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The sealing flow will inevitably affect the cooling airflow quality in a second air system of an aero-engine. In this study, theoretical derivation and numerical simulation were conducted to establish a modified mixing model that considers both the torque and the source of the mixing flow. Then, the effect of the sealing flow can be evaluated using the modified mixing model. The results demonstrate that the effects of the sealing outflow on the flow and temperature characteristics of the pre-swirl system are weak when the air supply mass flow rate and pressure are fixed. However, the effects of the sealing inflow are significant. When the inner sealing inflow mass flow rate is increased from 0 to 20%, the temperature drop effectiveness is decreased by 31.3%. The temperature drop effectiveness is decreased by 29.2% as the inner sealing inflow temperature rises by 37 K. Then, the temperature drop effectiveness is increased by 15.6% as the inner sealing inflow swirl ratio is increased from 0 to 0.8. The results of the modified mixing model are in satisfactory agreement with the numerical results, which show a maximum temperature drop deviation of 7.22%. Compared with the previous method, the prediction accuracy of the pre-swirl cavity temperature drop can be increased by 22.28%.

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... The aerodynamic performance of the receiver hole on the influence of the pre-swirl system temperature drop has been reported by Gong et al. [26,27]. The one-dimensional predicted model was built by Liu et al. to predict the velocity of the sealing flow and the swirl ratio at the receiver hole inlet [28]. It can be summarized that adjusting the swirl ratio distribution in the system is important to reduce the rotor entropy increase, and improve the system cooling performance. ...

... As shown in Fig. 13-c, the numerical model built by Liu et al. [28] was adopted to verify the accuracy of equation (18). Where σβ 1 in equation (18) is directly replaced by the effective swirl ratio obtained by the area-weighted average of swirl ratio at the receiver hole inlet. ...

... Where σβ 1 in equation (18) is directly replaced by the effective swirl ratio obtained by the area-weighted average of swirl ratio at the receiver hole inlet. The calculation conditions of Liu et al. [28] are that the rotating Mach number is 0.48 and the mass flow rate ratio is 0.14. In total, the predicted values attained by equation (18) have a good agreement with the numerical results. ...

The pre-swirl system has the ability to decrease the air supply temperature so as to improve the cooling performance and the operating life for turbine rotating blade. In this paper, a test rig was designed to reveal the aero-thermal characteristics in a cover-plate type pre-swirl system of gas turbine engines. Then, the theoretical derivation and experimental evaluation were conducted to reveal the variation of temperature drop and power consumption of a pre-swirl system with the mass flow rate ratio and rotating speed. Especially, the pressure and temperature on the rotating turbine disc were measured by a co-rotating data recorder. The theoretical and experimental analyses indicate that the temperature drop of pre-swirl system increases as the velocity coefficient of the pre-swirl nozzle outlet enhanced, but presenting a decrease with the increment of the rotating Mach number. Then, the ideal dimensionless temperature drop can be formally unified with the actual dimensionless temperature by defining the tangential velocity recovering coefficient, which is verified with the experimental results. Moreover, a linear relationship between the dimensionless temperature drop and the effective swirl ratio at the nozzle outlet can be deduced further. Especially, this relationship shows a good agreement between the predicted values and numerical results. Since the dimensionless temperature drop decreases with the increase of the dimensionless power consumption; an important discovery can be concluded that the algebraic sum of these two physical quantities is always equal to 1. Therefore, the results can offer a reference for the design and optimization of gas turbine cover-plate type pre-swirl system.

... As a result, the disk material will gradually deteriorate due to the accumulation of fatigue and thermal creep damage, thus endangering the safety of the gas turbine [3]. The rotating turbine disk cavity system is usually recognized as the most important and basic structure in the secondary air system of the aeroengine [4]. In general, several cooling technologies were developed on the turbine disk in order to decrease the thermal loading [5]. ...

... where T is the temperature and φ is a dissipation function that is related to the velocity distribution and the viscosity. (d) Ideal gas equation of state: (4) (e) Convective heat transfer equation (i.e., third kind of boundary condition): ...

Thermal loading management of turbine disks get important attention in the safety of aero-engines due to a large temperature level and gradient differences in the turbine disk cavity. This study conducts a comprehensive evaluation to address complex heat transfer problems in a high-speed rotating turbine disk cavity system, fully considering multiple factors. A theoretical derivation is conducted to fully elaborate the multifactor influencing mechanisms of the system based on similarity criteria and a dimensional analysis method. Notably, a high-speed rotational experimental platform of rotating disk is established to verify the research method's reasonability and the result's accuracy. Furthermore, four dimensionless operation cases are conducted to assess the correlation mechanism of the system performance with a strong rotating flow and heat transfer. The results indicate that the main correlation factors of the disk cavity system performance are the flowing Reynolds number, rotating Mach number, rotating Reynolds number, specific heat ratio, and wall temperature. Moreover, the Rossby number and the swirl ratio are used to evaluate the fluid flow characteristics. With the increase in the flowing Mach number from 0.006 to 0.15 and the rotating Reynolds number from 0.74 × 10⁶ to 14.80 × 10⁶ at 9000 rpm, the Nusselt number on the rotor disk wall enhances to 1639.4 and 1286.9, respectively. However, it decreases to 1001.91 for the rotating Mach numbers in the range of 1800–13,500 rpm. Particularly, the dimensionless heat flux is in the range of 0.0026–1.23 under multifactor effects. In summarizing, the present findings are of importance for improving the thermal management and performance reliability of aero-engines by developing an advanced turbine disk cooling system.

... In addition, Zhu et al. [24] numerically represented the influences of system temperature drop and total pressure loss characteristics under various rotating Reynolds numbers, mass flow rates, and swirl ratios. Simultaneously, Liu et al. [25] studied the influence of pressure ratio and entropy increment characteristics in the system and that of system seal flow on temperature drop characteristics [26]. Subsequently, an experimental analysis was conducted to determine the impact of the straight-hole type pre-swirl nozzle [27], which signified that the critical nozzle-pressure ratio was greater than the theoretical value of 1.89. ...

... In addition, the effect of seal flow should not be neglected, especially for a high-radius pre-swirl system. The previous work in Ref. [26] has conducted a prediction of the seal flow effect on tempeature drop characteristics of a pre-swirl system by a mixing model of the pre-swirl cavity based on conservation equations. However, there is still a lack of in-depth and comprehensive evaluation of the system performance. ...

Pre-swirl system has an indispensable role to supply enough cooling air with appropriate pressure, temperature, and mass flow rate to improve the life and the efficiency of turbine cooling blades and vanes. This study aimed to reveal the heat transfer mechanism and energy conversion characteristics of a multi-in and multi-out pre-swirl system. Subsequently, a novel modified prediction modeling was proposed to evaluate the system performance and energy conversion with complete consideration of multi-factors, especially for determining the influence of the seal flow, wall friction, work done by the rotating turbine disc, and rotor-stator moment. The results reveal that a high pre-swirl cooling performance and low-energy consumption can be obtained from the contribution of the airflow swirl ratio, whereas the swirl ratio was susceptible to the mixed seal flow. Thereafter, the seal outflow improved the system temperature-drop efficiency, whereas the seal inflow strongly influenced the heat transfer and energy consumption characteristics. The modified modeling resulted in a 56.89% increase in prediction accuracy relative to the Liu-model. Moreover, the nonlinear relationships between the seal flow and system performances can be comprehensively and accurately evaluated. In particular, a peak in a system temperature drop of 38.5 K can be realized with a low-energy consumption of − 133 kW and a 64% enhancement in the air-supply flow rate based on a contribution of the seal flow on airflow swirl ratio. Thus, the implementation of the modified modeling can prove significant in theoretical guidance and engineering applications.

... Poncet and Schietel [30] investigated the effects of rotation on the heat transfer in an enclosed rotor-stator disk cavity with a heated shroud. Moreover, Liu et al. [31][32] studied numerically the flow and heat transfer for a rotor-stator pre-swirl systems with experimental verification. Tan et al. [33] compared the RANS method and LES method in predicting the flow features in rotating cavities. ...

The rotor-stator disk system is of great importance for turbine blade cooling and preventing gas invasion in the aircraft engine. This study presents an experimental investigation on a high-speed rotor-stator disk cavity with axial throughflow. The aims are to experimentally measure and reveal the pressure characteristics, windage heating, swirl characteristics, and relative temperatures at a high rotational speed of 0-9000 rpm with mass flow rates of 0.05-0.15 kg/s. Especially, a new measurement idea was proposed and tested that relative temperature in the rotor system can be obtained by measuring absolute parameters in the stator system. Experiment results reveal that rotational speed and inlet mass flow are the main parameters to determine flow characteristics in the rotor-stator cavity. The increase of rotational speed will enhance the effect of centrifugal boosting, windage heating, and swirl characteristics. But increasing inlet mass flow rate will lead to the opposite effect. When the airflow is in the heat balance state, relative total temperature and adiabatic temperature can be acquired by measuring absolute temperature and swirl ratio at the same radius. The maximum deviation is below 2K. The results can be beneficial to the optimization design of rotor-stator disk cavity in the gas turbine engines.

... Deng et al. [28] analyzed the influence of pressure fluctuations in the compressor or combustion chamber on the stable leakage characteristics of the sealing sheets. The aerodynamic and thermodynamic performances are of importance for engine safety operation [29][30][31]. Zhang et al. [32] revealed the influence of sealed airflow on the turbine's flow field structure and aerodynamic performance. Especially, the thermal problem of high temperature is always a hot topic of engine research [33][34][35]. ...

The loss of cold air from the blade edge plates of the turbine has a negative impact on engine performance and safety. Using an experimental method, this paper investigates the effect of geometric and aerodynamic parameters on cold air leakage through pressure and mass flow measurements. Based on the results, it can be concluded that, with a change in sheet spacing, the proportion of bypass leakage and clearance leakage changes. At the same sheet spacing, the edge plate clearance is increased from 1 mm to 1.1 mm, resulting in a 30% increase of total leakage and a 25.7% increase of leakage equivalent mass flow. The edge plate clearance was increased from 1.1 mm to 1.2 mm, the total leakage increased by 19.2%, and the equivalent mass flow of leakage was 19%. The proportion of clearance leakage in the total leakage increased gradually for a given edge plate clearance. When the sheet spacing was 1 mm, bypass leakage accounted for 68% of the total leakage and was the primary source of leakage. The clearance leakage accounted for 83% of the total leakage with a plate spacing of 10 mm. When the sheet spacing is small, bypass leakage dominates; when it is large, clearance leakage dominates. The variation law of leakage with pressure, structural parameters and the ratio of sheet spacing to sealing slot length play an important role in the design of sealing structures.

... According to three-dimensional (3-D) numerical simulations for a pre-swirl system, [42][43][44] the interface in the rotor-stator cavity is suggested to apply the frozen-rotor method instead of the mixing plane method in the steady-state calculations. Liu et al. 45,46 conducted computational fluid dynamics (CFD) analysis on the pressure ratio and entropy increment in a coverplate pre-swirl system. Besides, a low-cost steady-state method for transient problems is provided. ...

The pre-swirl system is of great importance for temperature drop and cooling air supply. This study aims to investigate the influencing mechanism of heat transfer, nonuniform thermodynamic characteristics, and cooling air supply sensitivity in a pre-swirl system by the application of the flow control method of the pre-swirl nozzle. A novel test rig was proposed to actively control the supplied cooling air mass flow rate by three adjustable pre-swirl nozzles. Then, the transient problem of the pre-swirl system was numerically conducted by comparison with 60°, 120°, and 180° rotating disk cavity cases, which were verified with the experiment results. Results show that the partial nozzle closure will aggravate the fluctuation of air supply mass flow rate and temperature. When three parts of nozzles are closed evenly at 120° in the circumferential direction, the maximum value of the nonuniformity coefficient of air supply mass flow rate changes to 3.1% and that of temperature changes to 0.25%. When six parts of nozzles are closed evenly at 60° in the circumferential direction, the maximum nonuniformity coefficient of air supply mass flow rate changes to 1.4% and that of temperature changes to 0.20%. However, different partial nozzle closure modes have little effect on the average air supply parameters. Closing 14.3% of the nozzle area will reduce the air supply mass flow rate by 9.9% and the average air supply temperature by about 1 K.

... Liu et al. [35] found that the system performance using vane shaped receiver hole could be obviously improved by numerical simulations. The issues about the heat transfer and flow loss in the system were also studied [36][37][38][39][40][41][42][43]. ...

As a vital part of the pre-swirl air supply system, the rotating receiver hole will affect the cooling air quality supplied to turbine rotor blades of an aero-engine. It is concerned about the influence mechanism of the receiver hole on system performances. Thus, novel theoretical relations are proposed about the effect of both the mass flow rate ratio and rotating Mach number on the system pressure ratio, temperature ratio and temperature drop efficiency. Then, a comparative analysis is carried out to guide the structure optimization of the receiver hole through numerical methods with experimental verifications. Especially, a high-speed test rig is conducted to comprehensively evaluate the optimal rotating receiver hole about the system aerodynamic and thermodynamic characteristics. Numerical results show that the vane shaped receiver hole has the best system performance relative to both runway shaped and drilling shaped structure. The circumferential angle of the receiver hole can significantly reduce the system specific power consumption. Based on pressure and temperature measurement in the test rig, the vane shaped receiver hole can obviously improve the system performance, resulting in 13% increase in system temperature drop efficiency and 28% decrease in dimensionless system specific power consumption. Research conclusions can provide reference to enhance the pre-swirl system performance by optimizing design of the receiver hole.

... Increasing the turbine inlet temperature is an effective approach to improve the thermal efficiency of an engine cycle and thrust-to-weight ratio of the aero-engine [1] . A high inlet temperature will affect the turbine disk performance, which can provide thermal boundary conditions as a reliable basis for evaluating the strength and service life of a turbine disk. ...

【Published in Fundamental Research】
Thermal boundary conditions of the turbine disk cavity system are of great importance in the design of secondary air systems in aero-engines. This study aims to investigate the complex heat transfer mechanisms of a rotating turbine disk under high-speed conditions. A high-speed rotating free-disk model with Dorfman empirical solutions is developed to evaluate the heat transfer performance considering various factors. Specifically, the influence of compressibility, variable properties, and heat dissipation is determined using theoretical and numerical analyses. In particular, a novel combined solution method is proposed to simplify the complex heat transfer problem. The results indicate that the heat transfer performance of a free disk is primarily influenced by the rotating Mach number, rotating Reynolds number, Rossby number, and wall temperature ratio. The heat transfer temperature and Nusselt number of the free disk are strongly correlated with the rotating Mach number and rotating Reynolds number. Analysis reveals that heat dissipation is a critical factor affecting the accurate evaluation of the heat transfer performance of the turbine disk. Thus, the combined solution method can serve as a reference for future investigations of flow and heat transfer in high-speed rotating turbine disk cavity systems in aero-engines.

... 量、压力及温度等性能参数的影响。由此可见， 改善预旋供气系统性能对供气流量和系统温降的 品质具有重要作用。 在流阻和压力特性方面，Bricaud 等 [22] 实验 研究了预旋供气系统的气体动力损失和热力学损 失 。 预 旋 喷 嘴 的 流 阻 特 性 成 为 了关注对象 。 Mirzamoghadam 等 [23] 研究发现径向预旋喷嘴和轴 向预旋喷嘴的流量系数相差在 2%以内。Javiya 等 [24] 等对圆柱式、气动孔式及叶片式预旋喷嘴进 行了对比研究，指出叶型流道可显著改善预旋喷 嘴性能。针对叶型式预旋喷嘴，柴军生等 [25] 和刘 育心等 [26] 研究总结出，叶片式预旋喷嘴具有出口 气流角度变化小、总压损失系数小的特点。薛彪 [27] 和陈尧 [28] 通过数值模拟和实验测量，获得预旋 喷嘴流量系数及预旋效率随预旋角度及预旋喷嘴 长径比的变化规律。针对转动孔和转动盘腔元件 的流阻特性，Popp 等 [29] 和 Ditaman 等 [30] 分别开 展了盖板式和直接式预旋供气系统的接受孔流量 特性研究，定义了绝对坐标系和相对坐标系下转 动孔流量系数。在相对坐标系下流量系数可以不 考虑转子做功问题，转动孔流量系数小于 1 [31] 。 预旋喷嘴下游预旋腔内出现较大的总压损失，该 总压损失随流量和喷嘴出口旋转比的增大而增 大，随喷嘴数目的增大而减小；随着接受孔进口 旋转比接近 1 时，接受孔流量系数逐渐增大 [32] 。 基于相似分析法，冯青等 [33]- [34] 开展了转静腔流 阻特性研究。王锁芳等 [35] 揭示了旋转雷诺数和无 量纲流量对径向预旋供气系统温降和流阻特性的 影响。基于熵分析法，吴衡和刘高文等 [36] 发现系 统温降程度与熵增具有强关联，当熵增为 0 时温 降达到最大；并且预旋系统存在着温降与功耗的 关联 [37] 。龚文彬等 [38]- [39] 从热力学理论出发，建 立了预旋喷嘴、封严篦齿等流阻元件的质量流量 模型和熵产模型，揭示了流阻元件的损失机理。 由此可见，预旋供气系统并不仅仅是一个简单的 通流结构，其流阻熵增特性与供气流量、温度特 性有着关联机制。 综上阐述了国内外对预旋供气系统的研究现 状，针对系统供气流量和温降换热特性，国内外 已进行大量的研究。关于流阻和压比特性研究 中，主要关注预旋喷嘴、接受孔、转动盘腔等单 一元件的流动特性，而对预旋供气系统整体压比 航 空 学 报 3 的主要影响因素尚未有明确的结论。尽管前期西 北工业大学刘高文等 [5], [40]- [43] ...

Abstract: The pre-swirl system has the complex problem of power and heat conversion of rotating and stationary compo-nents, which provides an important guarantee for high-temperature thermal protection of turbine rotating blade. This study focuses on theoretical analysis, and then novelty reveals the correlation mechanism and evolution law of pressure ratio, entropy increase, and temperature drop characteristics of pre-swirl system. Moreover, the mathemat-ical model of pressure ratio efficiency is put forward. Especially, the influence mechanism of impeller effect of ro-tating component can be comprehensively evaluated. The formula derivation and theoretical analysis show that, under the condition of adiabatic constant specific heat, the pressure ratio and entropy increase of the station system decreases monotonously with the increase of air supply flow rate. The pressure ratio-entropy increase characteris-tic of rotor system depends on the effect of air supply flow rate, the rotation speed of turbine disc, and system tem-perature drop. Based on the decomposition of the mechanism of temperature drop into a strong correlation func-tion between the velocity coefficient and the rotating Mach number, it is clearly pointed out that the system pressure ratio decreases with the increase of the air supply flow rate, and basically increases with the increase of the turbine disc rotational speed. When the airflow swirl ratio of pre-swirl nozzle is greater than the reciprocal of pre-swirl radi-us ratio, the system pressure ratio decreases with the increase of turbine disc rotational speed. It can be revealed that the decrease of entropy loss is an important way to improve the system pressure ratio when the inlet flow con-dition and the pre-swirl radius ratio are constant. By systematically evaluating the impeller effect of rotor component, it is found that the impeller can increase the nozzle outlet velocity coefficient, increase the system temperature drop, and reduce the system power consumption without changing the rotating Mach number but keeping the system pressure ratio unchanged. Therefore, the correlation mechanism of pressure ratio and entropy increase character-istics can effectively evaluate the performance design of pre-swirl system.

... On the other hand, under the condition of close to the actual combat environment and the combat conditions, the overall combat effectiveness of weapon system is evaluated, which provides quantitative decision basis for the research of weapon system operation. Therefore, the evaluation method of weapon system effectiveness is studied [2]. ...

The evaluation of weapon system effectiveness can provide scientific basis for improving its own and operational effectiveness, and is of great significance to enrich the theory of weapon construction. Aiming at the complexity and uncertainty of weapon system, a comprehensive evaluation method based on cloud model and AHP is proposed to evaluate the effectiveness of weapon system. Firstly, the specific steps of cloud barycenter evaluation method based on cloud model are given; then, based on the requirement analysis of weapon system, the evaluation index system is established by using analytic hierarchy process; finally, the feasibility of the method is verified by a case. The proposed method provides a new idea for weapon system effectiveness evaluation.

Pre-swirl system has strong potential to improve the cooling performance and service life of high-pressure turbine rotor blades in gas turbine engines. This study is to evaluate and improve the temperature drop and power consumption characteristics of the pre-swirl system with multi-in and multi-out seal flow by theoretical and experimental analysis. Then, a high-speed rotating test rig of the pre-swirl rotor-stator system is established, considering the inner seal by-pass configuration to prevent the flow of hot gas into the pre-swirl cavity. In addition, the rotor-stator domain parameters in the pre-swirl system test rig are accurately measured at high-speed operating conditions. Three experimental schemes of pre-swirl systems are proposed for comparison under different operating conditions. The experimental results show that the temperature drop of the prototype pre-swirl system is in the range of 9.28–20.78 K, with the power consumption of the system ranging between −0.23 and −6.67 kW and the system pressure ratios being around 1.3–1.9. Because of the inner seal inflow ratio ranging within 0–15%, the system temperature drops for the improved pre-swirl system built-in inner seal by-pass passages notably reach a value between 12.12 K and 25.54 K with an average system power consumption within −0.41 to −8.21 kW. Thus, the improved pre-swirl system arrangement has dual advantages of a higher cooling effect and lower power consumption.

The precooled turbine engine is applied to overcome the limitation of Mach number due to high temperature inlet air. This paper aims to investigate the effect of water injection cooling on the high-temperature intake air. Then, the theory evaluation and Eulerian-Lagrangian multiphase flow method are conducted to explore the thermodynamic process and resistance characteristics of the pre-cooling section built-in even spray apparatus with a drag reduction. Results show that larger amount of the injection flow rate at higher Mach number will deteriorate total pressure loss and flow field uniformity. Evaporation cooling can decrease flow loss by 9.4%–60.7%. Within 27 ms, total-temperature drop is in 14–144 K range with a low total-pressure drop coefficient of 0.56%–1.29%. Especially, mass flow will increase by 1.15%–18.50%. Thus, water injection cooling is conducive to a higher acceleration, as well as for improving the thermodynamics characteristics of inlet air for a turbine engine at a high Mach number.

Personal Profile:
Dr. Aqiang Lin (林阿强) is currently an Associate Professor at School of Power and Energy of Northwestern Polytechnical University in P.R. China. He received a Ph.D. in 2020, M.S. in 2016, and B.S. in 2012 with a major of Power Engineering and Engineering Thermophysics. (a): And, his main research interests are Energy Conversion, Gas Turbine Engine, Secondary cooling air system, Turbine disc system, Turbomachinery, Heat and Mass Transfer, Multiphase Flow, etc. (b): By 2021, he has published 50+ papers in international refereed journals. He serves as a peer reviewer for 32 indexed international journals and completed more than 200 review records, such as Applied Energy, Energy Conversion and Management, Energy, International Journal of Hydrogen Energy, International Journal of Energy Research, Energy and Buildings, et al. (c): In addition, he acts as an Associate Editor in Energy and Thermofluids Engineering (ISSN 2716-8026) and Editorial Board in Journal of Internal Combustion Engine (Transactions of CSICE, ISSN 1000-0909) and International Journal of Energy and Power Engineering (ISSN 2326-957X). And, he also serves as a Bentham Science Ambassador for Bentham Science press. (d): In 2020, he has received the Global Peer Review Awards for the top 1% of reviewer from the Essential Science Indicators (ESI) research fields of Engineering and Cross-field, which is awarded by the Web of Science Group of Clarivate. As well, the title of an excellent reviewer of Elsevier was awarded to him in 2020.

According to the discontinuous structural characteristics of a gas turbine, by considering the contact thermal resistance of the rough surface, a contact thermal resistance measurement experiment was conducted in this study. The main objectives of this work were to investigate the influence mechanism and change law of the contact thermal resistance characteristics on flange installation. Furthermore, this study conducted a theoretical analysis of contact thermal resistance and the calculation of a typical flange mounting edge based on actual operating conditions. The research results show that the contact thermal resistance of a typical flange mounting edge increases with an increase in flange clearance under different tightening torques, which is essentially proportional to the flange clearance. As the flange clearance increases, the unit contact thermal conductivity firstly decreases rapidly. Then, as the flange clearance reaches 0.4 mm, the decreasing rate of unit contact thermal conductivity tends to flatten. In addition, the contact thermal resistance of the typical flange mounting edge decreases with the increase in the tightening torque under different flange clearances. Furthermore, the contact area ratio is not related to the material, and the contact thermal resistance under actual working conditions can be calculated using the unit contact area.

Casing treatment is a powerful method for improving the stability of aircraft compressors. An optimized slot-type casing treatment was tested on the first rotor of a highly-loaded two-stage compressor, and the results showed that the casing treatment could not increase the compressor stability at the design and off-design speeds. A coupled casing treatment (CCT), which is built with an injector, a bridge, a plenum chamber, and several slots for a recirculating loop, is proposed and optimized to enhance the stability of the compressor in the present study. The optimized CCT improves the compressor stability and efficiency under the design condition by 75.8 % and 0.71%, respectively. The coupling effect, which is established with an inner circulation in the slots and an outer circulation from the slots to the injectors, accounts for the excellent stability enhancement. The coupling effect reduces the amount of tip leakage flow, depresses the development of the tip leakage vortex (TLV), and greatly decreases the blockage in the rotor tip which is primarily induced by the interaction of the shock-wave and boundary-layer at the blade suction surface. The parametric study shows that improving the coupling effect has a positive effect on reducing the rotor tip blockage, but a negative effect on the stability of the compressor stage. This is because the inflow condition of the stator is tremendously distorted while the coupling effect is excessively strong, which can cause a stall in the stator rather than in the rotor. The compressor stability can be maximally enhanced by adjusting the strength of the coupling effect to make a compromise of the improved rotor tip flow and the deteriorated stator flow.

The porous heat shield installed in the afterburner can effectively prevent the afterburner cylinder from overheating. Impingement/effusion cooling is one composite cooling technique to effectively improve the overall cooling effectiveness of the heat shield. Designing effective and efficient double-wall configurations requires a detailed understanding of how geometry and operating conditions affect the way coolant cools the afterburner cylinder. In this study, conjugated heat transfer experiments were conducted using IR thermography for double-wall heat shields with three open areas of the impingement plate (σ = 0.5%, 0.7%, 0.8%). The momentum flux ratio was varied in the range 0.01≤I≤0.50. The mainstream Reynolds number, based on the diameter of the film hole, was varied in the range 800≤Reg≤2000. The effects of geometrical and aerodynamic parameters on overall cooling effectiveness were experimentally and numerically investigated with the comprehensive effects of solid heat conduction and convection heat transfer. The experiments were modeled in a low-temperature state (Tg = 603 K, Tc = 298 K), which was based on the analogy theory and matching principle, as if the experiments were conducted under engine operating conditions. The modeling accuracy of experimental results was analyzed by the analogy theory. Results show that the difference in the overall cooling effectiveness between “laboratory” conditions (Tg/Tc = 2) and “engine” conditions (Tg/Tc = 4) is within 0.048. The overall cooling effectiveness is mainly affected by the open area through adiabatic cooling effectiveness and internal heat transfer, and that is mainly affected by the mainstream Reynolds number through external heat transfer. According to the area-averaged results in given experimental conditions, the maximum overall cooling effectiveness raise and drop coefficients after increasing open area and mainstream Reynolds number are 17.3% and 6%, respectively. Thus, the high open area and low mainstream Reynolds number are beneficial to improve the overall cooling effectiveness of the afterburner double-wall heat shield. Furthermore, the experimental measurements provide an important database for the evaluation of computational fluid dynamics simulations of the conjugate heat transfer effects occurring in the double-wall heat shield.

The pre-swirl system can offer cooling air to improve the extreme thermal shock to the rotating turbine blades in a gas turbine engine. This study focuses on theoretical, experimental, and numerical analyses about the flow and entropy increment for a pre-swirl system at the high-speed test conditions (up to 10000 rpm). Especially, the pre-swirl system entropy increment was firstly measured in the experiment. Then, the experimental test and CFD analysis are conducted to reveal the pressure ratio characteristics and loss mechanism. Research suggests that the non-dimensional temperature drop and the rotating Mach number are major determinants for the ideal pressure ratio. However, the ratio of the actual system pressure ratio to the ideal pressure ratio only depends on the entropy increment. For a given rotating Mach number, the actual system pressure ratio decreases with the non-dimensional temperature drop increasing. The increment of mass flow rate results in an enhancement in the entropy increment. In addition, the entropy increment of the receiver hole can be minimal for the swirl ratio of pre-swirl nozzle outlet close to 1. Therefore, this study can provide the basis for designing and optimizing the pre-swirl system at a high rotation speed.

The pre-swirl system can transfer the cooling air from the compressor to the turbine rotor blades with a lower relative total temperature to avoid extreme thermal shock. This work proposes a novel test rig to investigate the flow and aero-thermal characteristics in a cover-plate type pre-swirl system. The performed experimental and numerical studies focus on the effects of the partial pre-swirl nozzle closing modes on the mass flow rate of air supply, temperature , and uniformities in a pre-swirl system by application of the pre-swirl nozzle adjustable flow path. Especially, the transient problem of the pre-swirl system with the time-space variation characteristics is approximately explored by changing the rotor-stator phases, within the framework of a frozen-rotor formulation. Results show that the opening of the pre-swirl nozzle is of great importance for flow uniformity. A pre-swirl nozzle closing of 14.3% will result in a 10.9% decrease in the mass flow rate of the pre-swirl nozzle and a 9.9% decrease in the mass flow rate of air supply at the system pressure ratio of 1.32 and the rotating Mach number of 0.678. The maximum amplitude of the non-uniformity coefficient of mass flow rate increases from 1.1% to 5.4% for a single supply hole. Moreover, the relative total temperature of air supply decreases by about 1 K with the increase of the fluctuation from 0.5 to 1.5 K. Thus, the performance of the aero-engine can be improved due to a reduction in the amount of cooling air into the rotating turbine blades. K E Y W O R D S air supply, non-uniformity, pre-swirl nozzle, pre-swirl system, rotor phase, turbine engine

Aero‐engine compressor is seriously threatened by the ingestion of liquid water. This article aims to deeply study the influences of different water contents and droplet diameters on the unsteady performance and thermodynamic parameters of compressor through frequency spectrum analysis. The accuracy of numerical calculation for compressor performance is verified by experimental data. Results show that the compression performance will be reduced and the unsteady fluctuations inside compressor will be aggravated after water ingestion. For some important parameters, such as mass flow rate, total pressure and temperature ratio, as well as efficiency, their main frequencies are changed from the original blade passing frequency to the rotor passing frequency (RPF), and their amplitudes are also significantly amplified. The working point of compressor will experience the nonoptimal state with large amplitude and period for a long time, which is not conducive to the stable operation of the compressor. Moreover, within the range of 2% to 8% water contents and 50 to 150 μm droplet diameters, the fluctuation amplitude is correspondingly exacerbated with the increase of water content or droplet size, but its main frequency is maintained at RPF. Particularly, the tip clearance is the most sensitive region affected by water ingestion where the fluctuations of static pressure and temperature are the largest. The point that water content has a greater influence on the performance fluctuation of compressor is also confirmed in this article. Unsteady performance of a single stage compressor under dry and wet conditions are numerically studied. Fast Fourier transform is introduced to perform spectrum analysis. Main frequencies of fluctuations are switched from the blade passing frequency to the rotor passing frequency. Larger water content or droplet size can aggravate the unsteady performance fluctuations.

This monograph presents results of the analytical and numerical modeling of convective heat and mass transfer in different rotating flows caused by (i) system rotation, (ii) swirl flows due to swirl generators, and (iii) surface curvature in turns and bends. Volume forces (i.e. centrifugal and Coriolis forces), which influence the flow pattern, emerge in all of these rotating flows. The main part of this work deals with rotating flows caused by system rotation, which includes several rotating-disk configurations and straight pipes rotating about a parallel axis. Swirl flows are studied in some of the configurations mentioned above. Curvilinear flows are investigated in different geometries of two-pass ribbed and smooth channels with 180° bends. The author demonstrates that the complex phenomena of fluid flow and convective heat transfer in rotating flows can be successfully simulated using not only the universal CFD methodology, but in certain cases by means of the integral methods, self-similar and analytical solutions. The book will be a valuable read for research experts and practitioners in the field of heat and mass transfer.

This paper describes the modelling of typical secondary air system elements such as rotating orifices, seals and flow passages with heat and work transfer from the surrounding surfaces. The modelling is carried out in an object-oriented simulation environment that allows the creation of different configurations in a simple and flexible manner. This makes possible to compare the performance between different designs of individual components or complete secondary air systems as well as integrate them directly in whole engine performance models. The modelling is validated against published experimental data and computational results. An example of implementation in an engine model is also presented.

The book describes results of investigations of a series of convective heat-and-mass transfer problems in rotating-disk systems, namely, over free rotating disks, under conditions of transient heat transfer, solid-body rotation of fluid, orthogonal flow impingement onto a disk, swirl radial flow between parallel co-rotating disks, in cone-disk systems and for Prandtl and Schmidt numbers larger than one. Methodology used included integral methods, self-similar and approximate analytical solutions, as well as CFD. The book is aimed at the professional audience of academic researchers, industrial R&D engineers, university lecturers and graduate/postgraduate students working in the area of rotating-disk systems.

The paper represents results of an exact solution of a laminar heat transfer problem for a rotating disk in a fluid co-rotating with the disk as a solid body. The angular speed of the fluid is less than the angular speed of the disk. Disks surface temperature varies radially accordingly to a power law. Results for the laminar regime are compared with computations for turbulent heat transfer obtained using an integral method developed earlier. On the basis of the exact solution for laminar flow and basic ideas of the integral methods solution for turbulent flow, an integral method for laminar regime is designed and an approximate analytical solution of the considered problem is derived. Inaccuracies of the laminar approximate solution over the main range of variation of the influencing parameters and Prandtl numbers from 0.71 to 1 do not exceed 2.5%. It is shown that the dependence of the Nusselt number on the ratio of the angular speeds of disk and fluid varying from 0 to 0.3 is weak and has a point of maximum within this region for laminar flow. The obtained results are important in predictions of fluid flow and heat transfer in different types of rotating machinery.

Thermal bridges are weakly insulated areas in the envelope of a building that can significantly increase the energy load due to heat dissipation. To improve energy efficiency, a thermal bridge model is established to simulate heat transfer through the column in a refrigeration room. The accuracy of the numerical simulation program is verified by experimental data. A heat preservation method for the column that minimizes the cooling loss is analyzed. The results show that the thermal bridging is mainly due to the steel bar in the column, because the share of the cooling loss attributed to the steel bars is 42.02-55.87%. Moreover, applying heat insulation on the column can provide more energy savings in low-temperature rooms than in high-temperature ones. The most economical thermal insulation method as a function of the height and thickness of the insulation layer is therefore proposed for the low-temperature column. By the optimum method, the amount of heat flux through the whole column section, which includes both reinforced and non-reinforced areas, decreases by 37.34%, and the total cooling loss decreases from 30.23 to 13.66 W, representing a 54.81% reduction. Therefore, a reduction in the cooling loss from thermal bridging is achieved for a low-temperature refrigeration room.

To explore the inlet air cooling effect in a precooled turbine-based combined cycle engine, a numerical investigation for air/droplet fully coupled cooling is performed in the cooling section with a spray system. The accuracy of numerical simulation program for mass injection cooling methodology is qualified with the experimental data. Results indicate that an even spray arrangement is beneficial to the uniform distribution of flow field, and it is also the major factor resulting in the flow loss. Although the flow loss of dry air is irreversible in the flow process, the additional new energy of water vapor can contribute total energy of wet air mixture. In contrast, under the lowest requirement qualified of mass injection cooling at two high-altitude simulation environments, the total-pressure drop coefficients are 3.22-4.22% before mist injection and 2.87-3.86% after mist injection; the total-temperature drop coefficient is 10.09% and 16.29%, respectively, for dry air and wet air conditions. After optimization for spray apparatus, the flow loss can decrease by about 55.84% before mist injection and about 64.53% after mist injection. Additionally, a little influence is for flow field temperature. Therefore, water injection cooling can effectively improve the flow field characteristics due to a larger total-temperature drop and a smaller total-pressure loss in the cooling section.

To investigate the effects of receiver holes on the flow characteristics of pre-swirl system, based on a 3D model, a steady state numerical simulation of the pre-swirl system with the receiver holes angles between 0°and 60°was carried out. The results show that when the circumferential velocity of airflow is higher than that of the receiver holes, the vortexes near the receiver holes disappear gradually, and the effective flow areas increase with the angle of the receiver holes increasing. When the circumferential velocity of airflow is lower than that of the receiver holes, the vortexes gradually become larger, and the guiding effect of the receiver holes on the airflow is strengthened with the receiver holes angle increasing. As the receiver holes angles increase, static temperature and static pressure of airflow near the receiver holes decrease, the dimensionless mass flow rate and the temperature drop coefficient of pre-swirl system increase, and the total pressure loss coefficient slightly rises. The temperature drop coefficient increases by 22.7%, and the total pressure loss coefficient increases by 1.31% as the receiver holes angles increase from 0°to 60°. © 2018, Editorial Department of Journal of Propulsion Technology. All right reserved.

The effect of different protrusion amounts on various parameters (static pressure, total pressure, sealing efficiency) was experimentally studied by measuring carbon dioxide volume fraction, so as to obtain the change rule of the sealing efficiency and the minimum flow rate of sealing air of different sealing structures. In the experiment, the experimental parameters of different dimensionless sealing flow rates were measured under the condition that the annulus Reynolds number and the rotating Reynolds number changed within a certain range. The results show that the change of the protrusions amount has little effect on the static pressure in the cavity, and the static pressure change near the sealing ring is almost negligible. The total pressure and sealing efficiency will increase with the increasing protrusion amount. However, the degree of change in the different sealing structures is different. As a whole, the efficiency of radial rim seal is most obvious, and the improvement of the axial rim seal and double teeth rim seal is less. For each additional protrusion, the minimum sealing flow rate required for each of the three structures can be reduced by 0.96%, 0.30%, 0.28%, respectively. In addition, the rotating Reynolds number will have a more significant effect on the sealing efficiency after the protrusions are installed. © 2018, Editorial Department of Journal of Aerospace Power. All right reserved.

A Pre-swirl system is used to supply cooling air to the rotating turbine blades where the pressure and temperature of the supplied air is crucial for blade cooling.
A test rig was designed to simulate the flow in a cover-plate Pre-swirl system. Some important performance parameters of a pre-swirl system were measured at different mass flow rate (Cw is up to 1.35 × 105), rotation speed (Maϕ is up to 0.744) and outlet pressure (210 kPa and 310 kPa). These parameters include discharge coefficient of pre-swirl nozzle, pressure ratios, temperature drop and rotor work consumption. To get rotor pressure boost ratio and temperature drop, pressures and temperatures on the rotating turbine disc were measured respectively by tiny pressure transducers and thermo-couples co-rotating with the axis and recorded by a customized data recorder co-rotating also. By measuring the inlet and outlet total temperature of the test rig, work consumption was estimated approximately with heat transfer ignored.

A feasible method of injecting water mist into the air can improve the operation performance of gas turbine. This study aims to develop a deeper understanding of aerodynamic characteristics of fluctuating quantities and its influence caused by air-mist two phase flow with conjugate the liquid film. The effect of various mist injection conditions on transient characteristics of compressor was investigated by the frequency attribute analysis. The results show that the film attached to the blade surfaces will aggravate the aerodynamic fluctuation. Notably, the fluctuating quantities, such as pressure, temperature, mass flow, flow loss and compression work, center on the lower frequency region, indicating that the dominant component of disturbance source appears a weak fluctuation because of unevenly distributed flow field after mist injection. Within the range of 0.5–5% mist concentrations and 1–9 μm mist diameters, mist injection can weaken the fluctuation of pressure and tip leakage flow, meanwhile the fluctuations of temperature and entropy increase are a good improvement in large mist ratio or small mist size. However, the fluctuation reduction is marginal as mist concentration and particle size increase. Therefore, the fluctuation characteristics in the compressor can be controlled by manipulating mist injection conditions.

This paper investigates the mainstream hot gas ingestion into a new stator-well cavity which consists of upstream and downstream rim cavities as well as a pre-swirl cavity. The effects of the radial location of sealing air inlet hole and the shape of sealing air supply geometry on the flow characteristics and sealing performance of the stator-well cavity have been investigated. Computations are performed for three radius ratios of sealing air inlet-to-rim seal periphery of 0.883, 0.909 and 0.935 and three sealing air supply geometries in terms of hole design and slot design with two height-to-width ratios of 12 and 21. The results indicate that both the radial location of sealing air inlet hole and the shape of sealing air supply geometry has a significant effect on the flow characteristics and sealing performance in the upstream rim cavity, while it negligibly affects the flow structure and sealing effectiveness in the downstream rim cavity. For upstream rim cavity, it is more effective to protect upper walls for the inlet hole at a higher radius, and the sealing effectiveness on inner walls is higher for the inlet hole at a lower radius. Additionally, the slot design shows a lower sealing effectiveness on upper walls than that of the hole design, and with an increase in height-to-width ratio it further decreases. However, the slot design is of benefit to the protection of inner walls as well as the performance of pre-swirl cavity, and as height-to-width ratio increases the sealing effectiveness on inner walls increases.

To find out the real reason of the flow losses in a cover-plate pre-swirl system and provide the optimization method, analysis of the entropy increment and entropy generation in a pre-swirl system was carried out based on the results of 3D aerodynamics computation. The results show that the pre-swirl system achieves the largest temperature-reduction only if the entropy increment is zero, with the parameters of the system inlet and outlet fixed and ignoring the heat transfer between the system and the outside. What is more, the temperature-reduction reduces with the entropy increment enlarging. About 37 percent of the system entropy increment, which is the largest part of all, generated by the supply holes. The entropy generation caused by the turbulent dissipation is two orders of magnitude higher than the one caused by the direct dissipation, and the main reason to cause the entropy generation to be large is the large difference of velocity between the flow and the wall in the inlet of supply holes. © 2016, Editorial Department of Journal of Propulsion Technology. All right reserved.

As a component of delivering cooling air to turbine rotor blade at appropriate pressure, temperature and mass flow rate, pre-swirl system is very important to the cooling of turbine blades. It is attractive to the designers and scholars for its potential ability to reduce relative total temperature of cooling air as large as 100K. A pre-swirl system is actually an aero-thermodynamic system with energy transformation between work and heat. Theoretical analysis was carried out on an isentropic pre-swirl system to deduce equations for ideal temperature drop and power consumption. For an actual pre-swirl system, correlation between the actual temperature drop and power consumption was deduced, and a temperature drop effectiveness was defined also. Theoretical analysis shows that the system’s temperature drop increases linearly with the reduction of the power consumption.
Numerical models were derived from a real engine pre-swirl system with small simplification. Standard k-ε turbulence model and Frozen-Rotor approach were applied in the three dimensional steady simulations. Inlet total pressure and total temperature, outlet static pressure, mass flow rate delivered to the blade and rotating speed of rotor were kept to be fixed for all the models. The influences of heat transfer and sealing flow coming from the inner seal were ignored in the simulations. Section averaged parameters like pressure, swirl ratio and total enthalpy were presented at each typical station throughout the flow path. The relationship between the temperature drop and the power consumption of all the models has been verified to be consistent with the deduced formula. For the pre-swirl system with low radial location of nozzle, these measures, such as adding impellers in the cover-plate cavity and inclining the receiver hole, were taken to reduce the power consumption and enlarge the temperature drop obviously. For this specific pre-swirl system, models with high radial location of nozzle are more recommended to decrease the loss caused by the large circumferential velocity difference between the airflow and the rotor.
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This paper conducts a numerical study to investigate the effect of the fillet radius at the junction of inlet cavity and nozzle on the flow and heat transfer characteristics of a radial pre-swirl system. The Reynolds-averaged Navier-Stokes equations, coupled with SST turbulence model, are adopted and solved. In this paper, four fillet radii at three nozzle length to diameter ratios are selected to study the flow dynamics of the radial pre-swirl rotor-stator system. The results obtained in this paper indicate that considering the effect of the ratio of fillet radius to nozzle diameter, _rf_/_D_, on the adiabatic effectiveness, the discharge coefficient of the receiver hole and the total pressure loss in the pre-swirl nozzle and the pre-swirl cavity, there is an optimum value of _rf_/_D_ which can provide the best performance of the pre-swirl system. The effect of _rf_/_D_ on the heat transfer coefficient _h_ is also conducted. Numerical results clearly show that _h_ on the rotor wall at low radius increases with _rf_/_D._ The uniform distribution of _h_ on the rotor wall at receiver hole radius can be observed as synchronous rotation between the receiver hole and the cooling air occurs.

Investigations on preswirl nozzle show that the cascade vane nozzle is the best one so far. While in the design of whole circular nozzle disc, the blade height and blade spacing will be settled with the throat area, preswirl angle, number and radial position of nozzle decided. If the ratio between blade height and blade spacing is too small, it will reduce the performance of nozzle significantly. Based on the vane nozzle, a new kind of preswirl nozzle called vane shaped hole preswirl nozzle (vsh nozzle for short) is proposed, with which the ratio of blade height against blade spacing can be adjusted to a more appropriate value. The flow characteristics of vane nozzle and vane shaped hole nozzle are compared numerically. To consider the mixing influence of preswirl cavity downstream the nozzle, the computational models contain not only the stationary inlet chamber and preswirl nozzle, but also the rotary preswirl cavity and receiver hole. Results show that the discharge coefficient and preswirl effectiveness of the vsh nozzle are higher remarkably than that of vane nozzle. The discharge coefficient of the vsh-52 preswirl nozzle increased by 9.14% comparing with that of the vane-52 nozzle, and the preswirl effectiveness increased by about 4.44%. Two new parameters called effective discharge coefficient and effective preswirl effectiveness are also proposed to reflect the comprehensive performance considering the mixing influence of preswirl cavity downstream the nozzle.

The effects of the center inflow on the flow and heat transfer characteristics in a pre-swirl rotor–stator system are numerically investigated using the CFD software ANSYS-CFX. The investigation of the pre-swirl system without center inflow is also conducted to be served as a contrast and these results are compared with experimental measurements to verify the computational method. In this paper, five mass flow rate ratio of the center flow to the pre-swirl flow, mf, four dimensionless mass flow rate of pre-swirl flow, Cw, and five rotation speeds, n, are selected to study the flow dynamics of the pre-swirl system in terms of the flow structure, the air swirl ratio, the total pressure loss coefficient, the discharge coefficient of the receiver holes and the adiabatic effectiveness. It shows that the maximum value of the discharge coefficient occurs as swirl ratio in the core at the receiver-hole radius equals 1 and mf reaches as a high value as possible, and the adiabatic effectiveness decreases as mf increases. In addition, the relation between the Nusselt number, Nu, and mf, Cw as well as n is also illustrated and discussed.

The three-dimensional numerical simulations of heat transfer in a rotor-stator cavity with pre-swirl nozzles at different radial positions in the stator were conducted in this paper. The standard k-ε turbulence model and unstructured grid were applied with the purpose of investigating the heat transfer characteristics. Under the constant mass flow rate and the different radial position of the pre-swirl nozzles, the outflow temperature and the effect of heat transfer on the rotor are greatly affected by the different rotational Reynolds number, pre-swirl angle and rotor-stator gap. The results show that the heat transfer of the rotor is enhanced with the increase of the rotational Reynolds number or the decrease of the rotor-stator gap. When the pre-swirl nozzles were moved out along the radial direction, the temperature difference between the inlet and the outlet and the averaged Nusselt number take on up-down tendency, that is, exists a optimum radial position of the pre-swirl nozzles.

A turbine disc-cavity cooling configuration of an aero-engine was simplified to a rotor-stator cavity model with high-positioned pre-swirl nozzle. The influences of rotor-stator gap, cooling air flux, rotational Reynolds number and swirl ratio on the drop of cooling air temperature and heat transfer on the rotor were experimentally investigated by using advanced temperature measurement technology of the thermochromic liquid crystal. The experimental results indicate that, the high-positioned pre-swirling inflow yields outstanding cooling effect on the rotor fringe, and the temperature of the rotor is distributed in the shape of concentric circle; the drop of cooling air temperature diminishes with the increase of rotational Reynolds number and rotor-stator gap, or with the decrease of cooling air flux, meanwhile, the cooling effect on the rotor becomes worse.

This paper presents a numerical investigation on the flow and heat transfer characteristics in a rotor-stator disc cavity. The Reynolds-averaged Navier–Stokes equations, coupled with standard k–ε turbulent model, are adopted and solved. Four different secondary air flow rates and five kinds of rotational Reynolds numbers have been examined to determine the effect on the flow and heat transfer. Some results obtained in this study indicate that the heat transfer coefficients increase with the increasing rotational Reynolds numbers except for some small radius region. The local Nusselt number could be correlated with the local rotational Reynolds number by power laws. The sealing effectiveness increases with the increasing secondary air flow rates and its decreasing drop at low flow rate decreases with the increase of rotational Reynolds numbers. The flow structure in the rotor-stator cavity does not remain unchanged and it could experience a transition from Batchelor-type to Stewartson-type outward along the radial direction. Pumping effect that the centrifugal forces in the boundary layer at the rotor surface drives the cavity fluid outward and induces the compensatory fluid at the stator surface flow inward. In final, a new fully-coupled heat transfer method has been firstly presented for a trial.

Three-dimensional viscous steady Reynolds Averaged Navier–Stokes (RANS) solutions are employed to investigate the flow and heat transfer characteristics of the pre-swirl rotor–stator system. The applicability of computational fluid dynamics (CFD) with Shear Stress Transport (SST) turbulence model is verified by a comparison of CFD results with experimental measurements. First, the influences of geometrical parameters, including the pre-swirl angle, the fillet and the ratio of length to diameter of pre-swirl nozzle, on the pre-swirl efficiency and total pressure loss have been numerically investigated to pick out an optimal structure. Then, eight different pressure ratios and four rotating speeds are selected to study the flow dynamics of the pre-swirl system in terms of the pre-swirl efficiency, total pressure loss, discharge coefficient of the pre-swirl nozzles and receiver holes, non-uniformity of velocity and flow angle at the outlet of nozzles, sealing leakage coefficient and technical work. It shows that the pressure ratio has a strong influence on all the flow parameters while the influence of the rotating speed on them looks different. Eventually, the relation between the heat transfer coefficient (HTC) and the pressure ratios as well as the rotating speeds is presented. Results show that the pressure ratio exerts an influence on the magnitude of HTC and the rotating speed has a significant effect on the movement of the regions with high HTC.

The urgent requirement to minimise the environmental impact and costs associated with gas turbine operation has provided the incentive for OEMs to design engines capable of performing at ever-increasing cycle pressure ratios, turbine inlet temperatures and rotational speeds. An inevitable consequence of this trend is the requirement for safe operation of gas turbine components in an increasingly hostile environment. The severity of the environment in which critical gas turbine components operate is such that even quite modest improvements in cooling effectiveness can result in a disproportionate improvement in component life. To this end, the technique of pre-swirling the cooling air delivered to rotating components, in order to reduce its relative total temperature and thereby increase cooling effectiveness, is well established [1]. The present work describes a novel pre-swirl arrangement which overcomes significant shortcomings found in more traditional systems. The benefits of the system and its sensitivity have been explored using CFD techniques. This investigation has shown that there are likely to be substantial benefits of up to 20K in relative total temperature from adopting such a system. The use of CFD to explore such a design allows considerable insight to be gained into its characteristics before investing heavily in experimental demonstration, on an engine or rig.

HP turbine cooling systems utilize a TOBI (tangential on-board injector) nozzle and seal-plate to deliver cooling air to the airfoils with minimal loss in pressure and a benefit in relative total temperature. It was necessary to have a low TOBI exit pressure to control excess leakage across adjacent labyrinth seals with a trade-off of maintaining adequate pressure to supply blade cooling. Consequently, pumping vanes were needed on the seal-plate to restore pressure, which adds parasitic work to the turbine and a corresponding loss of engine efficiency. Engine testing revealed recirculation zones attached to the radial pumping vanes. Subsequent numerical simulation corroborated the recirculation and resulting circumferential asymmetry in flow distribution to the cooled airfoils. As a consequence, excess cooling air is supplied to the HP rotor with some airfoils receiving the minimum amount of cooling air. This study seeks to improve the flow distribution and pumping effectiveness by means of contouring the pumping vanes, increasing pumping vane solidity and/or controlling diffusion by re-contouring the seal-plate surface. Design features that increase total through flow when overall pressure ratio is fixed are also explored.

Measurements and analysis for a pre-swirl cooling air delivery system are reported here. The experimental rig used is representative of aero-engine conditions, having 18 pre-swirl nozzles, 72 receiver holes, capable of speeds up to 11 000 rpm, and giving differences between total temperature upstream of the pre-swirl nozzles and relative total temperature measured in the receiver holes of up to 26K. Pressure and temperature measurements are reported. An elementary model is developed for calculation of the cooling air delivery temperature. This accounts for the pre-swirl nozzle velocity coefficient, moments on the stationary and rotating surfaces in the pre-swirl chamber, and flows through the inner and outer seals to the chamber. The model is shown to correlate the measurements well for a range of disc speeds and pre-swirl velocity to disc speed ratios.

The Internal Cooling Air Systems for Gas Turbines (ICAS-GT) research programme, sponsored by the European Commission, ran from January 1998 to December 2000, and was undertaken by a consortium of ten gas turbine manufacturing companies and four universities. Research was concentrated in five discrete but related areas of the air system including turbine rim seals, rotating cavity flow and heat transfer, and turbine pre-swirl system effectiveness. In each case, experiments were conducted to extend the database of pressure, temperature, flow and heat transfer measurements to engine representative non-dimensional conditions. The data was used to develop correlations, and to validate CFD and FE calculation methods, for internal fluid flow and heat transfer. This paper summarises the outcome of the project by presenting a sample of experimental results from each technical work package. Examples of the associated CFD calculations are included to illustrate the progress made in developing validated tools for predicting rotating cavity flow and heat transfer over an engine representative range of flow conditions.

This article presented detailed measurements of the pressure distribution and heat transfer in a rotor–stator cavity with inlet of orifices on the rotating disk and two outlets at both low radius and high radius. Transient thermochromic liquid crystal (TLC) technique was employed to determine the convective heat transfer characteristics on the test surface of the rotating disk. Rotational Reynolds numbers (Reφ) ranging from 4.9 × 105 to 2.47 × 106 and dimensionless flow rate (Cw) between 6.9 × 103 and 2.72 × 104 were considered. Experimental results indicated that the characteristics of the pressure loss coefficient between the inlet and the outlet was strongly dependent on the Reφ and Cw. Under the current operating conditions, the heat transfer on the surface of the rotating disk was weakened at both in the upper and lower edges for the case of r/R = 0.775 due to the existence of the recirculation. Whereas the heat transfer were enhanced near the upper radius with relatively low flow rate and high rotational speed, as well as on the middle radius with relatively high flow rate and low rotational speed.

The flow field in a preswirled cooling air supply to a turbine rotor has been investigated by means of CFD simulations. Coefficients for system efficiency are derived. The influences of various geometric parameters for different configurations have been correlated with the help of appropriate coefficients. For some of the most important geometric parameters of the coverplate receiver, design recommendations have been made. For the preswirl nozzles, the potential of efficiency improvement by contour design is highlighted.

Blade-cooling air for a high-pressure turbine is often supplied from pre-swirl nozzles attached to a stationary casing. By swirling the cooling air in the direction of rotation of the turbine disc, the temperature of the air relative to the blades can be reduced. The question addressed in this paper is: knowing the temperatures of the pre-swirl and disc-cooling flows, what is the temperature of the blade-cooling air?
A simple theoretical model, based on the Reynolds analogy applied to an adiabatic rotor-stator system, is used to calculate the pre-swirl effectiveness (that is, the reduction in the temperature of the blade-cooling air as a result of pre-swirling the flow). A mixing model is used to account for the ‘contamination’ of the blade-coolant with disc-cooling air, and an approximate solution is used to estimate the effect of frictional heating on the disc-cooling air.
Experiments were conducted in a rotor-stator rig which had pre-swirl nozzles in the stator and blade-cooling passages in the rotating disc. A radial outflow or inflow of disc-cooling air was also supplied, and measurements of the temperature difference between the pre-swirl and blade-cooling air were made for a range of flow rates and for rotational Reynolds numbers up to Reθ = 1.8 × 106. Considering the experimental errors in measuring the small temperature differences, good agreement between theory and experiment was achieved.

This paper describes an experimental study of the cooling efficiency of a preswirl rotor-stator system equipped with a small number of preswirl nozzles of circular shape, located on a radius equal to that of the receiver disk holes. In the direct transfer cooling air system, total air temperatures were measured in the relative frame, i.e. inside the receiver holes by means of small total temperature probes for different throughflow rates, rotational Reynolds numbers and swirl ratios. The experimental data were compared with a simple theoretical model which predicts air temperatures in an “ideal” preswirl system. This comparison served to quantify the efficiency of this cooling scheme. In a subsequent one-dimensional analysis which took into account flow data obtained in an earlier experimental study by the same authors, two different mechanisms responsible for the elevated cooling air temperatures were determined. The new model considers in addition to the observed reduction of swirl due to viscous drag on the stator and mixing inside the rotor-stator cavity, the work put in by the rotor at high disk rotational Reynolds numbers and low cooling air flow rates.

In a “direct-transfer” pre-swirl supply system, cooling air flows axially across the wheel-space from stationary pre-swirl nozzles to receiver holes located at a similar radius in the rotating turbine disc. This paper describes a combined computational and experimental study of the fluid dynamics of such a system. Measurements of total and static pressures have been made using a purpose-built rotor-stator rig, with 24 pre-swirl nozzles on the stator and 60 receiver holes in the rotor. The number of pre-swirl nozzles could be reduced, and it was possible to calculate CD , the discharge coefficient of the receiver holes. Information on the flowfield was also obtained from three-dimensional, incompressible steady turbulent flow computations. The measurements showed that there was a significant loss of total pressure between the outlet from the pre-swirl nozzles and the rotating core of fluid in the wheel-space. This loss increased as the pre-swirl flow-rate and inlet swirl ratio increased, and as the number of nozzles decreased. CD increased as the swirl ratio at the receiver hole radius approached unity; for the experiments, CD varied in the range 0.2 to 0.45. Computed pressures and tangential velocities were in mainly good agreement with the measurements. The computations help to explain the reasons for the significant losses in total pressure and for the relatively low values of CD in this pre-swirl system.

High inlet temperatures in a gas turbine lead to an increase in the thermal efficiency of the gas turbine. This results in the requirement of cooling of gas turbine blades/vanes. Internal cooling of the gas turbine blade/vanes with the help of two-pass channels is one of the effective methods to reduce the metal temperatures. In particular, the trailing edge of a turbine vane is a critical area, where effective cooling is required. The trailing edge can be modeled as a trapezoidal channel. This paper describes the numerical validation of the heat transfer and pressure drop in a trapezoidal channel with and without orthogonal ribs at the bottom surface. A new concept of ribbed trailing edge has been introduced in this paper which presents a numerical study of several trailing edge cooling configurations based on the placement of ribs at different walls. The baseline geometries are two-pass trapezoidal channels with and without orthogonal ribs at the bottom surface of the channel. Ribs induce secondary flow which results in enhancement of heat transfer; therefore, for enhancement of heat transfer at the trailing edge, ribs are placed at the trailing edge surface in three different configurations: first without ribs at the bottom surface, then ribs at the trailing edge surface in-line with the ribs at the bottom surface, and finally staggered ribs. Heat transfer and pressure drop is calculated at Reynolds number equal to 9400 for all configurations. Different turbulent models are used for the validation of the numerical results. For the smooth channel low-Re k- model, realizable k- model, the RNG k- model, low-Re k- model, and SST k- models are compared, whereas for ribbed channel, low-Re k- model and SST k- models are compared. The results show that the low-Re k- model, which predicts the heat transfer in outlet pass of the smooth channels with difference of +7%, underpredicts the heat transfer by −17% in case of ribbed channel compared to experimental data. Using the same turbulence model shows that the height of ribs used in the study is not suitable for inducing secondary flow. Also, the orthogonal rib does not strengthen the secondary flow rotational momentum. The comparison between the new designs for trailing edge shows that if pressure drop is acceptable, staggered arrangement is suitable for the outlet pass heat transfer. For the trailing edge wall, the thermal performance for the ribbed trailing edge only was found about 8% better than other configurations.

High inlet temperatures in a gas turbine lead to an increase in the thermal efficiency of the gas turbine. This results in the requirement of cooling of gas turbine blades/vanes. Internal cooling of the gas turbine blade/vanes with the help of two-pass channels is one of the effective methods to reduce the metal temperatures. Especially the trailing edge of a turbine vane is a critical area, where effective cooling is required. The trailing edge can be modeled as a trapezoidal channel. This paper describes the numerical validation of the heat transfer and pressure drop in a trapezoidal channel with and without orthogonal ribs at the bottom surface. A new concept of ribbed trailing edge has been introduced in this paper which presents a numerical study of several trailing edge cooling configurations based on the placement of ribs at different walls. The baseline geometries are two-pass trapezoidal channels with and without orthogonal ribs at the bottom surface of the channel. Ribs induce secondary flow which results in enhancement of heat transfer therefore for enhancement of heat transfer at the trailing edge, ribs are placed at the trailing edge surface in three different configurations: first without ribs at the bottom surface, then ribs at trailing edge surface in-line with the ribs at bottom surface and finally staggered ribs. Heat transfer and pressure drop is calculated at Reynolds number equal to 9400 for all configurations. Different turbulent models are used for the validation of the numerical results. For the smooth channel low-Re k-epsilon model, realizable k-epsilon model, the RNG k-omega model, low-Re k-omega model and SST k-omega models are compared, whereas for ribbed channel low-Re k-epsilon model and SST k-omega models are compared. The results show that the low-Re k-epsilon model, which predicts the heat transfer in outlet pass of the smooth channels with difference of +7%, underpredicts the heat transfer by −17% in case of ribbed channel compared to experimental data. Using the same turbulence model shows that the height of ribs used in the study is not suitable for inducing secondary flow. Also, the orthogonal rib does not strengthen the secondary flow rotational momentum. The comparison between the new designs for trailing edge shows that if pressure drop is acceptable, staggered arrangement is suitable for the outlet pass heat transfer. For the trailing edge wall, the thermal performance for ribbed trailing edge only, was found about 8% better than other configurations.

Application of CFD to assess the performance of a novel pre-swirl configuration

- G D Sonwsill
- C Young

G.D. Sonwsill, C. Young, Application of CFD to assess the performance of a novel
pre-swirl configuration. ASME Paper No. GT 2008-50684.

An investigation of a pre-swirled cooling airflow to a turbine disc by measuring the air temperature in the rotating channels

- B Meierhofer
- C Franklin

B. Meierhofer, C.J Franklin, An investigation of a pre-swirled cooling airflow to a
turbine disc by measuring the air temperature in the rotating channels, ASME
Paper No. GT1981-132.

Computational fluid dynamics simulations of flow and heat transfer in a pre-swirl system: influence of rotating-stationary domain interface

- J Karnahl
- J V Wolfersdorf
- K Tham
- M Wilson
- G Lock

J. Karnahl, J.V. Wolfersdorf, K. Tham, M. Wilson, G. Lock, Computational fluid
dynamics simulations of flow and heat transfer in a pre-swirl system: influence of
rotating-stationary domain interface, J. Eng. Gas Turbines Power 134 (2012)
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A comparative study on steady and unsteady calculations of a pre-swirl system

- L Liang
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L. Liang, G.W. Liu, Z. Lei, Q. Feng, A comparative study on steady and unsteady
calculations of a pre-swirl system, J. Propulsion Technol. 40 (2019) 2546-2553.

Numercial study on the similarity of flow and heat transfer on a high-speed rotating free disk

- R Chang
- G W Liu
- Q Chen
- Q Feng

R. Chang, G.W. Liu, Q. Chen, Q. Feng, Numercial study on the similarity of flow
and heat transfer on a high-speed rotating free disk, J. Eng. Thermophys. 41 (2020)
2561-2570.

Heat transfer and secondary air system of gas turbine engine

- S L Liu
- Z Tao

S.L. Liu, Z. Tao, Heat transfer and secondary air system of gas turbine engine,
Shanghai Jiao Tong University Press, Shanghai, 2018.

CFD analysis of flow and heat transfer in a direct transfer preswirl system

- U Javiya
- J W Chew
- N J Hills
- L Zhou
- M Wilson
- G D Lock

U. Javiya, J.W. Chew, N.J. Hills, L. Zhou, M. Wilson, G.D. Lock, CFD analysis of
flow and heat transfer in a direct transfer preswirl system, J. Turbomach. 134
(2012) 1-9.

Computational fluid dynamics simulations of flow and heat transfer in a pre-swirl system: influence of rotating-stationary domain interface

- Karnahl

A comparative study on steady and unsteady calculations of a pre-swirl system

- Liang

Numercial study on the similarity of flow and heat transfer on a high-speed rotating free disk

- Chang

CFD analysis of flow and heat transfer in a direct transfer preswirl system

- Javiya