Hangkong Dongli Xuebao/Journal of Aerospace Power

A 45° circumferential inlet pressure distortion screen was designed and the effects of screen-induced circumferential inlet pressure distortion on axial flow compressor stage were investigated at a high speed subsonic compressor test rig. The performance characteristics for the rotor with circumferential inlet pressure distortion and clean inlet flow were compared at middle-speed. The circumferential pressure distributions at three axial locations (rotor inlet, rotor outlet and stator outlet) were measured. The results show that the inlet flow distortion has weak effects on the compressor stage at middle-speed. In addition, the enlarging and moving of the distortion-section are not obvious at rotor outlet, but it is enlarged about 100 percent at stator outlet; the distortion is enhanced at rotor outlet and decayed at stator outlet. However, with inlet distortion the pressure ratio of this compressor rotor is improved 1.8 percent and the equivalent mass flow reduced 2.5 percent at near-stall condition in comparing with clean inlet flow.
Propeller acoustic experiments have been completed on the ground. The experimental results show that the aerodynamic and acoustic performances of 4-blade ARA-D propeller are better than that of the 3-blade NACA64 propeller. The sound field of propellers has directional properties, and it is dominated by discrete tones, especially the 1-5 x BPG tones. So, increase of the blade number and application of the advanced aerofoil will be very effective for improving aerodynamic and acoustic performances of the propeller. The best way to reduce propeller noise and suppress aircraft fuselage noise is to reduce the propeller discrete tones, especially the 1-5 x BPF tones.
A fiber-optic amplitude monitor has been developed as a non-contact vibration measuring system for rotator blades, in which a magnetic needle is adopted as a one-per-rotation sensor and a fiber-optical cable as a blade-passing sensor. Multiple application of the present monitor in the development of new-type engines demonstrates reliability and convenience in operation. It features high temperature resistance, it can work on temperatures up to 350 C and up to 400 C in the near future. This monitor has been put in service as a main instrumentation to monitor blade vibration in the high-pressure compressor of a new type of engine during its development.
Sources of compressor noise are usually considered as multiple pure tone noise, interaction noise, and broadband noise. In the paper, the noise propagation equation of steady force on the compressor rotor blade is derived. The numerical results are compared with the WP-11 compressor rotor acoustical experiment. The theoretical and experimental investigations indicate that the steady force noise on the compressor rotor blade is an important source of the compressor noise.
The flow-field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically studied. Results obtained from four combustion models, combined with the re-normalization group (RNG) k-ε turbulence model, discrete ordinates radiation model and enhanced wall treatment are presented and discussed. The results are compared with a comprehensive database obtained from a series of experimental measurements. The flow patterns and the recirculation zone length in the combustion chamber are accurately predicted, and the mean axial velocities are in fairly good agreement with the experimental data, particularly at downstream sections for all four combustion models. The mean temperature profiles are captured fairly well by the eddy dissipation (EDS) probability density function (PDF), and laminar flamelet combustion models. However, the EDS-finite-rate combustion model fails to provide an acceptable temperature field. In general, the flamelet model illustrates little superiority over the PDF model, and to some extent the PDF model shows better performance than the EDS model.
Two optical methods are studied which are used to visualize the flow field of exhaust free jet and jet impingement from a real solid rocket engine. One is the equal-thickness-fringe F-P interferometry which is constructed with two mirrors about 200 mm in diameter. The distance between two mirrors is more than 20 m and the resistance to vibration distortion is strong. Another is moire deflectometry which has an aperture over 400 mm in diameter. In this method, a large-diameter collimated light beam is used to expore the flow field, then it is reduced and recollimated into a small-diameter recollimated light beam, and detected by a two-gratings system to produce moire fringes. It is characterized by large aperture and simplicity. The experimental results show that the equal-thickness-fringe F-P interferometry can be used to visualize the flow field of the exhaust jet from a real solid rocket, and the moire deflectometry can be even used to visualize the extensive flow field of the rocket exhaust jet impingement.
A method for test and state analysis of simulation results was presented, which can not only effectively determine whether the simulation results are right or not, but also analyze every state of the simulation results when they are not completely correct, and point out which states have been simulated correctly and which have not. The method for test and state analysis of simulation results can guide the programming and the modification of simulation software system. Furthermore, a table of simulation results test and a table of simulation results state analysis was established, which makes the engineering application of the method more convenient.
An experimental investigation on the gas ingestion phenomenon was performed on the rig of 1.5 stage turbine with different rotating velocities and seal mass flow rates. The experimental measurements include time-average and unsteady pressure field measurements and carbon dioxide volume fraction technique. These data were used to find out the influence of the interaction between rotor blades and stator blades on the phenomenon of gas ingestion and investigate the details during the process of the main gas into the cavity. The study suggests that, some part of the pressure on the annulus out of the seal in higher than the pressure inside seal rim due to the circumferential variation following the vane pitch. And this part decreases as seal mass flow rate increases. An unsteady blade-periodic component is found in this experiment, which is also a key to ingestion. The minimum necessary value of seal mass flow rate is obtained by carbon dioxide volume fraction technique. And the fact that the path of the main gas ingestion into the disk cavity is arranged along the stator when seal mass flow rate is not enough can also be inferred.
The infrared integral radiant intensity of a typical fighter within the waveband between 8 μm and 14 μm and its detection range detected by infrared search/tracking system was calculated by taking into account the influence of the atmospheric transmissivity. The infrared stealth effect of the fighter with use of low emissivity materials was also analyzed. The flow field was calculated by Flunt software, while the infrared radiation characteristics and detection range were simulated by using self-developed software NUAA-IRSE. The results show that the infrared integral radiant intensity increases with the increasing of circumference angle and pitch angle. When applying low emissivity materials, the infrared integral radiant intensity decreases in all directions, leading to an improved infrared stealth effect.
A kind of unit cell for 2.5 dimension C/SiC composites was established by extracting the boundary of warp, fitting the curve using robust least square and simplifying the fitted curve. The elastic properties of 2.5 dimension C/SiC composites were predicted using dual-scale model; the dual-scale model was micro-scale which considered the scale of matrix/fiber/pore, and also meso-scale which considered the scale of warp/weft/cavity. The method for predicting the elastic properties of 2.5 dimension C/SiC composites was stiffness average method and energy method; finally the relationship between the porosity in the micro-scale and the elastic properties of 2.5 dimension C/SiC composites was discussed. Numerical results show that the theoretical results using energy method and stiffness average method have little difference; when considering the micro-scale porosity, the theoretical results can fit the experimental results better.
A fatigue life prediction method was developed to predict fatigue life of 2. 5 dimensional woven composites subjected to fatigue loading. This method consisted of unit-cell model, fatigue damage criterion and material property degradation technique. Stress analysis was performed by three dimensional finite element technology based on the unit-cell model. Modified three dimensional Hashin fatigue damage criterion and Mises criterion were adopted to identify fatigue damage separately for the yarns and matrix. The stiffness property sudden degradation rules were applied to establish the fatigue damaged material properties; the residual stiffness and strength models considering fiber volume fraction were used to establish the undamaged material properties. The coincidence of predicted fatigue life and experimental data was studied, and the comparison results validated the fatigue life prediction method. The results indicate that the tensile-tensile fatigue life in warp direction increases with the warp fiber volume fraction increasing, while weft fiber volume fraction has little effect on tensile-tensile fatigue life in weft direction.
From the perspective of macro and micro combinations, a series of failure criterions and corresponding stiffness reduction methods for multi-failure models of warps and wefts were developed based on modified Hashin criterion. Systematic static strength analytical method for 2.5 dimensional woven complex structures was presented based on gradually damage concept. Also, the tension stress-strain curves along the warp and weft were simulated, and the fitting curves were in good agreement with the experimental results with the errors of calculated stress less than 6.5% for given strains; and for 2.5 dimensional woven connection structure simulation of compressor, gradually damage process was simulated. The result shows that main damage of the structure occurs around the chamfer of the root; specifically, matrix compress failure on the root of suction surface can cause great deformation as a major cause of the destruction of the structure.
Based on the hypothesis of rectangle and biconvex section shape of the yarn, and different collocation between the inner warp and outer warp, thickness, section shape of the same structure being considered especially, a model for predicting the elastic property of 2.5-D woven composites was developed. To verify the elastic model, 62 samples of 2.5-D woven composites with 6 various structures were selected and the elastic properties were measured. Experiment results are in good agreement with the outcomes of the model. Further, it is shown that the difference between the inner warp and outer warp can't be ignored in predicting the elastic property of 2.5-D woven composites.
According to the micro-structure of 2.5-D self-healing C/SiC composite, a tensile mechanical model in weft and warp directions were established based on the damage mechanism including interfacial crack and matrix crack. The tensile nonlinear stress-strain functions in weft and warp directions were gained, and the predicted stress-strain curve agreed with the experiment very well. The result shows that, the largest error of the predicted stress-strain curve in weft direction is 8% to 9%. The largest error of the predicted stress-strain curve in warp direction is 10%. The stress-strain curve in weft direction is different from that in warp direction. By adopting tangent elasticity modulus and average crack distance, mass work to obtain strain is not needed and the model is simplified.
The mechanical properties and tension-tension fatigue life of 2.5D resin base woven composites at various temperatures, including room temperature (20℃) and high-temperature (180℃), were obtained by static tensile and tension-tension fatigue tests. Based on macroscopic tests, the damage modes and failure mechanism of the materials subjecting to static tensile and tension-tension fatigue loadings were discussed. Meanwhile, the relationship between residual strength and static strength was compared, and the influence of temperature on the static tensile and fatigue life was then analyzed. The results show that the weft modulus is not sensitive to temperature, ranging from 20℃ to 180℃, but the weft strength and fatigue life have a downward trend with the temperature increase. The weft fatigue life experiences a quite short cycle (less than 10⁴ cycles) prior to the ultimate failure at high temperature and high stress level (higher than 80% static strength), however, the corresponding life tends to be 10⁶ cycles when the stress level declines by only 2%. Additionally, the elevated residual strength is higher than the static strength tested at the same temperature. © 2017, Editorial Department of Journal of Aerospace Power. All right reserved.
The effect of component, temperature and flow on characteristic of methane/steam/carbon dioxide reforming reaction in the presence of oxygen in micro-annular chamber was numerically simulated using the surface elementary reaction mechanism. The results indicate that the effect of steam on the yields of H 2 is obvious but the effect of carbon dioxide is inconspicuous at low temperature. Increasing the content of steam (carbon dioxide) can improve the conversion efficiency of methane. As the temperature rises, the effect of steam (carbon dioxide) component on the characteristic of reforming reaction becomes more obvious. The content of hydrogen (carbon monoxide) and the conversion efficiency of methane at outlets obviously decrease with increasing flow rate. The effect of steam (carbon dioxide) on the conversion efficiency of methane becomes is no longer obvious at high flow rate. As a product of the reaction, the content of steam (carbon dioxide) at outlets maintains unchanged with increasing flow rate. On the contrary, as a reactant of the reaction, the content of steam (carbon dioxide) at outlets increases with increasing flow rate.
In order to get the distribution of cavitation flow field of N 2O in cavitation Venturi, governing equations of two-phase mixture flow were solved based on state equation for real gas and full cavitation model. According to the special properties of N 2O, numerical simulation was performed on a cavitation Venturi under three experimental states. Two different methods: with and without the influences of latent heat were used respectively and comparison and analysis of two different results were made. The cavitation area calculated by the method considering the influences of latent heat was smaller and obvious change of temperature in and around the cavitation area was found. The results indicate that the necessity and correctness of calculation considering the influences of latent heat, which can be a certain guide for the design of Venturi.
Fatigue experiments were carried out to investigate the effects of mean-stress and phase-difference on the tension-torsion fatigue life of 30CrMnSiA high strength steel, while the experimental data and plane stress characteristics of different mean stress and phase difference were analyzed. The test results showed that the fatigue life increased with the growing phase difference without mean stress, but decreased with the increase of phase difference when mean stress existed, whether mean normal stress or mean shear stress. Criteria based on the linear combination of the shear stress amplitude and normal stress on the maximum shear stress amplitude plane cannot reflect the test results correctly to some degree. Moreover, the initial crack angle was measured showing that its direction was close to the maximum shear stress amplitude plane. Finally, the defects of the criteria based on the linear combination shear stress amplitude and maximum normal stress on the maximum shear stress amplitude stress plane were explained by stress analysis. © 2018, Editorial Department of Journal of Aerospace Power. All right reserved.
The experimental research of low speed impact damage has been carried out on composite laminates with different geometries and layer direction angle, and the impact process was simulated by the progressive damage method. The geometries of composite laminates have much effect on the impact damage projected area. The layer direction angle of composite laminates has little effect on the impact damage projected area, but it has influence on the impact damage figure.
With the mesh generation method based on fin passages and element control equation, a new three-dimensional distributed-parameter model for compact heat exchangers was developed. On the basis of this model and the principle of minimum entropy generation, an optimization methodology was realized with genetic algorithm (GA), by which the geometry dimension of the heat exchanger and the fin surface type and sizing can be optimized simultaneously. The distributed-parameter model which takes account of the variation of local fluid physical properties in the heat exchanger can be applied to wet conditions or phase-change conditions. Moreover, because it avoids the complexity of CFD method and shortens the computer execution time greatly, the optimization based on distributed-parameter model is very practical. This optimization methodology can be extended to other kinds of heat exchangers and heat sinks.
Mathematical models for each component of aero engine based on S2 surface theory were analyzed, A full engine S2 flow simulation was performed using this method. High order Godunov's scheme was used, presenting good numerical stability and shock capturing capability. Viscous effects and secondary flow losses were treated as source terms. Their influence on the components and full engine system's performance were estimated effectively. A conservative process was taken to handle the parameter transfer between neighboring domains, ensuring the consistency of flux. The method features high accuracy by comparing the simulation and experimental results.
A stacked three-dimensional Laser Doppler Anemometer (LDA) system has been developed on the basis of a one-dimensional and a two-dimensional LDA system. This system was successfully used in the measurement of the rotational flowfield inside a small axial fan rotor. The measurements reveal rich and complex flow structures near the blade tip region. In particular, fine helical vortex structures are obtained which prove the system a useful tool in turbomachinery flow measurement.
With the vertical stacking of circuit layers, the power density of 3D-IC increases exponentially. Interlayer liquid cooling is a promising and scalable solution for high heat flux removal in 3D-IC (three-dimensional integration circuit). The flow and heat transfer performances of water through uniform and double-side heat flux 3D-IC of interlayer in-line micro-pin fins structure with heat transfer areas of 1 cm² and Reynolds number ranging from 150 to 900 were studied numerically. 3D-IC with in-line micro-pin fins for pitches of 200 μm, diameter of 100 μm and heights of 200 μm was analyzed. Results show that interlayer liquid cooling of 3D-IC with in-line micro-pin fins has better heat exchange effect than that with rectangular micro-channels. For the Reynolds number of 770, the power reaches to 250 W, which is equivalent to 8.3 kW/cm³ volumetric heat. Compared with rectangular micro-channels, the average temperature and the maximal junction temperature of the heater surface with in-line micro-pin fins are only 46.34, 13.96 K, down by 13.26, 21.34 K, respectively. © 2017, Editorial Department of Journal of Aerospace Power. All right reserved.
The NURBS (non-uniform rational B-spline) method was introduced for the 3D geometric optimization of axial flow compressor blade design. A set of optimization rule was developed by relating some aerodynamic performance parameters with the weights factor of NURBS. In the design of an axial compressor stator blade, the flow structures comparison have been made between the optimized new blade and the original one. The results show that this method could flexibly and rapidly optimize the blade shape to meet the aerodynamic requirements.
A parameter-based and geometry independent general method was developed for the simulation of 3D planar crack propagation by using finite element method (FEM). This method, on the basis of introducing a crack model containing whole crack surfaces, has a capability of creating cracked block automatically and simulating crack propagation in a multiple degree way. The accuracy, efficiency and versatility of the method were demonstrated by comparison with other analytical or experimental results available in the literature.
Flow characteristics of pre-swirl cavity and rotor-stator cavity of a cover-plate 45° pre-swirl system structure were studied experimentally. Static pressure distribution on the stator, total pressure distribution on the mid plane (z/S=0.326) and variations of the flow resistance coefficient in cavity and pre-nozzle discharge coefficient were obtained under high rotation speed. The results show that the pressure distribution in cavity is affected by the flow distribution weakly. The turbulent flow parameter is one of the primary control parameters of flow characteristics. The flow structure in cavity is mainly divided into two parts, the free vortex structures of rotor-stator cavity, and the recirculation and low pressure zones in pre-swirl cavity. The flow resistance coefficient of the cavity rise significantly with the increase of the turbulent flow parameter. The discharge coefficient of pre-swirl nozzle increases with the increasing pressure ratio of pre-swirl nozzle. © 2017, Editorial Department of Journal of Aerospace Power. All right reserved.
The goal of Collaborative Research Centre (SFB) 561 "thermally highly loaded, porous and cooled multi-layer systems for combined cycle power plants" is to expand the current technological and scientific knowledge on power plants in order to achieve total efficiencies of 65% in a combined cycle power plant in the year 2025. Therefore, the aero-thermomechanical, structural-mechanical, materials' scientific and production fundamentals for the development of steam and gas turbine components that are able to withstand highest thermal loads are being worked out within this SFB. This means for the gas turbine that combustion chamber outlet temperatures of 1520°C at 1.7 MPa are to be attained. In order to control these high temperatures, it is not only required to develop new materials' solutions, including thermal barrier coatings, but also to apply improved cooling techniques, as for example effusion cooling. This novel cooling concept is to be realised through open-porous structures. These structures can consist of drilled open-porous multi-layer systems or open-porous metallic foams. The development of graded multi-layer systems is also extremely important, as the grading will enable the use of coolant in dependence of the requirements. The live steam parameters in the high pressure turbine are expected to be increased up to approximately 700°C with pressure of 30 MPa. These elevated steam parameters can be encountered with Ni-base alloys, but this is a costly alternative, associated with many manufacturing difficulties. Therefore, the SFB proposes cooling the highly loaded turbines instead, as this would necessitate the application of far less Ni-base alloys. To protect the thermally highly loaded casing, a sandwich material consisting of two thin face sheets with a core of a woven wire mesh is used to cover the walls of the steam turbine casing. The current state of the research shows that by utilising innovative cooling technologies a total efficiency of 65% can be reached without exceeding the maximum allowable material temperature, thereby prolonging the life-span.
Laser shock processing of three categories of 7050-T7451 aluminum alloy samples was carried out, and their seven groups of fatigue life values were studied. To obtain the values of fatigue safe life of 7050-T7451 aluminum alloy specimens, the unilateral tolerance factor statistical analysis method and two-dimensional Weibull distribution method were used to predict the values of fatigue safe life, respectively, and these two kinds of calculation results were compared. The results show that: the fatigue life of aluminum alloy samples is enhanced greatly by laser shock processing, and in consideration of the confidence and reliability, the unilateral tolerance factor method can get an exact estimation value of the fatigue safe life, while the two-dimensional Weibull distribution method can get the range of values of fatigue safe life;considering different requirements of capital and safety, etc, on the fatigue safe life, the two-dimensional Weibull distribution method is more suitable for engineering applications.
Analysis on the hot deformation behavior of TiB2/7050 particle⁃reinforced aluminum⁃matrix composite and the influence of process parameters is significant for microstructure design and obtaining ideal performance after hot deformation.Based on this, related research on TiB2/7050 particle⁃reinforced aluminum⁃matrix composites was carried out.Hot compression experiments were carried out on Gleeble⁃3500 thermal simulator to study the hot deformation behavior of TiB2/7050 particle⁃reinforced aluminum⁃matrix composites at deformation temperature of 300-450 ℃ and strain rate of 0.001-1 s⁻¹, and the hyperbolic sine constitutive equation of the material was established.According to the dynamic material model, the processing map was calculated, and the processing window of the material was optimized.The mechanical properties and microstructure of the original extruded billet and the optimized hot pressed billet were analyzed.Results showed that, comparing these two processes, the strength index of hot pressed parts was slightly improved, but the plasticity was greatly improved, and the elongation after long transverse fracture was increased by 400%;the grain size of hot pressed parts was smaller and there was no obvious preferred orientation;the mechanism of tensile fracture was quasi cleavage fracture.The dimples of fracture surface of the hot pressed parts were deeper and the tearing edges were larger, indicating the longer duration of plastic tearing. © 2022, Editorial Department of Journal of Aerospace Power. All right reserved.
Performance parameter (exhaust temperature and fuel flow) correction formula of the GTCP131-9A auxiliary power unit(APU) was studied. A universal method of studying the gas turbine engine's comparability was proposed at fist. By using this method, the necessary conditions to make this single-rotor and fixed shaft gas turbine engine similar were three equal, independent similarity criterion numbers, namely, flight Mach number, corrected speed and corrected power; other similarity criterion parameters were the functions of these three similarity criterion numbers. Later, according to the similarity of this engine, by using small deviation method, small deviation correction equations of the additional exhaust resistance, fuel heat value deviation and power deviation existing in the process of engine test were given. Result showed that under the condition that the ratio of the output power to atmosphere pressure was constant, GTCP131-9A APU's performance parameter correction formula was the sum of the inlet total temperature polynomial, the correction term of additional exhaust resistance, the correction term of fuel heat variation and the correction term of power variation. © 2018, Editorial Department of Journal of Aerospace Power. All right reserved.
Self-designed oxygen-kerosene ablation system was employed to propose an ablation test method for testing the ablation property of the thermal structure and material of secondary combustion chamber in solid ducted rocket (SDR). Particle-free erosion and alumina particle erosion tests were performed on the silicone rubber insulation by using this method to analyze the erosion of particles on the surface micro-morphology of the silicone rubber material. Experiment results revealed that the samples without particle erosion swelled and delaminated after ablation, whose mean linear ablation rate was -0.025mm/s; the mean linear ablation rate of the samples with particle erosion was 1.901mm/s, the ceramic layer in center of samples was destroyed by particle absolutely, only the ultrathin pyrolytic layer and the head of carbon fiber (CF) were left, while the rubber matrix, particle fillers and aramid fiber (AF) around CF were oxidized and stripped by high speed flame flow, then the intense erosion damage effect of particle on insulation had been proved. The research shows that the method can simulate the ablation thermal condition of secondary combustion chamber in SDR, meanwhile, this method can also be applied to selection of insulation formula and ablation performance test of insulating materials. © 2018, Editorial Department of Journal of Aerospace Power. All right reserved.
Numerical simulation of combustion characteristics at wall burning condition in a diesel engine was conducted using software AVL FIRE, and the thermal boundary conditions of finite element calculation for piston at wall burning condition were obtained. Moreover, the finite element analysis of piston during ablation process was carried out using software ANSYS, and the rules of influence of wall burning on piston ablation were achieved. Meanwhile, a corresponding experiment of piston ablation was made on the diesel engine, and the calculated results accorded with the experimental results. The results show that the resolving method established can be used to simulate the ablation process of piston. The abrasion of injection nozzle, which leads to bigger gas temperature and wall heat transfer coefficient of gas on piston throat in a wide crank angle range, may cause ablation failure of piston. Meanwhile, the ablation amount firstly increases and then decreases with the increase of diameter of injection nozzle, and peaks when the diameter increases by 15%. The ablation amount increases with the ablation time, but the speed of ablation reduces slowly.
As for the ablation of hypersonic vehicles, the parabolized Navier-Stokes (PNS) equations of chemical non-equilibrium were calculated numerically based on a kind of Newton-type iteration method. The chemical model of 18 species 33 reactions containing alkali-metal impurities was established on the basis of a carbon-phenolic ablative material. Firstly, the wall temperature of small blunt cone was computed and the numerical results were validated by comparing with those in a reference. Then, the hypersonic ablation flow field containing alkali-metal impurities were simulated and the effects of ablation reactions on the flow parameters were deeply analyzed. The results show that compared with non-ablation condition, the temperature of flow field increases by 10% to 15% in ablation reactions. And the electron number densities increase by 1 to 2 orders of magnitude after taking alkali-metal Na into consideration.
A numerical method was developed to simulate the transient control ablation process by transpiration cooling. The influence of surface ablation and charring of thermal protective structure on cooling performance and the mass losses due to the ablation and charring was considered. In order to exactly predict the performance of the control ablation and cooling process, the influences of heat flux intensity, coolant injection velocity, initial temperatures of porous matrix and coolant on the cooling effect were discussed.
In order to investigate the nozzle thermal and ablation characteristics in dual-pulse solid rocket motors, the transient value of the throat diameter was obtained from the pressure and thrust measurements. Furthermore, the in-depth thermal response, pyrolysis/char profiles and surface recession of the nozzle assembly were predicted through fully coupled fluid-solid analysis using the commercial code FLUENT. Results show that during pulse operation, the insulation material pyrolysis/char profiles expand and the nozzle insert erosion rate increases. During pulse separation, heat conduction in the material leads to the decrease in the material temperature difference. The heat transfer and ablation processes of pulse 1 and pulse separation make the nozzle insert exhibit small heat sink, high surface temperature and large surface roughness, which would result in higher throat erosion rate when pulse 2 operates.
The thermal response simulation model and method of ablation thermal protection system were studied. Charred layer-pyrolysis surface-original material layer model was applied to establish physical and mathematical model of thermal response and the axis-symmetrical thermal response of thermal protection system of spacecraft was computed by finite element method. The calculational formulas of pyrolysis gas mass flux and mechanism of heat transfer during ablation course were studied and analyzed deeply. Convection heat transfer between pyrolysis gas and charred layer was treated as heat source and it could speed up convergence of temperature field calculation by keeping the conductance matrix and capacitance matrix positive definite symmetric. The calculation results demonstrate that the mass flow of prolysis gas in the direction of thickness is over 80%, and side direction part is very small. The ablation scale is approximately 10 mm, so the carton-carton material with good anti-ablation performance must be used in the tip of target; the ablation scale of body is less than 2 mm, so the carton-phenolic aldehyde of small density can be used in thermal protection system of body.
Tow-dimensional steady and unsteady numerical simulation was predicted by commercial softwave NUMECA when the stagger angle of cascade was abnormal. The main aim is to investigate cascade passage block resulting from abnormal stagger angle affecting the flow field and unsteady aerodynamic force of the blade and the adjacent cascade passage. The results show that it has an effect on the cascade field passage along the suction side when abnormal stagger angle is positive. With the increase of abnormal stagger angle, the flow is more deteriorated and the large scale of boundary layer separation is generated. The main frequency of vortex shedding decreases with the increase of abnormal stagger angle; but the secondary frequency of vortex shedding increases with the increase of abnormal stagger angle. And relative fluctuation quantity of unsteady aerodynamic force increases rapidly arising from the changing angle; accounting for the blade fatigue breakdown.
To research abnormal phenomenon of thrust reduction of a range rocket nozzle was chosen to study, nozzle with the same inlet pressure and different environment pressures were simulated numerically by applying the AUSM+ (advection upstream splitting method)scheme, SST(shear-stress transport) turbulence model and LU-SGS(lower-upper symmetric Gauss-Seidel)implicit algorithm were used to solve 2-D axial symmetry RANS(Reynolds-averaged Navier-Stokes) equations. The differences in thrust characteristics were obtained when the environment pressure varied from 50.67 kPa to 101.32 kPa, and the cause of these differences was analyzed. Results indicate that static thrust of the outer nozzle exit boundary rises toward the negative direction when the environment pressure gradually decreases, absolute value increases firstly and then decreases. Dynamic thrust and total thrust of the outer nozzle exit boundary slightly changes at the environment pressure ranging from 60. 80 kPa to 101.32 kPa, but dynamic thrust and total thrust of the outer nozzle declines sharply when the environment pressure is less than 60.80 kPa.
The abnormity of the axial-symmetric boundary in simulation of shock-induced combustion was discussed. Practice has shown that the abnormity (distortion of combustion front) may appear near the axis when the velocity was below the detonative speed. Four key factors, such as the solution method of the boundary, numerical scheme, chemical reaction model and mesh were analyzed. It is shown that all factors can cause the abnormity, but the numerical scheme should be the most fundamental one. The abnormity may be similar to the 'carbuncle' problem. Some reasonable measures are proposed, and numerical results show the availability of these proposals.
The damage evolution of blade coating in the erosion process was studied. Firstly, the flow field was measured; secondly, the erosion process of single solid particles was simulated to propose the concept Effective erosion region, allowing to simulate numerically the erosion process of multiple solid particles. Next, the erosion resistance performance of coating materials in the Effective erosion region was simulated. The results show the weak coating region and provide life prediction by simulating the erosion process of blade coating with the flow field data and erosion resistance performance parameters.
Given the complicated traditional abrasion computing process, the opposite direction to model the abrasion loss of the metering valve was studied. Three ways to compute the abrasion loss were found. The result of some model of the aero-engine fuel control unit's metering valve test data shows that, the model of the differential equation of first order based on the time series can accurately calculate the abrasion loss of the metering valve, with the relative error less than 5%. This had the practical meanings to the life prediction of abrasion in the fuel control unit metering valve, providing a basis for the useful life of the fuel control unit.
Mistuned integral bladed disk assemblies, including the mode, the vibration transmission localization and the localization factors, were elaborated. Besides, the modeling and solving methods of mistuned bladed disk assemblies were discussed. The mainly related hot topics, the latest research methods and their achievements in recent 10years, were reviewed and investigated in detail, including: nonlinearity, flutter, sensitivity, pneumatic and structure coupling, mistuning identification and prediction, mistuning optimization, intentionally mistuning, multi-stage and multi-component disks coupling, Coriolis forces, reliability and robustness etc. Finally, potential topics for future research work were proposed, for instance, building a more effective and applicative model with higher precision, verifying theoretical simulation with the test method, impact on multi-stage and multi-component integral bladed disk assemblies of pneumatic and structure coupling as well as the shroud tip and friction coupling, the principle of Coriolis forces, insensitivity and robustness to the mistuning of bladed disk assemblies and so on.
The characteristic atomic group of turbofan engine components was classified and exploited to the K-SVD(K-singular value decomposition) based on the sparse characteristics of gas path abrupt fault signals, then an improved K-SVD dictionary training algorithm was proposed and used for abrupt fault diagnosis. The compared results with EKF(extended Kalman filter) and UKF (unscented Kalman filter) showed that the improved K-SVD method was accurate for fault location, and the change of health parameters of no fault components was 0, which can improve the identification of fault components effectively and avoid misdiagnosis; the calculation time was basically the same as EKF method; under similar accuracy, the time consumption of this method was only 0.3% of UKF method, which can be adapted for engine gas path parameter tracking and abrupt faults diagnosis. © 2020, Editorial Department of Journal of Aerospace Power. All right reserved.
The problem of suppression of supersonic flutter of laminated composite panel using dynamic absorber device was investigated. The interaction forces between the panel and the dynamic absorber device were expressed as the functions of relative displacement and velocity of the panel and the absorber. Based on the von-Karman nonlinear deflection panel theory and the 3rd-order nonlinear piston theory, the equations of motion of the panel and the absorber were established according to the Hamilton principle and the Newton second law of motion. Then the assumed modal method was adopted in the discrete procedure, and the numerical simulation was conducted. The coordinate of the absorber was optimized. The simulation results indicate that the critical flutter dynamic pressure can be enhanced by 51.7% under certain parameters of the absorber, and the amplitude of the limit cycle oscillation can also be suppressed.
A kind of freely assembled dry friction vibration absorber was presented to solve the problems of instability and rubbing faults for a super-high speed rotor system based on theory of dry friction dissipating energy from rotor vibration. In this structure, a wave-shaped elastic pad and some dry friction pads were freely assembled on shaft, and axial normal force was provided for elastic pad and dry friction pads by pre-loaded moment for nut. When friction pads moved with shaft, the relative movements between them could dissipate vibration energy from rotor system, absorb vibration and enhance system stability. The configuration format meeting the stability in engineering for the damper of the studied rotor system has been acquired by testing different groups of dry friction pads and pre-loaded moment. The results show that dry friction damper is suitable for high speed and light loaded rotor system to restrain vibration and enhance its stability. The testing routine is helpful to find a comfortable configuration format in engineering of dry friction damper.
The application of ring dynamic vibration absorber in vibration control of rotor was studied by experiment. A kind of separable ring dynamic vibration absorber placed on bearing was designed based on single disc rotor model and vibration characteristics. Vibration absorber can be installed on optional position between two bearings without changing any support structure and affecting dynamic performance of rotor. The rotor experiment rig of vibration reduction with vibration absorber was built to measure the vibration with critical speed of rotor. The results show that vibration absorber can decrease vibration greatly, and the vibration amplitude is dropped by 70% at critical speed of rotor. The frequency range of vibration reduction can be broadened and the natural frequency of vibration absorber can be adjusted accurately by increasing the mass of vibration absorber. The relationship between vibration reduction effect and installation position of vibration absorber was studied by experiment. The results show that position of large amplitude is better than other area. The vibration reduction effect with different numbers of vibration absorbers was compared under rotor imbalance vibration, and the result indicates that the effect of two vibration absorbers is better than that of one.
The parameters of the dynamic vibration absorber used to suppress the excessive vibration of the rotor system were designed to optimize the vibration suppression. The dynamic equation of the dynamic vibration absorber-rotor coupling system was established by using the finite element method, and the response expression of the half-numerical half-resolution of the coupled system was obtained. The design optimization strategy was used to find the best design variable of the dynamic vibration absorber by combining the coordinate solution of the response solution and the bounded boundary. The sensitivity of the dynamic vibration absorber to the optimal deviation of different parameters was analyzed by comparing with the existing optimal design method of dynamic vibration absorber. The results show that the optimized the dynamic vibration absorber can reduce the amplitude of first order resonance by 45.4%, which shows the effectiveness of the method; this method is 11.2% and 9% higher than that of two effective conventional optimization methods, which can optimize the optimization effect of the dynamic vibration absorber; compared with the damped optimal deviation, the vibration suppression performance of the dynamic optimized vibration absorber has a higher sensitivity the optimal deviation of stiffness. © 2018, Editorial Department of Journal of Aerospace Power. All right reserved.
By numerical simulation of the heat transfer among nanoparticles, microencapsulated phase change material(MPCM) and liquid, the factors such as nanoparticle amount, diameter and thermal conductivity, which affect the MPCM-liquid heat transfer Nusselt number, were analyzed. When MPCM absorbed nanoparticles, the effect of the increase of the MPCM-liquid heat transfer coefficient on the phase change period was also studied numerically, providing a theoretical basis for the mechanism of enhancing the heat transfer with nanoparticle.
The numerical analysis is a very important work in the process of design on how composites resist the damage from bird impact. The paper analyzed and tested numerically the initial damage, stress and strain of every layer of laminates from bird impact using instantaneous non-linear FEM. It also analyzed how the changes of ply stacking sequence, parameter of laminates and birds affect the absorbing energy of laminates. The results of this paper provide a basis for further research on composite structures resisting bird impact.
For large aperture perforation plate, reducing acoustic mass is a way to realize broadband sound absorption. Meanwhile, the acoustic resistance can be enlarged due to the grazing flow effect as well as the reduction of the acoustic mass. Based on above results, the designing principle was proposed for the parameters of the perforation plate. Besides this, the perforated plate muffler experiment was also conducted. The experimental results show that broadband sound absorption can be achieved for large aperture perforation plate with low acoustic mass in the presence of grazing flow when compared with that of perforated lining without grazing flow. Such perforation plate can be applied to the noise reduction of the aircraft engine nacelle, inlet and exhaust pipe of motor engine, and all kinds of ventilation pipe with large air flow.
Top-cited authors
Jingzhou Zhang
  • Nanjing University of Aeronautics & Astronautics
Guoqiang Xu
  • Beihang University (BUAA)
Yuzhen Lin
  • Beihang University (BUAA)
Shuiting Ding
  • Beihang University (BUAA)
Yong Shan
  • Nanjing University of Aeronautics & Astronautics