Shiyan Liuti Lixue/Journal of Experiments in Fluid Mechanics

The 0.6m continuous transonic wind tunnel of CARDC, a circling wind tunnel, use dry air in variable density as working medium. The major components of the wind tunnel include broad-performance compressor, semi-flexible nozzle,lower-noise test section, re-entry flaps and slots, heat-exchange system and the second throat with wall flaps and center body. In order to get the general performance and the secure running boundary of the wind tunnel, the general performance calibration is carried out. Calibration results indicate that the general performances and each section of the wind tunnel agree well with the requirements. The compressor, heat-exchange system and other auxiliary equipments are all in working order. The range of total pressure in settling chamber is 15~250kPa and the control precision of the total pressure is better than 0.2%. The Mach number in the test section is in the range of 0.144~1.640 and the control precision of the Mach number is better than 0.002. The flow qualities such as the fluctuation of Mach number distribution have met the requirements(Ma≤1.0,σ Ma <0.002; 1.0<Ma≤1.6,σ Ma <0.008). When the Mach number is greater than 0.5, the flow fluctuation coefficient which is used to represent the noise level is below 0.8%. The design scheme's feasibility of the 0.6m continuous transonic wind tunnel is fully verified by the debugging results, which provide scientific guidance for the development of the large-scale continuous transonic wind tunnel. © 2018, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

In the wind tunnel tests, the method of decreasing stagnation pressure is usually adopted to expand the simulation scope of Reynolds number. Compared with the normal pressure test, in the low Reynolds number situation, the accuracy of the test data is directly affected by whether or not the change of the flow field is obviously and whether or not the quality of the flow field satisfies the index. In order to study the influence of Reynolds number on the 0.6m continuous wind tunnel performance, the relevant tests were carried out in the 0.6m continuous wind tunnel. Based on arrangement and analysis of the tests data, the results were given. It shows that: (1) The Reynolds number has obvious effect on the performance of the compressor, stagnation pressure control precision, Mach number control precision, the flow uniformity etc. When Rec<10⁵(c=0.1A½, A is the cross-sectional area of the test section), the effect of Reynolds number on the performance of wind tunnel is obvious. The smaller the Reynolds number is, the greater the effect is. (2) The 0.6m continuous wind tunnel can accuratly manifest the influence law of the effects of Reynolds number on the flow field performance of the wind tunnel and the force test data. Therefore, it is a good test platform for the capability research on aircraft, airfoil, engine, etc., at low Reynolds number. © 2017, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

For improving the measuring abilities of the weapons interference and separation testing in the 1.2 meter transonic wind tunnel and satisfying the customers' requirements constantly, a new six-degrees of freedom captive trajectory simulation (CTS) system has been designed in China Aerodynamics Research and Development Center (CARDC). This paper introduces the new CTS systems' construction design and realized technology targets as well as applications. The wind tunnel results show that the new CTS system has several improvements over the old CTS system in many aspects such as increased the movement ranges, productivity and the testing efficiency, and the range of testing Mach numbers.

In order to explore the phase split mechanism of two-phase flow at T-junction, a T-junction on a 180°return bend was employed to provide additional forces, such as centrifugal, gravitational and/or buoyant forces when two-phase mixture flows passing through it. The factors, such as the resultant force at the branch direction, inlet momentums of the two phases, and inlet flow patterns at the phase separation were investigated experimentally. Using air and water as two working fluids, the inlet flow patterns for the two-phase flows were set as bubble and annular flows, respectively, and the inlet tube for the bend was placed vertically upward or downward. The phase split data were measured under varying the inlet flow pattern and gas and/or liquid velocities and the flow pattern transition around the bend and at the T-junction was carefully examined. The results show that under the condition of vertically upward inlet tube and the bubble flow pattern, the gas is mainly subjected to buoyant force and the liquid to gravitational force. Thus gas takes off preferentially under the condition of the branch. Increasing gas or liquid velocity is harmful to the gas take-off. Whereas at vertically upward inlet tube and annular flow, the liquid is mainly subjected to centrifugal force, and thus the liquid preferentially takes off from the branch. Increasing gas or liquid velocity is beneficial to the liquid take-off. In the case of vertically downward annular flow, liquid is mainly subjected to downward centrifugal and gravitational forces, thus liquid preferentially takes off from the branch. Increasing gas or liquid velocity is harmful to the liquid take-off since the bubbles entrained in the liquid flow in the branch are increased and the liquid drops generated by the gas core at the bend are also increased. That which phase preferentially takes off depends mainly upon the resultant force at the branch direction. The phase split phenomena can be explained by analyzing the resultant forces, the flow pattern, and the momentums of the two phases at the T-junction. ©, 2015, Zhongguo Kongqi Dongli Yanjiu yu Fazhan Zhongxin. All right reserved.

The flow field in the 180° curved duct with the rectangular section was measured by Laser Doppler Velocimetry (LDV).The mean velocity and the turbulent intensity of the flow field were investigated. At the radial location, except for the r*=0.1 location, the tangential velocity changed a little along the Z direction, and the tangential velocity decreased gradually until zero near the upper wall. The tangential velocity increased between 0° and 60°, while the tangential velocity decreased between 60° and 180° near the inner wall. On the contrary, the tangential velocity decreased between 0° and 60°, but the tangential velocity increased between 60° and 180° near the outer wall. In the 180° curved duct, the tangential velocity near the inner wall was larger than the tangential velocity near the outer wall. At the r*=0.1 location of 90°~180° longitudinal section, the tangential velocity had obvious fluctuation due to the boundary layer and secondary flow. The axial velocity was much less than the tangential velocity, and had a little change along the Z direction. The axial velocity showed significant positive and negative values, which indicated the existence of the secondary flow, and the center of secondary flow moved from the outer wall to the inner wall. The tangential intensity and axial turbulent intensity were about 0.1Vi with the same order of magnitude. The tangential turbulent intensity had an obvious fluctuation at the r*=0.1 location between 150° and 180°. But the axial turbulent intensity changed a little along the axial and radial direction.

The Φ2.0 m high energy pulsed tunnel (FD-21) of CAAA is a free piston shock tunnel, which expands the test capability of CAAA. This paper mainly introduces the develop-ment process and key technologies of the FD-21 tunnel. Many key aerodynamic problems are settled independently. And the aerodynamic design is completed by the reverse design method. Based on these efforts, the engineering technical difficulties such as piston launch, piston stop, full floating support have been gradually overcome during the construction of the FD-21 tunnel. The successful development of the FD-21 tunnel marks the mastery of the free piston driving techno-logy, reduces the gap between China and some foreign countries, and improves the hypersonic research level in China greatly. Copyright ©2022 Journal of Experiments in Fluid Mechanics. All rights reserved.

The thrust vectoring control (TVC) technology enables aircraft to fly in post-stall maneuver, which is very important for breaking through obstacle stall, enhancing mobility and improving take-off/landing and cruise performance. For TVC test at 2.4m×2.4m transonic wind tunnel, three six-component strain-gauge balances and two separate air systems are applied to respectively measure the performance of the whole model and nozzles at the same time. The thrust vector test model is flat, so that the layout and structure design of the measurement system is constrained. In the small internal model, it is very difficult to set up three six-component balances, two separate air bridge systems and pipeline, a supporting system, a pressure measurement system and so on. The complex system design cannot be realized by traditional methods and neither can the matching design of the air bridge system and the force balance under the condition of high pressure be accomplished. In the development of the measurement system, the integrated design concept and the stiffness matching design method are adopted. Combined with ANSYS finite element software, the layout and structure optimization of each component of the system have been solved. The results of balance calibration and wind tunnel test prove that the measurement system meets the requirement of thrust vector test. © 2017, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

Two-hundred meter free flight ballistic range is the only one comprehensive ballistic range equipment in China that can carry out aerodynamics test, aero physics test, erosion and hypervelocity impact. In order to meet the demand of the hypervelocity aero craft development, the equipment has been upgraded since 2009. The upgraded equipment includes launch system, the chamber and vacuum system, velocity measurement and control system, photogram and orientation system. The launch system will be equipped with 203 mm and 120 mm bore two-stage light-gas guns. The weight of the model that the launchers can launch are from 0.5 kg to 30 kg, and the model velocity is from 0.3 km/s to 5 km/s. The diameter of the tank will be increased from 1.5 m to 3 m. At the same time, The range will equipped with new vacuum system, which can realize the simulation of altitude from 0 km to 80 km. Velocity measurement and control system will meet the big model measured requirement. Except shadow and schlieren equipment, the position system of double eyes front light imaging, X-ray imaging and measurement system will be constructed. After upgrading, from small to big bore two-stage light-gas guns will be equipped in the launcher system of 200 m free-flight ballistic range, and the test abilities of the range will be improved in aero-dynamic test, erosion, high and hypervelocity impact test.

In order to obtain the changes of model poses flying at hypervelocity accurately on the free flight ballistic range which was used for identifying the aerodynamic parameters, China Aerodynamics Research and Development Center (CARDC) developed the vision measurement technology of model poses, which combined the mature technologies of the binocular vision location and the front light photo. The binocular measurement stations were installed along the flying direction of model, which would be calibrated and correlated to the same base coordinate before model test. When the model with coded feature points on its surface entered the measurement field, it would be illuminated by the extended laser light beam with the pulse width of smaller than 10ns, meanwhile, the two front light images were obtained by the cameras of the binocular measurement station, then the model poses were obtained by identifying and calculating the coded feature points on its surface. Based on solving the key technologies of filtering the parasitic light in the chamber, homogenizing the exit facular of the front light source, correlating binocular measurement stations to the same base coordinate, dealing the model surface color and fabricating feature points, the vision measurement system of poses with high accuracy on the 200m free flight ballistic range was accomplished. The test on the 20° cone with the length of 165 mm was carried out on the ballistic range, which flew in the chamber with the pressure of 15kPa at the velocity of about 2.7km/s. According to the cone poses at different binocular measurement stations and the sequence time of lasers flashing obtained by the vision measurement system, the drag index and the dynamic derivative of the cone were obtained by identifying, the trends of which were basically in consistency with those of the AEDC G range. © 2018, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

As an important means of field testing, conventional two dimensional Particle Image Velocimetry (2D-PIV) has been widely applied to various flow measurements. Measurement error arises when 2D-PIV is applied to measure the cross section perpendicular to the flow due to geometric perspective relations. The error factors are analyzed and a model of the error in the measurement plane is established. The correctness of the error model is verified by experimental tests. It is concluded that the normal speed and off-axis angle of view are the key influencing factors. The calculation results show that the maximum perspective error can be up to 9.3% of normal speed. According to the analysis of error model, the effect of perspective error on measurement of streamwise vortex flow field mainly exhibits in three aspects: changing the velocity value of flow field, changing the shape of vortex, and changing the position of the vortex. Finally, some approaches to reduce the error are proposed, which can improve the measurement for the application of 2D-PIV in the cross section perpendicular to the flow. ©, 2014, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

The detail motions of vortices in a 2D scaled motor of SRM were studied by high speed visualization in this paper. The experimental data indicate that the flow start to separate right after the backward-facing step, which gives birth to periodically-shedding vortices. The scale of vortex increases with their convection downstream along the mean flow. Vortex breaks down due to its impingement on the submerged nozzle head, part of which exits in the motor directly through the nozzle throat while the other part flows into the cavity formed by submerged nozzle. Few of the vortices flow directly into the submerged nozzle cavity without impinging on the submerged nozzle head. The results obtained in this paper could improve the understanding of the flow in SRM and provide experimental validation for numerical simulation.

We develop a tunable diode laser absorption tomography algorithm for two-dimensional (2D) temperature reconstruction based on orthogonal optical paths. In order to evaluate the reconstruction method, we analyzed the 2D reconstruction results of two different temperature phantoms by means of numerical simulation of N×N uniform grid arrangement consisting of 2N (N≥3) light of sight (LOS) measurement path. The maximum deviation and the mean deviation were defined to describe the effect of the value of N on the reconstruction results. The results show that for the single symmetrical peak non-uniform temperature phantom, the maximum deviation of the reconstruction temperature is less than 50K(2.5%), the maximum deviation fluctuates with N parity and the overall trend is decrease with N increasing. The mean deviation is reduced as N increases, which means the reconstruction is better with N increasing. But when N≥9, the improvements are not distinct any more. For the bimodal temperature phantom, the maximum deviations of the results using this 2D reconstruction method are more than 350K(15.2%) and the mean deviations are greater than 0.03. What's worse, there is a serious distortion. However, the reconstruction results can be improved by added measurement path diagonally across the tested temperature field. The study is helpful for the real 2D measurement system setup and actual application.

The real time network is constructed by embedded RT controller and reflective shared-memory technique in measurement system of 2m×2m supersonic wind tunnel, and data acquisition devices of National Instruments Co. (NI) are adopted to acquire signals of balances and sensors pressure measurement through PSI 8400 DTC system. Operation management system implements operation, control and status surveillance of wind tunnel test, including software of operation system and status surveillance which are programmed through LabVIEW 8.6.1. The research contents, technique specifications, development scheme and the key technique issues and solutions are introduced in this paper. The system has characteristics of good performance, advanced technology, friendly operation interface and convenient maintenance.

The cloud calibration has been carried out under SAE ARP5905 standard for 3m×2m icing wind tunnel, results of which can be used for certificating icing wind tunnel performance and supplying data proof for obtaining icing flight certification. Based on the ice accretion mechanism, the phase doppler interference principle, and the hot-wire principle, the calibration work was completed in the main test section by using the icing grid, PDI-FPDR, the icing blade, and LWC-200. Methods and procedures are summarized to increase the efficiency of calibration. Typical cloud calibration results indicate that the icing cloud uniformity is good, 60% of the main test section could remain target LWC within ±20%. The MVD maximum deviation is smaller than ±10%. The LWC stability is greater than ±20%. All the cloud parameters could meet the requirements of ARP5905, which could be used for supplying data proof of 3m×2m icing wind tunnel certification © 2018, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

Additive manufacturing technology can be processed in any complex shape parts. The short manufacturing cycle and low cost are its unique advantages compared to the traditional machining, and thus it has wide application prospects in the wind tunnel test model manufacture. In view of the material 30CrMnSiA commonly used in the high speed wind tunnel model processing, the metal powder preparation, detection and material specimen manufacture are studied. On this basis, with test piece data as a yardstick for material performance, an AgardB model with hollow airfoil is designed based on the additive manufacturing process. Moreover, fluid-structure interaction analysis is conducted for the model using Ansys and the optimal design is carried out. The results indicate that the model structure can meet the requirement of high-speed wind tunnel testing. © 2017, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

The strain gauge balance is the main equipment used in wind tunnel test, which has an important influence on the quality of test data and operational efficiency. To improve the balance self-protection performance and lower balance failure rate in test operations, a quick development method based on three-dimensional (3D) printing for the wind tunnel strain gauge balance (SGB) protective device is proposed. By decomposing the design factors, the key factors pertaining to the design of balance protective device are studied. A design flow and method based on 3D printing is put forward. The 3D printing technology can be applied to the optimization of balance guards in two aspects: (1) to optimize and visualize design schemes; (2) to protect strain gauges and circuit on balances for wind tunnel tests. Both water-cooled balance protective device and assembly type mechanical protective device are designed. For the water-cooled device with complex internal structure, 3D printing technology makes design to be visualized, which is helpful for design verification before manufacturing. The assembly type product, manufactured by means of 3D printing technology, is applied in corresponding balance protection for wind tunnel force measurement test. The perfect combination of strain gauge balances with their highly customized, lightweight balance protective devices by 3D printing, serves not only to protect the strain gauges and wires from damages in the process of calibration, transportation, model assembly and testing, but also to make impressive visual artworks of the balances, rendering them functional, practical, economical and artistic. Compared with machining of a balance protective device in the traditional way, 3D printing can greatly reduce the processing cycle and the cost. Meanwhile design visualization can validate technical solutions in the design stage. Both applications promote the overall performance of the balance. © 2017, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

A 25 kHz picosecond pulsed digital off-axis holography system is applied to measure the near-nozzle atomization characteristics of an airblast swirl atomizer under low oil temperature conditions. Experiments are carried out for the near-nozzle atomization process 30 mm down-stream from the nozzle exit under air pressure of 1 kPa and oil pressure of 0.03 MPa. The oil temperature varies from -40 ℃ to 28 ℃. It is found that the atomization field in the near-nozzle region contains non-spherical droplets. Typical dynamic processes of atomization such as the breakup of films and filaments are visualized with clear images. The sizes and three-dimensional(3D) positions of droplets ranging from 30 to 1500 μm are obtained through particle identifica-tion and locating, thereafter statistics on 3D distribution of Sauter Mean Diameters(SMD) is obtained. It is found that under conditions of oil pressure of 0.03 MPa and air pressure of 1 kPa, the droplet diameter is mainly distributed within 200 μm, and droplets with size range 30-40 μm account for the largest proportion, above 15%. The 3D droplet size distribution is expressed as a cone where the central droplet size is larger than that on the edge; the decrease of oil temperature significantly deteriorates the atomization effect, which reduces the volume of the spray cone, and the density and the uniformity of atomized droplets; With oil temperature decreasing from 28 ℃ to -20 ℃, the central droplet diameter of the downstream cross-section increases from about 300 μm to over 450 μm and can be locally larger than 650 μm; with the oil temperature of -40 ℃, a large liquid core with multi-branched liquid films and filaments appears downstream of the nozzle, resulting in a longer breakup distance. The experimental results also demonstrate that the high-speed digital off-axis holography is a powerful tool for three-dimensional visualization and diagnostics of near-nozzle atomization under low oil temperatures conditions. This work can provide reference data for optimization of the nozzle structure design and the demonstration of the atomization model. Copyright ©2022 Journal of Experiments in Fluid Mechanics. All rights reserved.

This paper introduces the principle of the LIF technique to measure the water concentration, temperature and velocity fields,summarizes the LIF technology development from 1D to 3D, reviews the key issues of LIF to measure the scalar field in water, including laser and light-sheet sources, fluorescence material selections and calibration methods, and finally reviews various correction methods of PLIF and 3DLIF. Based on the 3DLIF techniques, this paper proposes an overall technical scheme, technical route and overall technical indicators of 3DLIF instrument, and then provides solutions of 3DLIF key techniques to meet the demand of engineering and industrialization. © 2017, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

This paper describes recent applications of particle image velocimetry(PIV) in Mach 4.0 flows in MMH(Multi-Mach number High-speed) intermittent wind tunnel of SJTU. To achieve this challenging progress in supersonic flow regime, appropriate seeding particles were selected and seeding dispersion of tracer particles was carefully developed to meet the requirements of high-speed and short-duration flow. In this paper, the measured velocity flowfield at Ma=4.0 was firstly discussed. The results showed that the flowfield at the nozzle exit was parallel to the nozzle axis and homogeneous as expected from supersonic nozzle theory. A ramp was further introduced into Mach 4.0 flow to study the typical shock wave flowfield with large velocity gradient and seed particle performance across an oblique shock. The PIV measured results were also in good agreement with calculated velocities from oblique shock theory. The flowfield over a corner was tested and the PIV results showed that the complex flow structures were clearly visible as schileren. Therefore, PIV has proved to be an effective technique for supersonic flow as well as for subsonic flow regimes.

The bridge aerodynamic stability research is an urgent topic since bridge construction has entered into a new era of crossing wider sea straits. In this paper, a trial design of a 5000 m suspension bridge with narrow and wide slotted steel boxes is conducted; then sectional model wind tunnel test is carried out as the first case of 5000 m suspension bridge, identifying the flutter derivatives, flutter frequencies and three dynamic coefficients. Also the influence of various combination of additional stabilizers on vibration control of the narrow slotted girder are checked, finding out that the horizontal stabilizer above the narrow slotted girder can increase the critical flutter speed by 50%. Finally the Straight-forward Method for analysis of two dimensional flutter of super long span suspension bridge is proposed to check the wind tunnel results and research shows the compatibility of wind tunnel test and Straight-forward Method. Total conclusions can be drawn that both the wide slotted girder and narrow slotted girder with additional stabilizers can be feasible solutions for 5000 m suspension bridge located in most of the typhoon prone areas around the world form the point of aerodynamic.

Three dimensional aerodynamic stability performances of super long span suspension bridge with a main span of 5000 m is studied by the following steps: Firstly, full mode flutter analysis method of super long span suspension bridge is developed by taking into account of the following effects, such as lateral, vertical and torsional self-excited forces and static wind loads. Then, numerical investigation is carried out using the previously described method to study the three dimensional flutter performances, and results from two dimensional and three dimensional approaches are compared in order to demonstrate their compatibility. Thereafter, three dimensions and three nonlinearities aerostatic stability analysis method are utilized to inspect the aerostatic stability of super long span suspension bridge, showing that 5000 m suspension bridge is controlled by aerodynamic stability problems. Total conclusions can be drawn that both the wide slotted girder and narrow slotted girder with additional stabilizers can be feasible solutions for 5000 m suspension bridge, which located in most of the typhoon prone areas around the world.

A historical review has been presented for the 50th anniversary of laser Doppler velocimetry. Main successes developed in this period are pointed out in memory with the important contributions from a number of scientists and engineers. It is noticed that the new age has already been opened up for the complex turbulent flow research with the accurate, quantitative and dynamical measurements. ©, 2014, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

The free to roll test, static force balance test and dynamic derivative test of 80°/65° double delta wing at high angle of attack are conducted in FL-23 high speed wind tunnel, which dynamic behaviors are forecast based on the static roll moment coefficients and dynamic derivative. The results show that dynamic motions obtained on a double delta wing was free to rotate about its longitudinal axis at different angles of attack. Different dynamic rolling motions including the static stability, double periodic oscillation, quasi-limit-cycle rock motion were observed. The forecast results meet the free to roll result well.

Through the established re-circulation water channel, the inner flow field in 90° bending duct of circular-section with a fore-end valve was measured by particle image velocimetry. Massive high-resolution data of transient flow field were obtained at different observation sections under diverse velocities. The transient and time-averaged flow fields after adaptive correlation calculation were analyzed. The POD modes were obtained after proper orthogonal decomposition of the flow fields, and the structural properties of vortex were further analyzed through the reconstruction of fluctuation field. Conclusions are drawn out that there exists Kármán vortex street in the bend after the butterfly valve, the vortex information is included in low proper orthogonal decomposition modes, and the flow properties of vortex can be restored through the reconstruction of fluctuation field.

The supersonic turbulent plate ablation test technology is an important method in arc-heater to study the ablation characteristic of thermal protection materials. In order to study the change of the flow field during the supersonic turbulence plate ablation, a numerical simulation method based on N-S equation is adopted. The simulation results of the initial model surface parameters are in good agreement with the experimental results. Then,the flow field simulation about the model contour is carried out in the experimental process, which is compared with the experimental flow field. The changes of surface pressure and heat flux on the model are analyzed. According to the analysis, if the maximum ablation position is in the high heat flux region of the initial model, the ablation rate can be calculated by using the maximum ablation amount. © 2018, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

The aerodynamic heat load on the surface of the non-ablative thermal protection materials which served in the chemical non-equilibrium flow field, is controlled by the coupling of chemical non-equilibrium degree of flow field and the surface catalytic reaction of the materials. If the coupled effect is neglected in the performance simulation, the effective service performance cannot be obtained through the ground simulation test. Therefore, according to the stagnation-point heat flux relationship within the boundary layer of the blunt body supersonic vehicle, the present paper analyzes the principal flow field parameters, the characteristics of high-enthalpy supersonic field provided by ground simulation equipment, and the differences between ground and flight environments. The validity of the Three-Parameter-Simulation method is analyzed by the CFD simulation. A Four-Parameter-Simulation method is presented for analyzing the heat transfer of the chemical non-equilibrium stagnation-point boundary layer. Besides, the properties of the thermal protection materials is analyzed and a preliminary solution is proposed when the dissociation enthalpy in the Four-Parameter-Simulation is unable to be simulated. © 2018, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

The test results of non-ablative ultra-high temperature ceramic materials (UHTC) in one of the plasma wind tunnels of CARDC are introduced in this paper. Three types of materials, namely model C(15, 10), Y and S(30, 15, 10), were tested under a subsonic condition with stagnation point heat flux of 478 W/cm2, enthalpy of 27.9 MJ/kg and stagnation point pressure of 18 kPa. The test models were in flat cylinder shape with a diameter of 20 mm. The length variation and mass loss and surface temperature of each test model were measured. Test results showed that model Y surface temperature reached 1930°C with little surface characteristics change, model S surface temperature reached 1964°C with an oxidation layer formed and model C surface temperature reached 2462°C yet experienced severe ablation. Preliminary analyses of the tested materials in terms of surface characteristics change, anti-oxidation characteristics and surface radiation characteristics are also presented.

Abnormal combustion phenomena like knock or super-knock are inherent constraint limiting the performance and efficiency of downsized spark ignition (SI) engines. Essentially, engine knock or super-knock is always accompanied by the interactions of turbulent flames and shock waves, as well as rapid chemical energy release. Thus, it is of great significance to investigate the interactions of turbulent flame and shock waves which are the key to reveal the mechanism of knock and super-knock. The major objective of the present work is to experimentally investigate the process of flame acceleration, shock wave formation and interactions of turbulent flame and shock wave in a newly designed constant volume combustion bomb (CVCB) mounted with a perforated plate. In the CVCB, the perforated plate is used to achieve flame acceleration and produce turbulent flame and shock wave. High-speed Schlieren photography was employed to capture the interactions of turbulent flame and shock wave. Hydrogen-air mixture was chosen as the test fuel due to its fast flame propagation velocity and easiness to form obvious shock wave ahead of the flame front. Interactions of turbulent flame and shock wave at different levels could be obtained by changing the initial thermodynamic conditions (including initial pressure and equivalence ratio) and parameters of the perforated plate (including hole size and porosity). Flame acceleration, formation of shock wave and flame-shock wave interactions are discussed in this paper. Depending on the interactions of turbulent flame and shock wave, five combustion modes are obtained by experiments, such as normal combustion, periodically decelerating combustion, oscillating combustion, flame-front autoiginiton and end-gas autoiginiton. The maximum amplitude of the pressure oscillation at combustion models with autoiginiton exceeded 4.5MPa, 4~40 times greater than those without ignition. Therefore, autoiginiton caused by the interactions of turbulent flame and shock wave is the root cause of the intense pressure oscillation in the combustion chamber © 2018, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

In order to breach the resistance wall phenomenon encountered by traditional amphibious vehicle, this paper puts forward a new technique of propulsion by studying the treading water mechanism of a basilisk lizard and the theory of solid-liquid mutual action on high speed. It can lift amphibious vehicle upon the water into the high speed sliding status depending on the upward lift force produced by the high speed action between the bionic impeller and the water thus obtaining a high speed and avoiding the resistance wall phenomenon. Through simulation analysis and theory experiments in advance, it is validated to be an efficient technique which can make the amphibious vehicle into the high speed sliding status, reduce the water resistance and increase the velocity on water.

Gas temperature and species number density are the key parameters to quantitatively assess the arc-heated wind tunnel operation and flow quality. Conventional techniques meet great challenge in high enthalpy flow diagnostics for arc-heated facilities under prolonged operation at high temperatures. Based on the local thermodynamic equilibrium plasma assumption, this paper presents in-situ diagnostics for the dissociated air (>5000K) in the arc heater by using laser absorption spectroscopy of atomic oxygen at the wavelength of 777.19nm. The gas temperature and the number density of atomic oxygen are measured under two operation conditions of H0=15.8MJ/kg and 17.4MJ/kg, respectively. The average temperatures are 5843K and 6047K, corresponding to 5950K and 6335K from charts for high temperature equilibrium flow properties of air. The number density of atomic oxygen is within (1.1~1.2)×10¹⁸cm⁻³ and is in consistency with the calculation via NASA-CEA program, while the number density of atomic oxygen (⁵S2⁰) is within (1.0~1.5)×10¹⁰cm⁻³. This work demonstrates that the laser absorption spectroscopy is applicable for high enthalpy flow diagnostics in the arc-heated wind tunnel as a new technique. © 2017, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

In this paper, JF-10 shock tunnel is driven by H2/O2 detonation and the free-stream contains some trace components which are generated by non-equilibrium processes such as ionization and dissociation. Tunable diode absorption spectroscopy (TDLAS) is used for temperature and concentration measurement of nitric oxide in the free-stream and this quantitative measurement is helpful to understand the non-equilibrium processes. In the experiments, the test section's static pressure of JF-10 shock tunnel is just several hPa. Thus, Doppler broadening dominates, which is caused by random thermal motion of the absorber species. The half width of Doppler broadening is temperature dependent and this functional relation provides a method for gas temperature and species concentration measurement. A mid-infrared quantum cascade laser of 5.2 μm central wavelength is used and gas temperature and nitric oxide concentration are measured using a single line of 1909.7 cm-1 wavelength by direct absorption-wavelength scanning method under 2 kHz scanning frequency. The measured partial pressure of nitric oxide is about 0.33 Pa which represents its concentration and the temperature is about 600 K in the free-stream. ©, 2015, Editorial Office of Journal of Experiments in Fluid Mechanics. All right reserved.

CO is one of the main products of hydrocarbon combustion. Accurate measurement of CO concentration at the scramjet outlet is an important basis for evaluating the combustion efficiency of the hydrocarbon fuel. Compared with the near infrared band, the CO absorption spectrum in the mid infrared band has the advantages of stronger absorption, rich spectral lines, relatively isolated spectral lines and no interference from other gases. Based on the mid infrared absorption spectrum technology, this paper studies the mid infrared spectrum characteristics of CO, selects the characteristic spectrum which is suitable for the measurement of CO in the high temperature flow field, designs and builds the CO concentration detection system in the high temperature flow field, carries out the CO measurement verification under different equivalence ratios of the plane flame, realizes the CO measurement of the high temperature flow field at the exit of a scramjet, and reflects the changes of concentration and temperature of CO during the combustion of aviation kerosene, thus providing powerful research means and abundant experimental data for the study of combustion and flow mechanism of the scramjet. © 2021, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

Tunable diode laser absorption spectroscopy (TDLAS), a line-of-sight technology, is used to measure the temperature, velocity, concentration and other parameters in the flow field. As a fast and efficient diagnostic tool, TDLAS sensors have wide applications in the development of the combustion and propulsion system. TDLAS sensors play more and more important role in the improvement of the system performance. When new concept propulsion appears, the sensors face new challenge, at the same time, relevant technology have been improved. The development of the TDLAS technique, applications in the combustion diagnosis and enormous potential have been summarized. This review can provide enlightenment and help for the researchers in this field.

ADN monopropellant green space propulsion is perceived as a focus of the space propulsion research worldwide. Experimental study is in urgent requirement for understanding the combustion process in the ADN based thruster and for quantitative evaluation and optimization of the combustion stability and the thruster performance. In this paper, experiments were conducted to measure the concentration of the key intermediate products(CO, N2O) and the temperature of the combustion gas flow based on the mid-infrared quantum cascade laser absorption spectroscopy (QCLAS). Two main ignition modes of the 1 N ADN based thruster are studied: the steady-state firing and the pulse-mode firing over the injection pressure of 0.5~1.2MPa bar with catalytic bed length of 19 mm, corresponding to a current thruster prototype. It is found in the steady-state firing experiments that the whole process can be divided into the catalytic decomposition stage and the combustion stage, and the combustion kinetics mechanism of the monopropellant is experimentally demonstrated. Experiments for the pulse-mode firing show the variance of the measured multispecies concentration and temperature in consistence with the pulse trains, verifying the good performance of the thruster pulse-mode firing operation. © 2017, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

The interactions of shock waves with density inhomogeneities are of fundamental importance in compressible turbulence. This interaction is often referred to as the Richtmyer-Meshkov (RM)instability. In the irregular refraction case, it is a more complicated vorticity distribution. We focus on the specific case of a Mach 1.23 and 1.41 shock wave irregular refraction at a Air/SF6 gaseous interface, inclined at an angle of β=60° to the plane of the shock. In these experiments, it is found that vortices formed by the incident shock-side shock-normal shock interaction. The transmitted shock culminates as a Mach stem at the lower boundary. This paper reports the results of interfacial evolution and mixing, obtained from flow visualization experiments by the shadowgraph method.

Aerodynamic characteristics of icing on different wing sections are one of the most important factors to be considered for designing anti/de-icing system. Wind tunnel routine force measure tests were carried out to obtain aerodynamic characteristics using simulation ice model on different wing sections of an airplane. Wing leading icing on different wing span sections would lead to different aerodynamic performance losses. Cruise and landing configurations were involved to study the lift, drag and pitch characteristics of the airplane. The results of the research showed that icing in the middle part of the wing lead to the greatest aerodynamic performance losses, and icing at the root and the tip of the wing leads to less aerodynamic performance losses which could be propitious to establish effective and efficient anti/de-icing system. © 2016, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

The conventional Cramér-Rao lower bounds method is too optimistic to be a good quantitative assessment of the accuracy of aerodynamic parameters identified from the wind tunnel free-flight test data, considering the colored noise in the measurement data. This paper introduces a technique, that modified covariance matrix method, to process the residuals from a conventional maximum likelihood estimation to compute the accurate Cramér-Rao lower bounds for colored residuals. The modified accuracy assessment method is validated by Monte Carlo simulation and wind tunnel tests of pointed cone models with the semi-cone angle being 10°. The identified results indicate that the Cramér-Rao lower bounds calculated by the modified covariance matrix method are 3~5 times the quantity of the conventional. The modified results can be used as an accurate and impersonal assessment of the aerodynamic parameters estimated, which are consistent with the sample standard errors for the estimated parameters for colored residuals. © 2017, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

The principle, test bench and method of the vectoring nozzle static thrust measurement experimental technology are introduced in this paper. The primary simulation parameters are the nozzle pressure ratio (NPR) and the Mach number at the nozzle exhaust. The nozzle model is installed in the vacuum cabin of the thrust test bench, and aerodynamic forces of the nozzle model are measured accurately by the wall balance. After the mass flow correction, installation position correction, and the correction of pressure effect and mass flow effect to the balance caused by the air bridge system based on the rubber membrane, the exact values of the vector nozzle static thrust, thrust coefficient and vector angles etc. are obtained. The experimental results show that the axial thrust coefficient, the normal thrust coefficient and the variation trend of vector angle with NPR, which is measured in the vector nozzle static thrust measurement experiment using the thrust test bench are correct,the test results precision can satisfy the GJB requirements for force-test precision, and the technique can be applied in project test © 2018, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

The mixing characteristics of an injector was studied using acetone planar laser induced fluorescence (PLIF) technique. Some technical comments on how to choose the tracer and the excited wavelength were put forward and the photophysical processes of acetone were studied preliminarily. Seven velocity ratios were tested in gas-gas mixing tests in order to get the concentration and mixing ratio distribution of the straight-swirl injector. The research shows that there is a critical velocity ratio vr,Cr, if vr < vr,Cr, the mixing is coarse, else the mixing is good. In addition we found that there are fluctuations of mixing ratio at downstream location.

The principle of free jet density flowfield measurement using an acetone planar laser-induced fluorescence (PLIF) technique was introduced, and then the density flowfield structure of under-expanded free jet adulterated with acetone vapor was visualized by the PLIF technique under the two injection stagnation pressure conditions. The PLIF images show the characteristic information of the flowfield including the barrel shock and the Mach disc clearly. The level of the under-expanded degree mostly influences the flowfield before the Mach disc. The higher level of the under-expanded degree is followed by the larger jet diameter, the farer distance between the Mach disc and the injection port, and the barrel shock expanding outward continuously. To examine the precision of using the acetone PLIF technique to measure density, the experimental flowfield was calculated by the numerical simulation method. The density flowfield structure and the profile of the normalized density along the injection axis obtained from the simulation agree well with those obtained from the experiment.

An experimental system including underwater plasma acoustic source, PCB pressure sensor and high speed camera was built up. The bubble dynamics induced by intensive acoustic pulse and its sound emission were studied. The typical waveform of the intensive acoustic pulse was captured, and the growing, expanding and collapsing process of the bubble and its emitted sound were observed. Theoretically, Gilmore equation and Bernoulli equation were used to simulate the bubble dynamics and sound emission, based on which the numerical calculation and analysis were performed. The results indicate that: (1) Bubble will be compressed and will oscillate around the "quasi-equilibrium radius" during the positive pressure phase of the incident pulse, and then the bubble will undergo the process of expanding, collapsing and rebounding during the negative pressure phase of the incident pulse; (2) The duration of the periodically radiated acoustic pulse of the collapsing bubble is very short, which exhibits the characteristic of a "shock wave".

The combustion of pyrotechnic composition underwater has ability to form a low-frequency underwater sound signal. The French defense company of Lacroix pyrotechnic Group developed a "pyrotechnic-acoustic transmitter" in 1995. However, until now this investigation has not been extensively studied and reported. In this paper, the research of mechanism of the acoustic radiation for pyrotechnic composition combustion underwater was conducted. The results show that the emission noise mainly includes turbulence noise and breakdown bubble noise. The further investigation also revealed that the breakdown bubble noise has the dominant effect comparing with the turbulent noise. In order to prove this viewpoint, the underwater combustion of pyrotechnic composition with pulsating combustion effect was studied through a deep experimental investigation.

This paper introduces a solution of mixing conductive liquids in the micro-channel, using the generated electromagnetic force caused by the effect of electric and magnetic fields coupling. The solution improves the mixing efficiency of fluids by increasing the contact area, which is caused by the reciprocating motion and the interface extending of the different fluids. Then the experimental platform is established and the detailed experimental studies are carried out using the micro-PIV system. The velocity field of fluid flow in the micro channel is got. The flow fields of different electrode arrangements are analyzed and compared. On the basis of experiment, the numerical simulation is carried out, and the mixing efficiencies of the different conditions are analysed. The results show that under the disturbance of electromagnetic force, the mixing efficiency of the fluids in the micro channel can be improved.

PIV investigation on flow induced by plasma aerodynamic actuation was presented in the paper to reveal the operation mechanism between plasma aerodynamic actuation and airflow. The experimental results show that the flow induced by millisecond and microsecond plasma aerodynamic actuation come out as starting vortex and wall jet. The maximal induced velocity is about 3m/s when the actuation voltage is 12kV. The higher the voltage is, the stronger the starting vortex and the wall jet. The intensity and the influence of the pulse actuation are higher than that of the steady actuation. The results are instructional for increasing the ability of plasma flow control.

Plasma flow control is an innovative active flow control technology that based on the plasma aerodynamic actuation, which has become a research hotspot of aerodynamics field presently. One of the physical principles is dynamic effect. Body force, as a very important parameter valuing dynamic effect, has significant meaning for investigating the principle of plasma flow control. Experimental principle and the basic composition of the experimental system are introduced, then the body force experimental measurement of plasma aerodynamic actuation were performed. The results indicate that the body force of plasma aerodynamic actuator is on mN magnitude; with fixed actuation frequency, the body force would increases linearly with the actuation voltage increases; with fixed voltage, the induced body force is not sensitive to actuation frequency.

A new designed multi-bipolar dielectric barrier discharge actuator was reported for controlling flow separation from a circular cylinder in cross-flow. This new type plasma actuator was adopted with the electrode of former covered electrode and later exposed electrode connected together. We used this new designed actuator to control flow separation of a circular cylinder in cross-flow. The experiment was performed in a low speed wind tunnel at Re=2.8×104. The near wake structure of a circular cylinder was studied using particle image velocimetry (PIV). It was shown that the flow separation was suppressed when the plasma actuators were activated either in steady mode or in unsteady pulsed mode. The strength of the actuation was an important factor for the control of flow separation. Interestingly, with this multi-bipolar dielectric barrier discharge actuator, we found the pulsed actuation frequency of StD=0.21 was more effective for the flow separation control in the case of unsteady plasma actuation.

Active flow control on a three-dimensional NACA633-421 airfoil has been investigated experimentally using beveled-slit-synthetic-jet-actuator (BSSJA). Balance force measurement results show that the synthetic jet can control the flow separation effectively, improve the maximum lift coefficient by 10.4% and increase the stall angle of attack by 4°. Both boundary layer velocity measurement and particle image velocimetry (PIV) technology have been performed under selected experimental conditions to investigate the mechanism of synthetic jet flow control. Results reveal that the shape factor of boundary layer velocity profile decreases with BSSJA control and the promotion of the power of the boundary layer is responsible for the control effect. The instantaneous flow maps and ensemble-averaged PIV results reveal that synthetic jet tends to enhance the flow dilution and transfer the mass flux so that the separated flow could attach to the wall of NACA633-421 airfoil again. In addition, the turbulent kinetic energy (TKE) and Reynolds stress are increased near the wall compared to the situation without control. ©, 2014, Editorial Department of JOURNAL OF EXPERIMENTS IN FLUID MECHANICS. All right reserved.

A new type of splayed-slit-synthetic-jet-actuator(SSSJA) which is useful for separation flow control was designed. The core component of the acoustic excitation type actuator was a powerful loudspeaker(4W). The jet velocity depends on two parameters of excitation frequency and voltage. Particle image velocimetry(PIV) and boundary layer probe was used to study the interaction between the jet flow and the main flow. Results revealed that the promotion of both flow dilution and the power of the boundary layer are responsible for the control effect. Flow control on a three-dimensional NACA633-421 airfoil was then conducted to investigate the effect of two parameters of dimensionless energy ratio Cμ and the location of the actuator array. Both pressure and force measurements data show the ability of SSSJA to reattach the separation flow and to delay the stall at high angles of attack. The control effect gets better along with the larger value of Cμ. At Cμ=0.00168, maximum of the lift coefficient and the stall angle were increased by 5.92% and 2.5°, respectively. Chordwise location of the actuator array was proved to be a vital parameter in separation flow control. The behavior of the array located at 0.3c is better than the one located at 0.55c. The difference in the control effect is determined by the relative position of the actuator array and the separation point. Experiments were conducted at the wind speed of v∞=16m/s and the chord-based Reynolds number of Re=2.7×105.

Influence of plasma actuators on the flow separation control of NACA 0015 airfoil was investigated in an open-circuit low-speed wind tunnel. Particle Image Velocimetry (PIV) technology was applied to visualize the modification of the flow structure over the airfoil by the plasma actuators. Lift and drag were measured by a five-component strain gauge balance to investigate the separation control effect of the actuator voltage and excitation frequency. The results show that the leading-edge plasma actuators are effective in controlling the flow separation over the airfoil at low wind speeds. The maximum lift coefficient and stall angle are increased by 11% and 6 deg respectively at the free-stream velocity of 20m/s. However, at a given flow state, there exists threshold values for both the actuator voltage and excitation frequency on the actuators. The threshold values are different with the changing attack angles. At the higher attack angles, the plasma actuator's authority must be increased due to the much stronger flow separation on the airfoil.

Based on the theory of rigid-flexible coupling dynamics, the dynamics simulation of flexible nozzle in wind tunnel is done by using the software of ADAMS and PATRAN/NASTRAN. At the same time, the nonlinear deformation of flexible wall is analyzed through the finite element software of NASTRAN. The comparison of these two results indicates that neglecting the nonlinear deformation of the flexible wall can bring big errors to the dynamics simulation. Therefore, the dynamics simulation model is improved by using the segmented linearization method and the nonlinear deformation of the flexible wall is reckoned in. The result shows that the improved dynamics simulation is accurate and is applicable for the control design of the flexible nozzle. Finally, the influence of the handspike drive on the structure strength of the flexible wall is analyzed which can provide essential basis for the control of the handspike drive and avoid the damage of the flexible wall.