实验流体力学

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2022, 36(4)

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2022, 36(4): 1-2.

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Direct connected experimental research on hydrocarbon-fueled rotating detonation

WANG Chao, ZHENG Yushan, CAI Jianhua, XIAO Baoguo, LIU Yu, LE Jialing

2022, 36(4): 1-9. doi: 10.11729/syltlx20210086

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Direct connected tests of rotating detonation were performed with ethylene and room-temperature kerosene adopted as fuel. The corresponding flight Mach number is 5.0, and the Mach number is 2.5 at the isolator entrance. Results show that the rotating detonation wave was sustained after initiation with the equivalent ratio of ethylene ranging from 0.43 to 0.99. The propagation frequency of detonation waves is 5.32–6.42 kHz, with a propagation cycle of 0.156–0.188 ms. As the equivalent ratio increases, the propagation velocity of the detonation wave and the pressure in the detonation combustor increase almost linearly. While the averaged pressure peaks of the dynamic pressure（PCB pressure sensor） first increase and then decrease. The pressure at the isolator exit also increases under a higher equivalent ratio, but the velocity remains unchanged at Ma=2.5. When the equivalent ratio of kerosene was about 0.70, the rotating detonation wave was also sustained.

Simulation and analysis on the motion characteristics of shock train under dynamic throttle

GAO Wenzhi, SONG Zhixiong, TIAN Ye, ZHAO Pengfei

2022, 36(4): 10-19. doi: 10.11729/syltlx20220022

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To investigate the shock train characteristics under the influence of dynamic backpressure, the dynamic throttle flows of a two-dimensional inlet/isolator configuration were simulated under Mach 6 free steam condition, where the throttle ratio increased from 0.20 to 0.32 and were kept constant. The effects of increasing time （varied from 1–10 ms） of the throttle ratio were analyzed. The results show that the amplitudes of the shock train downstream motion and the upstream motion are within 3 mm and about 18 mm, respectively, as the throttle ratio increases from 0.20 to 0.32 within 5 ms. The shock train motion lag behind the throttle process and the lag time decreases with the prolongation of the throttle variation time. When the increasing time of the throttle ratio was 6 ms and above, the shock train could move downstream to the middle of the cavity and the motion amplitude reached 31 mm, accompanied by flow oscillations. The upstream motion amplitude of the shock train was still about 18 mm and the shock train motion was approximately synchronized with the throttle process. The analysis showes that the lag of the shock train motion is related to the time intervals of back pressure increment and propagation, which is longer than the variation time of the throttle ratio under the condition of short increasing time. Under the long increasing time conditions, the flow oscillations are related to the increase of the mass flowrate in the subsonic section of the cavity, which dominates the shrinkage of the recirculating region in the cavity. This further causes the expansion of the supersonic flows near the cavity and generates choked flows near the throttle region. Therefore, flow oscillations are generated through the interactions between the separated shock wave flows of the choked flows and the cavity recirculating region. The lag of the shock train motion and its influence on flow performance should be considered in engineering design.

Flow and combustion characteristics of dual-mode scramjet under different flight conditions

HE Can, XIAO Baoguo, XING Jianwen, YI Miaorong

2022, 36(4): 20-29. doi: 10.11729/syltlx20220019

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In order to study the flow and combustion characteristics of kerosene fueled rectangular dual-mode scramjet under different flight conditions, the accuracy of the numerical method was verified by direct connect experiment. Three-dimensional steady numerical simulations were carried out for six cases with different equivalence ratio and Mach numbers. The distribution of the wall pressure and the one-dimensional mass average Mach number along the flow direction of the scramjet were given. The characteristics of the shock structure and heat release rate were analyzed. The results show that the scramjet works in two different combustion modes under different flight conditions. When the scramjet is in the ramjet-mode operation, the pre combustion shock trains propagate to the front of the fuel injector, and the shock system in the combustor is relatively weak; as the shock train moves forward, the separation vortex structure is formed in the isolator, and the fuel is rolled up to the upstream. Part of the combustion is completed before the injector. The separation of the combustor mainly occurs inside the cavities, and the heat release is concentrated in the head of the first cavity. When the scramjet is in the scramjet-mode operation without shock train forward propagation, the shock system in the cavity section is relatively stronger and the fluctuation of flow parameters is more severe. The combustion occurs downstream of the injector, and the separation vortex in the combustor has a long flow span, forming a continuous flow separation from the leading edge of the first cavity to the second cavity. The separation vortex helps the combustion to propagate downstream, so the heat release is more evenly distributed along the flow direction of the combustor. The flow separation induced in the section between two cavities promotes the formation of the separation vortex with large flow direction span in the combustor, which may help the combustion to propagate downstream, so as to realize distributed heat release and avoid shock train propagation caused by concentrated heat release.

Study on visualization of supersonic flame using Three Dimensional Laser–Induced Fluorescence （3DLIF）

YUAN Xun, YU Xin, PENG Jiangbo, QIN Fei, LIU Bing, CAO Zhen, GAO Long, HAN Minghong

2022, 36(4): 30-36. doi: 10.11729/syltlx20210150

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In view of the urgent need of scramjet combustion diagnosis, especially the visualization of flame space structure, it needs to realize three–dimensional measurement of the supersonic flames. The Three Dimensional Laser–Induced Fluorescence （3DLIF） technology can realize the visualization of the flame combustion space. For the supersonic coaxial jet combustion, a scanning galvanometer multi–plane 3DLIF experimental device was built, and a laser sheet shaping scheme with expanded scanning range was proposed, which realizes the multi–plane 3DLIF visualization of the supersonic flames. The interpolation algorithm was used to reconstruct the three–dimensional average image of supersonic flame with a spatial scale of 50 mm×85 mm×20 mm and a time scale of 5 ms, which verifies the feasibility of using the 3DLIF technology to visualize the combustion space structure of the scramjet test bench. The effect of the flame speed on the flame structure shape using the three–dimensional images is discussed.

Mixing characteristic and flow features of pylon-aided fuel injection into a supersonic crossflow

LIU Yuan, SUN Mingbo, LIANG Changhai, TIAN Ye, LI Ji

2022, 36(4): 37-44. doi: 10.11729/syltlx20220011

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Flowfield structures of pylon-aided fuel injection of a sonic jet into a supersonic crossflow with Ma_∞=2.95 have been investigated by RANS method. One case has been studied for jet-to-crossflow momentum flux ratios of 7.7, and the results are compared with those obtained by normal injection of a single jet from a flat plate without a pylon. Upstream of the jet orifice, the detached shock generated at the leading edge of the pylon is identified by inserting with the separation shock. Elevation of the jet plume height facilitates the mixing of the jet and the main flow. More CVP structures make pylon-aided fuel injection cases a better mixing performance. Besides, the mechanism of mixing enhancement resulting from the pylon is also elaborated in the present work.

Analysis of shock waves structure and its influencing factors in rectangular isolator

NIE Can, WANG Hongbo, SUN Mingbo

2022, 36(4): 45-55. doi: 10.11729/syltlx20210141

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The isolator is an important part of the scramjet engine, which mainly plays the role of isolating the interference between combustion and the intake duct. The complex flow phenomenon in the isolator has always been the focus of research and attention. In this paper, a three-dimensional numerical simulation method is used to study the influence factors of shock train characteristics of the rectangular isolator. The shock train characteristics under the influence of the factors such as different incoming Mach numbers, symmetry or single expansion angle, and wall cavity are analyzed. The results show that under the condition of high Mach number, the length of the shock train in the isolator becomes shorter, the anti-backpressure ability of the isolator is enhanced, and the total pressure loss increases; the shock train structures in the single expansion isolator and the symmetry expansion isolator are different, and the total pressure loss of the flow field after the isolator has nothing to do with the expansion form; after adding a wall cavity to the isolator, two different modes would appear according to the difference in the back pressure, namely the subcritical cavity mode and the supercritical cavity mode, and the shock train structure and flow field parameter characteristics in the isolator are different in the two modes. Under the supercritical cavity mode condition, the anti-backpressure ability of the isolator decreases, and the total pressure loss increases. The research results of this paper can provide reference for the design and test of the isolator and combustion chamber.

Thermophysical properties research progress of ferroelastic RETaO₄ ceramics

CHEN Lin, FENG Jing

2022, 36(4): 56-76. doi: 10.11729/syltlx20220020

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Working temperature is essential for the gas efficiency and energy conversion efficiency of multifarious aero engines, gas turbines, and hypersonic vehicle engines. Thermal barrier coatings （TBCs） are used in the high-temperature alloy components of aforementioned machines to provide thermal insulation and increase their working temperature. The most applied TBC is yttria stabilized zirconia （YSZ）, but it can no longer meet the demands of current industry due to its high thermal conductivity, mismatching thermal expansion coefficients （TECs）, and insufficient working temperature. It is urgent for scholars to investigate the next-generation TBC materials having low thermal conductivity, long lifetime, and high working temperature. The low fracture toughness, low TECs, weak high-temperature phase stability, and other weaknesses inhibit RE₂Zr₂O₇, REPO₄, RE₂SiO₅, RE₂Ce₂O₇, and RE–Al–O oxides from being applied as TBCs. Ferroelastic rare earth tantalates （RETaO₄） are considered as the next-generation TBCs with ultra-high working temperature based on their unique ferroelastic toughening, low thermal conductivity, high TECs, and low Young’s modulus. This paper reviews the thermophysical properties of RETaO₄ ceramics, including their crystal structures, microstructures, and mechanical/thermal properties （hardness, acoustic velocity, modulus, thermal conductivity, TECs, phase stability, and so on）. It is believed that RETaO₄ ceramics are candidate TBCs with high working temperature, and this paper provides scholars with some suggestions and future investigation directions on these series ceramics.

Research of simulation method for inlet flow steady-state distortion based on momentum exchange

ZHANG Xiaofei

2022, 36(4): 77-83. doi: 10.11729/syltlx20210070

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In order to simulate the steady-state total pressure distortion at the inlet of aero-engine, a new distortion generation method is studied and validated. After establishing the control model of steady state total pressure distortion generation in flow field, the distortion generator technical verification machine is developed, and the ground distortion simulation test-bed is built. Using it, three typical flow fields in different configuration of steady state total pressure distortion have generated demonstratively, and the simulation error is between 2.7% to 5.2%. The experimental results show that: The air jet distortion generator based on the airflow momentum exchange mechanism generates the expected steady-state total pressure distortion directly to flow field configuration, which can rapidly realize arbitrary flow field distortion by controlling the position and mass of the jet flow in the mainstream area by “soft adjustment”, and with low cost. It has obvious advantages and engineering practical value.

Influence of endwall suction slot arrangement on performance of the aspirated compressor plane cascade

LIU Bao, DU Zhengshuai, ZHOU Xun

2022, 36(4): 84-93. doi: 10.11729/syltlx20210015

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Boundary layer suction can control the flow separation in the compressor cascade and increase the aerodynamic load of the cascade. To investigate the influence of the arrangement of suction slots on the aerodynamic performance of the compressor cascade, blowing experiments were carried out in the transonic wind tunnel of the Engine Aerodynamic Research Center of Harbin Institute of Technology. At the same time, the numerical simulation of the cascade was carried out. The results show that the endwall boundary layer suction can effectively reduce the total pressure loss of cascades. The effect of boundary layer suction is related to the number of suction slots.

Transient velocity measurement of shear flow using Femtosecond Laser Electronic Excitation Tagging

YANG Wenbin, CHEN Li, YAN Bo, WANG Chaozong, ZHOU Jiangning, CHEN Shuang, MU Jinhe, WANG Jianxin, QIU Rong

2022, 36(4): 94-102. doi: 10.11729/syltlx20210060

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The measurement accuracy of flow velocity affects the prediction accuracy of aerodynamic performance of the aircraft. However, the current laser-spectroscopy-based velocity non-intrusive measurement technology can’t fully satisfy the requirement of high-precision flow velocity measurement, but the Femtosecond Laser Electronic Excitation Tagging （FLEET） measurement technology can. In this work, a FLEET system is developed based on a Ti:sapphire femtosecond laser. The electronic fluorescence of N₂, which is excited by the femtosecond laser, is analyzed. Based on the FLEET system, transient velocities of the shear flow within 30 m/s to 170 m/s, which is adjusted by the gas pressure or volume flow rate in the high-speed channel, are measured. Finally, the effect of delay time on velocity measurement is investigated. With the delay time increasing, the fluorescence image widens due to the diffusion of plasma, and the signal to noise ratio decreases due to the fluorescence intensity decay. However, the velocities measured at different delay times are basically consistent. The results show that FLEET is practicable to measure the velocity of the shear flow.

Research of scramjet thrust test in shock tunnel

ZHAO Rongjuan, LIU Shiran, ZHOU Zheng, WU Liyin, LYU Zhiguo

2022, 36(4): 103-108. doi: 10.11729/syltlx20210025

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In order to meet the need of high-Mach number scramjet development, the scramjet thrust test technique in the shock tunnel is studied. A piezoelectric balance is used to test the scramjet thrust in the shock tunnel. The research includes the balance design, calibration and thrust test in the shock tunnel. The finite element analysis method is used in the balance design to optimize the balance structure. The simulation results show that the sensitivity of the balance can reach 17.447 mV/N, and the first-order frequency mode can reach 1022.40 Hz. The validation test is conducted in the shock tunnel with the fuel and without the fuel injection. The test results show that, the difference of the drag force is about 220 N between two different experimental conditions. Which means the thrust of the scramjet under different conditions can be distin-guished with the new developed balance.

2022 Vol. 36, No. 4