实验流体力学

2021, 35(1): 1-4.

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Research advances in passive techniques for combustion diagnostics based on analysis of spontaneous emission radiation

LOU Chun, ZHANG Ludong, PU Yang, ZHANG Zhongnong, LI Zhicong, CHEN Pengfei

2021, 35(1): 1-17. doi: 10.11729/syltlx20200063

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Passive techniques for combustion diagnostics utilize flame spontaneous emission radiation information. The characteristics of this technique are noninvasive, low requirement on measurement environment, compact system, and easy to implement, and therefore it has unique advantages for online measurement of the combustion field. Firstly, the advantages and limitations of various combustion diagnosis technologies have been analyzed. Then, based on the work of passive combustion measurement diagnosis carried out by State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, the principles and state of the art of spontaneous emission radiation diagnostic are introduced according to the three aspects of flame emission spectroscopy, flame image processing, and thermal radiative imaging. Qualitative analysis of the combustion status and quantitative calculation of key combustion information such as the temperature and the species volume fraction in the combustion field can be achieved by using the three techniques above. Finally, the development trend of the spontaneous emission radiation diagnosis technology is presented, which is to obtain more plentiful measured signals, higher measurement resolution and accuracy, and more kinds of measured results.

Development of optically accessible gas turbine model combustor and its flow field testing

WANG Yulan, FAN Xiongjie, GAO Wei, LIU Cunxi, YANG Jinhu, LIU Fuqiang, MU yong, XU Gang

2021, 35(1): 18-33. doi: 10.11729/syltlx20190171

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The combustion in the chamber of aero-engine involving the aerodynamics of swirling air streams, fuel atomization, evaporation, the mixing of fuel droplets with air streams, and chemical reactions is a multiphase complex process under the conditions of high pressure and high temperature. The characteristics of the flow field play a significant role in determining combustion performances of the combustors by affecting the processes of fuel atomization and combustion. The interpretations off low mechanism and accurate tests of the highly swirling flows inside the combustors are always being one of the major challenges posed to the combustion researchers and engineers.In order to learn the knowledge of experimental setups of optically accessible gas turbine combustor facilities, and to have a grasp of swirling flow characteristics in swirl-cup traditional combustors and staged combustors combining premixed and diffusion combustion technologies, the design methods of the optically accessible model combustor, the organization mechanism of swirling flow, and the flow structures in typical combustors of aero-engines are analyzed and summarized in this study. The discussions in this paper may facilitate the research and development of aero-engine combustors.

Investigation of the combustion process in an ethylene-fueled scramjet combustor

ZHONG Fuyu, LE Jialing, TIAN Ye, YUE Maoxiong

2021, 35(1): 34-43. doi: 10.11729/syltlx20200093

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An experimental investigation was conducted in a direct-connect supersonic combustion facility simulating the inflow condition of Ma=2.0 to investigate the combustion process in an ethylene-fueled scramjet combustor with cavity and pilot hydrogen. The structure of the flow field and the flame development were visualized using the schlieren imaging, the flame luminosity imaging, the CH luminosity imaging and the planar laser-induced fluorescence (PLIF) of the OH radical. The equivalence ratios of pilot hydrogen and ethylene were about 0.33 and 0.10, respectively. The whole combustion process could be divided into six stages. In the first stage, there was a non-reaction cold flow before the hydrogen injection. And the frequency of oscillation was measured to be around 400 Hz, experimentally. In the second stage, the flow characteristics before the pilot hydrogen ignition were revealed, due to the hydrogen injection an oblique shock wave was generated, reflected on the bottom wall, and then interacted with the shock waves below the cavity, thus leading to the increase of the monitor pressure. The third stage was the hydrogen combustion, including ignition and flame stabilization. The process from the ignition of pilot hydrogen to the combustion stabilization lasted around 26.0 ms. In the first 0.1 ms, the ignition of pilot hydrogen had great effect on the flow field structures. The moving speed of the shock train caused by the combustion of pilot hydrogen was around 20 m/s. The stabilization mode of the pilot hydrogen flame was cavity recirculation stabilized combustion. The fourth stage was the intense combustion process of hydrogen and ethylene. The shock waves were pushed into the isolator, and thus exceeded the observation range. The ethylene flame stabilization mode was shear layer stabilized combustion. The combustion characteristics of ethylene were revealed in the fifth stage. When the pilot hydrogen was ceased, the ethylene flame moved from the cavity step to the cavity ramp. The last stage involved the combustion and flame blowout of pure ethylene. Preliminary analysis indicates that the CH luminosity images of ethylene combustion can be used to investigate combustion efficiency qualitatively.

Experimental investigation on thermoacoustic oscillation of a new dual-swirl combustor

HE Zuqiang, WANG Ping, Meenatchidevi Murugesan, Antonio Ferrante, LI Weichao, JIANG Linsong

2021, 35(1): 44-52. doi: 10.11729/syltlx20200021

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In this paper, a new type of dual-swirl combustor is tested. The effects of two varying processes of combustion state parameters on the thermoacoustic oscillation characteristics of flame are studied. The two processes are: keep methane volume flow rate constant and reduce the equivalence ratio from 0.900 to 0.725 and then increase it back to 0.925; keep the equivalence ratio constant as 0.850 and increase the premixed gas volume flow. The results show that there are two distinct flame patterns of M-shaped and V-shaped in this combustor. In process 1, the flame changes from unstable M-shaped flame to stable V-shaped flame with decreaseing equivalence ratio, and then changes to M-shaped flame with increaseing equivalence ratio, the combustor exists hysteresis phenomenon; In process 2, Thermoacoustic oscillation is only found at the initial flow rate, and the flame becomes stable with increaseing flow rate.Through the analysis of the power spectrum characteristics and phase space reconstruction of the pressure fluctuation signal, it is found that there are unstable frequencies around 400.0 and 256.0 Hz in this dual-swirl combustor.

Experimental investigation on high temperature deformation of regeneratively cooled combustor structure based on non-contact measurement

ZHANG Lei, ZHANG Ruoling, XIAO Shide, LIU Yu, XIONG Ying

2021, 35(1): 53-59. doi: 10.11729/syltlx20200051

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In order to obtain the high temperature deformation of the generatively cooled combustor structure in ground test, experimental investigation based on non-contact measurement was conducted. The speeded-up robust feature algorithm and the improved digital image correlation of cylindrical surface were used to measure the total deformation and the partial strain of the combustor, respectively. The results show that the experimental total deformations and partial strains of the combustor were about 4.8 mm and 0.0049 respectively under the stable working condition. The experimental results agree well with engineering rough estimated ones, which shows that the presented non-contact measurement is applicable for combustor structure design and the experimental data are useful for validating the numerical calculation of the three-dimensional structural strength analysis.

Measurement of CO concentration in flat flame based on mid-infrared absorption spectroscopy

HU Shangwei, YIN Kewei, TU Xiaobo, YANG Furong, CHEN Shuang

2021, 35(1): 60-66. doi: 10.11729/syltlx20190126

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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.

Advances in research on directional movement of droplets on wetted anisotropic surfaces

CAO Gang, HUANG Suhe, LI Mingsheng, HU Haibao

2021, 35(1): 67-85. doi: 10.11729/syltlx20200086

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Research of the droplet movement on the wetting of the heterogeneous surface has important application value in, for example, oil-water separation, water collection, etc., and has become a research hotspot in the field of surface interface. In addition, the research on the directional motion of the the droplets on wetting anisotropic surface is of great significance for understanding the solid-liquid interaction and developing a high-performance wetting anisotropic surface. This paper introduces the directional movement of droplets on the wetting anisotropic surface in detail including the wedge-shaped surface, groove surface, hydrophilic-hydrophobic surface, asymmetric topography surface and biological surface. The typical cases of directional movement of droplets on a wetting anisotropic surface at home and abroad are shown. Finally, a summary and prospect are provided for future research.

Research advances of tomographic particle image velocimetry

LI Xiaohui, WANG Hongwei, HUANG Zhan, ZHAO Junbo

2021, 35(1): 86-96. doi: 10.11729/syltlx20190160

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Tomographic Particle Image Velocimetry (Tomo-PIV) is an instantaneous three-dimensional velocity measurement technology which can provide detailed data support for complex flows with strong unsteady characteristics. A general review of the development and application of the technology at home and abroad is presented. The principle and characteristics of tomographic particle image velocimetry are introduced, and the current research situation is discussed, including especially the camera layout, particle density, calibration mapping function and 3D reconstruction algorithm. Then the typical application of Tomographic Particle Image Velocimetry is introduced, showing its advantages in the unsteady three-dimensional flow measurement and engineering applications. Finally, the application prospect and development trend of tomographic particle image velocimetry are discussed.

Investigation of mode transition and thrust performance in transient acceleration and deceleration experiments

LIAN Huan, GU Hongbin, ZHOU Ruixu, LI Tuo, LI Zhongpeng

2021, 35(1): 97-108. doi: 10.11729/syltlx20200069

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Experiments are designed to investigate the transient fluid-combustion phenomenon during simulated transient acceleration and deceleration between flight Ma5.0~6.0. Flow induced ram-scram mode transition and thrust abruption were observed. The transient fluid-combustion evolutions were characterized with high speed Schlieren imaging and summarized into four phases. The fluid phenomena were discussed based on the impulse function analysis. The accumulated heat release from the thermodynamic cycle analysis dominates the mode transition and thrust abruption process. The isolator pseudo-combustion shock train system is the dominating flow feature during the mode transition. The backpressure induced by the supersonic crossflow contributes to maintain thrust. In addition, the heat transfer and boundary layer disturbance could shift the combustion mode transition limits.

Standing stability enhancement method of oblique detonation waves in a confined space and its experimental validation

LIU Yu, XIAO Baoguo, WANG Lan, CHEN Weiqiang

2021, 35(1): 109-116. doi: 10.11729/syltlx20200084

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Hypersonic ramjets with the combustion mode of oblique detonation are promising in the high-Mach-number air-breathing propulsion field. It is very important to overcome the standing stability problem of oblique detonation waves for realizing this technical scheme. A standing stability enhancement method of oblique detonation waves in a confined space is proposed and validated in a direct-connect experiment under the Ma 8.0 near-real condition. Supersonic premixed gases are produced by using array nozzles and a non-reacting gas layer is formed by cutting off the fuel supply in the near-wall nozzle units. After the oblique detonation wave enters the near-wall region, it decays to an inert shock wave due to the presence of the non-reaction gas layer and therefore its Mach reflection on the wall can be significantly weakened to avoid choking flow. Through this method, the standing stability of oblique detonation waves is well enhanced and a long-time standing oblique detonation wave is obtained under the near-real condition.

TRPIV experimental investigation of drag reduction mechanism in turbulent boundary layer over superhydrophobic-riblet surface

LIU Lixia, WANG Kangjun, WANG Xinwei, TIAN Haiping, JIANG Nan

2021, 35(1): 117-125. doi: 10.11729/syltlx20200001

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The instantaneous velocity vector fields of turbulent boundary layers over the hydrophilic surface, the superhydrophobic (SH) surface and the superhydrophobic-riblet (SR) surface were measured using Time-Resolved Particle Image Velocimetry(TRPIV). Drag reduction rates of 14.6% and 20.7% for the SH surface and the SR surface respectively were acquired by comparing with the friction coefficient of the hydrophilic surface. By comparing the tendency of the turbulence intensity, it is found that the normal turbulence fluctuation intensity of the hydrophilic surface, the SH surface and the SR surface has no remarkable differences, but the streamwise turbulence fluctuation intensity shows a weakening trend in the region of y⁺ < 150 at the same wall-normal position. By using the spatial filtering method based on Fourier transform, the instantaneous fluctuating velocity field is divided into the large-scale part with the wavelength greater than δ and the small-scale part with the wavelength less than δ. It is found that the inhibitory effect of the SH surface and the SR surface on the streamwise turbulence fluctuation intensity of the large-scale part can reach the wall-normal position of y⁺=150, while the inhibitory effect on the streamwise turbulence fluctuation intensity of the small-scale part can only reach the normal position of y⁺=100. Through the conditional sampling and phase average methods, it is found that at the region of y_ref=0.1δ, compared with the hydrophilic surface, the positive large-scale streamwise fluctuating intensity and the negative wall-normal fluctuating intensity on the SH surface and the SR surface are increasing while the negative large-scale streamwise fluctuating and positive wall-normal fluctuating intensities on the SH surface and the SR surface are decreasing, and there is a gap between the contour with the value of zero and the reference position of the conditional sampling. Comparing the vortical strength of TBL on different wall, it is found that the vortex intensity value of the hydrophilic surface, the SH surface and the SR surface becomes weaker in turn, and hence we can conclude that the SR surface could acquire a higher drag reduction rate than the SH surface, via suppressing the motion of vortices at the near wall region.

China's first hypersonic wind tunnel dual CTS test capability formed in CARDC

LIN Jingzhou

2021, 35(1): 126-126.

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2021 Vol. 35, No. 1