Shock tubes are devices which are used in the investigation of high speed and high temperature flow of compressible gas. lnside a shock tube, the interaction between the reflected shock wave and boundary layer leads t...Shock tubes are devices which are used in the investigation of high speed and high temperature flow of compressible gas. lnside a shock tube, the interaction between the reflected shock wave and boundary layer leads to a complex flow phenomenon. Initially a normal shock wave is formed in the shock tube which migrates toward the closed end of the tube and that in turn leads to the reflection of shock. Due to the boundary layer interaction with the reflected shock, the bifurcation of shock wave takes place. The bifurcated shock wave then approaches the contact surface and shock train is generated. Till date only a few studies have been conducted to investigate this shock train phenomenon inside the shock tube. For the present study a computational fluid dynamics （CFD） analysis has been performed on a two dimensional axi-symmetric model of a shock tube using unsteady, compressible Navier-Stokes equations. In order to investigate the detailed characteristics of shock train, parametric studies have been performed by varying different parameters such as the shock tube length, diameter, pressure ratio used inside the shock tube.展开更多
In this paper,shock train motion in a Mach number 2.7 duct is studied experimentally,and large numbers of schlieren images are obtained by a high-speed camera.An image processing method based on Maximum Correlation De...In this paper,shock train motion in a Mach number 2.7 duct is studied experimentally,and large numbers of schlieren images are obtained by a high-speed camera.An image processing method based on Maximum Correlation Detection(MCD)is proposed to detect shock train motion from the schlieren images,based on which the key structures,e.g.,separation positions and separation shock angles on the top and bottom walls,can be analysed in detail.The oscillations of the shock train are generated by rhombus and ellipse shafts at various excitation frequencies.According to the analysis of MCD results,the distributions of the frequency components of shock train oscillation generated by the two shafts are distinctly different,in which the motion generated by the ellipse shaft is much smoother;shock train motion is mainly characterized by the oscillation of separation position while the separation shock strength is not so sensitive to downstream disturbance;there is a hysteresis loop relation between the downstream pressure and separation position.展开更多
The structure and dynamics of an oblique shock train in a duct model are investigated experimentally in a hypersonic wind tunnel.Measurements of the pressure distribution in front of and across the oblique shock train...The structure and dynamics of an oblique shock train in a duct model are investigated experimentally in a hypersonic wind tunnel.Measurements of the pressure distribution in front of and across the oblique shock train have been taken and the dynamics of upstream propagation of the oblique shock train have been analyzed from the synchronized schlieren imaging with the dynamic pressure measurements.The formation and propagation of the oblique shock train are initiated by the throttling device at the downstream end of the duct model.Multiple reflected shocks,expansion fans and separated flow bubbles exist in the unthrottled flow,causing three adversepressure-gradient phases and three favorable-pressure-gradient phases upstream the oblique shock train.The leading edge of the oblique shock train propagates upstream,and translates to be asymmetric with the increase of backpressure.The upstream propagation rate of the oblique shock train increases rapidly when the leading edge of the oblique shock train encounters the separation bubble near the shock reflection point and the adverse-pressure-gradient phase,while the oblique shock train slow movement when the leading edge of the oblique shock train is in the favorablepressure-gradient phase for unthrottled flow.The asymmetric flow pattern and oscillatory nature of the oblique shock train are observed throughout the whole upstream propagation process.展开更多
Scramjet is the main power device of hypersonic vehicles. With the gradual expansion of wide velocity domain, shock wave/shock wave and shock wave/boundary layer are the main phenomena in scramjet isolator. When the l...Scramjet is the main power device of hypersonic vehicles. With the gradual expansion of wide velocity domain, shock wave/shock wave and shock wave/boundary layer are the main phenomena in scramjet isolator. When the leading edge of the shock train is pushed out from the inlet of the isolator, the engine will not start. Therefore, it is very important to detect the flow field structure in the isolator and the leading edge position of the shock train. The traditional shock train detection methods have low detection accuracy and slow detection speed. This paper describes a method based on deep learning to reconstruct the flow field in the isolator and detect the leading edge of the shock train. Under various back pressure conditions, the flow field images of computational fluid dynamics (CFD) data and the corresponding upper and lower wall pressure data were obtained, and a data set corresponding to pressure and flow field was constructed. By constructing and training convolutional neural networks, a mapping model with pressure information as input and flow field image as output is obtained, and then the leading edge position of shock train is detected on the output flow field image. The experimental results show that the average structure similarity (SSIM) between the reconstructed flow field image and the CFD flow field image is 0.902, the average peak signal-to-noise ratio (PSNR) is 25.289, the average correlation coefficient (CORR) is 0.956, and the root mean square error of shock train leading edge detection is 3.28 mm. Moreover, if the total pressure input is appropriately reduced, the accuracy of flow field reconstruction does not decline significantly, which means that the model has a certain robustness. Finally, in order to improve the detection accuracy of the leading edge position, we fine tuned the model and obtained another detection method, which reduced the root mean square error of the detection results to 1.87 mm.展开更多
When a normal shock wave interacts with a boundary layer along a wall surface in supersonic internal flows and the shock is strong enough to separate the boundary layer, the shock is bifurcated and a series of shocks ...When a normal shock wave interacts with a boundary layer along a wall surface in supersonic internal flows and the shock is strong enough to separate the boundary layer, the shock is bifurcated and a series of shocks called “shock train” is formed. The flow is decelerated from supersonic to subsonic through the whole interaction region that is referred to as “pseudo-shock”. In the present paper some characteristics of the shock train and pseudo-shock and some examples of the pseudo-shocks in some flow devices are described.展开更多
目的观察冲击波联合表面肌电生物反馈训练对创伤后肘关节僵硬的治疗效果。方法选取2021年1-12月在杭州市富阳中医骨伤医院康复科收治的创伤后肘关节僵硬患者80例,采用抽签法随机分配至对照组和治疗组,每组40例。对照组采用常规康复治疗...目的观察冲击波联合表面肌电生物反馈训练对创伤后肘关节僵硬的治疗效果。方法选取2021年1-12月在杭州市富阳中医骨伤医院康复科收治的创伤后肘关节僵硬患者80例,采用抽签法随机分配至对照组和治疗组,每组40例。对照组采用常规康复治疗(软组织松解、关节松动术、关节连续被动运动和冷疗),治疗组在常规康复治疗后采用冲击波疗法联合表面肌电生物反馈训练。两组患者每天训练1次,每周5 d,持续8周。比较两组患者治疗前后的视觉模拟疼痛评分(visual analogue scale,VAS)、肘关节主动活动度(active range of motion,AROM)、Mayo肘关节功能评分情况。结果经过8周治疗,两组患者的VAS疼痛评分、AROM、Mayo肘关节功能评分均较治疗前好转(P<0.001),治疗组在治疗后的VAS评分、AROM、Mayo肘关节功能评分改善值均优于对照组(P<0.05,P<0.001,P<0.001),两组患者治疗后均未出现不适症状。结论冲击波配合表面肌电生物反馈训练可以有效缓解创伤后肘关节僵硬患者的疼痛,改善肘关节的功能,并提高肘关节的主动关节活动度。展开更多
The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct.Multiple shock waves are formed inside the duct at a shock Mach number of ...The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct.Multiple shock waves are formed inside the duct at a shock Mach number of 1.75.The duct has an exit height of H,and the effect of duct resonance on multiple shock oscillations is investigated by attaching exit ducts of lengths 0H,50H,and 150H.The downstream disturbance frequency varied from 10 Hz to 200 Hz to explore the oscillation characteristics of the multiple shock waves.The oscillatory response of shock waves under self-excited and forced oscillation conditions are analyzed in terms of wall static pressure,shock train leading-edge location,shock train length,and the size of the separation bubble.The extent of the initial shock location increases with an increase in exit duct length for the self-excited oscillation condition.The analysis of the shock train leading edge and the spectral analysis of wall static pressure variations are conducted.The variation in the shock train length is analyzed using the pressure ratio method for self-excited as well as forced oscillations.The RMS amplitude of the normalized shock train length(ζ_(ST))increases with an increase in the exit duct length for the self-excited oscillation condition.When the downstream perturbation frequency is increased,ζ_(ST)is decreased for exit duct configurations.For all exit duct designs and downstream forcing frequencies,the size of the separation bubble grows and shrinks during the shock oscillations,demonstrating the dependence on duct resonance and forced oscillations.展开更多
基金supported by the National Research Foundation(NRF)of Korea grant funded by the Korea government(MSIP)(NRF2016R1A2B3016436)
文摘Shock tubes are devices which are used in the investigation of high speed and high temperature flow of compressible gas. lnside a shock tube, the interaction between the reflected shock wave and boundary layer leads to a complex flow phenomenon. Initially a normal shock wave is formed in the shock tube which migrates toward the closed end of the tube and that in turn leads to the reflection of shock. Due to the boundary layer interaction with the reflected shock, the bifurcation of shock wave takes place. The bifurcated shock wave then approaches the contact surface and shock train is generated. Till date only a few studies have been conducted to investigate this shock train phenomenon inside the shock tube. For the present study a computational fluid dynamics （CFD） analysis has been performed on a two dimensional axi-symmetric model of a shock tube using unsteady, compressible Navier-Stokes equations. In order to investigate the detailed characteristics of shock train, parametric studies have been performed by varying different parameters such as the shock tube length, diameter, pressure ratio used inside the shock tube.
基金supported by the National Numerical Wind Tunnel Project of China,the National Natural Science Foundation of China(Nos.12002163 and 12072157)the Natural Science Foundation of Jiangsu Province,China(No.BK20200408)+1 种基金the China Postdoctoral Science Foundation(No.2022T150321)the Key Laboratory of Hypersonic Aerodynamic Force and Heat Technology,AVIC Aerodynamics Research Institute,China。
文摘In this paper,shock train motion in a Mach number 2.7 duct is studied experimentally,and large numbers of schlieren images are obtained by a high-speed camera.An image processing method based on Maximum Correlation Detection(MCD)is proposed to detect shock train motion from the schlieren images,based on which the key structures,e.g.,separation positions and separation shock angles on the top and bottom walls,can be analysed in detail.The oscillations of the shock train are generated by rhombus and ellipse shafts at various excitation frequencies.According to the analysis of MCD results,the distributions of the frequency components of shock train oscillation generated by the two shafts are distinctly different,in which the motion generated by the ellipse shaft is much smoother;shock train motion is mainly characterized by the oscillation of separation position while the separation shock strength is not so sensitive to downstream disturbance;there is a hysteresis loop relation between the downstream pressure and separation position.
基金supported by the National Natural Science Foundation of China(Nos.51476076 and 10702029)
文摘The structure and dynamics of an oblique shock train in a duct model are investigated experimentally in a hypersonic wind tunnel.Measurements of the pressure distribution in front of and across the oblique shock train have been taken and the dynamics of upstream propagation of the oblique shock train have been analyzed from the synchronized schlieren imaging with the dynamic pressure measurements.The formation and propagation of the oblique shock train are initiated by the throttling device at the downstream end of the duct model.Multiple reflected shocks,expansion fans and separated flow bubbles exist in the unthrottled flow,causing three adversepressure-gradient phases and three favorable-pressure-gradient phases upstream the oblique shock train.The leading edge of the oblique shock train propagates upstream,and translates to be asymmetric with the increase of backpressure.The upstream propagation rate of the oblique shock train increases rapidly when the leading edge of the oblique shock train encounters the separation bubble near the shock reflection point and the adverse-pressure-gradient phase,while the oblique shock train slow movement when the leading edge of the oblique shock train is in the favorablepressure-gradient phase for unthrottled flow.The asymmetric flow pattern and oscillatory nature of the oblique shock train are observed throughout the whole upstream propagation process.
基金National Natural Science Foundation of China(Grant No.51706237)CARDC Fundamental and Frontier Technology Research Fund,and the“1912 Program”(Grant No.001-060).
文摘Scramjet is the main power device of hypersonic vehicles. With the gradual expansion of wide velocity domain, shock wave/shock wave and shock wave/boundary layer are the main phenomena in scramjet isolator. When the leading edge of the shock train is pushed out from the inlet of the isolator, the engine will not start. Therefore, it is very important to detect the flow field structure in the isolator and the leading edge position of the shock train. The traditional shock train detection methods have low detection accuracy and slow detection speed. This paper describes a method based on deep learning to reconstruct the flow field in the isolator and detect the leading edge of the shock train. Under various back pressure conditions, the flow field images of computational fluid dynamics (CFD) data and the corresponding upper and lower wall pressure data were obtained, and a data set corresponding to pressure and flow field was constructed. By constructing and training convolutional neural networks, a mapping model with pressure information as input and flow field image as output is obtained, and then the leading edge position of shock train is detected on the output flow field image. The experimental results show that the average structure similarity (SSIM) between the reconstructed flow field image and the CFD flow field image is 0.902, the average peak signal-to-noise ratio (PSNR) is 25.289, the average correlation coefficient (CORR) is 0.956, and the root mean square error of shock train leading edge detection is 3.28 mm. Moreover, if the total pressure input is appropriately reduced, the accuracy of flow field reconstruction does not decline significantly, which means that the model has a certain robustness. Finally, in order to improve the detection accuracy of the leading edge position, we fine tuned the model and obtained another detection method, which reduced the root mean square error of the detection results to 1.87 mm.
文摘When a normal shock wave interacts with a boundary layer along a wall surface in supersonic internal flows and the shock is strong enough to separate the boundary layer, the shock is bifurcated and a series of shocks called “shock train” is formed. The flow is decelerated from supersonic to subsonic through the whole interaction region that is referred to as “pseudo-shock”. In the present paper some characteristics of the shock train and pseudo-shock and some examples of the pseudo-shocks in some flow devices are described.
文摘目的观察冲击波联合表面肌电生物反馈训练对创伤后肘关节僵硬的治疗效果。方法选取2021年1-12月在杭州市富阳中医骨伤医院康复科收治的创伤后肘关节僵硬患者80例,采用抽签法随机分配至对照组和治疗组,每组40例。对照组采用常规康复治疗(软组织松解、关节松动术、关节连续被动运动和冷疗),治疗组在常规康复治疗后采用冲击波疗法联合表面肌电生物反馈训练。两组患者每天训练1次,每周5 d,持续8周。比较两组患者治疗前后的视觉模拟疼痛评分(visual analogue scale,VAS)、肘关节主动活动度(active range of motion,AROM)、Mayo肘关节功能评分情况。结果经过8周治疗,两组患者的VAS疼痛评分、AROM、Mayo肘关节功能评分均较治疗前好转(P<0.001),治疗组在治疗后的VAS评分、AROM、Mayo肘关节功能评分改善值均优于对照组(P<0.05,P<0.001,P<0.001),两组患者治疗后均未出现不适症状。结论冲击波配合表面肌电生物反馈训练可以有效缓解创伤后肘关节僵硬患者的疼痛,改善肘关节的功能,并提高肘关节的主动关节活动度。
基金supported by Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(NRF-2021R1I1A3044216)。
文摘The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct.Multiple shock waves are formed inside the duct at a shock Mach number of 1.75.The duct has an exit height of H,and the effect of duct resonance on multiple shock oscillations is investigated by attaching exit ducts of lengths 0H,50H,and 150H.The downstream disturbance frequency varied from 10 Hz to 200 Hz to explore the oscillation characteristics of the multiple shock waves.The oscillatory response of shock waves under self-excited and forced oscillation conditions are analyzed in terms of wall static pressure,shock train leading-edge location,shock train length,and the size of the separation bubble.The extent of the initial shock location increases with an increase in exit duct length for the self-excited oscillation condition.The analysis of the shock train leading edge and the spectral analysis of wall static pressure variations are conducted.The variation in the shock train length is analyzed using the pressure ratio method for self-excited as well as forced oscillations.The RMS amplitude of the normalized shock train length(ζ_(ST))increases with an increase in the exit duct length for the self-excited oscillation condition.When the downstream perturbation frequency is increased,ζ_(ST)is decreased for exit duct configurations.For all exit duct designs and downstream forcing frequencies,the size of the separation bubble grows and shrinks during the shock oscillations,demonstrating the dependence on duct resonance and forced oscillations.
