Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to app...Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the practicability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disintegrates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17 % occurs with a triangular shape, while the maximum increase in aerodynamic efficiency（lift-to-drag ratio）of around 10 % happens with a rectangular shape at an angle of attack of 2.26？.展开更多
加氢装置是炼化企业典型的高危装置,涉及氢气等易燃易爆介质,安全风险较高。为研究加氢装置在开敞空间条件下氢气泄漏爆炸事故火焰及冲击波时空演化过程,基于FLACS三维模拟软件对某企业加氢装置建立了等比例模型,并对其进行氢气爆炸模...加氢装置是炼化企业典型的高危装置,涉及氢气等易燃易爆介质,安全风险较高。为研究加氢装置在开敞空间条件下氢气泄漏爆炸事故火焰及冲击波时空演化过程,基于FLACS三维模拟软件对某企业加氢装置建立了等比例模型,并对其进行氢气爆炸模拟研究,探究了不同当量比(ER)对氢气云燃爆超压值及温度的影响。研究结果表明,当量比(ER)在0.8~1.4范围内时,氢气爆炸的温度、超压峰值P max均随ER的增大呈先增大后减小的趋势,ER为1.05时,爆炸温度峰值及超压峰值最大,高温火焰传播范围半径约35 m,影响面积达到3800 m 2。此外,模拟结果为类似场景建筑物抗爆工程改造提供了理论指导。展开更多
针对推力状态控制时执行机构传感器发生故障影响发动机安全运行的问题,提出了一种非相似容错控制计划。该方法将燃油闭环/喷管开环和喷管闭环/燃油开环两种控制计划互为备份,并结合一种惯性切换逻辑,在执行机构传感器发生故障时切换控...针对推力状态控制时执行机构传感器发生故障影响发动机安全运行的问题,提出了一种非相似容错控制计划。该方法将燃油闭环/喷管开环和喷管闭环/燃油开环两种控制计划互为备份,并结合一种惯性切换逻辑,在执行机构传感器发生故障时切换控制计划以保障发动机的安全运行。面向串联式TBCC(Turbine Based Combined Cycle)发动机的冲压模态开展了仿真验证,结果表明,该容错控制计划能够实现发动机全包线范围内的推力状态容错控制,并且在传感器发生故障时能够平稳切换,推力波动小于1%,增强了控制系统的容错性。展开更多
A three-electrode high-energy plasma synthetic jet(PSJ) actuator was used for shock wave control. This actuator is an enhanced version of the two-electrode actuator as a high-voltage trigger electrode is added to incr...A three-electrode high-energy plasma synthetic jet(PSJ) actuator was used for shock wave control. This actuator is an enhanced version of the two-electrode actuator as a high-voltage trigger electrode is added to increase the cavity volume and the input energy while retaining a relatively low disruptive voltage. The electrical properties were studied using current-voltage measurements, and the energy consumption was calculated. To assess the jet strength, the penetration of PSJ was compared with empirical values, and the results show that the momentum flux ratio of PSJ for a capacitance of 0.96, 1.6, and 3 μF was approximately equal to 0.6, 1.0, and 1.3, respectively. The interaction of PSJ with shock waves was acquired using high-speed shadowgraph imaging. The shock was generated by a 25° compression ramp in Mach 2 flow, and PSJ actuator was placed up-stream of the compression ramp. Under the action of PSJ, the strength of the shock was notably weakened, and the near-wall part of the shock was entirely eliminated. The results show the good control effect of the three-electrode high-energy PSJ in high-speed flow.展开更多
This article is devoted to experimental study on the control of the oblique shock wave around the ramp in a low-temperature supersonic flow by means of the magnetohydrodynamic （MHD） flow control technique. The purpo...This article is devoted to experimental study on the control of the oblique shock wave around the ramp in a low-temperature supersonic flow by means of the magnetohydrodynamic （MHD） flow control technique. The purpose of the experiments is to take advantage of MHD interaction to weaken the oblique shock wave strength by changing the boundary flow characteristics around the ramp. Plasma columns are generated by pulsed direct current （ DC ） discharge, the magnetic fields are generated by Nd-Fe-B rare-earth permanent magnets and the oblique shock waves in supersonic flow are generated by the ramp. The Lorentz body force effect of MHD interaction on the plasma-induced airflow velocity is verified through particle image velocimetry（PIV）measurements. The experimental results from the supersonic wind tunnel indicate that the MHD flow control can drastically change the flow characteristics of the airflow around the ramp and decrease the ratio of the Pitot pressure after shock wave to that before it by up to 19.66% ,which leads to the decline in oblique shock wave strength. The oblique shock waves in front of the ramp move upstream by the action of the Lorentz body force. The discharge characteristics are analyzed and the MHD interaction time and consumed energy are determined with the help of the pulsed DC discharge images. The interaction parameter corresponding to the boundary layer velocity can reach 1.3 from the momentum conservation equation. The velocity of the plasma column in the magnetic field is much faster than that in the absence of magnetic field force. The plasma can strike the neutral gas molecules to transfer momentum and accelerate the flow around the ramp.展开更多
文摘Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the practicability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disintegrates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17 % occurs with a triangular shape, while the maximum increase in aerodynamic efficiency（lift-to-drag ratio）of around 10 % happens with a rectangular shape at an angle of attack of 2.26？.
文摘加氢装置是炼化企业典型的高危装置,涉及氢气等易燃易爆介质,安全风险较高。为研究加氢装置在开敞空间条件下氢气泄漏爆炸事故火焰及冲击波时空演化过程,基于FLACS三维模拟软件对某企业加氢装置建立了等比例模型,并对其进行氢气爆炸模拟研究,探究了不同当量比(ER)对氢气云燃爆超压值及温度的影响。研究结果表明,当量比(ER)在0.8~1.4范围内时,氢气爆炸的温度、超压峰值P max均随ER的增大呈先增大后减小的趋势,ER为1.05时,爆炸温度峰值及超压峰值最大,高温火焰传播范围半径约35 m,影响面积达到3800 m 2。此外,模拟结果为类似场景建筑物抗爆工程改造提供了理论指导。
文摘针对推力状态控制时执行机构传感器发生故障影响发动机安全运行的问题,提出了一种非相似容错控制计划。该方法将燃油闭环/喷管开环和喷管闭环/燃油开环两种控制计划互为备份,并结合一种惯性切换逻辑,在执行机构传感器发生故障时切换控制计划以保障发动机的安全运行。面向串联式TBCC(Turbine Based Combined Cycle)发动机的冲压模态开展了仿真验证,结果表明,该容错控制计划能够实现发动机全包线范围内的推力状态容错控制,并且在传感器发生故障时能够平稳切换,推力波动小于1%,增强了控制系统的容错性。
基金supported by the National Natural Science Foundation of China(Grant Nos.11372349&11502295)the Nature Science Fund for Distinguished Young Scholars of National University of Defense Technology(Grant No.CJ110101)
文摘A three-electrode high-energy plasma synthetic jet(PSJ) actuator was used for shock wave control. This actuator is an enhanced version of the two-electrode actuator as a high-voltage trigger electrode is added to increase the cavity volume and the input energy while retaining a relatively low disruptive voltage. The electrical properties were studied using current-voltage measurements, and the energy consumption was calculated. To assess the jet strength, the penetration of PSJ was compared with empirical values, and the results show that the momentum flux ratio of PSJ for a capacitance of 0.96, 1.6, and 3 μF was approximately equal to 0.6, 1.0, and 1.3, respectively. The interaction of PSJ with shock waves was acquired using high-speed shadowgraph imaging. The shock was generated by a 25° compression ramp in Mach 2 flow, and PSJ actuator was placed up-stream of the compression ramp. Under the action of PSJ, the strength of the shock was notably weakened, and the near-wall part of the shock was entirely eliminated. The results show the good control effect of the three-electrode high-energy PSJ in high-speed flow.
基金National Natural Science Foundation of China(50776100)
文摘This article is devoted to experimental study on the control of the oblique shock wave around the ramp in a low-temperature supersonic flow by means of the magnetohydrodynamic （MHD） flow control technique. The purpose of the experiments is to take advantage of MHD interaction to weaken the oblique shock wave strength by changing the boundary flow characteristics around the ramp. Plasma columns are generated by pulsed direct current （ DC ） discharge, the magnetic fields are generated by Nd-Fe-B rare-earth permanent magnets and the oblique shock waves in supersonic flow are generated by the ramp. The Lorentz body force effect of MHD interaction on the plasma-induced airflow velocity is verified through particle image velocimetry（PIV）measurements. The experimental results from the supersonic wind tunnel indicate that the MHD flow control can drastically change the flow characteristics of the airflow around the ramp and decrease the ratio of the Pitot pressure after shock wave to that before it by up to 19.66% ,which leads to the decline in oblique shock wave strength. The oblique shock waves in front of the ramp move upstream by the action of the Lorentz body force. The discharge characteristics are analyzed and the MHD interaction time and consumed energy are determined with the help of the pulsed DC discharge images. The interaction parameter corresponding to the boundary layer velocity can reach 1.3 from the momentum conservation equation. The velocity of the plasma column in the magnetic field is much faster than that in the absence of magnetic field force. The plasma can strike the neutral gas molecules to transfer momentum and accelerate the flow around the ramp.
