隔离段内激波串受稳态和脉动背压影响的数值研究

Numerical Study of Effects of Steady and Oscillating Back-Pressure on Shock Train in an Isolator

关键词:  隔离段  激波串  稳态背压  脉动背压  自激振荡  共振

Key words:  Isolator  Shock train  Steady back pressure  Oscillating back pressure  Self-excited oscillation  Resonance

摘要:

为了加深对背压影响下的隔离段工作特性的认识，基于非稳态雷诺平均的Navier-Stokes方程，探究在来流Ma=2.94条件下隔离段内激波串在稳态背压、脉动背压与共振状态下的振荡特性。结果表明：隔离段激波串的自激振荡频率受稳态背压大小的影响，激波串在9倍和10倍来流静压的稳态背压条件下会产生频率分别为506Hz和454 Hz的自激振荡，且激波串前缘位置呈周期振荡。在脉动背压条件下，激波串运动受脉动背压和自激振荡的共同作用，产生多个主导频率；当脉动背压振荡频率与自激振荡频率相近时，激波串运动达到共振状态，主要体现在激波串振幅的增强，振幅大小可以达到管道长度的33.5%，而受到100Hz的低频脉动背压影响时，振幅大小为管道长度的24%；同时共振状态下隔离段内上游的压升较受100Hz低频脉动背压影响下的压升更高；针对出口脉动背压的相位变化对共振状态下激波串运动的研究表明，相位变化对激波串运动的振幅几乎没有影响。

Abstract:

In order to have a better understanding of the effects of the back pressure on the working characteristics of isolator，a numerical simulation using the 2D unsteady Reynolds averaged Navier-Stokes equations was performed to study the characteristics of the shock train in the isolator with Mach number 2.94 incoming flow under the conditions of steady back-pressure， oscillating back-pressure and resonance oscillating. Results show that the self-excited oscillation frequency of the shock train in the isolator is affected by the steady back-pressure. The self-excited oscillation frequencies of the shock train are 506Hz and 454Hz， respectively at the steady back-pressure 9 times and 10 times of the incoming static pressure. The leading edge of the shock train is observed to oscillate periodically. Under the condition of oscillating back-pressure， the shock train is affected by both oscillating back-pressure and its self-excited oscillation， and is dominated by multiple frequencies. When the frequency of oscillating back-pressure is set to be close to the self-excited frequency， the shock train reaches resonance state， which is mainly reflected in the amplitude enhancement of the shock motion. The oscillation amplitude of the shock motion increased to 33.5% of the model length. However， the oscillation amplitude is only 24% of the model length with the forced oscillating frequency of 100Hz. Meanwhile， the pressure rise in the upstream of isolator at the resonance state is higher than that with the forced oscillating frequency of 100Hz. In addition， whether the oscillated back pressure’s phase change has effect on the resonant shock train motion was studied. Results show that phase change has no effect on the amplitude of the resonant shock train.