带抽吸二元进气道/隔离段激波串振荡特性

Shock Train Oscillations in a Two-Dimensional Inlet/Isolator with Suction

关键词:  二元进气道  隔离段  抽吸缝  激波串  振荡特性

Key words:  Two-dimensional inlet  Isolator  Suction slots  Shock train  Oscillation characteristics

摘要:

针对抽吸缝作用下激波串非定常振荡的复杂流动问题，采用高速纹影结合壁面动态压力测量的方法，在马赫数6的激波风洞中研究了高马赫数二元进气道/隔离段中激波串的自激振荡特性。隔离段出口不同堵塞度的实验结果表明：在低堵塞度下，隔离段内的分离激波无明显振荡；在中等堵塞度25.3%~32.3%和高堵塞度35.3%~38.2%工况下，隔离段内产生非定常激波串，受到隔离段内预先存在的背景波系以及抽吸缝泄流作用的影响，分别出现大幅度低频振荡和小幅度高频振荡；而当堵塞度超过临界值后，激波串被推出进气道，出现不起动。在大幅度振荡模式中，上壁面大分离区周期性地形成和消失，下壁面的激波串前沿分离激波在抽吸缝后缘到隔离段出口之间大幅度振荡，其振荡主频约为280Hz~480Hz，并且随着堵塞度升高而降低；在小幅度振荡模式中，上壁面始终存在大分离区，下壁面的激波串前沿分离激波在抽吸缝附近小幅振荡，其振荡主频约为900Hz~1800Hz。两种振荡模式均给隔离段壁面带来严酷的脉动压力载荷。

Abstract:

The characteristics of shock train oscillations in a two-dimensional inlet/isolator were investigated in a Mach 6 shock tunnel to reveal the complicated unsteady flow under the influence of suction slots. High-speed schlieren images and fluctuating wall pressure were acquired synchronously. Various throttling ratios were imposed at the isolator exit to simulate backpressure. The experimental results show that at low throttling ratios, non-oscillatory separation shocks are observed first. At medium throttling ratios of 25.3%~32.3% and high throttling ratios of 35.3%~38.2%, the unsteady shock train forms and presents a large-amplitude low-frequency oscillation mode and a small-amplitude high-frequency oscillation mode, respectively, under the effects of pre-exist background waves and boundary-layer suction in the isolator. When the throttling ratio exceeds a critical value, the shock train is pushed out of the inlet and an unstart occurs. In the large-amplitude oscillation mode, a large separation zone forms and vanishes periodically on the upper wall. As a result, on the lower wall, the leading separation shock of the shock train moves forward and backward repeatedly between the trailing edge of the suction slot and the isolator exit. The dominant frequencies of the large-amplitude oscillation mode are 280Hz~480Hz, which decrease with the increase of the throttling ratio. In the small-amplitude oscillation mode, a large separation zone on the upper wall persists throughout, whereas the leading separation shock of the shock train oscillates near the suction slots at the lower wall. The dominant frequencies of the small-amplitude oscillation mode are 900Hz~1800Hz. Both oscillation modes cause severe fluctuating pressure loads in the isolator.