Shock-wave/Boundary-Layer Interactions (SBLI): Physics and Control

激波/边界层干扰(SBLI)是未来所有航天系统发展的关键研究领域，因为它们普遍存在于高速空气动力流动中。SBLI区域的超常压力和热负荷造成了各种各样的问题，包括航空结构和相关保护系统的损坏/快速疲劳、进气扭曲和发动机不启动，所有这些都可能产生不利的后果。以前的研究指出，激波/分离区的低频不稳定是一种主要现象，并表明，如果不对不稳定有所了解，即使是平均性质的行为也不能完全理解。此外，计算研究发现，由于所用模型的局限性，很难准确地捕捉SBLIS的动态。因此，利用最先进的实验技术进行激波/边界层相互作用的实验研究是至关重要的。这个项目的目的是开发一种超音速设备，在那里可以使用最先进的实验方法来获得定性和定量的信息。发展先进的光学诊断技术，包括粒子图像加速度计(PIA)和多平面粒子图像测速(PIV)。高质量成像测量将与快速响应表面压力测量一起进行，以表征各种流动形态中激波/边界层相互作用的不稳定性和三维性质。测量将在上游超音速边界层、干扰区和激波诱导分离区进行。这些数据将被仔细分析，目的是建立一个物理框架，以解释导致不稳定的原因和流场的三维性质。将采用通用(涡流发生器、流向缝隙)和最先进的(压电致动器)控制方案来控制冲击波不稳定的频率和幅度。这些部件将被驱动，并将得到相位平均的速度、加速度和压力场。这些数据将被用来了解流量对控制方案的响应，这反过来又可以帮助开发改进的控制策略。此外，我们亦会探讨采用闭环系统以达致所需的局部控制的可行性。

Shock-wave/boundary-layer interaction (SBLI) is a critical area of research for the development of all future aerospace systems as they are ubiquitous in high-speed aerodynamic flows. The extraordinary pressure and thermal loads in the regions of SBLI poses a wide variety of problems including damage/rapid fatigue to aero-structures and associated protection systems, inlet flow distortion and engine unstart, all of which could have adverse consequences. Previous studies have noted that the low frequency unsteadiness of the shock-wave/separation region as a dominant phenomenon and indicated that even the behaviour of mean properties cannot be fully understood without some knowledge on the unsteadiness. Moreover, computational studies find it difficult to accurately capture the dynamics of SBLIs due to the limitations of the models employed. Therefore, it is vitally important to perform experimental investigations of shock-wave/boundary-layer interaction using state-of-the-art experimental techniques. The aim of this project is to develop a supersonic facility where state-of-the-art experimental methods can be employed to obtain qualitative and quantitative information. Advanced optical diagnostic techniques including Particle Image Accelerometry (PIA) and multiple-plane Particle Image Velocimetry (PIV) will be developed. High-quality imaging measurements will be performed together with fast-response surface pressure measurements to characterise the unsteadiness and the three-dimensional nature of shock-wave/boundary-layer interactions in a variety of flow configurations. Measurements will be obtained in the upstream supersonic boundary layer, the interaction region and in the shock induced separation region. The data will be carefully analysed with the aim of developing a physical framework to explain the causes responsible for the unsteadiness and the three-dimensional nature of the flow field.Generic (vortex generators, streamwise slots) and state-of-the-art (piezo actuators) control schemes will be employed to control the frequency and amplitude of shock-wave unsteadiness. The components will be actuated and phase-averaged velocity, acceleration and pressure fields will be obtained. The data will be used to understand the response of the flow to the control scheme, which in turn can help in development of improved control strategies. The feasibility of employing closed-loop schemes to achieve necessary localised control will also be explored.