Multiple Observation Scales Based Fundamental Investigations On The Shock Wave/turbulent Boundary-layer Interaction

The supersonic inlets are the key components for the air compression of high-speed flights and affect their aerodynamic performance obviously.Thus,the inner flow conditions of inlets have a vital effect on the propulsion systems and the overall performance of fights.The shock wave/turblent boundary-layer interactions(SWTBLI),a dominate flow phenomenon in supersonic inlets,play an important role in deciding key features of inlets.Consequently,SWTBLI has caused widespread concern and has been studied systematically.However,some uncovered and controversial topics still exist in this research field.Moreover,previous studies focused mainly on the macro-scale features.To further increase our understanding on SWTBLI,it is necessary to conduct investigations from different perspectives and on a broader measuring range.Two classic SWTBLIs,the compression ramp interaction(CR-SWTBLI)and the impinging interaction(I-SWTBLI),are selected as the objectives of study.Multiple measuring techniques,like the surface pressure measurement,the boundary-layer profile scanning,the schlieren visualization and the planar laser scattering(PLS),are applied to these two interaction flows.The fractal analysis and a machine-learning based character detection method are used in these studies.Based on these methods and analyses,several fundamental issues of SWTBLI are explained.G(?)rtler-like vortice(GLV)is one of the key features of separated SWTBLI flow and has a significant effect on multiple flow characters including the overall flow pattern.To deepen the insight into features of GLV in CR-SWTBLI flow,PLS visualization technique is applied on multiple directions and positions to acquire GLV's geometrical characters.At the same time,to cover the dispute about the existence of GLV in separated I-SWTBLI flow,a simplified model is introduced.Several model-based key parameters are acquired from experimental observations.Accordingly,the effect of G(?)rtler instability in the vicinity of the separation position and the reattachment position are analyzed.Meanwhile,large-scale streamwise vortices are directly observed on a surface parallel to the bottom surface.It is rational that these large streamwise vortices are GLVs according to previous analyses.This result support the presence of GLVs in the separated I-STBLI flow.Turbulent/nonturbulent interface(TNTI),the surface that separates the turbulent and irrotational flow regions,possesses information of the geometry of vortical structures in turbulence and is vital in understanding the development of turbulence.In order to conduct TNTI-based SWTBLI studies,it is necessary to first extend the study on the fractal features of TNTI to the supersonic regime.The result shows that the TNTI of a zero-pressure-gradient supersonic boundary-layer is a fractal with the fractal dimension of 2.31 and an upper-scale limitation.Further investigation on the effect of the separated CR-SWTBLI and the following relaxation on the fractal features of TNTI is conducted.The results show that both these two phenomena have significant effects on the fractal features of TNTI.Coherent vortical structure(CVS),the basic element of turbulence,is of fundamental importance to the understanding of turbulent boundary-layer dynamics.A CVS-based CR-SWTBLI study is conducted.Specifically,by dealing the PLS images with a machine-learning method,several features of 2-dimensional slices of CVS are acquired.The impacts of SWTBLI on the CVS is presented by comparing different features acquired before and after the interaction.An existing theoretical-model-based explanation on these impacts is demonstrated.The effects of rear expansion wave on I-SWTBLI flow is difficult to eliminate yet received little attention.In this paper,the distance between inviscid impinging point and the rear wave position is chosen as the key parameter to experimentally study the effect of rear expansion wave on separated I-SWTBLI.The overall flow structure and the influence of the distance on the separation pattern are obtained by optical visualization and wall-pressure measurement.The free-interaction theory combined with previous results are applied to explain the mechanism of the influence of downstream interference on the separated I-SWTBLI,and the corresponding physical model is established.