Structure And Mechanism On The Disturbed Supersonic Turbulent Boundary Layer

The disturbed supersonic turbulent boundary layer(BL)widely exists on the surface and inside the engine of hypersonic vehicles.Motivated by the development of scramjet engine combustor,the urgency of the study on the turbulent characteristics of various BL is gradually increased.The present study embarks from the practical application,combining the experimental(Nanoparticle-based Planar Laser Scattering,Particle Image Velocimetry and oil flow visualization)and numerical(Reynolds-averaged Navier–Stokes)method to clarify the structure and turbulence characteristics in the BL affected by internal wall injection and auxiliary injection of the scramjet.And in the meantime,the BL subjected to the changes of aircraft wall surface,combustion and inlet are also considered.To simplify the research,the object of the study is simplified from the complex multi-factor combination disturbed BL to the aerodynamic single-factor disturbed BL,then to the slightly simple lateral mechanical disturbed BL(the boundary layer disturbed by multiple pressure gradients together),and finally to the mechanical disturbed BL with one single pressure gradient.The disturbance mechanisms of the lateral disturbed cases are similar.The near-wall wake zone could be divided into three regions: the V-shape separation region behind the jet,followed by the reattachment region and the mixing and recovery zone further downstream.Root Mean Square(RMS)of NPLS images,PIV data and oil flow images exhibit that turbulent fluctuation is suppressed downstream of the horseshoe separation zone in the lateral region while it is enhanced in the wake region.As the distance away from the wall increases,the influences of the shock system,the expansion process,and the reflected shock in turbulence intensity and velocities of the crossflow BL is weakened gradually.A three-dimensional(3-D)schematic diagram of each disturbed turbulent BL is presented,explaining the formation of the turbulence decay zone in the lateral region.In the study of jet disturbed BL,lower jet-to-crossflow momentum flux ratio cases always have shorter distance from the orifice to the interaction position of the V-shape collision shock and the reflected shock.The angle between the main separation lines is found to be independent of J.Correlations for predicting the separation length and width are proposed based on the experiments of different momentum flux ratios.Different from the jet disturbed turbulent BL,the BL of pylon-aided one undergos two compression procsess,one from the tower itself to the flow channel,and the other from the jet expansion core to the fluid.Upstream of the jet orifice,the detached shock generated at the leading edge of the pylon is identified by inserting with the separation shock.Besides,the mechanism of mixing enhancement resulting from the pylon is also elaborated in the present work.In the turbulent BL subjected to concave curvature,the concave curvature disturbance causes the increase of the turbulence intensity,and the vortices are broken to smaller ones.It is found that the large-scale vortex structures in the turbulent BL show obvious queue characteristics,and the interaction between two adjacent vortex columns is gradually weakened and then recovered.In the turbulent BL subjected to expansion,the turbulence intensity of the BL is found decreased,the size of the vortex structure is enlarged,and the relaminaration of the BL flow occurs at the near wall region of the BL both in a steamwise and spanwise observation.In the spanwise direction,the interaction between vortex structures in the BL is weakened,and the vortex structures in the region near the wall have a striping trend,and then gradually recover to normal.