| The investigations of shock interaction and shock/turbulent boundary layer inter-action are of great importance for both development of high-speed vehicles and com-pressible turbulence flow.In this dissertation,large-eddy simulation is employed to study three typical flows including shock interactions on V shaped blunt leading edges,shock/turbulent boundary layer interactions near convex corners and shock train os-cillations in an axisymmetrical inlet.The results and conclusions are briefly given as follows:(1)The unsteady dynamics of shock interactions on the crotch of two typical V-shaped blunt leading edges have been investigated numerically and experimen-tally with a freestream Mach number 6 for different ratios(R),defined as the rounding radius at the crotch to the blunt radius at the leading edge.The pri-mary flow features observed in the shock tunnel experiments are reproduced with the present large-eddy simulations.Strikingly high wall pressure are found in the region where the transmitted shock impinges on the crotch.The time-averaged flow structures in the crotch are clearly shown as counterrotating vortices origi-nating from the collision of jets behind the transmitted shocks.These jets and vortices further undergo unsteady motions coupled with the dynamics of shock interactions.Two typical global oscillations of the flow,i.e.,swing oscillation and arch-recover oscillation corresponding to the two values of R,are identified,and the behaviors relevant to the oscillation flows are discussed.Moreover,the coherent structures of the flow motion are analyzed using the proper orthogonal decomposition technique.It is demonstrated that the swing oscillation is charac-terized by an antisymmetric mode,while the arch-recover oscillation is character-ized by a symmetrical mode.These two flow oscillations are also characterized by the energetic middle-frequency components of the broadband spectral of the wall pressure,which are associated with disturbance propagation in the overall crotch region.This finding has been confirmed by the spectral analysis of the wall pressure measured in the experiment.Two feedback models are proposed for the reasonable prediction of such dominant middle-frequency components.Com-parisons of the root-mean-square of the fluctuating pressure show that the swing oscillation for R = 1.75 causes much more severe pressure fluctuation,and the local impingement of the transmitted shock on the crotch is responsible for the peak value of the pressure fluctuation.The turbulent statistical quantities have been analyzed in the crotch region.The dilatational dissipation and pressure-dilatation correlation have exhibited that the compressibility effect is enhanced owing to the jet impingement and shock/reverse-flow interaction.(2)Large-eddy simulations are conducted on shock/convex-corner boundary layer in-teractions.Two typical convex corners with sharp corner and blunt corner are investigated.The effects of the two convex corners on the flow structures,bound-ary features,unsteady separation motions and turbulent statistical characteristic are systematically analyzed.For the sharp corner,strikingly high values of the favorable pressure gradient are generated near the corner.As a result,the wall friction coefficient increases to a high level,and the separation point of the separ ration bubble is restricted at downstream edge of the corner.Although the sep-aration point is motionless for sharp corner case,a contractile/dilative pulsation caused by the front/back motion of attachment point is illustrated by the analysis of flow evolution.However,for the blunt corner case,the separation point is not restricted by the favorable pressure gradient at the corner.As a consequence,the separation bubble not only undergoes a contractile and dilative pulsation,but also moves upstream and downstream integrally.The intensity of downstream flow fluctuation is enhanced by the incident shock interaction.The distribution of the fluctuating pressure for the blunt corner is similar to the canonical shock wave/turbulent boundary layer interaction,while for the sharp corner,a peak value appears at the corner.(3)The shock train oscillation in an axisymmetric inlet is investigated using large-eddy simulation.The back pressure is generated by a fixed block at the inlet exit with a throttling ratio of 0.508.Contributions of averaged wall pressure and frequencies of fluctuating pressure have been validated against experiment care-fully.Various fundamental phenomena,including the flow structures,unsteady shock wave behaviors and mechanisms,fluctuating pressure characteristics and kinematics of coherent structures,have been studied systematically.It is found that the shock train is induced in the inlet to match the backpressure,and thus three typical flow regions are classified as supersonic region,shock train region and subsonic region.Coupling and interaction between shock/shear-layer/separated boundary layer are formed in the shock train region,as the result of adverse pres-sure gradient.With the quasi-periodic unsteady motion of the flows in the shock train region,the fluctuating pressure exhibits a broadband spectral feature.The coherent structures of the flow motion are analyzed using the proper orthogonal decomposition technique,which indicates that the fluctuating pressure propagates in the subsonic with a form of disturbance wave.A feedback model is proposed for the reasonable prediction of dominant frequency in the downstream of shock train.According to correlation analysis,the motion of shock train is influenced by the coupling of the upstream and downstream flow.Correspondingly,the motion with frequency St = 0.7 is influenced by the upstream flow,while the motion with frequency St = 0.9 is influenced by the downstream flow.The turbulent statistical quantities have been analyzed in detail and different behaviors are found in the three flow regions.Both the turbulence kinetic energy and fluctuating pressure are enhanced by the interaction of the shock/turbulent separation. |
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