Detached Eddy Simulation (DES) Of Hypersonic Inlet Shock Oscillation

Supersonic and hypersonic turbulent flows are always very complex, involvingmany complicated phenomena such as shock wave, expansion wave, wave/waveinteraction, shock wave/turbulent boundary layer interaction and massively separatedflow. RANS methods are now generally used to calculate supersonic and hypersonicturbulent flows in practice applications, but incapable of simulating massivelyseparated flow accurately. LES methods do better than RANS methods, butcomputational resources at the moment keep off the whole field LES simulation ofhigh Reynolds number flows when wall effects are involved. Thus hybrid RANS/LESmethods are developed to arrive at a trade-off between accuracy and efficiency.DES-type methods are representatives of hybrid RANS/LES methods, aiming at theprediction of separated flows at unlimited Reynolds-numbers.Hypersonic inlet is the air breathing system of scramjet. When the inlet isunstarted, the phenomenon of periodic swallowing/disgorging of shock and separationbubble, which is named as shock oscillation, can appear. Shock oscillation alwayscontains massively separated flow, so RANS methods are not suitable for thesimulation, and DES-type methods are preferred.In present work, DES-type methods for supersonic and hypersonic turbulent flowsare established, based on three-dimensional, multi-block, parallel, structure grid, finitevolume methods. Then DES-type methods are validated with the simulation of severalclassic cases. Finally, oscillatory flow of a hypersonic inlet caused by downstreammass-flow choking is simulated using DES-type methods. Results of the simulationshow that the oscillation period is quite close to that of the experiment. Pressurecontours, Mach number contours, density gradient contours and large-scale vortexstructures of the simultaneous flow field can be clearly derived from the results. Thus itis concluded that DES-type methods have a good capability in simulating supersonicand hypersonic turbulent flow.In the first chapter, numerical methods for turbulent flows and the researchprogress of DES-type methods are introduced, and then, the research progress of shockoscillation is reviewed.In the second chapter, numerical methods are presented in detail, including thecontrol functions of DES-type methods, spatial and temporal discretization, initial andboundary conditions, etc.In the third chapter, seven classic cases are calculated to validate the methods.Spatial and Temporal discretization is verified through Sod’s shock tube problem,forward step problem, and laminar flow over a cylinder. The background RANS modelof DES-type methods is verified through a supersonic cavity flow. The capability ofDES-type methods in simulating turbulent flows are validated through several cases,including flow over a cylinder at high Reynolds-numbers, supersonic mixing layer andsupersonic base flow. In the fourth chapter, oscillatory flow of a hypersonic inlet caused by downstreammass-flow choking is simulated using DES-type methods. Results show that theoscillation period, the flow field evolution in an oscillation cycle and the pressuresignal evolution recorded by dynamic sensors are all quite in accordance with theexperiments, concluding that DES-type methods established in this thesis is credible inthe simulation of hypersonic inlet. Pressure contours, Mach number contours, densitygradient contours of the simultaneous flow field can be clearly derived from the results.Large-scale vortex structures can be captured with the help of the isosurface ofQ-criterion. Thus it can be inferred that DES-type methods are capable in the study ofhypersonic inlet flows.The fifth chapter is mainly the conclusions of this thesis and the plan for the nextstep work.