The Flow Structures And Dynamic Behavior Of Supersonic Flow Over Vortex Generators On The Wall

The mutual interference between the components of a vehicle in the supersonic orhypersonic flow field generates complex flow field structures, which contain theboundary layer transition, the interaction between shock waves, the boundary layerseparation, the reattached shock wave and the wake. Controlling and disturbing of theflow field by using vortex generator has been becoming a research hotspot but alsodifficulty in the study of the flow control. The study of the fine structures and dynamicbehaviors of the flow field has an important theoretical and engineering practical value.The influences of strong nonlinearity and diffusion factors, such as compressibility,turbulence, large scale structure, shock waves and slip line, make it difficult to study thefine structures of supersonic flow over a protuberance by means of high resolutionnumerical simulation and measurement. Based on the high resolution NPLS(Nano-tracer Planar Laser Scattering) technique, the spatial fine structures and temporalevolution characteristics of supersonic flow over various models (the delta wing, thecylinder and the hemisphere) on the flat plate were studied. The distortion of the flowstructures is rapider and the time correlation is worse near the vortex generators.Considering the difficulty of identifying the evolutionary characteristics of the flowstructures only using the experimental images, the method of numerical simulation isused in the thesis to mutually verify the results with the experimental.The complex flow field structures of supersonic flow over the varied vortexgenerator on the flate plate were observed based on the multi-view and multi-resolutionNPLS images, which contain the three-dimensional detached shock wave, the separationregion, the recirculating region in the downstream, the reattached shock wave, the wakeand so on. Based on the time correlation NPLS images, the temporal evolutioncharacteristics of supersonic flow over the various vortex generators weresystematically studied. According to the space-time structure characteristics of the flowfield, the modes of the vortexes shedding off were discovered. Naturally the shock wavestructures and the vortex structure modes in the wake flow were modeled.In general, the supersonic flow over a protuberance possesses the characteristics oflarger velocity gradient. The disconnected will be generated when the supersonic flowpasses through the shock wave, which makes the velocity field measurement verydifficult. Here, the high dynamic response characteristics of nanoparticles of NPLSsystem were used and associate the PIV (Particle Image Velocimetry) technique toprofoundly study the velocity distribution of supersonic flow over various models. Theanalysis of the velocity distribution at the different streamwise planes indicates that thevelocity field and the dynamics origin are different. According to the measurementresults of supersonic PIV in the streamwise planes at different positions, the velocity field structures of supersonic flow over the various vortex generators on the wall wereprofoundly studied. The vortex structure characteristics of the coherent structure werediscovered. And the mode of the coherent structures in the wake was modeled.The transient measurement of the density field on the supersonic flow over thevaried vortex generators was achieved. According to the density distributioncharacteristics of the flow field, a larger density gradient occurs in front and back of theshock waves, between the main stream flow and boundary layer/coherent structures inthe wake flow and in the vicinity of the vortex generators. The influences of the vortexstructures and the wall on the density fluctuation were studied. And the unsteady of thedensity fluctuation was also studied. Consequently the influences of the shock wavesand the coherent structures on the density fluctuation were analyzed. The spectrumanalysis indicates the large-scale vortex structures are the main carrier of mass,momentum and energy in the wake flow, and predominates the exchange of thembetween the main stream flow and the coherent structures. The evolution of thelarge-scale vortex structures is the major factor of the density fluctuation in the wakeflow.Based on the NPLS technique, the method of measuring the distribution of thevelocity and density on the supersonic flow over a vortex generator was put forward.The complex flow structures, such as the mutual interference between thethree-dimensional shock waves and the boundary layer, the interaction between wavesand vortexes, and the coherent structure in the wake flow, were discovered. And themodes of shock waves and flow structures in the wake flow were modeled. It ismeaningful to achieve the control and disturbance of the flow field by using vortexgenerator. Due to the complexity of supersonic flow over a vortex generator, it isnecessary to study further into the finer structures characteristics and the complexdynamic behavior.