| Supersonic turbulence is the issue that is paid highly attention to in the research of flow surrounding the supersonic/hypersonic aircraft and in the combustion chamber. Nevertheless, modeling incorrectness and result discrepancy with experimental measurements sometimes do exist in the prediction and analysis and simulation of supersonic turbulence by theory and turbulence modeling. Thus, in order to solve problems in supersonic aircraft turbulence more correctly, it is need to provide with exact and comprehensive data of supersonic turbulence for improving turbulence modeling and theory. As a classical turbulence, supersonic flow over a backward facing step usually exists in the complex flow field of supersonic/hypersonic aircraft and it is worth to be studied adequately. And in order to make experiments available and overcome the disadvantages of traditional experimental facilities and measurement techniques, it is indispensable to investigate the quiet wind tunnel which can reproduce the low-noise and low-turbulence flight environment and do researches on measurement techniques related to experiments.AΦ120 Ma = 6.0 hypersonic wind tunnel is designed in this dissertation and the holistic design, nozzle design and settling chamber design are discussed. It is a intermittent-flow and blowdown quiet wind tunnel. The quiet nozzle is designed by using the short nozzle designing technique based on Bézier curve and throat boundary layer suction technique. The corresponding numerical simulation is performed and the results show: the quality of flow field inside the nozzle is excellent. Pressure and Mach number both inside and at the exit of the nozzle change gradually; the bleed slot with a elliptical leading edge sucks the boundary layer moderately which guarantees the laminarization of the nozzle boundary layer. In order to reduce noise level and stabilize the flow, structures including porous tapers, damping meshes and muffles are setup in the setting section For the moment construction of the quiet wind tunnel is nearly complete, and the tunnel is about to be tested.NPLS (Nanoparticle-based Planar Laser Scattering) flow visualization technique together with the supersonic PIV technique and supersonic density measurement technique are newly developed by the research group consisted of the authors for supersonic turbulence experiments with high spatiotemporal resolution. Applications of these advanced techniques in experiments of Ma = 3.0 supersonic flow over a backward facing step are studied in this dissertation. NPLS which use nanoparticles as tracer can visualize the transient structure of a cross-section of supersonic 3D flow field at a time resolution of 6ns, and a temporal correlation resolution of 0.2μs high. The supersonic PIV based on NPLS resolve the problems of the following ability of nanoparticles in supersonic flow. After removing the influence from background, nonuniform distribution of laser sheet intensity, and some other factors, the relationship of NPLS image gray and local density in the flow field can be estimated by oblique shock wave calibration, and the density field can be measured quantitatively by the supersonic density measurement technique based on NPLS.NPLS is adopted in the flow structure visualization of the supersonic flow over a backward facing step in this dissertation. The panoramic and local fine structures of the supersonic flow over a backward facing step are revealed in NPLS images, which include the supersonic boundary layer upstream the step, recirculation region and shearing layer brought by the flow separation, compress wave, reattachment shock and so on. Comparing with supersonic turbulence, results show that flow structures of supersonic laminar flow over a backward facing step differ in many aspects such as thinner boundary layer, longer recirculation region and so on.The velocity field is obtained with the supersonic PIV system based on NPLS. The transient feature, mean feature and fluctuating feature of velocity field are obtained via plentiful measurements, which provide essential quantitative information for analyzing. POD is used to analyze the U, V velocity and vector features and reveal details concealed by statistical averaging. Based on the distributing of velocity fluctuating, turbulence intensity and turbulence kinetic energy can be gained. And it is found that shearing effects impact the flow greatly. Via large numbers of experimental measurements and statistical analysis, results show that the reattachment point is at around 8.47h and the reattachment region length is about 3.8h in the supersonic turbulence flow over a backward facing step while in the supersonic laminar flow they are 4.18h and 3.4h respectively, which is accordant with former results in other literatures.The supersonic density measurement technique based on NPLS is adopted in this paper to perform the density measurement in the regions of the supersonic flow over a backward facing step, obtaining the transient and mean density fields which supply important information for further study. Comparing the results with NPLS images and k -εturbulence modeling simulation, it can found that they reveal flow mechanism conformably, while the density technique with high spatio-temporal resolution can measure the density distributing of supersonic transient flow subtly.
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