The Design Of Ludwieg Tybe Hypersonic Facility For Boundary-layer Transition Study

At present,the experimental research on hypersonic boundary layer transition is mainly based on ground wind tunnel experiments.Conventional hypersonic wind tunnel equipment has complex structure,high construction and operation cost and low work efficiency,and it is not suitable for basic scientific research in institutes and universities.In view of the above problems,this paper refers to a wind tunnel design scheme proposed by professor Ludwieg in1955,which is simple in structure,low in construction cost and high in operation efficiency.In the aerospace design of Huazhong university of science and technology,a Mach 6 Ludwieg tube wind tunnel with and outlet diameter of 250mm is constructed.This wind tunnel is the first Ludwieg tube wind tunnel equipped with fast-acting valve in China,which provides reference for the design and construction of such wind tunnels in the future.In addition to the support of the wind tunnel platform,various flow field measurement technicals are also important.Nowadays the instruments used for hypersonic boundary layer flow field measurement are generally characterized by low response frequency and destructive flow field structure by intrusive measurement,such as pressure high-frequency pressure sensor and hot-wire instrument.Aiming at the hypersonic boundary layer flow field measurement problem,a set of non-intrusive focused Laser Differential Interferometer(FLDI)measurement system is built based on the light refraction and interference principle,which can effectively obtain the density variations at the spatial points of the flow field.In a conventional hypersonic wind tunnel with a Mach number of 8,FLDI was used to carry out the experiment of unsteady wave measurement for the boundary layer of inlet flow Reynolds number 10~7/m and 7°half cone Angle tip cone mode.The results showed that FLDI successfully captured the second mode transition and its harmonics(654 KHz)at the frequency of 327 KHz.By comparing with the PCB test results,the advantages of FLDI,such as high signal-to-noise ratio,high analytical frequency(1.5 MHz in the experiment)and high spatial resolution(less than 1 mm along the flow direction),were reflected.In view of its excellent characteristics such as high spatial and temporal resolution,FLDI is suitable for the study of unstable wave behavior and sensitivity in hypersonic boundary layer,and it provides an effective means for in-depth understanding of hypersonic boundary layer transition mechanism and sensitivity.