Abstract:
Hypersonic boundary-layer transition on a flat plate is fundamental research problem for both theoretical investigations and engineering applications, however, both theoretical evaluations and experimental estimations of the transition region have large discrepancies with the results in the real flight. With the development of the optical measurement techniques, the investigation level of the hypersonic aero-optics is gradually improved. In aero-optics, the effect of the boundary-layer flow to the light beam through the flow field, that is the distortions of the light beam including deflection, blur and jitter, is one of the important problems. Considering the above mentioned two problems, the hypersonic boundary-layer transition could result in the change of the distortion of the light beam, so that one could investigate the linkage between those two phenomena to built up one boundary-layer transition diagnostic technique based on the aero-optical measurement method. The linkage between the hypersonic boundary layer transition on a flat plate and the jittering characteristics of the small-aperture beam (SAB) is theoretically analyzed. Due to the concept of transitional aero-optics, a new idea which could diagnose the hypersonic boundary layer transition on a flat plate using SAB technique and HICS is suggested, and is preliminarily validated by those relative tests performed in FD-20 gun tunnel with the Mach number of 8 and the unit Reynolds number of 1×10
7/m. To investigate the effects of the boundary-layer transition on a flat plate to the jittering characteristics of the small-aperture beam, three polymethyl methacrylate windows are arranged in the centerline of the test model. The jittering of the small-aperture beam through the windows could be measured and the results validate the assumption that the standard deviation of the jittering data could be changed at the different streamwise locations in the boundary layer. The results are compared with the heat transfer measurements on the centerline of another same model, same trend between those two experimental results in the transitional region of the hypersonic boundary layer is found. Thus, it is feasible to diagnose the transition of the hypersonic boundary layer by those aero-optical techniques.