Experiments for reducing a flow field impacts on the light transmition by a guide plate

Experiments of researching the impacts of a supersonic flowfield with Ma=3 on light beam transmitting features were conducted in a small transonic wind tunnel.A Shack-Hartmann wavefront sensor was used to survey the aberrated optical wavefront under impacts.The test results showed that while a light beam traveling through the supersonic flowfield at Ma=3 in the wind tunnel test section without models,the optical wavefront would be disturbed remarkably by the turbulent boundary layers existing along the walls of the test section,thus the accuracy of measurements and the validity of flow field visualization that related to an optical measurement system would be suspicious.In order to remove the undesired influence of the turbulent boundary layers,a guide plate was installed parallel to one side wall of the test section,which was expected to replace the turbulent boundary layer with a rather steady laminar one.The obtained data was encouraging with apparent decreasing of the wavefront aberration.The average values of the peak variation(PV) and the Root-Mean-Square(RMS) of the wavefront aberration were reduced from 3.5λ and 0.73λ to 1.09λ and 0.22λ respectively,and the related PV fluctuations and RMS fluctuation were also decreased dramatically.The experiments have validated that a well-chosen guide plate can markedly reduce the impact of a supersonic flowfield on the light beam traveling through a wind tunnel,so that the validity of the flowfield visualization experiments conducted in the wind tunnel is guaranteed,and the accuracy of the measurement data could be improved.