利用导流板降低流场对光传输影响的试验研究

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

在一座小型跨超声速风洞上采用夏克-哈特曼波前传感器进行了Ma=3试验段流场对光传输特性影响的试验研究。空风洞流场的测试结果表明,由于试验段壁面湍流边界层中气流脉动与流场密度变化的影响,光波前会发生畸变。为了降低湍流边界层流场对光传输的影响,在风洞试验段单侧壁板上安装导流板进行了试验。测试数据表明,光波前畸变量的PV均值和RMS均值分别由3.5λ和0.73λ降低到了1.09λ和0.22λ,而且光波前畸变量的波动幅度也大为降低。初步研究结果说明,采用加装导流板等措施可以显著降低风洞流场对光传输的影响,有利于提高风洞试验时流场显示与测量结果的可靠性和有效性。

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.