Optical Skin Friction Measurement Using Liquid-crystal Coatings
Shear-sensitive liquid-crystal coatings (SSLCCs) have an optical characteristic that they are sensitive to the applied shear stress. Color-change response of a liquid-crystal coating (LCC) depends on both the magnitude of the applied shear vector and its direction. Images of spatial reflection spectrum of the LCC with illumination of white light can be gained utilizing a camera, and then processed to get the shear stress vector distribution on the coating surface. Based on the theory, detailed techniques on the measurement of skin friction by LCCs is investigated, including spraying of the liquid crystal, construction of the optical camera system, calibration (the Hue ~ t curve) of the shear stress by skin friction gauges, experiments in subsonic and supersonic flows. Surface shear stress vector distribution on a flat plate beneath tangential jet is gained in the low speed jet experiment. The magnitude of the stress vectors at points, symmetrical around the central line, differ with each other in less than 10 percent, and average error of the directions of the shear vectors on the central line is less than 5 degrees. The Ma=3.5 wind tunnel test provides plenty of images of LCC color-change response to the supersonic flow over another flat plate. So its feasible to qualitatively visualize the distribution of shear magnitude, and estimate boundary layer transition and existence of turbulence wedge.
liquid-crystal coatings shear stress flat plate supersonic
CHEN Xing BI Zhi-xian YAO Da-peng LIN Jian
China Academy of Aerospace Aerodynamics, Beijing 100074, China
国际会议
The 8th Sino-Russia High-speed Flow Conference(第八届中俄高超声速流体力学研讨会)
上海
英文
362-368
2011-11-21（万方平台首次上网日期，不代表论文的发表时间）