剪切敏感液晶涂层颜色变化特性及其用于壁面摩擦力场测量方法研究

Wall shear stress is an important fluid parameter, and much valuable information can be gained from visualizing and measuring shear stress patterns on solid surfaces. So any means to measure shear stress efficiently and with a high spatial resolution would be very interesting. .Shear-sensitive liquid crystal (SSLC) coating technique is a non-intrusive global wall shear stress measurement technique. The present project investigates the SSLC coating technique in wind tunnel test. Firstly, the color-play characteristic of SSLC coating under normal illumination is investigated. Then the multi-view measurement technique originally proposed by Reda et al. is improved by using several synchronized cameras placed at different circumferential angles but constant above plane angle, and a real-time measurement / display of wall shear stress vector field on planar surface is developed. After that, a novel approach based on surface matching is proposed for measurement of wall shear stress from images captured at variable above plane angles. Finally, the color-play characteristic of SSLC under oblique illumination is investigated and the approach based on surface matching is further extended to the measurement of wall shear stress on curved surface. Through this research project, a real-time measurement / display of shear stress vector field on a planar surface or curved surface is developed. .The achievements of the present project are expected to be used in boundary layer researches, flow control, aerodynamic drag reduction and other fields.

壁面摩擦力是空气动力学领域的一个重要参数，许多重要信息可以通过测量或者显示表面摩擦力分布获取，因此快速、准确测量摩擦力具有重要意义。.剪切敏感液晶（SSLC）涂层技术是一种能够测量壁面摩擦力矢量场的非接触式全局测量方法。本项目在风洞试验中开展SSLC涂层技术研究：对SSLC涂层相关基础技术和在法向光线照射下SSLC涂层颜色变化特性进行研究；对Reda等人提出的多视角测量方法进行了改进，采用多个相机同步工作，实时测量/显示平面摩擦力矢量场；对于相机俯视角可变情况，提出了基于曲面拟合的SSLC涂层颜色校准方法和基于曲面匹配的摩擦力矢量场测量方法；最后探索了在倾斜光线照射下SSLC涂层颜色变化特性，将曲面匹配法进一步推广用于测量曲面表面摩擦力矢量场。通过本项目研究，建立一种实时测量/显示平面和曲面表面摩擦力矢量场的方法。.本项目的研究成果有望在边界层理论研究、流动控制、气动减阻设计等领域得到应用。

壁面摩擦力是空气动力学领域的一个重要参数，许多重要信息可以通过测量或者显示表面摩擦力分布获取，但是摩擦力的测量一直是一项技术挑战极大的工作。.剪切敏感液晶（SSLC）涂层技术是一种能够测量壁面摩擦力矢量场的非接触式全局测量方法，通过测量SSLC涂层颜色解算壁面摩擦力场。本项目对基于SSLC涂层的摩擦力场测量方法进行研究，设计并搭建了一套基于六台同步相机的摩擦力场测量装置，基于曲线拟合法和曲面匹配法分别发展了壁面摩擦力场解算方法，应用所发展的方法测量了几种典型流动的壁面摩擦力矢量场，包括亚声速射流、超声速射流、圆柱绕流、突起物绕流等。实验结果表明，所发展的方法能够高分辨率测量亚声速流动和超声速流动的摩擦力矢量场，详细捕获了射流、激波和绕流等流动的特征，并且测量结果与采用传统流动显示技术（油流技术等）显示的结果比较一致。.本项目的研究工作从原理方法上和工程实践上将SSLC涂层测量技术向前推动了一步，研究工作经过进一步完善可用于风洞实验中测量壁面摩擦力矢量场。.