Windtunnel studies of surface shear stress vector distribution measurement using shear sensitive liquid crystal coatings

Abstract

Shear sensitive liquid crystal coating (SSLCC) can measure surface shear stress vector distribution efficiently with a high spatial resolution. The purpose of the present paper is to modify and extend the surface shear stress measurement technique determined by Reda et al. to wind tunnel studies. All the facilities employed in the technique are very common and simple. The measurement technique is applied to surface flow beneath a tangential jet and surface flow in a turbulence wedge generated by a small cylinder in windtunnel flow. Spatially resolved shear stresses over planar surface are obtained, although the magnitude is not fully calibrated.shear sensitive liquid crystal, surface shear stress measurement, tangential jet flow, turbulence wedge Citation:Zhao J S, Scholz P, Gu L X. Windtunnel studies of surface shear stress vector distribution measurement using shear sensitive liquid crystal coatings.

Measurement of Wall Shear Stress in High Speed Air Flow Using Shear-Sensitive Liquid Crystal Coating

“…The mean value and the standard deviation of the relative fit error for each dataset are −0.13% ± 2.24%, −0.11% ± 1.19%, and −0.16% ± 1.42%, respectively. Although no quantitative curve fit errors were given in literatures [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ], it is clear to see that the noises in the curve fits in Figure 3 are much smaller than that in literatures by simply comparing Figure 3 with the hue vs. φ plots in the literature [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. The improvement is attributed to the synchronous imaging system consisting of six digital cameras, the significant improvement in the imaging technique over the past two decades, and the higher shear stress levels, which are easier to measure.…”

“…In the literature, the SSLCC technique has been used in used in several measurements including shear stress over planar surface in the flow beneath a tangential wall jet [ 9 ] and an oblique impinging jet [ 10 ], shear stress over planar surface around a cylinder in steady flow [ 11 ], and instantaneous flow [ 12 ], and even shear stress over the curved surface [ 13 ]. Extension of the SSLCC technique to the general wind tunnel measurement is available in Zhao et al [ 14 , 15 , 16 , 17 ]. There are also other global wall shear stress measurement techniques, such as surface stress-sensitive film (S3F) technique [ 18 , 19 ], the oil-film interferometry (OFI) technique [ 20 ], the luminescent oil-film technique [ 21 , 22 ], the global skin friction diagnostic technique [ 23 , 24 , 25 ], and the global technique based on soft substrates [ 26 ].…”

“…Although some encouraging and impressive results have been obtained by the SSLCC technique under special arrangements, most wind tunnel studies of the SSLCC technique were performed in very low speed flow [ 11 , 12 , 13 , 14 , 15 , 16 , 17 ], exactly speaking, no more than 30 m/s. Some exceptions can be found in Disimile et al [ 34 ] and Zharkova et al [ 35 ], where only the shear magnitude field was measured.…”

“…Some exceptions can be found in Disimile et al [ 34 ] and Zharkova et al [ 35 ], where only the shear magnitude field was measured. Note that the wall shear stress in low speed flow is very small and it is not easy to measure, and so there are considerable noises in the measured wall shear stresses [ 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. It is believed that the shear stress that was measured using the SSLCC technique should be more accurate at higher wind tunnel velocities, because in that case the shear stresses are larger and thereby easier to measure.…”

高超声速飞行器表面对流气动加热快速预测方法

“…尽管目前实验流体力学领域出现了测量表面摩 擦阻力矢量场的方法 [23] , 但是准确、快速地确定边界 层外缘的流动方向仍然是比较困难的. 本文根据物 面法向与来流方向之间的几何关系估算飞行器表面 气流的速度方向, 即认为来流与物面碰撞后, 法向动 量损失, 气流沿着物面的切向方向运动, 那么 ,        n V n V V n V n (9) 其中 V 为飞行器表面气流的速度矢量.…”