Abstract
Wall shear stress is an important quantity in fluid mechanics, but its measurement is a challenging task. An approach to measure wall shear stress vector distribution using shear-sensitive liquid crystal coating (SSLCC) is described. The wall shear stress distribution on the test surface beneath high speed jet flow is measured while using the proposed technique. The flow structures inside the jet flow are captured and the results agree well with the streakline pattern that was visualized using the oil-flow technique. In addition, the shock diamonds inside the supersonic jet flow are visualized clearly using SSLCC and the results are compared with the velocity contour that was measured using the particle image velocimetry (PIV) technique. The work of this paper demonstrates the application of SSLCC in the measurement/visualization of wall shear stress in high speed flow.
Highlights
Wall shear stress is an important surface quantity in fluid mechanics
Various mechanical or electrical sensors has been developed for wall shear stress measurement, such as mechanical balances, intrusive probes [1,2], or micro-electro-mechanical systems (MEMS) [3,4,5], those methods are typically complicated, disturb the flow, destroy the surface, and measure point-wise
Quantitative comparison of the measured shear stress vectors against the data from other techniques was not made due to the limited research conditions. Work on this topic had been made by Reda et al [9,10], and the results showed very good overall agreement between shear vectors that were measured by the sensitive liquid crystal coating (SSLCC) technique and conventional point-measurement techniques
Summary
Wall shear stress is an important surface quantity in fluid mechanics. In aerodynamics research, much valuable information can be gained from visualizing and measuring shear stress patterns on solid surfaces. The main advantage of the SSLCC technique when compared with other techniques is that the responses of SSLCC to wall shear stress are colorful and visible with a high resolution both in space, and in time, can immediately reveal cause-and-effect relationships between changes in model or test condition and the resulting surface shear stress field. For these reasons, SSLCC has been extensively used in flow visualization [27,28,29,30,31,32,33]. Effort was made to visualize the shock waves in the supersonic jet flow using SSLCC
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