An Optical Measurement Method of Boundary Layer Shear Stress in Flow Field

Abstract

The invention discloses a method for optically measuring shear stress of boundary layers of flow fields, and relates to the technical field of wind tunnel tests. The method includes main steps of (1), anodizing and blackening wind tunnel test models; (2), smearing liquid crystal coatings; (3), acquiring relation curves of colors of the liquid crystal coatings and shear force; (4), mounting 6 test cameras; (5), simultaneously photographing the liquid crystal coatings by the 6 test cameras to obtain images of the liquid crystal coatings; (6), removing position difference of the images photographed by the different test cameras; (7), carrying out distortion removal processing; (8), correcting identical colors of the images photographed by the various cameras; (9), acquiring model surface shear stress vector distribution results. The method has the advantages that the obtained images are clear and visual, and the method is high in measurement accuracy and sensitivity and can be used for displaying the flow fields of wind tunnels, diagnosing transition and quantitatively measuring model surface friction drag.

Description

technical field [0001] The invention relates to the technical field of wind tunnel tests, in particular to an optical measurement method for flow field boundary layer shear stress. Background technique [0002] The shear stress in the boundary layer generated by the relative motion of the flow field and the object is one of the important aerodynamic parameters in the process of aircraft development. It has a great influence on the aerodynamic / thermal performance and is the basic work in fluid mechanics. However, due to the existence of complex flow phenomena such as boundary layer transition, the prediction of shear stress is difficult for numerical simulation. And because of its small absolute value, it is also a challenge for wind tunnel test measurement. [0003] Research on surface shear stress measurement technology mainly focuses on three areas: friction balance technology and oil film technology. Frictional balance technology uses strain electrical measurement techn...

AI Technical Summary

Problems solved by technology

Frictional balance technology uses strain electrical measurement technology to directly measure the shear stress acting on the balance sensing surface, and can directly obtain the absolute value of shear stress, but due to factors such as gap effects and temperature effects, its measurement sensitivity and accuracy are limited; The oil film technology determines the magnitude of the shear stress by detecting the change of the thickness of the thin oil film. The theoretical basis of the measurement and the mathematical derivation process are relatively complicated, and are seriously affected by the temperature.

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