Study on direct measurement method of vorticity from particle images

Abstract

To overcome the shortcomings of conventional methods for vorticity measurement, a new direct measurement of vorticity (DMV) method extracting vorticity from particle images was proposed. Based on the theory of fluid flow, two matched particle patterns were extracted from particle images in the DMV method. The pattern vorticity was determined from the average angular displacement of rotation between the two matched particle patterns. The method was applied on standard particle images, and was compared with the second and third order central finite difference methods. Results show that the accuracy of DMV method is independent of the spatial resolution of the sampling, and the uncertainty errors in the velocity measurement are not propagated into the vorticity. The method is applicable for measuring vorticity of a stronger rotational flow. The time interval of image sampling should be shortened to increase the measurement ranges for higher shearing distortion flows.