Image analysis of oil film interferometry — a method of measuring wall shear stress distributions |
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| Authors: | Henri A Siller Richard J Perkins and Gerd Janke |
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| Institution: | (1) Hermann Föttinger Institut für Thermo- und Fluiddynamik, Müller-Breslaustrasse 8, DW-1000 Berlin 12, Germany;(2) Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, U.K. |
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| Abstract: | A method is described of measuring a wall shear stress distribution that varies in the direction of the flow. Variations in the height of a very thin oil film moving under the boundary layer generate interference fringes, which are recorded and digitised using image processing equipment.The evolution of the film surface in space and time can be reconstructed from the interference fringe patterns and used to calculate the shear stress field. This reconstruction is achieved by comparing the picture data with images that were calculated for prescribed heights that are adjusted iteratively, until the calculated intensities match the data.The method is applied to a flow approaching a step, and the results are compared with pulsed-wire measurements. |
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| Keywords: | interferometry shear stress measurement image processing fringe patterns |
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