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Area Measurement of Skin Friction in Complex Three-Dimensional Flows |
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by Brown, James L |
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A surface-imaging skin-friction instrument provides |
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measurement of the wall shear-stress vector over a large |
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surface region during a single wind tunnel test using an |
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oil-film interference method. During a test, a camera |
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captures images of the fringe pattern produced by |
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illuminating an oil film with quasi-monochromatic light. |
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By using a visual tracer in the oil, the surface |
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streamlines can also be determined. Analysis of the |
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fringe images using a Hilbert-transform-based technique |
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determines the oil thickness distribution in the region |
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where fringes are visible. A combination of the oil |
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thickness and surface direction is then used to calculate |
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the surface shear-stress distribution by numerically |
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solving the thin-oil film equation: where tau(sub x) and |
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tau(sub z) are the x- and z-components of the surface |
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shear stress, and mu is the dynamic viscosity of the oil. |
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All quantities in this equation are known from the height |
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measurement except tau(sub x) and tau(sub z). However, an |
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additional piece of information is needed to solve this |
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equation. If the surface streamline direction gamma is |
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obtained from visual tracers or from a streamline image, |
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then tau(sub x) = tau cos(gamma) and tau(sub z) = tau |
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sin(gamma), and the equation may be solved for tau. To |
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test the technique in a demanding situation, it was |
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applied to a three-dimensional (3-D) flow in which a |
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cylinder is mounted normal to a flat plate. An incoming |
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turbulent boundary layer encounters the vertically |
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mounted cylinder and a highly complex 3-D flow results. |
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Date Published: 2011-06-02 08:33:55 |
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Identifier: nasa_techdoc_20040075818 |
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Item Size: 6602804 |
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Language: eng |
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Media Type: texts |
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# Topics |
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GALILEAN SATELLITES |
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EUROPA |
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CRATERING |
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GANYMEDE |
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IO |
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PLANETARY SURFACES |
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# Collections |
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nasa_techdocs |
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# Uploaded by |
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@greg_williamson |
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