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DTIC ADA1033541: Aerodynamics - Control of Surface Shear Stress of ... |
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by Defense Technical Information Center |
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An experimental study of techniques for modifying the |
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surface shear stress, both mean and fluctuating, in |
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turbulent boundary layers is reported. The surface shear |
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along the test section of a 45.7cm square wind tunnel, |
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with a downstream expansion section, was determined by |
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means of surface-hot-wire-heat-transfer-gauges. Turbulent |
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boundary layers in both zero and adverse pressure |
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gradients were evaluated. The mean and fluctuating |
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surface shear in a zero pressure gradient can be |
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effectively reduced by employing a set of closely spaced |
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fins. The fins protruded from the surface up through the |
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sublayer. The fins produced an effective momentum defect |
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for the boundary layer near the surface, which reduced |
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the surface shear fluctuations by as much as 75 percent, |
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two boundary layer thicknesses downstream, and 52 percent |
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15 boundary layer thicknesses downstream (the limit of |
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the present experiment). The mean surface shear was also |
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reduced by 35 to 25 percent for the same 2 to 15 boundary |
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thicknesses downstream. The fins do not appear to produce |
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a large increase in the thickness of the layer. No small |
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size device, which could be mounted in the sublayer, was |
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found that could develope a persistent increase in either |
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the mean or fluctuating surface shear. Small scale vortex |
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generators had no measureable effect on the flow for |
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downstream distances greater than approximately 4 to 5 |
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boundary layer thicknesses. Only the large scale vortex |
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generator, normally use to delay boundary layer |
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separation, produced an increase in surface shear at |
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large distances downstream. (Author) |
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Date Published: 2020-03-19 07:23:19 |
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Identifier: DTIC_ADA1033541 |
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Item Size: 18496461 |
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Language: english |
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Media Type: texts |
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