Reduction of Turbulent Skin Friction by Microbubbles
PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB
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Measurements of the effect of microbubbles on a zero pressure gradient turbulent boundary layer generated on the test section wall of a water tunnel are described. Microbubbles were created by injecting air through a 0.5 micron sintered stainless steel plate immediately upstream of a floating element drag balance. At the downstream edge of the balance the length Reynolds number was as high as ten million. Integrated skin friction reduction of greater than 80 was observed. The drag balance results were confirmed by measurements with surface hot film probes. For the case in which buoyancy tended to keep the bubbles in the boundary layer, the skin friction data was shown to collapse when plotted against the ratio of air to water volume flow rate. The effects of buoyancy on skin friction reduction were also documented.
- Fluid Mechanics