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Navy Lab Sets Record for Reynolds Numbers

NAVSEA News

By NSWC Carderock Division Public Affairs

MEMPHIS -- The U.S. Navy's William B. Morgan Large Cavitation Channel (LCC) in Memphis has enabled hydrodynamic experts to produce and measure two-dimensional flows at Reynolds Numbers up to 20 times higher than any previously achieved in a laboratory.

The Reynolds Number is among the most important non-dimensional parameters characterizing fluid flow. It combines the speed of the flow, size of the model or prototype and viscosity and density of the fluid. A classic challenge in the laboratory is getting sufficiently high Reynolds Numbers to adequately represent full-scale flows.

Naval Surface Warfare Center Carderock Division's Hydromechanics Directorate cooperated in two test programs with the University of Michigan's Mechanical Engineering Department using Office of Naval Research and Defense Advanced Research Projects Agency funding. One experiment made measurements on a National Advisory Committee for Aeronautics cambered foil with a ten-foot span and seven-foot chord weighing 14,000 pounds. Variations in trailing edge shape were incorporated. Lift on the bronze foil at a flow speed of 35 knots exceeded 150,000 pounds. The Reynolds Number of approximately 55 million is about 20 times greater than that for foil shapes in published literature.

The second (and different) experiment made detailed boundary layer and shear stress measurements on a 10 by 40-foot flat plate. The test involved both single-phase flow and flow with the injection of air microbubbles to study frictional drag reduction. Reynolds Numbers based on downstream length in this experiment were as high as 320 million and more than three times greater than similar measurements reported in the applicable scientific literature.

The LCC can simulate close to full-scale fluid effects in a boundary layer, for understanding the actual friction drag on a hull and potential ways to reduce it. Reducing drag either increases a vessel's range or speed, or reduces fuel costs. Before, no test could predict what was actually happening on a ship or submarine.

The LCC is the world's largest and most technically advanced high-speed, variable-pressure water channel. Using a stationary model in the 10 by 10 by 43 foot test section, water flow up to 35 knots (40 mph) combines with variable pressure to allow simultaneous measurements of forces, flows, cavitation and acoustics from a model's propulsion system, hull, and appendages. The facility allows tests on models of ships, submarines and torpedoes as well as basic and applied research on hydrodynamic components such as those at high Reynolds Numbers described above.