Supercavitation Drag Reduction in High-Mach-Number Liquid Flows
NAVAL UNDERSEA WARFARE CENTER DIV NEWPORT RI
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A review of supercavitation drag reduction in high-Mach-number liquid flows is presented in order to assess claims that experiments at such high speeds have been performed, and to provide a comparison between the drag of projectiles traveling in water at transonic speeds versus the drag of similar projectiles in air at the same speed. The physics of high-Mach-number flows are reviewed, including the equations of state in both air and water and the mechanics of shock and expansion waves. A review of literature discussing high-Mach-number supercavitating flows is presented, with a focus on the Nishiyama-Khan model for predicting the drag of supercavitating two-dimensional shapes at subsonic, transonic, and supersonic speeds. The flow in each of these regimes is described, and the drag components are discussed. Based on this background research, estimates of drag coefficients versus Mach number and dimensionalized drag versus speed in both air and water are presented for a wedge. It is concluded that, contrary to previous speculation, the drag of high-Mach-number projectiles in water is much higher than the drag at the same speed in air. Finally, upgrades to the Nishiyama-Khan model are recommended.
- Fluid Mechanics