Influence of Drag-Reducing Polymers on Hydrofoil Wakes.

摘要

The overall objective of this project was to demonstrate the plausibility of reducing or modifying hydrofoil noise through polymer ejection. A polymer ejecting hydrofoil was mounted in the Naval Undersea Warefare Center (NUWC) 12-inch water tunnel. A 1000-ppm solution of polyacrylamide was ejected through slots near the maximum thickness of the hydrofoil. The stream wise mean and root mean square fluctuation velocities and normal root mean square fluctuation velocities were measured in two planes downstream of the hydrofoil. The conclusions are that the data support the following hypotheses: (1) the drag-reducing polymers reduce the normal velocity fluctuations in the hydrofoil boundary layers; (2) this modification of the hydrofoil boundary layers leads to a reduction of all turbulent components in the far wake, and it also leads to a decrease in the normal turbulent fluctuations in a part of the near wake; (3) the momentum deficit in a hydrofoil wake can be reduced by ejection of drag-reduction polymers. These conclusions strongly suggest that ejection of drag-reducing polymers from hydrofoils will be beneficial in reducing propulsor noise.