Ship Air Wake Wind Tunnel Test Results (Invited)

Abstract

As part of a larger program to develop analytic and computational tools to predict the air wake characteristics of naval vessels, an experimental effort has been undertaken to map the air wake of a scaled patrol craft modified with a representative hangar structure and stern flight deck. A 4% scaled model of a United States Naval Academy YP (Patrol Craft, Training) was fabricated for wind tunnel testing at 0, 15, and 30 degrees of yaw at a Reynolds number of 7.6 million. The topside configuration of the vessel simulates that of larger destroyers and cruisers, which service rotorcraft from stern hangars and flight decks. Flow measurements were made in station planes from 0.45 to 5.14 hangar-heights downstream of the aft hangar face using an 18-hole Omniprobe. The 3D velocity measurements indicated that a recirculation zone occurred over the flight deck and extended from 1.5-3 hangar-heights downstream. The effect of yaw angle on the air wake was to consolidate and shift the rotationality of the flow into a large, leeward vortex with a size on the order of the superstructure height. Furthermore, the unsteadiness of the flow was independent of the survey plane position at zero yaw, but increased by 57% at 30 deg yaw, with a large band of high vorticity where the shear layer separated and rolled up. The velocity distributions, flow angles, and vorticity will be used to compare with computational fluid dynamics (CFD) and full-scale, in-situ measurements to portray a complete, Reynoldsscaled picture of the air wake.