Detached eddy simulations and tomographic PIV measurements of flows over surface combatant 5415 at straight-ahead and static drift conditions

Abstract

A coupled experimental and computational study is performed to discuss the overall trend in surface combatant 5512 forces and moment and flow pattern with the change in hull drift angle (β) from straight-ahead (β = 0°) to static drift β = 10°–20° conditions. The local flow measurements were performed using tomographic particle image velocimetry (TPIV), which involved uncertainties ranging from <1% to 17% and the uncertainties decreased with the vortex progression. The surge force increased quadratically with the drift angle, whereas the sway force and yaw moment increased cubically. The wave elevation showed diverging wave pattern from both starboard and port sides. The wave angle increased and decreased on the port and starboard sides, respectively, with the increase in β. But the total wave envelop angle remained almost constant. Both experiments and computational fluid dynamics (CFD) predictions showed very similar vortical structures. The β = 0° flow showed structures emanating from the sonar dome, forebody keel, and bilge keel aligned which progressed along the hull. The static drift flows showed structures emanating from the sonar dome tip, bilge keel tip, and aft body keel which advected away from the hull. The primary vortices for the static drift case were circular and showed Gaussian or bell-shaped planar distribution. The vortex strength increased with β, and decreased with progression as vortices diffused. The momentum deficit in vortex core was sustained for β = 0° due to interaction with boundary layer. Whereas for β = 10° and 20°, the deficit increased due to turbulence generation in the core because of helical instability. The TPIV measurements, for the first time, provided detailed measurements for the progression of the vortical structures and associated mean and turbulent flow characteristics for ship flows. However, they have larger uncertainties near the hull, which limits analysis of the vortex onset characteristics. Future work should focus on time resolved particle tracking velocimetry (PTV) to address these issues.