Asymmetries in the high Reynolds number wake of a submarine model in pitch

Experiments are reported in the wake of a submarine model (DARPA SUBOFF) over a wide range of Reynolds numbers based on the length Re$_{\mathrm{L}}$ between 10$^{5}$ and 30 x 10$^{6}$ at a pitch angle of 8 degrees. Two-component velocity measurements were taken at five cross-stream planes, downstream of the stern of the model (2\textless x/D\textless 14), using hot wire anemometry. The wake is distinguished by two principal vortex structures, but the strength of the two vortices are not equal, leading to an asymmetric wake that slowly rotates. The asymmetry appears to be endemic, and is not affected by freestream turbulence, changes in tripping, surface roughness, and small angles of yaw. They persist across all the Reynolds numbers measured, and the effects of Reynolds number are only important at low Reynolds number in that the wake becomes independent of Reynolds number when Re$_{\mathrm{L}} \ge $ 4.8 x 10$^{6}$. This work was supported under ONR Grant N00014-13-1-0174 (Ron Joslin).