Numerical investigation of three-dimensional separation on axisymmetric bodies at angle of attack

The understanding of three-dimensional separation is lagging behind the understanding of two-dimensional separation due to its greater complexity and the small number of universal or canonical flow problems. Three-dimensional separation occurs, for example, when low aspect ratio devices such as submarines and torpedoes are operated at large angles of attack, . Two low aspect ratio geometries, the DARPA Suboff bare hull geometry and a hemisphere-cylinder geometry were investigated. Numerical simulations and water tunnel experiments for the DARPA Suboff bare hull geometry which is a prototypical submarine shape, show little flow separation at = 30deg and for Reynolds numbers based on diameter of Re = 10, 000 and Re = 20, 000. A hemisphere-cylinder geometry was derived by replacing the Suboff forebody with a hemisphere. Simulations and water tunnel experiments were carried out for Re = 2000 and 5000 and for = 10deg and 30deg. For = 10deg a large separation bubble that is shedding is observed on the leeward side. For = 30deg two counter-rotating leeward vortices appear and shedding is suppressed. Proper orthogonal decomposition and Fourier analysis in time are employed for investigating the unsteady fluid dynamics. Conclusions are drawn with respect to the mean flow topology and possibly relevant hydrodynamic instabilities.