The spacing, position and strength of vortices in the wake of slender cylindrical bodies at large incidence

Abstract

Extensive schlieren studies and yawmeter traverses of the wake behind slender cone-cylinders at large angles of incidence have shown that the flow pattern is generally steady. Under certain flow conditions, however, the wake exhibits an instability which is not understood. For cross-flow Reynolds numbers in the subcritical region the wake can be described in terms of a cross-flow Strouhal number which has a constant value of 0·2 for cross-flow Mach number components (M_c) up to 0·7 and then increases steadily to a value of 0·6 at M_c = 1·6. The strength of the wake vortices varies substantially with M_c, increasing to a maximum at M_c ≈ 0·7 and then decreasing rapidly for higher values of M_c. Schlieren photographs of the wake have been analysed by means of the impulse flow analogy and also by considering the vortices to be part of a yawed infinite vortex street. The impulse flow analogy is shown to be of use in determining the cross-flow Strouhal number but estimates of vortex strength are too high. The Kármán vortex street theory combined with the sweepback principle leads to reliable estimates of vortex strength up to M_c = 1·0.Information is given on the spacing, path and strength of the vortices shed from the body for flow conditions varying from incompressible speeds up to M_c = 1·0. Finally this information is used to determine the vortex drag of a two-dimensional circular cylinder below M_c = 1·0.