Symmetric and Asymmetric Separation Patterns Over a Hemisphere Cylinder at Low Reynolds Numbers and High Incidences

Experimental flow study over a blunt-nosed axisymmetric body at incidence

“…It is also noteworthy that there is a local pressure minimum at j ¼ 1601, above which the vortex center is located. The same observations have been made by others (Chesnakas and Simpson, 1997;Hoang et al, 1997) calling this minimum the ''footprint'' of the vortex. Fig.…”

“…This pressure plateau is associated with a separation bubble that is a characteristic feature of the flow over hemisphere cylinders. This separation bubble has been documented by various researchers, like Hsieh and Wang (1996), Hoang et al (1997), Barberis (1986), who found that its shape depends on the angle of attack, Reynolds number and Mach number. In the present work, the pressure plateau along j ¼ 1801 moves upstream with increasing a: The existence of this bubble was also documented through flow visualization.…”

“…This type of 3-D separations is an open type (Wang, 1972) since fluid particles reach both sides of the separation line, originating from the same area. For one order of magnitude lower Re (2.7 Â 10 4 ) it was found by Hoang et al (1997) that, for the hemisphere cylinder and a4201, flow separation was of the closed type, since the nose separation bubble was connected with the downstream separated flow without any gap between them.…”

“…As has been documented (Hoang et al, 1997), small protuberances in the nose area of a hemispherical cylinder can cause strong flow asymmetries. However, in section D, since this was located at the end of the nose, it was decided to open more pressure taps, due to the fact that surface irregularities in this region do not affect the flow.…”

“…A common flow feature between sharp-and blunt-nosed inclined cylinders is the formation of two streamwise vortices on the leeside of the body. With respect to the symmetry plane, defined by the free-stream velocity and the longitudinal axis of the body, these vortices are symmetrically positioned for the blunt-nosed cylinders, independently of the angle of attack (Hoang et al, 1997), until the onset of shedding. However, for the sharp-nosed cylinders this symmetry breaks down beyond a certain angle, associated with the appearance of a significant side force (Ericson and Reding, 1986).…”