The influence of the thickness of the boundary layer developing over the surface of an axisymmetric bluff body upon its base pressure and near-wake flow is analysed experimentally. The model, whose diameter and length are d = 70 mm and l = 400 mm, has a forebody with an elliptical contour and a sharp-edged flat base; it is supported above a plate by means of a faired strut. The pressure distributions over the body lateral and base surfaces were obtained using numerous pressure taps, while the boundary layer profiles and wake velocity field were measured through hot-wire anemometry. The tests were carried out at Re = u∞ l/n = 5.50 x 10^5, at which the boundary layer over the lateral surface of the body becomes turbulent before reaching the base contour. Strips of emery cloth were wrapped in various positions around the body circumference in order to modify the thickness and characteristics of the boundary layer. The results show that the base suctions decrease with increasing boundary layer thickness. This variation is found to be connected with an increase of the length of the mean recirculation region behind the body and with a corresponding reduction of the curvature of the streamlines at separation.
Experimental characterization of the influence of boundary layer thickness on the base pressure and near-wake flow of a bluff body.
MARIOTTI, ALESSANDRO;BURESTI, GUIDO
2012-01-01
Abstract
The influence of the thickness of the boundary layer developing over the surface of an axisymmetric bluff body upon its base pressure and near-wake flow is analysed experimentally. The model, whose diameter and length are d = 70 mm and l = 400 mm, has a forebody with an elliptical contour and a sharp-edged flat base; it is supported above a plate by means of a faired strut. The pressure distributions over the body lateral and base surfaces were obtained using numerous pressure taps, while the boundary layer profiles and wake velocity field were measured through hot-wire anemometry. The tests were carried out at Re = u∞ l/n = 5.50 x 10^5, at which the boundary layer over the lateral surface of the body becomes turbulent before reaching the base contour. Strips of emery cloth were wrapped in various positions around the body circumference in order to modify the thickness and characteristics of the boundary layer. The results show that the base suctions decrease with increasing boundary layer thickness. This variation is found to be connected with an increase of the length of the mean recirculation region behind the body and with a corresponding reduction of the curvature of the streamlines at separation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
