Study of two-dimensional flow past an elliptic cylinder by discrete-vortex approximation

Abstract

Investigation of flow around an elliptic cylinder with the thickness ratio of 0.5 at an angle of attack of 45°, and 90°, having started impulsively, was carried out using the discrete-vortex approximation. The boundary layer along the body surface is divided into a finite number of elements and replaced by the same number of the corresponding vortex filaments, the circulations of which are determined to be equal to those of the elements. Usually, the arrays of the vortex filaments thus introduced separate alternatively from the surface of the cylinder, and form Karman vortex streets, that is, the familiar alternative separation process of the vortices was observed. At the angle of attack of 90°, the initial twin vortex separates from the cylinder simultaneously, but not alternatively. These vortex pairs eventually yield to the Karman vortex street, and this transition process successfully simulates the experimentally-observed phenomena. For this process it is essential to consider the boundary layer of the rear side of the cylinder and this consideration has been successfully carried out by the use of this method.