Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 07, 2019 - November 08, 2019
Separation of flows from a surface of an object is deeply related to aerodynamics itsself. In this study, a flow around a cylinder is considered as typical flow around the object. When a cylinder rotates, lift force is generated by the Magnus effect, meanwlie at a certain Reynolds number Re and spin ratio, it is reported that a negative Magnus effect (negative lift) is generated by the changes of separation points. And the behavior of the separation point is very important, however there are many unclear points on its fluctuations. Regarding to this, we assume the separations is closely related with the unsteady fluctuation of flow i.e. vortices. So we investigated flows around a cylinder by means of vortex method in order to clarify mechanisms of separations. Computations are performed at Re=2000, and agreements are obtained between the results with vortex method and a summary by Cantwell and Coles (1983). To estimate the location of flow separation we calculated velocity every π/180 rad on the circular arc whose radius is 1.02a (a is radius of the cylinder.). Then the angle θs at which the tangential velocity changes from positive to negative was detected on the condition that normal velocity is positive. As a result, the fluctuation of the separation point has been predicted. On the other hand, a relatively large velocity was observed behind the cylinder when vortices leave a cylinder. The influence of the velocity distribution and strength and position of vortices are discussed on the new vortices.
