On the Bi-stable Flows Around a Circuler Sylinder with a Semi-cerculer Rib

It is the purpose of this paper to make clear the condition required to bi-stable flow around a circuler cylinder with a semi-circuler riblet and the change of fluid forces by switching of flow patterns. We did a few measurements of fluid forces acting on a circuler cylinder with a semi-cerculer riblet. It is decided quantitatively the condition required to bi-stable flow and the change of fluid forces with switching of two flow patterns by analyesed the measured fluctuation of fluid forces transformed into low flequency fluctuation through the low pass filter with 2 or 3 times period of eddy shedding form a cerculer cylinder. And it became clear from discussion on the change of pressuer distribution at the surface of cerculer cylinder with the separetion region formed at vicinity of riblet that the relation between the change of fluid forces with a position of riblet and the flow pattern around a cerculer cylinder.