Title: Numerical study of transitions in lid-driven flows in semicircular cavities

Abstract: In this article, three-dimensional (3D) lid-driven flows in semicircular cavities are studied. The numerical solution of the Navier-Stokes equations modeling incompressible viscous fluid flow in cavities is obtained via a methodology combining a first-order accurate operator-splitting scheme, a fictitious domain formulation, and finite element space approximations. The critical Reynolds numbers (Re_{cr}) for having oscillatory flow (a Hopf bifurcation) are obtained. The associated oscillating motion in a semicircular cavity with length equal to width has been studied in detail. Based on the averaged velocity field in one period of oscillating motion, the flow difference (called oscillation mode) between the velocity field and averaged one at several time instances in such period shows almost the same flow pattern for the Reynolds numbers close to Re_{cr}. This oscillation mode in a semicircular cavity shows a close similarity to the one obtained in a shallow cavity, but with some difference in a shallow cavity which is triggered by the presence of two vertical side walls and downstream wall.