Inertial flow past a finite-length axisymmetric cylinder of aspect ratio 3: Effect of the yaw angle

Abstract

We study the flow past a finite-length yawed three-dimensional cylinder by a finite-volume–fictitious-domain method. We validate our non-boundary-fitted method against boundary-fitted numerical results for a finite-length cylinder whose axis is parallel to the streamwise direction. Drag and lift forces exerted on the cylinder and vortex shedding onset and frequency are carefully analyzed. Satisfactory agreement with published results gives strong confidence in the numerical methodology provided the boundary layer is accurately resolved. Then we carry out a detailed study of the flow past a yawed cylinder of aspect ratio L/D=3 (where L is the cylinder length and D is the cylinder diameter) at moderate Reynolds numbers (25≤Re≤250). We show that the wake patterns and the associated transitions depend strongly on Re and the yaw angle θ with respect to the streamwise direction. Various regimes are encountered including a standing-eddy pattern, steady shedding of one or two pairs of counterrotating vortices, periodic shedding of counterrotating vortices and unsteady shedding of hairpin-shaped vortices. The steady shedding of one or two pairs of counterrotating vortices prevails in the range of parameters studied. Hydrodynamic forces exerted on the cylinder are well approximated by laws derived in the Stokes flow regime, even for moderate Reynolds numbers. For the highest Reynolds numbers (Re=150,200,250) we show that the forces slowly depart from the Stokes-based laws. Simple modification of these laws is proposed, yielding a satisfactory match with the numerical results. An accurate way to compute the torque is also proposed based on the normal force to the cylinder.