Flow past a sphere up to a Reynolds number of 300

The flow of an incompressible viscous fluid past a sphere is investigated n umerically and experimentally over flow regimes including steady and unstea dy laminar flow at Reynolds numbers of up to 300. Flow-visualization experi ments are used to validate the numerical results and to provide additional insight into the behaviour of the how. Near-wake visualizations are present ed for both steady and unsteady flows. Calculations for Reynolds numbers of up to 200 show steady axisymmetric flow and compare well with previous exp erimental and numerical observations. For Reynolds numbers of 210 to 270, a steady non-axisymmetric regime is found, also in agreement with previous w ork. To advance the basic understanding of this transition, a symmetry brea king mechanism is proposed based on a detailed analysis of the calculated f low held. Unsteady flow is calculated at Reynolds numbers greater than 270. The resul ts at a Reynolds number of 300 show a highly organized periodic flow domina ted by vortex shedding. An analysis of the calculated vortical structure of the wake reveals a sequence of shed hairpin vortices in combination with a sequence of previously unidentified induced hairpin vortices. The numerica l results compare favourably with experimental flow visualizations which, i nterestingly, fail to reveal the induced vortices. Based on the deduced sym metry-breaking mechanism, an analysis of the unsteady kinematics, and the e xperimental results, a mechanism driving the transition to unsteady flow is proposed.