Effect of ventilation on the flowfield around a sphere

Suryanarayana, GK and Meier, GEA (1995) Effect of ventilation on the flowfield around a sphere. Experiments in Fluids, 19 (2). pp. 78-88. ISSN 0723-4864

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The flowfield around a sphere with and without ventilation was investigated in a wind tunnel over a range of Reynolds numbers in an incompressible flow. At supercritical Re, the pressure drag of a sphere can be nearly nullified by venting only 2 percent of the frontal area of the sphere to the base through a smooth internal duct.The drag reduction is achieved by increased pressures in the separated flow region close to the base. At high Re, the vent flow breaks through the near wake and brings about symmetry in the global flowfield. When the internal shear is increased by using a rough internal duct, the base pressure is unchanged, but the external flow is accelerated to velocities beyond that achieved by the potential flow around the basic sphere. The findings can be explained by a flow model in which the near wake is aerodynamically streamlined by a pair of counterrotating vortex rings at the base. A roughness element can be made to partially destroy the vortex system at the base and result in a steady asymmetric wake. A 1.2 mm diameter wire placed at 70 deg was found to overtrip the boundary layer and completely destroy the vortex system. Simultaneously, the turbulent separation is advanced and the drag increased.

Item Type: Article
Additional Information: Copy right for this article belongs to Springer-Verlag
Uncontrolled Keywords: Flow distribution;Spheres; Ventilation;Wind-tunnel-tests; Incompressible flow;Drag-reduction;Reynolds number;Air-flow; Bluff-bodies;Boundary-layer-flow
Subjects: ENGINEERING > Fluid Mechanics and Thermodynamics
Depositing User: M/S ICAST NAL
Date Deposited: 31 Dec 2007
Last Modified: 07 Jun 2010 10:32
URI: http://nal-ir.nal.res.in/id/eprint/4361

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