Effect of ventilation on the flowfield around a sphere
Syryanarayana, G.K. and Meier, G.E.A. (1995) Effect of ventilation on the flowfield around a sphere. Experiments in Fluids, Bd. 19 (1995), Heft 2, 78-88, pp. 78-88. Springer-Verlag.
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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% 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 1.2mm diameter wire placed at 70 was found to overtrip the boundary layer and completelydestroy the vortex system. Simultaneously, the turbulent separation is advanced and the drag increased.
|Title:||Effect of ventilation on the flowfield around a sphere|
|Journal or Publication Title:||Experiments in Fluids, Bd. 19 (1995), Heft 2, 78-88|
|In ISI Web of Science:||Yes|
|Page Range:||pp. 78-88|
|Keywords:||sphere with ventilation, incompressible flow, pressure drag, drag reduction, near wake, flow model, vortex rings, asymmetric wake, turbulent separation|
|HGF - Research field:||UNSPECIFIED|
|HGF - Program:||Aeronautics|
|HGF - Program Themes:||L - no assignement|
|DLR - Research area:||UNSPECIFIED|
|DLR - Program:||L TG - Querschnittstechnologien|
|DLR - Research theme (Project):||UNSPECIFIED|
|Location:||Köln-Porz , Braunschweig , Göttingen|
|Institutes and Institutions:||Institute of Aerodynamics and Flow Technology > Institut für Strömungsmechanik > Institut für Experimentelle Strömungsmechanik|
|Deposited By:||elib DLR-Beauftragter|
|Deposited On:||03 Apr 2006|
|Last Modified:||27 Apr 2009 10:08|
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