Effect of natural ventilation on the boundary layer separation and near-wake vortex shedding characteristics of a sphere

Suryanarayana, GK and Prabhu, A (2000) Effect of natural ventilation on the boundary layer separation and near-wake vortex shedding characteristics of a sphere. Experiments in Fluids, 29 (6). pp. 582-591.

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    Abstract

    Experiments were conducted in water and wind tunnels on spheres in the Reynolds number range 6 x 103 to 6.5 X 105 to study the effect of natural ventilation on the boundary layer separation and near-wake vortex shedding 13; characteristics. In the subcritical range of Re xAB;2 x 105),13; ventilation caused a marginal downstream shift in the location of laminar boundary layer separation, there was only a small change in the vortex shedding frequency. In the supercritical range (Re gt; 4 x 105), ventilation caused a downstream shift in the mean locations of boundary layer13; separation and reattachment; these lines showed significant13; axisymmetry in the presence of venting. No distinct vortex13; shedding frequency was found. Instead, a dramatic reduc13; tion occurred in the wake unsteadiness at all frequencies.13; The reduction of wake unsteadiness is consistent with the13; reduction in total drag already reported. Based on the13; present results and those reported earlier, the effects of13; natural ventilation on the flow past a sphere can be categorized in two broad regimes, viz., weak and strong interaction regimes. In the weak interaction regime (sub critical Re), the broad features of the basic sphere are largely unaltered despite the large addition of mass in the near wake. Strong interaction is promoted by the closer proximity of the inner and outer shear layers at supercritical Re. This results in a modified and steady near-wake flow, characterized by reduced unsteadiness and small drag.

    Item Type: Journal Article
    Additional Information: Copyright for this article belongs to Springer-Verlag
    Uncontrolled Keywords: Natural ventilation;Boundary layer;Shedding frequency
    Subjects: ENGINEERING > Fluid Mechanics and Thermodynamics
    Division/Department: National Trisonic Aerodynamic Facility, Other
    Depositing User: M/S ICAST NAL
    Date Deposited: 07 Sep 2006
    Last Modified: 24 May 2010 09:50
    URI: http://nal-ir.nal.res.in/id/eprint/2643

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