Title

The effects of freestream turbulence on the drag coefficient of a sphere

Document Type

Article

Publication Date

3-1-2009

Publication Title

Experimental Thermal and Fluid Science

Volume

33

Issue

3

First Page

460

Keywords

Drag, Integral length scale, Orifice perforated plate, Reynolds number, Sphere, Turbulence intensity

Last Page

471

Abstract

The effects of freestream turbulence intensity and integral length scale as freestream turbulent parameters on the drag coefficient of a sphere were experimentally investigated in a closed circuit wind tunnel. The Reynolds number, Re = Ud/ν, was varied from 2.2 × 104 to 8 × 104 by using spheres with diameter d of 20, 51 and 102 mm in addition to altering the freestream velocity, U. The freestream turbulence intensity Tu and flow integral length scale Λ were manipulated by the utilization of orifice perforated plates. The proper combination of orifice perforated plate hole diameter, sphere size, and sphere location along the center line of the wind tunnel enabled the independent alterations of turbulence intensity and relative integral length scale (Λ/d) from 1.8% to 10.7% and from 0.1 to 2.6, respectively, at each studied Reynolds number. Results show that over the range of conditions studied, the drag always decreases with increasing Tu and, the critical Reynolds number at which the drag coefficient is dramatically reduced is decreased by increasing Tu. Most interestingly, the drag at any particular Re and Tu may be significantly lowered by reducing Λ/d; this is particularly the case at high Re and Tu. © 2008 Elsevier Inc. All rights reserved.

DOI

10.1016/j.expthermflusci.2008.11.001

ISSN

08941777

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