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RESEARCH PAPERS

Flow Past a Sphere With Surface Blowing and Suction

[+] Author and Article Information
Prosenjit Bagchi

Department of Mechanical and Aerospace Engineering, Rutgers,  The State University of New Jersey, 98 Brett Road, Piscataway, NJ 08854pbagchi@jove.rutgers.edu

J. Fluids Eng 129(12), 1547-1558 (Jun 30, 2007) (12 pages) doi:10.1115/1.2801361 History: Received December 16, 2006; Revised June 30, 2007

The effect of uniform surface blowing and suction on the wake dynamics and the drag and lift forces on a sphere is studied using a high-resolution direct numerical simulation technique. The sphere Reynolds number Re, based on its diameter and the freestream velocity, is in the range 1–300. The onset of recirculation in the sphere wake occurs at higher Re, and the transition to nonaxisymmetry and unsteadiness occurs at lower Re in the presence of blowing. The size of the recirculation region increases with blowing, but it nearly disappears in the case of suction. Wake oscillation also increases in the presence of blowing. The drag coefficient in the presence of blowing is reduced compared to that in uniform flow, in the range 10<Re<250, whereas it is increased in the presence of suction. The reduction in the wake pressure minimum associated with the enhanced vortical structures is the primary cause for drag reduction in the case of blowing. In the case of suction, it is the increased surface vorticity associated with the reduction of the boundary layer that results into increased drag. The fluctuations in the instantaneous lift and drag coefficients are significant for blowing, and they result from the asymmetric movement of the wake pressure minimum associated with the shedding process.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Streamlines in the presence of surface blowing at B=0.2. (a)–(f) are for Re=10, 26, 38, 45, 50, and 100, respectively.

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Figure 2

Dimensionless length Le∕d of the recirculation region: (—○—) B=0, (—◻—) B=0.1, and (—▵—) B=0.2

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Figure 3

Streamlines for Re=150, B=0.2: (a) x-y plane, (b) x-z plane, and (c) 3D vortex topology

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Figure 4

((a) and (b)) Streamlines at Re=200, B=0.2 in the x-y plane for two time instants. (c) Streamlines in the x-z plane.

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Figure 5

3D vortex topology for Re=200, B=0.1

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Figure 6

3D vortex topology for Re=200, B=0.2 at various time instants

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Figure 7

Eigenfunctions corresponding to Kϕ=1 mode in the presence of surface blowing at B=0.2. (a)–(c) Imply streamwise, tangential, and azimuthal velocities, respectively, for Re=150. (d)–(f) Same for Re=200.

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Figure 8

3D vortex topology at Re=250, B=0.1

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Figure 9

3D vortex topology at Re=250, B=0.2

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Figure 10

Spectra of wake velocity fluctuations showing frequency content (St): (a) Re=300; (–∙–) B=0; (—) B=0.1; (------) B=0.2; (b) thick line Re=200, B=0.1; (⋯ ⋯) Re=200, B=0.2; (— —) Re=250, B=0.1; (– – –) Re=250, B=0.2

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Figure 11

Contours showing the rms of cross-stream velocity fluctuation at Re=300: (a) B=0, (b) B=0.1, and (c) B=0.2

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Figure 12

Effect of suction on the sphere wake. The top three figures are the streamline plots at Re=300 and for B=−0.05, −0.1, and −0.2, respectively.

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Figure 13

Streamlines based on perturbation field at Re=300; (a) B=0.2 and (b) B=−0.2

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Figure 14

Surface pressure coefficient. Thin lines are for B=0; thick lines are for B=0.2. Line symbols are as follows: (-----) Re=1, (—) Re=100. The right axis is for Re=1, and the left axis is for Re=100.

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Figure 15

Pressure contours for (a) Re=100, B=0 and (b) Re=100, B=0.2

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Figure 16

Instantaneous drag and lift for (a) Re=200, (b) Re=250, and (c) Re=300: (–∙–∙–) B=0; (—) B=0.1; (⋯ ⋯ ⋯) B=0.2

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