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Research Papers: Flows in Complex Systems

Mitigating Blockage Effects on Flow Over a Circular Cylinder in an Adaptive-Wall Wind Tunnel

[+] Author and Article Information
Michael Bishop

Department of Mechanical & Mechatronics Engineering,  University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada

Serhiy Yarusevych

Department of Mechanical & Mechatronics Engineering,  University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canadasyarus@uwaterloo.ca

J. Fluids Eng 133(8), 081101 (Aug 16, 2011) (7 pages) doi:10.1115/1.4004421 History: Received August 28, 2010; Accepted June 08, 2011; Published August 16, 2011; Online August 16, 2011

The effect of wall streamlining on flow development over a circular cylinder was investigated experimentally in an adaptive-wall wind tunnel. Experiments were carried out for a Reynolds number of 57,000 and three blockage ratios of 5%, 8%, and 17%. Three test section wall configurations were investigated, namely, geometrically straight walls (GSW), aerodynamically straight walls (ASW), and streamlined walls (SLW). The results show that solid blockage effects are evident in cylinder surface pressure distributions for the GSW and ASW configurations, manifested by an increased peak suction and base suction. Upon streamlining the walls, pressure distributions for each blockage ratio investigated closely match distributions expected for low blockage ratios. Wake blockage limits wake growth in the GSW configuration at 7.75 and 15 diameters downstream of the cylinder for blockages of 17% and 8%, respectively. This adverse effect can be rectified by streamlining the walls, with the resulting wake width development matching that expected for low blockage ratios. Wake vortex shedding frequency and shear layer instability frequency increase in the GSW and ASW configurations with increasing blockage ratio. The observed invariance of the near wake width with wall configuration suggests that the frequency increase is caused by the increased velocity due to solid blockage effects. For all the blockage ratios investigated, this increase is rectified in the SLW configuration, with the resulting Strouhal numbers of about 0.19 matching that expected for low blockage ratios at the corresponding Reynolds number. Blockage effects on the shear layer instability frequency are also successfully mitigated by streamlining the walls.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 5

Surface pressure distributions in the SLW configuration. The data from Okamoto and Takeuchi [12] pertains to Red  = 32,200 and B = 4.2%. Note the uncertainty is accommodated by the size of the legends.

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Figure 4

Surface pressure distributions in the GSW, ASW, and SLW configurations. Note the uncertainty is accommodated by the size of the legends.

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Figure 3

Wall deflections in GSW, ASW, and SLW configurations for B = 17%

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Figure 2

Wall pressure distributions in an empty test section

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Figure 1

Adaptive-wall wind tunnel with a cylinder installed in the contracted test section

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Figure 10

Normalized shear layer instability frequency

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Figure 9

Spectra of the streamwise fluctuating velocity component measured in the separated shear layer at x/d = 0.25 and y/d = 0.62

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Figure 8

Dependence of the Strouhal number on the blockage ratio and wall configuration

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Figure 7

Spectra of the vertical fluctuating velocity component measured at x/d = 2.5, y/d = 0.5. Note that x/d = 2.5 is located about one diameter downstream of the vortex formation region and y/d = 0.5 approximately corresponds to the location of maximum turbulent intensity at this x/d.

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Figure 6

Mean half-wake width growth in the GSW, ASW, and SLW configurations

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