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Wind and Structures
  Volume 12, Number 6, November 2009 , pages 541-551

Wind-tunnel blockage effect on drag coefficient of circular cylinders
J. Anthoine, D. Olivari and D. Portugaels

    This paper explains how to correctly measure the drag coefficient of a circular cylinder in wind tunnels with large blockage ratios and for the sub-critical to the super-critical flow regimes. When dealing with large blockage ratios, the drag has to be corrected for wall constraints. Different formulations for correcting blockage effect are compared for each flow regime based on drag measurements of smooth circular cylinders performed in a wind tunnel for three different blockage ratios. None of the correction model known in the literature is valid for all the flow regimes. To optimize the correction and reduce the scatter of the results, different correction models should be combined depending on the flow regime. In the sub-critical regime, the best results are obtained using Allen and Vincenti\'s formula or Maskell\'s theory with ?=0.96. In the super-critical regime, one should prefer using Glauert\'s formula with G=0.6 or the model of Modi and El-Sherbiny. The change in the formulations appears at the flow transition with a variation of the wake pattern when passing from sub-critical to super-critical flow regimes. This parameter being not considered in the known blockage corrections, these theories are not valid for all the flow regimes.
Key Words
    drag coefficient; blockage effect; wind tunnel measurement; bluff body; circular cylinder; flow transition.
J. Anthoine; Von Karman Institute for Fluid Dynamics - Chauss?e de Waterloo, 72 - B-1640 Rhode-St-Gen?se, Belgium
D. Olivari; AirSR, Belgium and von Karman Institute for Fluid Dynamics - Chauss?e de Waterloo, 72 - B-1640 Rhode-St-Gen?se, Belgium
D. Portugaels; Service Public de Wallonie, Namur, Belgium

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