Flow past a circular cylinder with a permeable wake splitter plate

Citation

Cardell, Gregory Scott (1993) Flow past a circular cylinder with a permeable wake splitter plate. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/25C5-1150. https://resolver.caltech.edu/CaltechETD:etd-04012005-092116

Abstract

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Measurements in the near wake region of a circular cylinder in a uniform flow in the Reynolds number range [...] with permeable splitter plates spanning the wake center plane are presented. Permeability is defined by the pressure drop across the plates, and the relationship between permeability and plate solidity is determined for a set of plates constructed from woven wire mesh, permitting unambiguous characterization of the splitter plates by the solidity. The effects of different solidities on the flow in the near wake are investigated using smoke wire flow visualization, hot-wire anemometry, and measurements of the mean pressure at the cylinder surface, and the results are related to cylinder flow without a splitter plate.

Flow visualization results demonstrate that the introduction of low solidity splitter plates does not change the basic near wake structure, and that sufficiently high solidity uncouples the large-scale wake instability from the body, with the primary vortex formation occurring downstream of the separation bubble due to instability of the wake profile. Hotwire and surface pressure measurements confirm and quantify the flow visualization results, showing that the permeable splitter plates reduce the drag and modify the primary wake frequency. When the solidity is high enough that the wake is convectively unstable, the base pressure is independent of the Reynolds number and solidity. For a wide range of solidities, the same asymptotic value of the Strouhal number is reached at high Reynolds numbers. The relationship between the Strouhal number and the base pressure is discussed.

Detailed measurements in the separating shear layers with splitter plates moderating the primary vortex formation show that in the mean the development of the separating shear layers is similar to that of the plane mixing layer. The presence of the splitter plates enhances shear layer development, and it is found that for all solidities the instability amplifies a broad frequency band without discrete spectral features. Turbulent transition in the shear layer and its role in the pronounced Reynolds number dependency of the flow in this Reynolds number range is discussed. Acoustic excitation of the separated shear layers confirms the broad band frequency response of the shear layer instability, and the effect of the driven shear layers on the near wake is investigated.

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