Abstract
thickness on the shedding frequency of these coherent structures. The experiments were conducted on a NACA 0018 airfoil at an angle of attack of ten degrees for a range of chord Reynolds numbers from 30,000 to 200,000. The experimental conditions were selected to ensure that both laminar boundary layer separation with and without reattachment could be produced and to enable a comparative analysis with data from previous studies. The results presented show that vortex shedding occurs in the airfoil wake for both flow regimes investigated. The dimensionless wake vortex shedding frequency is shown to vary linearly with the Reynolds number; however, the slope of the linear fit depends significantly on the shear layer behavior. When an increase in the Reynolds number results in shear layer reattachment on the upper surface of the airfoil, the wake shedding frequency decreases significantly, and the vortical structures become less coherent. The present results are compared to those available for NACA 0012 and 0025 profiles. The comparison demonstrates similar correlations and trends in the non-dimensional frequency from previous studies and the present investigation. Using a frequency scaling based on a characteristic wake length, the data for two different profiles are shown to collapse on to a Strouhal number of approximately 0.18.
Published Version
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