Investigations of Karman vortex street using flow visualization and image processing

A method of quantitative flow visualization of the Karman street is presented. Image processing creates the ability for quantitative evaluation of the phenomena and enables the determination of geometric parameters of the vortex street. The methodology and appropriate software for image processing are described, and the analysis of both individual pictures and a series of images was feasible. The distances between the adjoining vortices and the hydrodynamic wavelength have been calculated. The most fundamental conclusion is the experimental confirmation that in the close neighborhood of the bluff body, the vortices move slower than at a greater distance from their origin. A 7% decrease of the convection velocity was found in the closest neighborhood of the bluff body. The calculated ratios of wavelength to bluff body diameter, equal to 4.09 and 3.65 for the 10 mm and 12 mm bluff body diameter, respectively, are close to the theoretical values based on mathematical modeling.