Schlieren and Hot-Wire Investigation of Karman Vortex Streets

摘要

This thesis involved taking schlieren and hot-film anemometer data on Karman vortex streets, then developing a means of characterizing the individual vortices in a street using a schlieren picture and the corresponding anemometer trace. A ThermoSystems, Inc. IFA-100 anemometer system, with a Tektronix 425 oscilloscope, was used to record an anemometer trace. The trace was captured on photographic film. The oscilloscope also fired a Cordin Model 5401 spark lamp, which provided, via a schlieren optical system, a physical picture of the Karman streets formed behind a 5/16-inch dia cylinder in a 2-inch by 2-inch square cross-section test region with a Mach 0.43 flow. Distance and angle information were obtained from the schlieren photographs, and timing and anemometer output voltage were obtained from the anemometer trace photograph using an HP-9874A digitizer. The data were analyzed using a Newton-Raphson method to solve for two constants, which should have completely characterized the vortices in the vortex street, assuming the vortices followed the theoretical equation for a combined free and forced vortex. It was assumed that the superposition of two vortices plus the mean flow were the parameters influencing the flow at any point in space and time.