Measurements of Base Pressure and Energy Separation on a Circular Cylinder in Subsonic Cross Flow

Abstract

Experiments were conducted on the vortex shedding of a circular cylinder in cross flow, over the subsonic speed range. Although the phenomenon of energy separation behind bluff bodies had been discovered in 1943 no time-resolved temperature measurements had been achieved in the wake of a cylinder. Previous attempts to provide such measurements had been frustrated by the inadequate bandwidth of available temperature measurement instrumentation. New temperature measuring techniques gave a bandwidth of over 80 kHz, making it possible to investigate total temperature fluctuations behind the cylinder, in addition to total pressure and hence entropy. Timeresolved pressure distributions give information on surface pressure fluctuations and the corresponding drag and base drag coefficients are provided. Flow changes at higher subsonic velocities and into the transonic range are described and this should improve understanding of vortex shedding and base pressure. From time-resolved measurements of wake total pressure and temperature the phenomenon of energy separation was demonstrated. The vortex shedding was strongest and most coherent at a Mach number of 0.6. This condition became the focus of the investigation which linked the phenomena of energy separation and base pressure through the vortex shedding behavior.