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A circular cylinder is tested in crossflow over the subsonic speed range. Time-resolved pressure distributions give information on surface pressure fluctuations; the corresponding drag and base drag coefficients are provided. Measured base pressure fluctuations at low Mach numbers are in agreement with the findings of other researchers. Flow changes at higher subsonic velocities and into the transonic range are described. Illustrations are drawn from the observations of other researchers, enabling physical explanations to be given to assist toward a more general modeling of the problem. At Mach numbers above 0.6 the changing strength of the vortices reduces the base drag coefficient up to a Mach number of 0.9, at which the onset of sonic flow increases the drag. Strouhal number variation is compared with the measurements of other authors. The paper concentrates on providing reliable measurements of vortex shedding and base pressure over the subsonic speed range rather than attempting to provide universal correlations.

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