Three-dimensional nature of the flow past a fixed transverse cylinder

The flow past a fixed circular cylinder at Reynolds numbers of about 40,000, which is of a random three-dimensional nature, is analyzed on the basis of measurements of relevant velocities, pressure, and forces. It is shown that at Reynolds numbers of about 40,000, vortex shedding around a fixed cylinder has not the stability which characterizes it at low Reynolds number. This is marked by the onset of a slow variation of pressure at the cylinder base and by similar variations in the amplitude of fluctuations at the Strouhal frequency and at the second harmonic. These low-frequency modulations, being nonuniform along the cylinder, are associated with a lack of longitudinal correlation.