Strouhal number universality in high-speed cylinder wake flows

Flow oscillations in the near-wake region of a two-dimensional circular cylinder are experimentally investigated at Mach 6 over the Reynolds number range 2.3 x 105 to 5 x 105. The oscillation frequency is obtained by spectral proper orthogonal decomposition of high-speed schlieren data. The Strouhal number based on the length of the near-wake shear layers is found to exhibit universal behavior. This corroborates experimental findings at Mach 4 from recent literature, and furthermore, the universal behavior is also seen to hold with respect to Mach number. Time-resolved pressure measurements at the flow separation points on the cylinder aft surface show that coherent oscillatory activity occurs with a phase difference of pi radians between the two statistically symmetric halves of the flow. This aspect of the flow dynamics at high speeds is in common with its low-speed counterpart, i.e., the canonical problem of the cylinder wake in an incompressible flow.

Automated summary

Experimental investigation of flow oscillations in the near-wake region of a two-dimensional circular cylinder at Mach 6 reveals universal behavior in oscillation frequency and Strouhal number. Coherent oscillatory activity with a phase difference of pi radians is observed in time-resolved pressure measurements on the cylinder aft surface, similar to the low-speed counterpart of cylinder wake dynamics.