This Letter revisits the problem of the existence of a universal Strouhal number in the separated flow past a stationary bluff body. Physical hypotheses based on flow kinematics only are formulated on the phenomenom. They lead to a simple closed-form mathematical formulation. The model thus developped predicts a universal Strouhal number equal to $1/2\pi \approx 0.159$, whichmatches experimental observations. The model has been expanded to predict the Strouhal-Reynolds relationship in the supercritical regime. The formulation has a universal character since said relationship depends on the critical Strouhal and Reynolds numbers only. The circular, square, and triangular cross-section shapes have been used for validation purposes. The case on an accelerating incoming flow has also been considered. The theoretical model thus developed supports the idea, suggested experimentally by other researchers, that time-averaged flow speed during a vortex formation cycle governs vortex dynamics in this accelerating flow case. Lattice Boltzmann simulations were performed to validate the model.

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• Flow instability
• Vortex flows
• Vortex shedding