Constant-frequency time cells in the vortex-shedding from a square cylinder in accelerating flows

An extensive experimental campaign has been carried out in a multiple-fan wind tunnel to study the effects of flow acceleration on sectional model sharp-edged square cylinder. Different levels positive and negative are reproduced, which compatible with those induced by full-scale thunderstorm outflows. Various initial final conditions also explored and, all conditions, multiple test repeats order obtain satisfactory ensemble averages. Particular attention is devoted acquisition signals associated vortex-shedding, for tailored time-frequency analyses, based continuous wavelet Hilbert transforms, introduced. Sensitivity analyses selection relevant parameters that better allow tracing temporal variation shedding frequency. Time intervals frequency constant, separated discontinuities, found during transients. The number extent such constant-frequency time cells discontinuities seem be connected acceleration, but not strictly repetitive. For higher mean Strouhal comparable or moderately lower than steady-flow value corresponding instantaneous velocity.