Wavelet coherence of surface pressure fluctuations due to von Kármán vortex shedding near a hemispherical protuberance

Wavelet coherence analyses are done using fluctuating surface-pressure data, to reveal interesting aspects of von Kármán (vK) vortex shedding from a hydraulically smooth hemispherical protuberance. This study is conducted at a hemisphere-diameter ( D ) based Reynolds number of R e D = 6.36 × 10 4 , and for an oncoming turbulent boundary layer with thickness 0.16 D . Benefits of wavelet analysis are emphasised for these classes of flows. Aided with other published results where possible, it is found in this present study that: (1) span-wise coherency of vK vortex formation is aperiodic, with time intervals well approximated by a Markov process; (2) the predominant appearance of vK shedding for present conditions, as opposed to symmetric shedding, suggests an influence of the oncoming boundary-layer thickness and hence local turbulence intensity on shedding type; and (3) vK vortex convection velocity in the hemisphere near wake approximately collapses onto a power law as a function of stream-wise distance, with vortex incoherency occurring beyond two hemisphere diameters downstream. Graphical abstract