Last modified: 2018-04-14
Abstract
The mean and time-resolved flow behaviours within shallow cylindrical cavities, subject to grazing flows, have been known to exhibit a strong dependence on the cavity depth to diameter ratio. As this ratio is increased from zero to unity, the mean flow undergoes numerous transitions: starting from an initially symmetric pattern, the flow goes through an unstable flapping, followed by a bistable switching regime, and then returns to the symmetric behaviour. Furthermore, as the depth to diameter ratio for cylindrical cavities approaches one, the onset of cavity acoustic resonance is observed. Compared to rectangular cavities, very limited experimental data is available for shallow cylindrical cavities, with few authors interested in both internal flow features, and noise generation and propagation. In this work, the interplay between the internal flow behaviour, the cavity resonance modes and the tonal noise generation is explored experimentally. In particular, the focus is placed on cavity depth to diameter ratios of h/d = 0.5 to 1. Within this range, the shallower depths are associated with a bistable mean flow asymmetry and relatively weak far-field tonal noise propagation, and the deeper cavities are related to a symmetric mean flow pattern and higher amplitude tonal noise generation.