Flow features of shallow cylindrical cavities subject to grazing flow

Abstract

The flow behavior within shallow cavities of circular planform, subject to grazing flows, exhibits a strong dependence on the cavity depth ( h)-to-diameter ( d) ratio. In the present experimental study, the internal flow patterns within shallow circular cavities having a depth-to-diameter ratio of 0.15  ≤  h/d ≤ 1 have been extracted from mean static and unsteady surface pressure measurements collected on the cavity surfaces. In the literature, no comprehensive experimental study spanning this entire h/d range is available characterizing the flow behavior in shallow cylindrical cavities; only certain aspects of flow at select h/d are present in the current literature, and the present paper addresses this shortcoming. In agreement with the previous research on shallow cylindrical cavities, the mean flow orientation and the amplitude of large-scale pressure fluctuations within the cavity are observed to follow a non-monotonic function as the depth-to-diameter ratio is varied, with h/d = 0.5 exhibiting the greatest asymmetry in flow orientation. The division of the internal cavity flow into stable, switching, and flapping regimes established by previous related studies has been reevaluated, and utilizing a simple filtering technique, a modification to the classification of these flow regimes has been proposed for the present conditions. Furthermore, the observation of two high-frequency pressure oscillations, measured within the cavity for the flapping regime, has been linked to shear layer instabilities.