Sponsor: Office of Naval Research

The objective of this project is to gain an understanding of the unsteady flow characteristics of a stator-rotor combination. In liquid handling systems like pumps, low pressure fluctuations downstream of the rotor can induce cavitation which can sometimes lead to undesirable acoustic noise. It has been suggested that the low pressure fluctuations are caused by the "cutting" of vortex structures in the stator wakes by the rotor, as well as by the leakage vortices through the tip-gaps between the rotor blades and the endwall casing (Wenger et al. 1998).

The configuration of interest involves an incoming turbulent flow which first encounters a row of stator blades and subsequently convects downstream through a rotor. The stator blades have a small tip clearance at the end wall. The primary focus is on understanding the physical mechanisms that lead to low pressure fluctuations near the endwall a short distance downstream of the rotor. It is expected that such understanding will be useful in predicting and eventually controlling cavitation induced noise.

In order to analyze the temporal dynamics of this flow and determine the underlying mechanism for these low pressure fluctuations, a large eddy simulation (LES) solver has been developed. The presence of the tip-gap can significantly increase the complexity of the grid topology and this has been avoided by using a novel approach which combines an immersed boundary technique with a curvilinear mesh.