Details of Axial-Compressor Shrouded Stator Cavity Flows

Abstract

Data that reveal the structure and character of the flow in and near the cavities of compressor shrouded stators are reviewed. Results were obtained from low-speed multistage compressor measurements and simulations and generic high-speed cavity simulations. The experimental measurements were acquired with slow and fast response instrumentation. The numerical simulations were collected with two different flow solvers. The data are presented to provide compressor designers some indication of the complexities of the flow within shrouded stator cavities and to provide a datum for further studies on more complex geometries and flow conditions. The data suggest surprisingly similar flow structures within most cavities including spatial and temporal flow field variations. In general, the flow in the cavities involved fluid moving in the circumferential direction with lower momentum than powerstream fluid. The difference in momentum is adjusted through a shear layer in the radial direction near the powerstream/cavity interface. Circumferential variations in flow properties also exist, the most prominent being caused by the upstream potential influence of the downstream blade. This influence caused the fluid within the cavities near the leading edges of the airfoils to be driven radially inward relative to fluid near mid-pitch. Some data are presented that suggest powerstream secondary flows dictate which fluid particles are ingested in the downstream cavity across the stator pitch. Vortical flow structures, similar to those set up by a driven cavity, dominate the axial variations in flow. The position and structure of these vortical structures are dependent upon the powerstream flow field and the cavity geometry. Examining some interdependencies between cavity flow parameters concludes discussions of cavity flow field characteristics. A known relation between cavity leakage amount and tangential velocity is reiterated. Cavity rotational speed and stator exit swirl are also shown to influence the cavity tangential velocity. Increasing rotational speed tends to increase the tangential velocity through the cavity. Increasing the stator exit swirl reduces the tangential velocity increase.