Effect of Purge Flow Swirl on Hot-Gas Ingestion into Turbine Rim Cavities

摘要

A simplified turbine rim cavity is considered, with a focus on understanding the effects of purge flow swirl on main gas ingestion. Recent work has shown that introducing swirl into purge flow upstream of a blade row is desirable insofar as reducing viscous losses associated with purge flow interaction with the hot-gas path. However, computational fluid dynamics results suggest that, in the presence of the rotating external pressure nonunifonnity, due to the downstream blade row, swirled purge flow is less effective in preventing ingestion. This is reflected in higher purge air mass flow rates necessary to seal a given cavity, and that in turn diminishes the positive effect of preswirung purge flow in the first place. It is reasoned that swirled purge flow moves with the rotating pressure nonunifonnity and responds to it more readily than nonswirled purge flow, which sees the averaged effect of multiple blade passing events. A flow model based on this physical principle is developed, showing good agreement with computational results. The model yields an ingestion criterion with a parametric dependence on purge flow parameters. The analysis is extended to an unsteady situation, whereby the effects of both stationary and rotating pressure nonuniformities, from vanes and blades, respectively, are taken into account This unsteady flow model points to an optimal design space, in the context of minimizing purge flow losses while maintaining an appropriate margin with regard to hot-gas ingestion.