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

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 nonuniformity, 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 preswirling purge flow in the first place. It is reasoned that swirled purge flow moves with the rotating pressure nonuniformity 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 agreeme...