Control of a Turbine Tip Leakage Vortex Using Casing Vortex Generators

Abstract

An experiment was conducted in a linear cascade of Pak-B blades to simulate the ∞ow in the tip-gap region of a low pressure turbine blade row, and investigate the sensitivity of the ∞ow to casing-mounted passive and active vortex generators. The inlet Reynolds number was 5£10 5 corresponding to an inlet Mach number of 0.2 and an exit Mach number of 0.3. The gap-to-chord ratio was 5%. The ∞ow was documented using blade-tip static pressure measurements and downstream total pressure loss coe‐cients. Additionally, surface ∞ow visualization was performed on the cascade end-wall for a greater understanding of the gap∞ow behavior. These measurement techniques were used to investigate the response of the ∞ow to passive ∞ow control using vortex generators located on the cascade end-wall. The vortex generators were designed to produce vorticity of opposite sign of the tip-leakage vortex. Vortex generators that were of the height and roughly half the height of the clearance gap were investigated. Additionally, two placements of the vortex generator were investigated: on the wall directly across from the trailing edge of the blade and approximately 0.25cx upstream of the trailing edge. All investigated placements and sizes of the passive vortex generators reduced the total pressure loss associated with the tip leakage vortex. A 25% reduction was achieved with both heights of the vortex generators when placed at the upstream location. When placed at the trailing edge, the shorter vortex generator resulted in a 15% reduction of total pressure loss associated with the tip leakage vortex, and the taller vortex generator resulted in a 20% reduction. The sensitivity of the ∞ow to the passive devices was used to determine placement and design of a plasma actuator on the end-wall as an active ∞ow control mechanism. Three plasma actuators were investigated, one of which resulted in a 7% decrease in total pressure loss associated with the tip leakage vortex.