Experimental and numerical study on axially non-uniform clearances with a squealer cavity tip

Experimental method and numerical method were both used to study the effect and mechanism of the axially non-uniform clearances on turbine leakage flows with a squealer cavity tip. Two clearance heights and three clearance types: shrinking clearance, uniform clearance and expanding clearance, were investigated. The following findings were made. Firstly, there was no relation between the reduction of the leakage mass flowrate and the reduction of the total pressure loss. The leakage mass flow rate increased by 26.7% under the expanding clearance case, while the corresponding total pressure loss achieved a 2.44% reduction under small clearance and a 3.53% reduction under large clearance. Moreover, the reduction of the total pressure loss was obtained by the decrease of the scale of the passage vortex in pitch-wise and in span-wise directions and the decrease of the leakage vortex in pitch- wise direction. The arrangement of the expanding clearance strengthened the span-wise flows of the leakage flows in the squealer cavity, led to a closer reattachment line with the blade on the pressure side and a further back leakage vortex separation line, and finally restricted the leakage flows.