Effect of Inlet Mach Number on Aerothermodynamics of Sealing Leakage Flow Cooling on Endwall

Abstract

The gas turbine has an assembly gap between the combustion chamber and the first stage vane. The coolant air discharge from the gap can prevent the ingestion of the high temperature gas. This leakage flow also provides a cooling coverage on the vane endwall. Taking the cooling effect of the leakage flow on the endwall into consideration is very important for an efficient cooling design. In this paper, the cooling effect of leakage flow on endwall is studied by means of experimental and numerical methods. The study included slots at 30°, 45°, and 60° angles, and six blowing ratios of 0.3, 0.6, 1.0, 1.4, 1.7, and 2.0. The experiment and numerical calculation are conducted under the condition that the inlet Mach number is 0.125 and the outlet Mach number is 0.72, which is close to the working Mach number of the real gas turbine. Under the same slot inclination and blowing ratio, the distribution of endwall adiabatic cooling effectiveness is more nonuniform under the condition of near-real engine Mach number. This is because the passage vortex is weaker under the low Mach number condition, and the leakage flow has a better wall attachment effect. In terms of the spanwise average of endwall adiabatic cooling effectiveness, when the blowing ratio is small, the adiabatic cooling effectiveness is lower under the condition of near-real engine Mach number than that under the condition of low Mach number, but the opposite is true under the condition of large blowing ratio. This is because under the condition of large blowing ratio, the turbulence is stronger under the condition of Mach number of near-real engine. With the reduction of blowing ratio, the turbulent kinetic energy weakens more strongly. In the studied cases, there is a critical blowing ratio of 1.0, and the total endwall cooling adiabatic cooling effectiveness is not significantly affected by the Mach number when it is smaller than M1.0. The average adiabatic cooling effectiveness of the endwall under the condition of near-real engine Mach number is about 7% lower than that under the condition of low Mach number. It means that the experimental results of leakage flow cooling obtained under the condition of low inlet Mach number need to be corrected by a correction factor, which may be less than 1 to make it engine relevant.