Impact of Rotor-Casing Effusion Cooling on Turbine Performance and Operating Point: An Experimental, Computational, and Theoretical Study

Abstract

It is known that a secondary effect of rotor-casing effusion cooling is to modify and potentially spoil the rotor over-tip leakage flow. Studies have shown both positive and negative impacts on high-pressure stage aerodynamic performance and heat transfer, although there remains no consensus on whether the net effect is beneficial when both aerodynamic and thermal effects are accounted for simultaneously. An effect that has not been extensively discussed in the literature is the change in stage operating point that arises due to mass introduction midway through the machine. This effect complicates the analysis of the true performance impact on a turbine and must be accounted for in an assessment of the overall benefit of such a system. In this paper, we develop a low-order (“mean-line”) analysis in an attempt to bring clarity to this issue. We then present results from experiments conducted in the Oxford Turbine Research Facility, a 1.5-stage transonic rotating facility capable of matching non-dimensional engine conditions, with effusion cooling implemented over a sector of the rotor casing. Finally, we present steady and unsteady Reynolds-Averaged Navier-Stokes (RANS) simulations both with and without cooling. The results are used show that with cooling, there are flow changes both locally to the cooled casing (changes to the tip-leakage and secondary flow structures) and globally (changes to the bulk-flow velocity triangles). For the present configuration, both changes contribute positively to stage efficiency.

Blade tip leakage flow and heat transfer characteristics over a gas turbine blade at subsonic and transonic exit conditions

“…The experiments done by Kwak et al 28 showed that the suction side squealer tip had the lowest heat transfer rates on the blade tip and near tip regions compared to the camber line squealer, pressure side squealer, and cavity tips. It was shown by Adams et al 29 that rotor-casing effusion cooling changes the overall operation point of the turbine due to mass injection in the form of the coolant. Moreover, the cooling injection alters the effective flow characteristic and shock wave position.…”

Effect of casing purge flow on heat transfer and cooling performance of blade squealer tip for a gas turbine stage

“…Collins et al 30 used unsteady CFD method to describe the tip efficiency situation with film-cooling holes undertaken, the result showed the isentropic efficiency of the stage was improved by 0.55%. Adams et al 31 proposed the mean-line model to study the impact of rotor casing effect cooling on turbine performance and operating point. Abbasi and Gholamalipour 32 set coolant inlet on casing and found that setting coolant inlet at 9 mm upstream of tip leading edge obtained the best result.…”