Experimental Investigation of Rotor Tip Film Cooling at an Axial Turbine with Swirling Inflow Using Pressure Sensitive Paint

Manuel Wilhelm,Heinz-Peter Schiffer

doi:10.3390/ijtpp4030023

Abstract

Rotor tip film cooling is investigated at the Large Scale Turbine Rig, which is a 1.5-stage axial turbine rig operating at low speeds. Using pressure sensitive paint, the film cooling effectiveness η at a squealer-type blade tip with cylindrical pressure-side film cooling holes is obtained. The effect of turbine inlet swirl on η is examined in comparison to an axial inflow baseline case. Coolant-to-mainstream injection ratios are varied between 0.45% and 1.74% for an engine-realistic coolant-to-mainstream density ratio of 1.5. It is shown that inlet swirl causes a reduction in η for low injection ratios by up to 26%, with the trailing edge being especially susceptible to swirl. For injection ratios greater than 0.93%, however, η is increased by up to 11% for swirling inflow, while for axial inflow a further increase in coolant injection does not transfer into a gain in η .

Highlights

IntroductionBeing located downstream of the combustion chamber, the first stage of a high pressure turbine operates at hot gas temperatures that exceed the melting point of turbine materials
For a given cooling hole configuration, hole geometry and airfoil geometry, the film-cooling performance depends both on global parameters, i.e. the injection ratio IR = ṁc /ṁrotor,in and the main stream turbulence, as well as local parameters, i.e. the blowing ratio (BR) and the momentum flux ratio (MR) [26]
An axial inflow case (AX) is considered, which is compared to a high-turbulence swirling inflow case (SW), for which the swirler modules at the turbine inlet were installed

Summary

Introduction

Being located downstream of the combustion chamber, the first stage of a high pressure turbine operates at hot gas temperatures that exceed the melting point of turbine materials. The rotor blade tip is among the areas that experience the highest heat load due to hot fluid passing through the gap between tip and casing. If the tip is not cooled properly, its lifetime declines and tip oxidation may occur. Consequences include an increase in tip clearance and aerodynamic losses, leading to a reduction in turbine efficiency. The coolant acts as a protective layer between the hot gas and tip surface, reducing the thermal load

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