The Effect of Coolant Injection on the Endwall Flow of a High Pressure Turbine

This paper presents a study of the effects of two types of hub coolant injection on the rotor of a high pressure gas turbine stage. The first involves the leakage flow from the hub cavity into the mainstream. The second involves a deliberate injection of coolant from a row of angled holes from the edge of the stator hub. The aim of this study is to improve the distribution of the injected coolant on the rotor hub wall. To achieve this, it is necessary to understand how the coolant and leakage flows interact with the rotor secondary flows. The first part of the paper shows that the hub leakage flow is entrained into the rotor hub secondary flow and the negative incidence of the leakage strengthens the secondary flow and increases its penetration depth. Three dimensional unsteady calculations were found to agree with fast response pressure probe measurements at the rotor exit of a low speed test turbine. The second part of the paper shows that increasing the injected coolant swirl angle reduced the secondary flow penetration depth, improves the coolant distribution on the rotor hub and improves stage efficiency. Most of the coolant however, was still found to be entrained into the rotor secondary flow.