Repetitive tip convective transport and its flow physics in a large-scale turbine cascade

Abstract

In order to understand repetitive convective transport and its flow physics over the flat tip of a turbine blade, high-spatial resolution measurements of thermal load and aerodynamic loss are performed in a large-scale cascade. The thermal load distributions measured with the naphthalene sublimation technique show that for two tip gaps of h/s = 1.0% and 2.0%, there is a repetitive change of thermal load upstream of the mid-chord, and wider tip gap makes thermal load change more severe but less repetitive. The mean distance between the neighboring peaks of thermal load in the direction normal to local flow for h/s = 2.0% is twice the one for h/s = 1.0%. Present total pressure measurements show that in the area of repetitive thermal load change for h/s = 2.0%, there exists a distinct repetitive loss change only near the tip surface. A qualitative flow model in the area of repetitive change is proposed for h/s = 2.0%. According to the flow model, the separation bubble undergoes a wave-like repetitive change in its thickness and length. Just behind the ridge of the wave-like separation bubble, low thermal load coexists with high loss, whereas just behind its valley, high thermal load coexists with low loss.