Chord-wise repeated thermal load change on flat tip of a turbine blade

Abstract

Flow and heat transfer characteristics on the flat tip have been studied in a large-scale turbine blade cascade for a tip gap-to-span ratio of h/s = 1.5%. The present heat/mass transfer experiment by employing the naphthalene sublimation method with a high spatial resolution proves the existence of a chord-wise repeated thermal load change on the flat tip in the region between the leading edge and mid-chord. In this region, there are discrete local peaks of thermal load repeated along the pressure side, contrary to a continuous peak line downstream of the mid-chord. Each discrete peak has an aft ridge extending toward the suction side. The surface flow visualizations reveal that there exists a chord-wise repeated tip gap flow change between the leading edge tip gap vortex system and the stable separation bubble downstream of the mid-chord. The chord-wise repeated thermal load change seems to have a close relation to the chord-wise repeated flow change. Further investigations will be needed to understand exactly how, why, and when the repeated change happens.