Recent research developments for turbine blade tip heat transfer, including development and effects of tip leakage vortices

Currently, there is a deficit of experimental data for surface heat transfer characteristics and thermal transport process associated with tip gap flows, and a lack of understanding of performance and behavior of film cooling as applied to blade tip surfaces. As a result, many avenues of opportunity exist for development of creative tip configurations with innovative external cooling arrangements. Overall goals of recent investigation are to reduce cooling air requirements, and reduce thermal loading, with equivalent improvements of thermal protection and structural integrity. The present paper presents a survey of related research, considering these overall goals, including discussions of the development and effects of tip leakage vortices. Considered are surface heat transfer characteristics of transonic turbine blade tips, with a variety of innovative film cooling arrangements, as well as different tip configurations, including smooth, squealer, squealer with ribs, partial squealer, and winglet. Of particular interest in the present review are investigations which include transonic flows and their impact on blade tip surface heat transfer and tip gap aerodynamic losses, including the development and effects of tip leakage vortices. Associated investigations often include engine representative Mach numbers, Reynolds numbers, and film cooling parameters, including density ratios. In some cases, also considered are scaled engine components, which are modelled and tested with complete external cooling arrangements.