Film Cooling: Breaking the Limits of Diffusion Shaped Holes

Film cooling in all of its various formats has become a mainstay of turbine cooling technology today. Over the past 40 years, investigations have been performed by a broad spectrum of researchers to understand the fundamental physics of film cooling, and to improve the state-of-the-art with respect to actual gas turbine performance. The primary focus of most research has been on the use of discrete film holes, or rows of film holes, on the hot gas path surfaces of the turbine as seen in the vane and blade photos of Figure 1. Virtually all aspects of film cooling have been explored, some in great depth and others to a lesser extent, both experimentally and computationally. One of the goals of film cooling in gas turbines has been the achievement of ideal cooling films, such as those from two-dimensional continuous slots with uniformly distributed cooling supply. This ideal is held to be the entitlement of practical film cooling, or at least the much sought after goal. Due to the many competing constraints of turbine design, it is generally impractical to place such slots into the high temperature surfaces of the turbine components. As a consequence, film cooling is performed almost exclusively through the use of discrete holes and rows of evenly spaced holes. In practical applications, bot