Abstract
Over the past several decades, researchers from around the world have embraced the use of Pressure Sensitive Paint (PSP) to obtain detailed film cooling effectiveness distributions. Utilizing the mass transfer analogy along with the luminescence characteristics of PSP, the mixing behavior of the coolant and mainstream flows is easily quantified. As the method relies on tracking the concentration of various gases in contact with the paint, the measurements are not affected by thermal diffusion through the test surface. Therefore, researchers provide film cooling effectiveness distributions that are spatially, highly resolved, even in the near-hole regions. Such distributions are not only needed to visualize the three-dimensional mixing occurring near the holes, but the measurements can also be used to validate numerical simulations. When PSP was first introduced to the gas turbine and film cooling communities, steady, film cooling effectiveness distributions were primarily obtained in low-speed flows with simple geometries and coolant-to-mainstream density ratios of unity. However, as more researchers have integrated this measurement tool into their labs, the use of the paint has expanded to include flow conditions and cooling configurations relevant to advanced gas turbine engines. In this review, the mass transfer analogy for film cooling effectiveness measurements will be explained, and the recent, widespread deployment of the method will be discussed. Within the past decade, laboratories have successfully utilized traditional PSP for full coverage airfoil cooling over a range of coolant-to-mainstream density ratios simulating engine conditions. In addition, “binary” and “fast response” paints have gained popularity. The binary PSP is most often used in high speed flows, where viscous heating may affect the response of traditional PSP. A second luminophore in the binary paint allows for correction of the local temperature variation and improves the accuracy of the mass transfer analogy. Finally, fast response PSPs now allow researchers to visualize the unsteady interaction of the coolant and mainstream flows, yielding time-resolved film cooling effectiveness distributions. This review will discuss these developments and provide opportunities for further advancement into the future.
