Experimental investigation of the influence of freestream turbulence on an anti-vortex film cooling hole

Abstract

Film cooling is used in gas turbines to thermally protect combustor and turbine hot section components by creating a layer of relatively cooler air to insulate the components from the hot freestream gases. This relatively cooler air is taken from upstream in the compressor section at a loss to the engine efficiency and therefore must be used as effectively as possible. A novel anti-vortex hole (AVH) geometry has been investigated experimentally through a transient infrared thermography technique to study the film cooling effectiveness and heat transfer coefficient by varying blowing ratio and freestream turbulence intensity. The AVH geometry is designed with two secondary holes stemming from a main cooling hole that attempts to diffuse the coolant jet and mitigate the vorticity produced by conventional straight holes. The AVH geometry data collected showed improved cooling performance at low freestream turbulence intensities compared to conventional straight holes. Three turbulence intensities of 1, 7.5, and 11.7% were investigated for the AVH geometry at blowing ratios of 0.5, 1.0, 1.5, and 2.0 for a total of twelve different conditions. Results showed that higher freestream turbulence conditions were beneficial to the performance of the AVH. Increasing the blowing ratio at all turbulence levels also improved film cooling effectiveness, both span-averaged and on the centerline. The highest performing case was at a turbulence intensity of 7.5% and a blowing ratio of 2.0. The 11.7% cases outperformed the 1% cases, but it appears that at the 11.7% cases the higher freestream turbulence reduces the performance of the secondary holes compared to the 7.5% case. Increasing the blowing ratio and turbulence intensity will result in a higher heat transfer coefficient, which must be taken into account for future designs and overall reduction of heat load.