Experiments on Combustor Effusion Cooling Under Conditions of Very High Free-Stream Turbulence

Abstract

Full-coverage or effusion cooling is commonly used in the thermal management of gas turbine combustion systems. The combustor environment is characterised by highly turbulent freestream flow conditions and relatively large turbulent length scales (length scale-to-coolant hole diameter ratios in excess of 30) that are primarily created by the fuel injector and dilution jets; indeed, the available evidence suggests that large energetic eddies interact strongly with the coolant flows and may have a significant impact on the film-cooling performance. The desire to create compact low-emission combustion systems for aero gas turbine engines has also given rise to a desire to reduce the quantity of air used in wall cooling, and has led to the need for improved thermal design approaches, cooling correlations and validated computational methods. In order to establish a greater understanding of effusion cooling under conditions of very high freestream turbulence, a new laboratory-based test facility has been created that is capable of simulating representative combustor flow conditions, and that allows for a systematic investigation of film-cooling performance over a range of freestream turbulence conditions and coolant to mainstream density ratios. This paper describes the new test facility and its capabilities, including the method for generating combustor relevant flow conditions. Adiabatic film-cooling effectiveness data obtained at a range of blowing ratios are also presented for a typical combustor effusion cooling geometry that uses a twenty degree injection angle. The analysis of this data is supported by fluid temperature field measurements which are presented for low and high freestream turbulence conditions. The interpretation of the data has established the impact of turbulence intensity and integral length scale on the mixing processes between freestream and coolant flows.

The effect of effusion holes inclination angle on the adiabatic film cooling effectiveness in a three-sector gas turbine combustor rig with a realistic swirling flow

“…A reduction of film coverage is observed when turbulence increases, but the impact is largely reduced with blowing ratios approaching 1.0. More recently Martin and Thorpe [14] observed an increase of adiabatic effectiveness with realistic high free stream turbulence when using inclined holes at blowing ratio above 1.0: this is due to an increased mixing rate of the jet with the mainstream, which enhance the amount of coolant close to wall region. The investigation carried out by Scrittore et al [15] was focused on the measurement of adiabatic film effectiveness and flow field from inclined effusion cooling jets in a range of blowing ratios (3.2 to 5.0) that can be observed in actual combustors.…”

The Impact of Combustor Turbulence on Turbine Loss Mechanisms

“…The development of a combustor-style turbulence generator for cascade testing was first reported by Ames and Moffat [5]. A number of studies have since investigated the impact of combustor turbulence on downstream components [6][7][8][9][10][11][12][13]. These studies have mainly focused on the effect of combustor turbulence on wall shear stress and heat transfer on a flat plate.…”

Effects of Effusion Cooling Pattern Near the Dilution Hole for a Double-Walled Combustor Liner—Part 1: Overall Effectiveness Measurements

“…The conclusion that high freestream turbulence decreased the overall effectiveness is contradictory to previous studies that look at adiabatic effectiveness of effusion liners. As mentioned before, Martin and Thorpe [3] and Kakade et al [4] found that high freestream turbulence, compared to low freestream turbulence, resulted in a higher adiabatic effectiveness for effusion blowing ratios in the range of M eff,in ¼ 0.5-1.5. The reason given by each author for the increased effectiveness was that when there was jet lift off, the turbulent mixing brought some of the coolant back to the surface.…”

“…In a different study with only effusion cooling, Facchini et al [2] found that increasing the effusion blowing ratio generally led to decreased adiabatic effectiveness due to jet separation; however, overall effectiveness increased at high blowing ratios due to in-hole convection. Martin and Thorpe [3] studied the effects of freestream turbulence intensity on effusion cooling without dilution jets and found that at low blowing ratios of the effusion jets (M eff,in < 0.5), high freestream turbulence resulted in decreased adiabatic effectiveness; whereas at relatively high blowing ratios, up to M eff,in ¼ 1.4, high freestream turbulence caused an increase in adiabatic effectiveness. This phenomenon was attributed to the turbulent mixing that brought separated coolant back toward the surface.…”