Numerical study of effusion cooling flow and heat transfer

Abstract

An isothermal and non-isothermal numerical study of effusion cooling fl ow and heat transfer is conducted using a Reynolds-averaged Navier-Stokes (RANS) approach. A Reynolds stress transport (RST) turbulence model is used to predict the fl ow fi eld of a staggered array of 12 rows of effusion holes, each hole inclined at 30° to the fl at plate. The Reynolds number based on the hole diameter and jet exit velocity is 3800. The blowing ratio in both studies is 5. A conjugate heat transfer approach is adopted in the non-isothermal simulation. For the isothermal case, the RST model is shown to be capable of predicting the injection, penetration, downstream decay and lateral mixing of the effusion jets reasonably well. In addition, the numerical model captures the existence of two counter-rotating vortices emanating from each hole, which causes the entrainment of combustor fl ow towards the surface of the plate at the leading edge and downstream, infl uences the mixing of accumulated coolant fl ow, providing a more uniform surface temperature across the plate. The presence and characteristics of these vortices are in good agreement with previously published research. In the non-isothermal case, the laterally averaged cooling effectiveness across the plate is under-predicted but the trend conforms to that exhibited during experimentation. Keywords: Conjugate heat transfer, effusion cooling, RANS, RST turbulence model. INTRODUCTIONGas turbine engines operate at extremely high temperatures; thus, components such as combustion chamber walls, turbine endwalls, turbine blades and shrouds need to be cooled. The desire to increase the effi ciency, i.e. reducing the specifi c fuel consumption and raising the thrust-to-weight ratio of gas turbines, has led to an increase in pressure and temperature in the combustion chamber and turbine. The operational life of the combustion chamber walls decreases as the temperature increases; thus, a method of cooling must be used to protect the wall. Whilst wall cooling is essential, there is also a need to minimise the proportion of air used for cooling as air taken away from the combustion process increases nitrous oxide emissions. Amongst many techniques available, effusion cooling, also known as full coverage fi lm cooling (FCFC), is considered the most practical. In this approach, cooler air, usually bled from the latter stages of the compressor, is injected from the combustor outer casing side through thousands of sub-millimetric angled perforations and enters the boundary layer on the internal wall of the combustor. The cooling fi lm that protects the liner from the hot gases results from the coalescence of the discrete micro-jets emanating from the perforations.Engineers are always trying to extract greater cooling performance from less cooling air whilst also trying to maximise the overall fi lm-cooling effectiveness so that the amount of air used for cooling can be reduced. A fundamental understanding of the mechanisms involved in effusion fl ow fi elds is therefore requir...

Numerical Investigation of Effusion Cooling in Gas Turbine Combustor Liner

“…The study reported that wall cooling efficiency rises as the center-to-center spacing of neighbor holes gets smaller or the blowing ratios rises. Walton and Yang [19] argued that in the isothermal case, the Reynolds Stress Transport model can reasonably well predict the penetration, injection, downstream disruption, and lateral interactions of jets. Murray et al [20] experimentally investigated flat effusion plate effectiveness with two holes spacings 3.0D and 5.75D by pressure sensitive paint technique.…”