Modelling and Measurements of Combustor Cooling Tile Flows

Pressure to reduce available cooling air in modern combustors has driven recent interest in cooling technology based on double-skinned combustor liners, i.e. tiles containing multiple pin-type pedestals to enhance heat transfer. The design of such systems is, however, hampered by the multiplicity of parameters needing optimisation: feedhole configuration, pedestal configuration, tile configuration (e.g. tile overlap). Much experimental testing is currently needed. In addition, the simulation of flow and heat transfer in cooling tile geometries using RANS-based CFD is made particularly difficult by the impossibility of resolving every individual pin in the pedestal matrix whilst retaining an overall CFD problem of reasonable size. The present paper describes a mixture of experimental and computational work undertaken to explore cooling tile flows. On the experimental side, a large-scale Perspex aerodynamic rig of a cooling tile was constructed. Measurements at representative Reynolds numbers were possible and delivered information on discharge coefficients, pressure drops and flow splits for various tile configurations. The same tile geometries were subsequently modeled using a RANS-based CFD approach. The novelty in these simulations was the use of a ‘sub-grid-scale’ model for the pedestal flow and heat transfer. This approach has previously been used in combustor heatshield predictions; it is demonstrated in the present work how it may also be applied to cooling tiles.