Gas Turbine Combustor Wall Cooling

The need for better methods of cooling gas turbine
combustors and a review of current cooling techniques have been presented. Three cooling methods are investigated: (a) Full Coverage Discrete Hole Film Cooling (Effusion), (b) Impingement/Effusion Hybrid Cooling Systems, and (c) Transpiration Cooling.

The aim of these cooling techniques is to effectively and efficiently cool gas turbine combustors with a significant reduction in current cooling air requirements. The range of test conditions were coolant temperature, Tc, of 289 < Tc 710 K and combustion gases temperature, Tg, of 500 ^ Tg N< 1900 K. The discharge coefficients of the effusion and the impingement/effusion systemshave also been studied.

A detailed analysis has been made of the heat transfer of the cooling systems, jet penetration into the cross-stream, prediction of the cooling jet temperatures at various stages in the cooling process and the cooling film heat transfer coefficient.

The results of the discharge coefficient (Cd) indicate a decreasing C^ with increasing wall thickness to diameter ratio, t/D, and a weak effect of cross-stream flow. The results of both the effusion and the impingement/effusion hybrid systems indicate a high cooling performance of similar magnitude to that of the transpiration system. Graphical design correlations for the cooling wall have been made. The optimum hole geometries for both cooling configurations have been developed. The influence of the coolant to hot gas density ratio has been studied over the range 1.4-3.4.

In the design of effusion and impingement/effusion cooling systems, wall thickness, hole density, hole diameter and wall design pressure loss are significant parameters for cooling performance maximisation.