Experimental Investigation of Effusion Cooling Performance on the Liner of a Scaled Three Injector Annular Combustor

Abstract

Gas turbine combustors design nowadays is aimed at achieving extremely lower NOx emissions through involving more air into the combustor to perform lean combustion, which results in the reduction of cooling air ratio for the liner walls. In this context, effusion cooling, one of the most effective cooling strategies, is adopted on the liner for its advantages of providing well cooling protection with limited amount of air. The swirl flow structure generated by the injector to stabilize flame in most modern lean-burn combustor is very complex with recirculation and vortex breakdown. So the interaction between three dimensional main flow and jets issued from the effusion holes is significant when assessing effusion cooling performance on the liner. In the present work, detailed effusion cooling feature on both inner and outer liners of a scaled annular combustor equipped with three axial swirlers has been provided under non-reactive and reactive conditions. The main flow is electrically heated for the non-reactive condition, while premixed combustion is realized after methane is fueled into the injectors and mixed with the air in the surrounding passage for the reactive condition. Temperature distribution on the target bended plate with 7 rows of discrete cooling holes in an in-line layout is captured by infrared thermography, and the cooling effectiveness is then analyzed. Effects of coolant to mainstream flow rate ratio and equivalence ratio are evaluated respectively. Results show that the macro rotational flow generated by the swirl flows interacts with cooling film and leads to non-symmetric cooling protection circumferentially on both liners. Additionally, averaged cooling effectiveness is found to increase with the flow rate ratio. At reactive conditions, stagnation of the high temperature swirl flow impinging on the liner wall locates at X/D range of 0.4–0.5, which has not been observed at non-reactive conditions. Also cooling effectiveness results indicate that outer liner obtains better cooling protection than inner liner when reaction is activated. Finally, the effect of most interested parameter for combustion process equivalence ratio is surveyed at Φ=0.7, 0.8 and 0.9. With experimental results, the importance of the combustion is highlighted in weighing the effusion cooling performance on the real annular combustor liners, which can’t be predicted comprehensively by non-reactive investigations. To obtain more knowledge of this issue, future work concerned with the flow field and flame visualization needs to be done through experimental techniques and numerical methods.