Computational Analysis of Mixing in a Gas Turbine Combustor

This paper presents the computational analysis of the dilution process involved in gas turbines order to cool the combustion gases to the desired temperature before it enters the turbine. Here, it should be noted that in order to focus only on the dilution process, non-reacting flow conditions were simulated and the complete system was reduced to mixing of a primary (hot) stream and dilution (cold) stream of air. Four different schemes were investigated based on the layout of the dilution holes and use of a blunt body. A complete three dimensional analysis was carried out for each case in order to investigate its effectiveness to produce a more uniform temperature conditions at the exit of the combustor, so as to reduce the detrimental effect these temperature non-uniformities have on the turbine blades. For comparison of the proposed schemes, a parameter is defined in terms of the temperatures of the dilution and primary flow streams at the inlet and the exit plane, called the mixture fraction. Based on this parameter, it was found that the staggered dilution holes with the blunt body has the mixture fraction closest to the equilibrium mixture fraction (0.4), which implies that this scheme with the mixture fraction of 0.36, resulted in best mixing and produced the most uniform temperature distribution at the exit amongst the four proposed schemes.