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A numerical study has been performed in an axisymmetric diffuser followed by a casing-liner annulus of a typical gas turbine combustor to analyze the flow structure and pressure recovery in the geometry. Static pressure recovery in a gas turbine combustor is important to ensure high pressure of air around the liner. However, the irreversible pressure losses reduce the static pressure recovery from the ideal value. The presence of swirl in the flow from compressor and prediffuser geometry before the dump diffuser influences the flow pattern significantly. In this study, flow structures are numerically predicted with different prediffuser angles and inlet swirl levels for different dump gaps. Streamline distributions and pressure plots on the casing and liner walls are analyzed. Static pressure recovery coefficients are obtained from the pressure distributions across the combustor. The effect of dump gap on the static pressure recovery has also been evaluated. It is observed that the best static pressure recovery can be obtained at optimum values of inlet swirl level and prediffuser angle. Dump gap is found to have significant influence on the static pressure recovery only at small prediffuser angle.

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Numerical simulation employing different models is popularly used to predict spray combustion of liquid fuels. In the present work, we have compared the effects of three different combustion models, viz., eddy dissipation model, laminar flamelet model with detailed chemical reaction mechanism, and constrained equilibrium flamelet model, on the temperature, soot, and NOx distributions in an axisymmetric combustor burning kerosene spray. Experiments have also been performed in a combustor of the same geometry to validate some predictions from the models. The constraint condition for the equilibrium flamelet model has been adopted by suitably accounting the effects of scalar dissipation rate on the prediction of scalar variables in a laminar flamelet and by considering the mixture fraction and scalar dissipation rate distributions in the combustor under test. It is found that the results predicted by the two flamelet models agree closely between them and also with the experiments. On the other hand, the eddy dissipation model predicts a much higher flame temperature, soot, and NOx concentrations in the combustor. The results suggest the importance of chemistry in the prediction of the turbulent spray flame. It also suggests that with a proper choice of the constraint condition, the equilibrium flamelet model can address the nonequilibrium chemistry in the flame due to the high value of scalar dissipation rate.