Large Eddy Simulation for effect of number of microjets on flow in an axisymmetric dump combustor

Dump combustors with axisymmetric geometry is a viable design in both propulsion and general combustion systems. Sudden flow expansion over the geometry as a flame holding mechanisms created by the recirculation zones, is highly desired in the high-speed propulsion systems. Designs that successfully manipulate the fluidic shear layer without incurring significant drag penalty are the need of the hour. Microjets are one such type of fluid control mechanism traditionally used for noise reduction. Adding microjets to the axisymmetric dump combustor configuration increases mixing in the shear layer and helped as flame anchoring. Microjets tend to increase the mixing pattern in the step area leading to more fuel residence time in the combustor and consequently to decrease the percentage of unburnt fuel at the combustor exit. Previous investigations using asymmetric dump combustors studied the effect of the number of microjets and inlet flow velocity on the flow mixing characteristics, heat release rate, and the fraction of unburnt fuel at the combustor exit. In the current study, Large Eddy Simulation (LES) is used to investigate the influence of the number of microjets on the flow and energy fields. 3D Simulation of an axisymmetric dump combustor with microjets is conducted using ANSYS-FLUENT commercial code. Our results show that increasing the number of microjets increases the average combustor temperature, the mass flow at upstream locations. The combustion quality, represented by the mass fraction of the combustion products at the outlet, got enhanced due to better overall fuel-air mixing along the combustor due to the presence of microjets. Inclusion of microjets increased the average temperature gain to a maximum of 18.5% for the configuration with four microjets. The velocity at the outlet increased by 12.75% with the addition of 4 microjets in the domain when compared to the baseline case.