Numerical investigation of the flow and flame structure in an axisymmetric trapped vortex combustor

► Flow structure inside the cavity is considerably different for various momentum flux ratio (MFR) cases. ► Volume expansion due to combustion is the cause for the multiple vortices in the cavity for MFR∼0.82 and 1.8 cases. ► MFR∼1.8 case resulted in higher values of reaction rate. The main intention of the present investigation is to bring out the effect of the momentum flux ratio (MFR) on the flow and flame structure in an axisymmetric Trapped Vortex Combustor (TVC). In this study, the MFR was varied by changing the secondary air jet velocity, while keeping the fuel, primary and the mainstream air velocities constant. This study revealed that a single vortex, embedded within a flame on its edge was formed in the cavity for the low MFR case (MFR∼0.57) for which intense burning was observed at the shear layer. In contrast, for the higher MFR cases (MFR∼0.82 and 1.8), the flow and flame structures were altered considerably due to the occurrence of multiple vortices within the cavity. A comparison with the previous cold flow study revealed that the change in flow structure was attributed to the volume expansion due to the heat release during the combustion. Besides this, a counter rotating primary vortex was formed near the bottom wall, which grew in size with the MFR. As a result, the shape of the cavity flame was altered, which may protrude out of the cavity, leading to the local quenching of the flame. Hence, it could be concluded that the momentum flux ratio plays an important role in altering the flow and flame structures within the TVC cavity, thus affecting the performance of the combustor.