Effects of swirling motion on the cavity flow field and combustion performance

An investigation has been carried out through experimental and simulation analyses to evaluate the cold flow field and combustion performance of a novel trapped vortex combustor that incorporates swirling motion. The cavity is an annular region, and the swirling flow (swirl number is 0.0, 0.6, 0.8, 1.0, and 1.2) is in the central axis of the cavity region. The technique of particle image velocimetry (PIV) is employed to investigate the flow field, with a specific focus on the swirling flow configurations within cavities. Additionally, it serves as a reference point for verifying and enhancing simulation methods. Methane is being subjected to combustion experiments at atmospheric pressure, where the fuel is only introduced into the cavity region and the air used is at a temperature of 300 K. The results show that: the cavity vortices are squeezed due to the swirl jet dumping into the cavity region as a result of the overwhelmingly increased centrifugal forces with the strong swirling flow. Additionally, the vortices' tangential velocity within the cavity area undergoes a significant rise under the influence of swirling flow, ultimately leading to a prolonged residence time. A significant increase in turbulence intensity of cavity vortices is also achieved when the swirl number is increased. For combustion results, the average temperature of the cavity increases with an increase in the cavity rear flow equivalence ratio (Φr); as the Φr further increases, the temperature reduces. The maximum temperature is approximately 1600 K for the mainstream with a swirling flow, and it is about 1200 K for no swirling flow. Finally, the rich/lean blowout limit is extended when the swirl number increases.