Size Of Central Recirculation Zone Research Articles

Design and experimental evaluation of a plasma swirler with helical shaped actuators

In order to enhance the flow control effectiveness of the plasma swirl injector, dielectric barrier discharge (DBD) actuators with helical electrodes are developed and the performance is compared with that of straight actuators through flow field measurement. This new design can adjust the plasma distribution and increase the plasma intensity. More importantly, the design can be used to adjust the axial velocity besides the azimuthal velocity, therefore it can be used to mitigate flame blow-off or flashback. In addition, the plasma-induced flow can be aligned with the direction of flow moving out of the vane swirler accurately, which can reduce the pressure loss from the swirler. The helical shaped actuator is more suitable for working in conjunction with traditional mechanical swirlers, providing more flexibility in flow control. By changing the direction of the helical electrodes and their relative positions, four different plasma swirler configurations for flow control are considered, making flexible combinations with the vane swirler possible and providing more options for combustion control. Results of flow field measurement showed that a central recirculation zone (CRZ) appeared under the plasma actuation. Compared with that of the straight electrode actuation, the size of CRZ is increased and the back flow in CRZ is enhanced by the helical electrode actuation. Effect of CRZ on the azimuthal velocity dissipation is also observed.

Large eddy simulations of turbulent combustion of kerosene-air in a dual swirl gas turbine model combustor at high pressures

In advanced gas turbine engines, high-pressure combustion generally occurs with combustion chamber pressure exceeding the critical pressure of the engine fuel. In this paper, large eddy simulations are conducted in a dual swirl gas turbine model combustor to analyze the effects of different fuel-air equivalence ratios and chamber pressures on swirling injection and turbulent combustion. Numerical results reveal that intricate interactions exist between swirling flows and high-pressure turbulent flame. Strong swirling injection of air could cause reverse flows in the inner injector, which lead to a V shaped partially premixed turbulent flame at a chamber pressure of 3 MPa. As the operating pressure increases to 5 MPa, decreased injection velocity would prevent reverse flows in the inner injector, leading to the turbulent diffusive flame. On the other hand, combustion causes flow acceleration, gaseous expansion, and strong thermophysical property variations, which would influence the reverse flows, increase the expansion angle in swirling injection, and dictate the size of central recirculation zone and the oscillation frequency of precessing vortex core. Results obtained herein would help gain fundamental understanding on high-pressure swirling flows and flame dynamics in advanced gas turbine engines.