Design of a Swirl-Stabilized Burner With Fluidically Variable Swirl Number

Abstract

Abstract For flame stabilization, burner systems are usually equipped with swirlers which incite a defined air rotation, quantified by the swirl number. In consequence, the swirl number, which significantly influences the flame dynamics, is fixed. Applications exist in which the swirl number can be varied through mechanically adjustable swirler geometries. Such systems, however, comprise moving parts and actuators, the operation of which might be disadvantageous in a combustor environment. Hence, a swirler is developed that allows for continuous swirl number changes by means of fluidic flow control. The direction of a primary air flow is changed through the injection of an adjacent wall jet which follows a curved surface. This causes a directional change of the primary flow due to entrainment effects. The swirler consists of a cylindrical plenum into which a primary air flow is led through azimuthally distributed channels. Each channel comprises a slotted wall. A secondary air mass flow can be induced passing through the slots, hence creating an adjacent wall jet, which subsequently follows a curved surface. The resulting azimuthal direction change of the primary flow depends on the induced secondary air mass flow. The angular flow momentum and thus the swirl number can be therefore continuously changed. The development process of the proposed swirler is presented and the efficiency of swirl variation of different geometries is qualitatively assessed through computational flow simulations. The effects of stationary operation and unsteady swirl number variations are herein investigated and, moreover, the variation performance is assessed for a range of different air mass flows. The simulation results show the potential of a linear swirl number variation with respect to the induced secondary air mass flow. Moreover, the simulation results show that the achieved swirl numbers are comparable to those of state-of-the-art swirlers.