Flow Field in Swirl-Type Tabular Flame Burner

Abstract

The flow field in swirl-type tubular flame burners was measured using a Particle Imaging Velocimetry (PIV) system with an easily controlled kerosene droplet tracer generator. Through characterization of the flow field in two burners with different swirl numbers, it was found that the flow is an axisymmetric vortex flow. The tangential component of the velocity is zero at the tube center, and increases proportionally with radius at first, and then falls slowly in a radial direction. The gradient of the tangential component near the vortex center depends significantly on the swirl number and the flow rate. The vortex center oscillates around the tube center in a roughly circular area, and this precession is significantly sensitive to the swirl number. The radius of the precession area shrinks as the swirl number increases. The radial distributions of the axial velocity take a plateau-shape for the weak swirl burner (swirl number S = 0.21), whereas they take an M shape for the strong swirl burner (S = 0.78) with reverse flow in the vicinity of the burner axis. The occurrence of the axial reverse flow is dominated by the swirl number, and is affected by the flow rate as well. Finally, a comparison was made between the swirl numbers calculated with the measured velocity profiles in a cross section and those calculated from the input angular momentum.