Near-Field Aerodynamics of Swirl Burners : Part 3; Isothermal annular swirling flows with and without primary air injection

Abstract

Isothermal annular swirling flows were investigated to clarify the effects of a bluff body and a nonswirled central air jet upon the characteristics of swirl-induced recirculation zones. The velocity measurement using an LDA system revealed that the use of a bluff body increased the rate of recirculating mass flow and also the mass flow brought back into the quarl (or expansion) section. For flows with a primary air jet, two distinct flow patterns were observed: (I) ordinary IRZ (Internal Recirculation Zone) and (II) IRZ with primary air jet penetration. The IRZ strength could be determined by the combined parameter, Sa(D1/Do)², where the swirl number is Sa and the vortex diameter expansion ratio is D1/Do.