Effect of Flare Geometry on the Flow Field of Radial-Radial Swirlers

Abstract

In this study, an experimental investigation is conducted to assess the impact of the flare geometry on the mean flow field generated by radial-radial swirlers. Two-dimensional two-component PIV measurements are performed on the mid-plane of a non-reacting planar combustor test section. Three-dimensional numerical simulations are conducted for selected cases to support experimental observations. In a previous study conducted in the same setup, counter-rotating radial-radial swirlers without flare extension were investigated. In this study, in addition to the previously studied baseline swirler geometry, four different swirlers are investigated with three different flare geometries (a rounded flare geometry with a radius of 4 mm and two chamfered flares at angles of 27.5° and 45°) with the rounded one having both co- and counter-rotating configurations. Analysis of the time-averaged flow fields reveals that there is an increase in radial velocity values and a decrease in axial velocity values as a result of the introduction of the flare geometry, which results in a sudden expansion of the swirling jet. When different flare geometries are compared, almost identical flow fields are observed and the formation of a CRZ is not observed for any geometry that employs a flare geometry. Although the maximum negative axial velocity values decrease for geometries with flare, due to the increase of the recirculation radius, the recirculating mass flow rate is higher than the baseline swirler. On the other hand, the recirculating mass flow rate is higher in the co-rotating swirler configuration due to stronger adverse pressure gradient along the central axis of the jet when compared to counter-rotating configuration. Coherent flow structures are identified by using the snapshot POD method and different mode shapes obtained for swirlers with and without flare geometry are reported. It is shown that the change of the sense of rotation and flare geometry does not bring about any differences in the POD modes and their energy contents for the given swirl number and confinement conditions.