Effects of the Interaction Point of Multi-Passage Swirlers on the Swirling Flow Field

Abstract

An experimental study is conducted to understand the mean and instantaneous behavior of the swirling flow issued from a triple swirler influenced by a single critical geometrical parameter, termed as the passage length. The investigated geometrical parameter defines the interaction point of the inner axial swirlers with the outer radial swirler, which consequently defines the primary air–fuel mixture characteristics and the resultant combustion state. Experiments were performed under cold flow conditions, and planar particle image velocimetry was employed to measure the velocity field. The mean flow pattern exhibited significant differences in terms of the swirl-jet width and angle and altered the number of stagnation points on the swirler axis. When the passage length was reduced to half, two stagnation points appeared on the swirler axis due to an initially developed smaller recirculation zone at the swirler mouth. Also, the turbulent activity at the vicinity of the swirler increased with as the passage length reduced. Investigations on the relocation of the second stagnation point on the axis through an arbitrary window revealed identical standard deviation in x and y directions. The energetic coherent structures extracted from the proper orthogonal decomposition also identified major differences in terms of the spatial distribution of the modes and their corresponding energy levels. The experimental results indicated that if the passage length is altered, the number of stagnation points on the swirler axis increases, and a breakdown of both the bubble and cone vortex may appear at the same time as different energy levels.