A Flow-Visualization Study of an Elevated Jet in Crossflow

This paper presents the physics of a jet issuing from a circular stack orthogonal to crossflow. A circular pipe of thickness 2 mm and outer diameter of 12 mm, having an aspect ratio AR = 9, is modeled as a stack. The experiments are conducted for a fixed crossflow Reynolds number of ReD = 632 with a velocity ratio of R = 0.5. The quantitative measurements have been taken using Laser Doppler Velocimetry (LDV). Two types of flow-visualization techniques, namely (i) bulk flow visualization and (ii) Laser-Induced Fluorescence (LIF), have been used. The bulk flow visualization gives the volumetric visualization in the projected XY plane, where the clockwise rotating windward jet shear layer morphs into the shape of hairpin vortices in the downstream direction via a stretching mechanism. The LIF visualization in the XZ plane is done by traversing the laser sheet in various spanwise locations. The evolution of flow inside the stack gives rise to the formation of a concentric ring that transforms into counter-rotating vortex pair near the stack free-end. The flow field captured in this plane (XZ) reveals the switching of vortex shedding from an alternate to an arch-type vortex.