Image Analysis of Acoustically Excited Bluff Body Flames

Abstract

This thesis analyzes the effects of various bluff bodies on the downstream flow field. Bluff bodies, for example, those typically found in jet engine augmentors, are objects designed to impede the flow in order to stabilize a flame. The effects of different bluff body shapes (cylindrical and triangular), size (6.35 mm, 9.53 mm, 12.7 mm, and 19.1 mm) and heat release are examined with respect to their influence on downstream vorticity strength, vortex separation distance, and vorticity divergence angle. Particle Image Velocimetry (PIV) is used to obtain the velocity field data from which the vorticity field is calculated. The mean flow velocity, U∞ is 2.7 m/s, and the flow is acoustically excited at 300 Hz with a normalized acoustic velocity of u'/U∞ = 0.8. The vorticity divergence angle increases with increasing bluff body size, is not affected by bluff body shape, and has a non-linear correlation with heat release. Downstream vorticity strength is affected by all three parameters (bluff body shape, size and heat release) in a non-linear manner. Vortex separation distance is a function primarily of bluff body size, increasing for larger bodies; however, the separation distance decreases with increasing heat release. Bluff body shape also has an effect on vortex separation distance as the cylindrical bluff body creates a larger separation distance between vortices.