Effect of self-excited acoustic perturbations on flow characteristics around rectangular cylinders with varied geometrical aspects

Abstract

This study explores the effects of aspect ratio, edge geometry and incidence angles on the dynamic lift force, wake behaviors, and the susceptibility of such geometrical aspects to self-excited acoustic resonance in rectangular cylinders inside a high-speed wind tunnel. Experimental findings demonstrate a notable shift in both acoustic pressure and dynamic lift force during resonance excitation for rods characterized by an aspect ratio of l/h = 0.5. For cylinders with an aspect ratio of l/h = 2, there is unexpected excitation of the third acoustic mode, imposing a considerable reduction in the dynamic lift force and alteration in shear layer dynamics, which subsequently impacts the shedding pattern. The study reveals that modifying the shape of the upstream edges to be rounded can alter the shedding pattern and decrease dynamic the loading, whereas alterations to the downstream edges amplify the sound pressure level (SPL) during resonance. Particle image velocimetry (PIV) measurements further accentuate the crucial role of incidence angles in modulating flow structures, vortex generation, and wake dynamics. The combined effect of a small angle of incidence and self-excited acoustic resonance was found to have an added streamwise length effect. This research emphasizes the significant influence of incidence angles and self-induced acoustic resonance on the ILEV/TEVS shedding pattern, underscoring the importance of rod geometry and orientation in the mechanism of flow-sound interaction. Note: Rectangular rod and cylinder are used interchangeably in this thesis.