Keywords

Hydrodynamic stability, Flow control, CFD, Vortex Dynamics, Fluid dynamics

Abstract

This dissertation investigates the manipulation of global and three-dimensional instabilities in the wake of a circular cylinder through two separate flow control methods. This study first focuses on the influence of attached leading edge forebodies as a form of passive flow control designed to introduce upstream streamline curvature, where the curvature takes the form of a concave and convex case. We demonstrate that for both cases this induced curvature significantly modifies the primary instability, which suppresses periodic vortex shedding (Von Kármán vortex street). We found an increase in critical Reynolds number of 56.6 and 60.1 for the concave and convex cases respectively, whereas it is 47 for typical cylinder flow. Using local stability analysis we obtain maximum temporal growth rates of 0.099, 0.11, and 0.17 respectively for the convex, concave, and cylinder cases. In addition to passive modifications, we examine the role of localized harmonic forcing as an active control mechanism. The localized forcing is shown to primarily target and suppress the secondary instability corresponding to Mode A at a Reynolds number of 220, which governs the transition to three-dimensionality at intermediate Reynolds numbers. This work provides conclusive proof using Floquet stability analysis that localized forcing at twice the shedding frequency can be applied to suppress Mode A with a blowing ratio of 0.2 to 0.8, with the primary identified mechanism lying in the y-component of the tilting term of the vorticity perturbation evolution equation.

Completion Date

2026

Semester

Spring

Committee Chair

Bhattacharya, Samik

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Format

PDF

Document Type

Dissertation

Identifier

DP0053159

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