Vortex induced vibrations: Further contributions and an energy application

Abstract

Vortex shedding and Vortex Induced Vibrations (VIV) of bluff bodies is a fundamental problem in fluid mechanics. The ubiquity of vortex shedding and VIV in several engineering fields has meant that a significant amount of research has centered on this subject. Recent studies have focused on the extraction of energy from steady flow using bodies undergoing VIV. In this dissertation, a new model for flow around a circular cylinder called the Hybrid Potential Flow (HPF) model is presented. The HPF model incorporates potential flow methods, experimental data and von Karman’s representation of the vortex wake to construct a complete solution for flow around a circular cylinder in the sub-critical Reynolds number regime $300 \leq Re \leq 1.5 x 10^5).$ Shedding frequencies and forces due to vortex shedding are calculated and compared to published results. The HPF model is extended to other bluff body geometries using conformal mapping. A composition of Karman-Trefftz transformations and Fornberg’s method is used to construct a conformal map between the physical domain and the circle plane. The combination of the HPF model and conformal mapping can thus be used to quickly calculate vortex shedding behavior for various bluff bodies. Validation of theoretical results is done through experimental methods. A flow visualization technique to view the time-averaged wake behind bluff bodies is developed and presented. Wind tunnel tests are done to validate predicted shedding frequencies for various bluff body geometries. A proof-of-concept prototype of a device that extracts energy from steady flow using VIV is developed. Emphasis is laid on the device being of low cost and complexity. Finally, principal conclusions of this dissertation and recommendations for future work are presented.