DOI: https://doi.org/10.15368/theses.2018.154
Available at: https://digitalcommons.calpoly.edu/theses/1959
Date of Award
12-2018
Degree Name
MS in Aerospace Engineering
Department/Program
Aerospace Engineering
Advisor
Graham Doig
Abstract
This thesis documents a series of three dimensional unsteady Reynolds Averaged Navier-Stokes CFD simulations used to investigate the influence of an upstream prolate spheroid body on tandem pitching hydrofoils. The model is validated by performing separate CFD simulations on the body and pitching hydrofoils and comparing results to existing experimental data. The simulations were run for a range of Strouhal numbers (0.2-0.5) and phase differences (0-π). Results were compared to identical simulations without an upstream body to determine how the body affects thrust generation and the unsteady flow field.
The combined time-averaged thrust increases with Strouhal number, and is highest when the foils pitch out of phase with each other. At intermediate phase differences between φ = 0 and φ = π the leading foil produces significantly more thrust than the trailing foil, peaking at φ = π/2. For St = 0.5 this difference is 21.7%.
Results indicate that adding an upstream prolate spheroid body does not significantly alter thrust results, though it does provide a small (nearly negligible) boost. Vorticity from the body is pulled downstream from the pitching foils, which interacts with the vortex generation when the vortex being generated is of the same sign as the body vorticity. This body vorticity does not affect the vorticity magnitude of the downstream vortex pairs.