High-Reynolds Number Flow Past a Rotating Cylinder With and Without Thom Discs

Abstract

The present dissertation was written based on a computational fluid dynamics study of high-Reynolds number flow past a few different geometries of the Flettner rotor with and without Thom discs. The three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) equations were solved and descretized with a finite volume approach. Two separate types of flows were investigated; a 3D smooth cylinder flow investigating two different cylinder span lengths and a rotor with fixed circumferential discs (Thom discs) to investigate the idea introduced by Thom (1934).A high-Re k-ε eddy viscosity turbulence model resolved the turbulence while the near-wall motion was solved using an advanced log-law wall function. The simulations are run as if the rotor was instantaneously translated and rotated simultaneously. The 3D smooth cylinder simulations studied the span length dependencies of the cylinder's flow behaviour and aerodynamics. Two solution spaces were generated differing by span length. The grids modelled flows for Re = 140,000 and dimensionless rotation rates alpha = 2 and 5. The study revealed the three-dimensionality in the flow behaviour past the cylinder at both rotation rates and the formation of periodic spanwise undulation along the cylinder when the rotation rate is increased. Likewise, lift and drag coefficients were investigated where the smooth cylinder was found to be aerodynamically independent of span length. Thom discs of infinitesimally small thickness were fixed on the cylinder to investigate the possibility of aerodynamic improvements, as proposed by Thom but not convincingly detected in a preceding CFD study. The solution space models a single region between two discs referred to as the Thom disc cavity. The two simulations model flow for Re = 140,000 with alpha = 5, while of lower Re than those a Flettner rotor would typically experience, it was believed to be sufficiently high, nonetheless. A qualitative analysis of the flow behaviour revealed the fluid motion within the Thom disc cavity was highly complex and highly random in nature. This study found that a great deal of aerodynamic instability was exhibited as the radius of the Thom discs was increased.

Date of Award	1 Aug 2012
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Brian Launder (Supervisor)