Bluff Body Flows

Paul_bluffThe fluid flow past a bluff body is an important consideration in many engineering applications and can have a significant impact on design. However, to date, many aspects of the wake dynamics of such a flow are still to be fully understood. This is particularly true when the flow direction is not perpendicular to the axis of the bluff body and relatively little attention is paid to such cases in the literature. The so called Independence Principle has been proposed to relate the forces on a yawed cylinder to those on an unyawed cylinder with the same perpendicular inflow velocity component. For the case of a circular cylinder this has been investigated both experimentally and computationally in the literature; as yet no firm conclusion as to the validity of the Independence Principle has been reached.

Experimental studies have encountered obstacles in negating the impact of end effects and the intrinsic nature of vortex shedding not parallel to the cylinder axis is the topic of much debate. Full three-dimensional computational studies using periodic boundary conditions at low yaw angles have yet to show anything other than parallel shedding, however no thorough examination of the effect of spanwise cylinder length for the case of yawed cylinders has been undertaken.

The aim of this report is to improve the understanding of the flow over yawed bluff bodies and to establish whether significantly increasing the spanwise length produces slantwise shedding for low yaw angles. The results of this investigation will go some way to providing a firm conclusion as to whether slantwise shedding is intrinsic to the wake of a yawed circular cylinder and hence confirm or disprove the validity of the Independence Principle.

Spectral/hp element methods have been used to simulate the flow at various yaw angles and cylinder lengths. These simulations allow the full 3D flow field to be visualised, and various parameters to be calculated to allow comparisons with previous studies.