This thesis describes an experimental and theoretical investigation of the flow upstream and in the near wake of a fence attached to a plane wall on which exists a turbulent boundary layer. The study is conducted for a fence height comparable with the thickness of the approaching boundary layer. Comparative results were also obtained in the flow upstream of a forward facing step. The experimental investigation consists of measurements of mean flow and turbulent velocities using hot wire probes at selected locations in the flow. The hot wire results were analysed digitally to give all three components of mean velocity and Reynolds normal stress, and two components of Reynolds shear stress. Some flow visualisation studies using smoke were also undertaken. Results are presented of the theoretical investigation which extends through a range of models, including inviscid, laminar and turbulent flow simulations. All the models describe the flow by various forms of the elliptic Navier Stokes equations and solutions are obtained iteratively. It has been found that certain aspects of two-dimensional separation as described in the Stratford-Townsend model are identifiable well up to the separation point. However, additional three-dimensional motion is observed due to the presence of the fence or forward facing step, which induces significant increases in outer flow stress levels. It is suggested that these additional stresses appear in the downstream wake. The theoretical simulations have indicated that the gross features of the flow can be easily predicted, but that a very complex turbulence model would have to be employed to realise fully the flow mechanics observed in the experiment.
|Date of Award||1977|