Turbulent boundary layer: comparison between a flat plate and a rotating disk with and without periodic roughness

Abstract

In order to understand and predict the behavior of a flow around an object it is necessary to study the phenomenon present on the close-to-the-wall region of the flow, where the viscous forces cannot be neglected nor the variations of the properties of the flow. This region is called the boundary layer. In many situations, the contribution of the viscous friction in the boundary layer into the total drag can be substantial, and understanding of the effect of the roughness on the boundary layer is of importance. This project is focused on the study of the boundary layer created near two different objects: a flat plate and a rotating disk. The flat plate is widely used in fundamental studies and in the engineering industry as an approximation of more complex models, for instance the ship hull in the naval engineering. The influence of the roughness on the friction drag can be obtained from testing of different plate models in a towing tank. Although this approximation usually offers a good agreement, experimental data and measurements are expensive to obtain. In order to reduce the cost of the experiments, a rotating disk is used an approximation of a flat plate since the installation and design of the experiment is not only cheaper but also simpler. The validation of this approximation is the main objective of this project and it is carried out by a study which is focused on finding similarities between both boundary layer properties with the aid of Computational Fluid Dynamics (CFD). Also, experimental measurements are compared with CFD result with the aim of a validation of the CFD results.