Turbulent boundary layer perturbed by a hill

Abstract

Turbulent boundary layers over flat walls in the presence of a hill are frequently found in nature and industry. Some examples are the air and water flows over hills and dunes in deserts and in rivers, respectively, but also water flows over aquatic ripples inside closed conduits. The perturbation of a two-dimensional boundary layer by a hill introduces new scales in the problem, changing the way in which velocities and stresses are distributed along the flow. When in the presence of sediment transport, the stress distribution along the hill is strongly related to bed instabilities. This MSc thesis will consist of an experimental study on the perturbation of a fully-developed turbulent boundary layer by a two-dimensional hill. For the experiments, water flows will be imposed over a hill fixed on the bottom wall of a closed conduit and the flow field will be measured by PIV - Particle Image Velocimetry. From the flow measurements, mean and fluctuation fields will be computed. The velocities and stresses fields will be compared with analytical expressions and the surface shear stress will be analyzed in terms of instabilities of a granular bed. This project is related to the FAPESP Projeto Jovem Pesquisador No. 2012/19562-6.