Turbulent kinetic energy budget in a wall-mounted cylinder wake using PIV measurements

Abstract

In high flow velocity areas, turbulence intensity is high and flow variations may have a major impact on tidal turbines behaviour. Previous studies show that a square wall-mounted cylinder produces a very extended and energetic wake. In this work, two-component PIV measurements are conducted in the symmetry plane of the flow in order to evaluate the Turbulent Kinetic Energy (TKE) budget. This analysis enables to show how the TKE, produced in the shear-layer region, is re-distributed and dissipated within the flow. The Large-Eddy PIV method enables to obtain full spatial maps of dissipation and to assess the validity of the constant involved in the spectral method. Results show that the production occurs when the Reynolds shear stress is the more intense, so is the dissipation. Energy is then transported through turbulent motion into the outer flow and swept to the bottom due to the pressure gradient effects. Production is directly due to the periodic vortex shedding unlike for other terms. A better description of the energy exchanges in the turbulent wake flow is obtained. This knowledge is important for the performance determination of a tidal turbine positioned in such an obstacle wake which affects the flow-induced dynamic load on turbine.