Turbulent Flow
Considering Turbulent Flow
TEEDs are being used for projects such as the MeyGen Project, located around the Pentland Firth, an area with extreme environmental conditions, and therefore associated turbulent flows. These occur for many reasons including:
- Surface roughness of the seabed interrupting the flow profile, resulting in the creation of turbulent eddies [7].
- The local bathymetry (headlands and peninsulas) will cause transverse swirling motions
- Devices themselves, which contain turbulent boundary layers due to surface roughness. The image below highlights how the boundary layer develops into a turbulent one [7].
- As seen using Airy Wave theory, the orbital motion of wave particles, although not strictly turbulence, can add to the unsteady flow effects [14].
- If flow passes an airfoil, which has a significant Reynolds number associated, the point of separation could occur further away from the trailing edge, causing a turbulent wake [7]. This leads to formation of turbulent vortices, and pressures much lower than the stagnation point pressure.
Properties Of Turbulent Flow
Turbulence is a phenomenon which is present in all natural flows. Even though it does not have a firm definition, the flow can be defined as chaotic, stochastic property changes of fluid flow [15]. Unlike laminar flow, turbulent flow has random fluctuations in time and space so is a three-dimensional, time dependant phenomena. Generally the flow can be considered diffusive, irregular and has a spectrum of different scales. Turbulent flow is parameterised as being made up of a mean velocity component and a fluctuating component. This fluctuating component/perturbation acts as a dynamic load on the blade, with many cycles occurring within a short period of time [15]. As a result of this, turbulence intensity is given an important consideration when determining loads on a tidal turbine blade