Numerical Simulation On Hydrodynamic Response To Tidal Current Energy Extraction

As a kind of marine renewable energy, the use of tidal current energy resource has received attention recently. Research on hydro-dynamic response to tidal current energy extraction which makes a better understanding of the impact of tidal current turbines on the surrounding flow, plays a great role on choosing optimal layouts for tidal turbine "farms" and the protection of marine ecological environment.Both the near-field and far-field hydro-dynamic response to tidal current energy extraction are studied using different numerical methods. A3-dimension numerical channel is established by using the commercial computational dynamics (CFD) code FLUENT. The flow field of several schemes with single turbine and several turbines with different space between each other are simulated, and the results are compared. Based on a widely used2D mathematical model for tidal current, a mathematical model for far-field hydro-dynamic impact of tidal current energy extraction simulation is established, in which the presence of tidal current turbines are included as an additional bed friction source term. This model is then used on predicting the far-field hydro-dynamic impact of tidal current energy extraction in Guishan channel. The main conclusions are drawn as follows:1) Because of the blockage effect, the free surface upstream the turbine increases. But the energy extraction from tidal current will cause a free surface drop. There is a clear velocity reduction due to energy losses in the wake. However, the water speed is accelerated around the turbine and also along the downstream wake. The velocity recovers far away from certain distance downstream.2) Flow will be accelerated between the turbines, and the closer the two turbines are away from each other, the smaller the accelerated region will be. When the distance is farther than twice times diameter, it is proved to be suitable to position second row turbines. After setting2-row arrays, the wakes of the turbines are influenced by each other, and the wake of the downstream turbines is bigger than the upstream turbines’. The wakes formed by the3turbines merge with each other far away from20-diameter downstream, creating a large velocity decreased region. 3) The simulated results of tidal current energy extraction in Guishan Channel illustrate that the first scheme with a power coefficient0.3is found to have lower impact on original flow than the second scheme (the power coefficient equals0.5). In both schemes, the changes of water levels are less than5cm. The velocities reduce inside the array, and both upstream and downstream of the array, but increase along the sides of the array and in the neighboring channels. The impacts of mean tidal current power density are distributed inside and around the arrays, especially tending to the direction of the preferential flow. The mean tidal current power density also increase along the sides of the array and in the neighboring channels.