Power extraction calculation improvement when local parameters are included

The improvement of the tidal resource assessment will be studied by comparing two approaches in a two-dimensional, finite difference, hydrodynamic model DIVAST-ADI; in a channel of non-varying cross-sectional area that connects two large basins. The first strategy, considers a constant trust coefficient; the second one, use the local field parameters around the turbine. These parameters are obtained after applying the open channel theory in the tidal stream and after considering the turbine as a linear momentum actuator disk. The parameters correspond to the upstream and downstream, with respect to the turbine, speeds and depths; also the blockage ratio, the wake velocity and the bypass coefficients and they have already been incorporated in the model.

The figure (a) shows the numerical configuration at high tide developed with DIVAST-ADI. The experiment undertakes two open boundary conditions. The first one is a sinusoidal forcing introduced as a water level located at (I, J=1) and the second one, indicate that a zero velocity and a constant water depth were kept (I, J=362); when the turbine is introduced it is placed in the middle of the channel (I=161, J=181). The influence of the turbine in the velocity and elevation around the turbine region is evident; figure (b) and (c) shows that the turbine produces a discontinuity in the depth and velocity profile, when we plot a transect along the channel.

Finally, the configuration implemented reproduced with satisfactory accuracy the quasi-steady flow condition, even without presenting shock-capturing capability. Also, the range of the parameters $0.01<\alpha_4<0.55$, $0<Fr<0.14$ and $B=0.006$ is correct and produce roots for the $\beta_4$ quartic polynomial which fall into the subset input that produce physical admissible solutions. The results call upon continue the calculation of the power extraction, the thrust coefficient and also the water drop, the power lost by the wake mixing and the efficiency of the turbine. The comparison of the power, obtained with the open channel theory, with the one obtained with constant thrust coefficient will let us to determine the improvement that the inclusion of local parameters provide.