Embedding of a Blade-Element Analytical Model into the SHYFEM Marine Circulation Code to Predict the Performance of Cross-Flow Turbines

Abstract

Our aim was to embed a 2D analytical model of a cross-flow tidal turbine inside the open-source SHYFEM marine circulation code. Other studies on the environmental impact of Tidal Energy Converters use marine circulation codes with simplified approaches: performance coefficients are fixed a priori regardless of the operating conditions and turbine geometrical parameters, and usually, the computational grid is so coarse that the device occupies one or few cells. In this work, a hybrid analytical computational fluid dynamic model based on Blade Element Momentum theory is implemented: since the turbine blades are not present in the grid, the flow is slowed down by means of bottom frictions applied to the seabed corresponding to forces equal and opposite to those that the blades would experience during their rotation. This simplified approach allowed reproducing the turbine behavior for both mechanical power generation and the turbine effect on the surrounding flow field. Moreover, the model was able to predict the interaction between the turbines belonging to a small cluster with hugely shorter calculation time compared to pure Computational Fluid Dynamics.

A Double Multiple Stream Tube (DMST) routine for site assessment to select efficient turbine aspect ratios and solidities in real marine environments

“…When using a sliding mesh, to obtain a satisfactory numeric convergence the time-step should not be larger than the time required for advance the mobile interface by a distance corresponding to one cell thus, in order to consider the smallest cell at the interface, a time-step corresponding to 0.5° of revolution was adopted. The overall validation of the 2D CFD model has been described in a previous article [22] in comparison to the experimental data by Bravo et al [23], whereas the validation of the 3D CFD model has been done versus the wind-tunnel velocity profiles achieved by Vergaerde et al [24] at several locations downstream a two straight bladed turbine (details of the validation in [25]).…”

A Double Multiple Stream Tube (DMST) routine to identify efficient geometries of cross-flow tidal turbines in site assessment analyses

“…In this paper we describe an easy methodology based on this kind of approach. Only after the turbine concept has already been inferred, the chosen turbine can be checked inside the marine code (Thiébot et al 2020;Pucci et al 2020). This will require very fine grids and long computation times, to assess the environmental impacts of a certain tidal farm layout.…”