Developing a coupled turbine thrust methodology for floating tidal stream concepts: Verification under prescribed motion

Development of a fully nonlinear, coupled numerical model for assessment of floating tidal stream concepts

“…The software is written in C++ and is based around the Object Orientated Programming (OOP) paradigm, offering a large collection of solvers and shared libraries. Consequently, the new turbine library is easily coupled with many of the existing solvers as previously demonstrated on single phase steady (simpleFOAM) and transient (pisoFOAM) solvers (Brown et al, 2020b). However, this study uses a transient two-phase approach and hence the turbine methodology is coupled with interFOAM (Rusche, 2002) which solves the incompressible Reynolds-Averaged Navier-Stokes (RANS) equations for two, incompressible, isothermal and immiscible fluids using the Finite Volume Method (FVM).…”

“…In the present application where the turbine only forms a single component of the entire system, the computational expense of the blade-resolved approach is infeasibly large if all parts of the system are to be modelled simultaneously in a coupled approach. Hence, in this work, a more computationally efficient approach has been adopted using a 'weighted body force implementation' which, at each time step, identifies and applies weights to a region of the computational domain (representing the turbine), determines the local velocity at the turbine position and adds an additional, equal and opposite force, T (based on the thrust on the turbine), to the momentum equations (equation 1) (Brown et al, 2020b). A summary of the key steps of the method is given in this section with the reader referred to Brown et al (2020b) for full details.…”

“…where a is the axial induction factor, A is the swept area of the turbine and C t = 4a(1 − a) is the turbine thrust coefficient (Brown et al, 2020b). The local velocity, u t , is considered to be the axial component of the weighted average of the instantaneous velocity (relative to the platform's motion) in each of the mesh cells,…”

“…This is the second article in a series that document the development, demonstration and application of the complete tool. In the first article a methodology is demonstrated, for a computationally efficient HATT model that can predict accurately the coupled forces on the turbine as well as remain stable throughout arbitrary motion through the computational mesh (Brown et al, 2020b). In this article the HATT model is coupled with the existing rigidbody motion solver from the open-source Computational Fluid Dynamics (CFD) libraries of OpenFOAM.…”

Coupled Interactions Analysis of a Floating Tidal Current Power Station in Uniform Flow

“…They suggested that the rotor should be mounted close to the floater center to avoid the floater-motion-induced velocity on the blade section. Brown et al developed a computational HATT model for generalized incident flow conditions using the actuator theory [14]. The arbitrary movement of the turbine was modeled based on the 'weighted body force implementation'.…”