## CRES-flow NS

CRES-flow NS is an in-house RANS solver using the k-ω turbulence model for closure and the actuator disk theory for the simulation of the embedded wind turbines. The momentum equations are numerically integrated introducing a matrix-free pressure correction algorithm which maintains the compatibility of the velocity and pressure field corrections. Discretization is performed with a finite volume technique using a body-fitted coordinate transformation on a structured curvilinear mesh. Convection terns are handled by a second order upwind scheme bounded through a limiter, whereas centred second order schemes are employed for the diffusion terms. Velocity-pressure decoupling is prevented by a linear fourth order dissipation term added into the continuity equation. The k-ω turbulence model has been suitably modified for atmospheric conditions. Stratification is considered through an additional production term added to each one of the k and ω transport equations to account for the buoyancy effect.

The reference velocity for thrust calculation is estimated at the position of each wind turbine as if the specific turbine was absent. In offshore wind farms, wind turbines are mostly installed in parallel rows, so turbine rows can be considered instead of single turbines. Activation of the actuator disks in a row is realized when a certain convergence criterion is fulfilled for the velocities at the specific wind turbine positions of that row. The simulation continues and the reference velocities are estimated at the next row. This parabolic procedure is repeated until all turbine rows are added.

[1] Chaviaropoulos, P. K. and Douvikas, D. I., “Mean-flow-field Simulations over Complex Terrain Using a 3D Reynolds Averaged Navier–Stokes Solver,”Proceedings of ECCOMAS ’98, 1998, Vol. I, Part II, pp. 842-848

[2] Prospathopoulos, J.M., Politis, E.S., Rados, K.G., Chaviaropoulos, P.K., "Evaluation of the effects of turbulence model enhancements on wind turbine wake predictions", Wind Energy, 2011, 14, pp.285-300

[3] Politis, E.S., Prospathopoulos, J.M., Cabezon, D., Hansen, K.S., Chaviaropoulos, P.K, Barthelmie,R.J., "Modeling wake effects in large wind farms in complex terrain: the problem, the methods and the issues", Wind Energy, 2012, 15, pp.161-182

[4] Prospathopoulos, J.M., Politis, E.S., Chaviaropoulos, P.K., "Modelling Wind Turbine Wakes in Complex Terrain", Proceedings of EWEC 2008, Brussells, Belgium, pp. 42-46

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