RANS-Elliptic

CFDWind1.1

Submitted by Roberto A. Chav... on May 27, 2015 - 12:00am
Main hypothesis

This model is formulated with the assumptions of isotropic eddy-viscosity turbulence and the k-ε two-equation closure scheme modified for atmospheric flows.

CFDWind1 deals with surface boundary layer (SBL) by imposing a set of coefficients as well as proper modifications to the boundary conditions (inlet boundary and wall functions) in order to comply with the Monin-Obukhov Similarity Theory (MOST) as proposed by Richards & Hoxey (1993) and Parente et al. (2011). 

SemiParabollicFOAM

Daniel Cabezon's picture
Submitted by Daniel Cabezon on May 5, 2015 - 9:59am
Main hypothesis

The model derives from a previous elliptic model and it is inspired on the parabolic technique of other models such as UPMPARK and Windfarmer but using the actuator disk technique to represent the wind turbine instead of wind speed deficit. 

The wind turbine is represented as an actuator disk uniformly loaded. This means that the wind turbine acts as a sink of momentum, associated to the drag force exerted over the incoming flow. The reference wind speed for each disk is initially calculated from the wind speed at the position of the disk and corrected through the method proposed by Calaf et.al.

The solution algorithm consists of a decomposition of the domain into a finite number of adjacent subdomains that are solved sequentially in the axial direction, using the output of each subdomain as input for the next one. This is done until the end of the domain is reached. This way the computational time becomes significantly lower in comparison to the solution of a single domain by means of a purely elliptic approach.

CRES-flow NS

John Prospathopoulos's picture
Submitted by John Prospathopoulos on May 4, 2015 - 5:22pm
Main hypothesis

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.