Surface layer

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). 

CFDWind 1.0

Submitted by Roberto A. Chav... on May 16, 2015 - 12:00am
Main hypothesis

Steady-state, surface layer, isotropic eddy-viscosity turbulence, boussinesq approximation for air density.

In this first version of CFDWind1, the near wall inconsistency was solved by using the Blocken et al. 2007 approach which was inherited from the previous implementation in the commercial solver Fluent, which does not allow to access the source code in order to modify the wall functions.   Further versions (CFDWind1.1 and CFDWind2) have updated this condition to the more consistent formulation of Richards & Hoxey.

Windmodeller (Ansys-CFX)

Benjamin Martinez's picture
Submitted by Benjamin Martinez on May 5, 2015 - 10:49am
Main hypothesis

- Steady-state RANS for neutral simulations

- Accounts for atmospheric stability by adding an additional energy conversation equation formulated in terms of the potential temperature and using the k-epsilon closure scheme. Surface conditions are determined via heat flux or temperature gradient.

- Actuator Disk Modelling for Wakes

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.

Omnivor

Submitted by Emmanuel Branlard on May 4, 2015 - 6:11pm
Main hypothesis

Homogeneous Incompressible Newtonian fluid under conservative forces, viscous splitting assumption (separate convection/diffusion steps).

Omnivor is a vortex code that uses Lagrangian tracking of vorticity using low order singular and regularized vortex elements. Bodies may be represented using source elements.

Elements intensities may be a combination of prescribed intensities, intensities determined by solving of non-penetration condition or intensities determined using tabulated profile data and a Lifting line formulation.

ISOL RANS 0.1

Submitted by Carlos Peralta on May 4, 2015 - 6:02pm
Main hypothesis

Steady state solver based on OpenFOAM's simpleFoam (version 2.1.1). Isotropic eddy-viscosity turbulence using the Boussinesq approximation, homogeneous forest canopy and actuator disk solver.

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.

Waving Wheat Neutral

Javier Sanz Rodrigo's picture
Submitted by Javier Sanz Rodrigo on May 4, 2015 - 4:13pm

Scope

The benchmark is open to participants of the Wakebench project using canopy models. This is the first element of the building-block approach in this range, so it should be mandatory if you intend to participate with this model in other test cases down the line.

Objectives

Demonstrate the performance of the model at reproducing the mean flow and turbulent quantities of a horizontally-homogeneous canopy profile.

Data Accessibility

The benchmark is offered to participants of the IEA Task 31 Wakebench who agree with the terms and conditions described below.

Input data

The conditions for simulating the waving wheat canopy profile in neutral conditions are:

  • Free-stream wind speed: U0 = 10.2 m/s
  • Canopy height: hc = 0.047 m
  • Canopy drag coefficient: Cd = 0.68
  • Canopy-area-density: A = 0.1 m-1
  • Obukhov length: L0 = ∞
  • Use dry air with a density ρ = 1.225 kg/m3 and dynamic viscosity μ = 1.73e-5 kg/ms

Validation data

The validation consists on mean and standard deviation values for the horizontal wind speed (U) and mean values of the shear stress (uw).

Model runs

The user is free to define the computational domain and model settings that best fit with the validation data.