Computational Fluid Dynamics Setup

A simulation setup consists of couple of elements that don’t change for different airfoils.

They include a set of boundary conditions. At the boundaries of the computational domain and on the airfoil surface values for pressure, velocity and turbulence properties are specified. The size of the domain compared to the airfoil is visualised below:

The domain is made significantly larger (20 chord length on each side of airfoil) to ensure the airfoil remains unaffected by the presence of the boundaries, which are typically not important for wind turbine blades or air crafts.

The domain is discretised in a number of control volumes. These are smaller near the airfoil surface where sharper velocity gradients exist:

Mesh topology in the far field region. Based on the distance from the surface, different level of refinements are applied
A surface confining boundary layer mesh is added along the surface to resolve the boundary layer down to inner viscous dominated part. The average first cell height is around yPlus=0.3 for common geometries (max yPlus=2).

In each control volume, a continuity, two momentum equations (x- and y-direction) and a turbulence equation is solved. For these calculations, the Spalart-Allmares turbulence model is used (more very detailed info here).

More info coming…