CFD Online Discussion Forums - Actuator disc in 2d

This is accomplished by assigning proper materials. There are also a couple of approaches you can try:

1) For an actuator disk which experiences only drag you can assign a Resistance material. There are several ways to define the properties of this material including constant, free area ratio, friction factor, head capacity and permeability.

My experience is limited to free area ratio. This is exactly what it sounds like. For example, if you had a screen which had some known mesh size and diameter you can calculate the free area ratio which is open area to total area. This directly sets the pressure drop associated with this material. For a good discussion on screens and pressure drops see 'Low-Speed Wind Tunnel Testing' by Barlow, Rae and Pope.

The big problem with this is you can only acquire so much drag for a given free area ratio and actuator size. I had some limited success using this approach to analyze duct performance for ducted wind turbines. This is really more appropriate for modeling things like turbulence screens and honeycomb in wind tunnels.

2) Your other option is Internal Fan/Pump element. Again, there are several ways to define this material you can either specify flow rate (either constant or varying with head) or define a velocity profile which gives velocity vs radius.

We typically use this to model propellers on aircraft when we are concerned about power effects on wings and other structures. I have never used it to model a turbine (i.e. thrust points down stream rather than upstream for a prop). I would be interested to see how that worked out if you try it. The important thing here is to make sure that you define the flow direction properly.

Hope this helps,
Matt