Tower shadow model in Aerodyn


We are currently looking at the potential flow tower shadow model implemented in Aerodyn. Looking at the Aerodyn manual we understand that you are using the Bak model for upwind wind turbines. However in the FAST reference manual there is no mention to this model and the only parameters making reference to any tower shadow model are in our opinion used just for the Powles model (downwind wind turbines).

We would like to know:

  1. if our interpretation is correct
  2. if the upwind Bak model is always used by default or if it is possible to switch it on and off. In that case how can we do it?
  3. if it is possible to modify the drag coefficient parameter (Cd) in order to account for different tower geometries

Thank you so much and kind regards from Spain


Dear Mikel,

The current AeroDyn Theory Manual (dated January, 2005) includes documentation of both existing and proposed models. The description of the tower influence in that manual is one of the proposed models. In AeroDyn v12.58, the only tower influence model available is the one that is documented in Appendix A of the AeroDyn User’s Guide (dated December, 2002)–This is also the only model whose inputs are documented in the current FAST User’s Guide (dated August, 2005).

Pat Moriarty is currently working on AeroDyn v12.60, which among other things, includes the tower influence model described in the AeroDyn Theory Manual (this model is Bak’s adjustment to the potential flow model). You will have control over the drag coeffecient in this implementation of the tower influence. Although I cannot give a set date, AeroDyn v12.60 should be available shortly.

Best regards,

Hi everyone,

I reply in this topic to avoid multiplying useless topic.

I am currently working on a downwind turbine.
I read the aerodyn user’s guide and theory manual, but I still in difficulty to input my aerodyn ipt file.
I know my tower drag coefficient and its diameter (tubular tower), but I do not know how to exactly define the shadow.
Where can I find some sample or a way to get the input asked by aerodyn (TWRSHAD, SHADHWID, and T_Shad_Refpt)?

Thank you ahead.

Thomas Duffey

Dear Thomas,

The downwind tower shadow model in AeroDyn v12.58 (described in the AeroDyn User’s Manual on page 27) puts the burden on the user in that you have to know the size and magnitude of the wake ahead of time. The code assumes that you have some data or empirical relationships on which to base its shape in terms of TwrShad, ShadHWid, and T_Shad_Refpt.

The proposed downwind tower shadow model that will come in a future version of AeroDyn (described in the AeroDyn Theory Manual on page 31) makes it easier in that you only have to specify the drag coefficent and radius of the tower, from which the wake deficit is calculated. The two models are similar in form, but not identical. Although I haven’t tried this myself, I think that with a little algebra you could derive some relationships that would allow you to choose the model parameters in order get similar results between the models. This may be useful for you since you claim to already know the tower’s drag coefficent and diameter.

Best regards,

Thank you Jason for your quick answer,

I will try to use my known values (Cd and diameter) to find the TwrShad, ShadHWid, and T_Shad_Refpt.

Hi everyone,

I am currently working on a upwind turbine.
I read the aerodyn user’s guide and theory manual, but I still in difficulty to input my aerodyn ipt file.
How do I activate the descriped tower dam model for considering the upwind influence of the tower.

Thank you in advance.

Best regards,

Matthias Taubert

Hi, Matthias.

The tower influence model documented in the AeroDyn theory manual is available in AeroDyn v13.00.00a-bjj. You can read about the required inputs on pages 1 and 2 in There is also a sample input file in the AeroDyn v13.00.00a-bjj archive that uses this new feature (see “AeroDyn_TowerInfl.ipt” and “AeroDyn_Tower.dat” in the archive’s “Samples” folder).