Inflow direction and yawDOF


this is my first post in this helpfull forum. Thanks a lot for your generous work.

I am modeling a floating offshore upwind WT (5 MW reference wind turbine). Normally, waves will come from 0º direction and wind will come from ±45º sector. So I need to set nacelle yaw and wind mean flow horizontal direction inside this sector because, when analyzing the production cases, the rotor plane will be orthogonal to the mean wind direction in order to face the wind (misalignement = 0º).

The problem comes when I set HFlowAng to high values. In the case of 22.5º mean flow horizontal angle (generated using TurbSim v1.06.00 and without turbulence) because even FAST .out file does not calculate such angle, instead FAST returns as HorWndDir: -3.56º. Same thing happened when I changed the yaw DOF value to zero (and HFlowAng = 22.5º —>wind/nacelle misalignement).

I have looked at the .u, .v and .w files and the wind field is correctly generated according to the given values.

U component: 3 m/s
InfModel: EQUIL

I am using latest versions of the codes:

  • FAST_v7.02.00d-bjj_AeroDyn_v13.00.02a-bjj_BladedDLLInterface_OC3Hywind.exe
  • AeroDyn_v13.00.02a-bjj
  • InflowWind v1.01.00b-bjj
  • NWTC Subroutine Library v1.07.00b-mlb

I found the same problem using: FAST_v7.01.00a-bjj.exe

Have you got an idea of which could be the problem?

Thank you.

Dear Josean,

The scaling used to create the binary .u, .v, and .w data files breaks down at very low levels (or zero) turbulence and can lead to unexpected behavior. If you wish to generate wind without turbulence, use AeroDyn’s simple “hub-height” format wind data file instead. See the following forum topic for more information:

That said, when using FAST in conjunction with turbulent wind data files from TurbSim, the wind “grids” (“planes”) will propagate along the xi-axis regardless of the wind direction specified in TurbSim, which is why we always recommend setting the wind direction to zero when using TurbSim in conjunction with FAST. To model a floating offshore wind turbine with waves misaligned from turbulent wind, change the wave direction instead of the wind direction. When using AeroDyn’s so-called “hub-height wind files,” the wind direction need not align with the xi-axis.

See the TurbSim User’s Guide for more information.

Best regards,


thank you for your reply. I also thought that changing the wave diretion could be a solution, but it seems quite tedious work because the Wamit matrices that have to be provided to HydroDyn and the mooring definiton should be changed for each value of misalignement between waves and wind.

In my institution they have just bought OrcaFlex 9.6, which can be coupled (I am working on this) with FAST. Do I have to follow this procedure, for “misalignement cases”, when coupling FAST and OrcaFlex? I supposse that the answer is “YES”.

Thank you again.

Dear Josean,

The limitation regarding the fixed direction of turbulent wind is a limitation of FAST’s InflowWind module, so, any code that uses InflowWind, including the FAST-OrcaFlex coupling, will also have this limitation. We are aware of this limitation and will remedy it when we can.

HydroDyn allows one to import WAMIT data for a range of wave directions. So, you shouldn’t need to change the WAMIT matrices if you want to change the wave direction within HydroDyn. You would have to change the WAMIT matrices if you change the platform orientation instead of changing the wave direction.

Best regards,

Dear Jason,

thank you for your quick answer!