Effect of NumGrid_Z and NumGrid_Y

Hi everyone,

I got a question about the effect of parameters NumGrid_Z and NumGrid_Y in the TurbSim input file, which are the number of grid points to generate the inflow turbulence in the vertical direction and in the horizontal direction. My question is how would different input values of these two parameters affect the simulation output of TurbSim. I am wondering because according to the formula in TurbSim guidebook,

it seems that no matter how many gird points we choose to generate the inflow turbulence, i.e. what values of these two parameters are set, we will get identical mean wind speed at height z when mean wind speed at hub and parameter PLExp are the same. I did not find the formula that specifies how do the TurbSim output variables are related to these two parameters, so could anyone give me some information about this? Many thanks!

Sincere regards,
Qiyun Pan

NumGrid_Z and NumGrid_Y determine the number of points simulated. The height of the points will determine their mean wind speed, but each individual point on the NumGrid_Y x NumGrid_Z grid will have different random phases, so you will get different time series at each point (i.e., the instantaneous wind speeds will be different).

Hi Bonnie,

Sure, according to the equation the height of the points will determine their mean wind speed, but I was expecting the same result at the origin (0 0) what ever the grid size is, since the simulation is at the same hub height. So, is my assumption wrong?

2- Another question, I am conducting turbine load fatigue analysis (on single turbine) -can I use TurbSim output file as input for FAST V8 (replacing the corresponding file at inflowwind model) then the FAST output to MLife input?

Best regards


Single blade

TurbSim generates a random phase for each grid point, each wind component, and each analysis frequency. So, when you change any of those values, you will get different random phases, which then result in different time series. The way the points are currently numbered, point 1 is the lower left point on the grid, and that is the only point that may possibly have the same u-component time-series values when only the number grid points change. If you change the number of frequencies being analyzed, that time series will differ, too.

You can use TurbSim’s output files (.bts or .wnd) in InflowWind, which is then used in a FAST v8 simulation. Please see the InflowWind User Manual for details. And, yes, MLife can analyze FAST output. I have not used MLife, but I am sure this is described in its manual, too.

Thank you very much!!

Hi Bonnie,

I exported/pasted the u comp velocity in excel to get the contour plot and have a look the velocity distribution on the plane. However, my contour plot shows most of high velocities are accumulated at the lower height than the at the very highest point of the map (Grid point). For me it sounds like I am having a wrong result, since wind curve (naturally) shows wind velocity increases as the height increases, relatively. The orientation of the Y and Z axis on the plane (contour plot) is: Y is oriented horizontally from right (+) to left (-) and Z is oriented vertically from top (+) to bottom (-). Please, find attached the out put file.

Kind regards,


Hi, Tadele.

It is very difficult to tell if there is a problem given the instantaneous values on the grid at one time step. These values will vary greatly depending on the level of turbulence and shear you have set. I would first suggest that you turn off all turbulence (set TurbModel to “none”) and turn off the coherence (set SCMod1, SCMod2, and SCMod3 to “none”). Then, the output you get should be ONLY the velocities due to shear (and these velocities will not change over time).

Hi Bonnie,

Thank you for your help and suggestion. I have been working on the simulation varying the turbulence characteristics and type (don’t set any shear as I am using IEC model). When I set IEC turbulence characteristics to ‘TI in percent’ and the type to ‘NTM’ (as NTM is must when choosing ‘TI in percent’) the u comp output looks like fine; however, the variation of the speed at each timestep on the corresponding grid point is very very small (can say negligible -it seams the result is duplicating at each timestep).
Otherwise, I get a bit not-convincing result (at all timestep) for other setups.



I don’t understand what you mean by

Did you input a very small number for the TI so that the time series looks constant?

Hi Bonnie,

the u-comp is the simulation result for the u component velocity- like ‘Kaimal.u’. The result for each time step (speeds at each grid points of Y and Z coordinate) for example timestep 0.00, 0.05… is almost identical, in my case.
I used 16% TI then changed it to 20% then 24% to see the effect but still the variation of the result for each timestep is not changing significantly (i,e. result at timestep 0.00 is not different from 0.05 or 10.0…) please find attached the simulation result.



Hi Bonnie and all,

I found my problem. MY MESS!! It was the way I put the value of TI (I mean I have been setting it in fraction like 16/100=0.16 instead of just 16…). Sorry Bonnie for bothering you with my mess and confused results; I should have think and check twice before I post it as a problem :blush:



Hello everyone,

I am just getting used to FastV8. After running the CertTest files (There were no problems doing that) I just tried to modify the Wind input by changing the given “NRELOffshrBsline5MW_InflowWind_12mps.dat” input file “Wind/90m_12mps_twr.bts” to a input file “Wind/TurbSim.bts”. A direct comparison of the input files the bts files were created of looks like this:


I basically didnt change anything else, but a few seconds after I started running the Fastv8.exe the Fatal Error occurs:FATAL ERROR.PNG.

What did I do wrong? Thanks in advance for ur help!


Dear David,

I see that you disabled WrADTWR, which means that wind at the location of tower points will not be generated. Thus, FAST is complaining that AeroDyn’s tower analysis nodes are outside of the wind grid.

Best regards,