# Full 4D Velocity Field

Hello everyone,

I have generated a file using TurbSim 2.0 which generates a 3D wind profile for the rotor (y,z,t). What I am now interested in is obtaining a wind velocity profile (x,y,z,t). In InflowWind, the planar profile (y,z,t) generated by TurbSim is then propagated in the x-direction to create the full field using the frozen turbulence hypothesis.

I have several questions regarding InflowWind:
How do I tell InflowWind to output the entirety of the field (more than the 9 points found in the docs)?
Am I able to control how far InflowWind propagates downstream (say I want 8 diameters in the x-direction)?

Thanks,

Inflow only supports outputting 9 points, but you could always modify the source code to add more. But if your interest is in visualizing the full TurbSim wind field, you can bypass InflowWind altogether and use scripts such as readfile_BTS.m from the MATLAB Toolbox.

InflowWind uses Taylor’s frozen assumption to relate X and t. That is, the 2D plane of time-dependent wind data generated by TurbSim is propagated along X at the mean wind speed (Ubar), so, X = Ubar*t

Best regards,

Hello @Jason.Jonkman ,

I have written a script that does something like this and would like your input.

For my case, I want to propagate the field to be 8 diameters in length. So if I take a plane of velocity at one time instance, the same exact velocity plane would show up Ubar meters after 1 second in time.

Now, in order to generate 8 turbine diameters worth of data throughout the entire time simulation I would need to cycle through all the time at each point?

An example might be something like this:
Ubar(t) = [1 2 3 4 5 6 7 8]

Ubar(t,x=0) = [1 2 3 4 5 6 7 8]
Ubar(t,x=Ubar) = [8 1 2 3 4 5 6 7]
Ubar(t,x=2*Ubar) = [7 8 1 2 3 4 5 6], and so on…

Does this formulation of propagating the wind speed in the x-direction make sense?

Thanks,

I’m not sure I fully understand becuase you have Ubar appearing both as a constant and as something time-varying. Presumably the variable showing up as Ubar(t) should be some other variable? Please clarify.

Best regards,

Hello @Jason.Jonkman ,

I apologize for the confusion. The revised formulation should be,

U(t) = [1 2 3 4 5 6 7 8]

U(t,x=0) = [1 2 3 4 5 6 7 8]
U(t,x=Ubar) = [8 1 2 3 4 5 6 7]
U(t,x=2*Ubar) = [7 8 1 2 3 4 5 6], and so on…

With Ubar(x) simply being the time average. At the end of the day, all we are doing is simply cycling through the entire time varying plane for various locations in the streamwise.

Thanks,

Yes, I agree. The TurbSim output will be periodic in time/x when `UsableTime` is set to “ALL”.