Processing OpenFOAM VTK to bts format

[Derek03-pixel]

I have OpenFOAM VTK file that I need to convert ***.bts format. I have seen many python codes in wind tools folder, but couldn’t distinguish the one can be applied for my case. Would you suggest the specific python code please! Thank you!

[ewquon]

In the past I have found the bts format to be unnecessarily unwieldy. To specify custom inflow planes for openfast, I've instead used the HAWC format. Assuming that's what you're trying to do, you can use this https://github.com/NREL/windtools/blob/main/windtools/inflow/openfast.py#L29-L44. Note that HAWCInput.URef parameter is the speed at which the turbulence box is moved through the rotor, not necessarily the mean wind speed. As long as the URef used to define your box agrees with your InflowWind input, I believe this parameter doesn't matter.

Hopefully this helps.

[Derek03-pixel]

Thank you for the detailed guide; it has been very helpful. I am confused about the following points. When I run the code hawc = HAWCInput(); hawc.write_binary_from_netcdf(ds), the dataset (ds) has multiIndex coordinates containing (t, y, z) and data variables (u, v, w). However, the OpenFOAM output VTK files are saved in individual folders for each time step (in seconds). How does the code convert these outputs into the ds format, or do I need to preprocess the data?

[ewquon]

You would have to separately create the xarray dataset with inflow planes from the VTK files.

[Derek03-pixel]

Thank you so much. it works!

[Derek03-pixel]

Dear Ewquon,
I have used the following profile plot function code to produce the inflow profile attached on this page. However, the code gives the profile at all the y-mesh points of the yz-slice. Which part of the code should I modify to achieve the required flow-field profile at an arbitrary Y-point against height z? Thank you!

plot_profile(
    datasets=ds,              
    fields=['u', 'v', 'w'],   
    times=ds.time.isel(time=slice(0, 1)).values,     
    timerange=None,           
    fig=None,                 
    ax=None,                  
    fieldlimits= {'u': (0, 15), 'v': (-6, 6), 'w': (-6, 6)},         
    heightlimits=[0, 1000],   
    fieldlabels={'u': 'u (m/s)', 'v': 'v (m/s)', 'w': 'w (m/s)'},           
    cmap=None,                
    stack_by_datasets=False,  
    labelsubplots=True,       
    showlegend=True,          
    fieldorder='C',           
    ncols=3,                  
    subfigsize=(4, 5),        
    plot_local_time=False,    
    local_time_offset=0,      
    datasetkwargs={},         
    **{'linewidth': 1, 'alpha': 0.8} 
)

[ewquon]

The plotting code was developed with virtual met masts or planar-averaged data in mind. I would subset your xarray dataset in y (and/or x) so that the input to the plotting function has only time-height dimensions.

[Derek03-pixel]

Yes it worked. Thank you for the insight.

[Derek03-pixel]

Dear Ewquon,
I followed the steps below to run the code, but I ran into some issues.

1. ds = readVTK(VTK_YZ', sliceType='U_slice_streamwise_3D.vtk',dateref=pd.to_datetime('2025-10-15 12:00:00'), ti=18000, tf=18600, res=(100,100,100),squash='x', ang=15.52)

2. ds = ds.rename({'datetime': 't'}) # I was having error and renamed to 't'
After importing binary file, I excuted:

hawc = HAWCInput(
URef=URef, # The mean u(x_componenet) from flow field.
RefHt=90.0,
TipRad=63.0
)

3. hawc.write_binary_from_netcdf(
    ds=ds,
    prefix='./HAWC_',
    dy=4.6785,
    dz=4.6785,
    expand_rotor_radius=1.3
)
4. I experience the error with `get_delta()` and I replaced with
 `t_vals = ds.coords['t'].values
   if np.issubdtype(t_vals.dtype, np.datetime64):
       t_vals = (t_vals - t_vals[0]) / np.timedelta64(1, 's') `

dt = round(float(np.mean(np.diff(t_vals))), 10)
dx = dt * self.URef

5. After this change I run the ```
hawc.write_binary_from_netcdf(
    ds=ds,
    prefix='./HAWC_',
    dy=4.6785,
    dz=4.6785,
    expand_rotor_radius=1.3
)

...and the HAWC2-format file was generated successfully. However, OpenFAST fails to read it.
The error I receive is the following:

FAST_Solution:FAST_UpdateStates:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput
:InflowWind_GetRotorSpatialAverage:IfW_FlowField_GetVelAcc:Grid3DField_GetCell: Error: GF wind
array was exhausted at 6.25000E-03 seconds (trying to access data at NaN seconds).
IT_Lo=-2147483647, IT_HI=-2147483646
InflowWind_CalcOutput:InflowWind_GetHubValues:IfW_FlowField_GetVelAcc:Grid3DField_GetCell: Error:
GF wind array was exhausted at 6.25000E-03 seconds (trying to access data at NaN seconds).
IT_Lo=-2147483647, IT_HI=-2147483646
FAST_AdvanceStates:AD_UpdateStates:AD_CalcWind:AD_CalcWindRotor:IfW_FlowField_GetVelAcc:Grid3DFiel
d_GetCell: Error: GF wind array was exhausted at 6.25000E-03 seconds (trying to access data at
NaN seconds). IT_Lo=-2147483647, IT_HI=-2147483646

 OpenFAST encountered an error at simulation time 6.25000E-03 of 700 seconds.
 Simulation error level: FATAL ERROR

 Aborting OpenFAST.

Could you please help me understand how to solve this problem?
Best regards,