title: Save data to VTK using Python and tvtk with more than one vector field
body: <p>I'm trying to save three sets of vector quantities corresponding to the same structured grid (velocity, turbulence intensity and standard deviation of velocity fluctuations). Ideally, I'd like them to be a part of the same vtk file but so far I have only been able to get one of them into the file like so:</p>
  
  <pre><code>sg = tvtk.StructuredGrid(dimensions=x.shape, points=pts)
  sg.point_data.vectors = U
  sg.point_data.vectors.name = 'U'
  write_data(sg, 'vtktestWake.vtk')
  </code></pre>
  
  <p>I've spent past few hours searching for an example of how to add more then one vector or scalar field but failed and so thought I'd ask here. Any guidance will be most appreciated.</p>
  
  <p>Thanks,</p>
  
  <p>Artur</p>