code: def download_blood_vessels():
      
      local_path, _ = _download_file('pvtu_blood_vessels/blood_vessels.zip')
      filename = os.path.join(local_path, 'T0000000500.pvtu')
      mesh = vtki.read(filename)
      mesh.set_active_vectors('velocity')
      return mesh
docs: data representing the bifurcation of blood vessels.