import vtk

reader = vtk.vtkXMLUnstructuredGridReader()
reader.SetFileName('SimulationResults50.vtu')
reader.UpdateInformation()
arrayselect = reader.GetPointDataArraySelection()

for i in xrange(0, 501):
    stringi = '%06d' % i
    arrayname = 'V_' + stringi

    arrayselect.DisableAllArrays()
    arrayselect.EnableArray(arrayname)
    reader.Update()

    indata = reader.GetOutput()

    inarray = indata.GetPointData().GetArray(arrayname)
    outarray = inarray.NewInstance()
    outarray.DeepCopy(inarray)
    outarray.SetName('V')

    outdata = vtk.vtkUnstructuredGrid()
    outdata.CopyStructure(indata)
    outdata.GetPointData().AddArray(outarray)

    writer = vtk.vtkXMLUnstructuredGridWriter()
    writer.SetFileName('SimulationResults50_' + stringi + '.vtu')
    writer.SetInput(outdata)
    writer.Write()