Calculating time derivative of scalar field
 

I have an unsteady (time dependent) simulation to be analysed in paraview. I would like to calculate for instance but I can't find a good way to do it. I figured there must be a straightforward way to do this as it must be a common task in CFD.

The only way I can think of is to write a python programmable filter that loops over all points, and for each point calculates the time derivative using a finite difference scheme by accessing the time step of a simulation at that point. However this seems like its going to be very slow...