This is my first post so I will try my best to be concise. I use Paraview 5.0.1

I am working on a two-phase fluid flow simulation where I am post-processing using Paraview. I am trying to obtain the unit normal vector at the liquid-gas interface given by
n = grad(alpha)/|grad(alpha)|

I have been able to compute the normal by applying the Contour filter (set fluid = 0.5) and checking Compute Normals box.

Q1. Is this unit normal vector?

Q2. If it is, why am I not getting it shown in Calculator to calculate a different parameter?

Q3. If it is not, how can I use the unit normal vector equation above in Calculator or Python Calculator? I read that it is not possible to do gradient calculation with Calculator filter in the below post https://www.paraview.org/pipermail/paraview/2010-September/018776.html
but when I tried using Python Calculator, it crashes.

I have looked at different forums and have been unsuccessful so far.

If you apply the slice filter first, the result of the contour filter will be line segments, and since there are no surfaces, the normals cannot be calculated. Therefore, it is necessary to change the order of the contour filter and the slice filter.

You can use the mag function in the Calculator filter to compute the magnitude of a normal vector. Then, as shown below, in the Information tab, the maximum and minimum length of the normal vectors are both 1, which confirms that they are unit vectors.