Setting different source terms and properties for each scalar

[pasqualelapenna]

I'm trying to modify the lowMach example including an additional scalar. I want to set different source terms and properties between the scalar and the temperature and then (an other time) modify accordingly the thermal divergence. I've done this many time in nek5000 and now I'm trying to do the same in nekRS.

As far as I understood I should modify the .oudf in userQ and userVp.
How can I identify which scalar I'm assigning the source term QVOL[id]=... ?
How can assign SPROP (both udiff and utrans) to the scalar?

Thank you!

[pasqualelapenna]

Updates on this try

Here's my preliminary (first guess) modifications in .oudf, which are still giving me wrong results:

In userQ:
QVOL[id + 0*sOffset] = my_temp_source_term;
QVOL[id + 1*sOffset] = my_scal_source_term;

in userVp (with the nek5000 nomenclature commented):
UPROP[id + 0*uOffset] = my_viscosity; // udiff vel
UPROP[id + 1*uOffset] = EoS_density; // utrans vel
SPROP[id + 0*sOffset] = my_temp_diffusivity; // udiff temp
SPROP[id + 1*sOffset] = EoS_density; // utrans temp
SPROP[id + 2*sOffset] = my_scal_diffusivity; // udiff scal
SPROP[id + 3*sOffset] = EoS_density; // utrans scal

All the properties should then be included as function of both the temperature and the additional scalar.