What's the scalar variable "Tracer" in AMReX/IAMR?

[Bowen0330]

Hello AMReX Team!

I am considering using the level set method in AMReX and I found the "Tracer" scalar variable in it. I was wondering what it is used for? Can I use it directly or modify it to perform the level set method? Because I think I can take advantage of the scalar update procedure provided in AMReX/IAMR.

Thanks in advance for any suggestions!

Regards,
Bowen

[asalmgren]

HI Bowen! Tracer is there for exactly this purpose -- to be used as a model for generic scalar advection. So you could use this for your level set variable.

Note these lines in NS_setup.cpp:

advectionType[Tracer] = NonConservative;
diffusionType[Tracer] = Laplacian_S;
if (do_cons_trac) {
  advectionType[Tracer] = Conservative;
  diffusionType[Tracer] = Laplacian_SoverRho;
  amrex::Print() << "Using conservative advection update for tracer.\n";
}

This says that the default advection scheme is non-conservative, i.e. d/dt(phi) + u dot grad phi = 0 is used to update phi. And the diffusion term if you use one doesn't have any density-weighting. You can change that by setting do_cons_trac if you want to update in the form d/dt(phi) + del dot (u phi) = 0

[Bowen0330]

Thank you very much for the detailed explanation, I'll start it!

Regards,
Bowen