This action establishes the scales for dimensionalizing the NekRS solution. If nekRS is solving in non-dimensional form, this means that the nekRS solution is performed for:
- nondimensional temperature T^\dagger, defined as T^\dagger=\frac{T-T_{ref}}{\Delta T_{ref}}. The 'T' and 'dT' variables here represent these scales.
- nondimensional velocity U^\dagger=\frac{u}{U_{ref}}. The 'U' variable here represents this velocity scale.
- nondimensional pressure P^dagger=\frac{P}{\rho_{0}U_{ref}^2}. The 'rho' variable here represents this density parameter.
In terms of heat flux boundary conditions, the entire energy conservation equation in nekRS is multiplied by \frac{L_{ref}}{\rho_{0}C_{p,0}U_{ref}\Delta T_{ref}} in order to clear the coefficient on the convective. Therefore, the heat source in nekRS is expressed in nondimensional form as q^\dagger=\frac{q}{\rho_{0}C_{p,0}U_{ref}\Delta
T_{ref}}. Here, 'Cp' is the specific heat capacity scale.
Unfortunately, there is no systematic way to get these reference scales from nekRS, so we need to inform MOOSE of any possible scaling so that we can appropriately scale the nekRS temperature to the dimensional form that is usually expected in MOOSE. Therefore, these scales just need to match what is used in the nekRS input files used to specify boundary conditions. Conversion between dimensional MOOSE heat flux to dimensionless nekRS heat flux is performed automatically, and does not require any special treatment in the nekRS scalarNeumannBC kernel.
