Courant Number,

Unit: [-]

 

The Courant number or Courant-Friedrichs-Lewy Number (CFL Number) provides a measure for the spatio-temporal discretization of the transport equation. It represents the number of elements that the fluid moves in a single time step.

c = v (Δt / Δx)

A Courant number of 1 is typically known as a hard stability limit for explicit methods. The implicit formulation used by FEFLOW is more robust with this regard, but low Courant numbers are still beneficial for the result accuracy and numerical stability of transport calculations.

 

Furthermore, the CFL condition number for the Richards equation is also available. It similarly reflects the importance of the convective flux in the variable-saturation flow and is a function, in this case, of pressure, pressure-dependent hydraulic conductivity and pressure-dependent capacity.