Criterion of mass equation convergence
Let ρ0 be
the density at time t and ρk is
calculated approximation for the density at time (t + Δt).
While performing
the (k +1)-th
nested iteration, the residual
error (
) for the mass equation
is calculated and defined as follows:
 | (1) |
|---|
where 
means
summing over all control volumes in the domain (sub-domain) Ω and
the residual error at the control volume (“cv”)
is:
 | (2) |
|---|
where 
is
the mass flux at the control volume face (fcv).
To make decision if is small enough, a reference residual
value (
) is defined as:
 | (3) |
|---|
So a sum of absolute values of inlet and outlet fluxes at control volume faces can be considered as doubled mass flux through the control volume (“cv”).
At the end of the (k +1)-th nested iteration, a stopping criteria are checked. For the mass equation it is:
 | (4) |
|---|
and the stopping criteria Equation 4 can be treated as:
 | (5) |
|---|