Commit b5206472 authored by Henry Weller's avatar Henry Weller
Browse files

reactingEulerFoam: Corrected and rationalized pressure-work

In many publications and Euler-Euler codes the pressure-work term in the
total enthalpy is stated and implemented as -alpha*dp/dt rather than the
conservative form derived from the total internal energy equation
-d(alpha*p)/dt.  In order for the enthalpy and internal energy equations
to be consistent this error/simplification propagates to the total
internal energy equation as a spurious additional term p*d(alpha)/dt
which is included in the OpenFOAM Euler-Euler solvers and causes
stability and conservation issues.

I have now re-derived the energy equations for multiphase flow from
first-principles and implemented in the reactingEulerFoam solvers the
correct conservative form of pressure-work in both the internal energy
and enthalpy equations.

Additionally an optional limiter may be applied to the pressure-work
term in either of the energy forms to avoid spurious fluctuations in the
phase temperature in regions where the phase-fraction -> 0.  This may
specified in the "thermophysicalProperties.<phase>" file, e.g.

pressureWorkAlphaLimit 1e-3;

which sets the pressure work term to 0 for phase-fractions below 1e-3.
parent b4b4e1a0
......@@ -77,11 +77,39 @@ void Foam::AnisothermalPhaseModel<BasePhaseModel>::correctThermo()
}
template<class BasePhaseModel>
Foam::tmp<Foam::volScalarField>
Foam::AnisothermalPhaseModel<BasePhaseModel>::filterPressureWork
(
const tmp<volScalarField>& pressureWork
) const
{
const volScalarField& alpha = *this;
scalar pressureWorkAlphaLimit =
this->thermo_->lookupOrDefault("pressureWorkAlphaLimit", 0.0);
if (pressureWorkAlphaLimit > 0)
{
return
(
max(alpha - pressureWorkAlphaLimit, scalar(0))
/max(alpha - pressureWorkAlphaLimit, pressureWorkAlphaLimit)
)*pressureWork;
}
else
{
return pressureWork;
}
}
template<class BasePhaseModel>
Foam::tmp<Foam::fvScalarMatrix>
Foam::AnisothermalPhaseModel<BasePhaseModel>::heEqn()
{
const volScalarField& alpha = *this;
const volVectorField& U = this->U();
const surfaceScalarField& alphaPhi = this->alphaPhi();
const surfaceScalarField& alphaRhoPhi = this->alphaRhoPhi();
......@@ -93,7 +121,8 @@ Foam::AnisothermalPhaseModel<BasePhaseModel>::heEqn()
tmp<fvScalarMatrix> tEEqn
(
fvm::ddt(alpha, this->rho(), he) + fvm::div(alphaRhoPhi, he)
fvm::ddt(alpha, this->rho(), he)
+ fvm::div(alphaRhoPhi, he)
- fvm::Sp(contErr, he)
+ fvc::ddt(alpha, this->rho(), K_) + fvc::div(alphaRhoPhi, K_)
......@@ -112,13 +141,18 @@ Foam::AnisothermalPhaseModel<BasePhaseModel>::heEqn()
// Add the appropriate pressure-work term
if (he.name() == this->thermo_->phasePropertyName("e"))
{
tEEqn.ref() +=
fvc::ddt(alpha)*this->thermo().p()
+ fvc::div(alphaPhi, this->thermo().p());
tEEqn.ref() += filterPressureWork
(
fvc::div(fvc::absolute(alphaPhi, alpha, U), this->thermo().p())
);
}
else if (this->thermo_->dpdt())
{
tEEqn.ref() -= alpha*this->fluid().dpdt();
tEEqn.ref() -= filterPressureWork
(
fvc::ddt(alpha, this->thermo().p())
+ alpha*(this->fluid().dpdt() - fvc::ddt(this->thermo().p()))
);
}
return tEEqn;
......
......@@ -58,6 +58,15 @@ class AnisothermalPhaseModel
volScalarField K_;
// Private member functions
//- Optionally filter the pressure work term as the phase-fraction -> 0
tmp<volScalarField> filterPressureWork
(
const tmp<volScalarField>& pressureWork
) const;
public:
// Constructors
......
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