UEqns.H

mrfZones.correctBoundaryVelocity(U1);
mrfZones.correctBoundaryVelocity(U2);
mrfZones.correctBoundaryVelocity(U);

fvVectorMatrix U1Eqn(U1, U1.dimensions()*dimVol/dimTime);
fvVectorMatrix U2Eqn(U2, U2.dimensions()*dimVol/dimTime);

volScalarField dragCoeff(fluid.dragCoeff());

{
    volScalarField virtualMassCoeff(fluid.virtualMassCoeff());

    volVectorField liftForce(fluid.liftForce());
    volVectorField wallLubricationForce(fluid.wallLubricationForce());
    volVectorField turbulentDispersionForce(fluid.turbulentDispersionForce());

    {
        U1Eqn =
        (
            fvm::ddt(alpha1, U1)
          + fvm::div(alphaPhi1, U1)
          - fvm::Sp(fvc::ddt(alpha1) + fvc::div(alphaPhi1), U1)
          + phase1.turbulence().divDevReff(U1)
         ==
          - fvm::Sp(dragCoeff/rho1, U1)
          - (
                liftForce
              + wallLubricationForce
              + turbulentDispersionForce
            )/rho1
          - virtualMassCoeff/rho1
           *(
                fvm::ddt(U1)
              + fvm::div(phi1, U1)
              - fvm::Sp(fvc::div(phi1), U1)
              - DDtU2
            )
        );
        mrfZones.addCoriolis(alpha1 + virtualMassCoeff/rho1, U1Eqn);
        U1Eqn.relax();
    }

    {
        U2Eqn =
        (
            fvm::ddt(alpha2, U2)
          + fvm::div(alphaPhi2, U2)
          - fvm::Sp(fvc::ddt(alpha2) + fvc::div(alphaPhi2), U2)
          + phase2.turbulence().divDevReff(U2)
         ==
          - fvm::Sp(dragCoeff/rho2, U2)
          + (
                liftForce
              + wallLubricationForce
              + turbulentDispersionForce
            )/rho2
          - virtualMassCoeff/rho2
           *(
                fvm::ddt(U2)
              + fvm::div(phi2, U2)
              - fvm::Sp(fvc::div(phi2), U2)
              - DDtU1
            )
        );
        mrfZones.addCoriolis(alpha2 + virtualMassCoeff/rho2, U2Eqn);
        U2Eqn.relax();
    }
}