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.