Continue generalizing the supported flamelet equations

[michael-a-hansen]

Recently we have generalized our flamelet equations by adding the variable heat capacity and consistent enthalpy flux terms. This has been important in getting good results for both adiabatic and nonadiabatic flamelet libraries. There are more generalizations that should be supported in the future.

• Support a use_molar_flux entry in the Flamelet constructor that uses mole fraction gradients to determine diffusive fluxes.

• Support a use_Curtiss_Hirschfelder_approximation entry to the Flamelet constructor to compute all N mass fluxes and correct them for mass conservation according to Curtiss and Hirschfelder's procedure. The default will be the current behavior of forming N-1 fluxes and using mass conservation to directly set the N-th flux.

Note that these two choices (mass/mole, Curtiss_Hirschfelder/not) result in four diffusive flux models.

• Support a consistent nonunity, constant Lewis number formulation. This involves some care over the four different diffusion models.

• Support a nonconstant Lewis number formulation, with mixture-averaged transport properties. This is a big task requiring transport property evaluation in Griffon.