template<class TypeTag>
class Ewoms::FlashModel< TypeTag >
A compositional multi-phase model based on flash-calculations.
This model assumes a flow of fluid phases , each of which is assumed to be a mixture chemical species (denoted by the upper index ).
By default, the standard multi-phase Darcy approach is used to determine the velocity, i.e.
although the actual approach which is used can be specified via the FluxModule
property. For example, the velocity model can by changed to the Forchheimer approach by
The core of the model is the conservation mass of each component by means of the equation
To determine the quanties that occur in the equations above, this model uses flash calculations. A flash solver starts with the total mass or molar mass per volume for each component and, calculates the compositions, saturations and pressures of all phases at a given temperature. For this the flash solver has to use some model assumptions internally. (Often these are the same primary variable switching or NCP assumptions as used by the other fully implicit compositional multi-phase models provided by eWoms.)
Using flash calculations for the flow model has some disadvantages:
- The accuracy of the flash solver needs to be sufficient to calculate the parital derivatives using numerical differentiation which are required for the Newton scheme.
- Flash calculations tend to be quite computationally expensive and are often numerically unstable.
It is thus adviced to increase the target tolerance of the Newton scheme or a to use type for scalar values which exhibits higher precision than the standard double
(e.g. quad
) if this model ought to be used.
The model uses the following primary variables:
- The total molar concentration of each component:
- The absolute temperature $T$ in Kelvins if the energy equation enabled.