### 1.12.2. Porous Momentum Loss Models

The momentum loss models available for porous domains are identical to the loss models available with the superficial velocity formulation. In particular, two options are available:

- Isotropic Loss Model

- Directional Loss Model

Note that, in these models, the velocity may refer to either true velocity or superficial velocity. Changing from one to the other leads to different coefficients. For fluid domains, the solver assumes that the coefficients multiply the superficial velocity, while for porous domains, you may choose either true or superficial velocity.

For details on specifying fluid-specific sources in a multiphase flow, for a case involving a porous medium (and for other cases), see Fluid-Specific Sources in the CFX-Solver Modeling Guide.

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