******************************************** **Gas Phase Darcy Velocity in Porous Media** ******************************************** :: Gas phase Darcy velocity in porous media = {yes | no} ----------------------- **Description / Usage** ----------------------- This post-processing option will lead to the explicit calculation and storage of the Darcy velocity components in the gas phase, viz. the velocity of the gas phase due to gas-phase pressure gradients. This option is only available for *POROUS_TWO_PHASE* media types (cf. *Media Type* card). The velocity components appear in the output EXODUS II file as the nodal variables **Darcy_Vel_g_0, Darcy_Vel_g_1** and **Darcy_Vel_g_2**. The permissible values for this postprocessing option are: ============= ================================================================ **yes** Calculate the gas-phase Darcy velocity components and write to the output EXODUSII file. **no** Do not calculate the gas phase velocity components. ============= ================================================================ ------------ **Examples** ------------ This input example turns on calculation of the gas phase velocity components: :: Gas phase Darcy velocity in porous media =yes ------------------------- **Technical Discussion** ------------------------- The gas-phase Darcy velocity is given by the extended Darcy law, which accounts for the relative reduced flow due to the presence of another phase, viz. .. figure:: /figures/330_goma_physics.png :align: center :width: 90% Here :math:`\nu_g` represents the Darcy flux, or Darcy velocity, in the gas phase, k is the permeability of the porous medium, :math:`k_g` is the relative permeabilities for the gas and liquid phases respectively, :math:`\mu_g` are the gas viscosity, :math:`p_g` is the pressure in the gas phase, and g is the gravitational force vector. :math:`\rho_g` is the density of the gas phase and is equal to the sum of the partial densities of air and solvent vapor, .. figure:: /figures/331_goma_physics.png :align: center :width: 90% -------------- **References** -------------- GT-009.3: GOMA’s Capabilities for Partially Saturated Flow in Porous Media, September 1, 2002, P. R. Schunk .. TODO - Lines 48 and 52 are photos that need to be swapped with the equations.