# GfsSourceViscosity

### From Gerris

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- | [[SourceDiffusion]] solves the diffusion equation for a scalar quantity, while '''SourceViscosity''' solves the diffusion equation for the velocity (a vector quantity obviously). In the case of a spatially uniform viscosity the two are strictly equivalent since—in the case of an incompressible fluid—the vector diffusion equation for the velocity can be split in independent scalar diffusion equations for each of the Cartesian components of the velocities. | + | [[GfsSourceDiffusion]] solves the diffusion equation for a scalar quantity, while '''GfsSourceViscosity''' solves the diffusion equation for the velocity (a vector quantity obviously). In the case of a spatially uniform viscosity the two are strictly equivalent since—in the case of an incompressible fluid—the vector diffusion equation for the velocity can be split in independent scalar diffusion equations for each of the Cartesian components of the velocities. |

- | To sum up, using SourceViscosity is safe in all cases, regardless of whether the viscosity is uniform. | + | To sum up, using GfsSourceViscosity is safe in all cases, regardless of whether the viscosity is uniform. |

## Revision as of 08:57, 8 February 2008

GfsSourceDiffusion solves the diffusion equation for a scalar quantity, while **GfsSourceViscosity** solves the diffusion equation for the velocity (a vector quantity obviously). In the case of a spatially uniform viscosity the two are strictly equivalent since—in the case of an incompressible fluid—the vector diffusion equation for the velocity can be split in independent scalar diffusion equations for each of the Cartesian components of the velocities.

To sum up, using GfsSourceViscosity is safe in all cases, regardless of whether the viscosity is uniform.