Gravity#
The gravity model applies a gravitational body force to the fluid momentum and energy equations, enabling simulation of buoyancy-driven flows. Gravity is applied globally to all fluid zones in the simulation and is disabled by default.
Available Parameters#
Parameter |
Description |
|---|---|
Gravity (toggle) |
Enable or disable the gravitational body force |
Direction |
Unit vector defining the direction of gravitational acceleration [X, Y, Z] |
Magnitude |
Magnitude of the gravitational acceleration |
Detailed Descriptions#
Gravity (toggle)#
Enables or disables the gravitational body force. When enabled, gravity is applied globally to all fluid zones by adding a body force to the momentum equations and a work term to the energy equation: \(\mathbf{f}_{\text{mom}} = \rho \, \mathbf{g}, \qquad f_{\text{energy}} = \rho \, (\mathbf{g} \cdot \mathbf{u})\)
Default: Disabled (off)
Direction#
The unit vector specifying the direction of the gravitational acceleration. Defines the orientation of the gravity vector in the simulation coordinate system.
Default:
X: 0, Y: 0, Z: -1(pointing in the negative Z-direction)Example:
(0, 0, -1)for vertical-down in a Z-up coordinate system,(0, -1, 0)for a Y-up coordinate system
Notes:
The direction vector will be normalised automatically; you do not need to supply a unit vector.
Only available when the Gravity toggle is enabled.
Magnitude#
The magnitude of the gravitational acceleration.
Default:
9.81 m/s²(Earth surface gravity)Example:
9.81 m/s²,1.62 m/s²(lunar gravity)
Notes:
Must be a positive value.
Only available when the Gravity toggle is enabled.
💡 Tips
Enable gravity only when buoyancy effects are physically significant (e.g., natural convection, thermally stratified flows, or flows where density differences drive the motion).
For aerodynamic simulations where density variations are small and driven by compressibility rather than temperature gradients, gravity can typically be omitted.
Ensure the Direction vector is aligned with the physical orientation of your geometry in the simulation coordinate system.
When using a Z-up coordinate system, the default direction
(0, 0, -1)corresponds to Earth’s downward gravity and requires no adjustment.For conjugate heat transfer (CHT) simulations with buoyancy-driven convection, enabling gravity is essential for physically accurate results.