Namelist "Gravity"

This data set is related to the characteristics of the gravity force.
If no gravitational effect is considered, this namelist can be omitted.

Full data set of the namelist

&Gravity Gravity_Enabled= .true. ,
Gravity_Angle_IJ= 0.0 ,
Gravity_Angle_IK= 90.0 ,
Reference_Gravity_Constant= 9.81D+00/

Definition of the data set

Gravity_Enabled

Type : boolean value

The gravity effects are enabled or disabled

Default value= .false.

Gravity_Angle_IJ

Type : real value

Angle between the I-axis and of the projection of on the IJ-plan (in degrees). The I-axis is the origin axis.

Default value = 0.0

Gravity_Angle_IK

Type : real value

angle between the K-axis and (in degrees). The K-axis is the origin axis.

Default value = 0.0

Reference_Gravity_Constant

Type : real value

Reference value of the gravity constant

Default value = 9.81

IMPORTANT NOTE

The orientation of the gravity vector in the cartesian referential is defined from the below formulation (spherical coordinates) : Where is norm of the force of gravity (or the buoyancy force). The angle ranges are Gravity_Angle_IJ and Gravity_Angle_IJ . From the definitions for the angles, note that the vector is oriented along the axis while Gravity_Angle_IK= 0 and is in the plan IJ while Gravity_Angle_IK= 90. Following the type of simulation and the choice on the form of equations (dimensional, dimensionless, the scales used in order to define the non-dimensional form of equations, etc …), the term can be written following different ways. For instance, the buoyancy force can be read as : in the momentum equations under Low Mach number hypothesis. In this case where is the constant of gravity. is the reference density defined in the namelist "Fluid_Properties". The buoyancy force can also be read as : in the momentum equations for incompressible flows under Boussinesq hypothesis. In this case where is the thermal expansion coefficient of the fluid considered. is the reference temperature defined in the namelist "Fluid_Properties". As a consequence the generalized form of in the code is : where is defined from the data “Reference_Gravity_Constant” and from the data “Thermal_Expansion_Coefficient” (in the namelist "Fluid_Properties" ). The Default values of these variables are : Reference_Gravity_Constant= 9.81 Thermal_Expansion_Coefficient = 1.0 These values are automatically taken into account by the code if these variables are not explicitly modified by the user in the data file. Clearly, the variable “Thermal_Expansion_Coefficient” is only needed in the simulations of incompressible flows with thermal buoyancy effect . In every other cases, it can be omitted because the buoyancy/gravity force can be defined from the variable “Reference_Gravity_Constant” only.