Flow boundary condition along boundary i
DESCRIPTION
Selecting an option sets the type of boundary condition. Polydata will then prompt the user for the parameters associated with the boundary condition in use.
The user may also request the calculation of the force on the current boundary set.
NOTES
-2' Enable force postprocessor Allows user to switch on the force postprocessor on this boundary set. The integral of the force density will appear in the listing. -2" Disable force postprocessor Allows user to switch off the force postprocessor on this boundary set -1 Upper level menu The current flow boundary conditions are accepted on boundary set i 0 Interface Interface flow boundary conditions are available for multi-fluid flow problems. They require continuity of the velocity field along the interface, together with continuity of the interfacial force. Interfaces can be fixed (the position is known a priori) or mobile (a kinematic condition is added to the system).
Interface conditions are available along intersections of sub-domains only.
Interface conditions in domain A along domain B also require interface conditions in domain B along domain A.
In case of incompatibility, an error is reported at the level of the task.1 Normal and tangential velocities imposed (vn & vs) Default : vn = vs = 0 (no slip) 2 Normal and tangential forces imposed (fn & fs) Default : fn = fs = 0 3 Normal velocity and tangential force imposed (vn & fs) Default : fs = vn = 0 (full slip) 4 Normal force and tangential velocity imposed (fn & vs) Default : fn = vs = 0.
For free surface problems, this type of boundary conditions should be used along the outlet section.
Boundary conditions of the "Outflow" type cannot be used for viscoelastic free surfaces.5 Slip conditions Vanishing normal velocity is imposed, while the tangential force is a function of (Vfluid - Vwall). Navier slip equation and power-law slip equations are available.
Default : vn = fs =06 Plane (axis) of symmetry (fs=0 & vn=0) 7 Inflow Fully developed inlet velocity profile, calculated on the basis of the sub-task fluid model, is imposed. The flow rate is specified.
For viscoelastic flows, the hyperbolic character of the constitutive equations requires extra-stresses along entry sections. They are automatically imposed where inflow boundary conditions are specified.8 Outflow For generalized Newtonian flows : vanishing normal force and tangential velocities are imposed.
For viscoelastic flows : a fully developed outlet velocity profile (the flow rate is specified by the user), calculated on the basis of the sub-task fluid model, is imposed.
Outflow boundary conditions can not be imposed at the exit of free jets in viscoelastic flow problems.9 Free surface Holds for mobile boundaries: a kinematic condition is added to the system.
In 2-D flow problems, surface tension can be taken into account.10 Global force imposed Selecting this option allows the user to specify a constant force to be applied to a boundary set, the shape of which is a priori unknown. In fiber spinning, for example, this option allows the user to impose a global spinning force which does not change when the output diameter is updated. 11 Cartesian velocities imposed (vx, vy, vz) Available for 3D computations only, this option allows the user to impose boundary conditions in terms of cartesian velocities. 12 Interface with porous media Allows for coupling with porous media (Darcy) problem. Available when such a problem exists. 13 Porous wall Vanishing tangential velocity is imposed, while normal velocity vn = -k fn 14 Inlet of periodic condition Allows for defining symmetry or anti-symmetry constraints between two boundary sets 15 Outlet of periodic condition Never directly available. Imposed via the definition of a 'Inlet of periodic condition'
For physical reasons, the boundaries adjacent to an inflow/outflow boundary should preferably be orthogonal to the inflow/outflow boundary.