The specification of boundary conditions is usually an engineer’s interpretation of
the true behaviour. Real boundary conditions are generally defined by some
physical attributes rather than the numerical description as described of the
previous Section. In incompressible fluid flow there are the following physical
The velocity field at the inlet is supplied and, for consistency, the
boundary condition on pressure is zero gradient.
The pressure field at the outlet is supplied and a zero gradient
boundary condition on velocity is specified.
No-slip impermeable wall
The velocity of the fluid is equal to that of
the wall itself, i.e. a fixed value condition can be specified. The pressure
is specified zero gradient since the flux through the wall is zero.
In a problem whose solution domain and boundary conditions are symmetric
about a plane, we only need to model half the domain to one side of the symmetry
plane. The boundary condition on the plane must be specified according
The symmetry plane condition specifies the component
of the gradient normal to the plane should be zero. [Check**]