Boundary conditions in fluid dynamics

[1] This type of boundary conditions are common and specified mostly where inlet flow velocity is known.

This type of boundary conditions is common and specified mostly where outlet velocity is known.

In such region, an outlet could be outlined and the gradient of all variables could be equated to zero in the flow direction except pressure.

The most common boundary that comes upon in confined fluid flow problems is the wall of the conduit.

The appropriate requirement is called the no-slip boundary condition, wherein the normal component of velocity is fixed at zero, and the tangential component is set equal to the velocity of the wall.

[1] It may run counter to intuition, but the no-slip condition has been firmly established in both experiment and theory, though only after decades of controversy and debate.

This includes pressure inlet and outlet conditions mainly.

In this boundary condition, the model is axisymmetric with respect to the main axis such that at a particular r = R, all θs and each z = Z-slice, each flow variable has the same value.

A periodic or cyclic boundary condition arises from a different type of symmetry in a problem.

The cyclic-symmetric areas should have the same flow variables and distribution and should satisfy that in every Z-slice.