The normal and tangential velocity condition allows you to specify the normal and tangential velocity components on the boundary section. The normal velocity component is denoted by and the tangential component by . The default condition corresponds to , but you can assign nonzero values for one or both of the components. Note that, in 3D, is a vector with two components, not a scalar.

It is important to note the sign convention for and .

In 2D, a positive normal velocity points out of the domain, as well as a positive normal force. A positive means that the fluid emerges from the domain of the sub-task; therefore, in an entry section, will be assigned a negative value. A positive is oriented along the counter-clockwise direction on the closed curve surrounding the domain of the sub-task; for internal boundaries of 2D domains that are not simply connected (for example, a hole in the domain), the orientation of is reversed.

In 3D, a positive normal velocity points into the domain, as well as a positive normal force. In 3D, it is more complicated to assign a value of , primarily because the definition of relies on complex conventions of orientation. As a result, in 3D, the normal and tangential velocity condition is recommended for use only for a zero tangential velocity. If the tangential velocity in a 3D problem is nonzero, you should use the Cartesian velocity condition (described in Cartesian Velocity Condition) instead.

To define the normal and tangential velocity on a boundary section, select

the Normal and tangential velocities imposed (vn, vs) menu item in the list of boundary condition choices.

  Normal and tangential velocities imposed (vn, vs)

Then specify as a Constant, a Linear function of coordinates, a Map from CSV (Excel) file, or a User-defined function. When you select Upper level menu after specifying , Ansys Polydata will bring you to the menu where you can specify in the same manner.