As mentioned previously, the sliding mesh model is a special case of general dynamic mesh motion wherein the nodes move rigidly in a given dynamic mesh zone. Additionally, multiple cells zones are connected with each other through non-conformal interfaces. As the mesh motion is updated in time, the non-conformal interfaces are likewise updated to reflect the new positions each zone. It is important to note that the mesh motion must be prescribed such that zones linked through non-conformal interfaces remain in contact with each other (that is, “slide” along the interface boundary) if you want fluid to be able to flow from one mesh to the other. Any portion of the interface where there is no contact is treated as a wall, as described in Non-Conformal Meshes in the User's Guide.

The general conservation equation formulation for dynamic meshes, as expressed in Equation 3–1, is also used for sliding meshes. Because the mesh motion in the sliding mesh formulation is rigid, all cells retain their original shape and volume. As a result, the time rate of change of the cell volume is zero, and Equation 3–3 simplifies to:

(3–11)

and Equation 3–2 becomes:

(3–12)

Additionally, Equation 3–4 simplifies to

(3–13)

Equation 3–1, in conjunction with the above simplifications, permits the flow in the moving mesh zones to be updated, provided that an appropriate specification of the rigid mesh motion is defined for each zone (usually this is simple linear or rotation motion, but more complex motions can be used). Note that due to the fact that the mesh is moving, the solutions to Equation 3–1 for sliding mesh applications will be inherently unsteady (as they are for all dynamic meshes).