To model a problem involving multiple reference frames, follow the steps outlined below.
| The grid-setup constraints
for a rotating reference frame listed in Section
10.4 apply to multiple reference frames as well.
Define Models Solver...
(Note that this step is irrelevant if you are using one of the coupled solution algorithms; these algorithms always use an absolute velocity formulation.)
Define Boundary Conditions...
Details about these inputs are presented in Section 7.17.1 and in Section 7.18.1.
If the wall is moving at the speed of the moving frame (and hence stationary relative to the moving frame), it is convenient to specify a relative angular velocity of zero. Likewise, a wall that is stationary in the non-moving frame of reference should be given a velocity of zero in the absolute reference frame. Specifying the wall velocities in this manner obviates the need to modify these inputs later if a change is made in the rotational velocity of the fluid zone.
An example for which you would specify a relative velocity is as follows: If an impeller is defined as wall-3 and the fluid region within the impeller's radius is defined as fluid-5, you would need to specify the angular velocity and axis of rotation for fluid-5 and then assign wall-3 a relative velocity of 0. If you later wanted to model a different angular velocity for the impeller, you would need to change only the angular velocity of the fluid region; you would not need to modify the wall velocity conditions.
Details about these inputs are presented in Section 7.13.1.
Details about these inputs are presented in Sections 7.3.1 and 7.4.1.
Solve Initialize Initialize...
Select the Absolute option under Reference Frame. If the Relative to Cell Zone option is selected, the initial flow field can contain discontinuities, which can cause convergence problems in the first few iterations.