10.7 Setting Up a Single Rotating Reference Frame Problem

To model a problem involving a single rotating reference frame, follow the steps outlined below.

1.   Select the Velocity Formulation to be used when solving: either Relative or Absolute. (See Section  10.7.1 for details.)

General

(Note that this step is irrelevant if you are using one of the density-based solvers; these solvers always use an absolute velocity formulation.)

2.   For each cell zone in the domain, specify the angular velocity ( $\omega$) of the reference frame and the axis about which it rotates.

Cell Zone Conditions

(a)   In the Fluid or Solid dialog box, specify the Rotation-Axis Origin and Rotation-Axis Direction to define the axis of rotation.

(b)   Also in the Fluid (Figure  10.7.1) or Solid dialog box, select Moving Reference Frame in the Motion Type drop-down list and then set the Speed under Rotational Velocity in the expanded portion of the dialog box.

Details about these inputs are presented in Section  7.2.1 and in Section  7.2.2.

Figure 10.7.1: The Fluid Dialog Box with the Moving Reference Frame Selected

For solid zones, you only need to activate the Moving Reference Frame option if you intend to include the convective terms in the energy equation for the solid ( this equation (in the separate Theory Guide)). Normally, this is not required if you wish to do a conjugate heat transfer problem where the solid and fluid zones are moving together.

3.   Define the velocity boundary conditions at walls. You can choose to define either an absolute velocity or a velocity relative to the moving reference frame (i.e., relative to the velocity of the adjacent cell zone specified in step 2), as shown in Figure  10.6.2.

If the wall is moving at the speed of the rotating frame (and hence stationary in the rotating frame), it is convenient to specify a relative angular velocity of zero. Likewise, a wall that is stationary in the non-rotating 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.

Details about these inputs are presented in Section  7.3.14.

4.   Define the velocity at any velocity inlets and the flow direction and total pressure at any pressure inlets. For velocity inlets, you can choose to define either absolute velocities or velocities relative to the motion of the adjacent cell zone (specified in step 2). For pressure inlets, the specification of the flow direction and total pressure will be relative or absolute, depending on the velocity formulation you selected in step 1. See Section  10.7.1 for details. (If you use one of the coupled solution algorithms, the specification is always in the absolute frame.)

Details about these inputs are presented in Sections  7.3.3 and 7.3.4.