[Note - The capability to use the ROTATE keyword to specify rotating reference frames on a zonal basis has temporarily been removed. Until it is restored, the REL-ROT-ZONE keyword block will not work as advertised.]

For structured grids, the REL-ROT-ZONE keyword block, along with the ROTATE keyword, may be used to specify that one zone is rotating relative to another zone. This "relative rotating zone" capability is intended to simulate rotating devices such as compressor fans. The ROTATE keyword is used to specify which zone(s) are rotating, plus the rotation axis and rate. The REL-ROT-ZONE keyword block specifies the location of the interface between the two zones, and how flow conditions are to be transferred between zones.

Zones sharing an interface may have different circumferential extents. Thus, when modeling a turbomachinery component like a compressor, only one blade per stage is required. Multiple zones and zonal interfaces may be used to cover the radial extent of the stage-to-stage interface, but a single zone must be used in the circumferential direction. The interface surface must correspond to a surface of revolution and grid lines in the circumferential direction must be at a constant radius relative to the rotation axis. The rotation axis must correspond to a coordinate axis.

As noted above, this capability is intended to simulate rotating devices such as compressor fans. A typical configuration would be an upstream non-rotating zone covering the full 360° cross-section, and a rotating downstream zone (or zones, if multiple zones are used in the radial direction) with a circumferential extent of 360°/N corresponding to a single blade. Periodic boundary conditions would be set at the circumferential boundaries in the rotating zone(s), using GMAN's rotational coupling mode.

The coupling of the downstream face of the non-rotating zone to the upstream face of the rotating zone would also be done using GMAN's rotational coupling mode, repeated N - 1 times. This will couple all the points except for that portion of the face that corresponds to the downstream zone in its non-rotated position. These remaining points are then coupled using ordinary (i.e., non-rotated) coupling mode. [In Wind-US, non-zero rotation angles trigger the use of a rotationally periodic boundary condition. Since this is not what we want between two relative rotating zones, this "non-rotated" coupling should be done last, so that zero rotation angles are written into the common grid (.cgd) file.]

The elements of the REL-ROT-ZONE keyword block are defined as follows:

REL-ROT-ZONE

Defines the beginning of the relative rotating zone block.

ZONE iz1 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX} \      [SUBSET I range J range K range] ZONE iz2 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX} \      [SUBSET I range J range K range]

These two lines define the interface between the two zones. The relevant zones are given by the values of iz1 and iz2, and the relevant boundaries within zones iz1 and iz2 are specified via the BOUNDARY keyword parameter.

	iz1		Zone to which increments will be added when passing information to iz2
	iz2		Zone receiving positive increments, increments will be subtracted when passing information back to zone iz1

The SUBSET parameter may be used to specify that the change in properties occurs only over a part of the zone boundary. Otherwise, it is assumed that the change occurs over the entire boundary. The range parameters define the part of the zone boundary over which the change occurs, and take one of the following forms:

	index1 index2		Starting and ending indices in the specified direction. LAST may be used for the last index.
	ALL		Equivalent to 1 LAST.

The starting and ending indices for the appropriate I, J, or K parameter (depending on the boundary specified) must be the same, and correspond to that boundary.

ROTATING-ZONE flag

flag defines how data is to be communicated between the two zones. Currently the only valid values are:

	0		if the zones are not rotating relative to each other. This is the default.
	2		for circumferential averaging. This permits the communication of the bulk fluid properties between zones, while maintaining radial distributions and the efficiency of local time stepping.

ENDRRZ

Defines the end of the relative rotating zone block.

Example

The following figure shows a four-zone configuration. Zone 1 is non-rotating, and zones 2, 3, and 4 are rotating about the x axis at 1680 radians/sec in the counter-clockwise direction. The figure shows the grid from the side in a constant-θ plane, and at the interface plane between the non-rotating and rotating zones, looking downstream.

The non-rotating zone 1 covers the full 360° cross section, but the rotating zones 2-4 cover just 36°. As noted previously, zones sharing an interface may have different circumferential extents. This particular configuration is similar to one that might be used to model a single blade from a compressor blade row with 10 blades.

The indices i, j, and k are in the axial, radial, and circumferential directions, respectively.

For this configuration, the zone coupling was done in GMAN as described below. In this discussion, the "boundary zone" is the one containing grid points for which a boundary condition is being set. GMAN is used to set the connectivity between points in the boundary zone to points in the "source zone". The source zone is specified using GMAN's "SEL OTHER BND" menu choice.

1. Run "auto-couple", which results in the following coupling:
   
   

   	Zone		Boundary				Zone		Boundary
   	1		IMAX		<---		2		I1
   	1		IMAX		<---		3		I1
   	1		IMAX		<---		4		I1
   	2		JMAX		<--->		3		J1
   	3		JMAX		<--->		4		J1

   
   Note that "auto-couple" couples the upstream faces of zones 2-4 to the downstream face of zone 1, but not vice-versa.
   
   
2. Manually couple the zone 1 K1 surface (θ = 0°) to the zone 1 KMAX surface (θ = 360°), and vice versa, using ordinary coupling.
   
   
3. Couple the K1 and KMAX surfaces in zone 2 as periodic boundaries.
   
   
   1. Use zone 2, boundary K1, as the "boundary zone", and zone 2, boundary KMAX, as the "source zone".
   2. Use 1 (rotation) as the connection mode, a point on the x axis as the center of rotation, and 36.0 0.0 0.0 for the rotation angles (in degrees, without commas, and positive for the +K direction).
   3. Repeat the above two steps, but using zone 2, boundary K1, as the "boundary zone", zone 2, boundary KMAX, as the "source zone", and -36.0 0.0 0.0 for the rotation angles.
   4. Repeat the above three steps for zones 3 and 4.
   
   
4. Couple the zone 1 IMAX surface to the zone 2 I1 surface, using rotational coupling mode repeatedly. The procedure is very similar to specifying periodic coupling.
   
   
   1. For the first rotation:
      
      
      • In graphics mode, from GMAN's main menu select BOUNDARY COND.
      • Pick zone 1, boundary IMAX (the "boundary zone").
      • Select MODIFY BNDY.
      • Select COUPLE.
      • Select SEL OTHER BND.
      • Pick zone 2, boundary I1 (the "source zone").
      • Select SET COUP MODE.
      • Click on the choice under CONNECT MODE (initially ** NONE **).
      • Respond to the prompts at the bottom of the screen, using 1 (rotation) as the connection mode, a point on the x axis as the center of rotation, and 36.0 0.0 0.0 for the rotation angles.
      • Select CONNECT.
      
      
   2. For the next rotation:
      
      
      • Select COUPLE.
      • Select SEL OTHER BND.
      • Pick zone 2, boundary I1 (the "source zone").
      • Select SET COUP MODE.
      • Click on the choice under CONNECT MODE (now set to ROTATION).
      • Respond to the prompts at the bottom of the screen as before, except using 72.0 0.0 0.0 for the rotation angles.
      • Select CONNECT.
      
      
   3. Repeat the previous step for rotation angles of 108°, 144°, 180°, 216°, 252°, 288°, and 324°.
   
   
5. Couple the zone 1 IMAX surface to the zone 2 I1 surface in its non-rotated position.
   
   
   • Select BOUNDARY COND.
   • Pick zone 1, boundary IMAX (the "boundary zone").
   • Select MODIFY BNDY.
   • Select COUPLE.
   • Select SEL OTHER BND.
   • Pick zone 2, boundary I1 (the "source zone").
   • Select COUPLE.
   
   
6. Repeat steps 4 and 5 twice, coupling the zone 1 IMAX surface to the I1 surfaces in zones 3 and 4.
   
   
7. Whew!

The relevant keyword input in the input data (.dat) file would be

   ROTATE 0.0 0.0 0.0 -1680.0 0.0 0.0 ZONE 2:4

   REL-ROT-ZONE
      ZONE 1 BOUNDARY IMAX SUBSET I LAST LAST J  1   18 K ALL
      ZONE 2 BOUNDARY I1
      ROTATING-ZONE 2
   ENDRRZ
   REL-ROT-ZONE
      ZONE 1 BOUNDARY IMAX SUBSET I LAST LAST J 19   34 K ALL
      ZONE 3 BOUNDARY I1
      ROTATING-ZONE 2
   ENDRRZ
   REL-ROT-ZONE
      ZONE 1 BOUNDARY IMAX SUBSET I LAST LAST J 35 LAST K ALL
      ZONE 4 BOUNDARY I1
      ROTATING-ZONE 2
   ENDRRZ