How to prevent excessive twisting when extending the inlet/outlet far upstream of the airfoil

In some cases a user will want to extend the inlet or outlet of the domain far upstream of the airfoil.  This will normally cause Code Wand to generate a highly twisted mesh, but a duct mesh can be used to prevent this.

In this tutorial, the centrifugal compressor sample case included with the ADS installation will be modified to extend the upstream boundary.  To do this, navigate to the Example Cases --> 3D Single Runs directory and make a copy of the Centrifugal Compressor folder.  Rename the directory to InletDuct.  In the newly created directory open CentrifugalCompressor.AGF.  Change NHT to 102 and then modify the endwall definition to include the bolded line shown below.

> XL        RL         XU           RU
-30.000000  2.054000   -30.000000   4.567700
-3.870300   2.054000   -3.760100    4.567700
-3.727196   2.007644   -3.637952    4.535681
-3.583492   1.963179   -3.515567    4.504576

Next, change the upstream boundary specification to

-15     2.05400 -15    4.56770

Save the modifications and close the .AGF file.  Running Code Wand to generate the mesh will result in an upstream boundary as shown below.

In order to avoid generating a mesh with such extreme twist, the mesh we be broken up into two stages: an upstream duct and the downstream impeller.  The simulation will then be conducted as a multistage simulation.

Create the .AGF file for the Duct

In order to create the .AGF file for the duct, a copy of the compressor .AGF file should be made and renamed to Duct.AGF.  This new file should be opened and the following parameters set to zero: NSPAN, TCLS, HCLS, LETE, NSPLT.  Next the outlet static pressure, PSOT, should be set to 12.75 to give a realistic value for static pressure at the interface.  Finally, the downstream location should be set to

*XHDW       RHDW       XTDW        RTDW
-1.970615   1.602151   -2.152797   4.239365

Modify the .AGF for the Compressor

The upstream location for the compressor should be set the same as the downstream location for the duct.  No other changes are necessary.

Modify the .WAND file to include the Duct

The .WAND file should be modified as follows to include the Duct

-3       6        1       1       2      0      3
81       41       1
20       13       41      0
2        0
*IUP     IDW      JPITCH
13       13       41
*IUP     IDW      JPITCH
13       13       41

Note: If Code Wand prints out a message stating that it is having difficultly locating the intersection between the two meshes, set the variable IFACE to 1 which will switch the interface from the location automatically calculated by Code Wand to the interface specified in the .AGF file.

Resulting Mesh

The resulting mesh should look similar to the following

George Fan
Date Created
2013-06-21 05:08:51
Date Updated
2013-06-21 05:21:09