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.
*ENDWALL > 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
*XHUP RHUP XTUP RTUP -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
*ITYPE OUTYPE IGRID IPOSS ICLS IWAL IFAN -3 6 1 1 2 0 3 *MBLD KSPAN FUTURE 81 41 1 *IUP IDW JPITCH IFACE (OPTIONAL) 20 13 41 0 *NFILES IPLOT 2 0 FILENAME Duct.AGF *IUP IDW JPITCH 13 13 41 CentrifugalCompressor.AGF *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.
The resulting mesh should look similar to the following