The ERCOFTAC diffuser case study, geometry and base case set-up
Maryse Page, Hydro Quebec, Montreal, Canada
The ERCOFTAC diffuser is an axi-symmetric expansion of a circular pipe. Figure 1 shows a 3D view of the geometry. In this case an artificial extension of the domain has been added at the end of the expansion. In the experiments it was open air after the end of the expansion. The inlet is in this case located at the end of the honeycomb that was used in the experiments to generate a plug flow with a solid body rotation/swirl.
File:ERCOFTAC base case 3dView crop.jpgFigure 1. 3D view of the ERCOFTAC diffuser base case.
Figure 2 shows the definitions of the parameters rIn, diffuserLength, extensionLength and openingAngle.
Figure 2. 2D view of the ERCOFTAC diffuser base case.
Figure 3 shows the cross-sections A-G, that are used when making the mesh. The cross-sections refer to:
A: The outlet of the artificial extension. B: The outlet of the diffuser. C: The inlet of the diffuser. D: A measurement plane. E: The edge of a rotating part of the wall. F: The edge of a rotating part of the wall. G: The end of the honeycomb.
The number of cells in the z-direction between each cross-section is specified using parameters zABnumberOfCells (for the number of cells between cross-sections A and B), etc.
Figure 3. Planes used in the parametrization.
Figure 4 shows the parameters used for defining the O-grid throughout the domain. The figure is an example of the grid plane at cross-section A. The number of cells in the radial direction in the O-grid is specified using parameter rNumberOfCells, and the number of cells in the tangential direction is specified using parameter tNumberOfCells. The center block will get tNumberOfCells in both directions.
The radius of the cross-section is specified using parameter rA. The radius of the corners of the center block, relative to rA, is specified using the parameter rRelA, which should be between 0 and 1.
Figure 4. O-grid used in the parametrization.
