## 6.11. Predicting a Performance Map

An important requirement of the preliminary design of a centrifugal compressor is the calculation of a reliable performance map as a guide to the expected operating flow range and the sensitivity to speed variations when the design is completed. Such a performance map may be calculated using the Vista CCD (with CCM) system.

The resulting performance map is based on the following key non-dimensional parameters:

- The expected design point polytropic efficiency

- The power input factor

- The global volume flow coefficient

- The stage work coefficient

- The stage tip-speed Mach number

The predicted performance map is independent of any detailed geometry and shows the performance that may be feasible for a well-designed compressor exhibiting these key parameters. It is unlikely that the initial design produced by the upstream Blade Design cell will match this performance map without detailed modification of the geometry.

Note: Performance maps are not available with real gases.

Figure 6.9: Performance Prediction Module

Figure 6.9: Performance Prediction Module shows the user interface for the performance prediction.

The non-dimensional parameters, on which the calculation is based, are shown in the Stage Parameters section. These are derived from the upstream Blade Design cell and may not be edited. Likewise the data displayed in the Geometry section is also derived from the Blade Design cell and is included purely for reference purposes.

The data displayed in the Operating Conditions section is partially available for editing. If the Use Design Point Data check box is selected, you can modify only the number of speeds to be calculated with the remaining entries being derived from the upstream Blade Design cell.

Clearing the Use Design Point Data check box enables you to modify the minimum and maximum speed ranges so that you may obtain a more focused map over a limited range of speeds, enabling you to extend the map to show overspeed conditions. In addition, the inlet stagnation conditions are then also available for editing and could be used to assess the sensitivity of the performance map to variations in inlet temperatures and inlet pressures. Note that the design point is plotted as a datum point on the resulting performance map.

If the Performance Map cell becomes “out-of-date” with respect to the Blade Design cell (and the latter is up-to-date), then you can use the Refresh button to update all entries derived from the Blade Design cell. Calculations always start with an automatic refreshing of any derived entries.

The default setting for the performance chart is `Pressure ratio vs Mass flow`. By right-clicking the chart, you can select other types of comparisons from a context menu (Figure 6.10: Performance Chart Examples).

Figure 6.10: Performance Chart Examples

The performance chart itself features a menu bar that contains the following icons:

- Save

  This icon enables the current chart data to be exported as a comma separated variable (`*.csv`) file for import into 3rd-party tools such as Microsoft Excel.

- Maximize

  This icon enables the chart to be viewed in a full-screen view. The full-screen view contains a Restore down icon to restore the chart to its original size.

Release 18.2 - © ANSYS, Inc. All rights reserved.