### 6.2.1. Duty and Aerodynamic Data Tab

Figure 6.1: Duty and Aerodynamic Data Tab

Frame 1: Duty

This frame contains: Overall pressure ratio, Mass flow, and Rotational speed. The pressure ratio can be total-total or total-static but then the Stage efficiency must be on the same basis.

Frame 2: Inlet Stagnation Conditions

This frame contains: The stagnation Temperature and Pressure at the inlet to the machine.

Frame 3: Inlet Gas Angle

This frame contains the options for specifying the upstream flow angle. The RMS angle is specified along with a Radial distribution from hub to shroud. The distribution options are:

- Constant angle

- Free vortex

- Solid body rotation

- Linear variation of Vw

If the linear variation of the whirl velocity is selected, the Vw ratio must also be specified.

Frame 4: Incidence at Shroud

This frame contains the option to either specify the Incidence at shroud directly, or indirectly by specifying the choke margin for the machine and letting the program calculate the appropriate incidence to achieve this value.

Frame 5: Stage Efficiency

You may specify Stage efficiency (Select User specify, then choose Isentropic or Polytropic). Alternatively, the program will determine an efficiency appropriate to the compressor duty by means of built-in correlations (if you select Correlations). There is a choice of three correlations:

- Casey-Robinson [1]

- Casey-Marty [2]

- Rodgers [3]

Casey-Robinson is a combination of the other two older correlations, combining data from high Mach number compressors with data from lower-speed industrial machines. However, you may want to use one of the two classic methods, so both of these have been retained as options.

The correlations provide “base efficiency” for the following class of compressor stage:

- large size (at least 300 mm impeller diameter)

- low axial tip clearance (2% of axial tip width or less)

- unshrouded impeller

- vaned diffuser

- machined vane surface

For smaller machines or machines with higher clearances, you may select Reynolds no. correction and/or the Tip clearance and shroud correction.

If Reynolds no. correction is selected, then you should review the Vane roughness options on the Geometry tab.

If Tip clearance and shroud correction is selected, then you should review Tip clearance or Tip Clearance/vane height on the Geometry tab.

Corrections for vaneless diffusers and shrouded impellers may be applied by selecting the appropriate option on the Geometry tab.

Frame 6: Impeller Isentropic Efficiency

Impeller isentropic efficiency may be specified by you or set as linked to stage, where the latter has been selected to come from the correlations.

Frame 7: Power Input Factor

Power Input Factor (PIF) may be optionally specified by you or calculated automatically from a correlation by Vista CCD.

Frame 8: Other aerodynamic data

This frame contains: Meridional velocity gradient, and Relative velocity ratio.

Meridional velocity gradient is the ratio of the shroud station meridional velocity to the RMS station and meridional velocity at the impeller inlet plane.

Relative velocity ratio is the ratio of the relative exit velocity to the inlet shroud relative velocity and so is a measure of impeller diffusion.

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