## 6.3. Viewing the Results

The results are shown in the Vista Centrifugal Compressor Design dialog box, which you can apply by editing the Blade Design cell of the Vista CCD system.

To compute an impeller design, click Calculate. The Results tab is then automatically made visible (Figure 6.4: Results Tab) and the numerical results appear in its field.

Figure 6.4: Results Tab

The results are arranged in four sections:

- Input data and derived parameters

- Impeller leading edge

- Impeller exit

- Overall performance

At the three radial locations of hub, RMS and shroud, the Impeller leading edge section shows the principal aerodynamic and geometric data. The Impeller exit section shows aerodynamic and geometric data at the impeller tip. The Overall performance section includes specific speed, flow coefficient, stage loading, and other significant performance quantities.

The following table shows definitions for the parameters on the Results tab.

Table 6.2: Definition of Parameters on Results Tab

Abbreviated name | Parameter | SI units | Imperial units
--- | --- | --- | ---
Input data and derived parameters
Mass | Mass flow rate | kg/s | lb/s
N | Machine rotational speed | rpm | rpm
P0out/P0in | Total pressure ratio | — | —
Eta Poly | Polytropic stage efficiency | — | —
Eta Isen | Isentropic stage efficiency | — | —
Eta Imp | Isentropic impeller efficiency | — | —
T0in | Inlet stagnation temperature | K | °F
P0in | Inlet stagnation pressure | kPa | psi
Beta'5 | Blade backsweep angle | deg | deg
W ratio | Relative velocity ratio | — | —
Rgas | Gas constant | J/kg-K | btu/lb-°F
Gamma | Ratio of specific heats | — | —
Nu | Kinematic viscosity | m2/s | ft2/s
Main | Number of main vanes | — | —
Inter | Number of splitter vanes | — | —
Thub | Impeller hub thickness | mm | in
Tshr | Impeller shroud thickness | mm | in
Alpha3 | Inlet flow angle | deg | deg
PIF | Power input factor | — | —
k/h | Tip clearance to blade height ratio at outlet | — | —
RESULTS
Impeller leading edge
Vm ratio | Meridional velocity ratio at impeller inlet | — | —
Vw ratio | Whirl velocity ratio at impeller inlet | — | —
M_rms | RMS Mach number at impeller inlet | — | —
V_rms | RMS absolute velocity at impeller inlet | m/s | ft/s
A_throat | Throat area at impeller inlet | mm2 | in2
H0 | Total enthalpy at impeller inlet | kJ/kg | btu/lb
s | Specific entropy at impeller inlet | kJ/kg-K | btu/lb-°F
Inclination | Inclination angle of leading edge | deg | deg
Values at the impeller leading edge hub, rms, and shroud positions
Dia | Diameter | mm | in
Vw | Whirl velocity | m/s | ft/s
Vm | Meridional velocity | m/s | ft/s
Mrel | Relative Mach number | — | —
Beta | Relative flow angle | deg | deg
Inc | Incidence angle | deg | deg
Beta' | Blade angle | deg | deg
Impeller exit
Dia | Diameter at impeller exit | mm | in
Tip width | Distance between hub and shroud at the impeller exit | mm | in
P0 | Stagnation pressure at impeller exit | kPa | psi
P | Static pressure at impeller exit | kPa | psi
T0 | Stagnation temperature at impeller exit | K | °F
H0 | Stagnation enthalpy at impeller exit | kJ/kg | btu/lb
s | Specific entropy at impeller exit | kJ/kg-K | btu/lb-°F
U | Blade speed at impeller exit | m/s | ft/s
M_U | Blade Mach number at impeller exit | — | —
M_rms | Mach number at impeller exit | — | —
W_rms | RMS relative velocity at impeller exit | m/s | ft/s
V_rms | RMS absolute velocity at impeller exit | m/s | ft/s
Alpha_rms | RMS absolute flow angle at impeller exit | deg | deg
Beta_rms | RMS relative flow angle at impeller exit | deg | deg
W ratio modified | Relative velocity ratio with the modified leading edge location | — | —
Overall performance
Ns | Specific speed | — | —
phi | Flow coefficient | — | —
DelH/U2 | Loading parameter | — | —
m/mch | Choke ratio | — | —
m/mch_a | Annulus choke ratio | — | —
power | Power | kW | hp
Re tip width | Reynolds number using impeller exit tip width as the defining length | — | —
Re tip dia | Reynolds number using impeller exit diameter as the defining length | — | —

The efficiency correlation selected on the Geometry tab determines which chart is displayed on the Efficiency Chart tab at the bottom-right of the dialog box. One of the three charts shown in the following figures will be displayed. The current design is indicated by the circle symbol in each case.

Figure 6.5: Casey-Robinson stage efficiency correlation

Figure 6.6: Casey-Marty stage efficiency correlation

Figure 6.7: Rodgers stage efficiency correlation

In Figure 6.5: Casey-Robinson stage efficiency correlation, the legend shows values of tip speed Mach number, . In Figure 6.7: Rodgers stage efficiency correlation the legend shows values of stage pressure ratio, R. A sketch of the meridional view of the designed impeller appears in the Impeller Sketch tab at the bottom-right of the dialog box.

Figure 6.8: Impeller sketch

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