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► PROJECT  General  Performance prediction
The Performance prediction is an empirical based estimation of the performance map of the machine.
The performance prediction is not available for
•incomplete impellers
•impellers in "Manual dimensioning" mode (see Main dimensions/ Setup)
•axial gas turbines
Two approaches are used to estimate the characteristics:
•Euler: Losses are estimated and subtracted from the theoretical Eulerline.
•Casey/Robinson: Characteristics will be derived from similarity considerations. For details see Casey/Robinson. This model is applicable for compressors only.
Please note: This is an estimation. The actual performance may differ from the prediction.
A performance curve of the current design is estimated on the basis of the EulerEquation:

and 

respectively. 
In these and all the following equations all variables are averaged values. E.g. the circumferential velocity u2 is calculated with an average impeller diameter dM2 that is the impeller diameter d2 for centrifugal impeller and the area averaged diameter for axial impeller respectively. The latter reads as:
.
All types of turbo machines have in common: The characteristics can be displayed in a diagram with dimensions as well as without dimensions.
Variable 
Pump 
Fan 
Compressor 
Gas Turbine 
Hydro Turbine 
H 
head 
 
net head 

Δp 
pressure difference (totaltotal) 

Δpts 
 
pressure difference (totalstatic) 
 



ψ 
work coefficient 






H/Hopt 
head ratio 
 
head ratio 

Δp/Δpopt 
total pressure difference ratio 

πtt 
 
pressure ratio (totaltotal) 
 

πts 
 
pressure ratio (totalstatic) 
 

η 
efficiency 

η* 
efficiency incl. motor 
 

ηV 
volumetric efficiency 
 
volumetric efficiency 

P 
required driving power 
 
power output 








Q 
volume flow 






φm 
meridional flow coefficient 




φ 
flow coefficient 



 

Q/Qopt 
flow ratio 

Qt 
 
volume flow total 
 





mass flow 


 
reduced mass flow 
 




 
corrected mass flow 
 


All combinations of flow and energy variables are possible.
It is common practice in the case of gas turbines  contrary to all other type of turbo machines  that the flow variable is given as a function of the energy variable. Beyond it characteristics of different rotational speeds will not be displayed over the whole theoretical pressure interval but only piecewise.
The choice of the variables is to be made in the tab "Variables".
For comparison purposes with the present design saved designs can be loaded (soft button"configure").
On the right hand site in the panel information some design point information can be found. Beyond it also the mass flow (or equivalent) for the tangential (shockless) flow towards the leading edge of the impeller blades as well as its relative deviation from the design point is given. The value of the shockless flow is also represented as a vertical line in the performance diagram. The visibility of that line can be toggled by the display options (lower corner in the left).