<< Click to Display Table of Contents >> Parameters 

On page Parameters one has to put in or to modify parameters resulting from approximation functions in dependence on specific speed nq (see Approximation functions).
For details of how to handle the parameter edit fields please see Edit fields with empirical functions.
Parameter and efficiency values can be handled manually or can be switched to automatic update by the checkbox on top of the page. Then the default values are used always, even after design point modifications (see Global setup). 
If the automatic mode is not selected the current default values can be specified by one of the following options:
globally by the button on top of the page 

regionally by the default button within the Parameters or Efficiency region 

individually by the default button within the input field when selected 
The panel Parameters allows defining alternative values in each case for the calculation of the following rotor main dimensions: •suction diameter dS •rotor diameter d1 •inlet width b1 
For details of how to handle the parameter edit fields please see Edit fields with empirical functions.
The design concept is based on a mean flow area, therefore a mean blade angle βB1 as well as a mean incidence angle i has to be given. In order to yield best efficiency the angle of incidence should be 20..30°. The relative flow angle β1 based on these two parameters is:
.
One of the following parameters has to be specified for the calculation of the rotor diameter d1.
Work coefficient ψ (= pressure and head coefficient) 
▪dimensionless expression of the specific enthalpy ▪big → small d1 ▪Guideline ~ 2 
Flow coefficient φm 
▪dimensionless mass flow ▪in accordance to CordierDiagramm 
Tangential force coefficient ct = ψ/φm 
▪Coefficient of a flow force pointing in tangential direction 3 ... 4 Francis highspeed turbine 4 ... 8 Normalspeed turbine 8 ...10 Lowspeed turbine

Coefficient ratio cR = ψ/φm2 
▪Ratio of work to the square of the meridional speed 6 ...10 Francis highspeed turbine 10...12 Normalspeed turbine 12...30 Lowspeed turbine

Between the work coefficient ψ, the relative flow angle β1 and the tangential force coefficient ψ/φm there is the following relation:
At a relative flow angle of β1= 90° the work coefficient becomes ψ = 2. In this case the work coefficient should not be chosen as a design parameter in the tab sheet Parameters. Otherwise one has no influence on the meridional flow coefficient and therefore meridional flow, see last equation.
For all further geometric variables guess values have to be given:
Diameter ratio d2/d1 
~0.5 
Meridional acceleration 

Meridional acceleration (suction side) cmS/cm2 Diameter ratio dS/d1 
~0.7 
Diameter ratio dH/dS 
~0.3 
There are three modes for the definition of the hub diameter dH:
•Direct input in the tab sheet Dimensions (check box "Calculate hub diameter" deactivated)
•Combo box option "Diameter ratio dH/dS": automatic calculation with dH = dH/dS * dS.
•Combo box option "Diameter ratio d2/d1": automatic calculation with dH = dH/dS * dS. Here the diameter ratio dH/dS will be adjusted in a way that the guideline of the geometrical ratios will be met.
With option "diameter ratio dS/d1" for the dScalculation the option "Diameter ratio d2/d1" is not available.
In the group Efficiency the following efficiencies need to be given:
Design relevant
•Rotor efficiency ηtt (totaltotal)
Information only
•Mechanical efficiency ηm
Internal and mechanical efficiency form the overall efficiency (coupling efficiency):
PQ: (isentropic) Rotor power PD: Power output (coupling/ driving power) 
The rotor efficiency (or blade efficiency) ηtt describes the energy losses within the turbine caused by friction and vorticity. Friction losses mainly originate from shear stresses in boundary layers. Vorticity losses are caused by turbulence and on the other hand by changes of flow cross section and flow direction which may lead to secondary flow, flow separation, wake behind blades etc.. The rotor efficiency is the ratio between the actual specific work Y and the specific work at loss less transmission:
The mechanical efficiency mainly includes the friction losses in bearings and seals:
(rising with impeller size)
If the check box "Use η for main dimensions (otherwise for βB1 only)" is set, then main dimension calculation is done on the basis of Δh=Δhis·η. Otherwise Δhis  the isentropic specific enthalpy  is used.
In the right panel of the tab sheet Parameter some variables are displayed for Information:
actual Power PD 
PD = PQ·ηttSt 
Power loss PL 
PL = PQ  PD 
Flow Q 
calculated with total density in the outlet: 
Total pressure inlet pt1 
pt1 = π⋅pt2 
Pressure ratio totaltotal 

Pressure ratio totalstatic 

Stage efficiency totaltotal 
ηttSt 
Efficiency totalstatic 
ηts 
Polytropic efficiency 
(n .. polytropic exponent κ .. isentropic exponent) 
In general for cost reasons singlestage & singleintake machines are preferred covering a range of about 10 < nq < 400. In exceptional cases it may become necessary to design a rotor for extremely low specific speed values (nq < 10). These rotors are characterized by large rotor diameters and low rotor widths. The ratio of free flow cross section area to wetted surfaces becomes unfavorable and is causing high frictional losses. To prevent this one may increase either rotational speed n or mass flow rate ṁ if possible. An alternative solution could be the design of a multistage turbine reducing the pressure drop of a singlestage. If especially high specific speed values (nq > 400) do occur one can reduce rotational speed n or mass flow rate ṁ if feasible. Another option would be to operate several singlestage turbines  having a lower nq  in parallel.
Please note: CFturbo® is preferably used between 10 < nq < 150 – radial and mixedflow rotors.