Performance prediction

<< Click to Display Table of Contents >>

Navigation:  Menu > PROJECT > General >

Performance prediction

Previous pageReturn to chapter overviewNext page

► PROJECT | General | Performance prediction

The Performance prediction is an empirical based estimation of the performance map of the machine. Currently it is not available for axial turbines.

Two approaches are used to estimate the characteristics:

Euler: Losses are estimated and subtracted from the theoretical Euler-line.

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.

General

A performance curve of the current design is estimated on the basis of the Euler-Equation:

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:

.

Variables

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

Turbine

H

head

-

-

-

Δp

pressure difference (total-total)

Δpts

-

pressure difference (total-static)

-

ψ

work coefficient

H/Hopt

head ratio

-

-

-

Δp/Δpopt

total pressure difference ratio

πtt

-

-

pressure ratio (total-total)

πts

-

-

pressure ratio (total-static)

ηSt

stage efficiency

ηSt*

stage efficiency incl. motor

-

ηV

volumetric efficiency

-

P

required driving power

-

 

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 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".

Reference curves

For comparison purposes with the present design saved designs can be loaded (soft button"configure").

Information

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).