﻿ Impeller > Mean line design > Blade properties

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## Absolute and relative flow

 Absolute velocity Relative velocity Rotational speed

Fundamental kinematic equation
of Turbomachinery

## Significant cross sections

 Index Position 0 just before leading edge 1 just after 2 just before trailing edge 3 just after

Axial impeller

Pump, Fan, Compressor

Gas/Hydro turbine

## Specification of number of blades

 Pump 3 ... 7 Wastewater: 1 ... 3 Barske (low nq): 12 ... 24 Inducer: 1 ... 3 Fan 6 ... 10 Squirrel cage: 30 ... 60 Compressor Depending on blade exit angle ß2: •12 for ß2≈30° •16 for ß2≈45°...60° •20 for ß2≈70°...90° Radial-inflow gas turbine 12 ... 20 Axial gas turbine 30 .. 70 (100) Axial compressor 20 .. 40 Francis turbine 6 .. 16

The recommended number of blades according to Pfleiderer is displayed as a hint at the information image [ for centrifugal & mixed-flow pumps, fans, compressors only ]:

with kz = 6.5 ... 8.0 for compressors, else 5.0 ... 6.5.

The recommended number of blades using the Zweifel work coefficient is displayed as a hint at the information image [ for axial gas turbines only ]:

with Δz the axial chord length and dav the average impeller diameter.

The Zweifel work coefficient is in the range of ψ = 0.75..1.15 and is specified in the approximation functions.

## Information

In the right panel some information are displayed which result from calculated or determined values:

### (1) Velocity triangles

The velocity triangles of inflow and outflow are displayed.

Continuous lines represent flow velocities on hub (blue) and shroud (green).

Velocities directly before and behind blade area are displayed by dashed lines to show the influence of blockage in the flow domain.

Furthermore the blade angles are displayed by thick lines in order to see the incidence angle on the leading edge and the flow deviation caused by slip velocity on trailing edge.

### (2) Values

Numerical values of velocity components and flow angles are displayed in a table. A short description is at mouse cursor too:

 z Axial position d Diameter αF Angle of absolute flow to circumferential direction βF Angle of relative flow to circumferential direction u Circumferential velocity cm Meridional velocity  (cm=wm) cu Circumferential component of absolute velocity cr Radial component of absolute velocity cax Axial component of absolute velocity c Absolute velocity wu Circumferential component of relative velocity: wu+cu = u w Relative velocity τ Obstruction by blades (see below) i Incidence angle: i = β1B - β1 δ Deviation angle: δ = β2B - β2 w2/w1 Deceleration ratio of relative velocity c2/c1 Absolute velocity ratio ΔαF Abs. deflection angle: ΔαF= αF2 - αF1 ΔβF Rel. deflection angle: ΔβF= βF2 - βF1 φ=ΔβB Blade camber angle: φ=ΔβB= βB2 - βB1 γ Slip coefficient Δ(cu·r) Swirl difference T Torque H/Δpt Head/Pressure difference (total-total)

### (3) Default ßB, mean line design only

Default blade angles for the optimal Free-form 3D blade shape is displayed compared to the currently specified/ calculated angles. Deviations from default values are marked in red color. Default blade angles are calculated based on