<< Click to Display Table of Contents >> Blade properties 

► IMPELLER  Blade properties
Definition of blade properties is made in two steps:
(1) Blade setup
(2) Blade angles
Usual number of blades are:
Pump 
3 ... 7 Inducer: 1 ... 3 
Fan 
6 ... 10 
Compressor 
Depending on blade exit angle ß2: •12 for ß2≈30° •16 for ß2≈45°...60° •20 for ß2≈70°...90° 
Radial turbine 
12 ... 20 
Axial turbine 
30 .. 70 (100) 
Many blades  causing low blade loading  are related to higher friction losses. By choosing of fewer blades  leading to a higher blade loading  the hydraulic losses may rise due to increased secondary flow and stronger deviation between blade and flow direction.
The recommended number of blades according to Pfleiderer is displayed as a hint at the information image [ for centrifugal & mixedflow 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 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.
The span positions are illustrated as meridional lines in the Meridian diagram in the information area. By default the meridional lines are equally spaced between hub and shroud.
If the impeller has splitter blades then the shape of the splitter can be linked to the main blade optionally. If linked the splitter blades are truncated main blades. Otherwise the splitter blade can be designed completely independent.
In the right panel some information are displayed which result from calculated or determined values:
(1) Velocity trianglesThe 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) ValuesNumerical values of velocity components and flow angles are displayed in a table. A short description is at mouse cursor too:


(3) Default ßB, mean line design onlyDefault blade angles for the optimal Freeform 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
If the mean line design already exists in the component then these dependent angles are calculated automatically for information, otherwise the table cells remain empty. 

(4) MeridianThe Meridian with the locations of the spans is displayed in this diagram. Radial element blades For Radial element blades the number of spans is fixed to 11. Furthermore a Distribution exponent can be specified. This exponent has influence on the distribution of spans and herewith especially on the shape of the leading edge (turbine). For highly spatial curved blades the continuity of the blade surface can be influenced by this parameter. Impact: Distribution exponent = 1: spans uniformly distributed (default) Distribution exponent < 1: spans concentrated towards shroud Distribution exponent > 1: spans concentrated towards hub 