Impeller > Airfoil/ Hydrofoil design

► IMPELLER | Blade properties

Definition of blade properties is made in three steps:

Absolute and relative flow

Absolute velocity
Relative velocity
Rotational speed

Fundamental kinematic equation
of Turbomachinery

Velocity triangles

Radial impeller	Axial impeller

Specification of number of blades

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. The track bar on top of table can be used to get the values at any span. A short description is at mouse cursor too:

z	Axial co-ordinate
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 = βB1 - β1
δ	Deviation angle: δ = βB2 - β2
w2/w1	Deceleration ratio of relative velocity
ΔαF	Absolute deflection angle
ΔβF	Relative deflection angle
ΔβB	Blade deflection angle
γ	Slip coefficient
Δ(cu·r)	Swirl difference
M	Torque
Δpt	Pressure difference (total-total)

(3) Curves

Here blade angles as well as relative flow angles are displayed versus span.

Progressions of geometric parameters (angles):

β1/2	Angle of relative flow to circumferential direction
βB1/2	Blade angles at leading and trailing edge

(4) Criteria

Progressions of aerodynamic and airfoil parameters:

Re	Reynolds-number
l/t	solidity
DH	DeHaller critierion
ST	Strscheletzky critierion
DF01	diffusion number

Possible warnings

Problem	Possible solutions
Automated blade angles are active. Values may adapt to changing input parameters.
Stagger angles and chord length are updated automatically when input parameters are modified.	To fix stagger angles and chord length uncheck "Automatic" calculation. Then calculation must started manually if required.
Automated blade angles are NOT active. Values are fixed but may not reflect input parameters.
Stagger angles and chord length are not updated automatically if any input parameters are modified.	To be sure that all parameter modifications are considered you could switch to an automatic calculation by checking the "Automatic" option.
Swirl gradient violates Euler equation. Check blade angles and velocity triangles.
cu2r2 is lower than cu1r1 (turbines: cu2r2 is higher than cu1r1) resulting in energy transmission in the wrong direction (Euler equation of turbomachinery).	Recalculate and/or check stagger angles γ and chord length l, check cu-cm-specification or chosen profiles.
ΔβB1/2 (leading/trailing edge) = ... is larger than warning level of ...
Blade angle difference (highest - lowest value) at all spans exceeds the warning level (see Preferences: Warning level). The resulting blade could be highly twisted.	Check the resulting 3D blade shape and avoid high blade angle differences on spans if possible.
ΔβB (span) = ... is larger than warning level of ...
ΔβB = \|βB2 - βB1\| on one or more spans exceeds the warning level (see Preferences: Warning level). The resulting blade could be highly curved.	Check the resulting 3D blade shape and avoid high blade angle differences between leading and trailing edge if possible.
Blade angles βB1/2 cannot be determined. Thermodynamic state could not be calculated. Check main dimensions, meridional shape or global setup. [ for compressors and turbines only ]
The dimensions or meridional contour might be too tight for the specified mass flow and inlet conditions.	Increase the dimensions (width etc.), meridional contour or change the Global setup (e.g. decrease mass flow).