Blade properties

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Blade properties

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► STATOR | Blade properties

In principle, the same features are available as for the blade properties of impellers.

To support the selection of a suitable blade count a separate dialog can be used, which can be started by pressing the button right beside the edit field.

The outlet angles αTE are input values for most of the blade types according to the desired change of flow direction. Slip models are not available for stators. Some angle oversizing should be considered if necessary.

Two additional special blade shapes are available for "Radial diffuser" type stators (see Main dimensions):

1. Log. Spiral + Straight 2D

The inlet section of the vanes without overlapping is noneffective and configured as a logarithmic spiral (similar to spiral casing).

The diffuser part in the overlapping area is straight. The transition point between these areas can be moved along the logarithmic spiral curve (see mean line).

2. Circular + Free-form 2D

The inlet section of the vanes without overlapping is configured as a circular arc with the boundary conditions inlet radius r3, inlet angle α3 and ideal throat width a3.

The diffuser part in the overlapping area is designed by a Bezier curve with optionally 2 (straight), 3 or 4 Bezier points (selectable by context menu). The transition point between these areas can be moved along the circular arc curve (see mean line).  

Calculation of throat width a3 can be done using the conservation of angular momentum (const. swirl) or a specific deceleration ratio alternatively:

a) Constant swirl

Throat width corresponds to the dimensioning in accordance with the conservation of angular momentum, whereat the deceleration is increased by using the factor fa3 (1.1...1.3).

b) Deceleration

Alternatively one can use the deceleration ratio c3q/c2 (0.7...0.85) for throat width calculation.

 

Trailing edge angle αTE is a result of mean line design for these special blade shapes and therefore cannot be specified explicitly ("var.").

3. Straight 2D (axial)

A diffuser opening angle ϑ is calculated and displayed for information in accordance to Bohl with:

,

where a4 and  a5 are LE and TE blade passage distance (expressed by equivalent diameters) and l is the mean line length.

Warnings

Problem

Possible solution

A reasonable thermodynamic state could not be calculated.

[ for compressors and turbines only ]

The dimensions might be too tight for the specified mass flow and inlet conditions. The chosen blade angles might also yield this state.

Increase the dimensions (width etc.), change blade angle or change the Global setup (e.g. decrease mass flow).

Diffuser opening angle bigger than 10°. Flow separation possible.

[ for Straight 2D (axial) only ]

The diffuser opening angle is to big and might give room for flow separation.

Change αBLE, s1, s2, LE or TE radius (in meridian)