Spiral development areas

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Spiral development areas

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► VOLUTE | Spiral development areas

The spiral development areas can be designed and calculated in this dialog box.

Spiral contour

The wrap angle can be defined - default value is 360°.

Design rule

You can choose between two kinds of Design rules for volute calculation. Velocity-based rules are Pfleiderer and Stepanoff. Geometry-based rules are defined by outer radius, cross section area or ratio of area to center of mass.

¢ Details Design Rule

Cut-water compensation

In panel Cut-water compensation you can specify parameters for the cut-water design.

¢ Details Cut-water compensation

Circular arc approximation

For spirals with rectangular or trapezoidal cross sections, an approximation by circular arcs is provided. The arcs are optimized with respect to the maximal deviation from the initial contour, which is defined by the design rule. Information about the resulting circular arcs (e.g. midpoints, radii and angles) are shown in the "informational values" view. In addition, their details are given as hint of the arc in the diagram if enabled in display properties.

Note that further calculations are based on the initial contour.

Possible warnings


Possible solutions

Spiral contour could not be calculated exactly.
Check geometry and "Volute/ Inlet definition".

Spiral sections cannot be calculated due to unusual inflow direction or volute cross section definition.

Too narrow cross section shape can result in unreasonable high height-width-ratio. Try to select another cross section shape.

Volute end cross section not sensible.
Check geometry and  "Volute/ Inlet definition".

The properties of the end cross section are not reasonable, e.g. the ratio H5/B5 is too low or too high.

Check the properties of the end cross section.

See also the hints to the error "It's not possible to calculate spiral contour exactly.".

Flow angle at volute inlet is too large.
Check flow properties of design rule.

Spiral sections cannot be calculated due to invalid reference parameters with a resulting flow angle of more than 70°.

For velocity-based design rules the flow angle at inner radius results from cm and cu. While cm is calculated from volume flow Qi

cm = Qi / (d b π),

circumferential velocity is set directly. Increase cu or reduce Qi to decrease flow angle.

tan(α) = cm / cu

Spiral contour calculation failed due to invalid inflow conditions.
Check "Volute/ Inlet definition".

Spiral sections cannot be calculated due to invalid inflow direction.

The flow angle on volute inlet should be small (<~45°, 90° is completely invalid). It can be checked in "Volute/ Inlet definition", page "Volute" right at "Values": Flow angle α. The inlet flow angle is defined by the previous component. If no previous component exists, the inflow angle is defined by "Global setup/ Inflow".

Angle of last cross section definition is higher than spiral wrap angle.

One or more cross sections are defined at positions φ > spiral wrap angle φ

Adapt circumferential position of the cross section definition ("Volute/ Cross section") or spiral wrap angle ("Volute/ Spiral areas").

Automated contour update active.
Cross section sizes are not fixed and adapt to external flow properties.

Spiral cross section extents are updated automatically if anything on the inlet side or any spiral properties are modified.

To fix the spiral cross section extents you could uncheck the "Automatic" calculation right top. Then you have to manually start the calculation if required.

Automated contour update NOT active.
Cross section sizes are fixed but may be inappropriate for external flow properties.

Spiral cross section extents 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.