Double Volutes are used to compensate asymmetric casing forces that are inevitable for Single Volutes. Their design can be activated in the initial volute Setup.
Double volutes are calculated analogously to Single Volutes. The blockage at splitter leading edge has to be compensated by splitter compensation (see parameters below), exactly like Cut-water compensation. Furthermore, the calculation of the outer contour is considering the geometry of the splitter (position, fillet-radius, thickness).
The inner radius of the splitter ra,II and thus the Inner area (II) at φ is given by the outer radius ra at φ-φSpl.
The Outer area (I) is calculated based on the Design rule for
* a constant flow rate defined by the splitter start angle (normally 50% of overall flow rate)
* starting from the splitter outside radius ri,I = ra,II + Δr.
For double volutes you can define additional properties of the spiral and splitter.
•The start angle φSpl is the angular position where the splitter starts. It also determines the splitter contour.
•The angular offset ΔφSpl can be used to achieve a radial offset without changing the contour.
•The thickness eSpl defines the distance between the inner and outer splitter contour.
•The compensation φSpl,C is used analogous to the cut-water compensation.
•The fillet radius defines the radial corner radius between spiral and splitter surface.
The progression diagrams contain curves for each part of the volute, like the area progression below.
Beside the default informational values separate values for inner and outer part of the volute are reported.
Furthermore 2 additional ratios are displayed:
•Expansion of outer volute (using end point of blue curve / start point of blue curve)
•Ratio of outer to inner throat (using end point of blue curve / end point of green curve)