﻿ Impeller > Meridional contour > Primary flow path > Leading, Trailing edge

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Leading and trailing edge contour can be designed as:

Bezier curve
The Leading edge is defined by the position of the Bezier points.

Straight
The Leading edge is a straight connecting line between the endpoints on hub and shroud.

r = constant
The Leading edge runs on constant radius, i.e. parallel to rotational axis.

z = constant
The Leading edge runs on constant axial coordinate, i.e. perpendicular to rotational axis.

The trailing edge can not be designed, if Trailing edge fixed on outlet.

The position of the meridional blade leading edge on hub and shroud can be defined by its axial (z), radial (r) or relative position (rel.) optionally.

In case of Splitter blades each leading edge can be designed individually.

The radial-inflow gas turbine rotors and compressor impellers have straight leading edges by default, in case of radial-inflow gas turbines r = constant additionally.

Leading edge can be designed as a straight line by selecting Straight in the context menu of the curve (controlled by 2 Bezier points). Additionally the edge can be strictly axial or radial (z = const. or r = const, controlled by 1 Bezier point).

For centrifugal impellers having nq  10…30 the leading edge is often designed parallel to the z-axis. As the trailing edge is parallel to the axis too for such applications 2D-curved blades can be created. At higher specific speed nq or due to strength reasons the leading edge often is extended into the impeller suction area. Various diameters result in different leading edge blade angles - therefore 3D-curved blades are created. This leads to better performance curves, higher efficiencies and improved suction capacity for pumps.

The position of the leading edge should be chosen in a way that the energy transmission should be about equal on all meridional flow surfaces. A criterion is the approximately equal static moment S =  r dx of the meridional streamlines on hub and shroud between leading and trailing edge. In the Static moment section the corresponding numerical values are displayed. Both ends of the leading edge should be perpendicular to the meridional contours of hub and shroud if possible. To obtain equal static moments on hub and shroud the trailing edge is often not parallel to axial direction - particularly at higher specific speeds (mixed-flow impellers).

The leading edge can be designed by a 4th order Bezier curve. Regarding the Bezier points, the properties are similar to the hub/ shroud curves. The only difference is the manipulation of the end points, which are located on the hub/ shroud curves always. The position of the leading edge always appears at the same relative position in a primary CFturbo design but this not mean to be a suggestion.

## Leading/Trailing edge fixed on ...

The leading/trailing edge is fixed on meridional inlet/outlet and can not be designed.

Uncheck this option to detach the leading/trailing edge from meridional inlet/outlet and design its position and shape independently.