Blade edge

Ü Impeller | Blade edge

The previously designed blade has a blunt leading and trailing edge (connection line between endpoints of suction and pressure side).

The blade edges are designed by specifying its thickness distribution. The representation of the blade thickness s is made on 15% of the straight blade length l on leading and trailing edge.

If the complete thickness distribution including leading or trailing edge was already designed in the Blade profile dialog, then the Edge position (transition from blade edge to blade suction/pressure side) has to be defined only.

In panel Geometry the blade edge shape can be selected:

(1) Simple

le_sim te_sim

The blade edge has a blunt end.

A straight line is calculated from the endpoint of suction side perpendicular to the mean line.

Trimmed on inlet/outlet causes the blade being trimmed on the corresponding inlet or outlet surface. The trimming is possible on the trailing edge only (or on the leading edge of turbines).

(2) Ellipse

le_ell te_ell

The blade edge is rounded elliptically.

The semi-axis ratio can be defined. One axis runs on the mean line, the other perpendicular.

(3) Bezier

le_bez1 te_bez1

For this purpose 4th order Bezier splines are used.

Points 0 and 4 representing the transition between the blade sides and the rounded blade edge. You can move these points only along the corresponding blade side. Bezier points 1 and 3 can only be moved on straight lines which correspond to the gradient of the curve in points 0 or 4, respectively in order to guarantee smooth transition from the contour to the blade edge. Bezier point 2 is not restricted to move - it has the most influence to the shape of the blade edge. Its horizontal position is calculated automatically in such way that the leading edge starts at position l=0 and the trailing edge ends at position l=blade length. The blade edges are designed at the first or last 10% of the blade length.

Axis-Symmetric results in symmetric geometry, i.e. points 0/4 and 1/3 have the same horizontal position and point 2 is on the middle line.

There are two different possibilities to determine the shape of the blade edge. In the Bezier curve option panel you can select between:

▪	Coupled linear: only blade edges of hub and shroud will be fixed, while anything between will be interpolated linearly

▪	Uniform: when designing blade edge on hub or shroud then Bezier points of all other leading edges have the same relative positions

Info area represent information of Blade edge design.

Display options only influence the graphical representation. For instance, the visibility of the smallest cross section can be toggled.

LE_frontal

The Frontal view (switch above the diagram) represents the designed blades in a frontal view, including diameters dN und d2.

Furthermore the smallest cross section between 2 neighboring blades is displayed.

Possible warnings

Problem	Possible solutions
The blade exceeds the meridional boundaries.
The orthogonal application of thickness on the mean lines can result in some blade position outside the meridional boundaries. As a result the model finishing option 'solid trimming' will probably fail.	Dependent upon the location of these areas one have to modify leading or trailing edge. If the leading edge (or the trailing edge of turbines) exceeds the meridional boundaries you can adjust it in the Meridional contour dialog only. Exceeding trailing edge (or leading edge of turbines) can be corrected by trim on in/outlet.
Error Trim Hub/Shroud on Blade: Check blade angles and thickness.
The orthogonal blade thickness is added to the blade mean line to create the blade sides. Thereupon these blade sides are trimmed on hub and shroud automatically. In some cases this trimming can fail.	Meridional contour: Align leading edge towards the direction of the hub normal. Blade profile: Change blade thickness. Mean line: Check m-t and leanangle direction
Distance between blade and hub is higher than tolerance of ...
Distance between blade and hub after default blade trimming is higher than tolerance. Import of geometry in a CAE-program via point based interface could fail.	Trim geometry with Modell-finishing (Solid trimming) and use a surface based export (IGES, STEP, STL) Meridional contour: Align leading edge towards the direction of the hub normal. Blade profile: Change blade thickness.

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