Meridional contour

Ü Impeller | Meridional contour

The design of the meridional contour is the second important step to design the impeller.

Graphical elements can be manipulated not only by the computer mouse per drag and drop but also by using context menus. To this end a right click on the appropriate element is necessary. Doing so the mode of the leading edge can be changed as well as the coordinates of Bezier points for example.

Meridian_Popups

Hub and shroud can be designed as:

•	Bezier curve The curve is defined by the position of the Bezier points. ¢ Details

•	Circular Arc + Straight line The curve consists of a circular arc and a straight line. ¢ Details

•	Straight line The contour is defined by a straight line between start and endpoint.

•	Polyline The curve is fixed and cannot be modified interactively. Import of point sets from file is possible (Load polyline).

Leading edge 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.

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

Radial ventilator impellers are designed simply by arc and line by default (Circular Arc + Straight line), all other impeller types in Bezier mode (Bezier curve). The turbine rotors and compressor impellers have straight leading edges by default, in case of turbines z = const. additionally.

Special context menu features:

•	On the endpoints of hub and shroud the complete geometry can be shifted optionally (Shift complete geometry). Hence the geometry can be positioned on a specific axial position.

•	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 the panel General curve mode you can set the mode of hub and shroud simultaneously. But Bezier- and Arc+Line mode can be used in a mixed way too using the context menu of the curves.

meridian_prog

In the panel Progressions diagrams the following curves are displayed:

Curvature

·	Static moment

·	Area progression

It can be accessed by the tab on the right side of the diagram where the dialog is docked. When the dialog is open, it can be pinned on or undocked, for moving it. In undocked state the transparency of the dialog can be adjusted by the track bar above.

The static moment is the integral of the curve length (x) in the blade area multiplied by the radius (r). It should be similar at hub and shroud:

In the Display Options panel some graphical representations can be activated for illustration:

meridian_netz

Grid
for later blade design

meridian_kreise

Area circles
for calculation of cross section area

In the Information panel you can find some numerical values of above mentioned quantities.

Possible warnings

Problem	Possible solution
The blade exceeds the meridional boundaries caused by the blade thickness. Please check the meridional leading edge position.
The warning indicates that some parts of the blade leading edge are outside the meridional dimensions of the component. The leading edge position is defined in the meridional contour design – this is the start point of each blade mean line. To this mean line the blade thickness is added in orthogonal direction. If the mean line starts close to the inlet and the blade angle is low then small parts of the blade could be outside of meridional inlet to outlet region. The CAD model remains valid in general, only the “Solid trimming” in the Model finishing will fail due to this problem.	Move the meridional leading edge slightly away from the meridional inlet in the Meridional contour dialog.

Problem

Possible solution

The blade exceeds the meridional boundaries caused by the blade thickness. Please check the meridional leading edge position.

The warning indicates that some parts of the blade leading edge are outside the meridional dimensions of the component.

merLE_warning

The leading edge position is defined in the meridional contour design – this is the start point of each blade mean line. To this mean line the blade thickness is added in orthogonal direction. If the mean line starts close to the inlet and the blade angle is low then small parts of the blade could be outside of meridional inlet to outlet region. The CAD model remains valid in general, only the “Solid trimming” in the Model finishing will fail due to this problem.

Move the meridional leading edge slightly away from the meridional inlet in the Meridional contour dialog.

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