Freeform blades have the highest flexibility - the mean lines of all blade profile can be designed directly.

For 2D blades and radial element blades you can design the hub mean line only, all other mean lines are calculated automatically due to the constraints of the blade shape.

 

In general the mean lines are represented by 3rd order Bezier splines. Constraints are:

 

Start angle φ0 defines the starting point of the mean lines. The absolute value is irrelevant, only the position of the mean lines to each other can be influenced. If all mean lines have the same starting point then the leading edge starts on the same angular position on all mean lines (radial leading edge). On panel Leading edge points you can select, if the position of points 0 of the mean lines is Constant, Linear or User defined.

 

Wrap angle Δφ can be specified numerically for inner (hub) and outer (shroud) meanline, in between the values are interpolated.

For continuous transition between the separate mean lines (blade surface), the matching points of each mean line have to be Coupled linear. If you deactivate this option then you can modify all mean lines independently, inclusive individual wrap angles Δφ.

 

 

CFturbo's primary design is fixing point 0 (leading edge) for all cross sections due to wrap angle and meridian coordinate m=0, while point 3 is determined by the meridian coordinate of the trailing edge (dm) and t=0.

 

In case of Splitter blades the design options depends on the link between main and splitter blades in the Blade properties. If Splitter blade linked to Main blade is activated there, the splitter blade is a shortened main blade. The blade- and wrap-angles are calculated automatically. Under Constraints the relative position of the splitter blade between two main blades can be adjusted. It couldn't be set on all profiles user defined like the Start angle φ0.

 

If main and splitter blades are not linked there are all degrees of freedom in design for both.

 

The m-t-view of the splitter blades is shown on a separate tab (Splitter blade (m-t)). Additionally the profiles of the contiguous blades are shown. By default  they are positioned relatively by their m-coordinate. That can be changed under Display options by selecting another Splitter to main position (m-t).

 

In case of Turbines the situation is vice versa: The leading edge is located at high meridional coordinates whereas the trailing edge is at zero.

 

The wrap angle φ is initially constant for all cross sections, but it can be modified individually. The wrap angle tremendously influences the blade angle progression (βB) along the mean line. Beta-progression can be viewed in a separate diagram.

 

Two points in the middle, 1 and 2, must be on a straight line at an angle of βB1 or βB2 to the horizontal in order to fulfill the boundary condition: β = dm/dt

The primary design shows points 2  at 1/4 of the wrap angle, and points 1 at 3/4.

 

Individual mean lines can be designed separately. If the linear coupling mode is active you can move and rotate the connecting line. The positions of Bezier points of all mean lines are modified correspondingly, to get uniform profiles. If you select a point of the inner cross sections you can move the entire connecting line. On the other hand, if you select any point of the inner or outer cross sections, you can move this point along the related straight line. This line is given by βB1 or βB2 (rotation of the connecting line). Points 0 (leading edge) and 3 (trailing edge) can only be moved horizontally (m=const). Points 3 can be moved interactively (move/ rotate trailing edge). Points 0 (leading edge) can moved only by modifying wrap angles in table Boundary conditions.

By activating the Central Bezier point option a flexible central point is added for representing each mean line by an 4th order Bezier spline. As a result more flexibility is provided.

 

In panel Blade angles the blade angles βB1, βB2 (see Blade properties) and the angles in x,y-plane (frontal view) βB1,xy, βB2,xy are stated for information.

In panel Blade information the angles of overlap of neighboring blades φB and the incidence angle i (see Blade properties) are stated.

 

 

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