Impeller design using FreeCAD

[ferris12]

Hi everyone,

I am trying to CAD impeller with elliptical leading edge in FREECAD and running into some issues. I figured out a way to make 2-dimensional blades with elliptical leading edges, but it is a bit cumbersome and was hoping if someone can propose a simpler way of getting this done. The blades are 2-dimensional (made through circular arc method shown in snapshot attached). To get the elliptical leading edge, I insert a point (P1) on the circular arc that is 6 mm from the point of the leading edge (P0) (blade thickness is 6 mm), and then I insert two additional points (P2 & P3) on either side of the arc (both these points are 3 mm from P1) and I use the symmetry constraint on the points P2 and P3 with respect to P1 and then make a line passing through P1, P2 and P3 (see Snapshot_1). Thereafter, I use the option of the arc of ellipse by center, major radius and endpoints to make an elliptical edge passing through P0, P2, and P3 (P1 is center, P0 becomes the point to denote the major radius, while points P2 and P3 are the endpoints). I then insert two additional points (P4 and P5) at the other end of the arc (see Snapshot_2). Thereafter, using the option of circular arc using endpoints and rim point, I make an arc joining points P1 and P4 and points P3 and P5, so there is a circular arc on both sides. To ensure that the two arcs remain parallel to the arc in the middle, I make two lines joining the middle arc to the arc on either sides and apply the constraints so that both the lines are perpendicular to the two arcs they join and that the length of each line is 3 mm (see Snapshot_3).

This does result in a fully constrained sketch, however, I find it a bit cumbersome. Eventually, I have to be able to code all this process for optimization study and was hoping if someone can propose a simpler way to get the same CAD of the blades.

Also, I want to close the blade trailing edge defined by the four edges (see Snapshot_4) so that the blade interior doesn't get meshed for simulation. I am not sure how to do that. Can someone please suggest how this can be achieved?

Apologies if this is a really long post. In summary, I was wondering if anyone can suggest a better way to CAD blades with elliptical leading edges than the one described above (especially one that is easier to code) and a way to close the blade surface at the trailing edge.
Any help is greatly appreciated!

OS: Windows 10 Version 2009
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24267 +148 (Git)
Build type: Release
Branch: Branch_0.19.4
Hash: 476ecf091941bead59b14e44afa6064d5a66afa3
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.3
Locale: English/United States (en_US)

[Shalmeneser]

I don't understand your explanations, but :
* why are you working with surface and not solid ?
* your 1st sketch should not depend on the fillet radius.
* your 2nd sketch is not closed or with one line : Sketcher_ValidateSketch + Highlight ...

Do you just need 2 arcs with same center and an ellipse at the end ?
try Sketcher_ConstrainTangent

[NewJoker]

Perhaps this workbench could help you: https://forum.freecadweb.org/viewtopic.php?f=8&t=62056