Screw Impeller Example

[dave_w]

Hi,

I've searched around for an example of a screw impeller I could re-purpose. I'm not looking for a normal screw thread, though it might be similar to a self tapping screw. I've seen pictures of a pump which has an impeller similar to what I'm looking for by ppemawm (https://forum.freecadweb.org/viewtopic.php?f=24&t=11652), but no examples.

Anybody have a link I can follow?

Thanks!

Dave

[ppemawm]

Anybody have a link I can follow?

This is another example of a "screw" pump https://forum.freecadweb.org/viewtopic. ... 40#p363215.

The parametric model is for liquids only, but it may give you an idea how to get started on the work process.
Note that the model was created with an early version of 0.19. If you save this in a much later version the sketches are likely to break.
The file is included in the above link.

Questions or comments are welcome.

[chrisb]

Note that the model was created with an early version of 0.19. If you save this in a much later version the sketches are likely to break.

This shouldn't be a problem. But you cannot use sketches in files in 0.18 which were saved by a recent 0.19 version or higher.

[dave_w]

Thanks ppemawm and chrisb. I'll go and study this. Can't wait!

Dave

[dave_w]

ppemawm,

A question if I'm not imposing too much. How would I go about changing the diameter and length of the impeller? I can see how I can change the length and taper of the cone, but don't see how I can change the diameter of the blades and make the blades wrap along a longer cone. I can't quite follow some of the constraints, and I don't see dimensions I'm looking for.

Thanks. I'll work hard to not pester you.

Dave

[ppemawm]

I'll work hard to not pester you.

You're not. We are here to help.

How would I go about changing the diameter and length of the impeller...

and make the blades wrap along a longer cone?

This model is set up for common pump application parameters such as flow, speed, and inlet pressure (NPSHR). The physical dimensions are calculated from these parameters using the design constants. If you want to input specific dimensions then you have to delete the appropriate calculations in the variables table and replace those with your chosen values.

The blade wrap is controlled by the blade angle, solidity, and the blade number.

Please be advised that I sent you a PM with additional comments this morning US EDT.

[dave_w]

I think I posted a head exploding some months ago. Here I am again. I need to process this at a much slower rate.

Thanks Bill & Chris.

Bill, no, I hadn't noticed the PM until you said. I will go to it next.

Dave

[ppemawm]

head exploding... Here I am again.

I have simplified the model to be more suitable for your use. The variable input now consists of only geometry:

Parameter input should be self explanatory. The blade angle is with respect to the tangential direction at the outer diameter, OD.

The model may break if the parameters are not realistic, e.g. if the blade thickness is greater than the hub radius, the ID is greater than the OD, etc.

Incremental changes to the variables should be small to avoid flipping sketches or other strange things that may cause the model to break.

Capture.JPG (227.29 KiB) Viewed 2552 times

The model will accept 1 to 4 blades. Anything greater may give you unintended results.

Capture2.JPG (254.3 KiB) Viewed 2552 times

The model seems to be quite stable over a large range of all the variables as long as they make sense. If you change more than one variable it is probably safer to 'skip recomputes' and recompute manually after all the variables are defined.

Capture3.JPG (237.05 KiB) Viewed 2552 times

Generic Screw Pump.FCStd

(696.77 KiB) Downloaded 68 times

OS: Windows 10 Version 2004
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24276 (Git)
Build type: Release
Branch: releases/FreeCAD-0-19
Hash: a88db11e0a908f6e38f92bfc5187b13ebe470438
Python version: 3.8.6+
Qt version: 5.15.1
Coin version: 4.0.1
OCC version: 7.5.0
Locale: English/United States (en_US)

[dave_w]

Cool! Let me experiment.

Thanks Bill.

Dave

[Kunda1]

Nice!