V0.19 The Power of Parametrics: A High Head Low Flow Centrifugal Pump

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V0.19 The Power of Parametrics: A High Head Low Flow Centrifugal Pump

Postby ppemawm » Sun Feb 09, 2020 9:33 pm

This is a follow-on to the parametric inducer model previously created for a client https://forum.freecadweb.org/viewtopic. ... 40#p363215.

This new model includes the impeller, diffuser passages, and a generic pump housing. The hydraulic design is best suited for relatively low flow and high pressure (or headrise) generally requiring rotational speeds greater than 50 or 60 Hz. The unsophisticated flow passages in the impeller and diffusion system lend themselves nicely to a parametric approach and mass customization of hardware. Literally thousands of efficient operating points can be accommodated by machining a single casting each for the impeller and the pump housing. The constant-lead inducer can be easily machined as well since it is quite similar to a screw thread.

The design rules for the impeller and diffuser were taken from Lobanoff & Ross, Centrifugal Pumps: Design and Application, pp. 161-194, 1985, Gulf Publishing Co. This parametric model is suitable for flows of 30-200 gpm, headrise of 250-2500 ft, and speeds of 5000-17,500 rpm. The high speeds can be obtained with a turbine, gearbox, or or better yet, a high speed AC motor with a variable frequency inverter.

Several screenshots are as follows with a few comments about the modeling process:

The modelling process begins by defining the input variables, design constants (rules) and the calculations deriving the geometry and pump performance estimates.

Asssembly4 > Add variable table was used in this example rather than a spreadsheet.

Once the variables are defined they can be conveniently used in sketches, placements, and expressions.
Picture1.jpg (107.4 KiB) Viewed 822 times
All of the constraints, major dimensions, and interface location of each part can be controlled with a top-level master sketch as shown in this image. Note also the ability to capture specific design intent, e.g. the basic shape of the impeller.

The dimensions intended to be parametric shown in light orange are directly calculated with expressions or taken from the Variable table.

A second master sketch could be added in the YZ plane to control the exit flange size and location if desired.
Picture2.jpg (81.16 KiB) Viewed 822 times
All of the bodies were created in-context by referencing the master sketch with carbon copies in a single Assembly4 file.

This image shows the optimum geometry which produces the highest efficiency at a desired flow, head, and optimum speed. The diffuser can be step drilled and taper reamed from the discharge.
Picture4.jpg (96.82 KiB) Viewed 822 times
This image shows the effect of changing the pump operating point and the number of blades demonstrating the power of using a parametric manufacturing model. Note the fully parametric changes in the exit diffuser required by the head and flow operating point for the given speed.
Picture5.jpg (108.62 KiB) Viewed 822 times
It is best to use manual recompute and disable auto recompute of the file (right click > skip recomputes at top of tree) especially when changing multiple input parameters to avoid breaking the master sketch. It is also possible to break the model by specifying parameter values outside of the intended range of parametrics. Usually, once the input is corrected, however, the sketch will 'heal' itself, otherwise all you can do is close without saving and reopen to recover the master sketch.

The file is too large (1.85 Mb) to attach, but if you would like to review it please contact me via PM.
Any questions or comments are welcome.

OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.19311 (Git)
Build type: Release
Branch: master
Hash: 120b69c74f7dac8c4fa6dbc0a7e10674bde9216c
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United States (en_US)
"It is a poor workman who blames his tools..." ;)
Posts: 98
Joined: Fri Feb 03, 2017 2:55 pm

Re: V0.19 The Power of Parametrics: A High Head Low Flow Centrifugal Pump

Postby m0n5t3r » Tue Feb 11, 2020 5:28 pm

Very cool, thanks for sharing! I tend to use a similar approach, but didn't come across the parameter table until now, it looks like a huge usability boost (better than opening the master sketch to change constraint values or selecting a spreadsheet and losing sight of the model).