10 Replies Latest reply on Dec 2, 2013 3:01 AM by Luc Spruyt

# Determine rotation of flowmeter rotor

Dear members,

I'm working on a project with flowmeters.

The question is, what is the best design for the worm in order to get te best efficiency in a flow meter.

I've added a picture to show the model.

I know it is possible to determine equilibrium rotation of a propeller in ambient flow.

Set a goal for the torque around the axis for all the faces of the propeller and see if it's driving or resisting.

I did some testing to see the difference between selecting ALL faces or just ONE as a " sensor " face to determine the "+" or "-" vallue of the torque.

The vallues are quit different and therefore I'm doubting my analysis.

Question:

- Is it neccesary to select ALL the faces of the rotor?

- Is there an alternative for placing a sensor goal to measure the equilibrium rotation?

Luc Spruyt

3D Assist

• ###### Re: Determine rotation of flowmeter rotor

Best efficiency would be achieve by calibrating a low solidity rotor - that would be my guess - don't have a worm gear with high solidity (100%).

Flow sim is not hte best tool for this analysis. The rotating frame approximation is not well suited to this problem. However an iterative scheme (trail and error) may get you in the ball park but I am not even sure what you would look to compare the assumed rotor speed to the actual rotor speed to see when it would be balanced. It isn't initially obvious to me at least. The "efficieny" would be the pressure drop that the meter induces across it. You can always assume the rotor speed is the same as the pitch of the worm and go from there but that seems a bit dicy.

• ###### Re: Determine rotation of flowmeter rotor

Hello Bill,

The thing is I need a proper goal/sensor to determine wether the rotor is not causing any obstruction.

And there will be obstruction when the RPM of the rotor is much to high or to low.

The spiral/worm in front of the rotor is fixed and guiding the flow to achieve maximum thrust on the rotor.

I would like to see the effect of changing the angular twist of the spiral.

It would effect the RPM and therefore I need a goal to measure this change.

I am willing to run several trail and error analysis as long as I can rely on the goal/sensor value.

The advice of setting up a surface goal and measure driving or resisting troque is ok with me. (article ID x344 26-12-2006)

Is it neccesary to apply the surface goal on ALL the surfaces or will 1 surface do the job.

Eventually the only thing we need to know is if the torque will be "+" or "-".

Or is there another work around for this matter.

Is there another way to set up a reliable goal !!

Thanks again.

Regards Luc

• ###### Re: Determine rotation of flowmeter rotor

I think you are violating too many assumptions of the frozen rotor approach that flow uses. Would suggest setting up a know case before you try design with flow. Also, work with your var on this. I wouldn't spend too much time on it until you can confirm the application is applicable to frozen rotor.

The limitations are well defined in the kb, tech ref and solving eng problems docs.

If you're good with the ball park that bill describes, go for it. But don't be blown away by weird inconsistent results. If you want an opinion, build a sample model that you can post with your questions.

• ###### Re: Determine rotation of flowmeter rotor

Hi Jarred,

Ik do have a know case according to tests with the flow meter.

I know that with 1200ml the rotor will spin appr. 13725 rpm.

This with a 180 degr. spiral worm.

What will the rpm of the rotor be if we change to a 135 degr. spiral.

For sure it will have less pressure drop than the 180 degr. version of the worm.

Wich is good.

But how will it affect the rpm's of the rotor.

There are some things I don't understand ( my english...)

What do you mean with ...work with your VAR(?) on this..

I'll post a zip file with a sample and the main question.

Thanks for the support

• ###### Re: Determine rotation of flowmeter rotor

Var is your software provider, they provide you support and training on the tool

Frozen rotor is the method of moving the fluid around the part vs moving the part through the fluid, or moving mesh.

Have you confirmed your know condition works properly in flow?

• ###### Re: Determine rotation of flowmeter rotor

OK clear.

My software reseller is a good partner.

Though I thought this forum would be more helpfull and get me answers more quick.

The 1200 ml and 13750 rpm gives a clear analyses without warning and troubles.

Cut plots and flow trajectories looked plausible.

• ###### Re: Determine rotation of flowmeter rotor

If the flow analysis looks ok, is he question just how to measure the torque? The answer is select all of the faces. There is a really good example in the kb on this. It is the same concept as the selections for drag and lift.

However, as we discussed, check that your application of rotating regions is correct first.

• ###### Re: Determine rotation of flowmeter rotor

Thanks again Jared!

Two last questions and then I'm very pleased.

- What do you mean with the KB for the example? (sorry dutch guy)

- How can I check whether the rotor is Frozen Rotor proove?

Enjoy the day.

Regards

Luc

• ###### Re: Determine rotation of flowmeter rotor

Customerportal.solidworks.com > knowledgebase > search for rotating or rotation and read up

Then browse to your install directory > lang > English > docs and look at the sections on rotation in the technical reference and the solving engineering problems doc

• ###### Re: Determine rotation of flowmeter rotor

Ok Jared,

Thanks again.

I'll get into it.

Learned a lot.

Regards.

Luc