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 Mangnan May 14, 2004 09:25

constant rotation speed

Hi Robin:

Thanks for giving me very useful advices in the topic --very confused problem,Please help me.I am confused in the your last message--You could add expressions for torque to your solver run and compute the rotation rate accordingly. However, what one would typically do is run a speed line and determine where the operating point falls.

What does the "determine where the operating point falls" mean? Could you explain it in detail or just take an example?

Best Regards, Mangnan

 Robin May 17, 2004 22:21

Re: constant rotation speed

Hi Mangnan,

If you have a fixed pressure drop, run multiple speeds and record the power output. You can then interpolate along this curve to determine at what speed you will get the desired power output.

Regards, Robin

 Mangnan May 18, 2004 05:38

Re: constant rotation speed

Hi Robin:

Thanks for your return! My model has no power output. Whether can I calculate the pressure drop and record it?Then I interpolate along this curve to determine at what speed I will get the desired power output.

Best Regards, Mangnan

 Robin May 19, 2004 10:16

Re: constant rotation speed

Hi Mangnan,

I haven't a clue what you are doing! You have no power output and don't know what your pressure drop is? What do you know about your system?

Regardds, Robin

 Mangnan May 19, 2004 23:01

Re: constant rotation speed

Hi Robin:

I am sorry that I did not decribe my model detailly.Now I supply it.There is a micro-rotor in a pipe. The pipe is vertical,the water get in from the pipe bottom.Then the rotor rotate freely in the pipe. The buoyancy on the rotor balance with the rotor's gravity.The rotor float in the pipe and rotate aroud the axis of pipe.It does not get to the pipe top.So there is no output from the rotor.

Best Regards, Mangnan

 Glenn Horrocks May 20, 2004 18:43

Re: constant rotation speed

Hi Mangnan,

I think I said this to one of your requests over a week ago, but it all comes back to ensuring you have zero net torque on the rotor. When there is zero net torque on the rotor it will rotate at constant velocity.

I suggest you set up your flow, driven by pressure, mass flow rate or whatever; and do a series of runs where you assume the rotor has different rotational velocities. For the simulations where the rotor velocity is too slow you will get a net torque accelerating the rotor, and for the simulations where you are too fast you will get a net torque decelerating the rotor. You can then interpolate to find the zero net torque speed - that is the speed at which the rotor turns at constant velocity for that flow field.

Also, am I correct in reading that your rotor floats in the fluid such that the axial position of the rotor is determined by the balance between the weight of the rotor causing it to sink against the fluid pushing it back up again? If this is the case then you have a far more complicated situation as the position (and stability) of the rotor in three dimensions will be determined by rigid body dynamics. This would be tricky to do - but interesting!

Regards, Glenn

 Mangnan May 22, 2004 04:08

Re: constant rotation speed

Hi Glenn:

Thanks for your return. (1)In my model,the rotor rotates in fixed position for a simplified problem. (2)An question.How to interpolate find the zero net torque speed? We know that interpolation needs two variables.One is rotational velocities.But what is anther?Could you tell me?Is the acceleration of rotor or net torque?If then, how to get them?I think it is not a easy job.

Best Regards, Mangnan

 Glenn Horrocks May 23, 2004 18:49

Re: constant rotation speed

Hi Mangnan,

Plot net torque against rotational velocity. Interpolate to zero net torque.

Glenn

 Mangnan May 26, 2004 21:22

Re: constant rotation speed

Hi Glenn:

How should I calculate the net torque?

Is the net torque of the rotor including the axial torque and radial torque?

Best Regards, Mangnan

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