Rotor Stator Simulation Power curve issue for different RPM

AS_Aero · October 10, 2018, 10:45

Hi

I am using rotor-stator simulation with Frozen rotor and RANS computation with different RPM values and constant velocity. I wanted to calculate the power of the rotor and plot the power curve so that I can select the optimum RPM of the turbine. But unfortunately I am getting some crazy values like

RPM Power
100 0.5686 W
200 0.5743
300 0.035
500 1.8
600 2.91
800 6.59

For RPM of 100 the tip speed is 4m/s since rotor diameter is 750mm

So now the issue is I am not getting the parabolic curve where the Power reduces for increased RPM. So now my doubt is if I am making some mistake in this ? I have attached the power monitor for differert RPMs and for 300 the plot looks wierd as well, I havent changed anything here, except the rpm.

I have attached the image of the power expression and the rotor domain setup

ghorrocks · October 10, 2018, 19:27

Either you have a mistake in your modelling approach or your device's operating point is faster than 800rpm. Over to you to work out which.

AS_Aero · October 11, 2018, 04:17

The thing is its a quasi 2D model, that means its just one cell thickness of 2mm. And am running in steady RANS.
You mean my modelling approach for all RPM or just the 300 one ? What do you think about the power monitor plot for other rpms ? this small fluctuation is ok or ?

AS_Aero · October 11, 2018, 04:19

Also I tried to increase the thickness in direction from 2mm to 4mm and 8mm and the power value increases for same RPM. I just wanted to see if its linear so that I can do the 2D simulation and then somehow interpolate for the 1m length in Z direction

ghorrocks · October 11, 2018, 18:54

I recommend you ignore this issue and deal with the accuracy issue discussed on the other thread first. Until you have some trust in your results there is no point in interpreting the results.

AS_Aero · October 12, 2018, 04:53

Exactly, first I want to find the optimum RPM for a speed of 10m/s
But as I increase the RPM the power value is also increasing and for 300rpm some strange effect is seen in the monitor plot. Where the power value goes down and then from 350 its going on increasing. Nothing has been changed. And till 2000rpm its going on increasing. And running at 2000 rpm is not at all a physical one I would say.
Should I see changing the speed and running it ?

ghorrocks · October 12, 2018, 05:48

This thread is now asking the same question as your other thread (Negative value for torque).

Please post further discussion on this topic on the other thread. We don't want multiple threads on the same topic.

October 10, 2018, 19:27		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Either you have a mistake in your modelling approach or your device's operating point is faster than 800rpm. Over to you to work out which. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

October 11, 2018, 18:54		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	I recommend you ignore this issue and deal with the accuracy issue discussed on the other thread first. Until you have some trust in your results there is no point in interpreting the results. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

October 12, 2018, 05:48		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	This thread is now asking the same question as your other thread (Negative value for torque). Please post further discussion on this topic on the other thread. We don't want multiple threads on the same topic. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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October 11, 2018, 04:17		#3
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 14	The thing is its a quasi 2D model, that means its just one cell thickness of 2mm. And am running in steady RANS. You mean my modelling approach for all RPM or just the 300 one ? What do you think about the power monitor plot for other rpms ? this small fluctuation is ok or ?

October 11, 2018, 04:19		#4
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 14	Also I tried to increase the thickness in direction from 2mm to 4mm and 8mm and the power value increases for same RPM. I just wanted to see if its linear so that I can do the 2D simulation and then somehow interpolate for the 1m length in Z direction

October 12, 2018, 04:53		#6
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 14	Exactly, first I want to find the optimum RPM for a speed of 10m/s But as I increase the RPM the power value is also increasing and for 300rpm some strange effect is seen in the monitor plot. Where the power value goes down and then from 350 its going on increasing. Nothing has been changed. And till 2000rpm its going on increasing. And running at 2000 rpm is not at all a physical one I would say. Should I see changing the speed and running it ?