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-   -   rotor spins freely depending on the torque exerted by the wind? (http://www.cfd-online.com/Forums/star-ccm/97351-rotor-spins-freely-depending-torque-exerted-wind.html)

sanchovg2 February 15, 2012 08:39

rotor spins freely depending on the torque exerted by the wind?
 
hey everyone,
im simulating a wind turbine and still struggling with the motions and rotion of the rotor.
the question now is cn the rotor spin freely depending on the torque exerted by the wind? is this possible? and if it is how?
please help my time is runnig for my thesis :S

nomad February 15, 2012 15:32

You have to setup a DFBI case. There is a boat tutorial that shows you how to do this.
You will also need to enclose your rotor in a rotating region with an in-place interface with the rest of the domain that does not rotate.
This process is a little involved if you've never run the simpler MRF model for propellers. So, I'd suggest that you do that first.

sanchovg2 February 16, 2012 12:27

hi nomad,
thank you for your answer. ok i already did the MRF and it work really fine but now im having problems with the DFBI. i become an floating exeption error and i have simplified the definition from velocity and pressure as constant and not as field function. it is a problem if i extracted the turbine from the rotating region? should it be as a body? where else could i have made mistakes?

nomad February 16, 2012 13:03

There should be no prism layers near in your interface, otherwise it will lead to a non-conformal mesh when it rotates with respect to the non-rotating region. And make sure that your initial mesh has a conformal mapping of more than 99% at least.

sanchovg2 February 16, 2012 14:50

ahhh the prism layers are the problem!!! hehe thanks im not now at the office to try it but tomorrow i will.and when you say near the interface you mean direct on the interface between the rotating area and the flow or the prism layers direct on the wind turbine?

nomad February 16, 2012 15:27

I mean the prism layers at the rotating interface. You will need the prim layers on the turbine walls.

sanchovg2 February 16, 2012 15:35

ok thank very much for your help

abdul099 February 18, 2012 08:30

Prism layers at the interface don't cause a floating point exception. It doesn't matter if there are prism layers, as the turbine rotates, you will not have a conformal match.

Other question: Did you apply an appropriate moment of inertia to the 6DOF body? Did you apply any load moment? Did you choose an appropriate time step?

sail February 18, 2012 12:18

other things to keep in mind:
is your solution at least moderately converged before freeing the motion?

are you using ramps to allow for the movement to be smooth?

sanchovg2 February 20, 2012 05:05

so i deleted the prism layer between the interfaces and it work.the error with the floating ppint exception dint came any more and i could to a simulation but the turbine just rotated 25 deg with a time step=0.05s deg by 180 iterations
a maximum inner iteration 5 and maximum physical time 2s. im just trying some values but i dont know exactly how i should choose this values.
i dint used any ramp values but it converged,for the next try im going to smooth the residuals.
for the moment of inertia i got the values from pro-e so i hope they are ok.

sanchovg2 February 27, 2012 12:25

im still trying to make the turbine rotate but i doesn't work rigth :s it startīs to rotate in positive directions but after a couple of iteration it rotates in the other way, why? i have tried to redefine the rotation axis, the moments of inertia, time steps and nothing is working.i also design new wings because i thought the other ones weren't rigth. i also let the turbine rotate after iterations but nothing. HELP

sanchovg2 February 28, 2012 12:33

2 Attachment(s)
today i tried to fix the problem but its still there. i made now 2 simulations one with a wind velocity of 9 m/s and the second one without a wind velocity. i just gave an initial angular velocity for the turbine by the properties for 6-DOF-Body, to see how the rigid body plot looked like.i found a very intresting thing but im not sure how it really works.
the figure 1 shows the first sim. with the wind velocity the plot shows how it goes from + to - in just one step but ist not repetitive.
the figure 2 is the one just with the initial angular velocity.when the plot is nearing +/- 180 deg it just turn to -/+ angle
what can i do?im running out of ideas where the problem could be...


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