# Frozen Rotor Model CFX

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 July 24, 2011, 22:52 Frozen Rotor Model CFX #1 New Member   Join Date: Dec 2010 Posts: 6 Rep Power: 7 Hi I am designing the rotor blades for a coaxial MAV and was trying to run some simulations in CFX. I have read up on several methods for simulating the flow around the rotor blades and am trying to avoid using a sliding mesh for now as it is quite difficult. I am instead using the frozen rotor approach and have produced a mesh and have results below. Boundary Conditions for frozen rotor Rotor Blade: No Slip Wall Top and Bottom cylinder: Opening Periodic Conditions set Frozen Rotor Interface between disc and outer domain Pressure Contours with Velocity vectors on Spanwise plane Pressure Contours on chordwise plane I have followed the method used in tut12 Axial Rotor/Stator to set up the simulation. The obvious problem here is that the airfoil doesn't seem to have much of an effect and the rotating domain seems to be making much more contribution. It seems like the results are incorrect for the interface between the rotating and stationary domain. Either I am misunderstanding the frozen rotor model or I have made an error in my model set up.

 July 25, 2011, 02:43 hi #2 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 8 Hi Windsim I have few questions for you to clearly understand this problem.. 1st what are pressure boundary conditions u have applied 2nd please check the rotation axis and direction of frozen rotor

 July 25, 2011, 07:01 #3 New Member   Join Date: Dec 2010 Posts: 6 Rep Power: 7 Hi rahul, I have zero relative pressure on both openings and the axis of rotation for the frozen rotor is the global z axis. Thank you for your time.

 July 25, 2011, 07:20 hi #4 Member   Rahul Vaibhav Join Date: Nov 2009 Location: India Posts: 33 Rep Power: 8 Hi windsim I think u are trying to simulate the open to atmosphere condition. try these boundary conditions . Inlet: Total pressure 0 Pa Outlet : static pressure 0 Pa and please let me know flow rate developed by the rotor blade. rv

 July 25, 2011, 08:18 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,709 Rep Power: 98 Your image Velocity vectors on Spanwise plane shows the effect of the domain rotation. Is that what you mean by "the rotating domain seems to be making much more contribution"? If so then just plot the variables "Velocity in Stationary Frame" and they will probably make sense. You need to make sure you understand what frame of reference the velocities are being drawn with respect to.

 July 29, 2011, 19:53 #6 New Member   Join Date: Dec 2010 Posts: 6 Rep Power: 7 Thank you for your responses. I did plot the velocities in the stationary frame however, it was simply a linear velocity gradient. The problem with my above model set up is that it does not simulate any relative movement between the rotor blade and the fluid domain. Since the rotor blade is moving with the fluid disc, it appears that there is no relative motion between the disc and the blade. This definitely not the right way to set up the model. If someone could shed some light on how to simulate the motion of the rotor blade that would be most helpful.

 July 30, 2011, 08:04 #7 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,709 Rep Power: 98 I do not understand most of your last comment. What linear velocity gradient? Relative motion between the rotor blade and what fluid domain? Regardless, CFX comes with a few rotating domain examples. They are the easiest tutorials to do to see how to set up multiple domain of reference simulations.

 November 16, 2011, 18:15 #8 New Member   Join Date: Nov 2011 Posts: 2 Rep Power: 0 I am also made a similar project using the turbo mode on ansys, then with the one way fsi model i tried to show rotqation of the blade. i possibly can help you but would you be able to send me ur cfx file (geometry, mesh pre)

 November 17, 2011, 06:49 #9 New Member   ali abadi Join Date: Nov 2011 Posts: 3 Rep Power: 6 I used the same technique of frozen rotor for wind turbine but I got results about half of the experimental results is that ratio accepted

 November 22, 2011, 04:50 #10 New Member   Rachit Singh Join Date: Nov 2011 Posts: 7 Rep Power: 6 hi all, i am trying to simulate the same thing in cfx. but i am stuck at model. As shown in windsims image, how does one create such model having more than one parts (i.e. the outer domain-biggest, then a wedge inside it and then a blade inside the wedge). Are all these different parts made while modelling the geometry or they are made seperately and called in during meshing phase. i cannot get this, tho it is elementy question at this stage here, but your comments will helpfull. Thankyou.

 November 23, 2011, 12:14 wind turbines #11 New Member   ali abadi Join Date: Nov 2011 Posts: 3 Rep Power: 6 Hi all, I am working with Wind turbine simulation and I used the frozen rotor technique with the velocity inlet b.c. and the outlet and sides of the outer stationary domain I set them as opening and linked the stationary with rotating domains with interface, but i got results less than half of the theoretical torque which i calculated with blade element momentum theory, as in fig. below.. can anyone suggest me some different b.c.'s or another technique or any other suggestions with regards alix

 November 23, 2011, 23:40 #12 Member   DB Join Date: Apr 2011 Posts: 81 Rep Power: 7 Hi, How many blades are you modelling as against the actual number of blades..if you are modeeling just one blade try multiplying the torque by the number of blades. I know this is a trivial suggestion, but sometimes so are our mistakes.. __________________ -D.B

 November 24, 2011, 11:01 wind turbines #13 New Member   ali abadi Join Date: Nov 2011 Posts: 3 Rep Power: 6 hi, D.B and all and thank u for replying I simulated three blades and calculated directly the torque applied on the rotor, so I don't think this is the problem, but anyway thank you for the suggestion but what you and other says about the turbulent model SSt or SSG or k-e which one is preferred and what about the outer domain how big it supposed to be as compared to rotor dia. with regards Alix

 January 5, 2012, 14:25 #14 New Member   soni Join Date: Oct 2011 Posts: 25 Rep Power: 7 Hi everyone, I went through the thread and seems like this is a place where I can put my question which is pretty similar to the discussion above. I am simulating a water turbine.I have 3 rotor blades and 9 stator vanes.I am using steady state simulation with frozen rotor.I made the mesh for one rotor and one stator.My BCs are Pressure at inlet and mass flow outlet I calculated power developed by turbine by the Z component of teh torque value. But it did not match with the experimental data. Can anyone please suggest me if I am wrong in setting up the model. 1.Do we have to use one rotor and 3 stator blades? 2.Is power calculated from the resultant torque of the Z component of torque? I would really appreciate your help friends. Thank you

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