Translation of an airfoil

Phil_QM · November 3, 2011, 13:06

Hi all

I am having problems with getting a NACA 0012 airfoil to translate vertically with harmonic motion. I have followed the ANSYS tutorials and tried to set my problem up in a similar way.

I am using a tet c-mesh you can see attached. I have a problem when my airfoil oscillates as elements seem to fold rather than remesh, resulting in a negative volume error.
This is shown in the second attachment, you can see at the top of the airfoil the elements are folding and on the bottom of the airfoil the elongated elements.

I am using define_cg_motion to oscillate the airfoil.

Thanks in advance
Phil

swetkyz · November 5, 2011, 09:02

Would defining a UDF of the motion and applying it to Cell Zone Conditions > Mesh Motion > Translation work? I think this solves the same physics without the need for mesh adaptation.

-Zachariah

Phil_QM · November 7, 2011, 06:54

How would I go about defining a UDF for this as I have been using Define_CG_Motion which I dont think is suited to this case.

Also how would applying a cell zone motion solve the same physical problem?

Sorry if my questions seem basic but I am fairly new to CFD.

Thanks Phil

swetkyz · November 7, 2011, 09:18

According to the user guide, by using a Single Moving Reference Frame, the accelerations due to the motion of the frame are accounted for by the solver. This means that as long as your boundary conditions represent the problem correctly, the same physics will be solved.

As far as the UDF is concerned, my knowledge is limited. It seems to me that this is the only way to define non-constant motion for a moving frame is a UDF.

If this approach is too cumbersome, you may try implementing the non spring-based dynamic mesh method that removes cells once they become too small.

sail · November 7, 2011, 16:03

remeshing does not work on hexa cells. [Ref, Fluent guide]

to get some remeshing you need to mesh your bl and then some as hexa, and the farfield as tri. then set all the hexa domain as passive rigid body. there are quite a few tutorial for this on the web.

or, not using a c-type grid but a normal h-type, you could take advantage of the relayering option.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Natural convection in a closed domain STILL NEEDING help!	Yr0gErG	FLUENT	4	December 2, 2019 00:04
Low Speed Airfoil	Mancusi	FLUENT	7	April 3, 2014 06:11
[GAMBIT] Meshing airfoil using .dat file problem	creggie	ANSYS Meshing & Geometry	10	June 27, 2010 19:24
Modeling Backflow for a 3D Airfoil (Wing of Finite Span)	Josh	CFX	9	August 18, 2009 11:31
Airfoil boundary condition	Frank	Main CFD Forum	1	April 21, 2008 18:36

November 5, 2011, 09:02		#2
swetkyz Member Zachariah Swetky Join Date: Aug 2011 Posts: 36 Rep Power: 14	Would defining a UDF of the motion and applying it to Cell Zone Conditions > Mesh Motion > Translation work? I think this solves the same physics without the need for mesh adaptation. -Zachariah

November 7, 2011, 06:54		#3
Phil_QM New Member Join Date: Jul 2011 Location: London, UK Posts: 6 Rep Power: 14	How would I go about defining a UDF for this as I have been using Define_CG_Motion which I dont think is suited to this case. Also how would applying a cell zone motion solve the same physical problem? Sorry if my questions seem basic but I am fairly new to CFD. Thanks Phil

November 7, 2011, 09:18		#4
swetkyz Member Zachariah Swetky Join Date: Aug 2011 Posts: 36 Rep Power: 14	According to the user guide, by using a Single Moving Reference Frame, the accelerations due to the motion of the frame are accounted for by the solver. This means that as long as your boundary conditions represent the problem correctly, the same physics will be solved. As far as the UDF is concerned, my knowledge is limited. It seems to me that this is the only way to define non-constant motion for a moving frame is a UDF. If this approach is too cumbersome, you may try implementing the non spring-based dynamic mesh method that removes cells once they become too small.

November 7, 2011, 16:03		#5
sail Senior Member Vieri Abolaffio Join Date: Jul 2010 Location: Always on the move. Posts: 308 Rep Power: 16	remeshing does not work on hexa cells. [Ref, Fluent guide] to get some remeshing you need to mesh your bl and then some as hexa, and the farfield as tri. then set all the hexa domain as passive rigid body. there are quite a few tutorial for this on the web. or, not using a c-type grid but a normal h-type, you could take advantage of the relayering option.