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DELTA SHAPE FLAP IN WIND TUNNEL IMPORTANT!!

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Old   December 31, 2005, 03:58
Default DELTA SHAPE FLAP IN WIND TUNNEL IMPORTANT!!
  #1
eddie farid
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I LIKE TO GET HELP REGARDING THIS ISSUE I HAVE, I AM GRADUATE STUDENT AND I AM TRYING TO FINISH THIS PROJECT WHICH INVOLVES A DELTA OR TRIANGULAR SHAPED FLAP THAT IS MOVING FROM ZERO TO 90 DEGRESES IN A WINDTUNNEL THE FLAP IS IN THE MIDDLE OF THE TUNNEL AT THE SURFACE AND IT HAS UDF FILE THAT SIMULATES THE MOTION OF THE FLAP FROM ZERO TO 90 DEGREES CCW WHERE X,Y,Z AXES LOCATED ON THE FLAP FOR EASYING THE UDF FILE CODE. THE FLAP GOES AT 100 RAD/S AND THE WINDTUNNEL HAS 10 M/S AND WHEN I SETUP THE MODEL AND INITIALIZE AND MONITOR THE DRAG AND LIFT I DONT GET NOTHING BUT ZERO ON THE FLAP WALLS THE TOP AND BOTTOM WALLS OF FALP I MEAN AND I TREID HIGHER MESHING THEN I MADE FLAP BIGGER SINCE IT IS 10CM ISOSCELES AND THOUGHT DIMENSIONS TOO SMALL SO I CHANGED IT TO 40CM PER SIDE AND NO CHANGE I ALWAY GET ZERO LIFT AND ZERO DRAG ON FLAP WALLS, I ONLY GET LIFT ON THE WINDTUNNEL WALLS WHICH I DONT CARE FOR, PLEASE SOMEONE CAN HELP I TRIED TO ADAPT THE FLAP REGION AND MADE THE MESH FINE IN THAT AREA STILL NOTHING I WENT AND TRIED TO SETUP THE REFERENCE VALUES WHERE THE AREA IS THE FLAP AREA WHICH IS TRIANGUALR AREA OF ISOSCELES BUT NOTHING CHANGED I DONT KNOW WHATS WRONG AND I RAN OUT OF IDEAS THE UDF DOES SIMULATE THE MOTION CORRECTLY AND I HAVE THE CODE WHICH I VERY SIMPLE BUT NO RESULTS NOTHING AT ALL I ALWAY GET ZERO FORCES CAN ANYBOYD HELP
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Old   January 1, 2006, 22:25
Default Re: DELTA SHAPE FLAP IN WIND TUNNEL IMPORTANT!!
  #2
georgy
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I think you should make the mesh finer in the area of interest to be able to calculate the forces on the flap try and see and good luck hope it works and others to give more ideas
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Old   January 3, 2006, 11:34
Default Re: DELTA SHAPE FLAP IN WIND TUNNEL IMPORTANT!!
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Jason
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A quick note... go easy on the caps. Capital letters are a forums version of yelling, and no one likes getting yelled at. In your heading and in your post. A lot of people out here won't even read a post if the title is all in caps.

Anyway...

Look at the flow field. A traingle should be causing a large distubance in the flow field, especially at the higher AoAs. Make sure you're BCs are defined correctly (so that the flap is defined as walls and not and that the names are correct when you're reporting your values). Also, it's common to pick a couple steady state conditions to simulate before you try an unsteady, moving mesh case. This way you can debug your model setup and mesh dependencies without going through your entire unsteady solution.

Let me know what you find out when you look at the flow field and we'll see if we can figure it out from there.

Hope this helps, and good luck, Jason
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Old   January 3, 2006, 11:47
Default Re: DELTA SHAPE FLAP IN WIND TUNNEL IMPORTANT!!
  #4
Luca
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Just a doubt: how are you defing the motion of your flap? by dynamic mesh? if it is so, are you sure you're moving the flap correctly? Check the motion provided by your udf with the mesh preview command. Luca
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Old   January 3, 2006, 18:46
Default Re: DELTA SHAPE FLAP IN WIND TUNNEL IMPORTANT!!
  #5
eddie farid
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ok i did setup steady state models at 45,60,90 degress so flap was in these positions and solution was steady state(no dynamic mesh) and i setup up bc,s which i think are simple and they are velocity in at 10m/s and outflow and tunnel walls as wall bc and flap bottom wall and top wall as wall condition and also flap as solid and the volumetric flow rate for air as fluid bc and the udf motion i monitored the motion through mesh animation and it movies accordingly from zero to 90 degrees around z axis so it is in x-y plane and still nothing works but i notes couple of things: 1)that mesh in the flap region does not have enough nodes or cells and the best i could have done is 50 cells on surface when it is at zero position which could affect solution or you guys can tell me if it does.

2)when i plotted velocity i noted that outflow has higher velocity than inlet and that sounds like backflow to me and i couldnt understand why.

3)the velocity around flap is zero or close to it and i wonder why thats happening so it is confusing to me.

4)the reference values when they ask for projected area does not it change with motion since flap moves so whats the area to put initial area.

5)i have adapted region of flap to very high adaptaion and my memory usage went to 2gb and still no result i mean if i was close to reality wouldnt it at least show wrong values of drag and lift but it shows zero throughout solution whether it is steady or time dependent.

last note is i want some one to tell me how to mesh a certain region in volume with high mesh and keep the rest in coarser mesh is that possible should i create a small volume that includes the flap then mesh it at high density then add it to tunnel volume through boolean operation if any one interested i can send him case and udf files i really need this done it is over due project and i have a week to finish so anyhelp is more than welcome and sorry for being too long
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Old   January 5, 2006, 03:37
Default Re: DELTA SHAPE FLAP IN WIND TUNNEL IMPORTANT!!
  #6
eddie farid
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hi guys again, i have tried lots of scenarios from changing the boundary conditions from outflow to pressure outlet and also from velocity inlet to pressure outlet and i know it wont make difference but i ran out of ideas, i even meshed another volume inside the tunnel that encapsules the flap and it was highly meshed and still no change i am sure of the flap udf motion and i checked it but still i get zero lift and drag on flap top and bottom surfaces even fluent online help didnt give me a hint, i only have this hope is it needed to setup boundary layer at the velocity inlet and i did try to do one but it was lousy because i noticed the velocity in flap region is very low and i also tried steady state solution but still didnt work i only get results at the tunnel walls i really dont get it to why there is not forces on a moving flap in a windtunnel and last i tried bigger dimensions for flap and still didnt work. I would appreciate any help possible
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Old   January 5, 2006, 09:24
Default Re: DELTA SHAPE FLAP IN WIND TUNNEL IMPORTANT!!
  #7
Jason
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Grab pics of the flow field and send them to me at jason_at_bae@yahoo.com. Also, send me pics of your mesh.

Jason
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