# Question to liftDrag

 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 22, 2007, 03:47 Hello all, im trying to cal #1 hoochie Guest   Posts: n/a Hello all, im trying to calculate some cases from fluent, to evaluate the results of OpenFOAM. The cases consist of a wing (2D) in a flow and Im interested in the forces in X and Y-direction. So I changed the liftDrag-tool to print the vectors from the pressure-, visous- and turbulenceforce. With this vectors, I hoped to get more or less the same results than from fluent. In fact they are not, the forces are much to low. I filled in the right value of nue, because liftDrag is working with it. So, does anybody have a clue where could be the problem? And a second question, I raed in the forum, that calculating incompressible means to compute p* but not p. To get the real pressure I have to multiply p* with rho. But if p* isnt p, is the function pressureForce = sum ( p.boundaryField()[patchLabel] *mesh.Sf().boundaryField()[patchLabel] ); in liftDrag correct? Because p in this case is p* as far as I can see. thx in advance

 June 2, 2007, 02:45 There is a very detailed discu #2 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 698 Rep Power: 12 There is a very detailed discussion on lift/drag on the "Running/Solving CFD" forum. Check it out. For the record, I have compared the lift and drag coefficients using both OpenFOAM and Fluent for the case of 2D laminar unsteady vortex shedding past a square cylinder. They compare quite well!

 June 2, 2007, 05:25 And I compared lift/drag for a #3 Senior Member   Frank Bos Join Date: Mar 2009 Location: The Netherlands Posts: 338 Rep Power: 9 And I compared lift/drag for a 2D laminar flow around fixed and moving circular cylinders. Comparison with Fluent / Literature is quite good, and OpenFoam is faster, especially the new 1.4! __________________ Frank Bos

 June 2, 2007, 11:27 hi, I am new for OpenCFD. Ac #4 ranjan_1947yahoocom Guest   Posts: n/a hi, I am new for OpenCFD. Actually I have to do the simulation for flow past fixed circular cylinder of radius 10cm in 2D incompressible viscous laminar unsteady flow in water. Lift/drag has to compare with the fluent result. Can any one suggest that,which solver I have to use(simple or piso) and also which scheme and what value for other factor should be used or whole steps. My reynolds number is 3000. thanx Rk

 June 2, 2007, 13:45 Hi Ranjan, Welcome OpenFoa #5 Senior Member   Frank Bos Join Date: Mar 2009 Location: The Netherlands Posts: 338 Rep Power: 9 Hi Ranjan, Welcome OpenFoam, it is a very good piece of code and perfectly suitable for your problem. I am also dealing with laminar flows and performed certain tests using circular cylinders in a freestream at Re=150. For detailed info, take a look at: http://www.aero.lr.tudelft.nl/~frank/index.php?id=research/cfd/OpenFOAM/validati on/OpenFOAM For the problem of a static cylinder in a freestream, you'll have to use icoFoam with PISO and central discretisation. For a static cylinder I use the fully Crank Nicholson timescheme and for moving cylinders I use the backward scheme (with icoDyMFoam). From my experience, OpenFoam 1.4 is a lot faster than 1.3, so try this new version. One more question. You are aware that the flow around circular cylinders becomes turbulent at about Re=180, right? When you want to solve for turbulence you need the solver turbFoam..... Goodluck and keep me informed about your results! Regards, Frank __________________ Frank Bos

 June 2, 2007, 16:35 Hi Frank, I will be giving #6 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 698 Rep Power: 12 Hi Frank, I will be giving a presentation in my university concerning the use of GNU/Linux clusters in solving CFD problems. I was wondering if I could use your CFD movies from your webpage as examples. I will reference your movies to your webpage. Would that be OK?

 June 2, 2007, 17:00 Hi pUI, It OK with me. Just #7 Senior Member   Frank Bos Join Date: Mar 2009 Location: The Netherlands Posts: 338 Rep Power: 9 Hi pUI, It OK with me. Just refer to my website and mention the Delft University of Technology. Btw, which movies are you referring to? And what is your university? Frank __________________ Frank Bos

 June 2, 2007, 17:05 Will do Frank. Thanks! I'm fro #8 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 698 Rep Power: 12 Will do Frank. Thanks! I'm from University of Alberta (www.ualberta.ca), Chemical and Materials Engineering Department.

 June 6, 2007, 16:48 RW- I am also trying to get #10 Member   Doug Hunsaker Join Date: Mar 2009 Location: Logan, UT Posts: 63 Rep Power: 8 RW- I am also trying to get a 2D airfoil case running using a C-grid. I'm having a really tough time with the boundary conditions for some reason. I found this thread that suggests getting it running in potentialFoam first: http://www.cfd-online.com/OpenFOAM_D...tml?1181162568 but I haven't had any luck with that either. I've posted in two other threads along the same lines: http://www.cfd-online.com/OpenFOAM_D...tml?1179501415 and http://www.cfd-online.com/OpenFOAM_D...tml?1181080719 If you get something running, I'd be very interested in knowing what your using for initial conditions, boundary conditions, and the other initial setup files for the case. Thanks. -Doug

 June 6, 2007, 16:51 RW: Apologies for the delayed #11 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 698 Rep Power: 12 RW: Apologies for the delayed reply. Can you rephrase your question if possible in a single sentence. I'm unable to follow it at present.

 June 6, 2007, 17:02 Hello All- One more questio #12 Member   Doug Hunsaker Join Date: Mar 2009 Location: Logan, UT Posts: 63 Rep Power: 8 Hello All- One more question. OpenFOAM 1.4 doesn't come with a pre-compiled liftDrag executable. When I try to compile it, I get errors telling me: make: *** No rule to make target '/blah/blah/blah.h' needed by 'liftDrag.dep'. Stop I figured it wasn't finding the .h files and located a bunch of them. It seems that liftDrag.dep was written for 1.2 and that many of the files have been moved for 1.4. Locating the files alleviated the problem for most of the .h files. However, there are a bunch of .h files that I can't find anywhere in the OpenFOAM-1.4 installation. This includes liftDrag.h. I assume many of you are running liftDrag on 1.4 and just wondered how you got it to compile when so many of the .h files listed in liftDrag.dep don't even exist in the installation. Thanks for you help. -Doug

 June 6, 2007, 17:23 Yes, liftDrag compiles trivial #13 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 698 Rep Power: 12 Yes, liftDrag compiles trivially in OpenFOAM 1.4. I have given detailed instructions[1] in the forum on how to install it in OF 1.3. If you follow the same procedure for OF 1.4 it will work. I use it on OF 1.4 without any problems. [1] http://www.cfd-online.com/OpenFOAM_D...es/1/2299.html I read somewhere in the forum that it is on the TODO list for a future OpenFOAM version. So I'm guessing that we should have have native liftDrag support sooner or later. Good Luck!!!!

 June 6, 2007, 17:41 Yes, liftDrag compiles trivial #14 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 698 Rep Power: 12 Yes, liftDrag compiles trivially in OpenFOAM 1.4. I have given detailed instructions[1] in the forum on how to install it in OF 1.3. If you follow the same procedure for OF 1.4 it will work. I use it on OF 1.4 without any problems. [1] http://www.cfd-online.com/OpenFOAM_D...es/1/2299.html I read somewhere in the forum that it is on the TODO list for a future OpenFOAM version. So I'm guessing that we should have have native liftDrag support sooner or later. Good Luck!!!!

 June 6, 2007, 18:30 Thank you! I just compiled lif #15 Member   Doug Hunsaker Join Date: Mar 2009 Location: Logan, UT Posts: 63 Rep Power: 8 Thank you! I just compiled liftDrag in 1.4. Thanks for the detailed explanation of your other post in the other thread. -Doug

 June 6, 2007, 19:05 Hey there, pUI, no case to #16 hoochie Guest   Posts: n/a Hey there, pUI, no case to apologize, we all got our work to do. My question in one sentence would be: Did anyone of you tried to simulate an airfoil in 2D with simpleFoam or rhoSimpleFoam? Im getting always a velocity in z-direction which makes it hard to qualify my values for liftdrag, allthough they look good. As I said, I wrote about it in another thread, so it isnt wise to discuss it here, but unless I tried a lot with no success Im interested in the setup files, for 2D-cases in case of an airfoil, which got no velocity in z-direction. RW

 August 27, 2007, 10:02 Hello, all I just compiled #17 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: South Bend, IN, USA Posts: 688 Blog Entries: 9 Rep Power: 12 Hello, all I just compiled liftDrag in 1.4. And I found it is available for interFoam, but it cannot be applied to icoFoam and oodles, I guess the problem is around here: -------------------------------------------------- scalar Aref = sum ( (Uav & mesh.Sf().boundaryField()[patchI])* pos(Uav & mesh.Sf().boundaryField()[patchI]) ); // Reference length boundBox patchBounds ( mesh.boundaryMesh()[patchI].localPoints() ); scalar Lref = mag(Uav & (patchBounds.max() - patchBounds.min())) /(mag(Uav) + VSMALL); -------------------------------------------------- could anyone give some comments on these lines that why I cannot use liftDrag here and how to modify it. Thanks Have a good day! Daniel __________________ ~ Daniel WEI ------------- NatHaz Modeling Laboratory Department of Civil & Environmental Engineering & Earth Sciences University of Notre Dame, USA Email || My Personal CFD Blog

 October 29, 2007, 03:47 Hello Forum, I just install #18 Member   Alessandro Spadoni Join Date: Mar 2009 Location: Atlanta, GA Posts: 65 Rep Power: 8 Hello Forum, I just installed the utility liftDrag as suggested in: http://www.cfd-online.com/OpenFOAM_D...es/1/2299.html I am running a very simple case in simpleFoam. I have a naca0012 at 0 angle of attack, and k-epsilon for modeling turbulence. I get the analysis to converge nicely, pressure looks good, velocity, k, epsolin, etc. look very good. When I run liftDrag . naca0012 -time 700 for example, I get this output: [gtg627eOpenFOAM@ruzzene03 simpleFoam]\$ liftDrag . naca0012 -time 700 /*---------------------------------------------------------------------------*\ | ========= | | | \ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \ / O peration | Version: 1.4.1 | | \ / A nd | Web: http://www.openfoam.org | | \/ M anipulation | | \*---------------------------------------------------------------------------*/ Exec : liftDrag . naca0012 -time 700 Date : Oct 29 2007 Time : 03:42:42 Host : ruzzene03 PID : 9647 Root : /home/gtg627eOpenFOAM/OpenFOAM/gtg627eOpenFOAM-1.4.1/run/tutorials/simpleFoam Case : naca0012 Nprocs : 1 Create time Create mesh for time = 700 Time = 700 Reading U Reading p Inlet velocity: (50 0 0) Wall patch 1 named airfoiln : Reference area: 0.297421 Reference length: 1 Drag coefficient: 0.00116109 Lift coefficient: (0 8.21932e-05 -1.32776e-21) Moment coefficient: (-2.05483e-06 2.90273e-05 -1.95907e-05) This result seems to not include viscous forces. The drag for a naca0012 at 0 deg and Re ~ 3 million should be approximately 0.0058, from "theory of wing sections." Thank you in advance for any comments, Alessandro

 October 29, 2007, 03:48 Sorry I meant to post the abov #19 Member   Alessandro Spadoni Join Date: Mar 2009 Location: Atlanta, GA Posts: 65 Rep Power: 8 Sorry I meant to post the above message in the following thread: http://www.cfd-online.com/OpenFOAM_D...es/1/2299.html

 October 29, 2007, 04:20 I have performed a validation #20 Senior Member   Srinath Madhavan (a.k.a pUl|) Join Date: Mar 2009 Location: Edmonton, AB, Canada Posts: 698 Rep Power: 12 I have performed a validation for laminar flows and I am confident that the utility accounts for both components. For turbulence please see the other threads on liftDrag. You may have to add some features.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post nuovodna OpenFOAM Running, Solving & CFD 45 September 2, 2009 17:56 ryan_m OpenFOAM Running, Solving & CFD 2 August 24, 2009 21:26 fabian_korn OpenFOAM Post-Processing 1 September 22, 2008 02:34 msrinath80 OpenFOAM Running, Solving & CFD 8 March 28, 2008 11:55 guggi OpenFOAM Running, Solving & CFD 1 August 2, 2006 12:36

All times are GMT -4. The time now is 04:04.