# Force on body by velocity compared to force_y@...

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

 February 14, 2006, 12:57 Force on body by velocity compared to force_y@... #1 Stefan Guest   Posts: n/a Dear posters, it would really help me if anyone could give me a hint with this: in order to calculate the Force on a bluff body normaly one uses force_y@bluffBodyName. This shuould calculate the y component of Integral(sigma dot normal)*dS this integral is equal to areaInt((-p+2*Dynamic Viscosity*(Velocity u.Gradient X))*Normal X)@bluffBodyName + areaInt(Dynamic Viscosity*(Velocity u.Gradient Y+Velocity v.Gradient X)*-Normal Y)@bluffBodyName + areaInt(Dynamic Viscosity*(Velocity u.Gradient Z+Velocity w.Gradient X)*-Normal Z)@bluffBodyName But they are not equal! Question: Why? (I need to calculate the Integral this way, because in my application I need to direcly acsess the memory of the solver with Fortran routines and map forces from a deformed to a reference configuration)

 February 14, 2006, 13:08 Re: Force on body by velocity compared to force_y@ #2 opaque Guest   Posts: n/a Dear Stefan, I assume you are using a laminar model because otherwise you cannot assume that the shear force is visc*(grad vel + gradT vel).. Recall that the turbulence models use wall functions, and the expression for wall shear is C * (Vel Node - Vel Wall) or something in that direction.. Good luck, Opaque..

 February 15, 2006, 10:27 Re: Force on body by velocity compared to force_y@ #3 Stefan Guest   Posts: n/a Thank's a lot for your answer. Yes I am using a laminar model the reynolds number is only 20. no wall function or anything like that is used. using f_x@cylinder I get 5.56847e-005 [N] and using visc*(grad vel + gradT vel) leads to 5.48238e-005 [N] which is not the same and I need it to be exact. Really looks like I foregot something. Can you think of anything else that went wrong? greetings Stefan

 February 15, 2006, 10:29 Re: Force on body by velocity compared to force_y@ #4 Stefan Guest   Posts: n/a Foregot to say that the fluid is visous and incompressible

 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 enghamed CFX 3 November 27, 2010 05:28 Souviktor Fluent UDF and Scheme Programming 0 March 31, 2009 08:54 Mohammad Aghakhani FLUENT 0 May 21, 2007 17:01 Sandilya FLUENT 0 May 21, 2007 13:32 Abhi Main CFD Forum 12 July 8, 2002 09:11

All times are GMT -4. The time now is 01:31.