# Flow Past Cyilnder - Drag And Lift

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 October 18, 2009, 08:50 Flow Past Cyilnder - Drag And Lift #1 Member   Primoz Ternik Join Date: Apr 2009 Location: Maribor, Slovenia Posts: 65 Rep Power: 9 Hi all, I know that there has been a lot of discussion on this subject, but I still miss the following for the flow (2D, laminar) past cylinder (circular, square): lRef - is this the diameter (D=2R) and side (a) for circular and square cylinder? Aref - is this the lRef*dz, where dz is the length in z-direction? rhoInf - this is the reference (free stream) density. For SimpleFoam this value should be 1? magUInf - this is magnitude of free stream velocity. For the flow past cylnder in a BOUNDED channel this means an average velocity? Last but not least, is the "libforces.so" library universal - by that I mean that it can be applied to Newtonian and non-Newtonian (i.e. Power law) fluids within the SimpleFoam? Thanks in advance, Primoz.

 March 16, 2010, 13:49 #2 New Member   Evren Join Date: Mar 2010 Posts: 20 Rep Power: 8 Hi, lRef - is this the diameter (D=2R) and side (a) for circular and square cylinder? YES Aref - is this the lRef*dz, where dz is the length in z-direction? YES rhoInf - this is the reference (free stream) density. For SimpleFoam this value should be 1? A: It's the reference density and shall be the physical value unless you've done some scaling magUInf - this is magnitude of free stream velocity. For the flow past cylnder in a BOUNDED channel this means an average velocity? : I don't know. I'm looking forward to replies :-) . Nevertheless, if you're just interested in the forces, you dont need magUInf. Last but not least, is the "libforces.so" library universal - by that I mean that it can be applied to Newtonian and non-Newtonian (i.e. Power law) fluids within the SimpleFoam? I don't know exactly but it should be the force calculated by using the pressure gradient. In this manner, it can be general if you don't consider viscoelastic forces. But some expert shall answer this question. I would like to ask some questions, why do you use simpleFoam? It's supposed to be for steady-state solver for incompressible turbulent Newtonian flows. Doesn't icoFoam work better for this case? Which reynolds number are you interested in and which geometry you're using. I am interested in your problem because I try to solve the same problem and I suggest to compare the results.??? Cheers, Evren

March 18, 2010, 17:22
#3
Member

Primoz Ternik
Join Date: Apr 2009
Location: Maribor, Slovenia
Posts: 65
Rep Power: 9
Quote:
 Originally Posted by pbe_cfd Hi, lRef - is this the diameter (D=2R) and side (a) for circular and square cylinder? YES Aref - is this the lRef*dz, where dz is the length in z-direction? YES rhoInf - this is the reference (free stream) density. For SimpleFoam this value should be 1? A: It's the reference density and shall be the physical value unless you've done some scaling magUInf - this is magnitude of free stream velocity. For the flow past cylnder in a BOUNDED channel this means an average velocity? : I don't know. I'm looking forward to replies :-) . Nevertheless, if you're just interested in the forces, you dont need magUInf. Last but not least, is the "libforces.so" library universal - by that I mean that it can be applied to Newtonian and non-Newtonian (i.e. Power law) fluids within the SimpleFoam? I don't know exactly but it should be the force calculated by using the pressure gradient. In this manner, it can be general if you don't consider viscoelastic forces. But some expert shall answer this question. I would like to ask some questions, why do you use simpleFoam? It's supposed to be for steady-state solver for incompressible turbulent Newtonian flows. Doesn't icoFoam work better for this case? Which reynolds number are you interested in and which geometry you're using. I am interested in your problem because I try to solve the same problem and I suggest to compare the results.??? Cheers, Evren
Hi Evren,

Regarding the forces - in lift & drag calculation there are two components that contribute! One is due to the pressure (pressure lift and drag) and the other is due to the viscous forces (viscous drag and lift).

Why I am using simpleFoam? I found it nice (gives good results) for laminar and steady flow of non-Newtonian fluids! Of course, you have to set the "RASmodel" to laminar (in RASProperties dictionary) and choose appropriate "transportModel" (i.e. non-Newtonian model) in transportProperties dictionary! Another option is to use "nonNewtonianIcoFoam" which is useful for numerical modeling of transient flow of non-Newtonian fluids...

Regarding the "flow past cylinder case" - I am considering creeping and slowly moving flow conditions of non-Newtonian fluids! But, I am in a process of writing an article on this subject and therefore I rather do not post any results... I hope you understand. Of course, as soon as the paper is published (which sometimes takes quite some time) I can share it ("my personal copy") with you...

Cheers,
Primoz

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