Low reynolds number flow

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 February 5, 2011, 13:06 Low reynolds number flow #1 New Member   pranav r Join Date: Feb 2011 Location: INDIA Posts: 3 Rep Power: 7 What are the equations aplicable in the case of a low reynolds number flow as in the case of a flow past an airplane made of paper

 February 7, 2011, 16:50 #2 Senior Member     Join Date: Jan 2011 Posts: 246 Blog Entries: 5 Rep Power: 9 You should solve incompressible Navier-Stokes

 February 8, 2011, 05:29 #3 Member   Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 7 depends upon the problem and your area of interest.... Reynolds Averaged Navier Stroke's Equation(RANS).... is to be the best to catered flow separation

 February 16, 2011, 06:35 #4 New Member   Join Date: Feb 2011 Posts: 3 Rep Power: 7 hi, i want to calculate the Reynolds number of exhaust gas with a given temperature(°c) and massflow(g/s). What is the fastest way? thanks in advance

 February 17, 2011, 01:51 #5 Member   Muhammad Aqib Chishty Join Date: Nov 2010 Posts: 50 Rep Power: 7 i think as per my knowledge, your flow is compressible and their should be some laminar separation.... the best model to catered that is Menter Transition model of 4 four equations....

February 21, 2011, 10:53
#6
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Shenren Xu
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I'm afraid low-Re # does not imply low mach number.

You can get shock wave for inviscid fluid, where the Re # is zero.

Quote:
 Originally Posted by truffaldino You should solve incompressible Navier-Stokes

February 22, 2011, 11:42
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Quote:
 Originally Posted by Shenren_CN I'm afraid low-Re # does not imply low mach number. You can get shock wave for inviscid fluid, where the Re # is zero.

Have you seen shok waves past paper airplane?

BTW, for inviscid fluid RE=infinity

February 22, 2011, 12:04
#8
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Shenren Xu
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Hi truffaldino,
my apology... I didn't read it carefully.
And you are right, Re # is infinity.

Quote:
 Originally Posted by truffaldino This thread is about aerodynamics of a small (paper) airplane. Have you seen shok waves past paper airplane? BTW, for inviscid fluid RE=infinity

 February 22, 2011, 13:36 #9 New Member   Vasiliy Join Date: Feb 2011 Posts: 9 Rep Power: 7 Hi All, My opinion that transition model is not necessary in this case. As I understand air flows around paper plane. So velocity is small and we can use incompressible Navier Stokes equation. About turbulence models. I think SA model is good choise in this case. Flow is not very difficult. I am not sure about transition and separation on paper plane.

 February 22, 2011, 16:05 #10 Senior Member     Join Date: Jan 2011 Posts: 246 Blog Entries: 5 Rep Power: 9 I had quite extensive experience with model gliders, they fly at about the same order of RE as paper planes and there is almost always separation and transition there.

 February 23, 2011, 02:00 #11 New Member   Vasiliy Join Date: Feb 2011 Posts: 9 Rep Power: 7 Hi truffaldino, It looks like nice case. It would be interesting to have such model and experiment results. Could you provide it. Thanks

 February 23, 2011, 03:33 #12 Senior Member     Join Date: Jan 2011 Posts: 246 Blog Entries: 5 Rep Power: 9 Hi Vasiliy, Information about low reynolds number airfoil design and its peculiarities (due to separation/transition bubbles) is quite extensive and easily acessible over the web. As an example you could take a look at Martin Heppelere website, and in particular http://www.mh-aerotools.de/airfoils/ Data on very slow airfoils for Discus Launch Gliders (down to RE=40K) can be found here http://www.charlesriverrc.org/articl...t-airfoils.htm People from RC glider commmunity mainly use Mark Drela's xfoil and also XFLR5 software. These are nice programs that are free and increadibly easy to use: Xfoil analyses airfoils, while XFLR5 analyses an airplane as a whole. These programs are based on viscous-inviscid interaction method with boundary layer integral methods. They use e^n transition model and some turbulence model. One can also have a rough idea about presence of separation at low Re for 2D airfoils even without using the above software: one can use Thwaites integral BL method. It is very simple and takes a couple of hours to write a program in mathlab or maple. About experimental data: there has been an extencive testing by UIUC Applied Aerodynamics group, and measured polars were available free of charge on the web. Now they are selling them as reference books: see e.g. http://www.ae.illinois.edu/m-selig/uiuc_lsat.html but some of them are still scattered over the internet free of charge Truffaldino Last edited by truffaldino; February 23, 2011 at 07:16.

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