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Old   February 5, 2011, 12:06
Post Low reynolds number flow
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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
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Old   February 7, 2011, 15:50
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You should solve incompressible Navier-Stokes
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Old   February 8, 2011, 04:29
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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
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Old   February 16, 2011, 05:35
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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
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Old   February 17, 2011, 00:51
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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....
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Old   February 21, 2011, 09:53
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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.


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You should solve incompressible Navier-Stokes
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Old   February 22, 2011, 10:42
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Quote:
Originally Posted by Shenren_CN View Post
I'm afraid low-Re # does not imply low mach number.

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

This thread is about aerodynamics of a small (paper) airplane.
Have you seen shok waves past paper airplane?

BTW, for inviscid fluid RE=infinity
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Old   February 22, 2011, 11:04
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Hi truffaldino,
my apology... I didn't read it carefully.
And you are right, Re # is infinity.
hope my advisor is not reading this...

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This thread is about aerodynamics of a small (paper) airplane.
Have you seen shok waves past paper airplane?

BTW, for inviscid fluid RE=infinity
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Old   February 22, 2011, 12:36
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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.
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Old   February 22, 2011, 15:05
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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.
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Old   February 23, 2011, 01:00
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Hi truffaldino,

It looks like nice case. It would be interesting to have such model and experiment results. Could you provide it.

Thanks
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Old   February 23, 2011, 02:33
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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 06:16.
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