[pranavr]

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

[truffaldino]

You should solve incompressible Navier-Stokes

[aqib]

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

[jvr]

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

[aqib]

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....

[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.

Originally Posted by truffaldino

You should solve incompressible Navier-Stokes

[truffaldino]

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.

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

BTW, for inviscid fluid RE=infinity

[Shenren_CN]

Hi truffaldino,
my apology... I didn't read it carefully.
And you are right, Re # is infinity.
hope my advisor is not reading this...

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

[Vasiliy]

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.

[truffaldino]

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.

[Vasiliy]

Hi truffaldino,

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

Thanks

[truffaldino]

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