What to set the turbulence specification of airfoil
 

Hello,everyone.I'm simulating the airfoil flow field.However,I encountered some problems.
1.What to set the turbulence specification of airfoil, modified turbulent viscosity, intensity and length scale, turbulent viscosity ratio or intensity and hydraulic diameter?
2.The material you choose is air or ideal gas?

Thank you in advance.

I always use the turbulence intensity and viscosity ratio to specify turbulence because they are the most apparent parameters to me. Ideal gas is one way to relate the density with other quantities such pressure and temperature and is not a kind of material. If what you meant is how to choose between constant density and ideal gas, then it largely depends on your flow Mach number.

Keep the default condition if you are not trying to match some wind tunnel setup. Most appropriate parameters to me are : Turbulence intensity and length scale. While the data for turbulence intensity is available but length scale data is not. I can send you very relevant journal papers if needed.

Having said that, these parameters come into play at critical Reynolds number, otherwise default conditions should suffice.

daer...
 

if your mach number is:
less than 0.3, chose constant density,
bigger than 0.3 chose ideal gas.(Notice that if you select ideal gas, energy equation tuned on automatically and you should set temperature condition.

blackmask,thank you for your reply.Although I still have some problems on turbulence specification method, it's a matter of experience.

Thank you, Far.Your suggestion is useful.I really need some relevant journal papers.Could you send them to my email?

farza,thank you.

send your email id please

komega sst
 

hi dear Far
i want to simulat flow around an airfoil and using komega sst model.my mach number is 0.5 and Re=30*10^6
i dont now how estimate turbulence intensity and k and omega in boundary condition?
pleas can you help me?

use length of chord airfoil as length scale of turbulence and intensity 0.1%

I would suggest to use the default values if you are modeling transition or reprocuding alrady done wind tunnel experiment

Hello Sijal,

I have a quesion. How can I calculat the drag coefficient from the CFD Post for FLUENT?
I have created a post here, can you commented on it please?
http://www.cfd-online.com/Forums/flu...alidation.html

Thanks :)

CFD Post
 

Yes you can.
in expression tab you can define Drag coef:
Foorce X@airfoil/0.5*density*Velocity*Velocity*chord length*Span

Hi Farzad,

Thanks for the reply. But how come 2D smulation in FLUENT have span??


If you take "Force X/span" and evaluate expression you gave, you get cd, which is drag coefficient per span length . Will this equal to NASA data?

The same quetion I ask for lift coefficent, where Force X is replaced by Force Y.

Help is much appreciated :)