[Anna Tian]

Hi,

I'm doing CFD for light aircraft. I'm wondering what turbulent intensity and turbulent viscosity ratio shall I use for the external flow boundary conditions? What are the typical values used in this area?

[Anna Tian]

Originally Posted by Anna Tian

Hi,

I'm doing CFD for light aircraft. I'm wondering what turbulent intensity and turbulent viscosity ratio shall I use for the external flow boundary conditions? What are the typical values used in this area?

Could anyone answer me this question?

[shereez234]

for external aerodynamics of aircrafts usually turbulence intensity is below 1% according to what i have heard and seen. Some one more experienced here could guide you further..

Also for a fully developed flow, the T.I = (0.16) * (Reynolds number)^(-1/8) * (Length scale)

[Anna Tian]

Originally Posted by shereez234

for external aerodynamics of aircrafts usually turbulence intensity is below 1% according to what i have heard and seen. Some one more experienced here could guide you further..

Also for a fully developed flow, the T.I = (0.16) * (Reynolds number)^(-1/8) * (Length scale)

Thanks for your answer. And what is the typical turbulent viscosity ratio value?

Btw, what are the typical value of them in the wind tunnel? I heard about that, in wind tunnel, usually we have flow much more turbulent.

[truffaldino]

For numeric simulation one usually needs turbulent intensity at inlet: for a sailplane T.I free stream turbulence is of order of .01%. For a wind tunnel is about .1%.

For more info see recent post on the same topic

http://www.cfd-online.com/Forums/mai...intensity.html

[Anna Tian]

Originally Posted by truffaldino

For numeric simulation one usually needs turbulent intensity at inlet: for a sailplane T.I free stream turbulence is of order of .01%. For a wind tunnel is about .1%.

For more info see recent post on the same topic

http://www.cfd-online.com/Forums/mai...intensity.html

Thank you for your information. It's very helpful. Btw, what should be the value of the turbulent viscosity ratio?

[truffaldino]

Eddy viscosity has a simple relationship with turbulent energy and length ( http://www.cfd-online.com/Wiki/Turbu...ary_conditions ), so you need the turbulence length. This depends on your inlet conditions (whether this is a wind tunnel with or without grid, athmospheric turbulence etc). Some useful info can be found here:

http://www.cfd-online.com/Wiki/Turbulence_length_scale

I think instead looking for turbulence lenght in tables etc, it is better to do the following: If you to compare your results with measurement, just choose one measurement poit and vary the length until it fits this point, then, using the same length check if the other points will also fit.

[Anna Tian]

Originally Posted by truffaldino

Eddy viscosity has a simple relationship with turbulent energy and length ( http://www.cfd-online.com/Wiki/Turbu...ary_conditions ), so you need the turbulence length. This depends on your inlet conditions (whether this is a wind tunnel with or without grid, athmospheric turbulence etc). Some useful info can be found here:

http://www.cfd-online.com/Wiki/Turbulence_length_scale

I think instead looking for turbulence lenght in tables etc, it is better to do the following: If you to compare your results with measurement, just choose one measurement poit and vary the length until it fits this point, then, using the same length check if the other points will also fit.

I'm wondering, from your experience, will the wing numerical simulation results be sensitive to the inlet turbulence intensity value?

[truffaldino]

As you could see from the above posts, it will be something like logarithmic dependence, i.e. it is not very sensitive.

Sometimes it is sensitive (e.g. if one uses laminar flow airfoil in critical regime, where the flow is close to transition almost at every point).

[a.zareinezhad]

following link can help you for measuring Turbulence intensity:


How to estimate turbulence quantities to specify at inlet boundaries?


Turbulence intensity


10. Turbulence modeling