[sms1424]

Hey Guys,

So I did some CFD on turbulent flow analysis and want to reference some of the equations I used like:

Turbulence Intensity= 0.16 Re^(-1/8)
Length Scale= 0.07* d

Also, I read somewhere in here that inlet turbulent intensity for moderate flow applications like HVAC can be assumed as 5%. Do you guys have a good reference, like a book, so I could cite these above information to?

Thank you

[LuckyTran]

As far as I know, those two equations are from the Fluent User's Guide. Its source is not referenced in the Fluent manual. But if there is a solid reference, I would like to know. I would guess Batchelor or Shapiro. But most people know that the Reynolds stresses in pipe flows are not equal in all directions and that even k varies strongly across the dimensions of the pipe, which suggests that this result was derived from (CFD) experience.

In my opinion, turbulence intensity without a length scale attached to it is meaningless and the length scale is much more important. A fly buzzing around can just as easily generate as much turbulence intensity as a a T-rex running through a room. You can test this by running a simulation with a very high I 100 or 1000% and small L (the turbulence will decay rapidly and might not even transport anywhere) and compare it to a small I and large L.

If your problem is truly sensitive to these boundary conditions for I and L (or k and epsilon, or k and omega) then I would assume you have already put the effort into obtaining these parameters, which might even require its own CFD using BC's that you do know.

[sms1424]

Thank you for the reply.

Actually my problem is not sensitive to these BCs, I tried to vary them and almost got same results but my professor is insisting in getting " real" reference for them instead of " fluent user's guide"

[sbaffini]

A like for your professor. I haven't it now to check, but Schlichting is where I would first look for this. It's both autoritative and wide, well worth a try.