[Jem01]

Hello, im using the channel395 file and need to make several simulations with different reynoldnumbers. How do i Change the reynold's number?

I figured i can Change the Ubar and the reynolds number will Change, but what is the correlation between Ubar and Re?

Is there another way to Change Re?

Thank you for help!

[Tobi]

Hello,

I don´t know what you want to do but the definition of the Reynoldsnumber should be known:



And based on that equation, you can see how to change the Reynoldsnumber. Further information are here: http://bfy.tw/AtyL

But if this is not what you want to Do, I am sorry for the wrong Information.

[agustinvo]

Hello,

I think there are expressions to relate them, but I'd go to the Re_tau definition. In your case, Re_tau=395.

If you know the Re_tau definition, you can see how u_tau evolves, and then you can impose a certain pressure gradient, instead of the mean velocity.

[Jem01]

Hello Tobi!

your equation is exactly what im working with: Re_tau = u_tau * L / v. I wanna change u_tau in order to Change Re_tau.

The Problem is, in order to Change u_tau i Need to Change Ubar. But what is the relation of Ubar to u_tau? Or what is the relation of Ubar to Re_tau? Do you have an equation? I tried to make one out of Literatur but the results are not correct: Ubar = 5,5 + (Re_tau*v)/delta * (2,44*lnRe_tau -2,4)

Do you have a correct equation?

[Jem01]

Hello agustinvo!

The channel395 has cyclic boundaries. There are no inlet and outlet therefore you cant impose a pressure gradient.

[agustinvo]

Originally Posted by Jem01

Hello agustinvo!

The channel395 has cyclic boundaries. There are no inlet and outlet therefore you cant impose a pressure gradient.

Of course you can! Take alook into SemiImplicitSource fvOption. Then you only change yout u_tau, and add the pressure gradient in the fvOption, change the mesh resolution and run the case