[Mateja]

Hello, I am developing a FORTRAN code for flow in a channel and pipe. The equations are non dimensionalized. My question is which length should be taken as reference length to make the length and width of the channel non dimensionalized? diameter of the tube or height of channel would be an appropriate reference?
Also for velocity, Which reference velocity can be used to get the non dimensionalized numbers eg. Reynolds number?
Is there any reference for this?

Thank you.

[sbaffini]

While I am, typically, against writing nondimensional codes today (you get the confusion you have but not any practical advantage), I think you are overthinking this.

When doing a simulation, you need to have a dimension and a velocity that are both 1. Those will be the ones in your Re definition. Let's say you have a pipe diameter of 2 and a Re of 100, that Re necessarily refers to the pipe radius and not the diameter.

For channels and pipes you will likely find both cases (half height/radius and full height/diameter). Just stick to whatever reference you think is appropriate for your work.

[Mateja]

Thank you for your reply @sbaffini.