Reference length for y+ estimation
 

Hello.

I understand that reference length in case of a flat plate of length 1m would be 1m.

But I'm trying to mesh a whole pump. The overall length of the body is known but the shape is far from a flat plate or even a pipe.

How do I choose the reference size for such cases?

Thanks!

the function y+ is nothing else that the local Reynolds number measured using the distance from the wall in normal direction

what reference length has to do with y+ estimation?

And for reference length for meshing etc. consider smallest and more important feature of geometry. Like diameter of hole or diameter of pipe or width of some face etc.

So a good guess in my pump case would be inlet pipe diameter?

y+ is a function, not a value. For example, it starts from y+=0 at the wall pipe and reach the value of the Reynolds number (with radius as lenght) at the center of the pipe. The characteristic velocity u_tau is based on the stress at the wall

Huh, that explains many things.
I get it now, thanks!