Hello, can anybody tell me what is hydraulic diameter? if i am simulating a 2 dimensional air flow simualtion around a 4.465m length and 1.42m heigh car in a 60 x 35 meter square wind tunnel, what hydraulic diameter should i set? what are the area and length values should i set in the reference value? thanks.

hello

Hydraulic diameter- its a diameter with which you will calculate Reynolds number for the bodies like rectangular shape (Wind tunnel dimensions )

D_H= (4*Area )/perimeter

http://en.wikipedia.org/wiki/Hydraulic_diameter

lenght should be your highest dimension of the domain. Area will be used to compute the forces on the surface.

Length which is used in the computation of the moment coefficient.

thanks a lot, Pratik..it really help me a lot. i still not clear with the length u mention, may i know, what did u mean by the "highest dimension of the domain"? is't the car length? if for 2D simulation we need to set or not?

I think U = (4.465 +4.465 + 1.42 +1.42)

Lenght means the charactertic dimension ,here in your case it would mean Height of the car from the ground

ok..thanks a lot.

i see, thanks a lot.