Why do wind tunnels not have oval turns? Why do wind tunnel not have oval turns to reduce energy which is lost in sharp 90 degree turns and decrease turbulence?
Wind tunnel with oval turns:

Wind tunnel with 90 degree turns:
Some closed wind tunnels do have rounded corners, for instance the inner circuit (&quot;thermal test chamber&quot;) of the Jules Verne climatic wind tunnel in Nantes.
This plan view is from fig. 1 of &quot;Numerical modeling of the flow conditions in a closed-circuit low-speed wind tunnel&quot; by Moonen et al, J. Wind Eng. &amp; Industrial Aero. 94(10):699-723.

More diagrams of this wind tunnel are in &quot;Benefit of Wind Tunnels with Large Test Sections for Wind Engineering Applications&quot; by Flamand et al, Mathematical Modelling in Civil Engineering 15(2).