[Jongmin Choi]

Hi, I 'm doing ANSYS fluent tutorial


While I'm following 'chap. 7 using a non-conformal mesh,' I have been confused because of hydrulic diameter. It is little bit different from the knowledge that I 've learned from 'Fluid Mechanics' class in undergraduate, i.e.,

By using that equation, I could get a hydraulic diameter of 1.3 in but, the tutorial says that it should be 5 in.
I thought that the material that flows the main duct is air so I can use that equation.
I attach the captures of problem and tutorial.

Thank you all my ANSYS teachers!!