[CFDbeginer]

I previously posted a help post (Ansys Fluent's calculation results do not match the theoretical values) and I have also sought solutions on other professional forums, but so far I have tried all the methods but still haven't solved this problem. So I need someone to help me check where my mistake is. I know it's not good to do this, but since there are no people around me who are proficient in CFD, it seems to be my only choice at the moment. If this post violates relevant regulations, please delete my post by the administrator.

My Case file (generated by fluent 19.0): https://drive.google.com/file/d/1Mk9...usp=drive_link

Model and mesh files (generated by ICEM):https://drive.google.com/drive/folde...usp=drive_link

Problem: pressure drop friction factor is much smaller than the theoretical value (0.0055 vs 0.0066)

Model: 5m*0.5m*0.125m smooth duct, RNG ke with enhanced wall function, 320K air parameter

BCs: Re=20000,320K massflow inlet, 0 Pa Pressure outlet, periodic sidewalls, 300K top and bottom walls