OK, I suspect part of the problem is the operating density. Check https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v232/en/flu_ug/flu_ug_bcs_sec_operating.html You may want to initialise the domain to the outlet condition, and use the (hopefully uniform) density that's calculated by Fluent as the operating density. If you look at the (rho - rho_operating) you can explain why.
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