Keyur Kanade
Ansys Employee

I assume you are using watertight workflow.

Please check geometry in SpaceClaim. 
Select geometry in structure tree --> Use right click --> Select Check Geometry. (Or Tools - Fault Detection in DM)
The geometry should be error free to proceed. 
If geometry has any errors, please modify/recreate geometry at those places. 

Try to split any highly curved face into more number of faces. 

Please make sure that you define correct sizing. 

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v221/en/flu_ug/tgd_user_workflow_guided_tasks_setup_mesh_controls.html?q=curvature%20sizing

Please go through help manual for more details 

Regards,

Keyur

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