Usually aortic flow is challenging simulation because they can be unstable. Try with more underrealxation or ramp up the load with 'ramping' option.
Are you trying it in WB or Standalone System coupling application?
To diagnose the issue have a look at the system coupling log file (scLog.scl), fluent log file (.trn) and mechanical log file (.out)
Best practices can be found in system coupling manual. Best Practices for Coupled Fluid-Structure Interaction (FSI) (ansys.com)