Close the Model Editor, then click on Mesh in the workflow.
Set Mesh Size & Controls
Retain the default mesh settings. AIM will prompt the user to fix the boundary layer before generating the mesh. Click on Boundary Layer under Mesh Controls. Select the faces of the flow volume.
Return to the Mesh task and click Generate Mesh under Output or at the top of the Mesh panel. AIM should detect that you are ready to generate the mesh and highlight the buttons in blue.