Hello Emma, I only know a few words in French so let's use English.
This is the best platform to get help from experts. I have done a little bit of CFD and can help you get a model with an appropriate mesh and boundary conditions. When a question arises that I can't answer, you will click the Ask a Question button in the Fluids category on the Simulation page.
When you said you didn't succeed on the first model, what happened? Did you manage to make a solid body of the air to mesh? You can clear generated data on the Mesh, and in Workbench, use File Archive to make a .wbpz file that you can attach to your reply.
What version of ANSYS will you use? Is that the Student license or a Research license?
Airfoils often plot the Lift Coefficient and Drag Coefficient as a function of Angle of Attack. Do you have a single Angle of Attack you want to evaluate ribs vs no ribs?
What is the chord length of the airfoil? What is the free stream velocity of the air you want to use? Those two numbers along with some physical properties of air will let you calculate a Reynolds number. Have you done that? Another value to compute is the Y+ value to help decide on the thickness of the first cell in the boundary layer.
Best regards Peter