Emailing professor for help with (non class related) project
I want to do an analysis involving computational fluid dynamics (CFD)...and I would like to reach out to [a professor] to ask for suggestions on learning more about using CFD, and hopefully discuss it with them to get feedback on this particular project. 


As mentioned already, "Visit in office hours or make an appointment." Once you have demonstrated your abilities to the professor, you'll be in a stronger position to:


  get involved in this professor’s research


Although you won't express "both of [your] requests at once," you can present both of your requests in a short time frame. If this isn't an option, then start by discussing CFD and mention that you'd be interested in working with the professor at the end.


  Would it be more effective to only request some guidance on the project?


If you ask for both at the same time, then the professor mightn't know your strengths. Whereas, asking later lets you demonstrate yourself first. 


  Would it come across rude asking for guidance as well as ask to get involved in their research?


It isn't rude. You can ask for guidance and the professor can say "no." You can offer to be involved in their research and they can again say "no."