a lot of journals implicitly expect academic association
often though, including in technical engineering from my experience, it is not for people from industry to submit articles.
Basically..start by reading other articles in a journal you are interested in submitting to and getting a feel for how they work. Figure out what sections you will need to have, what prior work you can reference. Have you ever written something similar? Are you interested in publishing the model as a theoretical construction? If so, why does one not already exist? how confident are you in your math? Are you interested in publishing an implementation of the model?
It is worth noting that AIAA and arXiv are TOTALLY different beasts. arXiv is a pre-print repository, that is NOT a peer reviewed journal. On the other hand, AIAA publishes multiple journals with different specific areas. For AIAA, how
What is the value/relevance of the paepr? Not just...novelty...journals get hundreds of 'novel' submissions. What is the value of a model of drag in incompressible flow? can you cite others making that argument?
As someone who regularly reviews (although less now because I won't review paywalled articles anymore) a fair number of journal articles, the reason most get rejected is lack of adherence to field norms and poor writing. Norms aren't god, but they exist for a reason and speak to/provide evidence of credibility in what you are saying. Poor writing...well academic writing is HARD. everything you are doing contributes to building an argument and providing evidence for your key point. It has to be situated, claims have to be supported, references made, etc. There are many problems with academic publishing...and these issues can be applied in exclusionary ways, but they are generally useful. Often, people think that you need some crzy high minded writing for journal articles...you don't. What you are seeing is field norms operationalized. In a way it is a highly practical cargo cult. Each field has a ton of knowledge and needs a way to short hand all of it to their disciplinary peers.
Happy to answer more specific questions or similar off list if you want to get into specifics.