It is already some time ago when I worked together with DonVK and fluid investigating fin horns and especially finding methods how to simulate them properly with BEM. First, off I would like to mention that this collaboration was one of my highlight “diy” experiences. When three people with their respective strengths work together in a concentrated and constructive manner over a longer period of time this is a very good chance creating something special. It all started exploring the original Yuichi/Arai fin horn design and how to simulate it with BEM.
I had started developing my own fin horns already a few years before, but struggled to simulate these horns accordingly. Especially the individual fins or separate channels and their integration as BEM model at throat and at the end of the fins is tricky. You could either simulate them as individual channels but in this case several interfaces are necessary and you could end up with interface issues (one to many and many to one subdomain). Or the BEM model is one single mesh including the fins but then at fin start and end you encounter very close vertices when the fins are very sharp which is a problem with BEM. At that time more questions than answers left for me and these initial designs ended up in the drawer.