Strange drag coefficient analysis results

I’m trying to find the drag coefficient for a submarine model as it dives down horizontally, so I set up an incompressible steady-state simulation where the water is pushing up against the bottom of the submarine’s hull to simulate a descent; I double checked to make sure I had everything set up correctly. When I check the drag coefficient after the simulation, however, I get this weird sin curve like graph that I’ve never gotten before on my other drag simulations with this model and setup. I did almost the same process for the front profile drag coefficient for when the submarine is moving straight through water, and got a fine result of around 0.35, while for the bottom profile drag coefficient I ended up with here is about 0.02, which is clearly far too low. Can anyone tell me what I did wrong? Submarine body drag analysis (Bottom profile) by Masteriti | SimScale

I do not believe you are looking at converged results, your residuals are too high.

It looks like you will expect to have a lot of separated flow with this inflow direction and it will be hard to truly achieve convergence.