How Close Is Too Close? Applying Fluid Dynamics Research Methods to PC Cooling (opens in new tab)

I do CFD in my day job, though not for electronics cooling. I don't think this is as easy as you imagine. It's relatively easy to make pretty pictures, but just because the picture is pretty doesn't mean that it's physical accurate or mathematically correct. Lack of resolution could be an issue, but there are plenty of more subtle problems as well. Jet impingement is known to cause problems with turbulence models, though some models claim to solve the issue. Plus, turbulence modeling isn't always predictive, and might require a certain amount of calibration any time a model is used in a new scenario. Add on top of that the fact that the computational cost of these simulations often is extremely high, even with turbulence models. Maybe people building PCs have plenty of unused CPUs and GPUs, though.

Unfortunately, I don't think CFD and turbulence modeling are things that you can just start doing well without learning a lot before starting.

Yes, positive pressure is also essential for keeping dust off components, which becomes insulating if left unchecked. Make sure intake fans have filters and you're golden.