Best Fan Positions for Airflow in a Duct w/ Two 90° Angles

Question

A similar question was answered here. And while that did help me understand airflow, I have an even more specific question with a little different context.

So what I'm dealing with here is pulling fresh air in a vacuum duct through the front passenger door on a 1984 Volkswagen Vanagon. I have 2 sets of 3 vertically stacked 40mm computer fans, making 6 fans in total. You can read more about (and critique(please)) my ventilation system idea here.

As you can see, when the door is closed, air travels through two 90 degree angles. So the question is.... Where is the optimal placement of my fans. Should I put them both just before the first angle to give it the 'OOMPH' it needs? Or should I space them out, one at the beginning of the duct and another just before the angle? Or does it make any difference at all?

I tested it with just a single set of my stacked fans and I was able to feel a little bit of flow coming out of the vents. Can I expect to double that with my other set added?

Answer 1

One set of fans creates a pressure difference, so two will create double (assuming identical sets of fans), well close enough to double.

Will it be better to put one set close to the other? probably, but noise might then be an issue.

So, I may put one at the start, as you show, then the second halfway - depends on spacing etc but testing will give the best answer for the situation.