I have a fan on a stand, to circulate air in my home. The three fab blades are somewhat "D"-shaped, with one edge being rounded and one being straight-ish or even curving inward.
Now, from my sailing, as well as my understanding of wing and propeller (edit: and low-noise computer fan) design, I would expect the outward-curving edge to be the leading one, but it's not. In the photo*, the fan spins clockwise to push air towards me. *excuse potato quality, the fan was spinning so this is with reduced shutter time and high ISO.
In contrast, this low noise pc fan also spins clockwise, yet its blades do curve "backwards" in relation to their direction of spin (as I'd expect).
Wouldn't my fan be less noisy if it spun the other way, at least theoretically? Obviously, including inverting the blade tilt, in order to keep airflow direction.