The product: The NF-P12 is made with 9 blades, instead of the 7 blades we’ve seen on their previous fans, and the company states that it has been done for maximum airflow. Furthermore you’ll notice the 2 notches at the end of every blade, and Noctua says this has been done to decrease turbulence and thereby decrease the noise level. Another detail worth noticing is that the cable fitted on the fan is sleeved, which I personally think is a plus.
The 9 blade pressure optimized design, which the NF-P12 has (P means Power, Pressure and Performance) has been specially developed for CPU coolers, water cooling radiators, power supplies and cases. According to Noctua it should provide a stable pressure along with a high airflow at a low noise level.
typically more blades is associated with more noise, but the NF-P12 compensates for this with the Vortex-Control at the end of each blade. This should reduce noise and turbulence. The reason for this is that the air will be moved differently than in a traditional fan, which is illustrated below:
The rotational movement around the axel creates a pressure on the special oil inside the ball bearing. This results in the build-up of a dynamic pressure field, centring and stabilizing the axel. While other fluid based fans also use the dynamic pressure, the SSO ball bearing is equipped with an extra magnet that secures a quicker and more precise centring of the rotational axel and ensures a long-term stability of the ball bearing. This is illustrated below: