Why are most cooling fan blades singular?

The selection of odd fan blades (such as 3, 5, 7) is based on the optimal design requirements of mechanical balance, airflow efficiency, structural stability, etc., which can avoid the inherent defects of even number fan blades. The following is an explanation from three dimensions:

1. Core reason: To avoid "resonance risk" and reduce vibration and noise.

Resonance is a pain point in fan design. When the rotational frequency of the fan blades coincides with the overall "natural frequency" of the fan, it can cause vibration, noise, shorten the life of the motor, and even cause fan blade breakage.
Double fan blades are usually symmetrically distributed, and when rotating, symmetrical blades are subjected to the same airflow resistance and centrifugal force, which can easily trigger resonance;
The distribution of the center of gravity of odd numbered fan blades is scattered and irregular, and there are differences in the forces exerted on adjacent blades, which does not form a "synchronous external force" and reduces the probability of resonance. The rotation is smoother and the noise is lower.

2. Improve airflow efficiency: avoid "airflow reversal" and optimize the air supply effect.

The core function of a fan is to promote the formation of stable airflow, and the arrangement of odd numbered fan blades can reduce airflow interference and improve efficiency.
When a fan blade with even numbers rotates, the airflow trajectories of adjacent blades may overlap or clash, resulting in airflow disorder, wind force cancellation, shortened air supply distance, and decreased uniformity;
The asymmetrical spacing between odd numbered fan blades can reduce hedge losses, such as a 3-blade fan suitable for rapid cooling and a 5-blade fan with gentle airflow.

3. Structural stability: Reduce the impact of processing and installation errors.

The precision of fan blade processing and installation affects the rotational balance.
The symmetrical errors of even numbered fan blades will accumulate, causing the fan to shake, making it difficult to process and install, and increasing the cost;
The error of odd numbered fan blades is dispersed and will not be concentrated and stacked. The overall balance is easy to control, and the processing and installation costs are low and more durable.
The selection of fan blades is to find the optimal solution between balance, efficiency, cost, and stability, which can avoid resonance, reduce airflow loss, lower processing difficulty, and adapt to mainstream scenarios. It is the industry's default design solution.