How does a gear driven turbofan increase the bypass ratio?

The traditional fan and low-pressure compressor are one shaft. But the fan cannot rotate too fast, and the fan blades cannot be enlarged without restrictions, otherwise the edges of the fan blades will become supersonic and the resistance will increase. But the faster the low-pressure compressor rotates, the higher the compression efficiency. This is the contradiction.
Therefore, a star gear was added between the fan and the low-pressure compressor to achieve coaxial different speeds, with a speed ratio of approximately 1:3. This way, the fan can be made larger while ensuring the speed without affecting the efficiency of the low-pressure fan. The result is that the bypass ratio has increased. The bypass ratio of CFM56 is approximately 5.5:1, while the bypass ratio of PW1000G can reach 12:1.

The gear driven turbofan increases the bypass ratio by reducing the fan speed. During this process, adjustments are made to the design and operating conditions of the fan blades, which helps to improve efficiency.
Firstly, through gear transmission, the speed of the fan decreases but the torque increases. Enable the fan to provide sufficient thrust at lower speeds. As the torque increases, the angle of the fan blades can be adjusted to better adapt to low-speed operating conditions.
By adjusting the angle of the blades, the fan can more effectively suck in air. Helps to improve the suction efficiency of the turbofan, thereby increasing the bypass ratio.
Overall, through gear driven turbofans, fans can more effectively suck in air at low speeds, and improve bypass ratios by optimizing blade design and angle. This design helps to achieve better fuel efficiency and thrust performance under different flight conditions.