Turbofan engine!?

Question

What is the limiting factor, when it comes to fan size? And why dont we see twin counter rotating fans, like counter rotating propeller engines?

Answer 1

Landing gear length, aircraft height. You can put bigger diameter fans on without taller landing gear, and with taller landing gear the airframe needs significant modification or redesign. And with more thrust it must be ensured that the structure can adequately withstand it. Counter-rotating fans also do not have the same torque and gyroscopic force of a propeller and requiring opposite rotating engines would increase costs significantly

Answer 2

The limiting factor is the tip speed; where it reaches the speed of sound, there is additional issues with flow due to shock wave.



Propellers are more massive than fans and induces a gyroscopic effect and a sidewash that is contained in the case of a shrouded fan. Counter-rotating propeller minimize such effects that are only marginally present in the case of a fan.

Answer 3

I won't go any further that saying that counter-rotating turbine blades would create a physical rotation problem that would negate any benefit of counter rotating blades.

Answer 4

see how rotor and stator parts of turbine are shaped and setup. imagine the price for building that in the size of engine fan.