slater_just_slater t1_irq3c05 wrote on October 10, 2022 at 4:20 AM

Reply to comment by Boomshrooom in TIL that passenger jet engines produce most of their thrust from fan at the front, not from the jet exhaust, and that this is called a high-bypass engine. by Rilot

The fans don't actually spin very fast (compared to the compressor) fans only spin about 3000 rpm so the tips don't go supersonic. The compressor spins much faster (12,000 rpm is typical however small engines can spin much faster up to 50,000 rpm) they do this by using 2, sometimes 3 shafts in the engine (one shaft inside the other). The fan is powered by 1 or 2 turbine at the very back, the compressor is powered by separate turbines at the front of the turbine section, just ahead of the fan turbines

Boomshrooom t1_irqiqsl wrote on October 10, 2022 at 7:34 AM

I'm aware of this, my point is that the fan is still spinning at a very high speed, and moves a ridiculous amount of air. 3000rpm still gives 50 rps which is very high especially given the size of the fan.

BobbyP27 t1_irsbfwc wrote on October 10, 2022 at 5:39 PM

Typically the fan tips are supersonic at the design condition. Tip Mach numbers of about 1.3 are typical.