jetmech From Australia, joined Mar 2006, 2621 posts, RR: 53 Posted (3 years 7 months 3 weeks 2 days 10 hours ago) and read 8253 times:
I found an interesting diagram about the P&W F135 engine, which powers the F-35 aircraft. I find it interesting that the waste heat is supposedly the same wether the lift fan is operating or not. I thought the amount of waste heat may be less with the lift fan operating. What do you think?
tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81
Reply 1, posted (3 years 7 months 3 weeks 2 days 7 hours ago) and read 8233 times:
Quoting jetmech (Thread starter): I thought the amount of waste heat may be less with the lift fan operating. What do you think?
If the fan is running, it's extracting power from the turbines, which means less energy entering the nozzle, but it also means a bigger pressure drop in the turbines so the nozzle can do less work. At least as far as PW concerns, the energy extracted to the lift fan is exactly balanced by the energy not extracted by the nozzle, so the amount of waste heat holds constant. That makes some sense in my head, although I doubt it works out exactly that well in real life.
jetlife2 From United States of America, joined Jul 2006, 220 posts, RR: 25
Reply 5, posted (3 years 7 months 3 weeks 4 hours ago) and read 7807 times:
Horribly irrelevant diagram on wikipedia. Single shaft turbojet used to illustrate a turbofan - lift fan combination! LOL. Someone with the time and energy should replace it. JetMech you are just the man for the job.