Ok folks, here comes what might be a fairly rudimentary question, but one that I've been curious about and never bothered to ask.
Some modern turbofans, seem to collect all bipass and core exhaust into a single nozzle before it reaches the atmosphere, as on this 757:
Others (seems like MOST others) rout bypass and core exhaust seperately all the way to the atmosphere, as on this 777:
What are some of the factors that engineers consider when choosing one design over the other. I'm guessing noise may have something to do with it, since power rating is not consistent with the use of either design.
Also, on all wing-mounted engines, the pylon displaces bypass airflow at the 12 o-clock position. Obviuosly, this can't be avoided, and the overall thust of an engine as on the 777 couldn't be too bothered by a thin, aerodynamic obstruction, but does it reduce total thrust output at all? would engine #2 on a trijet like the MD-11 produce fractionally more thrust than the others? Thanks for any replies,