Turbo Fans With Very High Bypass Ratio but Acceptable Dimensions

Turbofan engines for commercial aircraft will have to improve substantially in fuel burn, noise level and NOx emissions to fulfil the ACARE 2020 environmental goals. No doubt very high bypass ratios (VHBR) will be necessary to achieve the ambitious noise reduction targets. But weight and drag of the nacelle cannot increase further and under wing installation must always be feasible. Several innovative design options such as counter rotating turbo components, air breathing nacelle, and off axis core are presented and discussed in the paper which could help to overcome the increasing dimensions of the fan and the nacelle with increasing bypass ratio.