Installed performance of ultra-high bypass turbofans: estimation of power saving in optimised configurations

The contemporary tendency for commercial transport to improve propulsion efficiency, reduce fuel consumption, and meet environmental requirements is to move towards the adoption of Ultra-High Bypass Ratio (UHBPR) turbofans mounted in compact nacelles under the aircraft wings. This paper describes a new approach for evaluating the performance of an installed UHBR nacelle under steady horizontal cruise conditions, where the net resulting force on the aircraft is balanced. The procedure to obtain this flight condition in numerical simulations is fully described and the new performance figures are defined. Exploiting the newly developed method, the results of the analyses obtained for two different nacelles within the IVANHOE project are presented. The reference nacelle is derived from state-of-the-art literature information, while the optimised is obtained through a multi-point and multi-objective algorithm aiming at maximising the installed net propulsive force. The effectiveness of the new approach in characterising the UHBPR engine performance is proven by the achieved improvement of the shaft power at steady cruise flight.