The results showed a net fuel burn reduction of approximately 9% because of the lower fan pressure ratio
and boundary layer ingestion.
Variable Lower bound Baseline Wing area ([m.sup.2]) 300 355.49 Wing sweep ([degrees]) 27 32.4 Wing aspect ratio 8 10.4672 Wing taper ratio 0.1 0.1062 Thickness to chord ratio at wing root 0.11 0.135 Maximum takeoff thrust (kN) 280 334 Engine bypass ratio 8 11 Fan pressure ratio
1.5 1.58 Low-pressure compressor pressure ratio 2.5 3.2 Overall pressure ratio 40 52 Turbine inlet temperature (K) 1650 1800 Variable Upper bound Wing area ([m.sup.2]) 400 Wing sweep ([degrees]) 36 Wing aspect ratio 13 Wing taper ratio 0.12 Thickness to chord ratio at wing root 0.15 Maximum takeoff thrust (kN) 420 Engine bypass ratio 15 Fan pressure ratio
1.75 Low-pressure compressor pressure ratio 4.5 Overall pressure ratio 60 Turbine inlet temperature (K) 1900 Table 4: Optimization problem constraints.
The new engine has internal variable geometry features that allow the system to vary the bypass ratio and fan pressure ratio
, optimizing engine operation for varying flight conditions.
Based on installed performance evaluation, this engine optimizes at a fan pressure ratio
of 1.3 and a bypass ratio in the range of 12 to 13.The comparable open rotor engine has an effective "bypass ratio" level in excess of 20.
(1) is largely determined by bypass flow in a high bypass engine the fan pressure ratio
(which could be 1.6 for a bypass ratio of 8:1) is the key parameter.