Optimum Mixing of Core and Bypass Streams in High-Bypass Civil Turbofan

In a mixed-stream turbofan, except for fan pressure ratio, the mission matched optimum selection of other basic cycle variables like bypass ratio, overall pressure ratio, throttle ratio, and turbine entry temperature depends upon engine-airframe interactions over the prescribed mission and the available technology level. The fan pressure ratio is decided by the mixing conditions that are internal to the engine. This paper, by utilizing a multidisciplinary cycle optimization software, performs a number of numerical experiments to determine a criterion for mixing of bypass and core streams, which results in an optimum fan pressure ratio. The use of optimum fan pressure ratio will aid the other basic cycle parameters in enhancing performance gains caused by mixing, thereby improving the engine-airframe-mission compatibility. The penalty of non- or suboptimal mixing, and savings in mission fuel consumption for a mixed-stream turbofan with respect to a separate exhaust turbofan, both at optimum fan pressure ratio, are also quantified. (Author)