Installation aerodynamics of civil aero-engine exhaust systems

Without careful consideration of aerodynamic installation effects on exhaust system performance the projected benefits of high bypass ratio engines may not be achievable. This work presents a computational study of propulsion system integration in order to quantify the effect that aircraft installation has on the aerodynamic performance of separate-jet aero-engine exhaust systems. Within this study the sensitivity of exhaust nozzle performance metrics to aircraft incidence and under wing position were investigated for two engines of different specific thrust. Upon installation, thrust generation was found to be beneficial or detrimental relative to an isolated engine depending on the position of the engine relative to the wing leading edge. The dominant installation effect was observed on the exhaust afterbodies and, over the range of engine positions investigated at cruise conditions, the installed modified velocity coefficient was shown to vary up to 1 % relative to an isolated engine. Furthermore, due to variations in the core nozzle mass flow rate by up to 10% relative to an isolated engine, it is concluded that aerodynamic installation effects need to be taken into consideration when sizing the core nozzle in order to ensure engine operability.