A Numerical Simulation on the Coupled Influence of the High Bypass Ratio Nacelle and Exhaust System

The aerodynamic performance and flow characteristics of high bypass ratio nacelle and exhaust system was studied by numerical simulation. The coupled influence of fan nozzle length-diameter ratio on the performance of nacelle and exhaust system was also studied. The results show that a low velocity zone exits at the lip of nacelle and there is a velocity peak on the forebody of nacelle. There are many complex flow phenomenon, such as shockwave, expansion wave, shear flow and shock wave boundary layer interaction, at the downstream of exit plane of fan nozzle. The engine effective thrust decreases by 3.2% with the fan nozzle length-diameter ratio increases. Nacelle drag is main factor which affects the engine effective thrust because of its large increase with the increase of fan nozzle length-diameter ratio. The decrease of supersonic zone, enhancement of fan nozzle flow expansion and shock wave strength at the downstream of fan nozzle exit plane, affected by the fan nozzle length-diameter ratio, lead to the decrease of static pressure on the core cowl and increase of main flow velocity near core cowl wall which increase the pressure drag and decrease the friction drag of core cowl. The friction drag of cowl increases because of the increase of its wetted area.