The influence of exhaust system on the performance of the high bypass ratio turbofan engine nacelle

In order to reduce specific fuel consumption, pollution emissions and engine jet noise, modern civil aircraft engine will employ high bypass ratio and low fan pressure ratio. Large fan diameters, which caused by the increase of bypass ratio, leads to the increase of size and weight of nacelle. At the same time, the interference among the nacelle, exhaust system, pylon, and wing becomes greater. Especially the high pressure flow exhausted from the nozzle can change the pressure distribution on the cowl. The aim of this paper is to study the influence of exhaust system on the performance of the nacelle for the high bypass ratio turbofan engine. Results show that the total drag coefficient of isolated nacelle decreases by 0.0415(36.7%) when considering the influence of exhaust system. The main aerodynamic mechanisms influencing the performance of nacelle are the increase of static pressure on the nacelle after body, which is caused by the flow exhausted from the nozzle and the ejector effect on the free stream of the high velocity flow, exhausted from the fan nozzle. The total drag coefficient decreases by 0.015(32.4%) with the fan nozzle pressure ratio increasing from 2.2 to 2.6, decreases by 0.012(25.9%) with the core nozzle pressure ratio increasing from 1.6 to 2.0 and increases by 0.0049(10.5%) with the flow swirl angle at the entrance of fan nozzle increasing from 0°to 9°.