Ultrahigh Bypass Ratio Propulsion Systems Studied

celerate a large mass of air by a small amount than to accelerate a small mass of air by a large amount. In a turbofan jet engine, the airflow rate that bypasses the engine core divided by the airflow rate that travels through the core is called the bypass ratio. The bypass ratio, or BPR, is one of the key indicators of turbofan engine efficiency. The desire for better fuel efficiency has resulted in the evolution of commercial aircraft gas turbine engines from early turbojets (BPR=0), to low bypass ratio, first generation turbofans (BPR=1-2), to today's high bypass ratio turbofans (BPR=5-10).Now, ultrahigh bypass ratio (UHB) turbofans (BPR=10-20) are being designed for a next-generation, intracontinental commercial aircraft. This aircraft could enter service as early as 2020. The Intercenter Systems Analysis Team, consisting of systems engineers from Glenn and Langley Research Centers, conducted an analytical feasibility study of UHB turbofans for NASA's Fundamental Aeronautics Prog ram. With a little math, it can be shown that fuel efficiency increases along with BPR.The engine core, however, has a limited supply of power available to propel the bypass air stream, so it can be difficult to simply increase BPR arbitrarily. One path to UHB engines and better efficiency is to reduce the fan's pressure ratio, which lowers the fan's power requirement and allows higher BPRs. Our analysis team designed nine notional UHB propulsion systems for this new aircraft along a parametric design sweep of fan pressure ratio. Using advanced computational tools, these propulsion systems were ana