An Ultra-High Bypass Turbofan is generally considered to be any turbofan with a bypass ratio of 10 or higher. The move towards ultra-high bypass ratios is a logical one based on the performance benefits (reduced TSFC, increased specific thrust, improved propulsion efficiency, and reduced noise) rendered from the use of turbofan engines.
With the ultra-high bypass turbofan, the jet noise becomes an almost negligible noise source, as compared to the fan noise. Thus, fan noise has become a major focus of UHB turbofan research.
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information on the potential fuel savings of UHB technology.