An Assessment of Ultra High Bypass Engine Architecture and Installation Considerations

Abstract

As commercial airliners push for reduction in aircraft noise, emissions, and fuel burn, aircraft and engine manufacturers are accelerating the development of technologies aimed to meet those goals. A reduction in fuel burn, in particular, has led to a trend of very high bypass engines (VHBR), such as the PW1100G and the GEnx. By increasing bypass ratio (BPR) and the fan diameter, higher propulsive efficiencies for turbofans are able to be met, in turn decreasing TSFC. Engines with BPR greater than 25 are now deemed to be achievable through installing variable geometry, removing the nacelle-based thrust reverser, and installing the engine on next generation aircraft configurations. The objective of this work is to develop and investigate different aircraft and engine combination concepts that will provide a reduction in fuel burn. More specifically, a variable pitch geared fan with an aircraft-based thrust reverser, defined as VPF in this study, and a geared fan with a variable area nozzle and a nacelle-based thrust reverser, defined here as VHBR, will be compared on a tube and wing aircraft. To perform this study, each engine model will be implemented within the Environmental Design Space (EDS) in order to receive integrated, relative performance impacts of the two engines. A tradeoff study was then performed with a Boeing 737-800 to obtain the net vehicle fuel burn. EDS was modified to better quantify installation effects in order to meet constraints as fan diameter increases with BPR. Constraints for tire clearance, ground clearance, and roll angle were assessed and the engine location and/or landing gear length were updated accordingly. In order to counteract the new moment caused by the change in engine location, the vertical tail was then resized based on the new engine location. The analysis concluded that the VPF resulted in lower fuel burn than the VHBR when compared with the same engine parameters, and both engines needed to move outboard at lower fan pressure ratios (FPR) to maintain installation constraints.

A Review of Novel and Non-Conventional Propulsion Integrations for Next-Generation Aircraft

“…It is therefore evident that in addition to performance trade-offs, space constraints may represent a blocking limitation for the maximum exploitation of UHBR technology. Similar considerations on installation constraints are discussed qualitatively in [80], where additional limitations are discussed, as the maximum roll angle available before the nacelle ground striking.…”

“…The selected reference aircraft features the typical specifications of the so-called middle of the market [82], with a number of passengers equal to 250, a design range of 4600 nm and a selected turbofan with a BPR equal to 16.3. A CFD RANS analysis Similar considerations on installation constraints are discussed qualitatively in [80], where additional limitations are discussed, as the maximum roll angle available before the nacelle ground striking.…”

System Architecture Optimization: An Open Source Multidisciplinary Aircraft Jet Engine Architecting Problem

“…The same principles apply to the geared turbofans: they seem to result in close to the lowest TSFC of all engine architectures, as compressors and fan rotate at optimal speeds, while simultaneously also providing low weight for the turbofan cluster. UHBR turbofans achieve a reduction in TSFC, but this comes at the price of higher weight due to the increased diameter of the engine [13]. The lowest TSFC in the entire optimization problem was also achieved by a UHBR turbofan at 6.7 g/kNs, and is indicated in Fig.…”

“…2)? Is the fan directly connected to the low-pressure compressor, or is a gearbox inserted [13]? At what stage is air bled off for the environmental control system (if at all)?…”