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Improvement of aeropropulsion fuel efficiency through engine design
Published in Emily S. Nelson, Dhanireddy R. Reddy, Green Aviation: Reduction of Environmental Impact Through Aircraft Technology and Alternative Fuels, 2018
Kenneth L. Suder, James D. Heidmann
NASA’s aggressive noise and fuel burn reduction goals are driving aircraft engine designs to higher bypass ratios and larger fan diameters. Aircraft engine noise and fuel burn reduction are directly correlated to fan size, fan pressure ratio and fan bypass ratio. As the fan size increases, there is a corresponding drop in fan pressure ratio and an increase in fan BPR. At some point, as the fan size continues to increase, a minimum is reached between fan size and weight and drag. The larger, heavier nacelle produces more drag during flight, and overcomes the advantages of a larger fan. Hence, a technology paradigm shift is needed to reduce the minimum point, which is produced by introducing advanced fan and core technology. A shift of this type was produced by Pratt & Whitney (P&W) with their geared-turbofan (GTF) UHB engine design. UHB engines are defined as engines with a fan BPR equal to or greater than 12. NASA in cooperation with P&W has been investigating UHB technology over the last 20 years, but the GTF is the first generation of UHB engines that will see EIS with an aircraft manufacturer. The paradigm shift produced by the GTF is achieved by operating the fan and core in such a way as to optimize the performance of both. Direct-drive turbofans necessarily operate the fan and low-pressure turbine at the same speed. At low fan speeds, the LPT is operating at faroff-design conditions, and its efficiency goes down, increasing fuel burn. P&W introduced a gearbox into their GTF engine design that allows the fan and LPT to operate at different speeds—thus more optimum, higher efficiency conditions—and so reduced fuel burn. As BPR increases, the mean radius ratio of the fan and LPT increases. Consequently, if the fan is to rotate at its optimum blade speed, the LPT will spin slowly so that additional LPT stages will be required to extract sufficient energy to drive the fan. Introducing a planetary reduction gearbox with a suitable gear ratio between the low-pressure shaft and the fan enables both the fan and LPT to operate at their optimum speeds. A geared turbofan uses a larger fan that moves more air at a lower speed, allowing the same thrust as its nongeared counterpart, but with less energy expended.
Turbofan Engines
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
There are several advantages to the turbofan engine over both turboprop and turbojet engines. The fan is not as large as the propeller, so the increase of speeds along the blade is less. Thus a turbofan engine can power civil transport flying at transonic speeds up to Mach 0.9. Also, by enclosing the fan inside a duct or cowling, the aerodynamics are better controlled. There is less flow separation at the higher speeds and less trouble with shock developing. The turbofan may suck in more air flow than a turbojet, and thus generate more thrust. Like the turboprop engine, the turbofan has low fuel consumption compared with the turbojet. The turbofan engine is the best choice for high-speed, subsonic commercial airplanes. The advantages of turbofan engines are as follows:The fan is not as large as the propeller; therefore, higher aircraft velocities can be reached before vibrations occur. The aircraft is able to reach transonic speeds of Mach 0.9.The fan is more stable than a single propeller; therefore, if the vibration velocity is reached, vibrations are less apparent and do not disrupt the airflow as significantly.The fan is encased in a duct or cowling; therefore, the aerodynamics of the airflow is controlled a lot better, providing greater efficiency.For geared turbofan engines, the gearbox required to translate the energy from the compressor/fan to the turbine is relatively small and less complex as the fan is smaller. This reduces the weight and aerodynamic drag loss that are present in the turboprop design.The smaller fan is more efficient and takes in air at a greater rate than the propeller, allowing the engine to produce greater thrust.The turbofan engine is a much more fuel-efficient design than the turbojet and is able to equal some of the high-performance velocities.As illustrated in Figure 1.51, in the classification section of Chapter 1, numerous types of turbofan exist. Next, we present a detailed analysis of a few types of turbofans.
State-of-the-art review of energy harvesting applications by using thermoelectric generators
Published in Mechanics of Advanced Materials and Structures, 2023
Babak Safaei, Sertan Erdem, Mohammad Karimzadeh Kolamroudi, Samaneh Arman
Based on a finite element method-based performance analysis, Bode et al. [175] reveals that TEG operation on a designed geared turbofan with an unmixed nozzle on cruise, where the speed is higher than 0.76 Mach and altitude is 35,000 ft., specific power of high pressure turbine (HPT) is 9 kW/m2 whereas the nozzle has 1 kW/m2 of specific power. Allmen et al. [70] showed using TEGs in a system which focuses on wireless sensor electronics can be run during a flight. It can be seen that TEG voltage behaves parallel to temperature on TEG hot-side when the cold-side temperature remains stable in Figure 35.