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Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
One of the main challenges for the aeroengine designer is to develop new power systems that fulfill the requirements of both civil and military aircraft. The main issues now are the reduction of fuel burn, emissions, and noise while maintaining very high power/thrust levels and high propulsive and thermal efficiencies. Such engines, characterized by great power/thrust and low fuel consumption, directly affect an aircraft’s payload, maneuverability, and maximum range. Perhaps the obvious way to reduce emission is to reduce the fuel burnt. Increasing the bypass ratio (BPR) of turbofan engines minimizes the kinetic energy of the exhaust gas and thus increases the propulsive efficiency. Then the value of the BPR is near its limit, and it is difficult to think of ways to continue this trend indefinitely [1]. However, the ultra-bypass ratio (UBPR) is a feasible proposal. With compressor and turbine efficiencies near plateauing, and turbine inlet temperatures paced by materials and blade cooling technologies, improvements in thrust specific fuel (SFC), specific power, and weight for conventional engines (including turboprop and turboshaft engines and larger turbofans) will likely be incremental compared with the past [2].
Fundamentals of human response to sound
Published in Frank Fahy, John Walker, Fundamentals of Noise and Vibration, 2003
Over the years since the Wilson Committee was appointed there has been a considerable amount of research and development work carried out into the problem of noise. Noise at source has been reduced, in some cases by considerable amounts. For example, modern high bypass ratio aircraft engines are much quieter than the low by-pass ratio aircraft engines used in the Boeing 707s and Comet aircraft used at the time of the Wilson Report, and there arc similar improvements in the noise generated by motor vehicle engines. Buildings can now be designed to exclude noise at relatively low cost, and there are numerous standards and regulations all designed to control or limit noise.
Environmental challenges and the aerospace industry
Published in Wesley Spreen, The Aerospace Business, 2019
Technical causes of aircraft noise are generally understood by design engineers, who have reduced noise levels by approximately 80% since the 1950s. However, due to trade-offs that are inevitably part of aircraft design, changes to reduce noise potentially entail degradation of other aspects of performance. Much of the noise reduction in recent decades is attributable to jet-noise reduction, a characteristic of high-bypass-ratio engines, which have also yielded greatly improved fuel efficiency. High-bypass-ratio engines, however, have increased fan diameters and large nacelles, which increase aircraft weight and aerodynamic drag. Thus, at some theoretical point the noise reduction and efficiency benefits of increasing bypass ratios will be offset by penalties imposed by larger nacelles. Numerous noise reduction opportunities involving airframe aerodynamic design also involve difficult trade-off decisions. For example, the noise from wing leading-edge slats separated by gaps is significantly higher than a ‘drooped leading edge’ design, which performs the same purpose as slats but has historically been less aerodynamically efficient, resulting in higher fuel consumption. Likewise, airframe noise can be reduced very effectively by reducing landing speed. However, slower landing speed requires a larger wing, which entails substantial weight and drag penalties. Another comparatively simple but effective technical solution for noise reduction involves the installation of aerodynamic fairings around landing gear components. The landing gear has historically not been designed with aerodynamic shape as a priority and consequently generates inordinate turbulence and commensurate noise. The noise problem is particularly problematic because, obviously, the landing gear is deployed when the aircraft is close to the ground. Testing by NASA and Boeing indicates that landing-gear noise can be greatly attenuated by means of relatively simple fairings that divert air to minimize turbulence.
Internal Ballistics of a Boron-Containing Solid Fuel Ramjet
Published in Combustion Science and Technology, 2021
Hertzel Kadosh, Benveniste Natan
As the bypass ratio increases, less air flows to the main combustor, the regression rate decreases and also do the fuel flow rate and thrust. Therefore, thrust regulation of ramjet engine is demonstrated using bypass air, mainly at high bypass ratio (BR > 0.5).