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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
with V in kt. Although the range is explicitly independent of V,V must have the value appropriate to the cruise (L/D). Increasing V by increasing the altitude or W/S will not increase the range but will decrease the flight time (and increase the power required). Although the maximum range occurs when (L/D) is at its maximum value, the associated airspeed, especially with an aspirated engine, is usually much lower than the maximum airspeed of the aircraft and the required power for cruise is below the best operating point for the engine. Consequently, the cruise of a piston-prop is customarily at 75% of the maximum power available to reduce flight time and favor the engine. With respect to other power plants, whereas a turbojet is a single-flow engine that produces only jet thrust, a turbofan is a multiflow engine that uses a turbine to drive a multibladed ducted fan that produces thrust power in addition to jet thrust. It has characteristics of both turbojet and propeller aircraft, and its performance (and specific fuel consumption) lies in the region between the two but closer to the turbojet. The turbojet range equation is normally used.
Engine performance
Published in Mohammad H. Sadraey, Aircraft Performance, 2017
Thus, a turbofan engine is a modified version of a turbojet engine to improve few performance characteristics. A turbofan engine is a gas turbine engine in which the turbine extracts gas power in excess of that required to drive a fan or low-pressure compressor in a fan (auxiliary) duct, usually annular around the primary duct (core). The turbofan engine imparts momentum to greater volume of air than a turbojet, but the velocity added is less.
Mobile sources
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
The sulphur content of aviation fuel is typically 400 ppm (i.e. 0.4 g S/kg fuel). Most fuel sulphur is expected to be emitted as SO2, with 2%–10% in the higher oxidised forms of H2SO4 and SO3. The turbofan uses the hot exhaust gas flow to drive a fan which draws a bypass flow through the engine and contributes to the thrust. The bypass ratio has been raised to increase engine efficiency, and along with this trend the combustion temperatures and pressures have also been increased. These high-bypass, more fuel efficient engines reduce CO2 and H2O emissions (due to greater fuel efficiency), and also HC and CO emissions. However, NOx emissions are increased, and there is an inevitable trade-off. One of the burning issues associated with aircraft emissions is the increased levels of ozone in the upper troposphere and lower stratosphere resulting from the atmospheric chemistry of emitted NOx. More recent detailed investigations using Chemical Transport Model (CTM), including detailed tropospheric and stratospheric chemistry have estimated the short-lived radiative forcing (RF) from O3 to range between 16.4 and 23.5 mW m−2. Generally, NOx contributes to production of O3 in the troposphere and to destruction of O3 in the stratosphere. Cruising at 2000 ft higher altitude increases the total RF due to aircraft NOx emissions by 2 ± 1 mW m−2, while cruising at 2000 ft lower altitude reduces RF by 2 ± 1 mW m−2, which is mainly controlled by short-lived O3 chemistry.
Influence of Mach number on the off-design performance of S-shaped compressor transition duct under the combined effect of curvature and pressure gradient
Published in Australian Journal of Mechanical Engineering, 2022
Manish Sharma, Beena D. Baloni
A turbofan engine bypasses some portion of the total airflow from the compressor, combustion chamber, turbine, and finally through a nozzle to meet the demand of lower noise and specific fuel consumption (SFC). A twin-spool arrangement is preferred due to the stability concerns of a high-pressure turbofan engine, which helps to obtain the desired bypass and pressure ratios (Saravanamuttoo, Rogers, and Cohen 2001). In a twin-spool turbofan engine, the flow must be directed from a low-pressure compressor (LPC) to a high-pressure compressor (HPC) through a substantial radial offset annular duct. This duct is generally referred to as a compressor transition duct and is designed with a constant area ratio and negligible diffusion (Norris 1998). Moreover, optimisation and weight restrictions dictate that the transition duct must be as short as possible (Sharma and Baloni 2019; Britchford et al. 1994), and optimisation helps to increase the radial offset, decreasing the axial design space between the fans and cores without affecting the performance of a turbofan engine (Lu, Zheng, and Li 2014). Hence, it is intentionally designed as an S-shaped form attaining a certain level of curvature; however, this curvature induces the secondary flow and three-dimensional effects on the flow (Ng et al. 2008; Bansod and Bradshaw 1972).