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Noise emissions from commercial aircraft
Published in Emily S. Nelson, Dhanireddy R. Reddy, Green Aviation: Reduction of Environmental Impact Through Aircraft Technology and Alternative Fuels, 2018
In the case of engine noise, power generation processes inside the engine, namely, compression, combustion and expansion, are mainly responsible for generation of pressure fluctuations in the airstream. In contrast, airframe noise is nonpropulsive and “self-generated” through the creation of unsteady flow and turbulence when the airstream interacts with the landing gear and the high- lift devices (i.e., trailing edge flaps and leading edge slats). Even when the landing gear and high-lift devices are retracted (the so-called clean configuration), the airflow over the fuselage and wing generates noise. However, airframe noise level increases substantially (by as much as 10 dB or more) when the landing gear and/or high-lift devices are deployed. The noise produced by the airframe components is mostly broadband, although some tones could also be generated by vortex shedding from sharp edges or from flow over cavities like fuel and anti-ice vents on the airframe. The relative importance of various airframe noise sources depends on the type of the aircraft.
Principles of flow visualization
Published in Stefano Discetti, Andrea Ianiro, Experimental Aerodynamics, 2017
But perhaps the most extended (and oldest) visualization technique in experimental aerodynamics consists in the use of small tufts with their tips pinned to an aerodynamic surface. Although the information that they yield is less quantitative than that obtained using liquid and/or sublimating coatings, the easiness to implement the technique has granted tufts their popularity. In the laboratory, they can be used to determine the flow direction at a surface and to spot regions of flow separation. For instance, Figure 4.6 shows a test model of an airplane being tested in a wind tunnel, using tufts to assess flow separation in different flow configurations: clean configuration, low angle of attack (a); clean configuration, high angle of attack (b); and with flaps partially deployed (c). In this example, it can be observed how the flow remains attached in configurations (a) and (c) but exhibits separation at different locations near the trailing edge (see (d) for a close-up view of the near-tip region).
Numerical simulation for the differences between FTN/WPN engine models aerodynamic influence on BWB300 airframe
Published in Engineering Applications of Computational Fluid Mechanics, 2020
From the comparison between pressure coefficient distribution of the three configurations at different angles of attack, it shows that: at angles of attack below 9°, the lower surface flows of the three configurations were the same and the upper surface flow of the WPN was always faster than the other two at the same angle. This was the main reason why the lift and drag of the WPN were bigger than that of the FTN and Clean configuration when the angle of attack was below 9°. The WPN configuration upper surface stream velocity initially decreased, then increased near the engine inlet to satisfy the powered engine air inlet requirement. However, at angles of attack above 11°, because of the flow separation, the engine capture flow needed greater velocity to balance the mass loss, thereby causing a suction peak at the upper surface in front of the engine. The pressure was lower as the angle increased, thus causing a larger flow separation area. This also caused the trailing edge pressure to decrease, which made the flow pressure distribution behind about 20% of the local chord on the lower surface of the WPN configuration and lower than those of the FTN and Clean configurations at the same angle. Moreover, the flow at the front of the engine on the upper surface of the WPN configuration was also not always lower than that of the FTN and Clean configurations. The lower surface pressure decrease and the upper surface pressure increase, causes the lift curve to flatten at 9°: 11°, but an increase in the lift and flow separation should increase the drag; therefore, the drag of the WPN configuration was still growing. Above 11°, except for the separated area, the other location also provided a lift, so the lift curve of the WPN configuration increased linearly again until 19°. The FTN configuration did not have any power influences and it maintained a nearly constant aerodynamic force curve trend as the Clean configuration.
Airline pilot perceptions and implementation of fuel saving actions
Published in International Journal of Sustainable Transportation, 2022
Seung Joon Jeon, Kwang Eui Yoo, Sihyun Yoo
Reduced Acceleration Altitude is a best practice for increasing fuel efficiency in the climbing phase. The principle is to accelerate at an altitude lower than what is usually done. By accelerating at a lower altitude, the clean configuration is reached earlier and drag is reduced2.