Abstract:The bypass ratio of newer turbofan engines has been increasing steadily and has reached $10; even higher bypass ratios are being considered for improving aircraft fuel efficiency. An accurate method for the prediction of jet noise over a wide range of bypass ratio, from $5 to ultra-high bypass ratios ($20), is required to address current and future needs. The main objective of the current study is the development of a procedure for real-world application that would permit the accurate prediction of jet noise, … Show more
“…As seen, there is good agreement at all angles of 80°, 110°, 130° and 150°. Several examples, with good agreement, shown in Viswanathan 165 at cycle conditions that match existing modern turbofan engines indicate that, the characteristic scales as well as the velocity ratio control the contributions from the different sub-components, at various angles.Figure 65.Comparison of spectral prediction with data. Symbols: data; lines: prediction.…”
Section: Practical Applicationsmentioning
confidence: 77%
“…Similarly good agreement is demonstrated for other airplane/engine combinations from approach to takeoff power. As stated in Viswanathan, 165 the practical benefits of the accurate prediction of jet noise are multifold: (1) it enables the identification and extraction of the individual noise components and helps establish their dominance as functions of frequency, angle and flight/engine conditions; (2) it allows the quantification of the sensitivities of the different components at various flight conditions;…”
Section: New Methods For Spectral Prediction Of Jet Noise From Turbof...mentioning
confidence: 99%
“…are provided in Viswanathan. 165 As noted, it is straightforward to calculate the characteristic scales from the conservation equations for mass, momentum, energy and the equation of state. Various regions of the jet contribute to different portions of the total spectrum at each angle.…”
It is a distinct privilege to produce this article to honor Professor Tam, the foremost authority on jet aeroacoustics. The fundamental characteristics of jet noise have been studied for 70 years, since the pioneering work of Lighthill in the 1950s. The acoustic analogy, with many variants, has served as the leading theory for nearly 50 years. Many leading researchers in the 1970s formulated theories to interpret the measured trends from subsonic and supersonic jets, using acoustic analogy and flow features as the framework. Quadrupoles, dipoles and monopoles were believed to constitute the sources of noise. The discovery of large-scale organized structures in free shear layers and jets sparked a different avenue of thinking about their importance for noise generation. Tam was the first to clearly demonstrate that these structures are efficient generators of noise and constitute the dominant noise sources, especially in the downstream direction. Now, two schools of thought emerged on the sources of jet noise. Experimental measurements showed that the mean flow as well as the turbulence statistics exhibit a self-similarity in the mixing layer and another similarity in the fully developed jet. Based on these observations, Tam proposed that since noise is generated by the turbulence of the jet, the noise spectra generated by fine-scale and large-scale turbulence should also exhibit self-similarity. By examining a large set of supersonic jet noise data acquired at NASA Langley, Tam offered evidence that the turbulent mixing noise of high-speed jets does consist of two independent self-similar components. In this paper, experimental evidence is compiled from an extensive database that quantifies the effect of several parameters that affect jet spectra. A new scaling method is developed and extended to noise predictions for realistic dual-stream nozzle geometries. The objectives of this paper are to serve as a synthesis of noise characteristics and to focus on application to real-world problems. Results from five different experimental measurements are examined: (1) farfield spectral characteristics; (2) azimuthal and polar correlations in the farfield; (3) correlations of jet turbulence fluctuations and farfield sound; (4) measurement of source distributions with an elliptic mirror; and (5) space-time correlation measurements in the nearfield with a cage array, and nearfield-farfield correlations. Two distinctly different trends are observed in the angular ranges of 50° – ∼120° and ∼120° – 165° for all the parameters investigated with the above five approaches. The salient observations are mutually supporting, and the cumulative weight lends credence to the proposition that there are two distinct sources of turbulent mixing noise.
“…As seen, there is good agreement at all angles of 80°, 110°, 130° and 150°. Several examples, with good agreement, shown in Viswanathan 165 at cycle conditions that match existing modern turbofan engines indicate that, the characteristic scales as well as the velocity ratio control the contributions from the different sub-components, at various angles.Figure 65.Comparison of spectral prediction with data. Symbols: data; lines: prediction.…”
Section: Practical Applicationsmentioning
confidence: 77%
“…Similarly good agreement is demonstrated for other airplane/engine combinations from approach to takeoff power. As stated in Viswanathan, 165 the practical benefits of the accurate prediction of jet noise are multifold: (1) it enables the identification and extraction of the individual noise components and helps establish their dominance as functions of frequency, angle and flight/engine conditions; (2) it allows the quantification of the sensitivities of the different components at various flight conditions;…”
Section: New Methods For Spectral Prediction Of Jet Noise From Turbof...mentioning
confidence: 99%
“…are provided in Viswanathan. 165 As noted, it is straightforward to calculate the characteristic scales from the conservation equations for mass, momentum, energy and the equation of state. Various regions of the jet contribute to different portions of the total spectrum at each angle.…”
It is a distinct privilege to produce this article to honor Professor Tam, the foremost authority on jet aeroacoustics. The fundamental characteristics of jet noise have been studied for 70 years, since the pioneering work of Lighthill in the 1950s. The acoustic analogy, with many variants, has served as the leading theory for nearly 50 years. Many leading researchers in the 1970s formulated theories to interpret the measured trends from subsonic and supersonic jets, using acoustic analogy and flow features as the framework. Quadrupoles, dipoles and monopoles were believed to constitute the sources of noise. The discovery of large-scale organized structures in free shear layers and jets sparked a different avenue of thinking about their importance for noise generation. Tam was the first to clearly demonstrate that these structures are efficient generators of noise and constitute the dominant noise sources, especially in the downstream direction. Now, two schools of thought emerged on the sources of jet noise. Experimental measurements showed that the mean flow as well as the turbulence statistics exhibit a self-similarity in the mixing layer and another similarity in the fully developed jet. Based on these observations, Tam proposed that since noise is generated by the turbulence of the jet, the noise spectra generated by fine-scale and large-scale turbulence should also exhibit self-similarity. By examining a large set of supersonic jet noise data acquired at NASA Langley, Tam offered evidence that the turbulent mixing noise of high-speed jets does consist of two independent self-similar components. In this paper, experimental evidence is compiled from an extensive database that quantifies the effect of several parameters that affect jet spectra. A new scaling method is developed and extended to noise predictions for realistic dual-stream nozzle geometries. The objectives of this paper are to serve as a synthesis of noise characteristics and to focus on application to real-world problems. Results from five different experimental measurements are examined: (1) farfield spectral characteristics; (2) azimuthal and polar correlations in the farfield; (3) correlations of jet turbulence fluctuations and farfield sound; (4) measurement of source distributions with an elliptic mirror; and (5) space-time correlation measurements in the nearfield with a cage array, and nearfield-farfield correlations. Two distinctly different trends are observed in the angular ranges of 50° – ∼120° and ∼120° – 165° for all the parameters investigated with the above five approaches. The salient observations are mutually supporting, and the cumulative weight lends credence to the proposition that there are two distinct sources of turbulent mixing noise.
“…2. When the aircraft is close to the ground, aircraft-induced noise has been evaluated under four main headings (Basner et al 2017;Franssen et al 2004;Klaeboe et al 2006;Viswanathan 2018):…”
Aircraft noise emissions are a problem that negatively affects human health, directly or indirectly. For this reason, examining and managing the noise effects caused by aircrafts at the airports is important for the sustainable development of aviation. In the present study, a noise management model based on the multiapproach method, including some actions related to aircraft noise, has been created. The model was applied to the International Eskisehir Hasan Polatkan Airport (LTBY). Within the scope of the model, in the first stage, in 365 days, day, evening and night noise levels around the airport were simulated using IMMI software under the European noise directive and European Civil Aviation Conference (ECAC) doc 29-interim was also used to measure aircraft noise. In the second stage, the noise generated by the Cessna 172-S aircraft under different operating conditions experimentally measured was carried out. After the model had been applied to LTBY, improvement opportunities for aircraft noise were evaluated. It is thought that the study and its results will help other civil airports on the issue of noise problem at airports.
“…In-flight jet mixing noise effects, measured in the acoustic far field, have been investigated extensively both in open jet wind tunnels [7][8][9] and full-scale turbojet engines [10]. Scarce amounts of experimental data, however, exist regarding the unsteady flow field of in-flight jets.…”
In this paper, insight is provided into the modelling of single-point and two-point statistics of a subsonic round jet discharged into a moving ambient medium. An experimental campaign has been performed comprising two round, unheated air flows-a central 'jet' at Mach number equal to 0.6 surrounded by a slower 'flight' flow. Constant temperature hot-wire anemometry was used to measure both the axial and radial velocity fluctuations within the turbulent jet flow field. A Mach 0.6 jet was discharged into the flight flow, which ranged from zero up to Mach 0.3. The data show that the degree to which the jet stretches with increasing flight velocity can be discerned with knowledge of the decay of the mean velocity field downstream of the end of the jet's potential core. This stretching factor can then be used to predict the changes
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