Journal articles on the topic 'Turbofan intake noise radiation'
To see the other types of publications on this topic, follow the link: Turbofan intake noise radiation.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 37 journal articles for your research on the topic 'Turbofan intake noise radiation.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Palma, Giorgio, Lorenzo Burghignoli, Francesco Centracchio, and Umberto Iemma. "Innovative Acoustic Treatments of Nacelle Intakes Based on Optimised Metamaterials." Aerospace 8, no. 10 (October 14, 2021): 296. http://dx.doi.org/10.3390/aerospace8100296.
Abstract:
Modern turbofans with high bypass ratios, low blade passage frequencies and short nacelles require continuous development of acoustic linings to achieve the noise reductions expected by the international aviation authorities. Metamaterials and metafluids have been recently proposed as promising technologies for designing innovative acoustic treatments dedicated to reducing aeronautic turbofan noise emissions. In this work, a phase-gradient metasurface treatment is investigated as a way to tackle the noise radiation from an axially symmetric nacelle. This paper aims to study the potential benefits of the mentioned technology, and is not an attempt to design a complete new liner or nacelle. The metasurface is modelled through an equivalent metafluid, and a simulation-based optimisation is used in defining the design parameters. The tonal contribution of the blade passage frequency is considered, and the numerical results with the metafluid optimised on one azimuthal mode at a time show a significant effect in terms of acoustic levels and directivity over an arc of virtual receivers.
2
Guérin, S., and A. Holewa. "Fan tonal noise from aircraft aeroengines with short intake: A study at approach." International Journal of Aeroacoustics 17, no. 6-8 (August 7, 2018): 600–623. http://dx.doi.org/10.1177/1475472x18789001.
Abstract:
This work assesses the risks of increased fan noise for high bypass ratio aeroengines with short intakes. The close proximity between the fan and inlet contributes to the increase in radiation of the rotor-alone tones and reinforces the interaction of the inflow distortion with the fan. Thus, the closer the fan is to the inlet, the higher the risk for noise generation. This article discusses the results of Harmonic Balance simulations performed on a conceptual turbofan operated at the approach condition. The inflow distortion created by the nacelle incidence is dominated by the circumferential component [Formula: see text] = 1. Its presence is visible throughout the nacelle. A thorough analysis of the unsteady pressure and velocity fields shows that the new acoustic source created by the periodic unsteady loading of the rotor cutting the inflow distortion is negligible compared to the rotor–stator interaction. But the amplitude of the rotor–stator interaction tones is affected by the unsteadiness of the rotor wake shape, particularly in the tip region where a pronounced flow separation on the rotor blade is created at a certain range of azimuthal position. The variations of the flow incidence at the rotor leading edge, due to the axial and tangential components of the mean velocity, cannot explain that flow separation. Instead, the origin is attributed to the azimuthal variations of the radial component of the mean flow velocity near the casing which slightly points inward to the spinner, i.e. in the opposite direction of the casing contour line. The flow separation induces a pronounced scattering of the wake azimuthal components mw = hB into [Formula: see text] in the tip region, whereas the same effect is rather limited on the rest of the blade height. This leads to a moderate increase of the tonal sound power level compared to the case with clean inflow. The azimuthal scattering due to the propagation of the sound waves through the distortion is found to be weak in the bypass duct. However, this effect is very important in the inlet lip vicinity, where the strong asymmetry of the flow modifies the path of the sound waves up to the far field.
3
Groeneweg, J. F., and E. J. Rice. "Aircraft Turbofan Noise." Journal of Turbomachinery 109, no. 1 (January 1, 1987): 130–41. http://dx.doi.org/10.1115/1.3262058.
Abstract:
Recent advances in the understanding of turbofan noise generation and suppression in aircraft engines are reviewed with particular emphasis on NASA research. The review addresses each link in the chain of physical processes which connect unsteady flow interactions with fan blades to far field noise. Mechanism identification and description, duct propagation, radiation, and acoustic suppression are discussed. Recent advances in the experimental technique of fan inflow control assure that inflight generation mechanisms are not masked by extraneous sources in static tests. Rotor blade surface pressure and wake velocity measurements aid the determination of the types and strengths of the generation mechanisms. Approaches to predicting or measuring acoustic mode content, optimizing treatment impedance to maximize attenuation, translating impedance into porous wall structure, and interpreting far field directivity patterns are illustrated by comparisons of analytical and experimental results. A persistent theme of the review is the interdependence of source and acoustic treatment design to minimize far field noise. Areas requiring further research are discussed and the relevance of aircraft turbofan results to quieting other turbomachinery installations is addressed.
4
Özyörük, Y., E. Alpman, V. Ahuja, and L. N. Long. "Frequency-domain prediction of turbofan noise radiation." Journal of Sound and Vibration 270, no. 4-5 (March 2004): 933–50. http://dx.doi.org/10.1016/s0022-460x(03)00640-0.
5
Korotin, P. I., O. A. Potapov, G. E. Fiks, I. S. Fiks, Ia S. Pochkin, and I. D. Khaletskii. "Active noise suppression in the model of turbofan intake duct." Aviation Engines, no. 2 (2021): 7–16. http://dx.doi.org/10.54349/26586061_2021_2_7.
6
Polacsek, C., and S. Burguburu. "Fan Interaction Noise Predictions Using RANS-BEM Coupling." International Journal of Aeroacoustics 4, no. 1-2 (January 2005): 153–67. http://dx.doi.org/10.1260/1475472053729987.
Abstract:
A source-to-far-field computation procedure aiming at predicting the noise generated by rotor-stator fan interactions and inlet noise radiation is presented here. It is applied to the NLR turbofan model, tested in DNW-LLF anechoic chamber under the framework of DUCAT project. The unsteady aerodynamic input for the acoustic computation is obtained using a 3D RANS code, CANARI, developed at ONERA for turbomachinery applications. The CFD solutions are coupled, using a modal expansion approach, to a BEM code, solving the Helmholtz equation in an arbitrary bounded space. A single interacting cut-on mode amplitude is either directly deduced from experiment or provided by post-processing the CFD data. With this approach, the predicted noise radiation can be related to the directivity patterns measured at several axial positions upstream of the turbofan inlet. A fairly good agreement is found using both experimental and CFD input data.
7
Rouvas, D.-M., and A. McAlpine. "Prediction of Fan Tone Radiation Scattered By A Cylindrical Fuselage." IOP Conference Series: Materials Science and Engineering 1226, no. 1 (February 1, 2022): 012050. http://dx.doi.org/10.1088/1757-899x/1226/1/012050.
Abstract:
Abstract A theoretical prediction method of the scattering of fan tone radiation from a turbofan inlet duct by the airframe fuselage is presented. The fan tone noise is modelled by an acoustic disc source that represents the sound field at the inlet duct termination. Adjacent to the source is a cylindrical fuselage that scatters the fan tone radiation. The prediction method is valid for upstream sound radiation. The acoustic pressure on the cylindrical fuselage is affected by refraction of the sound as it propagates through the fuselage boundary layer. This effect known as boundary layer shielding is more prominent forward of the turbofan, since the fan tone noise radiated from the inlet duct is propagating upstream. An asymptotic approach is used to model sound propagation through a boundary layer which is modelled by a thin linear shear velocity profile. Consequently the scattered pressure field can be computed very quickly, thus providing a fast and efficient prediction method. Although a realistic fuselage turbulent boundary layer does not resemble a linear shear layer, it is shown that the effect of acoustic shielding by a turbulent boundary layer can be modelled by taking a liner shear profile with a shape factor that matches the shape factor for a realistic turbulent profile.
8
Parrett, A. V., and W. Eversman. "Wave envelope and finite element approximations for turbofan noise radiation in flight." AIAA Journal 24, no. 5 (May 1986): 753–60. http://dx.doi.org/10.2514/3.9342.
9
Kholodov, Pavel, and Stéphane Moreau. "Identification of Noise Sources in a Realistic Turbofan Rotor Using Large Eddy Simulation." Acoustics 2, no. 3 (September 22, 2020): 691–706. http://dx.doi.org/10.3390/acoustics2030037.
Abstract:
Large Eddy Simulation is performed using the NASA Source Diagnostic Test turbofan at approach conditions (62% of the design speed). The simulation is performed in a periodic domain containing one fan blade (rotor-alone configuration). The aerodynamic and acoustic results are compared with experimental data. The dilatation field and the dynamic mode decomposition (DMD) are employed to reveal the noise sources around the rotor. The trailing-edge radiation is effective starting from 50% of span. The strongest DMD modes come from the tip region. Two major noise contributors are shown, the first being the tip noise and the second being the trailing-edge noise. The Ffowcs Williams and Hawkings’ (FWH) analogy is used to compute the far-field noise from the solid surface of the blade. The analogy is computed for the full blade, for its tip region (outer 20% of span) and for lower 80% of span to see the contribution of the latter. The acoustics spectrum below 6 kHz is dominated by the tip part (tip noise), whereas the rest of the blade (trailing-edge noise) contributes more beyond that frequency.
10
Duta, M. C., and M. B. Giles. "A three-dimensional hybrid finite element/spectral analysis of noise radiation from turbofan inlets." Journal of Sound and Vibration 296, no. 3 (September 2006): 623–42. http://dx.doi.org/10.1016/j.jsv.2006.03.006.
11
Wang, Ruichen, and Xun Huang. "Sound radiation from semi-infinite elliptical ducts with uniform subsonic jets: An analytical approach." Journal of the Acoustical Society of America 154, no. 4_supplement (October 1, 2023): A188—A189. http://dx.doi.org/10.1121/10.0023221.
Abstract:
This paper presents an analytical method for modeling the acoustic field radiation from a semi-infinite elliptical duct with a uniform subsonic jet. Elliptical ducts are often used as inlets for turbofan engines to take full advantage of the pre-compression effect of the fuselage and improve the stealth performance of the aircraft. The method accounts for the instability wave inside the vortex sheet induced by the shearing of jet and ambient flow and its effect to sound radiation. The method uses Mathieu functions to describe the incident and scattered sound in the elliptic cylindrical coordinates. A semi-analytical Wiener-Hopf approach with low computational cost is applied to obtain the near and far field solutions. The near field is illustrated by acoustic pressure maps at different modes and circumferential angles. The far field is shown by directivity patterns at single tones. Numerical simulations based on a finite element method are conducted to validate the accuracy of the analytical method. The results show good agreement between the analytical and numerical solutions. The proposed method can be used to analyze the acoustic characteristics of elliptical ducts with jets, which are relevant for noise control and optimization of turbofan engine inlets.
12
Dong, Thomas Z. "On Boundary Conditions for Acoustic Computations in Non-Uniform Mean Flows." Journal of Computational Acoustics 05, no. 03 (September 1997): 297–315. http://dx.doi.org/10.1142/s0218396x97000174.
Abstract:
Many acoustic problems involve acoustic wave radiation to the exterior field. A common approach in numerical simulations is to restrict the computational domain to a finite region with artificial boundaries. The so-called radiation or non-reflecting boundary conditions must be imposed at those artificial boundaries. Most existing non-reflecting boundary conditions are derived for computing disturbances propagating in a known uniform mean flow near the boundaries. In many applications such as the computation of jet noise or turbofan noise, the mean flow at an artificial boundary is non-uniform and unknown. The mean flow also needs to be computed in these cases. Incorrect computation of this mean flow at the boundary could directly affect the near field physics as well as the far field acoustics. In the present paper, a set of boundary conditions is proposed which focuses on computing the correct mean solution at an artificial boundary, while still maintaining the non-reflecting feature for the outgoing transient and acoustic waves.
13
Liu, Hongda, Dan Sun, Jingguo Sun, and Jianyuan He. "Numerical Analysis of Flow Field and Aerodynamic Noise in Intake Structure." Journal of Physics: Conference Series 2463, no. 1 (March 1, 2023): 012052. http://dx.doi.org/10.1088/1742-6596/2463/1/012052.
Abstract:
Abstract The CFD numerical simulation was used to simulate the flow field and sound field of the intake system, combined with the acoustic finite element method. Based on the Lighthill acoustic analogy and the Möhring acoustic analogy method, the internal sound source distribution of the intake system, the intensity of the nozzle noise and the acoustic directivity were analyzed. Improvement measures were proposed from the perspective of noise transmission, and the influence of different wall thicknesses on the wall stimulated radiation noise, as well as the effects of attaching sound absorbing materials and spraying damping materials on wall radiation noise were studied.
14
Qiu, S., WB Song, and H. Liu. "Shape optimization of a general bypass duct for tone noise reduction using continuous adjoint method." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 228, no. 1 (March 25, 2013): 119–34. http://dx.doi.org/10.1177/0954406213481915.
Abstract:
A novel continuous adjoint-based acoustic propagation method is proposed for low-noise turbofan duct design. A fan bypass duct tonal noise propagation model that is verified by comparison with an analytical solution of the modal radiation from a semi-infinite duct with the shear layer is enhanced with its continuous adjoint formulation, having been applied to design the bypass duct. First, this article presents the complete formulation of the time-dependent optimal design problem. Second, a continuous adjoint-based acoustic propagation method for two-dimensional bypass duct configurations is derived and presented. This article aims at describing the potential of the adjoint technique for aeroacoustic shape optimization. The implementation of the unsteady aeroacoustic adjoint method is validated by comparing the sensitivity derivative with that obtained by finite differences. Using a continuous adjoint formulation, the necessary aerodynamic gradient information is obtained with large computational savings over traditional finite-difference methods. The examples presented demonstrate that the combination of a continuous-adjoint algorithm with a noise prediction method can be an efficient design tool in the bypass duct noise design problem.
15
Simon, Frank, Noah H. Schiller, Nicole Pettingill, Nicolas Zawodny, and Matt Galles. "Measurement of airborne sound insulation of building components by near-field acoustic holography." INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, no. 7 (February 1, 2023): 657–67. http://dx.doi.org/10.3397/in_2022_0091.
Abstract:
Unmanned aerial vehicles (UAVs) are currently being used for reconnaissance missions, tactical surveillance, and infrastructure inspection. When legislation allows it, these devices will provide additional services close to inhabited areas, which could lead to noise complaints. On most UAVs, the propellers are the dominant source of noise. As a result, researchers have studied the impact of propeller shape and blade count on noise. Much of this work, however, has focused on isolated propellers. While different UAV concepts are equipped with ducts for aerodynamic and protection reasons, few studies focus on the acoustic benefit of ducts, as is achieved, for example, on turbofan aircraft. The objectives of this paper are: first, to simulate the noise radiation of a UAV propeller in static conditions based on its location in a hard wall duct; second, to analyze the contribution of the different acoustic source components (i.e., thrust, torque, and thickness); and third, to validate the approach with experiments conducted in the NASA Small Hover Anechoic Chamber over a range of propeller rotation rates. In this experiment, it is shown that the best attenuation is achieved when the propeller is centered, axially, in the duct because of interference between upstream and downstream radiated waves.
16
Choung, HanAhChim. "Numerical investigation on radiation characteristics of aero-intake noise with ground effects." Journal of the Acoustical Society of America 140, no. 4 (October 2016): 3141. http://dx.doi.org/10.1121/1.4969845.
17
Шмырев, Владимир Федорович. "ОСОБЛИВОСТІ ПРОЕКТУВАННЯ НОСКА ПОВІТРОЗАБІРНИКА ТУРБОВЕНТИЛЯТОРНОГО ДВИГУНА." Open Information and Computer Integrated Technologies, no. 86 (February 14, 2020): 25–36. http://dx.doi.org/10.32620/oikit.2019.86.02.
Abstract:
Optimization of turbofan engine air intake as well as geometry of intake lip, in-let cross-sectional area and its length is a relevant task in optimizing aerodynamic configuration of an aircraft. It is necessary to ensure a smooth entry of air flow into the engine at all modes of its operation and at various aircraft evolutions while minimizing impact on the overall aerodynamic efficiency of the aircraft. Development of engine air intake was once a very long, routine process that could last for months be-fore design completion, followed by expensive tests on determination of air intake performances on the engine test bench and in flight. Today, we can evaluate performances for a large number of air intake options using design software. The use of computational methods does not exclude tests of air intakes but dramatically reduces their quantity, testing costs and allows designers to focus mainly on the best candidates for air intakes avoiding potential surprises such as shock waves or flow separation caused by a shock wave. Optimal design of the air intake includes determining the right balance between the air intake characteristics, structural load and weight. An over-designed air intake will ultimately be overweight and thus more expensive in terms of flight cost. In a well-designed air intake the Mach number should not exceed 1, in order to avoid a sudden change in static pressure, temperature and density, which can lead to potential shock waves and flow separation caused by a shock wave in all areas throughout the flight. The use of computational fluid dynamics al-lows a better understanding of the conditions under which such adverse events occur. Adjacent to this task is the provision of necessary area on the inside of air intake to ensure sufficient noise absorption generated by the engine fan. The article considers evolution of research on the example of air intake of the D-436 engine of the An-148 aircraft.
18
Nuckolls, W. E., and W. F. Ng. "Fan Noise Reduction From a Supersonic Inlet During Simulated Aircraft Approach." Journal of Engineering for Gas Turbines and Power 117, no. 2 (April 1, 1995): 237–44. http://dx.doi.org/10.1115/1.2814086.
Abstract:
A series of experiments was conducted to investigate the radiation of fan noise from a supersonic inlet during a simulated aircraft approach. A scaled-down model of an axisymmetric, mixed-compression, supersonic inlet (P-inlet) was used in conjunction with a 10.4 cm (4.1 in) diameter turbofan engine simulator as the noise source. The tests were conducted at an outdoor facility under static conditions. The main goal of the experiment was to reduce the forward radiating fan noise by modifying the auxiliary inlet doors. The modified doors are designed to reduce the inlet distortion to the fan face. In addition, the new door design also uses a converging flow passage in order to take advantage of the noise attenuation due to the choking effect at the auxiliary door. The simulator was tested at 60 percent design speed in an attempt to match the simulator noise source to that of a real aircraft engine on approach. Both aerodynamic and acoustic measurements were taken in the experiments. The results show that when compared to the original design, the modified auxiliary inlet doors reduced the circumferential inlet distortion to the fan face by a factor of two. The key result is that the blade passing frequency tone has been decreased by an average of 6 dB in the forward sector for the modified door design. Results from the closed auxiliary inlet door case are also presented to provide additional comparisons.
19
Liu, Chen, Yipeng Cao, Yang Liu, Wenping Zhang, Pingjian Ming, and Sihui Ding. "Numerical and experimental analyses of intake silencer and its effects on turbocharger compressor performance." Advances in Mechanical Engineering 11, no. 3 (March 2019): 168781401982667. http://dx.doi.org/10.1177/1687814019826677.
Abstract:
Numerical studies of a marine diesel engine intake silencer are conducted to evaluate its performance, and effects of the silencer on the turbocharger compressor performance are also discussed. The results show that the duct acoustic mode method can be used in the silencer transmission loss prediction, and the predicted noise reduction and main frequency range agree with the measurements fairly well. However, it is found that the silencer compromises the compressor performance by shortening its operating range. It is found that the static pressure on the compressor blade surface is decreased, thus the compressor total-to-total pressure ratio and isentropic efficiency are reduced. Pressure fluctuations at compressor rotor and stator inlets enhanced when a silencer is installed, which means the trend of pressure spectrum in the rotor and stator passage is changed. Compared with the results of a compressor in natural aspiration, it is found that the silencer can significantly reduce high-frequency noise. In particular, it is quite effective in tonal noise reduction. In addition, the compressor inlet noise spectrum indicates that noise radiation characteristics are different with a silencer installed.
20
RICHTER, CHRISTOPH, HANNES LÜCK, ŁUKASZ PANEK, and FRANK THIELE. "METHODS FOR SUPPRESSING SHEAR LAYER INSTABILITIES FOR CAA." Journal of Computational Acoustics 19, no. 02 (June 2011): 181–203. http://dx.doi.org/10.1142/s0218396x11004420.
Abstract:
The rearward propagation of tonal noise from the main fan and the engine core of modern high bypass aeroengines is one of the current demanding applications of CAA methods. One of the main features of this problem is the radiation of tones from main fan and turbine through the shear layers of core and bypass jets. This can approximately be described by a solution of the linearized perturbed Euler equations over a sheared turbulent averaged base flow field. However, these equations not only describe sound propagation, but also provide a stability analysis for the sheared base flow. Three techniques with the potential to calculate an acoustic solution and at the same time to suppress the instability are compared in this paper. The radiation of a source from a two-dimensional hot jet, chosen from a CAA workshop on benchmark problems, is considered first. Then, the techniques are adopted for the simulation of a single azimuthal mode radiating from the bypass duct of a turbofan engine, as an example for the realistic application. The first technique is based on filtering the mean flow field, over which the perturbation equations are solved. A low-order filter is applied. Subsequently, an adaption of this method, which considers a filtering of the mean flow derivatives in addition, is proved to be very beneficial. The result then reflects the analytical solution of the benchmark problem very well. The second technique filters the source terms in the governing equations. In a first attempt, all mean flow derivatives are neglected to suppress the instability. A more physical motivated variant of the approach neglects only source terms in the momentum equations. However, both provide unsatisfactory predictions of the acoustic field for the benchmark. Finally, a third technique is implemented, which considers the modification of the velocity derivatives in the momentum equations, as this method has demonstrated one of the best predictions for the benchmark problem. Nevertheless, the latter technique has no 3D extension and thus fails in suppressing the instability waves in the turbofan application.
21
Vasilyev, Andrey. "AUTOMOBILE INTERNAL COMBUSTION ENGINE LOW FREQUENCY NOISE REDUCTION USING ACTIVE NOISE CONTROL SOLUTIONS." Akustika 34 (November 1, 2019): 113–17. http://dx.doi.org/10.36336/akustika201934113.
Abstract:
Increased level of automobile low-frequency noise may cause significant environmental pollution, driver and passenger discomfort etc. For automobile equipped with internal combustion engine forming of either internal or external noise is mainly caused by engine operation. Approaches to automobile low-frequency noise reduction are suggested using active noise control method. The different variants of principal schemes and constructions of electronic units of forming required vibroacoustic characteristic of active noise control system were developed by the author either for complex noise reduction of experimental unit or for investigation of the separate noise sources reduction. Intercommunication of engine compartment and passenger compartment and coherent low-frequency sound radiation by air-suctioning pipe and exhaust pipe are taking into consideration. Construction of active noise control unit designed by author for complex reduction of exhaust and intake engine low-frequency noise is described. The results described in this paper may be useful for further development and application of constructions of active noise control systems as for efficient complex engine noise reduction or for reduction of the separate automobile engine noise sources.
22
Gounet, Helene, and Serge Lewy. "Three-Dimensional Sound Directivity around a Helicopter Turboshaft Engine." Journal of the American Helicopter Society 57, no. 4 (October 1, 2012): 1–10. http://dx.doi.org/10.4050/jahs.57.042002.
Abstract:
Turboshaft engines can be the main source of noise due to a helicopter at takeoff. Some new silencing designs of the inlets and of the ejector were tested on a Turbomeca Arrius 2B2 engine in an open-air static facility. Intake and exhaust are not axisymmetric, and conventional directivity patterns of sound field on a horizontal arc of circle are insufficient. A special microphone array on a vertical half-circle translating axially was built. Data processing has been implemented to plot maps of sound pressure levels in third-octave bands and to compute sound power levels. Intake and exhaust radiations are separated thanks to mufflers on the other side. The lined fins in the secondary lateral inlet well reduce the compressor tone, which is largely dominant in intake radiation. Its sound power level is decreased by 7 dB. The novel ejector is also successful to reduce exhaust broadband noise above 1 kHz with a gain of 5 dB on sound power level. Finally, the benefit on the acoustic emission of the helicopter in flight is appraised.
23
Fedorov, Volodymyr, Oleksii Korpach, Dmytro Yashchenko, and Volodymyr Bosenko. "EXTERNAL NOISE REDUCTION “NOVATOR” ARMORED CAR USING A HIGHLY EFFICIENT SILENCER." Avtoshliakhovyk Ukrayiny 3, no. 275 (September 30, 2023): 36–41. http://dx.doi.org/10.33868/0365-8392-2023-3-275-36-41.
Abstract:
Armored vehicles are widely used for combat operations, for which it is extremely important to be as inconspicuous as possible. There are different types of masking, one of which is reducing the level of external noise. For the Novator armored car, a highly effective muffler of the exhaust gases of the internal combustion engine was devel-oped. The Novator armored car has a pickup-type body, a gross weight of 9,000 kg and a Ford F8 turbodiesel engine with a power of 300 hp. The uniqueness of the developed muffler is that it seeks to return all the sound waves that entered it back to the intake pipe. This effect is achieved due to the specific structure of the silencer housing. The case is an ellipsoid of rotation.At the same time, the section of the intake pipe (the pipe that goes into the muffler) is placed in the first focus of the ellipsoid of rotation, and the sound waves propagate to the inner wall of the elliptical body, reflect from it, con-verge at the second focus, and then continue to move to the opposite wall, reflect from it, converge in the first focus and spread further back into the intake pipe. In the intake pipe, there is partial interference of the reflected sound waves when they meet the incoming waves, and the final absorption by the sound-absorbing material. At the same time, exhaust gas-es, bouncing off the walls of the muffler, leave the latter through the exhaust pipe. At the same time, the exhaust pipe exits the ellipsoid of rotation coaxially with the intake pipe, which enters the pipe tel-escopically with a gap. Taking into account the directional diagram of sound energy radiation at the exit from the ex-haust pipe, a proposal was made to create a muffler not as a full ellipsoid of rotation, but in the form of a half ellipsoid of rotation. Such a solution will make the muffler significantly cheaper and much more compact, which is essential for a military vehicle. Keywords: armored car, “novator”, masking, camouflage, silencer, ellipsoid of rotation, directional diagram, acoustic efficiency, sound waves, sound absorbing material.
24
Chapman, C. J. "Sound radiation from a cylindrical duct. Part 2. Source modelling, nil-shielding directions, and the open-to-ducted transfer function." Journal of Fluid Mechanics 313 (April 25, 1996): 367–80. http://dx.doi.org/10.1017/s0022112096002248.
Abstract:
This paper analyses the sound radiated from the front face of a hard-walled circular cylindrical duct in a subsonic mean flow when the duct contains acoustic sources typical of those in a ducted-fan aeroengine. Two main results are established for modes of any given frequency and circumferential order. The first result is that in certain easily calculated directions, called here the nil-shielding directions, the sound radiated by ducted sources is the same as the sound radiated by the corresponding open sources, i.e. by unducted sources of the same distribution and strength radiating into free space. Thus in these special directions the duct has no noise-shielding effect. The second result is that, in the Kirchhoff approximation, the sound radiated by the open sources in the nil-shielding directions determines the sound radiated by the ducted sources in all directions; i.e. the sound fields radiated by open and ducted sources are related by an open-to-ducted transfer function. This function is such that the sound radiated by the ducted sources is a linear combination of certain diffraction functions, in which the coefficients are given by the sound radiated by the open sources in the nil-shielding directions. The diffraction functions do not depend on the sources and are here calculated explicitly in terms of Bessel functions. The method used in the paper is Kirchhoff's approximation; within linear theory this gives the nil-shielding directions exactly, i.e. in agreement with the Wiener—Hopf solution, and gives the main beam of the radiated field, including the major side-lobes, to good accuracy. The results are relevant to the sound radiated into the forward arc by a ducted turbofan aeroengine.
25
Vasilyev, A. V. "SOFTWARE DEVELOPMENT FOR ESTIMATION OF LOW FREQUENCY SOUND PROPAGATION IN GAS GUIDES OF POWER PLANTS TAKING TO ACCOUNT ACTIVE SOUND SOURCES." Journal of Dynamics and Vibroacoustics 5, no. 4 (March 12, 2020): 36–44. http://dx.doi.org/10.18287/2409-4579-2019-5-4-36-44.
Abstract:
This paper is devoted to the problems of modelling and calculation of propagation of low frequency sound in gas guides of power plants taking to account active sound sources. The structure of software for prediction and calculation of low-frequency sound propagation in gas guides have described. Software uses four-pole method and takes to account radiation from additional (active) sound course. By using software it is possible to estimate sound source parameters to provide efficient sound attenuation. Examples of software application to calculation of intake and exhaust noise of internal combustion engine are described. The results of calculations show the possibilities of four-pole method software using to design acoustically the parameters of gas guides and mufflers for the different fields of applications.
26
O, Zaporozhets, Karpenko S, Puzik S, and Sagaidak B. "MODEL OF SOUND LEVELS CALCULATION FOR NOISE FROM COMPRESSOR STATIONS FOR JUSTIFICATION OF SANITARY PROTECTION ZONE BOUNDARIES." National Transport University Bulletin 1, no. 50 (2021): 81–91. http://dx.doi.org/10.33744/2308-6645-2021-3-50-081-091.
Abstract:
This article is devoted to the study of sound levels for noise from a gas turbine plant and technological equipment of a compressor station in everyday operation, in order to assess the sustainability of the conditions of sanitary protection zones around the compressor station and in order to protect the population living near the compressor station. The main purpose of the study is to assess the compliance of the sizes of sanitary protection zones in terms of noise load on environment. The main source of noise at compressor gas-pumping stations is determined by the noise regime at the industrial site, in addition to auxiliary equipment; include gas-pumping devices, systems of technological gas discharge from the blower circuits, fuel and starting gas of gas-pumping devices. The dependence of the noise conditions at the production site and in the environment on the sound power level of gas-pumping apparatuses, the installed power of gas-turbine plants, the sound power of the turbocompressor, service life of gas-pumping apparatuses, the number of simultaneously operating gas-pumping apparatuses, the characteristics of production premises, the design of the gas-pumping apparatuses, the state of means of noise absorption of gas-pumping apparatuses. In gas turbine installations of compressor stations, intense noise occurs in the air intake and exhaust systems, in the cooling system fan, in the turbomachine housing and in the generator. To calculate the sound levels at a separate point, depending on the distance to the noise source, a model was used taking into account the effects of sound wave propagation in atmospheric air and the characteristics of the noise source, such as: directivity and spectral characteristics of radiation, the height of the source above the surface; distance from the source to the point of determining the sound level; absorption of sound in atmospheric air, depends on the frequency and parameters of the state of the atmosphere; the effect of the influence of the earth; weather effects and others. The methodology of the standard and the international method CONCAW were used based on the results of calculating sound levels at the border of the sanitary protection zone at the compressor station. The calculation results, for standard atmospheric conditions, according to the international CONCAW method indicate that at a distance of 700 m from the sound source, the sound propagation will be 50.0 dBA, which coincides with the calculation results using the standard method and also exceeds the night noise standard by 5 dBA for conditions in the residential area. Development even when only one gas compressor is in operation, which proves the relevance of studying the environmental risks of compressor stations. KEY WORDS: NOISE, ENVIRONMENTAL RISKS, NOISE SOURCE, COMPRESSOR STATIONS, GAS PUMPING UNIT, GAS PUMPING APPARATUS, SOUND.
27
Руденко, В. В., И. В. Калужинов, and Н. А. Андрущенко. "АКУСТИЧНА ПОМІТНІСТЬ БЕЗПІЛОТНИХ ЛІТАЛЬНИХ АПАРАТІВ З СИЛОВИМИ УСТАНОВКАМИ НА БАЗІ ПОРШНЕВИХ ДВИГУНІВ." Open Information and Computer Integrated Technologies, no. 88 (November 6, 2020): 62–80. http://dx.doi.org/10.32620/oikit.2020.88.05.
Abstract:
The presence in operation of many prototypes of UAVs with propeller propellers, the use of such devices at relatively low altitudes and flight speeds makes the problem of noise reduction from UAVs urgent both from the point of view of acoustic imperceptibility and ecology.The aim of the work is to determine a set of methods that help to reduce the visibility of UAVs in the acoustic range. It is shown that the main source of noise from the UAV on the ground is the power plant, which includes the engine and the propeller. The parameters of the power plants influencing the processes that determine the acoustic signature of the UAV were investigated. A comprehensive analysis of the factors affecting visibility was carried out. The power plants include two-stroke and four-stroke engines, internal combustion and two-blade propellers. The use of silencers on the exhaust of the internal combustion engine was considered. The spectral characteristics of the acoustic fields of the propeller-driven power plants for the operating sample of the UAV "Eco" were obtained. The measurements were carried out in one-third octave and 1/48 octave frequency bands under static conditions. The venue is the KhAI airfield. Note that the propellers that were part of the power plants operated at Reynolds numbers (Re0,75<2*105), which can significantly affect its aerodynamic and acoustic characteristics. It is shown that when choosing a UAV control system, one should take into account the fact that two-stroke piston engines are the dominant source in the noise of propeller-driven control systems in the absence of a hood and mufflers in the intake and exhaust tracts. The use of a four-stroke internal combustion engine significantly reduces the noise of the control system. In the general case, the position of the boundaries of the zone of acoustic visibility of a UAV at the location of the observer is determined by the ratio between the intensity of acoustic radiation perceived by the observer from the UAV and the intensity of sound corresponding to the natural acoustic background and depends on the degree of manifestation of acoustic effects accompanying the propagation of sound in a turbulent atmosphere - the refraction of sound waves. Absorption and dissipation of acoustic energy. The calculation and comparison of the UAV detection range was carried out taking into account the existing natural maskers.The results of experimental studies are presented that allow assessing the degree of acoustic signature of the UAV. A set of measures aimed at reducing the intensity of the acoustic signature of the UAV in various regions of the radiation spectrum has been determined.
28
Kondrat’ev, Konstantin V., Pavel F. Kiku, Svetlana N. Beniova, Marina V. Li, Ol’ga G. Tsygankova, Tat’yana V. Gorborukova, and Anna V. Sukhova. "Social and hygienic assessment of the spread of thyroid diseases." HEALTH CARE OF THE RUSSIAN FEDERATION 65, no. 1 (March 5, 2021): 37–44. http://dx.doi.org/10.47470/0044-197x-2021-65-1-37-44.
Abstract:
Introduction. Iodine deficiency diseases (IDD) are currently one of the most common pathologies of the endocrine system. The development of these diseases in the Primorsky region depends on the sufficient intake of iodine and various factors of exogenous and endogenous nature. The identification and establishment of the contribution of social and hygienic nature factors in the comprehensive impact to the occurrence and development of thyroid diseases, including IDD, is an important area of research. The aim of the study is to obtain information about the social and hygienic factors that influence the occurrence and development of thyroid pathology, including iodine deficiency diseases. Material and methods. Based on statistical data the dynamics in the population prevalence of diseases of the endocrine system in the Primorsky region was analyzed. To identify social and hygienic factors, a survey of 222 patients of the Center of Endocrinology Regional Clinical Hospital No. 2 (Vladivostok) was performed. Statistical processing of the results of the sociological survey was carried out using the Terentyev correlation pleiades method. Results. The development of thyroid pathology, including IDD, is influenced by unfavorable environmental conditions, physical inactivity and stressful situations in the workplace, unfavorable occupational factors including an exposure to noise, dust, radiation from a personal computer, lifestyle factors due to low physical activity, non-compliance with the waking and sleeping regime. More often, thyroid diseases develop in women and people over 50 years of age. The development of IDD is influenced by the observance of the principles of rational nutrition and the presence of certain foods in the diet. The contribution of these factors in the conditions of their combined impact on the human body is established. Conclusion. The identified complex of social and hygienic factors that are important for the occurrence and development of thyroid diseases can be further used to create targeted programs for the prevention of these diseases in the population of the Primorsky region.
29
Christophe, Julien, Julien de Decker, and Christophe Schram. "Jet Noise and Wing Installation Effects of Circular, Beveled and Rectangular Nozzles." Flow, Turbulence and Combustion, February 26, 2024. http://dx.doi.org/10.1007/s10494-024-00533-7.
Abstract:
AbstractWith the growth of modern turbofan engines, their integration under the wing becomes challenging and induces aerodynamic and acoustic interactions between the jet exhaust and the airframe. Jet noise reduction techniques have been widely studied over the past decades but their efficiency has still to be demonstrated once installed. The present lab-scale jet experiments at Mach 0.6 compare the noise radiated by beveled and rectangular installed nozzles to circular ones on a quarter-sphere radiation map using a microphone antenna. For all radiation angles, modified nozzles show an amplitude decrease of the jet-plate interaction tones of the noise spectra attributed to a strong coupling between the jet shear layers and the sound scattering at the plate trailing edge. Beveled nozzles achieve a noise reduction for all radiation angles with a maximum decrease up to 2 dB at receiver locations perpendicular to the plate. While rectangular nozzles show a similar behavior, a sound increase is observed for listeners parallel to the plate when the height-to-width ratio is small.
30
Nguyen, V. H. "Application of the “actuator disk” boundary condition to calculation of a non-uniform flow in the air intake of modern turbofan engines." Engineering Journal: Science and Innovation, no. 8 (92) (August 2019). http://dx.doi.org/10.18698/2308-6033-2019-8-1909.
Abstract:
As the degree of bypass ratio of modern aviation turbofan engines increases, their appearance and characteristics change as well: the nacelle diameter increases, the air intake length decreases, and the temperature and jet noise reduce. Due to these circumstances, the design must take into account the interaction between the fan and the air intake as part of configuration. An approach based on unsteady three-dimensional modeling with account for full blade tips is necessary for the analysis, but is resource-intensive. In some cases, an approach based on the “actuator disk” boundary condition can be used to study aerodynamic interference. The paper considers a validated computational technique based on the “actuator disk” boundary condition with flow structure in front of the fan taken into account. The results of the computational study of the characteristics of the fan model in the engine nacelle are given, as well as the analysis of options for the “actuator disk” boundary condition and their application to the calculation of a non-uniform flow in the air intake under side wind conditions.
31
Al-Am, Jean, Alexis Giauque, Vincent Clair, Jérôme Boudet, and Fernando Gea-Aguilera. "Direct-Noise of an Ultrahigh-Bypass-Ratio Turbofan: Periodic-Sector vs Full-Annulas Large-Eddy Simulations." AIAA Journal, May 8, 2024, 1–15. http://dx.doi.org/10.2514/1.j063596.
Abstract:
The tonal and broadband noise of an ultrahigh-bypass-ratio fan stage, which has been developed at École Centrale de Lyon, is studied using large-eddy simulations (LES). Wall-modeled LES of a periodic sector and a 360-deg full fan stage have been performed at approach conditions, which is a relevant operating point for aircraft noise certifications. The fan noise is directly obtained from the fully compressible LES, using a well-refined unstructured mesh, and compared with state-of-the-art analytical models. The impact of the periodic boundary conditions, which are often used for high-fidelity simulations of turbofan engines, is assessed. The results from the 360-deg and periodic-sector LES are compared from aerodynamic and acoustic perspectives, including an analysis of the mean and turbulent flow quantities and sound-pressure spectra. Aerodynamic parameters show similar results for both configurations. However, the fan blade loading is slightly reduced in the 360-deg- LES near the blade tip. Acoustically, lower sound power levels at the intake and exhaust sections of the fan stage are obtained in the 360-deg LES, when compared to the periodic sector LES, particularly at low and middle frequencies. This can be associated with lower coherence levels in the fan wakes and smaller spanwise correlation lengths at the trailing edge of the blades. The modal content of the acoustic field has also been analyzed in detail and shows that the periodic sector LES cannot correctly simulate the modal content of the fan noise.
32
Qiu, S. "Design of a low noise turbofan duct via an acoustic gradient-enhanced Kriging method." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, June 17, 2020, 095440622093364. http://dx.doi.org/10.1177/0954406220933640.
Abstract:
The Kriging models which are frequently used in aerodynamic shape optimization may become computationally inefficient when solving problems with large numbers of design variables. One solution to this problem would be the application of gradient-enhanced Kriging model. A gradient-enhanced Kriging and acoustic adjoint-method approach to duct acoustic problems is developed, aimed to improve the efficiency and accuracy of the existing Kriging approach at acoustic problems with many design parameters. To our knowledge, it is the first application of gradient-enhanced Kriging for duct acoustic problem. It employs a Kriging response surface in the parameter space, augmented with gradients obtained from the acoustic adjoint equations efficiently. The present paper aims at describing the potential of the gradient-enhanced Kriging method for low noise turbofan duct design. Prior to the optimization process, the implementation of the unsteady aeroacoustic adjoint method in shape optimization is validated by comparing the gradient values with that obtained by finite differences. In this work, the ordinary Kriging model and gradient-enhanced Kriging method are applied firstly to a benchmark functions and the results show that the additional gradient information can significantly enhance the accuracy of Kriging model. And then, the original Kriging-based, adjoint-based and the gradient-enhanced Kriging method are all used to model 50 variable duct acoustic problems, respectively. The test results show that this approach whose gradient information is introduced by using acoustic adjoint method developed from multimode LEE, named as acoustic gradient-enhanced Kriging, can significantly enhance the accuracy of Kriging models when the gradient data are available and thus provide an optimized low noise intake while maintaining the aerodynamic performance.
33
Polacsek, Cyril, Majd Daroukh, Benjamin Francois, and Raphaël Barrier. "Zonal Detached Eddy Simulation of the Fan-OGV Stage of a Turbofan Engine: PartII—Broadband Noise Predictions." Journal of Turbomachinery, June 9, 2022, 1–30. http://dx.doi.org/10.1115/1.4054764.
Abstract:
Abstract This part II paper presents the broadband noise predictions of a turbofan stage based on an hybrid method proposed by ONERA in the framework of the European project TurboNoiseBB. The numerical approach relies on a ZDES (Zonal Detached Eddy Simulation) strategy that is applied to a fan module at approach condition and tested in AneCom facility (Wildau, Germany). The ZDES method with main aerodynamic flow features are detailed in a companion paper (part I) and this one focuses on acoustic analyses. Acoustic codes based on Amiet's theory and FWH (Ffowcs-Williams and Hawkings) analogy, briefly described in the article, are chained to the CFD to assess the rotor-stator interaction noise. The required inputs are the turbulent wake information (issued either from RANS or ZDES) in front the stator and the unsteady pressure on the vane wall, respectively. Turbulent velocity profiles and velocity spectra are compared to hot-wire measurements in the interstage region. A nice agreement is globally observed with noticeable improvement compared to RANS solutions. Then, sound power spectra in the intake and bypass duct provided by acoustic post-processing are discussed and compared to the experiment. Reliable numerical predictions are obtained when undesirable additional sources (shown to be caused by local flow separation at the vane wall) are removed from the FWH surface integration. ZDES-FWH spectra are found to be not far from RANS-Amiet ones, with a best fitting to the experimental spectrum shape and level deviations within 3 dB.
34
Pan, Yuning, Aiqin Song, Shizhong Bu, Zhaoqian Chen, Qiuli Huang, and Aijing Li. "The feasibility of low-concentration contrast and low tube voltage in computed tomography perfusion imaging: an animal study." Bioscience Reports 38, no. 1 (January 10, 2018). http://dx.doi.org/10.1042/bsr20170977.
Abstract:
Aim: To investigate the feasibility of low-concentration contrast (270 mg/ml) together with low tube voltage (80 kV) and adaptive iterative dose reduction (AIDR)-3D reconstruction in liver computed tomography (CT) perfusion imaging. Method: A total of 15 healthy New Zealand rabbits received two CT scans each. The first scan (control) was acquired at 100 kV and 100 mA with iopromide (370 mg/ml), while the second scan (experimental) was acquired at 80 kV and 100 mA with iodixanol (270 mg/ml) 24 h after the first scan. The obtained images were reconstructed with filtered back projection (FBP) and AIDR-3D in the control and experimental groups respectively. The perfusion parameters (hepatic artery perfusion [HAP], portal vein perfusion [PVP], hepatic perfusion index [HPI], and total liver perfusion [TLP]) and image quality (image quality score, average CT value of abdomen aorta, signal-to-noise ratio [SNR], contrast-to-noise ratio [CNR], and figure of merit [FOM]) were compared using a paired t-test or Mann–Whitney U test between the two groups, when appropriate. The effective radiation dose and iodine intake were also recorded and compared. Results: With the exception of the FOM criteria, the image quality and perfusion parameters were not significantly different between the two groups. The effective radiation dose and iodine intake were 38.79% and 27.03% lower respectively, in the experimental group. Conclusion: Low-concentration contrast (iodixanol, 270 mg/ml) together with low tube voltage (80 kV) and AIDR-3D reconstruction help to reduce radiation dose and iodine intake without compromising perfusion parameters and image quality in liver CT perfusion imaging.
35
Liu, Zhi-Chao, Sai Zhao, Ze-Peng Ma, Tian-Le Zhang, and Yong-Xia Zhao. "Comparing feasibility of different tube voltages and different concentrations of contrast medium in coronary CT angiography of overweight patients." Journal of X-Ray Science and Technology, October 7, 2022, 1–12. http://dx.doi.org/10.3233/xst-221263.
Abstract:
OBJECTIVES: To compare image quality, radiation dose, and iodine intake of coronary computed tomography angiography (CCTA) acquired by wide-detector using different tube voltages and different concentrations of contrast medium (CM) for overweight patients. MATERIALS AND METHODS: A total of 150 overweight patients (body mass index≥25 kg/m2) who underwent CCTA are enrolled and divided into three groups according to scan protocols namely, group A (120 kVp, 370 mgI/ml CM); group B (100 kVp, 350 mgI/ml CM); and group C (80 kVp, 320 mgI/ml CM). The CT values, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure-of-merit (FOM) of all images are calculated. Images are subjectively assessed using a 5-point scale. In addition, the CT dose index volume (CTDIvol) and dose length product (DLP) of each patient are recorded. The effective radiation dose (ED) is also calculated. Above data are then statistically analyzed. RESULTS: The mean CT values, SNR, CNR, and subjective image quality of group A are significantly lower than those of groups B and C (P < 0.001), but there is no significant difference between groups B and C (P > 0.05). FOMs show a significantly increase trend from group A to C (P < 0.001). The ED values and total iodine intake in groups B and C are 30.34% and 68.53% and 10.22% and 16.85% lower than those in group A, respectively (P < 0.001). CONCLUSION: The lower tube voltage and lower concentration of CM based on wide-detector allows for significant reduction in iodine load and radiation dose in CCTA for overweight patients comparing to routine scan protocols. It also enhances signal intensity of CCTA and maintains image quality.
36
Gao, Kai, Ze-Peng Ma, Tian-Le Zhang, Yi-Wen Liu, and Yong-Xia Zhao. "Comparative study of abdominal CT enhancement in overweight and obese patients based on different scanning modes combined with different contrast medium concentrations." Journal of X-Ray Science and Technology, January 12, 2024, 1–13. http://dx.doi.org/10.3233/xst-230327.
Abstract:
PURPOSE: To compare image quality, iodine intake, and radiation dose in overweight and obese patients undergoing abdominal computed tomography (CT) enhancement using different scanning modes and contrast medium. METHODS: Ninety overweight and obese patients (25 kg/m2≤body mass index (BMI)< 30 kg/m2 and BMI≥30 kg/m2) who underwent abdominal CT-enhanced examinations were randomized into three groups (A, B, and C) of 30 each and scanned using gemstone spectral imaging (GSI) +320 mgI/ml, 100 kVp + 370 mgI/ml, and 120 kVp + 370 mgI/ml, respectively. Reconstruct monochromatic energy images of group A at 50–70 keV (5 keV interval). The iodine intake and radiation dose of each group were recorded and calculated. The CT values, contrast-to-noise ratios (CNRs), and subjective scores of each subgroup image in group A versus images in groups B and C were by using one-way analysis of variance or Kruskal–Wallis H test, and the optimal keV of group A was selected. RESULTS: The dual-phase CT values and CNRs of each part in group A were higher than or similar to those in groups B and C at 50–60 keV, and similar to or lower than those in groups B and C at 65 keV and 70 keV. The subjective scores of the dual-phase images in group A were lower than those of groups B and C at 50 keV and 55 keV, whereas no significant difference was seen at 60–70 keV. Compared to groups B and C, the iodine intake in group A decreased by 12.5% and 13.3%, respectively. The effective doses in groups A and B were 24.7% and 25.8% lower than those in group C, respectively. CONCLUSION: GSI +320 mgI/ml for abdominal CT-enhanced in overweight patients satisfies image quality while reducing iodine intake and radiation dose, and the optimal keV was 60 keV.
37
Zhao, Sai, Zhi-Chao Liu, Yong-Xia Zhao, Tian-Le Zhang, and Zi-Wei Zuo. "A feasibility study of different GSI noise indexes and concentrations of contrast medium in hepatic CT angiography of overweight patients: image quality, radiation dose, and iodine intake." Japanese Journal of Radiology, January 6, 2023. http://dx.doi.org/10.1007/s11604-022-01384-w.