# Improved noise predictions from subsonic jets at Mach 0.75 using URANS calculations

11 Aug 2009-Progress in Computational Fluid Dynamics (Inderscience Publishers)-Vol. 9, Iss: 8, pp 460-474

TL;DR: In this paper, a simulation of round, compressible, turbulent jets at Mach 0.75 have been carried out and two jets, one cold and hot, have been simulated.

Abstract: Numerical simulations of round, compressible, turbulent jets at Mach 0.75 have been carried out. Two jets, one cold and hot, have been simulated. Overall Sound Pressure Levels (SPL) at far-field observer locations have been calculated using Ffowcs Williams-Hawkings equation. Axial and radial variation of the mean axial velocity, axial variation of u′u′½, v′v′½, radial variation of u′v′ and overall SPL levels are compared with experimental data reported in the literature. The potential core length is predicted well, but the predicted centreline velocity decay is faster than the measured value. The URANS calculations are able to predict the absolute values for the overall SPL, and the trends to within ±4dB of the experimental value for most of the receivers. The calculations predict the trends as well as absolute values of the variations of the spectral amplitude for receivers at 30Dj but not 50Dj.

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01 Jan 2001

TL;DR: In this paper, the mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation and the results are validated against an experiment at the same flow conditions.

Abstract: The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation. Details of the numerical method are briefly outlined and results are validated against an experiment at the same flow conditions. Lighthill's theory is used to define a nominal acoustic source in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic source is Fourier transformed in the axial coordinate and time and then filtered in order to identify and separate components capable of radiating to the far field. This procedure indicates that the peak radiating component of the source is coincident with neither the peak of the full unfiltered source nor that of the turbulent kinetic energy. The phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed which calls into question the commonly made assumption that the noise sources convect at a single velocity. Space-time correlations demonstrate that the sources are not acoustically compact in the streamwise direction and that the portion of the source that radiates at angles greater than 45 deg. is stationary. Filtering non-radiating wavenumber components of the source at single frequencies reveals that a simple modulated wave forms for the source, as might be predicted by linear stability analysis. At small angles from the jet axis the noise from these modes is highly directional, better described by an exponential than a standard Doppler factor.

16 citations

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TL;DR: The double parabolic nozzle has been designed in such a way that the maximum slope of the divergent curve is taken as one-third of the Prandtl Meyer (PM) angle.

Abstract: The purpose of this paper is to design a double parabolic nozzle and to compare the performance with conventional nozzle designs.,The throat diameter and divergent length for Conical, Bell and Double Parabolic nozzles were kept same for the sake of comparison. The double parabolic nozzle has been designed in such a way that the maximum slope of the divergent curve is taken as one-third of the Prandtl Meyer (PM) angle. The studies were carried out at Nozzle Pressure Ratio (NPR) of 5 and also at design conditions (NPR = 3.7). Experimental measurements were carried out for all the three nozzle configurations and the performance parameters compared. Numerical simulations were also carried out in a two-dimensional computational domain incorporating density-based solver with RANS equations and SST k-ω turbulence model.,The numerical predictions were found to be in reasonable agreement with the measured experimental values. An enhancement in thrust was observed for double parabolic nozzle when compared with that of conical and bell nozzles.,Even though the present numerical simulations were capable of predicting shock cell parameters reasonably well, shock oscillations were not captured.,The double parabolic nozzle design has enormous practical importance as a small increase in thrust can result in a significant gain in pay load.,The thrust developed by the double parabolic nozzle is seen to be on the higher side than that of conventional nozzles with better fuel economy.,The overall performance of the double parabolic nozzle is better than conical and bell nozzles for the same throat diameter and length.

8 citations

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TL;DR: In this paper, the aerodynamic characteristics of corrugated lobed nozzles were investigated for subsonic turbulent jets with varying parameters such as lobe length, lobe penetration and lobe count at a Mach number of 0.75.

Abstract: The purpose of this study is to investigate the aerodynamic characteristics of subsonic jet emanating from corrugated lobed nozzle.,Numerical simulations of subsonic turbulent jets from corrugated lobed nozzles using shear stress transport k-ω turbulence model have been carried out. The analysis was carried out by varying parameters such as lobe length, lobe penetration and lobe count at a Mach number of 0.75. The numerical predictions of axial and radial variation of the mean axial velocity, u′u′ ¯ and v′v′ ¯ have been compared with experimental results of conventional round and chevron nozzles reported in the literature.,The centreline velocity at the exit of the corrugated lobed nozzle was found to be lower than the velocity at the outer edges of the nozzle. The predicted potential core length is lesser than the experimental results of the conventional round nozzle and hence the decay in centreline velocity is faster. The centreline velocity increases with the increase in lobe length and becomes more uniform at the exit. The potential core length increases with the increase in lobe count and decreases with the increase in lobe penetration. The turbulent kinetic energy region is narrower with early appearance of a stronger peak for higher lobe penetration. The centreline velocity degrades much faster in the corrugated nozzle than the chevron nozzle and the peak value of Reynolds stress appears in the vicinity of the nozzle exit.,The corrugated lobed nozzles are used for enhancing mixing without the thrust penalty inducing better acoustic benefits.,The prominent features of the corrugated lobed nozzle were obtained from the extensive study of variation of flow characteristics for different lobe parameters after making comparison with round and chevron nozzle, which paved the way to the utilization of these nozzles for various applications.

5 citations

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05 Jan 2009TL;DR: In this article, numerical simulations of compressible, turbulent jets using the Shear Stress Transport (SST) k− ω model have been carried out for baseline nozzle and chevron nozzles with 6 lobes for three different penetration angles.

Abstract: Numerical simulations of compressible, turbulent jets using the Shear Stress Transport (SST) k− ω model have been carried out for baseline nozzle and chevron nozzles with 6 lobes for three different penetration angles. The predicted flow performance and far-field noise production were compared with the experimental data available in the literature. The 3D calculations have been done on a hexahedral mesh with 1.1 million cells in a 30◦ pie sector for the baseline nozzle. A hybrid mesh of 1.5 million cells were used for chevron simulation in a view to keep the wall y less than 10. Both cold and hot jets have been simulated. The jet exit velocity simulated for both the cases are approximately 300 m/s. Overall sound pressure levels at far-field observer locations have been calculated using Ffowcs Williams-Hawkings equation. Numerical prediction of stagnation pressure, stagnation temperature, turbulent kinetic energy and 90◦ observer spectral trends were compared with experimental data. The potential core length is predicted well, but the predicted centerline velocity decay is faster than the measured value. The URANS calculations are able to predict the absolute values for the overall SPL, but the predicted spectral trends are very poor. The calculations predict the flow performance characteristics like stagnation pressure, temperature and peak values of turbulent kinetic energy reasonably well for both cold and hot jets.

1 citations

##### References

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••

TL;DR: In this article, the mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation and the results show that the phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed.

Abstract: The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation. Details of the numerical method are briefly outlined and results are validated against an experiment at the same flow conditions (Stromberg, McLaughlin & Troutt 1980). Lighthill's theory is used to define a nominal acoustic source in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic source is Fourier transformed in the axial coordinate and time and then filtered in order to identify and separate components capable of radiating to the far field. This procedure indicates that the peak radiating component of the source is coincident with neither the peak of the full unfiltered source nor that of the turbulent kinetic energy. The phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed which calls into question the commonly made assumption that the noise sources convect at a single velocity. Space–time correlations demonstrate that the sources are not acoustically compact in the streamwise direction and that the portion of the source that radiates at angles greater than 45° is stationary. Filtering non-radiating wavenumber components of the source at single frequencies reveals that a simple modulated wave forms for the source, as might be predicted by linear stability analysis. At small angles from the jet axis the noise from these modes is highly directional, better described by an exponential than a standard Doppler factor.

632 citations

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TL;DR: In this paper, a review of computational methods for computational aero-acoustics applications is presented, and some of the computational methods to be reviewed are quite different from traditional CFD methods.

Abstract: Computational fluid dynamics (CFD) has made tremendous progress especially in aerodynamics and aircraft design over the past 20 years. An obvious question to ask is "why not use CFD methods to solve aeroacoustics problems?" Most aerodynamics problems are time independent, whereas aeroacoustics problems are, by definition, time dependent. The nature, characteristics, and objectives of aeroacoustics problems are also quite different from the commonly encountered CFD problems. There are computational issues that are unique to aeroacoustics. For these reasons computational aeroacoustics requires somewhat independent thinking and development. The objectives of this paper are twofold. First, issues pertinent to aeroacoustics that may or may not be relevant to computational aerodynamics are discussed. The second objective is to review computational methods developed recently that are designed especially for computational aeroacoustics applications. Some of the computational methods to be reviewed are quite different from traditional CFD methods. They should be of interest to the CFD and fluid dynamics communities.

529 citations

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TL;DR: In this article, the authors investigated the noise radiated by a subsonic circular jet with a Mach number of 0.9 and a Reynolds number of 65000 computed by a compressible Large Eddy Simulation (LES) and demonstrated the feasibility of using LES to predict accurately both the flow field and sound radiation on a domain including the acoustic field.

Abstract: This study investigates the noise radiated by a subsonic circular jet with a Mach number of 0.9 and a Reynolds number of 65000 computed by a compressible Large Eddy Simulation (LES). First, it demonstrates the feasibility of using LES to predict accurately both the flow field and the sound radiation on a domain including the acoustic field. Mean flow parameters, turbulence intensities, velocity spectra and integral length scales are in very good agreement with experimental data. The noise generated by the jet, provided directly by the simulation, is also consistent with measurements in terms of sound pressure spectra, levels and directivity. The apparent location of the sound sources is at the end of the potential core in accordance with some experimental observations at similar Reynolds numbers and Mach numbers. Second, the noise generation mechanisms are discussed in an attempt to connect the flow field with the acoustic field. This study shows that for the simulated moderate Reynolds number jet, the predominant sound radiation in the downstream direction is associated with the breakdown of the shear layers in the central jet zone.

365 citations

### "Improved noise predictions from sub..." refers background or methods in this paper

...This approach can be regarded as a very LES where only the very large structures are resolved (Bogey et al., 2003)....

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...This was observed by Bogey et al. (2003) and Uzun et al....

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TL;DR: A survey of the current applications of large-eddy simulation for the prediction of noise from single stream turbulent jets is given in this paper, with special attention paid to relationship between numerical and/or modeling choices and the prediction accuracy.

Abstract: A survey of the current applications of large-eddy simulation for the prediction of noise from single stream turbulent jets is given. After summarizing the numerical techniques used, the data predicted by the simulations are given at conditions from subsonic, heated jets to supersonic, unheated jets. Mach numbers between 0.3 and 2.0 are considered. Following the data presentation, an analysis of the trends exhibited by the data is given, with special attention paid to relationship between numerical and/or modeling choices and the prediction accuracy. The data support the conclusion that the most limiting factor in current large-eddy simulations is the thickness of the initial shear layer, which is commonly one order of magnitude thicker than what is found experimentally. There is also a large amount of uncertainty regarding the influence of the subgrid scale model on the predictions. The influence of inflow conditions is discussed in depth. Uncertainties in the inflow conditions currently prohibit the simulations from reliably predicting the potential core length. The centerline evolution of the mean and fluctuating axial velocity is strongly coupled to the resolution of the initial shear layers, but can be made to agree within experimental uncertainty when sufficiently thin initial shear layers are used. The maximum achieved Strouhal number of the sound in the acoustic far field is 1.5-3.0, depending on flow condition; this limit is due to numerical resources. A listing of some of the open questions and future directions concerning jet noise predictions using large-eddy simulation concludes the survey.

287 citations

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TL;DR: A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-field CFD results to the acoustic far-field is given in this paper.

Abstract: A review of recent advances in the use of surface integral methods in Computational AeroAcoustics (CAA) for the extension of near-field CFD results to the acoustic far-field is given. These integral formulations (i.e. Kirchhoff's method, permeable (porous) surface FfowcsWilliams Hawkings (FW-H) equation) allow the radiating sound to be evaluated based on quantities on an arbitrary control surface if the wave equation is assumed outside. Thus only surface integrals are needed for the calculation of the far-field sound, instead of the volume integrals required by the traditional acoustic analogy method (i.e. Lighthill, rigid body FW-H equation). A numerical CFD method is used for the evaluation of the flow-field solution in the near field and thus on the control surface. Diffusion and dispersion errors associated with wave propagation in the far-field are avoided. The surface integrals and the first derivatives needed can be easily evaluated from the near-field CFD data. Both methods can be extended in orde...

263 citations

### "Improved noise predictions from sub..." refers methods in this paper

...The fluctuating acoustic pressure at the receiver locations were then calculated using the Ffowcs Williams-Hawkings integral method (Lyrintzis, 2003)....

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