Experimental investigations of sound reflection from hot and subsonic flow duct termination

Tiikoja, Heiki; Lavrentjev, Jüri; Rämmal, Hans; Åbom, Mats

doi:10.1016/j.jsv.2013.09.030

Cited by 11 publications

(6 citation statements)

References 23 publications

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“…where R c is the convective reflection coefficient. R c can be solved using the theory deduced by Munt [19] and has been proven to be applicable for pipe termination with hot and subsonic flow [20]. The expression can be written as follows:…”

Section: Functionsmentioning

confidence: 99%

Numerical and Experimental Analysis of the Effect of Acoustic Loads on the Source Characterization for an Internal Combustion Engine Exhaust System

2020

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The identification of source characteristics, commonly characterized as the source strength and source impedance, is essential for predicting the acoustic performance of an internal combustion (IC) engine exhaust system. This study contributes to a theoretical analysis of the effect of the acoustic parameters of loads (i.e., four-pole parameters, load impedance, and radiation impedance of the tailpipe) on the identification error of the source characteristics for an IC engine. A model based on the linear time-invariant hypothesis was constructed. A dispersion estimation function of the source strength and a deviation estimation function of the source impedance were established as indicators to test the identification accuracy. A three-dimensional (3D) multifield coupling numerical simulation method, which can thoroughly consider the influences of airflow and temperature, was applied to obtain the acoustic parameters of loads and compare them with those obtained by a one-dimensional (1D) analytical method. Then, the acoustic parameters of loads and the radiated sound pressure level of the tailpipe obtained in the measurement were substituted into the source characteristics identification model. Based on the analysis and calculation, the estimated error of the source characteristics acquired by using the 3D numerical simulation method is significantly lower than that by using the 1D analytical method. Moreover, the experiment and the 3D multifield coupling numerical simulation method were used to verify the identification results of the engine source characteristics. The results show that the far-field sound pressure level of the tailpipe predicted via the 3D numerical simulation method agrees well with the experimental results, indicating that accurate acoustic parameters of loads can effectively improve the source identification accuracy for an IC engine. INDEX TERMS IC engine, exhaust noise control, source characteristics identification, acoustic parameters of loads, error analysis, multifield coupling numerical simulation.

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Section: Functionsmentioning

confidence: 99%

Numerical and Experimental Analysis of the Effect of Acoustic Loads on the Source Characterization for an Internal Combustion Engine Exhaust System

2020

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“…The outlet pressure reflection coefficient is R 2 = −1. An end correction of 0.4 times of the diameter of the combustion chamber diameter is taken into account to consider the sound radiation at the outlet of the chamber [15,102,103].…”

Section: Low Order Combustion Instability Network Model Oscilos Andmentioning

confidence: 99%

Prediction of combustion instability limit cycle oscillations by combining flame describing function simulations with a thermoacoustic network model

Han

Morgans

2015

Combustion and Flame

196

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a b s t r a c t Accurate prediction of limit cycle oscillations resulting from combustion instability has been a long-standing challenge. The present work uses a coupled approach to predict the limit cycle characteristics of a combustor, developed at Cambridge University, for which experimental data are available (Balachandran, Ph.D. thesis, 2005). The combustor flame is bluff-body stabilised, turbulent and partially-premixed. The coupled approach combines Large Eddy Simulation (LES) in order to characterise the weakly non-linear response of the flame to acoustic perturbations (the Flame Describing Function (FDF)), with a low order thermoacoustic network model for capturing the acoustic wave behaviour. The LES utilises the open source Computational Fluid Dynamics (CFD) toolbox, OpenFOAM, with a low Mach number approximation for the flow-field and combustion modelled using the PaSR (Partially Stirred Reactor) model with a global one-step chemical reaction mechanism for ethylene/air. LES has not previously been applied to this partially-premixed flame, to our knowledge. Code validation against experimental data for unreacting and partially-premixed reacting flows without and with inlet velocity perturbations confirmed that both the qualitative flame dynamics and the quantitative response of the heat release rate were captured with very reasonable accuracy. The LES was then used to obtain the full FDF at conditions corresponding to combustion instability, using harmonic velocity forcing across six frequencies and four forcing amplitudes. The low order thermoacoustic network modelling tool used was the open source OSCILOS (http://www.oscilos.com). Validation of its use for limit cycle prediction was performed for a well-documented experimental configuration, for which both experimental FDF data and limit cycle data were available. The FDF data from the LES for the present test case was then imported into the OSCILOS geometry network and limit cycle oscillations of frequency 342 Hz and normalised velocity amplitude of 0.26 were predicted. These were in good agreement with the experimental values of 348 Hz and 0.21 respectively. This work thus confirms that a coupled numerical prediction of limit cycle behaviour is possible using an entirely open source numerical framework.

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“…Peters et al 6 propose to use the surface average outlet flow velocity. Allam and Å bom 7 and Tiikoja et al 12 claim that the centerline velocity U max should be used. The Vortex Sound Theory of Howe 13 helps evaluating such a choice.…”

Section: Theorymentioning

confidence: 99%

“…When the gas flow is hot as expected in combustion engine exhaust and other combustion systems the temperature contrast between the gas flow and the surroundings significantly increases the radiation impedance. [8][9][10][11][12] The measurements of Tiikoja et al…”

Section: Introductionmentioning

confidence: 99%

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Comments on the low frequency radiation impedance of a duct exhausting a hot gas

Hirschberg

Hoeijmakers

2014

The Journal of the Acoustical Society of America

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The influence of convection and temperature on the radiation impedance of an open duct termination exhausting a hot gas is commonly described by a complex theory. A simplified analytical expression is proposed for low frequencies. Both models assume a free jet with uniform velocity bounded by infinitely thin shear layers. The convective velocity that should be assumed when applying these models to a non-uniform outflow is uncertain. A simplified version of the so-called Vortex Sound Theory demonstrates that the convective velocity one should assume is lower than the jet centerline velocity.

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Experimental investigations of sound reflection from hot and subsonic flow duct termination

Cited by 11 publications

References 23 publications

Numerical and Experimental Analysis of the Effect of Acoustic Loads on the Source Characterization for an Internal Combustion Engine Exhaust System

Numerical and Experimental Analysis of the Effect of Acoustic Loads on the Source Characterization for an Internal Combustion Engine Exhaust System

Prediction of combustion instability limit cycle oscillations by combining flame describing function simulations with a thermoacoustic network model

Comments on the low frequency radiation impedance of a duct exhausting a hot gas

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