Indirect Combustion Noise: Noise Generation by Accelerated Vorticity in a Nozzle Flow

Kings, Nancy; Bake, Friedrich

doi:10.1260/1756-8277.2.3.253

Cited by 42 publications

(67 citation statements)

References 12 publications

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“…For M 1.3, they are close to 0.6u j at t t c − 10r 0 /u j , then increase and reach maximum values around 0.85u j near the time of potential-core closing, and finally diminish. As in spatially developing jets [18], these results suggest that the turbulent structures that enter in the potential core are accelerated, which may generate sound [67]. For M = 2, the convection velocities are lower compared to those at lower Mach numbers, and the peak values are obtained earlier, at t t c − 5r 0 /u j .…”

Section: B Properties Of the Velocity Fieldsmentioning

confidence: 74%

Potential-core closing of temporally developing jets at Mach numbers between 0.3 and 2: Scaling and conditional averaging of flow and sound fields

Bogey

Pineau

2019

Phys. Rev. Fluids

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In a previous work [Bogey, J. Fluid Mech. 859, 1022 (2019)], the potential-core closing of temporally developing isothermal round jets at a Mach number M = 0.9 was shown to generate a strong axisymmetric noise component in the downstream direction. The persistence of this component is investigated in the present work for jets at M = 0.3, 0.6, 1.3, and 2 computed by direct numerical simulation, from a low subsonic to a high supersonic Mach number. The flow and sound fields are presented, and the Mach number scaling of their magnitudes and spectral content is examined. The centerline velocity and hydrodynamic pressure spectra are close to each other using k z r 0 in abscissa, where k z and r 0 are the axial wave number and the initial jet radius, respectively. The sound spectra for M 1.3 collapse well when they are plotted as a function of k z r 0 M −1 and adjusted in amplitude using a M 7.5 power law, whereas a k z r 0 scaling and a lower power-law exponent seem to apply to the spectra for M 1.3. The flow and sound fields are then correlated with each other, and conditionally averaged based on a synchronization of the fields with the minimum values of centerline velocity at potential-core closing. The noise component radiated in the downstream direction for M = 0.9 is clearly identified for M = 0.6, 1.3, 2, and is also detected, albeit with more difficulty, for M = 0.3, indicating the presence of the associated sound source over a wide range of Mach numbers. In all cases, its generation process extracted by the conditional averaging consists in the growth of a spot of low velocity and a high vorticity level in the inner side of the mixing layer, reaching a peak intensity at its arrival on the axis and weakening subsequently. The use of different trigger conditions for the averaging suggests that, for a given Mach number, the amplitude of the acoustic waves radiated during that stage depends linearly on the velocity deficit and the strength of the vortical structures on the jet centerline at the time of potential-core closing.

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Section: B Properties Of the Velocity Fieldsmentioning

confidence: 74%

Potential-core closing of temporally developing jets at Mach numbers between 0.3 and 2: Scaling and conditional averaging of flow and sound fields

Bogey

Pineau

2019

Phys. Rev. Fluids

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“…Second, it includes the effect of a non-zero mean flow angle, which is of significant relevance in turbine stages. Third, it includes the vorticity wave, which is responsible for part of the indirect combustion noise, as shown by Kings & Bake (2010). Finally, it shows that circumferential entropy waves generate vorticity when accelerated; this vorticity wave, shown to originate due to the baroclinic torque of the vorticity equation, is of first order and can contribute to indirect vorticity noise when further accelerated and decelerated, as seen in the literature and in § 4.3.…”

Section: Discussionmentioning

confidence: 77%

“…A different source of indirect noise is vorticity waves, as explained theoretically by Cumpsty & Marble (1977) and shown experimentally by Kings & Bake (2010). These waves have also been found to affect combustion instabilities (Li & Sun 2014).…”

Section: Vorticity Transfer Functionsmentioning

confidence: 91%

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On the reflection and transmission of circumferential waves through nozzles

Durán

Morgans

2015

J. Fluid Mech.

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This paper presents a mathematical model for predicting the propagation of circumferential waves (acoustic, entropy and vorticity waves) through an annular nozzle. Combustion chambers in modern aero-engines are typically annular, and so a model for circumferential waves is essential for understanding and predicting both combustion noise and thermoacoustic instabilities for such geometries. The linearised Euler equations are solved using the Magnus expansion to obtain the reflection and transmission coefficients of the annular nozzle for acoustic, entropy and vorticity perturbations. Predictions which account for flow physics, such as a non-zero mean flow angle and the generation of vorticity noise, are obtained for the first time.Results are compared with two numerical methods, showing that the mathematical model is able to predict the transmission and reflection of waves for both compact and non-compact frequencies. The model is used to prove one particularly interesting and relevant feature of annular geometries: the generation of a vorticity wave by the acceleration of a circumferential entropy wave. It is shown that this phenomenon originates from the baroclinic torque in the vorticity equation.

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“…[3,5,6] Thec urrent work is focused on predicting the direct combustion noise emitted from unconfined,p remixed flames.I nl ow-Mach number (Ma) combustion flows,t he fluctuation in heat release,c aused by the interaction of the chemical reactions and the turbulent flow, represents the main noise-generating source. [7,8] As ac onsequence,c ombustion noise correlates strongly with turbulent fluctuations and is broadband in the spectral domain.…”

Section: Introductionmentioning

confidence: 99%

Combustion‐Generated Noise: An Environment‐Related Issue for Future Combustion Systems

et al. 2017

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A first‐order estimation of the prediction of combustion‐generated noise from turbulent premixed flames was explored. The method was based on Lighthill's acoustic analogy and used measurement data from high‐speed imaging of chemiluminescent emissions as input. To determine the noise‐generating source, that is, the overall heat release rate from the measured chemiluminescence signals, numerical simulations were performed for 1 D laminar and 3 D turbulent freely propagating flames by employing detailed transport models and reaction mechanisms, including the full reaction chain of the electronically excited hydroxyl radical (OH*). It was shown for both the 1 D and 3 D cases that the local generation of OH* correlated strongly with the heat released from the chemical reaction, especially in the fuel‐lean range. As the chemiluminescence measurements gathered light only along the viewing direction, the line‐of‐sight summed values of heat release rate and OH* concentration were evaluated from the 3 D simulation, and a quasilinear relationship was identified for these integral values. Hence, a proportionality relation was applied for computation of the integral heat release from measured chemiluminescence intensity. An analytical solution of Lighthill's wave equation served as a transfer function, which took fluctuations in the total heat release rate or light intensity as input to calculate the sound radiation in the far field. This approach was applied to a generic burner operated with premixed methane/air jet flames. Good quantitative agreement was obtained between the sound pressures derived from the chemiluminescence measurements and the microphone data, which highlights the potential of the method for applications to more complex flame configurations.

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Indirect Combustion Noise: Noise Generation by Accelerated Vorticity in a Nozzle Flow

Cited by 42 publications

References 12 publications

Potential-core closing of temporally developing jets at Mach numbers between 0.3 and 2: Scaling and conditional averaging of flow and sound fields

Potential-core closing of temporally developing jets at Mach numbers between 0.3 and 2: Scaling and conditional averaging of flow and sound fields

On the reflection and transmission of circumferential waves through nozzles

Combustion‐Generated Noise: An Environment‐Related Issue for Future Combustion Systems

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