Investigation of Entropy Noise in Aero-Engine Combustors

Bake, Friedrich; Michel, U.; Roehle, I.

doi:10.1115/1.2364193

Cited by 51 publications

(26 citation statements)

References 9 publications

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“…(20), which gives the ratio between acoustic and entropy waves produced by the combustion chamber (case CC), and Eqs. (21), (22), (28), and (29), which give the transmitted and generated waves by a compact nozzle (cases SA and AA. For this approach, the expression of is 1…”

Section: Resultsmentioning

confidence: 99%

“…More recently, Bake et al [21][22][23][24] worked on the subject, but the separation of direct and indirect combustion noise in a real case is still difficult to evaluate. On one hand, entropy fluctuations are controlled by complicated aerodynamical, thermal, and chemical phenomena.…”

Section: Leykomentioning

confidence: 98%

“…The set of equations (21), (22), (28), and (29) provides analytical expressions for the outgoing waves w 2 as a function of the incoming waves w 1 and w S 1 and the mean inlet M 1 and outlet M 2 Mach numbers for the compact nozzle.…”

Section: A Analytical Approachmentioning

confidence: 99%

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Comparison of Direct and Indirect Combustion Noise Mechanisms in a Model Combustor

Leyko¹,

2009

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Core noise in aeroengines is due to two main mechanisms: direct combustion noise, which is generated by the unsteady expansion of burning gases, and indirect combustion noise, which is due to the acceleration of entropy waves (temperature fluctuations generated by unsteady combustion) within the turbine stages. This paper shows how a simple burner model (a flame in a combustion chamber terminated by a nozzle) can be used to scale direct and indirect noise. An analytical formulation is used for waves generated by combustion. The transmission and generation of waves through the nozzle is calculated using both the analytical results of Marble and Candel (Marble, F. E., and Candel, S., "Acoustic Disturbances from Gas Nonuniformities Convected Through a Nozzle," Journal of Sound and Vibration, Vol. 55, 1977, pp. 225-243.) and a numerical tool. Numerical results for the nozzle verify and extend the analytical approach. The analytical relations for the combustion and the nozzle provide simple scaling laws for direct and indirect noise ratio as a function of the Mach number in the combustion chamber and at the nozzle outlet. Nomenclature A = nozzle cross-sectional area, m 2 A c = throat nozzle cross-sectional area, m 2 A f = combustor cross-sectional area, m 2 c = speed of sound, m=s c p = massic heat capacity at constant pressure, J=K=kg c v = massic heat capacity at constant volume, J=K=kg ' f = flame length, m ' n = nozzle length, m M = Mach number _ m = mass flow rate, kg=s PWfg = spectral power density of computed with Welch's method p = thermodynamic pressure, Pa _ Q = heat release rate, W _ q = heat release rate per volume unit, W=m 3 r = massic ideal gas constant, J=K=kg s = massic entropy, J=K=kg T = temperature, K t = time, s u = gas velocity, m=s w S = dimensionless entropy wave w = dimensionless acoustic wave propagating downstream w= dimensionless acoustic wave propagating upstream x = x-axis value, m y = y-axis value, m z = z-axis value, m = specific heat capacities ratio = Dirac distribution = ratio between indirect and direct noise = mass density, kg=m 3 = temporal mean value of 0 = temporal fluctuation value of = reduced angular pulsation ! = angular pulsation, rad=s Subscripts AA = acoustic response of the nozzle to an acoustic perturbation CC = response of the combustion chamber to a heat release fluctuation SA = acoustic response of the nozzle to an entropy perturbation t = total quantity of 0 = quantity upstream from the combustor 1 = quantity downstream from the combustor and upstream from the nozzle 2 = quantity downstream from the nozzle

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Section: Resultsmentioning

confidence: 99%

Section: Leykomentioning

confidence: 98%

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Comparison of Direct and Indirect Combustion Noise Mechanisms in a Model Combustor

Leyko¹,

2009

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“…The method revealed delay times from the internal combustor sensor to the far-field microphone, even though the correlated signal contained both periodic and random components. In addition, indirect combustion noise has been investigated numerically and with model-scale experiments by Schemel et al [32], Richter et al [33], and Bake et al [34][35][36].…”

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confidence: 98%

Core Noise Diagnostics of Turbofan Engine Noise Using Correlation and Coherence Functions

Miles

2010

Journal of Propulsion and Power

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Cross-correlation and coherence functions are used to look for periodic acoustic components in turbofan engine combustor time histories, to investigate direct and indirect combustion noise source separation based on signal propagation time delays, and to provide information on combustor acoustics. This investigation uses a combustor pressure sensor and a far-field microphone at 130 to study the change in propagation time to the far field of the direct and indirect combustion noise signal using a generalized cross-correlation function. Results are presented as a function of the cutoff frequency of the low-pass filter used to create the generalized cross-correlation function and engine operating condition. The filtering procedure used produces no phase distortion. As the low-pass-filter frequency is decreased, the travel time increases. The indirect combustion noise signal travels more slowly, because the entropy in the combustor moves with the flow, which has a low velocity. The indirect combustion noise signal travels at acoustic velocities after reaching the turbine and being converted into an acoustic signal. The direct combustion noise is always propagating at acoustic velocities. This is in agreement with previous investigations of delay times using a cross-spectrum phase-angle method with unfiltered signals that found indirect combustion noise to be in the 0-200 Hz frequency range and the direct combustion noise to be in the 200-400 Hz frequency range. Similar results obtained using the cross-spectrum phase-angle method with filtered signals are also shown. These results show that the low-pass filtering can be used with the cross-correlation function to separate this type of dependent source and confirm the cross-spectrum results. Although the results are based on a set of static engine tests conducted for one specific dual-spool turbofan engine configuration, they may lead to a better idea about the acoustics in the combustor turbine-tailpipe system and may help develop and validate improved reduced-order physics-based methods for predicting turbofan engine core noise. NomenclatureB e = resolution bandwidth, Hz, 1=T d r s =N 2 Hz c c = combustor-region speed of sound, m=s c o = ambient speed of sound, m=s D = propagation time delay or lag, s f c = upper frequency limit, 1=2t r s =2, Hz (32,768 Hz) f L = cutoff frequency of low-pass filter L c = combustor-region length, m L y = number of frequencies, f c =f N=2 (16,384) M c = combustor-region Mach number N = segment length, number of data points per segment (32,768) n o = number of overlapped data segments/blocks n s = number of disjoint (independent) data segments/ blocks, B e T total 128 P I = confidence-interval percent value used to calculate coherence threshold < = gas constant, 8314 J=k mol K R x = autocorrelation function R xy = cross-correlation function r = microphone radial location, m (30.48 m) r s = sample rate, samples/s (65,536) T c = temperature in combustor, K T d i = record length of segment i, N=r s , 0.5 s T total = total record length, s ...

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“…Miles et al (2010) has developed an experiment method to identify the indirect combustion noise and direct combustion noise into different frequency domain using aligned and unaligned coherence techniques. Bake et al (2007;2008; has also demonstrated the indirect combustion noise by using a electrically heated flow as a inlet flow for a convergent-divergent nozzle tube. A numerical simulation of this simple experimental setup was performed by Leykoa et al (2009)…”

Section: Introductionmentioning

confidence: 99%

Investigation of Tonal Noise in a High Pressure Turbine Stage Due to Temperature Inhomogeneous of the Inflow

Zhongqiang¹,

Qiao²,

Michel³

2012

MAS

Self Cite

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The tonal sound emission of a high pressure turbine stage due to total temperature inhomogeneous of the inflow investigated numerically. A non-uniform mean temperature made by a result of the discrete burners inside the annular combustion chamber. In present paper we made a setting that 14 periodic total temperature distribution in the azimuthal direction in the turbine inlet. Through comparison between non-uniform inlet temperature case and uniform inlet temperature case, the results show that the sound power emitted in the downstream direction is increased by 5.9 dB at the blade-passing frequency and by remarkably 11.6 dB at the first harmonic of the blade-passing frequency. This result indicated the total temperature fluctuation in the inlet of turbine stage would affect the sound field drastically.

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Investigation of Entropy Noise in Aero-Engine Combustors

Cited by 51 publications

References 9 publications

Comparison of Direct and Indirect Combustion Noise Mechanisms in a Model Combustor

Comparison of Direct and Indirect Combustion Noise Mechanisms in a Model Combustor

Core Noise Diagnostics of Turbofan Engine Noise Using Correlation and Coherence Functions

Investigation of Tonal Noise in a High Pressure Turbine Stage Due to Temperature Inhomogeneous of the Inflow

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