Jet Noise: Acoustic Analogy informed by Large Eddy Simulation

On the Space-Time Correlation of Heat Release Rate in Turbulent Premixed Flames

“…It is obviously shown in Figure 7 of the peak correlation are determined by ∆ + x =ū + τ + , which is in agreement with the convection characteristics observed in Figure 6(c) as well as the spatio-temporal correlations of jet noise sources (e.g. Karabasov et al, 2010Karabasov et al, , 2011Depuru Mohan et al, 2015), local burning area fluctuations (Hemchandra and Lieuwen, 2010), and local chemiluminescence fluctuations (Rajaram and Lieuwen, 2009). The envelope of the peak correlation values indicates the decay of Ω p (∆ + x , τ + ) with the separation distance ∆ + x and/or time delay τ + .…”

“…In a series of recent studies on modelling the two-point space-time correlation of jet noise sources (e.g. Karabasov et al, 2010Karabasov et al, , 2011Depuru Mohan et al, 2015), it was observed that this correlation can be well represented by the Gaussian-type function commonly used in classical turbulence. Tam (2015) recently proposed that the spectral shape of combustion noise from hydrocarbon fuels is the same as the similarity spectrum of the large turbulence structure noise from high-speed jets, regardless of the turbulence level or fuel properties.…”

“…One kind of temporal correlation of heat release rate fluctuations is the two-point space-time correlation which has been successfully applied to model the spectrum of fluid dynamic noise in non-reacting flows, for example jet noise spectrum (e.g. Karabasov et al, 2010Karabasov et al, , 2011Depuru Mohan et al, 2015). However, the two-point space-time correlation of the heat release rate fluctuation in turbulent flames has scarcely been reported in prior literature (Liu et al, 2011) primarily because reliable heat release rate data are absent in previous numerical simulations or measurements.…”

Spatial correlation of heat release rate and sound emission from turbulent premixed flames

“…They found that the two-point correlations of heat release rate, 33 Ω, and the rate of change of fluctuating heat release rate, Ω 1 , can be 34 well represented by Gaussian-type functions commonly used in classical 35 turbulence, and that the length scale of the correlation volume, v cor , is 36 0.5δ L . This model was then shown to give a good agreement with recent 37 experimental measurements [20] of the far-field overall sound pressure level The construction of Ω 1 requires the rate of change of fluctuating heat 40 release rate, which was calculated in Refs. [5,6] indirectly by using a balance equation for a progress variable and taking the instantaneous reaction rate 42 to be a function of the progress variable.…”

A second golden age of aeroacoustics?

“…As anticipated in previous studies [43,64,65], analysis of the recent databases is providing a comprehensive characterization of the jet noise source covariances. The structural differences in different Reynolds stress covariance [66][67][68] have been noted. More importantly, the often assumed independence among the different (source) components is shown to be flawed, particularly in relation to source terms involving enthalpy fluctuations [68,69].…”