Experimental investigation of the nonlinear response of turbulent premixed flames to imposed inlet velocity oscillations

Combining a Helmholtz solver with the flame describing function to assess combustion instability in a premixed swirled combustor

“…The output of this quasi-analytical approach are the growth rate of the acoustic modes, their frequency of oscillation and spatial structure as a function of the perturbation amplitude level. For a given frequency and for increasing values of the acoustic velocity amplitude, the gain and phase of the FDF evolve (Balachandran et al, 2005;Bellows et al, 2007;Durox et al, 2009;Schimek et al, 2011;Kim and Hochgreb, 2011). Depending on û , a mode may be found stable or unstable; when the growth rate ω i exceeds damping at small amplitude the mode is unstable and the limit cycle corresponds to the particular value of û for which the growth rate tends to the damping rate.…”

Use of filtered combustion light and backlit high-speed images in combustion stability studies

“…The chemiluminescence measurement is a line of sight technique used to determine the total heat release emitted by a §ame in the region of interest [411]. Balachandran et al studied both OH * and CH * simultaneously in a series of experiments and determined that both were in good agreement with each other and are a good indicator of global heat release [9]. The study found that the OH * and CH * global measurements correlated with the global heat release measurements, and the magnitude and the phase of the global OH * and CH * were in good agreement.…”

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

“…Both of the values are slightly larger than the values reported in an earlier study because correlation between the far-field acoustic power and burner geometry or 16 operating flow conditions. It has been recently noted [5,6] that the two-point 17 spatial correlation of the rate of change of fluctuating heat release rate, 18 and hence the associated correlation volume v cor and its length scale, is 19 crucial to predicting combustion noise. In previous studies, different length 20 scales have been suggested to estimate v cor empirically, ranging from the 21 laminar flame thickness δ L [12], turbulence integral length scale Λ [13] to the 22 turbulent flame-brush thickness [14,15] or a combination of them.…”

“…was derived indirectly from the DNS flames [16][17][18] whereas B was obtained 397 from the laser diagnostics data [19]. In addition, both K and B 1 were treated 398 in Refs.…”

“…27 Recently, it has become feasible to obtain high-fidelity information on the 28 correlation of fluctuating heat release rate because of the advancement in 29 computing technologies and techniques, and laser metrology. Swaminathan 30 et al [5,6] have attempted to analyse and model this two-point correlation 31 using DNS [16][17][18] and laser diagnostics [19] data of turbulent premixed 32 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 .…”