Does sensitivity of measured scaling exponents for turbulent burning velocity to flame configuration prove lack of generality of notion of turbulent burning velocity?

Direct numerical simulation study of statistically stationary propagation of a reaction wave in homogeneous turbulence

“…In particular, as shown by Lipatnikov and Chomiak [56], the three most extensive experimental databases obtained from expanding statistically spherical premixed flames [66][67][68] are reasonably well fitted with S T ∝ U Ka −1/3 or S T ∝ U Da 1/4 and, therefore, indicate a less pronounced dependence of S T /U on Ka or Da when compared to the present DNS. Differences between these measured data and the present DNS results could be attributed to a number of factors, such as (i) thermal expansion effects, reviewed elsewhere [69,70], (ii) differences between experimental and numerical flame configurations, (iii) differences between methods adopted to evaluate S T in the experiments and simulations [71], etc.…”

Improvement of Turbulent Burning Velocity Measurements by Schlieren Technique, for High Pressure Isooctane-Air Premixed Flames

“…The problem is particularly crucial due to the use or future use of premixed turbulent combustion in increasingly drastic conditions in terms of pressure, temperature and diluted environment. As underlined by Verma and Lipatnikov (Verma and Lipatnikov 2016) and Lawes et al(Lawes et al 2012), the notion of turbulent flame speed, or burning velocity, remains unresolved, despite the large amount of data available. Matalon and Creta (Matalon and Creta 2012) consider that represents the mean propagation speed of a premixed flame in a statistical steady state within a turbulent field, similar to the laminar flame speed.…”

A DNS Study of Sensitivity of Scaling Exponents for Premixed Turbulent Consumption Velocity to Transient Effects

“…In other words, the scaling exponents obtained from premixed turbulent flames of different configurations may be different not only due to the well-known effects of the mean-flame-brush curvature and the mean flow non-uniformities, but also due to the flame development, even if the different flames are at the same stage of their development. 2 Direct comparison of the scaling exponents reported in Table 2 with fits to various measured data may be misleading not only due to (i) simplicity of the simulated problem, (ii) the significant scatter of the fits, and (iii) the lack of detailed information on flame-development time in many experimental papers, but also and mainly due to (iv) substantial sensitivity [35] of the scaling exponents to three other effects (the influence of the mean curvature of a flame brush on U T , the influence of the divergence of the mean flow of fresh reactants on S T , and the influence of the growth of mean flame brush thickness on S T ), which are not addressed in the present study, but play an important role in various laboratory premixed turbulent flames. Such effects can, at least in part, explain significant scatter of the scaling exponents reported in different papers.…”

“…Third, S T characterizing different mean flame surfaces can be significantly different if the mean flame brush thickness δ T grows with time or distance from a flame-holder [28], with such a growth of δ T being well documented in a number of experiments with various premixed flames, as reviewed elsewhere [3,22,32], see also recent papers [10,16,33,34]. While the focus of studies [3,22,[26][27][28][29][30][31][32] was placed on the values of U T and S T , rather than the scaling exponents, a recent numerical work [35] has shown that the three aforementioned well-known effects can even cause substantial sensitivity of the scaling exponents q v , q s , and q r to methods used to evaluate U T or S T by processing raw experimental data.…”