Consumption speed and burning velocity in counter-gradient and gradient diffusion regimes of turbulent premixed combustion

The structure of turbulent flames in fractal- and regular-grid-generated turbulence

“…Whereas, in the near field the rod creates some flow disturbance, further downstream, where the flame images are acquired, the effect of the rod is largely nonexistent, as observed previously, e.g. [34].…”

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

“…Since the majority of measurements of turbulent burning velocity in V-shaped flames, e.g., [11,16,17], and, especially, in Bunsen (rim-stabilized) flames, e.g., [5,10,12,15,19,21,31], were performed by averaging experimental data over the entire flame volume or over a significant part of it, another method of processing the DNS data was also used in order to evaluate similarly averaged values of the developing U T . For this purpose, let us consider a simple mean-reaction-wave surface that has a conical shape, with the cone base radius and height being equal to R and H , respectively.…”

“…Finally, it is worth noting that the aforementioned model expressions for the transient U T (θ ) also predict variations in the scaling exponents during flame development. For instance, the following equation [70] U T (θ ) U T (θ → ∞) = 1+ 1 θ e −θ −1 1/2 (11) which was developed within the framework of the Flame Speed Closure (FSC) model [22,25] and was validated in RANS simulations [24,25,35,71] of various experiments with statistically stationary premixed turbulent flames, predicts that q v (θ → ∞) = q v (θ 1) + 0.5 and q L (θ → ∞) = q L (θ 1) + 0.5 also. Here, q L is the scaling exponent with respect to an integral length scale L. In other words, both scaling exponents increase during flame development, with the total increase in q v or q L being equal to 0.5.…”

“…Accordingly, as reviewed elsewhere [1][2][3], S T and U T were in the focus of experimental research into premixed combustion for many years. In particular, over the past decade, such measurements were conducted by various research groups, e.g., [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. However, values of U T and S T obtained from different experiments under similar conditions, i.e., comparable rms turbulent velocities u , close unburned gas temperatures, the same pressure, the same fuel, and the same equivalence ratio, are strongly scattered, e.g., see Fig.…”

“…Then, strictly speaking, research into turbulent burning velocity and flame speed is of minor fundamental value. On the other hand, while the scatter of measured U T , S T , and their scaling exponents seems to be a sufficient reason for expressing concern over the notions of these quantities, such a standpoint is not widely accepted and evaluation of U T and S T is still in the focus of experimental research into premixed combustion, e.g., see [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and references quoted therein. Moreover, U T and S T are widely used in numerical simulations of turbulent flames, as reviewed elsewhere [3,[22][23][24][25].…”