DNS analysis on the correlation between local burning velocity and flame displacement speed of turbulent premixed flames

The local burning velocity and flame displacement speed are the major properties of premixed flames. The local burning velocity, which is the instantaneous quantity based on the local consumption rate of the unburnt mixture, is considered to be the most appropriate burning velocity in terms of the definition. The local burning velocity can be evaluated theoretically and numerically; however, it is almost impossible to obtain it experimentally using the current technology of measurement. The flame displacement speed can be evaluated more easily than the local burning velocity and compared with the flame displacement speed obtained from experiments. However, the local burning velocity and flame displacement speed have been discussed separately in turbulent premixed flames. In this study, to clarify the relation between the local burning velocity and the flame displacement speed, numerical analyses were performed using the DNS database of statistically steady and fully developed turbulent premixed flames with different density ratios of the unburnt mixture to the burnt product and with different Lewis numbers. It was found that for different density ratios, the local burning velocity was little sensitive to the flame displacement speed in any case under the unity Lewis number. This means the correlation between the local burning velocity and the flame displacement speed is little affected by the dilation of a flame. For different Lewis numbers, the correlation between the local burning velocity and the flame displacement speed was negative in Le = 0.8, and positive in Le = 1.2. This can be explained by the effect of the Lewis number on the local burning velocity, and the flame displacement speed was little affected by the Lewis number in the correlation between the local burning velocity and the flame displacement speed.