Abstract
The effects of varying turbulence intensity and turbulence length scale on premixed turbulent flame propagation are investigated using Direct Numerical Simulation (DNS). The DNS dataset contains the results of a set of turbulent flame simulations based on separate and systematic changes in either turbulence intensity or turbulence integral length scale while keeping all other parameters constant. All flames considered are in the thin reaction zones regime. Several aspects of flame behaviour are analysed and compared, either by varying the turbulence intensity at constant integral length scale, or by varying the integral length scale at constant turbulence intensity. The turbulent flame speed is found to increase with increasing turbulence intensity and also with increasing integral length scale. Changes in the turbulent flame speed are generally accounted for by changes in the flame surface area, but some deviation is observed at high values of turbulence intensity. The probability density functions (pdfs) of tangential strain rate and mean flame curvature are found to broaden with increasing turbulence intensity and also with decreasing integral length scale. The response of the correlation between tangential strain rate and mean flame curvature is also investigated. The statistics of displacement speed and its components are analysed, and the findings indicate that changes in response to decreasing integral length scale are broadly similar to those observed for increasing turbulence intensity, although there are some interesting differences. These findings serve to improve current understanding of the role of turbulence length scales in flame propagation.
Highlights
The response of a premixed flame when subjected to increasingly intense turbulence has been the subject of many different experimental and theoretical studies (Bradley 1992; Driscoll 2008; Peters 1999; Poludnenko and Oran 2011, 2010)
A majority of related studies has focused on the variations in turbulence intensity (Driscoll 2008; Lipatnikov and Chomiak 2002), including Direct Numerical Simulation (DNS) studies which have been applied to investigate the effect of increasing the turbulence intensity u′ while holding all other parameters constant as far as possible (Nivarti and Cant 2017)
A set of Direct Numerical Simulations has been carried out in which the integral length scale 0∕ L as well as the turbulence intensity u ∕sL is varied in a systematic manner while keeping all other parameters constant
Summary
The response of a premixed flame when subjected to increasingly intense turbulence has been the subject of many different experimental and theoretical studies (Bradley 1992; Driscoll 2008; Peters 1999; Poludnenko and Oran 2011, 2010). There have been fewer studies which have produced information about the effect on the flame of varying the turbulence integral length scale l0 (Peters 1999; Lipatnikov and Chomiak 1999; Song et al 2021). The statistics of flame stretch for this dataset (Luca et al 2019) indicated that tangential strain rate and mean flame curvature normalised by the Kolmogorov length were found to have a weak dependence on Re. The present study aims to investigate the response of a turbulent premixed flame to variations in u′ and l0 , treating each of these quantities separately as an independent variable while holding all the other variables constant. The effects of varying u′ at constant l0 are compared with previous findings (Nivarti and Cant 2017), while results illustrating the effects of varying l0 at constant u′ are presented and discussed
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