Flow, Turbulence and Combustion ( IF 2.4 ) Pub Date : 2022-03-03 , DOI: 10.1007/s10494-022-00318-w Arun Ravi Varma 1 , Umair Ahmed 1 , Nilanjan Chakraborty 1
The effects of buoyancy on turbulent premixed flames are expected to be strong due to the large changes in density between the unburned and fully burned gases. The present work utilises three-dimensional direct numerical simulations of statistically planar turbulent premixed flames under decaying turbulence to study the influence of buoyancy on the evolution of turbulent kinetic energy within the flame brush. Four sets of turbulence parameters have been studied, with four different values of Froude number for each set. It is found that for a given set of turbulence parameters, flame wrinkling increases with an increase in body force magnitude in the case of unstable stratification, which is also reflected in the increased values of turbulent burning velocity and flame surface area. An increase in body force magnitude in the case of stable stratification acts to reduce the extent of flame wrinkling. Turbulent kinetic energy and its dissipation rate are found to be affected by both the magnitude and direction of the body force. For low turbulence intensities considered here, turbulent kinetic energy increases from the leading edge of the flame brush before decaying eventually towards the product side of the flame brush. For high turbulence intensities, the turbulent kinetic energy is found to decay across the flame brush, and it is also found that the effect of body force on the evolution of turbulent kinetic energy is marginal in the case of high turbulence intensities. The effects of body force magnitude and direction on the statistical behaviours and closures of the various terms of the turbulent kinetic energy transport equation are analysed, and existing models have been modified to account for Froude number effects, where necessary.
中文翻译:
体力对预混火焰中湍流动能传输的影响
由于未燃烧气体和完全燃烧气体之间的密度变化很大,预计浮力对湍流预混合火焰的影响会很大。目前的工作利用在衰减湍流下统计平面湍流预混合火焰的三维直接数值模拟来研究浮力对火焰刷内湍流动能演变的影响。已经研究了四组湍流参数,每组具有四个不同的弗劳德数值。研究发现,对于给定的湍流参数,在分层不稳定的情况下,火焰起皱随着体力大小的增加而增加,这也反映在湍流燃烧速度和火焰表面积值的增加上。在稳定分层的情况下,体力大小的增加可以减少火焰起皱的程度。发现湍流动能及其耗散率受体力大小和方向的影响。对于这里考虑的低湍流强度,湍流动能从火焰刷的前缘增加,然后最终向火焰刷的产品侧衰减。对于高湍流强度,发现湍流动能穿过火焰刷衰减,并且还发现在高湍流强度的情况下,体力对湍动能演化的影响是微不足道的。