Influence of Residence and Scalar Mixing Time Scales in Non-Premixed Combustion in Supersonic Turbulent Flows

Lagrangian modelling of turbulent spray combustion under liquid rocket engine conditions

“…It could also be the outcome of an unsatisfactory evaluation of the mixing time scale, which is supposed to be proportional to the turbulent time scale. This proportionality assumption should be seriously reconsidered in the present case since the usual scalar/velocity similarity assumption is not suited to the near injection, see for instance the recent investigation reported in [23]. In addition to this and as emphasized above, vaporizing droplets are also expected to modify the mean SDR level.…”

“…Such a closure does involve an assumed equilibrium between the production of SDR (through turbulent straining) and its dissipation. However, as recently confirmed by the study conducted in reference [23], the use of such an algebraic representation may raise some important issues, even for classical situations associated with the mixing of inert scalars. This seriously questions the use of the above closure for the present situation involving scalar quantities affected by vaporization processes.…”

“…As a consequence, since the mixture fraction is not affected by chemical reactions, there is no reactive contribution similar to the term labelled (IX) in references [25,26,27]. Most of the remaining contributions in the RHS of this transport equation have already concentrated a large amount of work, see for instance [23,25,26,27,28], and the reader is referred to the recent study conducted in reference [23] for further insights into their detailed modelling.…”

Self-similarity of fluid residence time statistics in a turbulent round jet

“…The stream-age equation is useful because a broad set of chemical processes require the presence of more than one reactant, so that reaction progress may be related to the time since individual streams were introduced, rather than the fluid age of the mixture (Mouangue et al 2014). For example, Gomet et al (2012) used an ensemble-averaged form of the stream-age equation in order to model the different residence times of fuel, air and fuel-air mixtures in an autoigniting flow, and subsequently obtained accurate predictions for the ignition locations.…”

“…As a second example, residence time is the principal indicator of where and when an ignitable mixture will autoignite, and Gomet, Robin & Mura (2012) used residence time statistics to predict the locus of autoignition in a supersonic non-premixed flow by comparing the residence time with the ignition delay time of the fuel-air mixture. A further example where residence time is used to characterise the extent of physical processes in combustion is given by Nambully et al (2014), who used the mean residence time to explain the accumulation of preferential diffusion effects in a bluff-body stabilised turbulent flame.…”