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abstract
A stochastic model is proposed to describe the correlation between the scalar fluctuations and their dissipation and the distribution of the conditional scalar dissipation in flows characterised by ‘young’ scalar turbulence, such as the mixing layer formed between opposed jets. It predicts the scalar field from an ensemble of instantaneous scalar interfaces of specified functional form, referred to as mixinglets, randomly displaced in space, and is shown to compare favourably with experimental data from counterflows and direct numerical simulations of scalar fields characterised by short residence times. The model is initially formulated to account for molecular diffusion and turbulent convection and then extended to include all turbulent transport processes by incorporating a description for the instantaneous turbulent strain rates. The contribution of each mechanism to the evolution of the single and joint statistics is quantified individually and the ability of the model to represent conditional scalar statistics with application to combustion modelling is addressed.