Similarities and dissimilarities in a spatially evolving turbulent reactive planar jet

Turbulent mixing of reactive scalars is fundamental to a range of engineering and environmental processes, yet accurately capturing its multi-scale dynamics remains challenging. This study employs quasi-direct numerical simulation to investigate the turbulent mixing characteristics of a planar turbulent jet undergoing an isothermal second-order chemical reaction, with a particular focus on the self-similar properties of the velocity and scalar fields. A novel transitional region where the turbulence dissipation coefficient increases streamwise is revealed. The streamwise increase of turbulence dissipation coefficient is attributed to the constant Taylor-scale Reynolds number ($R{e}_{\lambda }$) and the growing ratio of outer to inner length scales ($\delta /\lambda$, where $\delta$ represents the jet half-width and $\lambda$ the Taylor microscale). The interaction between turbulent transport and chemical reactions causes notable changes in the scalar distribution patterns, as evidenced by distinct scaling laws and flux profiles of reactive scalar compared to those of a scalar. Additionally, a persistent core region with nearly constant fluctuation covariance is observed. These findings offer novel insights into the interplay between reactions and turbulent mixing, which is essential for optimizing industrial processes and environmental assessments.