The role of friction on the annihilation of self-similarity in a scalar field

The self-similarity nature of a scalar field released from a wall source located at the bottom wall of a fully-developed turbulent channel flow is investigated. In pursuit of this objective, direct numerical simulation (DNS) was carried out for two distinct cases involving weak and strong source strengths. The findings show the absence of self-similarity in the distribution of mean concentration fields. Analysis carried out in both physical and spectral spaces revealed that the convection-diffusion mechanism and the development of short- and long- range dispersion play only a minor role in influencing the nature of self-similarity. Friction is shown to be the key factor in determining the emergence of self-similarity.