Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets

TL;DR

This paper uses DNS data to analyze how chemical reactions and heat release influence turbulence, scalar fields, and anisotropy in reacting wall-jets, revealing persistent small-scale anisotropy and Damkohler number effects near the wall.

Contribution

It provides a detailed DNS-based analysis of anisotropy and scalar field behavior in reacting turbulent wall-jets, highlighting the impact of heat release and Damkohler number on turbulence characteristics.

Findings

Heat release increases anisotropy near the wall.

Small-scale anisotropies persist throughout the domain.

Damkohler number significantly affects near-wall turbulence.

Abstract

The concept of local isotropy in a chemically reacting turbulent wall-jet flow is addressed using direct numerical simulation (DNS) data. Different DNS databases with isothermal and exothermic reactions are examined. The chemical reaction and heat release effects on the turbulent velocity, passive scalar and reactive species fields are studied using their probability density functions (PDF) and higher order moments for velocities and scalar fields, as well as their gradients. With the aid of the anisotropy invariant maps for the Reynolds stress tensor the heat release effects on the anisotropy level at different wall-normal locations are evaluated and found to be most accentuated in the near-wall region. It is observed that the small-scale anisotropies are persistent both in the near-wall region and inside the jet flame. Two exothermic cases with different Damkohler number are examined and the comparison revealed that the Damkohler number effects are most dominant in the near-wall region, where the wall cooling effects are influential. In addition, with the aid of PDFs conditioned on the mixture fraction, the significance of the reactive scalar characteristics in the reaction zone is illustrated. We argue that the combined effects of strong intermittency and strong persistency of anisotropy at the small scales in the entire domain can affect mixing and ultimately the combustion characteristics of the reacting flow.