Conditional statistics near the turbulent/non-turbulent interface in a planar liquid jet with a chemical reaction

Abstract

We measure concentrations of reactive species and streamwise velocity simultaneously near the turbulent/non-turbulent (T/NT) interface in a planar liquid jet with a second-order chemical reaction A + B → R. The reactants A and B are premixed into the jet and ambient flows, respectively. We use an I-type hot-film probe and an optical fiber probe based on the light absorption spectrometry to measure the streamwise velocity and the concentrations of the reactive species. We investigate the two interfaces perpendicular to the streamwise direction: leading edge, across which the turbulent region turns into the non-turbulent region toward streamwise direction, and trailing edge, across which the non-turbulent region turns into the turbulent region toward streamwise direction. We calculate the conditional statistics conditioned on the time elapsed from the time when the interface is detected. The results show that the conditional statistics of the concentrations vary drastically near the T/NT interface, and the variations in the conditional statistics near the leading edge are larger than those near the trailing edge. The width of the interface with the large variation in the conditional mean concentration near the T/NT interface is almost independent of the chemical species and the Damköhler number. Because the reactant A only exists in the turbulent region, the chemical reaction takes place in the turbulent region. The chemical reaction rate near the leading edge is larger than that near the trailing edge. This difference between the leading and trailing edges relates to the velocity near the T/NT interface.

Keywords

• jet
• chemical reaction
• turbulent flow
• mixing
• turbulent/non-turbulent interface