AN EXPERIMENTAL-STUDY OF A REACTIVE PLUME IN GRID TURBULENCE

Experimental results for a reactive non-buoyant plume of nitric oxide (NO) in a turbulent grid flow doped with ozone (O-3) are presented. Th e Damkohler number (N-D) for the experiment is of order unity indicati ng the turbulence and chemistry have similar timescales and both affec t the chemical reaction rate. Continuous measurements of two component s of velocity using hot-wire anemometry and the two reactants using ch emiluminescent analysers have been made. A spatial resolution for the reactants of four Kolmogorov scales has been possible because of the n ovel design of the experiment. Measurements at this resolution for a r eactive plume are not found in the literature. The experiment has been conducted relatively close to the grid in the region where self-simil arity of the plume has not yet developed. Statistics of a conserved sc alar, deduced from both reactive and non-reactive scalars by conserved scalar theory, are used to establish the mixing held of the plume, wh ich is found to be consistent with theoretical considerations and with those found by other investigators in non-reactive flows. Where appro priate the reactive species means and higher moments, probability dens ity functions, joint statistics and spectra are compared with their re spective frozen, equilibrium and reaction-dominated limits deduced fro m conserved scalar theory. The theoretical limits bracket reactive sca lar statistics where this should be so according to conserved scalar t heory. Both reactants approach their equilibrium limits with greater d istance downstream. In the region of measurement, the plume reactant b ehaves as the reactant not in excess and the ambient reactant behaves as the reactant in excess. The reactant covariance lies outside its fr ozen and equilibrium limits for this value of N-D. The reaction rate c losure of Toor (1969) is compared with the measured reaction rate. The gradient model is used to obtain turbulent diffusivities from turbule nt fluxes. Diffusivity of a non-reactive scalar is found to be close t o that measured in non-reactive hows by others.