Thermally stratified liquid turbulence with a chemical reaction

Effects of stable and unstable thermal stratifications on turbulent mixing and chemical reaction in liquid turbulence were investigated by both laboratory experiments and numerical simulations. Instantaneous velocity and concentration were simultaneously measured using a combined technique with a two-component laser-Doppler velocimeter (LDV) and a laser-induced fluorescence (LIF) method in two kinds of thermally stratified turbulent reacting flows: grid-generated turbulence and a mixing layer. The results show that turbulent mixing in the fully developed liquid turbulence is affected mainly at large scales by buoyancy. However, the maximum value of the mean concentration of chemical product is independent of thermal stratification. In addition, a large-eddy simulation (LES) based on a beta-pdf model was applied to the same thermally stratified reacting liquid flows as used in the experiments. The numerical results show that the stratification effects on the turbulent mixing and chemical reaction can be well predicted by the LES and the buoyancy effects are not significant in the subgrid-scale models for the LES. (c) 2005 American Institute of Chemical Engineers AIChE J, 52: 456-468, 2006