Hostname: page-component-5db6c4db9b-5lzww Total loading time: 0 Render date: 2023-03-26T04:00:51.705Z Has data issue: true Feature Flags: { "useRatesEcommerce": false } hasContentIssue true

The effects of unstable stratification and mean shear on the chemical reaction in grid turbulence

Published online by Cambridge University Press:  10 April 2000

Department of Mechanical Engineering, Kyoto University, Kyoto 606-8501, Japan
Department of Mechanical Engineering, Kyoto University, Kyoto 606-8501, Japan


The effects of unstable thermal stratification and mean shear on chemical reaction and turbulent mixing were experimentally investigated in reacting and non-reacting liquid mixing-layer flows downstream of a turbulence-generating grid. Experiments were carried out under three conditions: unsheared neutrally stratified, unsheared unstably stratified and sheared neutrally stratified. Instantaneous velocity and concentration were simultaneously measured using the combination of a laser-Doppler velocimeter and a laser-induced fluorescence technique. The results show that the turbulent mixing is enhanced at both large and small scales by buoyancy under unstably stratified conditions and therefore the chemical reaction is strongly promoted. The mean shear acts to enhance the turbulent mixing mainly at large scales. However, the chemical reaction rate in the sheared flow is not as large as in the unstably stratified case with the same turbulence level, since the mixing at small scales in the sheared neutrally stratified flow is weaker than that in the unsheared unstably stratified flow. The unstable stratification is regarded as a better tool to attain unsheared mixing since the shearing stress acting on the fluid is much weaker in the unstably stratified flow than in the sheared flow.

Research Article
© 2000 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)