Transient mixing in turbulent open channel subject to radiative heating
Abstract
The temporal evolution of initially neutral turbulent open channel flow subject to radiative surface heating through the Beer-Lambert law is examined through direct numerical simulations. As the flow transitions to stably stratified conditions we observe three distinct regimes in time. Initially the temperature field acts as a passive scalar growing directly in proportion to depth varying heat-source q (z) with turbulence largely unaffected. A second transient period is observed in which the flow begins to move towards local energetic equilibrium. During this regime a strong transient effect is observed whereby the turbulence micro-structure of the flow is still relatively unaffected by buoyancy, however the local buoyancy gradient N2 is significantly large. As stable stratification begins to affect the smallest scales of the flow a final temporal regime is observed whereby the flow becomes independent of transient effects and instantaneous mixing can be again be estimated from local measurements of Froude number Fr =ɛ/Nk .
- Publication:
-
APS Division of Fluid Dynamics Meeting Abstracts
- Pub Date:
- 2020
- Bibcode:
- 2020APS..DFDP17003I