| Popis: |
By using a thermally stratified wind tunnel, we have successfully simulated stably stratified boundary layers (SBL), in which the mean temperature increases upward almost linearly. We have investigated the flow structure and the effects of linear stable stratification on the transfer of momentum and heat fluxes. The vertical profiles of turbulence quantities exhibit different behavior in two distinct stability regimes of the SBL flows with weak and strong stability. For weak stability cases, the transfer of turbulent momentum and heat fluxes is basically similar to those for neutral turbulent boundary layers, although it is weaken with increasing stability. For strong stability cases, on the other hand, the time-mean transfer of turbulent fluxes is almost zero over the whole boundary layer depth. However, the instantaneous transfer of turbulent fluxes frequently occurs in the both gradient and counter-gradient directions in the lower part of boundary layer. This is due to the Kelvin-Helmholtz (K-H) shear instability and the rolling up and breaking of K-H waves. Moreover, the internal gravity waves are observed in the middle and upper parts of all stable boundary layers. |
