| Summary: | Coherent structures in the turbulent boundary layer were investigated under different stability conditions. Qualitative analyses of the flow field, spatial correlation coefficient field and pre-multiplied wind velocity spectrum showed that the dominant turbulent eddy structure changed from small-scale motions to large- and very-large-scale motions and then to thermal plumes as the stability changed from strong stable to neutral and then to strong unstable. A quantitative analysis of the size characteristics of the three-dimensional turbulent eddy structure based on the spatial correlation coefficient field showed that under near-neutral stability, the streamwise, wall-normal and spanwise extents remained constant at approximately 0.3<inline-formula> <math display="inline"> <semantics> <mi>δ</mi> </semantics> </math> </inline-formula>, 0.1<inline-formula> <math display="inline"> <semantics> <mi>δ</mi> </semantics> </math> </inline-formula> and 0.2<inline-formula> <math display="inline"> <semantics> <mi>δ</mi> </semantics> </math> </inline-formula> (<inline-formula> <math display="inline"> <semantics> <mi>δ</mi> </semantics> </math> </inline-formula>, boundary layer height), respectively, while for other conditions, the extent in each direction varied in a log-linear manner with stability; only the spanwise extent under stable conditions was also independent of stability. The peak wavenumber of the pre-multiplied wind velocity spectrum moves towards small values from stable conditions to neutral condition and then to unstable conditions; thus, for the wind velocity spectrum, another form is needed that takes account the effects of the stability condition.
|
|---|