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New expressions for the surface roughness length and displacement height in the atmospheric boundary layer 总被引:1,自引:0,他引:1 下载免费PDF全文
An alternative model for the prediction of surface roughness length
is developed. In the model a new factor is introduced to compensate
for the effects of wake diffusion and interactions between the wake
and roughness obstacles. The experiments are carried out by the use
of the hot wire anemometry in the simulated atmospheric boundary
layer in a wind tunnel. Based on the experimental data, a new
expression for the zero-plane displacement height is proposed for
the square arrays of roughness elements, which highlights the
influence of free-stream speed on the roughness length. It appears
that the displacement height increases with the wind speed while the
surface roughness length decreases with Reynolds number increasing.
It is shown that the calculation results based on the new
expressions are in reasonable agreement with the experimental data. 相似文献
2.
Effect of Surface Roughness and Reynolds Number on Self-Similarity of Velocity Profile in the Atmospheric Boundary Layer 总被引:1,自引:0,他引:1 下载免费PDF全文
Self-similarity of power law velocity profile of a simulated atmospheric boundary layer is studied experimentally. The results demonstrate that the self-similarity maintains very well along the streamwise direction for the same rough surface but changes significantly with the surface roughness at the same position. The self-similarity of the vertical velocity profiles is affected by enhancement of the free stream velocity when the roughness concentration is relatively denser. 相似文献
3.
In this paper the mixing of a sample in the curved microchannel with heterogeneous
surface potentials is analysed numerically by using the control-volume-based finite
difference method. The rigorous models for describing the wall potential and
external potential are solved to get the distribution of wall potential and external
potential, then momentum equation is solved to get the fully developed flow field.
Finally the mass transport equation is solved to get the concentration field. The
results show that the curved microchannel has an optimized capability of sample
mixing and transport when the heterogeneous surface is located at the left
conjunction between the curved part and straight part. The variation of
heterogeneous surface potential $\psi_{\rm n}$has more influence on the capability
of sample mixing than on that of sample transport. The ratio of the curved
microchannel's radius to width has a comparable effect on the capability of sample
mixing and transport. The conclusions above are helpful to the optimization of the
design of microfluidic devices for the improvement of the efficiency of sample
mixing. 相似文献
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