排序方式： 共有32条查询结果，搜索用时 31 毫秒
31.
Two-dimensional numerical simulations were conducted of the growth of thermal plumes from a point heat source at Rayleigh
numbers up to 108 and Prandtl numbers up to 1000. Scaling the convection equations by the free fall velocity rather than the
thermal diffusivity, increased the Prandtl number range available to numerical simulation by one order of magnitude from Prandtl
number 100 to 1000. We present animations showing how the plumes grow with time for different Prandtl numbers. Plumes with
Prandtl numbers around 7 (water) were found to be unstable to sinuous instabilities; whereas those at Prandtl numbers of 1000
had straight stems and fewer sinuous instabilities. Wavelet analysis was used to analyze the scales at which plumes initiated,
and the scales at which sinuous instabilities occurred. The scale of both the plume structures and instabilities was found
to decrease with Prandtl number. 相似文献
32.
This study, using an experimental approach, focuses on the effect of downward seepage on a threshold alluvial channel morphology and corresponding turbulent flow characteristics. In all the experiments, we observed that the streamwise time‐averaged velocities and Reynolds shear stresses were increased under the influence of downward seepage. Scales of eddy length and eddy turnover time were significantly increased with the application of downward seepage, leading to sediment transport and initiation of bedforms along the channel length. As the amount of seepage discharge increased, eddy length and turnover time were further increased, causing the development of larger bedforms. It was revealed that the geometry of bedforms was linked with the size of eddies. In this work, statistics of bedform dynamics are presented in terms of multi‐scalar bedforms in the presence of seepage. These multi‐scalar ubiquitous bedforms cast a potential impact on flow turbulence as well as stream bed morphology in channels. We used wavelet to analyse temporally lagged spatial bed elevation profiles that were obtained from a set of laboratory experiments and synchronized the wavelet coefficients with bed elevation fluctuations at different length scales. A spatial cross‐correlation analysis, based on the wavelet coefficients, was performed on these bed elevation datasets to observe the effect of downward seepage on the dynamic behaviour of bedforms at different length scales. It was found that celerity of bedforms reduced with increase in seepage percentage. Bedform celerity was best approximated by a probability density function such as Rayleigh distribution under varying downward seepage. Further, statistical analysis of physical parameters of bedforms ascertained that the reduction in bedform celerity was a result of increased bedform size. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献