Thermal Stratification Effects on Turbulence and Dispersion in Internal and External Boundary Layers
Thermal Stratification Effects on Turbulence and Dispersion in Internal and External Boundary Layers
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热分层对内外边界层湍流和色散的影响
DOI：
10.1007/s10546-020-00524-x
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发表时间：
2020
影响因子：
4.3
通讯作者：
S. Herring
中科院分区：
文献类型：
--
作者：
Vincenzo Sessa;Zheng;S. Herring
发展了一种合成湍流和温度脉动产生方法，并将其嵌入到大涡模拟中，以研究弱稳定层结(即Richardson数$$Ri\le1$$Ri≤1)对模拟的农村向城市过渡后的湍流和弥散的影响。通过将平均速度、湍流应力和点源弥散的预测与风洞实验的数据进行比较，验证了该模拟方法的有效性。风洞实验模拟了接近规则矩形块阵列的稳定大气边界层($$Ri=0.21$$Ri=0.21)。利用Sessa等人提出的壁法向湍流应力方法确定了从块体阵列前沿发展起来的内边界层(IBL)的深度。(《Wind Eng Ind Aerdyn 182：189-291,2018》)。这表明IBL的深度和增长速率对入口处的热稳定性和湍流动能(TKE)很敏感，使得IBL深度在保持相同Ri的情况下随着入流的TKE减小而减小，或者在保持相同的进气TKE的情况下随着Ri的增加而减小。当引入地面线源时，Ri的增加明显减少了冠层高度的垂直标量通量，而增加了街道内的平均浓度。此外，随着IBL的发展，发现对于给定的Ri值，随着TKE的流入水平的减少，层结的影响变得更加明显，从而影响到冠层内和冠层上方的标量通量，以及街道内的体积平均平均浓度。
A synthetic-turbulence and temperature-fluctuation-generation method is developed and embedded in large-eddy simulations to investigate the effects of weak stable stratification (i.e. Richardson number $$Ri\le 1$$ R i ≤ 1 ) on turbulence and dispersion following a simulated rural-to-urban transition. The modelling approach is validated by comparing predictions of mean velocity, turbulent stresses, and point-source dispersion against data from a wind-tunnel experiment that simulates a stable atmospheric boundary layer ( $$Ri=0.21$$ R i = 0.21 ) approaching a regular array of uniform rectangular blocks. The depth of the internal boundary layer (IBL) that develops from the leading edge of the block array is determined using the wall-normal turbulent stress method proposed by Sessa et al. (J Wind Eng Ind Aerodyn 182:189–291, 2018). This shows that the depth and growth rate of the IBL are sensitive to the thermal stability and the turbulence kinetic energy (TKE) prescribed at the inlet, such that the IBL depth reduces as the TKE of the inflow is reduced while maintaining the same Ri , or as the Ri is increased while maintaining the same inflow TKE. When a ground level line source is introduced it is found that increasing Ri evidently reduces the vertical scalar fluxes at the canopy height, while increasing the mean concentrations within the streets. Furthermore, as with IBL development it is found that for a given value of Ri the effect of stratification becomes more pronounced as the inflow level of TKE is reduced, affecting scalar fluxes within and above the canopy, and volume-averaged mean concentrations within the streets.
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