A control algorithm for statistically stationary large‐eddy simulations of thermally stratified boundary layers
A control algorithm for statistically stationary large‐eddy simulations of thermally stratified boundary layers
复制标题
热分层边界层实验稳态大涡模拟的控制算法
DOI：
10.1002/qj.2266
复制
发表时间：
2014
影响因子：
8.9
通讯作者：
C. Meneveau
中科院分区：
文献类型：
--
作者：
A. Sescu;C. Meneveau
热分层大气边界层（ABL）的大涡模拟（LES）通常涉及在地面施加加热或冷却，导致域内温度分布缓慢变化。虽然对于某些应用，将结果场解释为准稳态是可能的，但对于某些应用，缓慢的时间变化是一个严重的缺点。一个例子发生时，使用大涡模拟系统分析大型风电场对大气热通量的影响，静态统计分析大大有助于理解。为了在热分层边界层大涡模拟中获得统计上稳定的温度场，本文介绍了一种控制算法，并测试了它对不同水平的表面加热和冷却的有效性。该方法使用“比例积分”（PI）控制算法，旨在保持位于ABL感兴趣区域上方的计算边缘层中的水平平均温度恒定。对于由地转风驱动的流动，使用另一个控制器来调整ABL内指定高度处的平均流动角度，以实现规定的方向。这是通过控制动量方程中的源项（以附加科里奥利力的形式）来实现的。一旦统计数据变得稳定并且流与期望的方向对齐，则该项被停用。这两种控制方案共同实现了对热分层加热或冷却边界层的长时间模拟，显示出完全稳定的平均速度和温度分布。
Large‐eddy simulations (LESs) of thermally stratified atmospheric boundary layers (ABLs) typically involve imposed heating or cooling at the ground surface, leading to slowly varying temperature distributions in the domain. While for some applications an interpretation of the resulting fields as quasi‐stationary is possible, there are certain applications for which the slow temporal variations are a serious drawback. An example occurs when using LES for a systematic analysis of effects of large wind farms on atmospheric heat fluxes, where analysis of stationary statistics greatly facilitates understanding. In order to obtain statistically stationary temperature fields in LES of thermally stratified boundary layers, in this article we introduce a control algorithm, and test its effectiveness for various levels of surface heating and cooling. The method uses a ‘proportional‐integral’ (PI) control algorithm, designed to keep constant the horizontally averaged temperature in a computational fringe layer placed above the ABL region of interest. For flows driven by a geostrophic wind, another controller is used to adjust the mean flow angle within the ABL at a specified height to achieve a prescribed direction. This is done by controlling a source term (in the form of an additional Coriolis force) in the momentum equations. This term is deactivated once the statistics become stationary and the flow aligns with the desired direction. Together, these two control schemes enable very long‐time simulations of thermally stratified heated or cooled boundary layers displaying fully stationary distributions of mean velocity and temperature.