Large-Eddy Simulations of Air Flow and Turbulence within and around Low-Aspect-Ratio Cylindrical Open-Top Chambers

The flow around cylindrical open-top chambers (OTCs) with aspect ratios (i.e., height-to-diameter ratios) much less than unity is investigated using a large-eddy simulation (LES) model. The solid structures are represented using the immersed boundary method, and the ambient flow in which the OTCs are embedded is representative of a turbulent atmospheric boundary layer. Results from the LES model show that the flow inside OTCs depends strongly on the height of the chamber wall. In particular, as chamber height increases the flow impinging on the upstream wall is deflected more in the vertical direction, a stronger recirculation flow develops inside the chamber, turbulence intensities are greater, and there is stronger vertical transport and mixing within the OTC, even at or near the ground. For low wall heights (i.e., very low aspect ratios), however, the flow impinging on the OTC is only diverted weakly in the vertical direction; aside from a small recirculation zone inside the OTC near the upstream wall and a small region near the downstream wall as the flow separates from the ground, there is minimal vertical mixing and the turbulence intensities are small. The results of these simulations, while general in nature, are particularly relevant to design considerations for manipulative field experiments in highly heterogeneous, low-stature ecosystems such as Arctic shrubs and grasses.