The large eddy simulation (LES) module of the Virtual StreamLab (VSL3D) model is applied to simulate the flow and transport of a conservative tracer in a headwater stream in Minnesota, located in the south Twin Cities metropolitan area. The detailed geometry of the stream reach, which is ∼135 m long, ∼2.5 m wide, and ∼0.15 m deep, was surveyed and used as input to the computational model. The detailed geometry and location of large woody debris and bed roughness elements up to ∼0.1 m in size were also surveyed and incorporated in the numerical simulation using the Curvilinear Immersed Boundary approach employed in VSL3D. The resolution of the simulation, which employs up to a total of 25 million grid nodes to discretize the flow domain, is sufficiently fine to directly account for the effect of large woody debris and small cobbles (on the streambed) on the flow patterns and transport processes of conservative solutes. Two tracer injection conditions, a pulse and a plateau release, and two cross sections of measured velocity were used to validate the LES results. The computed results are shown to be in good agreement with the field measurements and tracer concentration time series. To our knowledge, the present study is the first attempt to simulate via high-resolution LES solute transport in a natural stream environment taking into account a range of roughness length scales spanning an order of magnitude: From small cobbles on the streambed (∼0.1 m in diameter) to large woody debris up to ∼3 m long.
Bibliographical noteFunding Information:
This work was supported by National Center for Earth-surface Dynamics (NCED), the NSF Science and Technology Center that operated from 2002 to 2012, and NSF PIF-BIC grant 1318201. Computational resources were provided by the University of Minnesota Supercomputing Institute. We thank Jovanny Velez and Guelord Mpagazihe for their extensive efforts to survey Eagle Creek and for their assistance with the tracer experiments. We thank Chip Small, Nolan Kleinjan, and Adam Eldeeb for helping to collect data during the tracer experiments. We also greatly appreciate Rob Runkel and Oliver Fringer and the anonymous reviewer for their contributions to improve the quality of this paper. For additional information regarding the data generated from these simulations, the reader can contact Fotis Sotiropoulos via e-mail: firstname.lastname@example.org. The VSL3D model is part of the Virtual Flow Simulator (VFS) suite of computational fluid dynamics solvers developed by the group of Fotis Sotiropoulos. The code is available as open source and can be downloaded, along with supporting documentation, from https://github.com/SAFL-CFD-Lab/ VFS-Rivers.
- forested stream
- large eddy simulation
- solute transport