Veröffentlichungen und Präsentationen

Soil pipes are large contiguous macropores that exist in soils or geological materials. These macropore features generally serve as conduits for rapid movement of water through soils or geological material, and are generally oriented nearly parallel to the land surface. Soil pipes are important with regard to the genesis of the landscape, leading to formation of gullies or sink holes, and also significantly increase the generation of rapid runoff in response to rainstorm events. They can also lead to dangerous natural hazards such as landslides, or to failures of human infrastructure including levees, dams, or structural surfaces. Soil pipes generally show evidence of erosion by the flow of water flow along pipe walls. The erosion process can lead to pipe enlargement and eventually to collapse of the material overlying the cavity formed by the pipe. Modeling the process of flow in soil pipes, and the erosion of the pipe walls and transport of sediment by the flowing water is complex. In this paper we present a model of pipe flow and pipe wall erosion based on the CFD Module of COMSOL Multiphysics^® simulation software. Various turbulent flow models are available within this module. In our application we use the k-ω approach. The erosion of the pipe walls is modelled using an equation referred to as the excess shear equation, and the transport of the eroded sediment is modelled using the Transport of Diluted Species physics interface. In our application the soil pipe is assumed to be straight and has uniform diameter. A finite element mesh was produced using triangular prisms for the central part of the pipe flow, and hexagonal elements for the boundary layer part of the flow. The Wall boundary condition was treated using the Automatic Wall Treatment option. Model simulations of pipe discharge were compared to calculations from the Darcy-Weisbach pipe hydraulics equation, and the turbulence model parameters in the COMSOL Multiphysics^® solution were adjusted to provide reasonable agreement. In our presentation we show the application of the coupled Turbulent Flow (k-ω) and Transport of Diluted Species interfaces for simulating the enlargement of a soil pipe resulting from erosion of the pipe walls, and compare the modeling results to experimental measurements conducted on a laboratory model of a soil pipe. The parameters for the excess shear equation were calibrated to yield reasonably agreeable comparisons.