Abstract
Exchange processes between a turbulent free flow and a porous media flow are sensitive to the flow dynamics in both flow regimes, as well as to the interface that separates them. Resolving these complex exchange processes across irregular interfaces is key in understanding many natural and engineered systems. With soil–water evaporation as the natural application of interest, the coupled behavior and exchange between flow regimes are investigated numerically, considering a turbulent free flow as well as interfacial forms and obstacles. Interfacial forms and obstacles will alter the flow conditions at the interface, creating flow structures that either enhance or reduce exchange rates based on their velocity conditions and their mixing with the main flow. To evaluate how these interfacial forms change the exchange rates, interfacial conditions are isolated and investigated numerically. First, different flow speeds are compared for a flat surface. Second, a porous obstacle of varied height is introduced at the interface, and the effects the flow structures that develop have on the interface are analyzed. The flow parameters of this obstacle are then varied and the interfacial exchange rates investigated. Next, to evaluate the interaction of flow structures between obstacles, a second obstacle is introduced, separated by a varied distance. Finally, the shape of these obstacles is modified to create different wave forms. Each of these interfacial forms and obstacles is shown to create different flow structures adjacent to the surface which alter the mass, momentum, and energy conditions at the interface. These changes will enhance the exchange rate in locations where higher velocity gradients and more mixing with the main flow develop, but will reduce the exchange rate in locations where low velocity gradients and limited mixing with the main flow occur.
Highlights
Throughout our natural and engineered surroundings, fluids flow in a multitude of different fashions, transporting mass, momentum, and energy to form the dynamic environment we know
A review: The flow dynamics in a free-flow domain play a large role in the exchange pro‐ cesses across the soil–atmosphere interface
Interfaces that include non-flat geometries, such as obstacles or interfacial forms, create flow structures adjacent to the domain inter‐ face that alter the transport of mass and energy in the free flow
Summary
Throughout our natural and engineered surroundings, fluids flow in a multitude of different fashions, transporting mass, momentum, and energy to form the dynamic environment we know. Impermeable surfaces reduce evaporation rates, where heat and air pollution can stagnate due to disturbed flow paths This causes the urban heat island (UHI) effect, where cities see larger increases in temperature than rural areas, reducing livability and adding economic strain (Allegrini et al 2015). Further applications, such as the salinization of agricultural land (Jambhekar et al 2015), flow through oil filters (Iliev and Laptev 2004), rocket cooling (Dahmen et al 2014), and nuclear waste storage (Masson et al 2016), all require an understanding of the coupled behaviors between porous media flow and free-flow domains. We perform a numerical investigation of the non-flat interface between a porous media flow and a free-flow domain, focusing on the exchange processes between a partially saturated bare soil and an atmospheric turbulent flow
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