Flow and transport at an interface between a turbulent flow and a porous medium

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This proposal deals with the exchange processes at a porous media/turbulent flow interface. We concentrate on the flow and mass transfer in the hyporheic zone in which streamborne surface waters and subsurface waters mix. This zone has a significant contribution to the ecological functioning of surface waters. We intend to perform Direct Numerical Simulations of the turbulent flow over a porous bed consisting of randomly packed spheres at various Reynolds numbers. In these simulations the pore space will be resolved. We cover the range from smooth to fully rough turbulent regimes. The simulations shall be validated with the help of recently published data from an experiment using state-of-the art experimental techniques thus providing detailed measurements of turbulent flow quantities. We extend the range of Reynolds numbers available from the experiment and perform additional simulations of the mass transfer over the interface. This will enable us to provide detailed information of turbulent momentum and mass transport by adopting a double-averaged approach. The latter will be used to distinguish between transport due to the time-averaged flow in the upper-most (Brinkman) layer and transport due to turbulent fluctuations. We hope that these simulations will provide essential information helpful for modelling mass and momentum transfer in the hyporheic zone that is applicable to other interfaces between porous media and turbulent flows.