We present a numerical study of mixing and reaction efficiency in closed domains. In particular we focus our attention on laminar flows. In the case of inert transport the mixing properties of the flows strongly depend on the details of the Lagrangian transport. We also study the reaction efficiency. Starting with a little spot of product we compute the time needed to complete the reaction in the container. We found that the reaction efficiency is not strictly related to the mixing properties of the flow. In particular, reaction acts as a "dynamical regulator".
[1] Rivers experience a wide range of discharges. It is nowadays acknowledged that is not realistic to assume that the morphology of a river is influenced by only a single formative discharge. Rather, it is the full range of flows that are able to move sediments and erode banks that affect the fluvial morphology. Thus, the channel morphology emerges from the interactions between different competent discharges. A goal that has still not been completely achieved in geomorphology is the understanding of the role of discharge variability on river morphological processes. In this paper, we present the results of an experimental investigation concerning the impact of the sequencing of two competent discharges on a self-forming pseudomeandering pattern. The inception of the pattern, the bar dynamics, and the bend erosion are investigated. A comparison of the experiments performed with steady and unsteady discharges has indicated the key role of the discharge variability in promoting and sustaining the pseudomeandering channel. These experimental findings shed light on some important morphological processes (bar deformation, low-flow channel incision, and triggering of the bend inception) that are affected by discharge variations to a great extent, in agreement with some field studies and conceptual models.
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