The Complexity of Nonlinear Flow and non‐Fickian Transport in Fractures Driven by Three‐Dimensional Recirculation Zones
Lichun Wang, M. Bayani Cardenas, Jiaqing Zhou, Richard A. Ketcham
Abstract
Abstract Although nonlinear fracture flow and non‐Fickian transport are common in natural settings, the mechanisms driving and controlling these intertwined phenomena are seldom scrutinized together. Here we investigated the critical role of recirculation zones (RZs) in controlling both nonlinear flow and non‐Fickian transport through numerical simulation experiments within three‐dimensional real fractures. RZs were quantitatively mapped from fully resolved flow fields directly simulated across increasing Reynolds number ( Re ). The development and growth of RZs, which are related to aperture expansion and contraction, determine the degree of flow nonlinearity. Moreover, expanding RZs have more capacity to capture and later release solutes back to the main flow. This always results in non‐Fickian transport with bimodal and sometimes multimodal breakthrough curves (BTCs). The time interval between the BTC modes is related via a power law. The Re and RZ volume are sufficient for characterizing the bimodal BTC.