Macro-scale effects over filtered and residual stresses in gas-solid riser flows

Sub-grid models for filtered and residual stresses are required as closures in filtered two-fluid modeling of gas-solid fluidized flows. An approach for deriving such models consists of filtering over results from highly resolved simulations with microscopic two-fluid modeling, which are mostly performed under suspension like conditions as separation of scales is assumed. This means that no macro-scale effects are accounted for. In this work effects of flow macro-scale are evaluated by practicing conditions from suspensions up to pneumatic transport, under solid concentrations typical of risers, applying highly resolved simulations with microscopic two-fluid modeling in periodic domains. Results show that the domain average gas Reynolds number and the domain average solid volume fraction both considerably affect filtered and residual stresses of both phases. It becomes evident that accurate sub-grid models require macro-scale effects to be accounted for. (C) 2018 Elsevier Ltd. All rights reserved.