This study introduced a four-way CFD-DEM coupling approach to simulate the shear-induced particle migration (SIPM) mechanism leading to formation of the lubrication layer (LL) during concrete pumping. The CFD-DEM simulations considered the coupled effect of concentration (10 %–40 %) and wide size distribution (1–17 mm) of aggregate and rheology of the mortar for forces between the suspending matrix and the particles (and vice versa), as well as force transmission directly between particles (and the pipe wall). The formation of the LL was successfully simulated through a more realistic understanding the SIPM mechanism and rheological evaluation across the pipe with comparable calculation times compared to the one-way coupled DEM approach, especially for high concentrations. The simulated LL thicknesses of 0.8–2.7 mm compared well with experimental values. The flow rate and rheological heterogeneity of pumped concrete, and rheology of the LL, were found mostly controlled by the granular-skeleton characteristics rather than the suspending-matrix rheology.

中文翻译：

---

四向CFD-DEM耦合模拟混凝土管流：润滑层形成机理

本研究引入了四向 CFD-DEM 耦合方法来模拟剪切诱导颗粒迁移 (SIPM) 机制，从而导致混凝土泵送期间形成润滑层 (LL)。 CFD-DEM 模拟考虑了骨料浓度 (10%–40%) 和宽尺寸分布 (1–17 mm) 以及砂浆流变学对悬浮基质和颗粒之间力的耦合效应（反之亦然），以及直接在颗粒（和管壁）之间传递力。与单向耦合 DEM 方法相比，通过更真实地理解 SIPM 机制和整个管道的流变评估，成功模拟了 LL 的形成，尤其是对于高浓度。模拟的 LL 厚度为 0.8-2.7 mm，与实验值吻合良好。研究发现，泵送混凝土的流量和流变不均匀性以及 LL 的流变性主要受颗粒骨架特性而非悬浮基质流变性的控制。