Lattice Boltzmann simulation of power-law fluid flow past fixed and counter-rotating tandem cylinders

Flow past tandem cylinders in non-Newtonian fluids represent a fundamental problem with significant engineering implications. In this study, we employ the multiple-relaxation-time lattice Boltzmann method with a single-node second-order curved boundary scheme to investigate power-law fluid flow past fixed and rotating tandem cylinders. The investigation covers power-law indices from 0.6 to 1.6 and spacing ratios from 1.2 to 8.0, focusing on the drag inversion phenomenon, force characteristics, and wake interference patterns. Our results reveal that fluid rheology significantly influences the critical spacing ratio for drag inversion, with shear-thickening fluids requiring smaller spacing ratios compared to shear-thinning fluids. For counter-rotating cylinders, we identify a novel rheology-dependent negative Magnus effect, where the lift force direction on the upstream cylinder can reverse depending on both spacing ratio and power-law index. The wake patterns demonstrate four distinct stages with increasing rotation rate, though highly shear-thickening fluids show delayed transitions between these stages. These findings provide valuable insights into the role of non-Newtonian effects in modifying wake interactions and force characteristics in multi-body flows.