AbstractWe perform three‐dimensional, time‐dependent simulations of dense, fluidized suspensions of solid cylindrical particles in a Newtonian liquid in fully periodic domains. The resolution of the flow field is an order of magnitude finer than the diameter of the cylindrical particles. At their surfaces no‐slip conditions are applied through an immersed boundary method (IBM), coupled to the lattice‐Boltzmann method that is used as the fluid flow solver. The marker points of the IBM are also used to detect and perform collisions between the cylinders. With these particle‐resolved simulations, we study the effects of the aspect ratio of the cylinders and the solids volume fraction on the superficial slip velocity between fluid and solids, on the solids velocity fluctuations, as well as on the orientation of the cylinders. The aspect ratio (length over diameter of the cylinders) ranges from 0.5 to 4, the solids volume fraction goes up to 0.48. Reynolds numbers based on average settling velocity are of the order of 1–10. At constant Archimedes number, we observe only minor sensitivities of the settling Reynolds number on the aspect ratio.