Imbibition dynamics in a rectangular U-groove that is connected to a sudden enlargement and complicated by the presence of Concus-Finn (CF) filaments is investigated using many-body dissipative particle dynamics. For open-ended sudden enlargement, four flow types are identified and depend on the contact angle θy, the critical angle θf associated with the occurrence of CF filaments, and the critical angle θc associated with the occurrence of main flow. First, for θy > θf and θy > θc, the corner flow is absent, and the main flow stops at the end of the small U-groove. Second, for θc > θy > θf, the corner flow vanishes, but the main flow occurs. Third, for θf > θy > θc, the corner flow takes place in the large U-groove, but the main flow is still absent. Fourth, for θy < θf and θy < θc, both the corner and main flows appear in the large U-groove. Additionally, the flow dynamics is greatly influenced by the length of the large U-groove (le). For closed-ended sudden enlargement, similar findings can be obtained. However, the outcome of the third case is altered for sufficiently small le, and the sudden enlargement can eventually be filled.