This investigation is aimed at studying the flow and velocity characteristics in an annular diffuser fitted with square twisted hub for different geometries. The study was numerically performed. The formulation was based on the steady-state Reynolds averaged Navier–Stokes equations with two-equation turbulence models. In this study, the effect of different twisted hub geometries was studied using three area ratios (AR) 2.4, 2.8 and 3.7 with air as the working fluid. The analysis of the flow features in an annular diffuser fitted with twisted hub showed that the insertion of twisted hub distributed the velocity as well as promoted the radial spread of the tangential velocity. The results show the development of the velocity distribution improved with the insertion of the square twisted hub. More importantly, the obtained results illustrate the velocity distribution through the annular diffuser increases with decreases the area ratio (AR). In addition, the results indicate that the square twisted hub with area ratio (AR) 2.4 offered a higher velocity distribution.