An experimental study was performed for the airflow between a pair of coaxial disks corotating in an axisymmetric enclosure with and without an obstruction in the form of a rigid flat rectangular bluff body (arm). Long-term averages of the pressure coefficient across the arm and of the circumferential velocity component in the space between the disks were obtained as a function of position and disk angular velocity in a system of fixed dimensions. The unobstructed configuration exhibits an inner flow region approaching solid body rotation and an outer strongly sheard region with high turbulence levels. For this case, the assumption of steady axisymmetric flow allowed numerical calculations to be perfomed using the procedures of Chang et. al. (1989). The calculations yield mean velocity distributions in good agreement with the unobstructed flow measurements but fail to reproduce some features of the velocity fluctuations that are believed to be due to circumferentially periodic mean flow structures. The measurements show that the presence of an arm has a profound effect on the flow. © 1991.