Curved diffusers are used in pipe lines or in some fluid machineries, such as blades of impeller, a volute casing, or suction duct. The performance of the curved diffuser has a considerable effect on the energy conversion in the pipe lines or the machineries. Furthermore, the volute casing in the pumps or blowers is generally attached to the radial diffuser, so that the flow in the volute or scroll casing has usually very high complexities. The flow in the volute casing will be moderated by the combination of the single curved diffuser and the longitudinal side wall slit duct. However, the studies to the flow in the curved diffuser with the longitudinal slit, were merely conducted in the past ages.
In this report, as a step of the study of the flow in the volute casing, experiments of flow in a two-dimensional curved diffuser, which has a small diverging angle and 90° turning angle, were carried out. The time average velocities and velocity fluctuations were measured using a constant temperature hot-wire or split film probe system. It is shown that the flow in the curved diffuser has velocity profiles with gradually variant gradients and attached to the outer side wall, and the profiles of velocity fluctuations have very interesting patterns concernig to the stall and the secondary flow
