Boundary Layer and Formation of Peripheral Nonuniformity in a Turbine Scroll

A detailed experimental investigation was carried out to examine the three-dimensional boundary layer characteristics in a radial inflow turbine scroll. Some basic flow phenomena and growth of secondary flow were also investigated. In the inlet region of the scroll, the incoming boundary layer begins to assume a skewed nature, namely the radially inward secondary flow caused by the radial pressure gradient. From the inlet region to one-third of the scroll circumference, the secondary flow increases largely that most of the low-momentum fluid in the incoming boundary layer is transported to the nozzle region. The succeeding elimination of the low-momentum fluid in the boundary layer suppresses growth of the boundary layer further downstream, where the boundary layer shows a self-similar velocity profile. The distributions of the boundary layer properties in the scroll correspond well to those of the flow properties at the nozzle. The behavior of the boundary layer in the scroll is found to affect the circumferential nonuniformity of the nozzle flow field.