Secondary flow in cascades with leaned and swept blades - a literature study

One goal in designing fluid machinery is to maximise the efficiency. The ro tor and the stator of such machines are comprised of rotating and stationar y cascades. In addition to the main flow a secondary flow develops which de pends on the operation point. The efficiency of the cascade is affected by this flow The secondary flow, including the gap flow, can reach up to 20-40 % of the total hydraulic losses in modern axial flow turbines. A reduction of these losses can remarkably affect the efficiency. In order to achieve t his an exact understanding of the formation and the development of the seco ndary flow is required. If the designer properly understands the secondary flows, the interaction between them and the parameters which influence the secondary flows, it: is possible to design cascades with reduced secondary losses by using proper design criteria. Shape and extend of the secondary f low mainly depend on flow parameters and geometric parameters. Flow paramet ers are, for example, the incidence angle, the boundary layer thickness and the turbulence. Geometric parameters are for example the distribution of t he blade load, shape and radius of the leading edge, the aspect ratio, boun dary layer fences, dihedral and sweep of the blade. The latter two geometri c criteria can be regarded efficient means to model the pressure on the end walls and, therefore, the development of the secondary flow.