Flow in regenerative compressors with aerofoil blading
Regenerative compressors are low specific speed, tangential flow turbomachines in which the working fluid follows an approximately toroidal-helical path around the machine. Although regenerative turbomachines have been in use for over fifty years, the use of aerofoil blades (as opposed to the more usual straight vanes) is a relatively new innovation designed to improve the internal flow. However, little work has been done on the details of this flow. This dissertation concentrates on the flow in the main region of the compressor, away from the inlet and exit ports. A simple, analytical model of the flow is developed; and it is shown that, under certain conditions, a similar flow pattern can be set up in a stationary model. Measurements of the flow in a machine are reported and a comparison is made with results from such a stationary model. It is concluded that, although discrepancies may arise from wall friction, Coriolis and centrifugal effects, or the variation in density, the stationary model is nevertheless capable of providing useful information about the loss-producing mechanisms in the flow. The results of more detailed measurements on stationary models of two different designs are presented, on the basis of which suggestions are made for an improved design of machine. The analysis is extended to include Coriolis and centrifugal effects, and the influence which the position of the blades relative to the machine axis has on the performance of the machine is examined. The presence of a uniform component of vorticity normal to the blade-to-blade plane is a characteristic feature of regenerative turbomachines. Some effects of this are discussed, and a computer program written to calculate the two-dimensional, inviscid, incompressible flow through a cascade with such a uniform spanwise vorticity is described.