In regenerative pumps or compressors of known form, fluid to be pressurised or compressed passes through an inlet port either axially or obliquely into an annular housing or shroud which surrounds a bladed rotor. Within the shroud there is also contained an annular core which is supported in such a way as to be spaced from the rotor blades and from the walls of the shroud. The blading is so designed that air (or other working fluid) is drawn into and passes around the annular shroud with a spiral motion around the core in the general direction of rotor rotation. In circulating around the core, the fluid makes repeated passes through the blading in a generally axial sense, and at each pass the pressure of the fluid is thereby increased. A fluid outlet port is provided just before the inlet port, by which the pressurised fluid can leave the shroud. Between the inlet and outlet ports there is provided a stripper which blocks passage of gas around the shroud, and conforms closely to the blade tips so as to minimise leakage of pressurised fluid, which has completed a circuit of the shroud, to the inlet port.
The conventional regenerative compressor is capable of generating a pressure ratio of the order of 2:1 but only at a low isothermal efficiency of the order of 25-35%, depending upon flowrate and design of machine. An isothermal efficiency approaching 60% is attainable, but only at a low pressure ratio, perhaps of the order of 1.2:1.
The conventional regenerative compressor is thus not a very efficient machine, and a great deal of the inefficiency is attributable to losses in the region of the stripper, in particular to
(i) leakage past the stripper which sustains the full pressure difference between inlet and outlet ports, and
(ii) carry-over in the blade pockets of fluid at outlet pressure back to the inlet.
Very high solidity designs have been produced with the object of reducing carry-over, but this has led to high viscous losses, and hence little or no net gain in efficiency. Similar considerations apply to conventional regenerative pumps.
The present invention aims to provide a regenerative turbomachine in which the need for a stripper is avoided, and hence the losses associated therewith can also be avoided.