Patent ID: 7794196

Claim:
Apparatus combining a water turbine and a guide-case, wherein: the turbine is an axial-flow propeller-type turbine; the turbine includes a rotor having a set of turbine blades, the blades having an inner diameter and an outer diameter; the guide-case includes an annular chamber, having an inlet port fed with water from a headrace; the annular chamber has an annular cross-section, having inner and outer tubes, for the conveyance of water therebetween, into the turbine; the inner and outer tubes of the annular chamber correspond to the inner and outer diameters of the turbine blades; the inlet port has an outside wall, an inside wall, a near end wall, and a far end wall; the inside wall of the inlet port merges into the inner tube of the annular chamber; the outside wall of the inlet port merges into the outer tube of the annular chamber; the annular chamber has a far wall, which is helical in configuration; the helical far wall spans radially between the inner and outer tubes of the annular chamber, and thereby closes off a far end of the annular chamber; the far end wall of the inlet port merges into the helical far wall of the annular chamber; the inner wall of the inlet port intersects the far wall of the annular chamber, along a line of intersection termed the inner-wall/far-wall intersection; the said inner-wall/far-wall intersection extends between the outer tube and the inner tube of the annular chamber; the guide-case includes an extension to the helical far wall; the extension extends beyond the said inner-wall/far-wall intersection in the downstream direction, helically towards the turbine; and the extension has a near side and a far side, and is arranged such that the extension is wetted on its far side by water entering the annular chamber from the near end of the inlet port, termed the near water, and is wetted on its near side by water entering from the far end of the inlet port, termed the far water.