Variable-throat spiral duct system for rotary stream-flow machines

A variable-throat spiral duct system for a stream-flow machine in which shaft motion is coupled to flow of a gas or liquid, comprising:

• a machine having an axial shaft and a rotor carrying thereon means for engaging a flow medium;
• at least one spiral duct leading spirally inwards to said rotor and having a radially outer wall and also a radially inner wall of less circumferential length than said radially outer wall;
• a tongue-bearing insert member (11) rotatably and coaxially mounted in the structure of said machine and formed as part of a tubular pipe forming part of the flow path of said medium on the axially and functionally opposite side of said machine from said spiral duct system;
• at least one tongue affixed to said insert member and thereby mounted slidably and snugly adjacent to the extremity of said inner wall and having a free end portion of spiral curvature and another portion having a surface of circular curvature, said inner wall extremity having a matching inwardfacing surface portion of circular curvature, and being tapered towards its circumferential extremity in the vicinity of said tongue, such a tongue (7,8) being provided for the inner wall (5,6) extremity of each said spiral duct (1,2), and
• means for so shifting each said tongue, by moving said tongue-bearing member, as to provide a variable extension of said inner wall(s) and thereby to reduce the throat cross-section of the duct between the tongue and said radially outer wall of the duct.