Vane assembly for an axial flow turbine

摘要

A vane assembly (21) for an axial flow turbine engine provides a plurality of nozzles (22) arranged symmetrically around a turbine axis formed by an inner hub (26), an outer casing (27) and vanes (23) intermediate pairs of adjacent nozzles. The nozzles have a cross-section normal to the turbine axis that changes smoothly with the position of the cross-section along the turbine axis from a first shape having a minimum radius of curvature of a first value that is no less than a limit L, providing the cross-section with no highly curved corners, to a second shape having a minimum radius of curvature of a second value less than the first value, providing corners. This allows the secondary flow structure to be designed to improve aerodynamic loss and cooling performance.

主权项

1. A vane assembly for an axial flow turbine, the vane assembly providing a plurality of nozzles arranged symmetrically around a turbine axis formed by an inner hub, an outer casing and vanes intermediate pairs of adjacent nozzles, the vanes providing a suction surface of one of the pair of adjacent nozzles and a pressure surface of the other of the pair of adjacent nozzles,
at least some of the nozzles having a cross-section normal to the turbine axis that changes smoothly with the position of the cross-section along the turbine axis from a first shape at an upstream end of the nozzle, the first shape having a minimum radius of curvature of a first value that is no less than a limit L, to a second shape at a downstream end of the nozzle, the second shape having a minimum radius of curvature of a second value less than the first value, where defining a reference plane normal to the turbine axis, which reference plane contains a circle that is centred on the turbine axis and touches the trailing edge of a vane at the most upstream position possible along the turbine axis in the direction of axial flow, defining a reference radius from the turbine axis that is the average of (a) the minimum radius from the turbine axis of the nozzle at the inner hub in the reference plane and (b) the maximum radius from the turbine axis of the nozzle at the outer casing in the reference plane, defining a reference cross-section of a nozzle normal to the turbine axis at a position along the turbine axis where an axial line parallel to the turbine axis at the reference radius from the turbine axis is tangential to the suction surface of a vane, defining a characteristic length a as half the difference between (c) the minimum radius from the turbine axis of the nozzle at the inner hub in the reference cross-section and (d) the maximum radius from the turbine axis of the nozzle at the outer casing in the reference cross-section, and defining a characteristic length b as the area of the reference cross-section divided by the product (π.a), the limit L is defined as k.min(a,b), where k is a constant of at least ⅓.