Method of designing guide vane formations

Abstract

A computer-based method of designing a guide vane formation is provided. The vane formation is for use in a gas turbine engine which has a cascade of circumferentially arranged identical guide vane formations. The vane formation has radially inner and radially outer chordal seals. The method allows the elimination of “saw-tooth” leakage gaps between inner chordal seals of neighbouring vane formations and between outer chordal seals of neighbouring vane formations even when the inner and outer chordal seals are axially offset from each other.

1 . A guide vane formation for use in a gas turbine engine as one of a cascade of n circumferentially arranged identical guide vane formations, the guide vane formation comprising:
 radially inner and outer platforms that each define an azimuthal portion of a gas annulus of the engine with respect to a center line of the engine, the radially inner and outer platforms each having a respective gas-washed surface, the gas-washed surfaces of the radially inner and outer platforms having a common wedge angle, and   one or more aerofoil bodies that each span between the radially inner and outer platforms,   wherein:
 the radially inner and outer platforms each have an inner and an outer chordal seal respectively that are mutually parallel and are mutually offset in a direction corresponding to the center line of the engine, and 
 each chordal seal extends along a respective straight line that intersects first and second planes containing side faces of the radially inner and outer platforms on suction and pressure sides respectively of the aerofoil bodies and each chordal seal lies in a respective plane that is substantially normal to the center line of the engine such that:
 points of intersection of the straight line with the first and second planes are substantially equidistant from the center line of the engine in the respective plane of each chordal seal, and 
 the first and second planes are (i) mutually inclined at an angle of substantially 360°/n, (ii) each substantially tangent to a surface of a cone having its axis coincident with the center line of the engine, its apex lying on another straight line that joins midpoints of the straight lines along which the chordal seals extend and having a semi-vertical angle equal to the wedge angle of the gas-washed surfaces of the radially inner and outer platforms, and (iii) each perpendicular to another respective plane containing the center line of the engine. 
 
   
     
     
         2 . The guide vane formation according to  claim 1 , wherein the guide vane formation is a high-pressure turbine nozzle guide vane formation. 
     
     
         3 . A nozzle guide vane system comprising a cascade of n circumferentially arranged identical guide vane formations each being a guide vane formation according to  claim 1 . 
     
     
         4 . A gas turbine engine comprising a guide vane formation according to  claim 1 .