Automated axial flow turbine design with performance prediction

Abstract

This paper describes the automation of preliminary 3D aerothermodynamic design and analysis of a single-stage axial flow turbine driving the compressor of the micro turbojet engine Jet Cat p200 using an analytical method. The geometrical parameters of the new design are based on the reverse engineering of the small gas turbine. Baseline stage dimensions and design parameters such as flow coefficient, stage loading factor are close to 0.5 and 1.14, respectively, with maximum expansion in the NGV (stator) row. In the thermal cycle and 1D analysis calculations, the turbine flow path and the meanline total conditions of all engine stations and all design controlling parameters are determined on the basis of mass, energy and momentum conservation. The results are compared with the published data in the engine manual and gave a good match. The axially symmetric assumption changes the 3D flow problem through the turbine stage into 2D problem, i.e. the flow through the profile cascade. Applying the simple radial equilibrium approach at the axial gapes with selecting the free vortex law of blading, the velocity triangles at different radii along the blade length are determined. The generated velocity triangles are used to design the profile cascades considering parabolic mean, convex and concave sides. The turbine stage performance is calculated at design point and off-design conditions based on the one-dimensional analytical approach with constant total pressure loss coefficient across the stator and constant relative velocity recovery factor across the rotor. A CFD model is constructed to evaluate the turbine stage performance numerically. The CFD results are compared with that of the analytical method which give a good match.