The Preliminary Analysis of Axial Turbines by a Simplified Throughflow Procedure

A new iterative scheme for calculating the axisymmetric flow through a turbine, which converges to a given value of turbine exit pressure, is described. It is intended to be used at a preliminary stage in a turbine design procedure instead of a one-dimensional calculation, since it enables spanwise variations of turbine performance to be calculated with reasonable accuracy and with minimum data preparation in approximately 1/30 of the computer time of a conventional axisymmetric calculation. The method solves the full axisymmetric flow equations on three streamlines through the machine at hub, midspan, and tip, although an approximation is introduced regarding the curvature of the centre streamline. Agreement with a full streamline curvature analysis is shown to be good, and comparisons with a one-dimensional Ainley-Mathieson based performance calculation show how the method is sensitive to root and tip behaviour.