Rotordynamic forces due to turbine tip leakage - Part I: Blade scale effects

Abstract

An experimental and theoretical investigation has been conducted on rotordynamic forces due to non-axisymmetric turbine tip leakage effects. This paper presents an actuator disc model which describes the flow response to a finite clearance at the rotor tip. The model simplifies the flow field by assuming that the radially uniform flow splits into two streams as it goes through the rotor. The stream associated with the tip clearance, or the undertumed stream, induces radially uniform unloading of the rest of the flow, called the bladed stream. Thus, a shear layer forms between the two streams. The fraction of each stream and the strength of shear layer between the two are found as functions of the turbine loading and flow parameters without resorting to empirical correlations. The results show that this model's efficiency predictions compare favorably with the experimental data and predictions from various correlations. A companion paper builds on this analysis to yield a model of the 3-D disturbances wound an offset turbine and to predict the subsequent cross forces.