Three-Dimensional Turbine Rotor Forcing Functions and Linear Theory Analysis

Abstract

Many turbomachine e owe elds are inherently three dimensional. Often, however, the data and methods used to analyze the unsteady aerodynamic forcing functions generated by these blade rows are two dimensional. This paper is directed at developing a three-dimensional compressible e ow forcing-function modeling technique to split forcing-function data into vortical and potential components. This is accomplished by extending current state-of-the-art two-dimensional methods to three dimensions in cylindrical coordinates. Three-dimensional unsteady forcing-function data, both unsteady pressure and velocity, generated by the e rst rotor of a low-speed, two-stage research turbine are used in the model development. Both the three-dimensional model developed herein and a two-dimensional model are then applied to the turbine rotor data. For the potential perturbation velocity, the three-dimensional method agrees well with the two-dimensional strip theory method in terms of both velocities and axial decay factors. For the vortical perturbation velocity, the correlations were inconsistent with the two-dimensional theory in that the vortical proportionality constant was not constant and the phasing of the velocity components was not zero.