Improved Methods for Modeling Dynamic Stage Characteristics

Abstract

An analytical investigation of dynamic compressor characteristics was conducted with the goal to make fundamental improvements in the modeling of dynamic compressor stage characteristics. It was determined that present state-of-the-art in modeling dynamic compressor stage characteristics is the use of steady-state characteristics derived from flow model calculations, with first-order time lag response functions applied to account for dynamic departures from the steady and quasi-steady performance predictions.

This investigation developed a blade frequency response function (FRF) method for describing the dynamic blade response. Once the frequency response function of a blade row has been determined, any time or spatially dependent, non-uniform flow can be applied and the model will predict the dynamic blade response.

The first step of this research was to develop FRFs based on first-order lag equations and to test the method using these simple transfer functions. The next step was to develop FRFs based on a dynamic blade lift model for a simple, idealized compressor blade row model. It was found that chord length has a strong influence on the FRF, which is related to the fluid transport time through the blade passage. The final step was to incorporate experimental data obtained from a study of dynamic wake response of an isolated rotor. It was assumed that the wake response was well correlated with the dynamic lift response of a blade row.

It was found that aerodynamic loading, distortion strength, and span position all influence the frequency response functions, which differ greatly from simple first-order lag equations. It was determined that a number of FRFs are needed to describe the dynamic blade response accurately.