A coupled mode method for multistage aeroelastic and aeroacoustic analysis of turbomachinery

A computational method for predicting the unsteady aerodynamic response of the blade rows in a multistage turbomachine is presented. Most current unsteady aerodynamic theories model a single blade row isolated in an infinitely long duct. This assumption, however, neglects the potentially important influence of neighboring blade rows. The Coupled Mode Method developed in this thesis is an elegant and computationally efficient method for modeling these neighboring blade row effects. The coupling between the blade rows is modeled using the pressure and vorticity "spinning modes" in the inter-row flow regions. The blade rows themselves are modeled in terms of reflection and transmission coefficients. These coefficients describe how spinning modes interact with and are scattered by a given blade row. The coefficients can be calculated using any standard isolated blade row model. The isolated blade row reflection and transmission coefficients, inter-row coupling relationships, and appropriate boundary conditions are all assembled into a small linear system of equations representing the unsteady multistage flow. The method is validated by comparison to several other analytical models of multistage flow, including a time marching vortex lattice simulation. Then, various multistage configurations are considered to demonstrate the method's capabilities and to investigate the importance of neighboring blade rows on the aeroelastic and aeroacoustic performance of a specific blade row. Both flutter (blade vibration) and forced response (incident gust) problems are examined. In particular, it is shown that the presence of neighboring blade rows can have a significant effect on the aerodynamic damping of vibrating blades. The Coupled Mode Method has a number of features which make it desirable for use in aeroelastic and aeroacoustic design/analysis systems. Specifically, this method is computationally fast and adaptable being able to accommodate a wide variety of blade row flow models and multistage geometries.