Showing papers by "Sanford Fleeter published in 2005"

Aerodynamic Damping Predictions in Turbomachines Using a Coupled Fluid-Structure Model

Abstract: Flow-induced vibration of turbomachine blade rows is a coupled fluid-structure problem. Thus, rather than separate fluid and structural models, a coupled interacting fluid-structures analysis is needed. This need is addressed by extending the finite element code ALE3D that solves the three-dimensional Euler equations to model the unsteady aerodynamics of turbomachine blade rows. The same finite element model is applied to both the blading and the fluid, which results in consistency between the fluid and structure. Such a coupled interacting fluid-structure analysis enables the aerodynamic damping of multiple vibration modes to be predicted from two time-domain simulations: one with the blading in a vacuum and one with the blading in flow. This novel approach to predict aerodynamic damping is demonstrated by the consideration of a modern transonic compressor blade row. The blading is first impulsed in its first bending and first torsion modes in a vacuum. It is then immersed in the design-point flowfield and impulsed in its first bending and first torsion modes again. Signal processing tools applied to the predicted blade response time history extract the difference in the decay rate of both modes.

Off-Design Transonic Rotor-Inlet Guide Vane Unsteady Aerodynamic Interactions

Abstract: The unsteady aerodynamic interactions of a transonic rotor with an upstream inlet guide vane (IGV) row under off-design operating conditions are investigated. The rotor-generated IGV unsteady aerodynamics are quantified when the IGV reset angle causes the rotor to be on the verge of becoming transonic and the vane exit metal angle is nearly aligned with the detached rotor shocks, that is, at the vane maximum modal force excitation. This is accomplished through experiments in a 1 1 2-stage axial-flow compressor, with detailed data acquired and analyzed. These data define the 90% span transonic rotor-generated forcing function to the IGVs, the resulting vane steady and unsteady aerodynamic response, and the time-variant vane-to-vane flow field over one interaction cycle.

Three-Dimensional Wake Forcing Functions Generated by a High-Speed Rotor

Abstract: A series of experiments are described that are directed at investigating and quantifying the inherent three-dimensionality and fundamental unsteady-flow characteristics of unsteady aerodynamic forcing functions generated by high-speed compressor rotors for application to forced response. With a midspan rotor-relative inlet Mach number of 0.6, three-component velocity and unsteady-static-pressure data defining the spanwise nature of the rotor wake are acquired and analyzed at two axial locations, in both the inlet guide vane freestream and wake regions. The slanted hot-film technique enables evaluation of the ensemble-averaged-velocity field and the rms of this ensemble-averaged velocity. Data show that the rotor-wake unsteadiness is highest in the blade wake, the vortex regions, and the casing boundary layer. A strip theory approach is used to analyze these three-dimensional data. The rotor-wake data are also correlated with empirical correlations. After Fourier decomposition of the axial and tangential velocity components, a two-dimensional vortical-potential gust splitting analysis is implemented, and the vortical and potential harmonic wake gust forcing functions are determined.