Aircraft intermittent combustion engines often incorporate turbochargers adapted from ground-based applications to improve their efficiency and performance. These turbochargers can operate at off-design conditions and experience blade failures brought on by aerodynamic-induced blade resonances. A reduced-order model of the aeroelastic response of general fluid-structural configurations is developed using the Euler-Lagrange equation informed by numerical data from uncoupled computational fluid dynamic (CFD) and computational structural dynamic calculations. The structural response is derived from a method of assumed-modes approach. The unsteady fluid response is described by a modified version of piston theory that approximates the local transient pressure fluctuation in conjunction with steady CFD solution data. The reduced-order model is first applied to a classical panel flutter scenario and found to predict a flutter boundary that compares favorably to the boundary identified by existing theory and experimental data. The model is then applied to the high-pressure turbine of a dual-stage turbocharger. The model predictions are shown to reliably determine the lack of turbine blade flutter, and rudimentary damping comparisons are performed to assess the ability of the model to ascertain the susceptibility of the turbine to forced response. Obstacles associated with the current experimental state of the art that impinge upon further numerical validation are discussed.

In order to improve their efficiency and performance, aircraft intermittent combustion engines often incorporate turbochargers that are adapted from ground-based applications. These turbochargers experience conditions outside of their design operating envelope and are found to experience high-cycle fatigue brought on by aerodynamically-induced blade resonances. The onset of fluid-structural interactions, such as flutter and forced response, in turbochargers at these conditions has not been extensively studied. A reduced-order model of the aeroelastic response of the turbine is developed using the Euler-Lagrange equation informed by numerical data from uncoupled computational fluid dynamic (CFD) and computational structural dynamic (CSD) calculations. The structural response of the reduced-order model is derived from a method of assumed modes approach. The unsteady fluid response is described by a modified version of piston theory as a first step towards including inhomogeneous aerodynamic forcing. Details of the reduced order model are given. The capability of the reduced-order model to predict the presence of flutter from a subset of the uncoupled numerical simulation data is discussed.

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To investigate the effect of altitude on vibrations in a turbocharger, an aircraft compression-ignition engine was operated in both a sea level cell and an altitude chamber up to 25,000 ft (7620 m). The turbocharger was instrumented with a nonintrusive stress measurement system to analyze the frequencies, magnitudes, and critical speeds of the blade bending modes as the ambient pressure, ambient temperature, and engine power varied. The measurements were also compared to data from accelerometers mounted on the compressor housing. At sea level conditions, the largest deflection amplitudes were associated with excitations of the first blade bending mode. These deflections grew in amplitude as the altitude increased and the turbocharger/engine worked harder to produce the required pressure rise and power. There was also evidence of a higher-order mode being excited at elevated altitudes. By understanding the factors contributing to resonance and flutter in aircraft turbomachinery, modeling and prediction tools can be improved to update operating envelopes for current designs and minimize these phenomena in future, aviation-specific designs.

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