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To assess the influence of mistuning on the vibration amplitudes of turbo-machinery rotors, reduced order models (ROMs) are widely used. A variety of methods are available for single-stage configurations and mostly aero-elastic effects can be taken into account. More recent research focusses on extending these methods to include multiple stages. However, due to the significantly increased computational effort of the aeroelastic simulations when adding more stages to the models, these ROMs are rarely applied with the inclusion of multistage aeroelastic effects. It is therefore desirable to develop reduction methods which minimize the number of these simulations to reduce the computational cost and thereby enable analyses of rotors with multiple stages including aeroelastic effects. In this paper, a cyclic Craig-Bampton reduction method with an a priori interface reduction for multistage rotors is extended with an additional a posteriori interface reduction to reduce the number of aeroelastic simulations necessary for a given accuracy level of the ROM. The interface degrees of freedom between stages are reduced using a modified version of Characteristic Constraint Modes, to yield a more efficient representation of their displacements while retaining their monoharmonic nature. The method is applied to a two-stage axial compressor with full aeroelastic coupling between the stages and its reduced computational effort is demonstrated. Additionally, two sorting methods for the degrees of freedom (DOFs) of the ROM are compared.

Im Rahmen des Auslegungsprozesses von Turbomaschinen können aerodynamisch optimale Designs oftmals nicht realisiert werden, da in der aeroelastischen Auslegung die strukturelle Integrität nicht gewährleistet ist. Problematisch sind dabei hohe Schwingungsamplituden, die beispielsweise durch selbsterregte Schwingungen (Flattern) oder zwangserregte Schwingungen (Forced Response) auftreten. Eine wichtige Einflussgröße bei der Vorhersage dieser Phänomene ist die Dämpfung. Allgemein wird angenommen, dass diese beim Fehlen von Reibkontakten normalerweise hauptsächlich aus der aerodynamischen Dämpfung besteht. In dieser Arbeit soll der Einfluss von zusätzlicher Dämpfung durch die Rotorlagerung auf die Gesamtdämpfung und auf das Schwingungsverhalten bei Forced Response untersucht werden. Dieser Einfluss kommt bei der Kopplung der Schaufelschwingungen in den Knotendurchmesser 1 und -1 mit den Rotorschwingungen zum Tragen, da die Dämpfung aus einer strukturdynamischen Interaktion dieser beiden Komponenten resultiert. Zu diesem Zweck wird eine Simulationskette aufgebaut, die die physikalischen Effekte im Betrieb bestmöglich abbildet. Die Simulationskette basiert im Wesentlichen auf einem strukturdynamischen Vollmodell des Blisk-Rotor-Verbundes und einem instationären CFD-Modell unter Nutzung der Harmonic Balance Methode zur Berücksichtigung der aeroelastischen Effekte. Zusätzlich erfolgt auf Basis einer experimentellen Modalanalyse im Stillstand eine Identifikation der Verstimmungsparameter der Beschaufelung. Alle Ergebnisse fließen in ein strukturdynamisches Modell reduzierter Ordnung ein, das das Schwingungsverhalten der Beschaufelung berechnet. Die numerischen Ergebnisse werden mit Messdaten verglichen. Dies umfasst insbesondere im Betrieb bestimmte Dämpfungen unter Nutzung eines akustischen Anregungssystems und gemessene Frequenzgänge bei Forced Response. Die numerischen Ergebnisse zeigen dabei im Rahmen der experimentellen Unsicherheiten eine sehr gute Übereinstimmung mit, During the design process of turbomachinery, it is often not possible to realize aerodynamically optimal designs due to aeroelastic constraints. The design choices are limited by possible structural failure, which can be caused by high vibration amplitudes, e.g. due to self-excited vibrations (flutter) or forced vibrations (forced response). In particular, the modal damping has an important impact on these phenomena. In the absence of frictional contacts, damping is mainly created by aerodynamics. In this work, the influence of additional damping due to the rotor bearing on the total damping and on the vibrational behavior in forced response will be investigated. This influence comes becomes relevant when blade vibrations in nodal diameters 1 and -1 couple with the rotor vibrations. This is caused by a structural dynamic interaction of these two components. For this purpose, a simulation process is set up to best represent the physical effects during operation. The simulation process is essentially based on a full structural dynamic model of the blisk-rotor assembly and an unsteady CFD model using the harmonic balance method to account for the aeroelastic effects. In addition, a mistuning identification of the blading is performed based on an experimental modal analysis at standstill. All results are incorporated into a structural dynamic reduced order model that calculates the vibrational behavior of the blading. The numerical results are compared with measurement data. In particular, this includes damping determined in operation using an acoustic excitation system and measured frequency responses due to forced response. The numerical results show very good agreement with the experimental results within the measurement uncertainty, both with respect to the damping and the mistuned frequency responses. Furthermore, the blade-rotor interaction results in significant changes of the eigenfrequencies and damping. As a consequence, damping increases by up to fifteen time

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Compact, electrically-driven compressors are a core component of a novel active high-lift system for future commercial aircraft. A newly-developed aeromechanical optimization process was used to design the compressor stage. The optimization resulted in an unusual mixed-flow compressor design with very low aspect ratio blades and a high rotational speed of up to 60,000 rpm. Due to the unusual design, experimental validation of the performance predictions by means of CFD is necessary. This paper presents the first experimental results obtained using a preliminary prototype at part-speed, i.e. rotational speeds from 20,000 to 30,000 rpm. The experimentally-determined pressure ratios deviate up to 1.5 %, the polytropic efficiencies up to 4 percentage points from the CFD predictions. Besides the deficiencies of available turbulence models, the underestimation of overall losses is presumably due to the omission of the volute in the CFD model. An experimental validation of the CFD predictions at full-speed is under way.