The present thesis discusses the forced response of a rotor’s bladed-disk when excited by the periodic force produced by a wake generator, or Inlet Guide Vane (IGV),with 8 equally-spaced blades. These components are part of an axial transonic compressor rig, moreover the Transonic Compressor Darmstadt 1 (TCD1), located at the Technical University of Darmstadt. The investigation is within the ARIAS (Advanced Research Into Aeromechanical Solutions) project, that aims to improve the predictive capabilities of the design methods used in the aircraft propulsion engine’s industry to study aerodynamically induced blade vibrations. The methodology comprised a set of numerical analyses that were conducted using the software Ansys, addressing both the structural and the aerodynamics sides of the aeroelastic problem, in a co-dependent way. At first, steady-state CFD simulations were conducted to study the mesh convergence and to analyse the operation of the compressor at N80 speed, obtaining its compressor map and its peak efficiency operation point. From these, the aerodynamic static force being applied on theblade was obtained, allowing to determine the pre-stresses of the bladed-disk, orblisk. With a modal analysis, the natural modes of the rotor blisk at N80 speed were obtained and the resonance crossing M2 EO8 was identified, plotting the Campbell and ZZENF diagrams. From the modal displacements of the critical mode, a blade flutter analysis was conducted in order to compute the aerodynamic damping ratio of the rotor blisk. With a transient CFD analysis, the periodic forcing being applied onthe rotor blisk that arises from the IGV wake pattern was determined and exported as Fourier coefficients. Finally, a harmonic simulation was carried out to analyse the forced response of the blisk, introducing both the aerodynamic damping value and the unsteady forcing mapped onto the blade. As a result, the frequency response of both the blade maximum alternating deflections and equivalent stresses was obtained, as well as the respective spatial contour plots at the obtained resonance frequency. Some of the results of the conducted analyses were investigated in order to analyse the aerodynamic phenomena occurring, where it was possible to identify vortex shedding, leading shock, tip-clearance and horse-shoe vortex.  Afterwards, the numerical results were compared to the experimental data optained from rig tests conducted at the TCD1 by partners of the ARIAS projects. The numerical model management to predict well the compressor map, thus the steady-state of the flow, as well as the resonance frequency. The aerodynamic damping value was over- predicted when compared to the entire data set. When it came to the harmonic analysis results, the numerical model under-predicted by one order of magnitude the maximum deflection, and the equivalent stress is, as well, far below the experimental results. These results led to conclude that the model is under-predicting the aerodynamix unsteady forcing that results from the wake pattern generated by the IGV and excites the rotor blades.

Forced response which is blade vibration due to an external excitation can lead to blade failure. The estimation of the level of vibration is dependent on the determination of aerodynamic damping. This thesisinvestigates the determination of aerodynamic damping at high reduced frequencies in turbomachines. The aerodynamic damping was calculated by a linearized Navier-Stokes flow solver with exact 3D non-reflecting boundary conditions. The method was validated using the two-dimensional test cases (Standard Configuration 5 and 8). Thereafter, two 3D profiles were also investigated: an aeroelastic turbine rig (AETR) which is a subsonic turbine case, and a virtual integrated compressor (VINK) which is a transonic compressor case. In AETR case, the first bending mode with reduced frequency 2.0 was studied. The 3D acoustic modes were calculated and the rate of decay was plotted as a function of nodal diameter and radial order. This plot identified six acoustic resonant points which included two points corresponding to the first radial order. The six resonance points correspond to six peaks in the damping curve. In VINK case, the fifth mode (1854 Hz, reduced frequency 3.1) was investigated. Acoustic resonance was predicted to occur for the first and second radial orders at the inlet. It was concluded that the higher order resonance points are influencing the damping curve. There were some inconsistencies in the results and grid convergence was not achieved. These inconsistencies were due to the difficulty in calculating the acoustic modes at the transonic inlet with an impinging shock. / Aerodynamiskt påtvingade vibrationer, som är bladvibrationer på grund av en extern excitation kan leda till haveri. Prediktering av vibrationen är beroende av bestämning av aerodynamisk dämpning. I detta arbete undersöks bestämningen av aerodynamisk dämpning vid höga reducerade frekvenser i turbomaskiner. Den aerodynamiska dämpningen beräknades genom en linjäriserad Navier-Stokeslösare med exakta 3D icke-reflekterande gränsvillkor. Metoden validerades med hjälp av de tvådimensionella testfallen (Standardkonfiguration 5 och 8). Därefter undersöktes två 3D-profiler: en aeroelastisk turbinrigg (AETR), som är en subsonisk turbinenhet och en virtuell integrerad kompressor (VINK) som är ett transoniskt kompressorfall. I AETRfallet undersöktes det första böjningsformen med reducerad frekvens 2.0. 3D akustiska lägen beräknades och graden av förfall visades som en funktion av noddiameter och radiell grad. Denna metod identifierade sex akustiska resonanspunkter som innehöll två punkter som motsvarade den första radiella graden. De sex resonanspunkterna motsvarar sex toppar i dämpningskurvan. I VINK-fallet undersöktes den femte svängningsformen (1854 Hz, reducerad frekvens 3.1). Akustisk resonans förutspåddes inträffa för första och andra radiella graden vid inloppet. Slutsatsen drogs att de högre ordningens resonanspunkter påverkar dämpningskurvan. Det fanns vissa inkonsekvenser i resultaten och gridkonvergens uppnåddes inte. Dessa inkonsekvenser berodde på svårigheten att beräkna de akustiska svängningsformerna vid det transoniska inloppet med en stötvåg.