Experimental findings point towards an acoustic resonance originating from separated flow in the variable inlet guide vanes. The mechanism of the fluid-structure-interaction behind the self-excited vibration is identified by means of unsteady compressor instrumentation data. Self-excited vibrations were finally initiated when the compressor was operated at part speed with fully open inlet guide vane along nominal and low operating line. The compressor was designed with the unconventional goal to encounter self-excited blade vibration within its regular operating domain.ĭespite the design target to have the rotor blades reach negative aerodamping in the near stall region for high speeds and open inlet guide vane, no vibration occurred in that area prior to the onset of rotating stall. This paper investigates the acoustically induced rotor blade vibration that occurred in a state-of-the-art 1.5-stage transonic research compressor. When decreasing the rotor tip gap size, the mechanism causing the vibration is alleviated. The tip clearance flow pattern travels in the backward direction, seen from the rotating frame of reference, andcauses a forward traveling structural vibration pattern with the same phase difference between blades. Numerical simulations and comparison with the experimental observations showed that vibrations occur near the compressor stability limit due to interaction of the blade movement with a pressure fluctuation pattern originating from the tip clearance flow. The vibration phenomenon shows similarities to flutter. The numerical simulation results are in close agreement with the experiment in both cases. The vibration was experimentally observed for the second eigenmode of the rotor blades at nonsynchronous frequencies and is simulated for two rotational speeds using a time-linearized approach. This paper presents a numerical study on blade vibration for the transonic compressor rig at the Technische Universität Darmstadt (TUD), Darmstadt, Germany. This paper concludes with a joint analytical interpretation of the shear layer fluctuations observed at the beginning of spike stall and during near stall NSV by basic flow principles. In this case, the compressor continues to operate on the aerodynamically stable characteristic and NSV might be excited due to the unsteady blade force. Already before the stall limit is reached such fluctuations can occur. The aerodynamic structure of shear layer fluctuations in the rotor tip region during the initial phase of spike stall inception is investigated. The simulations enable a detailed flow analysis during spike stall inception and non-synchronous vibrations (NSV) at operating points close to the stall limit. A comparison with previous experimental investigations shows close agreement for both steady and transient data. Simulations were carried out for the transonic compressor at the Technical University of Darmstadt using the AU3D flow solver. The aerodynamic and aeroelastic behavior of an engine-like transonic compressor stage is investigated in this paper. Meanwhile, the modal decomposition method and flow field reconstruction techniques are used to investigate the coherent flow structures caused by low frequency under different guide vane openings. A low frequency that has a great influence on the internal flow of the compressor stage is found, and the unstable flow caused by low frequency is analyzed by the combination of streamline distribution, spectrum analysis, vector, entropy increase, and modal decomposition method. ![]() The regulation of IGV can effectively improve the unstable flow of the compressor stage at low mass flow rates. In the three cases of positive pre-swirl, there was an improvement of approximately 9.95% of stall/surge margin greater than in conditions with no pre-swirl. Numerical results show that as positive pre-swirl increases, the aerodynamic performance curve of the stage moves in the low mass flow rate direction. The latter three positions of VIGV induce positive pre-swirl. Four positions of VIGV are considered, including 0◦, 30◦, 45◦, and 60◦ angles. This study numerically investigates the beneficial effects of positive pre-swirl on theĪerodynamic performance and internal flow field in a centrifugal compressor stage with variable inlet guide vanes (VIGVs) at low mass flow rates.
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