Blade Excitation by Aerodynamic Instabilities: A Compressor Blade Study

Abstract

In this paper, we investigate non-synchronous vibrations (NSV) in turbomachinery, an aeromechanic phenomenon in which rotor blades are driven by a fluid dynamic instability. Unlike flutter, a self-excited vibration in which vibrating rotor blades and the resulting unsteady aerodynamic forces are mutually reinforcing, NSV is primarily a fluid dynamic instability that can cause large amplitude vibrations if the natural frequency of the instability is near the natural frequency of the rotor blade. In this paper, we present both experimental and computational data. Experimental data was obtained from a full size compressor rig where the instrumentation consisted of blade-mounted strain gages and case-mounted unsteady pressure transducers. The computational simulation used a three-dimensional Reynolds averaged Navier-Stokes (RANS) time accurate flow solver. The computational results suggest that the primary flow features of NSV are a coupled suction side vortex shedding and a tip flow instability. The simulation predicts a fluid dynamic instability frequency that is in reasonable agreement with the experimentally measured value.

Investigation of the failure of the L-0 blades

“…On the other hand, prediction of the forced response of shrouded disc assemblies is still a challenging engineering task because of unknown excitation loads and friction damping effects [11]. Recently, a remarkable progress in transient flow calculations allowed the prediction of more realistic excitation forces acting on the rotating blades [12][13][14][15][16][17]. Nevertheless, due to some current uncertainties in transient flow calculation and forced response of shrouded disc assemblies, as was reported herein, some cases of steam turbine low pressure blades failures with a continuously-coupled connection structure have been recorded.…”

Investigation into Noise Frequency Spectrum Characteristics Corresponding to Blade Nonsynchronous Vibration in Multi-Stage Axial Compressor

“…i.e., the rotor blades vibrate at nonintegral multiples of the shaft rotational frequencies, and they occur in operating regimes not associated with classical flutter. This type of vibration was previously reported by Baumgartner et al [1] and Kielb et al [2]. Recent years, many scholars have paid attention to Rotating instabilities (RIs) as one of the unsteady flow phenomenon.…”

Mixing layer resonance under high-speed stream forcing

“…Second, the critical speed of occurrence varies with the operating temperature. Last but not least, discrete frequency and vibration mode shape shifts have been observed [2].…”

“…Since the NSV frequency is not synchronized to the rotating speed of the machine, phenomena like surrounding blade row, cavity, duct and cascade acoustics have been investigated to identify potential blade excitations [5][6][7][8][9][10]. Other researchers focused more on the blade tip clearance flow instabilities as the source of noise in turbomachinery but also established some links between tip clearance flow instabilities and blade vibrations [11][12][13][14], [2,15,3].…”

“…The phenomenon has [20] and (d) experimental [21] evidence of tangential tip clearance flow impingement at high aerodynamic loading. taken various names from non-engine order vibrations [1] to non-synchronous vibrations (NSV) and has been associated with important compressor blade fatigue problems [2][3][4]. Like the better known blade flutter phenomenon, nonsynchronous vibrations are asynchronous to the compressor rotating speed.…”