Abstract
Non-synchronous blade vibrations have been observed in an experimental multi-stage high-speed compressor setup at part-speed conditions. A detailed numerical study has been carried out to understand the observed phenomenon by performing unsteady full-annulus Reynolds-Averaged Navier–Stokes (RANS) simulations of the whole setup using the solver elsA. Several operating conditions have been simulated to observe this kind of phenomena along a speedline of interest. Based on the simulation results, the physical source of the non-synchronous blade vibration is identified: An aerodynamic disturbance appears in a highly loaded downstream rotor and excites a spinning acoustic mode. A “lock-in” phenomenon occurs between the blade boundary layer oscillations and the spinning acoustic mode. The establishment of axially propagating acoustic waves can lead to a complex coupling mechanism and this phenomenon is highly relevant in understanding the multi-physical interactions appearing in modern compressors. It is shown that aerodynamic disturbances occurring downstream can lead to critical excitation of rotor blades in upstream stages due to an axially propagating acoustic wave. The paper includes the analysis of a relevant transient test and a detailed analysis of the numerical results. The study shows the capability and necessity of a full-annulus multistage simulation to understand the phenomenon.
Highlights
Non-Synchronous Vibrations (NSV) have received much attention since the1990s [1–6]
They are respectively located near choke (OP0), near peak efficiency (OP1), and at a mass flow rate where strong non-synchronous pressure oscillations have been measured in the experiment (OP2)
The axial evolution of the modal amplitude of the dominant pressure mode at OP2 is presented in Figure 21 for the experiment (Na = +5, f ∗,stat = 6.4EO, see Figure 10) and the simulation (Na = +6, f ∗,stat = 6.7EO, see Figure 17), along the amplitude of the dominant mode (Na = −3, f ∗,stat = 2.3EO, see Figure 16) observed at OP1
Summary
Non-Synchronous Vibrations (NSV) have received much attention since the. The term of ‘NSV’ is used to describe a specific aeroelastic phenomenon where the characteristic frequency is not related to the shaft frequency. A multitude of phenomena can lead to non-synchronous blade vibrations in turbomachinery, as flutter [7], buffeting, or rotating stall. The term of ‘NSV’ has been widely used to identify an aeroelastic phenomenon where blade vibrations are measured without a precise terminology. According to cases of ‘NSV’ reported in literature, a characterization can be derived: .
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