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Centrifugal compressors can generate tonal pressure pulsations at low flow conditions [2-7]. Certain compressor designs can experience a flow Instability caused by rotating stall, which leads to a tonal pressure component at a sub-synchronous frequency (typically 10 - 80% of rotor speed). Even if the level of this excitation Is generally not high enough to lead to a rotor mechanical vibration problem, it can generate significant levels of pressure pulsation, particularly in the discharge piping, If it excites an acoustic natural frequency of the system. The susceptibility to rotating stall is a function of wheel geometry, speed and process conditions which should be addressed by the compressor designer. Typically the last wheel in a stage is the most susceptible.
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