Turbomachinery Rotordynamics With Case Studies Pdf Instant
A modern high-speed compressor exhibited strong subsynchronous vibration at a frequency of about 0.5 times running speed, causing high bearing loads and eventual machine trips. The vibration increased as discharge pressure was raised.
Metallurgical inspection of the fractured disc pack revealed textbook beach marks indicative of torsional fatigue failure. A transient torsional rotordynamic simulation uncovered that the VFD produced harmonic voltage ripples (specifically at the 6th and 12th line frequencies). During specific throughput rates, these electrical harmonics matched the first natural torsional frequency of the shaft assembly, causing a resonant condition known as torsional excitation. Engineering Solution:
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The oil whip phenomenon was completely eliminated, and the turbine resumed reliable, vibration-free operation across its entire speed envelope.
: This report details field problems involving rotordynamic instability in modern high-speed turbomachinery. It covers:
A novel swirl brake design tailored to the teeth-on-rotor geometry was developed. Computational fluid dynamics (CFD) was used to predict the swirl reduction, and the brake was then manufactured and installed. Post-installation testing showed a significant increase in the stability threshold speed, and the compressor was returned to service with stable vibration levels. This link or copies made by others cannot be deleted
Focuses on the radial bending vibration of the shaft. It determines critical speeds, unbalance responses, and stability margins (logarithmic decrements).
) of the first forward mode must be sufficiently positive under full aerodynamic loading to guarantee stability.
). This drove the system's logarithmic decrement into negative territory ( axes) at a bearing location
Oil seal related field problems and instability caused by aerodynamic cross-coupling in high-pressure compressors.
Engineers use this diagram to ensure that the operating speed range maintains a sufficient "separation margin" (typically 10% to 15%) from any critical speed. Synchronous vs. Asynchronous Vibration
These are the rotational speeds that match the rotor's natural frequencies. Modern machines often operate above the first critical speed (supercritical), requiring a safety margin (typically 15%) to avoid continuous operation at resonance.
axes) at a bearing location, engineers can view the actual path of the shaft centerline. The shape of this orbit (circular, elliptical, banana-shaped, or figure-eight) provides an immediate visual signature of unbalance, misalignment, rubbing, or oil whirl.
provides conference papers such as "Case Study Validation of Common Torsional Rotordynamic Practices for Integrally Geared Compressors" (DETC2017-67005).
