Vibration Signal Analysis of Fan Rotors
Fei
Xie, Zhuang Li,
Suri
Ganeriwala
SpectraQuest Inc., 8201 Hermitage Road, Richmond, VA 23228
Published: May 2007
Abstract
A fan rotor system can generate a large amplitude
blade-passing frequency (BPF) component if the gap between rotating
fans and stationary diffusers is not equal. A series of experiments
were conducted in this study using SpectraQuest’s Machinery Fault
SimulatorTM (MFS) to observe the behavioral changes of the BPF and
its harmonics before and after installing an obstruction nearby an
axial fan and a shroud around a paddle fan. The results show that
the obstruction had an obvious and consistent effect on the 1BPF and
2BPF components for the axial fan rotor system. However, for the two
paddle fans tested, the shroud does not have a large effect on the
1BPF, 2BPF behavioral changes.
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Introduction
During the operation of fluid turbo-machinery,
such as pumps, fans or turbines, fluid dynamic perturbations are
produced and can lead to vibration and noise emission. Typical
fluid-dynamic excitations in such machine are generally associated
with pure-tone (rotation frequency, blade-passing frequency) and
broadband frequency components. The rotation frequency is due to
small misalignments, unbalance or manufacturing imperfections of the
impeller. The broadband phenomena are usually caused by flow
turbulence and cavitation. In some cases, excitation at the blade
passing frequency is dominant. This study will focus on the issues
about the fan rotors and the blade passing frequency.
In this study, a series of tests were conducted
using the SpectraQuest’s MFS and fan kit to observe the changes of
the 1BPF and 2BPF components, with and without a discharge
obstruction and shroud. The running speeds were 1000 rpm, 2000 rpm
and 3000 rpm.
The fan kit of the SpectraQuest MFS contains:
One sheet
metal shroud
One
six-blade fan
One
ten-blade fan
One 12-blade
axial fan
One axial fan blade
obstruction
All experimental data were collected and analyzed
by SpectraQuest’s VibraQuest system. The VibraQuest system contains
portable multi-channel data acquisition front-end, and powerful
analysis functions. For each kind of fan test, the results before
and after installing the obstruction/ shroud have been compared
using the Comparison Panel of the VibraQuest system.
Fig 1:
Before and after installing the shroud in the 6-blade paddle fan
test
Fig 2:
Comparison of spectra for 12-blade axial
fan tests running at 3000 rpm before and after installing the
obstruction
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