Practical Solutions to Machinery and Maintenance Vibration Problems
Chapter 9, Fluid Flow
Section 3, Turbulence
Essentially, turbulence is caused by poor design of pipe and/or ductwork and is more common in air mover applications and fans than in pumping systems. It is induced when the fluid is forced to make abrupt changes in direction such as sharp 90° bends in discharge piping or passage through valves, etc. It usually does not cause excessive vibration unless a resonant frequency is excited. The vibration spectra look similar to those from cavitation. However, the broadband frequencies generated are generally lower than for cavitation, often with the most dominant peaks occurring in the sub-rotational range (less than 1 x rpm). The highest amplitudes are usually experienced immediately downstream from the cause. Whereas cavitation is normally related to the pump suction, the cure for turbulence is dependent on good design practice, such as avoiding sharp turns in piping and ducting, etc. Where such turns cannot be avoided, then flow modifiers may be used internally to smooth the fluid flow.
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