In-Situ Modal Response Characterization of Pipe-Structures Through Reynolds Number Variation

Abstract

In this investigation, an in-situ method of system excitation is explored experimentally. The modal characteristics of externally-supported pipe structures are investigated by varying the flow Reynolds number (Red) with hydrodynamic pressure fluctuations due to fully developed turbulent pipe-flow providing a varying excitation source on the internal pipe wall. During experiments, time series records of single-point fluctuating wall pressure and multi-point wall vibrations are collected. Power spectral density functions of both wall pressure fluctuation and wall vibration are computed at each discrete Reynolds number. Visualization of the computed power spectral density functions with flow Reynolds number are then used for system characterization. A comparative analysis of the data sets collected for both acrylic and ABS pipe show that the pressure spectra are similar, while the vibration spectra change significantly. Pressure spectra reveal a character whereby the magnitude of the spectra increase with increasing Reynolds number. A comparison of in-situ results to those obtained using traditional impact response tests show that the vibration spectra collected through Reynolds number variation successfully capture the modal characteristics of the pipe-structure. Both acoustic analysis to determine the vibration source and preliminary health diagnostics investigations for both loss-of-fluid and loss-of-material events are performed.