Acoustic source identification of an axial fan in a duct considering the rotation effect

Abstract

For developing the quiet axial fans, the spatial distribution of acoustic source parameters over the source plane provides essential information. In this study, the previously suggested source identification technique by authors is newly applied to an axial fan. To obtain the acoustic source parameters in a duct, one should overcome many technical difficulties related with: the turbulent flow, high order modes, rotating sources, inverse estimation. Measurements are conducted with several arrays of flush mounted microphones deployed on the periphery of the duct wall. A reference trigger signal obtained from the rotating blade is used to suppress the effect of turbulent flow in the measured pressure spectra with a reduction of about 25 dB in the present work. The maximum error between measurement and estimation is generally <-20 dB in the measurement plane in the very vicinity to the source. The visualized source images clearly indicate the locations and the strengths of main contributors to the radiated sound, e.g., for the inlet of the axial fan, the tip clearance between fan blades and shroud wall.

Implementation of X-Parameters Principle for Non-linear Vibroacoustic Membrane Using Two-Port Measurement

“…The microphone separation distance is s=300mm. According to the relationship 0.1π<ks<0.8π [19], the corresponding frequency region reckoned during the measurements ranges from 57 Hz to 457 Hz at the temperature of 20 °C. One of the two microphones (indicated as Mic.2) is located at the midsection of the duct (distance 1m from the end sections).…”

An Improved Time-Domain Inverse Technique for Localization and Quantification of Rotating Sound Sources

“…The pressure spectra at the positions of virtual rotating microphones were obtained from the spinning mode decomposition of pressure spectra measured by the actual fixed microphones. Since the virtual microphone data is prevented from the Doppler effect, it can be directly used as the input of the frequency-domain beamforming or inverse method to locate rotating sound sources [1][2][3][4][5][6]. Dougherty et al [7] and Jekosch et al [8,9] employed a time-domain interpolation method to eliminate the Doppler effect.…”