A method to predict the canceling response of flow-excited resonators for the reduction of axial turbomachine noise

摘要

Flow-excited, tunable quarter-wavelength resonators can be integrated into the shrouds of ductedsubsonic axial fans to generate a canceling secondary sound field. Arrays of resonators havebeen employed to reduce existing blade tone noise levels to within 5 dB of the broadband noisefloor, for both plane wave and higher order modal propagations. In previous work, experimentalmethods were used to determine the optimal positioning of resonator sources to achieve maximalnoise reductions for both monopole and dipole configurations of resonators. This study exploresa modeling technique that was developed to analytically determine an optimal configuration ofresonator sources for a given fan. A finite element method (FEM) propagation model isdeveloped to determine the sound pressure level (SPL) at the fan’s location from measurementstaken upstream and downstream of the source. Once SPL is known at the source, resonatorconfigurations can be optimized analytically to radiate anti-phase canceling tones. Flow drivenresponse of individual resonators is modeled using a method based on transmission line theory.Sources are then superimposed in the FEM model and propagated back to the measurementlocation. Analytical results are compared with measurements taken at the Deutsches ZentrumFür Luft Und Raumfahrt (DLR), verifying the efficacy of the modeling technique.