Abstract
The paper presents experimental results of the visualization of the
nonlinear aeroacoustic sound generation phenomena occurring in organ flue
pipe. The phase-locked particle image velocimetry technique is applied to
visualize the mixed velocity field in the transparent organ flue pipe
model made from Plexiglas. Presented measurements were done using
synchronization to the tone generated by the pipe itself sup- plied by
controlled air flow with seeding particles. The time series of raw
velocity field distribution images show nonlinear sound generation
mechanisms: the large amplitude of deflection of the mean flue jet and
vortex shedding in the region of pipe mouth. Proper Orthogonal
Decomposition (POD) was then applied to the experimental data to
separately visualize the mean mass flow, pulsating jet mass flow with
vortices and also sound waves near the generation region as well as inside
and outside of the pipe. The resulting POD spatial and temporal modes were
used to approximate the acoustic velocity field behaviour at the pipe
fundamental frequency. The temporal modes shapes are in a good agreement
with the microphone pressure signal shape registered from a distance.
Obtained decomposed spatial modes give interesting insight into sound
generating region of the organ pipe and the transition area towards the
pure acoustic field inside the resonance pipe. They can give qualitative
and quantitative data to verify existing sound generation models used in
Computational Fluid Dynamics (CFD) and Computational Aero-Acoustics (CAA).
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