Characterization of acoustic sources in a corrugated pipe flow with linear stochastic estimation

The intense whistling of corrugated pipe under flow is related to a coherence between the dynamics of structures developing in the shear layer over cavities and acoustic eigenmodes of the pipe. In order to highlight the coupling between aerodynamics and acoustics, three measurement systems with complementary characteristics in terms of space and time resolutions are synchronized. The simultaneity of the measurements of velocity and acoustic pressure provided by five local probes, as two hot-wires and three microphones, with the velocity fields measured by PIV in the same flow region is used to estimate the velocity fields at frequencies compatible with the space-time characterization of the acoustic sources. The linear stochastic estimation (LSE) is performed to reconstruct these high frequency velocity fields. Two rectangular corrugated pipes with different corrugation geometry are investigated. Thanks to the LSE velocity field reconstruction, the contribution of the flow structures, both jet flapping and vortex shedding, to acoustic level is highlighted.