Main flow oriented vorticity noise experiments

Lionel Hirschberg, Friedrich Bake, Karsten Knobloch, Seven J. Hulshoff

Research output: Chapter in Book/Report/Conference proceedingConference contributionAcademicpeer-review

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Entropy inhomogeneities and vorticity spots induce so-called indirect combustion noise when passing through a choked nozzle; referred to as entropy noise and vorticity noise, respectively. We note that vorticity noise depends on the orientation of the vorticity; viz., oriented normal or parallel to the axial main flow. An experimental investigation of parallel component vorticity noise is presented. In the experiment a time-dependent swirling flow was induced by unsteady tangential injection in the pipe upstream of a choked convergent-divergent nozzle. As the resulting swirling flow passes through the nozzle, the axial stretching of the fluid caused an increase in rotation energy. The steady energy conservation in an isentropic flow implies a Mach number higher than unity at the throat and an associated reduction of density. Ergo, the critical mass-flow rate (for fixed reservoir pressure and temperature) decreases quadratically with increasing swirl intensity. The acoustic waves radiated downstream of the nozzle are due to the change in the mass flow through the nozzle. These are a direct measure for this mass-flow modulation. Using a semi-empirical model, this sound production mechanism is demonstrated to be quasi steady.

Original languageEnglish
Title of host publicationInternoise 2022 - 51st International Congress and Exposition on Noise Control Engineering
PublisherThe Institute of Noise Control Engineering of the USA, Inc.
ISBN (Electronic)9781906913427
Publication statusPublished - 2022
Externally publishedYes
Event51st International Congress and Exposition on Noise Control Engineering, Internoise 2022 - Glasgow, United Kingdom
Duration: 21 Aug 202224 Aug 2022
Conference number: 51


Conference51st International Congress and Exposition on Noise Control Engineering, Internoise 2022
Abbreviated titleInternoise 2022
Country/TerritoryUnited Kingdom


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