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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union

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Nonlin. Processes Geophys., 23, 83-89, 2016
http://www.nonlin-processes-geophys.net/23/83/2016/
doi:10.5194/npg-23-83-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
04 Apr 2016
Dual-plane PIV investigation of acoustically excited jets in a swirl nozzle
Gavita S. Regunath1, William B. Zimmerman2, and Julia M. Rees3 1Department of Aeronautical and Automotive Engineering, Stewart Miller Building, Loughborough University, Leicestershire, LE11 3TU, UK
2Department of Chemical and Biological Engineering, The University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK
3School of Mathematics and Statistics, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK
Abstract. A novel dual-plane dye laser particle image velocimetry (PIV) technique used to analyze helicity and energy dissipation in an unexcited turbulent swirling jet of pressurized cold air has established that regions within the flow field of the jet exhibiting high helicity are correlated regions of high turbulent kinetic energy dissipation. This PIV configuration provides estimates of all components of the velocity gradient tensor, facilitating calculation of the helicity from the vorticity components. Application of this novel dual-plane PIV technique is extended in this study to investigate helical structures in a turbulent swirling jet where the underlying shear flow is subjected to external acoustic sinusoidal forcing in a plane perpendicular to the central axis of the jet. It was found that acoustic excitation had a significant effect on the mean velocity profile parallel to the direction of the jet. The horizontal forcing resulted in the generation of vorticity that was skewed with a pitch that favored a distribution of angles around 90° with respect to the velocity vector. The distribution of the time-averaged helicity angle indicated organized helical activity, but such activity is not dominated by large-scale coherent structures of maximal helicity.

Citation: Regunath, G. S., Zimmerman, W. B., and Rees, J. M.: Dual-plane PIV investigation of acoustically excited jets in a swirl nozzle, Nonlin. Processes Geophys., 23, 83-89, doi:10.5194/npg-23-83-2016, 2016.
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Short summary
Helical structures are commonplace in geophysical flows, but their effect on turbulence is still enigmatic. A novel PIV laser technique has been used to analyze helical structures in a turbulent swirling jet where the underlying shear flow is subjected to external acoustic forcing. Although the acoustic excitation had an effect on the flow field, no evidence for the existence of large-scale helical structures with maximal helicity was found.
Helical structures are commonplace in geophysical flows, but their effect on turbulence is still...
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