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Nozzle external geometry as a boundary condition for the azimuthal mode selection in an impinging underexpanded jet

Published online by Cambridge University Press:  11 January 2019

Joel L. Weightman*
Affiliation:
Laboratory for Turbulence Research in Aerospace and Combustion, Department of Mechanical and Aerospace Engineering, Monash University, Clayton, Victoria 3800, Australia
Omid Amili
Affiliation:
Laboratory for Turbulence Research in Aerospace and Combustion, Department of Mechanical and Aerospace Engineering, Monash University, Clayton, Victoria 3800, Australia Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis MN 55455, USA
Damon Honnery
Affiliation:
Laboratory for Turbulence Research in Aerospace and Combustion, Department of Mechanical and Aerospace Engineering, Monash University, Clayton, Victoria 3800, Australia
Daniel Edgington-Mitchell
Affiliation:
Laboratory for Turbulence Research in Aerospace and Combustion, Department of Mechanical and Aerospace Engineering, Monash University, Clayton, Victoria 3800, Australia
Julio Soria
Affiliation:
Laboratory for Turbulence Research in Aerospace and Combustion, Department of Mechanical and Aerospace Engineering, Monash University, Clayton, Victoria 3800, Australia
*
Email address for correspondence: joel.weightman@monash.edu

Abstract

The role of the external boundary conditions of the nozzle surface on the azimuthal mode selection of impinging supersonic jets is demonstrated for the first time. Jets emanating from thin- and infinite-lipped nozzles at a nozzle pressure ratio of $3.4$ and plate spacing of $5.0D$, where $D$ is the nozzle exit diameter, are investigated using high resolution particle image velocimetry (PIV) and acoustic measurements. Proper orthogonal decomposition is applied to the PIV fields and a difference in dominant instability mode is found. To investigate possible explanations for the change in instability mode, additional nozzle external boundary conditions are investigated, including the addition of acoustic dampening foam. A difference in acoustic feedback path is suggested to be the cause for the change in dominant azimuthal modes between the flows. This is due to the thin-lip case containing a feedback path that is concluded to be closed exclusively by a reflection from the nozzle base surface, rather than directly to the nozzle lip. The ability of the flow to form a feedback path that maximises the impingement tone gain is discussed with consideration of the numerous acoustic feedback paths possible for the given nozzle external boundary conditions.

Information

Type
JFM Papers
Copyright
© 2019 Cambridge University Press 

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Weightman et al. supplementary movie

Ultra high-speed schlieren of the sound generation at the standoff shock. The jet was emanating from the infinite-lip nozzle, at an NPR of 3.4 and z/D of 5.0.

Download Weightman et al. supplementary movie(Video)
Video 8.4 MB