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Aerospace 2018, 5(2), 35; https://doi.org/10.3390/aerospace5020035

Influence of Nozzle Exit Conditions on the Near-Field Development of High Subsonic and Underexpanded Axisymmetric Jets

1
Department of Aero & Auto Engineering, Loughborough University, Loughborough LE11 3TU, UK
2
Rolls-Royce Deutschland, Eschenweg 11, Dahlewitz, 15827 Blankenfelde-Mahlow, Germany
*
Author to whom correspondence should be addressed.
Received: 19 February 2018 / Revised: 17 March 2018 / Accepted: 19 March 2018 / Published: 29 March 2018
(This article belongs to the Special Issue Under-Expanded Jets)
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Abstract

Detailed knowledge of jet plume development in the near-field (the first 10–15 nozzle exit diameters for a round jet) is important in aero-engine propulsion system design, e.g., for jet noise and plume infrared (IR) signature assessment. Nozzle exit Mach numbers are often high subsonic but improperly expanded (e.g., shock-containing) plumes also occur; high Reynolds numbers (O (106)) are typical. The near-field is obviously influenced by nozzle exit conditions (velocity/turbulence profiles) so knowledge of exit boundary layer characteristics is desirable. Therefore, an experimental study was carried out to provide detailed data on nozzle inlet and exit conditions and near-field development for convergent round nozzles operated at Nozzle Pressure Ratios (NPRs) corresponding to high subsonic and supersonic (underexpanded) jet plumes. Both pneumatic probe and Laser Doppler Anemometry (LDA) measurements were made. The data revealed that internal nozzle acceleration led to a dramatic reduction in wall boundary layer thickness and a more laminar-like profile shape. The addition of a parallel wall extension to the end of the nozzle allowed the boundary layer to return to a turbulent state, increasing its thickness, and removing vena contracta effects. Differences in nozzle exit boundary layers exerted a noticeable influence but only in the first few diameters of plume development. The addition of the exit extension removed the vena contracta effects of the convergence only design. At underexpanded NPRs, this change to nozzle geometry modified the shock cell pattern and shortened the potential core length of the jet. View Full-Text
Keywords: nozzle exit profiles; near-field jet development; underexpanded jets nozzle exit profiles; near-field jet development; underexpanded jets
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Trumper, M.T.; Behrouzi, P.; McGuirk, J.J. Influence of Nozzle Exit Conditions on the Near-Field Development of High Subsonic and Underexpanded Axisymmetric Jets. Aerospace 2018, 5, 35.

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