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A Note on the Generation of a Compressible Vortex Rings Using Helium as Driver Gas.
University of Manchester.ORCID iD: 0000-0003-0820-7009
University of Manchester.
University of Manchester.
2012 (English)In: Proceedings of the Institution of Mechanical Engineers. Part G, Journal of Aerospace Engineering, ISSN 0954-4100, E-ISSN 2041-3025, Vol. 227, no 10, p. 1637-1645Article in journal (Refereed) Published
Abstract [en]

An experimental study has been conducted on the generation and propagation of compressible vortex rings using helium as a driver gas, with the aim of evaluating the effects of multi-gas operations for real-life applications. The advantage of such system, when compared to a constant gas system based on ambient air, is to effectively increase the Mach number while keeping the pressure ratio constant. Three pressure ratios of ~4, 8 and 12 were set, corresponding to experimental Mach numbers of approximately 1.50, 1.81 and 2.05. The increase in incident Mach number resulted in the variation of the vortex ring and trailing jet structure, and an increase in both the velocity magnitude and vorticity field. Results showed a transition from the regular-reflection shock-cell system at the experimental Mach number approximately 1.50 to the presence of a Mach reflection with a central Mach disc, which grew in size with further increase in incident Mach number. The presence of the Mach disc resulted in the formation of a subsonic jet, internal to the main trailing jet. Its velocity was measured to be in the order of magnitude of 550 m/s, with the speed of sound of helium at 1005 m/s. Results also demonstrated that shear layers formed between the subsonic and main trailing jet have opposing vorticity, with that of the subsonic jet being approximately half in magnitude. Secondary counter-rotating vortex rings were generated ahead of the main vortex and orbited around it. The analysis of the vorticity field has shown that these secondary vortices have a magnitude approximately half of that of the vorticity of the main vortex, and has confirmed that they have an opposite direction of rotation.

Place, publisher, year, edition, pages
Sage Publications, 2012. Vol. 227, no 10, p. 1637-1645
Keywords [en]
Vortex ring, compressible flow, helium driver
National Category
Fluid Mechanics and Acoustics
Research subject
Aerospace Engineering
Identifiers
URN: urn:nbn:se:kth:diva-263182DOI: 10.1177/0954410012465042ISI: 000324472000009Scopus ID: 2-s2.0-84889011016OAI: oai:DiVA.org:kth-263182DiVA, id: diva2:1367087
Note

QC 20191104

Available from: 2019-10-31 Created: 2019-10-31 Last updated: 2019-11-05Bibliographically approved

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Mariani, Raffaello
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