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Enhancement of disturbance wave amplification due to the intrinsic three-dimensionalisation of laminar separation bubbles

Part of: 31st Congress of The International Council of the Aeronautical Sciences (ICAS)

Published online by Cambridge University Press:  17 October 2018

D. Rodríguez Open the ORCID record for D. Rodríguez [Opens in a new window]  and
E. M. Gennaro
D. Rodríguez*
Affiliation:
Laboratory of Theoretical and Applied Mechanics (LMTA)Graduate Program in Mechanical Engineering (PGMEC)Department of Mechanical EngineeringUniversidade Federal Fluminense NiteróiRJ, Brazil
E. M. Gennaro*
Affiliation:
São Paulo State University (UNESP)Campus São João da Boa VistaSão João da Boa VistaSP, Brazil
*
danielrodriguez@id.uff.br
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Abstract

Previous studies demonstrated that laminar separation bubbles (LSBs) in the absence of external disturbances or forcing are intrinsically unstable with respect to a three-dimensional instability of centrifugal nature. This instability produces topological modifications of the recirculation region with the introduction of streamwise vorticity in an otherwise purely two-dimensional time-averaged flows. Concurrently, the existence of spanwise inhomogeneities in LSBs have been reported in experiments in which the amplification of convective instability waves dominates the physics. The co-existence of the two instability mechanisms is investigated herein by means of three-dimensional parabolised stability equations. The spanwise waviness of the LSB on account of the primary instability is found to modify the amplification of incoming disturbance waves in the linear regime, resulting in a remarkable enhancement of the amplitude growth and a three-dimensional arrangement of the disturbance waves in the aft portion of the bubble. Present findings suggest that the oblique transition scenario should be expected in LSBs dominated by the convective instability, unless high-amplitude disturbances are imposed.

Keywords

AerodynamicsLaminar separation bubblesFlow InstabilityLaminar–Turbulent transitionParabolised stability equations
Type
Research Article
Information
The Aeronautical Journal , Volume 123 , Issue 1268 , October 2019 , pp. 1492 - 1507
Copyright
© Royal Aeronautical Society 2018 

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Footnotes

A version of this paper first appeared at the ICAS 2018 Conference held in Belo Horizonte, Brazil, September 2018.

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