Olsman, W. F. J. and Willems, J. F. H. and Hirschberg, A. and Colonius, T. and Trieling, R. R. (2011) Flow around a NACA0018 airfoil with a cavity and its dynamical response to acoustic forcing. Experiments in Fluids, 51 (2). pp. 493-509. ISSN 0723-4864 http://resolver.caltech.edu/CaltechAUTHORS:20110812-110736366
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Trapping of vortices in a cavity has been explored in recent years as a drag reduction measure for thick airfoils. If, however, trapping fails, then oscillation of the cavity flow may couple with elastic vibration modes of the airfoil. To examine this scenario, the effect of small amplitude vertical motion on the oscillation of the shear layer above the cavity is studied by acoustic forcing simulating a vertical translation of a modified NACA0018 profile. At low Reynolds numbers based on the chord (O(10^4)), natural instability modes of this shear layer are observed for Strouhal numbers based on the cavity width of order unity. Acoustic forcing sufficiently close to the natural instability frequency induces a strong non-linear response due to lock-in of the shear layer. At higher Reynolds numbers (above 10^5) for Strouhal number 0.6 or lower, no natural instabilities of the shear layer and only a linear response to forcing were observed. The dynamical pressure difference across the airfoil is then dominated by added mass effects, as was confirmed by numerical simulations.
|Additional Information:||© 2011 The Author(s). Received: 20 May 2010; Revised: 23 February 2011; Accepted: 2 March 2011; Published online: 23 March 2011. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. The authors wish to acknowledge G.J.F. van Heijst, F.M.R. van Uittert, A.P.C. Holten and G.W.J.M. Oerlemans for support. Furthermore, the first author wishes to acknowledge the European Commission for partly sponsoring this research under the ’VortexCell2050 project’, contract number AST4-CT-2005-012139.|
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|Deposited By:||Tony Diaz|
|Deposited On:||18 Aug 2011 21:11|
|Last Modified:||26 Dec 2012 13:28|
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