Skip to main content Accessibility help
×
Home
Hostname: page-component-55597f9d44-5zjcf Total loading time: 0.224 Render date: 2022-08-12T02:37:45.343Z Has data issue: true Feature Flags: { "shouldUseShareProductTool": true, "shouldUseHypothesis": true, "isUnsiloEnabled": true, "useRatesEcommerce": false, "useNewApi": true } hasContentIssue true

MTV measurements of the vortical field in the wake of an airfoil oscillating at high reduced frequency

Published online by Cambridge University Press:  10 February 2009

DOUGLAS G. BOHL*
Affiliation:
Department of Mechanical and Aeronautical Engineering, Clarkson University, Potsdam, NY 13699USA
MANOOCHEHR M. KOOCHESFAHANI
Affiliation:
Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824, USA
*
Email address for correspondence: dbohl@clarkson.edu

Abstract

We present an experimental investigation of the flow structure and vorticity field in the wake of a NACA-0012 airfoil pitching sinusoidally at small amplitude and high reduced frequencies. Molecular tagging velocimetry is used to quantify the characteristics of the vortex array (circulation, peak vorticity, core size, spatial arrangement) and its downstream evolution over the first chord length as a function of reduced frequency. The measured mean and fluctuating velocity fields are used to estimate the mean force on the airfoil and explore the connection between flow structure and thrust generation.

Results show that strong concentrated vortices form very rapidly within the first wavelength of oscillation and exhibit interesting dynamics that depend on oscillation frequency. With increasing reduced frequency the transverse alignment of the vortex array changes from an orientation corresponding to velocity deficit (wake profile) to one with velocity excess (reverse Kármán street with jet profile). It is found, however, that the switch in the vortex array orientation does not coincide with the condition for crossover from drag to thrust. The mean force is estimated from a more complete control volume analysis, which takes into account the streamwise velocity fluctuations and the pressure term. Results clearly show that neglecting these terms can lead to a large overestimation of the mean force in strongly fluctuating velocity fields that are characteristic of airfoils executing highly unsteady motions. Our measurements show a decrease in the peak vorticity, as the vortices convect downstream, by an amount that is more than can be attributed to viscous diffusion. It is found that the presence of small levels of axial velocity gradients within the vortex cores, levels that can be difficult to measure experimentally, can lead to a measurable decrease in the peak vorticity even at the centre of the flow facility in a flow that is expected to be primarily two-dimensional.

Type
Papers
Copyright
Copyright © Cambridge University Press 2009

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Anderson, J. M., Streitlien, K., Barrett, D. S. & Triantafyllou, M. S. 1998 Oscillating foils of high propulsive efficiency. J. Fluid. Mech. 360, 41.CrossRefGoogle Scholar
Bohl, D. G. 2002 Experimental study of the 2-D and 3-D structure of a concentrated line vortex. PhD thesis, Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan.Google Scholar
Bohl, D. G. & Koochesfahani, M. M. 2004 MTV measurements of axial flow in a concentrated vortex core. Phys. Fluids. 16 (9), 4185.CrossRefGoogle Scholar
Cohn, R. K. 1999 Effects of forcing on the vorticity field in a confined wake. PhD thesis, Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan.Google Scholar
Cohn, R. K. & Koochesfahani, M. M. 1993 Effect of boundary conditions on axial flow in a concentrated vortex core. Phys. Fluids. A 5 (1), 280.CrossRefGoogle Scholar
Cohn, R. K. & Koochesfahani, M. M. 2000 The accuracy of remapping irregularly spaced velocity data onto a regular grid and the computation of vorticity. Experiments Fluids 29, S61.CrossRefGoogle Scholar
Dabiri, J. O., Colin, S. P., Costello, J. H. & Gharib, M. 2005 Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses. J. Exp. Biol. 208, 1257.CrossRefGoogle ScholarPubMed
DeLaurier, J. D. & Harris, J. M. 1982 Experimental study of oscillating-wing propulsion. J. Airc. 19 (5), 368.Google Scholar
Freymuth, P. 1988 Propulsive vortical signature of plunging and pitching airfoils. AIAA J. 26, 881.CrossRefGoogle Scholar
Gendrich, C. P. 1998 Dynamic stall of rapidly pitching airfoils: MTV experiments and Navier–Stokes simulations. PhD thesis, Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan.Google Scholar
Gendrich, C. P., Bohl, D. G. & Koochesfahani, M. M. 1997 Whole-field measurements of unsteady separation in a vortex ring wall interaction. AIAA Paper 97-1780.Google Scholar
Gendrich, C. P. & Koochesfahani, M. M. 1996 A spatial correlation technique for estimating velocity fields using molecular tagging velocimetry (MTV). Experiments Fluids 22, 67.CrossRefGoogle Scholar
Gendrich, C. P., Koochesfahani, M. M. & Nocera, D. G. 1997 Molecular tagging velocimetry and other novel applications of a new phosphorescent supramolecule. Experiments Fluids 23, 361.CrossRefGoogle Scholar
Jones, K. D. & Platzer, M. F. 1997 Numerical computation of flapping wing propulsion and power extraction. AIAA Paper 97-0826.Google Scholar
Katz, J. & Weihs, D. 1978 Behavior of vortex wakes from oscillating airfoils. J. Airc. 15 (12), 861.CrossRefGoogle Scholar
Koochesfahani, M. M. 1989 Vortical patterns in the wake of an oscillating airfoil. AIAA J. 27, 1200.CrossRefGoogle Scholar
Koochesfahani, M. M. (ed). 2000 Special feature: molecular tagging velocimetry. Meas Sci Technol. 11, 1235.Google Scholar
Koochesfahani, M. M. & Nocera, D. G. 2007 Molecular tagging velocimetry. In Handbook of Experimental Fluid Dynamics (ed. Foss, J., Tropea, C. & Yarin, A.), Chapter 5.4. Springer-Verlag.Google Scholar
Lighthill, J. 1975 Mathematical Biofluiddynamics, SIAM.CrossRefGoogle Scholar
Liu, H. & Kawachi, K. 1999 A numerical study of undulatory swimming. J. Comput. Phys. 155, 223.CrossRefGoogle Scholar
McCroskey, W. J. 1982 Unsteady airfoils. Annu. Rev. Fluid. Mech. 14, 285.CrossRefGoogle Scholar
Oshima, Y. & Oshima, K. 1980 Vortical flow behind an oscillating foil. In Proc. 15th IUTAM Intl Congress, North Holland, 357.Google Scholar
Platzer, M., Neace, K. & Pang, C. K. 1993 Aerodynamic analysis of flapping wing propulsion. AIAA Paper 93-0484.Google Scholar
Ramamurti, R. & Sandberg, W. 2001 Simulation of flow about flapping airfoils using finite element incompressible flow solver. AIAA J. 39, 253.CrossRefGoogle Scholar
Rosén, M., Spedding, G. R. & Hedenström, A. 2004 The relationship between wingbeat kinematics and vortex wake of a thrush nightingale. J. Exp. Biol. 207, 4255.CrossRefGoogle ScholarPubMed
Spedding, G. R., Hedenström, A. & Rosén, M. 2003 Quantitative studies of the wakes of freely flying birds in a low-turbulence wind tunnel. Experiments Fluids 34, 291.CrossRefGoogle Scholar
Stanek, M. J. & Visbal, M. R. Study of the vortical wake pattern of an oscillating airfoil. AIAA Paper 89-0554.Google Scholar
Streitlien, K. & Triantafyllou, G. S. 1998 On thrust estimates for flapping airfoils. J. Fluids Struct. 12, 47.CrossRefGoogle Scholar
Theodorsen, T. 1935 General theory of aerodynamic instability and the mechanism of flutter. NACA TR 496. http://ntrs.larc.nasa.gov/search.jsp.Google Scholar
Triantafyllou, G. S., Triantafyllou, M. S. & Grosenbaugh, M. A. 1993 Optimal thrust development in oscillating foils with application to fish propulsion. J. Fluids Struct. 7, 205.CrossRefGoogle Scholar
Von Kármán, T. & Burgers, J. M. 1943 General aerodynamic theory—perfect fluids. In Aerodynamic Theory (ed. Durand, W. F.), Division E, vol. II, p. 308. Springer-Verlag.Google Scholar
Von Kármán, T. & Sears, W. R. 1938 Airfoil theory for non-uniform motion. J. Aeronaut. Sci. 5 (10), 379.CrossRefGoogle Scholar
Wilder, M. C., Mathioulakis, D. S., Poling, D. R. & Telionis, D. P. 1996 The formation and internal structure of coherent vortices in the wake of a pitching airfoil. J. Fluids Struct. 10, 3.CrossRefGoogle Scholar
Wu, T. Y. 1971 Hydromechanics of swimming of fishes and cetaceans. Adv. Appl. Mech. 11, 1.CrossRefGoogle Scholar
143
Cited by

Save article to Kindle

To save this article to your Kindle, first ensure coreplatform@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

MTV measurements of the vortical field in the wake of an airfoil oscillating at high reduced frequency
Available formats
×

Save article to Dropbox

To save this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Dropbox account. Find out more about saving content to Dropbox.

MTV measurements of the vortical field in the wake of an airfoil oscillating at high reduced frequency
Available formats
×

Save article to Google Drive

To save this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Google Drive account. Find out more about saving content to Google Drive.

MTV measurements of the vortical field in the wake of an airfoil oscillating at high reduced frequency
Available formats
×
×

Reply to: Submit a response

Please enter your response.

Your details

Please enter a valid email address.

Conflicting interests

Do you have any conflicting interests? *