Hostname: page-component-78c5997874-t5tsf Total loading time: 0 Render date: 2024-11-19T04:43:17.019Z Has data issue: false hasContentIssue false
  • English
  • Français

A natural low-frequency oscillation of the flow over an airfoil near stalling conditions

Published online by Cambridge University Press:  26 April 2006

K. B. M. Q. Zaman ,
D. J. Mckinzie  and
C. L. Rumsey
K. B. M. Q. Zaman
Affiliation:
NASA Lewis Research Center, Cleveland, OH 44135, USA
D. J. Mckinzie
Affiliation:
NASA Lewis Research Center, Cleveland, OH 44135, USA
C. L. Rumsey
Affiliation:
NASA Langley Research Center, Hampton, VA 23665, USA
Get access Rights & Permissions [Opens in a new window]

Abstract

An unusually low-frequency oscillation in the flow over an airfoil is studied experimentally as well as computationally. Wind-tunnel measurements are carried out with two-dimensional airfoil models in the chord Reynolds number (Rc) range of 0.15 × 105−3.0 × 105. During deep stall, at α [gsim ] 18°, the usual ‘bluff-body shedding’ occurs at a Strouhal number, Sts ≈ 0.2. But at the onset of static stall around α = 15°, a low-frequency periodic oscillation is observed, the corresponding Sts being an order of magnitude lower. The phenomenon apparently takes place only with a transitional state of the separating boundary layer. Thus, on the one hand, it is not readily observed with a smooth airfoil in a clean wind tunnel, while on the other, it is easily removed by appropriate ‘acoustic tripping’. Details of the flow field for a typical case are compared with a case of bluff-body shedding. The flow field is different in many ways from the latter case and does not involve a Kármán Vortex street. The origin of the flow fluctuations traces to the upper surface of the airfoil and is associated with a periodic switching between stalled and unstalled states. The mechanism of the frequency selection remains unresolved, but any connection to blower instabilities, acoustic standing waves or structural resonances has been ruled out.

A similar result has been encountered computationally using a two-dimensional Navier–Stokes code. While with the assumption of laminar flow, wake oscillation akin to the bluff-body shedding has been observed previously, the Sts is found to drop to about 0.03 when a ‘turbulent’ boundary layer is assumed. Details of the flow field and unsteady forces, computed for the same conditions as in the experiment, compare reasonably well with the experimental data.

The phenomenon produces intense flow fluctuations imparting much larger unsteady forces to the airfoil than that experienced in bluff-body shedding, and may represent the primary aerodynamics of stall flutter of blades and wings.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 202 , May 1989 , pp. 403 - 442
Copyright
© 1989 Cambridge University Press

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, W. K., Thomas, J. L. & Rumsey, C. L., 1984 Application of thin layer Navier–Stokes equations near maximum lift. AIAA Paper 84–0049.Google Scholar
Armstrong, E. K. & Stevenson, M. A., 1960 Some practical aspects of compressor blade vibration. J. R. Aero. Soc. 64, 117–130.Google Scholar
Baker, J. E.: 1955 The effects of various parameters, including Mach number, on propeller blade flutter with emphasis on stall flutter. NACA TN-3357.Google Scholar
Brooks, T. F. & Schlinker, R. H., 1983 Progress in rotor broadband noise research. Vertica 7, 287–307.Google Scholar
Carmichael, B. H.: 1981 Low Reynolds number airfoil survey. vol. I. NASA Contractor Rep. 165803.Google Scholar
Cendenese, A., Cerri, G. & Ianetta, S., 1981 Experimental analysis of the wake behind an isolated cambered airfoil. Proc. IUTAM Symp. Unsteady Turbulent Shear Flows, pp. 272–284. Springer.
Ericsson, L. E.: 1986 Effect of Karman vortex shedding on airfoil flutter. AIAA Paper 86–1789.Google Scholar
Farren, W. S.: 1935 The reaction on a wing whose angle of incidence is changing rapidly. Wind tunnel experiments with a short period recording balance. Rep. & Mem. 1648. Aeronautics Laboratory, Cambridge.
Halfman, R. L., Johnson, H. C. & Haley, S. M., 1951 Evaluation of high-angle-of-attack aerodynamic-derivative data and stall-flutter prediction techniques. NACA TN-2533Google Scholar
Jones, B. M.: 1933 An experimental study of the stalling of wings. Aero. Res. Counc. R & M 1588. Aeronautics Laboratory, Cambridge.
Jones, B. M.: 1934 Stalling. J. R. Aeronaut. Soc. 38, 753–770.Google Scholar
Kibens, V.: 1979 Discrete noise spectrum generated by an acousically excited jet. AIAA Paper 79-0592.Google Scholar
Mangalam, S. M., Bar-Sever, A., Zaman, K. B. M. Q. & Harvey, W. D. 1986 Transition and separation control on a low-Reynolds-number airfoil. Proc. Intl Conf. on Aerodynamics at Low Reynolds Numbers, London.Google Scholar
McCroskey, W. J., Carr, L. W. & McAlister, K. W., 1975 Dynamic stall experiments on oscillating airfoils. AIAA Paper 75–125.Google Scholar
McCullough, G. B. & Gault, D. E., 1951 Examples of three representative types of airfoil-section stall at low speed. NACA TN-2502.Google Scholar
Moss, N. J.: 1979 Measurements of aerofoil unsteady stall properties with acoustic flow control. J. Sound Vib. 65, 505–520.Google Scholar
Motallebi, F. & Norbury, J. F., 1981 The effect of base bleed on vortex shedding and base pressure in compressible flow. J. Fluid Mech. 110, 273–292.Google Scholar
Mueller, T. J.: 1985 Low Reynolds number vehicles. AGARD-AG-288.Google Scholar
Parker, R.: 1966 Resonance effects in wake shedding from parallel plates: some experimental observations. J. Sound Vib. 4, 62–72.Google Scholar
Rockwell, D.: 1983 Oscillations of impinging shear layers. AIAA J. 21, 645–664.Google Scholar
Roshko, A.: 1954 On the drag and shedding frequency of two-dimensional bluff bodies. NACA TN-3169.Google Scholar
Rumsey, C. L.: 1987 A computational analysis of flow separation over five different airfoil geometries at high angles-of-attack. AIAA Paper 87-0188.Google Scholar
Rumsey, C. L., Thomas, J. L., Warren, G. P. & Liu, G. C., 1986 Upwind Navier–Stokes solutions for separated periodic flows. AIAA Paper 86-0247.Google Scholar
Schlichting, H.: 1979 Boundary Layer Theory. McGraw-Hill.
Simpson, R. L.: 1985 Two-dimensional turbulent separated flow. AGARDograph 287.Google Scholar
Sreenivasan, K. R.: 1985 Transitional and turbulent wakes and chaotic dynamical systems. In Nonlinear Dynamics of Transcritical Flows, pp. 59–80. Springer.
Thomas, A. S. W.: 1987 The unsteady characteristics of laminar juncture flow. Phys. Fluids 30, 283–285.Google Scholar
Townsend, J. C., Rudy, D. H. & Sirovich, L., 1987 Computation and analysis of a cylinder wake flow. Presented at the ASME Fluids Engineering Spring Conference, Cincinnati, Ohio, June 15–17.Google Scholar
Van Atta, C. W. & Gharib, M. 1987 Ordered and chaotic vortex streets behind circular cylinders at low Reynolds numbers. J. Fluid Mech. 174, 113–133.Google Scholar
Van Dyke, M. 1982 An Album of Fluid Motion. Parabolic.
Zaman, K. B. M. Q.: 1985 Far-field noise of a subsonic jet under controlled excitation. J. Fluid Mech. 152, 83–111.Google Scholar
Zaman, K. B. M. Q., Bar-Sever, A. & Mangalam, S. M. 1987 Effect of acoustic excitation on the flow over a low-Re airfoil. J. Fluid Mech. 182, 127–148.Google Scholar
Zaman, K. B. M. Q. & Hussain, A. K. M. F. 1981a Turbulence suppression in free shear flows by controlled excitation, J. Fluid Mech. 103, 133–159.Google Scholar
Zaman, K. B. M. Q. & Hussain, A. K. M. F. 1981b Taylor hypothesis and large-scale coherent structures. J. Fluid Mech. 112, 379–396.Google Scholar
Zaman, K. B. M. Q. & Hussain, A. K. M. F. 1984 Natural large-scale structures in the axisymmetric mixing layer. J. Fluid Mech. 138, 325–351.Google Scholar
Zaman, K. B. M. Q. & McKinzie, D. J. 1988 A natural low frequency oscillation in the wake of an airfoil near stalling conditions. AIAA Paper 88-0131.Google Scholar
Zaman, K. B. M. Q. & McKinzie, D. J. 1989 Control of ‘laminar separation’ over airfoils by acoustic excitation. AIAA Paper 89-0565.Google Scholar