Research Papers: Flows in Complex Systems

Detection of Laminar Flow Separation and Transition on a NACA-0012 Airfoil Using Surface Hot-Films

[+] Author and Article Information
Azemi Benaissa

e-mail: benaissa-a@rmc.ca

Dominique Poirel

Department of Mechanical and Aerospace Engineering,
Royal Military College of Canada,
Kingston, Ontario K7K 7B4, Canada

Contributed by the Fluids Engineering Division of ASME for publication in the Journal of Fluids Engineering. Manuscript received October 2, 2012; final manuscript received April 9, 2013; published online August 6, 2013. Assoc. Editor: Zvi Rusak.

J. Fluids Eng 135(10), 101104 (Aug 06, 2013) (6 pages) Paper No: FE-12-1490; doi: 10.1115/1.4024807 History: Received October 02, 2012; Revised April 09, 2013

A method for mapping the separation and transition of flow over a slowly pitching airfoil with high angular resolution is presented. An array of surface-mounted hot-film sensors is used to record simultaneous corresponding voltages. The method makes use of windowed correlation and spectral signatures of hot-film sensor voltages in synchronization with a servo-motor controlling airfoil pitch angle. Results are given for a NACA-0012 airfoil at three airspeeds at pitch angles of less than 6 deg. The airspeeds correspond to a region of known aeroelastic instability; they are situated between chord Reynolds numbers of 50,000 and 130,000. Tests in static and quasi-static pitch motion schedules were conducted. The quasi-static airfoil was sinusoidally pitching at 0.025 Hz between −6 deg and +6 deg (corresponding to a half-chord based reduced frequency between 0.0011 and 0.0020) and the detected separation and transition agreed very well with the static case. These results constitute a verification of the method used and provide insight into the size and location of the laminar separation bubble at transitional Reynolds numbers.

Copyright © 2013 by ASME
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Fig. 1

Aerodynamic efficiency of smooth airfoils as a function of the chord-based Reynolds number. (Adapted from McMasters and Henderson [3].)

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Fig. 2

Picture of the test section and the instrumented airfoil

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Fig. 3

Short sample of hot-film voltages near separation

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Fig. 4

Cross correlation coefficient for the static case

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Fig. 5

Spectra of the hot-film signals before and after separation

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Fig. 6

Trailing edge power spectra behind the sensor and the smooth area for α = 0

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Fig. 7

Hot-film signals (left) and corresponding spectra (right)

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Fig. 8

Hot-film voltage signals at a 0 deg angle of attack

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Fig. 9

Hot-film quasi-static signals

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Fig. 10

Cross correlation coefficient for the quasi-static case

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Fig. 11

Separation and transition localization on the airfoil surface; the dotted line represents the oil-flow results of Huang et al. [22]



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