The cancellation of a sound-excited Tollmien–Schlichting wave with plate vibration

Gedney, Charles

doi:10.1063/1.864275

Cited by 26 publications

(3 citation statements)

References 3 publications

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“…The twodimensional nature of TS waves allows cancellation using a simple linear wave superposition technique. The counter-disturbance wave has been generated using wall motion (Schilz 1965/66;Gedney 1983), a vibrating wire (Milling 1981;Thomas 1983) and surface heaters (Liepmann, Brown & Nosenchuck 1982). In all of these examples, the phase of the cancelling wave generator was tuned to achieve maximum attenuation of the TS wave.…”

Section: Transition Delaymentioning

confidence: 99%

Active control of streamwise vortices and streaks in boundary layers

1998

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Coherent structures play an important role in the dynamics of turbulent shear flows. The ability to control coherent structures could have significant technological benefits with respect to flow phenomena such as skin friction drag, transition, mixing, and separation. This paper describes the development of an actuator concept that could be used in large arrays for actively controlling transitional and turbulent boundary layers. The actuator consists of a piezoelectrically driven cantilever mounted flush with the flow wall. When driven, the resulting flow disturbance over the actuator is a quasi-steady pair of counter-rotating streamwise vortices with common-flow away from the wall. The vortices decay rapidly downstream of the actuator; however, they produce a set of high-and low-speed streaks that persist far downstream (well over 40 displacement thicknesses). The amplitude of the actuator drive signal controls the strength of the generated vortices. The actuator is fast, compact, and generates a substantial disturbance in the flow. Its performance has been demonstrated using a small array of sensors and actuators in low-speed water laminar boundary layers with imposed steady and unsteady disturbances. Experiments are reported in which transition from a large disturbance was delayed by 40 displacement thicknesses, and in which the mean and spanwise variation of wall shear under an array of high-and low-speed streaks was substantially reduced downstream of a single transverse array of actuators. † Present address:

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Section: Transition Delaymentioning

confidence: 99%

Active control of streamwise vortices and streaks in boundary layers

1998

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“…Even in the absence of tunnel resonance, an example of how the flow itself may interact with the sound field to set up a 'standing-wave' pattern is Leehey & Shapiro's (1977) boundary-layer experiment ; a streamwise interference pattern is observed by them, due to the difference in the phase velocities of the exciting sound wave and the resulting Tollmien-Schlichting waves. In passing, it is worth emphasizing that in calculating the fluid-particle velocity due to an imposed sound field, such as was done in the receptivity experiments of Gedney (1983) and Aizin & Polyakov (see Nishioka & Morkovin 1985), one must carefully avoid, or duly consider the presence of, any such standing wave.…”

Section: Effect Of Acoustic Excitation Onmentioning

confidence: 99%

Effect of acoustic excitation on the flow over a low- Re airfoil

1987

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Wind-tunnel measurements of lift, drag and wake velocity spectra were carried out under (tonal) acoustic excitation for a smooth airfoil in the chord-Reynolds-number (Rec) range of 4 × 104−1.4 × 105. The data are supported by smoke-wire flowvisualization pictures. Small-amplitude excitation in a wide, low-frequency range is found to eliminate laminar separation that otherwise degrades the airfoil performance at low Rec near the design angle of attack. Excitation at high frequencies, scaling as $U_{\infty}^{\frac{3}{2}}$, eliminates a pre-stall, periodic shedding of large-scale vortices; U∞ is the free-stream velocity. Significant improvement in lift is also achieved during post-stall, but with large-amplitude excitation. Wind-tunnel resonances strongly influence the results, especially in cases requiring large amplitudes. It is shown that large transverse velocity fluctuations, induced near the airfoil by specific cross-resonance modes, lead to the most effective separation control; resonances inducing only large-amplitude pressure fluctuations are demonstrated to be less effective.

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“…In this regard, the asymptotic analysis of Goldstein (1983aGoldstein ( , 1983b is encouraging in that it appears to be the first step in analyzing the leading-edge/acoustic-wave problem. The recent e..perimental work of Leehey and Shapiro (1980) and Gedney (1983) did not focus on the leading edge, and their results have not been completely conclusive. The recent work is summarized by Reshotko (1984) and Goldstein and Hultgren (1989).…”

Section: Completed Workmentioning

confidence: 97%

Navier-Stokes Simulation of Boundary-Layer Transition

Reed¹

1990

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The cancellation of a sound-excited Tollmien–Schlichting wave with plate vibration

Cited by 26 publications

References 3 publications

Active control of streamwise vortices and streaks in boundary layers

Active control of streamwise vortices and streaks in boundary layers

Effect of acoustic excitation on the flow over a low- Re airfoil

Navier-Stokes Simulation of Boundary-Layer Transition

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