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The control of transient disturbances in a flat plate boundary layer through active wall motion (1989)

Breuer, Kenneth S. ; Haritonidis, Joseph H. ; Landahl, Marten T.

New York, NY : American Institute of Physics (AIP)

Physics of Fluids 1 (1989), S. 574-582

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: Experimental results are presented demonstrating the evolution and control of a large amplitude and highly three-dimensional disturbance in a laminar boundary layer. A localized disturbance was introduced into a laminar boundary layer at Reδ* =1095 by means of a flexible membrane mounted on a flat plate. For low amplitudes, the disturbance initially decayed, leaving a slowly growing wave packet comprised of linearly unstable Orr–Sommerfeld modes. At higher amplitudes, the disturbance grew rapidly, leading to a turbulent spot. The high-amplitude disturbance was acted upon by an active wall counterdisturbance consisting of a traveling bump at the wall. The counterdisturbance was generated by an array of eight small flexible membranes mounted next to one another, flush with the wall and activated in rapid succession. The breakdown of the disturbance to a turbulent spot is shown to be delayed by the active wall motion by approximately 50δ@B|. The active wall motion is shown to inhibit the development of the initial disturbance and to decrease the amplification rate of spanwise vorticity by reducing the level of cross-stream stretching ∂w/∂z.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.857426

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Linear and non-linear mechanisms in boundary layer turbulence (1988)

Landahl, Marten T.

Chichester : Wiley-Blackwell

International Journal for Numerical Methods in Fluids 8 (1988), S. 1183-1193

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ISSN: 0271-2091

Keywords: Engineering ; Engineering General

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: The different stages of bursting and evolution of the fluctuation field in a turbulent boundary layer are governed by mechanisms that may be identified as either predominantly linear, i.e. governed by linear interaction with the mean shear flow, or non-linear, i.e. with interaction between the fluctuation components also being important. Wave number-frequency spectra reveal the presence of damped wave modes that may be modelled from the Orr-Sommerfeld equation. Conditional sampled experimental data for streamwise velocity fluctuations in the wall layer obtained using the variable interval time averaging (VITA) method scale with the threshold level in a manner consistent with linearity. High-amplitude wall pressure peaks show an approximately linear relationship with the associated vertical velocity fluctuations. Non-linearity acts primarily in the near-wall region where the fluctuation velocity is relatively the highest.

Additional Material: 6 Ill.