Some experimental observations of the law of the wall behind large eddy breakup devices using servo-controlled skin friction balances

Nguyen, Viet-Dung; Dickinson, J. T.; Chalifour, Y.; Anderson, J. D.; Lemay, J.; Haeberle, D.; Larose, Guy L.; Jean, Yves

doi:10.2514/6.1984-346

Cited by 15 publications

(3 citation statements)

References 3 publications

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“…Recently, Nguyen, Savill & Westphal (1987) have compared results from three independent manipulator experiments where direct local skin-friction measurements have been obtained using either a drag balance, as in the present experiment and those of Mumford & Savill (1984); Nguyen et al (1984a, b); Lemay et al (1985), or an oil film interferometer (Westphal 1986), and found very good agreement regarding the skin-friction distribution behind a single plate and a tandem configuration. This comparison is extended here by plotting further results from these other 'direct' investigations, together with some of the limited data from Sandborn (1981) on to figures 7 and 8.…”

Section: S K I N Frictionsupporting

confidence: 55%

Manipulation of turbulent boundary layers by outer-layer devices: skin-friction and flow-visualization results

Savill

Mumford

1988

J. Fluid Mech.

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Parametric studies have been made of devices introduced into the outer region of a low-Reynolds-number turbulent boundary layer (Reθ = 1000-3500) with a view to understanding the manner in which such ‘manipulators’ reduce the surface drag. The devices considered were single flat plates, a cylinder with the same drag as one of these, and two plates stacked, staggered, and in tandem, with chord Reynolds numbers Rec in the range 1000-100000. Direct measurements of local skin friction using a floating-plate drag balance are reported together with the results of laser- sheet smoke flow visualization. The skin-friction results are in good agreement with other floating-element data while the visual and photographic studies in both stationary and convected frames completely support the hairpin description of the boundary-layer structure, and reveal that the wake of the device may play a more important role than has previously been suggested. A picture is presented of the interaction of the devices and their wakes with the hairpin eddy structure which could explain the magnitudes and shapes of the skin-friction distributions observed downstream; their dependence on the height, thickness, and if appropriate, length and spacing of the device(s); the optimum values for these parameters; and the existence of a preferred, tandem plate configuration. The results suggest that such plates do not act primarily as large-eddy break-up systems (LEBUs). Instead several ‘active’ mechanisms are identified which supplement the ‘passive’ effect of the imposed momentum defect. The suppression of large-scale motions is one of these, but, a t least for our relatively thick devices, it would appear that it is an interaction between the vortices, introduced into the layer via the wake, and the near-wall structure that provides the principal mechanism for reducing the skin friction. The observation that the maximum skin-friction reduction always occurred close to the position where these vortices reached the sublayer provides strong evidence for such a view.

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Section: S K I N Frictionsupporting

confidence: 55%

Manipulation of turbulent boundary layers by outer-layer devices: skin-friction and flow-visualization results

Savill

Mumford

1988

J. Fluid Mech.

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“…Since the pioneering work of Hefner, Weinstein & Bushnell (1979) and Corke, Guezennec & Nagib (1979), this reduction in skin friction has been confirmed in many laboratory experiments throughout the world. See Nguyen et al (1984), Bandyopadhyay (1986) or Wilkinson et al (1987) for reviews of this experimental work. Typically a maximum local skin-friction reduction of between 15 and 40 % is achieved with some reduction in skin friction persisting over a downstream distance of lOOA-15OA, where A denotes the boundary-layer thickness.…”

Section: Introductionmentioning

confidence: 99%

The effect of large-eddy breakup devices on flow noise

Dowling

1989

J. Fluid Mech.

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The installation of large-eddy breakup devices (LEBUs) or ‘flow manipulators’ in a turbulent boundary layer over a rigid plane surface is known to lead to reductions in skin-friction coefficient, turbulence intensity and fluctuating Reynolds stress. We investigate the effect of such devices on the surface pressure spectrum and the far-field sound radiation. A model problem, in which a two-dimensional elliptical vortex is convected past a LEBU, is solved analytically in the low-Mach-number limit. The main noise source mechanisms are identified in this idealized problem and we go on to obtain scaling laws for the sound produced by a turbulent boundary-layer flow over a LEBU. The introduction of a LEBU reduces the strength of the Lighthill quadrupole source terms, but it produces an additional dipole source. However, the pressure fluctuations in this dipole field decay rapidly with distance from a LEBU, and we find that an array of LEBU's could have a beneficial effect on the flow noise for radian frequencies which are large in comparison with c/30Δ, where c is the sound speed and Δ denotes the boundary-layer thickness. At lower frequencies the LEBUs are predicted to increase the flow noise.

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“…Pineau Nguyen et al (1984), Brlanger (1987) and Pineau (1987). The k-type roughness consisted of 3.175 x 3.175 mm square ribs, distributed regularly normal to the main flow, with a longitudinal pitch of 12.7 m m giving a normalized wavelength 2 equal to 4.…”

Section: Introductionmentioning

confidence: 99%

Re-examination of the scaling roughness function for κ-type rough walls using a servo-controlled wall drag balance

Nguyen

Dickinson

Bélanger

et al. 1989

Experiments in Fluids

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Fig. 4. Velocity vector diagram obtained by the point-by-point analysisby a TV camera and transferred to a computer (Toyooka et al. 1985). A velocity vector diagram of the flow field obtained by the point-by-point analysis is shown in Fig. 4. In this vector diagram errors originate from the fan-like beam scanning in addition to errors from the processing of the fringes. The former errors are related to the distance separated the beam scanner and the plane of observation, angular velocity of the beam sweep and flow velocity, but nomally these errors are negligibly small. The accuracy of this method is expected to be of the same order as that of other methods using different techniques of illumination.The range of flow velocity suitable for this method is limited by the frequency of the beam scanner. The frequency range of the galvanometer scanner used in this experiment is 0-300 Hz, therefore, a practical upper limit of the velocity is about 0.2 m/s. However, it is possible to extend this value to 1 2 m/s by making use of high frequency scanners and a high power CW laser.In conclusion, the application of speckle velocimetry may be expanded with this method. References

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Some experimental observations of the law of the wall behind large eddy breakup devices using servo-controlled skin friction balances

Cited by 15 publications

References 3 publications

Manipulation of turbulent boundary layers by outer-layer devices: skin-friction and flow-visualization results

Manipulation of turbulent boundary layers by outer-layer devices: skin-friction and flow-visualization results

The effect of large-eddy breakup devices on flow noise

Re-examination of the scaling roughness function for κ-type rough walls using a servo-controlled wall drag balance

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