LEBU drag reduction in high Reynolds number boundary layers

Anders, J. B.

doi:10.2514/6.1989-1011

Cited by 15 publications

(9 citation statements)

References 5 publications

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“…First the maximum reduction appears to occur at about 60-706, rather further aft than might have been expected from low-speed results. Second the change in skin friction reduces with decrease in Mach Table 1 number, the measured reduction at M = 0.5 being far less than would be expected from the same low-speed tests, but apparently consistent with the high Reynolds number water tunnel tests by NASA Anders (1989). Locating the LEBU at a lower position in the boundary layer led to a more rapid recovery as expected from the low speed studies.…”

Section: Initial Testssupporting

confidence: 60%

“…chord c> 6 (typicaUy c= 1.5c~), thickness t=0.1 mm and height h =0.75c~ at low Reo, but possibly varying inversely with Re and, for the preferred tandem devices, spacing s = 10-126). Rather fewer experimental data are available for manipulators at high subsonic speeds and high Reynolds numbers, Bertelrud et al (1982) and Anders (1989). This report presents the results of an investigation made in the high-speed tunnels at Cambridge on the boundary-layer development and floating-head skinfriction balance readings downstream of a number of aerofoil (NACA0009) manipulators at Mach numbers between 0.5 and 0.88 in turbulent boundary layers with Ro in the range 10 000-20 000.…”

Section: Introductionmentioning

confidence: 99%

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Experimental results on aerofoil manipulators at high subsonic speeds

Squire

Savill

1996

Experiments in Fluids

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An extensive series of measurements of the boundary layer development and drag downstream of aerofoil manipulators have been made in the high speed tunnels at Cambridge. This work forms part of a combined study with the University of Poitiers into the possible drag reducing properties of manipulators and was supported by Airbus Industrie. Overall the test results showed that the reduction in turbulent skin-friction downstream of the device did not compensate for the drag of the device itself in any of the cases studied, thus no overall drag saving was possible although in certain cases the overall drag penalty was small. This finding suggests that such devices may have a use in regions where a local reduction in skin-friction (and hence possible heat transfer) is needed and a low level of loss can be accepted. However, the actual drag reduction obtained was found to be extremely sensitive to changes in the aerofoil shape and incidence.

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Section: Initial Testssupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Experimental results on aerofoil manipulators at high subsonic speeds

Squire

Savill

1996

Experiments in Fluids

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“…The large range of drag reductions reported in the literature has led to the general overestimation of the magnitude of the Although the data published in Anders (1989) indicate that at the lowest Reynolds number tested a small reduction is possible (approximately 3% ), the author pointed out that due to the large wave drag in the towing tank at these speeds, the error bars were much larger than the drag reduction. (1984); 9 Anders and Watson (1985); 10 Coustols and Cousteix (1985); 11 Lemay et al (1985); 12 Poddar and van Atta (1985); 13 Bandyopadhyay (1985); 14 Papathanasiou and Nagel (1986); 15 Rashidnia and Falco (1986); 16 Sahlin et al (1986); 17 Westphal (1986); 18 Lynn (1987); 19 Poll and Westland (1987); 20 Sahlin et al (1988); 21 Anders (1989); 22 Lynn et al (1989); 23 Present data effect to be expected from LEBU manipulators.…”

Section: Introductionmentioning

confidence: 99%

Direct drag measurements in a turbulent flat-plate boundary layer with turbulence manipulators

Lynn

Bechert²,

Gerich

1995

Experiments in Fluids

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The effect of turbulence manipulators on the turbulent boundary layer above a flat plate has been investigated. These turbulence manipulators are often referred to as Large Eddy Break Up (LEBU) devices. The basic idea is that thin blades or airfoils are inserted into the turbulent flow in order to reduce the fluctuating vertical velocity component v' above the flat plate. In this way, the turbulent momentum transfer and with it the wall shear stress downstream of the manipulator should be decreased. In our experiments, for comparison, a merely drag-producing wire also was inserted into the boundary layer.In particular, the trade-off between the drag of the turbulence manipulator and the drag reduction due to the shear-stress reduction on the flat plate downstream of the manipulator has been considered. The measurements were carried out with very accurate force balances for both the manipulator drag and the shear stress on the flat plate. As it turns out, no net drag reduction is found for a fairly large set of configurations. A single thin blade as a manipulator performed best, i.e., it was closest to break-even. However, a further improvement is unlikely, because the device drag of the thin blade elements used here has already been reduced to only that due to laminar skin friction, and is thus the minimum possible drag. Airfoils performed slightly worse, because their device drag was higher. A purely drag-producing wire device performed disastrously. The wire device, which consisted of a wire with another thin wire wound around it to suppress coherent vortex shedding and vibration, was designed to have (and did have) the same drag as the airfoil manipulator with which it was compared. The comparison showed that airfoil and blade manipulators recovered 75-90% of their device drag through a shear-stress reduction downstream, whereas the wire device recovered only about 25-30% of its device drag.Conventional LEBU manipulators with airfoils or thin blades produce between 0.25% and 1% net drag increase, whereas the wire device (with equal device drag) produces as much as 4% net drag increase. These data are valid for the specific plate length of our experiments, which was long enough in downstream extent to realize the full effect of the LEBU manipulators. Turbulence manipulators do indeed decrease the turbulent momentum exchange in the boundary layer by "rectifying" the turbulent fluctuations. This generates a significant shear-stress reduction downstream, which is much more than just the effect of the wake of the manipulator. However, the device drag of the manipulator cannot be reduced without simultaneously reducing the skin friction reduction. Thus, the manipulator's device drag exceeds, or at best cancels, the drag reduction achieved by the shear-stress reduction downstream. A critical survey of previous investigations shows that the suggestion that turbulence manipulators may produce net drag reduction is also not supported by the available previous drag force measurements. The issue had been stirred up by les...

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“…That is, device chord Reynolds numbers of less than 7 x 10 4 and host turbulent boundary-layer momentum thickness Reynolds numbers of less than 7 x 10 3 . Since application of manipulators to aircraft drag reduction will require operation at chord Reynolds numbers of 3-5 x 10 5 and momentum thickness Reynolds numbers of 3-7 x 10 4 , Anders 41 and Sahlin et al 40 have conducted experimental studies in water tow tanks to investigate manipulator performance at high Reynolds numbers. 21 Low values of the host boundary-layer momentum thickness Reynolds number are also of some concern.…”

Section: Turbulence Modifications and Possible Mechanismsmentioning

confidence: 99%

Outer-Layer Manipulators for Turbulent Drag Reduction

1990

Viscous Drag Reduction in Boundary Layers

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LEBU drag reduction in high Reynolds number boundary layers

Cited by 15 publications

References 5 publications

Experimental results on aerofoil manipulators at high subsonic speeds

Experimental results on aerofoil manipulators at high subsonic speeds

Direct drag measurements in a turbulent flat-plate boundary layer with turbulence manipulators

Outer-Layer Manipulators for Turbulent Drag Reduction

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