Skin friction drag measurements by LDV

Mazumder, Malay K.; Wanchoo, S.; McLeod, P. C.; Ballard, G. S.; Mozumdar, S.; Caraballo, Nemesio

doi:10.1364/ao.20.002832

Cited by 18 publications

(13 citation statements)

References 7 publications

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“…Near-wall LDA measurements do not suffer from the same difficulty as hot wire measurements (e.g. Mazumder et al, 1981) and should in principle allow a reasonably accurate estimate of U~ from (2) [e.g. Reischman and Tiederman, 1975;Neiderschulte et al, 1990].…”

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LDA measurements in low Reynolds number turbulent boundary layer

Djenidi

Antonia

1993

Experiments in Fluids

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LDA measurements of the mean velocity 0 in a low Reynolds number turbulent boundary layer allow a direct estimate of the friction velocity U~ from the value of ~O/~y at the wall. The trend of the Reynolds number dependence of O + = O/U~ is similar to the direct numerical simulations of Spalart (1988). I IntroductionA source of difficulty in low R o turbulent boundary layers is the accurate determination of the friction velocity U~. At such Reynolds numbers there is no rigorous basis for the log law, viz. + = x -i In y+ +C(1) (where x and C are constants; standard notation is used) and therefore no reason why low R o effects cannot penetrate well into the buffer layer. Consequently, the use of the Clauser chart technique [which is based on (1)] and of the Preston tube method may not be accurate. Under these conditions, a more direct and reliable estimate of U~ (=--w'rl/2, Tw is the kinematic wall shear stress) from the slope of the mean velocity profile at the wall using the relation rw = v .(2) y=0The use of (2) is prohibitive when a hot wire is used because of the wall conduction problem. Near-wall LDA measurements do not suffer from the same difficulty as hot wire measurements (e.g. Mazumder et al., 1981) and should in principle allow a reasonably accurate estimate of U~ from (2) [e.g. Reischman and Tiederman, 1975;Neiderschulte et al., 1990]. The purpose of this note is to show that U~ can be determined with sufficient accuracy from (2) to allow the effect of R o on 0 + to be assessed. Experimental conditions and procedure Experimental conditionsThe measurements were made in a closed circuit vertical water tunnel which consists of a constant head recirculating two-tank system (a brief description of the tunnel is given in Zhou and Antonia, 1992). The working section has a vertical square cross-section (0.26 m • 0.26 m) with a height of 2 m. All walls of the cross section are transparent (20 mm thick perspex). One of the walls, which is removable, was used as the smooth wall for the present boundary layer study. The maximum value of U1, the free stream velocity, is about 42 cm/s. At this speed, the boundary layers on the working section wall are laminar. Tripping was therefore required to achieve a turbulent regime. Three-dimensional roughness elements (pebbles of about 4.5 mm in height) were glued onto a 30 mm large perspex strip. This strip was recessed into a groove, located approx. 10 cm downstream of the contraction exit, so that the side of the strip onto which the pebbles were glued was flush with the working section wall. The measurement station was located 1,100 mm downstream of the trip. The boundary layer thickness 6 is about 35 mm at this station. Three values of R o (560, 1,033, 1,320) were used. Spalart (1988) reported direct numerical simulation (DNS) results for R o = 300, 670 and 1,410. In the present investigation, it was not possible to achieve Ro values less than about 500. Visualisations of dye injected at the wall and in the flow revealed that the boundary layer was laminar for R o < 500. ...

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confidence: 99%

LDA measurements in low Reynolds number turbulent boundary layer

Djenidi

Antonia

1993

Experiments in Fluids

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“…The skin friction coefficient C f is often used to describe the skin friction, which is the ratio between the shear stress and the dynamic pressure of the freestream [41,42,47]. The definition of C f in the wind channel is…”

Section: Bionic Wing Models Fabrication and Experimental Methodsmentioning

confidence: 99%

“…Here, wall shear stress τ w can be calculated by Eq. (3) as the following [41,46]:…”

Section: Bionic Wing Models Fabrication and Experimental Methodsmentioning

confidence: 99%

“…It is revealed that dragonfly wing has corrugated configuration, which could also improve the aerodynamic performance in the flow field of low Re [37][38][39][40]. It has been reported that the wavy structure on the skins of dolphin makes positive contribution on the drag reduction [41,42]. However, it remains unclear how the polygonal shapes of the wing indirectly affect the skin friction and the dragonfly aerodynamic behaviors.…”

Section: Introductionmentioning

confidence: 99%

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The Effect of Bionic 3D Printed Structure Morphology on Skin Friction

Zhang

Ito

Wang

et al. 2021

Journal of Tribology

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Dragonfly has remarkable flight efficiency, with unique wing structural properties such as the surface topological vein structures, corrugation, et al. The object of this paper is to identify how the polygonal patterns of the samples with bionic wing veins affected the skin friction. Four kinds of polygonal 3D patterns were designed and fabricated by additive manufacturing technology, and the skin friction coefficients (Cf) of various models were measured by the wind channel experiments. The quantitative effects of models on Cf with different Reynolds numbers (Re) in laminar, transitional and turbulent flow conditions were obtained. Results indicated that the law of whole change of the skin friction coefficient vs. Re is the same for all patterns which can be expressed by an empirical formula Cf = kReα. The model with mixed square and pentagonal patterns always generates the highest skin friction in the different flow conditions, which was speculated to play important role on the attenuation of the flow separation of the dragonfly wing.

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“…Methods (i) and (ii) require a small detection volume for high spatial resolution. This prerequisite has been fulfilled by a small cross section of the two laser beams [4], reduction of the measurement volume's extent by beam stops [5], the use of spatially low-coherent light [6] or coincident measurements of multi-component LDA systems [7]. The mechanical scanning of the detection volume necessary for method (i), does not allow real-time velocity measurements.…”

Section: Introductionmentioning

confidence: 99%

Measurement of velocity gradients in boundary layers by a spatially resolving laser Doppler sensor

et al. 2001

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A novel laser Doppler technique is presented to measure flow fields with micro-scale resolution. The realized laser Doppler sensor provides distributed velocity measurements inside a defined measurement volume. Two laser wavelengths are used to accomplish two Doppler frequency measurements, which determine the position and the velocity of a scattering particle. Repeating of these measurements determines the velocity gradient of the flow. One application area is the evaluation of the velocity variations in boundary layers of flows close to a wall. This contribution presents the principle and experimental results of the spatially resolving laser Doppler velocity sensor. Different concepts on the optical arrangements as well as the signal processing technique are discussed. A scheme for the construction of a miniaturized fiber-coupled sensor is presented, which allows its integration into flow channels.

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Skin friction drag measurements by LDV

Cited by 18 publications

References 7 publications

LDA measurements in low Reynolds number turbulent boundary layer

LDA measurements in low Reynolds number turbulent boundary layer

The Effect of Bionic 3D Printed Structure Morphology on Skin Friction

Measurement of velocity gradients in boundary layers by a spatially resolving laser Doppler sensor

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