New results, a review and synthesis of the mechanism of turbulence production in boundary layers and its modification

Falco, R. E.

doi:10.2514/6.1983-377

Cited by 38 publications

(39 citation statements)

References 16 publications

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“…[12][13][14] In this regard, Falco, Klewicki, and Pan 15 and later Klewicki and Falco, 16 and Klewicki and Hill 17 showed that the other, statistically more significant, contribution to the two-point z correlation comes from the inverse arrangement in which a patch of positive z (and in many cases positive z ) is positioned above a region of negative z . Consistent with previous observations of passive contaminants, 18,19 Falco,Klewicki,and Pan 15 proposed that these contributions to the correlation come from intermediate scale, positive z bearing motions, that are advected toward the surface from greater wallnormal locations, and in doing so invoke a sublayer response involving streaks, pockets, hairpin-like vortices, and shear layers. Examination of the near-wall z probability density function 20 (see also, Metzger and Klewicki, 14 Rajagopalan and Antonia 21 ) and employing the constraints imposed by the solenoidal condition on the vorticity field led Klewicki et al 20 to conclude that the simplest eddy bearing positive z comes in the form of a closed loop or ring-like motion.…”

Section: Introductionsupporting

confidence: 70%

“…In addition, Johansson, Alfredson, and Kim 25 were able to map out a number of the flow properties local to the shear layers as detected by their variable interval spatial averaging (VISA) technique: the spatial analog of the VITA technique. Interestingly, comparison indicates that the flows local to shear layers have a number of similarities with the flow fields local to sublayer pockets, 15,18,19,23,26 that have been visually detected using a distributed sheet of passive marker. As it relates to issues concerning probe-based versus visualbased event detections, Kline and Robinson 11 allude to the important point that, while probe sampling techniques inherently have a greater degree of quantitative statistical precision, by their very nature passive marker traces provide the visual assurance that one is indeed looking at the motion of interest.…”

Section: Introductionmentioning

confidence: 95%

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Flow field properties local to near-wall shear layers in a low Reynolds number turbulent boundary layer

Klewicki

Hirschi

2004

Physics of Fluids

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Combined hot-wire anemometry and flow visualizations are used to explore the properties of near-wall shear layers in a low Reynolds number turbulent boundary layer ͑R = U ϱ / Х 1200͒. The experiments employed two four-element probes positioned in the buffer layer. Data from these sensors were acquired synchronously with high speed, dual view, 35 mm movies of vaporized mineral oil fog illuminated via two orthogonal laser sheets. Near-wall shear layers were identified as satisfying the visual criterion of a narrow fissure of passive marker moving upward through the buffer layer in concert with a strong deceleration in the axial velocity trace. The present results reveal that the local flow fields satisfying these criteria regularly contain adjacent and spatially compact regions of opposing-sign spanwise vorticity z in the streamwise/wall-normal plane. A number of features were identified relative to whether z at the upper probe was positive or negative. In this regard, the configuration with positive z located above a region of negative z correlated with a more rapid wall-normal transport of the passive marker. Conditionally averaged measurements indicate that the flows local to near-wall shear layers have an attenuated opposing effect relative to the long time v z contribution to the Reynolds stress gradient. Overall, these observations point to the change-of-scale mechanism rather than gradient transport in establishing the large Reynolds stress gradient in the buffer layer. Both spatial configurations of z were revealed to have association with an advective acceleration upstream of the detected shear layer. The scale of this accelerated region was larger for the condition of negative z located above a region of positive z . The detection of near-wall shear layers had a strong visual correlation with clusters of spanwise vortices, often occurring in counter-rotating pairs.

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Section: Introductionsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 95%

Flow field properties local to near-wall shear layers in a low Reynolds number turbulent boundary layer

Klewicki

Hirschi

2004

Physics of Fluids

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“…As noted earlier, Falco (1977Falco ( , 1983Falco ( , 1991) present many flow visualizations and schematics of spatially coincident prograde and retrograde vortex cores in the streamwise-wall-normal plane, nearly always with the prograde core oriented above and downstream of the retrograde core. This arrangement is consistent with one of the preferred orientations presented herein.…”

Section: Discussionmentioning

confidence: 99%

“…The flow visualizations and an idealized schematic of these structures in Falco (1977) show that typical eddies appear as spatially coincident prograde and retrograde spanwise vortices when sliced in the streamwise-wall-normal plane. Falco (1977Falco ( , 1983Falco ( , 1991 offer little discussion regarding a preferred orientation for typical eddies except to state that the idealized schematic in Falco (1977) (which portrays the prograde core above and slightly downstream of the retrograde core) represents the "commonly-observed view" of such a structure in the streamwise-wall-normal plane. More recently, Klewicki & Hirschi (2004) observed that near-wall shear layers often occur in close proximity to clusters of prograde structures as well as adjacent regions of opposing-sign ω z , with the retrograde event either above or below the prograde event.…”

Section: Introductionmentioning

confidence: 99%

Spatial signatures of retrograde spanwise vortices in wall turbulence

Natrajan

Christensen

2007

J. Fluid Mech.

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The spatial signatures of retrograde spanwise vortices in wall turbulence are assessed from particle-image velocimetry measurements in the streamwise-wall-normal plane of a zero-pressure-gradient turbulent boundary layer at Re τ ≡ u * δ/ν = 2350. The present results suggest that a proportion of retrograde spanwise vortices have a welldefined spatial relationship with neighbouring prograde vortices. Two-point crosscorrelations and conditionally averaged velocity fields given a retrograde vortex reveal that such structures are typically oriented either upstream of and below or downstream of and above a prograde core. While these pairings are consistent with the typical-eddy patterns reported by Falco and co-workers, we offer an alternative interpretation for a proportion of these retrograde/prograde pairs. In particular, the arrangement of a retrograde spanwise vortex upstream of and below a prograde core is also consistent with the spatial signature revealed if an omega-shaped hairpin structure were sliced through its shoulder region by a fixed streamwise-wall-normal measurement plane.

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“…However, significant numbers of retrograde spanwise vortices, positive w. cores, were also observed, with their largest populations noted at the outer edge of the log layer. Observations of retrograde spanwise vortices have been reported by Falco (1977), Falco (1983) and Falco (1991), among others, and their occurrence spatially-coincident to prograde spanwise vortices in the outer layer of wall turbulence is often interpreted as the imprint of ring-like structures. More recently, Klewicki & Hirschi (2004) reported observations of hairpin vortices and retrograde structures clustered in the neighborhood of intense near-wall shear layers, with the influence of retrograde structures increasing with Reynolds number.…”

Section: "Outside the Roughness (Or Viscous) Sublayer The Turbulent mentioning

confidence: 99%

Studies of Real Roughness Effects for Improved Modeling and Control of Practical Wall-Bounded Turbulent Flows

Christensen¹,

Wu²

2008

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The public reporting burden for this collection of information is estimated to average 1 hour per response. including the time for reviewing instructions, sea"hing existing data soUrces, gathering and maintaining the data needed, and completing and reviewving the collection of infomation. Send comments regaliong this burden estimate or any otiler aspect of tts collection of information. including suggestions for reducing fhe burden, to the Department of Defense, Executive Service Directorate (0704-0188). Respondents should be aware that notwithstanding any other provision of law. no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a curently valid OMB control number. PLEASE DO NOT RETURN YOUR A F R L S R SUPPLEMENTARY NOTES ABSTRACTThe present effort investigates the effects of practical roughness replicated from a turbine blade damaged by deposition of foreign material. statistical and structural characteristics of wall turbulence. Two-dimensional particle image velocimetry (PIV) measurements are performed in the streamwise-wall-normal plane of turbulent boundary layers at momentum Reynolds numbers of 8000 and 13000. The surface conditions include a smooth wall and two highly-irregular rough walls. These rough surfaces have the same roughness topography but differ in spatial scaling. The validity of Townsend's wall similarity hypothesis in the presence of practical roughness is assessed and the impact of this roughness on the spatial structure of the flow is investigated. In addition, stereoscopic PIV measurements are made in streamwise-spanwise planes of smooth-and rough-wall turbulent boundary layers both within and at the outer edge of the roughness sublayer. This data is used to explore the impact of dominant topographical features on the near-wall flow as well as the influence of practical roughness on the spatial organization of the flow.Understanding such effects provides a stepping stone toward efficient modeling and control of practical flows in the presence of roughness. SUBJECT TERMS

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New results, a review and synthesis of the mechanism of turbulence production in boundary layers and its modification

Cited by 38 publications

References 16 publications

Flow field properties local to near-wall shear layers in a low Reynolds number turbulent boundary layer

Flow field properties local to near-wall shear layers in a low Reynolds number turbulent boundary layer

Spatial signatures of retrograde spanwise vortices in wall turbulence

Studies of Real Roughness Effects for Improved Modeling and Control of Practical Wall-Bounded Turbulent Flows

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