Near-field flow structure of a confined wall jet on flat and concave rough walls

Albayrak, Ismail; Hopfinger, Emil J.; Lemmin, Ulrich

doi:10.1017/s0022112008001444

Cited by 20 publications

(32 citation statements)

References 27 publications

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“…He reported the formation of Görtler instabilities in the outer part of the velocity profile (at the interface and above) where the density stratification is weak, which modify vertical mixing and the vertical turbulent transport. Albayrak, Hopfinger & Lemmin (2008) studied a wall jet on a concave boundary and reported significant changes in the boundary layer characteristics when Görtler instabilities were present. We performed cross-stream slit lighting and dye injections at the boundary but could not detect any Görtler vortices near the boundary for the parameter range investigated.…”

Section: Discussionmentioning

confidence: 99%

Development of gravity currents on rapidly changing slopes

2017

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Gravity currents often occur on complex topographies and are therefore subject to spatial development. We present experimental results on continuously supplied gravity currents moving from a horizontal to a sloping boundary, which is either concave or straight. The change in boundary slope and the consequent acceleration give rise to a transition from a stable subcritical current with a large Richardson number to a Kelvin–Helmholtz (KH) unstable current. It is shown here that depending on the overall acceleration parameter $\overline{T_{a}}$, expressing the rate of velocity increase, the currents can adjust gradually to the slope conditions (small $\overline{T_{a}}$) or go through acceleration–deceleration cycles (large $\overline{T_{a}}$). In the latter case, the KH billows at the interface have a strong effect on the flow dynamics, and are observed to cause boundary layer separation. Comparison of currents on concave and straight slopes reveals that the downhill deceleration on concave slopes has no qualitative influence, i.e. the dynamics is entirely dominated by the initial acceleration and ensuing KH billows. Following the similarity theory of Turner 1973 (Buoyancy Effects in Fluids. Cambridge University Press), we derive a general equation for the depth-integrated velocity that exhibits all driving and retarding forces. Comparison of this equation with the experimental velocity data shows that when $\overline{T_{a}}$ is large, bottom friction and entrainment are large in the region of appearance of KH billows. The large bottom friction is confirmed by the measured high Reynolds stresses in these regions. The head velocity does not exhibit the same behaviour as the layer velocity. It gradually approaches an equilibrium state even when the acceleration parameter of the layer is large.

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Section: Discussionmentioning

confidence: 99%

Development of gravity currents on rapidly changing slopes

2017

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“…Görtler vortices have been rarely and/or hardly identified in geophysical flows, such as boundary layer flow around a hill [Tani, 1962;Finnigan, 1983;Kaimal and Finnigan, 1994], gravity or stratified flows along a surface [Bradshaw, 1969;Scotti, 2008], and channel and tidal flows with sediment erosion [Hopfinger et al, 2004;Albayrak et al, 2008]. The present results bring a few ideas of how to track Görtler instability for in situ flow configurations.…”

Section: Toward In Situ Evidence Of Görtler Vortices?mentioning

confidence: 99%

“…For environmental fluid configurations, it is well known that Görtler instability exists in the nature and is strongly related to orographic and streamline curvature and wind shear [Bradshaw, 1969;Finnigan, 1983;Kaimal and Finnigan, 1994;Hopfinger et al, 2004;Albayrak et al, 2008;Scotti, 2008]. Many laboratory experiments have been designed to analyze precisely the effect of both concave and convex slopes on turbulent boundary layer development [Tani, 1962;Hoffmann et al, 1985;Muck et al, 1985;Swearingen and Blackwelder, 1987].…”

Section: Introductionmentioning

confidence: 99%

Large‐Eddy Simulation of a katabatic jet along a convexly curved slope: 2. Evidence of Görtler vortices

Brun

2017

JGR Atmospheres

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This paper is the second part of a study of katabatic jet along a convexly curved slope with a maximum angle of about 35.5°. Large‐Eddy Simulation (LES) is performed with a special focus on the outer‐layer shear of the katabatic jet. In the first part, a basic statistical quantitative analysis of the flow was performed. Here a qualitative and quantitative description of vortical structures is used to gain insight in the present 3‐D turbulent flow. It is shown that Görtler vortices oriented in the streamwise downslope direction develop in the shear layer. They spread with a specific mushroom shape in the vertical direction up to about 100 m height. They play a main role with respect to local turbulent mixing in the ground surface boundary layer. The present curved slope configuration constitutes a realistic model for alpine orography. This paper provides a procedure based on local turbulence anisotropy to track Görtler vortices for in situ measurements, which has never been proposed in the literature.

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“…If a boundary is artificially roughened by particles of a given diameter, then the bed roughness, k e , which is the length scale of protrusions into the flow, is simply proportional to the particle diameter. Albayraki et al [12] considered uniformly graded sand of mean diameter d 50 ¼ 2 mm that is equal to the roughness length k e used in the theoretical analysis. Strictly this eddy viscosity is given by s $ u s k e , where u s is the friction velocity, and Hogg et al [2] implies s $ U 0 k e over a rough wall.…”

Section: Analysis Of Turbulent Wall Jet Over Transitional Rough Surfacementioning

confidence: 99%

Parametric Analysis of Turbulent Wall Jet in Still Air Over a Transitional Rough, With Asymptotes of Fully Rough and Fully Smooth Wall Jets

Afzal¹,

Seena

2013

Journal of Fluids Engineering

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The novel scalings for streamwise variations of the flow in a turbulent wall jet over a fully smooth, transitional, and fully rough surfaces have been analyzed. The universal scaling for arbitrary wall roughness is considered in terms of the roughness friction Reynolds number (that arises from the stream wise variations of roughness in the flow direction) and roughness Reynolds number at the nozzle jet exit. The transitional rough wall jet functional forms have been proposed, whose numerical constants power law index and prefactor are estimated from best fit to the data for several variables, like, maximum wall jet velocity, boundary layer thickness at maxima of wall jet velocity, the jet half width, the friction factor and momentum integral, which are supported by the experimental data. The data shows that the two asymptotes of fully rough and fully smooth surfaces are co-linear with transitional rough surface, predicting same constants for any variable of flow for full smooth, fully rough and transitional rough surfaces. There is no universality of scalings in terms of traditional variables as different expressions are needed for each stage of the transitional roughness. The experimental data provides very good support to our universal relations.

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Near-field flow structure of a confined wall jet on flat and concave rough walls

Cited by 20 publications

References 27 publications

Development of gravity currents on rapidly changing slopes

Development of gravity currents on rapidly changing slopes

Large‐Eddy Simulation of a katabatic jet along a convexly curved slope: 2. Evidence of Görtler vortices

Parametric Analysis of Turbulent Wall Jet in Still Air Over a Transitional Rough, With Asymptotes of Fully Rough and Fully Smooth Wall Jets

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