1519 Large-scale feature in two-dimensional turbulent channel flow in the wide range of Reynolds number

An extended experimental method is presented in which the micro-pillar shear-stress sensor (MPS 3 ) and high-speed stereo particle-image velocimetry measurements are simultaneously performed in turbulent channel flow to conduct concurrent time-resolved measurements of the two-dimensional wall-shear stress (WSS) distribution and the velocity field in the outer flow. The extended experimental setup, which involves a modified MPS 3 measurement setup and data evaluation compared to the standard method, is presented and used to investigate the footprint of the outer, large-scale motions (LSM) onto the near-wall small-scale motions. The measurements were performed in a fully developed, turbulent channel flow at a friction Reynolds number R e τ = 969 . A separation between large and small scales of the velocity fluctuations and the WSS fluctuations was performed by two-dimensional empirical mode decomposition. A subsequent cross-correlation analysis between the large-scale velocity fluctuations and the large-scale WSS fluctuations shows that the streamwise inclination angle between the LSM in the outer layer and the large-scale footprint imposed onto the near-wall dynamics has a mean value of Θ ¯ x = 16.53 ∘ , which is consistent with the literature relying on direct numerical simulations and hot-wire anemometry data. When also considering the spatial shift in the spanwise direction, the mean inclination angle reduces to Θ ¯ x z = 13.92 ∘ .

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Turbulent channel flow of an elastoviscoplastic fluid

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.591 ◽

2018 ◽

Vol 853 ◽

pp. 488-514 ◽

Cited By ~ 11

Author(s):

Marco E. Rosti ◽

Daulet Izbassarov ◽

Outi Tammisola ◽

Sarah Hormozi ◽

Luca Brandt

Keyword(s):

Reynolds Number ◽

Turbulent Flow ◽

Friction Factor ◽

Channel Flow ◽

Viscosity Ratio ◽

Turbulent Channel Flow ◽

Turbulent Regime ◽

Bingham Number ◽

Wide Range ◽

Near Wall

We present numerical simulations of laminar and turbulent channel flow of an elastoviscoplastic fluid. The non-Newtonian flow is simulated by solving the full incompressible Navier–Stokes equations coupled with the evolution equation for the elastoviscoplastic stress tensor. The laminar simulations are carried out for a wide range of Reynolds numbers, Bingham numbers and ratios of the fluid and total viscosity, while the turbulent flow simulations are performed at a fixed bulk Reynolds number equal to 2800 and weak elasticity. We show that in the laminar flow regime the friction factor increases monotonically with the Bingham number (yield stress) and decreases with the viscosity ratio, while in the turbulent regime the friction factor is almost independent of the viscosity ratio and decreases with the Bingham number, until the flow eventually returns to a fully laminar condition for large enough yield stresses. Three main regimes are found in the turbulent case, depending on the Bingham number: for low values, the friction Reynolds number and the turbulent flow statistics only slightly differ from those of a Newtonian fluid; for intermediate values of the Bingham number, the fluctuations increase and the inertial equilibrium range is lost. Finally, for higher values the flow completely laminarizes. These different behaviours are associated with a progressive increases of the volume where the fluid is not yielded, growing from the centreline towards the walls as the Bingham number increases. The unyielded region interacts with the near-wall structures, forming preferentially above the high-speed streaks. In particular, the near-wall streaks and the associated quasi-streamwise vortices are strongly enhanced in an highly elastoviscoplastic fluid and the flow becomes more correlated in the streamwise direction.

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On the scaling of air entrainment from a ventilated partial cavity

Journal of Fluid Mechanics ◽

10.1017/jfm.2013.387 ◽

2013 ◽

Vol 732 ◽

pp. 47-76 ◽

Cited By ~ 32

Author(s):

Simo A. Mäkiharju ◽

Brian R. Elbing ◽

Andrew Wiggins ◽

Sarah Schinasi ◽

Jean-Marc Vanden-Broeck ◽

...

Keyword(s):

Reynolds Number ◽

Weber Number ◽

Large Scale ◽

Air Entrainment ◽

Small Scale ◽

Length Scale ◽

Entrainment Rate ◽

Two Dimensional ◽

Wide Range ◽

Stable Cavity

AbstractThe behaviour of a nominally two-dimensional ventilated partial cavity was examined over a wide range of size scales and flow speeds to determine the influence of Froude, Reynolds, and Weber number on the cavity shape, dynamics, and gas entrainment rate. Two geometrically similar experiments were conducted with a 14:1 length scale ratio. The results were compared to a two-dimensional semi-analytical model of the cavity flow, and Froude scaling was found to be sufficient to match basic cavity shapes. However, the air flux required to maintain a stable cavity did not scale with Froude number alone, as the dynamics of the cavity closure changed with increasing Reynolds number. The required air flux differed over one order of magnitude between the lowest and highest Reynolds number flows. But, for sufficiently high Reynolds numbers, the rate of scaled entrainment appeared to approach Reynolds number independence. Modest changes in surface tension of the small-scale experiment suggested that the Weber number was important only at the lowest speeds and smaller length scale. Otherwise, the Weber numbers of the flows were sufficiently high to make the effects of interfacial tension negligible. We also observed that modest unsteadiness in the inflow to the large-scale cavity led to a significant increase in the required air flux needed to maintain a stable cavity, with the required excess gas flux nominally proportional to the flow’s perturbation amplitude. Finally, discussion is provided on how these results relate to model testing of partial cavity drag reduction (PCDR) systems for surface ships.

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Statistics and structure of spanwise rotating turbulent channel flow at moderate Reynolds numbers

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.526 ◽

2017 ◽

Vol 828 ◽

pp. 424-458 ◽

Cited By ~ 18

Author(s):

Geert Brethouwer

Keyword(s):

Reynolds Number ◽

Channel Flow ◽

Large Scale ◽

Linear Part ◽

Turbulent Channel Flow ◽

Streamwise Velocity ◽

Reynolds Stresses ◽

System Rotation ◽

The Mean ◽

Spanwise Rotation

A study of fully developed plane turbulent channel flow subject to spanwise system rotation through direct numerical simulations is presented. In order to study both the influence of the Reynolds number and spanwise rotation on channel flow, the Reynolds number $Re=U_{b}h/\unicode[STIX]{x1D708}$ is varied from a low 3000 to a moderate 31 600 and the rotation number $Ro=2\unicode[STIX]{x1D6FA}h/U_{b}$ is varied from 0 to 2.7, where $U_{b}$ is the mean bulk velocity, $h$ the channel half-gap, $\unicode[STIX]{x1D708}$ the viscosity and $\unicode[STIX]{x1D6FA}$ the system rotation rate. The mean streamwise velocity profile displays also at higher $Re$ a characteristic linear part with a slope near to $2\unicode[STIX]{x1D6FA}$, and a corresponding linear part in the profiles of the production and dissipation rate of turbulent kinetic energy appears. With increasing $Ro$, a distinct unstable side with large spanwise and wall-normal Reynolds stresses and a stable side with much weaker turbulence develops in the channel. The flow starts to relaminarize on the stable side of the channel and persisting turbulent–laminar patterns appear at higher $Re$. If $Ro$ is further increased, the flow on the stable side becomes laminar-like while at yet higher $Ro$ the whole flow relaminarizes, although the calm periods might be disrupted by repeating bursts of turbulence, as explained by Brethouwer (Phys. Rev. Fluids, vol. 1, 2016, 054404). The influence of the Reynolds number is considerable, in particular on the stable side of the channel where velocity fluctuations are stronger and the flow relaminarizes less quickly at higher $Re$. Visualizations and statistics show that, at $Ro=0.15$ and 0.45, large-scale structures and large counter-rotating streamwise roll cells develop on the unstable side. These become less noticeable and eventually vanish when $Ro$ rises, especially at higher $Re$. At high $Ro$, the largest energetic structures are larger at lower $Re$.

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Reynolds number effects on the wall layer of two-dimensional turbulent channel flow

The Proceedings of Conference of Chugoku-Shikoku Branch ◽

10.1299/jsmecs.2019.57.503 ◽

2019 ◽

Vol 2019.57 (0) ◽

pp. 503

Author(s):

Mamoru WAKAMATSU ◽

Hiroki SUZUKI ◽

Shinsuke MOCHIZUKI

Keyword(s):

Reynolds Number ◽

Channel Flow ◽

Turbulent Channel Flow ◽

Wall Layer ◽

Two Dimensional ◽

Reynolds Number Effects

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On the universality of local dissipation scales in turbulent channel flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.664 ◽

2015 ◽

Vol 786 ◽

pp. 234-252 ◽

Cited By ~ 5

Author(s):

S. C. C. Bailey ◽

B. M. Witte

Keyword(s):

Reynolds Number ◽

Channel Flow ◽

Large Scale ◽

Isotropic Turbulence ◽

Turbulent Channel Flow ◽

Reynolds Numbers ◽

Small Scale ◽

Length Scale ◽

Scaling Behaviour ◽

Sixth Moment

Well-resolved measurements of the small-scale dissipation statistics within turbulent channel flow are reported for a range of Reynolds numbers from $Re_{{\it\tau}}\approx 500$ to 4000. In this flow, the local large-scale Reynolds number based on the longitudinal integral length scale is found to poorly describe the Reynolds number dependence of the small-scale statistics. When a length scale based on Townsend’s attached-eddy hypothesis is used to define the local large-scale Reynolds number, the Reynolds number scaling behaviour was found to be more consistent with that observed in homogeneous, isotropic turbulence. The Reynolds number scaling of the dissipation moments up to the sixth moment was examined and the results were found to be in good agreement with predicted scaling behaviour (Schumacher et al., Proc. Natl Acad. Sci. USA, vol. 111, 2014, pp. 10961–10965). The probability density functions of the local dissipation scales (Yakhot, Physica D, vol. 215 (2), 2006, pp. 166–174) were also determined and, when the revised local large-scale Reynolds number is used for normalization, provide support for the existence of a universal distribution which scales differently for inner and outer regions.

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