scholarly journals Laminar–turbulent coexistence in annular Couette flow

2019 ◽  
Vol 879 ◽  
pp. 579-603 ◽  
Author(s):  
Kohei Kunii ◽  
Takahiro Ishida ◽  
Yohann Duguet ◽  
Takahiro Tsukahara
Keyword(s):  
Phase Transition ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Couette Flow ◽  
Pipe Flow ◽  
Turbulent Structures ◽  
Coaxial Cylinders ◽  
Turbulent Fluctuations ◽  
Axial Translation ◽  
Planar Shear

Annular Couette flow is the flow between two coaxial cylinders driven by the axial translation of the inner cylinder. It is investigated using direct numerical simulation in long domains, with an emphasis on the laminar–turbulent coexistence regime found for marginally low values of the Reynolds number. Three distinct flow regimes are demonstrated as the radius ratio $\unicode[STIX]{x1D702}$ is decreased from 0.8 to 0.5 and finally to 0.1. The high-$\unicode[STIX]{x1D702}$ regime features helically shaped turbulent patches coexisting with laminar flow, as in planar shear flows. The moderate-$\unicode[STIX]{x1D702}$ regime does not feature any marked laminar–turbulent coexistence. In an effort to discard confinement effects, proper patterning is, however, recovered by artificially extending the azimuthal span beyond $2\unicode[STIX]{x03C0}$. Eventually, the low-$\unicode[STIX]{x1D702}$ regime features localised turbulent structures different from the puffs commonly encountered in transitional pipe flow. In this new coexistence regime, turbulent fluctuations are surprisingly short-ranged. Implications are discussed in terms of phase transition and critical scaling.

Direct numerical simulation of a puff and a slug in transitional cylindrical pipe flow

1999 ◽  
Vol 387 ◽  
pp. 39-60 ◽  
Author(s):  
H. SHAN ◽  
B. MA ◽  
Z. ZHANG ◽  
F. T. M. NIEUWSTADT
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Pipe Flow ◽  
Leading Edge ◽  
Transition Process ◽  
Axial Position ◽  
Trailing Edge ◽  
Mean Velocity ◽  
The Mean

A direct numerical simulation of transitional pipe flow is carried out with the help of a spectral element method and used to investigate the localized regions of ‘turbulent’ flow that are observed in experiments. Two types of such regions can be distinguished: the puff and the slug. The puff, which is generally found at low values of the Reynolds numbers, is simulated for Re = 2200 where the Reynolds number Re is based on the mean velocity UB and pipe diameter D. The slug occurs at a higher Reynolds number and it is simulated for Re = 5000. The computations start with a laminar pipe flow to which is added a prescribed velocity disturbance at a given axial position and for a finite time. The disturbance then evolves further into a puff or slug structure.The simulations confirm the experimentally observed fact that for a puff the velocity near the leading edge changes more gradually than for a slug where an almost discontinuous change is observed. The positions of the leading and trailing edges of the puff and slug are computed from the simulations as a function of time. The propagation velocity of the leading edge is found to be constant and equal to 1.56UB and 1.69UB for the puff and slug, respectively. For the trailing edge the velocity is found to be 0.73UB and 0.52UB, respectively. By rescaling the simulation results obtained at various times to a fixed length, we define an ensemble average. This method is used to compute the average characteristics of the puff and slug such as the spatial distribution of the mean velocity, the turbulent velocity fluctuations and also the wall shear stress. By computing particle trajectories we have investigated the entrainment and detrainment of fluid by a puff and slug. We find that the puff detrains through its trailing edge and entrains through its leading edge. The slug entrains fluid through its leading and through most of its trailing edge. As a consequence the fluid inside the puff is constantly exchanged with fluid outside whereas the fluid inside a slug remains there. These entrainment/detrainment properties which are in agreement with the measurements of Wygnanski & Champagne (1973) imply that the puff has the characteristics of a wave phenomenon while the slug can be characterized more as a material property which travels with the flow.Finally, we have investigated in more detail the velocity field within the puff. In a coordinate system that travels with the mean velocity we find recirculation regions both near the trailing and leading edges which agrees at least qualitatively with experimental data. We also find streamwise vortices, predominantly in the trailing-edge region which have been also observed in experiments and which are believed to play an important role in the dynamics of the transition process.

scholarly journals RANS Numerical Simulation of Turbulent Particulate Pipe Flow for Fixed Reynolds Number

10.5772/57216 ◽  
2014 ◽  
Author(s):  
Alexander Kartushinsky ◽  
Ylo Rudi ◽  
Igor Shcheglov ◽  
Sergei Tisler ◽  
Igor Krupenski
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Pipe Flow

Instability in Couette flow of solutions of macromolecules

1962 ◽  
Vol 13 (1) ◽  
pp. 86-90 ◽  
Author(s):  
E. W. Merrill ◽  
H. S. Mickley ◽  
A. Ram
Keyword(s):  
Reynolds Number ◽  
Couette Flow ◽  
Critical Reynolds Number ◽  
Vortex Formation ◽  
Newtonian Fluids ◽  
Coaxial Cylinders

In Couette flow between coaxial cylinders, ring-shaped vortices, illustrated schematically in figure 1, develop at a Reynolds number which depends strongly on the geometry of the system, as treated analytically for Newtonian fluids by Chandrasekhar (1958). The problem was first considered by Taylor (1923) who, examining simple (micromolecular) liquids, arrived at an equation for the critical Reynolds numberReiabove which instability (vortex formation) would occur when the inner cylinder rotated and the outer is stationary, and when the gap is small compared to the radius.

scholarly journals A theory for the streamwise turbulent fluctuations in high Reynolds number pipe flow

2012 ◽  
Vol 707 ◽  
pp. 575-584 ◽  
Author(s):  
Marcus Hultmark
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Pipe Flow ◽  
High Reynolds Number ◽  
Mean Flow ◽  
Mean Velocity ◽  
Theoretical Derivation ◽  
Turbulent Fluctuations ◽  
The Mean ◽  
High Reynolds

AbstractA new theory for the streamwise turbulent fluctuations in fully developed pipe flow is proposed. The theory extends the similarities between the mean flow and the streamwise turbulence fluctuations, as observed in experimental high Reynolds number data, to also include the theoretical derivation. Connecting the derivation of the fluctuations to that of the mean velocity at finite Reynolds number as introduced by Wosnik, Castillo & George (J. Fluid Mech., vol. 421, 2000, pp. 115–145) can explain the logarithmic behaviour as well as the coefficient of the logarithm. The slope of the logarithm, for the fluctuations, depends on the increase of the fluctuations with Reynolds number, which is shown to agree very well with the experimental data. A mesolayer, similar to that introduced by Wosnik et al., exists for the fluctuations for $300\gt {y}^{+ } \gt 800$, which coincides with the mesolayer for the mean velocities. In the mesolayer, the flow is still affected by viscosity, which shows up as a decrease in the fluctuations.

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