TY - JOUR
AB - In pipe, channel, and boundary layer flows turbulence first occurs intermittently in space and time: at moderate Reynolds numbers domains of disordered turbulent motion are separated by quiescent laminar regions. Based on direct numerical simulations of pipe flow we argue here that the spatial intermittency has its origin in a nearest neighbor interaction between turbulent regions. We further show that in this regime turbulent flows are intrinsically intermittent with a well-defined equilibrium turbulent fraction but without ever assuming a steady pattern. This transition scenario is analogous to that found in simple models such as coupled map lattices. The scaling observed implies that laminar intermissions of the turbulent flow will persist to arbitrarily large Reynolds numbers.
AU - Avila, Marc
AU - Hof, Björn
ID - 2811
IS - 6
JF - Physical Review E
TI - Nature of laminar-turbulence intermittency in shear flows
VL - 87
ER -
TY - JOUR
AB - Turbulence is ubiquitous in nature, yet even for the case of ordinary Newtonian fluids like water, our understanding of this phenomenon is limited. Many liquids of practical importance are more complicated (e.g., blood, polymer melts, paints), however; they exhibit elastic as well as viscous characteristics, and the relation between stress and strain is nonlinear. We demonstrate here for a model system of such complex fluids that at high shear rates, turbulence is not simply modified as previously believed but is suppressed and replaced by a different type of disordered motion, elasto-inertial turbulence. Elasto-inertial turbulence is found to occur at much lower Reynolds numbers than Newtonian turbulence, and the dynamical properties differ significantly. The friction scaling observed coincides with the so-called "maximum drag reduction" asymptote, which is exhibited by a wide range of viscoelastic fluids.
AU - Samanta, Devranjan
AU - Dubief, Yves
AU - Holzner, Markus
AU - Schäfer, Christof
AU - Morozov, Alexander
AU - Wagner, Christian
AU - Hof, Björn
ID - 2813
IS - 26
JF - PNAS
TI - Elasto-inertial turbulence
VL - 110
ER -
TY - JOUR
AB - Laminar-turbulent intermittency is intrinsic to the transitional regime of a wide range of fluid flows including pipe, channel, boundary layer, and Couette flow. In the latter turbulent spots can grow and form continuous stripes, yet in the stripe-normal direction they remain interspersed by laminar fluid. We carry out direct numerical simulations in a long narrow domain and observe that individual turbulent stripes are transient. In agreement with recent observations in pipe flow, we find that turbulence becomes sustained at a distinct critical point once the spatial proliferation outweighs the inherent decaying process. By resolving the asymptotic size distributions close to criticality we can for the first time demonstrate scale invariance at the onset of turbulence.
AU - Shi, Liang
AU - Avila, Marc
AU - Hof, Björn
ID - 2829
IS - 20
JF - Physical Review Letters
TI - Scale invariance at the onset of turbulence in couette flow
VL - 110
ER -
TY - JOUR
AB - Although the equations governing fluid flow are well known, there are no analytical expressions that describe the complexity of turbulent motion. A recent proposition is that in analogy to low dimensional chaotic systems, turbulence is organized around unstable solutions of the governing equations which provide the building blocks of the disordered dynamics. We report the discovery of periodic solutions which just like intermittent turbulence are spatially localized and show that turbulent transients arise from one such solution branch.
AU - Avila, Marc
AU - Mellibovsky, Fernando
AU - Roland, Nicolas
AU - Hof, Björn
ID - 2834
IS - 22
JF - Physical Review Letters
TI - Streamwise-localized solutions at the onset of turbulence in pipe flow
VL - 110
ER -