Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session A27: Flow Instability: Transition to Turbulence I |
Hide Abstracts |
Chair: Nigel Goldenfeld, University of Illinois at Urbana-Champaign Room: Georgia World Congress Center B315 |
Sunday, November 18, 2018 8:00AM - 8:13AM |
A27.00001: Laminar-turbulent transition in polymer solutions through micro-tubes Bidhan Chandra, Viswanathan Shankar Experiments are performed to characterize laminar-turbulent transition for the flow of polymer solutions through micro-tubes of size ~400µm using micro-PIV and dye stream visualization techniques. Using small diameter tubes enable us to probe high elasticity number. We observe that addition of small amounts of polymer (50ppm-100ppm) delays transition to turbulence as compared to a Newtonian fluid whereas addition of larger amounts of polymer (500ppm-800ppm) causes an early transition. It is observed that addition of polymer decreases velocity fluctuations in the post-transition regime irrespective of the concentration of polymer added for polyacrylamide solutions which may be linked to the drag reduction phenomena. The phenomena was corroborated by using a different polymer of a different molecular weight. Transition Re observed in our experiments (by varying polymer concentration, with tubes of different diameters and by using two different polymers) shows a remarkable data collapse. |
Sunday, November 18, 2018 8:13AM - 8:26AM |
A27.00002: Splitting of turbulent spots in transitional pipe flow. Ronald J Adrian, Xiaohua Wu, Parviz Moin Splitting of turbulent spots in a Re=2,300 transitional flow developing spatially from weakly perturbed laminar inflow in a 1000 radii long pipe is investigated by DNS, c.f. Wu et al (PNAS, 112, 7920, 2015). Spots are created by blobs of turbulence introduced from the inlet and developing through fully-developed laminar flow. Turbulent spots of scalars were first observed in Osborne Reynolds’ dye experiments, but the splitting phenomenon was not discovered until the work of E.R. Lindgren (Arkiv Fysik, 16, 101-112, 1959a). The center-line axial velocities ahead and behind a spot are very close to the expected laminar value=2 x bulk velocity. Passive scalar from the centerline occupies a smaller region than that impacted by the spot’s velocity field. A first-generation spot splits because a sustained speed difference between the front and middle of the spot pulls it apart. The separated front and back halves reform into 2nd generation spots that one might expect to repeat the process, thereby creating 3rd generation, and so on. In reality, 2nd generation turbulent spots enter an unexpected quasi-cyclic process containing previously unknown sub-processes of parent-child re-connection and re-splitting, rather than successive generational splitting. |
Sunday, November 18, 2018 8:26AM - 8:39AM |
A27.00003: Eigenfunctions of the Orr-Sommerfeld/Squire Operator for Channel Flow Anthony Leonard Knowledge of the eigenvalues and eigenfunctions of the Orr-Sommerfeld/Squire operator can be used in a variety of applications. They are relevant to the prediction of stability and transition in shear flows and could be used to construct the resolvent for turbulent wall-bounded flows. Rather than approximating the differential operators by a spectral expansion, |
Sunday, November 18, 2018 8:39AM - 8:52AM |
A27.00004: Statistical mechanics of puff-splitting in the transition to pipe turbulence Hong-Yan Shih, Gaute Linga, Grégoire Lemoult, Mukund Vasudevan, Björn Hof, Joachim Mathiesen, Nigel Goldenfeld Very close to the laminar-turbulent transition in pipe flow, localized regions of turbulence known as puffs proliferate and interact, leading to spatiotemporal intermittency. We develop a one-dimensional stochastic model of puff dynamics, taking into account puff decay, propagation and splitting, as well as short-range interactions whereby a puff experiences lifetime suppression and velocity pushing by a sufficiently close upstream puff. The universality class for the resulting laminar-turbulence transition in pipe flow is (1+1)-dimensional directed percolation, with puff-puff interactions irrelevant at the renormalization group fixed point. Continuum and discrete numerical simulations are in agreement with the theory, after taking into account finite-size and crossover effects. |
Sunday, November 18, 2018 8:52AM - 9:05AM |
A27.00005: Subcritical transition to turbulence in diverging pipe flows Dhanush Vittal Shenoy, Minh Quan Nguyen, Mostafa Safdari Shadloo, Abdellah Hadjadj, Jorge Peixinho, Omar K Matar Transition from laminar to turbulent regime is accompanied by a large change in flow related processes such as mixing, heat transfer and drag friction that increase dramatically. This work tries to addresses the fundamental question of the transition instability in diverging pipe flows of an ultimate active control strategy focusing on the fundamental understanding of the flow physics. From a theoretical point of view, the classical linear stability theory predicts large critical speeds for transition, whereas experiments indicate the occurrence of transition at lower flow rates. The current work intends to clarify this scientific ambiguity and to shade more lights into the transition mechanisms and their consequences on critical flows. Therefore, the proposed work uses direct numerical simulations (DNS) approach and compare the results with on-going well-designed experiments to better understand the effects of flow and geometrical parameters such as inlet imperfection and diverging angle on the transition to turbulence for such simple yet important geometries. In its extreme limit and in accordance with the experimental observation, we found a new transition mechanism as well as its dependency to wall imperfection. |
Sunday, November 18, 2018 9:05AM - 9:18AM |
A27.00006: Gradual development of perturbations toward a turbulent puff in pipe flows Yuji Tasaka, Jumpei Ohkubo, Kotaro Nakamura, Yuichi Murai Development of perturbations toward a turbulent puff in pipe flows was examined experimentally at moderate Reynolds numbers around 2000. Controlling amplitude of cross-flow jet as perturbations represented complex threshold for the transition that was also reported in Tasaka et al. Phys. Rev. Lett. (2010). Detailed measurements of local velocity fluctuations at pipe center by LDV elucidated two different routes toward a turbulent puff along the complex threshold. With relatively small amplitudes, transitions are accompanied by formation of hair-pin like vortices, and the transition process progresses gradually; a primary short puff grows up in both spatial extent and velocity defect. With relatively stronger perturbations, a short slug-like structure is formed, and relaminalization at the front of structure leads it toward a developed puff. These different routes were described as trajectories on phase space of magnitude of the velocity defect and intensity of the velocity fluctuations. |
Sunday, November 18, 2018 9:18AM - 9:31AM |
A27.00007: Directed percolation and the transition to turbulence Bjoern Hof, Mukund Vasudevan In pipe, channel and Couette flow turbulence does not arise from an instability of the laminar flow. Both states co-exist over a considerable Reynolds number range. Moreover the first turbulent structures that can be observed in experiments (depending on the flow referred to as puffs, spots or stripes) are essentially transients and decay after long times. Eventually however the proliferation of such turbulent patches outweighs their decay. At this point a non-equilibrium phase transition occurs which recently has been suggested to fall into the directed percolation universality class. In the light of the growth, decay and interaction mechanisms of turbulent patches in pipe, channel and Couette flow we discuss the correspondence to directed percolation and the conditions that must be fulfilled to fall into this universality class. In particular we discuss complications that arise in these flows and that are not part of simple percolation models, like for example puff-puff interactions. Finally we present data from a new pipe experiment, where the pipe length is order of 100 000 pipe diameters. The measured scaling of the turbulent fraction, the correlation length and correlation times are compared with the directed percolation predictions. |
Sunday, November 18, 2018 9:31AM - 9:44AM |
A27.00008: The origin of turbulent stripes in channel flow Chaitanya Paranjape, Yohann Duguet, Mukund Vasudevan, Bjoern Hof In plane Poiseuille flow turbulence first appears in the form of of oblique stripes that are separated by laminar regions. In experiments we find that stripes at low Reynolds numbers have an orientation of 45 degrees with respect to the streamwise direction. As shown, stripe patterns are statistically sustained even at Re as low as 675 which is considerably lower than a recent estimate for the onset of turbulence (Re = 830). Below Re~650 however stripes quickly decay and cannot be tracked to lower Re. Inspired by the experiments we perform direct numerical simulations in a rectangular domain tilted by 45 degrees (i.e. the preferred stripe angle) with respect to the streamwise direction. We find that in this case the turbulent stripes can be tracked to much lower Re, all the way to their origin. The turbulent flow in this limit turns into a localized non-turbulent stripe, which more precisely is a periodic orbit solution of the Navier Stokes equations. This stripe solution can be regarded as the precursor of turbulence and we investigate how turbulence develops from it. A notable feature is that a small increase in Re suffices to give rise to chaos and that subsequently the attractor dimension increases at an unprecedented rate. |
Sunday, November 18, 2018 9:44AM - 9:57AM |
A27.00009: Origin of the super-exponential scaling with Reynolds number of single turbulent puff lifetime in pipes Nigel Goldenfeld, Hong-Yan Shih In transitional Couette and 2D Waleffe flows, careful measurements and simulations provide strong evidence of power-law scaling of turbulent fraction and a diverging turbulent lifetime near the critical Reynolds number. These results are consistent with the laminar-turbulent transition being a non-equilibrium phase transition in the directed percolation (DP) universality class. In pipe flow, however, the lifetime of single turbulent puffs does not seem to diverge at a critical Reynolds number, even though the interaction between small-scale turbulence and a zonal flow coherent structure implies that the transition should follow DP. We resolve this paradox by arguing that near the transition, as the correlation length of turbulent fluctuations grows to the pipe diameter, the fluctuations in a single puff would follow a universal finite-size scaling distribution. We derive this distribution from DP and show that its asymptotics closely match extreme value distributions, giving rise to a super-exponential dependence of lifetime on Reynolds number, in agreement with observations on single puffs very close to the laminar-turbulent transition. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2023 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700