Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session F28: Turbulence: Wall-Bounded Flows IIBoundary Layers Turbulence
|
Hide Abstracts |
Chair: Martin Oberlack, Tech Univ Darmstadt Room: 207 |
Monday, November 20, 2017 8:00AM - 8:13AM |
F28.00001: Turbulent channel flow under moderate polymer drag reduction John Elsnab, Jason Monty, Christopher White, Manoochehr Koochesfahani, Joseph Klewicki Streamwise velocity profiles and their wall-normal derivatives are used to investigate the properties of turbulent channel flow under the moderate polymer drag reduction (DR) conditions of 6-27{\%}. Velocity data were obtained over a friction Reynolds number (Re) from 650-1800 using the single velocity component version of molecular tagging velocimetry (MTV). This adaptation of the MTV technique captures instantaneous profiles at high spatial resolution (\textgreater 800 data points per profile), thus generating well-resolved derivative information. The mean velocity profiles indicate that the extent of the logarithmic region diminishes with increasing polymer concentration, while the logarithmic profile slope increases for drag reductions greater than about 20{\%}. The measurements allow reconstruction of the mean momentum balance for channel flow that provides additional insights regarding the physics described by previous numerical simulation analyses that examined the mean dynamical structure of polymer laden channel flow at low Re. The present findings indicate that the polymer modifies the onset of the inertial domain, and that the extent of this domain shrinks with increasing DR. Once on the inertial domain, self-similar behaviors occur, but modified (sometimes subtly) by the modified distribution of characteristic y-scaling behavior of the Reynolds stress motions. [Preview Abstract] |
Monday, November 20, 2017 8:13AM - 8:26AM |
F28.00002: Response of turbulent pipe flow experiencing a rough-to-smooth step change Alexander Smits, Tyler Van Buren, Leo Hellström In this study, we consider fully-developed turbulent pipe flow (Re$_{\mathrm{D}}=$131000) subject to a step change in surface roughness, specifically a step change from rough to smooth. Velocity field measurements were taken downstream at (x-x$_{\mathrm{0}})$/D$=$0, 0.33, 1, 2, 4, 8, and 16 (x$_{\mathrm{0}}=$3.3D), using stereoscopic particle image velocimetry. We examine the downstream development of the relaxation of turbulence statistics including the Reynolds stresses, and explore how the change in roughness affects the large scale motions and the transfer of energy between scales. Supported under ONR Grant N00014-15-1-2402, Program Manager/Director Thomas Fu. [Preview Abstract] |
Monday, November 20, 2017 8:26AM - 8:39AM |
F28.00003: Surface roughness effects on turbulent Couette flow Young Mo Lee, Jae Hwa Lee Direct numerical simulation of a turbulent Couette flow with two-dimensional (2-D) rod roughness is performed to examine the effects of the surface roughness. The Reynolds number based on the channel centerline laminar velocity ($U_{co})$ and channel half height ($h)$ is \textit{Re}$=$7200. The 2-D rods are periodically arranged with a streamwise pitch of $\lambda =$8$k$ on the bottom wall, and the roughness height is $k=$0.12$h$. It is shown that the wall-normal extent for the logarithmic layer is significantly shortened in the rough-wall turbulent Couette flow, compared to a turbulent Couette flow with smooth wall. Although the Reynolds stresses are increased in a turbulent channel flow with surface roughness in the outer layer due to large-scale ejection motions produced by the 2-D rods, those of the rough-wall Couette flow are decreased. Isosurfaces of the $u$-structures averaged in time suggest that the decrease of the turbulent activity near the centerline is associated with weakened large-scale counter-rotating roll modes by the surface roughness. [Preview Abstract] |
Monday, November 20, 2017 8:39AM - 8:52AM |
F28.00004: On the persistence of large-scale turbulent structures in turbulent Couette flow with wall-transpiration Martin Oberlack, Sergio Hoyas, Stephani Kraheberger It has long been known that turbulent Couette flows (TCF) are dominated by large-scale turbulent structures of vortex-type in stream-wise direction (for an early experimental and numerical validation see e.g. Tillmark et al. 1995 and Bech et al. 1995), and a recent DNS study supports the persistence up to $Re_{\tau}=550$ (Avsarkisov et al. 2014). In an ongoing DNS study the TCF is extended towards wall transpiration, i.e. blowing from below and suction at the top at constant velocity $v_0$. Even at small transpiration rates, i.e. $v_o/u_w\ll 1$, where $u_w$ is the moving wall velocity, strong changes in the overall flow behavior is visible. E.g. a strong reduction of the mass-flux is observed. Beside interesting and new scaling issues, one of the most remarkable feature of this largely unexplored flow is, that even at the highest transpiration rates investigated so far, the footprints of the large turbulent rolls of the TCF are still visible at the highest Reynolds and transpiration number. Other quantities such as two-point auto-correlations, two-dimensional spectral energy densities and pre-multiplied spectra give a more detailed picture of the turbulent structure and support the finding of highly persisting large-scale turbulent structures in TCF with wall-transpiration. [Preview Abstract] |
Monday, November 20, 2017 8:52AM - 9:05AM |
F28.00005: Turbulent boundary layer measurements over permeable substrates Christoph Efstathiou, Mitul Luhar Turbulence flows of scientific and engineering interest are often bounded by permeable walls. Laser Doppler Velocimetry (LDV) measurements in turbulent boundary layers (upstream friction Reynolds number $Re_\tau=1690 \pm 70$) over foams with porosity $\phi=97.0\pm0.5\%$ and pore sizes ranging from $s=0.29\pm0.02$mm to $s=2.1\pm0.3$mm ($Re_k=1.9-8.2)$ showed substantial changes to the mean velocity and turbulence intensity profiles. A constant slip velocity ($\approx 0.3 U_e$) near the interface was measured for all substrates, while a mean velocity deficit was found for $0.004 \leq y/\delta \leq 0.4$. For the largest pore sizes, an outer peak in stream-wise turbulence intensity was observed at $y/\delta \approx 0.1$. Spectral analysis showed structures of 1-6$\delta$ in stream-wise length, extending from the interface to $y/\delta =0.4$ that are consistent with a Kelvin-Helmholtz type instability. The experiments described in this talk address how identical substrates of varying thickness affect flow structure at the limit where pore size and substrate thickness are comparable. Measurements are made in boundary layers over the same foams but with varying thickness $h/s=6-17$. Particle Image Velocimetry measurements will also be presented. [Preview Abstract] |
Monday, November 20, 2017 9:05AM - 9:18AM |
F28.00006: Multi-layer description of azimuthal velocity distribution in turbulent Taylor-Couette flow. Hong-Yue Zou, Zhen-Su She A quantitative multi-layer theory is developed for accurate description of mean azimuthal velocity profile (MAVP) in turbulent Taylor-Couette flow (TCF), validated by both experimental and numerical data over a wide range of Reynolds numbers (Re). In particular, the observations of a logarithmic law in MAVP by Sun et. al. is obtained, based on a similarity argument between the azimuthal velocity (instead of angular velocity) in TCF with temperature in Rayleigh-Benard convection. The theory allows to extract accurate Re scaling of the thicknesses of sub-layer, buffer layer, log-layer, and a linear layer from the empirical data, which successfully explain the observed variation of the log-law coefficient {\$}$\backslash $kappa{\$} from 0.32 for small Re to 0.40 for large Re. More interestingly, a linear layer is discovered in the MAVP far away from the wall, and an observed scaling of its coefficient A\textasciitilde Re$^{\mathrm{-0.65\thinspace }}$is explained by the scaling of the log-layer thickness, and an observed torque scaling, G\textasciitilde Re$^{\mathrm{1.794}}$, is explained by the scaling of the viscous sublayer, all validated by simulation data. In conclusion, the multi-layer thicknesses are shown to be important physical measures of the TCF. [Preview Abstract] |
Monday, November 20, 2017 9:18AM - 9:31AM |
F28.00007: Causal analysis of self-sustaining processes in the log-layer of wall-bounded turbulence Adrian Lozano-Duran, Hyunji Jane Bae, Miguel P. Encinar Despite the large amount of information provided by direct numerical simulations of turbulent flows, the underlying dynamics remain elusive even in the most simple and canonical configurations. Most standard methods used to investigate turbulence do not provide a clear causal inference between events, which is necessary to determine this dynamics, particularly in self-sustaning processes. In the present work, we examine the causal interactions between streaks and rolls in the logarithmic layer of minimal turbulent channel flow. Causality between structures is assessed in a non-intrusive manner by transfer entropy, i.e., how much the uncertainty of one structure is reduced by knowing the past states of the others. Streaks are represented by the first Fourier modes of the streamwise velocity, while rolls are defined by the wall-normal and spanwise velocities. The results show that the process is mainly unidirectional rather than cyclic, and that the log-layer motions are sustained by extracting energy from the mean shear, which controls the dynamics and time-scales. The well-known lift-up effect is shown to be not a key ingredient in the causal network between shear, streaks and rolls. [Preview Abstract] |
Monday, November 20, 2017 9:31AM - 9:44AM |
F28.00008: Statistical State Dynamics Based Study of the Role of Nonlinearity in the Maintenance of Turbulence in Couette Flow Brian Farrell, Petros Ioannou, Marios-Andreas Nikolaidis While linear non-normality underlies the mechanism of energy transfer from the externally driven flow to the perturbation field, nonlinearity is also known to play an essential role in sustaining turbulence. We report a study based on the statistical state dynamics of Couette flow turbulence with the goal of better understanding the role of nonlinearity in sustaining turbulence. The statistical state dynamics implementations used are ensemble closures at second order in a cumulant expansion of the Navier-Stokes equations in which the averaging operator is the streamwise mean. Two fundamentally non-normal mechanisms potentially contributing to maintaining the second cumulant are identified. These are essentially parametric perturbation growth arising from interaction of the perturbations with the fluctuating mean flow and transient growth of perturbations arising from nonlinear interaction between components of the perturbation field. By the method of selectively including these mechanisms parametric growth is found to maintain the perturbation field in the turbulent state while the more commonly invoked mechanism associated with transient growth of perturbations arising from scattering by nonlinear interaction is found to suppress perturbation variance. [Preview Abstract] |
Monday, November 20, 2017 9:44AM - 9:57AM |
F28.00009: On the dynamics and scales of Taylor-G\"ortler vortices in a channel subjected to high-speed streamwise system rotations Bing-Chen Wang, Zixuan Yang Direct numerical simulations (DNS) are performed to investigate the dynamics and precise scales of Taylor-G\"ortler-like (TG) vortices in a streamwise-rotating turbulent channel flow at moderate and high streamwise rotation numbers (up to $Ro = 150$). The highest rotation number tested in the current research far exceeds that reported in the existing literature ($Ro = 30$). In order to capture the TG vortices in the streamwise and spanwise directions, the streamwise domain size is stretched drastically to $512\pi h$, where h is one-half the channel height. A two-layer pattern of TG vortices is identified, and the characteristic length scales of TG vortices are quantified using the pre-multiplied two-dimensional energy spectra. The effects of streamwise system rotation on the scales and dynamics of TG vortices are investigated by comparing the statistical results of rotating and non-rotating channel flows, and through the analysis of pre-multiplied energy spectra and budget balance of turbulent stresses. [Preview Abstract] |
Monday, November 20, 2017 9:57AM - 10:10AM |
F28.00010: Modification of large-scale motions in a turbulent pipe flow Kohei Senshu, Hiroaki Shinozaki, Jun Sakakibara We performed experiments to modify the flow structures in a fully developed turbulent flow in a straight round pipe. The modification of the flow was achieved by installing a short coaxial inner pipe. The inner pipe has ability to add continuous suction or blowing disturbance through its outer surface. The experiments were conducted at a Reynolds number of 44,000 with seven different disturbance patterns. The wall static pressure was measured and pipe friction coefficient was evaluated. The velocity distribution was measured with PIV and very large scale motions (VLSMs) were visualized. Pipe friction coefficient was increased by installing the inner pipe, while turbulence intensities over the cross section were reduced. Slight change of the friction was observed if the disturbance was added. We decomposed fluctuating velocity field in the azimuthal direction by a Fourier series expansion. As a result, we obtained that contribution of lower azimuthal mode numbers (m $=$ 2, 3, 4) reduced while the higher modes increased. This was consistent with the observation of visualized very large scale motions. [Preview Abstract] |
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. |
© 2024 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
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700