Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session M32: Turbulent Boundary Layers: Structures II |
Hide Abstracts |
Chair: Julio Soria, Monash University Room: Oregon Ballroom 201 |
Tuesday, November 22, 2016 8:00AM - 8:13AM |
M32.00001: Wall parallel cross-correlations of volumetric PTV measurements in a perturbed turbulent boundary layer Yan Ming Tan, Ellen Longmire A canonical turbulent boundary layer (Re$_{\mathrm{\tau }}^{\mathrm{\thinspace }}=$ 2500) was perturbed by a narrowly spaced (0.2$\delta )$ array of cylinders extending normal to the wall. Two array heights were considered, H$=$ 0.2$\delta $ and H$=\delta $. Volumetric PTV measurements were acquired to understand 3-D variations in large scale structures within the log region of the unperturbed and perturbed flow. The recovery in the streamwise velocity coherence across the depth of the log region was analyzed using cross correlations between wall parallel planes. Conditional cross correlations are analyzed to examine the recovery in coherence specific to low momentum regions (LMRs), which can be signatures of vortex packets. The measurement volume was 0.70$\delta $ (streamwise,x), 0.90$\delta $ (spanwise,y), 0.12$\delta $ (wall-normal,z). In the unperturbed flow, LMRs frequently extended through the entire depth (155$\le $z$^{\mathrm{+}}\le $465). The cross correlations between planes at z$^{\mathrm{+}}=$ 155 and z$^{\mathrm{+}}=$ 465 exhibited strong skewness indicative of forward leaning structures. By comparison, downstream of the H$=\delta $ array, the wall normal extent of individual LMRs was frequently limited to the lower part of the measurement volume. The cross correlation magnitude and skewness remained suppressed relative to unperturbed flow up to 4.7$\delta $ downstream. These observations suggest reduced coherence of LMRs and high momentum regions across the log region. This result was consistent with previous planar PIV measurements at z$^{\mathrm{+}}=$ 500 that showed hardly any long LMRs over distances up to 7$\delta $ downstream of the H$=\delta $ array. [Preview Abstract] |
Tuesday, November 22, 2016 8:13AM - 8:26AM |
M32.00002: Analysis of coherent dynamical processes through computer vision M. J. Philipp Hack Visualizations of turbulent boundary layers show an abundance of characteristic arc-shaped structures whose apparent similarity suggests a common origin in a coherent dynamical process. While the structures have been likened to the hairpin vortices observed in the late stages of transitional flow, a consistent description of the underlying mechanism has remained elusive. Detailed studies are complicated by the chaotic nature of turbulence which modulates each manifestation of the process and which renders the isolation of individual structures a challenging task. The present study applies methods from the field of computer vision to capture the time evolution of turbulent flow features and explore the associated physical mechanisms. The algorithm uses morphological operations to condense the structure of the turbulent flow field into a graph described by nodes and links. The low-dimensional geometric information is stored in a database and allows the identification and analysis of equivalent dynamical processes across multiple scales. The framework is not limited to turbulent boundary layers and can also be applied to different types of flows as well as problems from other fields of science. [Preview Abstract] |
Tuesday, November 22, 2016 8:26AM - 8:39AM |
M32.00003: Evolution of vortex-surface fields in transitional boundary layers Yue Yang, Yaomin Zhao, Shiying Xiong We apply the vortex-surface field (VSF), a Lagrangian-based structure-identification method, to the DNS database of transitional boundary layers (Sayadi et al., J. Fluid Mech., 724, 2013). The VSFs are constructed from the vorticity fields within a sliding window at different times and locations using a recently developed boundary-constraint method. The isosurfaces of VSF, representing vortex surfaces consisting of vortex lines with different wall distances in the laminar stage, show different evolutionary geometries in transition. We observe that the vortex surfaces with significant deformation evolve from wall-parallel planar sheets through hairpin-like structures and packets into a turbulent spot with regeneration of small-scale hairpins. From quantitative analysis, we show that a small number of representative or influential vortex surfaces can contribute significantly to the increase of the drag coefficient in transition, which implies a reduced-order model based on VSF. [Preview Abstract] |
Tuesday, November 22, 2016 8:39AM - 8:52AM |
M32.00004: 3D critical layers in fully-developed turbulent flows Theresa Saxton-Fox, Beverley McKeon Recent work has shown that 3D critical layers drive self-sustaining behavior of exact coherent solutions of the Navier-Stokes equations (Wang et al 2007; Hall and Sherwin 2010; Park and Graham 2015). This study investigates the role of 3D critical layers in fully-developed turbulent flows. 3D critical layer effects are identified in instantaneous snapshots of turbulent boundary layers in both experimental and DNS data (Wu et al 2014). Additionally, a 3D critical layer effect is demonstrated to appear using only a few resolvent response modes from the resolvent analysis of McKeon and Sharma 2010, with phase relationships appropriately chosen. Connections are sought to the thin shear layers observed in turbulent boundary layers (Klewicki and Hirschi 2004; Eisma et al 2015) and to amplitude modulation observations (Mathis et al 2009; Duvvuri and McKeon 2014).\\ \\ The support of the Center for Turbulence Research (CTR) summer program at Stanford is gratefully acknowledged. [Preview Abstract] |
Tuesday, November 22, 2016 8:52AM - 9:05AM |
M32.00005: Coherent structures of a self-similar adverse pressure gradient turbulent boundary layer Atsushi Sekimoto, Vassili Kitsios, Callum Atkinson, Javier Jim\'enez, Julio Soria The turbulence statistics and structures are studied in direct numerical simulation (DNS) of a self-similar adverse pressure gradient turbulent boundary layer (APG-TBL). The self-similar APG-TBL at the verged of separation is achieved by a modification of the far-field boundary condition to produce the desired pressure gradient. The turbulence statistics in the self-similar region collapse by using the scaling of the external velocity and the displacement thickness. The coherent structures of the APG-TBL are investigated and compared to those of zero-pressure gradient case and homogeneous shear flow. [Preview Abstract] |
Tuesday, November 22, 2016 9:05AM - 9:18AM |
M32.00006: Turbulent Spots Inside the Turbulent Boundary Layer Jinhie Skarda, Xiaohua Wu, Parviz Moin, Adrian Lozano-Duran, James Wallace, Jean-Pierre Hickey We present evidence that the buffer region of the canonical turbulent boundary layer is populated by locally generated turbulent spots, which cause strong indentations on the near-wall low-momentum streaks. This evidence is obtained from a spatially-developing direct numerical simulation carrying the inlet Blasius boundary layer through a bypass transition to the turbulent boundary layer state over a moderate Reynolds number range. The turbulent spots are structurally analogous to their transitional counter-parts but without any direct causality connection. High-pass filtered time-history records are used to calculate the period of turbulent spot detection and this period is compared to the boundary layer bursting period reported in hot-wire experiments. The sensitivity of the results to parameters such as the high pass filter frequency and the amplitude discriminator level is examined. The characteristics of these turbulent spots are also quantified using a spatial connectivity based conditional sampling technique. This evidence seems to be at odds with the notion that the buffer region is dominated by quasi-streamwise vortices, and contributes to the potential unification of the studies on near-wall turbulent boundary layer dynamics. [Preview Abstract] |
Tuesday, November 22, 2016 9:18AM - 9:31AM |
M32.00007: Velocity-vorticity correlation structures in compressible turbulent boundary layer Jun Chen, Shi-Yao Li, Zhen-Su She A velocity-vorticity correlation structure (VVCS) analysis is applied to analyze data of 3-dimensional (3-D) direct numerical simulations (DNS), to investigate the quantitative properties of the most correlated vortex structures in compressible turbulent boundary layer (CTBL) at Mach numbers, $Ma=2.25$ and $6.0$. It is found that the geometry variation of the VVCS closely reflects the streamwise development of CTBL. In laminar region, the VVCS captures the instability wave number of the boundary layer. The transition region displays a distinct scaling change of the dimensions of VVCS. The developed turbulence region is characterized by a constant spatial extension of the VVCS. For various Mach numbers, the maximum correlation coefficient of the VVCS presents a clear multi-layer structure with the same scaling laws as a recent symmetry analysis proposed to quantifying the sublayer, the log-layer, and the wake flow. A surprising discovery is that the wall friction coefficient, $C_f$, holds a ``-1''-power law of the wall normal distance of the VVCS, $y_s$. This validates the speculation that the wall friction is determined by the near-wall coherent structure, which clarifies the correlation between statistical structures and the near-wall dynamics. [Preview Abstract] |
Tuesday, November 22, 2016 9:31AM - 9:44AM |
M32.00008: Evolution and formation of shear layers in a developing turbulent boundary layer JungHoon Lee, Jason Monty, Nicholas Hutchins The evolution and formation mechanism of shear layers in the outer region of a turbulent boundary layer are investigated using time-resolved PIV datasets of a developing turbulent boundary layer from inception at the trip up to $Re_\tau = 3000$. An analysis of a sequence of instantaneous streamwise velocity fluctuation fields reveals that strong streamwise velocity gradients are prevalent along interfaces where low- and high-speed regions interact. To provide an insight on how such regions are associated with the formation of shear layers in the outer regions, we compute conditional averages of streamwise velocity fluctuations based on a strong shear layer. Our results reveal that one possible mechanism for the generation of shear layers in the outer region is due to the mismatch in the convection velocities between low- and high-speed regions. The results also indicate that the angle of the inclined shear layer is developing in time. In addition, the conditionally averaged velocity fluctuations exhibit a local instability along these shear layers, leading to a shear layer roll-up event as the layers evolve in time. Based on these findings, we propose a conceptual model which describes dynamic interactions of shear layers and their associated large-scale coherent motions. [Preview Abstract] |
Tuesday, November 22, 2016 9:44AM - 9:57AM |
M32.00009: Traveling wave solutions of large-scale structures in turbulent channel flow at $Re_\tau=1000$. Yongyun Hwang, Ashley Willis, Carlo Cossu Recently, a set of stationary invariant solutions for the large-scale structures in turbulent Couette flow was computed at $Re_\tau\simeq 128$ using an over-damped LES with the Smagorinsky model which accounts the effect of the surrounding small-scale motions (Rawat et al., 2015, J. Fluid Mech., 782:515). In this talk, we show that this approach can be extended to $Re_\tau\simeq 1000$ in turbulent channel flow, towards the regime where the large-scale structures in the form of very-large-scale motions (long streaky motions) and large-scale motions (short vortical structures) energetically emerge. We demonstrate that a set of invariant solutions in the form of a traveling wave can be computed from simulations of the self-sustaining large-scale structures in the minimal unit with midplane reflection symmetry. By approximating the surrounding small scales with an artificially elevated Smagorinsky constant, a set of equilibrium states are found, labelled upper- and lower-branch according to their related wall shear stress. In particular, we will show that the upper-branch equilibrium state is a reasonable proxy for the spatial structure and the turbulent statistics of the self-sustaining large-scale structures. [Preview Abstract] |
Tuesday, November 22, 2016 9:57AM - 10:10AM |
M32.00010: Time-evolution of uniform momentum zones in a turbulent boundary layer Angeliki Laskari, R. Jason Hearst, Roeland de Kat, Bharathram Ganapathisubramani Time-resolved planar particle image velocimetry (PIV) is used to analyse the organisation and evolution of uniform momentum zones (UMZs) in a turbulent boundary layer. Experiments were performed in a recirculating water tunnel on a streamwise--wall-normal plane extending approximately $0.5 \delta \times 1.8 \delta $, in $x$ and $y$, respectively. In total 400,000 images were captured and for each of the resulting velocity fields, local peaks in the probability density distribution of the streamwise velocity were detected, indicating the instantaneous presence of UMZs throughout the boundary layer. The main characteristics of these zones are outlined and more specifically their velocity range and wall-normal extent. The variation of these characteristics with wall normal distance and total number of zones are also discussed. Exploiting the time information available, time-scales of zones that have a substantial coherence in time are analysed and results show that the zones' lifetime is dependent on both their momentum deficit level and the total number of zones present. Conditional averaging of the flow statistics seems to further indicate that a large number of zones is the result of a wall-dominant mechanism, while the opposite implies an outer-layer dominance. [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