Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H22: Turbulent Boundary Layers III |
Hide Abstracts |
Chair: Michele Guala, University of Minnesota Room: 210 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H22.00001: Scale contributions to inertial layer momentum transport in turbulent boundary layers Juan Carlos Cuevas-Bautista, Caleb Morril-Winter, Joseph Klewicki, Christopher White, Gregory Chini A weight of evidence indicates that the inertial region of the turbulent boundary layer is physically composed of large scale uniform momentum zones segregated by narrow \textit{fissures} of highly vortical flow. Relative to momentum transport, this physical structure predominantly stems from the correlation between the wall-normal velocity fluctuations, $v$, and the spanwise vorticity fluctuations, $\omega_z$. The present research seeks to better understand how the relative scales of the $v$ and $\omega_z$ motions contribute to this advective transport mechanism under increasing scale separation associated with increasing Reynolds number. The broader aim is to advance an asymptotically reduced partial differential equation model of the turbulent boundary layer. Here we report on spectral analyses of high resolution, high Reynolds number measurements acquired using a four wire hotwire sensor. The focus is on quantifying the scales associated with the individual $v$ and $\omega_z$ signals, as well as the predominant scales associated with their correlation. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H22.00002: A measure of scale-dependent asymmetry in turbulent boundary layer flows Michele Guala, Arvind Singh The distribution of scale-dependent, streamwise velocity increments is investigated in turbulent boundary layer flows at laboratory and atmospheric Reynolds number, using the SAFL wind tunnel (Singh et al. Phys. of Fluids 2014) and the SLTEST data (Metzger et al. Phil. Trans Royal Soc. A 2007). The third order moments of velocity increments, or asymmetry index As(a,z), is computed for varying wall distance z and scale separation a, where it was observed to leave a robust, distinct signature in the form of a hump, independent of Reynolds number and located across the inertial subrange. The hump is observed for z$+$ \textless 5000, with a tendency to increase in amplitude, and shift towards smaller timescales, as the wall is approached. Comparing the two datasets, the hump vertical location, obeying to inner wall scaling, is regarded to as a genuine feature of the canonical turbulent boundary layer. The magnitude cumulant analysis of the scale-dependent velocity increments indicates that intermittency is also enhanced in the same flow region. The combination of asymmetry and intermittency is inferred to point at non-local energy transfer across a range of scales and may thus be used to quantify interactions between structural types in boundary layer flows. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H22.00003: Non-linear scale interactions in a forced turbulent boundary layer Subrahmanyam Duvvuri, Beverley McKeon A strong phase-organizing influence exerted by a single synthetic large-scale spatio-temporal mode on directly-coupled (through triadic interactions) small scales in a turbulent boundary layer forced by a spatially-impulsive dynamic wall-roughness patch was previously demonstrated by the authors (\emph{J. Fluid Mech.} 2015, \emph{vol.} 767, R4). The experimental set-up was later enhanced to allow for simultaneous forcing of multiple scales in the flow. Results and analysis are presented from a new set of novel experiments where two distinct large scales are forced in the flow by a dynamic wall-roughness patch. The internal non-linear forcing of two other scales with triadic consistency to the artificially forced large scales, corresponding to sum and difference in wavenumbers, is dominated by the latter. This allows for a forcing-response (input-output) type analysis of the two triadic scales, and naturally lends itself to a resolvent operator based model (e.g. McKeon \& Sharma, \emph{J. Fluid Mech.} 2010, \emph{vol.} 658, \emph{pp.} 336-382) of the governing Navier-Stokes equations. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H22.00004: Spatio-temporal frequency responses of turbulent shear flows Armin Zare, Mihailo Jovanovic, Tryphon Georgiou Low-dimensional approximations of the Navier-Stokes equations are commonly used for the purpose of analysis and control of turbulent flows. In particular, stochastically-forced linearized models can capture statistical signatures observed in experiments and numerical simulations. In such models the dynamics of forcing play a critical role. It has been recently recognized that white-in-time forcing cannot explain the observed second-order statistics. In contrast, such statistics can be exactly matched with colored-in-time forcing. In order to account for partially-available second-order statistics of turbulent flows, we identify the dynamics of forcing using a convex-optimization procedure. We also provide a constructive method for designing linear filters that generate the colored-in-time forcing and show that our forcing models can be interpreted as perturbations to the original linearized dynamics subject to white-in-time stochastic excitation. Finally, we utilize spatio-temporal frequency response analysis to show that our models not only capture turbulent flow statistics but also identify energetically significant flow structures and provide reasonable estimation of the convection velocity of the individual modes. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H22.00005: Investigation of the temperature field in a turbulent boundary layer Clayton Byers, Marcus Hultmark The scaling and evolution of a developing turbulent thermal boundary layer is investigated. By allowing the temperature differences in the fluid to remain small enough to treat temperature as a passive scalar, the analysis can be extended to any turbulent convection/diffusion problem. Mean temperature scaling is developed and analyzed by utilizing the “Asymptotic Invariance Principle” developed by George and Castillo (1997). Possible effects of the Reynolds and Prandtl number are discussed. The derived power law solution for the inner and outer scaling is then used to develop a “heat transfer law” for the wall heat flux, $q_{w}$. Data collection is performed with a newly developed MEMS sensor, allowing improved performance and reduced spatial and temporal filtering of the signal. Integration with a PIV system will allow direct measurements of the turbulent heat flux $-\overline{\theta v}$ to investigate the extent of the overlap layer and validity of the proposed scaling laws. Temperature variance $\frac{1}{2}\overline{\theta^{2}}$ will also be investigated, with a possible scaling proposed. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H22.00006: Simultaneous wall-shear-stress and wide-field PIV measurements in a turbulent boundary layer Guillaume Gomit, Gregoire Fourrie, Roeland de Kat, Bharathram Ganapathisubramani Simultaneous particle image velocimetry (PIV) and hot-film shear stress sensor measurements were performed to study the large-scale structures associated with shear stress events in a flat plate turbulent boundary layer at a high Reynolds number ($Re_\tau \approx$ 4000). The PIV measurement was performed in a streamwise-wall normal plane using an array of six high resolution cameras (4$\times$16MP and 2$\times$29MP). The resulting field of view covers 8$\delta$ (where $\delta$ is the boundary layer thickness) in the streamwise direction and captures the entire boundary layer in the wall-normal direction. The spatial resolution of the measurement is approximately is approximately 70 wall units (1.8 mm) and sampled each 35 wall units (0.9 mm). In association with the PIV setup, a spanwise array of 10 skin-friction sensors (spanning one $\delta$) was used to capture the footprint of the large-scale structures. This combination of measurements allowed the analysis of the three-dimensional conditional structures in the boundary layer. Particularly, from conditional averages, the 3D organisation of the wall normal and streamwise velocity components ($u$ and $v$) and the Reynolds shear stress ($-u'v'$) related to a low and high shear stress events can be extracted. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H22.00007: Characteristics of turbulent spots in transitional boundary layers Olaf Marxen, Tamer Zaki The laminar-turbulent transition process in a flat-plate boundary layer beneath free-stream turbulence takes place through the inception and spreading of confined patches of turbulence in an otherwise laminar flow. These patches, also referred to as turbulent spots, result from a secondary instability of the Klebanoff streaks in the pre-transitional region. The dynamics of turbulence in the spots are investigated by analyzing data sets obtained from direct numerical simulations. Conditionally-averaged and spot-ensemble-averaged statistics are evaluated and describe the flow in the intermittent transition zone. Both mean-flow and disturbance root mean square levels obtained from conditional averaging agree very well with results for fully turbulent flows, in particular near the wall and at high intermittency levels. At relatively low intermittency, the spatial inhomogeneity of turbulence within the spots is important, and is examined using ensemble averaging of turbulent patches that have comparable volume and a similar streamwise location. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H22.00008: Characterization of coherent motions in cross flow via DNS Can Liu, Guillermo Araya, Stefano Leonardi, Murat Tutkun, Luciano Castillo Direct numerical simulations are performed at a friction Reynolds number of 394, based on the bulk velocity and half channel height. It is shown that small local blowing perturbations near the leading edge of the channel produced a secondary peak in turbulent production. This peak is attributed to the presence of a strong adverse pressure gradient that occurs in the outer part of the boundary layer. Furthermore, this secondary peak is produced by the energy enhancement of the presence of large-scale motions, which is a result of a shear layer located at about y$^{\mathrm{+}}=$60. It has been found that the pressure fluctuation is important in the energy distribution of small scale motions in the inner region and large scale motions. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H22.00009: Preponderance of hairpin vortices and their life cycles in the outer region of the canonical flat-plate boundary layer James Wallace, Xiaohua Wu While the dominance of hairpin vortices in the transitional and early turbulent regions of the zero-pressure-gradient, flat-plate boundary layer has been widely accepted, recent literature is divided on this issue at higher Reynolds numbers. Here we investigate the representative vortex structures in the outer region of the canonical boundary layer over the momentum thickness Reynolds number range of 1000 to 3000, using the DNS database of Wu, Moin and Hickey (Phys. Fluids 26, 091104). In the outer region of the boundary layer we observe that hairpin vortices comprise nearly fifty percent of all the vortical structures visualized with the swirling strength $\lambda_{ci}$. Furthermore, these hairpins remain identifiable while they are advected downstream over distances corresponding to increases of about 300 - 400 in momentum thickness Reynolds numbers. Therefore, over the Reynolds number range studied, approximately three generations of hairpins go through their life cycles. This demonstrates that many of these outer region hairpin vortices are generated in the fully-turbulent region, and thus are not the debris of the upstream transition to turbulence. Coherent structures in the near-wall region will also be discussed. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H22.00010: Identifying Orr-like behaviour in full-scale turbulent wall-bounded flows Miguel P. Encinar, Javier Jimenez The presence of linear, transient phenomena in fully developed non-linear turbulence is studied in the sense of relating the growth of the intensity of wall-normal velocity perturbations with their inclination angle. This phenomenon is predicted by the Orr-Sommerfield equation, and can explain the formation of the energy-containing scales when paired with the lift-up mechanism. This process has been previously identified in minimal channels in which structures are represented by individual Fourier modes, and is generalised here to extended ones that contain many individual structures at different scales and stages of development. We present a method based on wavelet projection that addresses both spatial and spectral locality. After filtering the flow with a given wavelet, a local optimum wavelength and wavefront inclination is computed at each point of the filtered flow, and used to trace the Orr-like behaviour. The relation of the measured perturbations with the rest of the flow properties is explored, showing good agreement with the predictions of the Orr mechanism. [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