Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G18: Turbulence: Environmental Flows |
Hide Abstracts |
Chair: Chandru Dhandapani, California Institute of Technology Room: 400 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G18.00001: A fresh look at an old problem: perturbed flow over uneven terrain Paolo Luchini, Franccois Charru Flow over an uneven terrain is classically first linearized about a flat bottom and a locally parallel flow, and then Fourier transformed and asymptotically approximated into an interactive representation that couples a boundary layer and an irrotational region through an intermediate inviscid but rotational layer. Or, since this is a one-dimensional Orr–Sommerfeld problem comparatively easy for any computer, one may decide to forgo the second sweep of approximation and solve the problem numerically. The hidden pitfalls of doing so, and the adopted solutions, are here examined and explained from the viewpoint of boundary-layer symmetries, while also providing a compact and accurate asymptotic approximation for the maximum laminar shear-stress response, whose wavenumber scales with a power of the boundary-layer thickness. In turbulent flow, the maximum shear-stress response occurs instead at a Reynolds-independent wavenumber; the question is still open, also in the light of recent numerical counterexamples, whether a fully developed turbulent regime, similar to the one predicted by a widely adopted eddy-viscosity or mixing-length model, even exists for open flow in the limit of infinite wavelength. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G18.00002: Turbulent intensity Enhancement by gaps in submerged Canopy Flows Hayoon Chung, Tracy Mandel, Margarita Dronov, Jeffrey Koseff Canopies such as seagrass alter their dynamical environment by impacting the flow and turbulent structures. However, unlike well-studied systems in which fully developed boundary layers encounter homogenous and uniform canopies, many aquatic canopy systems display patchiness, e.g. gaps and clearings, that impact the flow, and also interact with velocity fields that are still developing. Therefore, what are the impacts of gaps, both locally and at the canopy scale? We conducted experiments in a recirculating flume with a model vegetation canopy. The canopy is broken up by gaps of varying lengths, and velocity and turbulence measurements were made in the gaps and wakes. Observations suggest that gaps effect the decay of the mixing layer in the gap before it re-enters the downstream canopy segment. The ML decays into a more linear profile, and spreads more shear and turbulent intensities throughout the water column, particularly higher up away from the canopy roughness. Therefore, when compared to an uninterrupted homogenous canopy, the fragmented canopy experiences enhanced turbulent energy at various locations along the canopy. We studied the impact of gap lengths on the extent of turbulence enhancement, and the extent to which the disturbance propagates along the canopy. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G18.00003: Influence of plant flexibility on turbulent aquatic canopy flow Sida He, Lian Shen Aquatic plant plays an important role in the hydrodynamics of aquatic environments, such as river, lake, and ocean. We have simulated the turbulent flow in submerged aquatic canopy with plant flexibility varying from absolute rigid to extremely flexible. Different from the classical approach of modeling the hydrodynamic effect of canopy as a volume drag force, we resolved the hydrodynamic effect of every plant by an immersed boundary method. Our approach has two benefits: (1) the interaction between the turbulence and every plant can be inspected directly; (2) \textit{a priori} constant drag coefficient is not required. We then studied the influence of plant flexibility on the turbulent flow and canopy waving motion, i.e., \textit{monami}. For all canopy flexibility, the velocity profile is self-similar in the mixing layer, though it does not completely follow the hyperbolic tangent profile of pure mixing flow. Our comparison of the mean momentum transport in the flexible and rigid canopy shows the significance of Reynolds stress and dispersive flux in the flexible canopy. We also studied the dispersion relation of \textit{monami} and found that the wave speed of the high-wavenumber component depends on the plant flexibility. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G18.00004: Vibrational energy fluctuation in compressible isotropic turbulence with thermal non-equilibrium Qinmin Zheng, Jianchun Wang, Minping Wan, Shiyi Chen, Hui Li The vibrational energy fluctuation of compressible isotropic turbulent flows in vibrational non-equilibrium is investigated numerically at turbulent Mach numbers of 0.44 and 1.09, focusing on the effect of the characteristic vibrational relaxation time on statistical features of the dissipation/production components of vibrational energy fluctuation. The dissipation/production of vibrational energy fluctuation might result from effects of dilatation, thermal diffusion and vibrational relaxation. The dissipation component due to thermal diffusion always suppresses the vibrational energy fluctuation in both of compression and expansion regions for the weakly and highly compressible turbulences; but its effect is insignificant comparing to other two components. For the weakly compressible turbulence, the dissipation/production of vibrational energy fluctuation mainly comes from effects of dilatation and vibrational relaxation when the characteristic vibrational relaxation time is small; and the vibrational relaxation component loses its significance gradually with the increase of characteristic vibrational relaxation time. For the highly compressible turbulence, both of the dilatation and vibrational relaxation effects play an important role in the dissipation and production of vibrational energy fluctuation. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G18.00005: Enhanced Drag Reduction by High Mach Number Streaming Tapish Agarwal, Beni Cukurel, Ian Jacobi Significant drag reduction for a laminar boundary layer is predicted for high Mach number, travelling-wave flow actuation. Historically, low Mach number, temporal or standing waves were used to modify a base laminar flow by Stokes streaming. Predictions for the associated drag reduction were based on asymptotic, high frequency approximations of the governing momentum balance. We present a numeric solution of the full momentum balance for the streaming flow, based on Lin's Reynolds decomposition analysis, which allows for examination of the complete range of forcing frequencies. The solution also provides for analysis of travelling wave actuation, which is better suited for practical implementation in boundary layers and channels. The streaming-induced drag reduction is studied as a function of the Mach number, Reynolds number, forcing amplitude, and frequency. In particular, high Mach number, high frequency travelling waves are predicted to produce significant laminar drag reduction. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G18.00006: Laminar flow in planar Tee joints Marcos Vera, Gustavo A. Patiño, Immaculada Iglesias We present a numerical investigation of the laminar flow in planar Tee joints, a canonical flow of interest for the thermal-hydraulic design of oil power transformer windings. The steady, constant property flow in planar Tee joints is computed numerically by integrating a non dimensional formulation of the Navier-Stokes equations with fully developed upstream and downstream boundary conditions. The analysis assumes a straight-through configuration in which the straight duct holds flow in the same direction before and after the junction, whereas the flow from the side branch can combine with the incoming flow or divide from it. We present a description of the flow patterns that emerge in both cases for a full range of mass split ratios, $0\leq\beta\leq 1$, several values of straight duct to side branch width ratios, $1\leq\alpha\leq 3$, and Reynolds numbers of the common branch in the range $20 \leq {\rm Re} \leq 200$. Flow maps for planar Tee joints are presented, showing the existence of different regions in the (Re, $\beta$)-plane that exhibit different number and location of recirculation zones. From the pressure distribution, secondary loss coefficients are computed and used to fit pressure loss correlations useful for pipe-network modelling of oil power transformer windings. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G18.00007: Considering spatial inhomogeneities in forest canopies Ryan Scott, Hawwa Falih, Sarah Smith, Naseem Ali, Juliaan Bossuyt, Marc Calaf, Raul Cal Forest canopies serve a key role in determining regional climate and modify terrestrial surface roughness. Forests are typically considered large areas of contiguous roughness elements. While forest composition exists in a state of constant flux, human activities impose an ordered arrangement on local canopy structure. In particular, logging and development produce non-homogeneous patterns of canopy patches separated by regular gaps. To quantify the role of these patterns on the canopy sublayer, a series of wind tunnel experiments were performed with a scaled model forest canopy. The model forest was constructed of multiple patches spanning the width of the wind tunnel. Each patch was comprised of model conifers with a total height of 10 cm and cone diameter of 4 cm. Individual trees were realized by an interconnected reticulated foam canopy layer attached to evenly spaced tree trunks. Particle image velocimetry measurements were collected above the canopy and within gaps for both homogeneous and non-homogeneous canopies. From these measurements, the influence of non-homogeneous canopy patterns is quantified by computing relevant mean statistics and flow structures. In addition, the implications for local effects and land management practices will be discussed in presentation. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G18.00008: Implications of spatial heterogeneity on fluxes and dispersive stresses in a forest canopy Hawwa Kadum, Ryan Scott, Sarah Smith, Naseem Ali, Juliaan Bossuyt, Raúl Bayoán Cal, Marc Calaf The influence of canopy sublayer flow characteristics extends from locally deriving forest ecolog- ical processes to globally altering the atmospheric boundary layer. Here, implications of spatial heterogeneities and the impacts of unintended consequences caused by natural events and/or human intervention on the flow behavior in the canopy sublayer are considered. A series of experiments are conducted in Portland State University closed loop wind tunnel facility. Forest models consistent of alternating areas of forest patches and gaps in the streamwise direction are tested. The study covers various combinations of patch and gap lengths as well as a contiguous forest model with no gaps. Heterogeneity effects are examined through the quantification of dispersive stresses and terms associated with the momentum and mean kinetic energy equations. [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. |
© 2020 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