Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session L36: Boundary Layer Roughness Effect I |
Hide Abstracts |
Chair: Xiaowei Zhu, Portland State University Room: 355 B |
Monday, November 25, 2024 8:00AM - 8:13AM |
L36.00001: Experimental Characterization of Effects of Wall Inhomogeneity on Surface Deformation in a Turbulent Boundary Layer over a Compliant Wall Koustav Bandyopadhyay, Yuhui Lu, Joseph Katz Recent investigations have revealed that deformations of compliant surfaces have significant influence on the flow and turbulence in the inner part of the boundary layer, all the way to the logarithmic region. The two-way coupling between flow and deformation are affected by the Reynolds number, visco-elastic wall properties, and the wall thickness, with the wall longitudinal strain being proportional to the rms pressure divided by the storage modulus. Consistent with theoretical predictions, in homogeneous materials, the wavelength of wall deformation is equal to three times the compliant layer thickness (l0). This study attempts to modulate the surface wave characteristics by placing alternating strips of ‘high’ and ‘low’ stiffness, having a storage moduli of 930 kPa and 158 kPa, respectively (referred to ‘hard’ and ‘soft’ material) in the streamwise direction. The strip widths are 18 mm for a thickness of 5 mm, i.e. slightly larger than 3l0. Time-resolved Mach-Zehnder interferometry, which has a submicron resolution, is employed to map the surface deformation in a 65 mm diameter circular field of view, covering at least 1.5 times of the cycle of hard and soft strips. Applications of spectral and statistical data analysis tools, which are still in progress, show a series of effects, including attenuation, changes to the wavelength, as well as reflections and formation of standing waves at the interfaces. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L36.00002: Towards a new roughness parametrization through the Effective Distribution function Federica Bruno, Mauro De Marchis, Stefano Leonardi Many studies have explored the effects of different roughness shapes and distributions. Efforts have been aimed at finding a statistical descriptor of roughness geometry to replace the equivalent sand grain roughness ks, a hydraulic property estimable from the mean velocity profile. Despite advances in understanding of the flow over rough walls, a knowledge gap still remains, in particular how to parametrize the drag and roughness function. DNSs have been performed for a fully developed turbulent channel flow with triangular bars at Reτ up to 790. For a fixed pitch to height ratio w/k=4 two sets of simulations varying roughness height were analyzed. The first set had 16 triangular bars equally spaced in the streamwise direction w/h=0.4with a constant roughness height k/h=0.1. The second set halved the number of bars but doubled the roughness height to k/h=0.2. Other cases modified the baseline to highlight features like protuberances and wakes affecting downstream roughness. Plotting total drag and roughness function against ES, Sk, or Ku showed significant variation, about 30-40%. The results indicated that parametrization must consider: contribution of elements in larger elements' wake to drag is negligible, pattern and distance effects of roughness elements and the impact of flat regions between rough elements on velocity distribution. These factors were included in the Effective Distribution (ED), revising ES and improving drag correlation by accounting for peaks above mean roughness, wake regions from the highest elements and distances between elements. To further corroborate our previous finding and validate the ED, we applied it to a more complex irregular rough wall generated through the superimposition of sinusoidal functions with random amplitudes showing consistent results with the presented correlation. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L36.00003: Numerical simulations of oscillatory flow over rough beds with different shapes and angularity Umberto Ciri, Sylvia Rodriguez-Abudo, Stefano Leonardi The seabed hydrodynamics in coastal areas is characterized by the so-called wave bottom boundary layer, an oscillatory motion generated by free-surface gravity waves. The wave bottom boundary layer affects the whole seabed ecosystem, from remodeling the bed morphology to the transport of nutrients and substances dispersed in water. Despite significant research progress made over the years, a complete understanding of this flow is still lacking. A key challenge is that the seabed is typically rough and made of particles (sediments) that, depending on the location, have different shapes and angularities. Most of the previous work in the literature has focused spherical particles (representative of non-cohesive silica sands), while less attention has been devoted to other non-spherical sediment shapes that are common, for example, in tropical areas. Nevertheless, the particle geometry and spatial distribution are likely to have a significant impact on the bottom hydrodynamics. In this work, we consider beds with particles in the shapes of either ellipses, disks, or pyramids under the same oscillatory flow conditions. The study is conducted using direct numerical simulations coupled with an immersed boundary method to treat the bed. The oscillation is imposed through a sinusoidal velocity boundary condition on the rough bed, which mimics the shear-driven flow commonly observed in oscillating tray rigs experiments. The objective of this study is to investigate the dependence of turbulent flow statistics on the particle shape and angularity towards an improved understanding of the wave bottom boundary layer dynamics. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L36.00004: Effects of tilt angle on secondary motions over solar installation of E-type roughness Emma R Compton, Katie N Taylor, Sarah E Smith, Zein Ahmad Sadek, Ondrej Fercak, Abdelhalim Abdeldayem, Marc Calaf, Raúl Bayoán Cal For renewable energy to replace fossil fuels as the primary source of energy to fulfill the world's ever-increasing energy needs, the design of large-scale solar farms must reduce cost and undesirable changes to the atmospheric boundary layer (ABL). Photovoltaic (PV) technology can move towards cost parity by reducing efficiency losses due to working conditions; it has been shown the solar panel inclination greatly affects the convective heat transfer near the panels, allowing for thermal management of the PV modules. However, the effects of tilt angle on the secondary motions above the solar farm, which can affect the ABL, have yet to be investigated. The PV canopy is modeled as a novel type of roughness, referred to as elevated (or E-type) roughness. E-type roughness expands on other blunt roughness types (e.g. K-type or D-type) to include additional system variations known to affect local turbulence. This study utilizes Portland State University's wind tunnel to model an infinitely long solar farm with 4 tilt angles at variable wind speeds. Stereoscopic particle image velocimetry data will show the secondary and tertiary vortices extending into the ABL for each tilt angle. Results both inform the design of future PV systems and introduce E-type roughness as a model applicable to natural and industrial environments. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L36.00005: Scaling for Turbulent Flows Encountering Roughness Transitions Justin Patrick Cooke, George I Park, Douglas J Jerolmack, Paulo E. Arratia Roughness transitions in turbulent flows are widespread in nature and technology -- where ocean meets land, patchy bio-fouling on naval vessels, or deterioration of turbine blades. In such flows, an internal boundary layer (IBL) forms at the point of transition. The IBL introduces an unsteady region to the flow, as well as new time- and length-scales. This growing region complicates the scaling of these flows, as the IBL prevents mean velocity profiles from exhibiting self-similarity. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L36.00006: Physical Characterization of the University of New Hampshire’s Flow Physics Facility Wind Tunnel for Atmospheric Boundary Layers Simulation Christopher M White, Juan Carlos Cuevas-Bautista, Kofi Agyemang Amankwah, Maxx Parys The Flow Physics Facility (FPF) at the University of New Hampshire (UNH) was employed for Atmospheric BoundaryLayer (ABL) Simulation. The FPF, one of the largest boundary layer wind tunnels in the world, features a test section of 2.8m × 6m × 72m. This extensive flow development fetch is ideal for achieving a naturally developed simulated ABL thickness of O(2m). Pitot static tube and hot wire measurements of the streamwise velocity were collected at three speedsand three wall-roughness configurations. A rural terrain was simulated using Irwin triangular-shaped spires and a barrier of eight hundred 50mm cubical roughness elements with a fetch length of 5m after the spires, following the Counihan method. Experimental results showed good similarity with the rural models in the ASCE Standards (ASCE/SEI 49-12). Additionally, a porous disk turbine model of diameter 1m was placed within the denser rural terrain configuration to study near wake turbulence in a high Reynolds number environment. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L36.00007: Turbulent Boundary Layer Development over Flexible Roughness Patches Pratik Suhas Deshpande, Ebenezer P Gnanamanickam, Greeshma C Daniel Flexible roughness patches, in the form of micropillar arrays inspired by hair-like sensors found in various arthropods and aquatic species, were used to perturb a zero-pressure gradient turbulent boundary layer. Particle image velocimetry (PIV) measurements over a streamwise-wall-normal plane were carried out at a nominal friction Reynolds number of approximately 2400. The measurement window was centered over each flexible roughness patch and encompassed the length of the patch (≈1.5δ99) in the streamwise direction. The flow over several patches with varying micropillar stiffness and density was compared. The flow over a smooth wall was also used as a reference for comparison. Additionally, hot-wire measurements were carried out over the patches and downstream of the trailing edge of the patches. All arrays showed a shift in the near-wall peak away from the wall and above the micropillars. Generally, the near-wall turbulence intensity increased near the leading edge of the patch due to the abrupt introduction of the patch into the smooth wall flow. This near-wall turbulence intensity then decreased past the leading edge and gradually increased again towards the trailing edge. It was determined that the magnitude of these changes in the near-wall turbulence depended primarily on the spanwise and streamwise spacing. Downstream of the trailing edge, the increase in the near-wall peak observed over the patch shifted into the log region. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L36.00008: Refined Measurements of Turbulent Boundary Layer Statistics to Investigate Permeability Effects on Skin Friction Idan B Eizenberg, Mitul Luhar Hydrodynamic and aerodynamic surfaces in nature often feature anisotropic permeability. Previous modelling endeavours show that these surfaces can contribute to friction drag reduction (DR) in wall-bounded turbulent flows by producing direction-dependent slip. This work investigates the impact of such surfaces on turbulent skin friction via laboratory boundary layer experiments in a large-scale water channel facility. Drag forces were measured directly in several experiments, and velocity fields were measured using particle image velocimetry (PIV). |
Monday, November 25, 2024 9:44AM - 9:57AM |
L36.00009: Coherent turbulent heat transfer over a wall under pressure gradients with and without organized roughness Edgardo J Garcia, Fazle Hussain Bumps with roughness are prevalent in nature and technology. We study via DNS the flow over a heated wall of a channel having a simple large-scale spanwise bump overlaid with fine-scale longitudinal grooves (GW) used as an idealized roughness. Also, data are compared with a bump wall without grooves (SW). In SW, negative turbulent heat flux near the wall is found in the region of negative turbulence production despite also being where a local maximum of wall heat flux (qw) and wall shear stress (tw) occurs – notably further accentuated in GW. Another maximum of qw occurs at the point of flow reattachment downstream of the bump, with a higher magnitude in GW. In GW, qw decreases upstream of the bump and in the separation bubble (SB) region downstream of the bump; the thermal boundary layers are thicker in GW than in SW. The lower qw upstream is caused by the upstream streamline curvature-induced steady SB. In the SB downstream of the GW bump qw is particularly lower where secondary minibubbles, counter-rotating to SB appear – hence the decrease in qw under the entire SB. The turbulent Prandtl number (Prt) ranges from ~0.5 in the shear layer past the bump peak to ~2.5 in regions of adverse pressure gradient for both SW and GW – the peak of Prt is 25% higher in SW than in GW. qw/tw varies from 0.5 to 2.5 over the bump similarly in both SW and GW. This ratio upstream of the bump is 30% higher in GW. The instantaneous distributions of temperature, turbulent heat transfer and Prt are explained in terms of coherent structures in the vortical and thermal fields. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L36.00010: Input-output analysis of transitional channel flow over large-scale wavy walls Jino George, Chang Liu Flow over complex terrains is important in environmental applications such as understanding pollution transport in mountainous regions and flow over tree canopies. Surface roughness also plays an important role in industrial applications such as riblets that alter eddies in turbulent flows and potentially reduce the drag. This work analyzes flow over large-scale wavy walls as a low-order approximation to understand the roughness effect with a dominant wavelength. We conduct input-output analysis of transitional channel flow over large-scale wavy walls, where the wavy wall is included through implementing volume penalization method for the solid domain. The Chebyshev collocation method is used in wall-normal direction and the Fourier collocation method is employed in the wavy direction of the topography. Input-output analysis allows us to identify the dominant wavenumber frequency pair leading to the largest response. We also employ singular value decomposition to obtain the leading forcing and response mode, which shows a smaller wavelength than the length scale of the wavy wall. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L36.00011: “Superstructures” in turbulent boundary layers over rough walls up Reτ = 3,000 Ioannis Kaminaris, Elias Balaras The existence of large-scale structures, also known as "superstructures", in the instantaneous velocity field at high wall-normal distances has been reported by many studies in the literature so far, for both pipe and boundary layer configurations through primarily experimental studies. Computational works observing similar structures mainly rely on channel-flow configurations or boundary layers at relatively low Reτ, which thus do not allow for direct comparisons to the experimental datasets. In the present study we report evidence of "superstructures" in spatially developing boundary layers of at least 60δ streamwise extent over both regular and irregular rough-walls by performing direct numerical simulations (DNS) up to Reτ = 3,000. Rough-wall cases are compared to a refence smooth wall case at the same inflow Reτ. Detailed evolutions of the "superstructures’" lengthscales, as well as the corresponding time-scales are reported as a function of the streamwise and wall-normal distance through autocorrelation functions of the instantaneous velocity field. Results suggest that the structures formed over the rough-wall cases grow faster following the more rapid boundary layer evolution. Furthermore, "superstructures" have found to be clearly flanked by pairs of counter-rotating vortices when reduced order models (ROM) are constructed. Finally, the impact of "superstructures" to the instantaneous wall shear stress is reported, alongside the differences between the smooth and rough wall cases. |
Monday, November 25, 2024 10:23AM - 10:36AM |
L36.00012: Abstract Withdrawn |
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. |
© 2025 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