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 ZC35: Free-Surface Flows: Waves II |
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Chair: Cong Wang, University of Iowa Room: 355 A |
Tuesday, November 26, 2024 12:50PM - 1:03PM |
ZC35.00001: Physics of free-surface turbulent wake flow uncovered by three-dimensional defocusing particle image velocimetry (PIV) Cong Wang, Morteza Gharib, Chukwudum Eluchie, David Song Jeon The turbulent free surface wake is extremely complicated due to its multi-scale unsteady nature across two phases (air and water). The transport of mass, momentum, and energy results in phenomena such as air bubble entrainment, which critically affects the safety and performance capabilities of many maritime technologies. Here we present the physics of turbulent wake flow behind a partially submerged triangle wedge. Measurement results obtained by both the conventional 2D-PIV and the more advanced 3D defocusing PIV will be present. It was discovered that the wake flow has a wider wake angle with higher turbulence intensity when close to the free surface. These observations are likely due to the amplification of instability in the 3D wake flow caused by the unsteady free surface. These fundamental discoveries pave the way towards high-fidelity modeling of free surface turbulent wake. |
Tuesday, November 26, 2024 1:03PM - 1:16PM |
ZC35.00002: Frozen waves in the inertial regime Benoit-joseph Gréa, Antoine Briard, Andres Castillo-Castellanos Interfaces subjected to strong time-periodic horizontal accelerations exhibit remarkable patterns known as frozen waves. We have experimentally and numerically explored the formation of such structures within immiscible fluids under high forcing frequencies. It is demonstrated that in the inertial regime, characterized by large Reynolds and Weber numbers—where surface tension and viscosity effects become negligible—the amplitude of the frozen waves increases proportionally to the square of the forcing velocity. These findings are consistent with vibro-equilibria theory and confirm the predictions made by Grea & Briard (2019) for miscible fluids. Additionally, we have investigated the influence of Reynolds and Weber numbers on the secondary Faraday instabilities, illustrating the transition of frozen wave patterns toward a homogenized state. |
Tuesday, November 26, 2024 1:16PM - 1:29PM |
ZC35.00003: A new short-wave instability mode in gas-sheared falling liquid films Misa Ishimura, Sophie Mergui, Christian Ruyer-Quil, Georg F Dietze We study the linear stability of a laminar falling liquid film flowing in an inclined channel under the effect of a turbulent counter-current gas flow. In such systems, surface waves resulting from interfacial instability may strongly enhance interphase heat/mass transfer, but can also trigger flooding events, such as obstruction of the channel cross-section, droplet entrainment, or wave reversal. In a recent article (Ishimura et al., J. Fluid Mech., vol. 971, A37, 2023), we discovered, via linear stability calculations, a new short-wave instability mode, which is triggered by the turbulent gas flow. These calculations were based on the Navier-Stokes equations in the liquid and the Reynolds averaged Navier-Stokes (RANS) equations in the gas, using a temporal stability formulation. The short-wave instability mode gives rise to upward-travelling ripples, which have been observed in experiments, and our linear predictions were shown to be in good agreement with the measured wave speed and wavelength. Further, upon increasing the counter-current gas flow rate, the short-wave mode merges with the classical long-wave Kapitza mode, usually observed in falling liquid films. In the current contribution, we extend our previous work in two ways. Firstly, we determine how the onset of the short-wave instability is affected by the relevant control parameters, i.e. the liquid and gas Reynolds numbers, the channel height, the inclination angle, and the Kapitza number. In particular, we find that the short-wave mode disappears as the inclination angle is increased. Further, we perform stability calculations based on a spatio-temporal formulation, i.e. by differentiating the Orr-Sommerfeld eigenvalue problem with respect to the complex wavenumber, allowing to solve for the group velocity. Further, we show that the merged and long-wave modes can exhibit downward-convective, upward-convective, and absolute instability behavior, whereas the short wave mode is always upward convective. |
Tuesday, November 26, 2024 1:29PM - 1:42PM |
ZC35.00004: Restricted Euler dynamics in free-surface turbulence Yinghe Qi, Zhenwei Xu, Filippo Coletti The small-scale velocity gradient on the free surface is related to the large-scale properties of free-surface flows, such as the upwelling/downwelling motions from and into the fluid underneath and the transport along the free surface itself. The Lagrangian dynamics of the velocity gradient can be simplified and represented by a dynamic system using the restricted Euler model that neglects the viscous and nonlocal pressure Hessian terms in the Navier-Stokes equation. In this work, we derive the restricted Euler model for free-surface turbulence in the absence of surface deformation, and discuss the associated stable/unstable manifolds. The model is compared with the data collected on the free surface of a turbulent tank with negligible surface waves. We show that the joint probability density function of the velocity gradient invariants exhibits a distinct pattern, which differs from the one displayed by generic two-dimensional sections of three-dimensional turbulence and agrees with the predictions of the restricted Euler model. The latter, therefore, may be a powerful tool to examine the dynamics of free-surface turbulence. |
Tuesday, November 26, 2024 1:42PM - 1:55PM |
ZC35.00005: Turbulence Evolution under a Passing Wave Packet Anqing Xuan, Bing-qing Deng, Lian Shen In a realistic ocean environment, traveling wave groups can emerge from random surface waves, influencing the underlying turbulence. This simulation-based study investigates the turbulence response to a Gaussian wave packet, employing a Helmholtz decomposition-inspired method to capture turbulence-wave interactions with wave phase resolved. With this approach, the turbulence is simulated in a rigid-lid box, but the orbital motions of the wave packet can be directly resolved without wave-phase averaging, enabling accurate modeling of the wave packet effect on turbulence. Our results show that turbulence statistics, such as enstrophy and Reynolds normal stresses, experience significant variations during the wave packet passage, particularly around the packet core. The energy spectra indicate that the turbulence enhancement occurs across a wide range of scales, with the near-surface small-scale motions experiencing the most significant intensification. This work elucidates the dynamic interactions between transient wave forces and ocean turbulence. |
Tuesday, November 26, 2024 1:55PM - 2:08PM |
ZC35.00006: Influence of Riparian Vegetation on Turbulent Flow around Submerged Spur Dike Fields Divya Thokala, Soumendra Nath Kuiry Spur dikes extend from the riverbanks into the main channel to serve various purposes. These structures create stagnant water zones, which influence the river ecosystem, sediment dynamics, and pollutant transport. Additionally, riparian vegetation contributes to these river processes during flooding. This study investigates the flow interactions between spur dike fields and the main channel to examine the effects of floodplain vegetation on mixing and the momentum exchange processes. Large Eddy Simulations were conducted with and without vegetation in a simplified straight channel within the OpenFOAM computational fluid dynamics framework. The results were analyzed to assess coherent structures, distributions of flow patterns, turbulent kinetic energy, and Reynolds stresses. Findings indicate that the presence of vegetation in the floodplain significantly alters the evolution of flow structures and mixing dynamics during river flooding. It also amplifies bed shear stress and turbulence in the main channel, which may induce bed erosion. This research advances insights into the complex flow dynamics of this coupled system, enhancing our understanding of flood management and vegetation restoration strategies. |
Tuesday, November 26, 2024 2:08PM - 2:21PM |
ZC35.00007: Hydrodynamic impact of internal solitary waves on a cylinder close to free surface Sai Pramod Anumula, Xuanting Hao Surface currents generated by internal solitary waves (ISW) are known to induce a significant hydrodynamic force on surface platforms and offshore infrastructures, which can potentially affect their normal operations. Quantifying this force is challenging because ISW-induced flows are transient, and free surface proximity is known to cause complexity in the fluid dynamics. In this study, we perform direct numerical simulations (DNS) of a cylinder close to the free surface using the volume-of-fluid method. We first examine the hydrodynamic forces acting on the cylinder and the vortex shedding patterns for a steady inlet flow in different cases with varying cylinder submergence depths and Froude numbers. We then perform simulations where the inlet velocity is specified by the transient surface current adapted from the ISW solution computed from the classical Dubreil-Jacotin-Long (DJL) equation. Our analysis shows a notable difference in the hydrodynamic forces between the transient inlet case and their corresponding steady inlet cases. |
Tuesday, November 26, 2024 2:21PM - 2:34PM |
ZC35.00008: Abstract Withdrawn
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Tuesday, November 26, 2024 2:34PM - 2:47PM |
ZC35.00009: Waves, bubbles, and wake structures in liquid-gas flow past a cylinder Kuntal Patel, Xiaojue Zhu The interaction of free surface flow with solid bodies is ubiquitous in offshore structures. Motivated by this, in our numerical study, we consider a canonical setup involving a stationary circular cylinder in liquid-gas flow. The cylinder is immersed in the flowing liquid but kept close to the liquid-gas interface. In the unperturbed state, the liquid-gas interface spanning the horizontal direction is flat, and the flow profile within the liquid is uniform, which develops an interfacial boundary layer in the gas phase. The interplay between the liquid-gas interface and flow perturbations originating from the cylinder leads to three distinct regimes of interface dynamics: interfacial waves driven by Strouhal vortices, entrainment of multi-scale gas bubbles, and the reduced deformation state. These regimes exhibit markedly different wake structures, and the transition across these regimes is regulated by the Bond number and the submergence depth of the cylinder while keeping the Reynolds and Weber numbers fixed. We pay particular attention to bubble-size spectra and breakup mechanisms in the gas entrainment regime and assess the role of Reynolds and Weber numbers. Lastly, we show that the hydrodynamic lift force acting on the cylinder can be tuned using the deformability of the nearby liquid-gas interface. |
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