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 R02: Free-Surface Flows: General |
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Chair: Graham Benham, University College Dublin Room: Ballroom B |
Monday, November 25, 2024 1:50PM - 2:03PM |
R02.00001: Impact of a Plunging Breaker on a Cube at Various Streamwise Positions NAUMAN MALDAR, An Wang This study investigates the impact of a deep-water plunging breaker on a cube with a dimension of L = 30.5 cm and its bottom edge located 0.44L below the mean water level. A dispersive focusing technique is used to generate a wave packet with a nominal wavelength λ = 118 cm, resulting in a wave crest that reaches a maximum height at Xm = 643.9 cm relative to the wave maker and subsequently becomes a plunging breaker in open water. The front face of the cube is oriented vertically and its streamwise position is varied within a range from Xm-0.076λ to Xm+0.236λ. Synchronized time-resolved measurements of the free surface profiles and pressures on the cube front face are conducted using a laser induced fluorescent technique and piezoelectric sensors, respectively. Three distinct impact classifications—flip-through, low-aeration, and high-aeration—are identified based on the cube location and the unique characteristics of the wave impact. Notably, low-aeration impacts exhibit higher peak pressure values compared to the other classifications. In a flip-through condition, the velocity of the intersection between the free surface and the cube front face is found to follow a power law in time, similar to a finite-time singularity observed in some free-surface focusing phenomena. |
Monday, November 25, 2024 2:03PM - 2:16PM |
R02.00002: Experimental Investigation on the Deformation and Vibration Characteristics of Elastic/Hyperelastic Plates Under Water Jet Impact Qi Sun, An Wang The deformation and vibration characteristics of elastic/hyperelastic rubber plates subjected to water jet impact are investigated experimentally. A set of stereo high-speed cameras is used to capture the deformation of the plates and the recorded images are analyzed via a Digital Image Correlation (DIC) technique. Synchronized measurements of the impact force normal to the undeformed plates are conducted using force sensors. The rubber plates vary in elastic properties and different levels of in-plane tension are applied. The static and dynamic responses of these plates subjected to given loading functions are calibrated. Additionally, various speeds of the water jet are used. Literature suggests that the elastic properties of the plates significantly influence the characteristics of the impact load from the water jet, differing from the classic water hammer effect with rigid walls. In the present study, the relationship between the plate's effective bending stiffness, the impact force, the plate's vibration and the jet characteristics is explored. One of the goals of this research is to provide insights for manipulating the jet impact process through the control of the structural response. |
Monday, November 25, 2024 2:16PM - 2:29PM |
R02.00003: Abstract Withdrawn
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Monday, November 25, 2024 2:29PM - 2:42PM |
R02.00004: A delicate balance: How Faraday waves and vortex shedding drive air entrainment Sophia Relph, Kenneth Thomas Kiger Bubble-turbulence interactions are central to many processes of great fundamental interest, including ocean science, metal casting, and industrial power systems. A versatile yet simple analog for many of these processes is the plunging liquid jet, wherein bubbles are formed by the entrainment of air as the jet impinges upon a quiescent pool. The formation of these bubbles is initiated by the conditions of the jet and free surface, with major roles played by the dynamic effects of gravity, surface tension and the local subsurface flow. When air entrainment begins, it is the result of disturbances upon the interface overcoming surface tension via interactions with the subsurface flow. However, this competition of forces has escaped comprehensive description thus far. To better understand the inception of air entrainment, we employ time-resolved particle image velocimetry to extract pressure and velocity data from a well-characterized plunging jet flow that is well-controlled and harmonically perturbed. We fuse these data with high speed movies and quantitative bubble flow rate measurements to uncover the mechanisms that transform micron-scale free surface disturbances into centimeter-scale bubbles. |
Monday, November 25, 2024 2:42PM - 2:55PM |
R02.00005: Dynamics of gas exchange across the air-water interface: Insights from PIV and LIF measurements Adharsh Shankaran, R. Jason Hearst Understanding the mechanism of gas exchange across the air-water interface is crucial for improving prediction models of the global carbon cycle, climate change dynamics, and weather patterns. To contribute to this understanding, we conducted a series of simultaneous PIV/LIF experiments in an air-water channel. PIV was used for water velocity fields, oxygen LIF for capturing spatial and temporal dissolved oxygen data, and surface LIF for observing air-water interface deformation. The channel measures 1300 mm in length, 600 mm in width, and 106 mm in height, filled with water up to 50 mm. It is placed at the end of an air channel, allowing the inlet air to develop over 108 channel heights. The inlet air turbulence is quantified using a hot-wire before interacting with the water surface. Preliminary results indicate that increasing air velocity enhances the deformation of the air-water interface and the rate of oxygen dissolution. Furthermore, fluctuating velocity and vorticity components are high near the interface due to the wind-driven shear. Additional findings on the instantaneous structures of dissolved oxygen, the rate of oxygen dissolution, and the turbulence state of both air and water for different air velocities will be presented at the conference. |
Monday, November 25, 2024 2:55PM - 3:08PM |
R02.00006: Large- and very large-scale motions in open-channel flow: Spectra and structure functions Andrea Zampiron, Bastien Cerino, Celine Berni, Sebastian Proust, Vladimir Nikora Large-scale motions (LSMs) and very-large-scale motions (VLSMs) in open-channel flows are coherent structures that, in premultiplied streamwise velocity spectra, are represented by two “hills” at wavelengths of λx ≈ 2-4 and λx ≈ 20-50 flow depths, respectively. The origin of VLSMs remains unclear. Two main hypotheses suggest that VLSMs originate either from alignment of LSMs or as relatively independent structures. |
Monday, November 25, 2024 3:08PM - 3:21PM |
R02.00007: Wall Overflow to Free Overfall: Revisiting the Discharge Characteristics of Curvilinear Flows Over Thin Weirs Joseph Pugh, Karan Venayagamoorthy, Timothy K Gates The two-dimensional free-surface curvilinear flow over a thin weir was of much interest for early pioneers in fluid mechanics, due to the suitability of the problem to potential flow analysis and its practical application within the realm of hydraulic engineering for flow measurement. It is a complex problem, representing an amalgam of several canonical flows. 1D hydrostatic uniform open-channel flow exists upstream of the weir, and then separates into regions of rotational corner flow and convergent flow through an orifice, and finally transitions to a free-falling zero-pressure-gradient jet. More than a century onwards, we examine the same problem using a combination of experimental techniques and numerical simulations. These new data are analyzed in conjunction with the available historical data to examine the discharge characteristics of curvilinear weir flows in the limits of the wall overflow (i.e. where the weir height is very large) to the free overfall. Dimensional analysis reveals that the discharge coefficient in the classical form of the weir-discharge equation is best understood as a weir Froude number, Fr_h. The interaction between the coupled pressure and velocity fields is examined to elucidate the balance between inertial and gravitational effects as Fr_h varies. Based upon this, a new weir-discharge equation is proposed, where a logistic relationship is deduced to estimate Fr_h using readily measured hydraulic parameters. This yields a single monotonic curve over the full range of possible flows. Practical limitations on predicting weir discharge are set forward, defining regimes for scale effects due to viscosity and surface tension, as well as the transition from weir flow to sill flow, and ultimately the free overfall. The findings also hold potential for broader application to other common weir f low types. |
Monday, November 25, 2024 3:21PM - 3:34PM |
R02.00008: On wave-driven propulsion Graham P Benham, Olivier Devauchelle, Stuart J Thomson Wave-driven propulsion occurs when a floating body, driven into oscillations at the fluid interface, is propelled by the waves generated by its own motion. Wave-driven propulsion has been observed in the case of the waves generated by a honeybee trapped on the surface of water, in the case of “SurferBot”, a centimeter-scale interfacial robot that was inspired by the stricken honeybee, and at much larger scales, in the case of the waves generated by jumping up and down on a canoe, also known as “gunwale bobbing”. |
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