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 L38: Vortex Dynamics and Vortex Flows: Jets and Wakes |
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Chair: Francisco Huera-Huarte, Universitat Rovira i Virgili Room: 355 D |
Monday, November 25, 2024 8:00AM - 8:13AM |
L38.00001: The fluid dynamics of twin pulsed jets in an elastic cavity Lara Merlo, Lyes Kadem, Wael Saleh, Hoi Dick Ng, Giuseppe Di Labbio The interaction of multiple pulsed jets can be observed in cardiovascular flows as they occur naturally in the atria and as a result of treatments and diseases. Fundamentally, these flows possess two or more pulsed jets interacting within an expanding elastic environment. This study investigates the effects of interjet spacing on the fluid dynamics in an elastic hemisphere. The experimental setup includes two parallel jets ejected into a hemispherical elastic cavity filled with a water-glycerol mixture to match the refractive index and to operate at a lower Reynolds number (Re = 301). The experiment consists of four spacing ratios (1.5, 2.0, 2.5, 3.0). The velocity fields are captured via particle image velocimetry. The spacing between jets significantly influences vortex ring formation and interaction within the elastic cavity. For a spacing ratio of 1.5, the closest distance between the jets, the vortex rings compete until one of them dominates. However, for spacing ratios between 2.0 and 3.0, the vortex rings merge. At such low Reynolds numbers, the vortices ultimately decay without forming secondary or tertiary structures. This fundamental study can shed light on more complex flows such as aortic regurgitation in the left ventricle. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L38.00002: Abstract Withdrawn
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Monday, November 25, 2024 8:26AM - 8:39AM |
L38.00003: Laminar Flow Past Cylinder Arrays Tucker P Benton, Thomas Ward This research is focused on the solid-fluid interaction of arrays of axisymmetric cylinders at finite Reynolds numbers (< 100). This research aims to study how the spacing and arrangement between cylinders affect the fluid flow interaction in the array and downstream flow. These experiments are conducted using a soap film tunnel, which creates a thin water film, allowing vortex generation and evolution to be captured with a high-speed camera. The fluid in this experiment is a mixture of 3% to 5% soap in water, the velocity of the film is < 0.5 m/s and the axisymmetric cylinders range between 0.1 and 0.2 mm in diameter (45 < Re < 100). The solid-fluid interaction and the vortex generation and shedding frequency will be measured for arrays of variably spaced horizontal, vertical, and diagonal offset cylinders. These will be compared to the vortex shedding frequency of flow around a single cylinder with the same characteristics and fluid parameters. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L38.00004: Soap film visualization of low velocity flow over roughness elements Anwar Longi, Thomas Ward In this study we discuss estimates for the minimum Reynolds number at which vortex shedding occurs using a soap-film tunnel. The goal is to observe the flow over a series of roughness elements. The soap film tunnel generates a nearly two-dimensional fluid flow, achieving Reynolds numbers below 100 to study this phenomenon. A high-speed camera recording the thin film at 5000 fps, and MATLAB are the main tools used to extract data from the experiments. Test pieces with a length of 25.4 mm and width between 0.1194 mm and 0.1524 mm are inserted into the film. The boundary layer will be visualized, and the occurrence of vortex shedding will be determined. Measurements of the vortex speed and shedding frequency will be taken and compared with results from other studies. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L38.00005: ABSTRACT WITHDRAWN
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Monday, November 25, 2024 9:05AM - 9:18AM |
L38.00006: Vorticity distribution in the flow around a horizontal circular cylinder near a free surface Seolyeon Park, Dongmin Shin, Yeunwoo Cho We perform a numerical study to investigate the flow characteristics around a horizontal circular cylinder near a free surface. The incoming fluid with a uniform velocity (U) flows towards the horizontal cylinder (diameter: D) where the distance between the top position of the cylinder and the still free surface is h. According to the depth ratio (h/D) and the Froude number (U/(gD)1/2), four kinds of flow patterns are identified; no waves on the free surface, small-amplitude waves on the free surface, surging wave breaking on the free surface with a common vortex shedding behind the cylinder and a jet-like flow on the free surface with a suppressed vortex shedding behind the cylinder. In addition, the free-surface phenomena are all periodic. These numerical findings are compared to experiments and they agree with each other very well. For each experimentally validated numerical case, we check the vorticity distribution both on the free surface and inside the fluid to understand that how the vorticity is conserved. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L38.00007: Effects of Surface Roughness on a Pitching Foil in Quiescent Flow Conditions Rodrigo Vilumbrales Garcia, Lokesh Silwal, Anchal Sareen A pitching foil in quiescent flow conditions produces an unstable wake characterized by jet meandering and strong interactions between consecutively shed vortices. This can result in a chaotic and deflected wake, leading to low-performance scenarios. In this study, we explore the impact of surface dimples on the wake characteristics of a pitching foil using Particle Image Velocimetry (PIV). The dimple depth to chord ratio (k/c) is fixed at 0.003, while the Reynolds number, based on the trailing edge velocity, is varied from 3000 to 15000. Our findings reveal that surface roughness can have an influence on the jet characteristics past the pitching foil by increasing the jet velocity at locations far from the trailing edge. This enhancement boosts the longevity of the jet. Notably, the effect of roughness is dependent on the Reynolds number, becoming less pronounced at lower Reynolds numbers. In this presentation, we will discuss PIV results, focusing on the averaged wake shape and profile, as well as the instantaneous characteristics of the vortices shed by the foil. We will also examine the implications of these findings on the thrust production of the foil. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L38.00008: Two-way Coupling between the Wake of a D-shaped Cylinder and a Thrust-producing Pitching Plate James H. Buchholz For a cylinder in cross-flow, the phenomenon of vortex "lock-in" is the synchronization of vortex shedding with the vibration of a cylinder in the streamwise or transverse direction. On the other hand, an oscillating foil or fin immersed in the von Karman vortex street downstream of a cylinder can extract energy from the vortices, to reduce drag or enhance thrust, when the motion of the body is appropriately phased with the passing vortices. In the present study, the two-way coupling between a pitching plate and the vortex wake of a D-shaped cylinder is investigated under conditions in which the presence and motion of the plate influences the shedding behavior of the cylinder. The streamwise spacing between the cylinder and plate, as well as the pitching amplitude and frequency of the plate are systematically varied while visualizing the flow to understand how the motion of the plate influences vortex shedding from the cylinder and, subsequently, how the perturbed vortices interact with the plate. Measurements of the thrust and propulsive efficiency of the plate provide insight into how the fully-coupled system can be leveraged to maximize thrust performance of the plate under conditions in which it can modify the oncoming vortex street. |
Monday, November 25, 2024 9:44AM - 9:57AM |
L38.00009: 3D Effects on Fluctuating Pressure in Crossflow Rotary Device Wakes Duncan McIntyre, Chad Magas, Chanwoo Bae, Peter Oshkai Attempts to reduce noise pollution have historically focused on long-established technologies rather than up-and-coming ones. In underwater contexts, technologies such as sonar, drilling, and axial-flow rotary devices like propellers most often take the spotlight. Crossflow devices, including Darrius-type turbines and propulsive cyclorotors, are rising in popularity, but understanding of their acoustic behaviour lags more-established technologies. Turbomachines typically generate sound through vorticity and, where conditions are favourable for it, cavitation. High-fidelity solution of the shed vorticity in the wake of these devices is therefore a necessary precursor to physics-based acoustic models. Two-dimensional wake solutions of crossflow devices have revealed that fluctuating wake pressure is strongly influenced by blade-vortex interactions, suggesting that noise is unlikely to follow a monotonic trend with either flow speed or blade rate. In this investigation we applied LES solutions to examine the effects of three-dimensionality, with and without blade tip effects, on that two-dimensional behaviour. This work reveals the relative importance of three-dimensionality on the wake structures and fluctuating pressure behaviour of crossflow rotary devices across configurations and operating conditions, and further highlights the importance of blade-vortex interactions for acoustic prediction. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L38.00010: Parametric study of the flow over a 6:1 prolate spheroid Marc Plasseraud, Krishnan Mahesh
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Monday, November 25, 2024 10:10AM - 10:23AM |
L38.00011: The wake of a sphere in a chiral fluid Tali Khain, Michel Fruchart, Vincenzo Vitelli Systems composed of spinning particles or driven by a magnetic field break mirror symmetry at the microscopic level. These chiral fluids can be described by adding additional so-called “odd” viscosities, which do not dissipate energy, in the Navier-Stokes equation. Here, we ask: how does odd viscosity affect the wake of a sphere as the Reynolds number increases? In ordinary fluids, the wake undergoes several bifurcations, first from an axisymmetric to a non-axisymmetric steady state, and then to a state where it periodically sheds vortices, similar to the von Karman vortex street familiar from everyday fluid flows. Using a combination of numerical and analytical methods, we describe the transitional flow regime in a chiral fluid. We find that odd viscosity reshapes the vortex structure of the wake, which in turn affects the onset and nature of the periodic vortex shedding state. Our work sheds light on the transition to turbulence in chiral fluids, a regime that could be realized experimentally in collections of spinning inertial particles. |
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