Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session J28: Vortex Dynamics: General II |
Hide Abstracts |
Chair: Nils Tilton, Colorado School of Mines Room: 236 |
Sunday, November 20, 2022 4:35PM - 4:48PM |
J28.00001: Two-Dimensional Interactions in a Field of Vortices Scott Carlson, Keiko K Nomura A key aspect of decaying two-dimensional turbulence is the presence of coherent vortex structures. These vortices undergo mutual advection and participate in strong inelastic interactions which transfer energy and enstrophy across spatial scales thereby influencing the inverse and direct cascades. The coupled behavior of coherent structures and cascade processes depends on the various interactions occurring in the flow. While much has been learned from studies of isolated vortex pairs, and in particular symmetric merger, other interactions and outcomes are possible in a field of varying vortices. A more generalized characterization of interactions and their statistics is needed to better understand two-dimensional turbulent flows. |
Sunday, November 20, 2022 4:48PM - 5:01PM |
J28.00002: Numerical investigation of the 3D regularized Biot-Savart model towards vortex reconnection Yoshifumi Kimura, Hiroshi Fujiwara, Yu-Hsun Lee As the inverse of the curl operator, the Biot-Savart law calculates the velocity field produced by a vortex line, and plays a central role in the analysis of vortex motion. As is well-known that the Biot-Savart integral has a logarithmic divergence if the denominator of the integrand is close to zero. To avert this logarithmic singularity, Rosenhead (1930) introduced an artificial positive parameter μ in the denominator and regularized the singularity. In this paper, we investigate numerically the motion of two tilted circular vortex rings, which has been proposed as a model for the finite time singularity problem for the Navier-Stokes equation [1][2], using the regularized Biot-Savart model by Rosenhead. We observe that μ particularly moderates the development of curvature at the tipping points, the closest approach on the vortex rings. The moderation grows in a small circular region around a tipping point the extent of which is a function of μ. We demonstrate that a large value of μ distorts the development of curvature significantly to produce a spurious bubble around the tipping points. |
Sunday, November 20, 2022 5:01PM - 5:14PM |
J28.00003: Quantifying the finite wall effects in a vortex ring wall interaction William N McAtee, Sarah E Morris, Vrishank Raghav Vortex rings are a common flow feature found in various applications such as solar flares, the exhaust of an impulsively firing thruster, and in a human expiratory event such as coughing, sneezing, or speech. Such expiratory events, in addition to their vortical nature, are laden with aerosols that can spread infectious airborne diseases. Therefore, it is critical to understand vortex dynamics when evaluating the implementation of see-through barriers used to reduce the risk of exposure through direct contact. This study investigates the effectiveness of such strategies by studying the impingement of a vortex ring on a finite-size flat plate. Previous studies with 2D vortex dipoles indicate that finiteness can have a noticeable effect on the interaction. To understand this behavior in 3D, we study the impingement of vortex rings of varying circulation-based vortex Reynolds numbers on plates of various diameters. Flow visualization and particle image velocimetry are employed to quantify vortex ring trajectory, circulation, and secondary vorticity produced during the interaction. The effect of this finiteness is found to affect the roll up of secondary vorticity and the trajectory of the vortex rebound and could therefore influence the efficacy of barriers as a countermeasure. |
Sunday, November 20, 2022 5:14PM - 5:27PM |
J28.00004: An interactive geometrical organization of a vortex between vortical flow structure and bundle of vorticity lines Katsuyuki Nakayama The present study analyses geometrical characteristics of vortical flow structure and bundle of vorticity lines in the core region of a vortex and their relationships. A Galilei invariant coordinate system, vortex space, in a vortex center clarifies the vortical flow structure and associated vortex stretching, and local axis geometry theory specifies geometrical characteristics of the bundle with respect to the passage through the swirl plane in the vortical region, applying the geometrical quantities swirlity, sourcity, and vortical flow symmetry. It indicates that the vortex stretching swirls a bundle of the vorticity lines, and that its feature depends on the geometrical dynamics of the velocity structure along a vortical region. On the other hand, the velocity structure is influenced by the geometry of a bundle of the vorticity lines, and swirling or rotating feature of the bundle generates the axial flow of the vortex. An analysis of them in a homogeneous isotropic turbulence with the Direct Numerical Simulation shows these interactive characteristics. It indicates that a vortex may have a mutual geometrical organization system of them. |
Sunday, November 20, 2022 5:27PM - 5:40PM Author not Attending |
J28.00005: Investigation of Blade-Vortex Interaction using a Morphing Wing Carlos E Soto, Samik Bhattacharya The vortex dynamics and the unsteady forces on a morphing wing were studied during parallel blade-vortex interactions (BVIs) of a tandem-wing configuration. Investigations were carried out in a towing tank using particle image velocimetry (PIV) and force sensor data. Vortices were generated by applying a rapid pitching motion to a leading rigid flat plate using a servo motor. The generated vortices collide with a morphing flat plate undergoing dynamic twisting. The interaction between the vortex and leading edge, the interaction between the vortex and the boundary layer, and the subsequent evolution of the vortex over the surface of the trailing plate were investigated for varying twisting kinematics. Vortex trajectory, sense, and strength were obtained from PIV data. The results were used to study the mechanisms of vortex decay and the effects of key parameters on vortex dynamics. The subsequent effects on the hydrodynamic forces experienced by the trailing plate are studied by analyzing the force sensor data in conjunction with PIV results. |
Sunday, November 20, 2022 5:40PM - 5:53PM |
J28.00006: A reduced-order model of concentration boundary layers in reverse osmosis systems with vortical flow structures Nils Tilton, Jacob Johnston, Sarah Dischinger, Mostafa Nassr, Ji Yeon Lee, Benny D Freeman, Kris Gleason, Daniel Miller, Sergi Molins Rafa, Nicolas Spycher, William Stringfellow Reverse osmosis (RO) is a membrane desalination process that plays a central role in the energy-water-climate nexus due to its applications to desalinating seawater and treating complex wastewaters. RO operates by flowing a high-pressure feed solution (up to 80 bars) over a semipermeable membrane sheet that blocks solutes while allowing water to permeate. RO is energy intensive because the feed pressure must exceed the feed osmotic pressure to force permeate through the membrane. Moreover, the osmotic pressure at the membrane is much higher than that of the incoming feed due to the accumulation of solutes in a thin boundary layer growing along the membrane. This accumulation is not fully understood, and further complicated by the presence of "feed spacers," a plastic woven mesh that supports the membrane in the RO system. We perform a suite of time-resolved 2D CFD simulations of fluid flow and solute transport in an RO system with three different spacer geometries. We show that spacers generate vortical flow structures that generate regions of preferential solution accumulation within the concentration boundary. We then propose a reduced-order model that mimics the impact of spacers as a row of counter-rotating vortices near the membrane surface. We show that these vortices can be tuned to reproduce the key results of our CFD to high accuracy, for only a small fraction of the computational cost of CFD. |
Sunday, November 20, 2022 5:53PM - 6:06PM |
J28.00007: Vortex Breakdown in Shear-Driven Flow Over a Rectangular Cavity Haoyi Wang, Xinyi Yu, Jesse T Ault, Guillaume Durey The vortex dynamics of flow past a rectangular cavity is investigated using numerical simulations and microfluidic experiments. The flow is inherently three-dimensional and is characterized by a large, dominant eddy filling most of the cavity with weak, yet significant flow in the axial direction along the vortex core and symmetrical about the center plane. Classical bubble-type vortex breakdown is observed in this rather simple geometry at sufficiently high Reynolds numbers (Re), depending on the channel width. The critical Re for the onset of vortex breakdown is identified as a function of channel width, and the evolution of the breakdown region is investigated as the channel width and Re increase. Results confirm the emergence and bifurcation of stagnation points that bound the breakdown bubble. The results also corroborate findings about vortex breakdown previously observed in other geometries, such as the transition from stagnation points to stable/unstable orbits resulting from the merging of breakdown zones and the correlation between vortex breakdown and critical wave phenomena. |
Sunday, November 20, 2022 6:06PM - 6:19PM |
J28.00008: Forced Dissipative QG Simulation of Jupiter's Great Red Spot with Discrete Exterior Calculus Pankaj Jagad, Ravi Samtaney The giant vortex, Jupiter's great red spot (GRS) persists for over three hundred years, and is a research topic of interest for fluid dynamists apart from astrophysicists. Simulating GRS can shed some light on its existence and longevity. Previous work by (Marcus, P. S., & Lee, C. 1994) on the GRS, assumed a forced dissipative quasi-geostrophic flow limited to the beta-plane. Presently we consider the entire spherical geometry. We employ discrete exterior calculus (DEC) for the simulation. DEC retains at the discrete level many of the identities of its continuous counterpart (exterior calculus). It has superior conservation properties for the discretization of the physical problems. DEC is known for its structure preserving properties, and is an appropriate choice for investigating flows dominated by long-lived coherent structures such as GRS. We elucidate on the salient features of the GRS such as its shape, internal distribution of vorticity, and sign of rotation with respect to the shear of the surrounding zonal wind. |
Sunday, November 20, 2022 6:19PM - 6:32PM |
J28.00009: Stability of co-axial vortex rings with implications for hot spot formation in supernova remnants Michael Wadas, Heath J LeFevre, Subramaniam Balakrishna, Carolyn C Kuranz, Aaron S Towne, Eric Johnsen Perturbations along two interacting vortex cores can grow under the influence of their self- and mutually induced velocity fields in a process known as the Crow instability. While generally considered in the context of wingtip vortices (i.e., streamwise vortices in a planar geometry), other interacting vortex cores, including rings, can also demonstrate perturbation growth. In this study, we analyze the collision of two co-axial vortex rings of equal strength. We show that the zero-order motion of the flow, unlike the case of two interacting line vortices, causes the growth of different wavenumbers to vary in time, providing an explanation for the dominance of the low-frequency symmetric mode and the observed Reynolds-number dependence of the dominant wavenumber observed in experiments. Our results may have important implications related to the formation of hot spots along gaseous tori ejected from stars for which a supernova event is imminent; specifically, our analysis predicts maximum growth for a wavenumber consistent with the number of hot spots observed on the circumstellar ring of supernova 1987A. |
Sunday, November 20, 2022 6:32PM - 6:45PM |
J28.00010: Effect of Slip Flow on Vortex Ring Formation Paul S Krueger, Matt Saari, Haosen Tan, David A Willis Formation of vortex rings by transient jet ejection from a nozzle is governed by the formation of the boundary layer within the nozzle and its subsequent separation and rollup at the nozzle exit. Apparent slip flow on the nozzle surface may provide a significant impact on this process, particularly for lower Reynolds number flows where vorticity is more diffuse. In the present work, a novel approach to entrap air near the nozzle inner surface in order to provide apparent slip in an aqueous flow is used to experimentally investigate the influence of slip flow on vortex ring formation in comparison to the case with no-slip boundaries. Transient jets with ratios of the ejected jet slug length to jet diameter (L/D) in the range of 1 – 6 and jet Reynolds numbers of 350 – 400 were investigated using a nozzle with apparent slip from entrapped air on one side and a no-slip solid surface on the other. Apparent slip resulted in small but measurable effects on the resulting vortex, with generally higher peak vorticity and impulse than the vorticity associated with the no-slip surface. These results indicate the potential for manipulating vortex formation and propulsion at lower Reynolds numbers. |
Sunday, November 20, 2022 6:45PM - 6:58PM |
J28.00011: Generalization of vortex formation time for animal flight Yukun Sun, Morteza Gharib, Chris Roh Vortex formation is significantly related to propulsion of biological organisms. Specifically, vortices play an important role when aerial organisms generate lift and thrust. The dimensionless vortex formation time of an airborne biological system depends on wing kinematics and morphology, as well as its flight conditions. To generalize the dimensionless vortex formation time, we conducted meta-analysis of 11 literature with complete flight kinematics information of a wide range of biological flyers with Reynolds numbers ranging from $O(10^2)$ to $O(10^5)$. It is found that vortex formation time falls in a narrow range when defined as a function of velocity scale associated with vorticity generation, length scale that limits the growth of the vortex, and the time duration of the vorticity injection. Such findings suggest that instead of the optimization of frequency-based paramters, biological flyers optimize their wing kinematics for each cycle. |
Sunday, November 20, 2022 6:58PM - 7:11PM |
J28.00012: On the continuum of point vortex collapse configurations Sreethin Sreedharan Kallyadan, Priyanka Shukla A robust numerical algorithm is presented for finding the continuum of point vortex self-similar collapse configurations. Several numerical examples are constructed using the algorithm, and typical continua are shown to have vortices parametrized along closed curves. The specific conditions on the circulations for which the curves are not closed are analyzed in detail, along with the different properties of the limit configurations. |
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