Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session T38: Vortex Dynamics and Vortex Flows: Turbulence 
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Chair: Wei Zhang, Cleveland State University Room: 204A 
Monday, November 20, 2023 4:25PM  4:38PM 
T38.00001: Influence of rectangular cylinder array on vortex statistics in atmospheric boundary flow Yedam Lee, Sang Lee An atmospheric boundary flow was simulated using large eddy simulation, in which the presence of the rectangular cylinders was implemented via the immersed boundary method. The Rortexbased omega method was employed, which establishes a robust criterion capable of detecting rigid rotation while remaining invariant to arbitrary flow conditions and shear contamination. From the instantaneous flow, vortical structures were identified as individual entities using the connected component labeling method. Physical properties, such as the vortex size, convection speed, acceleration, and the vorticity magnitude, were collected to compute the vortex statistics. The key findings were the frequent occurrence of the longtailed rare events downstream of the rectangular cylinders by which the statistical distributions were considerably altered due to its geometrical features. 
Monday, November 20, 2023 4:38PM  4:51PM 
T38.00002: Vortexinduced vibration of a flexible cylinder under bidirectionally sheared flow Xuepeng Fu, Shixiao Fu, Mengmeng Zhang, Haojie Ren, Yuwang Xu We address the experimental investigation of the vortexinduced vibrations (VIV) of a tensioned flexible cylinder under bidirectionally sheared flow for the first time. The flow field is generated by a verified mechanical apparatus with a diameter of 8.00m. The Fiber Bragg Grating (FBG) strain sensors are applied for the measurement. The modal analysis approach is applied to determine the VIV response. The experiment reveals essential features of flexible cylinder VIV under bidirectionally sheared flow, including root mean square (RMS) VIV amplitudes, low Strouhal numbers and significant traveling wave phenomenon. 
Monday, November 20, 2023 4:51PM  5:04PM 
T38.00003: Flow Structure of Rooftop Vortices over a Lowrise Building at High Reynolds Number Wei Zhang, Erick Shelley, Huixuan Wu Severe windstorms cause enormous damage, destruction, and failure of civil structures in the United States, with lowrise buildings being among the most vulnerable structures. Roof failures account for most initial damage, which is often initiated at the windward roof edges and corners, due to peak suctions induced by flow separation and rooftop vortices. There is a need to improve the understanding of the link between rooftop vortical structures and the peak pressures to enhance wind loading design standards, advance flow modeling, and create effective mitigation strategies to reduce the peak suction. The research aims to determine the correlation of unsteady, 3D rooftop vortices with roof surface pressure at high Reynolds numbers. Wind tunnel testing was conducted to measure flow field over the roof and surface pressure distribution of a model lowrise building at Florida International University’s Wall of Wind facility. Data obtained by TomoPIV and pressure tap system were analyzed to correlate the rooftop vortices to peak suctions. This work intends to improve our understanding of flow physics behind rooftop vortices in relation to peak suction events and facilitate development of wind mitigation strategies for lowrise buildings. 
Monday, November 20, 2023 5:04PM  5:17PM 
T38.00004: Weaving classical turbulence with quantum skeletons Weiyu Shen, Yue Yang We construct classical fluid turbulent flow fields consisting of intertwined viscous vortex tubes whose centerlines are quantum vortex filaments. First, the homogeneous isotropic quantum turbulence is simulated using the vortex filament method. Then, we transform quantum vortex filaments into splinebased parametric equations. They serve as the centerlines of viscous vortex tubes. By precisely controlling the degree of entanglement, core size distribution, and internal twist of the vortex tubes, we can customize the generated turbulent field with different Reynolds numbers and helicities. The combination of the turbulence skeleton (represented by quantum vortex filaments) and the tunable vortextube thickness makes the constructed turbulent field satisfy a series of key statistics, e.g., the fivethirds scaling and bottleneck effect of the energy spectrum and negative skewness of the velocity fluctuation in classical turbulence. This elucidates the essential difference between structures/statistics in classical and quantum turbulence. 
Monday, November 20, 2023 5:17PM  5:30PM 
T38.00005: Coherent organizational states in turbulent pipe flow Robert Jäckel, Bruno Magacho, Bayode Emmanuel Owolabi, Luca Moriconi, Juliana B Loureiro

Monday, November 20, 2023 5:30PM  5:43PM 
T38.00006: Nonlinear Evolution of Helical Vortex Disturbed by LongWave Instability Yuji Hattori, Akihiro Hirano, Ivan Delbende, Maurice Rossi The nonlinear evolution of a helical vortex disturbed by a longwave instability mode is studied by direct numerical simulation. The 3D NavierStokes equations for an incompressible flow are solved using highly accurate numerical techniques assuming that the helical vortex extends periodically. Two values of the pitch are considered: L/R=0.2 and 0.3. The wavenumber of the longwave instability mode is set to k=1/2 and 3/2. The evolution and the topology of the resulting vortices depend crucially on the pitch L/R at the nonlinear stage. In both cases, the helical vortex deforms significantly so that vortex reconnection occurs. When L/R=0.3, a vortex ring is detached from the helical vortex after the vortex reconnection. As a result, the pitch of the helical vortex is doubled. A vortex ring is also created after the vortex reconnection when L/R=0.2; however, it is linked with the remaining helical vortex after the reconnection. This linkage makes the vortex tubes interact strongly, which leads to turbulent transition. 
Monday, November 20, 2023 5:43PM  5:56PM 
T38.00007: Turbulent drag reduction due to polymer additives, vorticity dynamics, and Lighthill mechanism Gregory L Eyink, Samvit Kumar, Simon Toedtli, Tamer A Zaki Turbulent drag reduction by polymer additives in channels is widely attributed to weakening of coherent vortices and reducing their number, especially quasistreamwise hairpin vortices in the buffer layer. Drag is due to the wallnormal flux of spanwise vorticity, with constant mean across the channel, and polymers must reduce this flux at all wall distances. However, another polymer effect is that the mean vorticity profile becomes more distributed, whereas it is strongly concentrated at the wall in Newtonian turbulence. Lighthill explained the latter by strong upgradient vorticity transport (into the wall), due to correlated inflow and spanwise stretching. This transport is due to pancaketype detached eddies [1]. The net downgradient transport (out from the wall) is due to even stronger transfer by viscous diffusion and turbulent advection. If the only polymer effect were to reduce the latter, however, then the mean vorticity profile would concentrate even more sharply at the wall! Direct numerical simulations of turbulent channel flow with FENEP show that the polymer damps out Lighthill’s upgradient transport, explaining the more distributed mean vorticity profile. The smallerscale downgradient vortices are damped out even more, however, explaining the net decrease in vorticity flux and drag. These effects are demonstrated by the 2D cospectra of the nonlinear vorticity flux. 
Monday, November 20, 2023 5:56PM  6:09PM 
T38.00008: Abstract Withdrawn 
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