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 T28: Vortex Dynamics: Wakes I |
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Chair: Matthew Bross, Pennsylvania State University Room: 236 |
Monday, November 21, 2022 4:10PM - 4:23PM |
T28.00001: An Experimental Investigation of Boundary Layer Ingestion and Aerodynamic Interactions Hulya Biler, Chaitanya Paruchuri, Bharathram Ganapathisubramani This study experimentally examines the aerodynamic interaction between a rotor and turbulent boundary layer. The fundamentals of this research are directly relevant to various applications, including over-the-wing propellers (aeronautics) and propeller-hull interactions (marine). The experiments are performed in the boundary layer wind tunnel (1.2m x 1m cross section) located at the University of Southampton at downstream location of 7.5 m from the beginning of the test section. A smooth-wall boundary layer develops over the bottom wall of the wind tunnel with a boundary layer thickness of 10 cm. A two-bladed 16-inch diameter propeller is installed in the wind tunnel such that the distance between the rotor and the wind tunnel floor could be altered. This enables us to examine the effect of tip-gap on the propeller/BL interaction. Phase-locked low-speed high-resolution stereoscopic particle image velocimetry is performed to examine the downstream development of the tip vortices generated by the propeller and its interaction with the boundary layer. We will present results where the evolution and the decay of the tip vortices ingested in the boundary layer are compared to tip vortex characteristics of a rotor in isolation (i.e., the rotor is outside of the boundary layer). |
Monday, November 21, 2022 4:23PM - 4:36PM |
T28.00002: Characterization of the three-dimensional velocity field of a propeller wake using Lagrangian particle tracking Matthew Bross, Jeff Harris, Adam Nickels A Lagrangian description of the vortical flow in the wake of a propeller is presented in this work. Data from a volumetric-PIV measurement performed in the historic Garfield Thomas Water Tunnel was re-processed using LaVision's implementation of the Shake-the-Box (STB) particle tracking algorithm. The data was acquired at 2500 fps using four Phantom v1212 cameras in a linear arrangement and a Photonics DM-50 to illuminate the volume. The measurement volume has dimensions of 140 x 180 x 40 mm^3. The generic propeller rotated at 625 rpm with a thrust of up to 30lbs. Lagrangian descriptions of flows are often not considered from experimental data due to the many challenges of dealing with sparse or uneven grid spacing. However, using even basic Lagrangian statistics, such as single or dual particle dispersion, distinct structural features of the wake flow can be highlighted and analyzed. Furthermore, a scheme to detect trajectories that are within coherent wake vortices and also ones that are entrained is presented. |
Monday, November 21, 2022 4:36PM - 4:49PM |
T28.00003: Wake Formations Behind a Multi-element Vertical Axis Wind Turbine David Charland, Colin M Parker, Megan C. Leftwich Vertical axis wind turbines (VAWT) are a potential energy solution for more urban environments because of their minimal size and noise pollution. While single airfoil VAWTs have been thoroughly studied, by introducing a multi-element airfoil VAWT there is a wide range of variables that are subject to change. Using particle image velocimetry (PIV) we aim to analyze the wake structures behind a scaled multi-element VAWT in a wind tunnel. Constant temperature anemometry along with the PIV results temporally resolve wake regions of interest chosen from the PIV analysis. A comparison will be made of the wake structure behind single airfoil and multi-element airfoil VAWTS. The multi-element airfoil VAWT produces significantly more vortex structures and patterns in the wake. In addition, multi-element airfoil VAWTs behave more like a solid cylinder due to the greater solidity compared to a single airfoil VAWT. Furthermore, the tip-to-speed ratio (TSR) is compared in two values to expand on existing research of the importance of TSR on single airfoil VAWT’s. |
Monday, November 21, 2022 4:49PM - 5:02PM |
T28.00004: On the coupling of vortex flow and whisker sensor in the wake of moving objects Pengyao Gong, Yaqing Jin In this study, we studied the wake-induced vibration (WIV) of a whisker model in the wake of a moving circular cylinder with various initial gap distances and moving speeds. Time-resolved particle image velocimetry was used to capture the synchronized wake dynamics and vibrations of whisker. Before the movement of circular cylinder, vibrations of whisker exhibited typical 'slaloming' patterns across all tested gap distance. After the movement of cylinder, the vibration amplitude decreased with the increasing gap distance, and the decaying rate was determined by the coupled influence of initial vortex strength and gap distance growth rate. A model based on harmonic oscillator with rational decaying force coefficient was provided to predict the time series of whisker WIV. To further explore the influence of vortex shedding patterns on WIV of whisker, off-centered whisker was placed in the wake of the moving cylinder as comparison. Before the movement of cylinder, the off-centered whisker vibrated at an equilibrium position that deflected toward the flow center; as the gap distance increased, whisker gradually moved back to its off-centered neutral, this trend was accompanied with faster vibration decaying due to lower initial vortex strength. |
Monday, November 21, 2022 5:02PM - 5:15PM |
T28.00005: Rounded Edge Effects on the Slanted Afterbody Aerodynamics Rhylan A Huss, Fernando Zigunov, Farrukh S Alvi Modern cargo aircraft such as the Boeing C-17 possess a large upswept angle on the fuselage afterbody. This angle, |
Monday, November 21, 2022 5:15PM - 5:28PM |
T28.00006: Assessment of vortex lock-in for circular cylinders in an in-line tandem configuration Girish K Jankee, Eirik Æsøy, Srikar Yadala Venkata, James R Dawson, Nicholas A Worth Understanding the characteristics of structures arising from vortex shedding in a tandem cylinder configuration is important in the design of wind turbine farms, bridges or offshore platforms. An experimental study is conducted on the interaction of the flow behind two circular cylinders in an in-line tandem configuration with an acoustically driven oscillating pipe flow. Three cylinder diameters, dc, are studied over a Reynolds number range of 900-9500. The flow has a non-zero mean velocity, ū, with forcing frequency of 760Hz while the forcing amplitude is varied between 0-30\% of ū. The downstream cylinder location is fixed at a velocity node of the acoustic mode while the upstream cylinder is positioned at distances of 1.5dc, 3dc and 6dc corresponding to the extended body, the reattachment and the co-shedding regimes respectively. Measurements of the flow was carried out through hot-wire anemometry and high speed planar PIV. Initial results show that cylinders in the extended body regime and a single cylinder at a velocity node share similar vortex lock-in behaviour. Further, in the co-shedding regime it is possible to induce vortex lock-in on a cylinder at the velocity node by having a second cylinder sufficiently far upstream. It is hypothesized that vortex shedding from the upstream cylinder is responsible for such a trend. PIV velocity fields will be analysed in order to better understand this behaviour. |
Monday, November 21, 2022 5:28PM - 5:41PM |
T28.00007: Dynamic mode decomposition and stability analyses of oscillating foil wakes Morgan Jones, Mitul Luhar, Eva Kanso Many swimming and flying animals make use of oscillating foils for efficient propulsion. Previous studies have shown that wake resonance plays an important role in determining hydrodynamic efficiency for oscillating foils. Optima in propulsive efficiency occur when the oscillation frequency coincides with the frequency corresponding to maximum spatial growth in the wake, as identified using linear stability analysis. Here, we combine linear stability analysis with Dynamic Mode Decomposition (DMD) to better understand the relationship between wake structure and propulsive efficiency. Experiments were performed using a NACA-0012 hydrofoil with heaving and pitching motions in a recirculating water channel. Direct measurements from a six-axis force sensor were used to determine thrust coefficients and Froude efficiencies for varying Strouhal number. 2D-2C Particle image velocimetry (PIV) measurements were carried out in the near-wake region of the oscillating foil to provide further insight into the wake structure. PIV time series data are used for DMD and the mean profiles are used for stability analyses. At peak Froude efficiencies, there is close correspondence between the DMD modes and stability analysis predictions. These observations are consistent with prior studies. |
Monday, November 21, 2022 5:41PM - 5:54PM |
T28.00008: Evolution of an unstable horizontal stratified vortex John P McHugh, Gabrielle Clause, Abdulaziz Alsamil A trailing vortex behind a wing moving through a stratified fluid will twist surfaces of constant density such that the density overturns along the axis of the vortex. Recent results indicate that this flow is unstable to a wide range of modes. This conclusion was limited by the presence of a rigid cylinder on the outer boundary. The base flow also was assumed to have constant axial vorticity. Evolution of the unstable flow in a more realistic vortex is treated here with numerical simulations. The initial velocity field matches a Rankine vortex, with constant axial vorticity in the core, and zero vorticity outside the core. The initial density field is constructed by rotating a statically stable density profile uniformly along the vortex axis such that the density field is axially periodic. Up to ten periods of this density field are included in each simulation. The results depend on the Froude number, the pitch of the density field, and the Reynolds number. Results with large Froude numbers experience strong mixing, resulting in the interior of the vortex becoming fully mixed, similar to previous simulations of a stratified vortex with uniform overturning. Results with smaller Froude numbers show strong dependence on the pitch of the density field, in agreement with the previous stability theory. |
Monday, November 21, 2022 5:54PM - 6:07PM |
T28.00009: Vortex Dynamics of a Smoldering Firebrand Particle Bikash Mahato, Saurabh Saxena, Neda Yaghoobian In wildfires, spotting is a complex process that is known as the major mechanism of propagation of fires to unburned areas and nearby communities. In this mechanism, burning debris (known as firebrand or flying ember) is transported by the turbulent wind and ignites local fuel upon landing. Firebrand flight behavior, their landing distribution, and thus, spot fire risks are critically dependent on the interaction of the evolving firebrands with the immediate wind field and the physical characteristics of the particles. Despite numerous research on firebrand transport, investigation of the effect of temperature on the aerodynamic forces acting on firebrand particles is lacking in the literature. In this study, we develop a Direct Numerical Simulation (DNS)-based computational model to investigate the effect of spatiotemporally evolving temperature of a spherical firebrand particle on its aerodynamic forces. The temperature evolution of the firebrand particle is obtained from a novel surface-energy balance model, which is capable of handling objects with complex-shape geometries and multiple material properties. |
Monday, November 21, 2022 6:07PM - 6:20PM |
T28.00010: The Dynamics of the Re-circulation Bubble behind a Bluff Body in a Flowing Soap Film Izhar H Khan, Manoj K, Sanjay Kumar, Kamal Poddar In the present investigation, we study the structure and evolution of the near wake of a circular cylinder experimentally in a flowing soap film at low Reynolds numbers. A high-speed camera is used to obtain instantaneous pictures of the formation and detachment of the vortices and capture the changes occurring within the recirculation bubble. Reynolds number is varied in small steps from Re = 150 to the point of no shedding. Two distinct regimes of the near wake structure are observed, the first one corresponds to the Benard von Karman vortex street in the wake region with a short near wake region comprising of continuous random motion of the fluid particles. Vortices are clearly observed to be peeling off from the shear layers alternately. The other regime is characterized by a significantly large recirculation bubble in the near wake and the wake vortices are seen to originate as a result of deflection of the tip of the recirculation region. The transition between these two regimes occurs for a short range of Reynolds numbers and is observed to display interesting phenomena such as the formation of a vortex chain along the elongated shear layers and upstream movement of the small-scale vortices to form two standing vortices eventually. |
Monday, November 21, 2022 6:20PM - 6:33PM |
T28.00011: Optimal forces of entrainment for the flow past inclined plate in a uniform flow Makoto Iima Phase reduction theory provides a simple and clear vision of the essential part of the dynamics around the limit cycle (LC), and has been applied to many rhythmic phenomena. LCs can be found in fluid mechanics problems, i.e. the Karman’s vortex street or the flow past the inclined plate in a uniform flow. Such periodic flows are also targets of the phase reduction theory which allows us to analyze the synchronization and the entrainment of the system. |
Monday, November 21, 2022 6:33PM - 6:46PM |
T28.00012: Experimental study on the wake of porous plates Murilo Cicolin, Simone Chellini, Bharathram Ganapathisubramani, Ian Castro This study focus on the wake of rectangular plates with different porosities in the moderate range of Reynolds number. It is well known from the literature that the typical Von Karman vortex street can be altered by interfering with the near wake of a bluff body. Past studies with porous plates have shown that the extra injection of fluid can delay the onset or even suppress the vortex shedding and the suppression is accompanied by a fall in drag. This series of experiments attempt to advance on remaining open questions on the topic. For example, how does the wake dynamics change as the porosity increases; can vortex shedding occur even in the absence of a recirculating bubble; how does the mean structure and geometry of the wake change with porosity; do the wakes display any other type of instability. The present work shows preliminary results on a series of experiments with several plates at Reynolds number between 15,000 and 35,000. All the perforated plates have a fixed width D, and their porosities vary according to the size of the holes, from the solid plate to 30% of open area exposed to the flow. High resolution planar PIV measurements were acquired covering a large field of view of approximately 6Dx20D. |
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