Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session M39: General Fluid Dynamics: Obstacles and Boundaries |
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Chair: Michael Plesniak, George Washington University Room: Sheraton Back Bay C |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M39.00001: Vortex propagation around a wall-mounted obstacle in pulsatile flow Ian A Carr, Michael W Plesniak Wall-mounted obstacles are prevalent in nature and engineering applications. Physiological flows observed in human vocal fold pathologies, such as polyps, can be modeled by flow over a wall-mounted protuberance. Despite their prevalence, studies of wall-mounted obstacles have been restricted to steady (constant velocity) freestream flow. In biological and geophysical applications, pulsatile flow is much more common, yet effects of pulsatility on the wake of a wall-mounted obstacle remain to be extensively studied. This study aims to characterize the complex physics produced in this unsteady, separated flow. Experiments were performed in a low-speed wind tunnel with a set of rotating vanes, which produce the pulsatile inflow waveform. Instantaneous and phase-averaged particle image velocimetry (PIV) results acquired around a hemispherical obstacle are presented and compared. A mechanism based on self-induced vortex propagation, analogous to that in vortex rings, is proposed to explain the observed dynamics of coherent structures. Predictions of the propagation velocity based on analytical expressions for vortex rings in a viscous fluid are compared to the experimentally measured propagation velocity. Effects of the unsteady boundary layer on the observed physics are explored. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M39.00002: Pressure-Velocity Correlations in the Cove of a Leading Edge Slat Stephen Wilkins, Patrick Richard, Joseph Hall One of the major sources of aircraft airframe noise is related to the deployment of high-lift devices, such as leading-edge slats, particularly when the aircraft is preparing to land. As the engines are throttled back, the noise produced by the airframe itself is of great concern, as the aircraft is low enough for the noise to impact civilian populations. In order to reduce the aeroacoustic noise sources associated with these high lift devices for the next generation of aircraft an experimental investigation of the correlation between multi-point surface-mounted fluctuating pressures measured via flush-mounted microphones and the simultaneously measured two-component velocity field measured via Particle Image Velocimetry (PIV) is studied. The development of the resulting shear-layer within the slat cove is studied for Re$=$80,000, based on the wing chord. For low Mach number flows in air, the major acoustic source is a dipole acoustic source tied to fluctuating surface pressures on solid boundaries, such as the underside of the slat itself. Regions of high correlations between the pressure and velocity field near the surface will likely indicate a strong acoustic dipole source. In order to study the underlying physical mechanisms and understand their role in the development of aeroacoustic noise, Proper Orthogonal Decomposition (POD) by the method of snapshots is employed on the velocity field. The correlation between low-order reconstructions and the surface-pressure measurements are also studied. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M39.00003: Structural Affects on the Slamming Pressures of High-Speed Planing Craft Christine Ikeda, Brandon Taravella, Carolyn Judge High-speed planing craft are subjected to repeated slamming events in waves that can be very extreme depending on the wave topography, impact angle of the ship, forward speed of the ship, encounter angle, and height out of the water. The current work examines this fluid-structure interaction problem through the use of wedge drop experiments and a CFD code. In the first set of experiments, a rigid 20-degree deadrise angle wedge was dropped from a range of heights ($0 \le H \le 0.6$~m) and while pressures and accelerations of the slam even were measured. The second set of experiments involved a flexible-bottom 15-degree deadrise angle wedge that was dropped from from the same range of heights. In these second experiments, the pressures, accelerations, and strain field were measured. Both experiments are compared with a non-linear boundary value flat cylinder theory code in order to compare the pressure loading. The code assumes a rigid structure, therefore, the results between the code and the first experiment are in good agreement. The second experiment shows pressure magnitudes that are lower than the predictions due to the energy required to deform the structure. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M39.00004: Experimental Investigations of Flow past Spinning Cylinders Pasquale Carlucci, Liam Buckley, Igbal Mehmedagic, Donald Carlucci, Siva Thangam Experimental investigations of flow past spinning cylinders is presented in the context of their application and relevance to flow past projectiles. A subsonic wind tunnel is used to perform experiments on flow past spinning cylinders that are sting-mounted and oriented such that their axis of rotation is aligned with the mean flow. The experiments cover a Reynolds number range of up to 300000 and rotation numbers of up to 2 (based on cylinder diameter). The experimental validation of the tunnel characteristics and the benchmarking of the flow field in the tunnel are described. The experimental results for spinning cylinders with both rear-mounted and fore-mounted stings are presented along with available computational and experimental findings. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M39.00005: Wave impact on walls with/without parapets Jannette Frandsen, Olivier Tremblay, Regis Xharde This work is concerned with coastline protection. The usage of vertical walls is examined for various wave trains. The effect of parapets is further studied to minimize overtopping. The results presented are based on large scale flume experiments (Quebec) with a geometric scaling of 1:4. The beach has a slope 1:10. The beach material is highly absorbing and contains a mix of sand-gravel-cobble. Steel plates are mounted locally at the beach top to eliminate effect from local scour. The critical cases found relates to the plunging breakers breaking directly impacting the wall. Entrapped air-pocket(s) under the breaking wave contribute to the run-up energy through compressibility effects and bubble burst physics even from relatively small air-pockets. Highly localized wall pressures greater than 1 MPa and 10 m run-up are easily developed even with moderate amplitude waves at the inlet. The max. peak pressure on the wall identified caused either by water or entrained air pressure is typically greater than 1 MPa occurring in the order of 0.1 ms. The pressure distributions contain either single, double or triple peaks occurring typically above/at mean flume water depth and at around the local water depth in front of the wall. Furthermore, it was identified that the cases with maximum pressure on the wall does not necessarily give the maximum jet velocity (equivalent to vertical force considered in design of parapets). [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M39.00006: Flow-induced vibration of an array of cylindrical pendulums Junyoung Kim, Hyeonseong Kim, Daegyoum Kim We investigated experimentally self-excited vibration of an array of cylindrical pendulums in a uniform flow in order to find its potential application to energy harvesting. A cylindrical pendulum is fixed to a rigid upper plate via a thin elastic sheet so that it can swing perpendicularly to the free stream. Although this type of model has been studied for electrical energy generation, few studies have been conducted in order to understand the detailed physics of fluid-structure interaction. In this study, the flow pattern and dynamics of pendulums were examined by varying distance among the pendulums, free-stream fluid velocity, density ratio of the fluid and the pendulums. The interaction of an upstream bluff body and pendulums was also considered to investigate how the wake of the bluff body affects the oscillations of cylinders. With this experimental setup, the pendulums show various patterns such as stationary mode and out-of-phase oscillation mode. [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M39.00007: Golf in the Wind: Exploring the Effect of Wind on the Accuracy of Golf Shots Neda Yaghoobian, Rajat Mittal Golf play is highly dependent on the weather conditions with wind being the most significant factor in the unpredictability of the ball landing position. The direction and strength of the wind alters the aerodynamic forces on a ball in flight, and consequently its speed, distance and direction of travel. The fact that local wind conditions on any particular hole change over times-scales ranging all the way from a few seconds to minutes, hours and days introduces an element of variability in the ball trajectory that is not understood. Any such analysis is complicated by the effect of the local terrestrial and vegetation topology, as well as the inherent complexity of golf-ball aerodynamics. In the current study, we use computational modeling to examine the unpredictability of the shots under different wind conditions over Hole-12 at the Augusta National Golf Club, where the Masters Golf Tournament takes place every year. Despite this being the shortest hole on the course, the presence of complex vegetation canopy around this hole introduces a spatial and temporal variability in wind conditions that evokes uncertainty and even fear among professional golfers. We use our model to examine the effect of wind direction and wind-speed on the accuracy of the golf shots at this hole and use the simulations to determine the key aerodynamic factors that affect the accuracy of the shot. [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M39.00008: Resonance wave pumping with surface waves Remi Carmigniani, Morteza Gharib, Damien Violeau The valveless impedance pump enables the production or amplification of a flow without the use of integrated mobile parts, thus delaying possible failures. It is usually composed of fluid-filled flexible tubing, closed by solid tubes. The flexible tube is pinched at an off-centered position relative to the tube ends. This generates a complex wave dynamic that results in a pumping phenomenon. It has been previously reported that pinching at intrinsic resonance frequencies of the system results in a strong pulsating flow. A case of a free surface wave pump is investigated. The resonance wave pump is composed of a rectangular tank with a submerged plate separating the water into a free surface and a recirculation rectangular section connected through two openings at each end of the tank. A paddle placed at an off-center position above the submerged plate is controlled in a heaving motion with different frequencies and amplitudes. Similar to the case of valveless impedance pump, we observed that near resonance frequencies strong pulsating flow is generated with almost no oscillations. A linear theory is developed to pseudo-analytically evaluate these frequencies. In addition, larger scale applications were simulated using Smoothed Particle Hydrodynamic codes. [Preview Abstract] |
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