Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E48: Flow over Complex ObjectsFocus
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Sponsoring Units: DFD DBIO GSNP Chair: Pejman Sanaei, Courant Institute of Mathematical Sciences Room: BCEC 251 |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E48.00001: Enhancement of lift to drag ratio for a wing using thermal forcing ANCHAL VARSHNEY, Mehul Varshney, MF Baig The aim is to enhance the lift to drag ratio produced by a wing with a cambered profile by thermal forcing its partial lower surface. Reynolds number is considered in the laminar regime. The efficacy of control technique has been checked at various Mach number and angle of attack. The overheat factor, which is the ratio of the temperature of the heated portion to free stream temperature has also been varied to study its role in the control technique. The governing equations of continuity, momentum, and energy have been solved using commercial package Fluent®. As of now, the proposed mechanism for the enhancement of lift to drag ratio is the increase in vorticity generation near the trailing edge because of the variation in viscosity. This brings about a net increase of circulation about the wing which results in higher lift. The other possible mechanism for the phenomenon is further being explored such that advancement in Micro-Air Vehicles technology can be done |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E48.00002: Turbulent Drag Reduction on an Aircraft Wing Mehul Varshney, MF Baig The aim of the present work is to reduce the turbulent drag induced on a supercritical aircraft wing at commercial flight scale conditions of Reynolds number and Mach number by using jets installed on the upper and lower surface of the wing. The present method is an active technique of viscous drag reduction. To the best of author’s knowledge, no such control technique has been explored at such conditions. The analysis considers jets in the stream-wise and span-wise direction incorporated on suction and pressure surfaces of the wing which tend to form a pair of colliding-jets in the span-wise direction. The efficacy of the control technique has been checked for jets with various emerging mass flux and inclination angle of the streams. The governing equation of continuity, RANS (using Spalart Allmaras as turbulence model) and the energy have been solved numerically using the commercial package Fluent®. The mechanism behind the control technique is the lifting of the boundary layer which brings about a reduction in the skin-friction component of the drag and the cross-diffusion of the near-wall streaks which brings about a decrease in the turbulent kinetic energy and hence viscous drag. Role of vorticity variation will also be explored. |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E48.00003: Stable flight of meteors Pejman Sanaei, Michael John Shelley, Leif Ristroph The atmospheric erosion of meteors is a splendid example of the reshaping of a solid object due to its motion through a fluid. Motivated by meteorite samples collected on Earth that suggest fixed orientation during flight--most notably the strikingly conical shape of so called oriented meteorite--here the hypothesis that such forms result from an aerodynamic stabilization of posture that may be achieved only by specific shapes, is explored. The laboratory- scale experiment is conducted for exploring systematic static stability tests on cones of varying apex angles in fast flows, and the resulting map of the orientational equilibria and their stability. A 2D mathematical model has been developed, and is compared with the experimental results. Armed with the simplified 2D model of oriented meteorites (with a conical shape), an isosceles triangle is considered in order to calculate its flow wake structure using free streamline theory and conclude that meteors are self-stabilizing in the sense that they seem to reshape themselves through erosion into a flight-stable form. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E48.00004: Vortex streets behind triangular objects Ildoo Kim When a triangular object, instead of a circular object, is used to produce a vortex street, an exotic vortex arrangement is observed in addition to the commonly observed mushroom-like structure. The exotic structure is morphologically distinctive from the classical von Karman vortex street and is characterized by a thin layer of irrotational fluid that separates two rows of vortices. This structure appears when a dimensionless ratio between the thickness of the boundary layer and the size of the object is less than a certain value, which is measured to be 0.4 in our experiment. The experiment is modeled by a double shear layer profile, whose linear stability is solved numerically. The theoretical consideration shows a rough agreement with the measurement. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E48.00005: Formation and propagation of a semi vortex-ring connected to a free surface Alexandre Vilquin, Vincent Pagneux, Agnès Maurel, Philippe Petitjeans The vortex rings are torus-shaped vortices existing in many different situations in fluid mechanics. They are involved in the locomotion of numerous animals like birds and fish. The understanding of their formation process is essential to optimize the propulsion in engineering. They also play a major role for blood pumping in left ventricle and are considered as an index of cardiac health in the human heart. As proof of the phenomenon diversity, the presence of charged vortex ring with a quantized circulation has also been identified in superfluid helium. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E48.00006: Heterogeneous dispersion of individual bacteria in micropillar arrays Pooja Chopra, David A Quint, Ajay Gopinathan, Bin Liu Transport through complex environments is paramount to microorganism propagation and survival. At the scale of a single bacterium, there can be environmental physical features that dramatically alter transport properties at the population level. In this work, we study the transportation of individual bacteria, here Escherichia coli (E. coli), through a lattice of micropillars which serve as structured obstacles with well-defined geometries. To fully account for single cell kinematics, we employ a 4D (3D+time) tracking microscope while imaging in the micropillar environment. Interestingly, we found that the micropillar arrays promote the dispersal of bacteria rather than serving as simple obstacles. We explore the mechanisms of such enhanced transport by studying the spatial dependence of the run-and-tumble statistics of E. coli, in part due to the hydrodynamic interactions between the bacteria and solid surfaces. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E48.00007: Is hummingbird's feeding mechanisms based on elasto-capillary ? Amandine Lechantre, Alejandro Rico Guevara, Pascal Damman Hummingbirds have a high metabolic rate requiring to feed on a very energetic resource: the nectar. For this purpose, they have developed a truly specialized nectar-feeding method. During the capture of the nectar, the hummingbird’s bill goes into the corolla of the flower. Then the tongue is protruded out and plunges into the nectar. After the loading, the tongue retracts and is unloaded in the bill. The mechanism of the tongue’s loading is still unresolved. At first, it was suggested that the tongue was composed of two thin tubes which was filled because of a capillary suction mechanism (Martin 1833, Scharnke 1931). But the morphological study of the tongue reveals that it is composed of two folded sheets and no closed tubes. In this talk, we will tackle the question: how a sheet can fold into a tube to capture viscous fluid. Several mechanisms were proposed: self-assembling capillary syphon (W. Kim et al. 2012) or elastic micropumps (A. R. Guevara et al. 2005). Based on elasto-capillary experiments and recording of living hummingbirds, the relevance of both models will be discussed. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E48.00008: Friction on water sliders Giuseppe Pucci, Ian Ho, Daniel M Harris A body in motion tends to stay in motion but is often slowed by friction. We investigate the friction experienced by centimeter-sized bodies sliding on water. We show that their motion is dominated by skin friction due to the boundary layer that forms in the fluid beneath the body. We develop a simple model that considers the boundary layer as quasi-steady, and is able to capture the experimental behaviour for a range of body sizes, masses, shapes and fluid viscosities. We define a dimensionless sliding number as the ratio between the fluid inertia and the body inertia, which allows us to assess the regime of validity of our model. Furthermore, we demonstrate that friction can be reduced by modification of the body's shape or bottom topography. Our results are significant for understanding natural and artificial bodies moving at the air-water interface, and can inform the design of aerial-aquatic microrobots for environmental exploration and monitoring. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E48.00009: Sedimentation of geometrically polar shapes Rahul Chajwa, Alyssa Conway, Rintaro Kirikawa, Narayanan Menon, Sriram Ramaswamy
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