Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session H12: Vortex Dynamics and Vortex Flows VI |
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Chair: William Irvine, University of Chicago Room: 336 |
Monday, November 25, 2013 10:30AM - 10:43AM |
H12.00001: Dynamics of Quasi 2D and 3D Co-rotating Vortex Merger Akshay Khandekar, Jamey Jacob Merger of vortices is examined experimentally to compare the merger of slender parallel vortices generated either coincidentally or continuously. It is known that like-sign vortices rotate around a common center of circulation and merger between the vortices may occur under certain conditions. This merger is dependent on the strength of the vortex circulation, distance of separation between the centers of the two vortices, $Re_\Gamma$, and vorticity distribution. Quasi-2D and 3D experimental data is examined and merger relations are derived. The former uses high aspect ratio rotating paddles in a tank and while the latter are from wing-tip vortices in a wind tunnel. The vortex merger tank generates slender co-rotating vortices and are examined using PIV, while in the wind tunnel two opposing wings are arranged at opposite angles of attack to generate a pair of vortices that merge downstream. A 5-hole probe is used to obtain 3D velocity vectors via wake survey, along with PIV. The procedure is performed in the wake at different distances to observe merger under different conditions. Temporally and spatially dependent relations in quasi-2D and 3D vortex merger are derived. Merger behavior is generally similar between the cases, but instabilities along quasi-2D vortices may affect [Preview Abstract] |
Monday, November 25, 2013 10:43AM - 10:56AM |
H12.00002: Interaction of a vortex ring with a natural convective layer C.A. Palacios-Morales, M. Salinas, F.J. Solorio-Ordaz, R. Zenit We study the dynamics and heat transfer resulting from the impact of a vortex ring with a vertical heated wall. Laminar vortex rings were generated in water with a piston- cylinder arrangement. The vertical wall is heated by a thermal bath which is held at constant temperature producing a laminar and stable thermal boundary layer. Measurements of the 2D velocity field were obtained with a TR-PIV technique and the scalar temperature field is obtained by the PLIF technique. To avoid azimuthal instabilities, we conducted experiments for small stroke rations and Re of O(1000). The initial circular shape evolves to an asymmetric shape after reaching the wall. The lower ring section thickens and separates from the wall while the upper part thins and is dragged by the thermal layer. On the sides, the vortex ring is stretched. The rate of change of circulation is small at the lower section of the ring indicating that the momentum transport and heat transfer is more significant in this region. The instantaneous heat transfer coefficient was obtained; as expected, when the vortex approaches the wall, the heat transfer increases mainly at the lower part of the ring. [Preview Abstract] |
Monday, November 25, 2013 10:56AM - 11:09AM |
H12.00003: Interactions of two unequal co-rotating viscous vortices in the presence of external shear Patrick Folz, Keiko Nomura The interaction of two co-rotating viscous vortices in linear background shear is investigated through two-dimensional numerical simulations. In general, equal co-rotating viscous vortices will merge if brought within a critical separation distance. This process occurs when the relative strain induced on one vortex by the other weakens it sufficiently, causing core fluid to detrain. The vortices are then mutually entrained and the flow transforms into a single vortex. In the absence of shear, when the vortices are unequal the outcome of the interaction is determined by the relative timing of core detrainment. Depending on the degree of asymmetry, merger may or may not occur. When background shear is present, advective motion of the vortices is altered. With sufficiently strong adverse shear, the vortices will separate. Otherwise, in the case of equal vortices, merger is enhanced or inhibited by favorable or adverse shear respectively. The onset of the merging process when shear is present is found to occur when the vortices reach the critical merging criterion for vortices without shear. For unequal vortices, the presence of the shear modifies the start of the detrainment process for each vortex and leads to varied outcomes. [Preview Abstract] |
Monday, November 25, 2013 11:09AM - 11:22AM |
H12.00004: Investigation of the Unsteady Total Pressure Profile Corresponding to Counter-Rotating Vortices in an Internal Flow Application Kathryn Gordon, Scott Morris, Aleksandar Jemcov, Joshua Cameron The interaction of components in a compressible, internal flow often results in unsteady interactions between the wakes and moving blades. A prime example in which this flow feature is of interest is the interaction between the downstream rotor blades in a transonic axial compressor with the wake vortices shed from the upstream inlet guide vane (IGV). Previous work shows that a double row of counter-rotating vortices convects downstream into the rotor passage as a result of the rotor blade bow shock impinging on the IGV. The rotor-relative time-mean total pressure distribution has a region of high total pressure corresponding to the pathline of the vortices. The present work focuses on the relationship between the magnitude of the time-mean rotor-relative total pressure profile and the axial spacing between the IGV and the rotor. A survey of different axial gap sizes is performed in a two-dimensional computational study to obtain the sensitivity of the pressure profile amplitude to IGV-rotor axial spacing. [Preview Abstract] |
Monday, November 25, 2013 11:22AM - 11:35AM |
H12.00005: Analysis of the formation and evolution of vortex rings in non Newtonian fluids using 3D PTV Abhishek Bajpayee, Alexandra Techet Formation and evolution of vortex rings have been studied for a long time but mostly only in Newtonian fluids. However, many fluids in nature and in the industry such as blood, crude oil, etc., exhibit non Newtonian characteristics. Palacios-Morales and Zenit recently studied the formation of vortex rings in shear thinning liquids for the first time using 2D PIV and compared experimental findings with theoretical predictions. The authors recently demonstrated the applicability of Light Field (LF) imaging to conduct 3D Particle Tracking Velocimetry (PTV) to study densely seeded flow fields and their evolution over time using synthetic data. LF based 3D PTV is now used to quantitatively study vortex rings created in Glycerin based on multiple parameters and the results are compared with previous findings. [Preview Abstract] |
Monday, November 25, 2013 11:35AM - 11:48AM |
H12.00006: Buoyancy-Induced Columnar Vortices Mark Simpson, Ari Glezer The formation of anchored, buoyancy-driven columnar vortices that is driven by the instability of a thermally stratified air layer and is sustained by entrainment of ground-heated air is investigated in a meter-scale laboratory facility using a heated ground plane and an azimuthal array of flow vanes. Naturally-occurring, buoyancy-driven columnar vortices (``dust devils'') spontaneously occur with core diameter of 1-50 m at the surface and heights up to one km, with considerable angular and axial momentum. Such vortices convert low-grade waste heat in an air layer overlying a warm surface into a flow with significant kinetic energy. The considerable kinetic energy of the vortex column cannot be explained by buoyancy alone and is a result of the production, concentration, and tilting of horizontal vorticity produced in the air layer over the heated ground plane. The present investigation focuses on the fundamental mechanisms of the formation, evolution, and dynamics of the available vorticity within the columnar vortex using stereo-PIV with specific emphasis on the scaling and distribution of the available kinetic energy flux. It is shown that the scaling and strength of these vortices can be significantly altered through adjustments of the flow vanes and the global sensible heat absorbed by the air flow. [Preview Abstract] |
Monday, November 25, 2013 11:48AM - 12:01PM |
H12.00007: ABSTRACT WITHDRAWN |
Monday, November 25, 2013 12:01PM - 12:14PM |
H12.00008: Numerical simulation of a spanwise vortex in a tidal induced flow Erick J. Lopez-Sanchez, Gerardo Ruiz-Chavarria The system formed by two counter-rotating vortices (known as a dipole) occurs often in geophysical flows and it has been the subject of some experimental and numerical investigations. In some previous works (e. g. Lacaze et. al. \textit{Exp. Fluids} \textbf{48} (2010) 225-231) a spanwise vortex in front of the dipole has been observed. In this work we study the evolution of this transversal vortex in a system consisting of a channel flushing into a open domain and subject to a periodic forcing. To this end the Navier-Stokes and continuity equations are solved with a finite volume code (OpenFOAM). The numerical solution has been obtained for a Reynolds number $Re=1000$ and two different values of the Strouhal number, namely $S=0.01$ and $S=0.02$, for which the dipole moves away from the channel. In addition two different aspect ratios (depth to channel width) are considered, these are 0.5 and 1. The horseshoe vortex forms near the bottom and it lifts as the dipole moves. We compare the evolution of the spanwise vortex with respect the case of a vortex produced by a impulsively jet and we highlight the effects of the periodic forcing. Finally we compare our results with some experimental data obtained in laboratory. [Preview Abstract] |
Monday, November 25, 2013 12:14PM - 12:27PM |
H12.00009: On Clarifying the Mechanisms for Persistent Asymmetries in Advecting Vortical Motions John Elsnab, Hurmat Ui Ain, Joseph Klewicki A challenge associated with the study of turbulence relates to determining how and why ensembles of instantaneous motions underlie the observed behaviors of the time averaged flow. It is important to distinguish between events that make a lasting and unique signature to the time average representation of the flow, and events that simply make instantaneous contributions. The present experiments establish when laminar vortex rings interact with a time evolving shear-layer that persistent asymmetries are generated. These asymmetries are dynamically significant as they modify the gradient of the Reynolds stress (RS), which is the relevant quantity that appears in the mean equations. In turbulent wall flows, the gradient of the RS acts as a net source or sink of mean momentum depending upon the position where the RS is maximum. Vortex rings subjected to an induced advection velocity (an additive perturbation) do not exhibit persistent asymmetries; however, when rings with modified advection velocities interact with a shear-layer, the ring dynamics exhibit enhanced asymmetries when compared to shear-layer interactions alone. Connections are drawn between the velocity and vorticity field correlations that are attributed to the RS gradient and its modification. [Preview Abstract] |
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