Effect of the Mitral Valve's Anterior Leaflet on Axisymmetry of Transmitral Vortex Ring.

PubMed

Falahatpisheh, Ahmad; Pahlevan, Niema M; Kheradvar, Arash

2015-10-01

The shape and formation of transmitral vortex ring are shown to be associated with diastolic function of the left ventricle (LV). Transmitral vortex ring is a flow feature that is observed to be non-axisymmetric in a healthy heart and its inherent asymmetry in the LV assists in efficient ejection of the blood during systole. This study is a first step towards understanding the effects of the mitral valve's anterior leaflet on transmitral flow. We experimentally study a single-leaflet model of the mitral valve to investigate the effect of the anterior leaflet on the axisymmetry of the generated vortex ring based on the three-dimensional data acquired using defocusing digital particle image velocimetry. Vortex rings form downstream of a D-shaped orifice in presence or absence of the anterior leaflet in various physiological stroke ratios. The results of the statistical analysis indicate that the formed vortex ring downstream of a D-shaped orifice is markedly non-axisymmetric, and presence of the anterior leaflet improves the ring's axisymmetry. This study suggests that the improvement of axisymmetry in presence of the anterior leaflet might be due to coupled dynamic interaction between rolling-up of the shear layer at the edges of the D-shaped orifice and the borders of the anterior leaflet. This interaction can reduce the non-uniformity in vorticity generation, which results in more axisymmetric behavior compared to the D-shaped orifice without the anterior leaflet.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mendenhall, M.R.

The present volume discusses tactical missile aerodynamic drag, drag-prediction methods for axisymmetric missile bodies, an aerodynamic heating analysis for supersonic missiles, a component buildup method for engineering analysis of missiles at low-to-high angles of attack, experimental and analytical methods for missiles with noncircular fuselages, and a vortex-cloud model for body vortex shedding and tracking. Also discussed are panel methods with vorticity effects and corrections for nonlinear compressibility, supersonic full-potential methods for missile body analysis, space-marching Euler solvers, the time-asymptotic Euler/Navier-Stokes methods for subsonic and transonic flows, 3D boundary layers on missiles, Navier-Stokes analyses of flows over slender airframes, and themore » interaction of exhaust plumes with missile airframes.« less

Transition and mixing in axisymmetric jets and vortex rings

NASA Technical Reports Server (NTRS)

Allen, G. A., Jr.; Cantwell, B. J.

1986-01-01

A class of impulsively started, axisymmetric, laminar jets produced by a time dependent joint source of momentum are considered. These jets are different flows, each initially at rest in an unbounded fluid. The study is conducted at three levels of detail. First, a generalized set of analytic creeping flow solutions are derived with a method of flow classification. Second, from this set, three specific creeping flow solutions are studied in detail: the vortex ring, the round jet, and the ramp jet. This study involves derivation of vorticity, stream function, entrainment diagrams, and evolution of time lines through computer animation. From entrainment diagrams, critical points are derived and analyzed. The flow geometry is dictated by the properties and location of critical points which undergo bifurcation and topological transformation (a form of transition) with changing Reynolds number. Transition Reynolds numbers were calculated. A state space trajectory was derived describing the topological behavior of these critical points. This state space derivation yielded three states of motion which are universal for all axisymmetric jets. Third, the axisymmetric round jet is solved numerically using the unsteady laminar Navier Stokes equations. These equations were shown to be self similar for the round jet. Numerical calculations were performed up to a Reynolds number of 30 for a 60x60 point mesh. Animations generated from numerical solution showed each of the three states of motion for the round jet, including the Re = 30 case.

Vortex motion in axisymmetric piston-cylinder configurations

NASA Technical Reports Server (NTRS)

Shih, T. I. P.; Smith, G. E.; Springer, G. S.

1982-01-01

By using the Beam and Warming implicit-factored method of solution of the Navier-Stokes equations, velocities were calculated inside axisymmetric piston cylinder configurations during the intake and compression strokes. Results are presented in graphical form which show the formation, growth and breakup of those vortices which form during the intake stroke by the jet issuing from the valve. It is shown that at bore-to-stroke ratio of less than unity, the vortices may breakup during the intake stroke. It is also shown that vortices which do not breakup during the intake stroke coalesce during the compression stroke.

Vortex breakdown simulation - A circumspect study of the steady, laminar, axisymmetric model

NASA Technical Reports Server (NTRS)

Salas, M. D.; Kuruvila, G.

1989-01-01

The incompressible axisymmetric steady Navier-Stokes equations are written using the streamfunction-vorticity formulation. The resulting equations are discretized using a second-order central-difference scheme. The discretized equations are linearized and then solved using an exact LU decomposition, Gaussian elimination, and Newton iteration. Solutions are presented for Reynolds numbers (based on vortex core radius) 100-1800 and swirl parameter 0.9-1.1. The effects of inflow boundary conditions, the location of farfield and outflow boundaries, and mesh refinement are examined. Finally, the stability of the steady solutions is investigated by solving the time-dependent equations.

The structure and dynamics of tornado-like vortices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nolan, D.S.; Farrell, B.F.

The structure and dynamics of axisymmetric tornado-like vortices are explored with a numerical model of axisymmetric incompressible flow based on recently developed numerical methods. The model is first shown to compare favorably with previous results and is then used to study the effects of varying the major parameters controlling the vortex: the strength of the convective forcing, the strength of the rotational forcing, and the magnitude of the model eddy viscosity. Dimensional analysis of the model problem indicates that the results must depend on only two dimensionless parameters. The natural choices for these two parameters are a convective Reynolds numbermore » (based on the velocity scale associated with the convective forcing) and a parameter analogous to the swirl ratio in laboratory models. However, by examining sets of simulations with different model parameters it is found that a dimensionless parameter known as the vortex Reynolds number, which is the ratio of the far-field circulation to the eddy viscosity, is more effective than the convention swirl ratio for predicting the structure of the vortex. The parameter space defined by the choices for model parameters is further explored with large sets of numerical simulations. For much of this parameter space it is confirmed that the vortex structure and time-dependent behavior depend strongly on the vortex Reynolds number and only weakly on the convective Reynolds number. The authors also find that for higher convective Reynolds numbers, the maximum possible wind speed increases, and the rotational forcing necessary to achieve that wind speed decreases. Physical reasoning is used to explain this behavior, and implications for tornado dynamics are discussed.« less

Prediction of subsonic vortex shedding from forebodies with chines

NASA Technical Reports Server (NTRS)

Mendenhall, Michael R.; Lesieutre, Daniel J.

1990-01-01

An engineering prediction method and associated computer code VTXCHN to predict nose vortex shedding from circular and noncircular forebodies with sharp chine edges in subsonic flow at angles of attack and roll are presented. Axisymmetric bodies are represented by point sources and doublets, and noncircular cross sections are transformed to a circle by either analytical or numerical conformal transformations. The lee side vortex wake is modeled by discrete vortices in crossflow planes along the body; thus the three-dimensional steady flow problem is reduced to a two-dimensional, unsteady, separated flow problem for solution. Comparison of measured and predicted surface pressure distributions, flow field surveys, and aerodynamic characteristics are presented for noncircular bodies alone and forebodies with sharp chines.

Steady axisymmetric vortex flows with swirl and shear

NASA Astrophysics Data System (ADS)

Elcrat, Alan R.; Fornberg, Bengt; Miller, Kenneth G.

A general procedure is presented for computing axisymmetric swirling vortices which are steady with respect to an inviscid flow that is either uniform at infinity or includes shear. We consider cases both with and without a spherical obstacle. Choices of numerical parameters are given which yield vortex rings with swirl, attached vortices with swirl analogous to spherical vortices found by Moffatt, tubes of vorticity extending to infinity and Beltrami flows. When there is a spherical obstacle we have found multiple solutions for each set of parameters. Flows are found by numerically solving the Bragg-Hawthorne equation using a non-Newton-based iterative procedure which is robust in its dependence on an initial guess.

Behavior of streamwise rib vortices in a three-dimensional mixing layer

NASA Technical Reports Server (NTRS)

Lopez, J. M.; Bulbeck, C. J.

1992-01-01

The structure and behavior of a streamwise rib vortex in a direct numerical simulation of a time-developing three-dimensional incompressible plane mixing layer is examined. Where the rib vortex is being stretched, the vorticity vector is primarily directed in the vortex axial direction and the radial and azimuthal velocity distribution is similar to that of a Burger's vortex. In the region where the vortex stretching is negative, there is a change in the local topology of the vortex. The axial flow is decelerated and a negative azimuthal component of vorticity is induced. These features are characteristic of vortex breakdown. The temporal evolution of the rib vortex is similar to the evolution of an axisymmetric vortex in the early stages of vortex breakdown. The effect of vortex breakdown on other parts of the flow is, however, not as significant as the interaction between the rib vortex and other vortices.

Development of a rotor wake-vortex model, volume 1

NASA Technical Reports Server (NTRS)

Majjigi, R. K.; Gliebe, P. R.

1984-01-01

Certain empirical rotor wake and turbulence relationships were developed using existing low speed rotor wave data. A tip vortex model was developed by replacing the annulus wall with a row of image vortices. An axisymmetric turbulence spectrum model, developed in the context of rotor inflow turbulence, was adapted to predicting the turbulence spectrum of the stator gust upwash.

Pattern formation and three-dimensional instability in rotating flows

NASA Astrophysics Data System (ADS)

Christensen, Erik A.; Aubry, Nadine; Sorensen, Jens N.

1997-03-01

A fluid flow enclosed in a cylindrical container where fluid motion is created by the rotation of one end wall as a centrifugal fan is studied. Direct numerical simulations and spatio-temporal analysis have been performed in the early transition scenario, which includes a steady-unsteady transition and a breakdown of axisymmetric to three-dimensional flow behavior. In the early unsteady regime of the flow, the central vortex undergoes a vertical beating motion, accompanied by axisymmetric spikes formation on the edge of the breakdown bubble. As traveling waves, the spikes move along the central vortex core toward the rotating end-wall. As the Reynolds number is increased further, the flow undergoes a three-dimensional instability. The influence of the latter on the previous patterns is studied.

The circumstellar disk response to the motion of the host star

NASA Astrophysics Data System (ADS)

Regály, Zs.; Vorobyov, E.

2017-05-01

Context. Grid-based hydrodynamics simulations of circumstellar disks are often performed in the curvilinear coordinate system, in which the center of the computational domain coincides with the motionless star. However, the center of mass may be shifted from the star due to the presence of any non-axisymmetric mass distribution. As a result, the system exerts a non-zero gravity force on the star, causing the star to move in response, which can in turn affect the evolution of the circumstellar disk. Aims: We aim at studying the effects of stellar motion on the evolution of protostellar and protoplanetary disks. In protostellar disks, a non-axisymmetric distribution of matter in the form of spiral arms and/or massive clumps can form due to gravitational instability. Protoplanetary disks can also feature non-axisymmetric structures caused by an embedded high-mass planet or a large-scale vortex formed at viscosity transitions. Methods: We use 2D grid-based numerical hydrodynamic simulations to explore the effect of stellar motion. We adopt a non-inertial polar coordinate system centered on the star, in which the stellar motion is taken into account by calculating the indirect potential caused by the non-axisymmetric disk, a high-mass planet, or a large-scale vortex. We compare the results of numerical simulations with and without stellar motion. Results: We found that the stellar motion has a moderate effect on the evolution history and the mass accretion rate in protostellar disks, reducing somewhat the disk size and mass, while having a profound effect on the collapsing envelope, changing its inner shape from an initially axisymmetric to a non-axisymmetric configuration. Protoplanetary disk simulations show that the stellar motion slightly reduces the width of the gap opened by a high-mass planet, decreases the planet migration rate, and strengthens the large-scale vortices formed at the viscosity transition. Conclusions: We conclude that the inclusion of the indirect potential is recommended in grid-based hydrodynamics simulations of circumstellar disks which use the curvilinear coordinate system.

A combined analytical and numerical analysis of the flow-acoustic coupling in a cavity-pipe system

NASA Astrophysics Data System (ADS)

Langthjem, Mikael A.; Nakano, Masami

2018-05-01

The generation of sound by flow through a closed, cylindrical cavity (expansion chamber) accommodated with a long tailpipe is investigated analytically and numerically. The sound generation is due to self-sustained flow oscillations in the cavity. These oscillations may, in turn, generate standing (resonant) acoustic waves in the tailpipe. The main interest of the paper is in the interaction between these two sound sources. An analytical, approximate solution of the acoustic part of the problem is obtained via the method of matched asymptotic expansions. The sound-generating flow is represented by a discrete vortex method, based on axisymmetric vortex rings. It is demonstrated through numerical examples that inclusion of acoustic feedback from the tailpipe is essential for a good representation of the sound characteristics.

Some experiments in swirling flows: Detailed velocity measurements of a vortex breakdown using a laser Doppler anemometer. Ph.D. Thesis - Cornell Univ. Final Report

NASA Technical Reports Server (NTRS)

Faler, J. H.

1976-01-01

The results of an experimental study of spiraling flows in a slightly diverging, circular duct are reported. Seven types of flow disturbances were observed. In addition to the spiral and axisymmetric vortex breakdowns and the double helix mode, four other forms were identified and are reported. The type and axial location of the disturbance depended on the Reynolds and circulation numbers of the flow. Detailed velocity measurements were made by using a laser Doppler anemometer. Measurements made far upstream of any disturbance showed that the introduction of swirl resulted in the formation of a high axial velocity jet centered around the vortex center. A mapping of the velocity field of a so-called axisymmetric breakdown, formed at a Reynolds number of 2560, revealed that the recirculation zone is a two-celled structure, with four stagnation points on the vortex axis marking the axial extremes of the concentric cells. The dominant feature of the flow inside the bubble was the strong, periodic velocity fluctuations. Existing theoretical models do not predict the two-celled structure and the temporal velocity fluctuations that were observed.

Prediction of vortex shedding from circular and noncircular bodies in subsonic flow

NASA Technical Reports Server (NTRS)

Mendenhall, Michael R.; Lesieutre, Daniel J.

1987-01-01

An engineering prediction method and associated computer code VTXCLD are presented which predict nose vortex shedding from circular and noncircular bodies in subsonic flow at angles of attack and roll. The axisymmetric body is represented by point sources and doublets, and noncircular cross sections are transformed to a circle by either analytical or numerical conformal transformations. The leeward vortices are modeled by discrete vortices in crossflow planes along the body; thus, the three-dimensional steady flow problem is reduced to a two-dimensional, unsteady, separated flow problem for solution. Comparison of measured and predicted surface pressure distributions, flowfield surveys, and aerodynamic characteristics are presented for bodies with circular and noncircular cross sectional shapes.

A numerical study of axisymmetric compressible non-isothermal and reactive swirling flow

NASA Astrophysics Data System (ADS)

Tavernetti, William E.; Hafez, Mohamed M.

2017-09-01

Non-linear dynamical phenomena in combustion processes is an active area of experimental and theoretical research. This is in large part due to increasingly strict environmental pressures to make gas turbine engines and industrial burners more efficient. Using numerical methods, for steady and unsteady confined and unconfined compressible flow, this study examines the modeling influence of compressibility for axisymmetric swirling flow. The compressible reactive Navier-Stokes equations in terms of stream function, vorticity, circulation are used. Results, details of the numerical algorithms, as well as numerical verification techniques and validation with sources from the literature will be presented. Understanding how vortex breakdown phenomena are affected by modeling reactant consumption with compressibility effect is the main goal of this study.

Analysis and control of supersonic vortex breakdown flows

NASA Technical Reports Server (NTRS)

Kandil, Osama A.

1990-01-01

Analysis and computation of steady, compressible, quasi-axisymmetric flow of an isolated, slender vortex are considered. The compressible, Navier-Stokes equations are reduced to a simpler set by using the slenderness and quasi-axisymmetry assumptions. The resulting set along with a compatibility equation are transformed from the diverging physical domain to a rectangular computational domain. Solving for a compatible set of initial profiles and specifying a compatible set of boundary conditions, the equations are solved using a type-differencing scheme. Vortex breakdown locations are detected by the failure of the scheme to converge. Computational examples include isolated vortex flows at different Mach numbers, external axial-pressure gradients and swirl ratios.

Experiments on the enhancement of compressible mixing via streamwise vorticity. II - Vortex strength assessment and seed particle dynamics

NASA Technical Reports Server (NTRS)

Naughton, J. W.; Cattafesta, L. N.; Settles, G. S.

1993-01-01

The effect of streamwise vorticity on compressible axisymmetric mixing layers is examined using vortex strength assessment and seed particle dynamics analysis. Experimental results indicate that the particles faithfully represent the dynamics of the turbulent swirling flow. A comparison of the previously determined mixing layer growth rates with the present vortex strength data reveals that the increase of turbulent mixing up to 60 percent scales with the degree of swirl. The mixing enhancement appears to be independent of the compressibility level of the mixing layer.

Helical solutions of the bidirectional vortex in a cylindrical cyclone: Beltramian and Trkalian motions

NASA Astrophysics Data System (ADS)

Majdalani, Joseph

2012-10-01

In this work, two families of helical motions are investigated as prospective candidates for describing the bidirectional vortex field in a right-cylindrical chamber. These basic solutions are relevant to cyclone separators and to idealized representations of vortex-fired liquid and hybrid rocket engines in which bidirectional vortex motion is established. To begin, the bulk fluid motion is taken to be isentropic along streamlines, with no concern for reactions, heat transfer, viscosity, compressibility or unsteadiness. Then using the Bragg-Hawthorne equation for steady, inviscid, axisymmetric motion, two families of Euler solutions are derived. Among the characteristics of the newly developed solutions one may note the axial dependence of the swirl velocity, the Trkalian and Beltramian types of the helical motions, the sensitivity of the solutions to the outlet radius, the alternate locations of the mantle, and the increased axial and radial velocity magnitudes, including the rate of mass transfer across the mantle, for which explicit approximations are obtained. Our results are compared to an existing, complex lamellar model of the bidirectional vortex in which the swirl velocity reduces to a free vortex. In this vein, we find the strictly Beltramian flows to share virtually identical pressure variations and radial pressure gradients with those associated with the complex lamellar motion. Furthermore, both families warrant an asymptotic treatment to overcome their endpoint limitations caused by their omission of viscous stresses. From a broader perspective, the work delineates a logical framework through which self-similar, axisymmetric solutions to bidirectional and multidirectional vortex motions may be pursued. It also illustrates the manner through which different formulations may be arrived at depending on the types of wall boundary conditions. For example, both the slip condition at the sidewall and the inlet flow pattern at the headwall may be enforced or relaxed.

The Complex Dynamics of the Precessing Vortex Rope in a Straight Diffuser

NASA Astrophysics Data System (ADS)

Stuparu, Adrian; Susan-Resiga, Romeo

2016-11-01

The decelerated swirling flow in the discharge cone of Francis turbines operated at partial discharge develops a self-induced instability with a precessing helical vortex (vortex rope). In an axisymmetric geometry, this phenomenon is expected to generate asynchronous pressure fluctuations as a result of the precessing motion. However, numerical and experimental data indicate that synchronous (plunging) fluctuations, with a frequency lower than the precessing frequency, also develops as a result of helical vortex filament dynamics. This paper presents a quantitative approach to describe the precessing vortex rope by properly fitting a three-dimensional logarithmic spiral model with the vortex filament computed from the velocity gradient tensor. We show that the slope coefficient of either curvature or torsion radii of the helix is a good indicator for the vortex rope dynamics, and it supports the stretching - breaking up - bouncing back mechanism that may explain the plunging oscillations.

Numerical studies of interacting vortices

NASA Technical Reports Server (NTRS)

Liu, G. C.; Hsu, C. H.

1985-01-01

To get a basic understanding of the physics of flowfields modeled by vortex filaments with finite vortical cores, systematic numerical studies of the interactions of two dimensional vortices and pairs of coaxial axisymmetric circular vortex rings were made. Finite difference solutions of the unsteady incompressible Navier-Stokes equations were carried out using vorticity and stream function as primary variables. Special emphasis was placed on the formulation of appropriate boundary conditions necessary for the calculations in a finite computational domain. Numerical results illustrate the interaction of vortex filaments, demonstrate when and how they merge with each other, and establish the region of validity for an asymptotic analysis.

Evolution of secondary whirls in thermoconvective vortices: Strengthening, weakening, and disappearance in the route to chaos

NASA Astrophysics Data System (ADS)

Castaño, D.; Navarro, M. C.; Herrero, H.

2016-01-01

The appearance, evolution, and disappearance of periodic and quasiperiodic dynamics of fluid flows in a cylindrical annulus locally heated from below are analyzed using nonlinear simulations. The results reveal a route of the transition from a steady axisymmetric vertical vortex to a chaotic flow. The chaotic flow regime is reached after a sequence of successive supercritical Hopf bifurcations to periodic, quasiperiodic, and chaotic flow regimes. A scenario similar to the Ruelle-Takens-Newhouse scenario is verified in this convective flow. In the transition to chaos we find the appearance of subvortices embedded in the primary axisymmetric vortex, flows where the subvortical structure strengthens and weakens, that almost disappears before reforming again, leading to a more disorganized flow to a final chaotic regime. Results are remarkable as they connect to observations describing formation, weakening, and virtual disappearance before revival of subvortices in some atmospheric swirls such as dust devils.

Analytical and numerical performance models of a Heisenberg Vortex Tube

NASA Astrophysics Data System (ADS)

Bunge, C. D.; Cavender, K. A.; Matveev, K. I.; Leachman, J. W.

2017-12-01

Analytical and numerical investigations of a Heisenberg Vortex Tube (HVT) are performed to estimate the cooling potential with cryogenic hydrogen. The Ranque-Hilsch Vortex Tube (RHVT) is a device that tangentially injects a compressed fluid stream into a cylindrical geometry to promote enthalpy streaming and temperature separation between inner and outer flows. The HVT is the result of lining the inside of a RHVT with a hydrogen catalyst. This is the first concept to utilize the endothermic heat of para-orthohydrogen conversion to aid primary cooling. A review of 1st order vortex tube models available in the literature is presented and adapted to accommodate cryogenic hydrogen properties. These first order model predictions are compared with 2-D axisymmetric Computational Fluid Dynamics (CFD) simulations.

Self-Similar Compressible Free Vortices

NASA Technical Reports Server (NTRS)

vonEllenrieder, Karl

1998-01-01

Lie group methods are used to find both exact and numerical similarity solutions for compressible perturbations to all incompressible, two-dimensional, axisymmetric vortex reference flow. The reference flow vorticity satisfies an eigenvalue problem for which the solutions are a set of two-dimensional, self-similar, incompressible vortices. These solutions are augmented by deriving a conserved quantity for each eigenvalue, and identifying a Lie group which leaves the reference flow equations invariant. The partial differential equations governing the compressible perturbations to these reference flows are also invariant under the action of the same group. The similarity variables found with this group are used to determine the decay rates of the velocities and thermodynamic variables in the self-similar flows, and to reduce the governing partial differential equations to a set of ordinary differential equations. The ODE's are solved analytically and numerically for a Taylor vortex reference flow, and numerically for an Oseen vortex reference flow. The solutions are used to examine the dependencies of the temperature, density, entropy, dissipation and radial velocity on the Prandtl number. Also, experimental data on compressible free vortex flow are compared to the analytical results, the evolution of vortices from initial states which are not self-similar is discussed, and the energy transfer in a slightly-compressible vortex is considered.

Effects of shape and stroke parameters on the propulsion performance of an axisymmetric swimmer.

PubMed

Peng, Jifeng; Alben, Silas

2012-03-01

In nature, there exists a special group of aquatic animals which have an axisymmetric body and whose primary swimming mechanism is to use periodic body contractions to generate vortex rings in the surrounding fluid. Using jellyfish medusae as an example, this study develops a mathematical model of body kinematics of an axisymmetric swimmer and uses a computational approach to investigate the induced vortex wakes. Wake characteristics are identified for swimmers using jet propulsion and rowing, two mechanisms identified in previous studies of medusan propulsion. The parameter space of body kinematics is explored through four quantities: a measure of body shape, stroke amplitude, the ratio between body contraction duration and extension duration, and the pulsing frequency. The effects of these parameters on thrust, input power requirement and circulation production are quantified. Two metrics, cruising speed and energy cost of locomotion, are used to evaluate the propulsion performance. The study finds that a more prolate-shaped swimmer with larger stroke amplitudes is able to swim faster, but its cost of locomotion is also higher. In contrast, a more oblate-shaped swimmer with smaller stroke amplitudes uses less energy for its locomotion, but swims more slowly. Compared with symmetric strokes with equal durations of contraction and extension, faster bell contractions increase the swimming speed whereas faster bell extensions decrease it, but both require a larger energy input. This study shows that besides the well-studied correlations between medusan body shape and locomotion, stroke variables also affect the propulsion performance. It provides a framework for comparing the propulsion performance of axisymmetric swimmers based on their body kinematics when it is difficult to measure and analyze their wakes empirically. The knowledge from this study is also useful for the design of robotic swimmers that use axisymmetric body contractions for propulsion.

Identification of vortexes obstructing the dynamo mechanism in laboratory experiments

NASA Astrophysics Data System (ADS)

Limone, A.; Hatch, D. R.; Forest, C. B.; Jenko, F.

2013-06-01

The magnetohydrodynamic dynamo effect explains the generation of self-sustained magnetic fields in electrically conducting flows, especially in geo- and astrophysical environments. Yet the details of this mechanism are still unknown, e.g., how and to which extent the geometry, the fluid topology, the forcing mechanism, and the turbulence can have a negative effect on this process. We report on numerical simulations carried out in spherical geometry, analyzing the predicted velocity flow with the so-called singular value decomposition, a powerful technique that allows us to precisely identify vortexes in the flow which would be difficult to characterize with conventional spectral methods. We then quantify the contribution of these vortexes to the growth rate of the magnetic energy in the system. We identify an axisymmetric vortex, whose rotational direction changes periodically in time, and whose dynamics are decoupled from those of the large scale background flow, that is detrimental for the dynamo effect. A comparison with experiments is carried out, showing that similar dynamics were observed in cylindrical geometry. These previously unexpected eddies, which impede the dynamo effect, offer an explanation for the experimental difficulties in attaining a dynamo in spherical geometry.

Structure of vortices in superfluid 3He A-like phase in uniaxially stretched aerogel

NASA Astrophysics Data System (ADS)

Aoyama, Kazushi; Ikeda, Ryusuke

2009-02-01

Possible vortex-core transitions in A-like phase of superfluid 3He in uniaxially stretched aerogel are investigated. Since the global anisotropy in this system induces the polar pairing state in a narrow range close to the superfluid transition in addition to the A-like and B-like phases, the polar state may occur in the core of a vortex in the A-like phase identified with the ABM pairing state, like in the case of the bulk B phase where a core including the ABM state is realized at higher pressures. We examine the core structure of a single vortex under the boundary condition compatible with the Mermin-Ho vortex in the presence of the dipole interaction. Following Salomaa and Volovik's approach, we numerically solve the Ginzburg-Landau equation for an axially symmetric vortex and, by examining its stability against nonaxisymmetric perturbations, discuss possible vortex core states. It is found that a first order transition on core states may occur on warming from an axisymmetric vortex with a nonunitary core to a singular vortex with the polar core.

Axisymmetric bluff-body flow: A vortex solver for thin shells

NASA Astrophysics Data System (ADS)

Strickland, J. H.

1992-05-01

A method which is capable of solving the axisymmetric flow field over bluff bodies consisting of thin shells such as disks, partial spheres, rings, and other such shapes is presented in this report. The body may be made up of several shells whose edges are separated by gaps. The body may be moved axially according to arbitrary velocity time histories. In addition, the surfaces may possess axial and radial degrees of flexibility such that points on the surfaces may be allowed to move relative to each other according to some specified function of time. The surfaces may be either porous or impervious. The present solution technique is based on the axisymmetric vorticity transport equation. Physically, this technique simulates the generation of vorticity at body surfaces in the form of discrete ring vortices which are subsequently diffused and convected into the boundary layers and wake of the body. Relatively large numbers of vortices (1000 or more) are required to obtain good simulations. Since the direct calculation of perturbations from large numbers of ring vortices is computationally intensive, a fast multipole method was used to greatly reduce computer processing time. Several example calculations are presented for disks, disks with holes, hemispheres, and vented hemispheres. These results are compared with steady and unsteady experimental data.

Vortex breakdown simulation

NASA Technical Reports Server (NTRS)

Hafez, M.; Ahmad, J.; Kuruvila, G.; Salas, M. D.

1987-01-01

In this paper, steady, axisymmetric inviscid, and viscous (laminar) swirling flows representing vortex breakdown phenomena are simulated using a stream function-vorticity-circulation formulation and two numerical methods. The first is based on an inverse iteration, where a norm of the solution is prescribed and the swirling parameter is calculated as a part of the output. The second is based on direct Newton iterations, where the linearized equations, for all the unknowns, are solved simultaneously by an efficient banded Gaussian elimination procedure. Several numerical solutions for inviscid and viscous flows are demonstrated, followed by a discussion of the results. Some improvements on previous work have been achieved: first order upwind differences are replaced by second order schemes, line relaxation procedure (with linear convergence rate) is replaced by Newton's iterations (which converge quadratically), and Reynolds numbers are extended from 200 up to 1000.

On the failure of the quasicylindrical approximation and the connection to vortex breakdown in turbulent swirling flow

NASA Astrophysics Data System (ADS)

Gyllenram, W.; Nilsson, H.; Davidson, L.

2007-04-01

This paper analyzes the properties of viscous swirling flow in a pipe. The analysis is based on the time-averaged quasicylindrical Navier-Stokes equations and is applicable to steady, unsteady, and turbulent swirling flow. A method is developed to determine the critical level of swirl (vortex breakdown) for an arbitrary vortex. The method can also be used for an estimation of the radial velocity profile if the other components are given or measured along a single radial line. The quasicylindrical equations are rearranged to yield a single ordinary differential equation for the radial distribution of the radial velocity component. The equation is singular for certain levels of swirl. It is shown that the lowest swirl level at which the equation is singular corresponds exactly to the sufficient condition for axisymmetric vortex breakdown as derived by Wang and Rusak [J. Fluid Mech. 340, 177 (1997)] and Rusak et al. [AIAA J. 36, 1848 (1998)]. In narrow regions around the critical levels of swirl, the solution violates the quasicylindrical assumptions and the flow must undergo a drastic change of structure. The critical swirl level is determined by the sign change of the smallest eigenvalue of the discrete linear operator which relates the radial velocities to effects of viscosity and turbulence. It is shown that neither viscosity nor turbulence directly alters the critical level of swirl.

An Experimental Investigation of Forced Mixing of a Turbulent Boundary Layer in an Annular Diffuser. Ph.D. Thesis - Ohio State Univ.; [for boundary layer control

NASA Technical Reports Server (NTRS)

Shaw, R. J.

1979-01-01

The forced mixing process of a turbulent boundary layer in an axisymmetric annular diffuser using conventional wing-like vortex generators was studied. Flow field measurements were made at four axial locations downstream of the vortex generators. At each axial location, a total of 25 equally spaced profiles were measured behind three consecutive vortex generators which formed two pairs of vortex generators. Hot film anemometry probes measured the boundary layer turbulence structure at the same locations where pressure measurements were made. Both single and cross film probes were used. The diffuser turbulence data was teken only for a nominal inlet Mach number of 0.3. Three vortex generator configurations were tested. The differences between configurations involved changes in size and relative vortex generator positions. All three vortex generator configurations tested provided increases in diffuser performance. Distinct differences in the boundary layer integral properties and skin friction levels were noted between configurations. The axial turbulence intensity and Reynolds stress profiles measured displayed similarities in trends but differences in levels for the three configurations.

Gas Dynamics of a Recessed Nozzle in Its Displacement in the Radial Direction

NASA Astrophysics Data System (ADS)

Volkov, K. N.; Denisikhin, S. V.; Emel'yanov, V. N.

2017-07-01

Numerical simulation of gasdynamic processes accompanying the operation of the recessed nozzle of a solid-propellant rocket motor in its linear displacement is carried out. Reynolds-averaged Navier-Stokes equations closed using the equations of a k-ɛ turbulence model are used for calculations. The calculations are done for different rates of flow of the gas in the main channel and in the over-nozzle gap, and also for different displacements of the nozzle from an axisymmetric position. The asymmetry of geometry gives rise to a complicated spatial flow pattern characterized by the presence of singular points of spreading and by substantially inhomogeneous velocity and pressure distributions. The vortex flow pattern resulting from the linear displacement of the nozzle from an axisymmetric position is compared with the data of experimental visualization. The change in the vortex pattern of the flow and in the position of the singular points as a function of the flow coefficient and the displacement of the nozzle from the symmetry axis is discussed.

Theoretical prediction of thick wing and pylon-fuselage-fanpod-nacelle aerodynamic characteristics at subcritical speeds. Part 1: Theory and results

NASA Technical Reports Server (NTRS)

Tulinius, J. R.

1974-01-01

The theoretical development and the comparison of results with data of a thick wing and pylon-fuselage-fanpod-nacelle analysis are presented. The analysis utilizes potential flow theory to compute the surface velocities and pressures, section lift and center of pressure, and the total configuration lift, moment, and vortex drag. The skin friction drag is also estimated in the analysis. The perturbation velocities induced by the wing and pylon, fuselage and fanpod, and nacelle are represented by source and vortex lattices, quadrilateral vortices, and source frustums, respectively. The strengths of these singularities are solved for simultaneously including all interference effects. The wing and pylon planforms, twists, cambers, and thickness distributions, and the fuselage and fanpod geometries can be arbitrary in shape, provided the surface gradients are smooth. The flow through nacelle is assumed to be axisymmetric. An axisymmetric center engine hub can also be included. The pylon and nacelle can be attached to the wing, fuselage, or fanpod.

Numerical investigation of a vortex ring impinging on a coaxial aperture

NASA Astrophysics Data System (ADS)

Hu, Jiacheng; Peterson, Sean D.

2017-11-01

Recent advancements in smart materials have sparked an interest in the development of small scale fluidic energy harvesters for powering distributed applications in aquatic environments, where coherent vortex structures are prevalent. Thus, it is crucial to investigate the interaction of viscous vortices in the proximity of a thin plate (a common harvester configuration). Hence, the present study systematically examines the interaction of a vortex ring impinging on an infinitesimally thin wall with a coaxially aligned annular aperture. The rigid aperture serves as an axisymmetric counterpart of the thin plate, and the vortex ring represents a typical coherent vortex structure. The results indicate that the vortex dynamics can be categorized into two regimes based on the aperture to ring radius ratio (Rr). The rebound regime (Rr < 0.9) exhibits the classical unsteady boundary layer interaction in a vortex ring-wall collision. The vortex ring is able to slip past the aperture when Rr >= 0.9 , and an increase in the vortex ring impulse is observed for 1.0 <= Rr <= 1.3 due to fluid entrainment. Furthermore, pressure loadings are also compared to elucidate an optimal energy harvesting strategy in vortex impact configurations. This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant (RGPIN-05778) and Alexander Graham Bell Canada Graduate Scholarship (CGS-D).

Numerical Simulation of Parachute Inflation Process by IB Method

NASA Astrophysics Data System (ADS)

Miyoshi, Masaya; Mori, Koichi; Nakamura, Yoshiaki

In the present study the deformation and motion of a parachute in the process of inflation are simulated by applying the immersed boundary technique in a fluid-structure coupling solver. It was found from simulated results that the canopy is first inflated in the normal direction to the uniform flow (in the lateral direction), and then its apex is pulled by a vortex ring generated near the canopy's outer surface due to its negative pressure. After the end of this inflation process, the canopy moves in the tangential direction to the spherical surface, the center of which is located at the payload location. This motion is caused by the breakup of an initial axisymmetric vortex, where many vortices are generated from the shear layer. The predicted maximum parachute opening force is twice as large as the payload force in the steady state, which is in good agreement with experiment.

Estimation of perspective errors in 2D2C-PIV measurements for 3D concentrated vortices

NASA Astrophysics Data System (ADS)

Ma, Bao-Feng; Jiang, Hong-Gang

2018-06-01

Two-dimensional planar PIV (2D2C) is still extensively employed in flow measurement owing to its availability and reliability, although more advanced PIVs have been developed. It has long been recognized that there exist perspective errors in velocity fields when employing the 2D2C PIV to measure three-dimensional (3D) flows, the magnitude of which depends on out-of-plane velocity and geometric layouts of the PIV. For a variety of vortex flows, however, the results are commonly represented by vorticity fields, instead of velocity fields. The present study indicates that the perspective error in vorticity fields relies on gradients of the out-of-plane velocity along a measurement plane, instead of the out-of-plane velocity itself. More importantly, an estimation approach to the perspective error in 3D vortex measurements was proposed based on a theoretical vortex model and an analysis on physical characteristics of the vortices, in which the gradient of out-of-plane velocity is uniquely determined by the ratio of the maximum out-of-plane velocity to maximum swirling velocity of the vortex; meanwhile, the ratio has upper limits for naturally formed vortices. Therefore, if the ratio is imposed with the upper limits, the perspective error will only rely on the geometric layouts of PIV that are known in practical measurements. Using this approach, the upper limits of perspective errors of a concentrated vortex can be estimated for vorticity and other characteristic quantities of the vortex. In addition, the study indicates that the perspective errors in vortex location, vortex strength, and vortex radius can be all zero for axisymmetric vortices if they are calculated by proper methods. The dynamic mode decomposition on an oscillatory vortex indicates that the perspective errors of each DMD mode are also only dependent on the gradient of out-of-plane velocity if the modes are represented by vorticity.

Observables for anticipating tornadogenesis in mesocyclones

NASA Technical Reports Server (NTRS)

Carrier, G.; Fendell, F.; Mitchell, J.; Bronstein, M.

1992-01-01

We seek to identify an observable for anticipating tornadogenesis in mesocyclones, because such tornadoes are characterized by particularly long life, long and wide path, and high wind speed. We associate tornadogenesis with the transition from a one-cell vortex to a two-cell vortex. In such a transition, 'insertion' of a virtually nonrotating, slowly recirculating core displaces that high-swirl-speed air which is rapidly ascending along a moist-adiabatic locus of thermodynamic states, to an annulus at small but finite distance from the axis of rotation. Such a transition, on a vastly larger lateral scale, is known to characterize intensification of a tropical storm to a typhoon. We examine analytically a quasisteady axisymmetric model of a four-part vortex structure consisting of a bulk potential vortex, near-ground inflow layer, 'eyewall', and 'eye'. We inquire whether such a four-part intense vortex, formed in convectively unstably stratified air, is self-sustaining. In particular, we inquire whether the vertical profile of the angular momentum at the periphery is a discriminant for identifying self-sustaining vortices.

Jet and Vortex Projectile Flows in Shock/bubble-on-wall Configuration

NASA Astrophysics Data System (ADS)

Peng, Gaozhu; Zabusky, Norman

2001-11-01

We observe intense coaxial upstream and radial flow structures from a shock in air interacting with a SF6 half-bubble placed against an ideally reflecting wall. Our axisymmetric numerical simulations were done with PPM and models a spherical bubble struck symmetrically by two identical approaching shocks . A "dual" vorticity deposition arises at early time and a coaxial upstream moving primary jet and radial vortex ring flow appears. A coherent vortex ring or vortex projectile (VP), with entrained shocklets originates from the vortex layer produced at the Mach stem (which arises from the primary reflected shock). This VP moves ahead of the jet. The original transmitted wave and other trapped waves in the expanding axial jet causes a collapsing and expanding cavity and other instabilities on the complex bubble interface. We present and analyze our results with different diagnostics: vorticity, density, divergence of velocity, and numerical shadowgraph patterns; global quantification of circulation, enstrophy and r-integrated vorticity; etc. We also discuss data projection and filtering for quantifying and validating complex flows.

An investigation of the effects of aft blowing on a 3.0 caliber tangent ogive body at high angles of attack. M.S. Thesis

NASA Technical Reports Server (NTRS)

Gittner, Nathan M.

1992-01-01

An experimental investigation of the effects of aft blowing on the asymmetric vortex flow of a slender, axisymmetric body at high angles of attack was conducted. A 3.0 caliber tangent ogive body fitted with a cylindrical afterbody was tested in a wind tunnel under subsonic, laminar flow test conditions. Asymmetric blowing from both a single nozzle and a double nozzle configuration, positioned near the body apex, was investigated. Aft blowing was observed to alter the vortex asymmetry by moving the blowing-side vortex closer to the body surface while moving the non-blowing-side vortex further away from the body. The effect of increasing the blowing coefficient was to move the blowing-side vortex closer to the body surface at a more upstream location. The data also showed that blowing was more effective in altering the initial vortex asymmetry at the higher angles of attack than at the lower. The effects of changing the nozzle exit geometry were investigated and it was observed that blowing from a nozzle with a low, broad exit geometry was more effective in reducing the vortex asymmetry than blowing from a high, narrow exit geometry.

Computation of aeroelastic characteristics and stress-strained state of parachutes

NASA Astrophysics Data System (ADS)

Dneprov, Igor'v.

The paper presents computation results of the stress-strained state and aeroelastic characteristics of different types of parachutes in the process of their interaction with a flow. Simulation of the aerodynamic part of the aeroelastic problem is based on the discrete vortex method, while the elastic part of the problem is solved by employing either the finite element method, or the finite difference method. The research covers the following problems of the axisymmetric parachutes dynamic aeroelasticity: parachute inflation, forebody influence on the aerodynamic characteristics of the object-parachute system, parachute disreefing, parachute inflation in the presence of the engagement parachute. The paper also presents the solution of the spatial problem of static aeroelasticity for a single-envelope ram-air parachute. Some practical recommendations are suggested.

Calculation of potential flow past non-lifting bodies at angle of attack using axial and surface singularity methods. M.S. Thesis. Contractor Report, 1 Jan. 1981 - 31 Aug. 1982

NASA Technical Reports Server (NTRS)

Shu, J. Y.

1983-01-01

Two different singularity methods have been utilized to calculate the potential flow past a three dimensional non-lifting body. Two separate FORTRAN computer programs have been developed to implement these theoretical models, which will in the future allow inclusion of the fuselage effect in a pair of existing subcritical wing design computer programs. The first method uses higher order axial singularity distributions to model axisymmetric bodies of revolution in an either axial or inclined uniform potential flow. Use of inset of the singularity line away from the body for blunt noses, and cosine-type element distributions have been applied to obtain the optimal results. Excellent agreement to five significant figures with the exact solution pressure coefficient value has been found for a series of ellipsoids at different angles of attack. Solutions obtained for other axisymmetric bodies compare well with available experimental data. The second method utilizes distributions of singularities on the body surface, in the form of a discrete vortex lattice. This program is capable of modeling arbitrary three dimensional non-lifting bodies. Much effort has been devoted to finding the optimal method of calculating the tangential velocity on the body surface, extending techniques previously developed by other workers.

Analysis of an open cycle gas core nuclear propulsion system using MHD driven vortices for fuel containment

NASA Astrophysics Data System (ADS)

Sedwick, Raymond John

1998-12-01

A novel method for containing gaseous uranium vapor in an open cycle nuclear space propulsion system is developed. In an attempt to increase the operating temperature of the nuclear reactor beyond the melting point of solid fuel rods (thus increasing specific impulse), the fuel is instead suspended as a vapor in the propellant using the pressure forces developed in a confined vortex flow. The introduction of the fuel as uranium hexafluoride is found to be effective in maintaining its vapor phase in the feed passages from the tank, but not in the main vortex. A mechanism by which the resulting condensation of the uranium may be tolerated is identified, and the electro- optical properties of the resulting mixture are investigated. Containment is modeled using a 1D- axisymmetric geometry, and radiative heat transfer is found to restrict the maximum specific impulse of the system to 1500 seconds using pumping pressures of 500 atm. The specific impulse is related to this pressure as pm1/4, allowing only marginal increases in Isp at increased pressure levels. Additional 2D- axisymmetric issues, such as non-uniform current distribution and bypass flows through the boundary layers, are investigated, with possible methods of solution cited. A two-group, two-region reactor analysis is performed, estimating the mass of the reactor to be about 10 metric tonnes, and establishing the thrust to weight ratio achievable by the system at about 50. To reduce the mass of the power system, a scheme for using cross-flow heat exchange with the propellant flow to minimize (and possibly eliminate) the need for radiators to reject waste heat is presented. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

Experimental investigation of the effects of aft blowing with various nozzle exit geometries on a 3.0 caliber tangent ogive at high angles of attack: Forebody pressure distributions

NASA Technical Reports Server (NTRS)

Chokani, Ndaona; Gittner, N. M.

1992-01-01

An experimental study of the effects of aft blowing on the asymmetric vortex flow of a slender, axisymmetric body at high angles of attack was conducted. A 3.0 caliber tangent ogive body fitted with a cylindrical afterbody was tested in a wind tunnel under subsonic, laminar flow test conditions. Asymmetric blowing from both a single nozzle and a double nozzle configuration, positioned near the body apex, was studied. Aft blowing was observed to alter the vortex asymmetry by moving the blowing-side vortex closer to the body surface while moving the non-blowing-side vortex further away from the body. The effect of increasing the blowing coefficient was to move the blowing-side vortex closer to the body surface at a more upstream location. The data also showed that blowing was more effective in altering the initial vortex asymmetry at the higher angles of attack than at the lower. The effects of changing the nozzle exit geometry were studied and it was observed that blowing from a nozzle with a low, broad exit geometry was more effective in reducing the vortex asymmetry than blowing from a high, narrow exit geometry.

On the three-dimensional interaction of a rotor-tip vortex with a cylindrical surface

NASA Astrophysics Data System (ADS)

Radcliff, Thomas D.; Burggraf, Odus R.; Conlisk, A. T.

2000-12-01

The collision of a strong vortex with a surface is an important problem because significant impulsive loads may be generated. Prediction of helicopter fatigue lifetime may be limited by an inability to predict these loads accurately. Experimental results for the impingement of a helicopter rotor-tip vortex on a cylindrical airframe show a suction peak on the top of the airframe that strengthens and then weakens within milliseconds. A simple line-vortex model can predict the experimental results if the vortex is at least two vortex-core radii away from the airframe. After this, the model predicts continually deepening rather than lessening suction as the vortex stretches. Experimental results suggest that axial flow within the core of a tip vortex has an impact on the airframe pressure distribution upon close approach. The mechanism for this is hypothesized to be the inviscid redistribution of the vorticity field within the vortex as the axial velocity stagnates. Two models of a tip vortex with axial flow are considered. First, a classical axisymmetric line vortex with a cutoff parameter is superimposed with vortex ringlets suitably placed to represent the helically wound vortex shed by the rotor tip. Thus, inclusion of axial flow is found to advect vortex core thinning away from the point of closest interaction as the vortex stretches around the cylindrical surface during the collision process. With less local thinning, vorticity in the cutoff parameter model significantly overlaps the solid cylinder in an unphysical manner, highlighting the fact that the vortex core must deform from its original cylindrical shape. A second model is then developed in which axial and azimuthal vorticity are confined within a rectangular-section vortex. Area and aspect ratio of this vortex can be varied independently to simulate deformation of the vortex core. Both axial velocity and core deformation are shown to be important to calculate the local induced pressure loads properly. The computational results are compared with experiments conducted at the Georgia Institute of Technology.

Program LRCDM2: Improved aerodynamic prediction program for supersonic canard-tail missiles with axisymmetric bodies

NASA Technical Reports Server (NTRS)

Dillenius, Marnix F. E.

1985-01-01

Program LRCDM2 was developed for supersonic missiles with axisymmetric bodies and up to two finned sections. Predicted are pressure distributions and loads acting on a complete configuration including effects of body separated flow vorticity and fin-edge vortices. The computer program is based on supersonic panelling and line singularity methods coupled with vortex tracking theory. Effects of afterbody shed vorticity on the afterbody and tail-fin pressure distributions can be optionally treated by companion program BDYSHD. Preliminary versions of combined shock expansion/linear theory and Newtonian/linear theory have been implemented as optional pressure calculation methods to extend the Mach number and angle-of-attack ranges of applicability into the nonlinear supersonic flow regime. Comparisons between program results and experimental data are given for a triform tail-finned configuration and for a canard controlled configuration with a long afterbody for Mach numbers up to 2.5. Initial tests of the nonlinear/linear theory approaches show good agreement for pressures acting on a rectangular wing and a delta wing with attached shocks for Mach numbers up to 4.6 and angles of attack up to 20 degrees.

Dynamic structure of confined shocks undergoing sudden expansion

NASA Astrophysics Data System (ADS)

Abate, G.; Shyy, W.

2002-01-01

The gas dynamic phenomenon associated with a normal shock wave within a tube undergoing a sudden area expansion consists of highly transient flow and diffraction that give rise to turbulent, compressible, vortical flows. These interactions can occur at time scales typically ranging from micro- to milliseconds. In this article, we review recent experimental and numerical results to highlight the flow phenomena and main physical mechanisms associated with this geometry. The topics addressed include time-accurate shock and vortex locations, flowfield evolution and structure, wall-shock Mach number, two- vs. three-dimensional sudden expansions, and the effect of viscous dissipation on planar shock-front expansions. Between axisymmetric and planar geometries, the flow structure evolves very similarly early on in the sudden expansion process (i.e., within the first two shock tube diameters). Both numerical and experimental studies confirm that the trajectory of the vortex formed at the expansion corner is convected into the flowfield faster in the axisymmetric case than the planar case. The lateral propagation of the vortices correlates very well between axisymmetric and planar geometries. In regard to the rate of dissipation of turbulent kinetic energy (TKE) for a two-dimensional planar shock undergoing a sudden expansion within a confined chamber, calculations show that the solenoidal dissipation is confined to the region of high strain rates arising from the expansion corner. Furthermore, the dilatational dissipation is concentrated mainly at the curvature of the incident, reflected, and barrel shock fronts. The multiple physical mechanisms identified, including shock-strain rate interaction, baroclinic effect, vorticity generation, and different aspects of viscous dissipation, have produced individual and collective flow structures observed experimentally.

Deceleration of a supersonic flow behind a curved shock wave with isentropic precompression

NASA Technical Reports Server (NTRS)

Dulov, V. G.; Shchepanovskiy, V. A.

1985-01-01

Three-dimensional supersonic flows of an ideal fluid in the neighborhood of bodies formed by being cut out along the streamlines of an axisymmetric flow are investigated. The flow consists of a region of isoentropic compression and a region of vortex flow. An exact solution with variable entropy is used to describe the flow in the vortex region. In the continuous flow region an approximate solution is constructed by expanding the solution in a series in a small parameter. The effect of the shape of the excision and the vorticity of the flow on compression of the jet and and the total pressure loss coefficient is studied.

Numerical Simulation of Vortex Ring Formation in the Presence of Background Flow: Implications for Squid Propulsion

NASA Astrophysics Data System (ADS)

Jiang, Houshuo; Grosenbaugh, Mark A.

2002-11-01

Numerical simulations are used to study the laminar vortex ring formation in the presence of background flow. The numerical setup includes a round-headed axisymmetric body with a sharp-wedged opening at the posterior end where a column of fluid is pushed out by a piston inside the body. The piston motion is explicitly included into the simulations by using a deforming mesh. The numerical method is verified by simulating the standard vortex ring formation process in quiescent fluid for a wide range of piston stroke to cylinder diameter ratios (Lm/D). The results from these simulations confirm the existence of a universal formation time scale (formation number) found by others from experimental and numerical studies. For the case of vortex ring formation by the piston/cylinder arrangement in a constant background flow (i.e. the background flow is in the direction of the piston motion), the results show that a smaller fraction of the ejected circulation is delivered into the leading vortex ring, thereby decreasing the formation number. The mechanism behind this reduction is believed to be related to the modification of the shear layer profile between the jet flow and the background flow by the external boundary layer on the outer surface of the cylinder. In effect, the vorticity in the jet is cancelled by the opposite signed vorticity in the external boundary layer. Simulations using different end geometries confirm the general nature of the phenomenon. The thrust generated from the jet and the drag forces acting on the body are calculated with and without background flow for different piston programs. The implications of these results for squid propulsion are discussed.

Self-sustaining intense vortices

NASA Astrophysics Data System (ADS)

Carrier, G.; Fendell, F.; Mitchell, J.; Bronstein, M.

1994-10-01

We seek to identify an accessible observable for anticipating tornadogenesis in mesocyclones, because such tornadoes are characterized by exceptionally extended lifespan, exceptionally long and wide path, and exceptionally high wind speed. We associate tornadogenesis with the transition from a one-cell vortex to a two-cell vortex. After such a transition, the core (“eye”) of the vortex consists of virtually nonrotating, slowly recirculating, relatively dry air. Rapidly swirling air swiftly ascends in an annulus (“eyewall”), situated at a small but finite distance from the axis of rotation. The swiftly ascending air is described by a locus of thermodynamic states well approximated by a moist adiabat. Such a transition from a one-cell vortex to a two-cell vortex, on vastly large lateral scale, is known to characterize the intensification of a tropical storm to a typhoon. We adopt a simplified, tractable model for our initial analytic efforts. We examine a quasisteady axisymmetric vortex with a four-part structure, consisting of a bulk potential vortex, a near-ground inflow layer, an “eyewall”, and an “eye”. We inquire under what conditions such a four-part intense vortex, formed in convectively unstable stratified air, is self-sustaining. In particular, we inquire whether the vertical profile of the angular momentum outside of the eyewall is a discriminant for identifying the conditions for which an intense (two-cell) vortex could be self-sustaining. Guidance from laboratory experiments would be helpful concerning the turnaround (the portion of the flow field in which the near-ground swirling inflow separates to form the swirling updraft of the eyewall annulus).

Drop impact into a deep pool: vortex shedding and jet formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agbaglah, G.; Thoraval, M. -J.; Thoroddsen, S. T.

2015-02-01

One of the simplest splashing scenarios results from the impact of a single drop on a deep pool. The traditional understanding of this process is that the impact generates an axisymmetric sheet-like jet that later breaks up into secondary droplets. Recently it was shown that even this simplest of scenarios is more complicated than expected because multiple jets can be generated from a single impact event and there are transitions in the multiplicity of jets as the experimental parameters are varied. Here, we use experiments and numerical simulations of a single drop impacting on a deep pool to examine themore » transition from impacts that produce a single jet to those that produce two jets. Using high-speed X-ray imaging methods we show that vortex separation within the drop leads to the formation of a second jet long after the formation of the ejecta sheet. Using numerical simulations we develop a phase diagram for this transition and show that the capillary number is the most appropriate order parameter for the transition.« less

Evolution of an electron plasma vortex in a strain flow

NASA Astrophysics Data System (ADS)

Danielson, J. R.

2016-10-01

Coherent vortex structures are ubiquitous in fluids and plasmas and are examples of self-organized structures in nonlinear dynamical systems. The fate of these structures in strain and shear flows is an important issue in many physical systems, including geophysical fluids and shear suppression of turbulence in plasmas. In two-dimensions, an inviscid, incompressible, ideal fluid can be modeled with the Euler equations, which is perhaps the simplest system that supports vortices. The Drift-Poisson equations for pure electron plasmas in a strong, uniform magnetic field are isomorphic to the Euler equations, and so electron plasmas are an excellent test bed for the study of 2D vortex dynamics. This talk will describe results from a new experiment using pure electron plasmas in a specially designed Penning-Malmberg (PM) trap to study the evolution of an initially axisymmetric 2D vortex subject to externally imposed strains. Complementary vortex-in-cell simulations are conducted to validate the 2D nature of the experimental results and to extend the parameter range of these studies. Data for vortex destruction using both instantaneously applied and time dependent strains with flat (constant vorticity) and extended radial profiles will be presented. The role of vortex self-organization will be discussed. A simple 2D model works well for flat vorticity profiles. However, extended profiles exhibit more complicated behavior, such as filamentation and stripping; and these effects and their consequences will be discussed. Work done in collaboration with N. C. Hurst, D. H. E. Dubin, and C. M. Surko.

Formation and behavior of counter-rotating vortex rings

NASA Astrophysics Data System (ADS)

Sadri, V.; Krueger, P. S.

2017-08-01

Concentric, counter-rotating vortex ring formation by transient jet ejection between concentric cylinders was studied numerically to determine the effects of cylinder gap ratio, Δ R/R, and jet stroke length-to-gap ratio, L/Δ R, on the evolution of the vorticity and the trajectories of the resulting axisymmetric vortex pair. The flow was simulated at a jet Reynolds number of 1000 (based on Δ R and the jet velocity), L/Δ R in the range 1-20, and Δ R/R in the range 0.05-0.25. Five characteristic flow evolution patterns were observed and classified based on L/Δ R and Δ R/R. The results showed that the relative position, relative strength, and radii of the vortex rings during and soon after formation played a prominent role in the evolution of the trajectories of their vorticity centroids at the later time. The conditions on relative strength of the vortices necessary for them to travel together as a pair following formation were studied, and factors affecting differences in vortex circulation following formation were investigated. In addition to the characteristics of the primary vortices, the stopping vortices had a strong influence on the initial vortex configuration and effected the long-time flow evolution at low L/Δ R and small Δ R/R. For long L/Δ R and small Δ R/R, shedding of vorticity was sometimes observed and this shedding was related to the Kelvin-Benjamin variational principle of maximal energy for steadily translating vortex rings.

Axisymmetric Vortices with Swirl

NASA Astrophysics Data System (ADS)

Elcrat, A.

2007-11-01

This talk is concerned with finding solutions of the Euler equations by solving elliptic boundary value problems for the Bragg-Hawthorne equation L u= -urr -(1/r)ur - = r^2f (u) + h(u). Theoretical results have been given for previously (Elcrat and Miller, Differential and Integral Equations 16(4) 2003, 949-968) for problems with swirl and general classes of profile functions f, h by iterating Lu(n+1)= rf(u)n)) + h(u(n)), and showing u(n) converges montonically to a solution. The solutions obtained depend on the initial guess, which can be thought of as prescribing level sets of the vortex. When a computational program was attempted these monotone iterations turned out to be numerically unstable, and a stable computation was acheived by fixing the moment of the cross section of a vortex in the merideanal plane. (This generalizes previous computational results in Elcrat, Fornberg and Miller, JFM 433 2001, (315-328) We obtain famillies of vortices related to vortex rings with swirl, Moffatt's generalization of Hill's vortex and tubes of vorticity with swirl wrapped around the symmetry axis. The vortices are embedded in either an irrotational flow or a flow with shear, and we deal with the transition form no swirl in the vortex to flow with only swirl, a Beltrami flow.

Transient growth in Taylor-Couette flow of a Bingham fluid.

PubMed

Chen, Cheng; Wan, Zhen-Hua; Zhang, Wei-Guo

2015-04-01

In this paper we investigate linear transient growth of perturbation energy in Taylor-Couette flow of a Bingham fluid. The effects of yield stress on transient growth and the structure of the optimal perturbation are mainly considered for both the wide-gap case and the narrow-gap case. For this purpose we complement the linear stability of this flow subjected to axisymmetric disturbances, presented by Landry et al. [M. P. Landry, I. A. Frigaard, and D. M. Martinez, J. Fluid Mech. 560, 321 (2006)], with the transient growth characteristics of both axisymmetric and nonaxisymmetric perturbations. We obtain the variations of the relative amplitude of optimal perturbation with yield stress, analyze the roles played by the Coriolis force and the additional stress in the evolution of meridional perturbations for the axisymmetric modes, and give the explanations for the possible change of the optimal azimuthal mode (featured by the maximum optimal energy growth G(opt)) with yield stress. These results might help us in the understanding of the effect of fluid rheology on transient growth mechanism in vortex flows.

Spectral Characteristics of Wake Vortex Sound During Roll-Up

NASA Technical Reports Server (NTRS)

Booth, Earl R., Jr. (Technical Monitor); Zhang, Yan; Wang, Frank Y.; Hardin, Jay C.

2003-01-01

This report presents an analysis of the sound spectra generated by a trailing aircraft vortex during its rolling-up process. The study demonstrates that a rolling-up vortex could produce low frequency (less than 100 Hz) sound with very high intensity (60 dB above threshold of human hearing) at a distance of 200 ft from the vortex core. The spectrum then drops o rapidly thereafter. A rigorous analytical approach has been adopted in this report to derive the spectrum of vortex sound. First, the sound pressure was solved from an alternative treatment of the Lighthill s acoustic analogy approach [1]. After the application of Green s function for free space, a tensor analysis was applied to permit the removal of the source term singularity of the wave equation in the far field. Consequently, the sound pressure is expressed in terms of the retarded time that indicates the time history and spacial distribution of the sound source. The Fourier transformation is then applied to the sound pressure to compute its spectrum. As a result, the Fourier transformation greatly simplifies the expression of the vortex sound pressure involving the retarded time, so that the numerical computation is applicable with ease for axisymmetric line vortices during the rolling-up process. The vortex model assumes that the vortex circulation is proportional to the time and the core radius is a constant. In addition, the velocity profile is assumed to be self-similar along the aircraft flight path, so that a benchmark vortex velocity profile can be devised to obtain a closed form solution, which is then used to validate the numerical calculations for other more realistic vortex profiles for which no closed form solutions are available. The study suggests that acoustic sensors operating at low frequency band could be profitably deployed for detecting the vortex sound during the rolling-up process.

Permeable disks at low Reynolds numbers

NASA Astrophysics Data System (ADS)

Viola, Ignazio Maria; Cummins, Cathal; Mastropaolo, Enrico; Nakayama, Naomi

2017-11-01

The wake of a permeable disk can be rather exceptional: a toroidal vortex can form and remains stably at a fixed distance from the disk. The streamwise length of the vortex depends on the Reynolds and Darcy numbers. We investigate this fascinating flow for Reynolds numbers from 10 to 130 and Darcy numbers (Da) from 10-9 to 1. Direct numerical simulations are performed on a 2D grid with axisymmetric boundary conditions. Three flow regimes are observed: for low Da (effectively impervious), the wake is characterized by the presence of a toroidal vortex whose length is approximately equal to that of an impervious disk. For 10-6 < Da <10-3 , the increase in Da causes the vortex to shorten, and eventually vanishes at a critical Darcy number. It is demonstrated that increasing the permeability can lead to large variations in the length of the recirculating wake but with minimal effect on the drag coefficient. For higher Da (highly permeable), there is no recirculation, and an analytical expression for the drag force on the disk is derived, showing good agreement with the numerical results. This work was supported by the Leverhulme Trust [RPG-2015-255].

Topology and stability of a water-soybean-oil swirling flow

NASA Astrophysics Data System (ADS)

Carrión, Luis; Herrada, Miguel A.; Shtern, Vladimir N.

2017-02-01

This paper reveals and explains the flow topology and instability hidden in an experimental study by Tsai et al. [Tsai et al., Phys. Rev. E 92, 031002(R) (2015)], 10.1103/PhysRevE.92.031002. Water and soybean oil fill a sealed vertical cylindrical container. The rotating top disk induces the meridional circulation and swirl of both fluids. The experiment shows a flattop interface shape and vortex breakdown in the oil flow developing as the rotation strength R eo increases. Our numerical study shows that vortex breakdown occurs in the water flow at R eo=300 and in the oil flow at R eo=941 . As R eo increases, the vortex breakdown cell occupies most of the water domain and approaches the interface at R eo around 600. The rest of the (countercirculating) water separates from the axis as the vortex breakdown cells in the oil and water meet at the interface-axis intersection. This topological transformation of water flow significantly contributes to the development of the flattop shape. It is also shown that the steady axisymmetric flow suffers from shear-layer instability, which emerges in the water domain at R eo=810 .

Studies of the relationship between environmental forcing and the structure and dynamics of tornado-like vortices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nolan, David S.; Almgren, Ann S.; Bell, John B.

Axisymmetric numerical simulations continue to provide insight into how the structure, dynamics, and maximum wind speeds of tornadoes, and other convectively-maintained vortices, are influenced by the surrounding environment. This work is continued with a new numerical model of axisymmetric incompressible flow that incorporates adaptive mesh refinement. The model dynamically increases or decreases the resolution in regions of interest as determined by a specified refinement criterion. Here, the criterion used is based on the cell Reynolds number dx dv / nu, so that the flow is guaranteed to be laminar on the scale of the local grid spacing. The model ismore » used to investigate how the altitude and shape of the convective forcing, the size of the domain, and the effective Reynolds number (based on the choice of the eddy viscosity nu) influence the structure and dynamics of the vortex. Over a wide variety of domain and forcing geometries,the vortex Reynolds number Gamma / nu (the ratio of the far-field circulation to the eddy viscosity) is shown to be the most important parameter for determining vortex structure and behavior. Furthermore,it is found that the vertical scale of the convective forcing only affects the vortex inasmuch as this vertical scale contributes to the total strength of the convective forcing. The horizontal scale of the convective forcing, however, is found to be the fundamental length scale in the problem, in that it can determine both the circulation of the fluid that is drawn into the vortex core, and also influences the depth of the swirling boundary layer. Higher mean wind speeds are sustained as the eddy viscosity is decreased; however, it is observed that the highest wind speeds are found in the high-swirl, two-celled vortex regime rather than in the low-swirl, one-celled regime, which is in contrast with some previous results. The conclusions drawn from these results are applied to dimensional simulations with scales similar to the mesocyclone/thunderstorm environment. Tornado-like vortices are reproduced, using a constant eddy viscosity with such values as 40 m2s-1, which have maximum wind speeds, radii of maximum winds, and boundary layer depths which are quite similar to those recently observed with portable Doppler radar. Based on the results of both nondimensional and tornado-scale simulations, scaling laws are empirically derived for the internal length scales in tornado-like vortices, such as the depth of the boundary layer and the radius of maximum winds.« less

Numerical investigation on nonlinear effect and vortex formation of oscillatory flow throughout a short tube in a thermoacoustic Stirling engine

NASA Astrophysics Data System (ADS)

Yang, Peng; Chen, Hui; Liu, Yingwen

2017-06-01

In this paper, a two-dimensional axisymmetric model of a thermoacoustic Stirling engine with a short tube where the cross section narrows has been developed. The transient streamlines and vortex formation through short tubes with different diameters in oscillatory flow have been investigated visually by computational fluid dynamics. Three dimensionless parameters, Reynolds number (Re), Keulegan-Carpenter number (KC), and Womersley number (Wo), are used to describe the flow regime and vortex characteristic throughout the short tube. High Re and Wo numbers indicate that the oscillatory flow develops into the turbulent flow through the short tube. The KC number has a direct effect on the transition of streamlines and the development of the vortex. For a small cross section where KC ≈ 1, streamlines rotate and the vortex forms at both sides of the short tube. The vortex stays in the main flow region, and intensity varies as streamlines are convected downstream. The velocity along the radius presents a Poiseuille profile within the influence of the vortex. For a large cross section where KC < 1, streamlines pass the short tube with little rotation and the vortex disappears in the main flow region and confines near the short tube. The velocity profile tends to be flat. The nonlinear effects including instantaneous pressure drop and power dissipation throughout the short tube are also discussed. It shows that the time averaged pressure drop is generated at the cost of power dissipation. Finally, the "effectiveness" is applied to evaluate the performance of the short tube. The results suggest that increasing the diameter of the short tube is in favor of reducing power dissipation, which is beneficial to improve "effectiveness."

RANS computations for identification of 1-D cavitation model parameters: application to full load cavitation vortex rope

NASA Astrophysics Data System (ADS)

Alligné, S.; Decaix, J.; Müller, A.; Nicolet, C.; Avellan, F.; Münch, C.

2017-04-01

Due to the massive penetration of alternative renewable energies, hydropower is a key energy conversion technology for stabilizing the electrical power network by using hydraulic machines at off design operating conditions. At full load, the axisymmetric cavitation vortex rope developing in Francis turbines acts as an internal source of energy, leading to an instability commonly referred to as self-excited surge. 1-D models are developed to predict this phenomenon and to define the range of safe operating points for a hydropower plant. These models require a calibration of several parameters. The present work aims at identifying these parameters by using CFD results as objective functions for an optimization process. A 2-D Venturi and 3-D Francis turbine are considered.

Effects of boundary layer forcing on wing-tip vortices

NASA Astrophysics Data System (ADS)

Shaw-Ward, Samantha

The nature of turbulence within wing-tip vortices has been a topic of research for decades, yet accurate measurements of Reynolds stresses within the core are inherently difficult due to the bulk motion wandering caused by initial and boundary conditions in wind tunnels. As a result, characterization of a vortex as laminar or turbulent is inconclusive and highly contradicting. This research uses several experimental techniques to study the effects of broadband turbulence, introduced within the wing boundary layer, on the development of wing-tip vortices. Two rectangular wings with a NACA 0012 profile were fabricated for the use of this research. One wing had a smooth finish and the other rough, introduced by P80 grade sandpaper. Force balance measurements showed a small reduction in wing performance due to surface roughness for both 2D and 3D configurations, although stall characteristics remained relatively unchanged. Seven-hole probes were purpose-built and used to assess the mean velocity profiles of the vortices five chord lengths downstream of the wing at multiple angles of attack. Above an incidence of 4 degrees, the vortices were nearly axisymmetric, and the wing roughness reduced both velocity gradients and peak velocity magnitudes within the vortex. Laser Doppler velocimetry was used to further assess the time-resolved vortex at an incidence of 5 degrees. Evidence of wake shedding frequencies and wing shear layer instabilities at higher frequencies were seen in power spectra within the vortex. Unlike the introduction of freestream turbulence, wing surface roughness did not appear to increase wandering amplitude. A new method for removing the effects of vortex wandering is proposed with the use of carefully selected high-pass filters. The filtered data revealed that the Reynolds stress profiles of the vortex produced by the smooth and rough wing were similar in shape, with a peak occurring away from the vortex centre but inside of the core. Single hot-wire measurements in the 2D wing wake revealed the potential origin of dominant length-scales observed in the vortex power spectra. At angles above 5 degrees, the 2D wing wake had both higher velocity deficits and higher levels of total wake kinetic energy for the rough wing as compared to the smooth wing.

Micro-Ramps for External Compression Low-Boom Inlets

NASA Technical Reports Server (NTRS)

Rybalko, Michael; Loth, Eric; Chima, Rodrick V.; Hirt, Stefanie M.; DeBonis, James R.

2010-01-01

The application of vortex generators for flow control in an external compression, axisymmetric, low-boom concept inlet was investigated using RANS simulations with three-dimensional (3-D), structured, chimera (overset) grids and the WIND-US code. The low-boom inlet design is based on previous scale model 1- by 1-ft wind tunnel tests and features a zero-angle cowl and relaxed isentropic compression centerbody spike, resulting in defocused oblique shocks and a weak terminating normal shock. Validation of the methodology was first performed for micro-ramps in supersonic flow on a flat plate with and without oblique shocks. For the inlet configuration, simulations with several types of vortex generators were conducted for positions both upstream and downstream of the terminating normal shock. The performance parameters included incompressible axisymmetric shape factor, separation area, inlet pressure recovery, and massflow ratio. The design of experiments (DOE) methodology was used to select device size and location, analyze the resulting data, and determine the optimal choice of device geometry. The optimum upstream configuration was found to substantially reduce the post-shock separation area but did not significantly impact recovery at the aerodynamic interface plane (AIP). Downstream device placement allowed for fuller boundary layer velocity profiles and reduced distortion. This resulted in an improved pressure recovery and massflow ratio at the AIP compared to the baseline solid-wall configuration.

Second order modeling of boundary-free turbulent shear flows

NASA Technical Reports Server (NTRS)

Shih, T.-H.; Chen, Y.-Y.; Lumley, J. L.

1991-01-01

A set of realizable second order models for boundary-free turbulent flows is presented. The constraints on second order models based on the realizability principle are re-examined. The rapid terms in the pressure correlations for both the Reynolds stress and the passive scalar flux equations are constructed to exactly satisfy the joint realizability. All other model terms (return-to-isotropy, third moments, and terms in the dissipation equations) already satisfy realizability. To correct the spreading rate of the axisymmetric jet, an extra term is added to the dissipation equation which accounts for the effect of mean vortex stretching on dissipation. The test flows used in this study are the mixing shear layer, plane jet, axisymmetric jet, and plane wake. The numerical solutions show that the unified model equations predict all these flows reasonably. It is expected that these models would be suitable for more complex and critical flows.

Dynamics and stability of a 2D ideal vortex under external strain

NASA Astrophysics Data System (ADS)

Hurst, N. C.; Danielson, J. R.; Dubin, D. H. E.; Surko, C. M.

2017-11-01

The behavior of an initially axisymmetric 2D ideal vortex under an externally imposed strain flow is studied experimentally. The experiments are carried out using electron plasmas confined in a Penning-Malmberg trap; here, the dynamics of the plasma density transverse to the field are directly analogous to the dynamics of vorticity in a 2D ideal fluid. An external strain flow is applied using boundary conditions in a way that is consistent with 2D fluid dynamics. Data are compared to predictions from a theory assuming a piecewise constant elliptical vorticity distribution. Excellent agreement is found for quasi-flat profiles, whereas the dynamics of smooth profiles feature modified stability limits and inviscid damping of periodic elliptical distortions. This work supported by U.S. DOE Grants DE-SC0002451 and DE-SC0016532, and NSF Grant PHY-1414570.

A numerical study of three-dimensional vortex breakdown

NASA Technical Reports Server (NTRS)

Spall, Robert E.; Ash, Robert L.

1987-01-01

A numerical simulation of bubble-type vortex breakdown using a unique discrete form of the full 3-D, unsteady incompressible Navier-Stokes equations was performed. The Navier-Stokes equations were written in a vorticity-velocity form and the physical problem was not restricted to axisymmetric flow. The problem was parametized on a Rossby- Reynolds-number basis. Utilization of this parameter duo was shown to dictate the form of the free-field boundary condition specification and allowed control of axial breakdown location within the computational domain. The structure of the breakdown bubble was studied through time evolution plots of planar projected velocity vectors as well as through plots of particle traces and vortex lines. These results compared favorably with previous experimental studies. In addition, profiles of all three velocity components are presented at various axial stations and a Fourier analysis was performed to identify the dominant circumferential modes. The dynamics of the breakdown process were studied through plots of axial variation of rate of change of integrated total energy and rate of change of integrated enstrophy, as well as through contour plots of velocity, vorticity and pressure.

Numerical studies of the formation and destruction of vortices in a motored four-stroke piston-cylinder configuration

NASA Technical Reports Server (NTRS)

Schock, H. J.; Sosoka, D. J.; Ramos, J. I.

1983-01-01

A finite-difference procedure which solves the conservation equations of mass, momentum, and energy is used to investigate the effects of the compression ratio, engine speed, bore-to-stroke ratio, and air intake flow angle on the turbulent flow field within an axisymmetric piston-cylinder configuration. It is shown that in a four-stroke piston-cylinder configuration, the intake stroke is characterized by the formation of a piston vortex. The piston vortex is stretched during the intake stroke, and the head vortex has an almost constant diameter. For a 0-deg air intake flow angle, both vortices disappear by the end of the compression stroke; for an air intake flow angle of 45 deg, the flow field within the cylinder shows three elongated vortices which persist into the compression stroke and then break up and merge. It is also shown that larger bore-to-stroke ratios give rise to lower turbulent levels than smaller bore-to-stroke ratios and that the turbulent intensity is almost independent of the rpm.

Experimental investigation on cavitating flow shedding over an axisymmetric blunt body

NASA Astrophysics Data System (ADS)

Hu, Changli; Wang, Guoyu; Huang, Biao

2015-03-01

Nowadays, most researchers focus on the cavity shedding mechanisms of unsteady cavitating flows over different objects, such as 2D/3D hydrofoils, venturi-type section, axisymmetric bodies with different headforms, and so on. But few of them pay attention to the differences of cavity shedding modality under different cavitation numbers in unsteady cavitating flows over the same object. In the present study, two kinds of shedding patterns are investigated experimentally. A high speed camera system is used to observe the cavitating flows over an axisymmetric blunt body and the velocity fields are measured by a particle image velocimetry (PIV) technique in a water tunnel for different cavitation conditions. The U-type cavitating vortex shedding is observed in unsteady cavitating flows. When the cavitation number is 0.7, there is a large scale cavity rolling up and shedding, which cause the instability and dramatic fluctuation of the flows, while at cavitation number of 0.6, the detached cavities can be conjunct with the attached part to induce the break-off behavior again at the tail of the attached cavity, as a result, the final shedding is in the form of small scale cavity and keeps a relatively steady flow field. It is also found that the interaction between the re-entrant flow and the attached cavity plays an important role in the unsteady cavity shedding modality. When the attached cavity scale is insufficient to overcome the re-entrant flow, it deserves the large cavity rolling up and shedding just as that at cavitation number of 0.7. Otherwise, the re-entrant flow is defeated by large enough cavity to induce the cavity-combined process and small scale cavity vortexes shedding just as that of the cavitation number of 0.6. This research shows the details of two different cavity shedding modalities which is worthful and meaningful for the further study of unsteady cavitation.

Nonlinear vortex dynamics in open nonequilibrium systems with bulk mass loss and a generation mechanism for tornadoes and typhoons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pashitskii, E. A., E-mail: pashitsk@iop.kiev.u

2010-06-15

Based on a general model of nonlinear vortex dynamics in open thermodynamically nonequilibrium systems with bulk or surface mass losses, an analysis is presented of the mechanism of generation of violent atmospheric vortices (tornadoes, typhoons, cyclones) associated with the formation of deep cloud systems by intense condensation of water vapor from moist air cooled below the dew point. Simple particular solutions to the Navier-Stokes equations are found that describe both axisymmetric and nonaxisymmetric incompressible vortex motions involving radial and vertical flows with viscous dissipation vanishing identically everywhere except for a thin shear layer at the boundary of the condensation region.more » It is shown that the nonlinear convective and local Coriolis forces generated by radial inflow in the presence of a background vorticity due to a global Coriolis force (the Earth's rotation) accelerate the solid-body rotation in the vortex core either exponentially or in a nonlinear regime of finite-time blow-up. Due to updrafts, such a vortex is characterized by a strong helicity. This mechanism explains a number of observed properties and characteristics of the structure and evolution of tornadoes and typhoons. Upper estimates are found for the kinetic energies of violent atmospheric vortices. It is shown that increase in rotational kinetic energy of atmospheric vortices with constant vortex-core radii is consistent with energy and momentum conservation, because radial inflow continually supplies the required amount of rotational kinetic energy drawn from the ambient atmosphere to an open system.« less

The Rapid Intensification of Hurricane Karl (2010): New Remote Sensing Observations of Convective Bursts from the Global Hawk Platform

NASA Technical Reports Server (NTRS)

Guimond, Stephen R.; Heymsfield, Gerald M.; Reasor, Paul; Didlake, Anthony C., Jr.

2016-01-01

The evolution of rapidly intensifying Hurricane Karl (2010) is examined from a suite of remote sensing observations during the NASA Genesis and Rapid Intensification Processes (GRIP) field experiment. The novelties of this study are in the analysis of data from the airborne Doppler radar HIWRAP and the new Global Hawk airborne platform that allows long endurance sampling of hurricanes. Supporting data from the HAMSR microwave sounder coincident with HIWRAP and coordinated flights with the NOAA WP-3D aircraft help to provide a comprehensive understanding of the storm. The focus of the analysis is on documenting and understanding the structure, evolution and role of small scale, deep convective forcing in the storm intensification process. Deep convective bursts are sporadically initiated in the downshear quadrants of the storm and rotate into the upshear quadrants for a period of 12 h during the rapid intensification. The aircraft data analysis indicates that the bursts are being formed and maintained through a combination of two main processes: (1) convergence generated from counter-rotating mesovortex circulations and the larger vortex-scale flow and (2) the turbulent (scales of 25 km) transport of anomalously warm, buoyant air from the eye to the eyewall at low levels. The turbulent mixing across the eyewall interface and forced convective descent adjacent to the bursts assists in carving out the eye of Karl, which leads to an asymmetric enhancement of the warm core. The mesovortices play a key role in the evolution of the features described above.The Global Hawk aircraft allowed an examination of the vortex response and axisymmetrization period in addition to the burst pulsing phase. A pronounced axisymmetric development of the vortex is observed following the pulsing phase that includes a sloped eyewall structure and formation of a clear, wide eye.

A comparison of predicted and measured inlet distortion flows in a subsonic axial inlet flow compressor rotor

NASA Technical Reports Server (NTRS)

Owen, Albert K.

1992-01-01

Detailed flow measurements were taken inside an isolated axial compressor rotor operating subsonically near peak efficiency. These Laser Anemometer measurements were made with two inlet velocity profiles. One profile consisted of an unmodified baseline flow, and the second profile was distorted by placing axisymmetric screens on the hub and shroud well upstream of the rotor. A detailed comparison in the rotor relative reference frame between a Navier-Stokes solver and the measured experimental results showed good agreement between the predicted and measured flows. A primary flow is defined in the rotor and deviations and the computed predictions is made to assess the development of a passage vortex due to the distortion of the inlet flow. Computer predictions indicate that a distorted inlet profile has a minimal effect on the development of the flow in the rotor passage and the resulting passage vortex.

Role of large-scale velocity fluctuations in a two-vortex kinematic dynamo.

PubMed

Kaplan, E J; Brown, B P; Rahbarnia, K; Forest, C B

2012-06-01

This paper presents an analysis of the Dudley-James two-vortex flow, which inspired several laboratory-scale liquid-metal experiments, in order to better demonstrate its relation to astrophysical dynamos. A coordinate transformation splits the flow into components that are axisymmetric and nonaxisymmetric relative to the induced magnetic dipole moment. The reformulation gives the flow the same dynamo ingredients as are present in more complicated convection-driven dynamo simulations. These ingredients are currents driven by the mean flow and currents driven by correlations between fluctuations in the flow and fluctuations in the magnetic field. The simple model allows us to isolate the dynamics of the growing eigenvector and trace them back to individual three-wave couplings between the magnetic field and the flow. This simple model demonstrates the necessity of poloidal advection in sustaining the dynamo and points to the effect of large-scale flow fluctuations in exciting a dynamo magnetic field.

Inertia-gravity wave radiation from the merging of two co-rotating vortices in the f-plane shallow water system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sugimoto, Norihiko, E-mail: nori@phys-h.keio.ac.jp

Inertia-gravity wave radiation from the merging of two co-rotating vortices is investigated numerically in a rotating shallow water system in order to focus on cyclone–anticyclone asymmetry at different values of the Rossby number (Ro). A numerical study is conducted on a model using a spectral method in an unbounded domain to estimate the gravity wave flux with high accuracy. Continuous gravity wave radiation is observed in three stages of vortical flows: co-rotating of the vortices, merging of the vortices, and unsteady motion of the merged vortex. A cyclone–anticyclone asymmetry appears at all stages at smaller Ro (≤20). Gravity waves frommore » anticyclones are always larger than those from cyclones and have a local maximum at smaller Ro (∼2) compared with that for an idealized case of a co-rotating vortex pair with a constant rotation rate. The source originating in the Coriolis acceleration has a key role in cyclone–anticyclone asymmetry in gravity waves. An additional important factor is that at later stages, the merged axisymmetric anticyclone rotates faster than the elliptical cyclone due to the effect of the Rossby deformation radius, since a rotation rate higher than the inertial cutoff frequency is required to radiate gravity waves.« less

Pressure Oscillations and Structural Vibrations in Space Shuttle RSRM and ETM-3 Motors

NASA Technical Reports Server (NTRS)

Mason, D. R.; Morstadt, R. A.; Cannon, S. M.; Gross, E. G.; Nielsen, D. B.

2004-01-01

The complex interactions between internal motor pressure oscillations resulting from vortex shedding, the motor's internal acoustic modes, and the motor's structural vibration modes were assessed for the Space Shuttle four-segment booster Reusable Solid Rocket Motor and for the five-segment engineering test motor ETM-3. Two approaches were applied 1) a predictive procedure based on numerically solving modal representations of a solid rocket motor s acoustic equations of motion and 2) a computational fluid dynamics two-dimensional axi-symmetric large eddy simulation at discrete motor burn times.

Pressure dependence of axisymmetric vortices in superfluid 3B

NASA Astrophysics Data System (ADS)

Fetter, Alexander L.

1985-06-01

The pressure dependence of the vortex core in rotating 3B is studied in the Ginzburg-Landau formalism with two distinct models of the strong-coupling corrections. The parametrization of Sauls and Serene [Phys. Rev. B 24, 183 (1981)] predicts a transition from a core with large magnetic moment below ~10 bars to one with small magnetic moment for higher pressures, in qualitative agreement with experiments. The earlier one-parameter model of Brinkman, Serene, and Anderson predicts no such transition, with the core having a large moment for all values of the parameter δ.

The three-dimensional evolution of a plane mixing layer. Part 1: The Kelvin-Helmholtz roll-up

NASA Technical Reports Server (NTRS)

Rogers, Michael M.; Moser, Robert D.

1991-01-01

The Kelvin Helmholtz roll up of three dimensional, temporally evolving, plane mixing layers were simulated numerically. All simulations were begun from a few low wavenumber disturbances, usually derived from linear stability theory, in addition to the mean velocity profile. The spanwise disturbance wavelength was taken to be less than or equal to the streamwise wavelength associated with the Kelvin Helmholtz roll up. A standard set of clean structures develop in most of the simulations. The spanwise vorticity rolls up into a corrugated spanwise roller, with vortex stretching creating strong spanwise vorticity in a cup shaped region at the vends of the roller. Predominantly streamwise rib vortices develop in the braid region between the rollers. For sufficiently strong initial three dimensional disturbances, these ribs collapse into compact axisymmetric vortices. The rib vortex lines connect to neighboring ribs and are kinked in the opposite direction of the roller vortex lines. Because of this, these two sets of vortex lines remain distinct. For certain initial conditions, persistent ribs do not develop. In such cases the development of significant three dimensionality is delayed. When the initial three dimensional disturbance energy is about equal to, or less than, the two dimensional fundamental disturbance energy, the evolution of the three dimensional disturbance is nearly linear (with respect to the mean and the two dimensional disturbances), at least until the first Kelvin Helmholtz roll up is completed.

Onset of chaos in helical vortex breakdown at low Reynolds number

NASA Astrophysics Data System (ADS)

Pasche, S.; Avellan, F.; Gallaire, F.

2018-06-01

The nonlinear dynamics of a swirling wake flow stemming from a Graboswksi-Berger vortex [Grabowski and Berger, J. Fluid Mech. 75, 525 (1976), 10.1017/S0022112076000360] in a semi-infinite domain is addressed at low Reynolds numbers for a fixed swirl number S =1.095 , defined as the ratio between the characteristic tangential velocity and the centerline axial velocity. In this system, only pure hydrodynamic instabilities develop and interact through the quadratic nonlinearities of the Navier-Stokes equations. Such interactions lead to the onset of chaos at a Reynolds value of Re=220 . This chaotic state is reached by following a Ruelle-Takens-Newhouse scenario, which is initiated by a Hopf bifurcation (the spiral vortex breakdown) as the Reynolds number increases. At larger Reynolds value, a frequency synchronization regime appears followed by a chaotic state again. This scenario is corroborated by nonlinear time series analyses. Stability analysis around the time-average flow and temporal-azimuthal Fourier decomposition of the nonlinear flow distributions both identify successfully the developing vortices and provide deeper insight into the development of the flow patterns leading to this route to chaos. Three single-helical vortices are involved: the primary spiral associated with the spiral vortex breakdown, a downstream spiral, and a near-wake spiral. As the Reynolds number increases, the frequencies of these vortices become closer, increasing their interactions by nonlinearity to eventually generate a strong chaotic axisymmetric oscillation.

Force Generation by Flapping Foils

NASA Astrophysics Data System (ADS)

Bandyopadhyay, P. R.; Donnelly, M.

1996-11-01

Aquatic animals like fish use flapping caudal fins to produce axial and cross-stream forces. During WW2, German scientists had built and tested an underwater vehicle powered by similar flapping foils. We have examined the forces produced by a pair of flapping foils. We have examined the forced produced by a pair of flapping foils attached to the tail end of a small axisymmetric cylinder. The foils operate in-phase (called waving), or in anti-phase (called clapping). In a low-speed water tunnel, we have undertaken time-dependent measurements of axial and cross-stream forces and moments that are exerted by the vortex shedding process over the entire body. Phase-matched LDV measurements of vorticity-velocity vectors, as well as limited flow visualization of the periodic vortex shedding process have also been carried out. The direction of the induced velocity within a pair of shed vortices determines the nature of the forces produced, viz., thrust or drag or cross-stream forces. The clapping mode produces a widely dispersed symmetric array of vortices which results in axial forces only (thrust and rag). On the other hand, the vortex array is staggered in the waving mode and cross-stream (maneuvering) forces are then generated.

Dipolar bright solitons and solitary vortices in a radial lattice

NASA Astrophysics Data System (ADS)

Huang, Chunqing; Lyu, Lin; Huang, Hao; Chen, Zhaopin; Fu, Shenhe; Tan, Haishu; Malomed, Boris A.; Li, Yongyao

2017-11-01

Stabilizing vortex solitons with high values of the topological charge S is a challenging issue in optics, studies of Bose-Einstein condensates (BECs), and other fields. To develop an approach to the solution of this problem, we consider a two-dimensional dipolar BEC under the action of an axisymmetric radially periodic lattice potential, V (r )˜cos(2 r +δ ) , with dipole moments polarized perpendicular to the system's plane, which gives rise to isotropic repulsive dipole-dipole interactions. Two radial lattices are considered, with δ =0 and π , i.e., a potential maximum or minimum at r =0 , respectively. Families of vortex gap soliton (GSs) with S =1 and S ≥2 , the latter ones often being unstable in other settings, are completely stable in the present system (at least up to S =11 ), being trapped in different annular troughs of the radial potential. The vortex solitons with different S may stably coexist in sufficiently far separated troughs. Fundamental GSs, with S =0 , are found too. In the case of δ =0 , the fundamental solitons are ring-shaped modes, with a local minimum at r =0 . At δ =π , they place a density peak at the center.

On the axisymmetric stability of heated supersonic round jets

PubMed Central

2016-01-01

We perform an inviscid, spatial stability analysis of supersonic, heated round jets with the mean properties assumed uniform on either side of the jet shear layer, modelled here via a cylindrical vortex sheet. Apart from the hydrodynamic Kelvin–Helmholtz (K–H) wave, the spatial growth rates of the acoustically coupled supersonic and subsonic instability waves are computed for axisymmetric conditions (m=0) to analyse their role on the jet stability, under increased heating and compressibility. With the ambient stationary, supersonic instability waves may exist for any jet Mach number Mj≥2, whereas the subsonic instability waves, in addition, require the core-to-ambient flow temperature ratio Tj/To>1. We show, for moderately heated jets at Tj/To>2, the acoustically coupled instability modes, once cut on, to govern the overall jet stability with the K–H wave having disappeared into the cluster of acoustic modes. Sufficiently high heating makes the subsonic modes dominate the jet near-field dynamics, whereas the supersonic instability modes form the primary Mach radiation at far field. PMID:27274691

Multiple Near Wake Patterns Behind Annular Rings

NASA Astrophysics Data System (ADS)

Zhang, Jinzhong; Higuchi, Hiroshi; Muzas, Brian K.; Furuya, Shojiro

1996-11-01

Wake interactions behind concentric annular rings at different spacing ratios were experimentally investigated. The flow visualization, laser Doppler velocimetry data and results from the particle tracking velocimetry are presented and discussed. Jets through individual slots merged in multiply-stable, axisymmetric manners. Most flow patterns were persistent unless the flow was strongly disturbed. The vortex interactions from individual annular elements were also axisymmetric in the near wake. This is in contrast to the asymmetric flows observed earlier behind two-dimensional slotted plates (Higuchi et al. J. Aircraft 26 1989, Phys. Fluids 6(1), 1994). The intermediate wake, however, was dominated by large scale, three-dimensional wake motions even at moderate porosity. Onset of the specific flow patterns was associated with the interactions among start-up vortices. Given model geometry, different turbulent structures and mean velocity profiles were observed in the intermediate wake depending on the near wake pattern. *BKM was a NSF-REU Program undergrad. from Princeton U. and SF was from Mitsubishi Heavy Industries. This work was suppoted in part by the Naval Air Warfare Center.

Evolution and transition mechanisms of internal swirling flows with tangential entry

NASA Astrophysics Data System (ADS)

Wang, Yanxing; Wang, Xingjian; Yang, Vigor

2018-01-01

The characteristics and transition mechanisms of different states of swirling flow in a cylindrical chamber have been numerically investigated using the Galerkin finite element method. The effects of the Reynolds number and swirl level were examined, and a unified theory connecting different flow states was established. The development of each flow state is considered as a result of the interaction and competition between basic mechanisms: (1) the centrifugal effect, which drives an axisymmetric central recirculation zone (CRZ); (2) flow instabilities, which develop at the free shear layer and the central solid-body rotating flow; (3) the bouncing and restoring effects of the injected flow, which facilitate the convergence of flow on the centerline and the formation of bubble-type vortex breakdown; and (4) the damping effect of the end-induced flow, which suppresses the development of the instability waves. The results show that the CRZ, together with the free shear layer on its surface, composes the basic structure of swirling flow. The development of instability waves produces a number of discrete vortex cores enclosing the CRZ. The azimuthal wave number is primarily determined by the injection angle. Generally, the wave number is smaller at a higher injection angle, due to the reduction of the perimeter of the free shear layer. At the same time, the increase in the Reynolds number facilitates the growth of the wave number. The end-induced flow tends to reduce the wave number near the head end and causes a change in wave number from the head end to the downstream region. Spiral-type vortex breakdown can be considered as a limiting case at a high injection angle, with a wave number equal to 0 near the head end and equal to 1 downstream. At lower Reynolds numbers, the bouncing and restoring effect of the injected flow generates bubble-type vortex breakdown.

Comparative assessment of pressure field reconstructions from particle image velocimetry measurements and Lagrangian particle tracking

NASA Astrophysics Data System (ADS)

van Gent, P. L.; Michaelis, D.; van Oudheusden, B. W.; Weiss, P.-É.; de Kat, R.; Laskari, A.; Jeon, Y. J.; David, L.; Schanz, D.; Huhn, F.; Gesemann, S.; Novara, M.; McPhaden, C.; Neeteson, N. J.; Rival, D. E.; Schneiders, J. F. G.; Schrijer, F. F. J.

2017-04-01

A test case for pressure field reconstruction from particle image velocimetry (PIV) and Lagrangian particle tracking (LPT) has been developed by constructing a simulated experiment from a zonal detached eddy simulation for an axisymmetric base flow at Mach 0.7. The test case comprises sequences of four subsequent particle images (representing multi-pulse data) as well as continuous time-resolved data which can realistically only be obtained for low-speed flows. Particle images were processed using tomographic PIV processing as well as the LPT algorithm `Shake-The-Box' (STB). Multiple pressure field reconstruction techniques have subsequently been applied to the PIV results (Eulerian approach, iterative least-square pseudo-tracking, Taylor's hypothesis approach, and instantaneous Vortex-in-Cell) and LPT results (FlowFit, Vortex-in-Cell-plus, Voronoi-based pressure evaluation, and iterative least-square pseudo-tracking). All methods were able to reconstruct the main features of the instantaneous pressure fields, including methods that reconstruct pressure from a single PIV velocity snapshot. Highly accurate reconstructed pressure fields could be obtained using LPT approaches in combination with more advanced techniques. In general, the use of longer series of time-resolved input data, when available, allows more accurate pressure field reconstruction. Noise in the input data typically reduces the accuracy of the reconstructed pressure fields, but none of the techniques proved to be critically sensitive to the amount of noise added in the present test case.

Coherent motion in excited free shear flows

NASA Technical Reports Server (NTRS)

Wygnanski, Israel J.; Petersen, Robert A.

1987-01-01

The application of the inviscid instability approach to externally excited turbulent free shear flows at high Reynolds numbers is explored. Attention is given to the cases of a small-deficit plane turbulent wake, a plane turbulent jet, an axisymmetric jet, the nonlinear evolution of instabilities in free shear flows, the concept of the 'preferred mode', vortex pairing in turbulent mixing layers, and experimental results for the control of free turbulent shear layers. The special features often attributed to pairing or to the preferred mode are found to be difficult to comprehend; the concept of feedback requires further substantiation in the case of incompressible flow.

Vortex/Flame Interactions in Microgravity Pulsed Jet Diffusion Flames

NASA Technical Reports Server (NTRS)

Bahadori, M. Y.; Hegde, U.; Stocker, D. P.

1999-01-01

The problem of vortex/flame interaction is of fundamental importance to turbulent combustion. These interactions have been studied in normal gravity. It was found that due to the interactions between the imposed disturbances and buoyancy induced instabilities, several overall length scales dominated the flame. The problem of multiple scales does not exist in microgravity for a pulsed laminar flame, since there are no buoyancy induced instabilities. The absence of buoyant convection therefore provides an environment to study the role of vortices interacting with flames in a controlled manner. There are strong similarities between imposed and naturally occurring perturbations, since both can be described by the same spatial instability theory. Hence, imposing a harmonic disturbance on a microgravity laminar flame creates effects similar to those occurring naturally in transitional/turbulent diffusion flames observed in microgravity. In this study, controlled, large-scale, axisymmetric vortices are imposed on a microgravity laminar diffusion flame. The experimental results and predictions from a numerical model of transient jet diffusion flames are presented and the characteristics of pulsed flame are described.

Effects of inlet distortion on the development of secondary flows in a subsonic axial inlet compressor rotor. Ph.D. Thesis - Toledo Univ., OH

NASA Technical Reports Server (NTRS)

Owen, Albert K.

1991-01-01

Detailed flow measurements were taken inside an isolated axial compressor rotor operating subsonically near peak efficiency. Laser anemometer measurements were made with two inlet velocity profiles. One profile consisted of an unmodified baseline flow, and the second profile was distorted by placing axisymmetric screens on the hub and shroud well upstream of the rotor. A primary flow is defined in the rotor and deviations from this primary flow for each inlet flow condition identified. A comparison between the two flow deviations is made to assess the development of a passage vortex due to the distortion of the inlet flow. A comparison of experimental results with computational predictions from a Navier-Stokes solver showed good agreement between predicted and measured flow. Measured results indicate that a distorted inlet profile has minimal effect on the development of the flow in the rotor passage and the resulting passage vortex.

The flows structure in unsteady gas flow in pipes with different cross-sections

NASA Astrophysics Data System (ADS)

Plotnikov, Leonid; Nevolin, Alexandr; Nikolaev, Dmitrij

2017-10-01

The results of numerical simulation and experimental study of the structure of unsteady flows in pipes with different cross sections are presented in the article. It is shown that the unsteady gas flow in a circular pipe is axisymmetric without secondary currents. Steady vortex structures (secondary flows) are observed in pipes with cross sections in the form of a square and an equilateral triangle. It was found that these secondary flows have a significant impact on gas flows in pipes of complex configuration. On the basis of experimental researches it is established that the strong oscillatory phenomena exist in the inlet pipe of the piston engine arising after the closing of the intake valve. The placement of the profiled plots (with a cross section of a square or an equilateral triangle) in the intake pipe leads to the damping of the oscillatory phenomena and a more rapid stabilization of pulsating flow. This is due to the stabilizing effect of the vortex structures formed in the corners of this configuration.

Controlled Growth of Gigantic Swirls in a Laboratory Magnetosphere

NASA Astrophysics Data System (ADS)

Worstell, M. W.; Mauel, M. E.; Roberts, T. M.

2012-10-01

Space and laboratory plasma confined by a strong magnetic field have remarkable properties. Low frequency mixing of the plasma occurs through the interchange of long plasma-filled tubes aligned with the magnetic field. The plasma dynamics becomes two-dimensional because these tubes can only move radially or circulate around the poles of the magnetic dipole. Studies of turbulent interchange dynamics made using the Collisionless Terella Experiment (CTX) show that turbulence appears as chaotic time-varying modes with broad global mode structures that interact nonlinearly and form an inverse cascade.footnotetextB.A. Grierson, M.W. Worstell, M.E. Mauel, Phys. Plasmas 16 055902 (2009) When we drive vortex mixing through the application of electrostatic bias to multiple probes, we break the rotational symmetry of the plasma and small vortex tubes are seen to drive larger ``gigantic'' swirls. Statistical analysis of the time-evolving spectra and measurement of the bicoherence of the turbulence show an increase of three wave coupling during non-axisymmetric electrostatic drive of the probe array.

Numerical and experimental investigation of VG flow control for a low-boom inlet

NASA Astrophysics Data System (ADS)

Rybalko, Michael

The application of vortex generators (VGs) for shock/boundary layer interaction flow control in a novel external compression, axisymmetric, low-boom concept inlet was studied using numerical and experimental methods. The low-boom inlet design features a zero-angle cowl and relaxed isentropic compression centerbody spike, resulting in defocused oblique shocks and a weak terminating normal shock. This allows reduced external gas dynamic waves at high mass flow rates but suffers from flow separation near the throat and a large hub-side boundary layer at the Aerodynamic Interface Plane (AIP), which marks the inflow to the jet engine turbo-machinery. Supersonic VGs were investigated to reduce the shock-induced flow separation near the throat while subsonic VGs were investigated to reduce boundary layer radial distortion at the AIP. To guide large-scale inlet experiments, Reynolds-Averaged Navier-Stokes (RANS) simulations using three-dimensional, structured, chimera (overset) grids and the WIND-US code were conducted. Flow control cases included conventional and novel types of vortex generators at positions both upstream of the terminating normal shock (supersonic VGs) and downstream (subsonic VGs). The performance parameters included incompressible axisymmetric shape factor, post-shock separation area, inlet pressure recovery, and mass flow ratio. The design of experiments (DOE) methodology was used to select device size and location, analyze the resulting data, and determine the optimal choice of device geometry. Based on the above studies, a test matrix of supersonic and subsonic VGs was adapted for a large-scale inlet test to be conducted at the 8'x6' supersonic wind tunnel at NASA Glenn Research Center (GRC). Comparisons of RANS simulations with data from the Fall 2010 8'x6' inlet test showed that predicted VG performance trends and case rankings for both supersonic and subsonic devices were consistent with experimental results. For example, experimental surface oil flow visualization revealed a significant post-shock separation bubble with flow recirculation for the baseline (no VG) case that was substantially broken up in the micro-ramp VG case, consistent with simulations. Furthermore, the predicted subsonic VG performance with respect to a reduction in radial distortion (quantified in terms of axisymmetric incompressible shape factor) was found to be consistent with boundary layer rake measurements. To investigate the unsteady turbulent flow features associated with the shock-induced flow separation and the hub-side boundary layer, a detached eddy simulation (DES) approach using the WIND-US code was employed to model the baseline inlet flow field. This approach yielded improved agreement with experimental data for time-averaged diffuser stagnation pressure profiles and allowed insight into the pressure fluctuations and turbulent kinetic energy distributions which may be present at the AIP. In addition, streamwise shock position statistics were obtained and compared with experimental Schlieren results. The predicted shock oscillations were much weaker than those seen experimentally (by a factor of four), which indicates that the mechanism for the experimental shock oscillations was not captured. In addition, the novel supersonic vortex generator geometries were investigated experimentally (prior to the large-scale inlet 8'x6' wind tunnel tests) in an inlet-relevant flow field containing a Mach 1.4 normal shock wave followed by a subsonic diffuser. A parametric study of device height and distance upstream of the normal shock was undertaken for split-ramp and ramped-vane geometries. Flow field diagnostics included high-speed Schlieren, oil flow visualization, and Pitot-static pressure measurements. Parameters including flow separation, pressure recovery, centerline incompressible boundary layer shape factor, and shock stability were analyzed and compared to the baseline uncontrolled case. While all vortex generators tested eliminated centerline flow separation, the presence of VGs also increased the significant three-dimensionality of the flow via increased side-wall interaction. The stronger streamwise vorticity generated by ramped-vanes also yielded improved pressure recovery and fuller boundary layer velocity profiles within the subsonic diffuser. (Abstract shortened by UMI.)

Connections between centrifugal, stratorotational, and radiative instabilities in viscous Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Leclercq, Colin; Nguyen, Florian; Kerswell, Rich R.

2016-10-01

The "Rayleigh line" μ =η2 , where μ =Ωo/Ωi and η =ri/ro are respectively the rotation and radius ratios between inner (subscript i ) and outer (subscript o ) cylinders, is regarded as marking the limit of centrifugal instability (CI) in unstratified inviscid Taylor-Couette flow, for both axisymmetric and nonaxisymmetric modes. Nonaxisymmetric stratorotational instability (SRI) is known to set in for anticyclonic rotation ratios beyond that line, i.e., η2<μ <1 for axially stably stratified Taylor-Couette flow, but the competition between CI and SRI in the range μ <η2 has not yet been addressed. In this paper, we establish continuous connections between the two instabilities at finite Reynolds number Re, as previously suggested by Le Bars and Le Gal [Phys. Rev. Lett. 99, 064502 (2007), 10.1103/PhysRevLett.99.064502], making them indistinguishable at onset. Both instabilities are also continuously connected to the radiative instability at finite Re. These results demonstrate the complex impact viscosity has on the linear stability properties of this flow. Several other qualitative differences with inviscid theory were found, among which are the instability of a nonaxisymmetric mode localized at the outer cylinder without stratification and the instability of a mode propagating against the inner cylinder rotation with stratification. The combination of viscosity and stratification can also lead to a "collision" between (axisymmetric) Taylor vortex branches, causing the axisymmetric oscillatory state already observed in past experiments. Perhaps more surprising is the instability of a centrifugal-like helical mode beyond the Rayleigh line, caused by the joint effects of stratification and viscosity. The threshold μ =η2 seems to remain, however, an impassable instability limit for axisymmetric modes, regardless of stratification, viscosity, and even disturbance amplitude.

Effect of vortical structures on velocity and turbulent fields in the near region of an impinging turbulent jet

NASA Astrophysics Data System (ADS)

Yadav, Harekrishna; Agrawal, Amit

2018-03-01

This experimental study pertains to the formation of a secondary peak in heat transfer distribution for an axisymmetric turbulent impinging submerged jet. The analysis of instantaneous fields is undertaken at various Reynolds numbers based upon the bulk velocity and nozzle diameter (Re = 1300-10 000) and surface spacings (L/D = 0.25-6). Our analysis shows that flow separation and reattachment correspond to decrease/increase in local pressure and are caused by primary vortices; these are further linked to the location of maxima in streamwise and cross-stream velocities. It is further observed that the locations of maxima and minima in velocities are linked to fluctuations in rms velocities and thickening/thinning of the boundary layer. The vortices transported along the surface either coalesce among themselves or combine with other eddies to form a primary vortex. The primary vortex while getting convected downstream makes multiple interactions with the inner shear layer and causes waviness in instantaneous flow fields. In their later stage, the primary vortex moves away from the wall and accelerates, while the flow decelerates in the inner shear layer. The accelerated fluid in the outer shear layer pulls the downstream fluid from the inner shear layer and leads to the formation of a secondary vortex. After a certain distance downstream, the secondary vortex rolling between the primary vortex and the wall eventually breaks down, while the flow reattaches to the wall. The behavior of time average and instantaneous velocity fields suggests that unsteadiness in the heat transfer is linked to the location of maximum streamwise velocity, location of flow attachment, location of rms velocity, and thickness of the boundary layer. The instantaneous velocity fields show that for a given surface spacing, the chances for the appearance of the secondary vortex reduce with an increase in Reynolds number because of the reduction in space available for the secondary vortex to develop. It is further deduced that the strength of the secondary vortex is primarily dependent upon the strength of the primary vortex. However, the velocity field estimated using the linear stochastic estimation technique shows a tendency for the formation of the secondary vortex at higher Reynolds number, suggesting that most measurements do not resolve them well. Our analysis explains the reason for the appearance of the secondary peak in heat transfer distribution and helps resolve the contradictions in the literature regarding this phenomenon.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majda, Andrew J.; Xing, Yulong; Mohammadian, Majid

Determining the finite-amplitude preconditioned states in the hurricane embryo, which lead to tropical cyclogenesis, is a central issue in contemporary meteorology. In the embryo there is competition between different preconditioning mechanisms involving hydrodynamics and moist thermodynamics, which can lead to cyclogenesis. Here systematic asymptotic methods from applied mathematics are utilized to develop new simplified moist multi-scale models starting from the moist anelastic equations. Three interesting multi-scale models emerge in the analysis. The balanced mesoscale vortex (BMV) dynamics and the microscale balanced hot tower (BHT) dynamics involve simplified balanced equations without gravity waves for vertical vorticity amplification due to moist heatmore » sources and incorporate nonlinear advective fluxes across scales. The BMV model is the central one for tropical cyclogenesis in the embryo. The moist mesoscale wave (MMW) dynamics involves simplified equations for mesoscale moisture fluctuations, as well as linear hydrostatic waves driven by heat sources from moisture and eddy flux divergences. A simplified cloud physics model for deep convection is introduced here and used to study moist axisymmetric plumes in the BHT model. A simple application in periodic geometry involving the effects of mesoscale vertical shear and moist microscale hot towers on vortex amplification is developed here to illustrate features of the coupled multi-scale models. These results illustrate the use of these models in isolating key mechanisms in the embryo in a simplified content.« less

Forcing scheme analysis for the axisymmetric lattice Boltzmann method under incompressible limit.

PubMed

Zhang, Liangqi; Yang, Shiliang; Zeng, Zhong; Chen, Jie; Yin, Linmao; Chew, Jia Wei

2017-04-01

Because the standard lattice Boltzmann (LB) method is proposed for Cartesian Navier-Stokes (NS) equations, additional source terms are necessary in the axisymmetric LB method for representing the axisymmetric effects. Therefore, the accuracy and applicability of the axisymmetric LB models depend on the forcing schemes adopted for discretization of the source terms. In this study, three forcing schemes, namely, the trapezium rule based scheme, the direct forcing scheme, and the semi-implicit centered scheme, are analyzed theoretically by investigating their derived macroscopic equations in the diffusive scale. Particularly, the finite difference interpretation of the standard LB method is extended to the LB equations with source terms, and then the accuracy of different forcing schemes is evaluated for the axisymmetric LB method. Theoretical analysis indicates that the discrete lattice effects arising from the direct forcing scheme are part of the truncation error terms and thus would not affect the overall accuracy of the standard LB method with general force term (i.e., only the source terms in the momentum equation are considered), but lead to incorrect macroscopic equations for the axisymmetric LB models. On the other hand, the trapezium rule based scheme and the semi-implicit centered scheme both have the advantage of avoiding the discrete lattice effects and recovering the correct macroscopic equations. Numerical tests applied for validating the theoretical analysis show that both the numerical stability and the accuracy of the axisymmetric LB simulations are affected by the direct forcing scheme, which indicate that forcing schemes free of the discrete lattice effects are necessary for the axisymmetric LB method.

The ground vortex flow field associated with a jet in a cross flow impinging on a ground plane for uniform and annular turbulent axisymmetric jets. M.S. Thesis

NASA Technical Reports Server (NTRS)

Cavage, William M.; Kuhlman, John M.

1993-01-01

An experimental study was conducted of the impingement of a single circular jet on a ground plane in a cross flow. This geometry is a simplified model of the interaction of propulsive jet exhaust from a V/STOL aircraft with the ground in forward flight. Jets were oriented normal to the cross flow and ground plane. Jet size, cross flow-to-jet velocity ratio, ground plane-to-jet board spacing, and jet exit turbulence level and mean velocity profile shape were all varied to determine their effects on the size of the ground vortex interaction region which forms on the ground plane, using smoke injection into the jet. Three component laser Doppler velocimeter measurements were made with a commercial three color system for the case of a uniform jet with exit spacing equal to 5.5 diameters and cross flow-to-jet velocity ratio equal to 0.11. The flow visualization data compared well for equivalent runs of the same nondimensional jet exit spacing and the same velocity ratio for different diameter nozzles, except at very low velocity ratios and for the larger nozzle, where tunnel blockage became significant. Variation of observed ground vortex size with cross flow-to-jet velocity ratio was consistent with previous studies. Observed effects of jet size and ground plane-to-jet board spacing were relatively small. Jet exit turbulence level effects were also small. However, an annular jet with a low velocity central core was found to have a significantly smaller ground vortex than an equivalent uniform jet at the same values of cross flow-to-jet velocity ratio and jet exit-to-ground plane spacing. This may suggest a means of altering ground vortex behavior somewhat, and points out the importance of proper simulation of jet exit velocity conditions. LV data indicated unsteady turbulence levels in the ground vortex in excess of 70 percent.

The turbomachine blading design using S2-S1 approach

NASA Technical Reports Server (NTRS)

Luu, T. S.; Bencherif, L.; Viney, B.; Duc, J. M. Nguyen

1991-01-01

The boundary conditions corresponding to the design problem when the blades being simulated by the bound vorticity distribution are presented. The 3D flow is analyzed by the two steps S2 - S1 approach. In the first step, the number of blades is supposed to be infinite, the vortex distribution is transformed into an axisymmetric one, so that the flow field can be analyzed in a meridional plane. The thickness distribution of the blade producing the flow channel striction is taken into account by the modification of metric tensor in the continuity equation. Using the meridional stream function to define the flow field, the mass conservation is satisfied automatically. The governing equation is deduced from the relation between the azimuthal component of the vorticity and the meridional velocity. The value of the azimuthal component of the vorticity is provided by the hub to shroud equilibrium condition. This step leads to the determination of the axisymmetric stream sheets as well as the approximate camber surface of the blade. In the second step, the finite number of blades is taken into account, the inverse problem corresponding to the blade to blade flow confined in each stream sheet is analyzed. The momentum equation implies that the free vortex of the absolute velocity must be tangential to the stream sheet. The governing equation for the blade to blade flow stream function is deduced from this condition. At the beginning, the upper and the lower surfaces of the blades are created from the camber surface obtained from the first step with the assigned thickness distribution. The bound vorticity distribution and the penetrating flux conservation applied on the presumed blade surface constitute the boundary conditions of the inverse problem. The detection of this flux leads to the rectification of the geometry of the blades.

Non-axisymmetric local magnetostatic equilibrium

DOE PAGES

Candy, Jefferey M.; Belli, Emily A.

2015-03-24

In this study, we outline an approach to the problem of local equilibrium in non-axisymmetric configurations that adheres closely to Miller's original method for axisymmetric plasmas. Importantly, this method is novel in that it allows not only specification of 3D shape, but also explicit specification of the shear in the 3D shape. A spectrally-accurate method for solution of the resulting nonlinear partial differential equations is also developed. We verify the correctness of the spectral method, in the axisymmetric limit, through comparisons with an independent numerical solution. Some analytic results for the two-dimensional case are given, and the connection to Boozermore » coordinates is clarified.« less

Flowfield Measurements in the Vortex Wake of a Missile at High Angle of Attack in Turbulence

DTIC Science & Technology

1988-12-01

pressure coefficient Cy: side force coefficient d: base diameter of the missile body F: blockage correction K: wind tunnel calibration factor LI : missile...and assistance in the wind tunnel apparatus and data acquisition s -;te1 m. I would like to thank Lt. Ao Chia-Ning. Republic of China Navy, Mr. Li ...axisymmetric missile configuration. 6- MO GRID + WIJS RE 1.33 E+05 z 2- Li 0- O C8 -C0 tq *tt~E I ’mtO0 E 5 , • r;.H/ 2 011USE 6 -6 x J! ’ 5SE 3 ,AHOSE

Uranium droplet core nuclear rocket

NASA Technical Reports Server (NTRS)

Anghaie, Samim

1991-01-01

Uranium droplet nuclear rocket is conceptually designed to utilize the broad temperature range ofthe liquid phase of metallic uranium in droplet configuration which maximizes the energy transfer area per unit fuel volume. In a baseline system dissociated hydrogen at 100 bar is heated to 6000 K, providing 2000 second of Isp. Fission fragments and intense radian field enhance the dissociation of molecular hydrogen beyond the equilibrium thermodynamic level. Uranium droplets in the core are confined and separated by an axisymmetric vortex flow generated by high velocity tangential injection of hydrogen in the mid-core regions. Droplet uranium flow to the core is controlled and adjusted by a twin flow nozzle injection system.

Excitation and propagation of nonlinear waves in a rotating fluid

NASA Astrophysics Data System (ADS)

Hanazaki, Hideshi

1993-09-01

A numerical study of the nonlinear waves excited in an axisymmetric rotating flow through a circular tube is described. The waves are excited by either an undulation of the tube wall or an obstacle on the axis of the tube. The results are compared with the weakly nonlinear theory (forced KdV equation). The computations are done when the upstream swirling velocity is that of Burgers' vortex type. The flow behaves like the solution of the forced KdV equation, and the upstream advancing of the waves appear even when the flow is critical or slightly supercritical to the fastest inertial wave mode.

Towards Perfectly Absorbing Boundary Conditions for Euler Equations

NASA Technical Reports Server (NTRS)

Hayder, M. Ehtesham; Hu, Fang Q.; Hussaini, M. Yousuff

1997-01-01

In this paper, we examine the effectiveness of absorbing layers as non-reflecting computational boundaries for the Euler equations. The absorbing-layer equations are simply obtained by splitting the governing equations in the coordinate directions and introducing absorption coefficients in each split equation. This methodology is similar to that used by Berenger for the numerical solutions of Maxwell's equations. Specifically, we apply this methodology to three physical problems shock-vortex interactions, a plane free shear flow and an axisymmetric jet- with emphasis on acoustic wave propagation. Our numerical results indicate that the use of absorbing layers effectively minimizes numerical reflection in all three problems considered.

Acoustic properties associated with rectangular geometry supersonic nozzles

NASA Technical Reports Server (NTRS)

Seiner, J. M.; Manning, J. C.; Ponton, M. K.

1986-01-01

Acoustic property experiments have been conducted to ascertain the behavior of rectangular geometry supersonic nozzles whose throat aspect ratios vary over a 2.0-7.6 range, and whose three partial sidewall geometries range from full to 75-percent cutback. The tests employed unheated air at static conditions for nozzle Mach numbers of 1.35-1.66. It is found that sonic fatigue failures are possible at certain partial sidewall geometries and high nozzle aspect ratios. Unlike axisymmetric supersonic nozzles, shock noise dominates both the rear and forward arc for throat aspect ratio cases greater than 5.6. Jet screech frequency was adequately predicted with a simple vortex sheel model.

High-resolution simulations of unstable cylindrical gravity currents undergoing wandering and splitting motions in a rotating system

NASA Astrophysics Data System (ADS)

Dai, Albert; Wu, Ching-Sen

2018-02-01

High-resolution simulations of unstable cylindrical gravity currents when wandering and splitting motions occur in a rotating system are reported. In this study, our attention is focused on the situation of unstable rotating cylindrical gravity currents when the ratio of Coriolis to inertia forces is larger, namely, 0.5 ≤ C ≤ 2.0, in comparison to the stable ones when C ≤ 0.3 as investigated previously by the authors. The simulations reproduce the major features of the unstable rotating cylindrical gravity currents observed in the laboratory, i.e., vortex-wandering or vortex-splitting following the contraction-relaxation motion, and good agreement is found when compared with the experimental results on the outrush radius of the advancing front and on the number of bulges. Furthermore, the simulations provide energy budget information which could not be attained in the laboratory. After the heavy fluid is released, the heavy fluid collapses and a contraction-relaxation motion is at work for approximately 2-3 revolutions of the system. During the contraction-relaxation motion of the heavy fluid, the unstable rotating cylindrical gravity currents behave similar to the stable ones. Towards the end of the contraction-relaxation motion, the dissipation rate in the system reaches a local minimum and a quasi-geostrophic equilibrium state is reached. After the quasi-geostrophic equilibrium state, vortex-wandering or vortex-splitting may occur depending on the ratio of Coriolis to inertia forces. The vortex-splitting process begins with non-axisymmetric bulges and, as the bulges grow, the kinetic energy increases at the expense of decreasing potential energy in the system. The completion of vortex-splitting is accompanied by a local maximum of dissipation rate and a local maximum of kinetic energy in the system. A striking feature of the unstable rotating cylindrical gravity currents is the persistent upwelling and downwelling motions, which are observed for both the vortex-wandering and vortex-splitting motions and were not previously documented for such flows. Depending on the Reynolds number, the bulges around the circumference of the unstable rotating cylindrical gravity currents may or may not develop into cutoff distinct circulations. The number of bulges is seen to be dependent on the ratio of Coriolis to inertia forces but independent of the Reynolds number for the range of Reynolds number considered in this study.

Spreading Characteristics and Thrust of Jets from Asymmetric Nozzles

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

1995-01-01

The spreading characteristics of jets from several asymmetric nozzles are studied in comparison to those of an axisymmetric jet, over the Mach number (M(sub J)) range of 0.3 to 1.96. The effect of tabs in two cases, the axisymmetric nozzle fitted with four tabs and a rectangular nozzle fitted with two large tabs, is also included in the comparison. Compared to the axisymmetric jet, the asymmetric jets spread only slightly faster at subsonic conditions, while at supersonic conditions, when screech occurs, they spread much faster. Screech profoundly increases the spreading of all jets. The effect varies in the different stages of screech, and the corresponding unsteady flowfield characteristics are documented via phase-averaged measurement of the fluctuating total pressure. An organization and intensification of the azimuthal vortical structures under the screeching condition is believed to be responsible for the increased spreading. Curiously, the jet from a 'lobed mixer' nozzle spreads much less at supersonic conditions compared to all other cases. This is due to the absence of screech with this nozzle. Jet spreading for the two tab configurations, on the other hand, is significantly more than any of the no-tab cases. This is true in the subsonic regime, as well as in the supersonic regime in spite of the fact that screech is essentially eliminated by the tabs. The dynamics of the streamwise vortex pairs produced by the tabs cause the most efficient jet spreading thus far observed in the study.

Development and application of a particle image velocimeter for high-speed flows

NASA Astrophysics Data System (ADS)

Molezzi, M. J.; Dutton, J. C.

1992-01-01

A particle image velocimetry (PIV) system has been developed for use in high-speed separated air flows. The image acquisition system uses two 550 mJ/pulse Nd:YAG lasers and is fully controlled by a host Macintosh computer. The interrogation system is also Macintosh-based and performs interrogations at approximately 2.3 sec/spot and 4.0 sec/spot when using the Young's fringe and autocorrelation methods, respectively. The system has been proven in preliminary experiments using known-displacement simulated PIV photographs and a simple axisymmetric jet flow. Further results have been obtained in a transonic wind tunnel operating at Mach 0.4 to 0.5 (135 m/s to 170 m/s). PIV experiments were done with an empty test section to provide uniform flow data for comparison with pressure and LDV data, then with a two-dimensional base model, revealing features of the von Karman vortex street wake and underlying small scale turbulence.

Strain dynamics for vortex ring mixing process

NASA Astrophysics Data System (ADS)

Bouremel, Yann; Yianneskis, Michael; Ducci, Andrea

2009-11-01

Simultaneous PIV-PLIF measurements were carried out to investigate the mixing occurring in a laminar vortex ring flow during the formation stage (Re=357-1072). In the first part of the work a control volume analysis was used to determine the variation in time of the scalar concentration mean, variance, and probability density function. In the second part the advection-diffusion differential equations of the scalar, ξ, and of its energy, 0.5 2̂, were studied in depth to gain insight into the effect of the strain rate tensor, S, on the local scalar concentration for increasing Re. The measurements were obtained with a high spatial resolution (12 μm for the PLIF) in order to resolve the scalar dissipative scales. Reliable estimates of the scalar dissipation rate (∇ξ.∇ξ), and of the symmetric contraction term (∇ξ.S .∇ξ), shown in equation 1, were obtained. ∇ξ.S .∇ξ accounts for the reduction of scalar dissipation due to the straining component directed as the local scalar gradient (see Southerland et al.footnotetextSoutherland K B., Porter III J. R., Dahm, W. J. A., Buch K. A., An experimental study of the molecular mixing process in an axisymmetric laminar vortex ring, Phys. Fluids A 3 (5), May 1991) Equation 1: ( t+u.∇+1ReSc∇^2 )12( ∇ξ.∇ξ )=-( ∇ξ.S.∇ξ )-1ReSc∇(∇ξ):∇(∇ξ)

Numerical 3D Hydrodynamics Study of Gravitational Instabilities in a Circumbinary Disk

NASA Astrophysics Data System (ADS)

Desai, Karna Mahadev; Steiman-Cameron, Thomas Y.; Michael, Scott; Cai, Kai; Durisen, Richard H.

2016-01-01

We present a 3D hydrodynamical study of gravitational instabilities (GIs) in a circumbinary protoplanetary disk around a Solar mass star and a brown dwarf companion (0.02 M⊙). GIs can play an important, and at times dominant, role in driving the structural evolution of protoplanetary disks. The reported simulations were performed employing CHYMERA, a radiative 3D hydrodynamics code developed by the Indiana University Hydrodynamics Group. The simulations include disk self-gravity and radiative cooling governed by realistic dust opacities. We examine the role of GIs in modulating the thermodynamic state of the disks, and determine the strengths of GI-induced density waves, non-axisymmetric density structures, radial mass transport, and gravitational torques. The principal goal of this study is to determine how the presence of the companion affects the nature and strength of GIs. Results are compared with a parallel simulation of a protoplanetary disk without the presence of the brown dwarf binary companion. We detect no fragmentation in either disk. A persistent vortex forms in the inner region of both disks. The vortex seems to be stabilized by the presence of the binary companion.

Dark matter cosmic string in the gravitational field of a black hole

NASA Astrophysics Data System (ADS)

Nakonieczny, Łukasz; Nakonieczna, Anna; Rogatko, Marek

2018-03-01

We examined analytically and proposed a numerical model of an Abelian Higgs dark matter vortex in the spacetime of a stationary axisymmetric Kerr black hole. In analytical calculations the dark matter sector was modeled by an addition of a U(1)-gauge field coupled to the visible sector. The backreaction analysis revealed that the impact of the dark vortex presence is far more complicated than causing only a deficit angle. The vortex causes an ergosphere shift and the event horizon velocity is also influenced by its presence. These phenomena are more significant than in the case of a visible vortex sector. The area of the event horizon of a black hole is diminished and this decline is larger in comparison to the Kerr black hole with an Abelian Higgs vortex case. After analyzing the gravitational properties for the general setup, we focused on the subset of models that are motivated by particle physics. We retained the Abelian Higgs model as a description of the dark matter sector (this sector contained a heavy dark photon and an additional complex scalar) and added a real scalar representing the real component of the Higgs doublet in the unitary gauge, as well as an additional U(1)-gauge field representing an ordinary electromagnetic field. Moreover, we considered two coupling channels between the visible and dark sectors, which were the kinetic mixing between the gauge fields and a quartic coupling between the scalar fields. After solving the equations of motion for the matter fields numerically we analyzed properties of the cosmic string in the dark matter sector and its influence on the visible sector fields that are directly coupled to it. We found out that the presence of the cosmic string induced spatial variation in the vacuum expectation value of the Higgs field and a nonzero electromagnetic field around the black hole.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pérez, Laura M.; Chandler, Claire J.; Isella, Andrea

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations in the dust continuum (690 GHz, 0.45 mm) and {sup 12}CO J = 6-5 spectral line emission of the transitional disks surrounding the stars SAO 206462 and SR 21. These ALMA observations resolve the dust-depleted disk cavities and extended gaseous disks, revealing large-scale asymmetries in the dust emission of both disks. We modeled these disk structures with a ring and an azimuthal Gaussian, where the azimuthal Gaussian is motivated by the steady-state vortex solution from Lyra and Lin. Compared to recent observations of HD 142527, Oph IRS 48, and LkHα 330, these are low-contrastmore » (≲ 2) asymmetries. Nevertheless, a ring alone is not a good fit, and the addition of a vortex prescription describes these data much better. The asymmetric component encompasses 15% and 28% of the total disk emission in SAO 206462 and SR 21, respectively, which corresponds to a lower limit of 2 M {sub Jup} of material within the asymmetry for both disks. Although the contrast in the dust asymmetry is low, we find that the turbulent velocity inside it must be large (∼20% of the sound speed) in order to drive these azimuthally wide and radially narrow vortex-like structures. We obtain residuals from the ring and vortex fitting that are still significant, tracing non-axisymmetric emission in both disks. We compared these submillimeter observations with recently published H-band scattered light observations. For SR 21 the scattered light emission is distributed quite differently from the submillimeter continuum emission, while for SAO 206462 the submillimeter residuals are suggestive of spiral-like structure similar to the near-IR emission.« less

Calculation of laminar heating rates on three-dimensional configurations using the axisymmetric analogue

NASA Technical Reports Server (NTRS)

Hamilton, H. H., II

1980-01-01

A theoretical method was developed for computing approximate laminar heating rates on three dimensional configurations at angle of attack. The method is based on the axisymmetric analogue which is used to reduce the three dimensional boundary layer equations along surface streamlines to an equivalent axisymmetric form by using the metric coefficient which describes streamline divergence (or convergence). The method was coupled with a three dimensional inviscid flow field program for computing surface streamline paths, metric coefficients, and boundary layer edge conditions.

Internal scanning method as unique imaging method of optical vortex scanning microscope

NASA Astrophysics Data System (ADS)

Popiołek-Masajada, Agnieszka; Masajada, Jan; Szatkowski, Mateusz

2018-06-01

The internal scanning method is specific for the optical vortex microscope. It allows to move the vortex point inside the focused vortex beam with nanometer resolution while the whole beam stays in place. Thus the sample illuminated by the focused vortex beam can be scanned just by the vortex point. We show that this method enables high resolution imaging. The paper presents the preliminary experimental results obtained with the first basic image recovery procedure. A prospect of developing more powerful tools for topography recovery with the optical vortex scanning microscope is discussed shortly.

A vortex-filament and core model for wings with edge vortex separation

NASA Technical Reports Server (NTRS)

Pao, J. L.; Lan, C. E.

1982-01-01

A vortex filament-vortex core method for predicting aerodynamic characteristics of slender wings with edge vortex separation was developed. Semi-empirical but simple methods were used to determine the initial positions of the free sheet and vortex core. Comparison with available data indicates that: (1) the present method is generally accurate in predicting the lift and induced drag coefficients but the predicted pitching moment is too positive; (2) the spanwise lifting pressure distributions estimated by the one vortex core solution of the present method are significantly better than the results of Mehrotra's method relative to the pressure peak values for the flat delta; (3) the two vortex core system applied to the double delta and strake wings produce overall aerodynamic characteristics which have good agreement with data except for the pitching moment; and (4) the computer time for the present method is about two thirds of that of Mehrotra's method.

Calculations of condensation and chemistry in an aircraft contrail

NASA Technical Reports Server (NTRS)

Miake-Lye, Richard C.; Brown, R. C.; Anderson, M. R.; Kolb, C. E.

1994-01-01

The flow field, chemistry, and condensation nucleation behind a transport airplane are calculated in two regimes using two separate reacting flow codes: first the axisymmetric plume, then the three dimensional vortex wake. The included chemical kinetics equations follow the evolution of the NO(y) and SO(x) chemical families. In the plume regime, the chemistry is coupled with the binary homogeneous formation of sulfate condensation nuclei, where the calculated nucleation rates predict that copious quantities of H2SO4/H2O nuclei are produced in subnanometer sizes. These sulfate aerosols could play a major role in the subsequent condensation of water vapor and the formation of contrails under favorable atmospheric conditions.

Simulation of a turbulent supersonic underexpanded jet flowing into a submerged space with the help of a shear stress transfer model

NASA Astrophysics Data System (ADS)

Isaev, S. A.; Lipnitskii, Yu. M.; Baranov, P. A.; Panasenko, A. V.; Usachov, A. E.

2012-11-01

We have calculated the flow of an axisymmetric turbulent supersonic underexpanded jet into a submerged space with the help of the VP2/3 package as part of the generalized pressure correction procedure. The shear stress transfer model modified with account for the curvature of streamlines has been verified on the basis of comparison with V. I. Zapryagaev's data obtained at the S. A. Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch of the Russian Academy of Sciences. The influence of the generated vortex viscosity on the shock-wave structure of the jet, the field of flow parameters, and the turbulence characteristics has been analyzed.

NLS clutching bearing cavity flow analysis

NASA Technical Reports Server (NTRS)

Tran, Ken; Chan, Daniel C.; Darian, Armen

1992-01-01

A flow model of the NLS clutching bearing cavity was built for 2-D axisymmetric viscous analysis. From the computational fluid dynamics (CFD) approach, the tangential force exerted on the surfaces of the inner race was integrated to calculate the dividing torque which, in conjunction with the resistance torque, was used to predict the operating speed of the inner race. In order to further reduce the inner race rotation, the swirling flow at the cavity inlet was partially redirected to generate an opposing torque. Thirty six slanted slots were incorporated into the anti-vortex rib to achieve this goal. A 3-D flow analysis performed on this configuration indicates a drastic reduction of the driving torque and inner race RPM.

Spinning superfluid 4He nanodroplets

NASA Astrophysics Data System (ADS)

Ancilotto, Francesco; Barranco, Manuel; Pi, Martí

2018-05-01

We have studied spinning superfluid 4He nanodroplets at zero temperature using density functional theory. Due to the irrotational character of the superfluid flow, the shapes of the spinning nanodroplets are very different from those of a viscous normal fluid drop in steady rotation. We show that when vortices are nucleated inside the superfluid droplets, their morphology, which evolves from axisymmetric oblate to triaxial prolate to two-lobed shapes, is in good agreement with experiments. The presence of vortex arrays confers to the superfluid droplets the rigid-body behavior of a normal fluid in steady rotation, and this is the ultimate reason for the surprising good agreement between recent experiments and the classical models used for their description.

Computer studies of baroclinic flow. [Atmospheric General Circulation Experiment

NASA Technical Reports Server (NTRS)

Gall, R.

1985-01-01

Programs necessary for computing the transition curve on the regime diagram for the atmospheric general circulation experiment (AGOE) were completed and used to determine the regime diagram for the rotating annulus and some axisymmetric flows for one possible AGOE configuration. The effect of geometrical constraints on the size of eddies developing from a basic state is being examined. In AGOE, the geometric constraint should be the width of the shear zone or the baroclinic zone. Linear and nonlinear models are to be used to examine both barotropic and baroclinic flows. The results should help explain the scale selection mechanism of baroclinic eddies in the atmosphere experimental models such as AGOE, and the multiple vortex phenomenon in tornadoes.

Numerical computation of gravitational field for general axisymmetric objects

NASA Astrophysics Data System (ADS)

Fukushima, Toshio

2016-10-01

We developed a numerical method to compute the gravitational field of a general axisymmetric object. The method (I) numerically evaluates a double integral of the ring potential by the split quadrature method using the double exponential rules, and (II) derives the acceleration vector by numerically differentiating the numerically integrated potential by Ridder's algorithm. Numerical comparison with the analytical solutions for a finite uniform spheroid and an infinitely extended object of the Miyamoto-Nagai density distribution confirmed the 13- and 11-digit accuracy of the potential and the acceleration vector computed by the method, respectively. By using the method, we present the gravitational potential contour map and/or the rotation curve of various axisymmetric objects: (I) finite uniform objects covering rhombic spindles and circular toroids, (II) infinitely extended spheroids including Sérsic and Navarro-Frenk-White spheroids, and (III) other axisymmetric objects such as an X/peanut-shaped object like NGC 128, a power-law disc with a central hole like the protoplanetary disc of TW Hya, and a tear-drop-shaped toroid like an axisymmetric equilibrium solution of plasma charge distribution in an International Thermonuclear Experimental Reactor-like tokamak. The method is directly applicable to the electrostatic field and will be easily extended for the magnetostatic field. The FORTRAN 90 programs of the new method and some test results are electronically available.

Development of axisymmetric lattice Boltzmann flux solver for complex multiphase flows

NASA Astrophysics Data System (ADS)

Wang, Yan; Shu, Chang; Yang, Li-Ming; Yuan, Hai-Zhuan

2018-05-01

This paper presents an axisymmetric lattice Boltzmann flux solver (LBFS) for simulating axisymmetric multiphase flows. In the solver, the two-dimensional (2D) multiphase LBFS is applied to reconstruct macroscopic fluxes excluding axisymmetric effects. Source terms accounting for axisymmetric effects are introduced directly into the governing equations. As compared to conventional axisymmetric multiphase lattice Boltzmann (LB) method, the present solver has the kinetic feature for flux evaluation and avoids complex derivations of external forcing terms. In addition, the present solver also saves considerable computational efforts in comparison with three-dimensional (3D) computations. The capability of the proposed solver in simulating complex multiphase flows is demonstrated by studying single bubble rising in a circular tube. The obtained results compare well with the published data.

Sensitivity of Tropical Cyclone Spinup Time to the Initial Entropy Deficit

NASA Astrophysics Data System (ADS)

Tang, B.; Corbosiero, K. L.; Rios-Berrios, R.; Alland, J.; Berman, J.

2014-12-01

The development timescale of a tropical cyclone from genesis to the start of rapid intensification in an axisymmetric model is hypothesized to be a function of the initial entropy deficit. We run a set of idealized simulations in which the initial entropy deficit between the boundary layer and free troposphere varies from 0 to 100 J kg-1 K-1. The development timescale is measured by changes in the integrated kinetic energy of the low-level vortex. This timescale is inversely related to the mean mass flux during the tropical cyclone gestation period. The mean mass flux, in turn, is a function of the statistics of convective updrafts and downdrafts. Contour frequency by altitude diagrams show that entrainment of dry air into updrafts is predominately responsible for differences in the mass flux between the experiments, while downdrafts play a secondary role. Analyses of the potential and kinetic energy budgets indicate less efficient conversion of available potential energy to kinetic energy in the experiments with higher entropy deficits. Entrainment leads to the loss of buoyancy and the destruction of available potential energy. In the presence of strong downdrafts, there can even be a reversal of the conversion term. Weaker and more radially confined radial inflow results in less convergence of angular momentum in the experiments with higher entropy deficits. The result is a slower vortex spinup and a reduction in steady-state vortex size, despite similar steady-state maximum intensities among the experiments.

An investigation of the vortex method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pryor, Jr., Duaine Wright

The vortex method is a numerical scheme for solving the vorticity transport equation. Chorin introduced modern vortex methods. The vortex method is a Lagrangian, grid free method which has less intrinsic diffusion than many grid schemes. It is adaptive in the sense that elements are needed only where the vorticity is non-zero. Our description of vortex methods begins with the point vortex method of Rosenhead for two dimensional inviscid flow, and builds upon it to eventually cover the case of three dimensional slightly viscous flow with boundaries. This section gives an introduction to the fundamentals of the vortex method. Thismore » is done in order to give a basic impression of the previous work and its line of development, as well as develop some notation and concepts which will be used later. The purpose here is not to give a full review of vortex methods or the contributions made by all the researchers in the field. Please refer to the excellent review papers in Sethian and Gustafson, chapters 1 Sethian, 2 Hald, 3 Sethian, 8 Chorin provide a solid introduction to vortex methods, including convergence theory, application in two dimensions and connection to statistical mechanics and polymers. Much of the information in this review is taken from those chapters, Chorin and Marsden and Batchelor, the chapters are also useful for their extensive bibliographies.« less

Consistent lattice Boltzmann methods for incompressible axisymmetric flows

NASA Astrophysics Data System (ADS)

Zhang, Liangqi; Yang, Shiliang; Zeng, Zhong; Yin, Linmao; Zhao, Ya; Chew, Jia Wei

2016-08-01

In this work, consistent lattice Boltzmann (LB) methods for incompressible axisymmetric flows are developed based on two efficient axisymmetric LB models available in the literature. In accord with their respective original models, the proposed axisymmetric models evolve within the framework of the standard LB method and the source terms contain no gradient calculations. Moreover, the incompressibility conditions are realized with the Hermite expansion, thus the compressibility errors arising in the existing models are expected to be reduced by the proposed incompressible models. In addition, an extra relaxation parameter is added to the Bhatnagar-Gross-Krook collision operator to suppress the effect of the ghost variable and thus the numerical stability of the present models is significantly improved. Theoretical analyses, based on the Chapman-Enskog expansion and the equivalent moment system, are performed to derive the macroscopic equations from the LB models and the resulting truncation terms (i.e., the compressibility errors) are investigated. In addition, numerical validations are carried out based on four well-acknowledged benchmark tests and the accuracy and applicability of the proposed incompressible axisymmetric LB models are verified.

A Laboratory Study of Vortical Structures in Rotating Convection Plumes

NASA Astrophysics Data System (ADS)

Fu, Hao; Sun, Shiwei; Wang, Yuan; Zhou, Bowen; Thermal Turbulence Research Team

2015-11-01

A laboratory study of the columnar vortex structure in rotating Rayleigh-Bénard convection is conducted. A rectangular water tank is uniformly heated from below and cooled from above, with Ra = (6 . 35 +/- 0 . 77) ×107 , Ta = 9 . 84 ×107 , Pr = 7 . 34 . The columnar vortices are vertically aligned and quasi steady. Two 2D PIV systems were used to measure velocity field. One system performs horizontal scans at 9 different heights every 13.6s, covering 62% of the total depth. The other system scans vertically to obtain the vertical velocity profile. The measured vertical vorticity profiles of most vortices are quasi-linear with height while the vertical velocities are nearly uniform with only a small curvature. A simple model to deduce vertical velocity profile from vertical vorticity profile is proposed. Under quasi-steady and axisymmetric conditions, a ``vortex core'' assumption is introduced to simplify vertical vorticity equation. A linear ODE about vertical velocity is obtained whenever a vertical vorticity profile is given and solved with experimental data as input. The result is approximately in agreement with the measurement. This work was supported by Undergraduates Training Project (J1103410).

Nonparallel linear stability analysis of unconfined vortices

NASA Astrophysics Data System (ADS)

Herrada, M. A.; Barrero, A.

2004-10-01

Parabolized stability equations [F. P. Bertolotti, Th. Herbert, and P. R. Spalart, J. Fluid. Mech. 242, 441 (1992)] have been used to study the stability of a family of swirling jets at high Reynolds numbers whose velocity and pressure fields decay far from the axis as rm-2 and r2(m-2), respectively [M. Pérez-Saborid, M. A. Herrada, A. Gómez-Barea, and A. Barrero, J. Fluid. Mech. 471, 51 (2002)]; r is the radial distance and m is a real number in the interval 0

Propagation of a premixed flame in a divided-chamber combustor

NASA Technical Reports Server (NTRS)

Cattolica, R. J.; Barr, P. K.; Mansour, N. N.

1989-01-01

Experimental observations on the propagation of lean premixed ethylene-air flames in a divided-chamber combustion vessel have been compared with the results of numerical simulations based on a flame sheet-vortex dynamics model in axisymmetric coordinates. Flame speeds were found to increase from 10-24 cm/s as the equivalence ratio was varied from 0.5-0.65 in the experiments. Using the associated increase in gas velocity with equivalence ratio, the estimated Reynolds number in the experiment was changed from 1870 to 8090. Good agreement between experimental and theoretical results was obtained for the prechamber flame propagation rates and for the spatial and temporal development of the flame in the main combustion chamber at the lowest Reynolds number.

Numerical investigation of separated nozzle flows

NASA Technical Reports Server (NTRS)

Chen, C. L.; Chakravarthy, S. R.; Hung, C. M.

1994-01-01

A numerical study of axisymmetric overexpanded nozzle is presented. The flow structure of the startup and throttle-down processes are examined. During the impulsive startup process, observed flow features include the Mach disk, separation shock, Mach stem, vortex core, contact surface, slip stream, initial shock front, and shocklet. Also the movement of the Mach disk is not monotonical in the downstream direction. For a range of pressure ratios, hysteresis phenomenon occurs; different solutions were obtained depending on different processes. Three types of flow structures were observed. The location of separation point and the lower end turning point of hysteresis are closely predicted. A high peak of pressure is associated with the nozzle flow reattachment. The reversed vortical structure and affects engine performance.

Development of a nonlinear vortex method. [steady and unsteady aerodynamic loads of highly sweptback wings

NASA Technical Reports Server (NTRS)

Kandil, O. A.

1981-01-01

Progress is reported in the development of reliable nonlinear vortex methods for predicting the steady and unsteady aerodynamic loads of highly sweptback wings at large angles of attack. Abstracts of the papers, talks, and theses produced through this research are included. The modified nonlinear discrete vortex method and the nonlinear hybrid vortex method are highlighted.

GRID3O- FAST GENERATION OF MULTILEVEL, THREE-DIMENSIONAL BOUNDARY-CONFORMING O-TYPE COMPUTATIONAL GRIDS

NASA Technical Reports Server (NTRS)

Dulikravich, D. S.

1994-01-01

A fast algorithm has been developed for accurately generating boundary-conforming, three-dimensional consecutively refined computational grids applicable to arbitrary wing-body and axial turbomachinery geometries. This algorithm has been incorporated into the GRID3O computer program. The method employed in GRID3O is based on using an analytic function to generate two-dimensional grids on a number of coaxial axisymmetric surfaces positioned between the centerbody and the outer radial boundary. These grids are of the O-type and are characterized by quasi-orthogonality, geometric periodicity, and an adequate resolution throughout the flow field. Because the built-in nonorthogonal coordinate stretching and shearing cause the grid lines leaving the blade or wing trailing-edge to end at downstream infinity, use of the generated grid simplifies the numerical treatment of three-dimensional trailing vortex sheets. The GRID3O program is written in FORTRAN IV for batch execution and has been implemented on an IBM 370 series computer with a central memory requirement of approximately 450K of 8 bit bytes. The GRID3O program was developed in 1981.

Vortex methods and vortex statistics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chorin, A.J.

Vortex methods originated from the observation that in incompressible, inviscid, isentropic flow vorticity (or, more accurately, circulation) is a conserved quantity, as can be readily deduced from the absence of tangential stresses. Thus if the vorticity is known at time t = 0, one can deduce the flow at a later time by simply following it around. In this narrow context, a vortex method is a numerical method that makes use of this observation. Even more generally, the analysis of vortex methods leads, to problems that are closely related to problems in quantum physics and field theory, as well asmore » in harmonic analysis. A broad enough definition of vortex methods ends up by encompassing much of science. Even the purely computational aspects of vortex methods encompass a range of ideas for which vorticity may not be the best unifying theme. The author restricts himself in these lectures to a special class of numerical vortex methods, those that are based on a Lagrangian transport of vorticity in hydrodynamics by smoothed particles (``blobs``) and those whose understanding contributes to the understanding of blob methods. Vortex methods for inviscid flow lead to systems of ordinary differential equations that can be readily clothed in Hamiltonian form, both in three and two space dimensions, and they can preserve exactly a number of invariants of the Euler equations, including topological invariants. Their viscous versions resemble Langevin equations. As a result, they provide a very useful cartoon of statistical hydrodynamics, i.e., of turbulence, one that can to some extent be analyzed analytically and more importantly, explored numerically, with important implications also for superfluids, superconductors, and even polymers. In the authors view, vortex ``blob`` methods provide the most promising path to the understanding of these phenomena.« less

Prediction of the vibroacoustic behavior of a submerged shell with non-axisymmetric internal substructures by a condensed transfer function method

NASA Astrophysics Data System (ADS)

Meyer, V.; Maxit, L.; Guyader, J.-L.; Leissing, T.

2016-01-01

The vibroacoustic behavior of axisymmetric stiffened shells immersed in water has been intensively studied in the past. On the contrary, little attention has been paid to the modeling of these shells coupled to non-axisymmetric internal frames. Indeed, breaking the axisymmetry couples the circumferential orders of the Fourier series and considerably increases the computational costs. In order to tackle this issue, we propose a sub-structuring approach called the Condensed Transfer Function (CTF) method that will allow assembling a model of axisymmetric stiffened shell with models of non-axisymmetric internal frames. The CTF method is developed in the general case of mechanical subsystems coupled along curves. A set of orthonormal functions called condensation functions, which depend on the curvilinear abscissa along the coupling line, is considered. This set is then used as a basis for approximating and decomposing the displacements and the applied forces at the line junctions. Thanks to the definition and calculation of condensed transfer functions for each uncoupled subsystem and by using the superposition principle for passive linear systems, the behavior of the coupled subsystems can be deduced. A plane plate is considered as a test case to study the convergence of the method with respect to the type and the number of condensation functions taken into account. The CTF method is then applied to couple a submerged non-periodically stiffened shell described using the Circumferential Admittance Approach (CAA) with internal substructures described by Finite Element Method (FEM). The influence of non-axisymmetric internal substructures can finally be studied and it is shown that it tends to increase the radiation efficiency of the shell and can modify the vibrational and acoustic energy distribution.

A 2.5D Computational Method to Simulate Cylindrical Fluidized Beds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Tingwen; Benyahia, Sofiane; Dietiker, Jeff

2015-02-17

In this paper, the limitations of axisymmetric and Cartesian two-dimensional (2D) simulations of cylindrical gas-solid fluidized beds are discussed. A new method has been proposed to carry out pseudo-two-dimensional (2.5D) simulations of a cylindrical fluidized bed by appropriately combining computational domains of Cartesian 2D and axisymmetric simulations. The proposed method was implemented in the open-source code MFIX and applied to the simulation of a lab-scale bubbling fluidized bed with necessary sensitivity study. After a careful grid study to ensure the numerical results are grid independent, detailed comparisons of the flow hydrodynamics were presented against axisymmetric and Cartesian 2D simulations. Furthermore,more » the 2.5D simulation results have been compared to the three-dimensional (3D) simulation for evaluation. This new approach yields better agreement with the 3D simulation results than with axisymmetric and Cartesian 2D simulations.« less

The effects of micro-vortex generators on normal shock wave/boundary layer interactions

NASA Astrophysics Data System (ADS)

Herges, Thomas G.

Shock wave/boundary-layer interactions (SWBLIs) are complex flow phenomena that are important in the design and performance of internal supersonic and transonic flow fields such as engine inlets. This investigation was undertaken to study the effects of passive flow control devices on normal shock wave/boundary layer interactions in an effort to gain insight into the physics that govern these complex interactions. The work concentrates on analyzing the effects of vortex generators (VGs) as a flow control method by contributing a greater understanding of the flowfield generated by these devices and characterizing their effects on the SWBLI. The vortex generators are utilized with the goal of improving boundary layer health (i.e., reducing/increasing the boundary-layer incompressible shape factor/skin friction coefficient) through a SWBLI, increasing pressure recovery, and reducing flow distortion at the aerodynamic interface plane while adding minimal drag to the system. The investigation encompasses experiments in both small-scale and large-scale inlet testing, allowing multiple test beds for improving the characterization and understanding of vortex generators. Small-scale facility experiments implemented instantaneous schlieren photography, surface oil-flow visualization, pressure-sensitive paint, and particle image velocimetry to characterize the effects of an array of microramps on a normal shock wave/boundary-layer interaction. These diagnostics measured the time-averaged and instantaneous flow organization in the vicinity of the microramps and SWBLI. The results reveal that a microramp produces a complex vortex structure in its wake with two primary counter-rotating vortices surrounded by a train of Kelvin- Helmholtz (K-H) vortices. A streamwise velocity deficit is observed in the region of the primary vortices in addition to an induced upwash/downwash which persists through the normal shock with reduced strength. The microramp flow control also increased the spanwise-averaged skin-friction coefficient and reduced the spanwise-averaged incompressible shape factor, thereby improving the health of the boundary layer. The velocity in the near-wall region appears to be the best indicator of microramp effectiveness at controlling SWBLIs. Continued analysis of additional micro-vortex generator designs in the small-scale facility revealed reduced separation within a subsonic diffuser downstream of the normal shock wave/boundary layer interaction. The resulting attached flow within the diffuser from the micro-vortex generator control devices reduces shock wave position and pressure RMS fluctuations within the diffuser along with increased pressure recovery through the shock and at the entrance of the diffuser. The largest effect was observed by the micro-vortex generators that produce the strongest streamwise vortices. High-speed pressure measurements also indicated that the vortex generators shift the energy of the pressure fluctuations to higher frequencies. Implementation of micro-vortex generators into a large-scale, supersonic, axisymmetric, relaxed-compression inlet have been investigated with the use of a unique and novel flow-visualization measurement system designed and successfully used for the analysis of both upstream micro-VGs (MVGs) and downstream VGs utilizing surface oil-flow visualization and pressure-sensitive paint measurements. The inlet centerbody and downstream diffuser vortex-generator regions were imaged during wind-tunnel testing internally through the inlet cowl with the diagnostic system attached to the cowl. Surface-flow visualization revealed separated regions along the inlet centerbody for large mass-flow rates without vortex generators. Upstream vortex generators did reduce separation in the subsonic diffuser, and a unique perspective of the flowfield produced by the downstream vortex generators was obtained. In addition, pressure distributions on the inlet centerbody and vortex generators were measured with pressure-sensitive paint. At low mass-flow ratios the onset of buzz occurs in the large-scale low-boom inlet. Inlet buzz and how it is affected by vortex generators was characterized using shock tracking through high-speed schlieren imaging and pressure fluctuation measurements. The analysis revealed a dominant low frequency oscillation at 21.0 Hz for the single-stream inlet, corresponding with the duration of one buzz cycle. Pressure oscillations prior to the onset of buzz were not detected, leaving the location where the shock wave triggers large separation on the compression spike as the best indicator for the onset of buzz. The driving mechanism for a buzz cycle has been confirmed as the rate of depressurization and repressurization of the inlet as the buzz cycle fluctuates between an effectively unstarted (blocked) inlet and supercritical operation (choked flow), respectively. High-frequency shock position oscillations/pulsations (spike buzz) were also observed throughout portions of the inlet buzz cycle. The primary effect of the VGs was to trigger buzz at a higher mass-flow ratio.

A vortex-filament and core model for wings with edge vortex separation

NASA Technical Reports Server (NTRS)

Pao, J. L.; Lan, C. E.

1981-01-01

A method for predicting aerodynamic characteristics of slender wings with edge vortex separation was developed. Semiempirical but simple methods were used to determine the initial positions of the free sheet and vortex core. Comparison with available data indicates that: the present method is generally accurate in predicting the lift and induced drag coefficients but the predicted pitching moment is too positive; the spanwise lifting pressure distributions estimated by the one vortex core solution of the present method are significantly better than the results of Mehrotra's method relative to the pressure peak values for the flat delta; the two vortex core system applied to the double delta and strake wing produce overall aerodynamic characteristics which have good agreement with data except for the pitching moment; and the computer time for the present method is about two thirds of that of Mehrotra's method.

User's manual for interfacing a leading edge, vortex rollup program with two linear panel methods

NASA Technical Reports Server (NTRS)

Desilva, B. M. E.; Medan, R. T.

1979-01-01

Sufficient instructions are provided for interfacing the Mangler-Smith, leading edge vortex rollup program with a vortex lattice (POTFAN) method and an advanced higher order, singularity linear analysis for computing the vortex effects for simple canard wing combinations.

Vortex-Airfoil Interaction and Application of Methods for Digital Fringe Analysis.

DTIC Science & Technology

1986-03-15

angles of attack. Different kinds of bluff bodies are used as vortex generators. Their wake is a Karman vortex street consisting of strong vortices of...Table of Contents 1. Introduction 1 2. A model for vortex paths around a profile and the sound generated by vortex -profile interaction 2"-- 3...I’ S.TTE(d~,t. TYPE OF PIrPORT a PERID COWERED ’. * Vortex -airfoil interaction and application of *methods for digital fringe analysis . 1 6

The Effect of the Air-Delivery Method on Parameters of the Precessing Vortex Core in a Hydrodynamic Vortex Chamber

NASA Astrophysics Data System (ADS)

Alekseenko, S. V.; Shtork, S. I.; Yusupov, R. R.

2018-03-01

The effect of the method of gas-phase injection into a swirled fluid flow on parameters of a precessing vortex core is studied experimentally. Conditions of the appearance of the vortex-core precession effect were modeled in a hydrodynamic sudden expansion vortex chamber. The dependences of the vortexcore precession frequency, flow-pulsation level, and full pressure differential in the vortex chamber on the consumption gas content in the flow have been obtained. The results of measurements permit one to determine optimum conditions for the most effective control of vortex-core precession.

Idealized Numerical Modeling Experiments of the Diurnal Cycle of Tropical Cyclones

NASA Astrophysics Data System (ADS)

Navarro, Erika L.

Numerical experiments are performed to evaluate the role of the daily cycle of radiation on axisymmetric hurricane structure. Although a diurnal response in the high cloudiness of tropical cyclones (TCs) has been well documented in the past, the impact to storm structure and intensity remains unknown. Previous modeling work attributes differences in results to experimental setup (e.g., initial and boundary conditions) as well as to radiative parameterization schemes. Here, a numerically-simulated TC in a statistical steady-state is examined to quantify the TC response to the daily cycle of radiation, and a modified, Sawyer-Eliassen approach is applied to evaluate the dynamical mechanism. Fourier analysis in time reveals a spatially coherent pattern in the temperature, wind, and latent heating tendency fields that is statistically significant at the 95% level. This signal accounts for up to 62% of the variance in the temperature field of the upper troposphere, and is mainly concentrated in the TC outflow layer. Composite analysis reveals a cycle in the storm intensity in the low-levels, which lags a periodic response in the latent heating tendency by 6 h. Average magnitudes of the azimuthal wind anomalies near the radius of maximum wind (RMW) are 1 m/s and account for 21% of the overall variance. A hypothesis is drawn from these results that the TC diurnal cycle is comprised of two distinct, periodic circulations: (1) a radiatively-driven circulation in the TC outflow layer due to absorption of solar radiation, and (2) a convectively-driven circulation in the lower and middle troposphere due to anomalous latent heating from convection. These responses are coupled and are periodic with respect to the diurnal cycle. Using a modified, Sawyer-Eliassen approach for time-varying heating, these hypotheses are evaluated to determine the impact of periodic diurnal heating on a balanced vortex. Periodic heating near the top of the vortex produces a local overturning circulation in the region of heating that manifests as inertia-buoyancy waves in the storm environment. Periodic heating in the lower troposphere drives an overturning circulation that resembles the Sawyer-Eliassen solution. This low-level heating induces a positive perturbation azimuthal wind response of 4 m/s near the RMW, which lags the maximum in streamfunction by 6 h. Comparison of these solutions to the numerically-simulated TC reveals a close correspondence of results, suggesting that the axisymmetric TC diurnal cycle is a balanced response driven by periodic heating. The sensitivity of these results to the length of the diurnal period and the vortex intensity are evaluated using the modified, Sawyer-Eliassen approach. Although the true diurnal period is fixed in nature, these experiments allow for the relationship between the magnitude and structure of the TC diurnal signal to the length of the diurnal period to be explored. Results demonstrate that the TC diurnal cycle exhibits large variance, even for the same heating distributions. High-frequency forcing projects mainly onto inertia-buoyancy waves, while low-frequency produces a balanced response resembling the Sawyer-Eliassen solution. Comparison to two, numerically simulated TCs with modified diurnal periods show similar results. In addition, stronger diurnal signals are observed for stronger vortices, suggesting a dependence of the TC diurnal signal on the underlying state of the vortex. These results imply that the magnitude and structure of the TC diurnal signal in nature varies throughout the storm lifetime, and is a function of the structure and intensity of the vortex.

Full-Potential Modeling of Blade-Vortex Interactions. Degree awarded by George Washington Univ., Feb. 1987

NASA Technical Reports Server (NTRS)

Jones, Henry E.

1997-01-01

A study of the full-potential modeling of a blade-vortex interaction was made. A primary goal of this study was to investigate the effectiveness of the various methods of modeling the vortex. The model problem restricts the interaction to that of an infinite wing with an infinite line vortex moving parallel to its leading edge. This problem provides a convenient testing ground for the various methods of modeling the vortex while retaining the essential physics of the full three-dimensional interaction. A full-potential algorithm specifically tailored to solve the blade-vortex interaction (BVI) was developed to solve this problem. The basic algorithm was modified to include the effect of a vortex passing near the airfoil. Four different methods of modeling the vortex were used: (1) the angle-of-attack method, (2) the lifting-surface method, (3) the branch-cut method, and (4) the split-potential method. A side-by-side comparison of the four models was conducted. These comparisons included comparing generated velocity fields, a subcritical interaction, and a critical interaction. The subcritical and critical interactions are compared with experimentally generated results. The split-potential model was used to make a survey of some of the more critical parameters which affect the BVI.

Eroding dipoles and vorticity growth for Euler flows in {{{R}}}^{3}: the hairpin geometry as a model for finite-time blowup

NASA Astrophysics Data System (ADS)

Childress, Stephen; Gilbert, Andrew D.

2018-02-01

A theory of an eroding ‘hairpin’ vortex dipole structure in three-dimensions is developed, extending our previous study of an axisymmetric eroding dipole without swirl. The axisymmetric toroidal dipole was found to lead to maximal growth of vorticity, as {t}4/3. The hairpin is here similarly proposed as a model to produce large ‘self-stretching’ of vorticity, with the possibility of finite-time blow-up. We derive a system of partial differential equations of ‘generalized’ form, involving contour averaging of a locally two-dimensional Euler flow. We do not attempt here to solve the system exactly, but point out that non-existence of physically acceptable solutions would most probably be a result of the axial flow. Because of the axial flow the vorticity distribution within the dipole eddies is no longer of the simple Sadovskii type (vorticity constant over a cross-section) obtained in the axisymmetric problem. Thus the solution of the system depends upon the existence of a larger class of propagating two-dimensional dipoles. The hairpin model is obtained by formal asymptotic analysis. As in the axisymmetric problem a local transformation to ‘shrinking’ coordinates is introduced, but now in a self-similar form appropriate to the study of a possible finite-time singularity. We discuss some properties of the model, including a study of the helicity and a first step in iterating toward a solution from the Sadovskii structure. We also present examples of two-dimensional propagating dipoles not previously studied, which have a vorticity profile consistent with our model. Although no rigorous results can be given, and analysis of the system is only partial, the formal calculations are consistent with the possibility of a finite time blowup of vorticity at a point of vanishing circulation of the dipole eddies, but depending upon the existence of the necessary two-dimensional propagating dipole. Our results also suggest that conservation of kinetic energy as realized in the eroding hairpin excludes a finite time blowup for the corresponding Navier-Stokes model.

The role of large eddy fluctuations in the magnetic dynamics of the Madison Dynamo Experiment

NASA Astrophysics Data System (ADS)

Kaplan, Elliot

The Madison Dynamo Experiment (MDE), a liquid sodium magnetohydrodynamics experiment in a 1 m diameter sphere at the University of Wisconsin-Madison, had measured [in Spence et al., 2006] diamagnetic electrical currents in the experiment that violated an anti dynamo theorem for axisymmetric flow. The diamagnetic currents were instead attributed to nonaxisymmetric turbulent fluctuations. The experimental apparatus has been modified to reduce the strength of the large-scale turbulence driven by the shear layer in its flow. A 7.62 cm baffle was affixed to the equator of the machine to stabilize the shear layer. This reduction has correlated with a decrease in the magnetic fields, induced by the flow, which had been associated with the α and β effects of mean-field magnetohydrodynamics. The research presented herein presents the experimental evidence for reduced fluctuations and reduced mean field emfs, and provides a theoretical framework—based upon mean-field MHD—that connects the observations. The shapes of the large-scale velocity fluctuations are inferred by the spectra of induced magnetic fluctuations and measured in a kinematically similar water experiment. The Bullard and Gellman [1954] formalism demonstrates that the large-scale velocity fluctuations that are inhibited by the baffle can beat with the large-scale magnetic fluctuations that they produce to generate a mean-field emf of the sort measured in Spence et al. [2006]. This shows that the reduction of these large-scale eddies has brought the MDE closer to exciting a dynamo magnetic field. We also examine the mean-field like effects of large-scale (stable) eddies in the Dudley-James [1989] two-vortex dynamo (that the MDE was based upon). Rotating the axis of symmetry redefines the problem from one of an axisymmetric flow exciting a nonaxisymmetric field to one of a combination of axisymmetric and nonaxisymmetric flows exciting a predominantly axisymmetric magnetic eigenmode. As a result, specific interactions between large-scale velocity modes and large-scale magnetic modes are shown to correspond to the Ω effect and the mean-field α and β effects.

Comparison of optical vortex detection methods for use with a Shack-Hartmann wavefront sensor.

PubMed

Murphy, Kevin; Dainty, Chris

2012-02-27

In this paper we compare experimentally two methods of detecting optical vortices from Shack-Hartmann wavefront sensor (SHWFS) data, the vortex potential and the contour sum methods. The experimental setup uses a spatial light modulator (SLM) to generate turbulent fields with vortices. In the experiment, many fields are generated and detected by a SHWFS, and data is analysed by the two vortex detection methods. We conclude that the vortex potential method is more successful in locating vortices in these fields.

Modification of vortex dynamics and transport properties of transitional axisymmetric jets using zero-net-mass-flux actuation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Önder, Asim; Meyers, Johan, E-mail: johan.meyers@mech.kuleuven.be

2014-07-15

We study the near field of a zero-net-mass-flux (ZNMF) actuated round jet using direct numerical simulations. The Reynolds number of the jet Re{sub D} = 2000 and three ZNMF actuators are used, evenly distributed over a circle, and directed towards the main jet. The actuators are triggered in phase, and have a relatively low momentum coefficient of C{sub μ} = 0.0049 each. We study four different control frequencies with Strouhal numbers ranging from St{sub D} = 0.165 to St{sub D} = 1.32; next to that, also two uncontrolled baseline cases are included in the study. We find that this typemore » of ZNMF actuation leads to strong deformations of the near-field jet region that are very similar to those observed for non-circular jets. At the end of the jet's potential core (x/D = 5), the jet-column cross section is deformed into a hexagram-like geometry that results from strong modifications of the vortex structures. Two mechanisms lead to these modifications, i.e., (i) self-deformation of the jet's primary vortex rings started by distortions in their azimuthal curvature by the actuation, and (ii) production of side jets by the development and subsequent detachment of secondary streamwise vortex pairs. Further downstream (x/D = 10), the jet transforms into a triangular pattern, as the sharp corner regions of the hexagram entrain fluid and spread. We further investigate the global characteristics of the actuated jets. In particular when using the jet preferred frequency, i.e., St{sub D} = 0.33, parameters such as entrainment, centerline decay rate, and mean turbulent kinetic energy are significantly increased. Furthermore, high frequency actuation, i.e., St{sub D} = 1.32, is found to suppress the mechanisms leading to large scale structure growth and turbulent kinetic energy production. The simulations further include a passive scalar equation, and passive scalar mixing is also quantified and visualized.« less

VORSTAB: A computer program for calculating lateral-directional stability derivatives with vortex flow effect

NASA Technical Reports Server (NTRS)

Lan, C. Edward

1985-01-01

A computer program based on the Quasi-Vortex-Lattice Method of Lan is presented for calculating longitudinal and lateral-directional aerodynamic characteristics of nonplanar wing-body combination. The method is based on the assumption of inviscid subsonic flow. Both attached and vortex-separated flows are treated. For the vortex-separated flow, the calculation is based on the method of suction analogy. The effect of vortex breakdown is accounted for by an empirical method. A summary of the theoretical method, program capabilities, input format, output variables and program job control set-up are described. Three test cases are presented as guides for potential users of the code.

Axisymmetric Lattice Boltzmann Model of Droplet Impact on Solid Surfaces

NASA Astrophysics Data System (ADS)

Dalgamoni, Hussein; Yong, Xin

2017-11-01

Droplet impact is a ubiquitous fluid phenomena encountered in scientific and engineering applications such as ink-jet printing, coating, electronics manufacturing, and many others. It is of great technological importance to understand the detailed dynamics of drop impact on various surfaces. The lattice Boltzmann method (LBM) emerges as an efficient method for modeling complex fluid systems involving rapidly evolving fluid-fluid and fluid-solid interfaces with complex geometries. In this work, we model droplet impact on flat solid substrates with well-defined wetting behavior using a two-phase axisymmetric LBM with high density and viscosity contrasts. We extend the two-dimensional Lee and Liu model to capture axisymmetric effect in the normal impact. First we compare the 2D axisymmetric results with the 2D and 3D results reported by Lee and Liu to probe the effect of axisymmetric terms. Then, we explore the effects of Weber number, Ohnesorge number, and droplet-surface equilibrium contact angle on the impact. The dynamic contact angle and spreading factor of the droplet during impact are investigated to qualitatively characterize the impact dynamics.

A generalized vortex lattice method for subsonic and supersonic flow applications

NASA Technical Reports Server (NTRS)

Miranda, L. R.; Elliot, R. D.; Baker, W. M.

1977-01-01

If the discrete vortex lattice is considered as an approximation to the surface-distributed vorticity, then the concept of the generalized principal part of an integral yields a residual term to the vorticity-induced velocity field. The proper incorporation of this term to the velocity field generated by the discrete vortex lines renders the present vortex lattice method valid for supersonic flow. Special techniques for simulating nonzero thickness lifting surfaces and fusiform bodies with vortex lattice elements are included. Thickness effects of wing-like components are simulated by a double (biplanar) vortex lattice layer, and fusiform bodies are represented by a vortex grid arranged on a series of concentrical cylindrical surfaces. The analysis of sideslip effects by the subject method is described. Numerical considerations peculiar to the application of these techniques are also discussed. The method has been implemented in a digital computer code. A users manual is included along with a complete FORTRAN compilation, an executed case, and conversion programs for transforming input for the NASA wave drag program.

On the combination of kinematics with flow visualization to compute total circulation - Application to vortex rings in a tube

NASA Technical Reports Server (NTRS)

Brasseur, J. G.; Chang, I.-D.

1980-01-01

To date the computation of the total circulation, or strength of a vortex has required detailed measurements of the velocity field within the vortex. In this paper a method is described in which the kinematics of the vortical flow field is exploited to calculate the strength of a vortex from relatively simple flow visualization measurements. There are several advantages in the technique, the most important being the newly acquired ability to calculate the transient changes in strength of a single vortex as it evolves. The method is applied to the study of vortex rings, although the development can be carried over directly to study vortex pairs, and it is expected that it can be generalized to other flows which contain regions of concentrated vorticity. The accuracy of the method as applied to vortex rings, assessed in part by comparing with the laser Doppler velocimeter (LDV) measurements of Sullivan et al., is shown to be excellent.

Aeroacoustics Computation for Nearly Fully Expanded Supersonic Jets Using the CE/SE Method

NASA Technical Reports Server (NTRS)

Loh, Ching Y.; Hultgren, Lennart S.; Wang, Xiao Y.; Chang, Sin-Chung; Jorgenson, Philip C. E.

2000-01-01

In this paper, the space-time conservation element solution element (CE/SE) method is tested in the classical axisymmetric jet instability problem, rendering good agreement with the linear theory. The CE/SE method is then applied to numerical simulations of several nearly fully expanded axisymmetric jet flows and their noise fields and qualitative agreement with available experimental and theoretical results is demonstrated.

Configuration of ripple domains and their topological defects formed under local mechanical stress on hexagonal monolayer graphene.

PubMed

Park, Yeonggu; Choi, Jin Sik; Choi, Taekjib; Lee, Mi Jung; Jia, Quanxi; Park, Minwoo; Lee, Hoonkyung; Park, Bae Ho

2015-03-24

Ripples in graphene are extensively investigated because they ensure the mechanical stability of two-dimensional graphene and affect its electronic properties. They arise from spontaneous symmetry breaking and are usually manifested in the form of domains with long-range order. It is expected that topological defects accompany a material exhibiting long-range order, whose functionality depends on characteristics of domains and topological defects. However, there remains a lack of understanding regarding ripple domains and their topological defects formed on monolayer graphene. Here we explore configuration of ripple domains and their topological defects in exfoliated monolayer graphenes on SiO2/Si substrates using transverse shear microscope. We observe three-color domains with three different ripple directions, which meet at a core. Furthermore, the closed domain is surrounded by an even number of cores connected together by domain boundaries, similar to topological vortex and anti-vortex pairs. In addition, we have found that axisymmetric three-color domains can be induced around nanoparticles underneath the graphene. This fascinating configuration of ripple domains may result from the intrinsic hexagonal symmetry of two-dimensional graphene, which is supported by theoretical simulation using molecular dynamics. Our findings are expected to play a key role in understanding of ripple physics in graphene and other two-dimensional materials.

Effects of general relativity on glitch amplitudes and pulsar mass upper bounds

NASA Astrophysics Data System (ADS)

Antonelli, M.; Montoli, A.; Pizzochero, P. M.

2018-04-01

Pinning of vortex lines in the inner crust of a spinning neutron star may be the mechanism that enhances the differential rotation of the internal neutron superfluid, making it possible to freeze some amount of angular momentum which eventually can be released, thus causing a pulsar glitch. We investigate the general relativistic corrections to pulsar glitch amplitudes in the slow-rotation approximation, consistently with the stratified structure of the star. We thus provide a relativistic generalization of a previous Newtonian model that was recently used to estimate upper bounds on the masses of glitching pulsars. We find that the effect of general relativity on the glitch amplitudes obtained by emptying the whole angular momentum reservoir is less than 30 per cent. Moreover, we show that the Newtonian upper bounds on the masses of large glitchers obtained from observations of their maximum recorded event differ by less than a few percent from those calculated within the relativistic framework. This work can also serve as a basis to construct more sophisticated models of angular momentum reservoir in a relativistic context: in particular, we present two alternative scenarios for macroscopically rigid and slack pinned vortex lines, and we generalize the Feynman-Onsager relation to the case when both entrainment coupling between the fluids and a strong axisymmetric gravitational field are present.

A Discrete-Vortex Method for Studying the Wing Rock of Delta Wings

NASA Technical Reports Server (NTRS)

Gainer, Thomas G.

2002-01-01

A discrete-vortex method is developed to investigate the wing rock problem associated with highly swept wings. The method uses two logarithmic vortices placed above the wing to represent the vortex flow field and uses boundary conditions based on conical flow, vortex rate of change of momentum, and other considerations to position the vortices and determine their strengths. A relationship based on the time analogy and conical-flow assumptions is used to determine the hysteretic positions of the vortices during roll oscillations. Static and dynamic vortex positions and wing rock amplitudes and frequencies calculated by using the method are generally in good agreement with available experimental data. The results verify that wing rock is caused by hysteretic deflections of the vortices and indicate that the stabilizing moments that limit wing rock amplitudes are the result of the one primary vortex moving outboard of the wing where it has little influence on the wing.

Calculation of two dimensional vortex/surface interference using panel methods

NASA Technical Reports Server (NTRS)

Maskew, B.

1980-01-01

The application of panel methods to the calculation of vortex/surface interference characteristics in two dimensional flow was studied over a range of situations starting with the simple case of a vortex above a plane and proceeding to the case of vortex separation from a prescribed point on a thick section. Low order and high order panel methods were examined, but the main factor influencing the accuracy of the solution was the distance between control stations in relation to the height of the vortex above the surface. Improvements over the basic solutions were demonstrated using a technique based on subpanels and an applied doublet distribution.

Vortex Analysis of Intra-Aneurismal Flow in Cerebral Aneurysms

PubMed Central

Sunderland, Kevin; Haferman, Christopher; Chintalapani, Gouthami

2016-01-01

This study aims to develop an alternative vortex analysis method by measuring structure ofIntracranial aneurysm (IA) flow vortexes across the cardiac cycle, to quantify temporal stability of aneurismal flow. Hemodynamics were modeled in “patient-specific” geometries, using computational fluid dynamics (CFD) simulations. Modified versions of known λ 2 and Q-criterion methods identified vortex regions; then regions were segmented out using the classical marching cube algorithm. Temporal stability was measured by the degree of vortex overlap (DVO) at each step of a cardiac cycle against a cycle-averaged vortex and by the change in number of cores over the cycle. No statistical differences exist in DVO or number of vortex cores between 5 terminal IAs and 5 sidewall IAs. No strong correlation exists between vortex core characteristics and geometric or hemodynamic characteristics of IAs. Statistical independence suggests this proposed method may provide novel IA information. However, threshold values used to determine the vortex core regions and resolution of velocity data influenced analysis outcomes and have to be addressed in future studies. In conclusions, preliminary results show that the proposed methodology may help give novel insight toward aneurismal flow characteristic and help in future risk assessment given more developments. PMID:27891172

Vortex Analysis of Intra-Aneurismal Flow in Cerebral Aneurysms.

PubMed

Sunderland, Kevin; Haferman, Christopher; Chintalapani, Gouthami; Jiang, Jingfeng

2016-01-01

This study aims to develop an alternative vortex analysis method by measuring structure ofIntracranial aneurysm (IA) flow vortexes across the cardiac cycle, to quantify temporal stability of aneurismal flow. Hemodynamics were modeled in "patient-specific" geometries, using computational fluid dynamics (CFD) simulations. Modified versions of known λ 2 and Q -criterion methods identified vortex regions; then regions were segmented out using the classical marching cube algorithm. Temporal stability was measured by the degree of vortex overlap (DVO) at each step of a cardiac cycle against a cycle-averaged vortex and by the change in number of cores over the cycle. No statistical differences exist in DVO or number of vortex cores between 5 terminal IAs and 5 sidewall IAs. No strong correlation exists between vortex core characteristics and geometric or hemodynamic characteristics of IAs. Statistical independence suggests this proposed method may provide novel IA information. However, threshold values used to determine the vortex core regions and resolution of velocity data influenced analysis outcomes and have to be addressed in future studies. In conclusions, preliminary results show that the proposed methodology may help give novel insight toward aneurismal flow characteristic and help in future risk assessment given more developments.

Combined stamping-forging for non-axisymmetric product

NASA Astrophysics Data System (ADS)

Taureza, Muhammad; Danno, Atsushi; Song, Xu; Oh, Jin An

2016-10-01

Successive combined stamping-forging (CSF) is proposed to produce multi-thickness non-axisymmetric components. This method involves successive compression to create exclusively outward metal flow. Hitherto, the development of CSF has been mostly done for axisymmetric geometry. Using this technique, defect-free rectangular case component with length to thickness ratio of 40 is produced with lower forging pressure. This technology has potential for high throughput production of parts with multiple thicknesses and high width to thickness ratio.

Numerical study of the vortex tube reconnection using vortex particle method on many graphics cards

NASA Astrophysics Data System (ADS)

Kudela, Henryk; Kosior, Andrzej

2014-08-01

Vortex Particle Methods are one of the most convenient ways of tracking the vorticity evolution. In the article we presented numerical recreation of the real life experiment concerning head-on collision of two vortex rings. In the experiment the evolution and reconnection of the vortex structures is tracked with passive markers (paint particles) which in viscous fluid does not follow the evolution of vorticity field. In numerical computations we showed the difference between vorticity evolution and movement of passive markers. The agreement with the experiment was very good. Due to problems with very long time of computations on a single processor the Vortex-in-Cell method was implemented on the multicore architecture of the graphics cards (GPUs). Vortex Particle Methods are very well suited for parallel computations. As there are myriads of particles in the flow and for each of them the same equations of motion have to be solved the SIMD architecture used in GPUs seems to be perfect. The main disadvantage in this case is the small amount of the RAM memory. To overcome this problem we created a multiGPU implementation of the VIC method. Some remarks on parallel computing are given in the article.

Passive control of base pressure on an axisymmetric blunt body using a perimetric slit

NASA Astrophysics Data System (ADS)

García de la Cruz, Juan Marcos; Oxlade, Anthony R.; Morrison, Jonathan F.

2017-04-01

The effect on the base pressure of a thin slit located at the base edge of a blunt axisymmetric body, communicating an internal cavity with the external flow, is investigated. A parametric study is performed of the effect on base pressure of changes in slit size and cavity depth. The base pressure increases initially with increasing cavity depth, but saturates at a depth which depends on the slit size. The base pressure increases monotonically up to 5 % with increasing slit size for the geometries tested. An upper limit of base pressure recovery of 20 % is extrapolated from the data. It is observed that the main effect of the slit is to reduce the instantaneous pressure asymmetry, which is linked to the total base pressure in a similar fashion for all the slit sizes. As a second-order effect, for highly asymmetric pressure distributions, the slit produces a base pressure increase not associated with the base pressure asymmetry. The results suggest a global effect of the slit on the wake due to a diametrical flow within the cavity driven by the pressure differences across the slit and regulated by the largest of the pressure drops between the slit and cavity. The slit also reduces the periodic base pressure fluctuations, corresponding mainly to the vortex shedding, and increases the rotational speed of the wake.

Method and apparatus for enhancing vortex pinning by conformal crystal arrays

DOEpatents

Janko, Boldizsar; Reichhardt, Cynthia; Reichhardt, Charles; Ray, Dipanjan

2015-07-14

Disclosed is a method and apparatus for strongly enhancing vortex pinning by conformal crystal arrays. The conformal crystal array is constructed by a conformal transformation of a hexagonal lattice, producing a non-uniform structure with a gradient where the local six-fold coordination of the pinning sites is preserved, and with an arching effect. The conformal pinning arrays produce significantly enhanced vortex pinning over a much wider range of field than that found for other vortex pinning geometries with an equivalent number of vortex pinning sites, such as random, square, and triangular.

Full-potential modeling of blade-vortex interactions

NASA Technical Reports Server (NTRS)

Jones, H. E.; Caradonna, F. X.

1986-01-01

A comparison is made of four different models for predicting the unsteady loading induced by a vortex passing close to an airfoil. (1) The first model approximates the vortex effect as a change in the airfoil angle of attack. (2) The second model is related to the first but, instead of imposing only a constant velocity on the airfoil, the distributed effect of the vortex is computed and used. This is analogous to a lifting surface method. (3) The third model is to specify a branch cut discontinuity in the potential field. The vortex is modeled as a jump in potential across the branch cut, the edge of which represents the center of the vortex. (4) The fourth method models the vortex expressing the potential as the sum of a known potential due to the vortex and an unknown perturbation due to the airfoil. The purpose of the current study is to investigate the four vortex models described above and to determine their relative merits and suitability for use in large three-dimensional codes.

Minnowbrook VI: 2009 Workshop on Flow Physics and Control for Internal and External Aerodynamics

NASA Technical Reports Server (NTRS)

LaGraff, John E.; Povinelli, Louis A.; Gostelow, J. Paul; Glauser, Mark

2010-01-01

Topics covered include: Flow Physics and control for Internal and External Aerodynamics (not in TOC...starts on pg13); Breaking CFD Bottlenecks in Gas-Turbine Flow-Path Design; Streamwise Vortices on the Convex Surfaces of Circular Cylinders and Turbomachinery Blading; DNS and Embedded DNS as Tools for Investigating Unsteady Heat Transfer Phenomena in Turbines; Cavitation, Flow Structure and Turbulence in the Tip Region of a Rotor Blade; Development and Application of Plasma Actuators for Active Control of High-Speed and High Reynolds Number Flows; Active Flow Control of Lifting Surface With Flap-Current Activities and Future Directions; Closed-Loop Control of Vortex Formation in Separated Flows; Global Instability on Laminar Separation Bubbles-Revisited; Very Large-Scale Motions in Smooth and Rough Wall Boundary Layers; Instability of a Supersonic Boundary-Layer With Localized Roughness; Active Control of Open Cavities; Amplitude Scaling of Active Separation Control; U.S. Air Force Research Laboratory's Need for Flow Physics and Control With Applications Involving Aero-Optics and Weapon Bay Cavities; Some Issues Related to Integrating Active Flow Control With Flight Control; Active Flow Control Strategies Using Surface Pressure Measurements; Reduction of Unsteady Forcing in a Vaned, Contra-Rotating Transonic Turbine Configuration; Active Flow Control Stator With Coanda Surface; Controlling Separation in Turbomachines; Flow Control on Low-Pressure Turbine Airfoils Using Vortex Generator Jets; Reduced Order Modeling Incompressible Flows; Study and Control of Flow Past Disk, and Circular and Rectangular Cylinders Aligned in the Flow; Periodic Forcing of a Turbulent Axisymmetric Wake; Control of Vortex Breakdown in Critical Swirl Regime Using Azimuthal Forcing; External and Turbomachinery Flow Control Working Group; Boundary Layers, Transitions and Separation; Efficiency Considerations in Low Pressure Turbines; Summary of Conference; and Final Plenary Session Transcript.

Direct observation of vortex structure in a high-{Tc} YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} thin film by Bitter decoration method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sugimoto, Akira; Yamaguchi, Tetsuji; Iguchi, Ienari

1999-12-01

The Bitter decoration technique is one of the most powerful techniques to study the vortex structure of superconductor. The authors report the observation of vortex structure in a high {Tc} YBa{sub 2}Cu{sub 3}O{sub 7{minus}y} (YBCO) thin film by Bitter decoration method. The image of vortex structure was monitored by SEM, AFM and high resolution optical microscope. For magnetic field about 4--6mT, a vortex structure is seen. The vortex image varied with changing magnetic field. As compared with the vortex image of a Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+y} single crystal, the observed image appeared to be more randomly distributed.

The Vortex Lattice Method for the Rotor-Vortex Interaction Problem

NASA Technical Reports Server (NTRS)

Padakannaya, R.

1974-01-01

The rotor blade-vortex interaction problem and the resulting impulsive airloads which generate undesirable noise levels are discussed. A numerical lifting surface method to predict unsteady aerodynamic forces induced on a finite aspect ratio rectangular wing by a straight, free vortex placed at an arbitrary angle in a subsonic incompressible free stream is developed first. Using a rigid wake assumption, the wake vortices are assumed to move downsteam with the free steam velocity. Unsteady load distributions are obtained which compare favorably with the results of planar lifting surface theory. The vortex lattice method has been extended to a single bladed rotor operating at high advance ratios and encountering a free vortex from a fixed wing upstream of the rotor. The predicted unsteady load distributions on the model rotor blade are generally in agreement with the experimental results. This method has also been extended to full scale rotor flight cases in which vortex induced loads near the tip of a rotor blade were indicated. In both the model and the full scale rotor blade airload calculations a flat planar wake was assumed which is a good approximation at large advance ratios because the downwash is small in comparison to the free stream at large advance ratios. The large fluctuations in the measured airloads near the tip of the rotor blade on the advance side is predicted closely by the vortex lattice method.

A Method for Computing the Core Flow in Three-Dimensional Leading-Edge Vortices. Ph.D. Thesis - North Carolina State Univ.

NASA Technical Reports Server (NTRS)

Luckring, J. M.

1985-01-01

A theory is presented for calculating the flow in the core of a separation-induced leading-edge vortex. The method is based on matching inner and outer representations of the vortex. The inner model of the vortex is based on the quasicylindrical Navier-Stokes equations; the flow is assumed to be steady, axially symmetric, and incompressible and in addition, gradients in the radial direction are assumed to be much larger then gradients in the axial direction. The outer model is based on the three-dimensional free-vortex-sheet theory, a higher-order panel method which solves the Prandtl-Glauert equation including nonlinear boundary conditions pertinent to the concentrated vorticity representation of the leading edge vortex. The resultant flow is evaluated a posteriori for evidence of incipient vortex breakdown and the critical helix angle concept, in conjunction with an adverse longitudinal pressure gradient, is found to correlate well with the occurrence of vortex breakdown at the trailing edge of delta, arrow, and diamond wings.

Vortex mass in a superfluid

NASA Astrophysics Data System (ADS)

Simula, Tapio

2018-02-01

We consider the inertial mass of a vortex in a superfluid. We obtain a vortex mass that is well defined and is determined microscopically and self-consistently by the elementary excitation energy of the kelvon quasiparticle localized within the vortex core. The obtained result for the vortex mass is found to be consistent with experimental observations on superfluid quantum gases and vortex rings in water. We propose a method to measure the inertial rest mass and Berry phase of a vortex in superfluid Bose and Fermi gases.

A new methodology for free wake analysis using curved vortex elements

NASA Technical Reports Server (NTRS)

Bliss, Donald B.; Teske, Milton E.; Quackenbush, Todd R.

1987-01-01

A method using curved vortex elements was developed for helicopter rotor free wake calculations. The Basic Curve Vortex Element (BCVE) is derived from the approximate Biot-Savart integration for a parabolic arc filament. When used in conjunction with a scheme to fit the elements along a vortex filament contour, this method has a significant advantage in overall accuracy and efficiency when compared to the traditional straight-line element approach. A theoretical and numerical analysis shows that free wake flows involving close interactions between filaments should utilize curved vortex elements in order to guarantee a consistent level of accuracy. The curved element method was implemented into a forward flight free wake analysis, featuring an adaptive far wake model that utilizes free wake information to extend the vortex filaments beyond the free wake regions. The curved vortex element free wake, coupled with this far wake model, exhibited rapid convergence, even in regions where the free wake and far wake turns are interlaced. Sample calculations are presented for tip vortex motion at various advance ratios for single and multiple blade rotors. Cross-flow plots reveal that the overall downstream wake flow resembles a trailing vortex pair. A preliminary assessment shows that the rotor downwash field is insensitive to element size, even for relatively large curved elements.

3D Lagrangian VPM: simulations of the near-wake of an actuator disc and horizontal axis wind turbine

NASA Astrophysics Data System (ADS)

Berdowski, T.; Ferreira, C.; Walther, J.

2016-09-01

The application of a 3-dimensional Lagrangian vortex particle method has been assessed for modelling the near-wake of an axisymmetrical actuator disc and 3-bladed horizontal axis wind turbine with prescribed circulation from the MEXICO (Model EXperiments In COntrolled conditions) experiment. The method was developed in the framework of the open- source Parallel Particle-Mesh library for handling the efficient data-parallelism on a CPU (Central Processing Unit) cluster, and utilized a O(N log N)-type fast multipole method for computational acceleration. Simulations with the actuator disc resulted in a wake expansion, velocity deficit profile, and induction factor that showed a close agreement with theoretical, numerical, and experimental results from literature. Also the shear layer expansion was present; the Kelvin-Helmholtz instability in the shear layer was triggered due to the round-off limitations of a numerical method, but this instability was delayed to beyond 1 diameter downstream due to the particle smoothing. Simulations with the 3-bladed turbine demonstrated that a purely 3-dimensional flow representation is challenging to model with particles. The manifestation of local complex flow structures of highly stretched vortices made the simulation unstable, but this was successfully counteracted by the application of a particle strength exchange scheme. The axial and radial velocity profile over the near wake have been compared to that of the original MEXICO experiment, which showed close agreement between results.

Preliminary study of the three-dimensional deformation of the vortex in Karman vortex street

NASA Astrophysics Data System (ADS)

Ling, Guocan; Guo, Liang; Wu, Zuobin; Ma, Huiyang

1992-03-01

The mechanism for 3D evolution of the isolated Karman vortex and the thin-vortex filament in a circular cylinder wake is studied numerically using the LIA method. The results show that the vortex motion is unstable for small 3D disturbances in the separated wake of a circular cylinder. Karman vortex in the time-averaged wake flowfield wolves into a horseshoe-spoon-like 3D structure. The thin vortex filament deforms three-dimensionally in the braid and generates streamwise vortex structures which incline to the region maximum-deformation direction of the flowfield.

3D visualization of unsteady 2D airplane wake vortices

NASA Technical Reports Server (NTRS)

Ma, Kwan-Liu; Zheng, Z. C.

1994-01-01

Air flowing around the wing tips of an airplane forms horizontal tornado-like vortices that can be dangerous to following aircraft. The dynamics of such vortices, including ground and atmospheric effects, can be predicted by numerical simulation, allowing the safety and capacity of airports to be improved. In this paper, we introduce three-dimensional techniques for visualizing time-dependent, two-dimensional wake vortex computations, and the hazard strength of such vortices near the ground. We describe a vortex core tracing algorithm and a local tiling method to visualize the vortex evolution. The tiling method converts time-dependent, two-dimensional vortex cores into three-dimensional vortex tubes. Finally, a novel approach calculates the induced rolling moment on the following airplane at each grid point within a region near the vortex tubes and thus allows three-dimensional visualization of the hazard strength of the vortices. We also suggest ways of combining multiple visualization methods to present more information simultaneously.

Visualization of flow separation and control by vortex generators on an single flap in landing configuration

NASA Astrophysics Data System (ADS)

Součková, Natálie; Kuklová, Jana; Popelka, Lukáš; Matějka, Milan

2012-04-01

This paper focuses on a suppression of the flow separation, which occurs on a deflected flap, by means of vortex generators (VG's). An airfoil NACA 63A421 with a simple flap and vane-type vortex generators were used. The investigation was carried out by using experimental and numerical methods. The data from the numerical simulation of the flapped airfoil without VG's control were used for the vortex generator design. Two sizes, two different shapes and various spacing of the vortex generators were tested. The flow past the airfoil was visualized through three methods, namely tuft filaments technique, oil and thermo camera visualization. The experiments were performed in closed circuit wind tunnels with closed and open test sections. The lift curves for both cases without and with vortex generators were acquired for a lift coefficient improvement determination. The improvement was achieved for several cases by means all of the applied methods.

New techniques for experimental generation of two-dimensional blade-vortex interaction at low Reynolds numbers

NASA Technical Reports Server (NTRS)

Booth, E., Jr.; Yu, J. C.

1986-01-01

An experimental investigation of two dimensional blade vortex interaction was held at NASA Langley Research Center. The first phase was a flow visualization study to document the approach process of a two dimensional vortex as it encountered a loaded blade model. To accomplish the flow visualization study, a method for generating two dimensional vortex filaments was required. The numerical study used to define a new vortex generation process and the use of this process in the flow visualization study were documented. Additionally, photographic techniques and data analysis methods used in the flow visualization study are examined.

Study on Prediction of Underwater Radiated Noise from Propeller Tip Vortex Cavitation

NASA Astrophysics Data System (ADS)

Yamada, Takuyoshi; Sato, Kei; Kawakita, Chiharu; Oshima, Akira

2015-12-01

The method to predict underwater radiated noise from tip vortex cavitation was studied. The growth of a single cavitation bubble in tip vortex was estimated by substituting the tip vortex to Rankine combined vortex. The ideal spectrum function for the sound pressure generated by a single cavitation bubble was used, also the empirical factor for the number of collapsed bubbles per unit time was introduced. The estimated noise data were compared with measured ship's ones and it was found out that this method can estimate noise data within 3dB difference.

Exact density-potential pairs from complex-shifted axisymmetric systems

NASA Astrophysics Data System (ADS)

Ciotti, Luca; Marinacci, Federico

2008-07-01

In a previous paper, the complex-shift method has been applied to self-gravitating spherical systems, producing new analytical axisymmetric density-potential pairs. We now extend the treatment to the Miyamoto-Nagai disc and the Binney logarithmic halo, and we study the resulting axisymmetric and triaxial analytical density-potential pairs; we also show how to obtain the surface density of shifted systems from the complex shift of the surface density of the parent model. In particular, the systems obtained from Miyamoto-Nagai discs can be used to describe disc galaxies with a peanut-shaped bulge or with a central triaxial bar, depending on the direction of the shift vector. By using a constructive method that can be applied to generic axisymmetric systems, we finally show that the Miyamoto-Nagai and the Satoh discs, and the Binney logarithmic halo cannot be obtained from the complex shift of any spherical parent distribution. As a by-product of this study, we also found two new generating functions in closed form for even and odd Legendre polynomials, respectively.

Development of a nonlinear vortex method

NASA Technical Reports Server (NTRS)

Kandil, O. A.

1982-01-01

Steady and unsteady Nonliner Hybrid Vortex (NHV) method, for low aspect ratio wings at large angles of attack, is developed. The method uses vortex panels with first-order vorticity distribution (equivalent to second-order doublet distribution) to calculate the induced velocity in the near field using closed form expressions. In the far field, the distributed vorticity is reduced to concentrated vortex lines and the simpler Biot-Savart's law is employed. The method is applied to rectangular wings in steady and unsteady flows without any restriction on the order of magnitude of the disturbances in the flow field. The numerical results show that the method accurately predicts the distributed aerodynamic loads and that it is of acceptable computational efficiency.

A vortex wake capturing method for potential flow calculations

NASA Technical Reports Server (NTRS)

Murman, E. M.; Stremel, P. M.

1982-01-01

A method is presented for modifying finite difference solutions of the potential equation to include the calculation of non-planar vortex wake features. The approach is an adaptation of Baker's 'cloud in cell' algorithm developed for the stream function-vorticity equations. The vortex wake is tracked in a Lagrangian frame of reference as a group of discrete vortex filaments. These are distributed to the Eulerian mesh system on which the velocity is calculated by a finite difference solution of the potential equation. An artificial viscosity introduced by the finite difference equations removes the singular nature of the vortex filaments. Computed examples are given for the two-dimensional time dependent roll-up of vortex wakes generated by wings with different spanwise loading distributions.

A Rotor Tip Vortex Tracing Algorithm for Image Post-Processing

NASA Technical Reports Server (NTRS)

Overmeyer, Austin D.

2015-01-01

A neurite tracing algorithm, originally developed for medical image processing, was used to trace the location of the rotor tip vortex in density gradient flow visualization images. The tracing algorithm was applied to several representative test images to form case studies. The accuracy of the tracing algorithm was compared to two current methods including a manual point and click method and a cross-correlation template method. It is shown that the neurite tracing algorithm can reduce the post-processing time to trace the vortex by a factor of 10 to 15 without compromising the accuracy of the tip vortex location compared to other methods presented in literature.

Vortex methods for separated flows

NASA Technical Reports Server (NTRS)

Spalart, Philippe R.

1988-01-01

The numerical solution of the Euler or Navier-Stokes equations by Lagrangian vortex methods is discussed. The mathematical background is presented and includes the relationship with traditional point-vortex studies, convergence to smooth solutions of the Euler equations, and the essential differences between two and three-dimensional cases. The difficulties in extending the method to viscous or compressible flows are explained. Two-dimensional flows around bluff bodies are emphasized. Robustness of the method and the assessment of accuracy, vortex-core profiles, time-marching schemes, numerical dissipation, and efficient programming are treated. Operation counts for unbounded and periodic flows are given, and two algorithms designed to speed up the calculations are described.

Apparatus and method for generating swirling flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haden, Robert E.; Lorentz, Donald G.

An apparatus and method for generating a swirl is disclosed that is used to induce an axi-symmetric swirling flow to an incoming flow. The disclosed subject matter induces a uniform and axi-symmetric swirl, circumferentially around a discharge location, thus imparting a more accurate, repeatable, continuous, and controllable swirl and mixing condition of interest. Moreover, the disclosed subject matter performs the swirl injection at a lower pressure drop in comparison to a more traditional methods and devices.

Full-Potential Modeling of Blade-Vortex Interactions

DTIC Science & Technology

1997-12-01

modeled by any arbitrary distribution. Stremel (ref. 23) uses a method in which the vortex is modeled with an area-weighted distribution of vorticity. A...Helicopter Rotor. Ph.D. Thesis, StanfordUniv., 1978. 23. Stremel , P. M.: Computational Methods for Non-Planar Vortex Wake Flow Fields. M.S. Thesis

Excitation of high density surface plasmon polariton vortex array

NASA Astrophysics Data System (ADS)

Kuo, Chun-Fu; Chu, Shu-Chun

2018-06-01

This study proposes a method to excite surface plasmon polariton (SPP) vortex array of high spatial density on metal/air interface. A doughnut vector beam was incident at four rectangularly arranged slits to excite SPP vortex array. The doughnut vector beam used in this study has the same field intensity distribution as the regular doughnut laser mode, TEM01* mode, but a different polarization distribution. The SPP vortex array is achieved through the matching of both polarization state and phase state of the incident doughnut vector beam with the four slits. The SPP field distribution excited in this study contains stable array-distributed time-varying optical vortices. Theoretical derivation, analytical calculation and numerical simulation were used to discuss the characteristics of the induced SPP vortex array. The period of the SPP vortex array induced by the proposed method had only half SPPs wavelength. In addition, the vortex number in an excited SPP vortex array can be increased by enlarging the structure.

Rotor Wake Vortex Definition Using 3C-PIV Measurements: Corrected for Vortex Orientation

NASA Technical Reports Server (NTRS)

Burley, Casey L.; Brooks, Thomas F.; vanderWall, Berend; Richard, Hughues Richard; Raffel, Markus; Beaumier, Philippe; Delrieux, Yves; Lim, Joon W.; Yu, Yung H.; Tung, Chee

2003-01-01

Three-component (3-C) particle image velocimetry (PIV) measurements, within the wake across a rotor disk plane, are used to determine wake vortex definitions important for BVI (Blade Vortex Interaction) and broadband noise prediction. This study is part of the HART II test program conducted using a 40 percent scale BO-105 helicopter main rotor in the German-Dutch Wind Tunnel (DNW). In this paper, measurements are presented of the wake vortex field over the advancing side of the rotor operating at a typical descent landing condition. The orientations of the vortex (tube) axes are found to have non-zero tilt angles with respect to the chosen PIV measurement cut planes, often on the order of 45 degrees. Methods for determining the orientation of the vortex axis and reorienting the measured PIV velocity maps (by rotation/projection) are presented. One method utilizes the vortex core axial velocity component, the other utilizes the swirl velocity components. Key vortex parameters such as vortex core size, strength, and core velocity distribution characteristics are determined from the reoriented PIV velocity maps. The results are compared with those determined from velocity maps that are not corrected for orientation. Knowledge of magnitudes and directions of the vortex axial and swirl velocity components as a function of streamwise location provide a basis for insight into the vortex evolution.

Large Eddy Simulation of Crashback in Marine Propulsors

NASA Astrophysics Data System (ADS)

Jang, Hyunchul

Crashback is an operating condition to quickly stop a propelled vehicle, where the propeller is rotated in the reverse direction to yield negative thrust. The crashback condition is dominated by the interaction of the free stream flow with the strong reverse flow. This interaction forms a highly unsteady vortex ring, which is a very prominent feature of crashback. Crashback causes highly unsteady loads and flow separation on the blade surface. The unsteady loads can cause propulsor blade damage, and also affect vehicle maneuverability. Crashback is therefore well known as one of the most challenging propeller states to analyze. This dissertation uses Large-Eddy Simulation (LES) to predict the highly unsteady flow field in crashback. A non-dissipative and robust finite volume method developed by Mahesh et al. (2004) for unstructured grids is applied to flow around marine propulsors. The LES equations are written in a rotating frame of reference. The objectives of this dissertation are: (1) to understand the flow physics of crashback in marine propulsors with and without a duct, (2) to develop a finite volume method for highly skewed meshes which usually occur in complex propulsor geometries, and (3) to develop a sliding interface method for simulations of rotor-stator propulsor on parallel platforms. LES is performed for an open propulsor in crashback and validated against experiments performed by Jessup et al. (2004). The LES results show good agreement with experiments. Effective pressures for thrust and side-force are introduced to more clearly understand the physical sources of thrust and side-force. Both thrust and side-force are seen to be mainly generated from the leading edge of the suction side of the propeller. This implies that thrust and side-force have the same source---the highly unsteady leading edge separation. Conditional averaging is performed to obtain quantitative information about the complex flow physics of high- or low-amplitude events. The events for thrust and side force show the same tendency. The conditional averages show that during high amplitude events, the vortex ring core is closer to the propeller blades, the reverse flow induced by the propeller rotation is lower, the forward flow is higher at the root of the blades, and leading and trailing edge flow separations are larger. The instantaneous flow field shows that during low amplitude events, the vortex ring is more axisymmetric and the stronger reverse flow induced by the vortex ring suppresses the forward flow so that flow separation on the blades is smaller. During high amplitude events, the vortex ring is less coherent and the weaker reverse flow cannot overcome the forward flow. The stronger forward flow makes flow separation on the blades larger. The effect of a duct on crashback is studied with LES. Thrust mostly arises from the blade surface, but most of side-force is generated from the duct surface. Both mean and RMS of pressure are much higher on inner surface of duct, especially near blade tips. This implies that side-force on the ducted propulsor is caused by the blade-duct interaction. Strong tip leakage flow is observed behind the suction side at the tip gap. The physical source of the tip leakage flow is seen to be the large pressure difference between pressure and suction sides. The conditional average for high amplitude event shows consistent results; the tip leakage flow and pressure difference are significantly higher when thrust and side-force are higher. A sliding interface method is developed to allow simulations of rotor-stator propulsor in crashback. The method allows relative rotations between different parts of the computational grid. Search algorithm for sliding elements, data structures for message passing, and accurate interpolation scheme at the sliding interface are developed for arbitrary shaped unstructured grids on parallel computing platforms. Preliminary simulations of open propulsor in crashback show reasonable performance.

Application of the vortex-lattice technique to the analysis of thin wings with vortex separation and thick multi-element wings

NASA Technical Reports Server (NTRS)

Smith, C. W.; Bhateley, I. C.

1976-01-01

Two techniques for extending the range of applicability of the basic vortex-lattice method are discussed. The first improves the computation of aerodynamic forces on thin, low-aspect-ratio wings of arbitrary planforms at subsonic Mach numbers by including the effects of leading-edge and tip vortex separation, characteristic of this type wing, through use of the well-known suction-analogy method of E. C. Polhamus. Comparisons with experimental data for a variety of planforms are presented. The second consists of the use of the vortex-lattice method to predict pressure distributions over thick multi-element wings (wings with leading- and trailing-edge devices). A method of laying out the lattice is described which gives accurate pressures on the top and part of the bottom surface of the wing. Limited comparisons between the result predicted by this method, the conventional lattice arrangement method, experimental data, and 2-D potential flow analysis techniques are presented.

Use of a microwave diagnostics technique to measure the temperature of an axisymmetric ionized gas flow

NASA Astrophysics Data System (ADS)

Tsel'Sov, Iu. G.; Kondrat'ev, A. S.

1990-12-01

A method is developed for determining the temperature of an ionized gas on the basis of electron-density sounding. This technique is used to measure the cross-sectional temperature distribution of an axisymmetric ionized gas flow using microwave diagnostics.

A vortex-lattice method for the mean camber shapes of trimmed noncoplanar planforms with minimum vortex drag

NASA Technical Reports Server (NTRS)

Lamar, J. E.

1976-01-01

A new subsonic method has been developed by which the mean camber surface can be determined for trimmed noncoplanar planforms with minimum vortex drag. This method uses a vortex lattice and overcomes previous difficulties with chord loading specification. A Trefftz plane analysis is utilized to determine the optimum span loading for minimum drag, then solved for the mean camber surface of the wing, which provides the required loading. Sensitivity studies, comparisons with other theories, and applications to configurations which include a tandem wing and a wing winglet combination have been made and are presented.

Frequency-feature based antistrong-disturbance signal processing method and system for vortex flowmeter with single sensor

NASA Astrophysics Data System (ADS)

Xu, Ke-Jun; Luo, Qing-Lin; Wang, Gang; Liu, San-Shan; Kang, Yi-Bo

2010-07-01

Digital signal processing methods have been applied to vortex flowmeter for extracting the useful information from noisy output of the vortex flow sensor. But these approaches are unavailable when the power of the mechanical vibration noise is larger than that of the vortex flow signal. In order to solve this problem, an antistrong-disturbance signal processing method is proposed based on frequency features of the vortex flow signal and mechanical vibration noise for the vortex flowmeter with single sensor. The frequency bandwidth of the vortex flow signal is different from that of the mechanical vibration noise. The autocorrelation function can represent bandwidth features of the signal and noise. The output of the vortex flow sensor is processed by the spectrum analysis, filtered by bandpass filters, and calculated by autocorrelation function at the fixed delaying time and at τ =0 to obtain ratios. The frequency corresponding to the minimal ratio is regarded as the vortex flow frequency. With an ultralow-power microcontroller, a digital signal processing system is developed to implement the antistrong-disturbance algorithm, and at the same time to ensure low-power and two-wire mode for meeting the requirement of process instrumentation. The water flow-rate calibration and vibration test experiments are conducted, and the experimental results show that both the algorithm and system are effective.

Frequency-feature based antistrong-disturbance signal processing method and system for vortex flowmeter with single sensor.

PubMed

Xu, Ke-Jun; Luo, Qing-Lin; Wang, Gang; Liu, San-Shan; Kang, Yi-Bo

2010-07-01

Digital signal processing methods have been applied to vortex flowmeter for extracting the useful information from noisy output of the vortex flow sensor. But these approaches are unavailable when the power of the mechanical vibration noise is larger than that of the vortex flow signal. In order to solve this problem, an antistrong-disturbance signal processing method is proposed based on frequency features of the vortex flow signal and mechanical vibration noise for the vortex flowmeter with single sensor. The frequency bandwidth of the vortex flow signal is different from that of the mechanical vibration noise. The autocorrelation function can represent bandwidth features of the signal and noise. The output of the vortex flow sensor is processed by the spectrum analysis, filtered by bandpass filters, and calculated by autocorrelation function at the fixed delaying time and at tau=0 to obtain ratios. The frequency corresponding to the minimal ratio is regarded as the vortex flow frequency. With an ultralow-power microcontroller, a digital signal processing system is developed to implement the antistrong-disturbance algorithm, and at the same time to ensure low-power and two-wire mode for meeting the requirement of process instrumentation. The water flow-rate calibration and vibration test experiments are conducted, and the experimental results show that both the algorithm and system are effective.

An improved panel method for the solution of three-dimensional leading-edge vortex flows. Volume 1: Theory document

NASA Technical Reports Server (NTRS)

Johnson, F. T.; Lu, P.; Tinoco, E. N.

1980-01-01

An improved panel method for the solution of three dimensional flow and wing and wing-body combinations with leading edge vortex separation is presented. The method employs a three dimensional inviscid flow model in which the configuration, the rolled-up vortex sheets, and the wake are represented by quadratic doublet distributions. The strength of the singularity distribution as well as shape and position of the vortex spirals are computed in an iterative fashion starting with an assumed initial sheet geometry. The method calculates forces and moments as well as detail surface pressure distributions. Improvements include the implementation of improved panel numerics for the purpose of elimination the highly nonlinear effects of ring vortices around double panel edges, and the development of a least squares procedure for damping vortex sheet geometry update instabilities. A complete description of the method is included. A variety of cases generated by the computer program implementing the method are presented which verify the mathematical assumptions of the method and which compare computed results with experimental data to verify the underlying physical assumptions made by the method.

Guiding principles for vortex flow controls

NASA Technical Reports Server (NTRS)

Wu, J. Z.; Wu, J. M.

1991-01-01

In the practice of vortex flow controls, the most important factor is that the persistency and obstinacy of a concentrated vortex depend on its stability and dissipation. In this paper, the modern nonlinear stability theory for circulation-preserving flows is summarized, and the dissipation for general viscous flows is analyzed in terms of the evolution of total enstrophy. These analyses provide a theoretical base for understanding relevant physics of vortex flows, and lead to some guiding principles and methods for their controls. Case studies taken from various theoretical and/or experimental works of vortex controls, due to the present authors as well as others, confirm the feasibility of the recommended principles and methods.

The challenges of simulating wake vortex encounters and assessing separation criteria

NASA Technical Reports Server (NTRS)

Dunham, R. E.; Stuever, Robert A.; Vicroy, Dan D.

1993-01-01

During landings and take-offs, the longitudinal spacing between airplanes is in part determined by the safe separation required to avoid the trailing vortex wake of the preceding aircraft. Safe exploration of the feasibility of reducing longitudinal separation standards will require use of aircraft simulators. This paper discusses the approaches to vortex modeling, methods for modeling the aircraft/vortex interaction, some of the previous attempts of defining vortex hazard criteria, and current understanding of the development of vortex hazard criteria.

A computational study on the interaction between a vortex and a shock wave

NASA Technical Reports Server (NTRS)

Meadows, Kristine R.; Kumar, Ajay; Hussaini, M. Y.

1989-01-01

A computational study of two-dimensional shock vortex interaction is discussed in this paper. A second order upwind finite volume method is used to solve the Euler equations in conservation form. In this method, the shock wave is captured rather than fitted so that the cases where shock vortex interaction may cause secondary shocks can also be investigated. The effects of vortex strength on the computed flow and acoustic field generated by the interaction are qualitatively evaluated.

Time-dependent solution for axisymmetric flow over a blunt body with ideal gas, CF4, or equilibrium air chemistry

NASA Technical Reports Server (NTRS)

Hamilton, H. H., II; Spall, J. R.

1986-01-01

A time-asymptotic method has been used to obtain steady-flow solutions for axisymmetric inviscid flow over several blunt bodies including spheres, paraboloids, ellipsoids, and spherically blunted cones. Comparisons with experimental data and results of other computational methods have demonstrated that accurate solutions can be obtained using this approach. The method should prove useful as an analysis tool for comparing with experimental data and for making engineering calculations for blunt reentry vehicles.

Time-dependent solution for axisymmetric flow over a blunt body with ideal gas, CF4, or equilibrium air chemistry

NASA Astrophysics Data System (ADS)

Hamilton, H. H., II; Spall, J. R.

1986-07-01

A time-asymptotic method has been used to obtain steady-flow solutions for axisymmetric inviscid flow over several blunt bodies including spheres, paraboloids, ellipsoids, and spherically blunted cones. Comparisons with experimental data and results of other computational methods have demonstrated that accurate solutions can be obtained using this approach. The method should prove useful as an analysis tool for comparing with experimental data and for making engineering calculations for blunt reentry vehicles.

Fast multipole methods on a cluster of GPUs for the meshless simulation of turbulence

NASA Astrophysics Data System (ADS)

Yokota, R.; Narumi, T.; Sakamaki, R.; Kameoka, S.; Obi, S.; Yasuoka, K.

2009-11-01

Recent advances in the parallelizability of fast N-body algorithms, and the programmability of graphics processing units (GPUs) have opened a new path for particle based simulations. For the simulation of turbulence, vortex methods can now be considered as an interesting alternative to finite difference and spectral methods. The present study focuses on the efficient implementation of the fast multipole method and pseudo-particle method on a cluster of NVIDIA GeForce 8800 GT GPUs, and applies this to a vortex method calculation of homogeneous isotropic turbulence. The results of the present vortex method agree quantitatively with that of the reference calculation using a spectral method. We achieved a maximum speed of 7.48 TFlops using 64 GPUs, and the cost performance was near 9.4/GFlops. The calculation of the present vortex method on 64 GPUs took 4120 s, while the spectral method on 32 CPUs took 4910 s.

Long-lived Dust Asymmetries at Dead Zone Edges in Protoplanetary Disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miranda, Ryan; Li, Hui; Li, Shengtai

A number of transition disks exhibit significant azimuthal asymmetries in thermal dust emission. One possible origin for these asymmetries is dust trapping in vortices formed at the edges of dead zones. We carry out high-resolution, two-dimensional hydrodynamic simulations of this scenario, including the effects of dust feedback. We find that, although feedback weakens the vortices and slows down the process of dust accumulation, the dust distribution in the disk can nonetheless remain asymmetric for many thousands of orbits. We show that even after 10{sup 4} orbits, or 2.5 Myr when scaled to the parameters of Oph IRS 48 (a significantmore » fraction of its age), the dust is not dispersed into an axisymmetric ring, in contrast to the case of a vortex formed by a planet. This is because accumulation of mass at the dead zone edge constantly replenishes the vortex, preventing it from being fully destroyed. We produce synthetic dust emission images using our simulation results. We find that multiple small clumps of dust may be distributed azimuthally. These clumps, if not resolved from one another, appear as a single large feature. A defining characteristic of a disk with a dead zone edge is that an asymmetric feature is accompanied by a ring of dust located about twice as far from the central star.« less

Configuration of ripple domains and their topological defects formed under local mechanical stress on hexagonal monolayer graphene

DOE PAGES

Park, Yeonggu; Choi, Jin Sik; Choi, Taekjib; ...

2015-03-24

Ripples in graphene are extensively investigated because they ensure the mechanical stability of two-dimensional graphene and affect its electronic properties. They arise from spontaneous symmetry breaking and are usually manifested in the form of domains with long-range order. It is expected that topological defects accompany a material exhibiting long-range order, whose functionality depends on characteristics of domains and topological defects. However, there remains a lack of understanding regarding ripple domains and their topological defects formed on monolayer graphene. Here we explore configuration of ripple domains and their topological defects in exfoliated monolayer graphenes on SiO₂/Si substrates using transverse shear microscope.more » We observe three-color domains with three different ripple directions, which meet at a core. Furthermore, the closed domain is surrounded by an even number of cores connected together by domain boundaries, similar to topological vortex and anti-vortex pairs. In addition, we have found that axisymmetric three-color domains can be induced around nanoparticles underneath the graphene. This fascinating configuration of ripple domains may result from the intrinsic hexagonal symmetry of two-dimensional graphene, which is supported by theoretical simulation using molecular dynamics. Our findings are expected to play a key role in understanding of ripple physics in graphene and other two-dimensional materials.« less

Configuration of ripple domains and their topological defects formed under local mechanical stress on hexagonal monolayer graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Yeonggu; Choi, Jin Sik; Choi, Taekjib

Ripples in graphene are extensively investigated because they ensure the mechanical stability of two-dimensional graphene and affect its electronic properties. They arise from spontaneous symmetry breaking and are usually manifested in the form of domains with long-range order. It is expected that topological defects accompany a material exhibiting long-range order, whose functionality depends on characteristics of domains and topological defects. However, there remains a lack of understanding regarding ripple domains and their topological defects formed on monolayer graphene. Here we explore configuration of ripple domains and their topological defects in exfoliated monolayer graphenes on SiO₂/Si substrates using transverse shear microscope.more » We observe three-color domains with three different ripple directions, which meet at a core. Furthermore, the closed domain is surrounded by an even number of cores connected together by domain boundaries, similar to topological vortex and anti-vortex pairs. In addition, we have found that axisymmetric three-color domains can be induced around nanoparticles underneath the graphene. This fascinating configuration of ripple domains may result from the intrinsic hexagonal symmetry of two-dimensional graphene, which is supported by theoretical simulation using molecular dynamics. Our findings are expected to play a key role in understanding of ripple physics in graphene and other two-dimensional materials.« less

An Approximate Axisymmetric Viscous Shock Layer Aeroheating Method for Three-Dimensional Bodies

NASA Technical Reports Server (NTRS)

Brykina, Irina G.; Scott, Carl D.

1998-01-01

A technique is implemented for computing hypersonic aeroheating, shear stress, and other flow properties on the windward side of a three-dimensional (3D) blunt body. The technique uses a 2D/axisymmetric flow solver modified by scale factors for a, corresponding equivalent axisymmetric body. Examples are given in which a 2D solver is used to calculate the flow at selected meridional planes on elliptic paraboloids in reentry flight. The report describes the equations and the codes used to convert the body surface parameters into input used to scale the 2D viscous shock layer equations in the axisymmetric viscous shock layer code. Very good agreement is obtained with solutions to finite rate chemistry 3D thin viscous shock layer equations for a finite rate catalytic body.

Recent theoretical developments and experimental studies pertinent to vortex flow aerodynamics - With a view towards design

NASA Technical Reports Server (NTRS)

Lamar, J. E.; Luckring, J. M.

1978-01-01

A review is presented of recent progress in a research program directed towards the development of an improved vortex-flow technology base. It is pointed out that separation induced vortex-flows from the leading and side edges play an important role in the high angle-of-attack aerodynamic characteristics of a wide range of modern aircraft. In the analysis and design of high-speed aircraft, a detailed knowledge of this type of separation is required, particularly with regard to critical wind loads and the stability and performance at various off-design conditions. A description of analytical methods is presented. The theoretical methods employed are divided into two classes which are dependent upon the underlying aerodynamic assumptions. One conical flow method is considered along with three different nonconical flow methods. Comparisons are conducted between the described methods and available aerodynamic data. Attention is also given to a vortex flow drag study and a vortex flow wing design using suction analogy.

A method for modeling finite-core vortices in wake-flow calculations

NASA Technical Reports Server (NTRS)

Stremel, P. M.

1984-01-01

A numerical method for computing nonplanar vortex wakes represented by finite-core vortices is presented. The approach solves for the velocity on an Eulerian grid, using standard finite-difference techniques; the vortex wake is tracked by Lagrangian methods. In this method, the distribution of continuous vorticity in the wake is replaced by a group of discrete vortices. An axially symmetric distribution of vorticity about the center of each discrete vortex is used to represent the finite-core model. Two distributions of vorticity, or core models, are investigated: a finite distribution of vorticity represented by a third-order polynomial, and a continuous distribution of vorticity throughout the wake. The method provides for a vortex-core model that is insensitive to the mesh spacing. Results for a simplified case are presented. Computed results for the roll-up of a vortex wake generated by wings with different spanwise load distributions are presented; contour plots of the flow-field velocities are included; and comparisons are made of the computed flow-field velocities with experimentally measured velocities.

Multimodel Ensemble Methods for Prediction of Wake-Vortex Transport and Decay Originating NASA

NASA Technical Reports Server (NTRS)

Korner, Stephan; Ahmad, Nashat N.; Holzapfel, Frank; VanValkenburg, Randal L.

2017-01-01

Several multimodel ensemble methods are selected and further developed to improve the deterministic and probabilistic prediction skills of individual wake-vortex transport and decay models. The different multimodel ensemble methods are introduced, and their suitability for wake applications is demonstrated. The selected methods include direct ensemble averaging, Bayesian model averaging, and Monte Carlo simulation. The different methodologies are evaluated employing data from wake-vortex field measurement campaigns conducted in the United States and Germany.

VORCOR: A computer program for calculating characteristics of wings with edge vortex separation by using a vortex-filament and-core model

NASA Technical Reports Server (NTRS)

Pao, J. L.; Mehrotra, S. C.; Lan, C. E.

1982-01-01

A computer code base on an improved vortex filament/vortex core method for predicting aerodynamic characteristics of slender wings with edge vortex separations is developed. The code is applicable to camber wings, straked wings or wings with leading edge vortex flaps at subsonic speeds. The prediction of lifting pressure distribution and the computer time are improved by using a pair of concentrated vortex cores above the wing surface. The main features of this computer program are: (1) arbitrary camber shape may be defined and an option for exactly defining leading edge flap geometry is also provided; (2) the side edge vortex system is incorporated.

Influence of Structural Parameters on the Performance of Vortex Valve Variable-Thrust Solid Rocket Motor

NASA Astrophysics Data System (ADS)

Wei, Xianggeng; Li, Jiang; He, Guoqiang

2017-04-01

The vortex valve solid variable thrust motor is a new solid motor which can achieve Vehicle system trajectory optimization and motor energy management. Numerical calculation was performed to investigate the influence of vortex chamber diameter, vortex chamber shape, and vortex chamber height of the vortex valve solid variable thrust motor on modulation performance. The test results verified that the calculation results are consistent with laboratory results with a maximum error of 9.5%. The research drew the following major conclusions: the optimal modulation performance was achieved in a cylindrical vortex chamber, increasing the vortex chamber diameter improved the modulation performance of the vortex valve solid variable thrust motor, optimal modulation performance could be achieved when the height of the vortex chamber is half of the vortex chamber outlet diameter, and the hot gas control flow could result in an enhancement of modulation performance. The results can provide the basis for establishing the design method of the vortex valve solid variable thrust motor.

The Fine Transverse Structure of a Vortex Flow Beyond the Edge of a Disc Rotating in a Stratified Fluid

NASA Astrophysics Data System (ADS)

Chashechkin, Yu. D.; Bardakov, R. N.

2018-02-01

By the methods of schlieren visualization, the evolution of elements of the fine structure of transverse vortex loops formed in the circular vortex behind the edge of a disk rotating in a continuously stratified fluid is traced for the first time. An inhomogeneous distribution of the density of a table-salt solution in a basin was formed by the continuous-squeezing method. The development of periodic perturbations at the outer boundary of the circular vortex and their transformation at the vortex-loop vertex are traced. A slow change in the angular size of the structural elements in the supercritical-flow mode is noted.

Large-eddy substitution via vortex cancellation for wall turbulence control

NASA Technical Reports Server (NTRS)

Mcginley, C. B.; Beeler, G. B.

1985-01-01

A system of co-rotating longitudinal vortices was used to introduce streamline (as opposed to wall) curvature into a turbulent wall flow. Two methods of vortex cancellation, unwinding and self-annihilation, were tested as a means of removing the vortices once they had processed most of the incoming turbulent boundary layer. Vortex unwinding, which uses vorticity of the opposite sign, was shown to be a viable method for cancelling the co-rotating vortices. Vortex self-annihilation, caused by interference effects resulting from a close initial spanwise vortex spacing, eliminated the vortices within 60 delta downstream. In each case, reductions in boundary layer entrainment were found once the vortices were cancelled.

Influence of air-jet vortex generator diameter on separation region

NASA Astrophysics Data System (ADS)

Szwaba, Ryszard

2013-08-01

Control of shock wave and boundary layer interaction continues to attract a lot of attention. In recent decades several methods of interaction control have been investigated. The research has mostly concerned solid (vane type) vortex generators and transpiration methods of suction and blowing. This investigation concerns interaction control using air-jets to generate streamwise vortices. The effectiveness of air-jet vortex generators in controlling separation has been proved in a previous research. The present paper focuses on the influence of the vortex generator diameter on the separation region. It presents the results of experimental investigations and provides new guidelines for the design of air-jet vortex generators to obtain more effective separation control.

Three-dimensional simulation of the free shear layer using the vortex-in-cell method

NASA Technical Reports Server (NTRS)

Couet, B.; Buneman, O.; Leonard, A.

1979-01-01

We present numerical simulations of the evolution of a mixing layer from an initial state of uniform vorticity with simple two- and three-dimensional small perturbations. A new method for tracing a large number of three-dimensional vortex filaments is used in the simulations. Vortex tracing by Biot-Savart interaction originally implied ideal (non-viscous) flow, but we use a 3-d mesh, Fourier transforms and filtering for vortex tracing, which implies 'modeling' of subgrid scale motion and hence some viscosity. Streamwise perturbations lead to the usual roll-up of vortex patterns with spanwise uniformity maintained. Remarkably, spanwise perturbations generate streamwise distortions of the vortex filaments and the combination of both perturbations leads to patterns with interesting features discernable in the movies and in the records of enstrophy and energy for the three components of the flow.

Dynamic Control of the Vortex Pinning Potential in a Superconductor Using Current Injection through Nanoscale Patterns.

PubMed

Kalcheim, Yoav; Katzir, Eran; Zeides, Felix; Katz, Nadav; Paltiel, Yossi; Millo, Oded

2017-05-10

Control over the vortex potential at the nanoscale in a superconductor is a subject of great interest for both fundamental and technological reasons. Many methods for achieving artificial pinning centers have been demonstrated, for example, with magnetic nanostructures or engineered imperfections, yielding many intriguing effects. However, these pinning mechanisms do not offer dynamic control over the strength of the patterned vortex potential because they involve static nanostructures created in or near the superconductor. Dynamic control has been achieved with scanning probe methods on the single vortex level but these are difficult so scale up. Here, we show that by applying controllable nanopatterned current injection, the superconductor can be locally driven out of equilibrium, creating an artificial vortex potential that can be tuned by the magnitude of the injected current, yielding a unique vortex channeling effect.

Effect of the pool depth on drop impact splashing

NASA Astrophysics Data System (ADS)

Chizari, Hossain; Thoraval, Marie-Jean

2017-11-01

We investigate the effect of the pool depth on the splashing dynamics of drop impact. The splashing of a single drop impacting into a deep pool or on wet surface has been investigated for many years both numerically and experimentally. However, recent results have demonstrated the importance of the vorticity produced during the impact on the splashing behavior. More specifically, the shedding of a vortex ring inside the liquid during the impact can separate the splash jet into several parts. The shedding of the vorticity can be influenced by the proximity of the bottom of the pool, if the pool depth is small enough. We study here how the pool depth can affect the vorticity shedding and the resulting splashing jets. We perform axisymmetric numerical simulations of the impacts with the open sources codes Gerris and Basilisk, and systematically vary the impact conditions, focusing on the effect of pool depth in the splashing regimes.

An Experimental Investigation of Jet Noise from Septa Nozzles

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Bridges, J. E.; Fagan, A. F.; Brown, C. A.

2016-01-01

Results of an experimental study with a large aspect ratio rectangular nozzle, divided into multiple compartments or septa, as pertinent to distributed propulsion, are presented. Noise measurements at high-subsonic conditions show that the nozzle with the septa is quieter than the corresponding baseline nozzle without the septa. At relatively lower Mach numbers a high-frequency tone is heard. This is shown to be due to Karmann vortex shedding from the trailing edge of the partitions that separate a septum from the adjacent ones. Flowfield measurements for a six septa case show that the cellular flow structure, issuing from the nozzle, goes through a curious coalescence with increasing downstream distance (x) from the nozzle. Adjacent cells pair to yield a three-cell structure by x/D =2, where D is the equivalent diameter of the baseline nozzle. By about x/D =16, both the septa case and the baseline case evolve to yield axisymmetric flowfields.

Mixing Enhancement by Tabs in Round Supersonic Jets

NASA Technical Reports Server (NTRS)

Seiner, John M.; Grosch, C. E.

1998-01-01

The objective of this study was to analyze jet plume mass flow entrainment rates associated with the introduction of counter-rotating streamwise vorticity by prism shaped devices (tabs) located at the lip of the nozzle. We have examined the resulting mixing process through coordinated experimental tests and numerical simulations of the supersonic flow from a model axisymmetric nozzle. In the numerical simulations, the total induced vorticity was held constant while varying the distribution of counter-rotating vorticity around the nozzle lip training edge. In the experiment, the number of tabs applied was varied while holding the total projected area constant. Evaluations were also conducted on initial vortex strength. The results of this work show that the initial growth rate of the jet shear layer is increasingly enhanced as more tabs are added, but that the lowest tab count results in the largest entrained mass flow. The numerical simulations confirm these results.

Fluid Mechanics Optimising Organic Synthesis

NASA Astrophysics Data System (ADS)

Leivadarou, Evgenia; Dalziel, Stuart

2015-11-01

The Vortex Fluidic Device (VFD) is a new ``green'' approach in the synthesis of organic chemicals with many industrial applications in biodiesel generation, cosmetics, protein folding and pharmaceutical production. The VFD is a rapidly rotating tube that can operate with a jet feeding drops of liquid reactants to the base of the tube. The aim of this project is to explain the fluid mechanics of the VFD that influence the rate of reactions. The reaction rate is intimately related to the intense shearing that promotes collision between reactant molecules. In the VFD, the highest shears are found at the bottom of the tube in the Rayleigh and the Ekman layer and at the walls in the Stewardson layers. As a step towards optimising the performance of the VFD we present experiments conducted in order to establish the minimum drop volume and maximum rotation rate for maximum axisymmetric spreading without fingering instability. PhD candidate, Department of Applied Mathematics and Theoretical Physics.

Vortex Thermometry for Turbulent Two-Dimensional Fluids.

PubMed

Groszek, Andrew J; Davis, Matthew J; Paganin, David M; Helmerson, Kristian; Simula, Tapio P

2018-01-19

We introduce a new method of statistical analysis to characterize the dynamics of turbulent fluids in two dimensions. We establish that, in equilibrium, the vortex distributions can be uniquely connected to the temperature of the vortex gas, and we apply this vortex thermometry to characterize simulations of decaying superfluid turbulence. We confirm the hypothesis of vortex evaporative heating leading to Onsager vortices proposed in Phys. Rev. Lett. 113, 165302 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.165302, and we find previously unidentified vortex power-law distributions that emerge from the dynamics.

Devices that Alter the Tip Vortex of a Rotor

NASA Technical Reports Server (NTRS)

McAlister, Kenneth W.; Tung, Chee; Heineck, James T.

2001-01-01

Small devices were attached near the tip of a hovering rotor blade 'in order to alter the structure and trajectory of the trailing vortex. Stereo particle image velocimetry (PIV) images were used to quantify the wake behind the rotor blade during the first revolution. A procedure for analyzing the 3D-velocity field is presented that includes a method for accounting for vortex wander. The results show that a vortex generator can alter the trajectory of the trailing vortex and that a major change in the size and intensity of the trailing vortex can be achieved by introducing a high level of turbulence into the core of the vortex.

Aperiodicity Correction for Rotor Tip Vortex Measurements

NASA Technical Reports Server (NTRS)

Ramasamy, Manikandan; Paetzel, Ryan; Bhagwat, Mahendra J.

2011-01-01

The initial roll-up of a tip vortex trailing from a model-scale, hovering rotor was measured using particle image velocimetry. The unique feature of the measurements was that a microscope was attached to the camera to allow much higher spatial resolution than hitherto possible. This also posed some unique challenges. In particular, the existing methodologies to correct for aperiodicity in the tip vortex locations could not be easily extended to the present measurements. The difficulty stemmed from the inability to accurately determine the vortex center, which is a prerequisite for the correction procedure. A new method is proposed for determining the vortex center, as well as the vortex core properties, using a least-squares fit approach. This approach has the obvious advantage that the properties are derived from not just a few points near the vortex core, but from a much larger area of flow measurements. Results clearly demonstrate the advantage in the form of reduced variation in the estimated core properties, and also the self-consistent results obtained using three different aperiodicity correction methods.

Photogrammetric technique for in-flight ranging of trailing vortices using entrained balloons

NASA Technical Reports Server (NTRS)

Snow, Walter L.; Burner, Alpheus W.; Goad, William K.

1989-01-01

A method for experimentally determining the radial distance of a probe aircraft from a trailing vortex is described. The method relies on photogrammetric triangulation of targets entrained in the vortex core. The theory and preliminary testing were described using laboratory mock-ups. Solid state video cameras were to provide data at 300 Hz rates. Practical methods for seeding the vortex are under separate investigation and are not addressed.

Boundary element analysis of corrosion problems for pumps and pipes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miyasaka, M.; Amaya, K.; Kishimoto, K.

1995-12-31

Three-dimensional (3D) and axi-symmetric boundary element methods (BEM) were developed to quantitatively estimate cathodic protection and macro-cell corrosion. For 3D analysis, a multiple-region method (MRM) was developed in addition to a single-region method (SRM). The validity and usefulness of the BEMs were demonstrated by comparing numerical results with experimental data from galvanic corrosion systems of a cylindrical model and a seawater pipe, and from a cathodic protection system of an actual seawater pump. It was shown that a highly accurate analysis could be performed for fluid machines handling seawater with complex 3D fields (e.g. seawater pump) by taking account ofmore » flow rate and time dependencies of polarization curve. Compared to the 3D BEM, the axi-symmetric BEM permitted large reductions in numbers of elements and nodes, which greatly simplified analysis of axi-symmetric fields such as pipes. Computational accuracy and CPU time were compared between analyses using two approximation methods for polarization curves: a logarithmic-approximation method and a linear-approximation method.« less

Multipole Vortex Blobs (MVB): Symplectic Geometry and Dynamics.

PubMed

Holm, Darryl D; Jacobs, Henry O

2017-01-01

Vortex blob methods are typically characterized by a regularization length scale, below which the dynamics are trivial for isolated blobs. In this article, we observe that the dynamics need not be trivial if one is willing to consider distributional derivatives of Dirac delta functionals as valid vorticity distributions. More specifically, a new singular vortex theory is presented for regularized Euler fluid equations of ideal incompressible flow in the plane. We determine the conditions under which such regularized Euler fluid equations may admit vorticity singularities which are stronger than delta functions, e.g., derivatives of delta functions. We also describe the symplectic geometry associated with these augmented vortex structures, and we characterize the dynamics as Hamiltonian. Applications to the design of numerical methods similar to vortex blob methods are also discussed. Such findings illuminate the rich dynamics which occur below the regularization length scale and enlighten our perspective on the potential for regularized fluid models to capture multiscale phenomena.

Vortices and turbulence (The 23rd Lanchester Memorial Lecture)

NASA Astrophysics Data System (ADS)

Lilley, G. M.

1983-12-01

A comprehensive discussion is presented concerning the phenomena characteristically treated in vortex and turbulence theory, as well as the degree of success achieved by various computation and visualization methods and theoretical models developed for vortex flow behavior prediction. Note is taken of the pioneering research conducted by F. W. Lanchester in 1893-1907, and attention is given to vortex tip and edge generation by rectangular and delta wings, the cool core effect of the Ranque-Hilsch vortex tube, the modeling of shear flows by means of vortex array methods, the classification and modelling of turbulent flows (together with a taxonomy of their calculation methods), and NASA ILLIAC IV computations of two-dimensional channel flow. Also noted are recent results concerning the boundary layer coherent structure of a flat plate at zero pressure gradient, including the regeneration structure and flow distortion and breakdown of a turbulent boundary layer.

An Organic Vortex Laser.

PubMed

Stellinga, Daan; Pietrzyk, Monika E; Glackin, James M E; Wang, Yue; Bansal, Ashu K; Turnbull, Graham A; Dholakia, Kishan; Samuel, Ifor D W; Krauss, Thomas F

2018-03-27

Optical vortex beams are at the heart of a number of novel research directions, both as carriers of information and for the investigation of optical activity and chiral molecules. Optical vortex beams are beams of light with a helical wavefront and associated orbital angular momentum. They are typically generated using bulk optics methods or by a passive element such as a forked grating or a metasurface to imprint the required phase distribution onto an incident beam. Since many applications benefit from further miniaturization, a more integrated yet scalable method is highly desirable. Here, we demonstrate the generation of an azimuthally polarized vortex beam directly by an organic semiconductor laser that meets these requirements. The organic vortex laser uses a spiral grating as a feedback element that gives control over phase, handedness, and degree of helicity of the emitted beam. We demonstrate vortex beams up to an azimuthal index l = 3 that can be readily multiplexed into an array configuration.

A theoretical method for the analysis and design of axisymmetric bodies. [flow distribution and incompressible fluids

NASA Technical Reports Server (NTRS)

Beatty, T. D.

1975-01-01

A theoretical method is presented for the computation of the flow field about an axisymmetric body operating in a viscous, incompressible fluid. A potential flow method was used to determine the inviscid flow field and to yield the boundary conditions for the boundary layer solutions. Boundary layer effects in the forces of displacement thickness and empirically modeled separation streamlines are accounted for in subsequent potential flow solutions. This procedure is repeated until the solutions converge. An empirical method was used to determine base drag allowing configuration drag to be computed.

Construction of higher order accurate vortex and particle methods

NASA Technical Reports Server (NTRS)

Nicolaides, R. A.

1986-01-01

The standard point vortex method has recently been shown to be of high order of accuracy for problems on the whole plane, when using a uniform initial subdivision for assigning the vorticity to the points. If obstacles are present in the flow, this high order deteriorates to first or second order. New vortex methods are introduced which are of arbitrary accuracy (under regularity assumptions) regardless of the presence of bodies and the uniformity of the initial subdivision.

Rotor Wake Vortex Definition: Initial Evaluation of 3-C PIV Results of the Hart-II Study

NASA Technical Reports Server (NTRS)

Burley, Casey L.; Brooks, Thomas F.; vanderWall, Berend; Richard, Hughes; Raffel, Markus; Beaumier, Philippe; Delrieux, Yves; Lim, Joon W.; Yu, Yung H.; Tung, Chee

2002-01-01

An initial evaluation is made of extensive three-component (3C) particle image velocimetry (PIV) measurements within the wake across a rotor disk plane. The model is a 40 percent scale BO-105 helicopter main rotor in forward flight simulation. This study is part of the HART II test program conducted in the German-Dutch Wind Tunnel (DNW). Included are wake vortex field measurements over the advancing and retreating sides of the rotor operating at a typical descent landing condition important for impulsive blade-vortex interaction (BVI) noise. Also included are advancing side results for rotor angle variations from climb to steep descent. Using detailed PIV vector maps of the vortex fields, methods of extracting key vortex parameters are examined and a new method was developed and evaluated. An objective processing method, involving a center-of-vorticity criterion and a vorticity 'disk' integration, was used to determine vortex core size, strength, core velocity distribution characteristics, and unsteadiness. These parameters are mapped over the rotor disk and offer unique physical insight for these parameters of importance for rotor noise and vibration prediction.

Subsonic aerodynamic characteristics of interacting lifting surfaces with separated flow around sharp edges predicted by a vortex-lattice method

NASA Technical Reports Server (NTRS)

Lamar, J. E.; Gloss, B. B.

1975-01-01

Because the potential flow suction along the leading and side edges of a planform can be used to determine both leading- and side-edge vortex lift, the present investigation was undertaken to apply the vortex-lattice method to computing side-edge suction force for isolated or interacting planforms. Although there is a small effect of bound vortex sweep on the computation of the side-edge suction force, the results obtained for a number of different isolated planforms produced acceptable agreement with results obtained from a method employing continuous induced-velocity distributions. By using the method outlined, better agreement between theory and experiment was noted for a wing in the presence of a canard than was previously obtained.

Wake vortex separation standards : analysis methods

DOT National Transportation Integrated Search

1997-01-01

Wake vortex separation standards are used to prevent hazardous wake vortex encounters. A "safe" separation model can be used to assess the safety of proposed changes in the standards. A safe separation model can be derived from an encounter hazard mo...

''Cloud in Cell'' technique applied to the roll up of vortex sheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, G.R.

The problem of the roll up of a two dimensional vortex sheet generated by a wing in an ideal fluid is phrased in terms of the streamfunction and the vortex sheet strength. A numerical method is used to calculate the time evolution of the vortex sheet by adapting the ''Cloud In Cell'' technique introduced in solving many particle simulations in plasma physics (see J. P. Christiansen, J. Computational Physics 13 (1973)). Two cases are considered for the initial distribution of circulation, one corresponding to an elliptically loaded wing and the other simulating the wing with a flap deployed. Results indicatemore » that small scale behaviour plays an important part in the roll up. Typically, small scale perturbations result in small structures which evolve into ever increasing larger structures by vortex amalgamation. Conclusions are given from a number of tests exploring the validity of the method. Briefly, small scale perturbations are introduced artificially by the grid; but once the process of vortex amalgamation is well underway, the emerging large scale behaviour is relatively insensitive to the precise details of the initial perturbations. Since clearly defined structures result from the application of this method, it promises to aid considerably in understanding the behaviour of vortex wakes.« less

Multi-Model Ensemble Wake Vortex Prediction

NASA Technical Reports Server (NTRS)

Koerner, Stephan; Holzaepfel, Frank; Ahmad, Nash'at N.

2015-01-01

Several multi-model ensemble methods are investigated for predicting wake vortex transport and decay. This study is a joint effort between National Aeronautics and Space Administration and Deutsches Zentrum fuer Luft- und Raumfahrt to develop a multi-model ensemble capability using their wake models. An overview of different multi-model ensemble methods and their feasibility for wake applications is presented. The methods include Reliability Ensemble Averaging, Bayesian Model Averaging, and Monte Carlo Simulations. The methodologies are evaluated using data from wake vortex field experiments.

Modeling Primary Breakup: A Three-Dimensional Eulerian Level Set/Vortex Sheet Method for Two-Phase Interface Dynamics

NASA Technical Reports Server (NTRS)

Herrmann, M.

2003-01-01

This paper is divided into four parts. First, the level set/vortex sheet method for three-dimensional two-phase interface dynamics is presented. Second, the LSS model for the primary breakup of turbulent liquid jets and sheets is outlined and all terms requiring subgrid modeling are identified. Then, preliminary three-dimensional results of the level set/vortex sheet method are presented and discussed. Finally, conclusions are drawn and an outlook to future work is given.

Numerical methods for axisymmetric and 3D nonlinear beams

NASA Astrophysics Data System (ADS)

Pinton, Gianmarco F.; Trahey, Gregg E.

2005-04-01

Time domain algorithms that solve the Khokhlov--Zabolotzskaya--Kuznetsov (KZK) equation are described and implemented. This equation represents the propagation of finite amplitude sound beams in a homogenous thermoviscous fluid for axisymmetric and fully three dimensional geometries. In the numerical solution each of the terms is considered separately and the numerical methods are compared with known solutions. First and second order operator splitting are used to combine the separate terms in the KZK equation and their convergence is examined.

Aerodynamic loads on a Darrieus rotor blade

NASA Astrophysics Data System (ADS)

Wilson, R. E.; McKie, W. R.; Lissaman, P. B. S.; James, M.

1983-03-01

A method is presented for the free vortex analysis of a Darrieus rotor blade in nonsteady motion, which employs the circle theorem to map the moving rotor airfoil into the circle plane and models the wake generated in terms of point vortices. Nascent vortex strength and position are taken from the Kutta condition, so that the nascent vortex has the same strength as a vortex sheet of uniform strength. Pressure integration over the plate and wake vortex impulse methods yields the same numerical results. The numerical results presented for a one-bladed Darrieus rotor at a tip/speed ratio of three, and two different chord sizes, indicate that the moment on the blade can be adequately approximated by quasi-steady relationships, although the accurate determination of local velocity and circulation are still required.

Calculation of wing response to gusts and blast waves with vortex lift effect

NASA Technical Reports Server (NTRS)

Chao, D. C.; Lan, C. E.

1983-01-01

A numerical study of the response of aircraft wings to atmospheric gusts and to nuclear explosions when flying at subsonic speeds is presented. The method is based upon unsteady quasi-vortex lattice method, unsteady suction analogy and Pade approximant. The calculated results, showing vortex lag effect, yield reasonable agreement with experimental data for incremental lift on wings in gust penetration and due to nuclear blast waves.

Calculation of wake vortex structures in the near-field wake behind cruising aircraft

NASA Astrophysics Data System (ADS)

Ehret, T.; Oertel, H.

Wake flows behind cruising aircraft influence the distribution of the exhaust gases. A three-dimensional vortex filament method was developed to calculate the vortex structures and the velocity field of the vorticity dominated wake flows as an integration of the Biot-Savart law. For three-dimensional vortex filament calculations, self-induction singularities were prevented using a finite vortex core for each vortex filament. Numerical simulations show the vortex structures and the velocity field in the wake behind a cruising Boeing 747 as a result of the integration of the Biot-Savart law. It is further shown how the structures of the fully rolled-up trailing vortices depend on the wing span loading, i.e. the circulation distribution.

Phase diagrams of vortex matter with multi-scale inter-vortex interactions in layered superconductors.

PubMed

Meng, Qingyou; Varney, Christopher N; Fangohr, Hans; Babaev, Egor

2017-01-25

It was recently proposed to use the stray magnetic fields of superconducting vortex lattices to trap ultracold atoms for building quantum emulators. This calls for new methods for engineering and manipulating of the vortex states. One of the possible routes utilizes type-1.5 superconducting layered systems with multi-scale inter-vortex interactions. In order to explore the possible vortex states that can be engineered, we present two phase diagrams of phenomenological vortex matter models with multi-scale inter-vortex interactions featuring several attractive and repulsive length scales. The phase diagrams exhibit a plethora of phases, including conventional 2D lattice phases, five stripe phases, dimer, trimer, and tetramer phases, void phases, and stable low-temperature disordered phases. The transitions between these states can be controlled by the value of an applied external field.

Optimization of steam-vortex plasma-torch start-up

NASA Astrophysics Data System (ADS)

Mikhailov, B. I.

2011-12-01

We propose a new optimal method of steam-vortex plasma-torches start-up; this method completely prevents the danger of water steam condensation in the arc chamber and all undesirable consequences of it.

Minimum trim drag design for interfering lifting surfaces using vortex-lattice methodology

NASA Technical Reports Server (NTRS)

Lamar, J. E.

1976-01-01

A new method has been developed by which the mean camber surface can be determined for trimmed noncoplanar planforms with minimum vortex drag under subsonic conditions. The method uses a vortex lattice and overcomes previous difficulties with chord loading specification; it uses a Trefftz plane analysis to determine the optimum span loading for minimum drag, then solves for the mean camber surface of the wing which will provide the required loading. Pitching-moment or root-bending-moment constraints can be employed as well at the design lift coefficient. Sensitivity studies of vortex-lattice arrangement have been made with this method and are presented. Comparisons with other theories show generally good agreement. The versatility of the method is demonstrated by applying it to (1) isolated wings, (2) wing-canard configurations, (3) a tandem wing, and (4) a wing-winglet configuration.

An axisymmetric PFEM formulation for bottle forming simulation

NASA Astrophysics Data System (ADS)

Ryzhakov, Pavel B.

2017-01-01

A numerical model for bottle forming simulation is proposed. It is based upon the Particle Finite Element Method (PFEM) and is developed for the simulation of bottles characterized by rotational symmetry. The PFEM strategy is adapted to suit the problem of interest. Axisymmetric version of the formulation is developed and a modified contact algorithm is applied. This results in a method characterized by excellent computational efficiency and volume conservation characteristics. The model is validated. An example modelling the final blow process is solved. Bottle wall thickness is estimated and the mass conservation of the method is analysed.

Farfield structure of an aircraft trailing vortex, including effects of mass injection

NASA Technical Reports Server (NTRS)

Mason, W. H.; Marchman, J. F., III

1972-01-01

Wind tunnel tests to predict the aircraft wake turbulence due to the tip trailing vortex are discussed. A yawhead pressure probe was used in a subsonic wind tunnel to obtain detailed mean flow measurements at stations up to 30 chordlengths downstream in an aircraft trailing vortex. Mass injection at the wingtip was shown to hasten the decay of the trailing vortex. A theoretical method is presented to show the effect which the circulation distribution on the wing has on the structure of the outer portion of the vortex.

Evolution of vortex-surface fields in transitional boundary layers

NASA Astrophysics Data System (ADS)

Yang, Yue; Zhao, Yaomin; Xiong, Shiying

2016-11-01

We apply the vortex-surface field (VSF), a Lagrangian-based structure-identification method, to the DNS database of transitional boundary layers. The VSFs are constructed from the vorticity fields within a sliding window at different times and locations using a recently developed boundary-constraint method. The isosurfaces of VSF, representing vortex surfaces consisting of vortex lines with different wall distances in the laminar stage, show different evolutionary geometries in transition. We observe that the vortex surfaces with significant deformation evolve from wall-parallel planar sheets through hairpin-like structures and packets into a turbulent spot with regeneration of small-scale hairpins. From quantitative analysis, we show that a small number of representative or influential vortex surfaces can contribute significantly to the increase of the drag coefficient in transition, which implies a reduced-order model based on VSF. This work has been supported in part by the National Natural Science Foundation of China (Grant Nos. 11472015, 11522215 and 11521091), and the Thousand Young Talents Program of China.

Vector spherical quasi-Gaussian vortex beams

NASA Astrophysics Data System (ADS)

Mitri, F. G.

2014-02-01

Model equations for describing and efficiently computing the radiation profiles of tightly spherically focused higher-order electromagnetic beams of vortex nature are derived stemming from a vectorial analysis with the complex-source-point method. This solution, termed as a high-order quasi-Gaussian (qG) vortex beam, exactly satisfies the vector Helmholtz and Maxwell's equations. It is characterized by a nonzero integer degree and order (n,m), respectively, an arbitrary waist w0, a diffraction convergence length known as the Rayleigh range zR, and an azimuthal phase dependency in the form of a complex exponential corresponding to a vortex beam. An attractive feature of the high-order solution is the rigorous description of strongly focused (or strongly divergent) vortex wave fields without the need of either the higher-order corrections or the numerically intensive methods. Closed-form expressions and computational results illustrate the analysis and some properties of the high-order qG vortex beams based on the axial and transverse polarization schemes of the vector potentials with emphasis on the beam waist.

Identification and tracking of hairpin vortex auto-generation in turbulent wall-bounded flow

NASA Astrophysics Data System (ADS)

Huang, Yangzi; Green, Melissa

2016-11-01

Hairpin vortices have been widely accepted as component structures of turbulent boundary layers. Their properties (size, vorticity, energy) and dynamic phenomena (origin, growth, breakdown) have been shown to correlate to the complex, multi-scaled turbulent motions observed in both experiments and simulations. As established in the literature, the passage of a hairpin vortex creates a wall-normal ejection of fluid, which encounters the high-speed freestream resulting in near-wall shear and increased drag. A previously generated simulation of an isolated hairpin vortex is used to study the auto-generation of a secondary vortex structure. Eulerian methods such as the Q criterion and Γ2 function, as well as Lagrangian methods are used to visualize the three-dimensional hairpin vortices and the auto-generation process. The circulation development and wall-normal location of both primary and secondary hairpin heads are studied to determine if there is a correlation between the strength and height of the primary hairpin vortex with the secondary hairpin vortex auto-generation.

Discrimination of orbital angular momentum modes of the terahertz vortex beam using a diffractive mode transformer.

PubMed

Liu, Changming; Wei, Xuli; Niu, Liting; Wang, Kejia; Yang, Zhengang; Liu, Jinsong

2016-06-13

We present an efficient method to discriminate orbital angular momentum (OAM) of the terahertz (THz) vortex beam using a diffractive mode transformer. The mode transformer performs a log-polar coordinate transformation of the input THz vortex beam, which consists of two 3D-printed diffractive elements. A following lens separates each transformed OAM mode to a different lateral position in its focal plane. This method enables a simultaneous measurement over multiple OAM modes of the THz vortex beam. We experimentally demonstrate the measurement of seven individual OAM modes and two multiplexed OAM modes, which is in good agreement with simulations.

Apparatus for and method of simulating turbulence

DOEpatents

Dimas, Athanassios; Lottati, Isaac; Bernard, Peter; Collins, James; Geiger, James C.

2003-01-01

In accordance with a preferred embodiment of the invention, a novel apparatus for and method of simulating physical processes such as fluid flow is provided. Fluid flow near a boundary or wall of an object is represented by a collection of vortex sheet layers. The layers are composed of a grid or mesh of one or more geometrically shaped space filling elements. In the preferred embodiment, the space filling elements take on a triangular shape. An Eulerian approach is employed for the vortex sheets, where a finite-volume scheme is used on the prismatic grid formed by the vortex sheet layers. A Lagrangian approach is employed for the vortical elements (e.g., vortex tubes or filaments) found in the remainder of the flow domain. To reduce the computational time, a hairpin removal scheme is employed to reduce the number of vortex filaments, and a Fast Multipole Method (FMM), preferably implemented using parallel processing techniques, reduces the computation of the velocity field.

The Impacts of Numerical Schemes on Asymmetric Hurricane Intensification

NASA Astrophysics Data System (ADS)

Guimond, S.; Reisner, J. M.; Marras, S.; Giraldo, F.

2015-12-01

The fundamental pathways for tropical cyclone (TC) intensification are explored by considering axisymmetric and asymmetric impulsive thermal perturbations to balanced, TC-like vortices using the dynamic cores of three different numerical models. Attempts at reproducing the results of previous work, which used the community atmospheric model WRF (Nolan and Grasso 2003; NG03), revealed a discrepancy with the impacts of purely asymmetric thermal forcing. The current study finds that thermal asymmetries can have an important, largely positive role on the vortex intensification whereas NG03 and other studies find that asymmetric impacts are negligible. Analysis of the spectral energetics of each numerical model indicates that the vortex response to asymmetric thermal perturbations is significantly damped in WRF relative to the other numerical models. Spectral kinetic energy budgets show that this anomalous damping is due to the increased removal of kinetic energy from the convergence of the vertical pressure flux, which is related to the flux of inertia-gravity wave energy. The increased kinetic energy in the other two models is shown to originate around the scales of the heating and propagate upscale with time. For very large thermal amplitudes (~ 50 K and above), the anomalous removal of kinetic energy due to inertia-gravity wave activity is much smaller resulting in little differences between models. The results of this paper indicate that the numerical treatment of small-scale processes that project strongly onto inertia-gravity wave energy are responsible for these differences, with potentially important impacts for the understanding and prediction of TC intensification.

Radiation Transport Around Axisymmetric Blunt Body Vehicles Using a Modified Differential Approximation

NASA Technical Reports Server (NTRS)

Hartung, Lin C.; Hassan, H. A.

1992-01-01

A moment method for computing 3-D radiative transport is applied to axisymmetric flows in thermochemical nonequilibrium. Such flows are representative of proposed aerobrake missions. The method uses the P-1 approximation to reduce the governing system of integro-di erential equations to a coupled set of partial di erential equations. A numerical solution method for these equations given actual variations of the radiation properties in thermochemical nonequilibrium blunt body flows is developed. Initial results from the method are shown and compared to tangent slab calculations. The agreement between the transport methods is found to be about 10 percent in the stagnation region, with the difference increasing along the flank of the vehicle.

An Eulerian/Lagrangian method for computing blade/vortex impingement

NASA Technical Reports Server (NTRS)

Steinhoff, John; Senge, Heinrich; Yonghu, Wenren

1991-01-01

A combined Eulerian/Lagrangian approach to calculating helicopter rotor flows with concentrated vortices is described. The method computes a general evolving vorticity distribution without any significant numerical diffusion. Concentrated vortices can be accurately propagated over long distances on relatively coarse grids with cores only several grid cells wide. The method is demonstrated for a blade/vortex impingement case in 2D and 3D where a vortex is cut by a rotor blade, and the results are compared to previous 2D calculations involving a fifth-order Navier-Stokes solver on a finer grid.

Calculation of symmetric and asymmetric vortex seperation on cones and tangent ogives based on discrete vortex models

NASA Technical Reports Server (NTRS)

Chin, S.; Lan, C. Edward

1988-01-01

An inviscid discrete vortex model, with newly derived expressions for the tangential velocity imposed at the separation points, is used to investigate the symmetric and asymmetric vortex separation on cones and tangent ogives. The circumferential locations of separation are taken from experimental data. Based on a slender body theory, the resulting simultaneous nonlinear algebraic equations in a cross-flow plane are solved with Broyden's modified Newton-Raphson method. Total force coefficients are obtained through momentum principle with new expressions for nonconical flow. It is shown through the method of function deflation that multiple solutions exist at large enough angles of attack, even with symmetric separation points. These additional solutions are asymmetric in vortex separation and produce side force coefficients which agree well with data for cones and tangent ogives.

Applicability of linearized-theory attached-flow methods to design and analysis of flap systems at low speeds for thin swept wings with sharp leading edges

NASA Technical Reports Server (NTRS)

Carlson, Harry W.; Darden, Christine M.

1987-01-01

Low-speed experimental force and data on a series of thin swept wings with sharp leading edges and leading and trailing-edge flaps are compared with predictions made using a linearized-theory method which includes estimates of vortex forces. These comparisons were made to assess the effectiveness of linearized-theory methods for use in the design and analysis of flap systems in subsonic flow. Results demonstrate that linearized-theory, attached-flow methods (with approximate representation of vortex forces) can form the basis of a rational system for flap design and analysis. Even attached-flow methods that do not take vortex forces into account can be used for the selection of optimized flap-system geometry, but design-point performance levels tend to be underestimated unless vortex forces are included. Illustrative examples of the use of these methods in the design of efficient low-speed flap systems are included.

Exact analytical formulae for linearly distributed vortex and source sheets in uence computation in 2D vortex methods

NASA Astrophysics Data System (ADS)

Kuzmina, K. S.; Marchevsky, I. K.; Ryatina, E. P.

2017-11-01

We consider the methodology of numerical schemes development for two-dimensional vortex method. We describe two different approaches to deriving integral equation for unknown vortex sheet intensity. We simulate the velocity of the surface line of an airfoil as the influence of attached vortex and source sheets. We consider a polygonal approximation of the airfoil and assume intensity distributions of free and attached vortex sheets and attached source sheet to be approximated with piecewise constant or piecewise linear (continuous or discontinuous) functions. We describe several specific numerical schemes that provide different accuracy and have a different computational cost. The study shows that a Galerkin-type approach to solving boundary integral equation requires computing several integrals and double integrals over the panels. We obtain exact analytical formulae for all the necessary integrals, which makes it possible to raise significantly the accuracy of vortex sheet intensity computation and improve the quality of velocity and vorticity field representation, especially in proximity to the surface line of the airfoil. All the formulae are written down in the invariant form and depend only on the geometric relationship between the positions of the beginnings and ends of the panels.

Symmetry investigations on the incompressible stationary axisymmetric Euler equations with swirl

NASA Astrophysics Data System (ADS)

Frewer, M.; Oberlack, M.; Guenther, S.

2007-08-01

We discuss the incompressible stationary axisymmetric Euler equations with swirl, for which we derive via a scalar stream function an equivalent representation, the Bragg-Hawthorne equation [Bragg, S.L., Hawthorne, W.R., 1950. Some exact solutions of the flow through annular cascade actuator discs. J. Aero. Sci. 17, 243]. Despite this obvious equivalence, we will show that under a local Lie point symmetry analysis the Bragg-Hawthorne equation exposes itself as not being fully equivalent to the original Euler equations. This is reflected in the way that it possesses additional symmetries not being admitted by its counterpart. In other words, a symmetry of the Bragg-Hawthorne equation is in general not a symmetry of the Euler equations. Not the differential Euler equations but rather a set of integro-differential equations attains full equivalence to the Bragg-Hawthorne equation. For these intermediate Euler equations, it is interesting to note that local symmetries of the Bragg-Hawthorne equation transform to local as well as to nonlocal symmetries. This behaviour, on the one hand, is in accordance with Zawistowski's result [Zawistowski, Z.J., 2001. Symmetries of integro-differential equations. Rep. Math. Phys. 48, 269; Zawistowski, Z.J., 2004. General criterion of invariance for integro-differential equations. Rep. Math. Phys. 54, 341] that it is possible for integro-differential equations to admit local Lie point symmetries. On the other hand, with this transformation process we collect symmetries which cannot be obtained when carrying out a usual local Lie point symmetry analysis. Finally, the symmetry classification of the Bragg-Hawthorne equation is used to find analytical solutions for the phenomenon of vortex breakdown.

Trimmed noncoplanar planforms with minimum vortex drag

NASA Technical Reports Server (NTRS)

Lamar, J. E.

1977-01-01

Vortex-lattice subsonic method determines mean camber surface for trimmed noncoplanar planforms with minimum vortex drag. Multiple surfaces can be designed together to yield trimmed configuration with minimum induced drag at some specified lift coefficient. Program is applicable to isolated wings, wing-canard configuration, tandem wing, and wing-winglet configuration.

Axisymmetric solid elements by a rational hybrid stress method

NASA Technical Reports Server (NTRS)

Tian, Z.; Pian, T. H. H.

1985-01-01

Four-node axisymmetric solid elements are derived by a new version of hybrid method for which the assumed stresses are expressed in complete polynomials in natural coordinates. The stress equilibrium conditions are introduced through the use of additional displacements as Lagrange multipliers. A rational procedure is to choose the displacement terms such that the resulting strains are also of complete polynomials of the same order. Example problems all indicate that elements obtained by this procedure lead to better results in displacements and stresses than that by other finite elements.

Helicity conservation under quantum reconnection of vortex rings.

PubMed

Zuccher, Simone; Ricca, Renzo L

2015-12-01

Here we show that under quantum reconnection, simulated by using the three-dimensional Gross-Pitaevskii equation, self-helicity of a system of two interacting vortex rings remains conserved. By resolving the fine structure of the vortex cores, we demonstrate that the total length of the vortex system reaches a maximum at the reconnection time, while both writhe helicity and twist helicity remain separately unchanged throughout the process. Self-helicity is computed by two independent methods, and topological information is based on the extraction and analysis of geometric quantities such as writhe, total torsion, and intrinsic twist of the reconnecting vortex rings.

Aeroelastic loads prediction for an arrow wing. Task 3: Evaluation of the Boeing three-dimensional leading-edge vortex code

NASA Technical Reports Server (NTRS)

Manro, M. E.

1983-01-01

Two separated flow computer programs and a semiempirical method for incorporating the experimentally measured separated flow effects into a linear aeroelastic analysis were evaluated. The three dimensional leading edge vortex (LEV) code is evaluated. This code is an improved panel method for three dimensional inviscid flow over a wing with leading edge vortex separation. The governing equations are the linear flow differential equation with nonlinear boundary conditions. The solution is iterative; the position as well as the strength of the vortex is determined. Cases for both full and partial span vortices were executed. The predicted pressures are good and adequately reflect changes in configuration.

Numerical restoration of surface vortices in Nb films measured by a scanning SQUID microscope

NASA Astrophysics Data System (ADS)

Ito, Atsuki; Thanh Huy, Ho; Dang, Vu The; Miyoshi, Hiroki; Hayashi, Masahiko; Ishida, Takekazu

2017-07-01

In the present work, we investigated a vortex profile appeared on a pure Nb film (500 nm in thickness, 10 mm x 10 mm) by using a scanning SQUID microscope. We found that the local magnetic distribution thus observed is broadened compared to a true vortex profile in the superconducting film. We therefore applied the numerical method to improve a spatial resolution of the scanning SQUID microscope. The method is based on the inverse Biot-Savart law and the Fourier transformation to recover a real-space image. We found that the numerical analyses give a smaller vortex than the raw vortex profile observed by the scanning microscope.

Aeroelastic loads prediction for an arrow wing. Task 1: Evaluation of R. P. White's method

NASA Technical Reports Server (NTRS)

Borland, C. J.; Manro, M. E.

1983-01-01

The separated flow method is evaluated. This method was developed for moderately swept wings with multiple, constant strength vortex systems. The flow on the highly swept wing used in this evaluation is characterized by a single vortex system of continuously varying strength.

Feasibility of wake vortex monitoring systems for air terminals

NASA Technical Reports Server (NTRS)

Wilson, D. J.; Shrider, K. R.; Lawrence, T. R.

1972-01-01

Wake vortex monitoring systems, especially those using laser Doppler sensors, were investigated. The initial phases of the effort involved talking with potential users (air traffic controllers, pilots, etc.) of a wake vortex monitoring system to determine system requirements from the user's viewpoint. These discussions involved the volumes of airspace to be monitored for vortices, and potential methods of using the monitored vortex data once the data are available. A subsequent task led to determining a suitable mathematical model of the vortex phenomena and developing a mathematical model of the laser Doppler sensor for monitoring the vortex flow field. The mathematical models were used in combination to help evaluate the capability of laser Doppler instrumentation in monitoring vortex flow fields both in the near vicinity of the sensor (within 1 kilometer and at long ranges(10 kilometers).

Mathematical modeling and simulation of aquatic and aerial animal locomotion

NASA Astrophysics Data System (ADS)

Hou, T. Y.; Stredie, V. G.; Wu, T. Y.

2007-08-01

In this paper, we investigate the locomotion of fish and birds by applying a new unsteady, flexible wing theory that takes into account the strong nonlinear dynamics semi-analytically. We also make extensive comparative study between the new approach and the modified vortex blob method inspired from Chorin's and Krasny's work. We first implement the modified vortex blob method for two examples and then discuss the numerical implementation of the nonlinear analytical mathematical model of Wu. We will demonstrate that Wu's method can capture the nonlinear effects very well by applying it to some specific cases and by comparing with the experiments available. In particular, we apply Wu's method to analyze Wagner's result for a wing abruptly undergoing an increase in incidence angle. Moreover, we study the vorticity generated by a wing in heaving, pitching and bending motion. In both cases, we show that the new method can accurately represent the vortex structure behind a flying wing and its influence on the bound vortex sheet on the wing.

A stochastic vortex structure method for interacting particles in turbulent shear flows

NASA Astrophysics Data System (ADS)

Dizaji, Farzad F.; Marshall, Jeffrey S.; Grant, John R.

2018-01-01

In a recent study, we have proposed a new synthetic turbulence method based on stochastic vortex structures (SVSs), and we have demonstrated that this method can accurately predict particle transport, collision, and agglomeration in homogeneous, isotropic turbulence in comparison to direct numerical simulation results. The current paper extends the SVS method to non-homogeneous, anisotropic turbulence. The key element of this extension is a new inversion procedure, by which the vortex initial orientation can be set so as to generate a prescribed Reynolds stress field. After validating this inversion procedure for simple problems, we apply the SVS method to the problem of interacting particle transport by a turbulent planar jet. Measures of the turbulent flow and of particle dispersion, clustering, and collision obtained by the new SVS simulations are shown to compare well with direct numerical simulation results. The influence of different numerical parameters, such as number of vortices and vortex lifetime, on the accuracy of the SVS predictions is also examined.

Some numerical methods for the Hele-Shaw equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whitaker, N.

1994-03-01

Tryggvason and Aref used a boundary integral method and the vortex-in-cell method to evolve the interface between two fluids in a Hele-Shaw cell. The method gives excellent results for intermediate values of the nondimensional surface tension parameter. The results are different from the predicted results of McLean and Saffman for small surface tension. For large surface tension, there are some numerical problems. In this paper, we implement the method of Tryggvason and Aref but use the point vortex method instead of the vortex-in-cell method. A parametric spline is used to represent the interface. The finger widths obtained agree well withmore » those predicted by McLean and Saffman. We conclude the the method of Tryggvason and Aref can provide excellent results but that the vortex-in-cell method may not be the method of choice for extreme values of the surface tension parameter. In a second method, we represent the interface with a Fourier representation. In addition, an alternative way of discretizing the boundary integral is used. Our results are compared to the linearized theory and the results of McLean and Saffman and are shown to be highly accurate. 21 refs., 4 figs., 2 tabs.« less

Influence of homogeneous magnetic fields on the flow of a ferrofluid in the Taylor-Couette system.

PubMed

Altmeyer, S; Hoffmann, Ch; Leschhorn, A; Lücke, M

2010-07-01

We investigate numerically the influence of a homogeneous magnetic field on a ferrofluid in the gap between two concentric, independently rotating cylinders. The full Navier-Stokes equations are solved with a combination of a finite difference method and a Galerkin method. Structure, dynamics, symmetry properties, bifurcation, and stability behavior of different vortex structures are investigated for axial and transversal magnetic fields, as well as combinations of them. We show that a transversal magnetic field modulates the Taylor vortex flow and the spiral vortex flow. Thus, a transversal magnetic field induces wavy structures: wavy Taylor vortex flow (wTVF) and wavy spiral vortex flow. In contrast to the classic wTVF, which is a secondarily bifurcating structure, these magnetically generated wavy Taylor vortices are pinned by the magnetic field, i.e., they are stationary and they appear via a primary forward bifurcation out of the basic state of circular Couette flow.

A simplified analytic form for generation of axisymmetric plasma boundaries

DOE PAGES

Luce, Timothy C.

2017-02-23

An improved method has been formulated for generating analytic boundary shapes as input for axisymmetric MHD equilibria. This method uses the family of superellipses as the basis function, as previously introduced. The improvements are a simplified notation, reduction of the number of simultaneous nonlinear equations to be solved, and the realization that not all combinations of input parameters admit a solution to the nonlinear constraint equations. The method tests for the existence of a self-consistent solution and, when no solution exists, it uses a deterministic method to find a nearby solution. As a result, examples of generation of boundaries, includingmore » tests with an equilibrium solver, are given.« less

A simplified analytic form for generation of axisymmetric plasma boundaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luce, Timothy C.

An improved method has been formulated for generating analytic boundary shapes as input for axisymmetric MHD equilibria. This method uses the family of superellipses as the basis function, as previously introduced. The improvements are a simplified notation, reduction of the number of simultaneous nonlinear equations to be solved, and the realization that not all combinations of input parameters admit a solution to the nonlinear constraint equations. The method tests for the existence of a self-consistent solution and, when no solution exists, it uses a deterministic method to find a nearby solution. As a result, examples of generation of boundaries, includingmore » tests with an equilibrium solver, are given.« less

Validation of Vortex-Lattice Method for Loads on Wings in Lift-Generated Wakes

NASA Technical Reports Server (NTRS)

Rossow, Vernon J.

1995-01-01

A study is described that evaluates the accuracy of vortex-lattice methods when they are used to compute the loads induced on aircraft as they encounter lift-generated wakes. The evaluation is accomplished by the use of measurements made in the 80 by 120 ft Wind Tunnel of the lift, rolling moment, and downwash in the wake of three configurations of a model of a subsonic transport aircraft. The downwash measurements are used as input for a vortex-lattice code in order to compute the lift and rolling moment induced on wings that have a span of 0.186, 0.510, or 1.022 times the span of the wake-generating model. Comparison of the computed results with the measured lift and rolling-moment distributions the vortex-lattice method is very reliable as long as the span of the encountering or following wing is less than about 0.2 of the generator span. As the span of the following wing increases above 0.2, the vortex-lattice method continues to correctly predict the trends and nature of the induced loads, but it overpredicts the magnitude of the loads by increasing amounts.

Extracting, Tracking, and Visualizing Magnetic Flux Vortices in 3D Complex-Valued Superconductor Simulation Data.

PubMed

Guo, Hanqi; Phillips, Carolyn L; Peterka, Tom; Karpeyev, Dmitry; Glatz, Andreas

2016-01-01

We propose a method for the vortex extraction and tracking of superconducting magnetic flux vortices for both structured and unstructured mesh data. In the Ginzburg-Landau theory, magnetic flux vortices are well-defined features in a complex-valued order parameter field, and their dynamics determine electromagnetic properties in type-II superconductors. Our method represents each vortex line (a 1D curve embedded in 3D space) as a connected graph extracted from the discretized field in both space and time. For a time-varying discrete dataset, our vortex extraction and tracking method is as accurate as the data discretization. We then apply 3D visualization and 2D event diagrams to the extraction and tracking results to help scientists understand vortex dynamics and macroscale superconductor behavior in greater detail than previously possible.

Kinematics and dynamics of vortex rings in a tube

NASA Technical Reports Server (NTRS)

Brasseur, J. G.

1979-01-01

Kinematic theory and flow visualization experiments were combined to examine the dynamic processes which control the evolution of vortex rings from very low to very high Reynolds numbers, and to assess the effects of the wall as a vortex ring travels up a tube. The kinematic relationships among the size, shape, speed, and strength of vortex rings in a tube were computed from the theory. Relatively simple flow visualization measurements were used to calculate the total circulation of a vortex rings at a given time. Using this method, the strength was computated and plotted as a function of time for experimentally produced vortex rings. Reynolds number relationships are established and quantitative differences among the three Reynolds number groups are discussed.

Vortex energy landscape from real space imaging analysis of YBa2Cu3O7 with different defect structures

NASA Astrophysics Data System (ADS)

Luccas, R. F.; Granados, X.; Obradors, X.; Puig, T.

2014-10-01

A methodology based on real space vortex image analysis is presented able to estimate semi-quantitatively the relevant energy densities of an arbitrary array of vortices, map the interaction energy distributions and evaluate the pinning energy associated to particular defects. The combined study using nanostructuration tools, a vortex visualization technique and the energy method is seen as an opportunity to estimate vortex pinning potentials strengths. Particularly, spatial distributions of vortex energy densities induced by surface nanoindented scratches are evaluated and compared to those of twin boundaries. This comparative study underlines the remarkable role of surface nanoscratches in pinning vortices and its potentiality in the design of novel devices for pinning and guiding vortex motion.

Visualization of vortex structures and analysis of frequency of PVC

NASA Astrophysics Data System (ADS)

Gesheva, E. S.; Shtork, S. I.; Alekseenko, S. V.

2018-03-01

The paper presents the results of the study of large-scale vortex structures in a model chamber. Methods of forming quasi-stationary vortices of various shapes by changing the geometric parameters of the chamber have been proposed. In the model chamber with a tangential swirl of the flow, a rectilinear vortex, single helical and double helical vortices were obtained. The double helical structure of the vortex is unique due to its immovability around the axis of the chamber. The resulting structures slowly oscillate around their own axes, which is called the vortex core precession; while the oscillation frequency depends linearly on the liquid flow rate. The use of stationary vortex structures in power plants will increase the efficiency of combustion chambers and reduce slagging.

Convergence characteristics of nonlinear vortex-lattice methods for configuration aerodynamics

NASA Technical Reports Server (NTRS)

Seginer, A.; Rusak, Z.; Wasserstrom, E.

1983-01-01

Nonlinear panel methods have no proof for the existence and uniqueness of their solutions. The convergence characteristics of an iterative, nonlinear vortex-lattice method are, therefore, carefully investigated. The effects of several parameters, including (1) the surface-paneling method, (2) an integration method of the trajectories of the wake vortices, (3) vortex-grid refinement, and (4) the initial conditions for the first iteration on the computed aerodynamic coefficients and on the flow-field details are presented. The convergence of the iterative-solution procedure is usually rapid. The solution converges with grid refinement to a constant value, but the final value is not unique and varies with the wing surface-paneling and wake-discretization methods within some range in the vicinity of the experimental result.

Finned Tube With Vortex Generators For A Heat Exchanger.

DOEpatents

Sohal, Manohar S.; O'Brien, James E.

2005-12-20

A system for and method of manufacturing a finned tube for a heat exchanger is disclosed herein. A continuous fin strip is provided with at one pair of vortex generators. A tube is rotated and linearly displaced while the continuous fin strip with vortex generators is spirally wrapped around the tube.

Finned Tube With Vortex Generators For A Heat Exchanger.

DOEpatents

Sohal, Monohar S.; O'Brien, James E.

2004-09-14

A system for and method of manufacturing a finned tube for a heat exchanger is disclosed herein. A continuous fin strip is provided with at least one pair of vortex generators. A tube is rotated and linearly displaced while the continuous fin strip with vortex generators is spirally wrapped around the tube.

Optical vortex beams: Generation, propagation and applications

NASA Astrophysics Data System (ADS)

Cheng, Wen

An optical vortex (also known as a screw dislocation or phase singularity) is one type of optical singularity that has a spiral phase wave front around a singularity point where the phase is undefined. Optical vortex beams have a lot of applications in areas such as optical communications, LADAR (laser detection and ranging) system, optical tweezers, optical trapping and laser beam shaping. The concepts of optical vortex beams and methods of generation are briefly discussed. The properties of optical vortex beams propagating through atmospheric turbulence have been studied. A numerical modeling is developed and validated which has been applied to study the high order properties of optical vortex beams propagating though a turbulent atmosphere. The simulation results demonstrate the advantage that vectorial vortex beams may be more stable and maintain beam integrity better when they propagate through turbulent atmosphere. As one important application of optical vortex beams, the laser beam shaping is introduced and studied. We propose and demonstrate a method to generate a 2D flat-top beam profile using the second order full Poincare beams. Its applications in two-dimensional flat-top beam shaping with spatially variant polarization under low numerical aperture focusing have been studied both theoretically and experimentally. A novel compact flat-top beam shaper based on the proposed method has been designed, fabricated and tested. Experimental results show that high quality flat-top profile can be obtained with steep edge roll-off. The tolerance to different input beam sizes of the beam shaper is also verified in the experimental demonstration. The proposed and experimentally verified LC beam shaper has the potential to become a promising candidate for compact and low-cost flat-top beam shaping in areas such as laser processing/machining, lithography and medical treatment.

Tip leakage vortex dynamics and inception

NASA Astrophysics Data System (ADS)

Oweis, Ghanem; Ceccio, Steven; Jessup, Stuart; Chesnakas, Christopher; Fry, David

2002-11-01

The McCormick rule for tip vortex cavitation scaling predicts that cavitation should take place in the vortex where the average core pressure deficit from the free stream is the largest along the vortex tube. The average core pressure deficit can be calculated from the vortex core size and circulation and these can be measured by LDV or hot wire, among other methods. The same rule applies to the tip vortex from a wall-bounded hydrofoil. Recent cavitation inception experiments on a ducted propeller in the NSWCCD 36 inch water tunnel combined with PIV and LDV measurements of the tip vortex flow are described. These tests reveal a disagreement between the actual inception location and that predicted by the McCormick rule. It is hypothesized that in this case the inception mechanism is related to local flow phenomena associated with local vortex unsteadiness, as opposed to the average vortex parameters (core size and circulation) used in the viscous scaling rule of McCormick. Discussion of the flow field measurements, bubble population, and the noise production from the inception events is given.

Animating Wall-Bounded Turbulent Smoke via Filament-Mesh Particle-Particle Method.

PubMed

Liao, Xiangyun; Si, Weixin; Yuan, Zhiyong; Sun, Hanqiu; Qin, Jing; Wang, Qiong; Heng, Pheng-Ann; Xiangyun Liao; Weixin Si; Zhiyong Yuan; Hanqiu Sun; Jing Qin; Qiong Wang; Pheng-Ann Heng

2018-03-01

Turbulent vortices in smoke flows are crucial for a visually interesting appearance. Unfortunately, it is challenging to efficiently simulate these appealing effects in the framework of vortex filament methods. The vortex filaments in grids scheme allows to efficiently generate turbulent smoke with macroscopic vortical structures, but suffers from the projection-related dissipation, and thus the small-scale vortical structures under grid resolution are hard to capture. In addition, this scheme cannot be applied in wall-bounded turbulent smoke simulation, which requires efficiently handling smoke-obstacle interaction and creating vorticity at the obstacle boundary. To tackle above issues, we propose an effective filament-mesh particle-particle (FMPP) method for fast wall-bounded turbulent smoke simulation with ample details. The Filament-Mesh component approximates the smooth long-range interactions by splatting vortex filaments on grid, solving the Poisson problem with a fast solver, and then interpolating back to smoke particles. The Particle-Particle component introduces smoothed particle hydrodynamics (SPH) turbulence model for particles in the same grid, where interactions between particles cannot be properly captured under grid resolution. Then, we sample the surface of obstacles with boundary particles, allowing the interaction between smoke and obstacle being treated as pressure forces in SPH. Besides, the vortex formation region is defined at the back of obstacles, providing smoke particles flowing by the separation particles with a vorticity force to simulate the subsequent vortex shedding phenomenon. The proposed approach can synthesize the lost small-scale vortical structures and also achieve the smoke-obstacle interaction with vortex shedding at obstacle boundaries in a lightweight manner. The experimental results demonstrate that our FMPP method can achieve more appealing visual effects than vortex filaments in grids scheme by efficiently simulating more vivid thin turbulent features.

A counter-rotating vortex pair in inviscid fluid

NASA Astrophysics Data System (ADS)

Habibah, Ummu; Fukumoto, Yasuhide

2017-12-01

We study the motion of a counter-rotating vortex pair with the circulations ±Γ move in incompressible fluid. The assumption is made that the core is very thin, that is the core radius σ is much smaller than the vortex radius d such that ɛ = σ/d ≪ 1. With this condition, the method of matched asymptotic expansion is employed. The solutions of the Navier-Stokes equations and the Biot-Savart law, regarding the inner and outer solutions respectively, are constructed in the form of a small parameter. An asymptotic expansion of the Biot-Savart law near the vortex core provides with the matching condition for an asymptotic expansion for limiting the Navier-Stokes equations for large radius r. The general formula of an anti-parallel vortex pair is established. At leading order O(ɛ0), we apply the special case in inviscid fluid, the Rankine vortex, a circular vortex of uniform vorticity. Furthermore at leading order O(ɛ5) we show the traveling speed of a vortex pair.

Microscale vortex laser with controlled topological charge

NASA Astrophysics Data System (ADS)

Wang, Xing-Yuan; Chen, Hua-Zhou; Li, Ying; Li, Bo; Ma, Ren-Min

2016-12-01

A microscale vortex laser is a new type of coherent light source with small footprint that can directly generate vector vortex beams. However, a microscale laser with controlled topological charge, which is crucial for virtually any of its application, is still unrevealed. Here we present a microscale vortex laser with controlled topological charge. The vortex laser eigenmode was synthesized in a metamaterial engineered non-Hermitian micro-ring cavity system at exceptional point. We also show that the vortex laser cavity can operate at exceptional point stably to lase under optical pumping. The microscale vortex laser with controlled topological charge can serve as a unique and general building block for next-generation photonic integrated circuits and coherent vortex beam sources. The method we used here can be employed to generate lasing eigenmode with other complex functionalities. Project supported by the “Youth 1000 Talent Plan” Fund, Ministry of Education of China (Grant No. 201421) and the National Natural Science Foundation of China (Grant Nos. 11574012 and 61521004).

Numerical study of the properties of optical vortex array laser tweezers.

PubMed

Kuo, Chun-Fu; Chu, Shu-Chun

2013-11-04

Chu et al. constructed a kind of Ince-Gaussian modes (IGM)-based vortex array laser beams consisting of p x p embedded optical vortexes from Ince-Gaussian modes, IG(e)(p,p) modes [Opt. Express 16, 19934 (2008)]. Such an IGM-based vortex array laser beams maintains its vortex array profile during both propagation and focusing, and is applicable to optical tweezers. This study uses the discrete dipole approximation (DDA) method to study the properties of the IGM-based vortex array laser tweezers while it traps dielectric particles. This study calculates the resultant force exerted on the spherical dielectric particles of different sizes situated at the IGM-based vortex array laser beam waist. Numerical results show that the number of trapping spots of a structure light (i.e. IGM-based vortex laser beam), is depended on the relation between the trapped particle size and the structure light beam size. While the trapped particle is small comparing to the beam size of the IGM-based vortex array laser beams, the IGM-based vortex array laser beams tweezers are suitable for multiple traps. Conversely, the tweezers is suitable for single traps. The results of this study is useful to the future development of the vortex array laser tweezers applications.

Signatures of two-step impurity mediated vortex lattice melting in Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Dey, Bishwajyoti

2017-04-01

We study impurity mediated vortex lattice melting in a rotating two-dimensional Bose-Einstein condensate (BEC). Impurities are introduced either through a protocol in which vortex lattice is produced in an impurity potential or first creating the vortex lattice in the absence of random pinning and then cranking up the impurity potential. These two protocols have obvious relation with the two commonly known protocols of creating vortex lattice in a type-II superconductor: zero field cooling protocol and the field cooling protocol respectively. Time-splitting Crank-Nicolson method has been used to numerically simulate the vortex lattice dynamics. It is shown that the vortex lattice follows a two-step melting via loss of positional and orientational order. This vortex lattice melting process in BEC closely mimics the recently observed two-step melting of vortex matter in weakly pinned type-II superconductor Co-intercalated NbSe2. Also, using numerical perturbation analysis, we compare between the states obtained in two protocols and show that the vortex lattice states are metastable and more disordered when impurities are introduced after the formation of an ordered vortex lattice. The author would like to thank SERB, Govt. of India and BCUD-SPPU for financial support through research Grants.

Computation of Incompressible Potential Flow over an Airfoil Using a High Order Aerodynamic Panel Method Based on Circular Arc Panels.

DTIC Science & Technology

1982-08-01

Vortex Sheet Figure 4 - Properties of Singularity Sheets they may be used to model different types of flow. Transfer of boundary... Vortex Sheet Equivalence Singularity Behavior Using Green’s theorem it is clear that the problem of potential flow over a body can be modeled using ...that source, doublet, or vortex singularities can be used to model potential flow problems, and that the doublet and vortex singularities are

Visualization and Quantification of Rotor Tip Vortices in Helicopter Flows

NASA Technical Reports Server (NTRS)

Kao, David L.; Ahmad, Jasim U.; Holst, Terry L.

2015-01-01

This paper presents an automated approach for effective extraction, visualization, and quantification of vortex core radii from the Navier-Stokes simulations of a UH-60A rotor in forward flight. We adopt a scaled Q-criterion to determine vortex regions and then perform vortex core profiling in these regions to calculate vortex core radii. This method provides an efficient way of visualizing and quantifying the blade tip vortices. Moreover, the vortices radii are displayed graphically in a plane.

An Investigation of the Effects of Discrete Wing Tip Jets on Wake Vortex Roll Up.

DTIC Science & Technology

1983-08-01

failure of these devices does not mean that the vortex structure cannot be altered such as to reduce rolling moment. On the contrary, Yuan and Bloom (43...which has demonstrated a capabilitv, to e:ra induced rolling moment - the downward blowing jet of .𔄁, ,and Bloom (43)- was also the only jet...eliminated the large vortex excursions associated with close approaches. Bloom and Jen (83) used the method of Kuwahara and Takami to calculate vortex roll up

Origin and dynamics of vortex rings in drop splashing

DOE PAGES

Lee, Ji San; Park, Su Ji; Lee, Jun Ho; ...

2015-09-04

A vortex is a flow phenomenon that is very commonly observed in nature. More than a century, a vortex ring that forms during drop splashing has caught the attention of many scientists due to its importance in understanding fluid mixing and mass transport processes. However, the origin of the vortices and their dynamics remain unclear, mostly due to the lack of appropriate visualization methods. Here, with ultrafast X-ray phase-contrast imaging, we show that the formation of vortex rings originates from the energy transfer by capillary waves generated at the moment of the drop impact. Interestingly, we find a row ofmore » vortex rings along the drop wall, as demonstrated by a phase diagram established here, with different power-law dependencies of the angular velocities on the Reynolds number. These results provide important insight that allows understanding and modelling any type of vortex rings in nature, beyond just vortex rings during drop splashing.« less

Origin and dynamics of vortex rings in drop splashing.

PubMed

Lee, Ji San; Park, Su Ji; Lee, Jun Ho; Weon, Byung Mook; Fezzaa, Kamel; Je, Jung Ho

2015-09-04

A vortex is a flow phenomenon that is very commonly observed in nature. More than a century, a vortex ring that forms during drop splashing has caught the attention of many scientists due to its importance in understanding fluid mixing and mass transport processes. However, the origin of the vortices and their dynamics remain unclear, mostly due to the lack of appropriate visualization methods. Here, with ultrafast X-ray phase-contrast imaging, we show that the formation of vortex rings originates from the energy transfer by capillary waves generated at the moment of the drop impact. Interestingly, we find a row of vortex rings along the drop wall, as demonstrated by a phase diagram established here, with different power-law dependencies of the angular velocities on the Reynolds number. These results provide important insight that allows understanding and modelling any type of vortex rings in nature, beyond just vortex rings during drop splashing.

Origin and dynamics of vortex rings in drop splashing

PubMed Central

Lee, Ji San; Park, Su Ji; Lee, Jun Ho; Weon, Byung Mook; Fezzaa, Kamel; Je, Jung Ho

2015-01-01

A vortex is a flow phenomenon that is very commonly observed in nature. More than a century, a vortex ring that forms during drop splashing has caught the attention of many scientists due to its importance in understanding fluid mixing and mass transport processes. However, the origin of the vortices and their dynamics remain unclear, mostly due to the lack of appropriate visualization methods. Here, with ultrafast X-ray phase-contrast imaging, we show that the formation of vortex rings originates from the energy transfer by capillary waves generated at the moment of the drop impact. Interestingly, we find a row of vortex rings along the drop wall, as demonstrated by a phase diagram established here, with different power-law dependencies of the angular velocities on the Reynolds number. These results provide important insight that allows understanding and modelling any type of vortex rings in nature, beyond just vortex rings during drop splashing. PMID:26337704

Induced Moment Effects of Formation Flight Using Two F/A-18 Aircraft

NASA Technical Reports Server (NTRS)

Hansen, Jennifer L.; Cobleigh, Brent R.

2002-01-01

Previous investigations into formation flight have shown the possibility for significant fuel savings through drag reduction. Using two F/A-18 aircraft, NASA Dryden Flight Research Center has investigated flying aircraft in autonomous formation. Positioning the trailing airplane for best drag reduction requires investigation of the wingtip vortex effects induced by the leading airplane. A full accounting of the vortex effect on the trailing airplane is desired to validate vortex-effect prediction methods and provide a database for the design of a formation flight autopilot. A recent flight phase has mapped the complete wingtip vortex effects at two flight conditions with the trailing airplane at varying distances behind the leading one. Force and moment data at Mach 0.56 and an altitude of 25,000 ft and Mach 0.86 and an altitude of 36,000 ft have been obtained with 20, 55, 110, and 190 ft of longitudinal distance between the aircraft. The moments induced by the vortex on the trailing airplane were well within the pilot's ability to control. This report discusses the data analysis methods and vortex-induced effects on moments and side force. An assessment of the impact of the nonlinear vortex effects on the design of a formation autopilot is offered.

Transition Delay in Hypersonic Boundary Layers via Optimal Perturbations

NASA Technical Reports Server (NTRS)

Paredes, Pedro; Choudhari, Meelan M.; Li, Fei

2016-01-01

The effect of nonlinear optimal streaks on disturbance growth in a Mach 6 axisymmetric flow over a 7deg half-angle cone is investigated in an e ort to expand the range of available techniques for transition control. Plane-marching parabolized stability equations are used to characterize the boundary layer instability in the presence of azimuthally periodic streaks. The streaks are observed to stabilize nominally planar Mack mode instabilities, although oblique Mack mode disturbances are destabilized. Experimentally measured transition onset in the absence of any streaks correlates with an amplification factor of N = 6 for the planar Mack modes. For high enough streak amplitudes, the transition threshold of N = 6 is not reached by the Mack mode instabilities within the length of the cone, but subharmonic first mode instabilities, which are destabilized by the presence of the streaks, reach N = 6 near the end of the cone. These results suggest a passive flow control strategy of using micro vortex generators to induce streaks that would delay transition in hypersonic boundary layers.

Research on aircraft trailing vortex detection based on laser's multiplex information echo

NASA Astrophysics Data System (ADS)

Zhao, Nan-xiang; Wu, Yong-hua; Hu, Yi-hua; Lei, Wu-hu

2010-10-01

Airfoil trailing vortex is an important reason for the crash, and vortex detection is the basic premise for the civil aeronautics boards to make the flight measures and protect civil aviation's security. So a new method of aircraft trailing vortex detection based on laser's multiplex information echo has been proposed in this paper. According to the classical aerodynamics theories, the formation mechanism of the trailing vortex from the airfoil wingtip has been analyzed, and the vortex model of Boeing 737 in the taking-off phase has also been established on the FLUENT software platform. Combining with the unique morphological structure characteristics of trailing vortex, we have discussed the vortex's possible impact on the frequency, amplitude and phase information of laser echo, and expounded the principle of detecting vortex based on fusing this information variation of laser echo. In order to prove the feasibility of this detecting technique, the field experiment of detecting the vortex of civil Boeing 737 by laser has been carried on. The experimental result has shown that the aircraft vortex could be found really in the laser scanning area, and its diffusion characteristic has been very similar to the previous simulation result. Therefore, this vortex detection means based on laser's multiplex information echo was proved to be practicable relatively in this paper. It will provide the detection and identification of aircraft's trailing vortex a new way, and have massive research value and extensive application prospect as well.

RAPID COMMUNICATION Time-resolved measurements with a vortex flowmeter in a pulsating turbulent flow using wavelet analysis

NASA Astrophysics Data System (ADS)

Laurantzon, F.; Örlü, R.; Segalini, A.; Alfredsson, P. H.

2010-12-01

Vortex flowmeters are commonly employed in technical applications and are obtainable in a variety of commercially available types. However their robustness and accuracy can easily be impaired by environmental conditions, such as inflow disturbances and/or pulsating conditions. Various post-processing techniques of the vortex signal have been used, but all of these methods are so far targeted on obtaining an improved estimate of the time-averaged bulk velocity. Here, on the other hand, we propose, based on wavelet analysis, a straightforward way to utilize the signal from a vortex shedder to extract the time-resolved and thereby the phase-averaged velocity under pulsatile flow conditions. The method was verified with hot-wire and laser Doppler velocimetry measurements.

3D Numerical Simulation versus Experimental Assessment of Pressure Pulsations Using a Passive Method for Swirling Flow Control in Conical Diffusers of Hydraulic Turbines

NASA Astrophysics Data System (ADS)

TANASA, C.; MUNTEAN, S.; CIOCAN, T.; SUSAN-RESIGA, R. F.

2016-11-01

The hydraulic turbines operated at partial discharge (especially hydraulic turbines with fixed blades, i.e. Francis turbine), developing a swirling flow in the conical diffuser of draft tube. As a result, the helical vortex breakdown, also known in the literature as “precessing vortex rope” is developed. A passive method to mitigate the pressure pulsations associated to the vortex rope in the draft tube cone of hydraulic turbines is presented in this paper. The method involves the development of a progressive and controlled throttling (shutter), of the flow cross section at the bottom of the conical diffuser. The adjustable cross section is made on the basis of the shutter-opening of circular diaphragms, while maintaining in all positions the circular cross-sectional shape, centred on the axis of the turbine. The stagnant region and the pressure pulsations associated to the vortex rope are mitigated when it is controlled with the turbine operating regime. Consequently, the severe flow deceleration and corresponding central stagnant are diminished with an efficient mitigation of the precessing helical vortex. Four cases (one without diaphragm and three with diaphragm), are numerically and experimentally investigated, respectively. The present paper focuses on a 3D turbulent swirling flow simulation in order to evaluate the control method. Numerical results are compared against measured pressure recovery coefficient and Fourier spectra. The results prove the vortex rope mitigation and its associated pressure pulsations when employing the diaphragm.

Non-axisymmetric flow characteristics in centrifugal compressor

NASA Astrophysics Data System (ADS)

Wang, Leilei; Lao, Dazhong; Liu, Yixiong; Yang, Ce

2015-06-01

The flow field distribution in centrifugal compressor is significantly affected by the non-axisymmetric geometry structure of the volute. The experimental and numerical simulation methods were adopted in this work to study the compressor flow field distribution with different flow conditions. The results show that the pressure distributionin volute is characterized by the circumferential non-uniform phenomenon and the pressure fluctuation on the high static pressure zone propagates reversely to upstream, which results in the non-axisymmetric flow inside the compressor. The non-uniform level of pressure distribution in large flow condition is higher than that in small flow condition, its effect on the upstream flow field is also stronger. Additionally, the non-uniform circumferential pressure distribution in volute brings the non-axisymmetric flow at impeller outlet. In different flow conditions,the circumferential variation of the absolute flow angle at impeller outlet is also different. Meanwhile, the non-axisymmetric flow characteristics in internal impeller can be also reflected by the distribution of the mass flow. The high static pressure region of the volute corresponds to the decrease of mass flow in upstream blade channel, while the low static pressure zone of the volute corresponds to the increase of the mass flow. In small flow condition, the mass flow difference in the blade channel is bigger than that in the large flow condition.

Simulation of moving flat plate with unsteady translational motion using vortex method

NASA Astrophysics Data System (ADS)

Widodo, A. F.; Zuhal, L. R.

2013-10-01

This paper presents simulation of moving flate plate with unsteady translational motion using Lagrangianmeshless numerical simulation named vortex method. The method solves Navier-Stokes equations in term of vorticity. The solving strategy is splitting the equation into diffusion and convection term to be solved separately. The diffusion term is modeled by particles strength exchange(PSE) which is the most accurate of diffusion modeling in vortex method. The convection term that represents transport of particles is calculated by time step integration of velocity. Velocity of particles is natively calculated using Biot-Savart relation but for acceleration, fastmultiple method(FMM) is employed. The simulation is validated experimentally using digital particle image velocimetry(DPIV) and the results give good agreement.

Analysis of the Vortex Wakes of the Boeing 727, Lockheed L-1011, McDonnell Douglas DC-10, and Boeing 747 Aircraft

DOT National Transportation Integrated Search

1975-07-01

A study has been made of the vortex wakes behind Boeing 727, Lockheed L-1011, McDonnell Douglas DC-10, and Boeing 747 aircraft in several flight configurations. An analytical method is developed for the computation of the wake vortex patterns and the...

Vortex diode jet

DOEpatents

Houck, Edward D.

1994-01-01

A fluid transfer system that combines a vortex diode with a jet ejector to transfer liquid from one tank to a second tank by a gas pressurization method having no moving mechanical parts in the fluid system. The vortex diode is a device that has a high resistance to flow in one direction and a low resistance to flow in the other.

The formation of new quasi-stationary vortex patterns from the interaction of two identical vortices in a rotating fluid

NASA Astrophysics Data System (ADS)

Sokolovskiy, Mikhail A.; Verron, Jacques; Carton, Xavier J.

2018-06-01

Within the framework of the quasi-geostrophic approximation, the interactions of two identical initially circular vortex patches are studied using the contour dynamics/surgery method. The cases of barotropic vortices and of vortices in the upper layer of a two-layer fluid are considered. Diagrams showing the end states of vortex interactions and, in particular, the new regime of vortex triplet formation are constructed for a wide range of external parameters. This paper shows that, in the nonlinear evolution of two such (like-signed) vortices, the filaments and vorticity fragments surrounding the merged vortex often collapse into satellite vortices. Therefore, the conditions for the formation and the quasi-steady motions of a new type of triplet-shaped vortex structure are obtained.

Emergency Entry with One Control Torque: Non-Axisymmetric Diagonal Inertia Matrix

NASA Technical Reports Server (NTRS)

Llama, Eduardo Garcia

2011-01-01

In another work, a method was presented, primarily conceived as an emergency backup system, that addressed the problem of a space capsule that needed to execute a safe atmospheric entry from an arbitrary initial attitude and angular rate in the absence of nominal control capability. The proposed concept permits the arrest of a tumbling motion, orientation to the heat shield forward position and the attainment of a ballistic roll rate of a rigid spacecraft with the use of control in one axis only. To show the feasibility of such concept, the technique of single input single output (SISO) feedback linearization using the Lie derivative method was employed and the problem was solved for different number of jets and for different configurations of the inertia matrix: the axisymmetric inertia matrix (I(sub xx) > I(sub yy) = I(sub zz)), a partially complete inertia matrix with I(sub xx) > I(sub yy) > I(sub zz), I(sub xz) not = 0 and a realistic complete inertia matrix with I(sub xx) > I(sub yy) > I)sub zz), I(sub ij) not= 0. The closed loop stability of the proposed non-linear control on the total angle of attack, Theta, was analyzed through the zero dynamics of the internal dynamics for the case where the inertia matrix is axisymmetric (I(sub xx) > I(sub yy) = I(sub zz)). This note focuses on the problem of the diagonal non-axisymmetric inertia matrix (I(sub xx) > I(sub yy) > I(sub zz)), which is half way between the axisymmetric and the partially complete inertia matrices. In this note, the control law for this type of inertia matrix will be determined and its closed-loop stability will be analyzed using the same methods that were used in the other work. In particular, it will be proven that the control system is stable in closed-loop when the actuators only provide a roll torque.

Experimental investigation about the effect of non-axisymmetric wake impact on a low speed axial compressor

NASA Astrophysics Data System (ADS)

Liu, Jianyong; Lu, Yajun; Li, Zhiping

2010-05-01

Non-axisymmetric wake impact experiments were carried out after the best exciting frequency for a low speed axial compressor had been found by axisymmetric wake impact experiments. When the number and circumferential distribution of inlet guide vanes (IGV) are logical the wakes of non-axisymmetric IGVs can exert beneficial unsteady exciting effect on their downstream rotor flow fields and improve the compressor’s performance. In the present paper, four non-axisymmetric wake impact plans were found working better than the axisymmetric wake impact plan. Compared with the base plan, the best non-axisymmetric plan increased the compressor’s peak efficiency, and the total pressure rise by 1.1 and 2%, and enhanced the stall margin by 4.4%. The main reason why non-axisymmetric plans worked better than the axisymmetric plan was explained as the change of the unsteady exciting signal arising from IGV wakes. Besides the high-frequency components, the non-axisymmetric plan generated a beneficial low-frequency square-wave exciting signal and other secondary frequency components. Compared with the axisymmetric plan, multi-frequency exciting wakes arising from the non-axisymmetric plans are easier to get coupling relation with complex vortices such as clearance vortices, passage vortices and shedding vortices.

Guided waves by axisymmetric and non-axisymmetric surface loading on hollow cylinders

PubMed

Shin; Rose

1999-06-01

Guided waves generated by axisymmetric and non-axisymmetric surface loading on a hollow cylinder are studied. For the theoretical analysis of the superposed guided waves, a normal mode concept is employed. The amplitude factors of individual guided wave modes are studied with respect to varying surface pressure loading profiles. Both theoretical and experimental focus is given to the guided waves generated by both axisymmetric and non-axisymmetric excitation. For the experiments, a comb transducer and high power tone burst function generator system are used on a sample Inconel tube. Surface loading conditions, such as circumferential loading angles and axial loading lengths, are used with the frequency and phase velocity to control the axisymmetric and non-axisymmetric mode excitations. The experimental study demonstrates the use of a practical non-axisymmetric partial loading technique in generating axisymmetric modes, particularly useful in the inspection of tubing and piping with limited circumferential access. From both theoretical and experimental studies, it also could be said that the amount of flexural modes reflected from a defect contains information on the reflector's circumferential angle, as well as potentially other classification and sizing feature information. The axisymmetric and non-axisymmetric guided wave modes should both be carefully considered for improvement of the overall analysis of guided waves generated in hollow cylinders.

A numerical investigation of viscous, incompressible flow past an axisymmetric body with and without spin

NASA Astrophysics Data System (ADS)

Weber, K. F.

1985-12-01

This study deals with a preliminary investigation of the effects of spin on the axisymmetric flow past a body of revolution. The study has its genesis larger problem of Magnus forces on spinning bodies at angle of attack. However, the fundamental behavior that arises when a spinning body is placed in a uniform stream is still not well understood; therefore, the problem of axisymmetric flow with spin was undertaken. The body consists of a 3-caliber cant-ogive blunted by a spherical nosecap, a 2-caliber cylindrical section, and a 1-caliber boattail. Numerical solutions of the compressible laminar Navier-Stokes equations are obtained using a modified version of the implicit-explicit method developed by MacCormack in 1981. The benchmark problem is the nonspinning body in uniform flow at a Reynolds number of 1.14. The results show that the modified method performs well and allows time steps that are in order of magnitude greater than those permitted by explicit stability criteria.

A point vortex model for the formation of ocean eddies by flow separation

NASA Astrophysics Data System (ADS)

Southwick, O. R.; Johnson, E. R.; McDonald, N. R.

2015-01-01

A simple model for the formation of ocean eddies by flow separation from sharply curved horizontal boundary topography is developed. This is based on the Brown-Michael model for two-dimensional vortex shedding, which is adapted to more realistically model mesoscale oceanic flow by including a deforming free surface. With a free surface, the streamfunction for the flow is not harmonic so the conformal mapping methods used in the standard Brown-Michael approach cannot be used and the problem must be solved numerically. A numerical scheme is developed based on a Chebyshev spectral method for the streamfunction partial differential equation and a second order implicit timestepping scheme for the vortex position ordinary differntial equations. This method is used to compute shed vortex trajectories for three background flows: (A) a steady flow around a semi-infinite plate, (B) a free vortex moving around a semi-infinite plate, and (C) a free vortex moving around a right-angled wedge. In (A), the inclusion of surface deformation dramatically slows the vortex and changes its trajectory from a straight path to a curved one. In (B) and (C), without the inclusion of flow separation, free vortices traverse fully around the tip along symmetrical trajectories. With the effects of flow separation included, very different trajectories are found: for all values of the model parameter—the Rossby radius—the free and shed vortices pair up and move off to infinity without passing around the tip. Their final propagation angle depends strongly and monotonically on the Rossby radius.

Intracardiac Vortex Dynamics by High-Frame-Rate Doppler Vortography-In Vivo Comparison With Vector Flow Mapping and 4-D Flow MRI.

PubMed

Faurie, Julia; Baudet, Mathilde; Assi, Kondo Claude; Auger, Dominique; Gilbert, Guillaume; Tournoux, Francois; Garcia, Damien

2017-02-01

Recent studies have suggested that intracardiac vortex flow imaging could be of clinical interest to early diagnose the diastolic heart function. Doppler vortography has been introduced as a simple color Doppler method to detect and quantify intraventricular vortices. This method is able to locate a vortex core based on the recognition of an antisymmetric pattern in the Doppler velocity field. Because the heart is a fast-moving organ, high frame rates are needed to decipher the whole blood vortex dynamics during diastole. In this paper, we adapted the vortography method to high-frame-rate echocardiography using circular waves. Time-resolved Doppler vortography was first validated in vitro in an ideal forced vortex. We observed a strong correlation between the core vorticity determined by high-frame-rate vortography and the ground-truth vorticity. Vortography was also tested in vivo in ten healthy volunteers using high-frame-rate duplex ultrasonography. The main vortex that forms during left ventricular filling was tracked during two-three successive cardiac cycles, and its core vorticity was determined at a sampling rate up to 80 duplex images per heartbeat. Three echocardiographic apical views were evaluated. Vortography-derived vorticities were compared with those returned by the 2-D vector flow mapping approach. Comparison with 4-D flow magnetic resonance imaging was also performed in four of the ten volunteers. Strong intermethod agreements were observed when determining the peak vorticity during early filling. It is concluded that high-frame-rate Doppler vortography can accurately investigate the diastolic vortex dynamics.

Gaps, rings, and non-axisymmetric structures in protoplanetary disks. From simulations to ALMA observations

NASA Astrophysics Data System (ADS)

Flock, M.; Ruge, J. P.; Dzyurkevich, N.; Henning, Th.; Klahr, H.; Wolf, S.

2015-02-01

Aims: Recent observations by the Atacama Large Millimeter/submillimeter Array (ALMA) of disks around young stars revealed distinct asymmetries in the dust continuum emission. In this work we wish to study axisymmetric and non-axisymmetric structures that are generated by the magneto-rotational instability in the outer regions of protoplanetary disks. We combine the results of state-of-the-art numerical simulations with post-processing radiative transfer (RT) to generate synthetic maps and predictions for ALMA. Methods: We performed non-ideal global 3D magneto-hydrodynamic (MHD) stratified simulations of the dead-zone outer edge using the FARGO MHD code PLUTO. The stellar and disk parameters were taken from a parameterized disk model applied for fitting high-angular resolution multi-wavelength observations of various circumstellar disks. We considered a stellar mass of M∗ = 0.5 M⊙ and a total disk mass of about 0.085 M∗. The 2D initial temperature and density profiles were calculated consistently from a given surface density profile and Monte Carlo radiative transfer. The 2D Ohmic resistivity profile was calculated using a dust chemistry model. We considered two values for the dust-to-gas mass ratio, 10-2 and 10-4, which resulted in two different levels of magnetic coupling. The initial magnetic field was a vertical net flux field. The radiative transfer simulations were performed with the Monte Carlo-based 3D continuum RT code MC3D. The resulting dust reemission provided the basis for the simulation of observations with ALMA. Results: All models quickly turned into a turbulent state. The fiducial model with a dust-to-gas mass ratio of 10-2 developed a large gap followed by a jump in surface density located at the dead-zone outer edge. The jump in density and pressure was strong enough to stop the radial drift of particles at this location. In addition, we observed the generation of vortices by the Rossby wave instability at the jump location close to 60 AU. The vortices were steadily generated and destroyed at a cycle of 40 local orbits. The RT results and simulated ALMA observations predict that it is feasible to observe these large-scale structures that appear in magnetized disks without planets. Neither the turbulent fluctuations in the disk nor specific times of the model can be distinguished on the basis of high-angular resolution submillimeter observations alone. The same applies to the distinction between gaps at the dead-zone edges and planetary gaps, to the distinction between turbulent and simple unperturbed disks, and to the asymmetry created by the vortex.

A volume-of-fluid method for simulation of compressible axisymmetric multi-material flow

NASA Astrophysics Data System (ADS)

de Niem, D.; Kührt, E.; Motschmann, U.

2007-02-01

A two-dimensional Eulerian hydrodynamic method for the numerical simulation of inviscid compressible axisymmetric multi-material flow in external force fields for the situation of pure fluids separated by macroscopic interfaces is presented. The method combines an implicit Lagrangian step with an explicit Eulerian advection step. Individual materials obey separate energy equations, fulfill general equations of state, and may possess different temperatures. Material volume is tracked using a piecewise linear volume-of-fluid method. An overshoot-free logically simple and economic material advection algorithm for cylinder coordinates is derived, in an algebraic formulation. New aspects arising in the case of more than two materials such as the material ordering strategy during transport are presented. One- and two-dimensional numerical examples are given.

Synchronized Schlieren method for vortex shedding in cascade during acoustic resonance

NASA Astrophysics Data System (ADS)

Nagashima, T.; Tanida, Y.

1986-10-01

An evaluation is made of synchronized schlieren optical system methods for the simultaneous visualization of both the acoustic wave and vortex shedding phenomena encountered during acoustic resonance excited by vortex shedding from the trailing edges of cascade blades. Attention is given to the case of parallel flat plate blades in throughflow velocities of up to 100 m/s. The acoustic wavefront is found to appear in the trailing edge region and travel upstream when a pair of vortices of opposite sign are fully developed at the trailing edge.

Analysis of the vortices in the inner flow of reversible pump turbine with the new omega vortex identification method

NASA Astrophysics Data System (ADS)

Zhang, Yu-ning; Liu, Kai-hua; Li, Jin-wei; Xian, Hai-zhen; Du, Xiao-ze

2018-05-01

Reversible pump turbines are widely employed in the pumped hydro energy storage power plants. The frequent shifts among various operational modes for the reversible pump turbines pose various instability problems, e.g., the strong pressure fluctuation, the shaft swing, and the impeller damage. The instability is related to the vortices generated in the channels of the reversible pump turbines in the generating mode. In the present paper, a new omega vortex identification method is applied to the vortex analysis of the reversible pump turbines. The main advantage of the adopted algorithm is that it is physically independent of the selected values for the vortex identification in different working modes. Both weak and strong vortices can be identified by setting the same omega value in the whole passage of the reversible pump turbine. Five typical modes (turbine mode, runaway mode, turbine brake mode, zero-flow-rate mode and reverse pump mode) at several typical guide vane openings are selected for the analysis and comparisons. The differences between various modes and different guide vane openings are compared both qualitatively in terms of the vortex distributions and quantitatively in terms of the areas of the vortices in the reversible pump turbines. Our findings indicate that the new omega method could be successfully applied to the vortex identification in the reversible pump turbines.

Non-axisymmetric annular curtain stability

NASA Astrophysics Data System (ADS)

Ahmed, Zahir U.; Khayat, Roger E.; Maissa, Philippe; Mathis, Christian

2013-08-01

A stability analysis of non-axisymmetric annular curtain is carried out for an axially moving viscous jet subject in surrounding viscous gas media. The effect of inertia, surface tension, gas-to-liquid density ratio, inner-to-outer radius ratio, and gas-to-liquid viscosity ratio on the stability of the jet is studied. In general, the axisymmetric disturbance is found to be the dominant mode. However, for small wavenumber, the non-axisymmetric mode is the most unstable mode and the one likely observed in reality. Inertia and the viscosity ratio for non-axisymmetric disturbances show a similar stability influence as observed for axisymmetric disturbances. The maximum growth rate in non-axisymmetric flow, interestingly, appears at very small wavenumber for all inertia levels. The dominant wavenumber increases (decreases) with inertia for non-axisymmetric (axisymmetric) flow. Gas-to-liquid density ratio, curvature effect, and surface tension, however, exhibit an opposite influence on growth rate compared to axisymmetric disturbances. Surface tension tends to stabilize the flow with reductions of the unstable wavenumber range and the maximum growth rate as well as the dominant wavenumber. The dominant wavenumber remains independent of viscosity ratio indicating the viscosity ratio increases the breakup length of the sheet with very little influence on the size of the drops. The range of unstable wavenumbers is affected only by curvature in axisymmetric flow, whereas all the stability parameters control the range of unstable wavenumbers in non-axisymmetric flow. Inertia and gas density increase the unstable wavenumber range, whereas the radius ratio, surface tension, and the viscosity ratio decrease the unstable wavenumber range. Neutral curves are plotted to separate the stable and unstable domains. Critical radius ratio decreases linearly and nonlinearly with the wavenumber for axisymmetric and non-axisymmetric disturbances, respectively. At smaller Weber numbers, a wider unstable domain is predicted for non-axisymmetric modes. For both axisymmetric and non-axisymmetric modes, the disturbance frequency is found to be the same and equal to the negative of axial wavenumber. Finally, comparison between theory and existing experiment leads to good qualitative agreement. A more accurate comparison is not possible given the difference in flow conditions.

Calculation of the flow field in supersonic mixed-compression inlets at angle of attack using the three-dimensional method of characteristics with discrete shock wave fitting

NASA Technical Reports Server (NTRS)

Vadyak, J.; Hoffman, J. D.

1978-01-01

The influence of molecular transport is included in the computation by treating viscous and thermal diffusion terms in the governing partial differential equations as correction terms in the method of characteristics scheme. The development of a production type computer program is reported which is capable of calculating the flow field in a variety of axisymmetric mixed-compression aircraft inlets. The results agreed well with those produced by the two-dimensional method characteristics when axisymmetric flow fields are computed. For three-dimensional flow fields, the results agree well with experimental data except in regions of high viscous interaction and boundary layer removal.

A high-order boundary integral method for surface diffusions on elastically stressed axisymmetric rods.

PubMed

Li, Xiaofan; Nie, Qing

2009-07-01

Many applications in materials involve surface diffusion of elastically stressed solids. Study of singularity formation and long-time behavior of such solid surfaces requires accurate simulations in both space and time. Here we present a high-order boundary integral method for an elastically stressed solid with axi-symmetry due to surface diffusions. In this method, the boundary integrals for isotropic elasticity in axi-symmetric geometry are approximated through modified alternating quadratures along with an extrapolation technique, leading to an arbitrarily high-order quadrature; in addition, a high-order (temporal) integration factor method, based on explicit representation of the mean curvature, is used to reduce the stability constraint on time-step. To apply this method to a periodic (in axial direction) and axi-symmetric elastically stressed cylinder, we also present a fast and accurate summation method for the periodic Green's functions of isotropic elasticity. Using the high-order boundary integral method, we demonstrate that in absence of elasticity the cylinder surface pinches in finite time at the axis of the symmetry and the universal cone angle of the pinching is found to be consistent with the previous studies based on a self-similar assumption. In the presence of elastic stress, we show that a finite time, geometrical singularity occurs well before the cylindrical solid collapses onto the axis of symmetry, and the angle of the corner singularity on the cylinder surface is also estimated.

Vortex flow during early and late left ventricular filling in normal subjects: quantitative characterization using retrospectively-gated 4D flow cardiovascular magnetic resonance and three-dimensional vortex core analysis.

PubMed

Elbaz, Mohammed S M; Calkoen, Emmeline E; Westenberg, Jos J M; Lelieveldt, Boudewijn P F; Roest, Arno A W; van der Geest, Rob J

2014-09-27

LV diastolic vortex formation has been suggested to critically contribute to efficient blood pumping function, while altered vortex formation has been associated with LV pathologies. Therefore, quantitative characterization of vortex flow might provide a novel objective tool for evaluating LV function. The objectives of this study were 1) assess feasibility of vortex flow analysis during both early and late diastolic filling in vivo in normal subjects using 4D Flow cardiovascular magnetic resonance (CMR) with retrospective cardiac gating and 3D vortex core analysis 2) establish normal quantitative parameters characterizing 3D LV vortex flow during both early and late ventricular filling in normal subjects. With full ethical approval, twenty-four healthy volunteers (mean age: 20±10 years) underwent whole-heart 4D Flow CMR. The Lambda2-method was used to extract 3D LV vortex ring cores from the blood flow velocity field during early (E) and late (A) diastolic filling. The 3D location of the center of vortex ring core was characterized using cylindrical cardiac coordinates (Circumferential, Longitudinal (L), Radial (R)). Comparison between E and A filling was done with a paired T-test. The orientation of the vortex ring core was measured and the ring shape was quantified by the circularity index (CI). Finally, the Spearman's correlation between the shapes of mitral inflow pattern and formed vortex ring cores was tested. Distinct E- and A-vortex ring cores were observed with centers of A-vortex rings significantly closer to the mitral valve annulus (E-vortex L=0.19±0.04 versus A-vortex L=0.15±0.05; p=0.0001), closer to the ventricle's long-axis (E-vortex: R=0.27±0.07, A-vortex: R=0.20±0.09, p=0.048) and more elliptical in shape (E-vortex: CI=0.79±0.09, A-vortex: CI=0.57±0.06; <0.001) compared to E-vortex. The circumferential location and orientation relative to LV long-axis for both E- and A-vortex ring cores were similar. Good to strong correlation was found between vortex shape and mitral inflow shape through both the annulus (r=0.66) and leaflet tips (r=0.83). Quantitative characterization and comparison of 3D vortex rings in LV inflow during both early and late diastolic phases is feasible in normal subjects using retrospectively-gated 4D Flow CMR, with distinct differences between early and late diastolic vortex rings.

Optimal homotopy asymptotic method for flow and heat transfer of a viscoelastic fluid in an axisymmetric channel with a porous wall.

PubMed

Mabood, Fazle; Khan, Waqar A; Ismail, Ahmad Izani Md

2013-01-01

In this article, an approximate analytical solution of flow and heat transfer for a viscoelastic fluid in an axisymmetric channel with porous wall is presented. The solution is obtained through the use of a powerful method known as Optimal Homotopy Asymptotic Method (OHAM). We obtained the approximate analytical solution for dimensionless velocity and temperature for various parameters. The influence and effect of different parameters on dimensionless velocity, temperature, friction factor, and rate of heat transfer are presented graphically. We also compared our solution with those obtained by other methods and it is found that OHAM solution is better than the other methods considered. This shows that OHAM is reliable for use to solve strongly nonlinear problems in heat transfer phenomena.

Optimal Homotopy Asymptotic Method for Flow and Heat Transfer of a Viscoelastic Fluid in an Axisymmetric Channel with a Porous Wall

PubMed Central

Mabood, Fazle; Khan, Waqar A.; Ismail, Ahmad Izani

2013-01-01

In this article, an approximate analytical solution of flow and heat transfer for a viscoelastic fluid in an axisymmetric channel with porous wall is presented. The solution is obtained through the use of a powerful method known as Optimal Homotopy Asymptotic Method (OHAM). We obtained the approximate analytical solution for dimensionless velocity and temperature for various parameters. The influence and effect of different parameters on dimensionless velocity, temperature, friction factor, and rate of heat transfer are presented graphically. We also compared our solution with those obtained by other methods and it is found that OHAM solution is better than the other methods considered. This shows that OHAM is reliable for use to solve strongly nonlinear problems in heat transfer phenomena. PMID:24376722

Beam shaping with vectorial vortex beams under low numerical aperture illumination condition

NASA Astrophysics Data System (ADS)

Dai, Jianning; Zhan, Qiwen

2008-08-01

In this paper we propose and demonstrate a novel beam shaping method using vectorial vortex beam. A vectorial vortex beam is laser beam with polarization singularity in the beam cross section. This type of beams can be decomposed into two orthogonally polarized components. Each of the polarized components could have different vortex characteristics, and consequently, different intensity distribution when focused by lens. Beam shaping in the far field can be achieved by adjusting the relative weighing of these two components. As one example, we study the vectorial vortex that consists of a linearly polarized Gaussian component and a vortex component polarized orthogonally. When such a vectorial vortex beam is focus by low NA lens, the Gaussian component gives rise to a focal intensity distribution with a solid centre while the vortex component gives rise to a donut distribution with hollow dark center. The shape of the focus can be continuously varied by continuously adjusting the relative weight of the two components. Under appropriate conditions, flat top focusing can be obtained. We experimentally demonstrate the creation of such beams with a liquid crystal spatial light modulator. Flattop focus obtained by vectorial vortex beams with topological charge of +1 has been obtained.

Tracking Blade Tip Vortices for Numerical Flow Simulations of Hovering Rotorcraft

NASA Technical Reports Server (NTRS)

Kao, David L.

2016-01-01

Blade tip vortices generated by a helicopter rotor blade are a major source of rotor noise and airframe vibration. This occurs when a vortex passes closely by, and interacts with, a rotor blade. The accurate prediction of Blade Vortex Interaction (BVI) continues to be a challenge for Computational Fluid Dynamics (CFD). Though considerable research has been devoted to BVI noise reduction and experimental techniques for measuring the blade tip vortices in a wind tunnel, there are only a handful of post-processing tools available for extracting vortex core lines from CFD simulation data. In order to calculate the vortex core radius, most of these tools require the user to manually select a vortex core to perform the calculation. Furthermore, none of them provide the capability to track the growth of a vortex core, which is a measure of how quickly the vortex diffuses over time. This paper introduces an automated approach for tracking the core growth of a blade tip vortex from CFD simulations of rotorcraft in hover. The proposed approach offers an effective method for the quantification and visualization of blade tip vortices in helicopter rotor wakes. Keywords: vortex core, feature extraction, CFD, numerical flow visualization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, M., E-mail: chengm@ihpc.a-star.edu.sg; Lou, J.; Lim, T. T.

A recent theoretical study [Borisov, Kilin, and Mamaev, “The dynamics of vortex rings: Leapfrogging, choreographies and the stability problem,” Regular Chaotic Dyn. 18, 33 (2013); Borisov et al., “The dynamics of vortex rings: Leapfrogging in an ideal and viscous fluid,” Fluid Dyn. Res. 46, 031415 (2014)] shows that when three coaxial vortex rings travel in the same direction in an incompressible ideal fluid, each of the vortex rings alternately slips through (or leapfrogs) the other two ahead. Here, we use a lattice Boltzmann method to simulate viscous vortex rings with an identical initial circulation, radius, and separation distance with themore » aim of studying how viscous effect influences the outcomes of the leapfrogging process. For the case of two identical vortex rings, our computation shows that leapfrogging can be achieved only under certain favorable conditions, which depend on Reynolds number, vortex core size, and initial separation distance between the two rings. For the case of three coaxial vortex rings, the result differs from the inviscid model and shows that the second vortex ring always slips through the leading ring first, followed by the third ring slipping through the other two ahead. A simple physical model is proposed to explain the observed behavior.« less

Investigation of Vortex Flaps and Other Flow Control Devices on Generic High-Speed Civil Transport Planforms

NASA Technical Reports Server (NTRS)

Kjerstad, Kevin J.; Campbell, Bryan A.; Gile, Brenda E.; Kemmerly, Guy T.

1999-01-01

A parametric cranked delta planform study has been conducted in the Langley 14- by 22-Foot Subsonic Tunnel with the following objectives: (1) to evaluate the vortex flap design methodology for cranked delta wings, (2) to determine the influence of leading-edge sweep and the outboard wing on vortex flap effectiveness, (3) to evaluate novel flow control concepts, and (4) to validate unstructured grid Euler computer code predictions with modeled vortex and trailing-edge flaps. Two families of cranked delta planforms were investigated. One family had constant aspect ratio, while the other had a constant nondimensional semispan location of the leading-edge break. The inboard leading-edge sweep of the planforms was varied between 68 deg., 71 deg., and 74 deg., while outboard leading-edge sweep was varied between 48 deg. and 61 deg. Vortex flaps for the different planforms were designed by an analytical vortex flap design method. The results indicate that the effectiveness of the vortex flaps was only slightly influenced by the variations in the parametric planforms. The unstructured grid Euler computer code was successfully used to model the configurations with vortex flaps. The vortex trap concept was successfully demonstrated.

OWC with vortex beams in data center networks

NASA Astrophysics Data System (ADS)

Kupferman, Judy; Arnon, Shlomi

2017-10-01

Data centers are a key building block in the rapidly growing area of internet technology. A typical data center has tens of thousands of servers, and communication between them must be flexible and robust. Vortex light beams have orbital angular momentum and can provide a useful and flexible method for optical wireless communication in data centers. Vortex beams can be generated with orbital angular momentum but independent of polarization, and used in a multiplexed system. We propose a multiplexing vortex system to increase the communication capacity using optical wireless communication for data center networks. We then evaluate performance. This paper is intended for use as an engineering guideline for design of vortex multiplexing in data center applications.

Design, fabrication, and measurement of reflective metasurface for orbital angular momentum vortex wave in radio frequency domain

NASA Astrophysics Data System (ADS)

Yu, Shixing; Li, Long; Shi, Guangming; Zhu, Cheng; Zhou, Xiaoxiao; Shi, Yan

2016-03-01

In this paper, a reflective metasurface is designed, fabricated, and experimentally demonstrated to generate an orbital angular momentum (OAM) vortex wave in radio frequency domain. Theoretical formula of phase-shift distribution is deduced and used to design the metasurface producing vortex radio waves. The prototype of a practical configuration is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that the vortex waves with different OAM mode numbers can be flexibly generated by using sub-wavelength reflective metasurfaces. The proposed method and metasurface pave a way to generate the OAM vortex waves for radio and microwave wireless communication applications.

Visualization of a vortex flow in a rotating tank

NASA Astrophysics Data System (ADS)

Kawano, Yosuke

Flow structures of a vortex in a rotating tank were studied employing tracer method. The velocity measurements were made by photographing the motions of small polystyrene particles and analyzing strobo flash light pictures. The vortex flow is confined to a cylindrical region which is composed of a spiral upward flow in the center surrounded by an annular downward flow.

Fast Multipole Methods for Three-Dimensional N-body Problems

NASA Technical Reports Server (NTRS)

Koumoutsakos, P.

1995-01-01

We are developing computational tools for the simulations of three-dimensional flows past bodies undergoing arbitrary motions. High resolution viscous vortex methods have been developed that allow for extended simulations of two-dimensional configurations such as vortex generators. Our objective is to extend this methodology to three dimensions and develop a robust computational scheme for the simulation of such flows. A fundamental issue in the use of vortex methods is the ability of employing efficiently large numbers of computational elements to resolve the large range of scales that exist in complex flows. The traditional cost of the method scales as Omicron (N(sup 2)) as the N computational elements/particles induce velocities at each other, making the method unacceptable for simulations involving more than a few tens of thousands of particles. In the last decade fast methods have been developed that have operation counts of Omicron (N log N) or Omicron (N) (referred to as BH and GR respectively) depending on the details of the algorithm. These methods are based on the observation that the effect of a cluster of particles at a certain distance may be approximated by a finite series expansion. In order to exploit this observation we need to decompose the element population spatially into clusters of particles and build a hierarchy of clusters (a tree data structure) - smaller neighboring clusters combine to form a cluster of the next size up in the hierarchy and so on. This hierarchy of clusters allows one to determine efficiently when the approximation is valid. This algorithm is an N-body solver that appears in many fields of engineering and science. Some examples of its diverse use are in astrophysics, molecular dynamics, micro-magnetics, boundary element simulations of electromagnetic problems, and computer animation. More recently these N-body solvers have been implemented and applied in simulations involving vortex methods. Koumoutsakos and Leonard (1995) implemented the GR scheme in two dimensions for vector computer architectures allowing for simulations of bluff body flows using millions of particles. Winckelmans presented three-dimensional, viscous simulations of interacting vortex rings, using vortons and an implementation of a BH scheme for parallel computer architectures. Bhatt presented a vortex filament method to perform inviscid vortex ring interactions, with an alternative implementation of a BH scheme for a Connection Machine parallel computer architecture.

Collapsing vortex filaments and the spectrum of quantum turbulence

NASA Astrophysics Data System (ADS)

Andryushchenko, V. A.; Nemirovskii, S. K.

2017-01-01

The method of correlation functions and the method of quantum vortex configurations are used to calculate the energy spectrum of a three-dimensional velocity field that is induced by collapsing (immediately before reconnection) vortex filaments. The formulation of this problem is motivated by the idea of modeling classical turbulence by a set of chaotic quantized vortex filaments. Among the various arguments that support the idea of quasi-classical behavior for quantum turbulence, the most persuasive is probably the resulting Kolmogorov energy spectrum resembling E ( k ) ∝ k - 5 / 3 that was obtained in a number of numerical studies. Another goal is associated with an important and intensely studied theme that relates to the role of hydrodynamic collapse in the formation of turbulence spectra. Calculations have demonstrated that vortex filaments create a velocity field at the moment of contact, which has a singularity. This configuration of vortex filaments generates the spectrum E(k), which bears the resemblance to the Kolmogorov law. A possible cause for this observation is discussed, as well as the likely reasons behind any deviations. The obtained results are discussed from the perspective of both classical and quantum turbulence.

Generation of Multiple Vortex Beams with Specified Vortex Number from Lasers with Controlled Ince-Gaussian Modes

NASA Astrophysics Data System (ADS)

Chu, Shu-Chun

2008-07-01

This study proposes a systematic method of selecting excitations of part of Ince-Gaussian modes (IGMs) and a three-lens configuration for generating multiple vortex beams with forced IGMs in the model of laser-diode (LD)-pumped solid-state lasers. Simply changing the lateral off-axis position of the tight pump beam focus on the laser crystal can produce the desired multiple optical vortex beam from the laser in a well-controlled manner using a proposed astigmatic mode converter assembled into one body with the laser cavity.

The Impacts of Dry Dynamic Cores on Asymmetric Hurricane Intensification

NASA Technical Reports Server (NTRS)

Guimond, Stephen R.; Reisner, Jon M.; Marras, Simone; Giraldo, Francis X.

2016-01-01

The fundamental pathways for tropical cyclone (TC) intensification are explored by considering axisymmetric and asymmetric impulsive thermal perturbations to balanced, TC-like vortices using the dynamic cores of three different nonlinear numerical models. Attempts at reproducing the results of previous work, which used the community WRF Model, revealed a discrepancy with the impacts of purely asymmetric thermal forcing. The current study finds that thermal asymmetries can have an important, largely positive role on the vortex intensification, whereas other studies find that asymmetric impacts are negligible. Analysis of the spectral energetics of each numerical model indicates that the vortex response to asymmetric thermal perturbations is significantly damped in WRF relative to the other models. Spectral kinetic energy budgets show that this anomalous damping is primarily due to the increased removal of kinetic energy from the vertical divergence of the vertical pressure flux, which is related to the flux of inertia-gravity wave energy. The increased kinetic energy in the other two models is shown to originate around the scales of the heating and propagate upscale with time from nonlinear effects. For very large thermal amplitudes (50 K), the anomalous removal of kinetic energy due to inertia-gravity wave activity is much smaller, resulting in good agreement between models. The results of this paper indicate that the numerical treatment of small-scale processes that project strongly onto inertia-gravity wave energy can lead to significant differences in asymmetric TC intensification. Sensitivity tests with different time integration schemes suggest that diffusion entering into the implicit solution procedure is partly responsible for the anomalous damping of energy.

Computational Simulations of Convergent Nozzles for the AIAA 1st Propulsion Aerodynamics Workshop

NASA Technical Reports Server (NTRS)

Dippold, Vance F., III

2014-01-01

Computational Fluid Dynamics (CFD) simulations were completed for a series of convergent nozzles in participation of the American Institute of Aeronautics and Astronautics (AIAA) 1st Propulsion Aerodynamics Workshop. The simulations were performed using the Wind-US flow solver. Discharge and thrust coefficients were computed for four axisymmetric nozzles with nozzle pressure ratios (NPR) ranging from 1.4 to 7.0. The computed discharge coefficients showed excellent agreement with available experimental data; the computed thrust coefficients captured trends observed in the experimental data, but over-predicted the thrust coefficient by 0.25 to 1.0 percent. Sonic lines were computed for cases with NPR >= 2.0 and agreed well with experimental data for NPR >= 2.5. Simulations were also performed for a 25 deg. conic nozzle bifurcated by a flat plate at NPR = 4.0. The jet plume shock structure was compared with and without the splitter plate to the experimental data. The Wind-US simulations predicted the shock structure well, though lack of grid resolution in the plume reduced the sharpness of the shock waves. Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations and Detached Eddy Simulations (DES) were performed at NPR = 1.6 for the 25 deg conic nozzle with splitter plate. The simulations predicted vortex shedding from the trailing edge of the splitter plate. However, the vortices of URANS and DES solutions appeared to dissipate earlier than observed experimentally. It is believed that a lack of grid resolution in the region of the vortex shedding may have caused the vortices to break down too soon

Study on Wind-induced Vibration and Fatigue Life of Cable-stayed Flexible Antenna

NASA Astrophysics Data System (ADS)

He, Kongde; He, Xuehui; Fang, Zifan; Zheng, Xiaowei; Yu, Hongchang

2018-03-01

The cable-stayed flexible antenna is a large-span space structure composed of flexible multibody, with low frequency of vibration, vortex-induced resonance can occur under the action of Stochastic wind, and a larger amplitude is generated when resonance occurs. To solve this problem, based on the theory of vortex-induced vibration, this paper analyzes the vortex-induced vibration of a cable-stayed flexible antenna under the action of Wind. Based on the sinusoidal force model and Autoregressive Model (AR) method, the vortex-induced force is simulated, then the fatigue analysis of the structure is based on the linear fatigue cumulative damage principle and the rain-flow method. The minimum fatigue life of the structure is calculated to verify the vibration fatigue performance of the structure.

Schlieren photography on freely flying hawkmoth.

PubMed

Liu, Yun; Roll, Jesse; Van Kooten, Stephen; Deng, Xinyan

2018-05-01

The aerodynamic force on flying insects results from the vortical flow structures that vary both spatially and temporally throughout flight. Due to these complexities and the inherent difficulties in studying flying insects in a natural setting, a complete picture of the vortical flow has been difficult to obtain experimentally. In this paper, Schlieren , a widely used technique for highspeed flow visualization, was adapted to capture the vortex structures around freely flying hawkmoth ( Manduca ). Flow features such as leading-edge vortex, trailing-edge vortex, as well as the full vortex system in the wake were visualized directly. Quantification of the flow from the Schlieren images was then obtained by applying a physics-based optical flow method, extending the potential applications of the method to further studies of flying insects. © 2018 The Author(s).

Discrete-vortex model for the symmetric-vortex flow on cones

NASA Technical Reports Server (NTRS)

Gainer, Thomas G.

1990-01-01

A relatively simple but accurate potential flow model was developed for studying the symmetric vortex flow on cones. The model is a modified version of the model first developed by Bryson, in which discrete vortices and straight-line feeding sheets were used to represent the flow field. It differs, however, in the zero-force condition used to position the vortices and determine their circulation strengths. The Bryson model imposed the condition that the net force on the feeding sheets and discrete vortices must be zero. The proposed model satisfies this zero-force condition by having the vortices move as free vortices, at a velocity equal to at the local crossflow velocity at their centers. When the free-vortex assumption is made, a solution is obtained in the form of two nonlinear algebraic equations that relate the vortex center coordinates and vortex strengths to the cone angle and angle of attack. The vortex center locations calculated using the model are in good agreement with experimental values. The cone normal forces as well as center locations are in good agreement with the vortex cloud method of calculating symmetric flow fields.

Random center vortex lines in continuous 3D space-time

DOE Office of Scientific and Technical Information (OSTI.GOV)

Höllwieser, Roman; Institute of Atomic and Subatomic Physics, Vienna University of Technology, Operngasse 9, 1040 Vienna; Altarawneh, Derar

2016-01-22

We present a model of center vortices, represented by closed random lines in continuous 2+1-dimensional space-time. These random lines are modeled as being piece-wise linear and an ensemble is generated by Monte Carlo methods. The physical space in which the vortex lines are defined is a cuboid with periodic boundary conditions. Besides moving, growing and shrinking of the vortex configuration, also reconnections are allowed. Our ensemble therefore contains not a fixed, but a variable number of closed vortex lines. This is expected to be important for realizing the deconfining phase transition. Using the model, we study both vortex percolation andmore » the potential V(R) between quark and anti-quark as a function of distance R at different vortex densities, vortex segment lengths, reconnection conditions and at different temperatures. We have found three deconfinement phase transitions, as a function of density, as a function of vortex segment length, and as a function of temperature. The model reproduces the qualitative features of confinement physics seen in SU(2) Yang-Mills theory.« less

Research of the Electron Cyclotron Emission with Vortex Property excited by high power high frequency Gyrotron

NASA Astrophysics Data System (ADS)

Goto, Yuki; Kubo, Shin; Tsujimura, Tohru; Takubo, Hidenori

2017-10-01

Recently, it has been shown that the radiation from a single electron in cyclotron motion has vortex property. Although the cyclotron emission exists universally in nature, the vortex property has not been featured because this property is normally cancelled out due to the randomness in gyro-phase of electrons and the development of detection of the vortex property has not been well motivated. In this research, we are developing a method to generate the vortex radiation from electrons in cyclotron motion with controlled gyro-phase. Electron that rotates around the uniform static magnetic field is accelerated by right-hand circular polarized (RHCP) radiation resonantly when the cyclotron frequency coincides with the applied RHCP radiation frequency. A large number of electrons can be coherently accelerated in gyro-phase by a RHCP high power radiation so that these electrons can radiate coherent emission with vortex feature. We will show that vortex radiation created by purely rotating electrons for the first time.

Stable dissipative optical vortex clusters by inhomogeneous effective diffusion.

PubMed

Li, Huishan; Lai, Shiquan; Qui, Yunli; Zhu, Xing; Xie, Jianing; Mihalache, Dumitru; He, Yingji

2017-10-30

We numerically show the generation of robust vortex clusters embedded in a two-dimensional beam propagating in a dissipative medium described by the generic cubic-quintic complex Ginzburg-Landau equation with an inhomogeneous effective diffusion term, which is asymmetrical in the two transverse directions and periodically modulated in the longitudinal direction. We show the generation of stable optical vortex clusters for different values of the winding number (topological charge) of the input optical beam. We have found that the number of individual vortex solitons that form the robust vortex cluster is equal to the winding number of the input beam. We have obtained the relationships between the amplitudes and oscillation periods of the inhomogeneous effective diffusion and the cubic gain and diffusion (viscosity) parameters, which depict the regions of existence and stability of vortex clusters. The obtained results offer a method to form robust vortex clusters embedded in two-dimensional optical beams, and we envisage potential applications in the area of structured light.

Characterizing the wake vortex signature for an active line of sight remote sensor. M.S. Thesis Technical Report No. 19

NASA Technical Reports Server (NTRS)

Heil, Robert Milton

1994-01-01

A recurring phenomenon, described as a wake vortex, develops as an aircraft approaches the runway to land. As the aircraft moves along the runway, each of the wing tips generates a spiraling and expanding cone of air. During the lifetime of this turbulent event, conditions exist over the runway which can be hazardous to following aircraft, particularly when a small aircraft is following a large aircraft. Left to themselves, these twin vortex patterns will converge toward each other near the center of the runway, harmlessly dissipating through interaction with each other or by contact with the ground. Unfortunately, the time necessary to disperse the vortex is often not predictable, and at busy airports can severely impact terminal area productivity. Rudimentary methods of avoidance are in place. Generally, time delays between landing aircraft are based on what is required to protect a small aircraft. Existing ambient wind conditions can complicate the situation. Reliable detection and tracking of a wake vortex hazard is a major technical problem which can significantly impact runway productivity. Landing minimums could be determined on the basis of the actual hazard rather than imposed on the basis of a worst case scenario. This work focuses on using a windfield description of a wake vortex to generate line-of-sight Doppler velocity truth data appropriate to an arbitrarily located active sensor such as a high resolution radar or lidar. The goal is to isolate a range Doppler signature of the vortex phenomenon that can be used to improve detection. Results are presented based on use of a simplified model of a wake vortex pattern. However, it is important to note that the method of analysis can easily be applied to any vortex model used to generate a windfield snapshot. Results involving several scan strategies are shown for a point sensor with a range resolution of 1 to 4 meters. Vortex signatures presented appear to offer potential for detection and tracking.

On the size and distribution of rings and coherent vortices in the Sargasso Sea

NASA Astrophysics Data System (ADS)

Luce, David L.; Rossby, Tom

2008-05-01

The container motor vessel CMV Oleander, which operates between New Jersey and Bermuda, crosses the Gulf Stream and Sargasso Sea all year round on a semiweekly schedule. Using an acoustic Doppler current profiler, measurements of upper ocean currents have been made on a regular basis since the fall of 1992. In this paper we examine the database for evidence of axisymmetric coherent vortices including the distribution and intensity of cold core rings. To detect the existence of coherent vortices, the patterns of current vectors averaged between 40 and 80 m depth were fit to an axisymmetric Gaussian vortex model. The parameters of the model were axis location, maximum tangential, or swirl, speed, and radius at which the maximum swirl was measured. We were able to distinguish between the well-known cold core "rings" (CCRs) pinched from the Gulf Stream, and a population of cyclonic and anticyclonic "vortices" in the Sargasso Sea. Both the rings and the Sargasso Sea vortices showed radii of 64 ± 18 km, albeit with different swirl speeds. The rings, close to the Gulf Stream, exhibited a typical maximum swirl speed of 0.98 ± 0.40 m s-1 and a center relative vorticity of 0.64 ± 0.35 × 10-4 s-1, almost 80% of the planetary vorticity for the region. The more uniform population of Sargasso Sea vortices contained approximately equal numbers of cyclones and anticyclones, with mean speeds of +0.43 and -0.55 m s-1, and center relative vorticities of +0.24 × 10-4 s-1 and -0.29 × 10-4 s-1, respectively.

Supersonic Wind Tunnel Tests of a Half-axisymmetric 12 Deg-spike Inlet to a Rocket-based Combined-cycle Propulsion System

NASA Technical Reports Server (NTRS)

DeBonis, J. R.; Trefny, C. J.

2001-01-01

Results of an isolated inlet test for NASA's GTX air-breathing launch vehicle concept are presented. The GTX is a Vertical Take-off/ Horizontal Landing reusable single-stage-to-orbit system powered by a rocket-based combined-cycle propulsion system. Tests were conducted in the NASA Glenn 1- by 1-Foot Supersonic Wind Tunnel during two entries in October 1998 and February 1999. Tests were run from Mach 2.8 to 6. Integrated performance parameters and static pressure distributions are reported. The maximum contraction ratios achieved in the tests were lower than predicted by axisymmetric Reynolds-averaged Navier-Stokes computational fluid dynamics (CFD). At Mach 6, the maximum contraction ratio was roughly one-half of the CFD value of 16. The addition of either boundary-layer trip strips or vortex generators had a negligible effect on the maximum contraction ratio. A shock boundary-layer interaction was also evident on the end-walls that terminate the annular flowpath cross section. Cut-back end-walls, designed to reduce the boundary-layer growth upstream of the shock and minimize the interaction, also had negligible effect on the maximum contraction ratio. Both the excessive turning of low-momentum comer flows and local over-contraction due to asymmetric end-walls were identified as possible reasons for the discrepancy between the CFD predictions and the experiment. It is recommended that the centerbody spike and throat angles be reduced in order to lessen the induced pressure rise. The addition of a step on the cowl surface, and planar end-walls more closely approximating a plane of symmetry are also recommended. Provisions for end-wall boundary-layer bleed should be incorporated.

Vortex methods for separated flows

NASA Technical Reports Server (NTRS)

Spalart, Philippe R.

1988-01-01

The numerical solution of the Euler or Navier-Stokes equations by Lagrangian vortex methods is discussed. The mathematical background is presented in an elementary fashion and includes the relationship with traditional point-vortex studies, the convergence to smooth solutions of the Euler equations, and the essential differences between two- and three-dimensional cases. The difficulties in extending the method to viscous or compressible flows are explained. The overlap with the excellent review articles available is kept to a minimum and more emphasis is placed on the area of expertise, namely two-dimensional flows around bluff bodies. When solid walls are present, complete mathematical models are not available and a more heuristic attitude must be adopted. The imposition of inviscid and viscous boundary conditions without conformal mappings or image vortices and the creation of vorticity along solid walls are examined in detail. Methods for boundary-layer treatment and the question of the Kutta condition are discussed. Practical aspects and tips helpful in creating a method that really works are explained. The topics include the robustness of the method and the assessment of accuracy, vortex-core profiles, timemarching schemes, numerical dissipation, and efficient programming. Calculations of flows past streamlined or bluff bodies are used as examples when appropriate.

A Numerical Model of Unsteady, Subsonic Aeroelastic Behavior. Ph.D Thesis

NASA Technical Reports Server (NTRS)

Strganac, Thomas W.

1987-01-01

A method for predicting unsteady, subsonic aeroelastic responses was developed. The technique accounts for aerodynamic nonlinearities associated with angles of attack, vortex-dominated flow, static deformations, and unsteady behavior. The fluid and the wing together are treated as a single dynamical system, and the equations of motion for the structure and flow field are integrated simultaneously and interactively in the time domain. The method employs an iterative scheme based on a predictor-corrector technique. The aerodynamic loads are computed by the general unsteady vortex-lattice method and are determined simultaneously with the motion of the wing. Because the unsteady vortex-lattice method predicts the wake as part of the solution, the history of the motion is taken into account; hysteresis is predicted. Two models are used to demonstrate the technique: a rigid wing on an elastic support experiencing plunge and pitch about the elastic axis, and an elastic wing rigidly supported at the root chord experiencing spanwise bending and twisting. The method can be readily extended to account for structural nonlinearities and/or substitute aerodynamic load models. The time domain solution coupled with the unsteady vortex-lattice method provides the capability of graphically depicting wing and wake motion.

A test of a vortex method for the computation of flap side edge noise

NASA Technical Reports Server (NTRS)

Martin, James E.

1995-01-01

Upon approach to landing, a major source location of airframe noise occurs at the side edges of the part span, trailing edge flaps. In the vicinity of these flaps, a complex arrangement of spanwise flow with primary and secondary tip vortices may form. Each of these vortices is observed to become fully three-dimensional. In the present study, a numerical model is developed to investigate the noise radiated from the side edge of a flap. The inherent three-dimensionality of this flow forces us to carefully consider a numerical scheme which will be both accurate in its prediction of the flow acoustics and also computationally efficient. Vortex methods have offered a fast and efficient means of simulating many two and three-dimensional, vortex dominated flows. In vortex methods, the time development of the flow is tracked by following exclusively the vorticity containing regions. Through the Biot-Savart law, knowledge of the vorticity field enables one to obtain flow quantities at any desired location during the flow evolution. In the present study, a numerical procedure has been developed which incorporates the Lagrangian approach of vortex methods into a calculation for the noise radiated by a flow-surface interaction. In particular, the noise generated by a vortex in the presence of a flat half plane is considered. This problem serves as a basic model of flap edge flow. It also permits the direct comparison between our computed results and previous acoustic analyses performed for this problem. In our numerical simulations, the mean flow is represented by the complex potential W(z) = Aiz(exp l/2), which is obtained through conformal mapping techniques. The magnitude of the mean flow is controlled by the parameter A. This mean flow has been used in the acoustic analysis by Hardin and is considered a reasonable model of the flow field in the vicinity of the edge and away from the leading and trailing edges of the flap. To represent the primary vortex which occurs near the flap, a point vortex is introduced just below the flat half plane. Using a technique from panel methods, boundary conditions on the flap surface are satisfied by the introduction of a row of stationary point vortices along the extent of the flap. At each time step in the calculation, the strength of these vortices is chosen to eliminate the normal velocity at intermediary collocation points. The time development of the overall flow field is then tracked using standard techniques from vortex methods. Vortex trajectories obtained through this computation are in good agreement with those predicted by the analytical solution given by Hardin, thus verifying the viability of this procedure for more complex flow arrangements. For the flow acoustics, the Ffowcs Williams-Hawkings equation is numerically integrated. This equation supplies the far field acoustic pressure based upon pressures occurring along the flap surface. With our vortex method solution, surface pressures may be obtained with exceptional resolution. The Ffowcs Williams-Hawkings equation is integrated using a spatially fourth order accurate Simpson's rule. Rational function interpolation is used to obtain the surface pressures at the appropriate retarded times. Comparisons between our numerical results for the acoustic pressure and those predicted by the Hardin analysis have been made. Preliminary results indicate the need for an improved integration technique. In the future, the numerical procedure developed in this study will be applied to the case of a rectangular flap of finite thickness and ultimately modified for application to the fully three-dimensional problem.

Vortex maneuver lift for super-cruise configurations

NASA Technical Reports Server (NTRS)

Campbell, J. F.; Gloss, B. B.; Lamar, J. E.

1976-01-01

Some of the theoretical and experimental research conducted at the NASA Langley Research Center is presented to investigate the subsonic vortex-lift producing capabilities for two classes of Super-Cruise designs: a close-coupled wing-canard arrangement and a slender wing configuration. In addition, several analytical methods are discussed for estimating critical structural design loads for thin, highly swept wings having separated leading-edge vortex flows.

Viscous and Interacting Flow Field Effects.

DTIC Science & Technology

1980-06-01

in the inviscid flow analysis using free vortex sheets whose shapes are determined by iteration. The outer iteration employs boundary layer...Methods, Inc. which replaces the source distribution in the separation zone by a vortex wake model . This model is described in some detail in (2), but...in the potential flow is obtained using linearly varying vortex singularities distributed on planar panels. The wake is represented by sheets of

Calculation of vortex lift effect for cambered wings by the suction analogy

NASA Technical Reports Server (NTRS)

Lan, C. E.; Chang, J. F.

1981-01-01

An improved version of Woodward's chord plane aerodynamic panel method for subsonic and supersonic flow is developed for cambered wings exhibiting edge separated vortex flow, including those with leading edge vortex flaps. The exact relation between leading edge thrust and suction force in potential flow is derived. Instead of assuming the rotated suction force to be normal to wing surface at the leading edge, new orientation for the rotated suction force is determined through consideration of the momentum principle. The supersonic suction analogy method is improved by using an effective angle of attack defined through a semi-empirical method. Comparisons of predicted results with available data in subsonic and supersonic flow are presented.

A static air flow visualization method to obtain a time history of the lift-induced vortex and circulation

NASA Technical Reports Server (NTRS)

Patterson, J. C., Jr.; Jordan, F. L., Jr.

1975-01-01

A recently proposed method of flow visualization was investigated at the National Aeronautics and Space Administration's Langley Research Center. This method of flow visualization is particularly applicable to the study of lift-induced wing tip vortices through which it is possible to record the entire life span of the vortex. To accomplish this, a vertical screen of smoke was produced perpendicular to the flight path and allowed to become stationary. A model was then driven through the screen of smoke producing the circular vortex motion made visible as the smoke was induced along the path taken by the flow and was recorded by highspeed motion pictures.

Research of the high performance low temperature vortex street flowmeter

NASA Astrophysics Data System (ADS)

Gao, Feng; Chen, Yang; Zhang, Zhen-peng; Geng, Wei-guo

2007-07-01

Flow measurement is the key method for R&D and operation monitoring of liquid rocket engine. Therefore, it is important to measure flux of low temperature liquid propellants for the liquid hydrogen/liquid oxygen or the liquid oxygen/kerosene rocket engine. Presently in China, the level meter and the turbine flowmeter are usually used in the experimentation of the liquid hydrogen/liquid oxygen rocket engine. The level meter can only scale average flux and the precision of the turbine flowmeter (the measuring wild point is 1.5%) can not be ensured due to the reason which there is not devices of low temperature real-time demarcation in China. Therefore, it is required to research the high performance low temperature flow measurement equipment and the vortex street flowmeter is selected because of its advantages. In the paper, some key techniques of low temperature vortex street flowmeter are researched from the design aspect. Firstly, the basic theoretical research of vortex street flowmeter includes signal detection method, shape of vortex producer and effects of dimension of vertex producer to vortex quality. Secondly, low temperature vortex street flowmeter adopts the method of piezoelectric components stress mode. As for the weakness of phase-change, lattice change and fragility for many piezoelectric materials in low temperature, it can not be fulfilled piezoelectric signal and mechanism performance under this condition. Some piezoelectric materials which can be used in low temperature are illustrated in the paper by lots of research in order for the farther research. The article places emphasis upon low temperature trait of piezoelectric materials, and the structure designs of signal detector and calculation of stress, electric charge quantity and heat transfer.

Stability of mechanical joints in launching vehicles: Local and global stationary values of energy density

NASA Astrophysics Data System (ADS)

Chue, Ching-Hwei

A method was developed for predicting the behavior of mechanical joints in launch vehicles with particular emphasis placed on how the combined effects of loading, geometry, and materials could be optimized in terms of structure instability and/or integrity. What was considered to be essential is the fluctuation of the volume energy density with time in the structure. The peaks and valleys of the volume energy density function will be associated with failure by fracture and/or yielding while the distance between their local and global stationary values govern the structure instability. The Solid Rocket Booster (SRB) of the space shuttle was analyzed under axisymmetric and non-axisymmetric loadings. A semi-analytical finite element program was developed for solving the case of non-axisymmetric loading. Following a dynamic stress analysis, contours of the volume energy density in the structure were obtained as a function of time. The magnitudes and locations of these stationary values were then calculated locally and globally and related to possible failure by fracture. In the case of axisymmetric flight, the local and global instability behavior do not change appreciably. Fluctuations in the energy density and the dynamic stability length parameter become appreciable when the non-axisymmetric loads are considered. The magnitude of the energy in the shell structure is sensitive to alterations in the gas pressure induced by the solid propellant.

Antenna design for microwave hepatic ablation using an axisymmetric electromagnetic model

PubMed Central

Bertram, John M; Yang, Deshan; Converse, Mark C; Webster, John G; Mahvi, David M

2006-01-01

Background An axisymmetric finite element method (FEM) model was employed to demonstrate important techniques used in the design of antennas for hepatic microwave ablation (MWA). To effectively treat deep-seated hepatic tumors, these antennas should produce a highly localized specific absorption rate (SAR) pattern and be efficient radiators at approved generator frequencies. Methods and results As an example, a double slot choked antenna for hepatic MWA was designed and implemented using FEMLAB™ 3.0. Discussion This paper emphasizes the importance of factors that can affect simulation accuracy, which include boundary conditions, the dielectric properties of liver tissue, and mesh resolution. PMID:16504153

Phase Correction for GPS Antenna with Nonunique Phase Center

NASA Technical Reports Server (NTRS)

Fink, Patrick W.; Dobbins, Justin

2005-01-01

A method of determining the position and attitude of a body equipped with a Global Positioning System (GPS) receiver includes an accounting for the location of the nonunique phase center of a distributed or wraparound GPS antenna. The method applies, more specifically, to the case in which (1) the GPS receiver utilizes measurements of the phases of GPS carrier signals in its position and attitude computations and (2) the body is axisymmetric (e.g., spherical or round cylindrical) and wrapped at its equator with a single- or multiple-element antenna, the radiation pattern of which is also axisymmetric with the same axis of symmetry as that of the body.

Fully Nonlinear Modeling and Analysis of Precision Membranes

NASA Technical Reports Server (NTRS)

Pai, P. Frank; Young, Leyland G.

2003-01-01

High precision membranes are used in many current space applications. This paper presents a fully nonlinear membrane theory with forward and inverse analyses of high precision membrane structures. The fully nonlinear membrane theory is derived from Jaumann strains and stresses, exact coordinate transformations, the concept of local relative displacements, and orthogonal virtual rotations. In this theory, energy and Newtonian formulations are fully correlated, and every structural term can be interpreted in terms of vectors. Fully nonlinear ordinary differential equations (ODES) governing the large static deformations of known axisymmetric membranes under known axisymmetric loading (i.e., forward problems) are presented as first-order ODES, and a method for obtaining numerically exact solutions using the multiple shooting procedure is shown. A method for obtaining the undeformed geometry of any axisymmetric membrane with a known inflated geometry and a known internal pressure (i.e., inverse problems) is also derived. Numerical results from forward analysis are verified using results in the literature, and results from inverse analysis are verified using known exact solutions and solutions from the forward analysis. Results show that the membrane theory and the proposed numerical methods for solving nonlinear forward and inverse membrane problems are accurate.

Generating multiple orbital angular momentum vortex beams using a metasurface in radio frequency domain

NASA Astrophysics Data System (ADS)

Yu, Shixing; Li, Long; Shi, Guangming; Zhu, Cheng; Shi, Yan

2016-06-01

In this paper, an electromagnetic metasurface is designed, fabricated, and experimentally demonstrated to generate multiple orbital angular momentum (OAM) vortex beams in radio frequency domain. Theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce multiple vortex radio waves in different directions with different OAM modes. The prototype of a practical configuration of square-patch metasurface is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that multiple OAM vortex waves can be simultaneously generated by using a single electromagnetic metasurface. The proposed method paves an effective way to generate multiple OAM vortex waves in radio and microwave wireless communication applications.

Petascale turbulence simulation using a highly parallel fast multipole method on GPUs

NASA Astrophysics Data System (ADS)

Yokota, Rio; Barba, L. A.; Narumi, Tetsu; Yasuoka, Kenji

2013-03-01

This paper reports large-scale direct numerical simulations of homogeneous-isotropic fluid turbulence, achieving sustained performance of 1.08 petaflop/s on GPU hardware using single precision. The simulations use a vortex particle method to solve the Navier-Stokes equations, with a highly parallel fast multipole method (FMM) as numerical engine, and match the current record in mesh size for this application, a cube of 40963 computational points solved with a spectral method. The standard numerical approach used in this field is the pseudo-spectral method, relying on the FFT algorithm as the numerical engine. The particle-based simulations presented in this paper quantitatively match the kinetic energy spectrum obtained with a pseudo-spectral method, using a trusted code. In terms of parallel performance, weak scaling results show the FMM-based vortex method achieving 74% parallel efficiency on 4096 processes (one GPU per MPI process, 3 GPUs per node of the TSUBAME-2.0 system). The FFT-based spectral method is able to achieve just 14% parallel efficiency on the same number of MPI processes (using only CPU cores), due to the all-to-all communication pattern of the FFT algorithm. The calculation time for one time step was 108 s for the vortex method and 154 s for the spectral method, under these conditions. Computing with 69 billion particles, this work exceeds by an order of magnitude the largest vortex-method calculations to date.

Optical superimposed vortex beams generated by integrated holographic plates with blazed grating

NASA Astrophysics Data System (ADS)

Zhang, Xue-Dong; Su, Ya-Hui; Ni, Jin-Cheng; Wang, Zhong-Yu; Wang, Yu-Long; Wang, Chao-Wei; Ren, Fei-Fei; Zhang, Zhen; Fan, Hua; Zhang, Wei-Jie; Li, Guo-Qiang; Hu, Yan-Lei; Li, Jia-Wen; Wu, Dong; Chu, Jia-Ru

2017-08-01

In this paper, we demonstrate that the superposition of two vortex beams with controlled topological charges can be realized by integrating two holographic plates with blazed grating. First, the holographic plate with blazed grating was designed and fabricated by laser direct writing for generating well-separated vortex beam. Then, the relationship between the periods of blazed grating and the discrete angles of vortex beams was systemically investigated. Finally, through setting the discrete angle and different revolving direction of the holographic plates, the composite fork-shaped field was realized by the superposition of two vortex beams in a particular position. The topological charges of composite fork-shaped field (l = 1, 0, 3, and 4) depend on the topological charges of compositional vortex beams, which are well agreed with the theoretical simulation. The method opens up a wide range of opportunities and possibilities for applying in optical communication, optical manipulations, and photonic integrated circuits.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Ji San; Park, Su Ji; Lee, Jun Ho

A vortex is a flow phenomenon that is very commonly observed in nature. More than a century, a vortex ring that forms during drop splashing has caught the attention of many scientists due to its importance in understanding fluid mixing and mass transport processes. However, the origin of the vortices and their dynamics remain unclear, mostly due to the lack of appropriate visualization methods. Here, with ultrafast X-ray phase-contrast imaging, we show that the formation of vortex rings originates from the energy transfer by capillary waves generated at the moment of the drop impact. Interestingly, we find a row ofmore » vortex rings along the drop wall, as demonstrated by a phase diagram established here, with different power-law dependencies of the angular velocities on the Reynolds number. These results provide important insight that allows understanding and modelling any type of vortex rings in nature, beyond just vortex rings during drop splashing.« less

Motion of a curved vortex filament with decaying vortical core and axial velocity

NASA Technical Reports Server (NTRS)

Callegari, A. J.; Ting, L.

1978-01-01

The motion and decay of a curved vortex filament having large axial and circumferential velocity components in a three-dimensional stream are analyzed by using the method of matched asymptotic expansions of the incompressible Navier-Stokes equations. The small parameter is the square root of the ratio of the kinematic viscosity to the circulation. The outer region is analyzed by the classical Biot-Savart law, and its solution is matched to that of the inner region, where viscous effects are important. Equations describing the coupling between the inner vortex structure and the motion of the vortex filament as well as the time evolution of the inner vortex structure are obtained. Equations are derived for the motion of the vortex filament and for the change and decay in time and space of the leading-order circumferential and axial velocity and vorticity components. Solutions are constructed for these components in terms of initial data.

Periodicity of the density wake past a vortex ring in a stratified liquid

NASA Astrophysics Data System (ADS)

Prokhorov, V.

2009-04-01

Spatial coherent structure of the density wake past a vortex ring moving horizontally in viscid stratified liquid is experimentally revealed. It follows from analysis that repetition period of the structure is determined by rotation radial frequency (or mean vorticity) of the vortex core and toward speed of the vortex ring. The wake formation of the ring is considered in respect to vorticity shedding which produces velocity disturbances in ambient medium. In case of stratified liquid velocity fluctuations, in their turn, cause density field distortion. This process is superimposed by vortex core oscillations, and, in result, vorticity shedding will be not monotonous but modulated at some frequency. So, the density wake is periodically structured, and the spatial period is defined by intrinsic frequency of the core and forward speed of the ring. To support analysis, experiments were conducted in which vortex rings excited by spring-piston generator were observed with high-sensitive Schlieren instrument and computer-controlled camera. Experimental tank was filled with salt-stratified water of constant buoyancy period, vortex ring velocities range from 3 to 16 cm/s. Spatial period is derived from schlieren image using two independent methods, both 2D spectral analysis and geometry calculations of the vortex core. Spatial periods and vortex intrinsic frequencies calculated by both algorithms are in good agreement; they vary in power lows depending on vortex speed

Model of random center vortex lines in continuous 2 +1 -dimensional spacetime

NASA Astrophysics Data System (ADS)

Altarawneh, Derar; Engelhardt, Michael; Höllwieser, Roman

2016-12-01

A picture of confinement in QCD based on a condensate of thick vortices with fluxes in the center of the gauge group (center vortices) is studied. Previous concrete model realizations of this picture utilized a hypercubic space-time scaffolding, which, together with many advantages, also has some disadvantages, e.g., in the treatment of vortex topological charge. In the present work, we explore a center vortex model which does not rely on such a scaffolding. Vortices are represented by closed random lines in continuous 2 +1 -dimensional space-time. These random lines are modeled as being piecewise linear, and an ensemble is generated by Monte Carlo methods. The physical space in which the vortex lines are defined is a torus with periodic boundary conditions. Besides moving, growing, and shrinking of the vortex configurations, also reconnections are allowed. Our ensemble therefore contains not a fixed but a variable number of closed vortex lines. This is expected to be important for realizing the deconfining phase transition. We study both vortex percolation and the potential V (R ) between the quark and antiquark as a function of distance R at different vortex densities, vortex segment lengths, reconnection conditions, and at different temperatures. We find three deconfinement phase transitions, as a function of density, as a function of vortex segment length, and as a function of temperature.

Numerical assessment of pulsating water jet in the conical diffusers

NASA Astrophysics Data System (ADS)

Tanasa, Constantin; Ciocan, Tiberiu; Muntean, Sebastian

2017-11-01

The hydraulic fluctuations associated with partial load operating conditions of Francis turbines are often periodic and characterized by the presence of a vortex rope. Two types of pressure fluctuations associated with the draft tube surge are identified in the literature. The first is an asynchronous (rotating) pressure fluctuation due to the precession of the helical vortex around the axis of the draft tube. The second type of fluctuation is a synchronous (plunging) fluctuation. The plunging fluctuations correspond to the flow field oscillations in the whole hydraulic passage, and are generally propagated overall in the hydraulic system. The paper introduced a new control method, which consists in injecting a pulsating axial water jet along to the draft tube axis. Nevertheless, the great calling of this control method is to mitigate the vortex rope effects targeting the vortex sheet and corresponding plunging component. In this paper, is presented our 3D numerical investigations with and without pulsating axial water jet control method in order to evaluate the concept.

Implicit Large Eddy Simulation of a wingtip vortex at Rec =1.2x106

NASA Astrophysics Data System (ADS)

Lombard, Jean-Eloi; Moxey, Dave; Sherwin, Spencer; SherwinLab Team

2015-11-01

We present recent developments in numerical methods for performing a Large Eddy Simulation (LES) of the formation and evolution of a wingtip vortex. The development of these vortices in the near wake, in combination with the large Reynolds numbers present in these cases, make these types of test cases particularly challenging to investigate numerically. To demonstrate the method's viability, we present results from numerical simulations of flow over a NACA 0012 profile wingtip at Rec = 1.2 x106 and compare them against experimental data, which is to date the highest Reynolds number achieved for a LES that has been correlated with experiments for this test case. Our model correlates favorably with experiment, both for the characteristic jetting in the primary vortex and pressure distribution on the wing surface. The proposed method is of general interest for the modeling of transitioning vortex dominated flows over complex geometries. McLaren Racing/Royal Academy of Engineering Research Chair.

Study on the generation of a vortex laser beam by using phase-only liquid crystal spatial light modulator

NASA Astrophysics Data System (ADS)

Ma, Haotong; Hu, Haojun; Xie, Wenke; Xu, Xiaojun

2013-09-01

The generation of vortex laser beam by using phase-only liquid crystal spatial light modulator (LC-SLM) combined with the spiral phase screen is experimentally and theoretically studied. Results show that Gaussian and dark hollow vortex laser beams can be generated by using this method successfully. Differing with the Gaussian and dark hollow beams, far field intensities of the generated vortex laser beams still exhibit dark hollow distributions. The comparisons between the ideal generation and experimental generation of vortex laser beams with different optical topological charges by using phase only LC-SLM is investigated in detail. Compared with the ideal generated vortex laser beam, phase distribution of the experimental generated vortex laser beam contains many phase singularities, the number of which is the same as that of the optical topological charges. The corresponding near field and far field dark hollow intensity distributions of the generated vortex laser beams exhibit discontinuous in rotational direction. Detailed theoretical analysis show that the main reason for the physical phenomenon mentioned above is the response error of phase only LC-SLM. These studies can provide effective guide for the generation of vortex laser beam by using phase only LC-SLM for optical tweezers and free space optical communication.

Nonlinear analysis of structures. [within framework of finite element method

NASA Technical Reports Server (NTRS)

Armen, H., Jr.; Levine, H.; Pifko, A.; Levy, A.

1974-01-01

The development of nonlinear analysis techniques within the framework of the finite-element method is reported. Although the emphasis is concerned with those nonlinearities associated with material behavior, a general treatment of geometric nonlinearity, alone or in combination with plasticity is included, and applications presented for a class of problems categorized as axisymmetric shells of revolution. The scope of the nonlinear analysis capabilities includes: (1) a membrane stress analysis, (2) bending and membrane stress analysis, (3) analysis of thick and thin axisymmetric bodies of revolution, (4) a general three dimensional analysis, and (5) analysis of laminated composites. Applications of the methods are made to a number of sample structures. Correlation with available analytic or experimental data range from good to excellent.

Numerical analysis of laser ablation using the axisymmetric two-temperature model

NASA Astrophysics Data System (ADS)

Dziatkiewicz, Jolanta; Majchrzak, Ewa

2018-01-01

Laser ablation of the axisymmetric micro-domain is analyzed. To describe the thermal processes occurring in the micro-domain the two-temperature hyperbolic model supplemented by the boundary and initial conditions is used. This model takes into account the phase changes of material (solid-liquid and liquid-vapour) and the ablation process. At the stage of numerical computations the finite difference method with staggered grid is used. In the final part the results of computations are shown.

Historical evolution of vortex-lattice methods

NASA Technical Reports Server (NTRS)

Deyoung, J.

1976-01-01

A review of the beginning and some orientation of the vortex-lattice method were given. The historical course of this method was followed in conjunction with its field of computational fluid dynamics, spanning the period from L.F. Richardson's paper in 1910 to 1975. The following landmarks were pointed out: numerical analysis of partial differential equations, lifting-line theory, finite-difference method, 1/4-3/4 rule, block relaxation technique, application of electronic computers, and advanced panel methods.

A Minimal Three-Dimensional Tropical Cyclone Model.

NASA Astrophysics Data System (ADS)

Zhu, Hongyan; Smith, Roger K.; Ulrich, Wolfgang

2001-07-01

A minimal 3D numerical model designed for basic studies of tropical cyclone behavior is described. The model is formulated in coordinates on an f or plane and has three vertical levels, one characterizing a shallow boundary layer and the other two representing the upper and lower troposphere, respectively. It has three options for treating cumulus convection on the subgrid scale and a simple scheme for the explicit release of latent heat on the grid scale. The subgrid-scale schemes are based on the mass-flux models suggested by Arakawa and Ooyama in the late 1960s, but modified to include the effects of precipitation-cooled downdrafts. They differ from one another in the closure that determines the cloud-base mass flux. One closure is based on the assumption of boundary layer quasi-equilibrium proposed by Raymond and Emanuel.It is shown that a realistic hurricane-like vortex develops from a moderate strength initial vortex, even when the initial environment is slightly stable to deep convection. This is true for all three cumulus schemes as well as in the case where only the explicit release of latent heat is included. In all cases there is a period of gestation during which the boundary layer moisture in the inner core region increases on account of surface moisture fluxes, followed by a period of rapid deepening. Precipitation from the convection scheme dominates the explicit precipitation in the early stages of development, but this situation is reversed as the vortex matures. These findings are similar to those of Baik et al., who used the Betts-Miller parameterization scheme in an axisymmetric model with 11 levels in the vertical. The most striking difference between the model results using different convection schemes is the length of the gestation period, whereas the maximum intensity attained is similar for the three schemes. The calculations suggest the hypothesis that the period of rapid development in tropical cyclones is accompanied by a change in the character of deep convection in the inner core region from buoyantly driven, predominantly upright convection to slantwise forced moist ascent.

Analytical investigation of aerodynamic characteristics of highly swept wings with separated flow

NASA Technical Reports Server (NTRS)

Reddy, C. S.

1980-01-01

Many modern aircraft designed for supersonic speeds employ highly swept-back and low-aspect-ratio wings with sharp or thin edges. Flow separation occurs near the leading and tip edges of such wings at moderate to high angles of attack. Attempts have been made over the years to develop analytical methods for predicting the aerodynamic characteristics of such aircraft. Before any method can really be useful, it must be tested against a standard set of data to determine its capabilities and limitations. The present work undertakes such an investigation. Three methods are considered: the free-vortex-sheet method (Weber et al., 1975), the vortex-lattice method with suction analogy (Lamar and Gloss, 1975), and the quasi-vortex lattice method of Mehrotra (1977). Both flat and cambered wings of different configurations, for which experimental data are available, are studied and comparisons made.

A Vortex Particle-Mesh method for subsonic compressible flows

NASA Astrophysics Data System (ADS)

Parmentier, Philippe; Winckelmans, Grégoire; Chatelain, Philippe

2018-02-01

This paper presents the implementation and validation of a remeshed Vortex Particle-Mesh (VPM) method capable of simulating complex compressible and viscous flows. It is supplemented with a radiation boundary condition in order for the method to accommodate the radiating quantities of the flow. The efficiency of the methodology relies on the use of an underlying grid; it allows the use of a FFT-based Poisson solver to calculate the velocity field, and the use of high-order isotropic finite differences to evaluate the non-advective terms in the Lagrangian form of the conservation equations. The Möhring analogy is then also used to further obtain the far-field sound produced by two co-rotating Gaussian vortices. It is demonstrated that the method is in excellent quantitative agreement with reference results that were obtained using a high-order Eulerian method and using a high-order remeshed Vortex Particle (VP) method.

Generation and characterization of a perfect vortex beam with a large topological charge through a digital micromirror device.

PubMed

Chen, Yue; Fang, Zhao-Xiang; Ren, Yu-Xuan; Gong, Lei; Lu, Rong-De

2015-09-20

Optical vortices are associated with a spatial phase singularity. Such a beam with a vortex is valuable in optical microscopy, hyper-entanglement, and optical levitation. In these applications, vortex beams with a perfect circle shape and a large topological charge are highly desirable. But the generation of perfect vortices with high topological charges is challenging. We present a novel method to create perfect vortex beams with large topological charges using a digital micromirror device (DMD) through binary amplitude modulation and a narrow Gaussian approximation. The DMD with binary holograms encoding both the spatial amplitude and the phase could generate fast switchable, reconfigurable optical vortex beams with significantly high quality and fidelity. With either the binary Lee hologram or the superpixel binary encoding technique, we were able to generate the corresponding hologram with high fidelity and create a perfect vortex with topological charge as large as 90. The physical properties of the perfect vortex beam produced were characterized through measurements of propagation dynamics and the focusing fields. The measurements show good consistency with the theoretical simulation. The perfect vortex beam produced satisfies high-demand utilization in optical manipulation and control, momentum transfer, quantum computing, and biophotonics.

Vortex Simulation of Turbulent Combustion

DTIC Science & Technology

1992-11-19

used in this simulation was more representative of that of a wake . The difference between the stability and long-time behavior of wakes and shear...several important issues, summarized next, cast some doubt on the conclusions of these simulations. Using desingularized vortex sheets to model shear...17, 1991. 8. Krishnan, A. and Ghoniem, A.F., "Simulation of the Roll-up and Mixing in Rayleigh- Taylor Flow using the Vortex /Transport Element Method

Modelling of Time-Variant Flows Using Vortex Dynamics.

DTIC Science & Technology

1987-02-01

eopennage.... ) avec nappes enroul~es et d~ chir ~cs. REFERENCES Ji .T. BEALE, A. MAJDA "Nigh order accurate vortex methods with explicit velocity kernel...discrete vortices. Two papers, Longuet- Higgins (37) and Smith and Stansby (38) deal with the problem. In (37) conformal transformation is used for the...Longuet- Higgins (37). Most experiments on separated flows undoubtedly contain three-dimensional effects and again vortex decay is occasionally put into the

Numerical Capture of Wing-tip Vortex Using Vorticity Confinement

NASA Astrophysics Data System (ADS)

Zhang, Baili; Lou, Jing; Kang, Chang Wei; Wilson, Alexander; Lundberg, Johan; Bensow, Rickard

2012-11-01

Tracking vortices accurately over large distances is very important in many areas of engineering, for instance flow over rotating helicopter blades, ship propeller blades and aircraft wings. However, due to the inherent numerical dissipation in the advection step of flow simulation, current Euler and RANS field solvers tend to damp these vortices too fast. One possible solution to reduce the unphysical decay of these vortices is the application of vorticity confinement methods. In this study, a vorticity confinement term is added to the momentum conservation equations which is a function of the local element size, the vorticity and the gradient of the absolute value of vorticity. The approach has been evaluated by a systematic numerical study on the tip vortex trailing from a rectangular NACA0012 half-wing. The simulated structure and development of the wing-tip vortex agree well with experiments both qualitatively and quantitatively without any adverse effects on the global flow field. It is shown that vorticity confinement can negate the effect of numerical dissipation, leading to a more or less constant vortex strength. This is an approximate method in that genuine viscous diffusion of the vortex is not modeled, but it can be appropriate for vortex dominant flows over short to medium length scales where viscous diffusion can be neglected.

Vortex Formation in the Wake of Dark Matter Propulsion

NASA Astrophysics Data System (ADS)

Robertson, G. A.; Pinheiro, M. J.

Future spaceflight will require a new theory of propulsion; specifically one that does not require mass ejection. A new theory is proposed that uses the general view that closed currents pervade the entire universe and, in particular, there is a cosmic mechanism to expel matter to large astronomical distances involving vortex currents as seen with blazars and blackholes. At the terrestrial level, force producing vortices have been related to the motion of wings (e.g., birds, duck paddles, fish's tail). In this paper, vortex structures are shown to exist in the streamlines aft of a spaceship moving at high velocity in the vacuum. This is accomplished using the density excitation method per a modified Chameleon Cosmology model. This vortex structure is then shown to have similarities to spacetime models as Warp-Drive and wormholes, giving rise to the natural extension of Hawking and Unruh radiation, which provides the propulsive method for space travel where virtual electron-positron pairs, absorbed by the gravitational expansion forward of the spaceship emerge from an annular vortex field aft of the spaceship as real particles, in-like to propellant mass ejection in conventional rocket theory.

A computer program for calculating the perfect gas inviscid flow field about blunt axisymmetric bodies at an angle of attack of 0 deg

NASA Technical Reports Server (NTRS)

Zoby, E. V.; Graves, R. A., Jr.

1973-01-01

A method for the rapid calculation of the inviscid shock layer about blunt axisymmetric bodies at an angle of attack of 0 deg has been developed. The procedure is of an inverse nature, that is, a shock wave is assumed and calculations proceed along rays normal to the shock. The solution is iterated until the given body is computed. The flow field solution procedure is programed at the Langley Research Center for the Control Data 6600 computer. The geometries specified in the program are sphores, ellipsoids, paraboloids, and hyperboloids which may conical afterbodies. The normal momentum equation is replaced with an approximate algebraic expression. This simplification significantly reduces machine computation time. Comparisons of the present results with shock shapes and surface pressure distributions obtained by the more exact methods indicate that the program provides reasonably accurate results for smooth bodies in axisymmetric flow. However, further research is required to establish the proper approximate form of the normal momentum equation for the two-dimensional case.

Numerical Study of Sound Emission by 2D Regular and Chaotic Vortex Configurations

NASA Astrophysics Data System (ADS)

Knio, Omar M.; Collorec, Luc; Juvé, Daniel

1995-02-01

The far-field noise generated by a system of three Gaussian vortices lying over a flat boundary is numerically investigated using a two-dimensional vortex element method. The method is based on the discretization of the vorticity field into a finite number of smoothed vortex elements of spherical overlapping cores. The elements are convected in a Lagrangian reference along particle trajectories using the local velocity vector, given in terms of a desingularized Biot-Savart law. The initial structure of the vortex system is triangular; a one-dimensional family of initial configurations is constructed by keeping one side of the triangle fixed and vertical, and varying the abscissa of the centroid of the remaining vortex. The inviscid dynamics of this vortex configuration are first investigated using non-deformable vortices. Depending on the aspect ratio of the initial system, regular or chaotic motion occurs. Due to wall-related symmetries, the far-field sound always exhibits a time-independent quadrupolar directivity with maxima parallel end perpendicular to the wall. When regular motion prevails, the noise spectrum is dominated by discrete frequencies which correspond to the fundamental system frequency and its superharmonics. For chaotic motion, a broadband spectrum is obtained; computed soundlevels are substantially higher than in non-chaotic systems. A more sophisticated analysis is then performed which accounts for vortex core dynamics. Results show that the vortex cores are susceptible to inviscid instability which leads to violent vorticity reorganization within the core. This phenomenon has little effect on the large-scale features of the motion of the system or on low frequency sound emission. However, it leads to the generation of a high-frequency noise band in the acoustic pressure spectrum. The latter is observed in both regular and chaotic system simulations.

The interaction between a propagating coastal vortex and topographic waves

NASA Astrophysics Data System (ADS)

Parry, Simon Wyn

This thesis investigates the motion of a point vortex near coastal topography in a rotating frame of reference at constant latitude (f-plane) in the linear and weakly nonlinear limits. Topography is considered in the form of an infinitely long escarpment running parallel to a wall. The vortex motion and topographic waves are governed by the conservation of quasi-geostrophic potential vorticity in shallow water, from which a nonlinear system of equations is derived. First the linear limit is studied for three cases; a weak vortex on- and off-shelf and a weak vortex close to the wall. For the first two cases it is shown that to leading order the vortex motion is stationary and a solution for the topographic waves at the escarpment can be found in terms of Fourier integrals. For a weak vortex close to a wall, the leading order solution is a steadily propagating vortex with a topographic wavetrain at the step. Numerical results for the higher order interactions are also presented and explained in terms of conservation of momentum in the along-shore direction. For the second case a resonant interaction between the vortex and the waves occurs when the vortex speed is equal to the maximum group velocity of the waves and the linear response becomes unbounded at large times. Thus it becomes necessary to examine the weakly nonlinear near-resonant case. Using a long wave approximation a nonlinear evolution equation for the interface separating the two regions of differing relative potential vorticity is derived and has similar form to the BDA (Benjamin, Davies, Acrivos 1967) equation. Results for the leading order steadily propagating vortex and for the vortex-wave feedback problem are calculated numerically using spectral multi-step Adams methods.

Vortex lattice prediction of subsonic aerodynamics of hypersonic vehicle concepts

NASA Technical Reports Server (NTRS)

Pittman, J. L.; Dillon, J. L.

1977-01-01

The vortex lattice method introduced by Lamar and Gloss (1975) was applied to the prediction of subsonic aerodynamic characteristics of hypersonic body-wing configurations. The reliability of the method was assessed through comparison of the calculated and observed aerodynamic performances of two National Hypersonic Flight Research Facility craft at Mach 0.2. The investigation indicated that a vortex lattice model involving 120 or more panel elements can give good results for the lift and induced drag coefficients of the craft, as well as for the pitching moment at angles of attack below 10 to 15 deg. Automated processes for calculating the local slopes of mean-camber surfaces may also render the method suitable for use in preliminary design phases.

Generating multiple orbital angular momentum vortex beams using a metasurface in radio frequency domain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Shixing; Li, Long, E-mail: lilong@mail.xidian.edu.cn, E-mail: gmshi@xidian.edu.cn; Shi, Guangming, E-mail: lilong@mail.xidian.edu.cn, E-mail: gmshi@xidian.edu.cn

In this paper, an electromagnetic metasurface is designed, fabricated, and experimentally demonstrated to generate multiple orbital angular momentum (OAM) vortex beams in radio frequency domain. Theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce multiple vortex radio waves in different directions with different OAM modes. The prototype of a practical configuration of square-patch metasurface is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that multiple OAM vortex waves can be simultaneously generated by using a single electromagnetic metasurface. The proposed method paves an effectivemore » way to generate multiple OAM vortex waves in radio and microwave wireless communication applications.« less

Vortex flows in the solar chromosphere. I. Automatic detection method

NASA Astrophysics Data System (ADS)

Kato, Y.; Wedemeyer, S.

2017-05-01

Solar "magnetic tornadoes" are produced by rotating magnetic field structures that extend from the upper convection zone and the photosphere to the corona of the Sun. Recent studies show that these kinds of rotating features are an integral part of atmospheric dynamics and occur on a large range of spatial scales. A systematic statistical study of magnetic tornadoes is a necessary next step towards understanding their formation and their role in mass and energy transport in the solar atmosphere. For this purpose, we develop a new automatic detection method for chromospheric swirls, meaning the observable signature of solar tornadoes or, more generally, chromospheric vortex flows and rotating motions. Unlike existing studies that rely on visual inspections, our new method combines a line integral convolution (LIC) imaging technique and a scalar quantity that represents a vortex flow on a two-dimensional plane. We have tested two detection algorithms, based on the enhanced vorticity and vorticity strength quantities, by applying them to three-dimensional numerical simulations of the solar atmosphere with CO5BOLD. We conclude that the vorticity strength method is superior compared to the enhanced vorticity method in all aspects. Applying the method to a numerical simulation of the solar atmosphere reveals very abundant small-scale, short-lived chromospheric vortex flows that have not been found previously by visual inspection.

Level set formulation of two-dimensional Lagrangian vortex detection methods

NASA Astrophysics Data System (ADS)

Hadjighasem, Alireza; Haller, George

2016-10-01

We propose here the use of the variational level set methodology to capture Lagrangian vortex boundaries in 2D unsteady velocity fields. This method reformulates earlier approaches that seek material vortex boundaries as extremum solutions of variational problems. We demonstrate the performance of this technique for two different variational formulations built upon different notions of coherence. The first formulation uses an energy functional that penalizes the deviation of a closed material line from piecewise uniform stretching [Haller and Beron-Vera, J. Fluid Mech. 731, R4 (2013)]. The second energy function is derived for a graph-based approach to vortex boundary detection [Hadjighasem et al., Phys. Rev. E 93, 063107 (2016)]. Our level-set formulation captures an a priori unknown number of vortices simultaneously at relatively low computational cost. We illustrate the approach by identifying vortices from different coherence principles in several examples.

Achromatic electromagnetic metasurface for generating a vortex wave with orbital angular momentum (OAM).

PubMed

Jiang, Shan; Chen, Chang; Zhang, Hualiang; Chen, Weidong

2018-03-05

The vortex wave that carries orbital angular momentum has attracted much attention due to the fact that it can provide an extra degree of freedom for optical communication, imaging and other applications. In spite of this, the method of OAM generation at high frequency still suffers from limitations, such as chromatic aberration and low efficiency. In this paper, an azimuthally symmetric electromagnetic metasurface with wide bandwidth is designed, fabricated and experimentally demonstrated to efficiently convert a left-handed (right-handed) circularly polarized incident plane wave (with a spin angular momentum (SAM) of ћ) to a right-handed (left-handed) circularly polarized vortex wave with OAM. The design methodology based on the field equivalence principle is discussed in detail. The simulation and measurement results confirm that the proposed method provides an effective way for generating OAM-carrying vortex wave with comparative performance across a broad bandwidth.

Spectrum study on unsteadiness of shock wave-vortex ring interaction

NASA Astrophysics Data System (ADS)

Dong, Xiangrui; Yan, Yonghua; Yang, Yong; Dong, Gang; Liu, Chaoqun

2018-05-01

Shock oscillation with low-frequency unsteadiness commonly occurs in supersonic flows and is a top priority for the control of flow separation caused by shock wave and boundary layer interaction. In this paper, the interaction of the shock caused by the compression ramp and the vortex rings generated by a micro-vortex generator (MVG) in a supersonic flow at Ma = 2.5 is simulated by the implicit large eddy simulation method. The analysis of observation and the frequency of both the vortex ring motion and the shock oscillation is carried out. The results show that the shock produced by a compression ramp flow at Ma = 2.5 has a dominant non-dimensional low frequency, which is around St = 0.002, while the vortex rings behind the MVG have a dominant high frequency which is around St = 0.038. The dominant low frequency of the shock, which is harmful, can be removed or weakened through the shock-vortex ring interaction by the vortex rings which generate high frequency fluctuations. In the shock and vortex ring interaction region, a dominant high frequency St = 0.037-0.038 has been detected rather than the low frequency St = 0.002, which indicates that the vortex ring is stiff enough to break or weaken the shock. This analysis could provide an effective tool to remove or weaken the low frequency pressure fluctuation below 500 Hz, which has a negative effect on the flight vehicle structures and the environmental protection, through the high frequency vortex generation.

Hydrostatic calculations of axisymmetric flow and its stability for the AGCE model

NASA Technical Reports Server (NTRS)

Miller, T. L.; Gall, R. L.

1981-01-01

Baroclinic waves in the atmospherics general circulation experiment (AGCE) apparatus by the use of numerical hydrostatic primitive equation models were determined. The calculation is accomplished by using an axisymmetric primitive equation model to compute, for a given set of experimental parameters, a steady state axisymmetric flow and then testing this axisymmetric flow for stability using a linear primitive equation model. Some axisymmetric flows are presented together with preliminary stability calculations.

Shielded beam delivery apparatus and method

DOEpatents

Hershcovitch, Ady; Montano, Rory Dominick

2006-07-11

An apparatus includes a plasma generator aligned with a beam generator for producing a plasma to shield an energized beam. An electrode is coaxially aligned with the plasma generator and followed in turn by a vortex generator coaxially aligned with the electrode. A target is spaced from the vortex generator inside a fluid environment. The electrode is electrically biased relative to the electrically grounded target for driving the plasma toward the target inside a vortex shield.

Correlation matching method for high-precision position detection of optical vortex using Shack-Hartmann wavefront sensor.

PubMed

Huang, Chenxi; Huang, Hongxin; Toyoda, Haruyoshi; Inoue, Takashi; Liu, Huafeng

2012-11-19

We propose a new method for realizing high-spatial-resolution detection of singularity points in optical vortex beams. The method uses a Shack-Hartmann wavefront sensor (SHWS) to record a Hartmanngram. A map of evaluation values related to phase slope is then calculated from the Hartmanngram. The position of an optical vortex is determined by comparing the map with reference maps that are calculated from numerically created spiral phases having various positions. Optical experiments were carried out to verify the method. We displayed various spiral phase distribution patterns on a phase-only spatial light modulator and measured the resulting singularity point using the proposed method. The results showed good linearity in detecting the position of singularity points. The RMS error of the measured position of the singularity point was approximately 0.056, in units normalized to the lens size of the lenslet array used in the SHWS.

Tactical missile aerodynamics

NASA Technical Reports Server (NTRS)

Hemsch, Michael J. (Editor); Nielsen, Jack N. (Editor)

1986-01-01

The present conference on tactical missile aerodynamics discusses autopilot-related aerodynamic design considerations, flow visualization methods' role in the study of high angle-of-attack aerodynamics, low aspect ratio wing behavior at high angle-of-attack, supersonic airbreathing propulsion system inlet design, missile bodies with noncircular cross section and bank-to-turn maneuvering capabilities, 'waverider' supersonic cruise missile concepts and design methods, asymmetric vortex sheding phenomena from bodies-of-revolution, and swept shock wave/boundary layer interaction phenomena. Also discussed are the assessment of aerodynamic drag in tactical missiles, the analysis of supersonic missile aerodynamic heating, the 'equivalent angle-of-attack' concept for engineering analysis, the vortex cloud model for body vortex shedding and tracking, paneling methods with vorticity effects and corrections for nonlinear compressibility, the application of supersonic full potential method to missile bodies, Euler space marching methods for missiles, three-dimensional missile boundary layers, and an analysis of exhaust plumes and their interaction with missile airframes.

A review on the solution of Grad-Shafranov equation in the cylindrical coordinates based on the Chebyshev collocation technique

NASA Astrophysics Data System (ADS)

Amerian, Z.; Salem, M. K.; Salar Elahi, A.; Ghoranneviss, M.

2017-03-01

Equilibrium reconstruction consists of identifying, from experimental measurements, a distribution of the plasma current density that satisfies the pressure balance constraint. Numerous methods exist to solve the Grad-Shafranov equation, describing the equilibrium of plasma confined by an axisymmetric magnetic field. In this paper, we have proposed a new numerical solution to the Grad-Shafranov equation (an axisymmetric, magnetic field transformed in cylindrical coordinates solved with the Chebyshev collocation method) when the source term (current density function) on the right-hand side is linear. The Chebyshev collocation method is a method for computing highly accurate numerical solutions of differential equations. We describe a circular cross-section of the tokamak and present numerical result of magnetic surfaces on the IR-T1 tokamak and then compare the results with an analytical solution.

Spectroscopy of Magnetic Excitations in Magnetic Superconductors Using Vortex Motion

NASA Astrophysics Data System (ADS)

Bulaevskii, L. N.; Hruška, M.; Maley, M. P.

2005-11-01

In magnetic superconductors a moving vortex lattice is accompanied by an ac magnetic field which leads to the generation of spin waves. At resonance conditions the dynamics of vortices in magnetic superconductors changes drastically, resulting in strong peaks in the dc I-V characteristics at voltages at which the washboard frequency of the vortex lattice matches the spin wave frequency ωs(g), where g are the reciprocal vortex lattice vectors. We show that if the washboard frequency lies above the magnetic gap, measurement of the I-V characteristics provides a new method to obtain information on the spectrum of magnetic excitations in borocarbides and cuprate layered magnetic superconductors.

Calculation of the force acting on a micro-sized particle with optical vortex array laser beam tweezers

NASA Astrophysics Data System (ADS)

Kuo, Chun-Fu; Chu, Shu-Chun

2013-03-01

Optical vortices possess several special properties, including carrying optical angular momentum (OAM) and exhibiting zero intensity. Vortex array laser beams have attracts many interests due to its special mesh field distributions, which show great potential in the application of multiple optical traps and dark optical traps. Previously study developed an Ince-Gaussian Mode (IGM)-based vortex array laser beam1. This study develops a simulation model based on the discrete dipole approximation (DDA) method for calculating the resultant force acting on a micro-sized spherical dielectric particle that situated at the beam waist of the IGM-based vortex array laser beams1.

Numerical experiments in homogeneous turbulence

NASA Technical Reports Server (NTRS)

Rogallo, R. S.

1981-01-01

The direct simulation methods developed by Orszag and Patternson (1972) for isotropic turbulence were extended to homogeneous turbulence in an incompressible fluid subjected to uniform deformation or rotation. The results of simulations for irrotational strain (plane and axisymmetric), shear, rotation, and relaxation toward isotropy following axisymmetric strain are compared with linear theory and experimental data. Emphasis is placed on the shear flow because of its importance and because of the availability of accurate and detailed experimental data. The computed results are used to assess the accuracy of two popular models used in the closure of the Reynolds-stress equations. Data from a variety of the computed fields and the details of the numerical methods used in the simulation are also presented.

Axisymmetric analysis of a tube-type acoustic levitator by a finite element method.

PubMed

Hatano, H

1994-01-01

A finite element approach was taken for the study of the sound field and positioning force in a tube-type acoustic levitator. An axisymmetric model, where a rigid sphere is suspended on the tube axis, was introduced to model a cylindrical chamber of a levitation tube furnace. Distributions of velocity potential, magnitudes of positioning force, and resonance frequency shifts of the chamber due to the presence of the sphere were numerically estimated in relation to the sphere's position and diameter. Experiments were additionally made to compare with the simulation. The finite element method proved to be a useful tool for analyzing and designing the tube-type levitator.

Effect of temperature, pH, and water activity on biofilm formation by Salmonella enterica enteritidis PT4 on stainless steel surfaces as indicated by the bead vortexing method and conductance measurements.

PubMed

Giaouris, E; Chorianopoulos, N; Nychas, G J E

2005-10-01

An assay was developed in an effort to elucidate the effect of important environmental parameters (temperature, pH, and water activity [aw]) on Salmonella Enteritidis biofilm formation on stainless steel surfaces. To achieve this, a modified microbiological technique used for biofilm studying (the bead vortexing method) and a rapid method based on conductivity measurements were used. The ability of the microorganism to generate biofilm on the stainless surfaces was studied at three temperatures (5, 20, and 37 degrees C), four pH values (4.5, 5.5, 6.5, and 7.4), and four aw values (0.5, 1.5, 5.5, and 10.5% NaCl). Results obtained by the bead vortexing method show that maximum numbers of adherent bacteria per square centimeter (106 CFU/cm2) were attained in 6 days at 20 degrees C. Biofilm formation after 7 days of incubation at 20 degrees C was found to be independent of the pH value. In addition, the high concentration of sodium chloride (10.5% NaCl, aw = 0.94) clearly inhibited the adherence of cells to the coupons. Conductance measurements were used as a supplementary tool to measure indirectly the attachment and biofilm formation of bacterial cells on stainless steel surfaces via their metabolic activity (i.e., changes in the conductance of the growth medium due to microbial growth or metabolism). Results obtained by conductance measurements corresponded well to those of the bead vortexing method. Furthermore, we were able to detect cells that remained attached on the metal surfaces even after vortexing via their metabolic activity. The results, except for demonstrating environmental-dependent Salmonella Enteritidis biofilm formation, indicated that traditional vortexing with beads did not remove completely biofilm cells from stainless steel; hence, conductance measurements seem to provide a more sensitive test capable to detect down to one single viable organism.

Rotorcraft acoustic radiation prediction based on a refined blade-vortex interaction model

NASA Astrophysics Data System (ADS)

Rule, John Allen

1997-08-01

The analysis of rotorcraft aerodynamics and acoustics is a challenging problem, primarily due to the fact that a rotorcraft continually flies through its own wake. The generation mechanism for a rotorcraft wake, which is dominated by strong, concentrated blade-tip trailing vortices, is similar to that in fixed wing aerodynamics. However, following blades encounter shed vortices from previous blades before they are swept downstream, resulting in sharp, impulsive loading on the blades. The blade/wake encounter, known as Blade-Vortex Interaction, or BVI, is responsible for a significant amount of vibratory loading and the characteristic rotorcraft acoustic signature in certain flight regimes. The present work addressed three different aspects of this interaction at a fundamental level. First, an analytical model for the prediction of trailing vortex structure is discussed. The model as presented is the culmination of a lengthy research effort to isolate the key physical mechanisms which govern vortex sheet rollup. Based on the Betz model, properties of the flow such as mass flux, axial momentum flux, and axial flux of angular momentum are conserved on either a differential or integral basis during the rollup process. The formation of a viscous central core was facilitated by the assumption of a turbulent mixing process with final vortex velocity profiles chosen to be consistent with a rotational flow mixing model and experimental observation. A general derivation of the method is outlined, followed by a comparison of model predictions with experimental vortex measurements, and finally a viscous blade drag model to account for additional effects of aerodynamic drag on vortex structure. The second phase of this program involved the development of a new formulation of lifting surface theory with the ultimate goal of an accurate, reduced order hybrid analytical/numerical model for fast rotorcraft load calculations. Currently, accurate rotorcraft airload analyses are limited by the massive computational power required to capture the small time scale events associated with BVI. This problem has two primary facets: accurate knowledge of the wake geometry, and accurate resolution of the impulsive loading imposed by a tip vortex on a blade. The present work addressed the second facet, providing a mathematical framework for solving the impulsive loading problem analytically, then asymptotically matching this solution to a low-resolution numerical calculation. A method was developed which uses continuous sheets of integrated boundary elements to model the lifting surface and wake. Special elements were developed to capture local behavior in high-gradient regions of the flow, thereby reducing the burden placed on the surrounding numerical method. Unsteady calculations for several classical cases were made in both frequency and time domain to demonstrate the performance of the method. Finally, a new unsteady, compressible boundary element method was applied to the problem of BVI acoustic radiation prediction. This numerical method, combined with the viscous core trailing vortex model, was used to duplicate the geometry and flight configuration of a detailed experimental BVI study carried out at NASA Ames Research Center. Blade surface pressure and near- and far-field acoustic radiation calculations were made. All calculations were shown to compare favorably with experimentally measured values. The linear boundary element method with non-linear corrections proved sufficient over most of the rotor azimuth, and particular in the region of the blade vortex interaction, suggesting that full non-linear CFD schemes are not necessary for rotorcraft noise prediction.

Axisymmetry breaking instabilities of natural convection in a vertical bridgman growth configuration

NASA Astrophysics Data System (ADS)

Gelfgat, A. Yu.; Bar-Yoseph, P. Z.; Solan, A.

2000-12-01

A study of the three-dimensional axisymmetry-breaking instability of an axisymmetric convective flow associated with crystal growth from bulk of melt is presented. Convection in a vertical cylinder with a parabolic temperature profile on the sidewall is considered as a representative model. The main objective is the calculation of critical parameters corresponding to a transition from the steady axisymmetric to the three-dimensional non-axisymmetric (steady or oscillatory) flow pattern. A parametric study of the dependence of the critical Grashof number Gr cr on the Prandtl number 0⩽Pr⩽0.05 (characteristic for semiconductor melts) and the aspect ratio of the cylinder 1⩽ A⩽4 ( A=height/radius) is carried out. The stability diagram Grcr(Pr, A) corresponding to the axisymmetric — three-dimensional transition is reported for the first time. The calculations are done using the spectral Galerkin method allowing an effective and accurate three-dimensional stability analysis. It is shown that the axisymmetric flow in relatively low cylinders tends to be oscillatory unstable, while in tall cylinders the instability sets in due to a steady bifurcation caused by the Rayleigh-Benard mechanism. The calculated neutral curves are non-monotonous and contain hysteresis loops. The strong dependence of the critical Grashof number and the azimuthal periodicity of the resulting three-dimensional flow indicate the importance of a comprehensive parametric stability analysis in different crystal growth configurations. In particular, it is shown that the first instability of the flow considered is always three-dimensional.

An annular superposition integral for axisymmetric radiators.

PubMed

Kelly, James F; McGough, Robert J

2007-02-01

A fast integral expression for computing the nearfield pressure is derived for axisymmetric radiators. This method replaces the sum of contributions from concentric annuli with an exact double integral that converges much faster than methods that evaluate the Rayleigh-Sommerfeld integral or the generalized King integral. Expressions are derived for plane circular pistons using both continuous wave and pulsed excitations. Several commonly used apodization schemes for the surface velocity distribution are considered, including polynomial functions and a "smooth piston" function. The effect of different apodization functions on the spectral content of the wave field is explored. Quantitative error and time comparisons between the new method, the Rayleigh-Sommerfeld integral, and the generalized King integral are discussed. At all error levels considered, the annular superposition method achieves a speed-up of at least a factor of 4 relative to the point-source method and a factor of 3 relative to the generalized King integral without increasing the computational complexity.

Research on the statically thrusting propeller

NASA Technical Reports Server (NTRS)

Eisenhuth, J. J.

1978-01-01

Methods for calculating the induced flow at propeller blades were analyzed by treating the wake formation as an initial problem in time. An unsteady vortex lattice technique was applied to the wake formation and the vortex core size was studied.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phillips, Carolyn L.; Guo, Hanqi; Peterka, Tom

In type-II superconductors, the dynamics of magnetic flux vortices determine their transport properties. In the Ginzburg-Landau theory, vortices correspond to topological defects in the complex order parameter field. Earlier, in Phillips et al. [Phys. Rev. E 91, 023311 (2015)], we introduced a method for extracting vortices from the discretized complex order parameter field generated by a large-scale simulation of vortex matter. With this method, at a fixed time step, each vortex [simplistically, a one-dimensional (1D) curve in 3D space] can be represented as a connected graph extracted from the discretized field. Here we extend this method as a function ofmore » time as well. A vortex now corresponds to a 2D space-time sheet embedded in 4D space time that can be represented as a connected graph extracted from the discretized field over both space and time. Vortices that interact by merging or splitting correspond to disappearance and appearance of holes in the connected graph in the time direction. This method of tracking vortices, which makes no assumptions about the scale or behavior of the vortices, can track the vortices with a resolution as good as the discretization of the temporally evolving complex scalar field. Additionally, even details of the trajectory between time steps can be reconstructed from the connected graph. With this form of vortex tracking, the details of vortex dynamics in a model of a superconducting materials can be understood in greater detail than previously possible.« less

Flow Separation Control Over a Ramp Using Sweeping Jet Actuators

NASA Technical Reports Server (NTRS)

Koklu, Mehti; Owens, Lewis R.

2014-01-01

Flow separation control on an adverse-pressure-gradient ramp model was investigated using various flow-control methods in the NASA Langley 15-Inch Wind Tunnel. The primary flow-control method studied used a sweeping jet actuator system to compare with more classic flow-control techniques such as micro-vortex generators, steady blowing, and steady- and unsteady-vortex generating jets. Surface pressure measurements and a new oilflow visualization technique were used to characterize the effects of these flow-control actuators. The sweeping jet actuators were run in three different modes to produce steady-straight, steady-angled, and unsteady-oscillating jets. It was observed that all of these flow-control methods are effective in controlling the separated flows on the ramp model. The steady-straight jet energizes the boundary layer by momentum addition and was found to be the least effective method for a fixed momentum coefficient. The steady-angled jets achieved better performance than the steady-straight jets because they generate streamwise vortices that energize the boundary layer by mixing high-momentum fluid with near wall low-momentum fluid. The unsteady-oscillating jets achieved the best performance by increasing the pressure recovery and reducing the downstream flow separation. Surface flow visualizations indicated that two out-of-phase counter-rotating vortices are generated per sweeping jet actuator, while one vortex is generated per vortex-generating jets. The extra vortex resulted in increased coverage, more pressure recovery, and reduced flow separation.

Tracking vortices in superconductors: Extracting singularities from a discretized complex scalar field evolving in time

DOE PAGES

Phillips, Carolyn L.; Guo, Hanqi; Peterka, Tom; ...

2016-02-19

In type-II superconductors, the dynamics of magnetic flux vortices determine their transport properties. In the Ginzburg-Landau theory, vortices correspond to topological defects in the complex order parameter field. Earlier, we introduced a method for extracting vortices from the discretized complex order parameter field generated by a large-scale simulation of vortex matter. With this method, at a fixed time step, each vortex [simplistically, a one-dimensional (1D) curve in 3D space] can be represented as a connected graph extracted from the discretized field. Here we extend this method as a function of time as well. A vortex now corresponds to a 2Dmore » space-time sheet embedded in 4D space time that can be represented as a connected graph extracted from the discretized field over both space and time. Vortices that interact by merging or splitting correspond to disappearance and appearance of holes in the connected graph in the time direction. This method of tracking vortices, which makes no assumptions about the scale or behavior of the vortices, can track the vortices with a resolution as good as the discretization of the temporally evolving complex scalar field. In addition, even details of the trajectory between time steps can be reconstructed from the connected graph. With this form of vortex tracking, the details of vortex dynamics in a model of a superconducting materials can be understood in greater detail than previously possible.« less

Linear nozzle with tailored gas plumes and method

DOEpatents

Leon, David D.; Kozarek, Robert L.; Mansour, Adel; Chigier, Norman

1999-01-01

There is claimed a method for depositing fluid material from a linear nozzle in a substantially uniform manner across and along a surface. The method includes directing gaseous medium through said nozzle to provide a gaseous stream at the nozzle exit that entrains fluid material supplied to the nozzle, said gaseous stream being provided with a velocity profile across the nozzle width that compensates for the gaseous medium's tendency to assume an axisymmetric configuration after leaving the nozzle and before reaching the surface. There is also claimed a nozzle divided into respective side-by-side zones, or preferably chambers, through which a gaseous stream can be delivered in various velocity profiles across the width of said nozzle to compensate for the tendency of this gaseous medium to assume an axisymmetric configuration.

Controlling abruptly autofocusing vortex beams to mitigate crosstalk and vortex splitting in free-space optical communication.

PubMed

Yan, Xu; Guo, Lixin; Cheng, Mingjian; Li, Jiangting

2018-05-14

Orbital angular momentum (OAM) mode crosstalk induced by atmospheric turbulence is a challenging phenomenon commonly occurring in OAM-based free-space optical (FSO) communication. Recent advances have facilitated new practicable methods using abruptly autofocusing light beams for weakening the turbulence effect on the FSO link. In this work, we show that a circular phase-locked Airy vortex beam array (AVBA) with sufficient elements has the inherent ability to form an abruptly autofocusing light beam carrying OAM, and its focusing properties can be controlled on demand by adjusting the topological charge values and locations of these vortices embedded in the array elements. The performance of a tailored Airy vortex beam array (TAVBA) through atmospheric turbulence is numerically studied. In a comparison with the ring Airy vortex beam (RAVB), the results indicate that TAVBA can be a superior light source for effectively reducing the intermodal crosstalk and vortex splitting, thus leading to improvement in the FSO system performance.

Simulations of vortices in a star-shaped plate with an artificial pin

NASA Astrophysics Data System (ADS)

Miyoshi, Hiroki; Ito, Atsuki; Dang, Vu The; Thanh Huy, Ho; Hayashi, Masahiko; Kato, Masaru; Ishida, Takekazu

2017-07-01

Although a triangular vortex lattice is stable in a bulk type-II superconductor, exotic vortex configurations are expected to appear in a small superconducting plate. Theoretical calculations on vortex structures in a star-shaped superconducting plate have been given in our preceding work. In this work, we extended our theoretical studies to the case of having an artificial pin. We performed the Ginzburg-Landau (GL) calculations systematically to compare with the pin-free case by using the finite element method. We found that a vortex tends to accommodate preferentially in an aritificial pin in the star-shaped plate. We found a systematic evolution of vortex structure with increaseing magnetic field. We compare our theoretical calculations with vortices in a star-shaped Mo80Ge20 plate with an artificial pin and without an artificial pin obtained by a scanning SQUID microscope. We reconstructed the vortex image on the sample surface by using the inverse Biot-Savart law and the Fourier transformation.

A Survey of the Isentropic Euler Vortex Problem Using High-Order Methods

NASA Technical Reports Server (NTRS)

Spiegel, Seth C.; Huynh, H. T.; DeBonis, James R.

2015-01-01

The flux reconstruction (FR) method offers a simple, efficient, and easy to implement method, and it has been shown to equate to a differential approach to discontinuous Galerkin (DG) methods. The FR method is also accurate to an arbitrary order and the isentropic Euler vortex problem is used here to empirically verify this claim. This problem is widely used in computational fluid dynamics (CFD) to verify the accuracy of a given numerical method due to its simplicity and known exact solution at any given time. While verifying our FR solver, multiple obstacles emerged that prevented us from achieving the expected order of accuracy over short and long amounts of simulation time. It was found that these complications stemmed from a few overlooked details in the original problem definition combined with the FR and DG methods achieving high-accuracy with minimal dissipation. This paper is intended to consolidate the many versions of the vortex problem found in literature and to highlight some of the consequences if these overlooked details remain neglected.

Coupling temporal and spatial gradient information in high-density unstructured Lagrangian measurements

NASA Astrophysics Data System (ADS)

Wong, Jaime G.; Rosi, Giuseppe A.; Rouhi, Amirreza; Rival, David E.

2017-10-01

Particle tracking velocimetry (PTV) produces high-quality temporal information that is often neglected when computing spatial gradients. A method is presented here to utilize this temporal information in order to improve the estimation of spatial gradients for spatially unstructured Lagrangian data sets. Starting with an initial guess, this method penalizes any gradient estimate where the substantial derivative of vorticity along a pathline is not equal to the local vortex stretching/tilting. Furthermore, given an initial guess, this method can proceed on an individual pathline without any further reference to neighbouring pathlines. The equivalence of the substantial derivative and vortex stretching/tilting is based on the vorticity transport equation, where viscous diffusion is neglected. By minimizing the residual of the vorticity-transport equation, the proposed method is first tested to reduce error and noise on a synthetic Taylor-Green vortex field dissipating in time. Furthermore, when the proposed method is applied to high-density experimental data collected with `Shake-the-Box' PTV, noise within the spatial gradients is significantly reduced. In the particular test case investigated here of an accelerating circular plate captured during a single run, the method acts to delineate the shear layer and vortex core, as well as resolve the Kelvin-Helmholtz instabilities, which were previously unidentifiable without the use of ensemble averaging. The proposed method shows promise for improving PTV measurements that require robust spatial gradients while retaining the unstructured Lagrangian perspective.

The Effects of Thermal Radiation on an Unsteady MHD Axisymmetric Stagnation-Point Flow over a Shrinking Sheet in Presence of Temperature Dependent Thermal Conductivity with Navier Slip

PubMed Central

Mondal, Sabyasachi; Haroun, Nageeb A. H.; Sibanda, Precious

2015-01-01

In this paper, the magnetohydrodynamic (MHD) axisymmetric stagnation-point flow of an unsteady and electrically conducting incompressible viscous fluid in with temperature dependent thermal conductivity, thermal radiation and Navier slip is investigated. The flow is due to a shrinking surface that is shrunk axisymmetrically in its own plane with a linear velocity. The magnetic field is imposed normally to the sheet. The model equations that describe this fluid flow are solved by using the spectral relaxation method. Here, heat transfer processes are discussed for two different types of wall heating; (a) a prescribed surface temperature and (b) a prescribed surface heat flux. We discuss and evaluate how the various parameters affect the fluid flow, heat transfer and the temperature field with the aid of different graphical presentations and tabulated results. PMID:26414006

Some Progress in Large-Eddy Simulation using the 3-D Vortex Particle Method

NASA Technical Reports Server (NTRS)

Winckelmans, G. S.

1995-01-01

This two-month visit at CTR was devoted to investigating possibilities in LES modeling in the context of the 3-D vortex particle method (=vortex element method, VEM) for unbounded flows. A dedicated code was developed for that purpose. Although O(N(sup 2)) and thus slow, it offers the advantage that it can easily be modified to try out many ideas on problems involving up to N approx. 10(exp 4) particles. Energy spectrums (which require O(N(sup 2)) operations per wavenumber) are also computed. Progress was realized in the following areas: particle redistribution schemes, relaxation schemes to maintain the solenoidal condition on the particle vorticity field, simple LES models and their VEM extension, possible new avenues in LES. Model problems that involve strong interaction between vortex tubes were computed, together with diagnostics: total vorticity, linear and angular impulse, energy and energy spectrum, enstrophy. More work is needed, however, especially regarding relaxation schemes and further validation and development of LES models for VEM. Finally, what works well will eventually have to be incorporated into the fast parallel tree code.

Sagnac interferometry with coherent vortex superposition states in exciton-polariton condensates

NASA Astrophysics Data System (ADS)

Moxley, Frederick Ira; Dowling, Jonathan P.; Dai, Weizhong; Byrnes, Tim

2016-05-01

We investigate prospects of using counter-rotating vortex superposition states in nonequilibrium exciton-polariton Bose-Einstein condensates for the purposes of Sagnac interferometry. We first investigate the stability of vortex-antivortex superposition states, and show that they survive at steady state in a variety of configurations. Counter-rotating vortex superpositions are of potential interest to gyroscope and seismometer applications for detecting rotations. Methods of improving the sensitivity are investigated by targeting high momentum states via metastable condensation, and the application of periodic lattices. The sensitivity of the polariton gyroscope is compared to its optical and atomic counterparts. Due to the large interferometer areas in optical systems and small de Broglie wavelengths for atomic BECs, the sensitivity per detected photon is found to be considerably less for the polariton gyroscope than with competing methods. However, polariton gyroscopes have an advantage over atomic BECs in a high signal-to-noise ratio, and have other practical advantages such as room-temperature operation, area independence, and robust design. We estimate that the final sensitivities including signal-to-noise aspects are competitive with existing methods.

Laser utilizing a gaseous lasing medium and method for operating the same

DOEpatents

Zerr, Bruce A.

1986-01-01

The invention relates to an improvement in gas lasers and a method of operating the same. In one aspect, the invention is an improved method for operating a high-power gas laser. The improvement comprises introducing the gas lasing medium tangentially to the laser tube at a pressure establishing a forced vortex in the tube. The vortex defines an axially extending core region characterized by a low pressure and temperature relative to the gas inlet and the exterior of the vortex. An electrical discharge is established in the core region to initiate lasing of the gas. The gas discharge from the tube is passed through a diffuser. As in conventional gas lasers, firing results in a very abrupt increase in gas temperature and in severe disruption of the gas. However, the gas vortex almost immediately restores the gas to its pre-firing condition. That is, almost all of the waste heat is transferred radially to the laser wall, and the original gas-flow pattern is restored. As a result, the power output of the laser is increased significantly, and the laser firing repetition rate is markedly increased.

Laser utilizing a gaseous lasing medium and method for operating the same

DOEpatents

Zerr, B.A.

1983-10-18

The invention relates to an improvement in gas lasers and a method of operating the same. In one aspect, the invention is an improved method for operating a high-power gas laser. The improvement comprises introducing the gas lasing medium tangentially to the laser tube at a pressure establishing a forced vortex in the tube. The vortex defines an axially extending core region characterized by a low pressure and temperature relative to the gas inlet and the exterior of the vortex. An electrical discharge is established in the core region to initiate lasing of the gas. The gas discharge from the tube is passed through a diffuser. As in conventional gas lasers, firing results in a very abrupt increase in gas temperature and in severe disruption of the gas. However, the gas vortex, almost immediately restores the gas to its prefiring condition. That is, almost all of the waste heat is transferred radially to the laser wall, and the original gas-flow pattern is restored. As a result, the power output of the laser is increased significantly, and the laser firing repetition rate is markedly increased.

Numerical study of vortex rope during load rejection of a prototype pump-turbine

NASA Astrophysics Data System (ADS)

Liu, J. T.; Liu, S. H.; Sun, Y. K.; Wu, Y. L.; Wang, L. Q.

2012-11-01

A transient process of load rejection of a prototype pump-turbine was studied by three dimensional, unsteady simulations, as well as steady calculations.Dynamic mesh (DM) method and remeshing method were used to simulate the rotation of guide vanes and runner. The rotational speed of the runner was predicted by fluid couplingmethod. Both the transient calculation and steady calculation were performed based on turbulence model. Results show that steady calculation results have large error in the prediction of the external characteristics of the transient process. The runaway speed can reach 1.15 times the initial rotational speed during the transient process. The vortex rope occurs before the pump-turbine runs at zero moment point. Vortex rope has the same rotating direction with the runner. The vortex rope is separated into two parts as the flow rate decreases to 0. Pressure level decreases during the whole transient process.The transient simulation result were also compared and verified by experimental results. This computational method could be used in the fault diagnosis of transient operation, as well as the optimization of a transient process.

An experimental and theoretical study of the flow phenomena within a vortex sink rate sensor

NASA Technical Reports Server (NTRS)

Goglia, G. L.; Patel, D. K.

1974-01-01

Tests were conducted to obtain a description of the flow field within a vortex sink rate sensor and to observe the influence of viscous effects on its performance. The characteristics of the sensor are described. The method for conducting the test is reported. It was determined that for a specific mass flow rate and the geometry of the vortex chamber, the flow in the vortex chamber was only affected, locally, by the size of the sink tube diameter. Within the sink tube, all three velocity components were found to be higher for the small sink tube diameters. As the speed of rotation of the sensor was increased, the tangential velocities within the vortex chamber, as well as in the sink tube, increased in proportion to the speed of rotation.

Formation of eyes in large-scale cyclonic vortices

NASA Astrophysics Data System (ADS)

Oruba, L.; Davidson, P. A.; Dormy, E.

2018-01-01

We present numerical simulations of steady, laminar, axisymmetric convection of a Boussinesq fluid in a shallow, rotating, cylindrical domain. The flow is driven by an imposed vertical heat flux and shaped by the background rotation of the domain. The geometry is inspired by that of tropical cyclones and the global flow pattern consists of a shallow swirling vortex combined with a poloidal flow in the r -z plane which is predominantly inward near the bottom boundary and outward along the upper surface. Our numerical experiments confirm that, as suggested in our recent work [L. Oruba et al., J. Fluid Mech. 812, 890 (2017), 10.1017/jfm.2016.846], an eye forms at the center of the vortex which is reminiscent of that seen in a tropical cyclone and is characterized by a local reversal in the direction of the poloidal flow. We establish scaling laws for the flow and map out the conditions under which an eye will, or will not, form. We show that, to leading order, the velocity scales with V =(αg β ) 1 /2H , where g is gravity, α is the expansion coefficient, β is the background temperature gradient, and H is the depth of the domain. We also show that the two most important parameters controlling the flow are Re =V H /ν and Ro =V /(Ω H ) , where Ω is the background rotation rate and ν the viscosity. The Prandtl number and aspect ratio also play an important, if secondary, role. Finally, and most importantly, we establish the criteria required for eye formation. These consist of a lower bound on Re , upper and lower bounds on Ro , and an upper bound on the Ekman number.

Non-equilibrium effects of diatomic and polyatomic gases on the shock-vortex interaction based on the second-order constitutive model of the Boltzmann-Curtiss equation

NASA Astrophysics Data System (ADS)

Singh, S.; Karchani, A.; Myong, R. S.

2018-01-01

The rotational mode of molecules plays a critical role in the behavior of diatomic and polyatomic gases away from equilibrium. In order to investigate the essence of the non-equilibrium effects, the shock-vortex interaction problem was investigated by employing an explicit modal discontinuous Galerkin method. In particular, the first- and second-order constitutive models for diatomic and polyatomic gases derived rigorously from the Boltzmann-Curtiss kinetic equation were solved in conjunction with the physical conservation laws. As compared with a monatomic gas, the non-equilibrium effects result in a substantial change in flow fields in both macroscale and microscale shock-vortex interactions. Specifically, the computational results showed three major effects of diatomic and polyatomic gases on the shock-vortex interaction: (i) the generation of the third sound waves and additional reflected shock waves with strong and enlarged expansion, (ii) the dominance of viscous vorticity generation, and (iii) an increase in enstrophy with increasing bulk viscosity, related to the rotational mode of gas molecules. Moreover, it was shown that there is a significant discrepancy in flow fields between the microscale and macroscale shock-vortex interactions in diatomic and polyatomic gases. The quadrupolar acoustic wave source structures, which are typically observed in macroscale shock-vortex interactions, were not found in any microscale shock-vortex interactions. The physics of the shock-vortex interaction was also investigated in detail to examine vortex deformation and evolution dynamics over an incident shock wave. A comparative study of first- and second-order constitutive models was also conducted for the enstrophy and dissipation rate. Finally, the study was extended to the shock-vortex pair interaction case to examine the effects of pair interaction on vortex deformation and evolution dynamics.

An immersed boundary method for simulating vesicle dynamics in three dimensions

NASA Astrophysics Data System (ADS)

Seol, Yunchang; Hu, Wei-Fan; Kim, Yongsam; Lai, Ming-Chih

2016-10-01

We extend our previous immersed boundary (IB) method for 3D axisymmetric inextensible vesicle in Navier-Stokes flows (Hu et al., 2014 [17]) to general three dimensions. Despite a similar spirit in numerical algorithms to the axisymmetric case, the fully 3D numerical implementation is much more complicated and is far from straightforward. A vesicle membrane surface is known to be incompressible and exhibits bending resistance. As in 3D axisymmetric case, instead of keeping the vesicle locally incompressible, we adopt a modified elastic tension energy to make the vesicle surface patch nearly incompressible so that solving the unknown tension (Lagrange multiplier for the incompressible constraint) can be avoided. Nevertheless, the new elastic force derived from the modified tension energy has exactly the same mathematical form as the original one except the different definitions of tension. The vesicle surface is discretized on a triangular mesh where the elastic tension and bending force are calculated on each vertex (Lagrangian marker in the IB method) of the triangulation. A series of numerical tests on the present scheme are conducted to illustrate the robustness and applicability of the method. We perform the convergence study for the immersed boundary forces and the fluid velocity field. We then study the vesicle dynamics in various flows such as quiescent, simple shear, and gravitational flows. Our numerical results show good agreements with those obtained in previous theoretical, experimental and numerical studies.

Pseudospectral method for gravitational wave collapse

NASA Astrophysics Data System (ADS)

Hilditch, David; Weyhausen, Andreas; Brügmann, Bernd

2016-03-01

We present a new pseudospectral code, bamps, for numerical relativity written with the evolution of collapsing gravitational waves in mind. We employ the first-order generalized harmonic gauge formulation. The relevant theory is reviewed, and the numerical method is critically examined and specialized for the task at hand. In particular, we investigate formulation parameters—gauge- and constraint-preserving boundary conditions well suited to nonvanishing gauge source functions. Different types of axisymmetric twist-free moment-of-time-symmetry gravitational wave initial data are discussed. A treatment of the axisymmetric apparent horizon condition is presented with careful attention to regularity on axis. Our apparent horizon finder is then evaluated in a number of test cases. Moving on to evolutions, we investigate modifications to the generalized harmonic gauge constraint damping scheme to improve conservation in the strong-field regime. We demonstrate strong-scaling of our pseudospectral penalty code. We employ the Cartoon method to efficiently evolve axisymmetric data in our 3 +1 -dimensional code. We perform test evolutions of the Schwarzschild spacetime perturbed by gravitational waves and by gauge pulses, both to demonstrate the use of our black-hole excision scheme and for comparison with earlier results. Finally, numerical evolutions of supercritical Brill waves are presented to demonstrate durability of the excision scheme for the dynamical formation of a black hole.

A Three-Dimensional Solution of Flows over Wings with Leading-Edge Vortex Separation. Part 1: Engineering Document

NASA Technical Reports Server (NTRS)

Brune, G. W.; Weber, J. A.; Johnson, F. T.; Lu, P.; Rubbert, P. E.

1975-01-01

A method of predicting forces, moments, and detailed surface pressures on thin, sharp-edged wings with leading-edge vortex separation in incompressible flow is presented. The method employs an inviscid flow model in which the wing and the rolled-up vortex sheets are represented by piecewise, continuous quadratic doublet sheet distributions. The Kutta condition is imposed on all wing edges. Computed results are compared with experimental data and with the predictions of the leading-edge suction analogy for a selected number of wing planforms over a wide range of angle of attack. These comparisons show the method to be very promising, capable of producing not only force predictions, but also accurate predictions of detailed surface pressure distributions, loads, and moments.

Iterative adaption of the bidimensional wall of the French T2 wind tunnel around a C5 axisymmetrical model: Infinite variation of the Mach number at zero incidence and a test at increased incidence

NASA Technical Reports Server (NTRS)

Archambaud, J. P.; Dor, J. B.; Payry, M. J.; Lamarche, L.

1986-01-01

The top and bottom two-dimensional walls of the T2 wind tunnel are adapted through an iterative process. The adaptation calculation takes into account the flow three-dimensionally. This method makes it possible to start with any shape of walls. The tests were performed with a C5 axisymmetric model at ambient temperature. Comparisons are made with the results of a true three-dimensional adaptation.

Parametric resonance in acoustically levitated water drops

NASA Astrophysics Data System (ADS)

Shen, C. L.; Xie, W. J.; Wei, B.

2010-05-01

Liquid drops can be suspended in air with acoustic levitation method. When the sound pressure is periodically modulated, the levitated drop is usually forced into an axisymmetric oscillation. However, a transition from axisymmetric oscillation into sectorial oscillation occurs when the modulation frequency approaches some specific values. The frequency of the sectorial oscillation is almost exactly half of the modulation frequency. It is demonstrated that this transition is induced by the parametric resonance of levitated drop. The natural frequency of sectorial oscillation is found to decrease with the increase of drop distortion extent.

Wake Vortex Avoidance System and Method

NASA Technical Reports Server (NTRS)

Shams, Qamar A. (Inventor); Zuckerwar, Allan J. (Inventor); Knight, Howard K. (Inventor)

2017-01-01

A wake vortex avoidance system includes a microphone array configured to detect low frequency sounds. A signal processor determines a geometric mean coherence based on the detected low frequency sounds. A display displays wake vortices based on the determined geometric mean coherence.

Magnetic control of magnetohydrodynamic instabilities in tokamaks

DOE PAGES

Strait, Edward J.

2014-11-24

Externally applied, non-axisymmetric magnetic fields form the basis of several relatively simple and direct methods to control magnetohydrodynamic (MHD) instabilities in a tokamak, and most present and planned tokamaks now include a set of non-axisymmetric control coils for application of fields with low toroidal mode numbers. Non-axisymmetric applied fields are routinely used to compensate small asymmetries ( δB/B ~ 10 -3 to 10 -4) of the nominally axisymmetric field, which otherwise can lead to instabilities through braking of plasma rotation and through direct stimulus of tearing modes or kink modes. This compensation may be feedback-controlled, based on the magnetic responsemore » of the plasma to the external fields. Non-axisymmetric fields are used for direct magnetic stabilization of the resistive wall mode — a kink instability with a growth rate slow enough that feedback control is practical. Saturated magnetic islands are also manipulated directly with non-axisymmetric fields, in order to unlock them from the wall and spin them to aid stabilization, or position them for suppression by localized current drive. Several recent scientific advances form the foundation of these developments in the control of instabilities. Most fundamental is the understanding that stable kink modes play a crucial role in the coupling of non-axisymmetric fields to the plasma, determining which field configurations couple most strongly, how the coupling depends on plasma conditions, and whether external asymmetries are amplified by the plasma. A major advance for the physics of high-beta plasmas ( β = plasma pressure/magnetic field pressure) has been the understanding that drift-kinetic resonances can stabilize the resistive wall mode at pressures well above the ideal-MHD stability limit, but also that such discharges can be very sensitive to external asymmetries. The common physics of stable kink modes has brought significant unification to the topics of static error fields at low beta and resistive wall modes at high beta. Furthermore, these and other scientific advances, and their application to control of MHD instabilities, will be reviewed with emphasis on the most recent results and their applicability to ITER.« less

Orbital tori for non-axisymmetric galaxies

NASA Astrophysics Data System (ADS)

Binney, James

2018-02-01

Our Galaxy's bar makes the Galaxy's potential distinctly non-axisymmetric. All orbits are affected by non-axisymmetry, and significant numbers are qualitatively changed by being trapped at a resonance with the bar. Orbital tori are used to compute these effects. Thick-disc orbits are no less likely to be trapped by corotation or a Lindblad resonance than thin-disc orbits. Perturbation theory is used to create non-axisymmetric orbital tori from standard axisymmetric tori, and both trapped and untrapped orbits are recovered to surprising accuracy. Code is added to the TorusModeller library that makes it as easy to manipulate non-axisymmetric tori as axisymmetric ones. The augmented TorusModeller is used to compute the velocity structure of the solar neighbourhood for bars of different pattern speeds and a simple action-based distribution function. The technique developed here can be applied to any non-axisymmetric potential that is stationary in a rotating from - hence also to classical spiral structure.

Effect of a crystal-melt interface on Taylor-vortex flow

NASA Technical Reports Server (NTRS)

Mcfadden, G. B.; Coriell, S. R.; Murray, B. T.; Glicksman, M. E.; Selleck, M. E.

1990-01-01

The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case that the stationary outer cylinder is a crystal-melt interface rather than a rigid surface. A radial temperature difference is maintained across the liquid gap, and equations for heat transport in the crystal and melt phases are included to extend the ordinary formulation of this problem. The stability of this two-phase system depends on the Prandtl number. For small Prandtl number the linear stability of the two-phase system is given by the classical results for a rigid-walled system. For increasing values of the Prandtl number, convective heat transport becomes significant and the system becomes increasingly less stable. Previous results in a narrow-gap approximation are extended to the case of a finite gap, and both axisymmetric and nonaxisymmetric disturbance modes are considered. The two-phase system becomes less stable as the finite gap tends to the narrow-gap limit. The two-phase system is more stable to nonaxisymmetric modes with azimuthal wavenumber n = 1; the stability of these n = 1 modes is sensitive to the latent heat of fusion.

Fast generation of three-dimensional computational boundary-conforming periodic grids of C-type. [for turbine blades and propellers

NASA Technical Reports Server (NTRS)

Dulikravich, D. S.

1982-01-01

A fast computer program, GRID3C, was developed to generate multilevel three dimensional, C type, periodic, boundary conforming grids for the calculation of realistic turbomachinery and propeller flow fields. The technique is based on two analytic functions that conformally map a cascade of semi-infinite slits to a cascade of doubly infinite strips on different Riemann sheets. Up to four consecutively refined three dimensional grids are automatically generated and permanently stored on four different computer tapes. Grid nonorthogonality is introduced by a separate coordinate shearing and stretching performed in each of three coordinate directions. The grids are easily clustered closer to the blade surface, the trailing and leading edges and the hub or shroud regions by changing appropriate input parameters. Hub and duct (or outer free boundary) have different axisymmetric shapes. A vortex sheet of arbitrary thickness emanating smoothly from the blade trailing edge is generated automatically by GRID3C. Blade cross sectional shape, chord length, twist angle, sweep angle, and dihedral angle can vary in an arbitrary smooth fashion in the spanwise direction.

Five-hole pitot probe time-mean velocity measurements in confined swirling flows

NASA Technical Reports Server (NTRS)

Yoon, H. K.; Lilley, D. G.

1983-01-01

Nonswirling and swirling nonreacting flows in an axisymmetric test section with an expansion ratio D/d = 2, which may be equipped with contraction nozzles of area ratios 2 and 4, are investigated. The effects of a number of geometric parameters on the flow-field are investigated, among them side-wall expansion angles of 90 and 45 deg, swirl vane angles of 0, 38, 45, 60, and 70 deg, and contraction nozzle locations L/D = 1 and 2 (if present). Data are acquired by means of a five-hole pitot probe enabling three time-mean velocity components in the axial, radial, and azimuthal directions to be measured. The velocities are extensively plotted and artistic impressions of recirculation zones are set forth. The presence of a swirler is found to shorten the corner recirculation zone and to generate a central recirculation zone followed by a precessing vortex core. A gradual inlet expansion has the effect of encouraging the flow to remain close to the sidewall and shortening the extent of the corner recirculation zone in all cases investigated.

Computational study of the interaction between a shock and a near-wall vortex using a weighted compact nonlinear scheme

NASA Astrophysics Data System (ADS)

Zuo, Zhifeng; Maekawa, Hiroshi

2014-02-01

The interaction between a moderate-strength shock wave and a near-wall vortex is studied numerically by solving the two-dimensional, unsteady compressible Navier-Stokes equations using a weighted compact nonlinear scheme with a simple low-dissipation advection upstream splitting method for flux splitting. Our main purpose is to clarify the development of the flow field and the generation of sound waves resulting from the interaction. The effects of the vortex-wall distance on the sound generation associated with variations in the flow structures are also examined. The computational results show that three sound sources are involved in this problem: (i) a quadrupolar sound source due to the shock-vortex interaction; (ii) a dipolar sound source due to the vortex-wall interaction; and (iii) a dipolar sound source due to unsteady wall shear stress. The sound field is the combination of the sound waves produced by all three sound sources. In addition to the interaction of the incident shock with the vortex, a secondary shock-vortex interaction is caused by the reflection of the reflected shock (MR2) from the wall. The flow field is dominated by the primary and secondary shock-vortex interactions. The generation mechanism of the third sound, which is newly discovered, due to the MR2-vortex interaction is presented. The pressure variations generated by (ii) become significant with decreasing vortex-wall distance. The sound waves caused by (iii) are extremely weak compared with those caused by (i) and (ii) and are negligible in the computed sound field.

Focus detection by shearing interference of vortex beams for non-imaging systems.

PubMed

Li, Xiongfeng; Zhan, Shichao; Liang, Yiyong

2018-02-10

In focus detection of non-imaging systems, the common image-based methods are not available. Also, interference techniques are seldom used because only the degree with hardly any direction of defocus can be derived from the fringe spacing. In this paper, we propose a vortex-beam-based shearing interference system to do focus detection for a focused laser direct-writing system, where a vortex beam is already involved. Both simulated and experimental results show that fork-like features are added in the interference patterns due to the existence of an optical vortex, which makes it possible to distinguish the degree and direction of defocus simultaneously. The theoretical fringe spacing and resolution of this method are derived. A resolution of 0.79 μm can be achieved under the experimental combination of parameters, and it can be further improved with the help of the image processing algorithm and closed-loop controlling in the future. Finally, the influence of incomplete collimation and the wedge angle of the shear plate is discussed. This focus detection approach is extremely appropriate for those non-imaging systems containing one or more focused vortex beams.

Reduced-order aeroelastic model for limit-cycle oscillations in vortex-dominated unsteady airfoil flows

NASA Astrophysics Data System (ADS)

Suresh Babu, Arun Vishnu; Ramesh, Kiran; Gopalarathnam, Ashok

2017-11-01

In previous research, Ramesh et al. (JFM,2014) developed a low-order discrete vortex method for modeling unsteady airfoil flows with intermittent leading edge vortex (LEV) shedding using a leading edge suction parameter (LESP). LEV shedding is initiated using discrete vortices (DVs) whenever the Leading Edge Suction Parameter (LESP) exceeds a critical value. In subsequent research, the method was successfully employed by Ramesh et al. (JFS, 2015) to predict aeroelastic limit-cycle oscillations in airfoil flows dominated by intermittent LEV shedding. When applied to flows that require large number of time steps, the computational cost increases due to the increasing vortex count. In this research, we apply an amalgamation strategy to actively control the DV count, and thereby reduce simulation time. A pair each of LEVs and TEVs are amalgamated at every time step. The ideal pairs for amalgamation are identified based on the requirement that the flowfield in the vicinity of the airfoil is least affected (Spalart, 1988). Instead of placing the amalgamated vortex at the centroid, we place it at an optimal location to ensure that the leading-edge suction and the airfoil bound circulation are conserved. Results of the initial study are promising.

Vortex ring motions in stratified media

NASA Astrophysics Data System (ADS)

Auvity, Bruno; Koulal, Mokrane; Dupont, Pascal; Peerhossaini, Hassan

2003-11-01

The behavior of vortex rings generated in a stably stratified media has received only weak treatment in the literature. This configuration is believed to shed light on the basic phenomena involved in the collapse of wake in stratified fluid. The present study focused on experimental observations of the formation, the advection and the collapse of horizontal vortex rings in stratified media. Stable continuous vertical stratification was produced in a tank using the well-known two-tanks method. The generation of vortex ring was realized moving a piston through a tube. The maximum piston stroke achievable was seven tube diameters. The problem is mainly characterized by two parameters : the initial Reynolds number and the initial Froude number of the vortex ring. Both these numbers were varied in the study. The Reynolds number based on the tube diameter and piston velocity was in the range 1,500 - 5,500 and the Froude number based on the same parameters in the range 1.4 - 4.7. Dye visualizations were performed from the top and the side of the tank showing the vortex ring may develop an important asymmetry. Different processes to the complete collapse of the vortex ring were identified.

Vortex wake control via smart structures technology

NASA Astrophysics Data System (ADS)

Quackenbush, Todd R.; Bilanin, Alan J.; McKillip, Robert M., Jr.

1996-05-01

Control of trailing vortex wakes is an important challenges for both military and civilian applications. This paper summarizes an assessment of the feasibility of mitigating adverse vortex wake effects using control surfaces actuated via Shape Memory Alloy (SMA) technology. The assessment involved a combined computational/design analysis that identified methods for introducing small secondary vortices to promote the deintensification of vortex wakes of submarines and aircraft. Computational analyses of wake breakup using this `vortex leveraging' strategy were undertaken, and showed dramatic increases in the dissipation rate of concentrated vortex wakes. This paper briefly summarizes these results and describes the preliminary design of actuation mechanisms for the deflectable surfaces that effect the required time-varying wake perturbations. These surfaces, which build on the high-force, high- deflection capabilities of SMA materials, are shown to be well suited for the very low frequency actuation requirements of the wake deintensification mission. The paper outlines the assessment of device performance capabilities and describes the sizing studies undertaken for full-scale Vortex Leveraging Tabs (VLTs) designed for use in hydrodynamic and aerodynamic applications. Results obtained to date indicate that the proposed VLTs can accelerate wake breakup by over a factor of three and can be implemented using deflectable surfaces actuated using SMAs.

A regularized vortex-particle mesh method for large eddy simulation

NASA Astrophysics Data System (ADS)

Spietz, H. J.; Walther, J. H.; Hejlesen, M. M.

2017-11-01

We present recent developments of the remeshed vortex particle-mesh method for simulating incompressible fluid flow. The presented method relies on a parallel higher-order FFT based solver for the Poisson equation. Arbitrary high order is achieved through regularization of singular Green's function solutions to the Poisson equation and recently we have derived novel high order solutions for a mixture of open and periodic domains. With this approach the simulated variables may formally be viewed as the approximate solution to the filtered Navier Stokes equations, hence we use the method for Large Eddy Simulation by including a dynamic subfilter-scale model based on test-filters compatible with the aforementioned regularization functions. Further the subfilter-scale model uses Lagrangian averaging, which is a natural candidate in light of the Lagrangian nature of vortex particle methods. A multiresolution variation of the method is applied to simulate the benchmark problem of the flow past a square cylinder at Re = 22000 and the obtained results are compared to results from the literature.

Prediction of vortex shedding from circular and noncircular bodies in supersonic flow

NASA Technical Reports Server (NTRS)

Mendenhall, M. R.; Perkins, S. C., Jr.

1984-01-01

An engineering prediction method and associated computer code NOZVTX to predict nose vortex shedding from circular and noncircular bodies in supersonic flow at angles of attack and roll are presented. The body is represented by either a supersonic panel method for noncircular cross sections or line sources and doublets for circular cross sections, and the lee side vortex wake is modeled by discrete vortices in crossflow planes. The three-dimensional steady flow problem is reduced to a two-dimensional, unsteady, separated flow problem for solution. Comparison of measured and predicted surface pressure distributions, flow field surveys, and aerodynamic characteristics is presented for bodies with circular and noncircular cross-sectional shapes.

Airfoil self-noise and prediction

NASA Technical Reports Server (NTRS)

Brooks, Thomas F.; Pope, D. Stuart; Marcolini, Michael A.

1989-01-01

A prediction method is developed for the self-generated noise of an airfoil blade encountering smooth flow. The prediction methods for the individual self-noise mechanisms are semiempirical and are based on previous theoretical studies and data obtained from tests of two- and three-dimensional airfoil blade sections. The self-noise mechanisms are due to specific boundary-layer phenomena, that is, the boundary-layer turbulence passing the trailing edge, separated-boundary-layer and stalled flow over an airfoil, vortex shedding due to laminar boundary layer instabilities, vortex shedding from blunt trailing edges, and the turbulent vortex flow existing near the tip of lifting blades. The predictions are compared successfully with published data from three self-noise studies of different airfoil shapes. An application of the prediction method is reported for a large scale-model helicopter rotor, and the predictions compared well with experimental broadband noise measurements. A computer code of the method is given.

Solution of axisymmetric and two-dimensional inviscid flow over blunt bodies by the method of lines

NASA Technical Reports Server (NTRS)

Hamilton, H. H., II

1978-01-01

Comparisons with experimental data and the results of other computational methods demonstrated that very accurate solutions can be obtained by using relatively few lines with the method of lines approach. This method is semidiscrete and has relatively low core storage requirements as compared with fully discrete methods since very little data were stored across the shock layer. This feature is very attractive for three dimensional problems because it enables computer storage requirements to be reduced by approximately an order of magnitude. In the present study it was found that nine lines was a practical upper limit for two dimensional and axisymmetric problems. This condition limits application of the method to smooth body geometries where relatively few lines would be adequate to describe changes in the flow variables around the body. Extension of the method to three dimensions was conceptually straightforward; however, three dimensional applications would also be limited to smooth body geometries although not necessarily to total of nine lines.

Solution of steady and unsteady transonic-vortex flows using Euler and full-potential equations

NASA Technical Reports Server (NTRS)

Kandil, Osama A.; Chuang, Andrew H.; Hu, Hong

1989-01-01

Two methods are presented for inviscid transonic flows: unsteady Euler equations in a rotating frame of reference for transonic-vortex flows and integral solution of full-potential equation with and without embedded Euler domains for transonic airfoil flows. The computational results covered: steady and unsteady conical vortex flows; 3-D steady transonic vortex flow; and transonic airfoil flows. The results are in good agreement with other computational results and experimental data. The rotating frame of reference solution is potentially efficient as compared with the space fixed reference formulation with dynamic gridding. The integral equation solution with embedded Euler domain is computationally efficient and as accurate as the Euler equations.

Dual-polarization and dual-mode orbital angular momentum radio vortex beam generated by using reflective metasurface

NASA Astrophysics Data System (ADS)

Yu, Shixing; Li, Long; Shi, Guangming

2016-08-01

A metasurface, which is composed of printed cross-dipole elements with different arm lengths, is designed, fabricated, and experimentally demonstrated to generate orbital angular momentum (OAM) vortex waves of dual polarizations and dual modes in the radio frequency domain simultaneously. The prototype of a practical metasurface is fabricated and measured to validate the results of theoretical analysis and design at 5.8 GHz. Numerical and experimental results verify that vortex waves with dual OAM modes and dual polarizations can be flexibly generated by using a reflective metasurface. The proposed method paves a way to generate diverse OAM vortex waves for radio frequency and microwave wireless communication applications.

Computing Trimmed, Mean-Camber Surfaces At Minimum Drag

NASA Technical Reports Server (NTRS)

Lamar, John E.; Hodges, William T.

1995-01-01

VLMD computer program determines subsonic mean-camber surfaces of trimmed noncoplanar planforms with minimum vortex drag at specified lift coefficient. Up to two planforms designed together. Method used that of subsonic vortex lattice method of chord loading specification, ranging from rectangular to triangular, left specified by user. Program versatile and applied to isolated wings, wing/canard configurations, tandem wing, and wing/-winglet configuration. Written in FORTRAN.

Scattering of a vortex pair by a single quantum vortex in a Bose–Einstein condensate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smirnov, L. A., E-mail: smirnov-lev@allp.sci-nnov.ru; Smirnov, A. I., E-mail: smirnov@appl.sci-nnov.ru; Mironov, V. A.

We analyze the scattering of vortex pairs (the particular case of 2D dark solitons) by a single quantum vortex in a Bose–Einstein condensate with repulsive interaction between atoms. For this purpose, an asymptotic theory describing the dynamics of such 2D soliton-like formations in an arbitrary smoothly nonuniform flow of a ultracold Bose gas is developed. Disregarding the radiation loss associated with acoustic wave emission, we demonstrate that vortex–antivortex pairs can be put in correspondence with quasiparticles, and their behavior can be described by canonical Hamilton equations. For these equations, we determine the integrals of motion that can be used tomore » classify various regimes of scattering of vortex pairs by a single quantum vortex. Theoretical constructions are confirmed by numerical calculations performed directly in terms of the Gross–Pitaevskii equation. We propose a method for estimating the radiation loss in a collision of a soliton-like formation with a phase singularity. It is shown by direct numerical simulation that under certain conditions, the interaction of vortex pairs with a core of a single quantum vortex is accompanied by quite intense acoustic wave emission; as a result, the conditions for applicability of the asymptotic theory developed here are violated. In particular, it is visually demonstrated by a specific example how radiation losses lead to a transformation of a vortex–antivortex pair into a vortex-free 2D dark soliton (i.e., to the annihilation of phase singularities).« less

Interaction of ions, atoms, and small molecules with quantized vortex lines in superfluid (4)He.

PubMed

Mateo, David; Eloranta, Jussi; Williams, Gary A

2015-02-14

The interaction of a number of impurities (H2, Ag, Cu, Ag2, Cu2, Li, He3 (+), He(*) ((3)S), He2 (∗) ((3)Σu), and e(-)) with quantized rectilinear vortex lines in superfluid (4)He is calculated by using the Orsay-Trento density functional theory (DFT) method at 0 K. The Donnelly-Parks (DP) potential function binding ions to the vortex is combined with DFT data, yielding the impurity radius as well as the vortex line core parameter. The vortex core parameter at 0 K (0.74 Å) obtained either directly from the vortex line geometry or through the DP potential fitting is smaller than previously suggested but is compatible with the value obtained from re-analysis of the Rayfield-Reif experiment. All of the impurities have significantly higher binding energies to vortex lines below 1 K than the available thermal energy, where the thermally assisted escape process becomes exponentially negligible. Even at higher temperatures 1.5-2.0 K, the trapping times for larger metal clusters are sufficiently long that the previously observed metal nanowire assembly in superfluid helium can take place at vortex lines. The binding energy of the electron bubble is predicted to decrease as a function of both temperature and pressure, which allows adjusting the trap depth for either permanent trapping or to allow thermally assisted escape. Finally, a new scheme for determining the trapping of impurities on vortex lines by optical absorption spectroscopy is outlined and demonstrated for He(*).

Interaction of ions, atoms, and small molecules with quantized vortex lines in superfluid 4He

NASA Astrophysics Data System (ADS)

Mateo, David; Eloranta, Jussi; Williams, Gary A.

2015-02-01

The interaction of a number of impurities (H2, Ag, Cu, Ag2, Cu2, Li, He3 + , He* (3S), He2∗ (3Σu), and e-) with quantized rectilinear vortex lines in superfluid 4He is calculated by using the Orsay-Trento density functional theory (DFT) method at 0 K. The Donnelly-Parks (DP) potential function binding ions to the vortex is combined with DFT data, yielding the impurity radius as well as the vortex line core parameter. The vortex core parameter at 0 K (0.74 Å) obtained either directly from the vortex line geometry or through the DP potential fitting is smaller than previously suggested but is compatible with the value obtained from re-analysis of the Rayfield-Reif experiment. All of the impurities have significantly higher binding energies to vortex lines below 1 K than the available thermal energy, where the thermally assisted escape process becomes exponentially negligible. Even at higher temperatures 1.5-2.0 K, the trapping times for larger metal clusters are sufficiently long that the previously observed metal nanowire assembly in superfluid helium can take place at vortex lines. The binding energy of the electron bubble is predicted to decrease as a function of both temperature and pressure, which allows adjusting the trap depth for either permanent trapping or to allow thermally assisted escape. Finally, a new scheme for determining the trapping of impurities on vortex lines by optical absorption spectroscopy is outlined and demonstrated for He*.

Characterization of Pulsed Vortex Generator Jets for Active Flow Control

DTIC Science & Technology

2001-06-01

approaches to calculating these quantities shown to not to play a significant role in the developing vortex, were assessed; most of which used Amtec ...obtained very close to Since this method was developed. Amtec Engineering’s CFD the wall, but not completely through the laminar sub-layer. The...Francisco, California, July 18-23 1999. 31 "’Khan, Z.U. & Jolmston, J.P., "On Vortex Generating Jets," " Amtec Engineering Inc., ©1988-2000 [http

Investigation of inner aerodynamics of the four-vortex furnace model

NASA Astrophysics Data System (ADS)

Anufriev, I. S.; Shadrin, E. Yu; Sharypov, O. V.

2018-03-01

The internal aerodynamics of a perspective vortex furnace chamber of a pulverized coal boiler with a diagonal arrangement of burners is studied using the non-contact optical method of flow diagnostics. The results of laser Doppler anemometry, characterizing the complex spatial structure of a swirling flow in an isothermal laboratory model of the furnace device, are presented. The velocity distribution in the vortex chamber volume is obtained, and the flow structure in the form of four conjugate closed vortices with curved axes is visualized.

An approximate theoretical method for modeling the static thrust performance of non-axisymmetric two-dimensional convergent-divergent nozzles. M.S. Thesis - George Washington Univ.

NASA Technical Reports Server (NTRS)

Hunter, Craig A.

1995-01-01

An analytical/numerical method has been developed to predict the static thrust performance of non-axisymmetric, two-dimensional convergent-divergent exhaust nozzles. Thermodynamic nozzle performance effects due to over- and underexpansion are modeled using one-dimensional compressible flow theory. Boundary layer development and skin friction losses are calculated using an approximate integral momentum method based on the classic karman-Polhausen solution. Angularity effects are included with these two models in a computational Nozzle Performance Analysis Code, NPAC. In four different case studies, results from NPAC are compared to experimental data obtained from subscale nozzle testing to demonstrate the capabilities and limitations of the NPAC method. In several cases, the NPAC prediction matched experimental gross thrust efficiency data to within 0.1 percent at a design NPR, and to within 0.5 percent at off-design conditions.

MODFLOW equipped with a new method for the accurate simulation of axisymmetric flow

NASA Astrophysics Data System (ADS)

Samani, N.; Kompani-Zare, M.; Barry, D. A.

2004-01-01

Axisymmetric flow to a well is an important topic of groundwater hydraulics, the simulation of which depends on accurate computation of head gradients. Groundwater numerical models with conventional rectilinear grid geometry such as MODFLOW (in contrast to analytical models) generally have not been used to simulate aquifer test results at a pumping well because they are not designed or expected to closely simulate the head gradient near the well. A scaling method is proposed based on mapping the governing flow equation from cylindrical to Cartesian coordinates, and vice versa. A set of relationships and scales is derived to implement the conversion. The proposed scaling method is then embedded in MODFLOW 2000. To verify the accuracy of the method steady and unsteady flows in confined and unconfined aquifers with fully or partially penetrating pumping wells are simulated and compared with the corresponding analytical solutions. In all cases a high degree of accuracy is achieved.

Chaotic vortex filaments in a Bose–Einstein condensate and in superfluid helium

NASA Astrophysics Data System (ADS)

Nemirovskii, S. K.

2018-05-01

A statement of the quantum turbulence problem in both a Bose–Einstein condensate (BEC) and superfluid helium is formulated. In superfluid helium use is made of a so-called vortex filament method, in which quantum vortices are represented by stringlike objects, i.e. vortex lines. The dynamics of the vortex lines is determined by deterministic equations of motion, supplemented by random reconnections. Unlike He II, the laws of the dynamics of quantum vortices in BEC are based on the nonlinear Schrödinger equation. This makes it possible to obtain a microscopic description of the collision of vortices, the structure of a vortex filament, etc. A comparative analysis of these complementary approaches is carried out. It is shown that there are some features that do not automatically transfer the results obtained for BEC to vortices in He II and vice versa.

Tip/tilt optimizations for polynomial apodized vortex coronagraphs on obscured telescope pupils

NASA Astrophysics Data System (ADS)

Fogarty, Kevin; Pueyo, Laurent; Mazoyer, Johan; N'Diaye, Mamadou

2017-09-01

Obstructions due to large secondary mirrors, primary mirror segmentation, and secondary mirror support struts all introduce diffraction artifacts that limit the performance offered by coronagraphs. However, just as vortex coronagraphs provides theoretically ideal cancellation of on-axis starlight for clear apertures, the Polynomial Apodized Vortex Coronagraph (PAVC) completely blocks on-axis light for apertures with central obscurations, and delivers off-axis throughput that improves as the topological charge of the vortex increases. We examine the sensitivity of PAVC designs to tip/tilt aberrations and stellar angular size, and discuss methods for mitigating these effects. By imposing additional constraints on the pupil plane apodization, we decrease the sensitivity of the PAVC to the small positional shifts of the on-axis source induced by either tip/tilt or stellar angular size; providing a route to overcoming an important hurdle facing the performance of vortex coronagraphs on telescopes with complicated pupils.

Wake Geometry Measurements and Analytical Calculations on a Small-Scale Rotor Model

NASA Technical Reports Server (NTRS)

Ghee, Terence A.; Berry, John D.; Zori, Laith A. J.; Elliott, Joe W.

1996-01-01

An experimental investigation was conducted in the Langley 14- by 22-Foot Subsonic Tunnel to quantify the rotor wake behind a scale model helicopter rotor in forward level flight at one thrust level. The rotor system in this test consisted of a four-bladed fully articulated hub with blades of rectangular planform and an NACA 0012 airfoil section. A laser light sheet, seeded with propylene glycol smoke, was used to visualize the vortex geometry in the flow in planes parallel and perpendicular to the free-stream flow. Quantitative measurements of wake geometric proper- ties, such as vortex location, vertical skew angle, and vortex particle void radius, were obtained as well as convective velocities for blade tip vortices. Comparisons were made between experimental data and four computational method predictions of experimental tip vortex locations, vortex vertical skew angles, and wake geometries. The results of these comparisons highlight difficulties of accurate wake geometry predictions.

Radiative modelling by the zonal method and WSGG model in inhomogeneous axisymmetric cylindrical enclosure

NASA Astrophysics Data System (ADS)

Méchi, Rachid; Farhat, Habib; Said, Rachid

2016-01-01

Nongray radiation calculations are carried out for a case problem available in the literature. The problem is a non-isothermal and inhomogeneous CO2-H2O- N2 gas mixture confined within an axisymmetric cylindrical furnace. The numerical procedure is based on the zonal method associated with the weighted sum of gray gases (WSGG) model. The effect of the wall emissivity on the heat flux losses is discussed. It is shown that this property affects strongly the furnace efficiency and that the most important heat fluxes are those leaving through the circumferential boundary. The numerical procedure adopted in this work is found to be effective and may be relied on to simulate coupled turbulent combustion-radiation in fired furnaces.

An analysis of turbulent diffusion flame in axisymmetric jet

NASA Technical Reports Server (NTRS)

Chung, P. M.; Im, K. H.

1980-01-01

The kinetic theory of turbulent flow was employed to study the mixing limited combustion of hydrogen in axisymmetric jets. The integro-differential equations in two spatial and three velocity coordinates describing the combustion were reduced to a set of hyperbolic partial differential equations in the two spatial coordinates by a binodal approximation. The MacCormick's finite difference method was then employed for solution. The flame length was longer than that predicted by the flame-sheet analysis, and was found to be in general agreement with a recent experimental result. Increase of the turbulence energy and scale resulted in an enhancement of the combustion rate and, hence, in a shorter flame length. Details of the numerical method as well as of the physical findings are discussed.

Spatial Dynamics Methods for Solitary Waves on a Ferrofluid Jet

NASA Astrophysics Data System (ADS)

Groves, M. D.; Nilsson, D. V.

2018-04-01

This paper presents existence theories for several families of axisymmetric solitary waves on the surface of an otherwise cylindrical ferrofluid jet surrounding a stationary metal rod. The ferrofluid, which is governed by a general (nonlinear) magnetisation law, is subject to an azimuthal magnetic field generated by an electric current flowing along the rod. The ferrohydrodynamic problem for axisymmetric travelling waves is formulated as an infinite-dimensional Hamiltonian system in which the axial direction is the time-like variable. A centre-manifold reduction technique is employed to reduce the system to a locally equivalent Hamiltonian system with a finite number of degrees of freedom, and homoclinic solutions to the reduced system, which correspond to solitary waves, are detected by dynamical-systems methods.

Non-ionic detergent Triton X-114 Based vortex- synchronized matrix solid-phase dispersion method for the simultaneous determination of six compounds with various polarities from Forsythiae Fructus by ultra high-performance liquid chromatography.

PubMed

Du, Kunze; Li, Jin; Tian, Fei; Chang, Yan-Xu

2018-02-20

A simple nonionic detergent - based vortex- synchronized matrix solid-phase dispersion (ND-VSMSPD) method was developed to extract bioactive compounds in Forsythiae Fructus coupled with ultra high-performance liquid chromatography (UHPLC). Nonionic detergent Triton 114 was firstly used as a green elution reagent in vortex- synchronized MSPD procedure. The optimum parameters were investigated to attain the best results, including Florisil as sorbent, 2mL 10% (v/v) nonionic detergent Triton X-114 as the elution reagent, 1:1 of sample/sorbent ratio, grinding for 3min, and whirling for 2min. The recoveries of the six compounds in Forsythiae Fructus were in the range of 95-104% (RSD <4.6%) and the method displayed a good linearity within the range of 0.08-20μgmL -1 for caffeic acid, 0.6-150μgmL -1 for forsythoside A, 0.4-100μgmL -1 phillyrin, 0.2-50μgmL -1 for quercetin, isorhamnetin and arctigenin (r≥0.999). It was proved that the extraction yields of almost all compounds attained by the established vortex- synchronized MSPD, which required lower sample, reagent and time, were higher than the normal MSPD and the traditional ultrasonic-assisted extraction. Consequently, this developed vortex- synchronized MSPD coupled with simple UHPLC method could be efficiently applies to extract and analyze the target compounds in real Forsythiae Fructus samples. Copyright © 2017 Elsevier B.V. All rights reserved.

Combination of Kinematics with Flow Visualization to Compute Total Circulation

NASA Technical Reports Server (NTRS)

Brasseur, J. G; Chang, I-Dee

1981-01-01

A method is described in which kinematics is exploited to compute the total circulation of a vortex from relatively simple flow visualization experiments. There are several advantages in the technique, including the newly acquired ability to calculate the changes in strength of a single vortex as it evolves. The main concepts and methodology are discussed in a general way for application to vortices which carry along with them definable regions of essentially irrotational fluid; however, the approach might be generalized to other flows which contain regions of concentrated vorticity. As an illustrative example, an application to the study of the transient changes in total circulation of individual vortex rings as they travel up a tube is described, taking into account the effect of the tube boundary. The accuracy of the method, assessed in part by a direct comparison with a laser Doppler measurement is felt to be well within experimental precision for vortex rings over a wide range of Reynolds numbers.

A design strategy for the use of vortex generators to manage inlet-engine distortion using computational fluid dynamics

NASA Technical Reports Server (NTRS)

Anderson, Bernhard H.; Levy, Ralph

1991-01-01

A reduced Navier-Stokes solution technique was successfully used to design vortex generator installations for the purpose of minimizing engine face distortion by restructuring the development of secondary flow that is induced in typical 3-D curved inlet ducts. The results indicate that there exists an optimum axial location for this installation of corotating vortex generators, and within this configuration, there exists a maximum spacing between generator blades above which the engine face distortion increases rapidly. Installed vortex generator performance, as measured by engine face circumferential distortion descriptors, is sensitive to Reynolds number and thereby the generator scale, i.e., the ratio of generator blade height to local boundary layer thickness. Installations of corotating vortex generators work well in terms of minimizing engine face distortion within a limited range of generator scales. Hence, the design of vortex generator installations is a point design, and all other conditions are off design. In general, the loss levels associated with a properly designed vortex generator installation are very small; thus, they represent a very good method to manage engine face distortion. This study also showed that the vortex strength, generator scale, and secondary flow field structure have a complicated and interrelated influence over engine face distortion, over and above the influence of the initial arrangement of generators.

Heat transfer and pressure drop characteristics of the tube bank fin heat exchanger with fin punched with flow redistributors and curved triangular vortex generators

NASA Astrophysics Data System (ADS)

Liu, Song; Jin, Hua; Song, KeWei; Wang, LiangChen; Wu, Xiang; Wang, LiangBi

2017-10-01

The heat transfer performance of the tube bank fin heat exchanger is limited by the air-side thermal resistance. Thus, enhancing the air-side heat transfer is an effective method to improve the performance of the heat exchanger. A new fin pattern with flow redistributors and curved triangular vortex generators is experimentally studied in this paper. The effects of the flow redistributors located in front of the tube stagnation point and the curved vortex generators located around the tube on the characteristics of heat transfer and pressure drop are discussed in detail. A performance comparison is also carried out between the fins with and without flow redistributors. The experimental results show that the flow redistributors stamped out from the fin in front of the tube stagnation points can decrease the friction factor at the cost of decreasing the heat transfer performance. Whether the combination of the flow redistributors and the curved vortex generators will present a better heat transfer performance depends on the size of the curved vortex generators. As for the studied two sizes of vortex generators, the heat transfer performance is promoted by the flow redistributors for the fin with larger size of vortex generators and the performance is suppressed by the flow redistributors for the fin with smaller vortex generators.

Extended Glauert tip correction to include vortex rollup effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maniaci, David; Schmitz, Sven

Wind turbine loads predictions by blade-element momentum theory using the standard tip-loss correction have been shown to over-predict loading near the blade tip in comparison to experimental data. This over-prediction is theorized to be due to the assumption of light rotor loading, inherent in the standard tip-loss correction model of Glauert. A higher- order free-wake method, WindDVE, is used to compute the rollup process of the trailing vortex sheets downstream of wind turbine blades. Results obtained serve an exact correction function to the Glauert tip correction used in blade-element momentum methods. Lastly, it is found that accounting for the effectsmore » of tip vortex rollup within the Glauert tip correction indeed results in improved prediction of blade tip loads computed by blade-element momentum methods.« less

Extended Glauert tip correction to include vortex rollup effects

DOE PAGES

Maniaci, David; Schmitz, Sven

2016-10-03

Wind turbine loads predictions by blade-element momentum theory using the standard tip-loss correction have been shown to over-predict loading near the blade tip in comparison to experimental data. This over-prediction is theorized to be due to the assumption of light rotor loading, inherent in the standard tip-loss correction model of Glauert. A higher- order free-wake method, WindDVE, is used to compute the rollup process of the trailing vortex sheets downstream of wind turbine blades. Results obtained serve an exact correction function to the Glauert tip correction used in blade-element momentum methods. Lastly, it is found that accounting for the effectsmore » of tip vortex rollup within the Glauert tip correction indeed results in improved prediction of blade tip loads computed by blade-element momentum methods.« less

Relationship Between Vortex Meander and Ambient Turbulence

NASA Technical Reports Server (NTRS)

Rossow, Vernon J.; Hardy, Gordon H.; Meyn, Larry A.

2006-01-01

Efforts are currently underway to increase the capacity of airports by use of closely-spaced parallel runways. If such an objective is to be achieved safely and efficiently during both visual and instrument flight conditions, it will be necessary to develop more precise methods for the prediction of the motion and spread of the hazard posed by the lift-generated vortex-wakes of aircraft, and their uncertainties. The purpose of the present study is to relate the motion induced in vortex filaments by turbulence in the ambient flow field to the measured turbulence in the flow field. The problem came about when observations made in the two largest NASA wind tunnels indicated that extended exposure of vortex wakes to the turbulence in the wind tunnel air stream causes the centers of the vortices to meander about with time at a given downstream station where wake measurements are being made. Although such a behavior was expected, the turbulence level based on the maximum amplitude of meander was much less than the root-mean-squared value measured in the free-stream of the wind tunnel by use of hot-film anemometers. An analysis of the time-dependent motion of segments of vortex filaments as they interact with an eddy, indicates that the inertia of the filaments retards their motion enough in the early part of their travel to account for a large part of the difference in the two determinations of turbulence level. Migration of vortex filaments from one turbulent eddy to another (probably with a different orientation), is believed to account for the remainder of the difference. Methods that may possibly be developed for use in the measurement of the magnitude of the more intense eddies in turbulent flow fields and how they should be adjusted to predict vortex meander are then discussed.

Rapid and selective brain cooling method using vortex tube: A feasibility study.

PubMed

Bakhsheshi, Mohammad Fazel; Keenliside, Lynn; Lee, Ting-Yim

2016-05-01

Vortex tubes are simple mechanical devices to produce cold air from a stream of compressed air without any moving parts. The primary focus of the current study is to investigate the feasibility and efficiency of nasopharyngeal brain cooling method using a vortex tube. Experiments were conducted on 5 juvenile pigs. Nasopharygeal brain cooling was achieved by directing cooled air via a catheter in each nostril into the nasal cavities. A vortex tube was used to generate cold air using various sources of compressed air: (I) hospital medical air outlet (n = 1); (II) medical air cylinders (n = 3); and (III) scuba (diving) cylinders (n = 1). By using compressed air from a hospital medical air outlet at fixed inlet pressure of 50 PSI, maximum brain-rectal temperature gradient of -2°C was reached about 45-60 minutes by setting the flow rate of 25 L/min and temperature of -7°C at the cold air outlet. Similarly, by using medical air cylinders at fill-pressure of 2265 PSI and down regulate the inlet pressure to the vortex tube to 50 PSI, brain temperature could be reduced more rapidly by blowing -22°C ± 2°C air at a flow rate of 50 L/min; brain-body temperature gradient of -8°C was obtained about 30 minutes. Furthermore, we examined scuba cylinders as a portable source of compressed gas supply to the vortex tube. Likewise, by setting up the vortex tube to have an inlet pressure of 25 PSI and 50 L/min and -3°C at the cold air outlet, brain temperature decreased 4.5°C within 10-20 min. Copyright © 2016 Elsevier Inc. All rights reserved.

A method for the estimate of the wall diffusion for non-axisymmetric fields using rotating external fields

NASA Astrophysics Data System (ADS)

Frassinetti, L.; Olofsson, K. E. J.; Fridström, R.; Setiadi, A. C.; Brunsell, P. R.; Volpe, F. A.; Drake, J.

2013-08-01

A new method for the estimate of the wall diffusion time of non-axisymmetric fields is developed. The method based on rotating external fields and on the measurement of the wall frequency response is developed and tested in EXTRAP T2R. The method allows the experimental estimate of the wall diffusion time for each Fourier harmonic and the estimate of the wall diffusion toroidal asymmetries. The method intrinsically considers the effects of three-dimensional structures and of the shell gaps. Far from the gaps, experimental results are in good agreement with the diffusion time estimated with a simple cylindrical model that assumes a homogeneous wall. The method is also applied with non-standard configurations of the coil array, in order to mimic tokamak-relevant settings with a partial wall coverage and active coils of large toroidal extent. The comparison with the full coverage results shows good agreement if the effects of the relevant sidebands are considered.

Vortex dynamics and surface pressure fluctuations on a normal flat plate

NASA Astrophysics Data System (ADS)

Hemmati, Arman; Wood, David H.; Martinuzzi, Robert J.; Ferrari, Simon W.; Hu, Yaoping

2016-11-01

The effect of vortex formation and interactions on surface pressure fluctuations is examined in the wake of a normal flat plate by analyzing Direct Numerical Simulations at Re =1200. A novel local maximum score-based 3D method is used to track vortex development in the region close to the plate where the major contributions to the surface pressure are generated. Three distinct vortex shedding regimes are identified by changes in the lift and drag fluctuations. The instances of maximum drag coincide with impingement of newly formed vortices on the plate. This results in large and concentrated areas of rotational and strain contributions to generation of pressure fluctuations. Streamwise vortex straining and chordwise stretching are correlated with the large ratios of streamwise to chordwise normal stresses and regions of significant rotational contribution to the pressure. In contrast at the minimum drag, the vorticity field close to the plate is disorganized, and vortex roll-up occurs farther downstream. This leads to a uniform distribution of pressure. This study was supported by Alberta Innovates Technology Futures (AITF) and Natural Sciences and Engineering Research Council of Canada (NSERC).

Effect of cavitation on flow structure of a tip vortex

NASA Astrophysics Data System (ADS)

Matthieu, Dreyer; Reclari, Martino; Farhat, Mohamed

2013-11-01

Tip vortices, which may develop in axial turbines and marine propellers, are often associated with the occurrence of cavitation because of the low pressure in their core. Although this issue has received a great deal of attention, it is still unclear how the phase transition affects the flow structure of such a vortex. In the present work, we investigate the change of the vortex structure due to cavitation incipience. The measurement of the velocity field is performed in the case of a tip vortex generated by an elliptical hydrofoil placed in the test section of EPFL high speed cavitation tunnel. To this end, a 3D stereo PIV is used with fluorescent seeding particles. A cost effective method is developed to produce in-house fluorescent seeding material, based on polyamide particles and Rhodamine-B dye. The amount of cavitation in the vortex core is controlled by the inlet pressure in the test section, starting with the non-cavitating case. We present an extensive analysis of the vorticity distribution, the vortex intensity and core size for various cavitation developments. This research is supported by CCEM and swisselectric research.

Simulation of Rotary-Wing Near-Wake Vortex Structures Using Navier-Stokes CFD Methods

NASA Technical Reports Server (NTRS)

Kenwright, David; Strawn, Roger; Ahmad, Jasim; Duque, Earl; Warmbrodt, William (Technical Monitor)

1997-01-01

This paper will use high-resolution Navier-Stokes computational fluid dynamics (CFD) simulations to model the near-wake vortex roll-up behind rotor blades. The locations and strengths of the trailing vortices will be determined from newly-developed visualization and analysis software tools applied to the CFD solutions. Computational results for rotor nearwake vortices will be used to study the near-wake vortex roll up for highly-twisted tiltrotor blades. These rotor blades typically have combinations of positive and negative spanwise loading and complex vortex wake interactions. Results of the computational studies will be compared to vortex-lattice wake models that are frequently used in rotorcraft comprehensive codes. Information from these comparisons will be used to improve the rotor wake models in the Tilt-Rotor Acoustic Code (TRAC) portion of NASA's Short Haul Civil Transport program (SHCT). Accurate modeling of the rotor wake is an important part of this program and crucial to the successful design of future civil tiltrotor aircraft. The rotor wake system plays an important role in blade-vortex interaction noise, a major problem for all rotorcraft including tiltrotors.

Modeling quantum fluid dynamics at nonzero temperatures

PubMed Central

Berloff, Natalia G.; Brachet, Marc; Proukakis, Nick P.

2014-01-01

The detailed understanding of the intricate dynamics of quantum fluids, in particular in the rapidly growing subfield of quantum turbulence which elucidates the evolution of a vortex tangle in a superfluid, requires an in-depth understanding of the role of finite temperature in such systems. The Landau two-fluid model is the most successful hydrodynamical theory of superfluid helium, but by the nature of the scale separations it cannot give an adequate description of the processes involving vortex dynamics and interactions. In our contribution we introduce a framework based on a nonlinear classical-field equation that is mathematically identical to the Landau model and provides a mechanism for severing and coalescence of vortex lines, so that the questions related to the behavior of quantized vortices can be addressed self-consistently. The correct equation of state as well as nonlocality of interactions that leads to the existence of the roton minimum can also be introduced in such description. We review and apply the ideas developed for finite-temperature description of weakly interacting Bose gases as possible extensions and numerical refinements of the proposed method. We apply this method to elucidate the behavior of the vortices during expansion and contraction following the change in applied pressure. We show that at low temperatures, during the contraction of the vortex core as the negative pressure grows back to positive values, the vortex line density grows through a mechanism of vortex multiplication. This mechanism is suppressed at high temperatures. PMID:24704874

Pitching effect on transonic wing stall of a blended flying wing with low aspect ratio

NASA Astrophysics Data System (ADS)

Tao, Yang; Zhao, Zhongliang; Wu, Junqiang; Fan, Zhaolin; Zhang, Yi

2018-05-01

Numerical simulation of the pitching effect on transonic wing stall of a blended flying wing with low aspect ratio was performed using improved delayed detached eddy simulation (IDDES). To capture the discontinuity caused by shock wave, a second-order upwind scheme with Roe’s flux-difference splitting is introduced into the inviscid flux. The artificial dissipation is also turned off in the region where the upwind scheme is applied. To reveal the pitching effect, the implicit approximate-factorization method with sub-iterations and second-order temporal accuracy is employed to avoid the time integration of the unsteady Navier-Stokes equations solved by finite volume method at Arbitrary Lagrange-Euler (ALE) form. The leading edge vortex (LEV) development and LEV circulation of pitch-up wings at a free-stream Mach number M = 0.9 and a Reynolds number Re = 9.6 × 106 is studied. The Q-criterion is used to capture the LEV structure from shear layer. The result shows that a shock wave/vortex interaction is responsible for the vortex breakdown which eventually causes the wing stall. The balance of the vortex strength and axial flow, and the shock strength, is examined to provide an explanation of the sensitivity of the breakdown location. Pitching motion has great influence on shock wave and shock wave/vortex interactions, which can significantly affect the vortex breakdown behavior and wing stall onset of low aspect ratio blended flying wing.

Flows about a rotating circular cylinder by the discrete-vortex method

NASA Astrophysics Data System (ADS)

Kimura, Takeyoshi; Tsutahara, Michihisa

1987-01-01

A numerical study has been conducted for flows past a rotating circular cylinder at high Reynolds numbers, using the discrete-vortex method. It is noted that the reverse Magnus effect is caused by the retreat of the separation point on the acceleration side. At high rotating speed, the nascent vortices of opposite directions are mixed faster, the wake becomes narrower, and predominating frequencies in the lift force disappear.

Physical and numerical aspects of the high-speed unsteady flow around concave axisymmetric bodies

NASA Astrophysics Data System (ADS)

Panaras, Argyris; Drikakis, Dimitris

2011-09-01

The axisymmetric concave body is a typical configuration about which shock/shock interactions appear. Various shapes of axisymmetric concave bodies are used in a variety of applications in aeronautics, for example, axisymmetric jet inlets with conical centerbody, ballistic missiles drag reduction by spike, plasma or hot gas injection, parachutes for pilot-ejection capsules. However, it is well known that two distinct modes of instability appear around a concave body in the high-speed flow regime for a certain range of geometric parameters. These instabilities can cause undesirable effects such as severe vibration of the structure, heating and pressure loads. According to the experimental evidence, the unsteady flow is characterised by periodic radial inflation and collapse of the conical separation bubble formed around the forebody (pulsation). Various explanations have been given for the driving mechanism of the instabilities. In the present, merging of the leading explanations is done, and basic rules for the passive suppression of the instabilities are applied, in order to enforce their proposed driving. In addition, the effect of the flow initialisation method on the flow structure predicted by numerical simulations is examined. For certain configurations, bifurcation of the time-dependent flow has been found. This behaviour is explained with recourse to the phenomenon of hysteresis, which is an inherent feature of the examined flows.

The shear-Hall instability in newborn neutron stars

NASA Astrophysics Data System (ADS)

Kondić, T.; Rüdiger, G.; Hollerbach, R.

2011-11-01

Aims: In the first few minutes of a newborn neutron star's life the Hall effect and differential rotation may both be important. We demonstrate that these two ingredients are sufficient for generating a "shear-Hall instability" and for studying its excitation conditions, growth rates, and characteristic magnetic field patterns. Methods: We numerically solve the induction equation in a spherical shell, with a kinematically prescribed differential rotation profile Ω(s), where s is the cylindrical radius. The Hall term is linearized about an imposed uniform axial field. The linear stability of individual azimuthal modes, both axisymmetric and non-axisymmetric, is then investigated. Results: For the shear-Hall instability to occur, the axial field must be parallel to the rotation axis if Ω(s) decreases outward, whereas if Ω(s) increases outward it must be anti-parallel. The instability draws its energy from the differential rotation, and occurs on the short rotational timescale rather than on the much longer Hall timescale. It operates most efficiently if the Hall time is comparable to the diffusion time. Depending on the precise field strengths B0, either axisymmetric or non-axisymmetric modes may be the most unstable. Conclusions: Even if the differential rotation in newborn neutron stars is quenched within minutes, the shear-Hall instability may nevertheless amplify any seed magnetic fields by many orders of magnitude.

PREFACE: Special section on vortex rings Special section on vortex rings

NASA Astrophysics Data System (ADS)

Fukumoto, Yasuhide

2009-10-01

This special section of Fluid Dynamics Research includes five articles on vortex rings in both classical and quantum fluids. The leading scientists of the field describe the trends in and the state-of-the-art development of experiments, theories and numerical simulations of vortex rings. The year 2008 was the 150th anniversary of 'vortex motion' since Hermann von Helmholtz opened up this field. In 1858, Helmholtz published a paper in Crelle's Journal which put forward the concept of 'vorticity' and made the first analysis of vortex motion. Fluid mechanics before that was limited to irrotational motion. In the absence of vorticity, the motion of an incompressible homogeneous fluid is virtually equivalent to a rigid-body motion in the sense that the fluid motion is determined once the boundary configuration is specified. Helmholtz proved, among other things, that, without viscosity, a vortex line is frozen into the fluid. This Helmholtz's law immediately implies the preservation of knots and links of vortex lines and its implication is enormous. One of the major trends of fluid mechanics since the latter half of the 20th century is to clarify the topological meaning of Helmholtz's law and to exploit it to develop theoretical and numerical methods to find the solutions of the Euler equations and to develop experimental techniques to gain an insight into fluid motion. Vortex rings are prominent coherent structures in a variety of fluid motions from the microscopic scale, through human and mesoscale to astrophysical scales, and have attracted people's interest. The late professor Philip G Saffman (1981) emphasized the significance of studies on vortex rings. One particular motion exemplifies the whole range of problems of vortex motion and is also a commonly known phenomenon, namely the vortex ring or smoke ring. Vortex rings are easily produced by dropping drops of one liquid into another, or by puffing fluid out of a hole, or by exhaling smoke if one has the skill. Their formation is a problem of vortex sheet dynamics, the steady state is a problem of existence, their duration is a problem of stability, and if there are several we have the problem of vortex interactions. Helmholtz himself, in the same paper (1858), devoted a few pages to an analysis of the motion of a vortex ring, and made substantial contributions. Since then, theoretical, experimental and numerical treatments of vortex rings have been developing continuously, yet we encounter mysteries and novel phenomena, with which vortex rings find new applications in, say, bio-fluid mechanics. Recently vortex rings have enlarged their scope beyond classical fluids to encompass super-fluids and Bose-Einstein condensates. On the occasion of the 150th anniversary of Helmholtz's theory on a vortex ring, it is worthwhile to bring together, in one issue, the latest understandings of and open problems in vortex rings from various aspects. The topics in this issue include development of theories and experiments for motion of vortex rings and their interaction with other vortex rings, flows and boundaries, with application to vortex-ring manipulation for flow control, original experiments on collision of vortex rings with a porous boundary, a novel numerical technique to simulate three-dimensional motion of vortex rings and new theories of dynamics of quantum vortex rings governed by nonlinear Schrödinger equations. I hope that this special section gives a sketch, in some proportion, of the current frontier of the field and provides a means to tackle future problems. References Saffman P G 1981 Dynamics of vorticity J. Fluid Mech. 106 49-58 von Helmholtz H 1858 Über Integrale der hydrodynamischen Gleichungen welche den Wirbelbewegungen entsprechen J. Reine Angew. Math. 55 25-55 (Engl. transl.: Tait P G 1867 On the integrals of the hydrodynamical equations which express vortex-motion Phil. Mag. 33 (4) 485-512)

Numerical computation of gravitational field of general extended body and its application to rotation curve study of galaxies

NASA Astrophysics Data System (ADS)

Fukushima, Toshio

2017-06-01

Reviewed are recently developed methods of the numerical integration of the gravitational field of general two- or three-dimensional bodies with arbitrary shape and mass density distribution: (i) an axisymmetric infinitely-thin disc (Fukushima 2016a, MNRAS, 456, 3702), (ii) a general infinitely-thin plate (Fukushima 2016b, MNRAS, 459, 3825), (iii) a plane-symmetric and axisymmetric ring-like object (Fukushima 2016c, AJ, 152, 35), (iv) an axisymmetric thick disc (Fukushima 2016d, MNRAS, 462, 2138), and (v) a general three-dimensional body (Fukushima 2016e, MNRAS, 463, 1500). The key techniques employed are (a) the split quadrature method using the double exponential rule (Takahashi and Mori, 1973, Numer. Math., 21, 206), (b) the precise and fast computation of complete elliptic integrals (Fukushima 2015, J. Comp. Appl. Math., 282, 71), (c) Ridder's algorithm of numerical differentiaion (Ridder 1982, Adv. Eng. Softw., 4, 75), (d) the recursive computation of the zonal toroidal harmonics, and (e) the integration variable transformation to the local spherical polar coordinates. These devices succesfully regularize the Newton kernel in the integrands so as to provide accurate integral values. For example, the general 3D potential is regularly integrated as Φ (\\vec{x}) = - G \\int_0^∞ ( \\int_{-1}^1 ( \\int_0^{2π} ρ (\\vec{x}+\\vec{q}) dψ ) dγ ) q dq, where \\vec{q} = q (√{1-γ^2} cos ψ, √{1-γ^2} sin ψ, γ), is the relative position vector referred to \\vec{x}, the position vector at which the potential is evaluated. As a result, the new methods can compute the potential and acceleration vector very accurately. In fact, the axisymmetric integration reproduces the Miyamoto-Nagai potential with 14 correct digits. The developed methods are applied to the gravitational field study of galaxies and protoplanetary discs. Among them, the investigation on the rotation curve of M33 supports a disc-like structure of the dark matter with a double-power-law surface mass density distribution. Fortran 90 subroutines to execute these methods and their test programs and sample outputs are available from the author's WEB site: https://www.researchgate.net/profile/Toshio_Fukushima/

A green ionic liquid-based vortex-forced MSPD method for the simultaneous determination of 5-HMF and iridoid glycosides from Fructus Corni by ultra-high performance liquid chromatography.

PubMed

Du, Kunze; Li, Jin; Bai, Yun; An, Mingrui; Gao, Xiu-Mei; Chang, Yan-Xu

2018-04-01

A simple and green ionic liquid-based vortex-forced matrix solid phase dispersion (IL-VFMSPD) method was presented to simultaneously extract 5-hydroxymethyl furfurol (5-HMF) and iridoid glycosides in Fructus Corni by ultra-high performance liquid chromatography. Ionic liquid was used as a green elution reagent in vortex-forced MSPD process. A few parameters such as the type of ionic liquid, the type of sorbent, ratio of sample to sorbent, the concentration and volume of ionic liquid, grinding time and vortex time, were investigated in detail and an orthogonal design experiment was introduced to confirm the best conditions in this procedure. With the final optimized method, the recoveries of the target compounds in Fructus Corni were in the range of 95.2-103% (RSD<5.0%) and the method displayed a good linearity within the range of 0.8-200 μg mL -1 for morroniside, sweroside, loganin, cornuside and 1.2-300 μg mL -1 for 5-HMF. The limits of detection ranged from 0.02 to 0.08 μg mL -1 for all compounds. The results showed that the newly established method was efficiently applied to extract and determine iridoid glycosides and 5-HMF for quality control of Fructus Corni. Copyright © 2017 Elsevier Ltd. All rights reserved.

The application of experimental data to blade wake interaction noise prediction

NASA Technical Reports Server (NTRS)

Glegg, Stewart A. L.; Devenport, William J.

1991-01-01

Blade wake interaction noise (BWI) has been defined as the broadband noise generated by the ingestion of turbulent trailing tip vortices by helicopter rotors. This has been shown to be the dominant contributor to the subjectively important part of the acoustic spectrum for the approach stage of a helicopter flyover. A prediction method for BWI noise based on the calculated trailing vortex trajectories has been developed and estimates of the vortex turbulence have been made. These measurements were made on a trailing vortex from a split wing arrangement and did not give the spectrum of the velocity fluctuations. A recent experiment carried out to measure the turbulence associated with a trailing vortex and the application of the results to BWI noise prediction is described.

Theoretical study of aerodynamic characteristics of wings having vortex flow

NASA Technical Reports Server (NTRS)

Reddy, C. S.

1979-01-01

The aerodynamic characteristics of slender wings having separation induced vortex flows are investigated by employing three different computer codes--free vortex sheet, quasi vortex lattice, and suction analogy methods. Their capabilities and limitations are examined, and modifications are discussed. Flat wings of different configurations: arrow, delta, and diamond shapes, as well as cambered delta wings, are studied. The effect of notch ratio on the load distributions and the longitudinal characteristics of a family of arrow and diamond wings is explored. The sectional lift coefficients and the accumulated span loadings are determined for an arrow wing and are seen to be unusual in comparison with the attached flow results. The theoretically predicted results are compared with the existing experimental values.

F/A-18 and F-16 forebody vortex control, static and rotary-balance results

NASA Technical Reports Server (NTRS)

Kramer, Brian; Smith, Brooke

1994-01-01

The results from research on forebody vortex control on both the F/A-18 and the F-16 aircraft will be shown. Several methods of forebody vortex control, including mechanical and pneumatic schemes, will be discussed. The wind tunnel data includes both static and rotary balance data for forebody vortex control. Time lags between activation or deactivation of the pneumatic control and when the aircraft experiences the resultant forces are also discussed. The static (non-rotating) forces and pressures are then compared to similar configurations tested in the NASA Langley and DTRC Wind Tunnel, the NASA Ames 80'x120' Wind Tunnel, and in flight on the High Angle of Attack Research Vehicle (HARV).

Development of the Technology of Vortex Diagnostics to Improve the Safety of Operation of Nuclear Reactors

NASA Astrophysics Data System (ADS)

Mitrofanova, O. V.; Ivlev, O. A.; Pozdeeva, I. G.; Urtenov, D. S.

2017-11-01

The results of studies are aimed at developing theoretical foundations and instrumentation system to ensure a technology of vortex diagnostics of the state of flows of fluids for nuclear power installations with power water reactors and fast neutrons reactors with liquid-metal coolants. The technology of vortex diagnostics is based on the study of acoustic, magneto-hydrodynamic and resonant effects related to the formation of stable vortex structures. For creation a system of monitoring and diagnostics of the crisis phenomena due to hydrodynamics of the flow, it is proposed to use acoustic method to record the radiation of elastic waves in the fluids caused by the dynamic local rearrangement of its structure.

CFD Modelling of a Quadrupole Vortex Inside a Cylindrical Channel for Research into Advanced Hybrid Rocket Designs

NASA Astrophysics Data System (ADS)

Godfrey, B.; Majdalani, J.

2014-11-01

This study relies on computational fluid dynamics (CFD) tools to analyse a possible method for creating a stable quadrupole vortex within a simulated, circular-port, cylindrical rocket chamber. A model of the vortex generator is created in a SolidWorks CAD program and then the grid is generated using the Pointwise mesh generation software. The non-reactive flowfield is simulated using an open source computational program, Stanford University Unstructured (SU2). Subsequent analysis and visualization are performed using ParaView. The vortex generation approach that we employ consists of four tangentially injected monopole vortex generators that are arranged symmetrically with respect to the center of the chamber in such a way to produce a quadrupole vortex with a common downwash. The present investigation focuses on characterizing the flow dynamics so that future investigations can be undertaken with increasing levels of complexity. Our CFD simulations help to elucidate the onset of vortex filaments within the monopole tubes, and the evolution of quadrupole vortices downstream of the injection faceplate. Our results indicate that the quadrupole vortices produced using the present injection pattern can become quickly unstable to the extent of dissipating soon after being introduced into simulated rocket chamber. We conclude that a change in the geometrical configuration will be necessary to produce more stable quadrupoles.

A new approach on anti-vortex devices at water intakes including a submerged water jet

NASA Astrophysics Data System (ADS)

Tahershamsi, Ahmad; Rahimzadeh, Hassan; Monshizadeh, Morteza; Sarkardeh, Hamed

2018-04-01

A new approach on anti-vortex methods as hydraulic-based anti-vortex was investigated experimentally in the present study. In the investigated method, a submerged water jet is used as the anti-vortex mechanism. The added jet acts as a source of external momentum. This leads to change the intake-induced hydrodynamic pattern in the near-field of the intake structure, which can prevent formation of undesirable intake vortices. The experiments were carried out on a horizontal pipe intake. By performing 570 test cases in two different categories, including the inclined jet with respect to the axis of the intake, and the inclined jet with respect to the water surface, the effects of the jet inclination angle on the anti-vortex performance were investigated. It was found that the inclined jet with respect to the water surface is the best alternative to consider as the water jet injection pattern. Results showed that using the inclined jet with respect to the water surface can simply reduce the amounts of the expected water jet momentum more than 50% compared to that of the similar condition of the horizontal injection pattern. Moreover, it was concluded that the intake critical submergence can easily be minimized using the inclined jet with respect to the water surface.

Experimental and Theoretical Study of a Rectangular Wing in a Vortical Wake at Low Speed

NASA Technical Reports Server (NTRS)

Smith, Willard G.; Lazzeroni, Frank A.

1960-01-01

A systematic study has been made, experimentally and theoretically, of the effects of a vortical wake on the aerodynamic characteristics of a rectangular wing at subsonic speed. The vortex generator and wing were mounted on a reflection plane to avoid body-wing interference. Vortex position, relative to the wing, was varied both in the spanwise direction and normal to the wing. Angle of attack of the wing was varied from -40 to +60. Both chordwise and spanwise pressure distributions were obtained with the wing in uniform and vortical flow fields. Stream surveys were made to determine the flow characteristics in the vortical wake. The vortex-induced lift was calculated by several theoretical methods including strip theory, reverse-flow theory, and reverse-flow theory including a finite vortex core. In addition, the Prandtl lifting-line theory and the Weissinger theory were used to calculate the spanwise distribution of vortex-induced loads. With reverse-flow theory, predictions of the interference lift were generally good, and with Weissinger's theory the agreement between the theoretical spanwise variation of induced load and the experimental variation was good. Results of the stream survey show that the vortex generated by a lifting surface of rectangular plan form tends to trail back streamwise from the tip and does not approach the theoretical location, or centroid of circulation, given by theory. This discrepancy introduced errors in the prediction of vortex interference, especially when the vortex core passed immediately outboard of the wing tip. The wake produced by the vortex generator in these tests was not fully rolled up into a circular vortex, and so lacked symmetry in the vertical direction of the transverse plane. It was found that the direction of circulation affected the induced loads on the wing either when the wing was at angle of attack or when the vortex was some distance away from the plane of the wing.

Cut-and-connect of two antiparallel vortex tubes

NASA Technical Reports Server (NTRS)

Melander, Mogens V.; Hussain, Fazle

1988-01-01

Motivated by an early conjecture that vortex cut-and-connect plays a key role in mixing and production of turbulence, helicity and aerodynamic noise, the cross-linking of two antiparallel viscous vortex tubes via direct numerical simulation is studied. The Navier-Stokes equations are solved by a dealiased pseudo-spectral method with 64 cubed grid points in a periodic domain for initial Reynolds numbers Re up to 1000. The vortex tubes are given an initial sinusoidal perturbation to induce a collision and keep the two tubes pressed against each other as annihilation continues. Cross-sectional and wire plots of various properties depict three stages of evolution: (1) Inviscid induction causing vortex cores to first approach and form a contact zone with a dipole cross-section, and then to flatten and stretch; (2) Vorticity annihilation in the contact zone accompanied by bridging between the two vortices at both ends of the contact zone due to a collection of cross-linked vortex lines, now orthogonal to the initial vortex tubes. The direction of dipole advection in the contact zone reverses; and (3) Threading of the remnants of the original vortices in between the bridges as they pull apart. The crucial stage 2 is shown to be a simple consequence of vorticity annihilation in the contact zone, link-up of the un-annihilated parts of vortex lines, and stretching and advection by the vortex tube swirl of the cross-linked lines, which accumulate at stagnation points in front of the annihilating vortex dipole. It is claimed that bridging is the essence of any vorticity cross-linking and that annihilation is sustained by stretching of the dipole by the bridges. Vortex reconnection details are found to be insensitive to asymmetry. Modeling of the reconnection process is briefly examined. The 3D spatial details of scalar transport (at unity Schmidt number), enstrophy production, dissipation and helicity are also examined.

Vortex-Lattice Utilization. [in aeronautical engineering and aircraft design

NASA Technical Reports Server (NTRS)

1976-01-01

The many novel, innovative, and unique implementations and applications of the vortex-lattice method to aerodynamic design and analysis which have been performed by Industry, Government, and Universities were presented. Although this analytical tool is not new, it continues to be utilized and refined in the aeronautical community.

Characterization of Pulsed Vortex Generator Jets for Active Flow Control

DTIC Science & Technology

2003-10-01

significant role in the developing vortex, were assessed; most of which used Amtec Engineering’s provided the net momentum flux rate is maintained. 7 The...incorporated in a single Tecplot macro, system allowed experimental data to be obtained very close to Since this method was developed, Amtec

Numerical simulation of convection and heat transfer in Czochralski crystal growth by multiple-relaxation-time LBM

NASA Astrophysics Data System (ADS)

Liu, Ding; Huang, Weichao; Zhang, Ni

2017-07-01

A two-dimensional axisymmetric swirling model based on the lattice Boltzmann method (LBM) in a pseudo Cartesian coordinate system is posited to simulate Czochralski (Cz) crystal growth in this paper. Specifically, the multiple-relaxation-time LBM (MRT-LBM) combined with the finite difference method (FDM) is used to analyze the melt convection and heat transfer in the process of Cz crystal growth. An incompressible axisymmetric swirling MRT-LB D2Q9 model is applied to solve for the axial and radial velocities by inserting thermal buoyancy and rotational inertial force into the two-dimensional lattice Boltzmann equation. In addition, the melt temperature and the azimuthal velocity are solved by MRT-LB D2Q5 models, and the crystal temperature is solved by FDM. The comparison results of stream functions values of different methods demonstrate that our hybrid model can be used to simulate the fluid-thermal coupling in the axisymmetric swirling model correctly and effectively. Furthermore, numerical simulations of melt convection and heat transfer are conducted under the conditions of high Grashof (Gr) numbers, within the range of 105 ˜ 107, and different high Reynolds (Re) numbers. The experimental results show our hybrid model can obtain the exact solution of complex crystal-growth models and analyze the fluid-thermal coupling effectively under the combined action of natural convection and forced convection.

Investigations of formation of quasi-static vortex-structures in granular bodies using DEM

NASA Astrophysics Data System (ADS)

Kozicki, Jan; Tejchman, Jacek

2017-06-01

The paper presents some two-dimensional simulation results of vortex-structures in cohesionless initially dense sand during quasi-static passive wall translation. The sand behaviour was simulated using the discrete element method (DEM). Sand grains were modelled by spheres with contact moments to approximately capture the irregular grain shape. In order to detect vortex-structures, the Helmholtz-Hodge decomposition of a flow displacement field from DEM calculations was used. This approach enabled us to distinguish both incompressibility and vorticity in the granular displacement field.

Bound states and interactions of vortex solitons in the discrete Ginzburg-Landau equation

NASA Astrophysics Data System (ADS)

Mejía-Cortés, C.; Soto-Crespo, J. M.; Vicencio, Rodrigo A.; Molina, Mario I.

2012-08-01

By using different continuation methods, we unveil a wide region in the parameter space of the discrete cubic-quintic complex Ginzburg-Landau equation, where several families of stable vortex solitons coexist. All these stationary solutions have a symmetric amplitude profile and two different topological charges. We also observe the dynamical formation of a variety of “bound-state” solutions composed of two or more of these vortex solitons. All of these stable composite structures persist in the conservative cubic limit for high values of their power content.

Multiple-Star System Adaptive Vortex Coronagraphy Using a Liquid Crystal Light Valve

NASA Astrophysics Data System (ADS)

Aleksanyan, Artur; Kravets, Nina; Brasselet, Etienne

2017-05-01

We propose the development of a high-contrast imaging technique enabling the simultaneous and selective nulling of several light sources. This is done by realizing a reconfigurable multiple-vortex phase mask made of a liquid crystal thin film on which local topological features can be addressed electro-optically. The method is illustrated by reporting on a triple-star optical vortex coronagraphy laboratory demonstration, which can be easily extended to higher multiplicity. These results allow considering the direct observation and analysis of worlds with multiple suns and more complex extrasolar planetary systems.

An annular superposition integral for axisymmetric radiators

PubMed Central

Kelly, James F.; McGough, Robert J.

2007-01-01

A fast integral expression for computing the nearfield pressure is derived for axisymmetric radiators. This method replaces the sum of contributions from concentric annuli with an exact double integral that converges much faster than methods that evaluate the Rayleigh-Sommerfeld integral or the generalized King integral. Expressions are derived for plane circular pistons using both continuous wave and pulsed excitations. Several commonly used apodization schemes for the surface velocity distribution are considered, including polynomial functions and a “smooth piston” function. The effect of different apodization functions on the spectral content of the wave field is explored. Quantitative error and time comparisons between the new method, the Rayleigh-Sommerfeld integral, and the generalized King integral are discussed. At all error levels considered, the annular superposition method achieves a speed-up of at least a factor of 4 relative to the point-source method and a factor of 3 relative to the generalized King integral without increasing the computational complexity. PMID:17348500

Vortex/boundary-layer interactions: Data report, volume 1

NASA Technical Reports Server (NTRS)

Cutler, A. D.; Bradshaw, P.

1987-01-01

This report summarizes the work done under NASA Grant NAGw-581, Vortex/Boundary Layer Interactions. The experimental methods are discussed in detail and numerical results are presented, but are not fully interpreted. This report should be useful to anyone who wishes to make further use of the data (available on floppy disc or magnetic tape) for the development of turbulence models or the validation of predictive methods. Journal papers are in course of preparation.

Flight Dynamics and Control of a Morphing UAV: Bio inspired by Natural Fliers

DTIC Science & Technology

2017-02-17

Approved for public release: distribution unlimited. IV Modelling and Sizing Tornado Vortex Lattice Method (VLM) was used for aerodynamic prediction... Tornado is a Vortex Lattice Method software programmed in MATLAB; it was selected due to its fast solving time and ability to be controlled through...custom MATLAB scripts. Tornado VLM models the wing as thin sheet of discrete vortices and computes the pressure and force distributions around the

Stability of stationary-axisymmetric black holes in vacuum general relativity to axisymmetric electromagnetic perturbations

NASA Astrophysics Data System (ADS)

Prabhu, Kartik; Wald, Robert M.

2018-01-01

We consider arbitrary stationary and axisymmetric black holes in general relativity in (d +1) dimensions (with d ≥slant 3 ) that satisfy the vacuum Einstein equation and have a non-degenerate horizon. We prove that the canonical energy of axisymmetric electromagnetic perturbations is positive definite. This establishes that all vacuum black holes are stable to axisymmetric electromagnetic perturbations. Our results also hold for asymptotically de Sitter black holes that satisfy the vacuum Einstein equation with a positive cosmological constant. Our results also apply to extremal black holes provided that the initial perturbation vanishes in a neighborhood of the horizon.

Unsteady aerodynamics and vortex-sheet formation of a two-dimensional airfoil

NASA Astrophysics Data System (ADS)

Xia, X.; Mohseni, K.

2017-11-01

Unsteady inviscid flow models of wings and airfoils have been developed to study the aerodynamics of natural and man-made flyers. Vortex methods have been extensively applied to reduce the dimensionality of these aerodynamic models, based on the proper estimation of the strength and distribution of the vortices in the wake. In such modeling approaches, one of the most fundamental questions is how the vortex sheets are generated and released from sharp edges. To determine the formation of the trailing-edge vortex sheet, the classical Kutta condition can be extended to unsteady situations by realizing that a flow cannot turn abruptly around a sharp edge. This condition can be readily applied to a flat plate or an airfoil with cusped trailing edge since the direction of the forming vortex sheet is known to be tangential to the trailing edge. However, for a finite-angle trailing edge, or in the case of flow separation away from a sharp corner, the direction of the forming vortex sheet is ambiguous. To remove any ad-hoc implementation, the unsteady Kutta condition, the conservation of circulation, as well as the conservation laws of mass and momentum are coupled to analytically solve for the angle, strength, and relative velocity of the trailing-edge vortex sheet. The two-dimensional aerodynamic model together with the proposed vortex-sheet formation condition is verified by comparing flow structures and force calculations with experimental results for airfoils in steady and unsteady background flows.

Axisymmetric shell analysis of the Space Shuttle solid rocket booster field joint

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.; Anderson, Melvin S.

1989-01-01

The Space Shuttle Challenger (STS 51-L) accident led to an intense investigation of the structural behavior of the solid rocket booster (SRB) tang and clevis field joints. The presence of structural deformations between the clevis inner leg and the tang, substantial enough to prevent the O-ring seals from eliminating hot gas flow through the joints, has emerged as a likely cause of the vehicle failure. This paper presents results of axisymmetric shell analyses that parametrically assess the structural behavior of SRB field joints subjected to quasi-steady-state internal pressure loading for both the original joint flown on mission STS 51-L and the redesigned joint recently flown on the Space Shuttle Discovery. Discussion of axisymmetric shell modeling issues and details is presented and a generic method for simulating contact between adjacent shells of revolution is described. Results are presented that identify the performance trends of the joints for a wide range of joint parameters.

Acoustic intensity calculations for axisymmetrically modeled fluid regions

NASA Technical Reports Server (NTRS)

Hambric, Stephen A.; Everstine, Gordon C.

1992-01-01

An algorithm for calculating acoustic intensities from a time harmonic pressure field in an axisymmetric fluid region is presented. Acoustic pressures are computed in a mesh of NASTRAN triangular finite elements of revolution (TRIAAX) using an analogy between the scalar wave equation and elasticity equations. Acoustic intensities are then calculated from pressures and pressure derivatives taken over the mesh of TRIAAX elements. Intensities are displayed as vectors indicating the directions and magnitudes of energy flow at all mesh points in the acoustic field. A prolate spheroidal shell is modeled with axisymmetric shell elements (CONEAX) and submerged in a fluid region of TRIAAX elements. The model is analyzed to illustrate the acoustic intensity method and the usefulness of energy flow paths in the understanding of the response of fluid-structure interaction problems. The structural-acoustic analogy used is summarized for completeness. This study uncovered a NASTRAN limitation involving numerical precision issues in the CONEAX stiffness calculation causing large errors in the system matrices for nearly cylindrical cones.

An Assessment of the Ozone Loss During the 1999-2000 SOLVE Arctic Campaign

NASA Technical Reports Server (NTRS)

Schoeberl, Mark R.; Newman, Paul A.; Lait, Leslie R.; McGee, Thomas J.; Burris, John F.; Browell, Edward V.; Grant, William B.; Richard, Eric; VonderGathen, Peter; Bevilacqua, Richard;

Computing Axisymmetric Jet Screech Tones Using Unstructured Grids

NASA Technical Reports Server (NTRS)

Jorgenson, Philip C. E.; Loh, Ching Y.

2002-01-01

The space-time conservation element and solution element (CE/SE) method is used to solve the conservation law form of the compressible axisymmetric Navier-Stokes equations. The equations are time marched to predict the unsteady flow and the near-field screech tone noise issuing from an underexpanded circular jet. The CE/SE method uses an unstructured grid based data structure. The unstructured grids for these calculations are generated based on the method of Delaunay triangulation. The purpose of this paper is to show that an acoustics solution with a feedback loop can be obtained using truly unstructured grid technology. Numerical results are presented for two different nozzle geometries. The first is considered to have a thin nozzle lip and the second has a thick nozzle lip. Comparisons with available experimental data are shown for flows corresponding to several different jet Mach numbers. Generally good agreement is obtained in terms of flow physics, screech tone frequency, and sound pressure level.

Non-invasive determination of external forces in vortex-pair-cylinder interactions

NASA Astrophysics Data System (ADS)

Hartmann, D.; Schröder, W.; Shashikanth, B. N.

2012-06-01

Expressions for the conserved linear and angular momenta of a dynamically coupled fluid + solid system are derived. Based on the knowledge of the flow velocity field, these expressions allow the determination of the external forces exerted on a body moving in the fluid such as, e.g., swimming fish. The verification of the derived conserved quantities is done numerically. The interaction of a vortex pair with a circular cylinder in various configurations of motions representing a generic test case for a dynamically coupled fluid + solid system is investigated in a weakly compressible Navier-Stokes setting using a Cartesian cut-cell method, i.e., the moving circular cylinder is represented by cut cells on a moving mesh. The objectives of this study are twofold. The first objective is to show the robustness of the derived expressions for the conserved linear and angular momenta with respect to bounded and discrete data sets. The second objective is to study the coupled dynamics of the vortex pair and a neutrally buoyant cylinder free to move in response to the fluid stresses exerted on its surface. A comparison of the vortex-body interaction with the case of a fixed circular cylinder evidences significant differences in the vortex dynamics. When the cylinder is fixed strong secondary vorticity is generated resulting in a repeating process between the primary vortex pair and the cylinder. In the neutrally buoyant cylinder case, a stable structure consisting of the primary vortex pair and secondary vorticity shear layers stays attached to the moving cylinder. In addition to these fundamental cases, the vortex-pair-cylinder interaction is studied for locomotion at constant speed and locomotion at constant thrust. It is shown that a similar vortex structure like in the neutrally buoyant cylinder case is obtained when the cylinder moves away from the approaching vortex pair at a constant speed smaller than the vortex pair translational velocity. Finally, the idealized symmetric settings are complemented by an asymmetric interaction of a vortex pair and a cylinder. This case is discussed for a fixed and a neutrally buoyant cylinder to show the validity of the derived relations for multi-dimensional body dynamics.

Linear nozzle with tailored gas plumes

DOEpatents

Leon, David D.; Kozarek, Robert L.; Mansour, Adel; Chigier, Norman

2001-01-01

There is claimed a method for depositing fluid material from a linear nozzle in a substantially uniform manner across and along a surface. The method includes directing gaseous medium through said nozzle to provide a gaseous stream at the nozzle exit that entrains fluid material supplied to the nozzle, said gaseous stream being provided with a velocity profile across the nozzle width that compensates for the gaseous medium's tendency to assume an axisymmetric configuration after leaving the nozzle and before reaching the surface. There is also claimed a nozzle divided into respective side-by-side zones, or preferably chambers, through which a gaseous stream can be delivered in various velocity profiles across the width of said nozzle to compensate for the tendency of this gaseous medium to assume an axisymmetric configuration.