High Gravity (g) Combustion

National Research Council Canada - National Science Library

Zelina, Joseph

2006-01-01

.... The Ultra-Compact Combustor (UCC), a novel design based on trapped-vortex combustor (TVC) work that uses high swirl in a circumferential cavity to enhance reaction rates via high cavity g-loading on the order of 3000 g's...

Three-vortex configurations in trapped Bose-Einstein condensates

International Nuclear Information System (INIS)

Seman, J. A.; Henn, E. A. L.; Shiozaki, R. F.; Ramos, E. R. F.; Caracanhas, M.; Castilho, P.; Castelo Branco, C.; Tavares, P. E. S.; Poveda-Cuevas, F. J.; Magalhaes, K. M. F.; Bagnato, V. S.; Haque, M.; Roati, G.

2010-01-01

We report on the creation of three-vortex clusters in a 87 Rb Bose-Einstein condensate by oscillatory excitation of the condensate. This procedure can create vortices of both circulations, so that we are able to create several types of vortex clusters using the same mechanism. The three-vortex configurations are dominated by two types, namely, an equilateral-triangle arrangement and a linear arrangement. We interpret these most stable configurations respectively as three vortices with the same circulation and as a vortex-antivortex-vortex cluster. The linear configurations are very likely experimental signatures of predicted stationary vortex clusters.

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

Science.gov (United States)

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.

The pollution reduction technology program for can-annular combustor engines - Description and results

Science.gov (United States)

Roberts, R.; Fiorentino, A. J.; Diehl, L.

1976-01-01

Pollutant reduction and performance characteristics were determined for three successively more advanced combustor concepts. Program Element I consisted of minor modifications to the current production JT8D combustor and fuel system to evaluate means of improved fuel preparation and changes to the basic airflow distribution. Element II addressed versions of the two-staged Vorbix (vortex burning and mixing) combustor and represented a moderate increase in hardware complexity and difficulty of development. The concept selected for Element III employed vaporized fuel as a means of achieving minimum emission levels and represented the greatest difficulty of development and adaptation to the JT8D engine. Test results indicate that the Element I single-stage combustors were capable of dramatic improvement in idle pollutants. The multistage combustors evaluated in Program Elements II and III simultaneously reduced CO, THC and NOx emissions, but were unable to satisfy the current 1979 EPA standards.

Deflection and trapping of a counter-rotating vortex pair by a flat plate

Science.gov (United States)

Nitsche, Monika

2017-12-01

The interaction of a counter-rotating vortex pair (dipole) with a flat plate in its path is studied numerically. The vortices are initially separated by a distance D (dipole size) and placed far upstream of a plate of length L . The plate is centered on the dipole path and inclined relative to it at an incident angle βi. At first, the plate is held fixed in place. The vortices approach the plate, travel around it, and then leave as a dipole with unchanged velocity but generally a different travel direction, measured by a transmitted angle βt. For certain plate angles the transmitted angle is highly sensitive to changes in the incident angle. The sensitivity increases as the dipole size decreases relative to the plate length. In fact, for sufficiently small values of D /L , singularities appear: near critical values of βi, the dipole trajectory undergoes a topological discontinuity under changes of βi or D /L . The discontinuity is characterized by a jump in the winding number of one vortex around the plate, and in the time that the vortices take to leave the plate. The jumps occur repeatedly in a self-similar, fractal fashion, within a region near the critical values of βi, showing the existence of incident angles that trap the vortices, which never leave the plate. The number of these trapping regions increases as the parameter D /L decreases, and the dependence of the motion on βi becomes increasingly complex. The simulations thus show that even in this apparently simple scenario, the inviscid dynamics of a two-point-vortex system interacting with a stationary wall is surprisingly rich. The results are then applied to separate an incoming stream of dipoles by an oscillating plate.

Effects of a trapped vortex cell on a thick wing airfoil

Energy Technology Data Exchange (ETDEWEB)

Lasagna, Davide; Iuso, Gaetano [Politecnico di Torino, Dipartimento di Ingegneria Aeronautica e Spaziale, Torino (Italy); Donelli, Raffaele; De Gregorio, Fabrizio [Centro Italiano di Ricerca Aerospaziale (C.I.R.A), Capua (Italy)

2011-11-15

The effects of a trapped vortex cell (TVC) on the aerodynamic performance of a NACA0024 wing model were investigated experimentally at Re = 10{sup 6} and 6.67 x 10{sup 5}. The static pressure distributions around the model and the wake velocity profiles were measured to obtain lift and drag coefficients, for both the clean airfoil and the controlled configurations. Suction was applied in the cavity region to stabilize the trapped vortex. For comparison, a classical boundary layer suction configuration was also tested. The drag coefficient curve of the TVC-controlled airfoil showed sharp discontinuities and bifurcative behavior, generating two drag modes. A strong influence of the angle of attack, the suction rate and the Reynolds number on the drag coefficient was observed. With respect to the clean airfoil, the control led to a drag reduction only if the suction was high enough. Compared to the classical boundary layer suction configuration, the drag reduction was higher for the same amount of suction only in a specific range of incidence, i.e., {alpha} = -2 to {alpha} = 6 and only for the higher Reynolds number. For all the other conditions, the classical boundary layer suction configuration gave better drag performances. Moderate increments of lift were observed for the TVC-controlled airfoil at low incidence, while a 20% lift enhancement was observed in the stall region with respect to the baseline. However, the same lift increments were also observed for the classical boundary layer suction configuration. Pressure fluctuation measurements in the cavity region suggested a very complex interaction of several flow features. The two drag modes were characterized by typical unsteady phenomena observed in rectangular cavity flows, namely the shear layer mode and the wake mode. (orig.)

A multi-objective CFD optimization of liquid fuel spray injection in dry-low-emission gas-turbine combustors

International Nuclear Information System (INIS)

Asgari, Behrad; Amani, Ehsan

2017-01-01

Highlights: •An Eulerian-Lagrangian model for the fuel spray injection is evaluated. •The drop breakup, spray-vortex interaction, and wall-wetting play the key roles. •The injection location and direction are the most important parameters. •The best design candidates are proposed using multi-objective optimizations. •A large central perpendicular injection with high co-rotating swirls is optimal. -- Abstract: The main goal of this research is to investigate the effects of fuel injection strategy on the performance of the premixing chamber of modern Dry-Low-Emission (DLE) Gas-Turbine (GT) combustors. Here, an Eulerian-Lagrangian model for multi-phase multi-component flows is evaluated and used to investigate the effects of different fuel spray design parameters, including the injection location, direction, mass-flow-rate partitioning, and flow Swirl number, on the performance of the premixing chamber. The analysis is enriched by multi-objective optimizations accounting for several goals, including the evaporation efficiency, mixture stratification, entropy generation, and flow recirculation. It is observed that the droplet breakup, spray-vortex interactions, and wall-wetting have significant influences on the performance objectives while the droplet residence time effect is minor. Among the design parameters, the injection location and direction have a profound impact on the droplet breakup which predominately controls the evaporation efficiency. In addition, the interactions between the spray and the two swirling vertices inside the chamber strongly affect the mixture stratification (uniformity), e.g. the location and direction of the injection should not be chosen such that a large proportion of fuel droplets are trapped in the shear layer between the two vortices (otherwise the evaporation efficiency drops significantly) or trapped in the strong outer swirling vortex (if large mixture non-uniformity should be avoided). Finally, the best designs meeting

The nonlinear dirac equation in Bose-Einstein condensates: vortex solutions and spectra in a weak harmonic trap

Science.gov (United States)

Haddad, L. H.; Carr, Lincoln D.

2015-11-01

We analyze the vortex solution space of the (2+1)-dimensional nonlinear Dirac equation for bosons in a honeycomb optical lattice at length scales much larger than the lattice spacing. Dirac point relativistic covariance combined with s-wave scattering for bosons leads to a large number of vortex solutions characterized by different functional forms for the internal spin and overall phase of the order parameter. We present a detailed derivation of these solutions which include skyrmions, half-quantum vortices, Mermin-Ho and Anderson-Toulouse vortices for vortex winding {\\ell }=1. For {\\ell }≥slant 2 we obtain topological as well as non-topological solutions defined by the asymptotic radial dependence. For arbitrary values of ℓ the non-topological solutions include bright ring-vortices which explicitly demonstrate the confining effects of the Dirac operator. We arrive at solutions through an asymptotic Bessel series, algebraic closed-forms, and using standard numerical shooting methods. By including a harmonic potential to simulate a finite trap we compute the discrete spectra associated with radially quantized modes. We demonstrate the continuous spectral mapping between the vortex and free particle limits for all of our solutions.

Flow structures in a lean-premixed swirl-stabilized combustor with microjet air injection

KAUST Repository

LaBry, Zachary A.

2011-01-01

The major challenge facing the development of low-emission combustors is combustion instability. By lowering flame temperatures, lean-premixed combustion has the potential to nearly eliminate emissions of thermally generated nitric oxides, but the chamber acoustics and heat release rate are highly susceptible to coupling in ways that lead to sustained, high-amplitude pressure oscillations, known as combustion instability. At different operating conditions, different modes of instability are observed, corresponding to particular flame shapes and resonant acoustic modes. Here we show that in a swirl-stabilized combustor, these instability modes also correspond to particular interactions between the flame and the inner recirculation zone. Two stable and two unstable modes are examined. At lean equivalence ratios, a stable conical flame anchors on the upstream edge of the inner recirculation zone and extends several diameters downstream along the wall. At higher equivalence ratios, with the injection of counter-swirling microjet air flow, another stable flame is observed. This flame is anchored along the upstream edge of a stronger recirculation zone, extending less than one diameter downstream along the wall. Without the microjets, a stationary instability coupled to the 1/4 wave mode of the combustor shows weak velocity oscillations and a stable configuration of the inner and outer recirculation zones. Another instability, coupled to the 3/4 wave mode of the combustor, exhibits periodic vortex breakdown in which the core flow alternates between a columnar mode and a vortex breakdown mode. © 2010 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved.

Three-dimensional parallel vortex rings in Bose-Einstein condensates

International Nuclear Information System (INIS)

Crasovan, Lucian-Cornel; Perez-Garcia, Victor M.; Danaila, Ionut; Mihalache, Dumitru; Torner, Lluis

2004-01-01

We construct three-dimensional structures of topological defects hosted in trapped wave fields, in the form of vortex stars, vortex cages, parallel vortex lines, perpendicular vortex rings, and parallel vortex rings, and we show that the latter exist as robust stationary, collective states of nonrotating Bose-Einstein condensates. We discuss the stability properties of excited states containing several parallel vortex rings hosted by the condensate, including their dynamical and structural stability

Characterization of nonequilibrium states of trapped Bose–Einstein condensates

Science.gov (United States)

Yukalov, V. I.; Novikov, A. N.; Bagnato, V. S.

2018-06-01

The generation of different nonequilibrium states in trapped Bose–Einstein condensates is studied by numerically solving the nonlinear Schrödinger equation. Inducing nonequilibrium states by shaking a trap creates the following states: weak nonequilibrium, the state of vortex germs, the state of vortex rings, the state of straight vortex lines, the state of deformed vortices, vortex turbulence, grain turbulence, and wave turbulence. A characterization of nonequilibrium states is advanced by introducing effective temperature, Fresnel number, and Mach number.

Formation of quasistationary vortex and transient hole patterns through vortex merger

International Nuclear Information System (INIS)

Ganesh, R.; Lee, J.K.

2002-01-01

Collection of point-like intense vortices arranged symmetrically outside of a uniform circular vortex patch, both enclosed in a free-slip circular boundary, are numerically time evolved for up to 10-15 patch turnover times. These patterns are found to merge with the patch by successively inducing nonlinear dispersive modes (V-states) on the surface of the patch, draw off fingers of vorticity (filamentation), trap the irrotational regions as the fingers symmetrize under the shear flow of the patch and point-like vortices (wave breaking) followed by the vortex-hole capture. While the hole patterns are observed to break up over several turnover periods the vortex patterns appear to evolve into quasistationary patterns for some cases of an initial number of point-like vortices N pv . The bounded V-states, filamentation, and vortex (hole) pattern formation are discussed in some detail and their possible connection to recently observed vortex 'crystals' is pointed out

Non-coaxial superposition of vector vortex beams.

Science.gov (United States)

Aadhi, A; Vaity, Pravin; Chithrabhanu, P; Reddy, Salla Gangi; Prabakar, Shashi; Singh, R P

2016-02-10

Vector vortex beams are classified into four types depending upon spatial variation in their polarization vector. We have generated all four of these types of vector vortex beams by using a modified polarization Sagnac interferometer with a vortex lens. Further, we have studied the non-coaxial superposition of two vector vortex beams. It is observed that the superposition of two vector vortex beams with same polarization singularity leads to a beam with another kind of polarization singularity in their interaction region. The results may be of importance in ultrahigh security of the polarization-encrypted data that utilizes vector vortex beams and multiple optical trapping with non-coaxial superposition of vector vortex beams. We verified our experimental results with theory.

Effects of streamwise vortex breakdown on supersonic combustion.

Science.gov (United States)

Hiejima, Toshihiko

2016-04-01

This paper presents a numerical simulation study of the combustion structure of streamwise vortex breakdown at Mach number 2.48. Hydrogen fuel is injected into a combustor at sonic speed from the rear of a hypermixer strut that can generate streamwise vortices. The results show that the burning behavior is enhanced at the points of the shock waves that are incident on the vortex and therefore the vortex breakdown in the subsonic region occurs due to combustion. The breakdown domain in the mainstream is found to form a flame-holding region suited to combustion and to lead to a stable combustion field with detached flames. In this way, streamwise vortex breakdown has an essential role in combustion enhancement and the formation of flames that hold under supersonic inflow conditions. Finally, the combustion property defined here is shown to coincide with the produced-water mass flow. This property shows that the amount of combustion is saturated at equivalence ratios over 0.4, although there is a slight increase beyond 1.

Vortex capturing vertical axis wind turbine

International Nuclear Information System (INIS)

Zannetti, L; Gallizio, F; Ottino, G

2007-01-01

An analytical-numerical study is presented for an innovative lift vertical axis turbine whose blades are designed with vortex trapping cavities that act as passive flow control devices. The unsteady flow field past one-bladed and two-bladed turbines is described by a combined analytical and numerical method based on conformal mapping and on a blob vortex method

Optically induced rotation of Rayleigh particles by vortex beams with different states of polarization

International Nuclear Information System (INIS)

Li, Manman; Yan, Shaohui; Yao, Baoli; Liang, Yansheng; Lei, Ming; Yang, Yanlong

2016-01-01

Optical vortex beams carry optical orbital angular momentum (OAM) and can induce an orbital motion of trapped particles in optical trapping. We show that the state of polarization (SOP) of vortex beams will affect the details of this optically induced orbital motion to some extent. Numerical results demonstrate that focusing the vortex beams with circular, radial or azimuthal polarizations can induce a uniform orbital motion on a trapped Rayleigh particle, while in the focal field of the vortex beam with linear polarization the particle experiences a non-uniform orbital motion. Among the formers, the vortex beam with circular polarization induces a maximum optical torque on the particle. Furthermore, by varying the topological charge of the vortex beams, the vortex beam with circular polarization gives rise to an optimum torque superior to those given by the other three vortex beams. These facts suggest that the circularly polarized vortex beam is more suitable for rotating particles. - Highlights: • States of polarization of vortex beams affect the optically induced orbital motion of particles. • The dependences of the force and orbital torque on the topological charge, the size and the absorptivity of particles were calculated. • Focused vortex beams with circular, radial or azimuthal polarizations induce a uniform orbital motion on particles. • Particles experience a non-uniform orbital motion in the focused linearly polarized vortex beam. • The circularly polarized vortex beam is a superior candidate for rotating particles.

CHARACTERIZATION OF CATALYTIC COMBUSTOR TURBULENCE AND ITS INFLUENCE ON VANE AND ENDWALL HEAT TRANSFER AND ENDWALL FILM COOLING

Energy Technology Data Exchange (ETDEWEB)

Forrest E. Ames

2002-10-01

Endwall heat transfer distributions taken in a large-scale low speed linear cascade facility are documented for mock catalytic and dry low NOx (DLN) combustion systems. Inlet turbulence levels range from about 1.0 percent for the mock Catalytic combustor condition to 14 percent for the mock dry low NOx combustor system. Stanton number contours are presented at both turbulence conditions for Reynolds numbers based on true chord length and exit conditions ranging from 500,000 to 2,000,000. Catalytic combustor endwall heat transfer shows the influence of the complex three-dimensional flow field, while the effects of individual vortex systems are less evident for the mock dry low NOx cases. Turbulence scales have been documented for both cases. Inlet boundary layers are relatively thin for the mock catalytic combustor case while inlet flow approximates a channel flow with high turbulence for the mock DLN combustor case. Inlet boundary layer parameters are presented across the inlet passage for the three Reynolds numbers and both the mock catalytic and DLN combustor inlet cases. Both midspan and 95 percent span pressure contours are included. This research provides a well-documented database taken across a range of Reynolds numbers and turbulence conditions for assessment of endwall heat transfer predictive capabilities.

Experiments and computations on coaxial swirling jets with centerbody in an axisymmetric combustor

International Nuclear Information System (INIS)

Chao, Y.C.; Ho, W.C.; Lin, S.K.

1987-01-01

Experiments and computations of turbulent, confined, coannular swirling flows have been performed in a model combustor. Numerical results are obtained by means of a revised two-equation model of turbulence. The combustor consists of two confined, concentric, swirling jets and a centerbody at the center of the inlet. Results are reported for cold flow conditions under co- and counter-swirl. The numerical results agree with the experimental data under both conditions. The size of the central recirculation zone is dominated by the strength of the outer swirl. A two-cell recirculation zone may be formed due to the presence of the swirler hub. The mechanism of interaction between the separation bubble at the hub of the swirler and the central recirculation zone due to vortex breakdown is also investigated. 18 references

Combustion Dynamic Characteristics Identification in a 9-point LDI Combustor Under Choked Outlet Boundary Conditions

Science.gov (United States)

He, Zhuohui J.; Chang, Clarence T.

2017-01-01

Combustion dynamics data were collected at the NASA Glenn Research Center's CE-5 flame tube test facility under combustor outlet choked conditions. Two 9-point Swirl-Venturi Lean Direct Injection (SV-LDI) configurations were tested in a rectangular cuboid combustor geometry. Combustion dynamic data were measured at different engine operational conditions up to inlet air pressure and temperature of 24.13 bar and 828 K, respectively. In this study, the effects of acoustic cavity resonance, precessing vortex core (PVC), and non-uniform thermal expansion on the dynamic noise spectrum are identified by comparing the dynamic data that collected at various combustor inlet conditions along with combustor geometric calculations. The results show that the acoustic cavity resonance noises were seen in the counter-rotating pilot configuration but not in the co-rotating pilot configuration. Dynamic pressure noise band at around 0.9 kHz was only detected at the P'41 location (9.8 cm after fuel injector face) but not at the P'42 location (29 cm after the fuel injector face); the amplitude of this noise band depended on the thermal expansion ratio (T4/T3). The noise band at around 1.8 kHz was found to depend on the inlet air pressure or the air density inside the combustor. The PVC frequency was not observed in these two configurations.

Interaction of ions, atoms, and small molecules with quantized vortex lines in superfluid (4)He.

Science.gov (United States)

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(*).

Numerical study of the effect of inlet geometry on combustion instabilities in a lean premixed swirl combustor

Energy Technology Data Exchange (ETDEWEB)

Lee, Chang Eon [Dept. of Mechanical Engineering, Inha University, Incheon (Korea, Republic of); Park, Seul Hyun [Dept. of Mechanical Systems Engineering, Chosun University, Gwangju (Korea, Republic of); Hwang, Cheol Hong [Dept. of Fire and Disaster Prevention, Daejeon University, Daejeon (Korea, Republic of)

2016-11-15

The effects of flow structure and flame dynamics on combustion instabilities in a lean premixed swirl combustor were numerically investigated using Large eddy simulation (LES) by varying the inlet geometry of combustor. The dynamic ksgs-equation and G-equation flamelet models were respectively employed as the LES subgrid models of turbulence and combustion. The divergent half angle (α) in the combustor inlet was varied systematically from 30° to 90° to quantify the effect of inlet geometry on the combustion instabilities. This variation caused considerable deformation in recirculation zones in terms of their size and location, leading to significant changes in flame dynamics. Analysis of unsteady pressure distributions in the combustor showed that the largest damping caused by combustion instabilities takes place at α = 45°, and the amplitude of acoustic pressure oscillation is largest at α = 30°. Examination of local Rayleigh parameters indicated that controlling flame-vortex interactions by modifying inlet geometry can change the local characteristics of combustion instabilities in terms of their amplification and suppression, and thus serve as a useful approach to reduce the instabilities in a lean premixed swirl combustor. These phenomena were studied in detail through unsteady analysis associated with flow and flame dynamics.

Numerical study of the effect of inlet geometry on combustion instabilities in a lean premixed swirl combustor

International Nuclear Information System (INIS)

Lee, Chang Eon; Park, Seul Hyun; Hwang, Cheol Hong

2016-01-01

The effects of flow structure and flame dynamics on combustion instabilities in a lean premixed swirl combustor were numerically investigated using Large eddy simulation (LES) by varying the inlet geometry of combustor. The dynamic ksgs-equation and G-equation flamelet models were respectively employed as the LES subgrid models of turbulence and combustion. The divergent half angle (α) in the combustor inlet was varied systematically from 30° to 90° to quantify the effect of inlet geometry on the combustion instabilities. This variation caused considerable deformation in recirculation zones in terms of their size and location, leading to significant changes in flame dynamics. Analysis of unsteady pressure distributions in the combustor showed that the largest damping caused by combustion instabilities takes place at α = 45°, and the amplitude of acoustic pressure oscillation is largest at α = 30°. Examination of local Rayleigh parameters indicated that controlling flame-vortex interactions by modifying inlet geometry can change the local characteristics of combustion instabilities in terms of their amplification and suppression, and thus serve as a useful approach to reduce the instabilities in a lean premixed swirl combustor. These phenomena were studied in detail through unsteady analysis associated with flow and flame dynamics

Combustor and combustor screech mitigation methods

Science.gov (United States)

Kim, Kwanwoo; Johnson, Thomas Edward; Uhm, Jong Ho; Kraemer, Gilbert Otto

2014-05-27

The present application provides for a combustor for use with a gas turbine engine. The combustor may include a cap member and a number of fuel nozzles extending through the cap member. One or more of the fuel nozzles may be provided in a non-flush position with respect to the cap member.

Vortex nucleation in Bose-Einstein condensates in time-dependent traps

International Nuclear Information System (INIS)

Lundh, Emil; Martikainen, J.-P.; Suominen, Kalle-Antti

2003-01-01

Vortex nucleation in a Bose-Einstein condensate subject to a stirring potential is studied numerically using the zero-temperature, two-dimensional Gross-Pitaevskii equation. In the case of a rotating, slightly anisotropic harmonic potential, the numerical results reproduce experimental findings, thereby showing that finite temperatures are not necessary for vortex excitation below the quadrupole frequency. In the case of a condensate subject to stirring by a narrow rotating potential, the process of vortex excitation is described by a classical model that treats the multitude of vortices created by the stirrer as a continuously distributed vorticity at the center of the cloud, but retains a potential flow pattern at large distances from the center

An Experimental Study of Swirling Flows as Applied to Annular Combustors

Science.gov (United States)

Seal, Michael Damian, II

1997-01-01

This thesis presents an experimental study of swirling flows with direct applications to gas turbine combustors. Two separate flowfields were investigated: a round, swirling jet and a non-combusting annular combustor model. These studies were intended to allow both a further understanding of the behavior of general swirling flow characteristics, such as the recirculation zone, as well as to provide a base for the development of computational models. In order to determine the characteristics of swirling flows the concentration fields of a round, swirling jet were analyzed for varying amount of swirl. The experimental method used was a light scattering concentration measurement technique known as marker nephelometry. Results indicated the formation of a zone of recirculating fluid for swirl ratios (rotational speed x jet radius over mass average axial velocity) above a certain critical value. The size of this recirculation zone, as well as the spread angle of the jet, was found to increase with increase in the amount of applied swirl. The annular combustor model flowfield simulated the cold-flow characteristics of typical current annular combustors: swirl, recirculation, primary air cross jets and high levels of turbulence. The measurements in the combustor model made by the Laser Doppler Velocimetry technique, allowed the evaluation of the mean and rms velocities in the three coordinate directions, one Reynold's shear stress component and the turbulence kinetic energy: The primary cross jets were found to have a very strong effect on both the mean and turbulence flowfields. These cross jets, along with a large step change in area and wall jet inlet flow pattern, reduced the overall swirl in the test section to negligible levels. The formation of the strong recirculation zone is due mainly to the cross jets and the large step change in area. The cross jets were also found to drive a four-celled vortex-type motion (parallel to the combustor longitudinal axis) near the

Radial midframe baffle for can-annular combustor arrangement having tangentially oriented combustor cans

Science.gov (United States)

Rodriguez, Jose L.

2015-09-15

A can-annular gas turbine engine combustion arrangement (10), including: a combustor can (12) comprising a combustor inlet (38) and a combustor outlet circumferentially and axially offset from the combustor inlet; an outer casing (24) defining a plenum (22) in which the combustor can is disposed; and baffles (70) configured to divide the plenum into radial sectors (72) and configured to inhibit circumferential motion of compressed air (16) within the plenum.

Large Eddy Simulations and Experimental Investigation of Flow in a Swirl Stabilized Combustor

KAUST Repository

Kewlani, Gaurav

2012-01-09

Swirling flows are the preferred mode of flame stabilization in lean premixed gas turbine engine combustors. Developing a fundamental understanding of combustion dynamics and flame stability in such systems requires a detailed investigation of the complex interactions between fluid mechanics and combustion. The turbulent reacting flow in a sudden expansion swirl combustor is studied using compressible large eddy simulations (LES) and compared with experimental data measured using PIV. Different vortex breakdown structures are observed, as the mixture equivalence ratio is reduced, that progressively diminish the stability of the flame. Sub-grid scale combustion models such as the artificially thickened flame method and the partially stirred reactor approach, along with appropriate chemical schemes, are implemented to describe the flame. The numerical predictions for average velocity correspond well with experimental results, and higher accuracy is obtained using the more detailed reaction mechanism. Copyright © 2012 American Institute of Aeronautics and Astronautics, Inc.

Alternate-Fueled Combustor-Sector Performance. Parts A and B; (A) Combustor Performance; (B) Combustor Emissions

Science.gov (United States)

Shouse, D. T.; Hendricks, R. C.; Lynch, A.; Frayne, C. W.; Stutrud, J. S.; Corporan, E.; Hankins, T.

2012-01-01

Alternate aviation fuels for military or commercial use are required to satisfy MIL-DTL-83133F(2008) or ASTM D 7566 (2010) standards, respectively, and are classified as "drop-in" fuel replacements. To satisfy legacy issues, blends to 50% alternate fuel with petroleum fuels are certified individually on the basis of processing and assumed to be feedstock agnostic. Adherence to alternate fuels and fuel blends requires "smart fueling systems" or advanced fuel-flexible systems, including combustors and engines, without significant sacrifice in performance or emissions requirements. This paper provides preliminary performance (Part A) and emissions and particulates (Part B) combustor sector data. The data are for nominal inlet conditions at 225 psia and 800 F (1.551 MPa and 700 K), for synthetic-paraffinic-kerosene- (SPK-) type (Fisher-Tropsch (FT)) fuel and blends with JP-8+100 relative to JP-8+100 as baseline fueling. Assessments are made of the change in combustor efficiency, wall temperatures, emissions, and luminosity with SPK of 0%, 50%, and 100% fueling composition at 3% combustor pressure drop. The performance results (Part A) indicate no quantifiable differences in combustor efficiency, a general trend to lower liner and higher core flow temperatures with increased FT fuel blends. In general, emissions data (Part B) show little differences, but with percent increase in FT-SPK-type fueling, particulate emissions and wall temperatures are less than with baseline JP-8. High-speed photography illustrates both luminosity and combustor dynamic flame characteristics.

Radiation from an excited vortex in the Abelian Higgs model

Science.gov (United States)

Arodź, H.; Hadasz, L.

1996-09-01

An excited vortex in the Abelian Higgs model is investigated with the help of a polynomial approximation. The excitation consists of the longitudinal component of a vector field trapped by the vortex. The energy and profile of the excitation as well as its back reaction on the vortex are found in the case of small κ. It turns out that the width of the excited vortex oscillates in time. Moreover, the vector field has a radiative long range component. Also, an upper bound on the amplitude of the excitation is found.

Vortex lattices in a rotating Fermi superfluid in the BCS–BEC crossover with many Landau levels

International Nuclear Information System (INIS)

Song, Tie-ling; Ma, C.R.; Ma, Yong-li

2012-01-01

We present an explicit analytical analysis of the ground state of vortex lattice structure, based on a minimization of the generalized Gross–Pitaevskii energy functional in a trapped rotating Fermi superfluid gas. By a Bogoliubov-like transformation we find that the coarse-grained average of the atomic density varies as inverted parabola in three dimensional cases; the Fermi superfluid in the BEC regime enters into the lowest Landau level at fast rotation, in which the vortices form an almost regular triangular lattice over a central region and the vortex lattice is expanded along the radial direction in the outer region; the fluid in the unitarity and BCS regimes occupies many low-lying Landau levels, in which a trapped gas with a triangular vortex lattice has a superfluid core surrounded by a normal gas. The calculation is qualitatively consistent with recent numerical and experimental data both in the vortex lattice structure and vortex numbers and in the density profiles versus the stirring frequency in the whole BCS–BEC crossover. - Highlights: ► We present an analysis of vortex lattice in an interacting trapped rotating Fermi superfluid gas. ► Decomposing the vortex from the condensate, we can explain the vortex lattice. ► The calculation is consistent with numerical and experimental data. ► It can characterize experimentally properties in different regimes of the BCS–BEC crossover.

Mode Selection in Flame-Vortex driven Combustion Instabilities

KAUST Repository

Speth, Ray

2011-01-04

In this paper, we investigate flame-vortex interaction in a lean premixed, laboratory scale, backward-facing step combustor. Two series of tests were conducted, using propane/hydrogen mixtures and carbon monoxide/hydrogen mixtures as fuels, respectively. Pressure measurements and high speed particle imaging velocimetry (PIV) were employed to generate pressure response curves as well as the images of the velocity field and the flame brush. We demonstrate that the step combustor exhibits several operating modes depending on the inlet conditions and fuel composition, characterized by the amplitude and frequency of pressure oscillations along with distinct dynamic flame shapes. We propose a model in which the combustor\\'s selection of the acoustic mode is governed by a combustion-related time delay inversely proportional to the flame speed. Our model predicts the transition between distinct operating modes. We introduce non-dimensional parameters characterizing the flame speed and stretch rate, and develop a relationship between these quantities at the operating conditions corresponding to each mode transition. Based on this relationship, we show that numerically-calculated density-weighted strained flame speed can be used to collapse the combustion dynamics data over the full range of conditions (inlet temperature, fuel composition, and equivalence ratio). Finally, we validate our strain flame based model by measuring the strain rate using the flame image and the velocity field from the PIV measurement. Our results show that the measured strain rates lie in the same range as the critical values at the transitions among distinct modes as those predicted by our model.

Design of an Open-Cycle, Vortex MHD Generator

Energy Technology Data Exchange (ETDEWEB)

Thalimer, J. R.; Kurtzrock, R. C.; Simons, W. H.; Bienstock, D. [Pittsburgh Coal Research Center, US Bureau Of Mines, Pittsburgh, PA (United States); Hughes, W. F. [Carnegie-Mellon University, Pittsburgh, PA (United States)

1968-11-15

The US Bureau of Mines has built a vortex MHD generator which combines the combustor-nozzle-duct combination into one integral unit. The vortex MHD generator consists of a cyclone burner, 7.5 in. diameter, 21 in. in length, with the inner wall used as one electrode together with a coaxial centre electrode. Power is obtained by impressing an axial field of 3000 G from an air solenoid magnet. Electrical output is expected to be one kilowatt. For the initial runs natural gas will be burned in oxygen-enriched, preheated air with a subsequent change to coal as a fuel. A theoretical analysis has been completed which predicts the velocity profiles and the electrical output characteristics of the generator. This analysis assumes variations in the radial and axial directions for all variables, steady state inviscid flow, constant electrical conductivity and a small magnetic Reynolds number. (author)

Acoustic Virtual Vortices with Tunable Orbital Angular Momentum for Trapping of Mie Particles

Science.gov (United States)

Marzo, Asier; Caleap, Mihai; Drinkwater, Bruce W.

2018-01-01

Acoustic vortices can transfer angular momentum and trap particles. Here, we show that particles trapped in airborne acoustic vortices orbit at high speeds, leading to dynamic instability and ejection. We demonstrate stable trapping inside acoustic vortices by generating sequences of short-pulsed vortices of equal helicity but opposite chirality. This produces a "virtual vortex" with an orbital angular momentum that can be tuned independently of the trapping force. We use this method to adjust the rotational speed of particles inside a vortex beam and, for the first time, create three-dimensional acoustics traps for particles of wavelength order (i.e., Mie particles).

Radiation from an excited vortex in the Abelian Higgs model

International Nuclear Information System (INIS)

Arodz, H.; Hadasz, L.

1996-01-01

An excited vortex in the Abelian Higgs model is investigated with the help of a polynomial approximation. The excitation consists of the longitudinal component of a vector field trapped by the vortex. The energy and profile of the excitation as well as its back reaction on the vortex are found in the case of small κ. It turns out that the width of the excited vortex oscillates in time. Moreover, the vector field has a radiative long range component. Also, an upper bound on the amplitude of the excitation is found. copyright 1996 The American Physical Society

Mobility of ions trapped on vortex lines in pure 4He and 3He--4He solutions

International Nuclear Information System (INIS)

Ostermeier, R.M.; Glaberson, W.I.

1976-01-01

Measurements have been made of the mobility of positive and negative ions trapped on vortex lines in pure 4 He and dilute 3 He-- 4 He solutions over the temperature range 1.6 greater than T greater than 0.3 K. In pure 4 He below about 0.7 K, several new effects not seen at higher temperatures are observed and are not easily explained with existing theories. Most notable are an enhanced broadening of the ion pulse and a rapid increase in the mobility with decreasing temperature. Measurements of the electric field dependence of the drift velocity in pure 4 He at low temperatures show a limiting velocity for sufficiently large fields. This behavior can be explained using a simple resonance theory. The inverse mobility data for solutions show sharp increases at certain critical temperatures, which are interpreted as being associated with the condensation of 3 He atoms onto the vortex cores. The dependence of the critical temperature on the bulk 3 He concentration is found to be in good agreement with a simple condensation theory. An extension of arguments used in this theory to lower temperatures leads to the picture of a 3 He-rich core growing with decreasing temperature, consistent with our lower temperature experimental data

Probing the dynamic response of antivortex, interstitial and trapped vortex lattices on magnetic periodic pinning potentials

International Nuclear Information System (INIS)

Gomez, A; Gonzalez, E M; Vicent, J L; Gilbert, D A; Liu Kai; Milošević, M V

2013-01-01

The dynamics of the pinned vortex, antivortex and interstitial vortex have been studied in superconducting/magnetic hybrids consisting of arrays of Co/Pd multilayer nanodots embedded in Nb films. The magnetic nanodots show out-of-plane magnetization at the remanent state. This magnetic state allows for superconducting vortex lattices of different types in an applied homogeneous magnetic field. We experimentally and theoretically show three such lattices: (i) a lattice containing only antivortices; (ii) a vortex lattice entirely pinned on the dots; and (iii) a vortex lattice with pinned and interstitial vortices. Between the flux creep (low vortex velocity) and the free flux flow (high vortex velocity) regimes the interaction between the magnetic array and the vortex lattice governs the vortex dynamics, which in turn enables distinguishing experimentally the type of vortex lattice which governs the dissipation. We show that the vortex lattice with interstitial vortices has the highest onset velocity where the lattice becomes ordered, whereas the pinned vortex lattice has the smallest onset velocity. Further, for this system, we directly estimate that the external force needed to depin vortices is 60% larger than the one needed to depin antivortices; therefore we are able to decouple the antivortex–vortex motion. (paper)

Dynamically controlled energy dissipation for fast magnetic vortex switching

Science.gov (United States)

Badea, R.; Berezovsky, J.

2017-09-01

Manipulation of vortex states in magnetic media provides new routes towards information storage and processing technology. The typical slow relaxation times (˜100 ns) of magnetic vortex dynamics may present an obstacle to the realization of these applications. Here, we investigate how a vortex state in a ferromagnetic microdisk can be manipulated in a way that translates the vortex core while enhancing energy dissipation to rapidly damp the vortex dynamics. We use time-resolved differential magneto-optical Kerr effect microscopy to measure the motion of the vortex core in response to applied magnetic fields. We first map out how the vortex core becomes sequentially trapped by pinning sites as it translates across the disk. After applying a fast magnetic field step to translate the vortex from one pinning site to another, we observe long-lived dynamics of the vortex as it settles to the new equilibrium. We then demonstrate how the addition of a short (<10 ns) magnetic field pulse can induce additional energy dissipation, strongly damping the long-lived dynamics. A model of the vortex dynamics using the Thiele equation of motion explains the mechanism behind this effect.

Elementary pinning force for a superconducting vortex

International Nuclear Information System (INIS)

Hyun, O.B.; Finnemore, D.K.; Schwartzkopf, L.; Clem, J.R.

1987-01-01

The elementary pinning force f/sub p/ has been measured for a single vortex trapped in one of the superconducting layers of a cross-strip Josephson junction. At temperatures close to the transition temperature the vortex can be pushed across the junction by a transport current. The vortex is found to move in a small number of discrete steps before it exits the junction. The pinning force for each site is found to be asymmetric and to have a value of about 10/sup -6/ N/m at the reduced temperature, t = T/T/sub c/ = 0.95. As a function of temperature, f/sub p/ is found to vary approximately as (1-t)/sup 3/2/. .AE

Simple point vortex model for the relaxation of 2D superfluid turbulence in a Bose-Einstein condensate

Science.gov (United States)

Kim, Joon Hyun; Kwon, Woo Jin; Shin, Yong-Il

2016-05-01

In a recent experiment, it was found that the dissipative evolution of a corotating vortex pair in a trapped Bose-Einstein condensate is well described by a point vortex model with longitudinal friction on the vortex motion and the thermal friction coefficient was determined as a function of sample temperature. In this poster, we present a numerical study on the relaxation of 2D superfluid turbulence based on the dissipative point vortex model. We consider a homogeneous system in a cylindrical trap having randomly distributed vortices and implement the vortex-antivortex pair annihilation by removing a pair when its separation becomes smaller than a certain threshold value. We characterize the relaxation of the turbulent vortex states with the decay time required for the vortex number to be reduced to a quarter of initial number. We find the vortex decay time is inversely proportional to the thermal friction coefficient. In particular, we observe the decay times obtained from this work show good quantitative agreement with the experimental results in, indicating that in spite of its simplicity, the point vortex model reasonably captures the physics in the relaxation dynamics of the real system.

Numerical simulation of a precessing vortex breakdown

International Nuclear Information System (INIS)

Jochmann, P.; Sinigersky, A.; Hehle, M.; Schaefer, O.; Koch, R.; Bauer, H.-J.

2006-01-01

The objective of this work is to present the results of time-dependent numerical predictions of a turbulent symmetry breaking vortex breakdown in a realistic gas turbine combustor. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations are solved by using the k-ε two-equation model as well as by a full second-order closure using the Reynolds stress model of Speziale, Sarkar and Gatski (SSG). The results for a Reynolds number of 5.2 x 10 4 , a swirl number of 0.52 and an expansion ratio of 5 show that the flow is emerging from the swirler as a spiral gyrating around a zone of strong recirculation which is also asymmetric and precessing. These flow structures which are typical for the spiral type (S-type) vortex breakdown have been confirmed by PIV and local LDA measurements in a corresponding experimental setup. Provided that high resolution meshes are employed the calculations with both turbulence models are capable to reproduce the spatial and temporal dynamics of the flow

Near-zero emissions combustor system for syngas and biofuels

International Nuclear Information System (INIS)

Yongho, Kim; Rosocha, Louis

2010-01-01

research necessary to develop a novel, high-efficiency, low-emissions (near-zero, or as low as reasonably achievable), advanced combustion technology for electricity and heat production from biofuels and fuels derived from MSW. For any type of combustion technology, including the advanced technology of this project, two problems of special interest must be addressed: developing and optimizing the combustion chambers and the systems for igniting and sustaining the fuel-burning process. For MSW in particular, there are new challenges over gaseous or liquid fuels because solid fuels must be ground into fine particulates (∼ 10 (micro)m diameter), fed into the advanced combustor, and combusted under plasma-assisted conditions that are quite different than gaseous or liquid fuels. The principal idea of the combustion chamber design is to use so-called reverse vortex gas flow, which allows efficient cooling of the chamber wall and flame stabilization in the central area of the combustor (Tornado chamber). Considerable progress has been made in design ing an advanced, reverse vortex flow combustion chamber for biofuels, although it was not tested on biofuels and a system that could be fully commercialized has never been completed.

Vortex survival in 3D self-gravitating accretion discs

Science.gov (United States)

Lin, Min-Kai; Pierens, Arnaud

2018-04-01

Large-scale, dust-trapping vortices may account for observations of asymmetric protoplanetary discs. Disc vortices are also potential sites for accelerated planetesimal formation by concentrating dust grains. However, in 3D discs vortices are subject to destructive `elliptic instabilities', which reduces their viability as dust traps. The survival of vortices in 3D accretion discs is thus an important issue to address. In this work, we perform shearing box simulations to show that disc self-gravity enhances the survival of 3D vortices, even when self-gravity is weak in the classic sense (e.g. with a Toomre Q ≃ 5). We find a 3D, self-gravitating vortex can grow on secular timescales in spite of the elliptic instability. The vortex aspect-ratio decreases as it strengthens, which feeds the elliptic instability. The result is a 3D vortex with a turbulent core that persists for ˜103 orbits. We find when gravitational and hydrodynamic stresses become comparable, the vortex may undergo episodic bursts, which we interpret as interaction between elliptic and gravitational instabilities. We estimate the distribution of dust particles in self-gravitating, turbulent vortices. Our results suggest large-scale vortices in protoplanetary discs are more easily observed at large radii.

Dual-Mode Combustor

Science.gov (United States)

Trefny, Charles J (Inventor); Dippold, Vance F (Inventor)

2013-01-01

A new dual-mode ramjet combustor used for operation over a wide flight Mach number range is described. Subsonic combustion mode is usable to lower flight Mach numbers than current dual-mode scramjets. High speed mode is characterized by supersonic combustion in a free-jet that traverses the subsonic combustion chamber to a variable nozzle throat. Although a variable combustor exit aperture is required, the need for fuel staging to accommodate the combustion process is eliminated. Local heating from shock-boundary-layer interactions on combustor walls is also eliminated.

Vectorial diffraction properties of THz vortex Bessel beams.

Science.gov (United States)

Wu, Zhen; Wang, Xinke; Sun, Wenfeng; Feng, Shengfei; Han, Peng; Ye, Jiasheng; Yu, Yue; Zhang, Yan

2018-01-22

A vortex Bessel beam combines the merits of an optical vortex and a Bessel beam, including a spiral wave front and a non-diffractive feature, which has immense application potentials in optical trapping, optical fabrication, optical communications, and so on. Here, linearly and circularly polarized vortex Bessel beams in the terahertz (THz) frequency range are generated by utilizing a THz quarter wave plate, a spiral phase plate, and Teflon axicons with different opening angles. Taking advantage of a THz focal-plane imaging system, vectorial diffraction properties of the THz vortex Bessel beams are comprehensively characterized and discussed, including the transverse (Ex, Ey) and longitudinal (Ez) polarization components. The experimental phenomena are accurately simulated by adopting the vectorial Rayleigh diffraction integral. By varying the opening angle of the axicon, the characteristic parameters of these THz vortex Bessel beams are exhibited and compared, including the light spot size, the diffraction-free range, and the phase evolution process. This work provides the precise experimental and theoretical bases for the comprehension and application of a THz vortex Bessel beam.

Steam reformer with catalytic combustor

Science.gov (United States)

Voecks, Gerald E. (Inventor)

1990-01-01

A steam reformer is disclosed having an annular steam reforming catalyst bed formed by concentric cylinders and having a catalytic combustor located at the center of the innermost cylinder. Fuel is fed into the interior of the catalytic combustor and air is directed at the top of the combustor, creating a catalytic reaction which provides sufficient heat so as to maintain the catalytic reaction in the steam reforming catalyst bed. Alternatively, air is fed into the interior of the catalytic combustor and a fuel mixture is directed at the top. The catalytic combustor provides enhanced radiant and convective heat transfer to the reformer catalyst bed.

Combustor and method for distributing fuel in the combustor

Science.gov (United States)

Uhm, Jong Ho; Ziminsky, Willy Steve; Johnson, Thomas Edward; York, William David

2016-04-26

A combustor includes a tube bundle that extends radially across at least a portion of the combustor. The tube bundle includes an upstream surface axially separated from a downstream surface. A plurality of tubes extends from the upstream surface through the downstream surface, and each tube provides fluid communication through the tube bundle. A baffle extends axially inside the tube bundle between adjacent tubes. A method for distributing fuel in a combustor includes flowing a fuel into a fuel plenum defined at least in part by an upstream surface, a downstream surface, a shroud, and a plurality of tubes that extend from the upstream surface to the downstream surface. The method further includes impinging the fuel against a baffle that extends axially inside the fuel plenum between adjacent tubes.

Vortex core structure and global properties of rapidly rotating Bose-Einstein condensates

International Nuclear Information System (INIS)

Baym, Gordon; Pethick, C.J.

2004-01-01

We develop an approach for calculating stationary states of rotating Bose-Einstein condensates in harmonic traps which is applicable for arbitrary ratios of the rotation frequency to the transverse frequency of the trap ω perpendicular . Assuming the number of vortices to be large, we write the condensate wave function as the product of a function that describes the structure of individual vortices times an envelope function varying slowly on the scale of the vortex spacing. By minimizing the energy, we derive Gross-Pitaevskii equations that determine the properties of individual vortices and the global structure of the cloud. For low rotation rates, the structure of a vortex is that of an isolated vortex in a uniform medium, while for rotation rates approaching the frequency of the trap (the mean-field lowest-Landau-level regime), the structure is that of the lowest p-wave state of a particle in a harmonic trap with frequency ω perpendicular . The global structure of the cloud is determined by minimizing the energy with respect to variations of the envelope function; for conditions appropriate to most experimental investigations to date, we predict that the transverse density profile of the cloud will be of the Thomas-Fermi form, rather than the Gaussian structure predicted on the assumption that the wave function consists only of components in the lowest Landau level for a regular array of vortices

Variable volume combustor

Science.gov (United States)

Ostebee, Heath Michael; Ziminsky, Willy Steve; Johnson, Thomas Edward; Keener, Christopher Paul

2017-01-17

The present application provides a variable volume combustor for use with a gas turbine engine. The variable volume combustor may include a liner, a number of micro-mixer fuel nozzles positioned within the liner, and a linear actuator so as to maneuver the micro-mixer fuel nozzles axially along the liner.

Design of a multipurpose laboratory scale analytical combustor

International Nuclear Information System (INIS)

Mohd Fairus Abdul Farid; Sivapalan Kathiravale; Muhd Noor Muhd Yunus; Mohamad Puad Abu; Norasalwa Zakaria; Khaironie Mohd Takip; Rohyiza Ba'an; Mohamad Azman Che Mat Isa

2005-01-01

The current method of digestion in order to determine the content of heavy metals and other elements in Municipal Solid Waste (MSW) is either too long or dangerous due to the usage of concentrated acids. As such, a Multi Purpose Portable Lab Scale Combustor was developed. It could also be used as a test rig under the various combustion conditions i.e. excess air combustion, gasification and pyrolysis. Another future of this rig, is to trap and analyse the combustion gasses produced from the different types of combustion processes. The rig can also be used to monitor weight loss against time during a combustion process. (Author)

Vortices trapped in discrete Josephson rings

International Nuclear Information System (INIS)

Van der Zanta, H.S.J.; Orlando, T.P.; Watanabe, Shinya; Strogatz, S.H.

1994-01-01

We report the first measurements of current- (I-V) characteristics of discrete rings of Josephson junctions. As I is increased, resonant steps appear in the I-V curve, due to phase-locking between a propagating, trapped vortex and the linear waves excited in its wake. Unexpectedly, the phase velocity of the linear waves, not the group velocity, is the physically important quantity and mode numbers outside the Brillouin zone are relevant. Our measurements show that away from the resonant steps, a single vortex can move in an environment with very little damping, making the discrete one-dimensional ring a well-defined model system for the study of ballistic and quantum vortex experiments. ((orig.))

Vortices trapped in discrete Josephson rings

Energy Technology Data Exchange (ETDEWEB)

Van der Zanta, H.S.J. [Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Orlando, T.P. [Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Watanabe, Shinya [Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Strogatz, S.H. [Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

1994-12-01

We report the first measurements of current- (I-V) characteristics of discrete rings of Josephson junctions. As I is increased, resonant steps appear in the I-V curve, due to phase-locking between a propagating, trapped vortex and the linear waves excited in its wake. Unexpectedly, the phase velocity of the linear waves, not the group velocity, is the physically important quantity and mode numbers outside the Brillouin zone are relevant. Our measurements show that away from the resonant steps, a single vortex can move in an environment with very little damping, making the discrete one-dimensional ring a well-defined model system for the study of ballistic and quantum vortex experiments. ((orig.)).

Experiments and numerical studies on a Syngas-fired Ultra low NOx combustor

KAUST Repository

S, Krishna; Ravikrishna, R. V.

2017-01-01

Exhaust measurements of temperature and pollutants in a syngas-fired model trapped vortex combustor for stationary power generation applications are reported. The performance was further evaluated for configurations where mixing enhancement was obtained using struts in the mainstream flow. Mainstream premixing of fuel was also studied to investigate its effect on emissions. The exhaust temperature pattern factor was found to be poor for baseline cases, but improved with the introduction of struts. NO emissions were steadily below 3-ppm across various flow conditions, whereas CO emissions tended to increase with increasing Momentum Flux Ratios (MFRs) and mainstream fuel addition. Combustion efficiencies ~96% were observed for all conditions. The performance characteristics were found to be favourable at higher MFRs with low pattern factors and high combustion efficiencies. Numerical simulations employing RANS and LES with Presumed Probability Distribution Function (PPDF) model were also carried out. Mixture fraction profiles in the TVC cavity for non-reacting conditions show that LES simulations are able to capture the mean mixing field better than the RANS-based approach. This is attributed to the prediction of the jet decay rate and is reflected on the mean velocity magnitude fields, which reinforce this observation at different sections in the cavity. Both RANS and LES simulations show close agreement with the experimentally measured OH concentration, however, the RANS approach does not perform satisfactorily in capturing the trend of velocity magnitude. LES simulations clearly capture the trend observed in exhaust measurements which is primarily attributed to the flame stabilization mechanism.

Experiments and numerical studies on a Syngas-fired Ultra low NOx combustor

KAUST Repository

S, Krishna

2017-06-06

Exhaust measurements of temperature and pollutants in a syngas-fired model trapped vortex combustor for stationary power generation applications are reported. The performance was further evaluated for configurations where mixing enhancement was obtained using struts in the mainstream flow. Mainstream premixing of fuel was also studied to investigate its effect on emissions. The exhaust temperature pattern factor was found to be poor for baseline cases, but improved with the introduction of struts. NO emissions were steadily below 3-ppm across various flow conditions, whereas CO emissions tended to increase with increasing Momentum Flux Ratios (MFRs) and mainstream fuel addition. Combustion efficiencies ~96% were observed for all conditions. The performance characteristics were found to be favourable at higher MFRs with low pattern factors and high combustion efficiencies. Numerical simulations employing RANS and LES with Presumed Probability Distribution Function (PPDF) model were also carried out. Mixture fraction profiles in the TVC cavity for non-reacting conditions show that LES simulations are able to capture the mean mixing field better than the RANS-based approach. This is attributed to the prediction of the jet decay rate and is reflected on the mean velocity magnitude fields, which reinforce this observation at different sections in the cavity. Both RANS and LES simulations show close agreement with the experimentally measured OH concentration, however, the RANS approach does not perform satisfactorily in capturing the trend of velocity magnitude. LES simulations clearly capture the trend observed in exhaust measurements which is primarily attributed to the flame stabilization mechanism.

Pulsed-Field Magnetization Properties of Bulk Superconductors by Employment of Vortex-Type Coils

Science.gov (United States)

Deng, Z.; Shinohara, N.; Miki, M.; Felder, B.; Tsuzuki, K.; Watasaki, M.; Kawabe, S.; Taguchi, R.; Izumi, M.

Vortex-type magnetizing coils are gaining more and more attention to activate bulk superconductors in pulsed-field magnetization (PFM) studies, compared with solenoid-type ones. Following existing reports, we present experimental results of the different penetration patterns of magnetic flux between the two kinds of coils. It was found that the magnetic flux will primarily penetrate inside the bulk from the upper and lower surfaces by using vortex coils, rather than from the periphery in the case of solenoid coils. Moreover, the bulk submitted to a small pulsed-field excitation exhibits a similar field profile as the excitation field (convex or concave shape); a phenomenon named field memory effect. The use of vortex- or solenoid-type coils in PFM will pose an influence on the initial flux penetration patterns during the flux trapping processes, but both coils can finally excite the best conical trapped field shape of the bulk.

Observations of electron vortex magnetic holes and related wave-particle interactions in the turbulent magnetosheath

Science.gov (United States)

Huang, S.; Sahraoui, F.; Yuan, Z.; He, J.; Zhao, J.; Du, J.; Le Contel, O.; Wang, X.; Deng, X.; Fu, H.; Zhou, M.; Shi, Q.; Breuillard, H.; Pang, Y.; Yu, X.; Wang, D.

2017-12-01

Magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the core region of the magnetic hole and a peak in the outer region of the magnetic hole. There is an enhancement in the perpendicular electron fluxes at 90° pitch angles inside the magnetic hole, implying that the electrons are trapped within it. The variations of the electron velocity components Vem and Ven suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the circular cross-section. These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations. We perform a statistically study using high time solution data from the MMS mission. The magnetic holes with short duration (i.e., < 0.5 s) have their cross section smaller than the ion gyro-radius. Superposed epoch analysis of all events reveals that an increase in the electron density and total temperature, significantly increase (resp. decrease) the electron perpendicular (resp. parallel) temperature, and an electron vortex inside the holes. Electron fluxes at 90° pitch angles with selective energies increase in the KSMHs, are trapped inside KSMHs and form the electron vortex due to their collective motion. All these features are consistent with the electron vortex magnetic holes obtained in 2D and 3D particle-in-cell simulations, indicating that the observed the magnetic holes seem to be best explained as electron vortex magnetic holes. It is furthermore shown that the magnetic holes are likely to heat and accelerate the electrons. We also investigate the coupling between whistler waves and electron vortex magnetic holes. These whistler waves can be locally generated inside electron

Fuel and Combustor Concerns for Future Commercial Combustors

Science.gov (United States)

Chang, Clarence T.

2017-01-01

Civil aircraft combustor designs will move from rich-burn to lean-burn due to the latter's advantage in low NOx and nvPM emissions. However, the operating range of lean-burn is narrower, requiring premium mixing performance from the fuel injectors. As the OPR increases, the corresponding combustor inlet temperature increase can benefit greatly with fuel composition improvements. Hydro-treatment can improve coking resistance, allowing finer fuel injection orifices to speed up mixing. Selective cetane number control across the fuel carbon-number distribution may allow delayed ignition at high power while maintaining low-power ignition characteristics.

Alternate-Fueled Combustor-Sector Performance: Part A: Combustor Performance Part B: Combustor Emissions

Science.gov (United States)

Shouse, D. T.; Neuroth, C.; Henricks, R. C.; Lynch, A.; Frayne, C.; Stutrud, J. S.; Corporan, E.; Hankins, T.

2010-01-01

Alternate aviation fuels for military or commercial use are required to satisfy MIL-DTL-83133F(2008) or ASTM D 7566 (2010) standards, respectively, and are classified as drop-in fuel replacements. To satisfy legacy issues, blends to 50% alternate fuel with petroleum fuels are certified individually on the basis of feedstock. Adherence to alternate fuels and fuel blends requires smart fueling systems or advanced fuel-flexible systems, including combustors and engines without significant sacrifice in performance or emissions requirements. This paper provides preliminary performance (Part A) and emissions and particulates (Part B) combustor sector data for synthetic-parafinic-kerosene- (SPK-) type fuel and blends with JP-8+100 relative to JP-8+100 as baseline fueling.

Composite vortex ordering in superconducting films with arrays of blind holes

International Nuclear Information System (INIS)

Berdiyorov, G R; Milosevic, M V; Peeters, F M

2009-01-01

The pinning properties of a superconducting thin film with a square array of blind holes are studied using the nonlinear Ginzburg-Landau theory. Although blind holes provide a weaker pinning potential than holes (also called antidots), several novel vortex structures are predicted for different size and thickness of the blind holes. Orientational dimer and trimer vortex states as well as concentric vortex shells can nucleate in the blind holes. In addition, we predict the stabilization of giant vortices that may be located both in the pinning centers and/or at the interstitial sites, as well as the combination of giant vortices with sets of individual vortices. For large blind holes, local vortex shell structures inside the blind holes may transfer their symmetry to interstitial vortices as well. The subtle interplay of shell formation and traditional Abrikosov vortex lattices inside the blind holes is also studied for different numbers of trapped vortices.

Laser-based investigations in gas turbine model combustors

Science.gov (United States)

Meier, W.; Boxx, I.; Stöhr, M.; Carter, C. D.

2010-10-01

Dynamic processes in gas turbine (GT) combustors play a key role in flame stabilization and extinction, combustion instabilities and pollutant formation, and present a challenge for experimental as well as numerical investigations. These phenomena were investigated in two gas turbine model combustors for premixed and partially premixed CH4/air swirl flames at atmospheric pressure. Optical access through large quartz windows enabled the application of laser Raman scattering, planar laser-induced fluorescence (PLIF) of OH, particle image velocimetry (PIV) at repetition rates up to 10 kHz and the simultaneous application of OH PLIF and PIV at a repetition rate of 5 kHz. Effects of unmixedness and reaction progress in lean premixed GT flames were revealed and quantified by Raman scattering. In a thermo-acoustically unstable flame, the cyclic variation in mixture fraction and its role for the feedback mechanism of the instability are addressed. In a partially premixed oscillating swirl flame, the cyclic variations of the heat release and the flow field were characterized by chemiluminescence imaging and PIV, respectively. Using phase-correlated Raman scattering measurements, significant phase-dependent variations of the mixture fraction and fuel distributions were revealed. The flame structures and the shape of the reaction zones were visualized by planar imaging of OH distribution. The simultaneous OH PLIF/PIV high-speed measurements revealed the time history of the flow field-flame interaction and demonstrated the development of a local flame extinction event. Further, the influence of a precessing vortex core on the flame topology and its dynamics is discussed.

Vortex dynamics during blade-vortex interactions

Science.gov (United States)

Peng, Di; Gregory, James W.

2015-05-01

Vortex dynamics during parallel blade-vortex interactions (BVIs) were investigated in a subsonic wind tunnel using particle image velocimetry (PIV). Vortices were generated by applying a rapid pitch-up motion to an airfoil through a pneumatic system, and the subsequent interactions with a downstream, unloaded target airfoil were studied. The blade-vortex interactions may be classified into three categories in terms of vortex behavior: close interaction, very close interaction, and collision. For each type of interaction, the vortex trajectory and strength variation were obtained from phase-averaged PIV data. The PIV results revealed the mechanisms of vortex decay and the effects of several key parameters on vortex dynamics, including separation distance (h/c), Reynolds number, and vortex sense. Generally, BVI has two main stages: interaction between vortex and leading edge (vortex-LE interaction) and interaction between vortex and boundary layer (vortex-BL interaction). Vortex-LE interaction, with its small separation distance, is dominated by inviscid decay of vortex strength due to pressure gradients near the leading edge. Therefore, the decay rate is determined by separation distance and vortex strength, but it is relatively insensitive to Reynolds number. Vortex-LE interaction will become a viscous-type interaction if there is enough separation distance. Vortex-BL interaction is inherently dominated by viscous effects, so the decay rate is dependent on Reynolds number. Vortex sense also has great impact on vortex-BL interaction because it changes the velocity field and shear stress near the surface.

Photographs of quantized vortex lines in rotating superfluid helium

International Nuclear Information System (INIS)

Williams, G.A.

1974-01-01

The spatial positions of quantized vortex lines in rotating He II have been determined using a photographic technique. Electrons are trapped on the vortices and then extracted through the liquid surface and accelerated into a phosphor screen. The light from the phosphor is transmitted to room temperature with coherent fiber optics and photographed with an image intensifier camera. Photographs taken with pure 4 He at T = 0.3 K were complete blurs. These blurs are attributed to nonequilibrium motion of the vortices, arising from the lack of normal fluid damping at this temperature. To resolve the individual vortex lines it was found necessary to add 3 He to the 4 He sample to damp the vortex motion. Photographs are presented for 3 He concentrations up to 1.6 percent. The number of vortices visible varies linearly with rotation speed, but is only about one-half the number expected from theory. The vortex lines in the apparatus were not observed to form a stable array

Vortex dynamics in coherently coupled Bose-Einstein condensates

Science.gov (United States)

Calderaro, Luca; Fetter, Alexander L.; Massignan, Pietro; Wittek, Peter

2017-02-01

In classical hydrodynamics with uniform density, vortices move with the local fluid velocity. This description is rewritten in terms of forces arising from the interaction with other vortices. Two such positive straight vortices experience a repulsive interaction and precess in a positive (anticlockwise) sense around their common centroid. A similar picture applies to vortices in a two-component, two-dimensional uniform Bose-Einstein condensate (BEC) coherently coupled through rf Rabi fields. Unlike the classical case, however, the rf Rabi coupling induces an attractive interaction and two such vortices with positive signs now rotate in the negative (clockwise) sense. Pairs of counter-rotating vortices are instead found to translate with uniform velocity perpendicular to the line joining their cores. This picture is extended to a single vortex in a two-component trapped BEC. Although two uniform vortex-free components experience familiar Rabi oscillations of particle-number difference, such behavior is absent for a vortex in one component because of the nonuniform vortex phase. Instead the coherent Rabi coupling induces a periodic vorticity transfer between the two components.

Pulse combustors for unpulverized solid fuels; Combustor pulsante para solidos nao pulverizados

Energy Technology Data Exchange (ETDEWEB)

Ferreira, Marco Aurelio; Carvalho Junior, Joao Andrade de [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil)

1988-12-31

This work presents results of performance evaluation of an experimental pulsating combustor developed to burn unpulverized solid fuels. The fuels tested were sized wood blocks and coal lumps. The results for coal show a clear maximum combustion efficiency as a function of fuel loading within the combustor. For an excess of air of 10%, a maximum combustion efficiency of 94% was obtained. (author) 38 refs., 10 figs., 2 tabs.

Mapping travelling convection vortex events with respect to energetic particle boundaries

DEFF Research Database (Denmark)

Moretto, T.; Yahnin, A.

1998-01-01

Thirteen events of high-latitude ionospheric travelling convection vortices during very quiet conditions were identified in the Greenland magnetometer data during 1990 and 1991. The latitudes of the vortex centres for these events are compared to the energetic electron trapping boundaries...

Intrinsic and extrinsic mechanisms of vortex formation in superfluid 3He-B

International Nuclear Information System (INIS)

Ruutu, V.M.H.; Parts, Ue.; Krusius, M.

1997-01-01

The authors report on the first comprehensive measurements of critical superflow velocities in 3 He-B which allow different mechanisms of vortex formation to be identified. As a function of temperature T and pressure P, they measure the critical angular velocity Ω c (T,P) at which vortices start to form in slowly accelerating rotation in a cylindrical container filled with 3 He-B. Owing to the long coherence length ξ(T,P) ∼ 10-100 nm, either trapped remanent vorticity or intrinsic nucleation may dominate vortex formation, depending on the roughness of the container wall and the presence of loaded traps. NMR measurement with a resolution of one single vortex line allows the authors to distinguish between different processes: (1) Three extrinsic mechanisms of vortex formation have been observed. One of them is the vortex mill, a continuous periodic source which is activated in a rough-walled container well below the limit for intrinsic nucleation. (2) In a closed smooth-walled container intrinsic nucleation is the only mechanism available, with a critical velocity v c (T,P) = Ω c (T,P) R, where R is the radius of the container. The authors find v c (T,P) to be related to the calculated intrinsic stability limit v c (T,P) of homogeneous superflow. The existence of this connection in the form of a scaling law implies that nucleation takes place at an instability, rather than by thermal activation or quantum tunneling which become impossible because of an inaccessibly high energy barrier

Alternate-Fueled Combustor-Sector Performance

Science.gov (United States)

Thomas, Anna E.; Saxena, Nikita T.; Shouse, Dale T.; Neuroth, Craig; Hendricks, Robert C.; Lynch, Amy; Frayne, Charles W.; Stutrud, Jeffrey S.; Corporan, Edwin; Hankins, Terry

2013-01-01

In order to realize alternative fueling for military and commercial use, the industry has set forth guidelines that must be met by each fuel. These aviation fueling requirements are outlined in MIL-DTL-83133F(2008) or ASTM D 7566 Annex (2011) standards, and are classified as "drop-in" fuel replacements. This report provides combustor performance data for synthetic-paraffinic-kerosene- (SPK-) type (Fischer-Tropsch (FT)) fuel and blends with JP-8+100, relative to JP-8+100 as baseline fueling. Data were taken at various nominal inlet conditions: 75 psia (0.52 MPa) at 500 degF (533 K), 125 psia (0.86 MPa) at 625 degF (603 K), 175 psia (1.21 MPa) at 725 degF (658 K), and 225 psia (1.55 MPa) at 790 degF (694 K). Combustor performance analysis assessments were made for the change in flame temperatures, combustor efficiency, wall temperatures, and exhaust plane temperatures at 3, 4, and 5 percent combustor pressure drop (DP) for fuel:air ratios (F/A) ranging from 0.010 to 0.025. Significant general trends show lower liner temperatures and higher flame and combustor outlet temperatures with increases in FT fueling relative to JP-8+100 fueling. The latter affects both turbine efficiency and blade and vane lives.

Mobilities of ions trapped on vortex lines in dilute 3He--4He solutions

International Nuclear Information System (INIS)

Huang, W.; Dahm, A.J.

1976-01-01

A model calculation of the mobility of a positive ion in the presence of 3 He atoms condensed on a vortex core is presented. Reasonable qualitative and quantitative agreement between theory and experiment is obtained, and reasons for differences are discussed. A reason for the larger mobility of the negative ion in comparison to the smaller positive ion is suggested. The contribution of vortex waves to the scattering of ions is addressed

Experimental clean combustor program, alternate fuels addendum, phase 2

Science.gov (United States)

Gleason, C. C.; Bahr, D. W.

1976-01-01

The characteristics of current and advanced low-emissions combustors when operated with special test fuels simulating broader range combustion properties of petroleum or coal derived fuels were studied. Five fuels were evaluated; conventional JP-5, conventional No. 2 Diesel, two different blends of Jet A and commercial aromatic mixtures - zylene bottoms and haphthalene charge stock, and a fuel derived from shale oil crude which was refined to Jet A specifications. Three CF6-50 engine size combustor types were evaluated; the standard production combustor, a radial/axial staged combustor, and a double annular combustor. Performance and pollutant emissons characteristics at idle and simulated takeoff conditions were evaluated in a full annular combustor rig. Altitude relight characteristics were evaluated in a 60 degree sector combustor rig. Carboning and flashback characteristics at simulated takeoff conditions were evaluated in a 12 degree sector combustor rig. For the five fuels tested, effects were moderate, but well defined.

Optical vortex beams: Generation, propagation and applications

Science.gov (United States)

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.

Ejector-Enhanced, Pulsed, Pressure-Gain Combustor

Science.gov (United States)

Paxson, Daniel E.; Dougherty, Kevin T.

2009-01-01

An experimental combination of an off-the-shelf valved pulsejet combustor and an aerodynamically optimized ejector has shown promise as a prototype of improved combustors for gas turbine engines. Despite their name, the constant pressure combustors heretofore used in gas turbine engines exhibit typical pressure losses ranging from 4 to 8 percent of the total pressures delivered by upstream compressors. In contrast, the present ejector-enhanced pulsejet combustor exhibits a pressure rise of about 3.5 percent at overall enthalpy and temperature ratios compatible with those of modern turbomachines. The modest pressure rise translates to a comparable increase in overall engine efficiency and, consequently, a comparable decrease in specific fuel consumption. The ejector-enhanced pulsejet combustor may also offer potential for reducing the emission of harmful exhaust compounds by making it practical to employ a low-loss rich-burn/quench/lean-burn sequence. Like all prior concepts for pressure-gain combustion, the present concept involves an approximation of constant-volume combustion, which is inherently unsteady (in this case, more specifically, cyclic). The consequent unsteadiness in combustor exit flow is generally regarded as detrimental to the performance of downstream turbomachinery. Among other adverse effects, this unsteadiness tends to detract from the thermodynamic benefits of pressure gain. Therefore, it is desirable in any intermittent combustion process to minimize unsteadiness in the exhaust path.

System and method for controlling a combustor assembly

Science.gov (United States)

York, William David; Ziminsky, Willy Steve; Johnson, Thomas Edward; Stevenson, Christian Xavier

2013-03-05

A system and method for controlling a combustor assembly are disclosed. The system includes a combustor assembly. The combustor assembly includes a combustor and a fuel nozzle assembly. The combustor includes a casing. The fuel nozzle assembly is positioned at least partially within the casing and includes a fuel nozzle. The fuel nozzle assembly further defines a head end. The system further includes a viewing device configured for capturing an image of at least a portion of the head end, and a processor communicatively coupled to the viewing device, the processor configured to compare the image to a standard image for the head end.

Ceramic combustor mounting

Science.gov (United States)

Hoffman, Melvin G.; Janneck, Frank W.

1982-01-01

A combustor for a gas turbine engine includes a metal engine block including a wall portion defining a housing for a combustor having ceramic liner components. A ceramic outlet duct is supported by a compliant seal on the metal block and a reaction chamber liner is stacked thereon and partly closed at one end by a ceramic bypass swirl plate which is spring loaded by a plurality of circumferentially spaced, spring loaded guide rods and wherein each of the guide rods has one end thereof directed exteriorly of a metal cover plate on the engine block to react against externally located biasing springs cooled by ambient air and wherein the rod spring support arrangement maintains the stacked ceramic components together so that a normal force is maintained on the seal between the outlet duct and the engine block under all operating conditions. The support arrangement also is operative to accommodate a substantial difference in thermal expansion between the ceramic liner components of the combustor and the metal material of the engine block.

Vortex phase-induced changes of the statistical properties of a partially coherent radially polarized beam.

Science.gov (United States)

Guo, Lina; Chen, Yahong; Liu, Xianlong; Liu, Lin; Cai, Yangjian

2016-06-27

Partially coherent radially polarized (PCRP) beam was introduced and generated in recent years. In this paper, we investigate the statistical properties of a PCRP beam embedded with a vortex phase (i.e., PCRP vortex beam). We derive the analytical formula for the cross-spectral density matrix of a PCRP vortex beam propagating through a paraxial ABCD optical system and analyze the statistical properties of a PCRP vortex beam focused by a thin lens. It is found that the statistical properties of a PCRP vortex beam on propagation are much different from those of a PCRP beam. The vortex phase induces not only the rotation of the beam spot, but also the changes of the beam shape, the degree of polarization and the state of polarization. We also find that the vortex phase plays a role of resisting the coherence-induced degradation of the intensity distribution and the coherence-induced depolarization. Furthermore, we report experimental generation of a PCRP vortex beam for the first time. Our results will be useful for trapping and rotating particles, free-space optical communications and detection of phase object.

Scramjet Combustor Characteristics at Hypervelocity Condition over Mach 10 Flight

Science.gov (United States)

Takahashi, M.; Komuro, T.; Sato, K.; Kodera, M.; Tanno, H.; Itoh, K.

2009-01-01

To investigate possibility of reduction of a scramjet combustor size without thrust performance loss, a two-dimensional constant-area combustor of a previous engine model was replaced with the one with 23% lower-height. With the application of the lower-height combustor, the pressure in the combustor becomes 50% higher and the combustor length for the optimal performance becomes 43% shorter than the original combustor. The combustion tests of the modified engine model were conducted using a large free-piston driven shock tunnel at flow conditions corresponding to the flight Mach number from 9 to 14. CFD was also applied to the engine internal flows. The results showed that the mixing and combustion heat release progress faster to the distance and the combustor performance similar to that of the previous engine was obtained with the modified engine. The reduction of the combustor size without the thrust performance loss is successfully achieved by applying the lower-height combustor.

Non-linear dynamics in pulse combustor: A review

Indian Academy of Sciences (India)

idea of pressure gain combustion (i.e., combustion with gain in total pressure across the combustor as opposed to pressure-loss combustion experienced in constant pressure devices like conventional gas turbine combustors) is gaining popularity for propulsion devices [2]. Thus pulse combustors, which provide a practical ...

Controlled pilot oxidizer for a gas turbine combustor

Science.gov (United States)

Laster, Walter R.; Bandaru, Ramarao V.

2010-07-13

A combustor (22) for a gas turbine (10) includes a main burner oxidizer flow path (34) delivering a first portion (32) of an oxidizer flow (e.g., 16) to a main burner (28) of the combustor and a pilot oxidizer flow path (38) delivering a second portion (36) of the oxidizer flow to a pilot (30) of the combustor. The combustor also includes a flow controller (42) disposed in the pilot oxidizer flow path for controlling an amount of the second portion delivered to the pilot.

High pressure MHD coal combustors investigation, phase 2

Science.gov (United States)

Iwata, H.; Hamberg, R.

1981-05-01

A high pressure MHD coal combustor was investigated. The purpose was to acquire basic design and support engineering data through systematic combustion experiments at the 10 and 20 thermal megawatt size and to design a 50 MW/sub t/ combustor. This combustor is to produce an electrically conductive plasma generated by the direct combustion of pulverized coal with hot oxygen enriched vitiated air that is seeded with potassium carbonate. Vitiated air and oxygen are used as the oxidizer, however, preheated air will ultimately be used as the oxidizer in coal fired MHD combustors.

Vortex line topology during vortex tube reconnection

Science.gov (United States)

McGavin, P.; Pontin, D. I.

2018-05-01

This paper addresses reconnection of vortex tubes, with particular focus on the topology of the vortex lines (field lines of the vorticity). This analysis of vortex line topology reveals key features of the reconnection process, such as the generation of many small flux rings, formed when reconnection occurs in multiple locations in the vortex sheet between the tubes. Consideration of three-dimensional reconnection principles leads to a robust measurement of the reconnection rate, even once instabilities break the symmetry. It also allows us to identify internal reconnection of vortex lines within the individual vortex tubes. Finally, the introduction of a third vortex tube is shown to render the vortex reconnection process fully three-dimensional, leading to a fundamental change in the topological structure of the process. An additional interesting feature is the generation of vorticity null points.

Gas turbine topping combustor

Science.gov (United States)

Beer, J.; Dowdy, T.E.; Bachovchin, D.M.

1997-06-10

A combustor is described for burning a mixture of fuel and air in a rich combustion zone, in which the fuel bound nitrogen in converted to molecular nitrogen. The fuel rich combustion is followed by lean combustion. The products of combustion from the lean combustion are rapidly quenched so as to convert the fuel bound nitrogen to molecular nitrogen without forming NOx. The combustor has an air radial swirler that directs the air radially inward while swirling it in the circumferential direction and a radial fuel swirler that directs the fuel radially outward while swirling it in the same circumferential direction, thereby promoting vigorous mixing of the fuel and air. The air inlet has a variable flow area that is responsive to variations in the heating value of the fuel, which may be a coal-derived fuel gas. A diverging passage in the combustor in front of a bluff body causes the fuel/air mixture to recirculate with the rich combustion zone. 14 figs.

Assessment of Combustor Working Environments

Directory of Open Access Journals (Sweden)

Leiyong Jiang

2012-01-01

Full Text Available In order to assess the remaining life of gas turbine critical components, it is vital to accurately define the aerothermodynamic working environments and service histories. As a part of a major multidisciplinary collaboration program, a benchmark modeling on a practical gas turbine combustor is successfully carried out, and the two-phase, steady, turbulent, compressible, reacting flow fields at both cruise and takeoff are obtained. The results show the complicated flow features inside the combustor. The airflow over each flow element of the combustor can or liner is not evenly distributed, and considerable variations, ±25%, around the average values, are observed. It is more important to note that the temperatures at the combustor can and cooling wiggle strips vary significantly, which can significantly affect fatigue life of engine critical components. The present study suggests that to develop an adequate aerothermodynamics tool, it is necessary to carry out a further systematic study, including validation of numerical results, simulations at typical engine operating conditions, and development of simple correlations between engine operating conditions and component working environments. As an ultimate goal, the cost and time of gas turbine engine fleet management must be significantly reduced.

Vortex profiles and vortex interactions at the electroweak crossover

OpenAIRE

Chernodub, M. N.; Ilgenfritz, E. -M.; Schiller, A.

1999-01-01

Local correlations of Z-vortex operators with gauge and Higgs fields (lattice quantum vortex profiles) as well as vortex two-point functions are studied in the crossover region near a Higgs mass of 100 GeV within the 3D SU(2) Higgs model. The vortex profiles resemble certain features of the classical vortex solutions in the continuum. The vortex-vortex interactions are analogous to the interactions of Abrikosov vortices in a type-I superconductor.

An experimental study of interacting swirl flows in a model gas turbine combustor

Science.gov (United States)

Vishwanath, Rahul B.; Tilak, Paidipati Mallikarjuna; Chaudhuri, Swetaprovo

2018-03-01

In this experimental work, we analyze the flow structures emerging from the mutual interaction between adjacent swirling flows at variable degrees of swirl, issued into a semi-confined chamber, as it could happen in a three cup sector of an annular premixed combustor of a modern gas turbine engine. Stereoscopic particle image velocimetry ( sPIV) is used to characterize both the non-reacting and reacting flow fields in the central diametrical (vertical) plane of the swirlers and the corresponding transverse (horizontal) planes at different heights above the swirlers. A central swirling flow with a fixed swirl vane angle is allowed to interact with its neighboring flows of varied swirl levels, with constant inlet bulk flow velocity through the central port. It is found that the presence of straight jets with zero swirl or co-rotating swirling jets with increasing swirl on both sides of the central swirling jet, significantly alters its structures. As such, an increase in the amount of swirl in the neighboring flows increases the recirculation levels in central swirling flow leading to a bubble-type vortex breakdown, not formed otherwise. It is shown with the aid of Helmholtz decomposition that the transition from conical to bubble-type breakdown is captured well by the radial momentum induced by the azimuthal vorticity. Simultaneous sPIV and OH-planar laser-induced fluorescence (PLIF) are employed to identify the influence of the neighboring jets on the reacting vortex breakdown states. Significant changes in the vortex breakdown size and structure are observed due to variation in swirl levels of the neighboring jets alongside reaction and concomitant flow dilatation.

Low pollution combustor designs for CTOL engines - Results of the Experimental Clean Combustor Program

Science.gov (United States)

Roberts, R.; Peduzzi, A.; Niedzwiecki, R. W.

1976-01-01

The NASA/Pratt & Whitney Aircraft Experimental Clean Combustor Program is a multi-year, major contract effort. Primary program objectives are the generation of combustor technology for development of advanced commercial CTOL engines with lower exhaust emissions than current aircraft and demonstration of this technology in a full-scale JT9D engine in 1976. This paper describes the pollution and performance goals, Phase I and II test results, and the Phase III combustor hardware, pollution sampling techniques, and test plans. Best results were obtained with the Vorbix concept which employs multiple burning zones and improved fuel preparation and distribution. Substantial reductions were achieved in all pollutant categories, meeting the 1979 EPA standards for NOx, THC, and smoke when extrapolated to JT9D cycle conditions. The Vorbix concept additionally demonstrated the capability for acceptable altitude relight and did not appear to have unsolvable durability or exit temperature distribution problems.

Thermal performance of a micro-combustor for micro-gas turbine system

International Nuclear Information System (INIS)

Cao, H.L.; Xu, J.L.

2007-01-01

Premixed combustion of hydrogen gas and air was performed in a stainless steel based micro-annular combustor for a micro-gas turbine system. Micro-scale combustion has proved to be stable in the micro-combustor with a gap of 2 mm. The operating range of the micro-combustor was measured, and the maximum excess air ratio is up to 4.5. The distribution of the outer wall temperature and the temperature of exhaust gas of the micro-combustor with excess air ratio were obtained, and the wall temperature of the micro-combustor reaches its maximum value at the excess air ratio of 0.9 instead of 1 (stoichiometric ratio). The heat loss of the micro-combustor to the environment was calculated and even exceeds 70% of the total thermal power computed from the consumed hydrogen mass flow rate. Moreover, radiant heat transfer covers a large fraction of the total heat loss. Measures used to reduce the heat loss were proposed to improve the thermal performance of the micro-combustor. The optimal operating status of the micro-combustor and micro-gas turbine is analyzed and proposed by analyzing the relationship of the temperature of the exhaust gas of the micro-combustor with thermal power and excess air ratio. The investigation of the thermal performance of the micro-combustor is helpful to design an improved micro-combustor

Fabrication and Characterization of Carbon-Based Nanofluids through the Water Vortex Trap Method

Directory of Open Access Journals (Sweden)

Ching-Min Cheng

2018-01-01

Full Text Available This study designed an efficient one-step method for synthesizing carbon-based nanofluids (CBNFs. The method employs the vortex trap method (VTM and an oxygen-acetylene flame, serving as a carbon source, in a manufacturing system of the VTM (MSVTM. The flow rate ratio of O2 and C2H2 was adjusted to form suitable combustion conditions for the reduced flame. Four flow rate ratios of O2 and C2H2 were used: 1.5 : 2.5 (V1, 1.0 : 2.5 (V2, 0.5 : 2.5 (V3, and 0 : 2.5 (V4. The morphology, structure, particle size, stability, and basic physicochemical characteristics of the obtained carbon-based nanomaterials (CBNMs and CBNFs were investigated using transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, Raman spectrometry, ultraviolet–visible–near-infrared spectrophotometry, and a particle size-zeta potential analyzer. The static positioning method was utilized to evaluate the stability of the CBNFs with added EP dispersants. The evaluation results revealed the morphologies, compositions, and concentrations of the CBNFs obtained using various process parameters, and the relation between processing time and production rate was determined. Among the CBNMs synthesized, those obtained using the V4-0 flow rate ratio had the highest stability when no EP dispersant was added. Moreover, the maximum enhancement ratios of the viscosity and thermal conductivity were also obtained for V4-0: 4.65% and 1.29%, respectively. Different types and concentrations of dispersants should be considered in future research to enhance the stability of CBNFs for further application.

Thermal performance of a meso-scale liquid-fuel combustor

International Nuclear Information System (INIS)

Vijayan, V.; Gupta, A.K.

2011-01-01

Research highlights: → Demonstrated successful combustion of liquid fuel-air mixtures in a novel meso-scale combustor. → Flame quenching was eliminated using heat recirculation in a swiss roll type combustor that also extended the flammability limits. → Liquid fuel was rapidly vaporized with the use of hot narrow channel walls that eliminated the need of a fuel atomizer. → Maximum power density of the combustor was estimated to be about 8.5 GW/m3 and heat load in the range of 50-280W. → Overall efficiency of the combustor was estimated in the range of 12 to 20%. - Abstract: Combustion in small scale devices poses significant challenges due to the quenching of reactions from wall heat losses as well as the significantly reduced time available for mixing and combustion. In the case of liquid fuels there are additional challenges related to atomization, vaporization and mixing with the oxidant in the very short time-scale liquid-fuel combustor. The liquid fuel employed here is methanol with air as the oxidizer. The combustor was designed based on the heat recirculating concept wherein the incoming reactants are preheated by the combustion products through heat exchange occurring via combustor walls. The combustor was fabricated from Zirconium phosphate, a ceramic with very low thermal conductivity (0.8 W m -1 K -1 ). The combustor had rectangular shaped double spiral geometry with combustion chamber in the center of the spiral formed by inlet and exhaust channels. Methanol and air were introduced immediately upstream at inlet of the combustor. The preheated walls of the inlet channel also act as a pre-vaporizer for liquid fuel which vaporizes the liquid fuel and then mixes with air prior to the fuel-air mixture reaching the combustion chamber. Rapid pre-vaporization of the liquid fuel by the hot narrow channel walls eliminated the necessity for a fuel atomizer. Self-sustained combustion of methanol-air was achieved in a chamber volume as small as 32.6 mm 3

Tailoring optical complex field with spiral blade plasmonic vortex lens

Science.gov (United States)

Rui, Guanghao; Zhan, Qiwen; Cui, Yiping

2015-01-01

Optical complex fields have attracted increasing interests because of the novel effects and phenomena arising from the spatially inhomogeneous state of polarizations and optical singularities of the light beam. In this work, we propose a spiral blade plasmonic vortex lens (SBPVL) that offers unique opportunities to manipulate these novel fields. The strong interaction between the SBPVL and the optical complex fields enable the synthesis of highly tunable plasmonic vortex. Through theoretical derivations and numerical simulations we demonstrated that the characteristics of the plasmonic vortex are determined by the angular momentum (AM) of the light, and the geometrical topological charge of the SBPVL, which is govern by the nonlinear superposition of the pitch and the number of blade element. In addition, it is also shown that by adjusting the geometric parameters, SBPVL can be utilized to focus and manipulate optical complex field with fractional AM. This miniature plasmonic device may find potential applications in optical trapping, optical data storage and many other related fields. PMID:26335894

Chaos in an imperfectly premixed model combustor.

Science.gov (United States)

Kabiraj, Lipika; Saurabh, Aditya; Karimi, Nader; Sailor, Anna; Mastorakos, Epaminondas; Dowling, Ann P; Paschereit, Christian O

2015-02-01

This article reports nonlinear bifurcations observed in a laboratory scale, turbulent combustor operating under imperfectly premixed mode with global equivalence ratio as the control parameter. The results indicate that the dynamics of thermoacoustic instability correspond to quasi-periodic bifurcation to low-dimensional, deterministic chaos, a route that is common to a variety of dissipative nonlinear systems. The results support the recent identification of bifurcation scenarios in a laminar premixed flame combustor (Kabiraj et al., Chaos: Interdiscip. J. Nonlinear Sci. 22, 023129 (2012)) and extend the observation to a practically relevant combustor configuration.

Low NOx Fuel Flexible Combustor Integration Project Overview

Science.gov (United States)

Walton, Joanne C.; Chang, Clarence T.; Lee, Chi-Ming; Kramer, Stephen

2015-01-01

The Integrated Technology Demonstration (ITD) 40A Low NOx Fuel Flexible Combustor Integration development is being conducted as part of the NASA Environmentally Responsible Aviation (ERA) Project. Phase 2 of this effort began in 2012 and will end in 2015. This document describes the ERA goals, how the fuel flexible combustor integration development fulfills the ERA combustor goals, and outlines the work to be conducted during project execution.

Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

Energy Technology Data Exchange (ETDEWEB)

Galvis, J.A. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Departamento de Ciencias Naturales, Facultad de ingeniería y Ciencias Básicas, Universidad Central, Bogotá (Colombia); National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310 (United States); Herrera, E.; Guillamón, I.; Vieira, S. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain); Suderow, H., E-mail: hermann.suderow@uam.es [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain)

2017-02-15

Highlights: • The observation of vortex cores is reviewed, with emphasis in new experiments. • Vortex cores are follow superconducting gap and Fermi surface shapes. • The vortex core shape influences vortex dynamics. - Abstract: Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

International Nuclear Information System (INIS)

Galvis, J.A.; Herrera, E.; Guillamón, I.; Vieira, S.; Suderow, H.

2017-01-01

Highlights: • The observation of vortex cores is reviewed, with emphasis in new experiments. • Vortex cores are follow superconducting gap and Fermi surface shapes. • The vortex core shape influences vortex dynamics. - Abstract: Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

Nonlinear quantum piston for the controlled generation of vortex rings and soliton trains

KAUST Repository

Pinsker, Florian; Berloff, Natalia G.; Pé rez-Garcí a, Ví ctor M.

2013-01-01

We propose a simple way to generate nonlinear excitations in a controllable way by managing interactions in Bose-Einstein condensates. Under the action of a quantum analog of a classical piston, the condensed atoms are pushed through the trap, generating vortex rings infully three-dimensional condensates or soliton trains in quasi-one-dimensional scenarios. The vortex rings form due to transverse instability of the shock-wave train, enhanced and supported by the energy transfer between waves. We elucidate in what sense the self-interactions within the atom cloud define the properties of the generated vortex rings and soliton trains. Based on the quantum-piston scheme we study the behavior of two-component Bose-Einstein condensates and analyze how the presence of an additional superfluid influences the generation of vortex rings or solitons in the other component, and vice versa. Finally, we show the dynamical emergence of skyrmions within two-component systems in the immiscible regime. © 2013 American Physical Society.

Nonlinear quantum piston for the controlled generation of vortex rings and soliton trains

KAUST Repository

Pinsker, Florian

2013-05-29

We propose a simple way to generate nonlinear excitations in a controllable way by managing interactions in Bose-Einstein condensates. Under the action of a quantum analog of a classical piston, the condensed atoms are pushed through the trap, generating vortex rings infully three-dimensional condensates or soliton trains in quasi-one-dimensional scenarios. The vortex rings form due to transverse instability of the shock-wave train, enhanced and supported by the energy transfer between waves. We elucidate in what sense the self-interactions within the atom cloud define the properties of the generated vortex rings and soliton trains. Based on the quantum-piston scheme we study the behavior of two-component Bose-Einstein condensates and analyze how the presence of an additional superfluid influences the generation of vortex rings or solitons in the other component, and vice versa. Finally, we show the dynamical emergence of skyrmions within two-component systems in the immiscible regime. © 2013 American Physical Society.

Vortex methods and vortex statistics

International Nuclear Information System (INIS)

Chorin, A.J.

1993-05-01

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 as 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

Vortex coupling in trailing vortex-wing interactions

Science.gov (United States)

Chen, C.; Wang, Z.; Gursul, I.

2018-03-01

The interaction of trailing vortices of an upstream wing with rigid and flexible downstream wings has been investigated experimentally in a wind tunnel, using particle image velocimetry, hot-wire, force, and deformation measurements. Counter-rotating upstream vortices exhibit increased meandering when they are close to the tip of the downstream wing. The upstream vortex forms a pair with the vortex shed from the downstream wing and then exhibits large displacements around the wing tip. This coupled motion of the pair has been found to cause large lift fluctuations on the downstream wing. The meandering of the vortex pair occurs at the natural meandering frequency of the isolated vortex, with a low Strouhal number, and is not affected by the frequency of the large-amplitude wing oscillations if the downstream wing is flexible. The displacement of the leading vortex is larger than that of the trailing vortex; however, it causes highly correlated variations of the core radius, core vorticity, and circulation of the trailing vortex with the coupled meandering motion. In contrast, co-rotating vortices do not exhibit any increased meandering.

Feasibility study of ultra-low NOx Gas turbine combustor using the RML combustion concept

Energy Technology Data Exchange (ETDEWEB)

Van, Tien Giap; Hwang, Jeong Jae; Kim, Min Kuk; Ahn, Kook Young [Environment and Energy Research Division, Korea Institute of Machinery and Materials (KIMM), Daejeon (Korea, Republic of)

2016-12-15

A new combustion concept, the so called RML, was investigated to validate its application as a gas turbine combustor for combustor outlet temperatures over 1973 K. The feasibility study of the RML combustor was conducted with zero dimensional combustion calculations. The emission characteristics of RQL, LEAN, EGR and RML combustors were compared. The calculation results showed that the RQL combustor has lower NOx emissions than the LEAN at high outlet temperature. NOx emissions of the RML combustor at equivalence ratio of the rich chamber of 2.0 can be reduced by 30 % compared with the EGR combustor, and lower than the RQL combustor at a combustor outlet temperature over 1973 K. However, the CO emissions of the RML combustor were higher than those of the LEAN and EGR combustors. Also, the possibility of applying the RML combustor to gas turbines was discussed considering residence time, equivalence ratio of the rich chamber and recirculation rate. Although further research to design and realize the proposed RML combustor is needed, this study verified that the RML concept can be successfully used in a gas turbine combustor.

Feasibility study of ultra-low NOx Gas turbine combustor using the RML combustion concept

International Nuclear Information System (INIS)

Van, Tien Giap; Hwang, Jeong Jae; Kim, Min Kuk; Ahn, Kook Young

2016-01-01

A new combustion concept, the so called RML, was investigated to validate its application as a gas turbine combustor for combustor outlet temperatures over 1973 K. The feasibility study of the RML combustor was conducted with zero dimensional combustion calculations. The emission characteristics of RQL, LEAN, EGR and RML combustors were compared. The calculation results showed that the RQL combustor has lower NOx emissions than the LEAN at high outlet temperature. NOx emissions of the RML combustor at equivalence ratio of the rich chamber of 2.0 can be reduced by 30 % compared with the EGR combustor, and lower than the RQL combustor at a combustor outlet temperature over 1973 K. However, the CO emissions of the RML combustor were higher than those of the LEAN and EGR combustors. Also, the possibility of applying the RML combustor to gas turbines was discussed considering residence time, equivalence ratio of the rich chamber and recirculation rate. Although further research to design and realize the proposed RML combustor is needed, this study verified that the RML concept can be successfully used in a gas turbine combustor

Can Water-Injected Turbomachines Provide Cost-Effective Emissions and Maintenance Reductions?

Science.gov (United States)

Hendricks, Robert C.; Daggett, David L.; Shouse, Dale T.; Roquemore, William M.; Brankovic, Andreja; Ryder, Robert C., Jr.

2011-01-01

An investigation has been performed to evaluate the effect of water injection on the performance of the Air Force Research Laboratory (AFRL, Wright-Patterson Air Force Base (WPAFB)) experimental trapped vortex combustor (TVC) over a range of fuel-to-air and water-to-fuel ratios. Performance is characterized by combustor exit quantities: temperature and emissions measurements using rakes, and overall pressure drop, from upstream plenum to combustor exit. Combustor visualization is performed using gray-scale and color still photographs and high-frame-rate videos. A parallel investigation evaluated the performance of a computational fluid dynamics (CFD) tool for the prediction of the reacting flow in a liquid fueled combustor (e.g., TVC) that uses water injection for control of pollutant emissions and turbine inlet temperature. Generally, reasonable agreement is found between data and NO(x) computations. Based on a study assessing the feasibility and performance impact of using water injection on a Boeing 747-400 aircraft to reduce NO(x) emissions during takeoff, retrofitting does not appear to be cost effective; however, an operator of a newly designed engine and airframe might be able to save up to 1.0 percent in operating costs. Other challenges of water injection will be discussed.

Evolution of an electron plasma vortex in a strain flow

Science.gov (United States)

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.

Core Noise: Overview of Upcoming LDI Combustor Test

Science.gov (United States)

Hultgren, Lennart S.

2012-01-01

This presentation is a technical summary of and outlook for NASA-internal and NASA-sponsored external research on core (combustor and turbine) noise funded by the Fundamental Aeronautics Program Fixed Wing Project. The presentation covers: the emerging importance of core noise due to turbofan design trends and its relevance to the NASA N+3 noise-reduction goal; the core noise components and the rationale for the current emphasis on combustor noise; and the current and planned research activities in the combustor-noise area. Two NASA-sponsored research programs, with particular emphasis on indirect combustor noise, "Acoustic Database for Core Noise Sources", Honeywell Aerospace (NNC11TA40T) and "Measurement and Modeling of Entropic Noise Sources in a Single-Stage Low-Pressure Turbine", U. Illinois/U. Notre Dame (NNX11AI74A) are briefly described. Recent progress in the development of CMC-based acoustic liners for broadband noise reduction suitable for turbofan-core application is outlined. Combustor-design trends and the potential impacts on combustor acoustics are discussed. A NASA GRC developed nine-point lean-direct-injection (LDI) fuel injector is briefly described. The modification of an upcoming thermo-acoustic instability evaluation of the GRC injector in a combustor rig to also provide acoustic information relevant to community noise is presented. The NASA Fundamental Aeronautics Program has the principal objective of overcoming today's national challenges in air transportation. The reduction of aircraft noise is critical to enabling the anticipated large increase in future air traffic. The Quiet Performance Research Theme of the Fixed Wing Project aims to develop concepts and technologies to dramatically reduce the perceived community noise attributable to aircraft with minimal impact on weight and performance.

Dust trapping by vortices in transitional disks: evidence for non-ideal magnetohydrodynamic effects in protoplanetary disks

International Nuclear Information System (INIS)

Zhu, Zhaohuan; Stone, James M.

2014-01-01

We study particle trapping at the edge of a gap opened by a planet in a protoplanetary disk. In particular, we explore the effects of turbulence driven by the magnetorotational instability on particle trapping, using global three-dimensional magnetohydrodynamic (MHD) simulations including Lagrangian dust particles. We study disks either in the ideal MHD limit or dominated by ambipolar diffusion (AD) which plays an essential role at the outer regions of a protoplanetary disk. With ideal MHD, strong turbulence (the equivalent viscosity parameter α ∼ 10 –2 ) in disks prevents vortex formation at the edge of the gap opened by a 9 M J planet, and most particles (except the particles that drift fastest) pile up at the outer gap edge almost axisymmetrically. When AD is considered, turbulence is significantly suppressed (α ≲ 10 –3 ), and a large vortex forms at the edge of the planet induced gap, which survives ∼1000 orbits. The vortex can efficiently trap dust particles that span 3 orders of magnitude in size within 100 planetary orbits. We have also carried out two-dimensional hydrodynamical (HD) simulations using viscosity as an approximation to MHD turbulence. These HD simulations can reproduce vortex generation at the gap edge as seen in MHD simulations. Finally, we use our simulation results to generate synthetic images for ALMA dust continuum observations on Oph IRS 48 and HD 142527, which show good agreement with existing observations. Predictions for future ALMA cycle 2 observations have been made. We conclude that the asymmetry in ALMA observations can be explained by dust trapping vortices and the existence of vortices could be the evidence that the outer protoplanetary disks are dominated by AD with α < 10 –3 at the disk midplane.

Micro-mixer/combustor

KAUST Repository

Badra, Jihad Ahmad; Masri, Assaad Rachid

2014-01-01

A micro-mixer/combustor to mix fuel and oxidant streams into combustible mixtures where flames resulting from combustion of the mixture can be sustained inside its combustion chamber is provided. The present design is particularly suitable

Near-field multiple traps of paraxial acoustic vortices with strengthened gradient force generated by sector transducer array

Science.gov (United States)

Wang, Qingdong; Li, Yuzhi; Ma, Qingyu; Guo, Gepu; Tu, Juan; Zhang, Dong

2018-01-01

In order to improve the capability of particle trapping close to the source plane, theoretical and experimental studies on near-field multiple traps of paraxial acoustic vortices (AVs) with a strengthened acoustic gradient force (AGF) generated by a sector transducer array were conducted. By applying the integration of point source radiation, numerical simulations for the acoustic fields generated by the sector transducer array were conducted and compared with those produced by the circular transducer array. It was proved that strengthened AGFs of near-field multiple AVs with higher peak pressures and smaller vortex radii could be produced by the sector transducer array with a small topological charge. The axial distributions of the equivalent potential gradient indicated that the AGFs of paraxial AVs in the near field were much higher than those in the far field, and the distances at the near-field vortex antinodes were also proved to be the ideal trapping positions with relatively higher AGFs. With the established 8-channel AV generation system, theoretical studies were also verified by the experimental measurements of pressure and phase for AVs with various topological charges. The formation of near-field multiple paraxial AVs was verified by the cross-sectional circular pressure distributions with perfect phase spirals around central pressure nulls, and was also proved by the vortex nodes and antinodes along the center axis. The favorable results demonstrated the feasibility of generating near-field multiple traps of paraxial AVs with strengthened AGF using the sector transducer array, and suggested the potential applications of close-range particle trapping in biomedical engineering.

System and method for reducing combustion dynamics in a combustor

Science.gov (United States)

Uhm, Jong Ho; Ziminsky, Willy Steve; Johnson, Thomas Edward; Srinivasan, Shiva; York, William David

2016-11-29

A system for reducing combustion dynamics in a combustor includes an end cap that extends radially across the combustor and includes an upstream surface axially separated from a downstream surface. A combustion chamber is downstream of the end cap, and tubes extend from the upstream surface through the downstream surface. Each tube provides fluid communication through the end cap to the combustion chamber. The system further includes means for reducing combustion dynamics in the combustor. A method for reducing combustion dynamics in a combustor includes flowing a working fluid through tubes that extend axially through an end cap that extends radially across the combustor and obstructing at least a portion of the working fluid flowing through a first set of the tubes.

High-speed laser diagnostics for the study of flame dynamics in a lean premixed gas turbine model combustor

Science.gov (United States)

Boxx, Isaac; Arndt, Christoph M.; Carter, Campbell D.; Meier, Wolfgang

2012-03-01

A series of measurements was taken on two technically premixed, swirl-stabilized methane-air flames (at overall equivalence ratios of ϕ = 0.73 and 0.83) in an optically accessible gas turbine model combustor. The primary diagnostics used were combined planar laser-induced fluorescence of the OH radical and stereoscopic particle image velocimetry (PIV) with simultaneous repetition rates of 10 kHz and a measurement duration of 0.8 s. Also measured were acoustic pulsations and OH chemiluminescence. Analysis revealed strong local periodicity in the thermoacoustically self-excited (or ` noisy') flame (ϕ = 0.73) in the regions of the flow corresponding to the inner shear layer and the jet-inflow. This periodicity appears to be the result of a helical precessing vortex core (PVC) present in that region of the combustor. The PVC has a precession frequency double (at 570 Hz) that of the thermo-acoustic pulsation (at 288 Hz). A comparison of the various data sets and analysis techniques applied to each flame suggests a strong coupling between the PVC and the thermo-acoustic pulsation in the noisy flame. Measurements of the stable (` quiet') flame (ϕ = 0.83) revealed a global fluctuation in both velocity and heat-release around 364 Hz, but no clear evidence of a PVC.

Influence of the shear flow on electron cyclotron resonance plasma confinement in an axisymmetric magnetic mirror trap of the electron cyclotron resonance ion source.

Science.gov (United States)

Izotov, I V; Razin, S V; Sidorov, A V; Skalyga, V A; Zorin, V G; Bagryansky, P A; Beklemishev, A D; Prikhodko, V V

2012-02-01

Influence of shear flows of the dense plasma created under conditions of the electron cyclotron resonance (ECR) gas breakdown on the plasma confinement in the axisymmetric mirror trap ("vortex" confinement) was studied experimentally and theoretically. A limiter with bias potential was set inside the mirror trap for plasma rotation. The limiter construction and the optimal value of the potential were chosen according to the results of the preliminary theoretical analysis. This method of "vortex" confinement realization in an axisymmetric mirror trap for non-equilibrium heavy-ion plasmas seems to be promising for creation of ECR multicharged ion sources with high magnetic fields, more than 1 T.

Influence of the shear flow on electron cyclotron resonance plasma confinement in an axisymmetric magnetic mirror trap of the electron cyclotron resonance ion source

International Nuclear Information System (INIS)

Izotov, I. V.; Razin, S. V.; Sidorov, A. V.; Skalyga, V. A.; Zorin, V. G.; Bagryansky, P. A.; Beklemishev, A. D.; Prikhodko, V. V.

2012-01-01

Influence of shear flows of the dense plasma created under conditions of the electron cyclotron resonance (ECR) gas breakdown on the plasma confinement in the axisymmetric mirror trap (''vortex'' confinement) was studied experimentally and theoretically. A limiter with bias potential was set inside the mirror trap for plasma rotation. The limiter construction and the optimal value of the potential were chosen according to the results of the preliminary theoretical analysis. This method of ''vortex'' confinement realization in an axisymmetric mirror trap for non-equilibrium heavy-ion plasmas seems to be promising for creation of ECR multicharged ion sources with high magnetic fields, more than 1 T.

Method for controlling incineration in combustor for radioactive wastes

International Nuclear Information System (INIS)

Takaoku, Y.; Uehara, A.

1991-01-01

This invention relates to a method for controlling incineration in a combustor for low-level radioactive wastes. In particular, it relates to a method for economizing in the consumption of supplemental fuel while maintaining a stable incineration state by controlling the amount of fuel and of radioactive wastes fed to the combustor. The amount of fuel supplied is determined by the outlet gas temperature of the combustor. (L.L.)

Single particle behaviour in circulating fluidized bed combustors

DEFF Research Database (Denmark)

Erik Weinell, Claus

1994-01-01

An investigation of single particle behaviour in a circulating fluidized bed combustor is described, relating to sulphur capture reactions by limestone under alternate oxidizing and reducing conditions present in a circulating fluidized bed combustor, and to the devolatilization and burn out...

Hypersonic Combustor Model Inlet CFD Simulations and Experimental Comparisons

Science.gov (United States)

Venkatapathy, E.; TokarcikPolsky, S.; Deiwert, G. S.; Edwards, Thomas A. (Technical Monitor)

1995-01-01

Numerous two-and three-dimensional computational simulations were performed for the inlet associated with the combustor model for the hypersonic propulsion experiment in the NASA Ames 16-Inch Shock Tunnel. The inlet was designed to produce a combustor-inlet flow that is nearly two-dimensional and of sufficient mass flow rate for large scale combustor testing. The three-dimensional simulations demonstrated that the inlet design met all the design objectives and that the inlet produced a very nearly two-dimensional combustor inflow profile. Numerous two-dimensional simulations were performed with various levels of approximations such as in the choice of chemical and physical models, as well as numerical approximations. Parametric studies were conducted to better understand and to characterize the inlet flow. Results from the two-and three-dimensional simulations were used to predict the mass flux entering the combustor and a mass flux correlation as a function of facility stagnation pressure was developed. Surface heat flux and pressure measurements were compared with the computed results and good agreement was found. The computational simulations helped determine the inlet low characteristics in the high enthalpy environment, the important parameters that affect the combustor-inlet flow, and the sensitivity of the inlet flow to various modeling assumptions.

Vortices in trapped Bose-Einstein condensates

International Nuclear Information System (INIS)

Jackson, B.

2000-09-01

In this thesis we solve the Gross-Pitaevskii equation numerically in order to model the response of trapped Bose-Einstein condensed gases to perturbations by electromagnetic fields. First, we simulate output coupling of pulses from the condensate and compare our results to experiments. The excitation and separation of eigenmodes on flow through a constriction is also studied. We then move on to the main theme of this thesis: the important subject of quantised vortices in Bose condensates, and the relation between Bose-Einstein condensation and superfluidity. We propose methods of producing vortex pairs and rings by controlled motion of objects. Full three-dimensional simulations under realistic experimental conditions are performed in order to test the validity of these ideas. We link vortex formation to drag forces on the object, which in turn is connected with energy transfer to the condensate. We therefore argue that vortex formation by moving objects is intimately related to the onset of dissipation in superfluids. We discuss this idea in the context of a recent experiment, using simulations to provide evidence of vortex formation in the experimental scenario. Superfluidity is also manifest in the property of persistent currents, which is linked to vortex stability and dynamics. We simulate vortex line and ring motion, and find in both cases precessional motion and thermodynamic instability to dissipation. Strictly speaking, the Gross-Pitaevskii equation is valid only for temperatures far below the BEC transition. We end the thesis by describing a simple finite-temperature model to describe mean-field coupling between condensed and non-condensed components of the gas. We show that our hybrid Monte-Carlo/FFT technique can describe damping of the lowest energy excitations of the system. Extensions to this model and future research directions are discussed in the conclusion. (author)

Turbine combustor with fuel nozzles having inner and outer fuel circuits

Science.gov (United States)

Uhm, Jong Ho; Johnson, Thomas Edward; Kim, Kwanwoo

2013-12-24

A combustor cap assembly for a turbine engine includes a combustor cap and a plurality of fuel nozzles mounted on the combustor cap. One or more of the fuel nozzles would include two separate fuel circuits which are individually controllable. The combustor cap assembly would be controlled so that individual fuel circuits of the fuel nozzles are operated or deliberately shut off to provide for physical separation between the flow of fuel delivered by adjacent fuel nozzles and/or so that adjacent fuel nozzles operate at different pressure differentials. Operating a combustor cap assembly in this fashion helps to reduce or eliminate the generation of undesirable and potentially harmful noise.

Optimal combustor dimensions for the catalytic combustion of methane-air mixtures in micro-channels

International Nuclear Information System (INIS)

Chen, Junjie; Song, Wenya; Xu, Deguang

2017-01-01

Highlights: • The effect of combustor dimensions on the combustion stability was elucidated. • Wall thermal properties are important for optimizing combustor dimensions. • The optimal wall thickness increases with flow velocity. • The optimal combustor length depends on the wall thermal conductivity. • Stability diagrams were constructed and design recommendations were made. - Abstract: This paper addresses the question of choosing appropriate combustor dimensions for the self-sustained catalytic combustion in parallel plate micro-channels. The combustion characteristics and stability of methane-air mixtures over platinum in catalytic micro-combustors were studied, using a two-dimensional computational fluid dynamics (CFD) model with detailed chemistry and transport. The effects of gap size, wall thickness, and combustor length on the combustion stability and combustor performance were explored to provide guidelines for optimal design of combustor dimensions. Combustion stability diagrams were constructed, and design recommendations were made. The effect of wall thermal conductivity on the mechanisms of extinction and blowout, and its implications on optimal combustor geometry were studied. It was shown that combustor dimensions are vital in determining the combustion stability of the system. The choice of appropriate combustor dimensions is crucial in achieving stable combustion, due to a rather narrow operating space determined by stability, material, and conversion constraints. The optimal gap size depends on whether the flow velocity or flow rate is kept constant. For most practical wall materials in the range of metals to highly conductive ceramics, larger combustors are more stable at a fixed flow velocity, whereas smaller combustors are recommended for a fixed flow rate at the expense of hot spots. The optimal wall thickness increases with flow velocity. Higher flow velocities can be sustained in combustors with low-conductivity materials using

Vortex-induced phase slip dissipation in a torioidal Bose-Einstein condensate flowing through a barrier

Energy Technology Data Exchange (ETDEWEB)

Collins, Lee A [Los Alamos National Laboratory

2009-01-01

We study the phase slips superfluid dissipation mechanism with a BEC flowing through a repulsive barrier inside a torus. The barrier is adiabatically raised across the annulus while the condensate is flowing with a finite quantized angular momentum. We found that, at a critical height, a vortex reaches the barrier moving radially from the inner region to eventually circulate along the annulus. At a slightly higher barrier, an anti-vortex also enters into the annulus from the outward region. The vortex and anti-vortex decrease the total angular momentum by leaving behind their respective paths a 2{pi} phase slip. When they collide or orbit along the same loop, the condensate suffers a global 2{pi} phase slip and the total angular momentum decreases by one quantum. The analysis is based on numerical simulations of the dynamical Gross-Pitaevskii equation both in two- and three-dimensions, the latter with the experimental parameters of the torus trap recently created at the NIST institute.

Development of a catalytically assisted combustor for a gas turbine

Energy Technology Data Exchange (ETDEWEB)

Ozawa, Yasushi; Fujii, Tomoharu; Sato, Mikio [Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa 240-01 (Japan); Kanazawa, Takaaki; Inoue, Hitoshi [Kansai Electric Power Company, Inc., 3-11-20 Nakoji, Amagasaki, Hyoho 661 (Japan)

1999-01-01

A catalytically assisted low NO{sub x} combustor has been developed which has the advantage of catalyst durability. This combustor is composed of a burner section and a premixed combustion section behind the burner section. The burner system consists of six catalytic combustor segments and six premixing nozzles, which are arranged alternately and in parallel. Fuel flow rate for the catalysts and the premixing nozzles are controlled independently. The catalytic combustion temperature is maintained under 1000C, additional premixed gas is injected from the premixing nozzles into the catalytic combustion gas, and lean premixed combustion at 1300C is carried out in the premixed combustion section. This system was designed to avoid catalytic deactivation at high temperature and thermal or mechanical shock fracture of the honeycomb monolith. In order to maintain the catalyst temperature under 1000C, the combustion characteristics of catalysts at high pressure were investigated using a bench scale reactor and an improved catalyst was selected for the combustor test. A combustor for a 20MW class multi-can type gas turbine was designed and tested under high pressure conditions using LNG fuel. Measurements of NO{sub x}, CO and unburned hydrocarbon were made and other measurements were made to evaluate combustor performance under various combustion temperatures and pressures. As a result of the tests, it was proved that NO{sub x} emission was lower than 10ppm converted at 16% O{sub 2}, combustion efficiency was almost 100% at 1300C of combustor outlet temperature and 13.5ata of combustor inlet pressure

Variable volume combustor with a conical liner support

Science.gov (United States)

Johnson, Thomas Edward; McConnaughhay, Johnie Franklin; Keener, Chrisophter Paul; Ostebee, Heath Michael

2017-06-27

The present application provides a variable volume combustor for use with a gas turbine engine. The variable volume combustor may include a liner, a number of micro-mixer fuel nozzles positioned within the liner, and a conical liner support supporting the liner.

Pumping vortex into a Bose-Einstein condensate of heteronuclear molecules

International Nuclear Information System (INIS)

Xu, Z F; Wang, R Q; You, L

2009-01-01

Heteronuclear molecules have attracted wide attention due to their permanent electric dipole moments. Analogous to atoms with magnetic dipoles, the existence of nonzero electric dipoles significantly enhances the possibilities and mechanisms for the control and design of quantum degenerate molecule systems with electric (E) fields. This work proposes a vortex creation mechanism inside a condensate of heteronuclear molecules through the adiabatic flipping of the axial bias of an analogous E-field Ioffe-Pritchard trap (IPT), extending the original protocol of Isoshima et al (2000 Phys. Rev. A 61 063610) for an atomic spinor condensate inside a magnetic (B)-field IPT. We provide both analytic proof and numerical simulations to illustrate the high fidelity operation of this vortex pump protocol. We hope our work provides stimulating experimental possibilities for active investigations in quantum degenerate molecule systems.

Design and fabrication of a 50 MWt prototypical MHD coal-fired combustor

International Nuclear Information System (INIS)

Albright, J.; Braswell, R.; Listvinsky, G.; McAllister, M.; Myrick, S.; Ono, D.; Thom, H.

1992-01-01

A prototypical 50 MWt coal-fired combustor has been designed and fabricated as part of the Magnetohydrodynamic (MHD) Integrated Topping Cycle (ITC) Program. This is a DOE-funded program to develop a prototypical MHD power train to be tested at the Component Development and Integration Facility (CDIF) in Butte, Montana. The prototypical combustor is an outgrowth of the 50 MWt workhorse combustor which has previously been tested at the CDIF. In addition to meeting established performance criteria of the existing 50 MWt workhorse combustor, the prototypical combustor design is required to be scaleable for use at the 250 MWt retrofit level. This paper presents an overview of the mechanical design of the prototypical combustor and a description of its fabrication. Fabrication of the 50 MWt prototypical coal-fired combustor was completed in February 1992 and hot-fire testing is scheduled to begin in May 1992

Parametric Study of Pulse-Combustor-Driven Ejectors at High-Pressure

Science.gov (United States)

Yungster, Shaye; Paxson, Daniel E.; Perkins, Hugh D.

2015-01-01

Pulse-combustor configurations developed in recent studies have demonstrated performance levels at high-pressure operating conditions comparable to those observed at atmospheric conditions. However, problems related to the way fuel was being distributed within the pulse combustor were still limiting performance. In the first part of this study, new configurations are investigated computationally aimed at improving the fuel distribution and performance of the pulse-combustor. Subsequent sections investigate the performance of various pulse-combustor driven ejector configurations operating at highpressure conditions, focusing on the effects of fuel equivalence ratio and ejector throat area. The goal is to design pulse-combustor-ejector configurations that maximize pressure gain while achieving a thermal environment acceptable to a turbine, and at the same time maintain acceptable levels of NOx emissions and flow non-uniformities. The computations presented here have demonstrated pressure gains of up to 2.8%.

Simulation of the flow inside an annular can combustor

OpenAIRE

Alqaraghuli, W; Alkhafagiy, D; Shires, A

2014-01-01

In the gas turbine combustion system, the external flows in annuli play one of the key roles in controlling pressure loss, air flow distribution around the combustor liner, and the attendant effects on performance, durability, and stability.  This paper describes a computational fluid dynamics (CFD) simulation of the flow in the outer annulus of a can combustor. Validating this simulation was done with experimental results obtained from analyzing the flow inside a can combustor annulus that w...

The interaction of counter-rotating strained vortex pairs with a third vortex

International Nuclear Information System (INIS)

Higgins, Keith; Ooi, Andrew; Chong, M S; Ruetten, Markus

2009-01-01

The vortex dynamics caused by the interaction of counter-rotating Burgers vortex pairs with a third Burgers vortex in a straining flow is investigated numerically. These interactions blend vortex merging and cancellation effects, and the aim is to investigate how the third vortex might influence the evolution of the vortex pair. Many different choices of initial conditions for the pair and third vortex exist, so attention is restricted to a class of initial conditions in which the vortex pair initially moves in the general direction of vortex 3, and the distance from vortex 3 to the line of free propagation of the vortex pair is the 'offset' parameter δ. A series of calculations with 0≤δ≤4 reveals three types of intermediate-time vortex dynamics that are called merging, swapping and switching. The evolution of the vortex core separation and core vorticity level diagnostics are used to determine the points of transition from merging to swapping and switching. In the longer term, vortex merging, cancellation and straining reduces the three vortices to a single vortex. Other diagnostics of interest are also monitored, including the spatial distributions of the rate of viscous dissipation and terms contributing to the vorticity transport equation. During the merging phase for the case with δ=0, double-peak and double-trough structures are observed in the dissipation-rate contours. In addition, the diffusion of vorticity dominates the vortex-stretching effect near vortex 1 during its absorbtion by vortex 3. Finally, the dynamics of the three vortices are also examined by computing a co-rotating angular velocity and stream function. A series of peaks in the co-rotating angular velocity is found to be associated with the conservation of angular momentum and interactions with a 'ghost' vortex in the co-rotating stream function.

Combustion Dynamics in Multi-Nozzle Combustors Operating on High-Hydrogen Fuels

Energy Technology Data Exchange (ETDEWEB)

Santavicca, Dom; Lieuwen, Tim

2013-09-30

Actual gas turbine combustors for power generation applications employ multi-nozzle combustor configurations. Researchers at Penn State and Georgia Tech have extended previous work on the flame response in single-nozzle combustors to the more realistic case of multi-nozzle combustors. Research at Georgia Tech has shown that asymmetry of both the flow field and the acoustic forcing can have a significant effect on flame response and that such behavior is important in multi-flame configurations. As a result, the structure of the flame and its response to forcing is three-dimensional. Research at Penn State has led to the development of a three-dimensional chemiluminescence flame imaging technique that can be used to characterize the unforced (steady) and forced (unsteady) flame structure of multi-nozzle combustors. Important aspects of the flame response in multi-nozzle combustors which are being studied include flame-flame and flame-wall interactions. Research at Penn State using the recently developed three-dimensional flame imaging technique has shown that spatial variations in local flame confinement must be accounted for to accurately predict global flame response in a multi-nozzle can combustor.

Computer simulation of vortex pinning in type II superconductors. II. Random point pins

International Nuclear Information System (INIS)

Brandt, E.H.

1983-01-01

Pinning of vortices in a type II superconductor by randomly positioned identical point pins is simulated using the two-dimensional method described in a previous paper (Part I). The system is characterized by the vortex and pin numbers (N/sub v/, N/sub p/), the vortex and pin interaction ranges (R/sub v/, R/sub p/), and the amplitude of the pin potential A/sub p/. The computation is performed for many cases: dilute or dense, sharp or soft, attractive or repulsive, weak or strong pins, and ideal or amorphous vortex lattice. The total pinning force F as a function of the mean vortex displacment X increases first linearly (over a distance usually much smaller than the vortex spacing and than R/sub p/) and then saturates, fluctuating about its averaging F-bar. We interpret F-bar as the maximum pinning force j/sub c/B of a large specimen. For weak pins the prediction of Larkin and Ovchinnikov for two-dimensional collective pinning is confirmed: F-bar = const. iW/R/sub p/c 66 , where W-bar is the mean square pinning force and c 66 is the shear modulus of the vortex lattice. If the initial vortex lattice is chosen highly defective (''amorphous'') the constant is 1.3--3 times larger than for the ideal triangular lattice. This finding may explain the often observed ''history effect.'' The function F-bar(A/sub p/) exhibits a jump, which for dilute, sharp, attractive pins occurs close to the ''threshold value'' predicted for isolated pins by Labusch. This jump reflects the onset of plastic deformation of the vortex lattice, and in some cases of vortex trapping, but is not a genuine threshold

Compressible Vortex Ring

Science.gov (United States)

Elavarasan, Ramasamy; Arakeri, Jayawant; Krothapalli, Anjaneyulu

1999-11-01

The interaction of a high-speed vortex ring with a shock wave is one of the fundamental issues as it is a source of sound in supersonic jets. The complex flow field induced by the vortex alters the propagation of the shock wave greatly. In order to understand the process, a compressible vortex ring is studied in detail using Particle Image Velocimetry (PIV) and shadowgraphic techniques. The high-speed vortex ring is generated from a shock tube and the shock wave, which precedes the vortex, is reflected back by a plate and made to interact with the vortex. The shadowgraph images indicate that the reflected shock front is influenced by the non-uniform flow induced by the vortex and is decelerated while passing through the vortex. It appears that after the interaction the shock is "split" into two. The PIV measurements provided clear picture about the evolution of the vortex at different time interval. The centerline velocity traces show the maximum velocity to be around 350 m/s. The velocity field, unlike in incompressible rings, contains contributions from both the shock and the vortex ring. The velocity distribution across the vortex core, core diameter and circulation are also calculated from the PIV data.

DART Core/Combustor-Noise Initial Test Results

Science.gov (United States)

Boyle, Devin K.; Henderson, Brenda S.; Hultgren, Lennart S.

2017-01-01

Contributions from the combustor to the overall propulsion noise of civilian transport aircraft are starting to become important due to turbofan design trends and advances in mitigation of other noise sources. Future propulsion systems for ultra-efficient commercial air vehicles are projected to be of increasingly higher bypass ratio from larger fans combined with much smaller cores, with ultra-clean burning fuel-flexible combustors. Unless effective noise-reduction strategies are developed, combustor noise is likely to become a prominent contributor to overall airport community noise in the future. The new NASA DGEN Aero0propulsion Research Turbofan (DART) is a cost-efficient testbed for the study of core-noise physics and mitigation. This presentation gives a brief description of the recently completed DART core combustor-noise baseline test in the NASA GRC Aero-Acoustic Propulsion Laboratory (AAPL). Acoustic data was simultaneously acquired using the AAPL overhead microphone array in the engine aft quadrant far field, a single midfield microphone, and two semi-infinite-tube unsteady pressure sensors at the core-nozzle exit. An initial assessment shows that the data is of high quality and compares well with results from a quick 2014 feasibility test. Combustor noise components of measured total-noise signatures were educed using a two-signal source-separation method an dare found to occur in the expected frequency range. The research described herein is aligned with the NASA Ultra-Efficient Commercial Transport strategic thrust and is supported by the NASA Advanced Air Vehicle Program, Advanced Air Transport Technology Project, under the Aircraft Noise Reduction Subproject.

Magnetospheric Multiscale Observations of Electron Vortex Magnetic Hole in the Turbulent Magnetosheath Plasma

Energy Technology Data Exchange (ETDEWEB)

Huang, S. Y.; Yuan, Z. G.; Wang, D. D.; Yu, X. D. [School of Electronic Information, Wuhan University, Wuhan (China); Sahraoui, F.; Contel, O. Le [Laboratoire de Physique des Plasmas, CNRS-Ecole Polytechnique-UPMC, Palaiseau (France); He, J. S. [School of Earth and Space Sciences, Peking University, Beijing (China); Zhao, J. S. [Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing (China); Deng, X. H.; Pang, Y.; Li, H. M. [Institute of Space Science and Technology, Nanchang University, Nanchang (China); Zhou, M. [Department of Physics and Astronomy, University of California, Los Angeles, CA (United States); Fu, H. S.; Yang, J. [School of Space and Environment, Beihang University, Beijing (China); Shi, Q. Q. [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai (China); Lavraud, B. [Institut de Recherche and Astrophysique et Planétologie, Université de Toulouse (UPS), Toulouse (France); Pollock, C. J.; Giles, B. L. [NASA, Goddard Space Flight Center, Greenbelt, MD (United States); Torbert, R. B. [University of New Hampshire, Durham, NH (United States); Russell, C. T., E-mail: shiyonghuang@whu.edu.cn [Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA (United States); and others

2017-02-20

We report on the observations of an electron vortex magnetic hole corresponding to a new type of coherent structure in the turbulent magnetosheath plasma using the Magnetospheric Multiscale mission data. The magnetic hole is characterized by a magnetic depression, a density peak, a total electron temperature increase (with a parallel temperature decrease but a perpendicular temperature increase), and strong currents carried by the electrons. The current has a dip in the core region and a peak in the outer region of the magnetic hole. The estimated size of the magnetic hole is about 0.23 ρ {sub i} (∼30 ρ {sub e}) in the quasi-circular cross-section perpendicular to its axis, where ρ {sub i} and ρ {sub e} are respectively the proton and electron gyroradius. There are no clear enhancements seen in high-energy electron fluxes. However, there is an enhancement in the perpendicular electron fluxes at 90° pitch angle inside the magnetic hole, implying that the electrons are trapped within it. The variations of the electron velocity components V {sub em} and V {sub en} suggest that an electron vortex is formed by trapping electrons inside the magnetic hole in the cross-section in the M – N plane. These observations demonstrate the existence of a new type of coherent structures behaving as an electron vortex magnetic hole in turbulent space plasmas as predicted by recent kinetic simulations.

Design Optimization of a Micro-Combustor for Lean, Premixed Fuel-Air Mixtures

Science.gov (United States)

Powell, Leigh Theresa

Present technology has been shifting towards miniaturization of devices for energy production for portable electronics. Micro-combustors, when incorporated into a micro-power generation system, provide the energy desired in the form of hot gases to power such technology. This creates the need for a design optimization of the micro-combustor in terms of geometry, fuel choice, and material selection. A total of five micro-combustor geometries, three fuels, and three materials were computationally simulated in different configurations in order to determine the optimal micro-combustor design for highest efficiency. Inlet velocity, equivalence ratio, and wall heat transfer coefficient were varied in order to test a comprehensive range of micro-combustor parameters. All simulations completed for the optimization study used ANSYS Fluent v16.1 and post-processing of the data was done in CFD Post v16.1. It was found that for lean, premixed fuel-air mixtures (φ = 0.6 - 0.9) ethane (C 2H6) provided the highest flame temperatures when ignited within the micro-combustor geometries. An aluminum oxide converging micro-combustor burning ethane and air at an equivalence ratio of 0.9, an inlet velocity of 0.5 m/s, and heat transfer coefficient of 5 W/m2-K was found to produce the highest combustor efficiency, making it the optimal choice for a micro-combustor design. It is proposed that this geometry be experimentally and computationally investigated further in order to determine if additional optimization can be achieved.

Effect of boundary conditions on downstream vorticity from counter-rotating swirlers

Directory of Open Access Journals (Sweden)

Weiye Huo

2015-02-01

Full Text Available Particle image velocimetry (PIV is utilized to measure the non-reacting flow field in a reflow combustor with multiple and single swirlers. The velocity field, vortex structure and total vorticity levels are experimentally obtained using two different boundary conditions, representing a single confined swirler and multiple swirlers in an annular combustor. The influence of the boundary conditions on the flow field at several locations downstream of the swirlers is experimentally investigated, showing that the central vortex in the multi-swirler case is more concentrated than in the single-swirler case. The vorticity of the central vortex and average cross-sectional vorticity are relatively low at the swirler outlet in both cases. Both of these statistics gradually increase to the maximum values near 20 mm downstream of the swirler outlet, and subsequently decrease. It is also found that the central vortex in the multi-swirler case is consistently greater than the single-swirler case. These results demonstrate the critical influence of boundary conditions on flow characteristic of swirling flow, providing insight into the difference of the experiments on test-bed combustor and the full-scale annular combustors.

Experimental study on premixed CH{sub 4}/air mixture combustion in micro Swiss-roll combustors

Energy Technology Data Exchange (ETDEWEB)

Zhong, Bei-Jing; Wang, Jian-Hua [Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics, Tsinghua University, Beijing 100084 (China)

2010-12-15

Excess enthalpy combustion is a promising approach to stabilize flame in micro-combustors. Using a Swiss-roll combustor configuration, excess enthalpy combustion can be conveniently achieved. In this work, three types of Swiss-roll combustors with double spiral-shaped channels were designed and fabricated. The combustors were tested using methane/air mixtures of various equivalence ratios. Both temperature distributions and extinction limits were determined for each combustor configuration at different methane mass flow rates. Results indicate that the Swiss-roll combustors developed in the current study greatly enhance combustion stability in center regions of the combustors. At the same time, excess enthalpy combustors of the Swiss-roll configuration significantly extend the extinction limits of methane/air mixtures. In addition, the effects of combustor configurations and thermal insulation arrangements on temperature distributions and extinction limits were evaluated. With heat losses to the environment being significant, the use of thermal insulations further enhances the flame stability in center regions of the Swiss-roll combustors and extends flammable ranges. (author)

Vortex configuration and vortex-vortex interaction in nano-structured superconductors

International Nuclear Information System (INIS)

Kato, Masaru; Niwa, Yuhei; Suematsu, Hisataka; Ishida, Takekazu

2012-01-01

We study the vortex structures and quasi-particle structures in nano-structured superconductors. We used the Bogoliubov-de Gennes equation and the finite element method and obtained stable magnetic flux structures and the quasi-particle states. We found the vortex configurations are affected by the interference of the quasi-particle bound states around the vortices. In order to clarify the interference between the quasi-particle wave-functions around two vortices we have developed a numerical method using the elliptic coordinates and the Mathieu functions. We apply this method to two singly quantized vortex state in a conventional s-wave superconductor and a pair of half-quantum vortices in a chiral p-wave superconductor.

Alternate-Fueled Combustor-Sector Performance—Part A: Combustor Performance and Part B: Combustor Emissions

OpenAIRE

Shouse, D. T.; Neuroth, C.; Hendricks, R. C.; Lynch, A.; Frayne, C. W.; Stutrud, J. S.; Corporan, E.; Hankins, Capt. T.

2012-01-01

Alternate aviation fuels for military or commercial use are required to satisfy MIL-DTL-83133F or ASTM D 7566 standards, respectively, and are classified as “drop-in’’ fuel replacements. To satisfy legacy issues, blends to 50% alternate fuel with petroleum fuels are acceptable. Adherence to alternate fuels and fuel blends requires “smart fueling systems’’ or advanced fuel-flexible systems, including combustors and engines, without significant sacrifice in performance or emissions requirements...

PREFACE: Special section on vortex rings Special section on vortex rings

Science.gov (United States)

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

Hybrid Optical-Magnetic Traps for Studies of 2D Quantum Turbulence in Bose-Einstein Condensates

Science.gov (United States)

Myers, Jessica Ann

Turbulence appears in most natural and man-made flows. However, the analysis of turbulence is particularly difficult. Links between microscopic fluid dynamics and statistical signatures of turbulence appear unobtainable from the postulates of fluid dynamics making turbulence one of the most important unsolved theoretical problems in physics. Two-dimensional quantum turbulence (2DQT), an emerging field of study, involves turbulence in two-dimensional (2D) flows in superfluids, such as Bose-Einstein condensates (BECs). In 2D superfluids, a turbulent state can be characterized by a disordered distribution of numerous vortex cores. The question of how to effectively and efficiently generate turbulent states in superfluids is a fundamental question in the field of quantum turbulence. Therefore, experimental studies of vortex nucleation and the onset of turbulence in a superfluid are important for achieving a deeper understanding of the overall problem of turbulence. My PhD dissertation involves the study of vortex nucleation and the onset of turbulence in quasi-2D BECs. First, I discuss experimental apparatus advancements that now enable BECs to be created in a hybrid optical-magnetic trap, an atom trapping configuration conducive to 2DQT experiments. Next, I discuss the design and construction of a quantum vortex microscope and initial vortex detection tests. Finally, I present the first experiments aimed at studying 2DQT carried out in the updated apparatus. Thermal counterflow in superfluid helium, in which the normal and superfluid components flow in opposite directions, is known to create turbulence in the superfluid. However, this phenomenon has not been simulated or studied in dilute-gas BECs as a possible vortex nucleation method. In this dissertation, I present preliminary data from the first experiments aimed at understanding thermal counterflow turbulence in dilute-gas BECs.

Flame stabilization and mixing characteristics in a Stagnation Point Reverse Flow combustor

Science.gov (United States)

Bobba, Mohan K.

A novel combustor design, referred to as the Stagnation Point Reverse-Flow (SPRF) combustor, was recently developed that is able to operate stably at very lean fuel-air mixtures and with low NOx emissions even when the fuel and air are not premixed before entering the combustor. The primary objective of this work is to elucidate the underlying physics behind the excellent stability and emissions performance of the SPRF combustor. The approach is to experimentally characterize velocities, species mixing, heat release and flame structure in an atmospheric pressure SPRF combustor with the help of various optical diagnostic techniques: OH PLIF, chemiluminescence imaging, PIV and Spontaneous Raman Scattering. Results indicate that the combustor is primarily stabilized in a region downstream of the injector that is characterized by low average velocities and high turbulence levels; this is also the region where most of the heat release occurs. High turbulence levels in the shear layer lead to increased product entrainment levels, elevating the reaction rates and thereby enhancing the combustor stability. The effect of product entrainment on chemical timescales and the flame structure is illustrated with simple reactor models. Although reactants are found to burn in a highly preheated (1300 K) and turbulent environment due to mixing with hot product gases, the residence times are sufficiently long compared to the ignition timescales such that the reactants do not autoignite. Turbulent flame structure analysis indicates that the flame is primarily in the thin reaction zones regime throughout the combustor, and it tends to become more flamelet like with increasing distance from the injector. Fuel-air mixing measurements in case of non-premixed operation indicate that the fuel is shielded from hot products until it is fully mixed with air, providing nearly premixed performance without the safety issues associated with premixing. The reduction in NOx emissions in the SPRF

Josephson oscillation and self-trapping in momentum space

Science.gov (United States)

Zheng, Yi; Feng, Shiping; Yang, Shi-Jie

2018-04-01

The Creutz ladder model is studied in the presence of unconventional flux induced by complex tunneling rates along and between the two legs. In the vortex phase, the double-minima band structure is regarded as a double well. By introducing a tunable coupling between the two momentum minima, we demonstrate a phenomenon of Josephson oscillations in momentum space. The condensate density locked in one of the momentum valleys is referred to as macroscopic quantum self-trapping. The on-site interaction of the lattice provides an effective analogy to the double-well model within the two-mode approximation which allows for a quantitative understanding of the Josephson effect and the self-trapping in momentum space.

Variable volume combustor with nested fuel manifold system

Science.gov (United States)

McConnaughhay, Johnie Franklin; Keener, Christopher Paul; Johnson, Thomas Edward; Ostebee, Heath Michael

2016-09-13

The present application provides a combustor for use with a gas turbine engine. The combustor may include a number of micro-mixer fuel nozzles, a fuel manifold system in communication with the micro-mixer fuel nozzles to deliver a flow of fuel thereto, and a linear actuator to maneuver the micro-mixer fuel nozzles and the fuel manifold system.

Estimating the uncertainty in thermochemical calculations for oxygen-hydrogen combustors

Science.gov (United States)

Sims, Joseph David

The thermochemistry program CEA2 was combined with the statistical thermodynamics program PAC99 in a Monte Carlo simulation to determine the uncertainty in several CEA2 output variables due to uncertainty in thermodynamic reference values for the reactant and combustion species. In all, six typical performance parameters were examined, along with the required intermediate calculations (five gas properties and eight stoichiometric coefficients), for three hydrogen-oxygen combustors: a main combustor, an oxidizer preburner and a fuel preburner. The three combustors were analyzed in two different modes: design mode, where, for the first time, the uncertainty in thermodynamic reference values---taken from the literature---was considered (inputs to CEA2 were specified and so had no uncertainty); and data reduction mode, where inputs to CEA2 did have uncertainty. The inputs to CEA2 were contrived experimental measurements that were intended to represent the typical combustor testing facility. In design mode, uncertainties in the performance parameters were on the order of 0.1% for the main combustor, on the order of 0.05% for the oxidizer preburner and on the order of 0.01% for the fuel preburner. Thermodynamic reference values for H2O were the dominant sources of uncertainty, as was the assigned enthalpy for liquid oxygen. In data reduction mode, uncertainties in performance parameters increased significantly as a result of the uncertainties in experimental measurements compared to uncertainties in thermodynamic reference values. Main combustor and fuel preburner theoretical performance values had uncertainties of about 0.5%, while the oxidizer preburner had nearly 2%. Associated experimentally-determined performance values for all three combustors were 3% to 4%. The dominant sources of uncertainty in this mode were the propellant flowrates. These results only apply to hydrogen-oxygen combustors and should not be generalized to every propellant combination. Species for

Effect of ramp-cavity on hydrogen fueled scramjet combustor

Directory of Open Access Journals (Sweden)

J.V.S. Moorthy

2014-03-01

Full Text Available Sustained combustion and optimization of combustor are the two challenges being faced by combustion scientists working in the area of supersonic combustion. Thorough mixing, lower stagnation pressure losses, positive thrust and sustained combustion are the key issues in the field of supersonic combustion. Special fluid mechanism is required to achieve good mixing. To induce such mechanisms in supersonic inflows, the fuel injectors should be critically shaped incurring less flow losses. Present investigations are focused on the effect of fuel injection scheme on a model scramjet combustor performance. Ramps at supersonic flow generate axial vortices that help in macro-mixing of fuel with air. Interaction of shocks generated by ramps with the fuel stream generates boro-clinic torque at the air & liquid fuel interface, enhancing micro-mixing. Recirculation zones present in cavities increase the residence time of the combustible mixture. Making use of the advantageous features of both, a ramp-cavity combustor is designed. The combustor has two sections. First, constant height section consists of a backward facing step followed by ramps and cavities on both the top and bottom walls. The ramps are located alternately on top and bottom walls. The complete combustor width is utilized for the cavities. The second section of the combustor is diverging area section. This is provided to avoid thermal choking. In the present work gaseous hydrogen is considered as fuel. This study was mainly focused on the mixing characteristics of four different fuel injection locations. It was found that injecting fuel upstream of the ramp was beneficial from fuel spread point of view.

NONEQUILIBRIUM SULFUR CAPTURE & RETENTION IN AN AIR COOLED SLAGGING COAL COMBUSTOR

Energy Technology Data Exchange (ETDEWEB)

Bert Zauderer

2003-04-21

Calcium oxide injected in a slagging combustor reacts with the sulfur from coal combustion to form sulfur-bearing particles. The reacted particles impact and melt in the liquid slag layer on the combustor wall by the centrifugal force of the swirling combustion gases. Due to the low solubility of sulfur in slag, it must be rapidly drained from the combustor to limit sulfur gas re-evolution. Prior analyses and laboratory scale data indicated that for Coal Tech's 20 MMBtu/hour, air-cooled, slagging coal combustor slag mass flow rates in excess of 400 lb/hr should limit sulfur re-evolution. The objective of this 42-month project was to validate this sulfur-in-slag model in a group of combustor tests. A total of 36 days of testing on the combustor were completed during the period of performance of this project. This was more that double the 16 test days that were required in the original work statement. The extra tests were made possible by cost saving innovations that were made in the operation of the combustor test facility and in additional investment of Coal Tech resources in the test effort. The original project plan called for two groups of tests. The first group of tests involved the injection of calcium sulfate particles in the form of gypsum or plaster of Paris with the coal into the 20 MMBtu/hour-combustor. The second group of tests consisted of the entire two-step process, in which lime or limestone is co-injected with coal and reacts with the sulfur gas released during combustion to form calcium sulfate particles that impact and dissolve in the slag layer. Since this sulfur capture process has been validated in numerous prior tests in this combustor, the primary effort in the present project was on achieving the high slag flow rates needed to retain the sulfur in the slag.

ProFile Vortex and Vortex Blue Nickel-Titanium Rotary Instruments after Clinical Use.

Science.gov (United States)

Shen, Ya; Zhou, Huimin; Coil, Jeffrey M; Aljazaeri, Bassim; Buttar, Rene; Wang, Zhejun; Zheng, Yu-feng; Haapasalo, Markus

2015-06-01

The aim of this study was to analyze the incidence and mode of ProFile Vortex and Vortex Blue instrument defects after clinical use in a graduate endodontic program and to examine the impact of clinical use on the instruments' metallurgical properties. A total of 330 ProFile Vortex and 1136 Vortex Blue instruments from the graduate program were collected after each had been used in 3 teeth. The incidence and type of instrument defects were analyzed. The lateral surfaces and fracture surfaces of the fractured files were examined by using scanning electron microscopy. Unused and used instruments were examined by full and partial differential scanning calorimetry. No fractures were observed in the 330 ProFile Vortex instruments, whereas 20 (6.1%) revealed bent or blunt defects. Only 2 of the 1136 Vortex Blue files fractured during clinical use. The cause of fracture was shear stress. The fractures occurred at the tip end of the spirals. Only 1.8% (21 of 1136) of the Vortex Blue files had blunt tips. Austenite-finish temperatures were very similar for unused and used ProFile Vortex files and were all greater than 50°C. The austenite-finish temperatures of used and unused Vortex Blue files (38.5°C) were lower than those in ProFile Vortex instruments (P Vortex Blue files had an obvious 2-stage transformation, martensite-to-R phase and R-to-austenite phase. The trends of differential scanning calorimetry plots of unused Vortex Blue instruments and clinically used instruments were very similar. The risk of ProFile Vortex and Vortex Blue instrument fracture is very low when instruments are discarded after clinical use in the graduate endodontic program. The Vortex Blue files have metallurgical behavior different from ProFile Vortex instruments. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

The Instituto de Investigaciones Electricas fluidized bed combustor; El combustor de lecho fluidizado del Instituto de Investigaciones Electricas

Energy Technology Data Exchange (ETDEWEB)

Milan Foressi, Julio [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)

1991-12-31

After synthesizing the most important aspects of the combustion technology in fluidized bed, the experimental combustor developed at the Instituto de Investigaciones Electricas (IIE) is described, as well as the test results of the experiences carried out with coal from Rio Escondido, Coahuila. [Espanol] Tras sintetizar los aspectos mas importantes de la tecnologia de combustion en lecho fluidizado, se describe el combustor experimental desarrollado en el Instituto de Investigaciones Electricas (IIE), asi como los resultados de las experiencias realizadas con carbon proveniente de Rio Escondido, Coahuila.

The Instituto de Investigaciones Electricas fluidized bed combustor; El combustor de lecho fluidizado del Instituto de Investigaciones Electricas

Energy Technology Data Exchange (ETDEWEB)

Milan Foressi, Julio [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)

1992-12-31

After synthesizing the most important aspects of the combustion technology in fluidized bed, the experimental combustor developed at the Instituto de Investigaciones Electricas (IIE) is described, as well as the test results of the experiences carried out with coal from Rio Escondido, Coahuila. [Espanol] Tras sintetizar los aspectos mas importantes de la tecnologia de combustion en lecho fluidizado, se describe el combustor experimental desarrollado en el Instituto de Investigaciones Electricas (IIE), asi como los resultados de las experiencias realizadas con carbon proveniente de Rio Escondido, Coahuila.

Variable volume combustor with pre-nozzle fuel injection system

Science.gov (United States)

Keener, Christopher Paul; Johnson, Thomas Edward; McConnaughhay, Johnie Franklin; Ostebee, Heath Michael

2016-09-06

The present application provides a combustor for use with a gas turbine engine. The combustor may include a number of fuel nozzles, a pre-nozzle fuel injection system supporting the fuel nozzles, and a linear actuator to maneuver the fuel nozzles and the pre-nozzle fuel injection system.

Quantum Monte Carlo study of the superconductor-insulator transition in the dual vortex representation

Science.gov (United States)

Khan, Hasan; Gazit, Snir; Randeria, Mohit; Trivedi, Nandini

The superconductor-insulator transition (SIT) in two dimensions is a paradigm for quantum criticality that has been observed experimentally in Josephson junction arrays, superconducting thin films, and cold atoms trapped in an optical lattice. The conventional picture of the transition is in terms of the condensation of bosonic degrees of freedom (Cooper pairs in superconductors). Interestingly, the transition has a dual description, where the insulating phase is a Bose condensate of vortices. We study the SIT numerically by means of a large-scale quantum Monte Carlo (QMC) simulation in the vortex representation. This provides direct access to both the boson and vortex degrees of freedom and allows us to numerically test the duality and quantify deviations from self-duality. Our main focus is on critical properties such as the vortex and the boson phase stiffness. We compare our results to previous studies in the bosonic representation. We acknowledge support from Grant DOE-BES DE-FG02-07ER46423 (HK, NT).

Study of the mechanisms for flame stabilization in gas turbine model combustors using kHz laser diagnostics

Science.gov (United States)

Boxx, Isaac; Carter, Campbell D.; Stöhr, Michael; Meier, Wolfgang

2013-05-01

An image-processing routine was developed to autonomously identify and statistically characterize flame-kernel events, wherein OH (from a planar laser-induced fluorescence, PLIF, measurement) appears in the probe region away from the contiguous OH layer. This routine was applied to datasets from two gas turbine model combustors that consist of thousands of joint OH-velocity images from kHz framerate OH-PLIF and particle image velocimetry (PIV). Phase sorting of the kernel centroids with respect to the dominant fluid-dynamic structure of the combustors (a helical precessing vortex core, PVC) indicates through-plane transport of reacting fluid best explains their sudden appearance in the PLIF images. The concentration of flame-kernel events around the periphery of the mean location of the PVC indicates they are likely the result of wrinkling and/or breakup of the primary flame sheet associated with the passage of the PVC as it circumscribes the burner centerline. The prevailing through-plane velocity of the swirling flow-field transports these fragments into the imaging plane of the OH-PLIF system. The lack of flame-kernel events near the center of the PVC (in which there is lower strain and longer fluid-dynamic residence times) indicates that auto-ignition is not a likely explanation for these flame kernels in a majority of cases. The lack of flame-kernel centroid variation in one flame in which there is no PVC further supports this explanation.

Electron vortex magnetic holes: A nonlinear coherent plasma structure

Energy Technology Data Exchange (ETDEWEB)

Haynes, Christopher T., E-mail: c.t.haynes@qmul.ac.uk; Burgess, David; Sundberg, Torbjorn [School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom); Camporeale, Enrico [Multiscale Dynamics, Centrum Wiskunde and Informatica (CWI), Amsterdam (Netherlands)

2015-01-15

We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

Vortex Matter dynamics in a thin film of Nb with columnar indentations

Energy Technology Data Exchange (ETDEWEB)

Nunes, J.S. [Grupo de Supercondutividade e Magnetism, Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos, SP (Brazil)], E-mail: julianakapp@gmail.com; Zadorosny, R.; Oliveira, A.A.M. [Grupo de Supercondutividade e Magnetism, Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos, SP (Brazil); Lepienski, C.M. [Departamento de Fisica, Universidade Federal do Parana, Curitiba, PR (Brazil); Patino, E.J.; Blamire, M.G. [Department of Materials Science, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); Ortiz, W.A. [Grupo de Supercondutividade e Magnetism, Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos, SP (Brazil)

2008-07-15

A superconducting film with columnar defects constitutes a rich scenario for studying Vortex Matter dynamics. This paper reports on the magnetic response of a 200 nm thick Nb film, pierced with a set of 900 columnar indentations of nearly triangular cross section, forming a square lattice. The column diameter is 1 {mu}m and the distance between columns is 10 {mu}m. To probe the interaction of Vortex Matter with the array of antidots, we have excited the sample with a significantly large AC-field, so that flux originally trapped by the columns could be unpinned and admitted into the superconducting sea surrounding the defects. The melting line of this system has a kink separating two different regimes, suggesting a crossover from the efficient pinning regime, at lower temperatures, to a temperature-induced depinning.

Vortex Matter dynamics in a thin film of Nb with columnar indentations

International Nuclear Information System (INIS)

Nunes, J.S.; Zadorosny, R.; Oliveira, A.A.M.; Lepienski, C.M.; Patino, E.J.; Blamire, M.G.; Ortiz, W.A.

2008-01-01

A superconducting film with columnar defects constitutes a rich scenario for studying Vortex Matter dynamics. This paper reports on the magnetic response of a 200 nm thick Nb film, pierced with a set of 900 columnar indentations of nearly triangular cross section, forming a square lattice. The column diameter is 1 μm and the distance between columns is 10 μm. To probe the interaction of Vortex Matter with the array of antidots, we have excited the sample with a significantly large AC-field, so that flux originally trapped by the columns could be unpinned and admitted into the superconducting sea surrounding the defects. The melting line of this system has a kink separating two different regimes, suggesting a crossover from the efficient pinning regime, at lower temperatures, to a temperature-induced depinning

Mapping travelling convection vortex events with respect to energetic particle boundaries

Directory of Open Access Journals (Sweden)

T. Moretto

1998-08-01

Full Text Available Thirteen events of high-latitude ionospheric travelling convection vortices during very quiet conditions were identified in the Greenland magnetometer data during 1990 and 1991. The latitudes of the vortex centres for these events are compared to the energetic electron trapping boundaries as identified by the particle measurements of the NOAA 10 satellite. In addition, for all events at least one close DMSP overpass was available. All but one of the 13 cases agree to an exceptional degree that: the TCV centres are located within the region of trapped, high energy electrons close to the trapping boundary for the population of electrons with energy greater than >100 keV. Correspondingly, from the DMSP data they are located within the region of plasmasheet-type precipitation close to the CPS/BPS precipitation boundary. That is, the TCV centres map to deep inside the magnetosphere and not to the magnetopause.Key Words. Ionosphere (Electric fields and currents; Particle precipitation · Magnetospheric physics (Magnetosphere-ionosphere interaction

Combustor nozzle for a fuel-flexible combustion system

Science.gov (United States)

Haynes, Joel Meier [Niskayuna, NY; Mosbacher, David Matthew [Cohoes, NY; Janssen, Jonathan Sebastian [Troy, NY; Iyer, Venkatraman Ananthakrishnan [Mason, OH

2011-03-22

A combustor nozzle is provided. The combustor nozzle includes a first fuel system configured to introduce a syngas fuel into a combustion chamber to enable lean premixed combustion within the combustion chamber and a second fuel system configured to introduce the syngas fuel, or a hydrocarbon fuel, or diluents, or combinations thereof into the combustion chamber to enable diffusion combustion within the combustion chamber.

Variable volume combustor with an air bypass system

Science.gov (United States)

Johnson, Thomas Edward; Ziminsky, Willy Steve; Ostebee, Heath Michael; Keener, Christopher Paul

2017-02-07

The present application provides a combustor for use with flow of fuel and a flow of air in a gas turbine engine. The combustor may include a number of micro-mixer fuel nozzles positioned within a liner and an air bypass system position about the liner. The air bypass system variably allows a bypass portion of the flow of air to bypass the micro-mixer fuel nozzles.

Thermodynamics of premixed combustion in a heat recirculating micro combustor

International Nuclear Information System (INIS)

Rana, Uttam; Chakraborty, Suman; Som, S.K.

2014-01-01

A thermodynamic model has been developed to evaluate exergy transfer and its destruction in the process of premixed combustion in a heat recirculating micro combustor. Exergy destruction caused by process irreversibilities is characterized by entropy generation in the process. The entropy transport equation along with the solution of temperature and species concentration fields in the wake of flame sheet assumptions have been used to determine the different components of entropy generation. The role of thermal conductivity and thickness of combustor wall, and Peclet number on transfer and destruction rate of exergy is depicted in the process of flame stabilization via heat recirculation. The entropy generations due to gas phase heat conduction and chemical reaction are identified as the major sources of exergy destruction. The total irreversibility in pre-flame region is confined only within a small distance upstream of the flame. It has been observed that the local volumetric entropy generation is higher near the axis than that near the combustor wall. The second law efficiency is almost invariant with heat loss from the combustor, Peclet number, and thermal conductivity and thickness of combustor wall. - Highlights: • Irreversibility in the combustor is mainly due to conduction and chemical reaction. • Entropy generation near the axis is higher compared to that near the wall. • Heat recirculation and process irreversibility decrease with heat loss. • The second law efficiency is almost independent of Peclet number. • Second law efficiency is almost independent of wall thermal conductivity

Point vortex modelling of the wake dynamics behind asymmetric vortex generator arrays

NARCIS (Netherlands)

Baldacchino, D.; Simao Ferreira, C.; Ragni, D.; van Bussel, G.J.W.

2016-01-01

In this work, we present a simple inviscid point vortex model to study the dynamics of asymmetric vortex rows, as might appear behind misaligned vortex generator vanes. Starting from the existing solution of the in_nite vortex cascade, a numerical model of four base-vortices is chosen to represent

Superfluid transition of homogeneous and trapped two-dimensional Bose gases.

Science.gov (United States)

Holzmann, Markus; Baym, Gordon; Blaizot, Jean-Paul; Laloë, Franck

2007-01-30

Current experiments on atomic gases in highly anisotropic traps present the opportunity to study in detail the low temperature phases of two-dimensional inhomogeneous systems. Although, in an ideal gas, the trapping potential favors Bose-Einstein condensation at finite temperature, interactions tend to destabilize the condensate, leading to a superfluid Kosterlitz-Thouless-Berezinskii phase with a finite superfluid mass density but no long-range order, as in homogeneous fluids. The transition in homogeneous systems is conveniently described in terms of dissociation of topological defects (vortex-antivortex pairs). However, trapped two-dimensional gases are more directly approached by generalizing the microscopic theory of the homogeneous gas. In this paper, we first derive, via a diagrammatic expansion, the scaling structure near the phase transition in a homogeneous system, and then study the effects of a trapping potential in the local density approximation. We find that a weakly interacting trapped gas undergoes a Kosterlitz-Thouless-Berezinskii transition from the normal state at a temperature slightly below the Bose-Einstein transition temperature of the ideal gas. The characteristic finite superfluid mass density of a homogeneous system just below the transition becomes strongly suppressed in a trapped gas.

Variable volume combustor with aerodynamic support struts

Science.gov (United States)

Ostebee, Heath Michael; Johnson, Thomas Edward; Stewart, Jason Thurman; Keener, Christopher Paul

2017-03-07

The present application provides a combustor for use with a gas turbine engine. The combustor may include a number of micro-mixer fuel nozzles and a fuel injection system for providing a flow of fuel to the micro-mixer fuel nozzles. The fuel injection system may include a number of support struts supporting the fuel nozzles and providing the flow of fuel therethrough. The support struts may include an aerodynamic contoured shape so as to distribute evenly a flow of air to the micro-mixer fuel nozzles.

A Coaxial Vortex Ring Model for Vortex Breakdown

OpenAIRE

Blackmore, Denis; Brons, Morten; Goullet, Arnaud

2008-01-01

A simple - yet plausible - model for B-type vortex breakdown flows is postulated; one that is based on the immersion of a pair of slender coaxial vortex rings in a swirling flow of an ideal fluid rotating around the axis of symmetry of the rings. It is shown that this model exhibits in the advection of passive fluid particles (kinematics) just about all of the characteristics that have been observed in what is now a substantial body of published research on the phenomenon of vortex breakdown....

NONEQUILIBRIUM SULFUR CAPTURE AND RETENTION IN AN AIR COOLED SLAGGING COAL COMBUSTOR

International Nuclear Information System (INIS)

Dr. Bert Zauderer

1999-01-01

Calcium oxide injected in a slagging combustor reacts with the sulfur from coal combustion to form sulfur-bearing particles. They are deposited on the liquid slag layer on the combustor wall. Due to the low solubility of sulfur in slag, slag must be rapidly drained from the combustor to limit sulfur gas re-evolution. Analysis indicated that slag mass flow rates in excess of 400 lb/hr should limit sulfur re-evolution. The objective of this 42-month project was to perform a series of tests to determine the factors that control the retention of the sulfur in the slag. 36 days of testing on the combustor were completed prior to the end of this reporting period, 12/31/98. This compares with 16 tests required in the original project plan. Combustor tests in early 1997 with high (37%) ash, Indian coal confirmed that high slag mass flow rates of about 500 lb/hr resulted in retention in the slag of up to 20% of the injected sulfur content mineral matter. To further increase the slag flow rate, rice husks, which contain 20% ash, and rice husk char, which contain 70% ash, were co-fired with coal in the combustor. A series of 13 combustor tests were performed in fourth quarter of 1997 and a further 6 tests were performed in January 1998 and in the summer of 1998. The test objective was to achieve slag flow rates between 500 and 1,000 lb/hr. Due to the very low bulk density of rice husk, compared to pulverized coal, almost the entire test effort focused on developing methods for feeding the rice husks into combustor. In the last test of December 1997, a peak mineral matter, injection rate of 592 lb/hr was briefly achieved by injection of coal, rice husk char, gypsum, and limestone into the combustor. However, no significant sulfur concentration was measured in the slag removed from the combustor. The peak injection rate reached with biomass in the 1997 tests was 310 lb/hr with rice husk, and 584 lb/hr with rice husk char

Fuel properties effect on the performance of a small high temperature rise combustor

Science.gov (United States)

Acosta, Waldo A.; Beckel, Stephen A.

1989-01-01

The performance of an advanced small high temperature rise combustor was experimentally determined at NASA-Lewis. The combustor was designed to meet the requirements of advanced high temperature, high pressure ratio turboshaft engines. The combustor featured an advanced fuel injector and an advanced segmented liner design. The full size combustor was evaluated at power conditions ranging from idle to maximum power. The effect of broad fuel properties was studied by evaluating the combustor with three different fuels. The fuels used were JP-5, a blend of Diesel Fuel Marine/Home Heating Oil, and a blend of Suntec C/Home Heating Oil. The fuel properties effect on the performance of the combustion in terms of pattern factor, liner temperatures, and exhaust emissions are documented.

Vortex breakdown in simple pipe bends

Science.gov (United States)

Ault, Jesse; Shin, Sangwoo; Stone, Howard

2016-11-01

Pipe bends and elbows are one of the most common fluid mechanics elements that exists. However, despite their ubiquity and the extensive amount of research related to these common, simple geometries, unexpected complexities still remain. We show that for a range of geometries and flow conditions, these simple flows experience unexpected fluid dynamical bifurcations resembling the bubble-type vortex breakdown phenomenon. Specifically, we show with simulations and experiments that recirculation zones develop within the bends under certain conditions. As a consequence, fluid and particles can remain trapped within these structures for unexpectedly-long time scales. We also present simple techniques to mitigate this recirculation effect which can potentially have impact across industries ranging from biomedical and chemical processing to food and health sciences.

Vortex cutting in superconductors

Science.gov (United States)

Vlasko-Vlasov, Vitalii K.; Koshelev, Alexei E.; Glatz, Andreas; Welp, Ulrich; Kwok, Wai-K.

2015-03-01

Unlike illusive magnetic field lines in vacuum, magnetic vortices in superconductors are real physical strings, which interact with the sample surface, crystal structure defects, and with each other. We address the complex and poorly understood process of vortex cutting via a comprehensive set of magneto-optic experiments which allow us to visualize vortex patterns at magnetization of a nearly twin-free YBCO crystal by crossing magnetic fields of different orientations. We observe a pronounced anisotropy in the flux dynamics under crossing fields and the filamentation of induced supercurrents associated with the staircase vortex structure expected in layered cuprates, flux cutting effects, and angular vortex instabilities predicted for anisotropic superconductors. At some field angles, we find formation of the vortex domains following a type-I phase transition in the vortex state accompanied by an abrupt change in the vortex orientation. To clarify the vortex cutting scenario we performed time-dependent Ginzburg-Landau simulations, which confirmed formation of sharp vortex fronts observed in the experiment and revealed a left-handed helical instability responsible for the rotation of vortices. This work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division.

Active Combustion Control for Aircraft Gas-Turbine Engines-Experimental Results for an Advanced, Low-Emissions Combustor Prototype

Science.gov (United States)

DeLaat, John C.; Kopasakis, George; Saus, Joseph R.; Chang, Clarence T.; Wey, Changlie

2012-01-01

Lean combustion concepts for aircraft engine combustors are prone to combustion instabilities. Mitigation of instabilities is an enabling technology for these low-emissions combustors. NASA Glenn Research Center s prior activity has demonstrated active control to suppress a high-frequency combustion instability in a combustor rig designed to emulate an actual aircraft engine instability experience with a conventional, rich-front-end combustor. The current effort is developing further understanding of the problem specifically as applied to future lean-burning, very low-emissions combustors. A prototype advanced, low-emissions aircraft engine combustor with a combustion instability has been identified and previous work has characterized the dynamic behavior of that combustor prototype. The combustor exhibits thermoacoustic instabilities that are related to increasing fuel flow and that potentially prevent full-power operation. A simplified, non-linear oscillator model and a more physics-based sectored 1-D dynamic model have been developed to capture the combustor prototype s instability behavior. Utilizing these models, the NASA Adaptive Sliding Phasor Average Control (ASPAC) instability control method has been updated for the low-emissions combustor prototype. Active combustion instability suppression using the ASPAC control method has been demonstrated experimentally with this combustor prototype in a NASA combustion test cell operating at engine pressures, temperatures, and flows. A high-frequency fuel valve was utilized to perturb the combustor fuel flow. Successful instability suppression was shown using a dynamic pressure sensor in the combustor for controller feedback. Instability control was also shown with a pressure feedback sensor in the lower temperature region upstream of the combustor. It was also demonstrated that the controller can prevent the instability from occurring while combustor operation was transitioning from a stable, low-power condition to

Structures of single vortex and vortex lattice in a d-wave superconductor

International Nuclear Information System (INIS)

Xu, J.; Ren, Y.; Ting, C.

1996-01-01

The structures of a single vortex and vortex lattice in a superconductor with d x 2 -y 2 symmetry are studied self-consistently employing a recently developed Ginzburg-Landau theory. Near a single vortex, we found that an s-wave component of the order parameter is always induced, and it causes the local magnetic-field distribution and the d-wave order parameter to have a fourfold anisotropy. It is shown that there is a strong correlation between the structure of a single vortex and the shape of the vortex lattice. Our numerical calculation indicates that the structure of the vortex lattice is always oblique except for temperatures very close to T c where it becomes triangular. The possible connection of the result with experiment is also discussed. copyright 1996 The American Physical Society

Aerotrace. Measurement of particulates from an engine combustor

Energy Technology Data Exchange (ETDEWEB)

Hurley, C D [DRA, Farnborough (United Kingdom)

1998-12-31

The effect of gas turbine operating conditions, inlet temperature, pressure and overall air fuel ratio, on particulate number density has been measured. Particulate number density was found to be proportional to combustor inlet pressure and decrease with increasing combustor inlet temperature. The relationship with air fuel ratio is more complex. The mechanism of particulate loss down sample lines has been elucidated and equations are presented to predict particulate losses for stainless steel and PTFE sample lines. (author) 3 refs.

Aerotrace. Measurement of particulates from an engine combustor

Energy Technology Data Exchange (ETDEWEB)

Hurley, C.D. [DRA, Farnborough (United Kingdom)

1997-12-31

The effect of gas turbine operating conditions, inlet temperature, pressure and overall air fuel ratio, on particulate number density has been measured. Particulate number density was found to be proportional to combustor inlet pressure and decrease with increasing combustor inlet temperature. The relationship with air fuel ratio is more complex. The mechanism of particulate loss down sample lines has been elucidated and equations are presented to predict particulate losses for stainless steel and PTFE sample lines. (author) 3 refs.

Onsager Vortex Formation in Two-component Bose-Einstein Condensates

Science.gov (United States)

Han, Junsik; Tsubota, Makoto

2018-06-01

We numerically study the dynamics of quantized vortices in two-dimensional two-component Bose-Einstein condensates (BECs) trapped by a box potential. For one-component BECs in a box potential, it is known that quantized vortices form Onsager vortices, which are clusters of same-sign vortices. We confirm that the vortices of the two components spatially separate from each other — even for miscible two-component BECs — suppressing the formation of Onsager vortices. This phenomenon is caused by the repulsive interaction between vortices belonging to different components, hence, suggesting a new possibility for vortex phase separation.

Vortex rings

CERN Document Server

Akhmetov, D G

2009-01-01

This text on vortex rings covers their theoretical foundation, systematic investigations, and practical applications such as the extinction of fires at gushing oil wells. It pays special attention to the formation and motion of turbulent vortex rings.

The effect of inlet conditions on lean premixed gas turbine combustor performance

Science.gov (United States)

Vilayanur, Suresh Ravi

The combustion community is today faced with the goal to reduce NOx at high efficiencies. This requirement has directed attention to the manner by which air and fuel are treated prior to and at the combustor inlet. This dissertation is directed to establishing the role of combustor inlet conditions on combustor performance, and to deriving an understanding of the relationship between inlet conditions and combustion performance. To investigate the complex effect of inlet parameters on combustor performance, (1) a test facility was designed and constructed, (2) hardware was designed and fabricated, (3) a statistically based technique was designed and applied, and (4) detailed in-situ measurements were acquired. Atmospheric tests were performed at conditions representative of industrial combustors: 670 K inlet preheat and an equivalence ratio of 0.47, and make the study immediately relevant to the combustion community. The effects of premixing length, fuel distribution, swirl angle, swirl vane thickness and swirl solidity were investigated. The detailed in-situ measurements were performed to form the database necessary to study the responsible mechanisms. A host of conventional and advanced diagnostics were used for the investigation. In situ measurements included the mapping of the thermal and velocity fields of the combustor, obtaining species concentrations inside the combustor, and quantifying the fuel-air mixing entering the combustor. Acoustic behavior of the combustor was studied, including the application of high speed videography. The results reveal that the principal statistically significant effect on NOx production is the inlet fuel distribution, and the principal statistically significant effect on CO production is the swirl strength. Elevated levels of NOx emission result when the fuel is weighted to the centerline. Eddies shedding off the swirler hub ignite as discrete packets, and due to the elevated concentrations of fuel, reach higher temperatures

Tunable quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors.

Science.gov (United States)

Taupin, M; Khaymovich, I M; Meschke, M; Mel'nikov, A S; Pekola, J P

2016-03-16

Nowadays, superconductors serve in numerous applications, from high-field magnets to ultrasensitive detectors of radiation. Mesoscopic superconducting devices, referring to those with nanoscale dimensions, are in a special position as they are easily driven out of equilibrium under typical operating conditions. The out-of-equilibrium superconductors are characterized by non-equilibrium quasiparticles. These extra excitations can compromise the performance of mesoscopic devices by introducing, for example, leakage currents or decreased coherence time in quantum devices. By applying an external magnetic field, one can conveniently suppress or redistribute the population of excess quasiparticles. In this article, we present an experimental demonstration and a theoretical analysis of such effective control of quasiparticles, resulting in electron cooling both in the Meissner and vortex states of a mesoscopic superconductor. We introduce a theoretical model of quasiparticle dynamics, which is in quantitative agreement with the experimental data.

A study of air breathing rockets. 3: Supersonic mode combustors

Science.gov (United States)

Masuya, G.; Chinzel, N.; Kudo, K.; Murakami, A.; Komuro, T.; Ishii, S.

An experimental study was made on supersonic mode combustors of an air breathing rocket engine. Supersonic streams of room-temperature air and hot fuel-rich rocket exhaust were coaxially mixed and burned in a concially diverging duct of 2 deg half-angle. The effect of air inlet Mach number and excess air ratio was investigated. Axial wall pressure distribution was measured to calculate one dimensional change of Mach number and stagnation temperature. Calculated results showed that supersonic combustion occurred in the duct. At the exit of the duct, gas sampling and Pitot pressure measurement was made, from which radial distributions of various properties were deduced. The distribution of mass fraction of elements from rocket exhaust showed poor mixing performance in the supersonic mode combustors compared with the previously investigated cylindrical subsonic mode combustors. Secondary combustion efficiency correlated well with the centerline mixing parameter, but not with Annushkin's non-dimensional combustor length. No major effect of air inlet Mach number or excess air ratio was seen within the range of conditions under which the experiment was conducted.

Vortex mass in a superfluid

Science.gov (United States)

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.

Thermo-acoustic cross-talk between cans in a can-annular combustor

NARCIS (Netherlands)

Farisco, Federica; Panek, Lukasz; Kok, Jim B.W.

2017-01-01

Thermo-acoustic instabilities in gas turbine engines are studied to avoid engine failure. Compared to the engines with annular combustors, the can-annular combustor design should be less vulnerable to acoustic burner-to-burner interaction, since the burners are acoustically coupled only by the

Experimental study of a plat-flame micro combustor burning DME for thermoelectric power generation

Energy Technology Data Exchange (ETDEWEB)

Jiang, L.Q.; Zhao, D.Q.; Guo, C.M.; Wang, X.H. [Key Laboratory of Renewable Energy and Gas Hydrate, CAS, Guangzhou Institute of Energy Conversion of CAS, Guangzhou 510640 (China)

2011-01-15

A centimeter magnitude thermoelectric (TE) power generation system based on a plat-flame micro combustor burning DME (dimethyl ether) has been developed. The chamber wall of this micro combustor was made of two parallel sintered porous plates which acted as mixture inlet. The main virtue of this combustor is that it can keep combustor wall at lower temperature for reducing heat loss when sustaining a stable flame. Experimental test results showed it was feasible to obtain stable DME/air premixed flame at lean combustion situations in the micro combustor. The combustion load of this 0.48 cm{sup 3} chamber capacity was 20-200 W at equivalence ratio {phi} = 0.6. Though the flame temperature was above 1000 C, the combustor's wall temperature was near 600 C lower than flame temperature. In the demonstrated TE power generation system which integrated the plat-flame micro combustor, a heat spreader had good effect on uniforming the hot side temperature field of TE modules. Cooled by water and with 150 W input power at {phi} = 0.7, the system produced 10 V output at open circuit and 4 V at 10 {omega} load. The maximum power output was above 2 W, and the maximum overall chemical-electric energy conversion efficiency was 1.25%. (author)

CFD analysis of a scramjet combustor with cavity based flame holders

Science.gov (United States)

Kummitha, Obula Reddy; Pandey, Krishna Murari; Gupta, Rajat

2018-03-01

Numerical analysis of a scramjet combustor with different cavity flame holders has been carried out using ANSYS 16 - FLUENT tool. In this research article the internal fluid flow behaviour of the scramjet combustor with different cavity based flame holders have been discussed in detail. Two dimensional Reynolds-Averaged Navier-Stokes governing(RANS) equations and shear stress turbulence (SST) k - ω model along with finite rate/eddy dissipation chemistry turbulence have been considered for modelling chemical reacting flows. Due to the advantage of less computational time, global one step reaction mechanism has been used for combustion modelling of hydrogen and air. The performance of the scramjet combustor with two different cavities namely spherical and step cavity has been compared with the standard DLR scramjet. From the comparison of numerical results, it is found that the development of recirculation regions and additional shock waves from the edge of cavity flame holder is increased. And also it is observed that with the cavity flame holder the residence time of air in the scramjet combustor is also increased and achieved stabilized combustion. From this research analysis, it has been found that the mixing and combustion efficiency of scramjet combustor with step cavity design is optimum as compared to other models.

Influence of the inductor shape, and the magnetization processes on a trapped magnetic flux in a superconducting bulk

Energy Technology Data Exchange (ETDEWEB)

Gony, B., E-mail: bashar.gony@univ-lorraine.fr; Linares, R.; Lin, Q.; Berger, K.; Douine, B.; Leveque, J.

2014-08-15

Highlights: • We tested two inductors: vortex coil and system of three coils. • The system of three coils is better than the vortex coil. • We presented and compared two processes of PFM method. • Similar results were found for the two processes. - Abstract: In this paper, we study the form of the inductor for producing a magnetic field in a superconductor bulk by using a method of PFM (Pulsed Field Magnetization). We tested two inductors: vortex coil and system of three coils, where we found the best results with the system of three coils. After that, we presented two processes for trapping a magnetic field in the bulk: direct magnetization and successive magnetization where we found similar results.

Transient Heat Transfer Properties in a Pulse Detonation Combustor

Science.gov (United States)

2011-03-01

appreciation to my wife Shelly , and my sons Cody, Brandon, and Tyler for their encouragement, support, and understanding during this challenging time...operation frequencies. 56 B. FUTURE WORK A redesign of the cooled combustor chamber is currently in progress and will result in a cast mold. A...water-cooled combustor with casted swept ramps in the combustion chamber that are cooled as well maximizes the amount cooling to the ramps to help

Effects of Burning Alternative Fuel in a 5-Cup Combustor Sector

Science.gov (United States)

Tacina, K. M.; Chang, C. T.; Lee, C.-M.; He, Z.; Herbon, J.

2015-01-01

A goal of NASA's Environmentally Responsible Aviation (ERA) program is to develop a combustor that will reduce the NOx emissions and that can burn both standard and alternative fuels. To meet this goal, NASA partnered with General Electric Aviation to develop a 5-cup combustor sector; this sector was tested in NASA Glenn's Advanced Subsonic Combustion Rig (ASCR). To verify that the combustor sector was fuel-flexible, it was tested with a 50-50 blend of JP-8 and a biofuel made from the camelina sativa plant. Results from this test were compared to results from tests where the fuel was neat JP-8. Testing was done at three combustor inlet conditions: cruise, 30% power, and 7% power. When compared to burning JP-8, burning the 50-50 blend did not significantly affect emissions of NOx, CO, or total hydrocarbons. Furthermore, it did not significantly affect the magnitude and frequency of the dynamic pressure fluctuations.

Focusing properties of cylindrical vector vortex beams

Science.gov (United States)

Xiaoqiang, Zhang; Ruishan, Chen; Anting, Wang

2018-05-01

In this paper, following Richards and Wolf vectorial diffraction theory, the focusing properties of cylindrical vector vortex beams (CVVB) are investigated, and a diffractive optical element (DOE) is designed to spatially modulate the amplitude of the CVVB. Simulated results show that the CVVB focused by an objective also carry orbital angular momentum (OAM), and the optical fields near the focal region can be modulated by changing the topological charge of the CVVB. We numerically simulate the focus properties of radially and azimuthally polarized beams with topological charge equal to 0, 1, 2 and 10 respectively. As a result, a dark channel with a length about 20 λ can be obtained. These new properties have the potential applications such as particle acceleration, optical trapping and material processing.

Front propagation in a regular vortex lattice: Dependence on the vortex structure.

Science.gov (United States)

Beauvier, E; Bodea, S; Pocheau, A

2017-11-01

We investigate the dependence on the vortex structure of the propagation of fronts in stirred flows. For this, we consider a regular set of vortices whose structure is changed by varying both their boundary conditions and their aspect ratios. These configurations are investigated experimentally in autocatalytic solutions stirred by electroconvective flows and numerically from kinematic simulations based on the determination of the dominant Fourier mode of the vortex stream function in each of them. For free lateral boundary conditions, i.e., in an extended vortex lattice, it is found that both the flow structure and the front propagation negligibly depend on vortex aspect ratios. For rigid lateral boundary conditions, i.e., in a vortex chain, vortices involve a slight dependence on their aspect ratios which surprisingly yields a noticeable decrease of the enhancement of front velocity by flow advection. These different behaviors reveal a sensitivity of the mean front velocity on the flow subscales. It emphasizes the intrinsic multiscale nature of front propagation in stirred flows and the need to take into account not only the intensity of vortex flows but also their inner structure to determine front propagation at a large scale. Differences between experiments and simulations suggest the occurrence of secondary flows in vortex chains at large velocity and large aspect ratios.

Plasmonic vortex generator without polarization dependence

Science.gov (United States)

Wang, Han; Liu, Lixia; Liu, Chunxiang; Li, Xing; Wang, Shuyun; Xu, Qing; Teng, Shuyun

2018-03-01

In view of the limitations of vortex generators with polarization dependence at present, we propose a plasmonic vortex generator composed of rectangular holes etched in silver film, in which the optical vortex can be generated under arbitrary linearly polarized light illumination. Two sets of rectangular holes are arranged equidistantly on a circle and rotate in postulate directions. Theoretical analysis provides the design principle for the vortex generator, and numerical simulations give guidance on designating the vortex generator parameters. Experimental measurements verify the performance of the proposed vortex generator. Moreover, two alternative structures for the generation of a plasmonic vortex are also provided in this paper. The resulting perfect vortex, compact structure and flexible illumination conditions will lead to wide applications of this plasmonic vortex generator.

Tight focusing of radially polarized circular Airy vortex beams

Science.gov (United States)

Chen, Musheng; Huang, Sujuan; Shao, Wei

2017-11-01

Tight focusing properties of radially polarized circular Airy vortex beams (CAVB) are studied numerically. The light field expressions for the focused fields are derived based on vectorial Debye theory. We also study the relationship between focal profiles, such as light intensity distribution, radius of focal spot and focal length, and the parameters of CAVB. Numerical results demonstrate that we can generate a radially polarized CAVB with super-long focal length, super-strong longitudinal intensity or subwavelength focused spot at the focal plane by properly choosing the parameters of incident light and high numerical aperture (NA) lens. These results have potential applications for optical trapping, optical storage and particle acceleration.

The singing vortex

Science.gov (United States)

Arndt, R.; Pennings, P.; Bosschers, J.; van Terwisga, T.

2015-01-01

Marine propellers display several forms of cavitation. Of these, propeller-tip vortex cavitation is one of the important factors in propeller design. The dynamic behaviour of the tip vortex is responsible for hull vibration and noise. Thus, cavitation in the vortices trailing from tips of propeller blades has been studied extensively. Under certain circumstances cavitating vortices have been observed to have wave-like disturbances on the surfaces of vapour cores. Intense sound at discrete frequencies can result from a coupling between tip vortex disturbances and oscillating sheet cavitation on the surfaces of the propeller blades. This research article focuses on the dynamics of vortex cavitation and more in particular on the energy and frequency content of the radiated pressures. PMID:26442147

DNS of droplet-vortex interaction with a Karman vortex street

International Nuclear Information System (INIS)

Burger, M.; Schmehl, R.; Koch, R.; Wittig, S.; Bauer, H.-J.

2006-01-01

Predicting fuel spray interaction with large scale vortex structures still is a major challenge for state-of-the-art CFD codes. In order to elucidate the mechanisms involved, a fundamental study has been carried out in which the interaction of water droplets with a Karman vortex street is investigated. The disperse two-phase flow around a cylinder has been computed taking into account the mass, momentum and heat transfer between both phases. Flow conditions are chosen such that large scale vortices are generated by periodic flow separations of the well known Karman vortex street. A homogeneous distribution of water droplets is injected into the hot air up-stream of the computational domain. The mixing process as well as the impact of the droplets on the gas phase instabilities is analyzed in the downstream region where large scale vortex structures are present

Investigation and demonstration of a rich combustor cold-start device for alcohol-fueled engines

Energy Technology Data Exchange (ETDEWEB)

Hodgson, J W; Irick, D K [Univ. of Tennessee, Knoxville, TN (United States)

1998-04-01

The authors have completed a study in which they investigated the use of a rich combustor to aid in cold starting spark-ignition engines fueled with either neat ethanol or neat methanol. The rich combustor burns the alcohol fuel outside the engine under fuel-rich conditions to produce a combustible product stream that is fed to the engine for cold starting. The rich combustor approach significantly extends the cold starting capability of alcohol-fueled engines. A design tool was developed that simulates the operation of the combustor and couples it to an engine/vehicle model. This tool allows the user to determine the fuel requirements of the rich combustor as the vehicle executes a given driving mission. The design tool was used to design and fabricate a rich combustor for use on a 2.8 L automotive engine. The system was tested using a unique cold room that allows the engine to be coupled to an electric dynamometer. The engine was fitted with an aftermarket engine control system that permitted the fuel flow to the rich combustor to be programmed as a function of engine speed and intake manifold pressure. Testing indicated that reliable cold starts were achieved on both neat methanol and neat ethanol at temperatures as low as {minus}20 C. Although starts were experienced at temperatures as low as {minus}30 C, these were erratic. They believe that an important factor at the very low temperatures is the balance between the high mechanical friction of the engine and the low energy density of the combustible mixture fed to the engine from the rich combustor.

Trapping Dust to Form Planets

Science.gov (United States)

Kohler, Susanna

2017-10-01

Growing a planet from a dust grain is hard work! A new study explores how vortices in protoplanetary disks can assist this process.When Dust Growth FailsTop: ALMA image of the protoplanetary disk of V1247 Orionis, with different emission components labeled. Bottom: Synthetic image constructed from the best-fit model. [Kraus et al. 2017]Gradual accretion onto a seed particle seems like a reasonable way to grow a planet from a grain of dust; after all, planetary embryos orbit within dusty protoplanetary disks, which provides them with plenty of fuel to accrete so they can grow. Theres a challenge to this picture, though: the radial drift problem.The radial drift problem acknowledges that, as growing dust grains orbit within the disk, the drag force on them continues to grow as well. For large enough dust grains perhaps around 1 millimeter the drag force will cause the grains orbits to decay, and the particles drift into the star before they are able to grow into planetesimals and planets.A Close-Up Look with ALMASo how do we overcome the radial drift problem in order to form planets? A commonly proposed mechanism is dust trapping, in which long-lived vortices in the disk trap the dust particles, preventing them from falling inwards. This allows the particles to persist for millions of years long enough to grow beyond the radial drift barrier.Observationally, these dust-trapping vortices should have signatures: we would expect to see, at millimeter wavelengths, specific bright, asymmetric structures where the trapping occurs in protoplanetary disks. Such disk structures have been difficult to spot with past instrumentation, but the Atacama Large Millimeter/submillimeter Array (ALMA) has made some new observations of the disk V1247 Orionis that might be just what were looking for.Schematic of the authors model for the disk of V1247 Orionis. [Kraus et al. 2017]Trapped in a Vortex?ALMAs observations of V1247 Orionis are reported by a team of scientists led by Stefan

Cylindrical vortex wake model: right cylinder

DEFF Research Database (Denmark)

Branlard, Emmanuel; Gaunaa, Mac

2015-01-01

The vortex system consisting of a bound vortex disk, a root vortex and a vortex cylinder as introduced by Joukowski in 1912 is further studied in this paper. This system can be used for simple modeling of rotors (e.g. wind turbines) with infinite number of blades and finite tip-speed ratios....... For each vortex element, the velocity components in all directions and in the entire domain are computed analytically in a novel approach. In particular, the velocity field from the vortex actuator disk is derived for the first time. The induction from the entire vortex system is studied and is seen...

Modeling and Simulation of Swirl Stabilized Turbulent Non-Premixed Flames

Science.gov (United States)

Badillo-Rios, Salvador; Karagozian, Ann

2017-11-01

Flame stabilization is an important design criterion for many combustion chambers, especially at lean conditions and/or high power output, where insufficient stabilization can result in dangerous oscillations and noisy or damaged combustors. At high flow rates, swirling flow can offer a suitable stabilization mechanism, although understanding the dynamics of swirl-stabilized turbulent flames remains a significant challenge. Utilizing the General Equation and Mesh Solver (GEMS) code, which solves the Navier-Stokes equations along with the energy equation and five species equations, 2D axisymmetric and full 3D parametric studies and simulations are performed to guide the design and development of an experimental swirl combustor configuration and to study the effects of swirl on statistically stationary combustion. Results show that as the momentum of air is directed into the inner air inlet rather than the outer inlet of the swirl combustor, the central recirculating region becomes stronger and more unsteady, improving mixing and burning efficiency in that region. A high temperature region is found to occur as a result of burning of the trapped fuel from the central toroidal vortex. The effects of other parameters on flowfield and flame-stabilization dynamics are explored. Supported by ERC, Inc. (PS150006) and AFOSR (Dr. Chiping Li).

Combustor

Energy Technology Data Exchange (ETDEWEB)

Boden, J C; Fuller, J; Styles, A C

1987-02-18

A combustor suitable for disposing of lean fuel gas mixtures, e.g. solvent-laden exhaust streams, has a combustion chamber, a heat exchanger comprising a matrix of elongate tubes for supplying lean fuel gas to the combustion chamber and a burner located within the combustion chamber. The burner is adapted to mix fuel gas and the lean fuel gas which enters at an inlet and issues from the elongate tube outlets. The heat exchanger is in an heat exchange relationship with flue gas emerging from the outlet and the combustion chamber. The passage of the flue gases from the combustion chamber over the external surfaces of the tubes of the heat exchanger enables the pre-heating of the lean fuel gas mixture prior to its entry into the combustion chamber.

A vortex ring interacting with a vortex filament and its deformation near the two-dimensional stagnation point

International Nuclear Information System (INIS)

Kiya, M.; Sato, T.

1986-01-01

In this paper the interaction between vortex filaments and vortex rings and the deformation of vortex rings near the two-dimensional stagnation point are simulated by a three-dimensional vortex method. The two problems are respectively concerned with the effect of free-stream turbulence on turbulent plane mixing layers and the production of turbulence by the vortex stretching near saddles associated with large-scale coherent structures. The authors assume that the first step to understand the free-stream turbulence effect is to study the interaction between a vortex ring and a vortex filament and that the process of deformation of a vortex ring gives us a clue to understand physical processes occurring near the saddles

Imaging of artificially induced vortex structures

International Nuclear Information System (INIS)

Fasano, Yanina; Menghini, M.; Cruz, F. de la

2004-01-01

The combination of engineered pinning potentials in superconducting crystals, the detection of the liquid-solid vortex transition and the observation of the vortex structure with single vortex sensitivity allow the microscopic analysis of the response of 3D elastic systems to the presence of these potentials. In this work we review recent results obtained by a combination of those techniques studying different vortex structure induced transformations. On the one hand, we have visualized the transformation, along the vortex direction, of a bulk vortex single crystal with hexagonal symmetry into another crystal with square symmetry induced by an engineered Fe-dot lattice deposited on a surface of the vortex single crystal. On the other hand, we found an infrequent first-order phase transition where a vortex liquid under the presence of a random correlated potential (columnar defects) transforms into a vortex solid with no change of topological order

Ground-state and rotational properties of a two-component Bose–Einstein condensate in a harmonic plus quartic trap

Energy Technology Data Exchange (ETDEWEB)

Chen, Guang-Ping [Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi' an 710600 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zhang, Zhi-Yuan [The School of Physics and Mech-tronic Engineering, Sichuan University of Art and Science, DaZhou 635000 (China); Dong, Biao [Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi' an 710600 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Wang, Lin-Xue [College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Zhang, Xiao-Fei, E-mail: xfzhang@ntsc.ac.cn [Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi' an 710600 (China); Zhang, Shou-Gang, E-mail: szhang@ntsc.ac.cn [Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Chinese Academy of Sciences, Xi' an 710600 (China)

2015-10-02

We consider a two-component Bose–Einstein condensate under extreme elongation in a harmonic plus quartic trap. The ground-state and rotational properties of such a system are numerically studied as a function of intra- and inter-component contact interactions, and of the rotational frequency. For the nonrotational case, we obtain the exact phase diagram showing the ground-state density distributions as contact-interactions varied. For both slowly and ultrarapidly rotational cases, we demonstrate that the vortex configurations depend strongly on the relative strength of the contact interactions, as well as on the rotational frequency. The controllable system may be used to investigate the interplay of interaction and rotation, and to explore more exotic quantum phases. - Highlights: • Quartic trap extends the parameter space to a fast rotating region. • Different ground state density distributions and novel vortex structures are obtained within the full parameter space. • Effects of the contact interactions and rotation are discussed in detail.

Ground-state and rotational properties of a two-component Bose–Einstein condensate in a harmonic plus quartic trap

International Nuclear Information System (INIS)

Chen, Guang-Ping; Zhang, Zhi-Yuan; Dong, Biao; Wang, Lin-Xue; Zhang, Xiao-Fei; Zhang, Shou-Gang

2015-01-01

We consider a two-component Bose–Einstein condensate under extreme elongation in a harmonic plus quartic trap. The ground-state and rotational properties of such a system are numerically studied as a function of intra- and inter-component contact interactions, and of the rotational frequency. For the nonrotational case, we obtain the exact phase diagram showing the ground-state density distributions as contact-interactions varied. For both slowly and ultrarapidly rotational cases, we demonstrate that the vortex configurations depend strongly on the relative strength of the contact interactions, as well as on the rotational frequency. The controllable system may be used to investigate the interplay of interaction and rotation, and to explore more exotic quantum phases. - Highlights: • Quartic trap extends the parameter space to a fast rotating region. • Different ground state density distributions and novel vortex structures are obtained within the full parameter space. • Effects of the contact interactions and rotation are discussed in detail

The preliminary design of an annular combustor for a mini gas turbine

CSIR Research Space (South Africa)

Meyers, Bronwyn C

2015-10-01

Full Text Available This study involves the redesign of the combustor liner for a 200N mini gas turbine engine using first principles and the design methods of the NREC series as shown in Figure 1. The combustor design was performed using five different operating...

Design and preliminary results of a fuel flexible industrial gas turbine combustor

Science.gov (United States)

Novick, A. S.; Troth, D. L.; Yacobucci, H. G.

1981-01-01

The design characteristics are presented of a fuel tolerant variable geometry staged air combustor using regenerative/convective cooling. The rich/quench/lean variable geometry combustor is designed to achieve low NO(x) emission from fuels containing fuel bound nitrogen. The physical size of the combustor was calculated for a can-annular combustion system with associated operating conditions for the Allison 570-K engine. Preliminary test results indicate that the concept has the potential to meet emission requirements at maximum continuous power operation. However, airflow sealing and improved fuel/air mixing are necessary to meet Department of Energy program goals.

Effect of Fuel Injection and Mixing Characteristics on Pulse-Combustor Performance at High-Pressure

Science.gov (United States)

Yungster, Shaye; Paxson, Daniel E.; Perkins, Hugh D.

2014-01-01

Recent calculations of pulse-combustors operating at high-pressure conditions produced pressure gains significantly lower than those observed experimentally and computationally at atmospheric conditions. The factors limiting the pressure-gain at high-pressure conditions are identified, and the effects of fuel injection and air mixing characteristics on performance are investigated. New pulse-combustor configurations were developed, and the results show that by suitable changes to the combustor geometry, fuel injection scheme and valve dynamics the performance of the pulse-combustor operating at high-pressure conditions can be increased to levels comparable to those observed at atmospheric conditions. In addition, the new configurations can significantly reduce the levels of NOx emissions. One particular configuration resulted in extremely low levels of NO, producing an emission index much less than one, although at a lower pressure-gain. Calculations at representative cruise conditions demonstrated that pulse-combustors can achieve a high level of performance at such conditions.

The effect of vortex merging and non-merging on the transfer of modal turbulent kinetic energy content

Science.gov (United States)

Ground, Cody; Vergine, Fabrizio; Maddalena, Luca

2016-08-01

A defining feature of the turbulent free shear layer is that its growth is hindered by compressibility effects, thus limiting its potential to sufficiently mix the injected fuel and surrounding airstream at the supersonic Mach numbers intrinsic to the combustor of air-breathing hypersonic vehicles. The introduction of streamwise vorticity is often proposed in an attempt to counteract these undesired effects. This fact makes the strategy of introducing multiple streamwise vortices and imposing upon them certain modes of mutual interaction in order to potentially enhance mixing an intriguing concept. However, many underlying fundamental characteristics of the flowfields in the presence such interactions are not yet well understood; therefore, the fundamental physics of these flowfields should be independently investigated before the explicit mixing performance is characterized. In this work, experimental measurements are taken with the stereoscopic particle image velocimetry technique on two specifically targeted modes of vortex interaction—the merging and non-merging of two corotating vortices. The fluctuating velocity fields are analyzed utilizing the proper orthogonal decomposition (POD) in order to identify the content, organization, and distribution of the modal turbulent kinetic energy content of the fluctuating velocity eigenmodes. The effects of the two modes of vortex interaction are revealed by the POD analysis which shows distinct differences in the modal features of the two cases. When comparing the low-order eigenmodes of the two cases, the size of the structures contained within the first ten modes is seen to increase as the flow progresses downstream for the merging case, whereas the opposite is true for the non-merging case. Additionally, the relative modal energy contribution of the first ten eigenmodes increases as the vortices evolve downstream for the merging case, whereas in the non-merging case the relative modal energy contribution decreases

Persistence of metastable vortex lattice domains in MgB2 in the presence of vortex motion.

Science.gov (United States)

Rastovski, C; Schlesinger, K J; Gannon, W J; Dewhurst, C D; DeBeer-Schmitt, L; Zhigadlo, N D; Karpinski, J; Eskildsen, M R

2013-09-06

Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.

Examining flow-flame interaction and the characteristic stretch rate in vortex-driven combustion dynamics using PIV and numerical simulation

KAUST Repository

Hong, Seunghyuck; Speth, Raymond L.; Shanbhogue, Santosh J.; Ghoniem, Ahmed F.

2013-01-01

In this paper, we experimentally investigate the combustion dynamics in lean premixed flames in a laboratory scale backward-facing step combustor in which flame-vortex driven dynamics are observed. A series of tests was conducted using propane/hydrogen/air mixtures for various mixture compositions at the inlet temperature ranging from 300K to 500K and at atmospheric pressure. Pressure measurements and high speed particle image velocimetry (PIV) are used to generate pressure response curves and phase-averaged vorticity and streamlines as well as the instantaneous flame front, respectively, which describe unsteady flame and flow dynamics in each operating regime. This work was motivated in part by our earlier study where we showed that the strained flame consumption speed Sc can be used to collapse the pressure response curves over a wide range of operating conditions. In previous studies, the stretch rate at which Sc was computed was determined by trial and error. In this study, flame stretch is estimated using the instantaneous flame front and velocity field from the PIV measurement. Independently, we also use computed strained flame speed and the experimental data to determine the characteristic values of stretch rate near the mode transition points at which the flame configuration changes. We show that a common value of the characteristic stretch rate exists across all the flame configurations. The consumption speed computed at the characteristic stretch rate captures the impact of different operating parameters on the combustor dynamics. These results suggest that the unsteady interactions between the turbulent flow and the flame dynamics can be encapsulated in the characteristic stretch rate, which governs the critical flame speed at the mode transitions and thereby plays an important role in determining the stability characteristics of the combustor. © 2013 The Combustion Institute.

Examining flow-flame interaction and the characteristic stretch rate in vortex-driven combustion dynamics using PIV and numerical simulation

KAUST Repository

Hong, Seunghyuck

2013-08-01

In this paper, we experimentally investigate the combustion dynamics in lean premixed flames in a laboratory scale backward-facing step combustor in which flame-vortex driven dynamics are observed. A series of tests was conducted using propane/hydrogen/air mixtures for various mixture compositions at the inlet temperature ranging from 300K to 500K and at atmospheric pressure. Pressure measurements and high speed particle image velocimetry (PIV) are used to generate pressure response curves and phase-averaged vorticity and streamlines as well as the instantaneous flame front, respectively, which describe unsteady flame and flow dynamics in each operating regime. This work was motivated in part by our earlier study where we showed that the strained flame consumption speed Sc can be used to collapse the pressure response curves over a wide range of operating conditions. In previous studies, the stretch rate at which Sc was computed was determined by trial and error. In this study, flame stretch is estimated using the instantaneous flame front and velocity field from the PIV measurement. Independently, we also use computed strained flame speed and the experimental data to determine the characteristic values of stretch rate near the mode transition points at which the flame configuration changes. We show that a common value of the characteristic stretch rate exists across all the flame configurations. The consumption speed computed at the characteristic stretch rate captures the impact of different operating parameters on the combustor dynamics. These results suggest that the unsteady interactions between the turbulent flow and the flame dynamics can be encapsulated in the characteristic stretch rate, which governs the critical flame speed at the mode transitions and thereby plays an important role in determining the stability characteristics of the combustor. © 2013 The Combustion Institute.

Co-combustor: the solid waste thermal treatment plant in MINT

International Nuclear Information System (INIS)

Norasalwa Zakaria; Mohd Azman Che Mat Isa; Sivapalan Kathiravale; Mohd Fairus Abdul Farid; Mohamad Puad Hj Abu; Rosli Darmawan; Muhd Noor Muhd Yunus

2005-01-01

MINT has geared up into the field of solid waste thermal treatment processing back in 1999 when a new unit known as MIREC was established. Since then, a fast progress has taken place including the design and construction of a pilot scale incinerator, named as the Co-Combustor. The Co-combustor was designed and developed based on the gasification principles, which employs combustion in starved air condition. In year 2001, this plant was commissioned. To date, it has been running quite well according to its design values. Several test runs were also performed in order to collect and gather data, which serve as a background or backtrack record for upgrading purposes and optimizing its performance in future. On going research is also conducted on this plant especially on the study of the waste's behaviors under combustion. Besides the typical RND activities, the Co-combustor is also currently being used to burn waste paper especially to dispose restricted and confidential documents. This paper will highlight on the design, performance, application and usage of the co-combustor. The direction for research and development activities for this plant is also discussed in this paper so as to strengthen the knowledge and build up expertise in the field of incineration

Development of an analytical model to assess fuel property effects on combustor performance

Science.gov (United States)

Sutton, R. D.; Troth, D. L.; Miles, G. A.; Riddlebaugh, S. M.

1987-01-01

A generalized first-order computer model has been developed in order to analytically evaluate the potential effect of alternative fuels' effects on gas turbine combustors. The model assesses the size, configuration, combustion reliability, and durability of the combustors required to meet performance and emission standards while operating on a broad range of fuels. Predictions predicated on combustor flow-field determinations by the model indicate that fuel chemistry, as defined by hydrogen content, exerts a significant influence on flame retardation, liner wall temperature, and smoke emission.

Design and evaluation of combustors for reducing aircraft engine pollution

Science.gov (United States)

Jones, R. E.; Grobman, J.

1973-01-01

Various techniques and test results are briefly described and referenced for detail. The effort arises from the increasing concern for the measurement and control of emissions from gas turbine engines. The greater part of this research is focused on reducing the oxides of nitrogen formed during takeoff and cruise in both advanced CTOL, high pressure ratio engines, and advanced supersonic aircraft engines. The experimental approaches taken to reduce oxides of nitrogen emissions include the use of: multizone combustors incorporating reduced dwell time, fuel-air premixing, air atomization, fuel prevaporization, water injection, and gaseous fuels. In the experiments conducted to date, some of these techniques were more successful than others in reducing oxides of nitrogen emissions. Tests are being conducted on full-annular combustors at pressures up to 6 atmospheres and on combustor segments at pressures up to 30 atmospheres.

Propagation of optical vortex beams and nucleation of vortex-antivortex pairs in disordered nonlinear photonic lattices

International Nuclear Information System (INIS)

Cho, Yeong-Kwon; Kim, Ki-Hong

2014-01-01

The propagation of optical vortex beams through disordered nonlinear photonic lattices is numerically studied. The vortex beams are generated by using a superposition of several Gaussian laser beams arranged in a radially-symmetric manner. The paraxial nonlinear Schroedinger equation describing the longitudinal propagation of the beam array through nonlinear triangular photonic lattices with two-dimensional disorder is solved numerically by using the split-step Fourier method. We find that due to the spatial disorder, the vortex beam is destabilized after propagating a finite distance and new vortex-antivortex pairs are nucleated at the positions of perfect destructive interference. We also find that in the presence of a self-focusing nonlinearity, the vortex-antivortex pair nucleation is suppressed and the vortex beam becomes more stable, while a self-defocusing nonlinearity enhances the vortex-antivortex pair nucleation.

Simulation Investigation on Combustion Characteristics in a Four-Point Lean Direct Injection Combustor with Hydrogen/Air

Directory of Open Access Journals (Sweden)

Jianzhong Li

2017-06-01

Full Text Available To investigate the combustion characteristics in multi-point lean direct injection (LDI combustors with hydrogen/air, two swirl–venturi 2 × 2 array four-point LDI combustors were designed. The four-point LDI combustor consists of injector assembly, swirl–venturi array and combustion chamber. The injector, swirler and venturi together govern the rapid mixing of hydrogen and air to form the mixture for combustion. Using clockwise swirlers and anticlockwise swirlers, the co-swirling and count-swirling swirler arrays LDI combustors were achieved. Using Reynolds-Averaged Navier–Stokes (RANS code for steady-state reacting flow computations, the four-point LDI combustors with hydrogen/air were simulated with an 11 species and 23 lumped reaction steps H2/Air reaction mechanism. The axial velocity, turbulence kinetic energy, total pressure drop coefficient, outlet temperature, mass fraction of OH and emission of pollutant NO of four-point LDI combustors, with different equivalence ratios, are here presented and discussed. As the equivalence ratios increased, the total pressure drop coefficient became higher because of increasing heat loss. Increasing equivalence ratios also corresponded with the rise in outlet temperature of the four-point LDI combustors, as well as an increase in the emission index of NO EINO in the four-point LDI combustors. Along the axial distance, the EINO always increased and was at maximum at the exit of the dump. Along the chamber, the EINO gradually increased, maximizing at the exit of chamber. The total temperature of four-point LDI combustors with different equivalence ratios was identical to the theoretical equilibrium temperature. The EINO was an exponential function of the equivalence ratio.

Vortex and half-vortex dynamics in a nonlinear spinor quantum fluid.

Science.gov (United States)

Dominici, Lorenzo; Dagvadorj, Galbadrakh; Fellows, Jonathan M; Ballarini, Dario; De Giorgi, Milena; Marchetti, Francesca M; Piccirillo, Bruno; Marrucci, Lorenzo; Bramati, Alberto; Gigli, Giuseppe; Szymańska, Marzena H; Sanvitto, Daniele

2015-12-01

Vortices are archetypal objects that recur in the universe across the scale of complexity, from subatomic particles to galaxies and black holes. Their appearance is connected with spontaneous symmetry breaking and phase transitions. In Bose-Einstein condensates and superfluids, vortices are both point-like and quantized quasiparticles. We use a two-dimensional (2D) fluid of polaritons, bosonic particles constituted by hybrid photonic and electronic oscillations, to study quantum vortex dynamics. Polaritons benefit from easiness of wave function phase detection, a spinor nature sustaining half-integer vorticity, strong nonlinearity, and tuning of the background disorder. We can directly generate by resonant pulsed excitations a polariton condensate carrying either a full or half-integer vortex as initial condition and follow their coherent evolution using ultrafast imaging on the picosecond scale. The observations highlight a rich phenomenology, such as the spiraling of the half-vortex and the joint path of the twin charges of a full vortex, until the moment of their splitting. Furthermore, we observe the ordered branching into newly generated secondary couples, associated with the breaking of radial and azimuthal symmetries. This allows us to devise the interplay of nonlinearity and sample disorder in shaping the fluid and driving the vortex dynamics. In addition, our observations suggest that phase singularities may be seen as fundamental particles whose quantized events span from pair creation and recombination to 2D+t topological vortex strings.

Vortex generation and wave-vortex interaction over a concave plate with roughness and suction

Science.gov (United States)

Bertolotti, Fabio

1993-01-01

The generation and amplification of vortices by surface homogeneities, both in the form of surface waviness and of wall-normal velocity, is investigated using the nonlinear parabolic stability equations. Transients and issues of algebraic growth are avoided through the use of a similarity solution as initial condition for the vortex. In the absence of curvature, the vortex decays as the square root of 1/x when flowing over streamwise aligned riblets of constant height, and grows as the square root of x when flowing over a corresponding streamwise aligned variation of blowing/suction transpiration velocity. However, in the presence of wall inhomogeneities having both streamwise and spanwise periodicity, the growth of the vortex can be much larger. In the presence of curvature, the vortex develops into a Gortler vortex. The 'direct' and 'indirect' interaction mechanisms possible in wave-vortex interaction are presented. The 'direct' interaction does not lead to strong resonance with the flow conditions investigated. The 'indirect' interaction leads to K-type transition.

Manipulation of vortex rings for flow control

International Nuclear Information System (INIS)

Toyoda, Kuniaki; Hiramoto, Riho

2009-01-01

This paper reviews the dynamics of vortex rings and the control of flow by the manipulation of vortex rings. Vortex rings play key roles in many flows; hence, the understanding of the dynamics of vortex rings is crucial for scientists and engineers dealing with flow phenomena. We describe the structures and motions of vortex rings in circular and noncircular jets, which are typical examples of flows evolving into vortex rings. For circular jets the mechanism of evolving, merging and breakdown of vortex rings is described, and for noncircular jets the dynamics of three-dimensional deformation and interaction of noncircular vortex rings under the effect of self- and mutual induction is discussed. The application of vortex-ring manipulation to the control of various flows is reviewed with successful examples, based on the relationship between the vortex ring dynamics and the flow properties. (invited paper)

Three-dimensional particle image velocimetry in a generic can-type gas turbine combustor

CSIR Research Space (South Africa)

Meyers, BC

2009-09-01

Full Text Available The three-dimensional flow field inside a generic can-type, forward flow, experimental combustor was measured. A stereoscopic Particle Image Velocimetry (PIV) system was used to obtain the flow field of the combustor in the non-reacting condition...

Nonintrusive transceiver and method for characterizing temperature and velocity fields in a gas turbine combustor

Science.gov (United States)

DeSilva, Upul P.; Claussen, Heiko

2017-09-05

An acoustic transceiver is implemented for measuring acoustic properties of a gas in a turbine engine combustor. The transceiver housing defines a measurement chamber and has an opening adapted for attachment to a turbine engine combustor wall. The opening permits propagation of acoustic signals between the gas in the turbine engine combustor and gas in the measurement chamber. An acoustic sensor mounted to the housing receives acoustic signals propagating in the measurement chamber, and an acoustic transmitter mounted to the housing creates acoustic signals within the measurement chamber. An acoustic measurement system includes at least two such transceivers attached to a turbine engine combustor wall and connected to a controller.

Optical vortex scanning inside the Gaussian beam

International Nuclear Information System (INIS)

Masajada, J; Leniec, M; Augustyniak, I

2011-01-01

We discussed a new scanning method for optical vortex-based scanning microscopy. The optical vortex is introduced into the incident Gaussian beam by a vortex lens. Then the beam with the optical vortex is focused by an objective and illuminates the sample. By changing the position of the vortex lens we can shift the optical vortex position at the sample plane. By adjusting system parameters we can get 30 times smaller shift at the sample plane compared to the vortex lens shift. Moreover, if the range of vortex shifts is smaller than 3% of the beam radius in the sample plane the amplitude and phase distribution around the phase dislocation remains practically unchanged. Thus we can scan the sample topography precisely with an optical vortex

Multiple helical modes of vortex breakdown

DEFF Research Database (Denmark)

Sørensen, Jens Nørkær; Naumov, I. V.; Okulov, Valery

2011-01-01

Experimental observations of vortex breakdown in a rotating lid-driven cavity are presented. The results show that vortex breakdown for cavities with high aspect ratios is associated with the appearance of stable helical vortex multiplets. By using results from stability theory generalizing Kelvi......’s problem on vortex polygon stability, and systematically exploring the cavity flow, we succeeded in identifying two new stable vortex breakdown states consisting of triple and quadruple helical multiplets....

Optimization high vortex finder of cyclone separator with computational fluids dynamics simulation

Directory of Open Access Journals (Sweden)

Ni Ketut Caturwati

2017-01-01

Full Text Available Cyclone separator is an equipment that separates particles contained in the fluid without using filters. The dust particles in the flue gases can be separated by utilizing centrifugal forces and different densities of particles, so that the exhaust gases to be cleaner before discharged into the environment. In this paper carried out a simulation by Computational of Fluids Dynamics to determine the number of particles that can be separated in several cyclone separator which has a ratio body diameter against vortex finder high varied as : 1:0.5 ; 1:0.75 ; 1:1 ; 1:1.25 and 1:1.5. Fluid inlet are air with antrachite impurity particles that are commonly found in the exhaust gases from tire manufacturers with inlet velocities varied as: 15 m/s and 30 m/s. The results of simulation show the fluids with 15 m/s of inlet velocity is generate particle separation value is higher than the fluids with 30 m/s inlet velocity for ratio of body diameter and height vortex finder a: 1:0.5 and 1:1.5. For both of inlet velocities the best ratio of body diameter and height vortex finder is 1:1.25, where it has the highest values of percentage trapped particles about 86% for 30 m/s input velocity and also for 15 m/s input velocity.

Cryptanalysis of Vortex

DEFF Research Database (Denmark)

Aumasson, Jean-Philippe; Dunkelman, Orr; Mendel, Florian

2009-01-01

Vortex is a hash function that was first presented at ISC'2008, then submitted to the NIST SHA-3 competition after some modifications. This paper describes several attacks on both versions of Vortex, including collisions, second preimages, preimages, and distinguishers. Our attacks exploit flaws...

Combustion of hydrogen-air in micro combustors with catalytic Pt layer

Energy Technology Data Exchange (ETDEWEB)

Yang Wang; Zhijun Zhou; Weijuan Yang; Junhu Zhou; Jianzhong Liu; Zhihua Wang; Cen, Kefa [State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, Zhejiang (China)

2010-06-15

Micro power generators have high power density. However, their key components micro combustors have low stability. In this experiment, catalyst is applied to improve the stability. The catalytic micro combustor is made from an alumina ceramic tube. It has inner diameter of 1 mm, outer diameter of 2.02 mm and length of 24.5 mm. It is prepared through impregnation of aqueous solution of H{sub 2}PtCl{sub 6}. The flammability limits and surface temperatures under different operation conditions are measured. The flow rates range from 0.08 to 0.4 L/min. According to the experimental results, catalyst is effective to inhibit extinction. For example, At 0.8 L/min, the stability limit is 0.193-14.9 in the non-catalytic combustor. After applying catalyst, the lean limit is near 0, and the rich limit is 29.3. But catalyst is less effective to inhibit blow out. Increasing flow rates also inhibits extinction. In the non-catalytic combustor, while the flow rates increase from 0.08 to 0.2 L/min, the lean stability limit decreases from 0.193 to 0.125. The experimental results indicate that catalyst induces shift downstream in the stoichiometric and rich cases. The numeric simulation verifies that the heterogeneous reaction weakens the homogeneous reaction through consuming fuels. Thus, the insufficient heat recirculation makes the reaction region shift downstream. However, lean mixture has intense reaction in the catalytic combustor. It is attributed to the high mass diffusion and low thermal diffusion of lean mixture. (author)

Combustion of hydrogen-air in micro combustors with catalytic Pt layer

Energy Technology Data Exchange (ETDEWEB)

Wang Yang; Zhou Zhijun [State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, Zhejiang (China); Yang Weijuan, E-mail: 10508107@zju.edu.c [State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, Zhejiang (China); Zhou Junhu; Liu Jianzhong; Wang Zhihua; Cen Kefa [State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, Zhejiang (China)

2010-06-15

Micro power generators have high power density. However, their key components micro combustors have low stability. In this experiment, catalyst is applied to improve the stability. The catalytic micro combustor is made from an alumina ceramic tube. It has inner diameter of 1 mm, outer diameter of 2.02 mm and length of 24.5 mm. It is prepared through impregnation of aqueous solution of H{sub 2}PtCl{sub 6}. The flammability limits and surface temperatures under different operation conditions are measured. The flow rates range from 0.08 to 0.4 L/min. According to the experimental results, catalyst is effective to inhibit extinction. For example, At 0.8 L/min, the stability limit is 0.193-14.9 in the non-catalytic combustor. After applying catalyst, the lean limit is near 0, and the rich limit is 29.3. But catalyst is less effective to inhibit blow out. Increasing flow rates also inhibits extinction. In the non-catalytic combustor, while the flow rates increase from 0.08 to 0.2 L/min, the lean stability limit decreases from 0.193 to 0.125. The experimental results indicate that catalyst induces shift downstream in the stoichiometric and rich cases. The numeric simulation verifies that the heterogeneous reaction weakens the homogeneous reaction through consuming fuels. Thus, the insufficient heat recirculation makes the reaction region shift downstream. However, lean mixture has intense reaction in the catalytic combustor. It is attributed to the high mass diffusion and low thermal diffusion of lean mixture.

Combustion of hydrogen-air in micro combustors with catalytic Pt layer

International Nuclear Information System (INIS)

Wang Yang; Zhou Zhijun; Yang Weijuan; Zhou Junhu; Liu Jianzhong; Wang Zhihua; Cen Kefa

2010-01-01

Micro power generators have high power density. However, their key components micro combustors have low stability. In this experiment, catalyst is applied to improve the stability. The catalytic micro combustor is made from an alumina ceramic tube. It has inner diameter of 1 mm, outer diameter of 2.02 mm and length of 24.5 mm. It is prepared through impregnation of aqueous solution of H 2 PtCl 6 . The flammability limits and surface temperatures under different operation conditions are measured. The flow rates range from 0.08 to 0.4 L/min. According to the experimental results, catalyst is effective to inhibit extinction. For example, At 0.8 L/min, the stability limit is 0.193-14.9 in the non-catalytic combustor. After applying catalyst, the lean limit is near 0, and the rich limit is 29.3. But catalyst is less effective to inhibit blow out. Increasing flow rates also inhibits extinction. In the non-catalytic combustor, while the flow rates increase from 0.08 to 0.2 L/min, the lean stability limit decreases from 0.193 to 0.125. The experimental results indicate that catalyst induces shift downstream in the stoichiometric and rich cases. The numeric simulation verifies that the heterogeneous reaction weakens the homogeneous reaction through consuming fuels. Thus, the insufficient heat recirculation makes the reaction region shift downstream. However, lean mixture has intense reaction in the catalytic combustor. It is attributed to the high mass diffusion and low thermal diffusion of lean mixture.

An Organic Vortex Laser.

Science.gov (United States)

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.

Coal-based oxy-fuel system evaluation and combustor development

Energy Technology Data Exchange (ETDEWEB)

MacAdam, S.; Biebuyck, C.; Anderson, R.; Pronske, K. [Clean Energy Systems Inc., Rancho Cordova, CA (United States)

2007-07-01

The core of the Clean Energy Systems, Inc. (CES) process is an oxy-combustor adapted from rocket engine technology. This combustor burns gaseous or liquid fuels with gaseous oxygen in the presence of water. Fuels include syngas from coal, refinery residues, or biomass; natural gas; landfill gas; glycoal solutions and oil/water emulsions. The combustion is performed at near-stoichiometric conditions in the presence of recycled water to produce a steam/CO{sub 2} mixture at high temperature and pressure. These combustion products power conventional or advanced steam turbines and may use modified gas turbines operating at high-temperatures for expansion at intermediate pressures. The gas exiting the turbines enter a condenser/separator where it is cooled, separating into its components, water and CO{sub 2}. The recovered CO{sub 2} is conditioned and purified as appropriate and sold or sequestered. Most of the water is recycled to the gas generator but excess high-purity water is produced and available for export. The development, evaluation and demonstration of the CES combustor are described. 8 refs., 4 figs., 1 tab.

Dynamic signatures of driven vortex motion.

Energy Technology Data Exchange (ETDEWEB)

Crabtree, G. W.; Kwok, W. K.; Lopez, D.; Olsson, R. J.; Paulius, L. M.; Petrean, A. M.; Safar, H.

1999-09-16

We probe the dynamic nature of driven vortex motion in superconductors with a new type of transport experiment. An inhomogeneous Lorentz driving force is applied to the sample, inducing vortex velocity gradients that distinguish the hydrodynamic motion of the vortex liquid from the elastic and-plastic motion of the vortex solid. We observe elastic depinning of the vortex lattice at the critical current, and shear induced plastic slip of the lattice at high Lorentz force gradients.

Numerical simulations of the internal flow pattern of a vortex pump compared to the Hamel-Oseen vortex

International Nuclear Information System (INIS)

Gerlach, Angela; Preuss, Enrico; Thamsen, Paul Uwe; Lykholt-Ustrup, Flemming

2017-01-01

We did a numerical study of the internal flow field of a vortex pump. Five operating points were considered and validated through a measured characteristic curve. The internal flow pattern of a vortex pump was analyzed and compared to the Hamel-Oseen vortex model. The calculated flow field was assessed with respect to the circumferential velocity, the vorticity and the axial velocity. Whereas the trajectories of the circumferential velocity were largely in line with the Hamel-Oseen vortex model, the opposite was true for vorticity. Only the vorticity at strong part load was in line with the predictions of the Hamel-Oseen vortex model. We therefore compared the circumferential velocity and vorticity for strong part load operation to the analytical predictions of the Hamel-Oseen vortex model. The simulated values were below the analytical values. The study therefore suggests that a vortex similar to the Hamel-Oseen vortex is only present at the strong part load operation

Numerical simulations of the internal flow pattern of a vortex pump compared to the Hamel-Oseen vortex

Energy Technology Data Exchange (ETDEWEB)

Gerlach, Angela; Preuss, Enrico; Thamsen, Paul Uwe [Institute of Fluid System Dynamics, Technische Universitaet, Berlin (Germany); Lykholt-Ustrup, Flemming [Grundfos Holding A/S, Bjerringbro (Denmark)

2017-04-15

We did a numerical study of the internal flow field of a vortex pump. Five operating points were considered and validated through a measured characteristic curve. The internal flow pattern of a vortex pump was analyzed and compared to the Hamel-Oseen vortex model. The calculated flow field was assessed with respect to the circumferential velocity, the vorticity and the axial velocity. Whereas the trajectories of the circumferential velocity were largely in line with the Hamel-Oseen vortex model, the opposite was true for vorticity. Only the vorticity at strong part load was in line with the predictions of the Hamel-Oseen vortex model. We therefore compared the circumferential velocity and vorticity for strong part load operation to the analytical predictions of the Hamel-Oseen vortex model. The simulated values were below the analytical values. The study therefore suggests that a vortex similar to the Hamel-Oseen vortex is only present at the strong part load operation.

Vortex shaking study of REBCO tape with consideration of anisotropic characteristics

Science.gov (United States)

Liang, Fei; Qu, Timing; Zhang, Zhenyu; Sheng, Jie; Yuan, Weijia; Iwasa, Yukikazu; Zhang, Min

2017-09-01

The second generation high temperature superconductor, specifically REBCO, has become a new research focus in the development of a new generation of high-field (>25 T) magnets. One of the main challenges in the application of the magnets is the current screening problem. Previous research shows that for magnetized superconducting stacks and bulks the application of an AC field in plane with the circulating current will lead to demagnetization due to vortex shaking, which provides a possible solution to remove the shielding current. This paper provides an in-depth study, both experimentally and numerically, to unveil the vortex shaking mechanism of REBCO stacks. A new experiment was carried out to measure the demagnetization rate of REBCO stacks exposed to an in-plane AC magnetic field. Meanwhile, 2D finite element models, based on the E-J power law, are developed for simulating the vortex shaking effect of the AC magnetic field. Qualitative agreement was obtained between the experimental and the simulation results. Our results show that the applied in-plane magnetic field leads to a sudden decay of trapped magnetic field in the first half shaking cycle, which is caused by the magnetic field dependence of critical current. Furthermore, the decline of demagnetization rate with the increase of tape number is mainly due to the cross-magnetic field being screened by the top and bottom stacks during the shaking process, which leads to lower demagnetization rate of inner layers. We also demonstrate that the frequency of the applied AC magnetic field has little impact on the demagnetization process. Our modeling tool and findings perfect the vortex shaking theory and provide helpful guidance for eliminating screening current in the new generation REBCO magnets.

The pitfalls of short-range endemism: high vulnerability to ecological and landscape traps

Directory of Open Access Journals (Sweden)

Leanda D. Mason

2018-05-01

Full Text Available Ecological traps attract biota to low-quality habitats. Landscape traps are zones caught in a vortex of spiralling degradation. Here, we demonstrate how short-range endemic (SRE traits may make such taxa vulnerable to ecological and landscape traps. Three SRE species of mygalomorph spider were used in this study: Idiommata blackwalli, Idiosoma sigillatum and an undescribed Aganippe sp. Mygalomorphs can be long-lived (>43 years and select sites for permanent burrows in their early dispersal phase. Spiderlings from two species, I. blackwalli (n = 20 and Aganippe sp. (n = 50, demonstrated choice for microhabitats under experimental conditions, that correspond to where adults typically occur in situ. An invasive veldt grass microhabitat was selected almost exclusively by spiderlings of I. sigillatum. At present, habitat dominated by veldt grass in Perth, Western Australia, has lower prey diversity and abundance than undisturbed habitats and therefore may act as an ecological trap for this species. Furthermore, as a homogenising force, veldt grass can spread to form a landscape trap in naturally heterogeneous ecosystems. Selection of specialised microhabitats of SREs may explain high extinction rates in old, stable landscapes undergoing (human-induced rapid change.

Sensitivity of the Numerical Prediction of Turbulent Combustion Dynamics in the LIMOUSINE Combustor

NARCIS (Netherlands)

Shahi, Mina; Kok, Jacobus B.W.; Pozarlik, Artur Krzysztof; Roman Casado, J.C.; Sponfeldner, T.

2014-01-01

The objective of this study is to investigate the sensitivity and accuracy of the reaction flow-field prediction for the LIMOUSINE combustor with regard to choices in computational mesh and turbulent combustion model. The LIMOUSINE combustor is a partially premixed, bluff body-stabilized natural gas

Preliminary investigation of the performance of a single tubular combustor at pressure up to 12 atmospheres

Science.gov (United States)

Wear, Jerrold D; Butze, Helmut F

1954-01-01

The effects of combustor operation at conditions representative of those encountered in high pressure-ratio turbojet engines or at high flight speeds on carbon deposition, exhaust smoke, and combustion efficiency were studied in a single tubular combustor. Carbon deposition and smoke formation tests were conducted over a range of combustor-inlet pressures from 33 to 173 pounds per square inch absolute and combustor reference velocities from 78 to 143 feet per second. Combustion efficiency tests were conducted over a range of pressures from 58 to 117 pounds per square inch absolute and velocities from 89 to 172 feet per second.

Aircraft Wake Vortex Deformation in Turbulent Atmosphere

OpenAIRE

Hennemann, Ingo; Holzaepfel, Frank

2007-01-01

Large-scale distortion of aircraft wake vortices appears to play a crucial role for aircraft safety during approach and landing. Vortex distortion is investigated based on large eddy simulations of wake vortex evolution in a turbulent atmosphere. A vortex identification method is developed that can be adapted to the vortex scales of interest. Based on the identified vortex center tracks, a statistics of vortex curvature radii is established. This statistics constitutes the basis for understan...

High-charge and multiple-star vortex coronagraphy from stacked vector vortex phase masks.

Science.gov (United States)

Aleksanyan, Artur; Brasselet, Etienne

2018-02-01

Optical vortex phase masks are now installed at many ground-based large telescopes for high-contrast astronomical imaging. To date, such instrumental advances have been restricted to the use of helical phase masks of the lowest even order, while future giant telescopes will require high-order masks. Here we propose a single-stage on-axis scheme to create high-order vortex coronagraphs based on second-order vortex phase masks. By extending our approach to an off-axis design, we also explore the implementation of multiple-star vortex coronagraphy. An experimental laboratory demonstration is reported and supported by numerical simulations. These results offer a practical roadmap to the development of future coronagraphic tools with enhanced performances.

Scale and material effects on flame characteristics in small heat recirculation combustors of a counter-current channel type

International Nuclear Information System (INIS)

Lee, Min Jung; Cho, Sang Moon; Choi, Byung Il; Kim, Nam Il

2010-01-01

Small energy sources have been interested with the recent development of small-scale mechanical systems. With the purpose of developing a basic model of micro-combustors of heat recirculation, small combustors of a counter-current channel type were fabricated, and the premixed flame stabilization characteristics were investigated experimentally. Each combustor consists of a combustion space and a pair of counter-current channels for heat recirculation. The channel gap was less than the ordinary quenching distance of a stoichiometric methane-air premixed flame. Depending on the flame locations and structures, flame stabilization was classified into four modes: an ordinary mode, a channel mode, a radiation mode, and a well-stirred reaction mode. Base-scale combustors of stainless steel were initially examined. Additional half-scale combustors of stainless steel and quartz were fabricated and their flame stabilization conditions were compared. Consequently, a change of the material of the combustor significantly affected the flame stabilization compared to the effects of a scale-down design. A half-scale quartz combustor had a wide range of flame stabilization conditions. Surface temperatures and the composition of the emission gas were measured. At a higher flow rate, the combustor temperature increases and the light emission from the middle wall is enhanced to extend the flame stabilization conditions. The combustion efficiency and the composition of emitted gas were feasible. These results provide useful information for the design of small-scale combustors.

40 CFR 62.14103 - Emission limits for municipal waste combustor metals, acid gases, organics, and nitrogen oxides.

Science.gov (United States)

2010-07-01

... combustor metals, acid gases, organics, and nitrogen oxides. 62.14103 Section 62.14103 Protection of... combustor metals, acid gases, organics, and nitrogen oxides. (a) The emission limits for municipal waste combustor metals are specified in paragraphs (a)(1) through (a)(3) of this section. (1) The owner or...

Vortex rings in classical and quantum systems

International Nuclear Information System (INIS)

Barenghi, C F; Donnelly, R J

2009-01-01

The study of vortex rings has been pursued for decades and is a particularly difficult subject. However, the discovery of quantized vortex rings in superfluid helium has greatly increased interest in vortex rings with very thin cores. While rapid progress has been made in the simulation of quantized vortex rings, there has not been comparable progress in laboratory studies of vortex rings in a viscous fluid such as water. This article overviews the history and current frontiers of classical and quantum vortex rings. After introducing the classical results, this review discusses thin-cored vortex rings in superfluid helium in section 2, and recent progress in understanding vortex rings of very thin cores propagating in water in section 3. (invited paper)

3D micro-optical elements for generation of tightly focused vortex beams

Directory of Open Access Journals (Sweden)

Balčytis Armandas

2015-01-01

Full Text Available Orbital angular momentum carrying light beams are usedfor optical trapping and manipulation. This emerging trend provides new challenges involving device miniaturization for improved performance and enhanced functionality at the microscale. Here we discus a new fabrication method based on combining the additive 3D structuring capability laser photopolymerization and the substractive sub-wavelength resolution patterning of focused ion beam lithography to produce micro-optical elements capable of compound functionality. As a case in point of this approach binary spiral zone pattern based high numerical aperture micro-lenses capable of generating topological charge carrying tightly focused vortex beams in a single wavefront transformation step are presented. The devices were modelled using finite-difference time-domain simulations, and the theoretical predictions were verified by optically characterizing the propagation properties of light transmitted through the fabricated structures. The resulting devices had focal lengths close to the predicted values of f = 18 µm and f = 13 µm as well as topological charge ℓ dependent vortex focal spot sizes of ~ 1:3 µm and ~ 2:0 µm for ℓ = 1 and ℓ = 2 respectively.

On vortex shedding and prediction of vortex-induced vibrations of circular cylinders

Energy Technology Data Exchange (ETDEWEB)

Halse, Karl Henning

1998-12-31

In offshore installations, many crucial components can be classified as slender marine structures: risers, mooring lines, umbilicals and cables, pipelines. This thesis studies the vortex shedding phenomenon and the problem of predicting vortex-induced vibrations of such structures. As the development of hydrocarbons move to deeper waters, the importance of accurately predicting the vortex-induced response has increased and so the need for proper response prediction methods is large. This work presents an extensive review of existing research publications about vortex shedding from circular cylinders and the vortex-induced vibrations of cylinders and the different numerical approaches to modelling the fluid flow. The response predictions from different methods are found to disagree, both in response shapes and in vibration amplitudes. This work presents a prediction method that uses a fully three-dimensional structural finite element model integrated with a laminar two-dimensional Navier-Stokes solution modelling the fluid flow. This solution is used to study the flow both around a fixed cylinder and in a flexibly mounted one-degree-of-freedom system. It is found that the vortex-shedding process (in the low Reynolds number regime) is well described by the computer program, and that the vortex-induced vibration of the flexibly mounted section do reflect the typical dynamic characteristics of lock-in oscillations. However, the exact behaviour of the experimental results found in the literature was not reproduced. The response of the three-dimensional structural model is larger than the expected difference between a mode shape and a flexibly mounted section. This is due to the use of independent hydrodynamic sections along the cylinder. The predicted response is not unrealistic, and the method is considered a powerful tool. 221 refs., 138 figs., 36 tabs.

On vortex shedding and prediction of vortex-induced vibrations of circular cylinders

Energy Technology Data Exchange (ETDEWEB)

Halse, Karl Henning

1997-12-31

In offshore installations, many crucial components can be classified as slender marine structures: risers, mooring lines, umbilicals and cables, pipelines. This thesis studies the vortex shedding phenomenon and the problem of predicting vortex-induced vibrations of such structures. As the development of hydrocarbons move to deeper waters, the importance of accurately predicting the vortex-induced response has increased and so the need for proper response prediction methods is large. This work presents an extensive review of existing research publications about vortex shedding from circular cylinders and the vortex-induced vibrations of cylinders and the different numerical approaches to modelling the fluid flow. The response predictions from different methods are found to disagree, both in response shapes and in vibration amplitudes. This work presents a prediction method that uses a fully three-dimensional structural finite element model integrated with a laminar two-dimensional Navier-Stokes solution modelling the fluid flow. This solution is used to study the flow both around a fixed cylinder and in a flexibly mounted one-degree-of-freedom system. It is found that the vortex-shedding process (in the low Reynolds number regime) is well described by the computer program, and that the vortex-induced vibration of the flexibly mounted section do reflect the typical dynamic characteristics of lock-in oscillations. However, the exact behaviour of the experimental results found in the literature was not reproduced. The response of the three-dimensional structural model is larger than the expected difference between a mode shape and a flexibly mounted section. This is due to the use of independent hydrodynamic sections along the cylinder. The predicted response is not unrealistic, and the method is considered a powerful tool. 221 refs., 138 figs., 36 tabs.

Stationary states and rotational properties of spin-orbit-coupled Bose-Einstein condensates held under a toroidal trap

Science.gov (United States)

He, Zhang-Ming; Zhang, Xiao-Fei; Kato, Masaya; Han, Wei; Saito, Hiroki

2018-06-01

We consider a pseudospin-1/2 Bose-Einstein condensate with Rashba spin-orbit coupling in a two-dimensional toroidal trap. By solving the damped Gross-Pitaevskii equations for this system, we show that the system exhibits a rich variety of stationary states, such as vehicle wheel and flower-petal stripe patterns. These stationary states are stable against perturbation with thermal energy and can survive for a long time. In the presence of rotation, our results show that the rotating systems have exotic vortex configurations. These phenomenon originates from the interplay among spin-orbit coupling, trap geometry, and rotation.

Variable volume combustor with aerodynamic fuel flanges for nozzle mounting

Science.gov (United States)

McConnaughhay, Johnie Franklin; Keener, Christopher Paul; Johnson, Thomas Edward; Ostebee, Heath Michael

2016-09-20

The present application provides a combustor for use with a gas turbine engine. The combustor may include a number of micro-mixer fuel nozzles and a fuel injection system for providing a flow of fuel to the micro-mixer fuel nozzles. The fuel injection system may include a number of support struts supporting the fuel nozzles and for providing the flow of fuel therethrough. The fuel injection system also may include a number of aerodynamic fuel flanges connecting the micro-mixer fuel nozzles and the support struts.

System and method for reducing combustion dynamics and NO.sub.x in a combustor

Science.gov (United States)

Uhm, Jong H.; Johnson, Thomas Edward

2015-11-20

A system for reducing combustion dynamics and NO.sub.x in a combustor includes a tube bundle that extends radially across at least a portion of the combustor, wherein the tube bundle comprises an upstream surface axially separated from a downstream surface. A shroud circumferentially surrounds the upstream and downstream surfaces. A plurality of tubes extends through the tube bundle from the upstream surface through the downstream surface, wherein the downstream surface is stepped to produce tubes having different lengths through the tube bundle. A method for reducing combustion dynamics and NO.sub.x in a combustor includes flowing a working fluid through a plurality of tubes radially arranged between an upstream surface and a downstream surface of an end cap that extends radially across at least a portion of the combustor, wherein the downstream surface is stepped.

An emissions audit of a biomass combustor burning treated wood waste

International Nuclear Information System (INIS)

Jackson, P.M.; Jones, H.H.; King, P.G.

1993-01-01

This report describes the Emissions Audit carried out on a Biomass Combustor burning treated wood waste at the premises of a furniture manufacturer. The Biomass Combustor was tested in two firing modes; continuous fire and modulating fire. Combustion chamber temperatures and gas residence times were not measured. Boiler efficiencies were very good at greater than 75% in both tests. However, analysis of the flue gases indicated that improved efficiencies are possible. The average concentrations of CO (512mgm -3 ) and THC (34mgm -3 ) for Test 1 were high, indicating that combustion was poor. The combustor clearly does not meet the requirements of the Guidance Note for the Combustion of Wood Waste. CO 2 and O 2 concentrations were quite variable showing that combustion conditions were fairly unstable. Improved control of combustion should lead to acceptable emission concentrations. (Author)

Vortex Ring Dynamics in Radially Confined Domains

Science.gov (United States)

Stewart, Kelley; Niebel, Casandra; Jung, Sunghwan; Vlachos, Pavlos

2010-11-01

Vortex ring dynamics have been studied extensively in semi-infinite quiescent volumes. However, very little is known about vortex-ring formation in wall-bounded domains where vortex wall interaction will affect both the vortex ring pinch-off and propagation velocity. This study addresses this limitation and studies vortex formation in radially confined domains to analyze the affect of vortex-ring wall interaction on the formation and propagation of the vortex ring. Vortex rings were produced using a pneumatically driven piston cylinder arrangement and were ejected into a long cylindrical tube which defined the confined downstream domain. A range of confinement domains were studied with varying confinement diameters Velocity field measurements were performed using planar Time Resolved Digital Particle Image Velocimetry (TRDPIV) and were processed using an in-house developed cross-correlation PIV algorithm. The experimental analysis was used to facilitate the development of a theoretical model to predict the variations in vortex ring circulation over time within confined domains.

An experimental study of the stable and unstable operation of an LPP gas turbine combustor

Science.gov (United States)

Dhanuka, Sulabh Kumar

A study was performed to better understand the stable operation of an LPP combustor and formulate a mechanism behind the unstable operation. A unique combustor facility was developed at the University of Michigan that incorporates the latest injector developed by GE Aircraft Engines and enables operation at elevated pressures with preheated air at flow-rates reflective of actual conditions. The large optical access has enabled the use of a multitude of state-of-the-art laser diagnostics such as PIV and PLIF, and has shed invaluable light not only into the GE injector specifically but also into gas turbine combustors in general. Results from Particle Imaging Velocimetry (PIV) have illustrated the role of velocity, instantaneous vortices, and key recirculation zones that are all critical to the combustor's operation. It was found that considerable differences exist between the iso-thermal and reacting flows, and between the instantaneous and mean flow fields. To image the flame, Planar Laser Induced Fluorescence (PLIF) of the formaldehyde radical was successfully utilized for the first time in a Jet-A flame. Parameters regarding the flame's location and structure have been obtained that assist in interpreting the velocity results. These results have also shown that some of the fuel injected from the main fuel injectors actually reacts in the diffusion flame of the pilot. The unstable operation of the combustor was studied in depth to obtain the stability limits of the combustor, behavior of the flame dynamics, and frequencies of the oscillations. Results from simultaneous pressure and high speed chemiluminescence images have shown that the low frequency dynamics can be characterized as flashback oscillations. The results have also shown that the stability of the combustor can be explained by simple and well established premixed flame stability mechanisms. This study has allowed the development of a model that describes the instability mechanism and accurately

A vortex dynamics perspective on stratospheric sudden warmings

OpenAIRE

Matthewman, N. J.

2009-01-01

A vortex dynamics approach is used to study the underlying mechanisms leading to polar vortex breakdown during stratospheric sudden warmings (SSWs). Observational data are used in chapter 2 to construct climatologies of the Arctic polar vortex structure during vortex-splitting and vortex-displacement SSWs occurring between 1958 and 2002. During vortex-splitting SSWs, polar vortex breakdown is shown to be typically independent of height (barotropic), whereas breakdown during vor...

Controlling vortex motion and vortex kinetic friction

International Nuclear Information System (INIS)

Nori, Franco; Savel'ev, Sergey

2006-01-01

We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcia, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves

Controlling vortex motion and vortex kinetic friction

Science.gov (United States)

Nori, Franco; Savel'ev, Sergey

2006-05-01

We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcìa, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves.

Vortex formation and instability in the left ventricle

Science.gov (United States)

Le, Trung Bao; Sotiropoulos, Fotis; Coffey, Dane; Keefe, Daniel

2012-09-01

We study the formation of the mitral vortex ring during early diastolic filling in a patient-specific left ventricle (LV) using direct numerical simulation. The geometry of the left ventricle is reconstructed from Magnetic Resonance Imaging (MRI) data of a healthy human subject. The left ventricular kinematics is modeled via a cell-based activation methodology, which is inspired by cardiac electro-physiology and yields physiologic LV wall motion. In the fluid dynamics videos, we describe in detail the three-dimensional structure of the mitral vortex ring, which is formed during early diastolic filling. The ring starts to deform as it propagates toward the apex of the heart and becomes inclined. The trailing secondary vortex tubes are formed as the result of interaction between the vortex ring and the LV wall. These vortex tubes wrap around the circumference and begin to interact with and destabilize the mitral vortex ring. At the end of diastole, the vortex ring impinges on the LV wall and the large-scale intraventricular flow rotates in clockwise direction. We show for the first time that the mitral vortex ring evolution is dominated by a number of vortex-vortex and vortex-wall interactions, including lateral straining and deformation of vortex ring, the interaction of two vortex tubes with unequal strengths, helicity polarization of vortex tubes and twisting instabilities of the vortex cores.

Interaction of Vortex Ring with Cutting Plate

Science.gov (United States)

Musta, Mustafa

2015-11-01

The interaction of a vortex ring impinging on a thin cutting plate was made experimentally using Volumetric 3-component Velocitmetry (v3v) technique. The vortex rings were generated with piston-cylinder vortex ring generator using piston stroke-to-diameter ratios and Re at 2-3 and 1500 - 3000, respectively. The cutting of vortex rings below center line leads to the formation of secondary vortices on each side of the plate which is look like two vortex rings, and a third vortex ring propagates further downstream in the direction of the initial vortex ring, which is previously showed by flow visualization study of Weigand (1993) and called ``trifurcation''. Trifurcation is very sensitive to the initial Reynolds number and the position of the plate with respect to the vortex ring generator pipe. The present work seeks more detailed investigation on the trifurcation using V3V technique. Conditions for the formation of trifurcation is analyzed and compared with Weigand (1993). The formed secondary vortex rings and the propagation of initial vortex ring in the downstream of the plate are analyzed by calculating their circulation, energy and trajectories.

Electric vortex in MHD flow

International Nuclear Information System (INIS)

Garcia, M.

1995-01-01

An electric vortex is the circulation of electron space charge about a magnetic field line that is transported by ion momentum. In cold, or low β flow the vortex diameter is the minimum length scale of charge neutrality. The distinctive feature of the vortex is its radial electric field which manifests the interplay of electrostatics, magnetism, and motion

Combustion and direct energy conversion inside a micro-combustor

International Nuclear Information System (INIS)

Lei, Yafeng; Chen, Wei; Lei, Jiang

2016-01-01

Highlights: • The flammability range of micro-combustor was broadened with heat recirculation. • The quenching diameter decreased with heat recirculation compared to without recirculation. • The surface areas to volume ratio was the most important parameter affecting the energy conversion efficiency. • The maximum conversion efficiency (3.15%) was achieved with 1 mm inner diameter. - Abstract: Electrical energy can be generated by employing a micro-thermophotovoltaic (TPV) cell which absorbs thermal radiation from combustion taking place in a micro-combustor. The stability of combustion in a micro-combustor is essential for operating a micro-power system using hydrogen and hydrocarbon fuels as energy source. To understand the mechanism of sustaining combustion within the quenching distance of fuel, this study proposed an annular micro combustion tube with recirculation of exhaust heat. To explore the feasibility of combustion in the micro annular tube, the parameters influencing the combustion namely, quenching diameter, and flammability were studied through numerical simulation. The results indicated that combustion could be realized in micro- combustor using heat recirculation. Following results were obtained from simulation. The quenching diameter reduced from 1.3 mm to 0.9 mm for heat recirculation at equivalence ratio of 1; the lean flammability was 2.5%–5% lower than that of without heat recirculation for quenching diameters between 2 mm and 5 mm. The overall energy conversion efficiency varied at different inner diameters. A maximum efficiency of 3.15% was achieved at an inner diameter of 1 mm. The studies indicated that heat recirculation is an effective strategy to maintain combustion and to improve combustion limits in micro-scale system.

Influence of the burner swirl on the azimuthal instabilities in an annular combustor

Science.gov (United States)

Mazur, Marek; Nygård, Håkon; Worth, Nicholas; Dawson, James

2017-11-01

Improving our fundamental understanding of thermoacoustic instabilities will aid the development of new low emission gas turbine combustors. In the present investigation the effects of swirl on the self-excited azimuthal combustion instabilities in a multi-burner annular annular combustor are investigated experimentally. Each of the burners features a bluff body and a swirler to stabilize the flame. The combustor is operated with an ethylene-air premixture at powers up to 100 kW. The swirl number of the burners is varied in these tests. For each case, dynamic pressure measurements at different azimuthal positions, as well as overhead imaging of OH* of the entire combustor are conducted simultaneously and at a high sampling frequency. The measurements are then used to determine the azimuthal acoustic and heat release rate modes in the chamber and to determine whether these modes are standing, spinning or mixed. Furthermore, the phase shift between the heat release rate and pressure and the shape of these two signals are analysed at different azimuthal positions. Based on the Rayleigh criterion, these investigations allow to obtain an insight about the effects of the swirl on the instability margins of the combustor. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant agreement n° 677931 TAIAC).

Some observations of tip-vortex cavitation

Science.gov (United States)

Arndt, R. E. A.; Arakeri, V. H.; Higuchi, H.

1991-08-01

Cavitation has been observed in the trailing vortex system of an elliptic platform hydrofoil. A complex dependence on Reynolds number and gas content is noted at inception. Some of the observations can be related to tension effects associated with the lack of sufficiently large-sized nuclei. Inception measurements are compared with estimates of pressure in the vortex obtained from LDV measurements of velocity within the vortex. It is concluded that a complete correlation is not possible without knowledge of the fluctuating levels of pressure in tip-vortex flows. When cavitation is fully developed, the observed tip-vortex trajectory flows. When cavitation is fully developed, the observed tip-vortex trajectory shows a surprising lack of dependence on any of the physical parameters varied, such as angle of attack, Reynolds number, cavitation number, and dissolved gas content.

The NASA Ames Hypersonic Combustor-Model Inlet CFD Simulations and Experimental Comparisons

Science.gov (United States)

Venkatapathy, E.; Tokarcik-Polsky, S.; Deiwert, G. S.; Edwards, Thomas A. (Technical Monitor)

1995-01-01

Computations have been performed on a three-dimensional inlet associated with the NASA Ames combustor model for the hypersonic propulsion experiment in the 16-inch shock tunnel. The 3-dimensional inlet was designed to have the combustor inlet flow nearly two-dimensional and of sufficient mass flow necessary for combustion. The 16-inch shock tunnel experiment is a short duration test with test time of the order of milliseconds. The flow through the inlet is in chemical non-equilibrium. Two test entries have been completed and limited experimental results for the inlet region of the combustor-model are available. A number of CFD simulations, with various levels of simplifications such as 2-D simulations, 3-D simulations with and without chemical reactions, simulations with and without turbulent conditions, etc., have been performed. These simulations have helped determine the model inlet flow characteristics and the important factors that affect the combustor inlet flow and the sensitivity of the flow field to these simplifications. In the proposed paper, CFD modeling of the hypersonic inlet, results from the simulations and comparison with available experimental results will be presented.

Thermal characteristics of various biomass fuels in a small-scale biomass combustor

International Nuclear Information System (INIS)

Al-Shemmeri, T.T.; Yedla, R.; Wardle, D.

2015-01-01

Biomass combustion is a mature and reliable technology, which has been used for heating and cooking. In the UK, biomass currently qualifies for financial incentives such as the Renewable Heat Incentive (RHI). Therefore, it is vital to select the right type of fuel for a small-scale combustor to address different types of heat energy needs. In this paper, the authors attempt to investigate the performance of a small-scale biomass combustor for heating, and the impact of burning different biomass fuels on useful output energy from the combustor. The test results of moisture content, calorific value and combustion products of various biomass samples were presented. Results from this study are in general agreement with published data as far as the calorific values and moisture contents are concerned. Six commonly available biomass fuels were tested in a small-scale combustion system, and the factors that affect the performance of the system were analysed. In addition, the study has extended to examine the magnitude and proportion of useful heat, dissipated by convection and radiation while burning different biomass fuels in the small-scale combustor. It is concluded that some crucial factors have to be carefully considered before selecting biomass fuels for any particular heating application. - Highlights: • Six biomass materials combustion performance in a small combustor was examined. • Fuel combustion rate and amount of heat release has varied between materials. • Heat release by radiation, convection and flue gasses varied between materials. • Study helps engineers and users of biomass systems to select right materials

Experimental Study of Annulus Flow for Can Combustor with Vibration Influence

Directory of Open Access Journals (Sweden)

Rami. Y. Dahham

2018-01-01

Full Text Available This paper concentrate on studying the behavior of velocity profile under the influence of different frequency (34, 48, 65 and 80 Hz in each of the upper and lower annulus of Can Combustor.An experimental rig was designed to simulate the annulus flow inside a Can Combustor.The Can Combustor tested in this study is real part collected from Al-Khairat/Iraq gas turbine power station.The velocity profiles are investigated at three positions in the annular for upper and lower region.The axial velocity and turbulence intensity are calculating with different frequency for upper and lower annulus.The results were shown that the increase of frequency lead to increase the velocity profile and large recirculation zone will build in some points.Reynolds number increasing with raise of axial velocity. Also the increasing in vibration level cause non-uniform velocity profile which affect on distribution of cooling effectiveness.

Numerical exploration of mixing and combustion in ethylene fueled scramjet combustor

Science.gov (United States)

Dharavath, Malsur; Manna, P.; Chakraborty, Debasis

2015-12-01

Numerical simulations are performed for full scale scramjet combustor of a hypersonic airbreathing vehicle with ethylene fuel at ground test conditions corresponding to flight Mach number, altitude and stagnation enthalpy of 6.0, 30 km and 1.61 MJ/kg respectively. Three dimensional RANS equations are solved along with species transport equations and SST-kω turbulence model using Commercial CFD software CFX-11. Both nonreacting (with fuel injection) and reacting flow simulations [using a single step global reaction of ethylene-air with combined combustion model (CCM)] are carried out. The computational methodology is first validated against experimental results available in the literature and the performance parameters of full scale combustor in terms of thrust, combustion efficiency and total pressure loss are estimated from the simulation results. Parametric studies are conducted to study the effect of fuel equivalence ratio on the mixing and combustion behavior of the combustor.

Two-stage combustion for reducing pollutant emissions from gas turbine combustors

Science.gov (United States)

Clayton, R. M.; Lewis, D. H.

1981-01-01

Combustion and emission results are presented for a premix combustor fueled with admixtures of JP5 with neat H2 and of JP5 with simulated partial-oxidation product gas. The combustor was operated with inlet-air state conditions typical of cruise power for high performance aviation engines. Ultralow NOx, CO and HC emissions and extended lean burning limits were achieved simultaneously. Laboratory scale studies of the non-catalyzed rich-burning characteristics of several paraffin-series hydrocarbon fuels and of JP5 showed sooting limits at equivalence ratios of about 2.0 and that in order to achieve very rich sootless burning it is necessary to premix the reactants thoroughly and to use high levels of air preheat. The application of two-stage combustion for the reduction of fuel NOx was reviewed. An experimental combustor designed and constructed for two-stage combustion experiments is described.

Regimes of flow past a vortex generator

DEFF Research Database (Denmark)

Velte, Clara Marika; Okulov, V.L.; Naumov, I.V.

2012-01-01

A complete parametric investigation of the development of multi-vortex regimes in a wake past simple vortex generator has been carried out. It is established that the vortex structure in the wake is much more complicated than a simple monopole tip vortex. The vortices were studied by stereoscopic...... particle image velocimetry (SPIV). Based on the obtained SPIV data, a map of the regimes of flow past the vortex generator has been constructed. One region with a developed stable multivortex system on this map reaches the vicinity of the optimum angle of attack of the vortex generator....

Steam Reformer With Fibrous Catalytic Combustor

Science.gov (United States)

Voecks, Gerald E.

1987-01-01

Proposed steam-reforming reactor derives heat from internal combustion on fibrous catalyst. Supplies of fuel and air to combustor controlled to meet demand for heat for steam-reforming reaction. Enables use of less expensive reactor-tube material by limiting temperature to value safe for material yet not so low as to reduce reactor efficiency.

Large eddy simulation of combustion characteristics in a kerosene fueled rocket-based combined-cycle engine combustor

Science.gov (United States)

Huang, Zhi-wei; He, Guo-qiang; Qin, Fei; Cao, Dong-gang; Wei, Xiang-geng; Shi, Lei

2016-10-01

This study reports combustion characteristics of a rocket-based combined-cycle engine combustor operating at ramjet mode numerically. Compressible large eddy simulation with liquid kerosene sprayed and vaporized is used to study the intrinsic unsteadiness of combustion in such a propulsion system. Results for the pressure oscillation amplitude and frequency in the combustor as well as the wall pressure distribution along the flow-path, are validated using experimental data, and they show acceptable agreement. Coupled with reduced chemical kinetics of kerosene, results are compared with the simultaneously obtained Reynolds-Averaged Navier-Stokes results, and show significant differences. A flow field analysis is also carried out for further study of the turbulent flame structures. Mixture fraction is used to determine the most probable flame location in the combustor at stoichiometric condition. Spatial distributions of the Takeno flame index, scalar dissipation rate, and heat release rate reveal that different combustion modes, such as premixed and non-premixed modes, coexisted at different sections of the combustor. The RBCC combustor is divided into different regions characterized by their non-uniform features. Flame stabilization mechanism, i.e., flame propagation or fuel auto-ignition, and their relative importance, is also determined at different regions in the combustor.

Spectral analysis of point-vortex dynamics: first application to vortex polygons in a circular domain

International Nuclear Information System (INIS)

Speetjens, M F M; Meleshko, V V; Van Heijst, G J F

2014-01-01

The present study addresses the classical problem of the dynamics and stability of a cluster of N-point vortices of equal strength arranged in a polygonal configuration (‘N-vortex polygons’). In unbounded domains, such N-vortex polygons are unconditionally stable for N⩽7. Confinement in a circular domain tightens the stability conditions to N⩽6 and a maximum polygon size relative to the domain radius. This work expands on existing studies on stability and integrability by a first giving an exploratory spectral analysis of the dynamics of N vortex polygons in circular domains. Key to this is that the spectral signature of the time evolution of vortex positions reflects their qualitative behaviour. Expressing vortex motion by a generic evolution operator (the so-called Koopman operator) provides a rigorous framework for such spectral analyses. This paves the way to further differentiation and classification of point-vortex behaviour beyond stability and integrability. The concept of Koopman-based spectral analysis is demonstrated for N-vortex polygons. This reveals that conditional stability can be seen as a local form of integrability and confirms an important generic link between spectrum and dynamics: discrete spectra imply regular (quasi-periodic) motion; continuous (sub-)spectra imply chaotic motion. Moreover, this exposes rich nonlinear dynamics as intermittency between regular and chaotic motion and quasi-coherent structures formed by chaotic vortices. (ss 1)

Vortex diode jet

Science.gov (United States)

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.

Emission control by cyclone combustor technology

Energy Technology Data Exchange (ETDEWEB)

Syred, N; Styles, A C; Sahatimehr, A

1983-09-01

Recent work carried out on a multi-inlet gas-fired cyclone combustor has shown that NO formation is reduced to negligible proportions when operated at mixture ratios 1.5 < PHI < 2.2 with combustion occurring under fully premixed fuel conditions. Elimination of hot spots, common to partial premixed systems, has been achieved with mean temperatures below 1300 C, thereby reducing NO emissions (1.5 ppm) by preventing the onset of Zeldovich and prompt mechanisms. The low NO levels are therefore dependent on a combination of low flame front temperature (about 1100 C) and premixed combustion conditions. Owing to the operating mode of combustion, heat transfer at the walls plays an important role in flame stability. Insulation of the cyclone chamber by refractory has been found to extend the operating range to higher mixture ratios. Conversely, it is expected that heat removal from the walls would enable the combustor to operate at mixture ratios nearer to stoichiometric, whilst still giving rise to low levels of NO emission. 17 references.

Decreasing vortex flux in channels

International Nuclear Information System (INIS)

Migaj, V.K.; Nosova, I.S.

1979-01-01

A new method for reducing vortex flow losses in power plant channels is suggested. The method is based on vortex splitting in vortex flow areas with transverse barriers placed on the channel walls. The upper barrier ends are at the level of the upper boundary of the vortex area and don't protrude to the active flow beyond this boundary. The effectiveness of the method suggested is illustrated taking as an example the investigation of square and flat channels with abrupt widening in one plane, diffusers with widening in one plane, or a rectangualr bend. It is shown that splitting the vortex areas with transverse barriers in the channels results in reduction of hydraulic losses by 10-25%. The above method is characteristic of an extreme simplicity, its application doesn't require changes in the channel shape nor installation of any devices in the flow

40 CFR 60.33b - Emission guidelines for municipal waste combustor metals, acid gases, organics, and nitrogen oxides.

Science.gov (United States)

2010-07-01

... combustor metals, acid gases, organics, and nitrogen oxides. 60.33b Section 60.33b Protection of Environment... Constructed on or Before September 20, 1994 § 60.33b Emission guidelines for municipal waste combustor metals, acid gases, organics, and nitrogen oxides. (a) The emission limits for municipal waste combustor metals...

Comparative study of non-premixed and partially-premixed combustion simulations in a realistic Tay model combustor

OpenAIRE

Zhang, K.; Ghobadian, A.; Nouri, J. M.

2017-01-01

A comparative study of two combustion models based on non-premixed assumption and partially premixed assumptions using the overall models of Zimont Turbulent Flame Speed Closure Method (ZTFSC) and Extended Coherent Flamelet Method (ECFM) are conducted through Reynolds stress turbulence modelling of Tay model gas turbine combustor for the first time. The Tay model combustor retains all essential features of a realistic gas turbine combustor. It is seen that the non-premixed combustion model fa...

Dissipative flow and vortex shedding in the Painleve boundary layer of a Bose-Einstein condensate

International Nuclear Information System (INIS)

Aftalion, Amandine; Du Qiang; Pomeau, Yves

2003-01-01

This paper addresses the drag force and formation of vortices in the boundary layer of a Bose-Einstein condensate stirred by a laser beam following the experiments of C. Raman et al., Phys. Rev. Lett. 83, 2502 (1999)10.1103/PhysRevLett.83.2502. We make our analysis in the frame moving at constant speed where the beam is fixed. We find that there is always a drag around the laser beam. We also analyze the mechanism of vortex nucleation. At low velocity, there are no vortices and the drag has its origin in a wakelike phenomenon: This is a particularity of trapped systems since the density gets small in an extended region. The shedding of vortices starts only at a threshold velocity and is responsible for a large increase in drag. This critical velocity for vortex nucleation is lower than the critical velocity computed for the corresponding 2D problem at the center of the cloud

A three-dimensional algebraic grid generation scheme for gas turbine combustors with inclined slots

Science.gov (United States)

Yang, S. L.; Cline, M. C.; Chen, R.; Chang, Y. L.

1993-01-01

A 3D algebraic grid generation scheme is presented for generating the grid points inside gas turbine combustors with inclined slots. The scheme is based on the 2D transfinite interpolation method. Since the scheme is a 2D approach, it is very efficient and can easily be extended to gas turbine combustors with either dilution hole or slot configurations. To demonstrate the feasibility and the usefulness of the technique, a numerical study of the quick-quench/lean-combustion (QQ/LC) zones of a staged turbine combustor is given. Preliminary results illustrate some of the major features of the flow and temperature fields in the QQ/LC zones. Formation of co- and counter-rotating bulk flow and shape temperature fields can be observed clearly, and the resulting patterns are consistent with experimental observations typical of the confined slanted jet-in-cross flow. Numerical solutions show the method to be an efficient and reliable tool for generating computational grids for analyzing gas turbine combustors with slanted slots.

Backreaction of excitations on a vortex

OpenAIRE

Arodz, Henryk; Hadasz, Leszek

1996-01-01

Excitations of a vortex are usually considered in a linear approximation neglecting their backreaction on the vortex. In the present paper we investigate backreaction of Proca type excitations on a straightlinear vortex in the Abelian Higgs model. We propose exact Ansatz for fields of the excited vortex. From initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the backreaction corrections. Their approximate solutions are found ...

Forced and self-excited oscillations in a natural gas fired lean premixed combustor

Energy Technology Data Exchange (ETDEWEB)

Kim, Daesik; Park, Sung Wook

2010-11-15

An experimental study of the flame response in a premixed gas turbine combustor has been conducted at room temperature and under atmospheric pressure inlet conditions using natural gas. The fuel is premixed with the air upstream of a choked inlet to avoid equivalence ratio fluctuations. Therefore the observed flame response is only the result of the imposed velocity fluctuations, which are produced using a variable-speed siren. Also, a variable length combustor is designed for investigating characteristics of self-excited instabilities. Measurements are made of the velocity fluctuation in the mixing section using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The results are analyzed to determine the phase and gain of the flame transfer function. The results show that the gain of flame transfer function is closely associated both with inlet flow forcing conditions such as frequency and amplitude of modulation as well as the operating conditions such as equivalence ratio. In order to predict the operating conditions where the combustor goes stable or unstable at given combustor and nozzle designs, time-lag analysis was tried using convection time delay measured from the phase information of the transfer function. The model prediction was in very good agreement with the self-excited instability measurement. However, spatial heat release distribution became more significant in long flames than in short flames and also had an important influence on the system damping procedure. (author)

Numerical optimization of laboratory combustor geometry for NO suppression

International Nuclear Information System (INIS)

Mazaheri, Karim; Shakeri, Alireza

2016-01-01

Highlights: • A five-step kinetics for NO and CO prediction is extracted from GRI-3.0 mechanism. • Accuracy and applicability of this kinetics for numerical optimization were shown. • Optimized geometry for a combustor was determined using the combined process. • NO emission from optimized geometry is found 10.3% lower than the basis geometry. - Abstract: In this article, geometry optimization of a jet stirred reactor (JSR) combustor has been carried out for minimum NO emissions in methane oxidation using a combined numerical algorithm based on computational fluid dynamics (CFD) and differential evolution (DE) optimization. The optimization algorithm is also used to find a fairly accurate reduced mechanism. The combustion kinetics is based on a five-step mechanism with 17 unknowns which is obtained using an optimization DE algorithm for a PSR–PFR reactor based on GRI-3.0 full mechanism. The optimization design variables are the unknowns of the five-step mechanism and the cost function is the concentration difference of pollutants obtained from the 5-step mechanism and the full mechanism. To validate the flow solver and the chemical kinetics, the computed NO at the outlet of the JSR is compared with experiments. To optimize the geometry of a combustor, the JSR combustor geometry is modeled using three parameters (i.e., design variables). An integrated approach using a flow solver and the DE optimization algorithm produces the lowest NO concentrations. Results show that the exhaust NO emission for the optimized geometry is 10.3% lower than the original geometry, while the inlet temperature of the working fluid and the concentration of O_2 are operating constraints. In addition, the concentration of CO pollutant is also much less than the original chamber.

An investigation of the vortex method

Energy Technology Data Exchange (ETDEWEB)

Pryor, Jr., Duaine Wright [Univ. of California, Berkeley, CA (United States)

1994-05-01

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. This 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.

Instability of vortex pair leapfrogging

DEFF Research Database (Denmark)

Tophøj, Laust; Aref, Hassan

2013-01-01

Leapfrogging is a periodic solution of the four-vortex problem with two positive and two negative point vortices all of the same absolute circulation arranged as co-axial vortex pairs. The set of co-axial motions can be parameterized by the ratio 0 vortex pair sizes at the time when one...... pair passes through the other. Leapfrogging occurs for α > σ2, where is the silver ratio. The motion is known in full analytical detail since the 1877 thesis of Gröbli and a well known 1894 paper by Love. Acheson ["Instability of vortex leapfrogging," Eur. J. Phys.21, 269-273 (2000...... pairs fly off to infinity, and a "walkabout" mode, where the vortices depart from leapfrogging but still remain within a finite distance of one another. We show numerically that this transition is more gradual, a result that we relate to earlier investigations of chaotic scattering of vortex pairs [L...

Soliton on thin vortex filament

International Nuclear Information System (INIS)

Konno, Kimiaki; Mituhashi, Masahiko; Ichikawa, Y.H.

1990-12-01

Showing that one of the equations found by Wadati, Konno and Ichikawa is equivalent to the equation of motion of a thin vortex filament, we investigate solitons on the vortex filament. N vortex soliton solution is given in terms of the inverse scattering method. We examine two soliton collision processes on the filament. Our analysis provides the theoretical foundation of two soliton collision processes observed numerically by Aref and Flinchem. (author)

ASRS Reports on Wake Vortex Encounters

Science.gov (United States)

Connell, Linda J.; Taube, Elisa Ann; Drew, Charles Robert; Barclay, Tommy Earl

2010-01-01

ASRS is conducting a structured callback research project of wake vortex incidents reported to the ASRS at all US airports, as well as wake encounters in the enroute environment. This study has three objectives: (1) Utilize the established ASRS supplemental data collection methodology and provide ongoing analysis of wake vortex encounter reports; (2) Document event dynamics and contributing factors underlying wake vortex encounter events; and (3) Support ongoing FAA efforts to address pre-emptive wake vortex risk reduction by utilizing ASRS reporting contributions.

New scanning technique for the optical vortex microscope.

Science.gov (United States)

Augustyniak, Ireneusz; Popiołek-Masajada, Agnieszka; Masajada, Jan; Drobczyński, Sławomir

2012-04-01

In the optical vortex microscopy the focused Gaussian beam with optical vortex scans a sample. An optical vortex can be introduced into a laser beam with the use of a special optical element--a vortex lens. When moving the vortex lens, the optical vortex changes its position inside the spot formed by a focused laser beam. This effect can be used as a new precise scanning technique. In this paper, we study the optical vortex behavior at the sample plane. We also estimate if the new scanning technique results in observable effects that could be used for a phase object detection.

Moving vortex matter with coexisting vortices and anti-vortices

International Nuclear Information System (INIS)

Carneiro, Gilson

2009-01-01

Moving vortex matter, driven by transport currents independent of time, in which vortices and anti-vortices coexist is investigated theoretically in thin superconducting films with nanostructured defects. A simple London model is proposed for the vortex dynamics in films with periodic arrays of nanomagnets or cylindrical holes (antidots). Common to these films is that vortex anti-vortex pairs may be created in the vicinity of the defects by relatively small transport currents, because it adds to the current generated by the defects - the nanomagnets screening current, or the antidots backflow current - and may exceed locally the critical value for vortex anti-vortex pair creation. The model assumes that vortex matter dynamics is governed by Langevin equations, modified to account for creation and annihilation of vortex anti-vortex pairs. For pair creation, it is assumed that whenever the total current at some location exceeds a critical value, equal to that needed to separate a vortex from an anti-vortex by a vortex core diameter, a pair is created instantaneously around this location. Pair annihilation occurs by vortex anti-vortex collisions. The model is applied to films at zero external magnetic field and low temperatures. It is found that several moving vortex matter steady-states with equal numbers of vortices and anti-vortices are possible.

Review of Idealized Aircraft Wake Vortex Models

Science.gov (United States)

Ahmad, Nashat N.; Proctor, Fred H.; Duparcmeur, Fanny M. Limon; Jacob, Don

2014-01-01

Properties of three aircraft wake vortex models, Lamb-Oseen, Burnham-Hallock, and Proctor are reviewed. These idealized models are often used to initialize the aircraft wake vortex pair in large eddy simulations and in wake encounter hazard models, as well as to define matched filters for processing lidar observations of aircraft wake vortices. Basic parameters for each vortex model, such as peak tangential velocity and circulation strength as a function of vortex core radius size, are examined. The models are also compared using different vortex characterizations, such as the vorticity magnitude. Results of Euler and large eddy simulations are presented. The application of vortex models in the postprocessing of lidar observations is discussed.

Optical force and torque on a dielectric Rayleigh particle by a circular Airy vortex beam

Science.gov (United States)

Chen, Musheng; Huang, Sujuan; Shao, Wei; Liu, Xianpeng

2018-03-01

Optical force and torque exerted on the Rayleigh particles by tightly focused circularly polarized circular Airy vortex beams (CAVB) in the far field are studied in this paper. The relation between parameters of circularly polarized CAVB and the trapping properties is numerically analyzed based on Rayleigh models and the Debye diffraction theory. The results show that both the high refractive index and low refractive index particles can be fully stably trapped in three dimensions by circularly polarized CAVB. The parameters of circularly polarized CAVB greatly affect the optical force. The longitudinal and transverse gradient force increase with the increase of decay factor and scaling factor, and decrease with the increase of the radius of the first primary ring and topological charges. The positions of the longitudinal stable equilibrium move toward the high numerical aperture lens when the scaling factor and the radius of the primary ring increase. The trapping range is broadened with the decrease of scaling factor. The optical orbital torque (OOT) of circularly polarized CAVB has circular symmetry and remains positive or negative. With the increase of topological charges, the peak value of OOT first increases and then decreases after reaches a maximum. These results are useful for optical trapping, optical levitation and particle acceleration.

Low-threshold, nanosecond, high-repetition-rate vortex pulses with controllable helicity generated in Cr,Nd:YAG self-Q-switched microchip laser

Science.gov (United States)

He, Hong-Sen; Chen, Zhen; Li, Hong-Bin; Dong, Jun

2018-05-01

A high repetition rate, nanosecond, pulsed optical vortex beam has been generated in a Cr,Nd:YAG self-Q-switched microchip laser pumped by the annular-beam formed with a hollow focus lens. The lasing threshold for vortex pulses is 0.9 W. A pulse width of 6.5 ns and a repetition rate of over 330 kHz have been achieved. The average output power of 1 W and the slope efficiency of 46.6% have been obtained. The helicity of the optical vortices has been controlled by adjusting the tilted angle between Cr,Nd:YAG crystal and output coupler. The work provides a new method for developing pulsed optical vortices for potential applications on quantum communication and optical trapping.

Emissions from laboratory combustor tests of manufactured wood products

Energy Technology Data Exchange (ETDEWEB)

Wilkening, R.; Evans, M.; Ragland, K. [Univ. of Wisconsin, Madison, WI (United States); Baker, A. [USDA Forest Products Lab., Madison, WI (United States)

1993-12-31

Manufactured wood products contain wood, wood fiber, and materials added during manufacture of the product. Manufacturing residues and the used products are burned in a furnace or boiler instead of landfilling. Emissions from combustion of these products contain additional compounds from the combustion of non-wood material which have not been adequately characterized to specify the best combustion conditions, emissions control equipment, and disposal procedures. Total hydrocarbons, formaldehyde, higher aldehydes and carbon monoxide emissions from aspen flakeboard and aspen cubes were measured in a 76 mm i.d. by 1.5 m long fixed bed combustor as a function of excess oxygen, and temperature. Emissions of hydrocarbons, aldehydes and CO from flakeboard and from clean aspen were very sensitive to average combustor temperature and excess oxygen. Hydrocarbon and aldehyde emissions below 10 ppM were achieved with 5% excess oxygen and 1,200{degrees}C average temperature for aspen flakeboard and 1,100{degrees}C for clean aspen at a 0.9 s residence time. When the average temperature decreased below these levels, the emissions increased rapidly. For example, at 950{degrees}C and 5% excess oxygen the formaldehyde emissions were over 1,000 ppM. These laboratory tests reinforce the need to carefully control the temperature and excess oxygen in full-scale wood combustors.

Flame dynamics of a meso-scale heat recirculating combustor

Energy Technology Data Exchange (ETDEWEB)

Vijayan, V.; Gupta, A.K. [Department of Mechanical Engineering, University of Maryland, College Park, MD 20742 (United States)

2010-12-15

The dynamics of premixed propane-air flame in a meso-scale ceramic combustor has been examined here. The flame characteristics in the combustor were examined by measuring the acoustic emissions and preheat temperatures together with high-speed cinematography. For the small-scale combustor, the volume to surface area ratio is small and hence the walls have significant effect on the global flame structure, flame location and flame dynamics. In addition to the flame-wall thermal coupling there is a coupling between flame and acoustics in the case of confined flames. Flame-wall thermal interactions lead to low frequency flame fluctuations ({proportional_to}100 Hz) depending upon the thermal response of the wall. However, the flame-acoustic interactions can result in a wide range of flame fluctuations ranging from few hundred Hz to few kHz. Wall temperature distribution is one of the factors that control the amount of reactant preheating which in turn effects the location of flame stabilization. Acoustic emission signals and high-speed flame imaging confirmed that for the present case flame-acoustic interactions have more significant effect on flame dynamics. Based on the acoustic emissions, five different flame regimes have been identified; whistling/harmonic mode, rich instability mode, lean instability mode, silent mode and pulsating flame mode. (author)

Meissner effects, vortex core states, and the vortex glass phase transition

International Nuclear Information System (INIS)

Huang, Ming.

1991-01-01

This thesis covers three topics involving Meissner effects and the resulting defect structures. The first is a study of Meissner effects in superconductivity and in systems with broken translational symmetry. The Meissner effect in the superconductors is a rigidity against external magnetic field caused by the breaking of the gauge symmetry. Other condensed matter systems also exhibit rigidities like this: The breaking of the translational symmetry in a cubic-liquid-crystal causes the system to expel twist deformations and the breaking of the translational symmetry in a nematic liquid crystal gives it a tendency to expel twist and bend deformations. In this thesis, the author studies these generalized Meissner effects in detail. The second is a study of the quasiparticle states bound to the vortex defect in superconductors. Scanning-tunneling-microscope measurements by Harald Hess et al. of the local density of states in a vortex core show a pronounced peak at small bias. These measurements contradict with previous theoretical calculations. Here, he solves the Bogoliubov equations to obtain the local density of states in the core and satisfactorily explain the experimental observations. He also predicted additional structure in the local density of states which were later observed in experiments. The third is a study of vortex dynamics in the presence of disorder. A mean field theory is developed for the recently proposed normal to superconducting vortex glass transition. Using techniques developed to study the critical dynamics of spin glasses, he calculates the mean field vortex glass phase boundary and the critical exponents

Leapfrogging of multiple coaxial viscous vortex rings

International Nuclear Information System (INIS)

Cheng, M.; Lou, J.; Lim, T. T.

2015-01-01

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 the 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

Aerodynamically shaped vortex generators

DEFF Research Database (Denmark)

Hansen, Martin Otto Laver; Velte, Clara Marika; Øye, Stig

2016-01-01

An aerodynamically shaped vortex generator has been proposed, manufactured and tested in a wind tunnel. The effect on the overall performance when applied on a thick airfoil is an increased lift to drag ratio compared with standard vortex generators. Copyright © 2015 John Wiley & Sons, Ltd....

Experiments concerning the theories of vortex breakdown

Science.gov (United States)

Panton, Ronald L.; Stifle, Kirk E.

1991-01-01

An experimental project was undertaken to investigate the character of vortex breakdown with particular regard to the stagnation and wave guide theories of vortex breakdown. Three different wings were used to produce a trailing vortex which convected downstream without undergoing breakdown. Disturbances were then introduced onto the vortex using a moving wire to 'cut' the vortex. The development of upstream and downstream propagating disturbance waves was observed and the propagation velocities measured. A downstream traveling wave was observed to produce a structure similar in appearance to a vortex breakdown. An upstream traveling wave produced a moving turbulent region. The upstream disturbance moved into an axial velocity profile that had a wake-like defect while the downstream moving vortex breakdown moved against a jet-like overshoot. The longitudinal and swirl velocity profiles were documented by LDV measurement. Wave velocities, swirl angles, and swirl parameters are reported.

Magnetic vortex racetrack memory

Energy Technology Data Exchange (ETDEWEB)

Geng, Liwei D.; Jin, Yongmei M., E-mail: ymjin@mtu.edu

2017-02-01

We report a new type of racetrack memory based on current-controlled movement of magnetic vortices in magnetic nanowires with rectangular cross-section and weak perpendicular anisotropy. Data are stored through the core polarity of vortices and each vortex carries a data bit. Besides high density, non-volatility, fast data access, and low power as offered by domain wall racetrack memory, magnetic vortex racetrack memory has additional advantages of no need for constrictions to define data bits, changeable information density, adjustable current magnitude for data propagation, and versatile means of ultrafast vortex core switching. By using micromagnetic simulations, current-controlled motion of magnetic vortices in cobalt nanowire is demonstrated for racetrack memory applications. - Highlights: • Advance fundamental knowledge of current-driven magnetic vortex phenomena. • Report appealing new magnetic racetrack memory based on current-controlled magnetic vortices in nanowires. • Provide a novel approach to adjust current magnitude for data propagation. • Overcome the limitations of domain wall racetrack memory.

Propeller and inflow vortex interaction : vortex response and impact on the propeller performance

NARCIS (Netherlands)

Yang, Y.; Zhou, T; Sciacchitano, A.; Veldhuis, L.L.M.; Eitelberg, G.

2016-01-01

The aerodynamic operating conditions of a propeller can include complex situations where vorticity from sources upstream can enter the propeller plane. In general, when the vorticity enters in a concentrated form of a vortex, the interaction between the vortex and blade is referred to as

Vortex Thermometry for Turbulent Two-Dimensional Fluids.

Science.gov (United States)

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.

Criterion for vortex breakdown on shock wave and streamwise vortex interactions.

Science.gov (United States)

Hiejima, Toshihiko

2014-05-01

The interactions between supersonic streamwise vortices and oblique shock waves are theoretically and numerically investigated by three-dimensional (3D) Navier-Stokes equations. Based on the two inequalities, a criterion for shock-induced breakdown of the streamwise vortex is proposed. The simple breakdown condition depends on the Mach number, the swirl number, the velocity deficit, and the shock angle. According to the proposed criterion, the breakdown region expands as the Mach number increases. In numerical simulations, vortex breakdown appeared under conditions of multiple pressure increases and the helicity disappeared behind the oblique shock wave along the line of the vortex center. The numerical results are consistent with the predicted breakdown condition at Mach numbers 2.0 and 3.0. This study also found that the axial velocity deficit is important for classifying the breakdown configuration.

Experimental Study of Shock Generated Compressible Vortex Ring

Science.gov (United States)

Das, Debopam; Arakeri, Jaywant H.; Krothapalli, Anjaneyulu

2000-11-01

Formation of a compressible vortex ring and generation of sound associated with it is studied experimentally. Impulse of a shock wave is used to generate a vortex ring from the open end of a shock-tube. Vortex ring formation process has been studied in details using particle image Velocimetry (PIV). As the shock wave exits the tube it diffracts and expands. A circular vortex sheet forms at the edge and rolls up into a vortex ring. Far field microphone measurement shows that the acoustic pressure consists of a spike due to shock wave followed by a low frequency pressure wave of decaying nature, superimposed with high frequency pressure wave. Acoustic waves consist of waves due to expansion, waves formed in the tube during diaphragm breakage and waves associated with the vortex ring and shear-layer vortices. Unsteady evolution of the vortex ring and shear-layer vortices in the jet behind the ring is studied by measuring the velocity field using PIV. Corresponding vorticity field, circulation around the vortex core and growth rate of the vortex core is calculated from the measured velocity field. The velocity field in a compressible vortex ring differs from that of an incompressible ring due to the contribution from both shock and vortex ring.

Techniques for enhancing durability and equivalence ratio control in a rich-lean, three-stage ground power gas turbine combustor

Science.gov (United States)

Schultz, D. F.

1982-01-01

Rig tests of a can-type combustor were performed to demonstrate two advanced ground power engine combustor concepts: steam cooled rich-burn combustor primary zones for enhanced durability; and variable combustor geometry for three stage combustion equivalence ratio control. Both concepts proved to be highly successful in achieving their desired objectives. The steam cooling reduced peak liner temperatures to less than 800 K. This offers the potential of both long life and reduced use of strategic materials for liner fabrication. Three degrees of variable geometry were successfully implemented to control airflow distribution within the combustor. One was a variable blade angle axial flow air swirler to control primary airflow while the other two consisted of rotating bands to control secondary and tertiary or dilution air flow.

Analytical model of the optical vortex microscope.

Science.gov (United States)

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

2016-04-20

This paper presents an analytical model of the optical vortex scanning microscope. In this microscope the Gaussian beam with an embedded optical vortex is focused into the sample plane. Additionally, the optical vortex can be moved inside the beam, which allows fine scanning of the sample. We provide an analytical solution of the whole path of the beam in the system (within paraxial approximation)-from the vortex lens to the observation plane situated on the CCD camera. The calculations are performed step by step from one optical element to the next. We show that at each step, the expression for light complex amplitude has the same form with only four coefficients modified. We also derive a simple expression for the vortex trajectory of small vortex displacements.

An Experimental Study on Axial Temperature Distribution of Combustion of Dewatered Poultry Sludge in Fluidized bed combustor

Directory of Open Access Journals (Sweden)

Abbas A.H.

2016-01-01

Full Text Available A laboratory scale bubbling fluidized bed combustor was designed and fabricated to study the combustion of dewatered poultry sludge at different operational parameters. This paper present a study on the influence of equivalent ratio, secondary to primary air ratio and the fuel feed rate on the temperature distribution along the combustor. The equivalent ratio has been changed between 0.8 to 1.4% under poultry sludge feed rate of 10 kg/h and from 0.8 to 1 under poultry sludge feed rate of 15 kg/h. The secondary to primary air ratio was varied from 0.1 to 0.5 at 0.65 m injection height and 1.25 equivalent ratio. The results showed that these factors had a significant influence on the combustion characteristics of poultry sludge. The temperature distribution along the combustor was found to be strongly dependent on the fuel feed rate and the equivalent ratio and it increased when these two factors increased. However, the secondary air ratio increased the temperature in the lower region of the combustor while no significant effect was observed at the upper region of the combustor. The results suggested that the poultry sludge can be used as a fuel with high thermal combustor efficiency.

Microscale vortex laser with controlled topological charge

Science.gov (United States)

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).

A note on integral vortex strength

Czech Academy of Sciences Publication Activity Database

Kolář, Václav

2010-01-01

Roč. 58, č. 1 (2010), s. 23-28 ISSN 0042-790X R&D Projects: GA AV ČR IAA200600801 Institutional research plan: CEZ:AV0Z20600510 Keywords : circulation * unsteady Taylor vortex * vortex intensity * vortex strength * vorticity * vorticity decomposition Subject RIV: BK - Fluid Dynamics Impact factor: 0.553, year: 2010

Large eddy simulation of soot evolution in an aircraft combustor

Science.gov (United States)

Mueller, Michael E.; Pitsch, Heinz

2013-11-01

An integrated kinetics-based Large Eddy Simulation (LES) approach for soot evolution in turbulent reacting flows is applied to the simulation of a Pratt & Whitney aircraft gas turbine combustor, and the results are analyzed to provide insights into the complex interactions of the hydrodynamics, mixing, chemistry, and soot. The integrated approach includes detailed models for soot, combustion, and the unresolved interactions between soot, chemistry, and turbulence. The soot model is based on the Hybrid Method of Moments and detailed descriptions of soot aggregates and the various physical and chemical processes governing their evolution. The detailed kinetics of jet fuel oxidation and soot precursor formation is described with the Radiation Flamelet/Progress Variable model, which has been modified to account for the removal of soot precursors from the gas-phase. The unclosed filtered quantities in the soot and combustion models, such as source terms, are closed with a novel presumed subfilter PDF approach that accounts for the high subfilter spatial intermittency of soot. For the combustor simulation, the integrated approach is combined with a Lagrangian parcel method for the liquid spray and state-of-the-art unstructured LES technology for complex geometries. Two overall fuel-to-air ratios are simulated to evaluate the ability of the model to make not only absolute predictions but also quantitative predictions of trends. The Pratt & Whitney combustor is a Rich-Quench-Lean combustor in which combustion first occurs in a fuel-rich primary zone characterized by a large recirculation zone. Dilution air is then added downstream of the recirculation zone, and combustion continues in a fuel-lean secondary zone. The simulations show that large quantities of soot are formed in the fuel-rich recirculation zone, and, furthermore, the overall fuel-to-air ratio dictates both the dominant soot growth process and the location of maximum soot volume fraction. At the higher fuel

Obstacle-induced spiral vortex breakdown

OpenAIRE

Pasche, Simon; Gallaire, François; Dreyer, Matthieu; Farhat, Mohamed

2014-01-01

An experimental investigation on vortex breakdown dynamics is performed. An adverse pressure gradient is created along the axis of a wing-tip vortex by introducing a sphere downstream of an elliptical hydrofoil. The instrumentation involves high-speed visualizations with air bubbles used as tracers and 2D Laser Doppler Velocimeter (LDV). Two key parameters are identified and varied to control the onset of vortex breakdown: the swirl number, defined as the maximum azimuthal velocity divided by...

Concentric catalytic combustor

Science.gov (United States)

Bruck, Gerald J [Oviedo, FL; Laster, Walter R [Oviedo, FL

2009-03-24

A catalytic combustor (28) includes a tubular pressure boundary element (90) having a longitudinal flow axis (e.g., 56) separating a first portion (94) of a first fluid flow (e.g., 24) from a second portion (95) of the first fluid flow. The pressure boundary element includes a wall (96) having a plurality of separate longitudinally oriented flow paths (98) annularly disposed within the wall and conducting respective portions (100, 101) of a second fluid flow (e.g., 26) therethrough. A catalytic material (32) is disposed on a surface (e.g., 102, 103) of the pressure boundary element exposed to at least one of the first and second portions of the first fluid flow.

Vortex and source rings

DEFF Research Database (Denmark)

Branlard, Emmanuel Simon Pierre

2017-01-01

The velocity field, vector potential and velocity gradient of a vortex ring is derived in this chapter. The Biot-Savart law for the vector potential and velocity is expressed in a first section. Then, the flow is derived at specific locations: on the axis, near the axis and in the far field where...... the analogy to a doublet field is made. The following section derive the value of the vector potential and velocity field in the full domain. The expression for the velocity gradient is also provided since it may be relevant in a simulation with vortex particles and vortex rings. Most of this chapter...

Development of vortex model with realistic axial velocity distribution

International Nuclear Information System (INIS)

Ito, Kei; Ezure, Toshiki; Ohshima, Hiroyuki

2014-01-01

A vortex is considered as one of significant phenomena which may cause gas entrainment (GE) and/or vortex cavitation in sodium-cooled fast reactors. In our past studies, the vortex is assumed to be approximated by the well-known Burgers vortex model. However, the Burgers vortex model has a simple but unreal assumption that the axial velocity component is horizontally constant, while in real the free surface vortex has the axial velocity distribution which shows large gradient in radial direction near the vortex center. In this study, a new vortex model with realistic axial velocity distribution is proposed. This model is derived from the steady axisymmetric Navier-Stokes equation as well as the Burgers vortex model, but the realistic axial velocity distribution in radial direction is considered, which is defined to be zero at the vortex center and to approach asymptotically to zero at infinity. As the verification, the new vortex model is applied to the evaluation of a simple vortex experiment, and shows good agreements with the experimental data in terms of the circumferential velocity distribution and the free surface shape. In addition, it is confirmed that the Burgers vortex model fails to calculate accurate velocity distribution with the assumption of uniform axial velocity. However, the calculation accuracy of the Burgers vortex model can be enhanced close to that of the new vortex model in consideration of the effective axial velocity which is calculated as the average value only in the vicinity of the vortex center. (author)

Experimental study on the heavy-duty gas turbine combustor

International Nuclear Information System (INIS)

Antonovsky, V.; Ahn, Kook Young

2000-01-01

The results of stand and field testing of a combustion chamber for a heavy-duty 150 MW gas turbine are discussed. The model represented one of 14 identical segments of a tubular multican combustor constructed in the scale 1:1. The model experiments were executed at a pressure smaller than in the real gas turbine. The combustion efficiency, pressure loss factor, pattern factor, liner wall temperature, flame radiation, fluctuating pressure, and NOx emission were measured at partial and full load for both model and on-site testing. The comparison of these items of information, received on similar modes in the stand and field tests, has allowed the development of a method of calculation and the improvement of gas turbine combustors

Measurement of vortex velocities over a wide range of vortex age, downstream distance and free stream velocity

Science.gov (United States)

Rorke, J. B.; Moffett, R. C.

1977-01-01

A wind tunnel test was conducted to obtain vortex velocity signatures over a wide parameter range encompassing the data conditions of several previous researchers while maintaining a common instrumentation and test facility. The generating wing panel was configured with both a revolved airfoil tip shape and a square tip shape and had a semispan aspect of 4.05/1.0 with a 121.9 cm span. Free stream velocity was varied from 6.1 m/sec to 76.2 m/sec and the vortex core velocities were measured at locations 3, 6, 12, 24 and 48 chordlengths downstream of the wing trailing edge, yielding vortex ages up to 2.0 seconds. Wing pitch angles of 6, 8, 9 and 12 deg were investigated. Detailed surface pressure distributions and wing force measurements were obtained for each wing tip configuration. Correlation with vortex velocity data taken in previous experiments is good. During the rollup process, vortex core parameters appear to be dependent primarily on vortex age. Trending in the plateau and decay regions is more complex and the machanisms appear to be more unstable.

Shock/vortex interaction and vortex-breakdown modes

Science.gov (United States)

Kandil, Osama A.; Kandil, H. A.; Liu, C. H.

1992-01-01

Computational simulation and study of shock/vortex interaction and vortex-breakdown modes are considered for bound (internal) and unbound (external) flow domains. The problem is formulated using the unsteady, compressible, full Navier-Stokes (NS) equations which are solved using an implicit, flux-difference splitting, finite-volume scheme. For the bound flow domain, a supersonic swirling flow is considered in a configured circular duct and the problem is solved for quasi-axisymmetric and three-dimensional flows. For the unbound domain, a supersonic swirling flow issued from a nozzle into a uniform supersonic flow of lower Mach number is considered for quasi-axisymmetric and three-dimensional flows. The results show several modes of breakdown; e.g., no-breakdown, transient single-bubble breakdown, transient multi-bubble breakdown, periodic multi-bubble multi-frequency breakdown and helical breakdown.

Large-scale vortex structures and local heat release in lean turbulent swirling jet-flames under vortex breakdown conditions

Science.gov (United States)

Chikishev, Leonid; Lobasov, Aleksei; Sharaborin, Dmitriy; Markovich, Dmitriy; Dulin, Vladimir; Hanjalic, Kemal

2017-11-01

We investigate flame-flow interactions in an atmospheric turbulent high-swirl methane/air lean jet-flame at Re from 5,000 to 10,000 and equivalence ratio below 0.75 at the conditions of vortex breakdown. The focus is on the spatial correlation between the propagation of large-scale vortex structures, including precessing vortex core, and the variations of the local heat release. The measurements are performed by planar laser-induced fluorescence of hydroxyl and formaldehyde, applied simultaneously with the stereoscopic particle image velocimetry technique. The data are processed by the proper orthogonal decomposition. The swirl rate exceeded critical value for the vortex breakdown resulting in the formation of a processing vortex core and secondary helical vortex filaments that dominate the unsteady flow dynamics both of the non-reacting and reacting jet flows. The flame front is located in the inner mixing layer between the recirculation zone and the annular swirling jet. A pair of helical vortex structures, surrounding the flame, stretch it and cause local flame extinction before the flame is blown away. This work is supported by Russian Science Foundation (Grant No 16-19-10566).

On the evolution of vortex rings with swirl

International Nuclear Information System (INIS)

Naitoh, Takashi; Okura, Nobuyuki; Gotoh, Toshiyuki; Kato, Yusuke

2014-01-01

A laminar vortex ring with swirl, which has the meridional velocity component inside the vortex core, was experimentally generated by the brief fluid ejection from a rotating outlet. The evolution of the vortex ring was investigated with flow visualizations and particle image velocimetry measurements in order to find the influence of swirling flow in particular upon the transition to turbulence. Immediately after the formation of a vortex ring with swirl, a columnar strong vortex along the symmetric axis is observed in all cases of the present experiment. Then the characteristic fluid discharging from a vortex ring with swirl referred to as “peeling off” appears. The amount of discharging fluid due to the “peeling off” increases with the angular velocity of the rotating outlet. We conjectured that the mechanism generating the “peeling off” is related to the columnar strong vortex by close observations of the spatio-temporal development of the vorticity distribution and the cutting 3D images constructed from the successive cross sections of a vortex ring. While a laminar vortex ring without swirl may develop azimuthal waves around its circumference at some later time and the ring structure subsequently breaks, the swirling flow in a vortex ring core reduces the amplification rate of the azimuthal wavy deformation and preserved its ring structure. Then the traveling distance of a vortex ring can be extended using the swirl flow under certain conditions

On the evolution of vortex rings with swirl

Energy Technology Data Exchange (ETDEWEB)

Naitoh, Takashi, E-mail: naitoh.takashi@nitech.ac.jp [Department of Engineering Physics, Electronics and Mechanics, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Okura, Nobuyuki, E-mail: ohkura@meijo-u.ac.jp [Department of Vehicle and Mechanical Engineering, Meijo University, 1-501 Shiogamaguchi Tempaku-ku, Nagoya 468-8502 (Japan); Gotoh, Toshiyuki, E-mail: gotoh.toshiyuki@nitech.ac.jp [Department of Scientific and Engineering Simulation, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Kato, Yusuke [Controller Business Unit Engineering Division 1, Engineering Department 3, Denso Wave Incorporated, 1 Yoshiike Kusagi Agui-cho, Chita-gun Aichi 470-2297 (Japan)

2014-06-15

A laminar vortex ring with swirl, which has the meridional velocity component inside the vortex core, was experimentally generated by the brief fluid ejection from a rotating outlet. The evolution of the vortex ring was investigated with flow visualizations and particle image velocimetry measurements in order to find the influence of swirling flow in particular upon the transition to turbulence. Immediately after the formation of a vortex ring with swirl, a columnar strong vortex along the symmetric axis is observed in all cases of the present experiment. Then the characteristic fluid discharging from a vortex ring with swirl referred to as “peeling off” appears. The amount of discharging fluid due to the “peeling off” increases with the angular velocity of the rotating outlet. We conjectured that the mechanism generating the “peeling off” is related to the columnar strong vortex by close observations of the spatio-temporal development of the vorticity distribution and the cutting 3D images constructed from the successive cross sections of a vortex ring. While a laminar vortex ring without swirl may develop azimuthal waves around its circumference at some later time and the ring structure subsequently breaks, the swirling flow in a vortex ring core reduces the amplification rate of the azimuthal wavy deformation and preserved its ring structure. Then the traveling distance of a vortex ring can be extended using the swirl flow under certain conditions.

Magnetic vortex racetrack memory

Science.gov (United States)

Geng, Liwei D.; Jin, Yongmei M.

2017-02-01

We report a new type of racetrack memory based on current-controlled movement of magnetic vortices in magnetic nanowires with rectangular cross-section and weak perpendicular anisotropy. Data are stored through the core polarity of vortices and each vortex carries a data bit. Besides high density, non-volatility, fast data access, and low power as offered by domain wall racetrack memory, magnetic vortex racetrack memory has additional advantages of no need for constrictions to define data bits, changeable information density, adjustable current magnitude for data propagation, and versatile means of ultrafast vortex core switching. By using micromagnetic simulations, current-controlled motion of magnetic vortices in cobalt nanowire is demonstrated for racetrack memory applications.

Phase diagram of a lattice of pancake vortex molecules

International Nuclear Information System (INIS)

Tanaka, Y.; Crisan, A.; Shivagan, D.D.; Iyo, A.; Shirage, P.M.; Tokiwa, K.; Watanabe, T.; Terada, N.

2009-01-01

On a superconducting bi-layer with thickness much smaller than the penetration depth, λ, a vortex molecule might form. A vortex molecule is composed of two fractional vortices and a soliton wall. The soliton wall can be regarded as a Josephson vortex missing magnetic flux (degenerate Josephson vortex) due to an incomplete shielding. The magnetic energy carried by fractional vortices is less than in the conventional vortex. This energy gain can pay a cost to form a degenerate Josephson vortex. The phase diagram of the vortex molecule is rich because of its rotational freedom.

Phenomenological Model of Vortex Generators

DEFF Research Database (Denmark)

Hansen, Martin Otto Laver; Westergaard, C.

1995-01-01

For some time attempts have been made to improve the power curve of stall regulated wind turbines by using devices like vortex generators VG and Gurney flaps. The vortex produces an additional mixing of the boundary layer and the free stream and thereby increasing the momentum close to the wall......, which again delays separation in adverse pressure gradient regions. A model is needed to include the effect of vortex generators in numerical computations of the viscous flow past rotors. In this paper a simple model is proposed....

Rewritable ferroelectric vortex pairs in BiFeO3

Science.gov (United States)

Li, Yang; Jin, Yaming; Lu, Xiaomei; Yang, Jan-Chi; Chu, Ying-Hao; Huang, Fengzhen; Zhu, Jinsong; Cheong, Sang-Wook

2017-08-01

Ferroelectric vortex in multiferroic materials has been considered as a promising alternative to current memory cells for the merit of high storage density. However, the formation of regular natural ferroelectric vortex is difficult, restricting the achievement of vortex memory device. Here, we demonstrated the creation of ferroelectric vortex-antivortex pairs in BiFeO3 thin films by using local electric field. The evolution of the polar vortex structure is studied by piezoresponse force microscopy at nanoscale. The results reveal that the patterns and stability of vortex structures are sensitive to the poling position. Consecutive writing and erasing processes cause no influence on the original domain configuration. The Z4 proper coloring vortex-antivortex network is then analyzed by graph theory, which verifies the rationality of artificial vortex-antivortex pairs. This study paves a foundation for artificial regulation of vortex, which provides a possible pathway for the design and realization of non-volatile vortex memory devices and logical devices.

Experimental and numerical studies in a vortex tube

International Nuclear Information System (INIS)

Sohn, Chang Hyun; Kim, Chang Soo; Gowda, B. H. L Lakshmana; Jung, Ui Hyun

2006-01-01

The present investigation deals with the study of the internal flow phenomena of the counter-flow type vortex tube using experimental testing and numerical simulation. Visualization was carried out using the surface tracing method, injecting dye on the vortex tube wall using a needle. Vortex tube is made of acrylic to visualize the surface particle tracing and the input air pressure was varied from 0.1 MPa to 0.3 MPa. The experimentally visualized results on the tube show that there is an apparent sudden changing of the trajectory on the vortex tube wall which was observed in every experimental test case. This may indicate the stagnation position of the vortex flow. The visualized stagnation position moves towards the vortex generator with increase in cold flow ratio and input pressure. Three-dimensional computational study is also conducted to obtain more detailed flow information in the vortex tube. Calculated total pressure, static pressure and total temperature distributions in the vortex tube were in good agreement with the experimental data. The computational particle trace on the vortex tube wall is very similar to that observed in experiments

Modeling the integration of thermoelectrics in anode exhaust combustors for waste heat recovery in fuel cell systems

Science.gov (United States)

Maghdouri Moghaddam, Anita

Recently developed small-scale hydrocarbon-fueled fuel cell systems for portable power under 1 kW have overall system efficiencies typically no higher than 30-35%. This study explores the possibility of using of thermoelectric waste heat recovery in anode exhaust combustors to improve the fuel cell system efficiencies by as much as 4-5% points and further to reduce required battery power during system start-up. Two models were used to explore this. The first model simulated an integrated SOFC system with a simplified catalytic combustor model with TEs integrated between the combustor and air preheating channels for waste heat recovery. This model provided the basis for assessing how much additional power can achieve during SOFC operation as a function of fuel cell operating conditions. Results for the SOFC system indicate that while the TEs may recover as much as 4% of the total fuel energy into the system, their benefit is reduced in part because they reduce the waste heat transferred back to the incoming air stream and thereby lower the SOFC operating temperatures and operating efficiencies. A second model transient model of a TE-integrated catalytic combustor explored the performance of the TEs during transient start-up of the combustor. This model incorporated more detailed catalytic combustion chemistry and enhanced cooling air fin heat transfer to show the dynamic heating of the integrated combustor. This detailed model provided a basis for exploring combustor designs and showed the importance of adequate reactant preheating when burning exhaust from a reformer during start-up for the TEs to produce significant power to reduce the size of system batteries for start-up.

Vortex phase diagram and vortex dynamics at low temperature in a thick a-MgxB1-x film

International Nuclear Information System (INIS)

Okuma, S.; Kohara, M.

2007-01-01

We report on the equilibrium vortex phase diagram and vortex dynamics at low temperature T in a thick amorphous (a-)Mg x B 1-x film based on the measurements of the dc resistivity ρ and time (t)-dependent component of the flux-flow voltage, δV(t), respectively. Both ρ(T) in perpendicular fields and the vortex phase diagram are qualitatively similar to those for the a-Mo x Si 1-x films, in which evidence for the quantum-vortex-liquid (QVL) phase has been obtained. In either material system we observe anomalous vortex flow with the asymmetric distribution of δV(t) in the QVL phase, suggesting that the anomalous flow is a universal phenomenon commonly observed for disordered amorphous films, independent of material

Green functions of vortex operators

International Nuclear Information System (INIS)

Polchinski, J.; California Univ., Berkeley

1981-01-01

We study the euclidean Green functions of the 't Hooft vortex operator, primarly for abelian gauge theories. The operator is written in terms of elementary fields, with emphasis on a form in which it appears as the exponential of a surface integral. We explore the requirement that the Green functions depend only on the boundary of this surface. The Dirac veto problem appears in a new guise. We present a two-dimensional solvable model of a Dirac string, which suggests a new solution of the veto problem. The renormalization of the Green functions of the abelian Wilson loop and abelian vortex operator is studied with the aid of the operator product expansion. In each case, an overall multiplication of the operator makes all Green functions finite; a surprising cancellation of divergences occurs with the vortex operator. We present a brief discussion of the relation between the nature of the vacuum and the cluster properties of the Green functions of the Wilson and vortex operators, for a general gauge theory. The surface-like cluster property of the vortex operator in an abelian Higgs theory is explored in more detail. (orig.)

Conjugate gradient minimisation approach to generating holographic traps for ultracold atoms.

Science.gov (United States)

Harte, Tiffany; Bruce, Graham D; Keeling, Jonathan; Cassettari, Donatella

2014-11-03

Direct minimisation of a cost function can in principle provide a versatile and highly controllable route to computational hologram generation. Here we show that the careful design of cost functions, combined with numerically efficient conjugate gradient minimisation, establishes a practical method for the generation of holograms for a wide range of target light distributions. This results in a guided optimisation process, with a crucial advantage illustrated by the ability to circumvent optical vortex formation during hologram calculation. We demonstrate the implementation of the conjugate gradient method for both discrete and continuous intensity distributions and discuss its applicability to optical trapping of ultracold atoms.

Investigations on the Influence of the In-Stream Pylon and Strut on the Performance of a Scramjet Combustor

Directory of Open Access Journals (Sweden)

Hao Ouyang

2014-01-01

Full Text Available The influence of the in-stream pylon and strut on the performance of scramjet combustor was experimentally and numerically investigated. The experiments were conducted with a direct-connect supersonic model combustor equipped with multiple cavities. The entrance parameter of combustor corresponds to scramjet flight Mach number 4.0 with a total temperature of 947 K. The research results show that, compared with the scramjet combustor without pylon and strut, the wall pressure and the thrust of the scramjet increase due to the improvement of mixing and combustion effect due to the pylon and strut. The total pressure loss caused by the strut is considerable whereas pylon influence is slight.

Single vortex states in a confined Bose-Einstein condensate

International Nuclear Information System (INIS)

Komineas, S.; Cooper, N. R.; Papanicolaou, N.

2005-01-01

It has been demonstrated experimentally that non-axisymmetric vortices precess around the center of a Bose-Einstein condensate. Two types of single vortex states have been observed, usually referred to as the S vortex and the U vortex. We study theoretically the single vortex excitations in spherical and elongated condensates as a function of the interaction strength. We solve numerically the Gross-Pitaevskii equation and calculate the angular momentum as a function of precession frequency. The existence of two types of vortices means that we have two different precession frequencies for each angular momentum value. As the interaction strength increases the vortex lines bend and the precession frequencies shift to lower values. We establish that for given angular momentum the S vortex has higher energy than the U vortex in a rotating elongated condensate. We show that the S vortex is related to the solitonic vortex, which is a nonlinear excitation in the nonrotating system. For small interaction strengths the S vortex is related to the dark soliton. In the dilute limit a lowest Landau level calculation provides an analytic description of these vortex modes in terms of the harmonic oscillator states

Vortex dynamics in the wake of a pivoted cylinder undergoing vortex-induced vibrations with elliptic trajectories

Science.gov (United States)

Marble, Erik; Morton, Christopher; Yarusevych, Serhiy

2018-05-01

Vortex-induced vibrations of a pivoted cylinder are investigated experimentally at a fixed Reynolds number of 3100, a mass ratio of 10.8, and a range of reduced velocities, 4.42 ≤ U^* ≤ 9.05. For these conditions, the cylinder traces elliptic trajectories, with the experimental conditions producing three out of four possible combinations of orbiting direction and primary axis alignment relative to the incoming flow. The study focuses on the quantitative analysis of wake topology and its relation to this type of structural response. Velocity fields were measured using time-resolved, two-component particle image velocimetry (TR-PIV). These results show that phase-averaged wake topology generally agrees with the Morse and Williamson (J Fluids Struct 25(4):697-712, 2009) shedding map for one-degree-of-freedom vortex-induced vibrations, with 2S, 2{P}o, and 2P shedding patterns observed within the range of reduced velocities studied here. Vortex tracking and vortex strength quantification are used to analyze the vortex shedding process and how it relates to cylinder response. In the case of 2S vortex shedding, vortices are shed when the cylinder is approaching the maximum transverse displacement and reaches the streamwise equilibrium. 2P vortices are shed approximately half a period earlier in the cylinder's elliptic trajectory. Leading vortices shed immediately after the peak in transverse oscillation and trailing vortices shed near the equilibrium of transverse oscillation. The orientation and direction of the cylinder's elliptic trajectory are shown to influence the timing of vortex shedding, inducing changes in the 2P wake topology.

Vortex matter stabilized by many-body interactions

Science.gov (United States)

Wolf, S.; Vagov, A.; Shanenko, A. A.; Axt, V. M.; Aguiar, J. Albino

2017-10-01

This work investigates interactions of vortices in superconducting materials between standard types I and II, in the domain of the so-called intertype (IT) superconductivity. Contrary to common expectations, the many-body (many-vortex) contribution is not a correction to the pair-vortex interaction here but plays a crucial role in the formation of the IT vortex matter. In particular, the many-body interactions stabilize vortex clusters that otherwise could not exist. Furthermore, clusters with large numbers of vortices become more stable when approaching the boundary between the intertype domain and type I. This indicates that IT superconductors develop a peculiar unconventional type of the vortex matter governed by the many-body interactions of vortices.

Back reaction of excitations on a vortex

Science.gov (United States)

Arodź, Henryk; Hadasz, Leszek

1997-01-01

Excitations of a vortex are usually considered in a linear approximation neglecting their back reaction on the vortex. In the present paper we investigate back reaction of Proca-type excitations on a straight linear vortex in the Abelian Higgs model. We propose an exact ansatz for fields of the excited vortex. From an initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the back reaction corrections. Their approximate solutions are found in the cases of plane wave and wave-packet-type excitations. We find that the excited vortex radiates the vector field and that the Higgs field has a very broad oscillating component.

Development and testing of pulsed and rotating detonation combustors

Science.gov (United States)

St. George, Andrew C.

Detonation is a self-sustaining, supersonic, shock-driven, exothermic reaction. Detonation combustion can theoretically provide significant improvements in thermodynamic efficiency over constant pressure combustion when incorporated into existing cycles. To harness this potential performance benefit, countless studies have worked to develop detonation combustors and integrate these devices into existing systems. This dissertation consists of a series of investigations on two types of detonation combustors: the pulse detonation combustor (PDC) and the rotating detonation combustor (RDC). In the first two investigations, an array of air-breathing PDCs is integrated with an axial power turbine. The system is initially operated with steady and pulsed cold air flow to determine the effect of pulsed flow on turbine performance. Various averaging approaches are employed to calculate turbine efficiency, but only flow-weighted (e.g., mass or work averaging) definitions have physical significance. Pulsed flow turbine efficiency is comparable to steady flow efficiency at high corrected flow rates and low rotor speeds. At these conditions, the pulse duty cycle expands and the variation of the rotor incidence angle is constrained to a favorable range. The system is operated with pulsed detonating flow to determine the effect of frequency, fill fraction, and rotor speed on turbine performance. For some conditions, output power exceeds the maximum attainable value from steady constant pressure combustion due to a significant increase in available power from the detonation products. However, the turbine component efficiency estimated from classical thermodynamic analysis is four times lower than the steady design point efficiency. Analysis of blade angles shows a significant penalty due to the detonation, fill, and purge processes simultaneously imposed on the rotor. The latter six investigations focus on fundamental research of the RDC concept. A specially-tailored RDC data

Generalized Kutta–Joukowski theorem for multi-vortex and multi-airfoil flow (a lumped vortex model

Directory of Open Access Journals (Sweden)

Bai Chenyuan

2014-02-01

Full Text Available For purpose of easy identification of the role of free vortices on the lift and drag and for purpose of fast or engineering evaluation of forces for each individual body, we will extend in this paper the Kutta–Joukowski (KJ theorem to the case of inviscid flow with multiple free vortices and multiple airfoils. The major simplification used in this paper is that each airfoil is represented by a lumped vortex, which may hold true when the distances between vortices and bodies are large enough. It is found that the Kutta–Joukowski theorem still holds provided that the local freestream velocity and the circulation of the bound vortex are modified by the induced velocity due to the outside vortices and airfoils. We will demonstrate how to use the present result to identify the role of vortices on the forces according to their position, strength and rotation direction. Moreover, we will apply the present results to a two-cylinder example of Crowdy and the Wagner example to demonstrate how to perform fast force approximation for multi-body and multi-vortex problems. The lumped vortex assumption has the advantage of giving such kinds of approximate results which are very easy to use. The lack of accuracy for such a fast evaluation will be compensated by a rigorous extension, with the lumped vortex assumption removed and with vortex production included, in a forthcoming paper.

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

Science.gov (United States)

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.

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

International Nuclear Information System (INIS)

Kudela, Henryk; Kosior, Andrzej

2014-01-01

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.

Ozone and water vapour in the austral polar stratospheric vortex and sub-vortex

Directory of Open Access Journals (Sweden)

E. Peet

2004-12-01

Full Text Available In-situ measurements of ozone and water vapour, in the Antarctic lower stratosphere, were made as part of the APE-GAIA mission in September and October 1999. The measurements show a distinct difference above and below the 415K isentrope. Above 415K, the chemically perturbed region of low ozone and water vapour is clearly evident. Below 415K, but still above the tropopause, no sharp meridional gradients in ozone and water vapour were observed. The observations are consistent with analyses of potential vorticity from the European Centre for Medium Range Weather Forecasting, which show smaller radial gradients at 380K than at 450K potential temperature. Ozone loss in the chemically perturbed region above 415K averages 5ppbv per day for mid-September to mid-October. Apparent ozone loss rates in the sub-vortex region are greater, at 7ppbv per day. The data support, therefore, the existence of a sub-vortex region in which meridional transport is more efficient than in the vortex above. The low ozone mixing ratios in the sub-vortex region may be due to in-situ chemical destruction of ozone or transport of ozone-poor air out of the bottom of the vortex. The aircraft data we use cannot distinguish between these two processes. Key words. Meteorology and atmospheric dynamics polar meteorology – Atmospheric composition and structure (middle atmosphere–composition and chemistry

Vortex Ring Interaction with a Heated Screen

Science.gov (United States)

Smith, Jason; Krueger, Paul S.

2008-11-01

Previous examinations of vortex rings impinging on porous screens has shown the reformation of the vortex ring with a lower velocity after passing through the screen, the creation of secondary vortices, and mixing. A heated screen could, in principle, alter the vortex-screen interaction by changing the local liquid viscosity and density. In the present investigation, a mechanical piston-cylinder vortex ring generator was used to create vortex rings in an aqueous sucrose solution. The rings impinged on a screen of horizontal wires that were heated using electrical current. The flow was visualized with food color and video imaging. Tests with and without heat were conducted at a piston stroke-to-jet diameter ratio of 4 and a jet Reynolds number (Re) of 1000. The vortex rings slowed after passing through the screen, but in tests with heat, they maintained a higher fraction of their before-screen velocity due to reduction in fluid viscosity near the wires. In addition, small ``fingers'' that developed on the front of the vortex rings as they passed through the screen exhibited positive buoyancy effects in the heated case.

Flame Propagation in a Dump Combustor with Shear Layer Excitation

Data.gov (United States)

National Aeronautics and Space Administration — This experimentation looks to investigate the use of fluidic oscillators to attenuate combustion instability in a naturally unstable rocket combustor. Since...

Vortex dynamics in superconducting Corbino disk at zero field

International Nuclear Information System (INIS)

Enomoto, Y.; Ohta, M.

2007-01-01

We study the radial current driven vortex dynamics in the Corbino disk sample at zero field, by using a logarithmically interacting point vortex model involving effect of temperature, random pinning centers, and disk wall confinement force. We also take into account both the current induced vortex pair nucleation and the vortex pair annihilation processes in the model. Simulation results demonstrate that the vortex motion induced voltage exhibits almost periodic pulse behavior in time, observed experimentally, for a certain range of the model parameters. Such an anomalous behavior is thought to originate from large fluctuations of the vortex number due to the collective dynamics of this vortex system

Square vortex lattice in p-wave superconductors

International Nuclear Information System (INIS)

Shiraishi, J.

1999-01-01

Making use of the Ginzburg Landau equation for isotropic p-wave superconductors, we construct the single vortex solution in part analytically. The fourfold symmetry breaking term arising from the tetragonal symmetry distortion of the Fermi surface is crucial, since this term indicates a fourfold distortion of the vortex core somewhat similar to the one found in d-wave superconductors. This fourfold distortion of the vortex core in turn favors the square vortex lattice as observed recently by small angle neutron scattering (SANS) experiment from Sr 2 RuO 4 . We find that the hexagonal vortex lattice at H = H c1 transforms into the square one for H = H cr = 0.26 H c2 . On the other hand the SANS data does not reveal such transition. The square vortex covers everywhere studied by the SANS implying H cr is very close to H c1 . Therefore some improvement in the present model is certainly desirable. (orig.)

Guiding-center dynamics of vortex dipoles in Bose-Einstein condensates

International Nuclear Information System (INIS)

Middelkamp, S.; Schmelcher, P.; Torres, P. J.; Kevrekidis, P. G.; Frantzeskakis, D. J.; Carretero-Gonzalez, R.; Freilich, D. V.; Hall, D. S.

2011-01-01

A quantized vortex dipole is the simplest vortex molecule, comprising two countercirculating vortex lines in a superfluid. Although vortex dipoles are endemic in two-dimensional superfluids, the precise details of their dynamics have remained largely unexplored. We present here several striking observations of vortex dipoles in dilute-gas Bose-Einstein condensates, and develop a vortex-particle model that generates vortex line trajectories that are in good agreement with the experimental data. Interestingly, these diverse trajectories exhibit essentially identical quasiperiodic behavior, in which the vortex lines undergo stable epicyclic orbits.

Vortex sorter for Bose-Einstein condensates

International Nuclear Information System (INIS)

Whyte, Graeme; Veitch, John; Courtial, Johannes; Oehberg, Patrik

2004-01-01

We have designed interferometers that sort Bose-Einstein condensates into their vortex components. The Bose-Einstein condensates in the two arms of the interferometer are rotated with respect to each other through fixed angles; different vortex components then exit the interferometer in different directions. The method we use to rotate the Bose-Einstein condensates involves asymmetric phase imprinting and is itself new. We have modeled rotation through fixed angles and sorting into vortex components with even and odd values of the topological charge of two-dimensional Bose-Einstein condensates in a number of states (pure or superposition vortex states for different values of the scattering length). Our scheme may have applications for quantum information processing

Vortex 'puddles' and magic vortex numbers in mesoscopic superconducting disks

Energy Technology Data Exchange (ETDEWEB)

Connolly, M R; Milosevic, M V; Bending, S J [Department of Physics, University of Bath - Claverton Down, Bath, BA2 7AY (United Kingdom); Clem, J R [Ames Laboratory Department of Physics and Astronomy - Iowa State University, Ames, IA 50011-3160 (United States); Tamegai, T, E-mail: mrc61@cam.ac.u [Department of Applied Physics, University of Tokyo - Hongo, Bunkyo-ku, Tokyo 113-8627 (Japan)

2009-03-01

The magnetic properties of a superconducting disk change dramatically when its dimensions become mesoscopic. Unlike large disks, where the screening currents induced by an applied magnetic field are strong enough to force vortices to accumulate in a 'puddle' at the centre, in a mesoscopic disk the interaction between one of these vortices and the edge currents can be comparable to the intervortex repulsion, resulting in a destruction of the ordered triangular vortex lattice structure at the centre. Vortices instead form clusters which adopt polygonal and shell-like structures which exhibit magic number states similar to those of charged particles in a confining potential, and electrons in artificial atoms. We have fabricated mesoscopic high temperature superconducting Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+delta} disks and investigated their magnetic properties using magneto-optical imaging (MOI) and high resolution scanning Hall probe microscopy (SHPM). The temperature dependence of the vortex penetration field measured using MOI is in excellent agreement with models of the thermal excitation of pancake vortices over edge barriers. The growth of the central vortex puddle has been directly imaged using SHPM and magic vortex numbers showing higher stability have been correlated with abrupt jumps in the measured local magnetisation curves.

Interaction of a strong vortex with decaying turbulence

International Nuclear Information System (INIS)

Terry, P.W.

1988-01-01

The evolution of a localized, axially symmetric vortex under the action of shear stresses associated with decaying two-dimensional turbulent vorticity which is inhomogeneous in the presence of the vortex is studied analytically. For a vortex which is sufficiently strong relative to the coefficient of turbulent eddy viscosity, it is shown that turbulent fluctuations in the vortex interior and diffusion of coherent vorticity by the turbulence localize to the vortex periphery. It is also found that the coefficient of diffusion is small compared to the coefficient of eddy viscosity. 8 refs

Ring vortex solitons in nonlocal nonlinear media

DEFF Research Database (Denmark)

Briedis, D.; Petersen, D.E.; Edmundson, D.

2005-01-01

We study the formation and propagation of two-dimensional vortex solitons, i.e. solitons with a phase singularity, in optical materials with a nonlocal focusing nonlinearity. We show that nonlocality stabilizes the dynamics of an otherwise unstable vortex beam. This occurs for either single...... or higher charge fundamental vortices as well as higher order (multiple ring) vortex solitons. Our results pave the way for experimental observation of stable vortex rings in other nonlocal nonlinear systems including Bose-Einstein condensates with pronounced long-range interparticle interaction....

Back reaction of excitations on a vortex

International Nuclear Information System (INIS)

Arodz, H.; Hadasz, L.

1997-01-01

Excitations of a vortex are usually considered in a linear approximation neglecting their back reaction on the vortex. In the present paper we investigate back reaction of Proca-type excitations on a straight linear vortex in the Abelian Higgs model. We propose an exact ansatz for fields of the excited vortex. From an initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the back reaction corrections. Their approximate solutions are found in the cases of plane wave and wave-packet-type excitations. We find that the excited vortex radiates the vector field and that the Higgs field has a very broad oscillating component. copyright 1997 The American Physical Society

Spectral analysis of point-vortex dynamics : first application to vortex polygons in a circular domain

NARCIS (Netherlands)

Speetjens, M.F.M.; Meleshko, V.V.; Heijst, van G.J.F.

2014-01-01

The present study addresses the classical problem of the dynamics and stability of a cluster of N point vortices of equal strength arranged in a polygonal configuration ("N-vortex polygons"). In unbounded domains, such N-vortex polygons are unconditionally stable for N

Computational simulation of multi-strut central lobed injection of hydrogen in a scramjet combustor

Directory of Open Access Journals (Sweden)

Gautam Choubey

2016-09-01

Full Text Available Multi-strut injection is an approach to increase the overall performance of Scramjet while reducing the risk of thermal choking in a supersonic combustor. Hence computational simulation of Scramjet combustor at Mach 2.5 through multiple central lobed struts (three struts have been presented and discussed in the present research article. The geometry and model used here is slight modification of the DLR (German Aerospace Center scramjet model. Present results show that the presence of three struts injector improves the performance of scramjet combustor as compared to single strut injector. The combustion efficiency is also found to be highest in case of three strut fuel injection system. In order to validate the results, the numerical data for single strut injection is compared with experimental result which is taken from the literature.

Numerical study of effect of compressor swirling flow on combustor design in a MTE

Science.gov (United States)

Mu, Yong; Wang, Chengdong; Liu, Cunxi; Liu, Fuqiang; Hu, Chunyan; Xu, Gang; Zhu, Junqiang

2017-08-01

An effect of the swirling flow on the combustion performance is studied by the computational fluid dynamics (CFD) in a micro-gas turbine with a centrifugal compressor, dump diffuser and forward-flow combustor. The distributions of air mass and the Temperature Pattern Factor (as: Overall Temperature Distribution Factor -OTDF) in outlet are investigated with two different swirling angles of compressed air as 0° and 15° in three combustors. The results show that the influences of swirling flow on the air distribution and OTDF cannot be neglected. Compared with no-swirling flow, the air through outer liner is more, and the air through the inner liner is less, and the pressure loss is bigger under the swirling condition in the same combustor. The Temperature Pattern Factor changes under the different swirling conditions.

Vortex Filaments in Grids for Scalable, Fine Smoke Simulation.

Science.gov (United States)

Meng, Zhang; Weixin, Si; Yinling, Qian; Hanqiu, Sun; Jing, Qin; Heng, Pheng-Ann

2015-01-01

Vortex modeling can produce attractive visual effects of dynamic fluids, which are widely applicable for dynamic media, computer games, special effects, and virtual reality systems. However, it is challenging to effectively simulate intensive and fine detailed fluids such as smoke with fast increasing vortex filaments and smoke particles. The authors propose a novel vortex filaments in grids scheme in which the uniform grids dynamically bridge the vortex filaments and smoke particles for scalable, fine smoke simulation with macroscopic vortex structures. Using the vortex model, their approach supports the trade-off between simulation speed and scale of details. After computing the whole velocity, external control can be easily exerted on the embedded grid to guide the vortex-based smoke motion. The experimental results demonstrate the efficiency of using the proposed scheme for a visually plausible smoke simulation with macroscopic vortex structures.

Giant moving vortex mass in thick magnetic nanodots.

Science.gov (United States)

Guslienko, K Y; Kakazei, G N; Ding, J; Liu, X M; Adeyeye, A O

2015-09-10

Magnetic vortex is one of the simplest topologically non-trivial textures in condensed matter physics. It is the ground state of submicron magnetic elements (dots) of different shapes: cylindrical, square etc. So far, the vast majority of the vortex dynamics studies were focused on thin dots with thickness 5-50 nm and only uniform across the thickness vortex excitation modes were observed. Here we explore the fundamental vortex mode in relatively thick (50-100 nm) dots using broadband ferromagnetic resonance and show that dimensionality increase leads to qualitatively new excitation spectra. We demonstrate that the fundamental mode frequency cannot be explained without introducing a giant vortex mass, which is a result of the vortex distortion due to interaction with spin waves. The vortex mass depends on the system geometry and is non-local because of important role of the dipolar interaction. The mass is rather small for thin dots. However, its importance increases drastically with the dot thickness increasing.

Modeling Vortex Generators in a Navier-Stokes Code

Science.gov (United States)

Dudek, Julianne C.

2011-01-01

A source-term model that simulates the effects of vortex generators was implemented into the Wind-US Navier-Stokes code. The source term added to the Navier-Stokes equations simulates the lift force that would result from a vane-type vortex generator in the flowfield. The implementation is user-friendly, requiring the user to specify only three quantities for each desired vortex generator: the range of grid points over which the force is to be applied and the planform area and angle of incidence of the physical vane. The model behavior was evaluated for subsonic flow in a rectangular duct with a single vane vortex generator, subsonic flow in an S-duct with 22 corotating vortex generators, and supersonic flow in a rectangular duct with a counter-rotating vortex-generator pair. The model was also used to successfully simulate microramps in supersonic flow by treating each microramp as a pair of vanes with opposite angles of incidence. The validation results indicate that the source-term vortex-generator model provides a useful tool for screening vortex-generator configurations and gives comparable results to solutions computed using gridded vanes.

Non-Abelian vortex lattices

Science.gov (United States)

Tallarita, Gianni; Peterson, Adam

2018-04-01

We perform a numerical study of the phase diagram of the model proposed in [M. Shifman, Phys. Rev. D 87, 025025 (2013)., 10.1103/PhysRevD.87.025025], which is a simple model containing non-Abelian vortices. As per the case of Abrikosov vortices, we map out a region of parameter space in which the system prefers the formation of vortices in ordered lattice structures. These are generalizations of Abrikosov vortex lattices with extra orientational moduli in the vortex cores. At sufficiently large lattice spacing the low energy theory is described by a sum of C P (1 ) theories, each located on a vortex site. As the lattice spacing becomes smaller, when the self-interaction of the orientational field becomes relevant, only an overall rotation in internal space survives.

Vorticity and vortex dynamics

CERN Document Server

Wu, Jie-Zhi; Zhou, M-D

2006-01-01

The importance of vorticity and vortex dynamics has now been well rec- nized at both fundamental and applied levels of ?uid dynamics, as already anticipatedbyTruesdellhalfcenturyagowhenhewrotethe?rstmonograph onthesubject, The Kinematics of Vorticity(1954);andasalsoevidencedby the appearance of several books on this ?eld in 1990s. The present book is characterizedbythefollowingfeatures: 1. A basic physical guide throughout the book. The material is directed by a basic observation on the splitting and coupling of two fundamental processes in ?uid motion, i.e., shearing (unique to ?uid) and compre- ing/expanding.Thevorticityplaysakeyroleintheformer,andavortex isnothingbuta?uidbodywithhighconcentrationofvorticitycompared to its surrounding ?uid. Thus, the vorticity and vortex dynamics is - cordinglyde?nedasthetheoryofshearingprocessanditscouplingwith compressing/expandingprocess. 2. A description of the vortex evolution following its entire life.Thisbegins from the generation of vorticity to the formation of thi...

Three-dimensional supersonic vortex breakdown

Science.gov (United States)

Kandil, Osama A.; Kandil, Hamdy A.; Liu, C. H.

1993-01-01

Three-dimensional supersonic vortex-breakdown problems in bound and unbound domains are solved. The solutions are obtained using the time-accurate integration of the unsteady, compressible, full Navier-Stokes (NS) equations. The computational scheme is an implicit, upwind, flux-difference splitting, finite-volume scheme. Two vortex-breakdown applications are considered in the present paper. The first is for a supersonic swirling jet which is issued from a nozzle into a supersonic uniform flow at a lower Mach number than that of the swirling jet. The second is for a supersonic swirling flow in a configured circular duct. In the first application, an extensive study of the effects of grid fineness, shape and grid-point distribution on the vortex breakdown is presented. Four grids are used in this study and they show a substantial dependence of the breakdown bubble and shock wave on the grid used. In the second application, the bubble-type and helix-type vortex breakdown have been captured.

High Magnetic Field Vortex Microscopy by NMR

Science.gov (United States)

Mitrović, V. F.; Sigmund, E. E.; Bachman, H. N.; Halperin, W. P.; Reyes, A. P.; Kuhns, P.; Moulton, W. G.

2001-03-01

At low temperatures the ^17O NMR spectrum of HTS exhibits a characteristic vortex lattice line shape. Measurements of spin-lattice relaxation rate, T_1-1, across the vortex spectrum represent a probe of low-energy quasiparticle excitations as a function of distance from the vortex core. We report ^17O(2,3) T_1-1 measurements of YBa_2Cu_3O7 at low temperatures in magnetic fields up to 37 T. We find that the rate increases on approaching the vortex core. In the vortex core region at 37 T we observe an additional increase in the relaxation rate. The temperature dependence of the rate will also be discussed. Work at Northwestern University is supported by the NSF (DMR 91-20000) through the Science and Technology Center for Superconductivity.

Vortex molecule in a nanoscopic square superconducting plate

International Nuclear Information System (INIS)

Suematsu, Hisataka; Kato, Masaru; Ishida, Takekazu; Koyama, Tomio; Machida, Masahiko

2010-01-01

Using the finite element method and solving the Bogoliubov-de Gennes equation, we have investigated magnetic field dependence of the stable vortex structures in a mesoscopic superconducting plate at low temperature (T = 0.1T c ). Because of the compactness of vortex configuration, there is interference between bound states around vortices and such quasi-particle structure affects the vortex configuration. Especially in two-vortices state, vortices form a molecule-like state, where bound states of each vortex form molecular orbital like bonding and anti-bonding states. The vortex configuration is different from that, which is expected from the repulsive interaction between vortices. (author)

Tunable magnetic vortex resonance in a potential well

Science.gov (United States)

Warnicke, P.; Wohlhüter, P.; Suszka, A. K.; Stevenson, S. E.; Heyderman, L. J.; Raabe, J.

2017-11-01

We use frequency-resolved x-ray microscopy to fully characterize the potential well of a magnetic vortex in a soft ferromagnetic permalloy square. The vortex core is excited with magnetic broadband pulses and simultaneously displaced with a static magnetic field. We observe a frequency increase (blueshift) in the gyrotropic mode of the vortex core with increasing bias field. Supported by micromagnetic simulations, we show that this frequency increase is accompanied by internal deformation of the vortex core. The ability to modify the inner structure of the vortex core provides a mechanism to control the dynamics of magnetic vortices.

Dynamic Control of Collapse in a Vortex Airy Beam

Science.gov (United States)

Chen, Rui-Pin; Chew, Khian-Hooi; He, Sailing

2013-01-01

Here we study systematically the self-focusing dynamics and collapse of vortex Airy optical beams in a Kerr medium. The collapse is suppressed compared to a non-vortex Airy beam in a Kerr medium due to the existence of vortex fields. The locations of collapse depend sensitively on the initial power, vortex order, and modulation parameters. The collapse may occur in a position where the initial field is nearly zero, while no collapse appears in the region where the initial field is mainly distributed. Compared with a non-vortex Airy beam, the collapse of a vortex Airy beam can occur at a position away from the area of the initial field distribution. Our study shows the possibility of controlling and manipulating the collapse, especially the precise position of collapse, by purposely choosing appropriate initial power, vortex order or modulation parameters of a vortex Airy beam. PMID:23518858

Vortex-line fluctuations in model high-temperature superconductors

International Nuclear Information System (INIS)

Li, Y.; Teitel, S.

1993-01-01

We carry out Monte Carlo simulations of the uniformly frustrated three-dimensional XY model, as a model for vortex-line fluctuations in a high-T c superconductor in an external magnetic field. A density of vortex lines of f=1/25 is considered. We find two sharp phase transitions. The low-T superconducting phase is an ordered vortex-line lattice. The high-T normal phase is a vortex-line liquid, with much entangling, cutting, and loop excitations. An intermediate phase is found, which is characterized as a vortex-line liquid of disentangled, approximately straight, lines. In this phase, the system displays superconducting properties in the direction parallel to the magnetic field, but normal behavior in planes perpendicular to the field. A detailed analysis of the vortex structure function is carried out

Aperiodicity Correction for Rotor Tip Vortex Measurements

Science.gov (United States)

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.

Superconductivity and vortex properties in various multilayers

International Nuclear Information System (INIS)

Koorevaar, P.

1994-01-01

In this thesis three qualitatively different type of superconducting multilayers are studied. We discuss the vortex lattice structure in Nb/NbZr multilayers, a system where both type of constituting layers are superconducting. At certain temperatures and for parallel fields close to H c2parallel , the Nb/NbZr system has a strongly modulated order parameter, and in this aspect resembles the high-Tc materials. By lowering the field the modulation decreases, having important consequences for the vortex lattice structure. By studying the transport critical currents we show that in the case of strong modulation the vortex lattice has a kinked structure, but at weaker modulations the vortices are straight, and the change in modulation actually results in a vortex lattice transition. Our study confirms the picture of the existence of kinked vortex lattices, but it is rather surprising that these kinked structures can exist in a system which in itself is not at all that anisotropic. It indicates the relevance of other parameters governing the vortex lattice structure. (orig.)

Study on mechanism of combustion instability in a dump gas turbine combustor

International Nuclear Information System (INIS)

Lee, Yeon Joo; Lee, Jong Ho; Jeon, Chong Hwan; Chang, Yonng June

2002-01-01

Combustion instabilities are an important concern associated with lean premixed combustion. Laboratory-scale dump combustor was used to understand the underlying mechanisms causing combustion instabilities. Experiments were conducted at atmospheric pressure and sound level meter was used to track the pressure fluctuations inside the combustor. Instability maps and phase-resolved OH chemiluminescence images were obtained at several conditions to investigate the mechanism of combustion instability and relations between pressure wave and heat release rate. It showed that combustion instability was susceptible to occur at higher value of equivalence ratio (>0.6) as the mean velocity was decreased. Instabilities exhibited a longitudinal mode with a dominant frequency of ∼341.8 Hz, which corresponded to a quarter wave mode of combustor. Heat release and pressure waves were in-phase when instabilities occurred. Rayleigh index distribution gave a hint about the location where the strong coherence of pressure and heat release existed. These results also give an insight to the control scheme of combustion instabilities. Emission test revealed that NO x emissions were affected by not only equivalence but also combustion instability

Experimental study on combustion modes and thrust performance of a staged-combustor of the scramjet with dual-strut

Science.gov (United States)

Yang, Qingchun; Chetehouna, Khaled; Gascoin, Nicolas; Bao, Wen

2016-05-01

To enable the scramjet operate in a wider flight Mach number, a staged-combustor with dual-strut is introduced to hold more heat release at low flight Mach conditions. The behavior of mode transition was examined using a direct-connect model scramjet experiment along with pressure measurements. The typical operating modes of the staged-combustor are analyzed. Fuel injection scheme has a significant effect on the combustor operating modes, particularly for the supersonic combustion mode. Thrust performances of the combustor with different combustion modes and fuel distributions are reported in this paper. The first-staged strut injection has a better engine performance in the operation of subsonic combustion mode. On the contrast, the second-staged strut injection has a better engine performance in the operation of supersonic combustion mode.

Computational investigation of the temperature separation in vortex chamber

International Nuclear Information System (INIS)

Anish, S.; Setoguchi, T.; Kim, H. D.

2014-01-01

The vortex chamber is a mechanical device, without any moving parts that separates compressed gas into a high temperature region and a low temperature region. Functionally vortex chamber is similar to a Ranque-Hilsch vortex tube (RVHT), but it is a simpler and compact structure. The objective of the present study is to investigate computationally the physical reasoning behind the energy separation mechanism inside a vortex chamber. A computational analysis has been performed using three-dimensional compressible Navier Stokes equations. A fully implicit finite volume scheme was used to solve the governing equations. A commercial software ANSYS CFX is used for this purpose. The computational predictions were validated with existing experimental data. The results obtained show that the vortex chamber contains a large free vortex zone and a comparatively smaller forced vortex region. The physical mechanism that causes the heating towards periphery of the vortex chamber is identified as the work done by the viscous force. The cooling at the center may be due to expansion of the flow. The extent of temperature separation greatly depends on the outer diameter of the vortex chamber. A small amount of compression is observed towards the periphery of the vortex chamber when the outer diameter is reduced.

Topological Vortex and Knotted Dissipative Optical 3D Solitons Generated by 2D Vortex Solitons.

Science.gov (United States)

Veretenov, N A; Fedorov, S V; Rosanov, N N

2017-12-29

We predict a new class of three-dimensional (3D) topological dissipative optical one-component solitons in homogeneous laser media with fast saturable absorption. Their skeletons formed by vortex lines where the field vanishes are tangles, i.e., N_{c} knotted or unknotted, linked or unlinked closed lines and M unclosed lines that thread all the closed lines and end at the infinitely far soliton periphery. They are generated by embedding two-dimensional laser solitons or their complexes in 3D space after their rotation around an unclosed, infinite vortex line with topological charge M_{0} (N_{c}, M, and M_{0} are integers). With such structure propagation, the "hula-hoop" solitons form; their stability is confirmed numerically. For the solitons found, all vortex lines have unit topological charge: the number of closed lines N_{c}=1 and 2 (unknots, trefoils, and Solomon knots links); unclosed vortex lines are unknotted and unlinked, their number M=1, 2, and 3.

Multiscale Software Tool for Controls Prototyping in Supersonic Combustors

National Research Council Canada - National Science Library

Pindera, M

2004-01-01

.... In Phase I we have developed a proof-of-concept version of such a tool. We have developed a model-free direct control strategy with on-line training and demonstrated its capabilities in controlling isolator unstart in a hypersonic combustor...

Investigation of Methane Oxy-Fuel Combustion in a Swirl-Stabilised Gas Turbine Model Combustor

Directory of Open Access Journals (Sweden)

Mao Li

2017-05-01

Full Text Available CO2 has a strong impact on both operability and emission behaviours in gas turbine combustors. In the present study, an atmospheric, preheated, swirl-stabilised optical gas turbine model combustor rig was employed. The primary objectives were to analyse the influence of CO2 on the fundamental characteristics of combustion, lean blowout (LBO limits, CO emission and flame structures. CO2 dilution effects were examined with three preheating temperatures (396.15, 431.15, and 466.15 K. The fundamental combustion characteristics were studied utilising chemical kinetic simulations. To study the influence of CO2 on the operational range of the combustor, equivalence ratio (Ф was varied from stoichiometric conditions to the LBO limits. CO emissions were measured at the exit of the combustor using a water-cooled probe over the entire operational range. The flame structures and locations were characterised by performing CH chemiluminescence imaging. The inverse Abel transformation was used to analyse the CH distribution on the axisymmetric plane of the combustor. Chemical kinetic modelling indicated that the CO2 resulted in a lower reaction rate compared with the CH4/air flame. Fundamental combustion properties such as laminar flame speed, ignition delay time and blowout residence time were found to be affected by CO2. The experimental results revealed that CO2 dilution resulted in a narrower operational range for the equivalence ratio. It was also found that CO2 had a strong inhibiting effect on CO burnout, which led to a higher concentration of CO in the combustion exhaust. CH chemiluminescence showed that the CO2 dilution did not have a significant impact on the flame structure.

Experimental results showing the internal three-component velocity field and outlet temperature contours for a model gas turbine combustor

CSIR Research Space (South Africa)

Meyers, BC

2011-09-01

Full Text Available by the American Institute of Aeronautics and Astronautics Inc. All rights reserved ISABE-2011-1129 EXPERIMENTAL RESULTS SHOWING THE INTERNAL THREE-COMPONENT VELOCITY FIELD AND OUTLET TEMPERATURE CONTOURS FOR A MODEL GAS TURBINE COMBUSTOR BC Meyers*, GC... identifier c Position identifier F Fuel i Index L (Combustor) Liner OP Orifice plate Introduction There are often inconsistencies when comparing experimental and Computational Fluid Dynamics (CFD) simulations for gas turbine combustors [1...

Design and fabrication of a meso-scale stirling engine and combustor.

Energy Technology Data Exchange (ETDEWEB)

Echekki, Tarek (Sandia National Laboratories, Livermore, CA); Haroldsen, Brent L. (Sandia National Laboratories, Livermore, CA); Krafcik, Karen L. (Sandia National Laboratories, Livermore, CA); Morales, Alfredo Martin (Sandia National Laboratories, Livermore, CA); Mills, Bernice E. (Sandia National Laboratories, Livermore, CA); Liu, Shiling (Sandia National Laboratories, Livermore, CA); Lee, Jeremiah C. (Sandia National Laboratories, Livermore, CA); Karpetis, Adionos N. (Sandia National Laboratories, Livermore, CA); Chen, Jacqueline H. (Sandia National Laboratories, Livermore, CA); Ceremuga, Joseph T. (Sandia National Laboratories, Livermore, CA); Raber, Thomas N. (Sandia National Laboratories, Livermore, CA); Hekmuuaty, Michelle A. (Sandia National Laboratories, Livermore, CA)

2005-05-01

Power sources capable of supplying tens of watts are needed for a wide variety of applications including portable electronics, sensors, micro aerial vehicles, and mini-robotics systems. The utility of these devices is often limited by the energy and power density capabilities of batteries. A small combustion engine using liquid hydrocarbon fuel could potentially increase both power and energy density by an order of magnitude or more. This report describes initial development work on a meso-scale external combustion engine based on the Stirling cycle. Although other engine designs perform better at macro-scales, we believe the Stirling engine cycle is better suited to small-scale applications. The ideal Stirling cycle requires efficient heat transfer. Consequently, unlike other thermodynamic cycles, the high heat transfer rates that are inherent with miniature devices are an advantage for the Stirling cycle. Furthermore, since the Stirling engine uses external combustion, the combustor and engine can be scaled and optimized semi-independently. Continuous combustion minimizes issues with flame initiation and propagation. It also allows consideration of a variety of techniques to promote combustion that would be difficult in a miniature internal combustion engine. The project included design and fabrication of both the engine and the combustor. Two engine designs were developed. The first used a cylindrical piston design fabricated with conventional machining processes. The second design, based on the Wankel rotor geometry, was fabricated by through-mold electroforming of nickel in SU8 and LIGA micromolds. These technologies provided the requisite precision and tight tolerances needed for efficient micro-engine operation. Electroformed nickel is ideal for micro-engine applications because of its high strength and ductility. A rotary geometry was chosen because its planar geometry was more compatible with the fabrication process. SU8 lithography provided rapid

The bathtub vortex in a rotating container

DEFF Research Database (Denmark)

Andersen, Anders Peter; Bohr, Tomas; Stenum, B.

2006-01-01

We study the time-independent free-surface flow which forms when a fluid drains out of a container, a so-called bathtub vortex. We focus on the bathtub vortex in a rotating container and describe the free-surface shape and the complex flow structure using photographs of the free surface, flow...... expansion approximation of the central vortex core and reduce the model to a single first-order equation. We solve the equation numerically and find that the axial velocity depends linearly on height whereas the azimuthal velocity is almost independent of height. We discuss the model of the bathtub vortex...

Pulse Combustor Driven Pressure Gain Combustion for High Efficiency Gas Turbine Engines

KAUST Repository

Lisanti, Joel

2017-02-01

The gas turbine engine is an essential component of the global energy infrastructure which accounts for a significant portion of the total fossil fuel consumption in transportation and electric power generation sectors. For this reason there is significant interest in further increasing the efficiency and reducing the pollutant emissions of these devices. Conventional approaches to this goal, which include increasing the compression ratio, turbine inlet temperature, and turbine/compressor efficiency, have brought modern gas turbine engines near the limits of what may be achieved with the conventionally applied Brayton cycle. If a significant future step increase in gas turbine efficiency is to be realized some deviation from this convention is necessary. The pressure gain gas turbine concept is a well established new combustion technology that promises to provide a dramatic increase in gas turbine efficiency by replacing the isobaric heat addition process found in conventional technology with an isochoric process. The thermodynamic benefit of even a small increase in stagnation pressure across a gas turbine combustor translates to a significant increase in cycle efficiency. To date there have been a variety of methods proposed for achieving stagnation pressure gains across a gas turbine combustor and these concepts have seen a broad spectrum of levels of success. The following chapter provides an introduction to one of the proposed pressure gain methods that may be most easily realized in a practical application. This approach, known as pulse combustor driven pressure gain combustion, utilizes an acoustically resonant pulse combustor to approximate isochoric heat release and thus produce a rise in stagnation pressure.

A counter-rotating vortex pair in inviscid fluid

Science.gov (United States)

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.

Quantum Kinematics of Bosonic Vortex Loops

International Nuclear Information System (INIS)

Goldin, G.A.; Owczarek, R.; Sharp, D.H.

1999-01-01

Poisson structure for vortex filaments (loops and arcs) in 2D ideal incompressible fluid is analyzed in detail. Canonical coordinates and momenta on coadjoint orbits of the area-preserving diffeomorphism group, associated with such vortices, are found. The quantum space of states in the simplest case of ''bosonic'' vortex loops is built within a geometric quantization approach to the description of a quantum fluid. Fock-like structure and non-local creation and annihilation operators of quantum vortex filaments are introduced

Bifurcation and instability problems in vortex wakes

DEFF Research Database (Denmark)

Aref, Hassan; Brøns, Morten; Stremler, Mark A.

2007-01-01

A number of instability and bifurcation problems related to the dynamics of vortex wake flows are addressed using various analytical tools and approaches. We discuss the bifurcations of the streamline pattern behind a bluff body as a vortex wake is produced, a theory of the universal Strouhal......-Reynolds number relation for vortex wakes, the bifurcation diagram for "exotic" wake patterns behind an oscillating cylinder first determined experimentally by Williamson & Roshko, and the bifurcations in topology of the streamlines pattern in point vortex streets. The Hamiltonian dynamics of point vortices...... in a periodic strip is considered. The classical results of von Kármán concerning the structure of the vortex street follow from the two-vortices-in-a-strip problem, while the stability results follow largely from a four-vortices-in-a-strip analysis. The three-vortices-in-a-strip problem is argued...

An Experimental Investigation of Self-Excited Combustion Dynamics in a Single Element Lean Direct Injection (LDI) Combustor

Science.gov (United States)

Gejji, Rohan M.

The management of combustion dynamics in gas turbine combustors has become more challenging as strict NOx/CO emission standards have led to engine operation in a narrow, lean regime. While premixed or partially premixed combustor configurations such as the Lean Premixed Pre-vaporized (LPP), Rich Quench Lean burn (RQL), and Lean Direct Injection (LDI) have shown a potential for reduced NOx emissions, they promote a coupling between acoustics, hydrodynamics and combustion that can lead to combustion instabilities. These couplings can be quite complex, and their detailed understanding is a pre-requisite to any engine development program and for the development of predictive capability for combustion instabilities through high-fidelity models. The overarching goal of this project is to assess the capability of high-fidelity simulation to predict combustion dynamics in low-emissions gas turbine combustors. A prototypical lean-direct-inject combustor was designed in a modular configuration so that a suitable geometry could be found by test. The combustor comprised a variable length air plenum and combustion chamber, air swirler, and fuel nozzle located inside a subsonic venturi. The venturi cross section and the fuel nozzle were consistent with previous studies. Test pressure was 1 MPa and variables included geometry and acoustic resonance, inlet temperatures, equivalence ratio, and type of liquid fuel. High-frequency pressure measurements in a well-instrumented metal chamber yielded frequencies and mode shapes as a function of inlet air temperature, equivalence ratio, fuel nozzle placement, and combustor acoustic resonances. The parametric survey was a significant effort, with over 105 tests on eight geometric configurations. A good dataset was obtained that could be used for both operating-point-dependent quantitative comparisons, and testing the ability of the simulation to predict more global trends. Results showed a very strong dependence of instability amplitude on

Computational model of a whole tree combustor

Energy Technology Data Exchange (ETDEWEB)

Bryden, K.M.; Ragland, K.W. [Univ. of Wisconsin, Madison, WI (United States)

1993-12-31

A preliminary computational model has been developed for the whole tree combustor and compared to test results. In the simulation model presented hardwood logs, 15 cm in diameter are burned in a 4 m deep fuel bed. Solid and gas temperature, solid and gas velocity, CO, CO{sub 2}, H{sub 2}O, HC and O{sub 2} profiles are calculated. This deep, fixed bed combustor obtains high energy release rates per unit area due to the high inlet air velocity and extended reaction zone. The lowest portion of the overall bed is an oxidizing region and the remainder of the bed acts as a gasification and drying region. The overfire air region completes the combustion. Approximately 40% of the energy is released in the lower oxidizing region. The wood consumption rate obtained from the computational model is 4,110 kg/m{sup 2}-hr which matches well the consumption rate of 3,770 kg/m{sup 2}-hr observed during the peak test period of the Aurora, MN test. The predicted heat release rate is 16 MW/m{sup 2} (5.0*10{sup 6} Btu/hr-ft{sup 2}).

System for reducing combustion dynamics and NO.sub.x in a combustor

Science.gov (United States)

Uhm, Jong Ho; Ziminsky, Willy Steve; Johnson, Thomas Edward; Hughes, Michael John; York, William David

2016-05-31

A combustor includes an end cap that extends radially across at least a portion of the combustor. The end cap includes an upstream surface axially separated from a downstream surface. A plurality of tubes extend from the upstream surface through the downstream surface of the end cap to provide fluid communication through the end cap. Each tube in a first set of the plurality of tubes has an inlet proximate to the upstream surface and an outlet downstream from the downstream surface. Each outlet has a first portion that extends a different axial distance from the inlet than a second portion.

On the self-induced motion of a helical vortex

NARCIS (Netherlands)

Boersma, J.; Wood, D.H.

1999-01-01

The velocity field in the immediate vicinity of a curved vortex comprises a circulation around the vortex, a component due to the vortex curvature, and a ‘remainder’ due to the more distant parts of the vortex. The first two components are relatively well understood but the remainder is known only

Melting of heterogeneous vortex matter: The vortex 'nanoliquid'

Indian Academy of Sciences (India)

E ZELDOV2, A SOIBEL3, F de la CRUZ4,CJ van der BEEK5,. M KONCZYKOWSKI5, T ... 2Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot. 76100, Israel ..... heterogeneous nature of the vortex nanoliquid.

Genetic algorithm to optimize the design of main combustor and gas generator in liquid rocket engines

Science.gov (United States)

Son, Min; Ko, Sangho; Koo, Jaye

2014-06-01

A genetic algorithm was used to develop optimal design methods for the regenerative cooled combustor and fuel-rich gas generator of a liquid rocket engine. For the combustor design, a chemical equilibrium analysis was applied, and the profile was calculated using Rao's method. One-dimensional heat transfer was assumed along the profile, and cooling channels were designed. For the gas-generator design, non-equilibrium properties were derived from a counterflow analysis, and a vaporization model for the fuel droplet was adopted to calculate residence time. Finally, a genetic algorithm was adopted to optimize the designs. The combustor and gas generator were optimally designed for 30-tonf, 75-tonf, and 150-tonf engines. The optimized combustors demonstrated superior design characteristics when compared with previous non-optimized results. Wall temperatures at the nozzle throat were optimized to satisfy the requirement of 800 K, and specific impulses were maximized. In addition, the target turbine power and a burned-gas temperature of 1000 K were obtained from the optimized gas-generator design.

Nonlinear dynamics in a trapped atomic Bose-Einstein condensate induced by an oscillating Gaussian potential

International Nuclear Information System (INIS)

Fujimoto, Kazuya; Tsubota, Makoto

2011-01-01

We consider a trapped atomic Bose-Einstein condensate penetrated by a repulsive Gaussian potential and theoretically investigate the dynamics induced by oscillating the Gaussian potential. Our study is based on the numerical calculation of the two-dimensional Gross-Pitaevskii equation. Our calculation reveals the dependence of the characteristic behavior of the condensate on the amplitude and frequency of the oscillating potential. These dynamics are deeply related to the nucleation and dynamics of quantized vortices and solitons. When the potential oscillates with a large amplitude, it nucleates many vortex pairs that move away from the potential. When the amplitude of the oscillation is small, it nucleates solitons through an annihilation of vortex pairs. We discuss three issues concerning the nucleation of vortices. The first is the phase diagram for the nucleation of vortices and solitons near the oscillating potential. The second is the mechanism and critical velocity of the nucleation. The critical velocity of the nucleation is an important issue in quantum fluids, and we propose an expression for the velocity containing both the coherence length and the size of the potential. The third is the divergence of the nucleation time, which is the time it takes for the potential to nucleate vortices, near the critical parameters for vortex nucleation.

Motion of a single quantized vortex in an orifice

International Nuclear Information System (INIS)

Schwarz, K.W.

1993-01-01

Discrete phase-slip events are observed when superfluid 4 He moves through a microscopic orifice. In order to understand such behavior, one must know (a) how a quantized vortex is introduced into the orifice, and (b) how such a vortex evolves fluid dynamically so as to absorb energy from the applied flow field. To begin the study of the latter question, the authors present calculations done with an idealized orifice geometry. It is found that vortex loops larger than a critical size are carried out of the orifice and stretched by the diverging flow. As it stretches, such a vortex will cross the orifice, the energy required to stretch the vortex being absorbed from the flow field. Both a vortex loop introduced directly into the orifice and a remanent vortex extending to infinity will be discussed

Theory of vortex flows in partially ionized magnetoplasmas

Energy Technology Data Exchange (ETDEWEB)

Jovanovic, D.; Shukla, P.K

2004-06-07

A complete theory for vortex flows in partially ionized magnetoplasmas is presented. Accurate analytical and numerical results are obtained concerning the structure of a Burger's vortex and a tripolar vortex. A novel type of rotating tripolar vortices with elliptic cores are found in the systems dominated by the convection in incompressible flows, but whose generation is triggered by the diffusive and compressible effects. Our vortex flow models successfully explain recent observations from laboratory magnetoplasmas and geophysical flows.

Vortex Lattices in the Bose-Fermi Superfluid Mixture.

Science.gov (United States)

Jiang, Yuzhu; Qi, Ran; Shi, Zhe-Yu; Zhai, Hui

2017-02-24

In this Letter we show that the vortex lattice structure in the Bose-Fermi superfluid mixture can undergo a sequence of structure transitions when the Fermi superfluid is tuned from the BCS regime to the BEC regime. This is due to the difference in the vortex core structure of a Fermi superfluid in the BCS regime and in the BEC regime. In the BCS regime the vortex core is nearly filled, while the density at the vortex core gradually decreases until it empties out in the BEC regime. Therefore, with the density-density interaction between the Bose and the Fermi superfluids, interaction between the two sets of vortex lattices gets stronger in the BEC regime, which yields the structure transition of vortex lattices. In view of the recent realization of this superfluid mixture and vortices therein, our theoretical predication can be verified experimentally in the near future.

Generalized Kutta–Joukowski theorem for multi-vortex and multi-airfoil flow with vortex production — A general model

Directory of Open Access Journals (Sweden)

Bai Chenyuan

2014-10-01

Full Text Available By using a special momentum approach and with the help of interchange between singularity velocity and induced flow velocity, we derive in a physical way explicit force formulas for two-dimensional inviscid flow involving multiple bound and free vortices, multiple airfoils, and vortex production. These force formulas hold individually for each airfoil thus allowing for force decomposition, and the contributions to forces from singularities (such as bound and image vortices, sources, and doublets and bodies out of an airfoil are related to their induced velocities at the locations of singularities inside this airfoil. The force contribution due to vortex production is related to the vortex production rate and the distance between each pair of vortices in production, thus frame-independent. The formulas are validated against a number of standard problems. These force formulas, which generalize the classic Kutta–Joukowski theorem (for a single bound vortex and the recent generalized Lagally theorem (for problems without a bound vortex and vortex production to more general cases, can be used to identify or understand the roles of outside vortices and bodies on the forces of the actual body, optimize arrangement of outside vortices and bodies for force enhancement or reduction, and derive analytical force formulas once the flow field is given or known.

Systems and methods for preventing flashback in a combustor assembly

Science.gov (United States)

Johnson, Thomas Edward; Ziminsky, Willy Steve; Stevenson, Christian Xavier

2016-04-05

Embodiments of the present application include a combustor assembly. The combustor assembly may include a combustion chamber, a first plenum, a second plenum, and one or more elongate air/fuel premixing injection tubes. Each of the elongate air/fuel premixing injection tubes may include a first length at least partially disposed within the first plenum and configured to receive a first fluid from the first plenum. Moreover, each of the elongate air/fuel premixing injection tubes may include a second length disposed downstream of the first length and at least partially disposed within the second plenum. The second length may be formed of a porous wall configured to allow a second fluid from the second plenum to enter the second length and create a boundary layer about the porous wall.

Modeling of aerodynamics in vortex furnace

Energy Technology Data Exchange (ETDEWEB)

Anufriev, I.; Krasinsky, D. [Russian Academy of Sciences, Novosibirsk (Russian Federation). Inst. of Thermophysics; Salomatov, V.; Anikin, Y.; Sharypov, O. [Russian Academy of Sciences, Novosibirsk (Russian Federation). Inst. of Thermophysics; Novosibirsk State Univ. (Russian Federation); Enkhjargal, Kh. [Mongol Univ. of Science and Technology, Ulan Bator (Mongolia)

2013-07-01

At present, the torch burning technology of pulverized-coal fuel in vortex flow is one of the most prospective and environmentally-friendly combustion technologies of low-grade coals. Appropriate organization of aerodynamics may influence stability of temperature and heat flux distributions, increase slag catching, and reduce toxic emissions. Therefore, from scientific point of view it is interesting to investigate aerodynamics in the devices aiming at justification of design and operating parameters for new steam generators with vortex furnace, and upgrade of existing boiler equipment. The present work is devoted to physical and mathematical modeling of interior aerodynamics of vortex furnace of steam generator of thermal power plants. Research was carried out on the air isothermal model which geometry was similar to one section of the experimental- industrial boiler TPE-427 of Novosibirsk TPS-3. Main elements of vortex furnace structure are combustion chamber, diffuser, and cooling chamber. The model is made from organic glass; on the front wall two rectangular nozzles (through which compressed air is injected) are placed symmetrically at 15 to the horizon. The Laser Doppler Velocimeter LAD-05 was used for non-contact measurement of vortex flow characteristics. Two velocity components in the XY-plane (in different cross- sections of the model) were measured in these experiments. Reynolds number was 3.10{sup 5}. Numerical simulation of 3-D turbulent isothermal flow was performed with the use of CFD package FLUENT. Detailed structure of the flow in vortex furnace model has been obtained in predictions. The distributions of main flow characteristics (pressure, velocity and vorticity fields, turbulent kinetic energy) are presented. The obtained results may be used at designing boilers with vortex furnace. Computations were performed using the supercomputer NKS-160.

Vortex operators in gauge field theories

International Nuclear Information System (INIS)

Polchinski, J.

1980-07-01

Several related aspects of the 't Hooft vortex operator are studied. The current picture of the vacuum of quantum chromodynamics, the idea of dual field theories, and the idea of the vortex operator are reviewed first. The Abelian vortex operator written in terms of elementary fields and the calculation of its Green's functions are considered. A two-dimensional solvable model of a Dirac string is presented. The expression of the Green's functions more neatly in terms of Wu and Yang's geometrical idea of sections is addressed. The renormalization of the Green's functions of two kinds of Abelian looplike operators, the Wilson loop and the vortex operator, is studied; for both operators only an overall multiplicative renormalization is needed. In the case of the vortex this involves a surprising cancellation. Next, the dependence of the Green's functions of the Wilson and 't Hooft operators on the nature of the vacuum is discussed. The cluster properties of the Green's functions are emphasized. It is seen that the vortex operator in a massive Abelian theory always has surface-like clustering. The form of Green's functions in terms of Feynman graphs is the same in Higgs and symmetric phases; the difference appears in the sum over all tadpole trees. Finally, systems having fields in the fundamental representation are considered. When these fields enter only weakly into the dynamics, a vortex-like operator is anticipated. Any such operator can no longer be local looplike, but must have commutators at long range. A U(1) lattice gauge theory with two matter fields, one singly charged (fundamental) and one doubly charged (adjoint), is examined. When the fundamental field is weakly coupled, the expected phase transitions are found. When it is strongly coupled, the operator still appears to be a good order parameter, a discontinuous change in its behavior leads to a new phase transition. 18 figures

Trapping saturation of the bump-on-tail instability and electrostatic harmonic excitation in Earth's foreshock

International Nuclear Information System (INIS)

Klimas, A.J.

1990-01-01

Trapping saturation of the bump-on-tail instability is discussed using electron plasma Vlasov simulation results. The role of electrostatic harmonic excitation is considered in detail and shown to play a decisive role in the saturation of the instability. An extensive discussion of the simulation results is given to show that the results are not significantly limited by the finite number of Fourier modes used nor by the discrete distribution of those modes in wave number. It is argued that in the leading edge of Earth's electron foreshock a narrow wave number band of unstable field modes leads to trapping saturation of the bump-on-tail instability while simultaneously exciting electrostatic plasma waves at harmonics of the plasma frequency in simialr narrow bands of shorter wavelengths. The argument is based (1) on the observations of Lacombe et al. (1985), who found intense plasma waves at the leading edge of the foreshock with a spectral distribution sufficiently narrow to trap particles in resonance with the waves, and (2) on numerical simulations of the foreshock electron plasma which indicate that trapping saturation of the bump-on-tail instability leads to phase space vortex formation with consequent excitation of electrostatic harmonics. Thus it is suggested that observations of electrostatic harmonics in the leading edge of the foreshock would strongly implicate trapping as the saturation mechanism for the bump-on-tail instability in that region

Vorticity budget of a tornado-like vortex

Energy Technology Data Exchange (ETDEWEB)

Sassa, Koji; Takemura, Saki, E-mail: sassa@kochi-u.ac.jp [Department of Applied Science, Kochi University (Japan)

2011-12-22

We evaluated the vorticity budget of a tornado-like vortex by measuring vertical and horizontal circulations of it. Though spiral horizontal vortices are clearly observed to converge and tilted into the tornado-like vortex, their circulation is quite small. The conversion of the vertical vorticity concentrated at the side of the spiral horizontal vortices was found to mainly contribute to the maintenance of the tornado-like vortex.

Distributed amplifier using Josephson vortex flow transistors

International Nuclear Information System (INIS)

McGinnis, D.P.; Beyer, J.B.; Nordman, J.E.

1986-01-01

A wide-band traveling wave amplifier using vortex flow transistors is proposed. A vortex flow transistor is a long Josephson junction used as a current controlled voltage source. The dual nature of this device to the field effect transistor is exploited. A circuit model of this device is proposed and a distributed amplifier utilizing 50 vortex flow transistors is predicted to have useful gain to 100 GHz

Nonlinear Binormal Flow of Vortex Filaments

Science.gov (United States)

Strong, Scott; Carr, Lincoln

2015-11-01

With the current advances in vortex imaging of Bose-Einstein condensates occurring at the Universities of Arizona, São Paulo and Cambridge, interest in vortex filament dynamics is experiencing a resurgence. Recent simulations, Salman (2013), depict dissipative mechanisms resulting from vortex ring emissions and Kelvin wave generation associated with vortex self-intersections. As the local induction approximation fails to capture reconnection events, it lacks a similar dissipative mechanism. On the other hand, Strong&Carr (2012) showed that the exact representation of the velocity field induced by a curved segment of vortex contains higher-order corrections expressed in powers of curvature. This nonlinear binormal flow can be transformed, Hasimoto (1972), into a fully nonlinear equation of Schrödinger type. Continued transformation, Madelung (1926), reveals that the filament's square curvature obeys a quasilinear scalar conservation law with source term. This implies a broader range of filament dynamics than is possible with the integrable linear binormal flow. In this talk we show the affect higher-order corrections have on filament dynamics and discuss physical scales for which they may be witnessed in future experiments. Partially supported by NSF.

The Acoustically Driven Vortex Cannon

Science.gov (United States)

Perry, Spencer B.; Gee, Kent L.

2014-01-01

Vortex cannons have been used by physics teachers for years, mostly to teach the continuity principle. In its simplest form, a vortex cannon is an empty coffee can with a hole cut in the bottom and the lid replaced. More elaborate models can be purchased through various scientific suppliers under names such as "Air Cannon" and…

Vortex lattices in layered superconductors

International Nuclear Information System (INIS)

Prokic, V.; Davidovic, D.; Dobrosavljevic-Grujic, L.

1995-01-01

We study vortex lattices in a superconductor--normal-metal superlattice in a parallel magnetic field. Distorted lattices, resulting from the shear deformations along the layers, are found to be unstable. Under field variation, nonequilibrium configurations undergo an infinite sequence of continuous transitions, typical for soft lattices. The equilibrium vortex arrangement is always a lattice of isocell triangles, without shear

Vortex particle method in parallel computations on graphical processing units used in study of the evolution of vortex structures

International Nuclear Information System (INIS)

Kudela, Henryk; Kosior, Andrzej

2014-01-01

Understanding the dynamics and the mutual interaction among various types of vortical motions is a key ingredient in clarifying and controlling fluid motion. In the paper several different cases related to vortex tube interactions are presented. Due to problems with very long computation times on the single processor, the vortex-in-cell (VIC) method is implemented on the multicore architecture of a graphics processing unit (GPU). Numerical results of leapfrogging of two vortex rings for inviscid and viscous fluid are presented as test cases for the new multi-GPU implementation of the VIC method. Influence of the Reynolds number on the reconnection process is shown for two examples: antiparallel vortex tubes and orthogonally offset vortex tubes. Our aim is to show the great potential of the VIC method for solutions of three-dimensional flow problems and that the VIC method is very well suited for parallel computation. (paper)

A Model for the Onset of Vortex Breakdown

Science.gov (United States)

Mahesh, K.

1996-01-01

A large body of information exists on the breakdown of incompressible streamwise vortices. Less is known about vortex breakdown at high speeds. An interesting example of supersonic vortex breakdown is the breakdown induced by the interaction of vortices with shock waves. The flow in supersonic engine inlets and over high-speed delta wings constitute technologically important examples of this phenomenon, which is termed 'shock-induced vortex breakdown'. In this report, we propose a model to predict the onset of shock-induced vortex breakdown. The proposed model has no adjustable constants, and is compared to both experiment and computation. The model is then extended to consider two other problems: the breakdown of a free compressible vortex, and free incompressible vortex breakdown. The same breakdown criterion is used in all three problems to predict the onset of breakdown. Finally, a new breakdown map is proposed that allows the simultaneous comparison of data from flows ranging from incompressible breakdown to breakdown induced by a shock wave.

Examples of Applications of Vortex Methods to Wind Energy

DEFF Research Database (Denmark)

Branlard, Emmanuel Simon Pierre

2017-01-01

The current chapter presents wind-energy simulations obtained with the vortex code OmniVor (described in Chap. 44 ) and compared to BEM, CFD and measurements. The chapter begins by comparing rotor loads obtained with vortex methods, BEM and actuator-line simulations of wind turbines under uniform...... and yawed inflows. The second section compares wakes and flow fields obtained by actuator-disk simulations and a free-wake vortex code that uses vortex segments and vortex particles. The third section compares different implementations of viscous diffusion models and investigate their effects...

Controlling abruptly autofocusing vortex beams to mitigate crosstalk and vortex splitting in free-space optical communication.

Science.gov (United States)

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.

Experimental investigations on effect of different materials and varying depths of one turn exhaust channel swiss roll combustor on its thermal performance

Science.gov (United States)

Mane Deshmukh, Sagar B.; Krishnamoorthy, A.; Bhojwani, V. K.; Pawane, Ashwini

2017-05-01

More energy density of hydrocarbon fuels compared to advanced batteries available in the market demands for development of systems which will use hydrocarbon fuels at small scale to generate power in small quantity (i.e. in few watts) and device efficiency should be reasonably good, but the basic requirement is to generate heat from the fuels like methane, propane, hydrogen, LPG and converting into power. Swiss roll combustor has proved to be best combustor at small scale. Present work is carried out on one turn exhaust channel and half turn of inlet mixture channel Swiss roll combustor. Purpose of keeping exhaust channel length more than the inlet mixture channel to ensure sufficient time for heat exchange between burned and unburned gases, which is not reported in earlier studies. Experimental study mentions effects of different design parameters like materials of combustor, various depths, equivalence ratio, mass flow rates of liquefied petroleum gas (LPG), volume of combustion space and environmental conditions (with insulation and without insulation to combustors) on fuel lean limit and fuel rich limit, temperature profile obtained on all external surfaces, in the main combustion chamber, in the channel carrying unburned gas mixture and burned gas mixture, heat loss to atmosphere from all the walls of combustor, flame location. Different combustor materials tested were stainless steel, Aluminum, copper, brass, bronze, Granite. Depths considered were 22mm, 15mm, 10mm and 5mm. It was observed that flame stability inside the combustion chamber is affected by materials, depths and flow rates. Unburned mixture carrying channel was kept below quenching distance of flame to avoid flash back. Burned gas carrying channel dimension was more than the quenching distance. Considerable temperature rise was observed with insulation to combustors. But combustors with more thermal conductivity showed more heat loss to atmosphere which led to instability of flame.

Vortex Shedding Inside a Baffled Air Duct

Science.gov (United States)

Davis, Philip; Kenny, R. Jeremy

2010-01-01

Common in the operation of both segmented and un-segmented large solid rocket motors is the occurrence of vortex shedding within the motor chamber. A portion of the energy within a shed vortex is converted to acoustic energy, potentially driving the longitudinal acoustic modes of the motor in a quasi-discrete fashion. This vortex shedding-acoustic mode excitation event occurs for every Reusable Solid Rocket Motor (RSRM) operation, giving rise to subsequent axial thrust oscillations. In order to better understand this vortex shedding/acoustic mode excitation phenomena, unsteady CFD simulations were run for both a test geometry and the full scale RSRM geometry. This paper covers the results from the subscale geometry runs, which were based on work focusing on the RSRM hydrodynamics. Unsteady CFD simulation parameters, including boundary conditions and post-processing returns, are reviewed. The results were further post-processed to identify active acoustic modes and vortex shedding characteristics. Probable locations for acoustic energy generation, and subsequent acoustic mode excitation, are discussed.

Phenomena, dynamics and instabilities of vortex pairs

International Nuclear Information System (INIS)

Williamson, C H K; Asselin, D J; Leweke, T; Harris, D M

2014-01-01

Our motivation for studying the dynamics of vortex pairs stems initially from an interest in the trailing wake vortices from aircraft and the dynamics of longitudinal vortices close to a vehicle surface. However, our motivation also comes from the fact that vortex–vortex interactions and vortex–wall interactions are fundamental to many turbulent flows. The intent of the paper is to present an overview of some of our recent work concerning the formation and structure of counter-rotating vortex pairs. We are interested in the long-wave and short-wave three-dimensional instabilities that evolve for an isolated vortex pair, but also we would like to know how vortex pairs interact with a wall, including both two-dimensional interactions, and also the influence of the surface on the three-dimensional instabilities. The emphasis of this presentation is on physical mechanisms by which vortices interact with each other and with surfaces, principally from an experimental approach, but also coupled with analytical studies. (paper)

Stochastic modelling of turbulent combustion for design optimization of gas turbine combustors

Science.gov (United States)

Mehanna Ismail, Mohammed Ali

The present work covers the development and the implementation of an efficient algorithm for the design optimization of gas turbine combustors. The purpose is to explore the possibilities and indicate constructive suggestions for optimization techniques as alternative methods for designing gas turbine combustors. The algorithm is general to the extent that no constraints are imposed on the combustion phenomena or on the combustor configuration. The optimization problem is broken down into two elementary problems: the first is the optimum search algorithm, and the second is the turbulent combustion model used to determine the combustor performance parameters. These performance parameters constitute the objective and physical constraints in the optimization problem formulation. The examination of both turbulent combustion phenomena and the gas turbine design process suggests that the turbulent combustion model represents a crucial part of the optimization algorithm. The basic requirements needed for a turbulent combustion model to be successfully used in a practical optimization algorithm are discussed. In principle, the combustion model should comply with the conflicting requirements of high fidelity, robustness and computational efficiency. To that end, the problem of turbulent combustion is discussed and the current state of the art of turbulent combustion modelling is reviewed. According to this review, turbulent combustion models based on the composition PDF transport equation are found to be good candidates for application in the present context. However, these models are computationally expensive. To overcome this difficulty, two different models based on the composition PDF transport equation were developed: an improved Lagrangian Monte Carlo composition PDF algorithm and the generalized stochastic reactor model. Improvements in the Lagrangian Monte Carlo composition PDF model performance and its computational efficiency were achieved through the

Vortex dynamics in nonrelativistic version of Abelian Higgs model: Effects of the medium on the vortex motion

Directory of Open Access Journals (Sweden)

Kozhevnikov Arkadii

2016-01-01

Full Text Available The closed vortex dynamics is considered in the nonrelativistic version of the Abelian Higgs Model. The effect of the exchange of excitations propagating in the medium on the vortex string motion is taken into account. The obtained are the effective action and the equation of motion both including the exchange of the propagating excitations between the distant segments of the vortex and the possibility of its interaction with the static fermion asymmetric background. They are applied to the derivation of the time dependence of the basic geometrical contour characteristics.

Formation Number Of Laminar Vortex Rings. Numerical Simulations

International Nuclear Information System (INIS)

Rosenfeld, M.; Rambod, E.; Gharib, M.

1998-01-01

The formation time scale of axisymmetric vortex rings is studied numerically for relatively long discharge times. Experimental findings on the existence and universality of a formation time scale, referred to as the formation number, are confirmed. The formation number is indicative of the time a vortex ring acquires its maximal circulation. For vortex rings generated by impulsive motion of a piston, the formation number was found experimentally to be approximately 4. Numerical extension of the experimental study to thick shear layers indicates that the scaled circulation of the pinched-off vortex is relatively insensitive of the details of the formation process, such as the velocity program, velocity profile or vortex generator geometry. In contrast, the formation number does depend on the velocity profile

NASA One-Dimensional Combustor Simulation--User Manual for S1D_ML

Science.gov (United States)

Stueber, Thomas J.; Paxson, Daniel E.

2014-01-01

The work presented in this paper is to promote research leading to a closed-loop control system to actively suppress thermo-acoustic instabilities. To serve as a model for such a closed-loop control system, a one-dimensional combustor simulation composed using MATLAB software tools has been written. This MATLAB based process is similar to a precursor one-dimensional combustor simulation that was formatted as FORTRAN 77 source code. The previous simulation process requires modification to the FORTRAN 77 source code, compiling, and linking when creating a new combustor simulation executable file. The MATLAB based simulation does not require making changes to the source code, recompiling, or linking. Furthermore, the MATLAB based simulation can be run from script files within the MATLAB environment or with a compiled copy of the executable file running in the Command Prompt window without requiring a licensed copy of MATLAB. This report presents a general simulation overview. Details regarding how to setup and initiate a simulation are also presented. Finally, the post-processing section describes the two types of files created while running the simulation and it also includes simulation results for a default simulation included with the source code.

Excitation of high density surface plasmon polariton vortex array

Science.gov (United States)

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.

The mechanism of char ignition in fluidized bed combustors

NARCIS (Netherlands)

Siemons, R.V.

1987-01-01

Knowledge about ignition processes of coal in fluidized beds is of importance for the start-up and dynamic control of these combustors. Initial experiments in a transparent fluidized bed scale model showed the existence of a considerable induction period for the ignition of char, especially at low

Vortex Analysis of Intra-Aneurismal Flow in Cerebral Aneurysms.

Science.gov (United States)

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.

Vortex deformation and reduction of the Lorentz force

International Nuclear Information System (INIS)

Vuorio, M.

1977-01-01

A vortex of an extreme II-type superconductor is considered in the presence of a transport current. The equivalence of Magnus and Lorentz forces in a static vortex is discussed and the effect of vortex deformation is included in calculating corrections to the conventional expression of the Lorentz force. (author)

Fundamental vortices, wall-crossing, and particle-vortex duality

Energy Technology Data Exchange (ETDEWEB)

Hwang, Chiung; Yi, Piljin [School of Physics, Korea Institute for Advanced Study,Seoul 02455 (Korea, Republic of); Yoshida, Yutaka [Research Institute for Mathematical Sciences, Kyoto University,Kyoto 606-8502 (Japan)

2017-05-18

We explore 1d vortex dynamics of 3d supersymmetric Yang-Mills theories, as inferred from factorization of exact partition functions. Under Seiberg-like dualities, the 3d partition function must remain invariant, yet it is not a priori clear what should happen to the vortex dynamics. We observe that the 1d quivers for the vortices remain the same, and the net effect of the 3d duality map manifests as 1d Wall-Crossing phenomenon; although the vortex number can shift along such duality maps, the ranks of the 1d quiver theory are unaffected, leading to a notion of fundamental vortices as basic building blocks for topological sectors. For Aharony-type duality, in particular, where one must supply extra chiral fields to couple with monopole operators on the dual side, 1d wall-crossings of an infinite number of vortex quiver theories are neatly and collectively encoded by 3d determinant of such extra chiral fields. As such, 1d wall-crossing of the vortex theory encodes the particle-vortex duality embedded in the 3d Seiberg-like duality. For N=4, the D-brane picture is used to motivate this 3d/1d connection, while, for N=2, this 3d/1d connection is used to fine-tune otherwise ambiguous vortex dynamics. We also prove some identities of 3d supersymmetric partition functions for the Aharony duality using this vortex wall-crossing interpretation.

Evaluation of Aircraft Wing-Tip Vortex Using PIV

Science.gov (United States)

Alsayed, Omer A.; Asrar, Waqar; Omar, Ashraf A.

2010-06-01

The formation and development of a wing-tip vortex in a near and extended near filed were studied experimentally. Particle image velocimetry was used in a wind tunnel to measure the tip vortex velocity field and hence investigate the flow structure in a wake of aircraft half-wing model. The purpose of this investigation is to evaluate the main features of the lift generated vortices in order to find ways to alleviate hazardous wake vortex encounters for follower airplanes during start and approach such that the increase in airport capacity can be achieved. First the wake structure at successive downstream planes crosswise to the axis of the wake vortices was investigated by measuring parameters such as core radius, maximum tangential velocities, vorticities and circulation distributions. The effect of different angles of attack setting on vortex parameters was examined at one downstream location. In very early stages the vortex sheet evolution makes the tip vortex to move inward and to the suction side of the wing. While the core radius and circulation distributions hardly vary with the downstream distance, noticeable differences for the same vortex parameters at different angles of attack settings were observed. The center of the wing tip vortices scatter in a circle of radius nearly equal to 1% of the mean wing chord and wandering amplitudes shows no direct dependence on the vortex strength but linearly increase with the downstream distance.

Flow aerodynamics modeling of an MHD swirl combustor - calculations and experimental verification

International Nuclear Information System (INIS)

Gupta, A.K.; Beer, J.M.; Louis, J.F.; Busnaina, A.A.; Lilley, D.G.

1981-01-01

This paper describes a computer code for calculating the flow dynamics of constant density flow in the second stage trumpet shaped nozzle section of a two stage MHD swirl combustor for application to a disk generator. The primitive pressure-velocity variable, finite difference computer code has been developed to allow the computation of inert nonreacting turbulent swirling flows in an axisymmetric MHD model swirl combustor. The method and program involve a staggered grid system for axial and radial velocities, and a line relaxation technique for efficient solution of the equations. Tue produces as output the flow field map of the non-dimensional stream function, axial and swirl velocity. 19 refs

Stability of barotropic vortex strip on a rotating sphere.

Science.gov (United States)

Sohn, Sung-Ik; Sakajo, Takashi; Kim, Sun-Chul

2018-02-01

We study the stability of a barotropic vortex strip on a rotating sphere, as a simple model of jet streams. The flow is approximated by a piecewise-continuous vorticity distribution by zonal bands of uniform vorticity. The linear stability analysis shows that the vortex strip becomes stable as the strip widens or the rotation speed increases. When the vorticity constants in the upper and the lower regions of the vortex strip have the same positive value, the inner flow region of the vortex strip becomes the most unstable. However, when the upper and the lower vorticity constants in the polar regions have different signs, a complex pattern of instability is found, depending on the wavenumber of perturbations, and interestingly, a boundary far away from the vortex strip can be unstable. We also compute the nonlinear evolution of the vortex strip on the rotating sphere and compare with the linear stability analysis. When the width of the vortex strip is small, we observe a good agreement in the growth rate of perturbation at an early time, and the eigenvector corresponding to the unstable eigenvalue coincides with the most unstable part of the flow. We demonstrate that a large structure of rolling-up vortex cores appears in the vortex strip after a long-time evolution. Furthermore, the geophysical relevance of the model to jet streams of Jupiter, Saturn and Earth is examined.

Stability of barotropic vortex strip on a rotating sphere

Science.gov (United States)

Sohn, Sung-Ik; Sakajo, Takashi; Kim, Sun-Chul

2018-02-01

We study the stability of a barotropic vortex strip on a rotating sphere, as a simple model of jet streams. The flow is approximated by a piecewise-continuous vorticity distribution by zonal bands of uniform vorticity. The linear stability analysis shows that the vortex strip becomes stable as the strip widens or the rotation speed increases. When the vorticity constants in the upper and the lower regions of the vortex strip have the same positive value, the inner flow region of the vortex strip becomes the most unstable. However, when the upper and the lower vorticity constants in the polar regions have different signs, a complex pattern of instability is found, depending on the wavenumber of perturbations, and interestingly, a boundary far away from the vortex strip can be unstable. We also compute the nonlinear evolution of the vortex strip on the rotating sphere and compare with the linear stability analysis. When the width of the vortex strip is small, we observe a good agreement in the growth rate of perturbation at an early time, and the eigenvector corresponding to the unstable eigenvalue coincides with the most unstable part of the flow. We demonstrate that a large structure of rolling-up vortex cores appears in the vortex strip after a long-time evolution. Furthermore, the geophysical relevance of the model to jet streams of Jupiter, Saturn and Earth is examined.

Vortex dynamics in Josephson junctions arrays

International Nuclear Information System (INIS)

Shalom, Diego Edgar

2005-01-01

In this work we study the dynamics of vortices in two-dimensional overdamped Josephson Junctions Arrays (JJA) driven by dc current in a wide range of conditions varying magnetic field and temperature using experiments, numerical simulations and analytic studies.We develop the Fixed Phase method, a variation of numeric relaxation techniques in which we fix and control the phase of some islands, adjacent to the vortex center, while allowing all other phases in the system to relax.In this way we are able to pull and push the vortex uphill, as we are forcing the center of rotation of the vortex currents to be in a defined location, allowing us to calculate the potential energy of a vortex located in any arbitrary position.We use this method to study the potential energy of a vortex in a variety of situations in homogeneous and non-homogeneous JJA, such as arrays with defects, channel arrays and ratchets.We study the finite size effects in JJA by means of analytic and numerical tools.We implement the rings model, in which we replace the two-dimensional square array by a series of square, concentric, uncoupled rings. This is equivalent to disregarding the radial junctions that couple consecutive rings.In spite of its extreme simplicity, this model holds the main ingredients of the magnetic dependence of the energy.We combine this model with other terms that take into account the dependence in the position of the vortex to obtain a general expression for the potential energy of a vortex in a finite JJA with applied magnetic field.We also present an expression for the first critical field, corresponding to the value of the magnetic field in which the entrance of the first vortex becomes energetically favorable.We build and study JJA modulated to form periodic and asymmetrical potentials for the vortices, named ratchet potentials.The experimental results clearly show the existence of a rectification in the motion of vortices in these potentials.Under certain conditions we

Review of Vortex Methods for Simulation of Vortex Breakdown

National Research Council Canada - National Science Library

Levinski, Oleg

2001-01-01

The aim of this work is to identify current developments in the field of vortex breakdown modelling in order to initiate the development of a numerical model for the simulation of F/A-18 empennage buffet...

Rotation of a single vortex in dusty plasma

International Nuclear Information System (INIS)

Yan Jia; Feng Fan; Liu Fu-Cheng; He Ya-Feng

2017-01-01

A single vortex is obtained in radio-frequency capacitive discharge in argon gas. The dust subsystem is confined in the horizontal plane with an asymmetrical saw structure placed on the lower electrode. The vortex rotates as a whole along the long side of the saw-teeth. Asymmetry of the saw structure plays an important role in the rotation of the vortex. Nonzero curl of the total force resulting from the local ion flow and the electric field in the plasma sheath could be attributed to the persistent rotation of vortex. (paper)

Experimental evaluation of sorbents for sulfur control in a coal-fueled gas turbine slagging combustor

International Nuclear Information System (INIS)

Cowell, L.H.; Wen, C.S.; LeCren, R.T.

1992-01-01

This paper reports on a slagging combustor that has been used to evaluate three calcium-based sorbents for sulfur capture efficiency in order to assess their applicability for use in a oil-fueled gas turbine. Testing is competed in a bench-scale combustor with one-tenth the heat input needed for the full-scale gas turbine. The bench-scale rig is a two-stage combustor featuring a fuel-rich primary zone an a fuel-lean secondary zone. The combustor is operated at 6.5 bars with inlet air preheated to 600 K. Gas temperatures of 1840 K are generated in the primary zone and 1280 K in the secondary zone. Sorbents are either fed into the secondary zone or mixed with the coal-water mixture and fed into the primary zone. Dry powered sorbents are fed into the secondary zone by an auger into one of six secondary air inlet ports. The three sorbents tested in the secondary zone include dolomite, pressure-hydrated dolomitic lime, and hydrated lime. Sorbents have been tested while burning coal-water mixtures with coal sulfur loadings of 0.56 to 3.13 weight percent sulfur. Sorbents are injected into the secondary zone at varying flow rates such that the calcium/sulfur ratio varies from 0.5 to 10.0

Proposed thermodynamic method to determine the vortex mass in layered superconductors

International Nuclear Information System (INIS)

Moler, K.A.; Fetter, A.L.; Kapitulnik, A.

1995-01-01

The authors describe a simple method to study vortex dynamics that can determine or set an upper limit on the vortex mass. The specific heat of the vortex lattice in layered superconductors has a classical limit of 1 k B per pancake vortex if the vortex mass is zero. If the vortex mass m v is finite, a new Einstein branch of normal modes will appear with a crossover temperature Θ E ∝ m v -1 , and the specific heat will saturate at a new classical limit of 2 k B per pancake vortex

Ultra low injection angle fuel holes in a combustor fuel nozzle

Science.gov (United States)

York, William David

2012-10-23

A fuel nozzle for a combustor includes a mixing passage through which fluid is directed toward a combustion area and a plurality of swirler vanes disposed in the mixing passage. Each swirler vane of the plurality of swirler vanes includes at least one fuel hole through which fuel enters the mixing passage in an injection direction substantially parallel to an outer surface of the plurality of swirler vanes thereby decreasing a flameholding tendency of the fuel nozzle. A method of operating a fuel nozzle for a combustor includes flowing a fluid through a mixing passage past a plurality of swirler vanes and injecting a fuel into the mixing passage in an injection direction substantially parallel to an outer surface of the plurality of swirler vanes.

Transverse force on a moving vortex with the acoustic geometry

International Nuclear Information System (INIS)

Zhang Pengming; Cao Liming; Duan Yishi; Zhong Chengkui

2004-01-01

We consider the transverse force on a moving vortex with the acoustic metric using the phi-mapping topological current theory. In the frame of effective space-time geometry the vortex appear naturally by virtue of the vortex tensor in the Lorentz space-time and we show that it is just the vortex derived with the order parameter in the condensed matter. With the usual Lagrangian we obtain the equation of motion for the vortex. At last, we show that the transverse force on the moving vortex in our equation is just the usual Magnus force in a simple model

RANS computations of tip vortex cavitation

Science.gov (United States)

Decaix, Jean; Balarac, Guillaume; Dreyer, Matthieu; Farhat, Mohamed; Münch, Cécile

2015-12-01

The present study is related to the development of the tip vortex cavitation in Kaplan turbines. The investigation is carried out on a simplified test case consisting of a NACA0009 blade with a gap between the blade tip and the side wall. Computations with and without cavitation are performed using a R ANS modelling and a transport equation for the liquid volume fraction. Compared with experimental data, the R ANS computations turn out to be able to capture accurately the development of the tip vortex. The simulations have also highlighted the influence of cavitation on the tip vortex trajectory.

Vortex breakdown in a supersonic jet

Science.gov (United States)

Cutler, Andrew D.; Levey, Brian S.

1991-01-01

This paper reports a study of a vortex breakdown in a supersonic jet. A supersonic vortical jets were created by tangential injection and acceleration through a convergent-divergent nozzle. Vortex circulation was varied, and the nature of the flow in vortical jets was investigated using several types of flow visualization, including focusing schlieren and imaging of Rayleigh scattering from a laser light sheet. Results show that the vortical jet mixed much more rapidly with the ambient air than a comparable straight jet. When overexpanded, the vortical jet exhibited considerable unsteadiness and showed signs of vortex breakdown.

Experimental and Modeling Investigation of the Effect of Air Preheat on the Formation of NOx in an RQL Combustor

Science.gov (United States)

Samuelsen, G. S.; Brouwer, J.; Vardakas, M. A.; Holderman, J. D.

2012-01-01

The Rich-burn/Quick-mix/Lean-burn (RQL) combustor concept has been proposed to minimize the formation of oxides of nitrogen (NOx) in gas turbine systems. The success of this low-NOx combustor strategy is dependent upon the links between the formation of NOx, inlet air preheat temperature, and the mixing of the jet air and fuel-rich streams. Chemical equilibrium and kinetics modeling calculations and experiments were performed to further understand NOx emissions in an RQL combustor. The results indicate that as the temperature at the inlet to the mixing zone increases (due to preheating and/or operating conditions) the fuel-rich zone equivalence ratio must be increased to achieve minimum NOx formation in the primary zone of the combustor. The chemical kinetics model illustrates that there is sufficient residence time to produce NOx at concentrations that agree well with the NOx measurements. Air preheat was found to have very little effect on mixing, but preheating the air did increase NOx emissions significantly. By understanding the mechanisms governing NOx formation and the temperature dependence of key reactions in the RQL combustor, a strategy can be devised to further reduce NOx emissions using the RQL concept.

Aerosol Effects on Microphysical Processes, Storm Structure, and Cold Pool Strength in Simulated Supercell Thunderstorms from VORTEX-2 and VORTEX-SE

Science.gov (United States)

Guo, M.; Dawson, D. T., II; Baldwin, M. E.; Mansell, E. R.

2017-12-01

The cloud condensation nuclei (CCN) concentration has been found to strongly affect microphysical, dynamical and thermodynamical processes in supercells and other deep convective storms. Moreover, recent simulation studies have shown aerosols effects differ between higher- and lower-CAPE environments. Owing to the known sensitivity of severe storms to microphysical differences, studying the impact of aerosols supercell storms different environments is of clear societal importance. Tornadic environments in the southwastern U.S. are generally characterized by lower magnitudes CAPE and deeper tropospheric moisture than those in the Great Plains. These two regions were the focus of Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX)-2 and VORTEX-Southeast (SE) field campaigns, respectively. In our study, we simulate several cases from VORTEX-2 and -SE with the Advanced Regional Prediction System (ARPS) Model at 6 different CCN concentrations (100-3000 cm-3). We use NSSL 3-moment microphysics parameterization schemeto explicitly predict precipitation particle size distributions and microphysirocess rates. Overall, storms under the higher-CAPE VORTEX-2 environments are more sensitiveto the change of CCN than those under the lower-CAPE VORTEX-SE environments. Updraft volume decreases as CCN increases for the VORTEX-2 cases, whereas the opposite is true but with a much weaker trend for the VORTEX-SE cases. Moreover, the cold pool strength drops dramatically as CCN surpasses 1000 cm-3n the VORTEX-2 cases but barely changes for the VORTEX-SE cases. Through a microphysics budget analysis, we show the change of the importance of ice processes is key to the differing sensitivities. in the VORTEX-2 cases, deposition to ice nuclei, cloud drop freezing and rain drop freezing in the upper levels (5-11km) contribute more to latent heating since more rain and cloud drops are lifted above the freezing level due to stronger updrafts. For CCN concentration over 1000

MERCURY CONTROL IN MUNICIPAL WASTE COMBUSTORS AND COAL-FIRED UTILITIES

Science.gov (United States)

Control of mercury (Hg) emissions from municipal waste combustors (MWCs) and coal-fired utilities has attracted attention due to current and potential regulations. Among several techniques evaluated for Hg control, dry sorbent injection (primarily injection of activated carbon) h...

Drift wave coherent vortex structures in inhomogeneous plasmas

International Nuclear Information System (INIS)

Su, X.N.

1992-01-01

Nonlinear drift wave vortex structures in magnetized plasmas are studied theoretically and numerically in the various physical environments. The effects of density and temperature gradients on drift wave vortex dynamics are analyzed using a fully nonlinear model with the Boltzmann density distribution. The equation, based on the full Boltzmann relation, possess no localized monopole solution in the short wavelength (∼ρ s ) region, while in the longer wavelength (∼(ρ s (r) n ) 1/2 ) region the density profile governs the existence of monopole-like solutions. In the longer wavelength regime, however, the monopoles cannot be localized sufficiently to avoid coupling to propagating drift waves due to the inhomogeneity of the plasma. Thus, the monopole vortex is a long lived coherent structure, but it is not precisely a stationary structure since the coupling results in a open-quote flapping close-quote tail. The tail causes energy of the vortex to leak out, but the effect of the temperature gradient is to reduce the leaking of this energy. Nonlinear coherent structures governing by the coupled drift wave-ion acoustic mode equations in sheared magnetic field are studied analytically and numerically. A solitary vortex equation that includes the effects of density and temperature gradients and magnetic shear is derived and analyzed. The results show that for a plasma in a sheared magnetic field, there exist the solitary vortex solutions. The new vortex structures are dipole-like in their symmetry, but not the modon type of dipoles. The numerical simulations are performed in 2-D with the coupled vorticity and parallel mass flow equations. The vortex structures in an unstable drift wave system driven by parallel shear flow are studied. The nonlinear solitary vortex solutions are given and the formation of the vortices from a turbulent state is observed from the numerical simulations

Evaluation of Turner relaxed state as a model of long-lived ion-trapping structures in plasma focus and Z-pinches

Science.gov (United States)

Auluck, S. K. H.

2011-03-01

Relatively long-lived spheroidal structures coincident with the neutron emission phase have been observed in frozen deuterium fiber Z-pinch and some plasma focus devices. Existence of energetic ion-trapping mechanism in plasma focus has also been inferred from experimental data. It has been conjectured that these are related phenomena. This paper applies Turner's theory [L. Turner, IEEE Trans. Plasma Sci. 14, 849 (1986)] of relaxation of a Hall magnetofluid to construct a model of these structures and ion-trapping mechanism. Turner's solution modified for a finite-length plasma is used to obtain expressions for the magnetic field, velocity, and equilibrium pressure fields and is shown to represent an entity which is simultaneously a fluid vortex, a force-free magnetic field, a confined finite-pressure plasma, a charged object, and a trapped energetic ion beam. Characteristic features expected from diagnostic experiments are evaluated and shown to resemble experimental observations.

Theory of pairing symmetry in the vortex states

NARCIS (Netherlands)

Yokoyama, Takehito; Ichioka, Yukio; Yanaka, Yukio; Golubov, Alexandre Avraamovitch

2010-01-01

We investigate pairing symmetry in an Abrikosov vortex and vortex lattice. It is shown that the Cooper pair wave function at the center of an Abrikosov vortex with vorticity m has a different parity with respect to frequency from that in the bulk if m is an odd number, while it has the same parity

The Vortex and the Line: Performative Gestures in Allen Ginsberg's ‘Wichita Vortex Sutra’

DEFF Research Database (Denmark)

Sørensen, Bent

and their identity politics… Queering the straight lines of Modernism, Allen Ginsberg suggests in his long poem about America and the Vietnam War, ‘Wichita Vortex Sutra’, that lying media discourses and corrupt political and military statements about the necessity of participation in the war may be cancelled out...... by a poet performing the simple, yet impossible speech act of declaring the end of the war, and in doing so queering the original declaratory speech act of the executive power. The poet must enter intrepidly the vortex of lies told by the voices disseminated by the media on behalf of politicians, authority...... to provide the reader of the Sutra with the possibility of Enlightenment. While the poet may be forced to travel along straight lines to penetrate the vortex, he should at any given opportunity queer these lines as much as possible....

Direct visualization of the vortex distributions in a superconducting film with a Penrose array of magnetic pinning centers: Symmetry induced giant vortex state

International Nuclear Information System (INIS)

Kramer, R.B.G.; Silhanek, A.V.; Van de Vondel, J.; Raes, B.; Moshchalkov, V.V.

2010-01-01

Using scanning Hall probe microscopy a direct visualization of the flux distribution in a Pb film covering a fivefold Penrose array of Co dots is obtained. We demonstrate that stable vortex configurations can be found for fields H ∼ 0.8H 1 , H 1 and 1.6H 1 , where H 1 corresponds to one flux quantum per pinning site. The vortex pattern at 0.8H 1 corresponds to one vacancy in one of the vertices of the thin tiles whereas at 1.6H 1 the vortex structure can be associated with one interstitial vortex inside each thick tile. Strikingly, for H = 1.6H 1 interstitial and pinned vortices arrange themselves in ring-like structures ('vortex corrals') which favor the formation of a giant vortex state at their center.

Superconducting coherence in a vortex line liquid

International Nuclear Information System (INIS)

Chen, T.; Teitel, S.

1995-01-01

We carry out simulations of the anisotropic uniformly frustrated 3d XY model, as a model for vortex line fluctuations in high T c superconductors. We compute the phase diagram as a function of temperature and anisotropy, for a fixed applied magnetic field B. We find two distinct phase transitions. Upon heating, there is first a lower T c perpendicular where the vortex line lattice melts and super-conducting coherence perpendicular to the applied magnetic field vanishes. At a higher T cz , within the vortex line liquid, superconducting coherence parallel to the applied magnetic field vanishes. For finite anisotropy, both T c perpendicular and T cz lie well below the crossover from the vortex line liquid to the normal state

Formation of Ion Phase-Space Vortexes

DEFF Research Database (Denmark)

Pécseli, Hans; Trulsen, J.; Armstrong, R. J.

1984-01-01

The formation of ion phase space vortexes in the ion two stream region behind electrostatic ion acoustic shocks are observed in a laboratory experiment. A detailed analysis demonstrates that the evolution of such vortexes is associated with ion-ion beam instabilities and a nonlinear equation for ...

Longitudinal vortex control - Techniques and applications (The 32nd Lanchester Lecture)

Science.gov (United States)

Bushnell, D. M.

1992-01-01

A summary is presented of vortex control applications and current techniques for the control of longitudinal vortices produced by bodies, leading edges, tips and intersections. Vortex control has up till now been performed by many approaches in an empirical fashion, assisted by the essentially inviscid nature of much of longitudinal vortex behavior. Attention is given to Reynolds number sensitivities, vortex breakdown and interactions, vortex control on highly swept wings, and vortex control in juncture flows.

Vortex flow in acoustically levitated drops

Energy Technology Data Exchange (ETDEWEB)

Yan, Z.L.; Xie, W.J. [Department of Applied Physics, Northwestern Polytechnical University, Xi' an 710072 (China); Wei, B., E-mail: bbwei@nwpu.edu.cn [Department of Applied Physics, Northwestern Polytechnical University, Xi' an 710072 (China)

2011-08-29

The internal flow of acoustically levitated water drops is investigated experimentally. This study reveals a kind of vortex flow which rotates in the meridional plane of the levitated drop. The magnitude of fluid velocity is nearly vanishing at the drop center, whereas it increases toward the free surface of a levitated drop until the maximum value of about 80 mm/s. A transition of streamline shapes from concentric circles to ellipses takes place at the distance of about 1.2 mm from the drop center. The fluid velocity distribution is plotted as a function of polar angle for seven characteristic streamlines. -- Highlights: → We experimentally observe the internal flow of acoustically levitated water drops. → We present a fascinating structure of vortex flow inside the levitated water drop. → This vortex flow rotates around the drop center in the meridional plane. → Velocity distribution information of this vortex flow is quantitatively analyzed.

Vortex flow in acoustically levitated drops

International Nuclear Information System (INIS)

Yan, Z.L.; Xie, W.J.; Wei, B.

2011-01-01

The internal flow of acoustically levitated water drops is investigated experimentally. This study reveals a kind of vortex flow which rotates in the meridional plane of the levitated drop. The magnitude of fluid velocity is nearly vanishing at the drop center, whereas it increases toward the free surface of a levitated drop until the maximum value of about 80 mm/s. A transition of streamline shapes from concentric circles to ellipses takes place at the distance of about 1.2 mm from the drop center. The fluid velocity distribution is plotted as a function of polar angle for seven characteristic streamlines. -- Highlights: → We experimentally observe the internal flow of acoustically levitated water drops. → We present a fascinating structure of vortex flow inside the levitated water drop. → This vortex flow rotates around the drop center in the meridional plane. → Velocity distribution information of this vortex flow is quantitatively analyzed.

The observation of a triangular vortex in a rotating fluid

NARCIS (Netherlands)

Beckers, M.; Heijst, van G.J.F.

1998-01-01

A dye visualization study of a triangular vortex in a rotating fluid is presented. The emergence and subsequent break-up of the vortex structure are described. Soon after the generation of the triangular vortex it becomes unstable: two satellite vortices merge and pair with the core vortex into an

Vortex phase diagram and vortex dynamics at low temperature in a thick a-Mg{sub x}B{sub 1-x} film

Energy Technology Data Exchange (ETDEWEB)

Okuma, S. [Research Center for Low Temperature Physics, Tokyo Institute of Technology, 2-12-1, Ohokayama, Meguro-ku, Tokyo 152-8551 (Japan)], E-mail: sokuma@o.cc.titech.ac.jp; Kohara, M. [Research Center for Low Temperature Physics, Tokyo Institute of Technology, 2-12-1, Ohokayama, Meguro-ku, Tokyo 152-8551 (Japan)

2007-09-01

We report on the equilibrium vortex phase diagram and vortex dynamics at low temperature T in a thick amorphous (a-)Mg{sub x}B{sub 1-x} film based on the measurements of the dc resistivity {rho} and time (t)-dependent component of the flux-flow voltage, {delta}V(t), respectively. Both {rho}(T) in perpendicular fields and the vortex phase diagram are qualitatively similar to those for the a-Mo{sub x}Si{sub 1-x} films, in which evidence for the quantum-vortex-liquid (QVL) phase has been obtained. In either material system we observe anomalous vortex flow with the asymmetric distribution of {delta}V(t) in the QVL phase, suggesting that the anomalous flow is a universal phenomenon commonly observed for disordered amorphous films, independent of material.

Inclined Jet in Crossflow Interacting with a Vortex Generator

Science.gov (United States)

Zaman, K. B. M. Q.; Rigby, D .L.; Heidmann, J. D.

2011-01-01

An experiment is conducted on the effectiveness of a vortex generator in preventing liftoff of a jet in crossflow, with possible relevance to film-cooling applications. The jet issues into the boundary layer at an angle of 20 degreees to the freestream. The effect of a triangular ramp-shaped vortex generator is studied while varying its geometry and location. Detailed flowfield properties are obtained for a case in which the height of the vortex generator and the diameter of the orifice are comparable with the approach boundary-layer thickness. The vortex generator produces a streamwise vortex pair with a vorticity magnitude 3 times larger (and of opposite sense) than that found in the jet in crossflow alone. Such a vortex generator appears to be most effective in keeping the jet attached to the wall. The effect of parametric variation is studied mostly from surveys 10 diameters downstream from the orifice. Results over a range of jet-to-freestream momentum flux ratio (1 vortex generator has a significant effect even at the highest J covered in the experiment. When the vortex generator height is halved, there is a liftoff of the jet. On the other hand, when the height is doubled, the jet core is dissipated due to larger turbulence intensity. Varying the location of the vortex generator, over a distance of three diameters from the orifice, is found to have little impact. Rounding off the edges of the vortex generator with the increasing radius of curvature progressively diminishes its effect. However, allowing for a small radius of curvature may be quite tolerable in practice.

Helicity conservation under quantum reconnection of vortex rings.

Science.gov (United States)

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.

Three-wave electron vortex lattices for measuring nanofields.

Science.gov (United States)

Dwyer, C; Boothroyd, C B; Chang, S L Y; Dunin-Borkowski, R E

2015-01-01

It is demonstrated how an electron-optical arrangement consisting of two electron biprisms can be used to generate three-wave vortex lattices with effective lattice spacings between 0.1 and 1 nm. The presence of vortices in these lattices was verified by using a third biprism to perform direct phase measurements via off-axis electron holography. The use of three-wave lattices for nanoscale electromagnetic field measurements via vortex interferometry is discussed, including the accuracy of vortex position measurements and the interpretation of three-wave vortex lattices in the presence of partial spatial coherence. Copyright © 2014 Elsevier B.V. All rights reserved.

The development of an ultra-low-emission gas-fired cyclonic combustor

International Nuclear Information System (INIS)

Xiong, Tian-yu; Khinkis, M.J.; Coppin, W.P.

1991-01-01

A gas-fired cyclonic combustor has been developed for relatively low-temperature direct-air heating applications that require ultra-low pollutant emissions. High-lean premixed combustion with a flame stabilizer is adopted to achieve ultra-low emissions and high turndown operation. On the basis of analytical studies and cold modeling, a 350-kW test combustor was designed and successfully tested. Experimental results obtained using natural gas and ambient air demonstrated that the test combustor can operate steadily at high excess air up to 80% to 100% over a large turndown range up to 40:1. At design operating conditions, NO x emissions as low as 0.6 vppm and CO and total hydrocarbon (THC) emissions below 3 vppm were achieved. Over the full operating range, NO x emissions from 0.3 to 1.0 vppm and CO and THC emissions below 4 vppm were demonstrated. In all tests, concentrations of NO 2 were less than 40% of the total NO x emissions -- lower than the level of NO 2 emissions from combustion processes required for good indoor air quality (0.5 vppm). This paper presents the concept of high-lean premixed ultra-low-emission cyclonic combustion, design specifications for the combustion system, and the major experimental results, including flame stability, emissions, and turndown performance. 13 refs., 12 figs., 1 tab

Vortex operators in gauge field theories

International Nuclear Information System (INIS)

Polchinski, J.G.

1980-01-01

We study several related aspects of the t Hooft vortex operator. The first chapter reviews the current picture of the vacuum of quantum chromodynamics, the idea of dual field theories, and the idea of the vortex operator. The second chapter deals with the Abelian vortex operator written in terms of elementary fields and with the calculation of its Green's functions. The Dirac veto problem appears in a new guise. We present a two dimensional solvable model of a Dirac string. This leads us to a new solution of the veto problem; we discuss its extension to four dimensions. We then show how the Green's functions can be expressed more neatly in terms of Wu and Yang's geometrical idea of sections. In the third chapter we discuss the dependence of the Green's functions of the Wilson and t Hooft operators on the nature of the vacuum. In the fourth chapter we consider systems which have fields in the fundamental representation, so that there are no vortex operators. When these fields enter only weakly into the dynamics, as is the case in QCD and in real superconductors, we would expect to be able to define a vortex-like operator. We show that any such operator can no longer be local looplike, but must have commutators at long range. We can still find an operator with useful properties, its cluster property, though more complicated than that of the usual vortex operator, still appears to distinguish Higgs, confining and perturbative phases. To test this, we consider a U(1) lattice gauge theory with two matter fields, one singly charged (fundamental) and one doubly charged (adjoint)

Formation of vortex breakdown in conical–cylindrical cavities

International Nuclear Information System (INIS)

Martins, Diego Alves de Moro; Souza, Francisco José de; Salvo, Ricardo de Vasconcelos

2014-01-01

Highlights: • Rotating flows in conical–cylindrical cavities were simulated via an in-house code using unstructured meshes. • The vortex breakdown phenomenon was verified in the geometries analyzed. • The influence of Stewartson and Bödewadt layers was observed in the vortex breakdown formation. • A curve of stability and number of breakdowns was obtained as a function of Reynolds number. • Spiral vortex breakdown was observed in some situations. - Abstract: Numerical simulations in confined rotating flows were performed in this work, in order to verify and characterize the formation of the vortex breakdown phenomenon. Cylindrical and conical–cylindrical geometries, both closed, were used in the simulations. The rotating flow is induced by the bottom wall, which rotates at constant angular velocity. Firstly the numerical results were compared to experimental results available in references, with the purpose to verify the capacity of the computational code to predict the vortex breakdown phenomenon. Further, several simulations varying the parameters which govern the characteristics of the flows analyzed in this work, i.e., the Reynolds number and the aspect ratio, were performed. In these simulations, the limits for the transitional regime and the vortex breakdown formation were verified. Steady and transient cases, with and without turbulence modeling, were simulated. In general, some aspects of the process of vortex breakdown in conical–cylindrical geometries were observed to be different from that in cylinders

A new look at sound generation by blade/vortex interaction

Science.gov (United States)

Hardin, J. C.; Mason, J. P.

1985-01-01

As a preliminary attempt to understand the dynamics of blade/vortex interaction, the two-dimensional problem of a rectilinear vortex filament interacting with a Joukowski airfoil is analyzed in both the lifting and nonlifting cases. The vortex velocity components could be obtained analytically and integrated to determine the vortex trajectory. With this information, the aeroacoustic low-frequency Green's function approach could then be employed to calculate the sound produced during the encounter. The results indicate that the vortex path deviates considerably from simple convection due to the presence of the airfoil and that a reasonably sharp sound pulse is radiated during the interaction whose fundamental frequency is critically dependent upon whether the vortex passes above or below the airfoil. Determination of this gross parameter of the interaction is shown to be highly nonlinearly dependent upon airfoil circulation, vortex circulation, and initial position.

Emission performance and combustion efficiency of a conical fluidized-bed combustor firing various biomass fuels

International Nuclear Information System (INIS)

Permchart, W.; Kouprianov, V.I.

2004-01-01

This paper summarizes the results of an experimental study on combustion of three distinct biomass fuels (sawdust, rice husk and pre-dried sugar cane bagasse) in a single fluidized-bed combustor (FBC) with a conical bed using silica sand as the inert bed material. Temperature, CO, NO and O 2 concentrations along the combustor height as well as in flue (stack) gas were measured in the experimental tests. The effects of fuel properties and operating conditions (load and excess air) on these variables were investigated. Both CO and NO axial profiles were found to have a maximum whose location divides conventionally the combustor volume into formation (lower) and reduction (upper) regions for these pollutants. Based on CO emission and unburned carbon content in fly ash, the combustion efficiency of the conical FBC was quantified for the selected biomass fuels fired under different operating conditions. (Author)

Vortex dynamics in ferromagnetic/superconducting bilayers

Energy Technology Data Exchange (ETDEWEB)

Cieplak, M.Z.; Adamus, Z. [Polish Acad Sci, Inst Phys, PL-02668 Warsaw, (Poland); Konczykowski, M. [CEA, DSM, DRECAM, Lab Solides Irradies, Ecole Polytechnique, CNRS-UMR 7642, F-91128 Palaiseau (France); Zhu, L.Y.; Chien, C.L. [Johns Hopkins Univ, Dept Phys and Astron, Baltimore, MD 21218 (United States)

2008-07-01

The dependence of vortex dynamics on the geometry of magnetic domain pattern is studied in the superconducting/ferromagnetic bilayers, in which niobium is a superconductor, and Co/Pt multilayer with perpendicular magnetic anisotropy serves as a ferromagnetic layer. Magnetic domain patterns with different density of domains per surface area and different domain size, w, are obtained for Co/Pt with different thickness of Pt. The dense patterns of domains with the size comparable to the magnetic penetration depth (w {>=} {lambda}) produce large vortex pinning and smooth vortex penetration, while less dense patterns with larger domains (w {>=}{>=} {lambda}) enhance pinning less effectively and result in flux jumps during flux motion. (authors)

Chaotic diffusion in steady wavy vortex flow-Dependence on wave state and correlation with Eulerian symmetry measures

Energy Technology Data Exchange (ETDEWEB)

King, G P [Instituto de Oceanografia, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa (Portugal); Rudman, Murray [CSIRO Manufacturing and Infrastructure Technology, P.O. Box 56, Highett, Vic. 3190 (Australia); Rowlands, G [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)], E-mail: gkinglisboa@gmail.com, E-mail: Murray.Rudman@csiro.au, E-mail: G.Rowlands@warwick.ac.uk

2008-01-31

The dimensionless effective axial diffusion coefficient, D{sub z}, calculated from particle trajectories in steady wavy vortex flow in a narrow gap Taylor-Couette system, has been determined as a function of Reynolds number (R = Re/Re{sub c}), axial wavelength ({lambda}{sub z}), and the number of azimuthal waves (m). Two regimes of Reynolds number were found: (i) when R < 3.5, D{sub z} has a complex and sometimes multi-modal dependence on Reynolds number; (ii) when R > 3.5, D{sub z} decreases monotonically. Eulerian quantities measuring the departure from rotational symmetry, {psi}{sub {theta}}, and flexion-free flow, {psi}{sub {nu}}, were calculated. The space-averaged quantities {phi}-bar{sub {theta}} and {phi}-bar{sub {nu}} were found to have, unlike D{sub z}, a simple unimodal dependence on R. In the low R regime the correlation between D{sub z} and {psi}{sub {theta}}{psi}{sub {nu}} was complicated and was attributed to variations in the spatial distribution of the wavy disturbance occurring in this range of R. In the large R regime, however, the correlation simplified to D{sub z}{approx}{phi}-bar{sub {theta}}{phi}-bar{sub {nu}} for all wave states, and this was attributed to the growth of an integrable vortex core and the concentration of the wavy disturbance into narrow regions near the outflow and inflow jets. A reservoir model of a wavy vortex was used to determine the rate of escape across the outflow and inflow boundaries, the size of the 'escape basins' (associated with escape across the outflow and inflow boundaries), and the size of the trapping region in the vortex core. In the low R regime after the breakup of all KAM tori, the outflow basin ({gamma}{sub O}) is larger than the inflow basin ({gamma}{sub I}), and both {gamma}{sub O} and {gamma}{sub I} are (approximately) independent of R. In the large R regime, with increasing Reynolds number the trapping region grows, the outflow basin decreases, and the inflow basin shows a slight increase

Combustor nozzles in gas turbine engines

Science.gov (United States)

Johnson, Thomas Edward; Keener, Christopher Paul; Stewart, Jason Thurman; Ostebee, Heath Michael

2017-09-12

A micro-mixer nozzle for use in a combustor of a combustion turbine engine, the micro-mixer nozzle including: a fuel plenum defined by a shroud wall connecting a periphery of a forward tube sheet to a periphery of an aft tubesheet; a plurality of mixing tubes extending across the fuel plenum for mixing a supply of compressed air and fuel, each of the mixing tubes forming a passageway between an inlet formed through the forward tubesheet and an outlet formed through the aft tubesheet; and a wall mixing tube formed in the shroud wall.

Vortex matter in the presence of an array of pinning centers of variable strength

International Nuclear Information System (INIS)

Nunes, J.S.; Zadorosny, R.; Oliveira, A.A.M.; Lepienski, C.M.; Patino, E.J.; Blamire, M.G.; Ortiz, W.A.

2008-01-01

This contribution reports on the magnetic response of a 200 nm thick Nb film, pierced with a set of 900 columnar indentations of nearly triangular cross section, forming a square lattice. The column effective diameter is 1 μm and the array lattice parameter is 10 μm. To probe the interaction of vortex matter with the array of antidots, we have excited the sample with an AC-field, so that flux trapped by the columns could be unpinned and admitted into the superconducting sea surrounding the defects. An order-disorder line was determined for this system, with a kink separating two regimes, suggesting a crossover from the efficient pinning regime, at lower temperatures, to a temperature-induced depinning. To exploit the influence of pinning efficiency on vortex dynamics, we have determined the order-disorder line at different angles between the applied field and the plane of the film. A plot of the field component perpendicular to the film versus temperature, gives a collapsed response near T c , which splits for lower temperatures, as a consequence of pinning weakening due to the component of the applied AC-field perpendicular to the columns. Consistently, the kink tends to progressively disappear as the pinning strength decreases

Vortex matter in the presence of an array of pinning centers of variable strength

Energy Technology Data Exchange (ETDEWEB)

Nunes, J.S.; Zadorosny, R.; Oliveira, A.A.M. [Grupo de Supercondutividade e Magnetismo, Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos, SP (Brazil); Lepienski, C.M. [Departamento de Fisica, Universidade Federal do Parana, Curitiba, PR (Brazil); Patino, E.J.; Blamire, M.G. [Department of Materials Science, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); Ortiz, W.A. [Grupo de Supercondutividade e Magnetismo, Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos, SP (Brazil)], E-mail: wortiz@df.ufscar.br

2008-04-01

This contribution reports on the magnetic response of a 200 nm thick Nb film, pierced with a set of 900 columnar indentations of nearly triangular cross section, forming a square lattice. The column effective diameter is 1 {mu}m and the array lattice parameter is 10 {mu}m. To probe the interaction of vortex matter with the array of antidots, we have excited the sample with an AC-field, so that flux trapped by the columns could be unpinned and admitted into the superconducting sea surrounding the defects. An order-disorder line was determined for this system, with a kink separating two regimes, suggesting a crossover from the efficient pinning regime, at lower temperatures, to a temperature-induced depinning. To exploit the influence of pinning efficiency on vortex dynamics, we have determined the order-disorder line at different angles between the applied field and the plane of the film. A plot of the field component perpendicular to the film versus temperature, gives a collapsed response near T{sub c}, which splits for lower temperatures, as a consequence of pinning weakening due to the component of the applied AC-field perpendicular to the columns. Consistently, the kink tends to progressively disappear as the pinning strength decreases.