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Sample records for jet optimised shear

  1. Motional Stark Effect Measurements of q-Profiles in JET Optimised Shear Plasmas

    NASA Astrophysics Data System (ADS)

    Stratton, B. C.; Hawkes, N. C.; Challis, C. D.; Drozdov, V.; Lomas, P.; Joffrin, E.; Litaudon, X.; Lotte, P.; Mazon, D.; Deangelis, R.; Rachlew, E.; Reyes-Cortes, S.

    2000-10-01

    A Motional Stark Effect (MSE) diagnostic is used to measure the magnetic field pitch angle in JET discharges. The q-profile is deduced from EFIT magnetic equilibrium reconstructions constrained by MSE data. Measurements have concentrated primarily on the Optimised Shear (OS) regime in which the details of the q-profile play an important role in the formation of internal transport barriers, leading to improved confinement. q-profiles in the target and high-power phases of OS plasmas with various heating scenarios (NBI + ICRF, NBI only, and NBI + LHCD) and pre-heat timings are presented and are correlated with ITB formation in the high-power phase.

  2. Jet momentum balance independent of shear viscosity

    NASA Astrophysics Data System (ADS)

    Neufeld, R. B.

    2012-03-01

    Jet momentum balance measurements, such as those recently performed by the CMS collaboration, provide an opportunity to quantify the energy transferred from a parton shower to the underlying medium in heavy-ion collisions. Specifically, I argue that the Cooper-Frye freeze-out distribution associated with the energy and momentum deposited by the parton shower is controlled to a significant extent by the distribution of the underlying bulk matter and independent of the details of how deposited energy is redistributed in the medium, which is largely determined by transport coefficients such as shear viscosity. Thus, by matching the distribution of momentum associated with the secondary jet in such measurements to the thermal distribution of the underlying medium, one can obtain a model-independent estimate on the amount of parton shower energy deposited.

  3. Shear layer characteristics of supersonic free and impinging jets

    NASA Astrophysics Data System (ADS)

    Davis, T. B.; Kumar, R.

    2015-09-01

    The initial shear layer characteristics of a jet play an important role in the initiation and development of instabilities and hence radiated noise. Particle image velocimetry has been utilized to study the initial shear layer development of supersonic free and impinging jets. Microjet control employed to reduce flow unsteadiness and jet noise appears to affect the development of the shear layer, particularly near the nozzle exit. Velocity field measurements near the nozzle exit show that the initially thin, uncontrolled shear layer develops at a constant rate while microjet control is characterized by a rapid nonlinear thickening that asymptotes downstream. The shear layer linear growth rate with microjet control, in both the free and the impinging jet, is diminished. In addition, the thickened shear layer with control leads to a reduction in azimuthal vorticity for both free and impinging jets. Linear stability theory is used to compute unstable growth rates and convection velocities of the resultant velocity profiles. The results show that while the convection velocity is largely unaffected, the unstable growth rates are significantly reduced over all frequencies with microjet injection. For the case of the impinging jet, microjet control leads to near elimination of the impingement tones and an appreciable reduction in broadband levels. Similarly, for the free jet, significant reduction in overall sound pressure levels in the peak radiation direction is observed.

  4. Mixing in Shear Coaxial Jets with and without Acoustics

    DTIC Science & Technology

    2012-03-29

    Briefing Charts 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Mixing in Shear Coaxial Jets with and without...Modern rockets operate at supercritical pressures with respect to the propellants . Researchers need to understand mixing and combustion...beyond liquid, gas states. Shear coaxial injectors are a common choice for cryogenic liquid rocket engines. Interactions of transverse acoustics with

  5. Jetting of a shear banding fluid in rectangular ducts

    PubMed Central

    Salipante, Paul F.; Little, Charles A. E.; Hudson, Steven D.

    2017-01-01

    Non-Newtonian fluids are susceptible to flow instabilities such as shear banding, in which the fluid may exhibit a markedly discontinuous viscosity at a critical stress. Here we report the characteristics and causes of a jetting flow instability of shear banding wormlike micelle solutions in microfluidic channels with rectangular cross sections over an intermediate volumetric flow regime. Particle-tracking methods are used to measure the three-dimensional flow field in channels of differing aspect ratios, sizes, and wall materials. When jetting occurs, it is self-contained within a portion of the channel where the flow velocity is greater than the surroundings. We observe that the instability forms in channels with aspect ratio greater than 5, and that the location of the high-velocity jet appears to be sensitive to stress localizations. Jetting is not observed in a lower concentration solution without shear banding. Simulations using the Johnson-Segalman viscoelastic model show a qualitatively similar behavior to the experimental observations and indicate that compressive normal stresses in the cross-stream directions support the development of the jetting flow. Our results show that nonuniform flow of shear thinning fluids can develop across the wide dimension in rectangular microfluidic channels, with implications for microfluidic rheometry. PMID:28691108

  6. Jetting of a shear banding fluid in rectangular ducts

    NASA Astrophysics Data System (ADS)

    Salipante, Paul F.; Little, Charles A. E.; Hudson, Steven D.

    2017-03-01

    Non-Newtonian fluids are susceptible to flow instabilities such as shear banding, in which the fluid may exhibit a markedly discontinuous viscosity at a critical stress. Here we report the characteristics and causes of a jetting flow instability of shear banding wormlike micelle solutions in microfluidic channels with rectangular cross sections over an intermediate volumetric flow regime. Particle-tracking methods are used to measure the three-dimensional flow field in channels of differing aspect ratios, sizes, and wall materials. When jetting occurs, it is self-contained within a portion of the channel where the flow velocity is greater than the surroundings. We observe that the instability forms in channels with aspect ratio greater than 5, and that the location of the high-velocity jet appears to be sensitive to stress localizations. Jetting is not observed in a lower concentration solution without shear banding. Simulations using the Johnson-Segalman viscoelastic model show a qualitatively similar behavior to the experimental observations and indicate that compressive normal stresses in the cross-stream directions support the development of the jetting flow. Our results show that nonuniform flow of shear thinning fluids can develop across the wide dimension in rectangular microfluidic channels, with implications for microfluidic rheometry.

  7. Jetting of a shear banding fluid in rectangular ducts.

    PubMed

    Salipante, Paul F; Little, Charles A E; Hudson, Steven D

    2017-03-01

    Non-Newtonian fluids are susceptible to flow instabilities such as shear banding, in which the fluid may exhibit a markedly discontinuous viscosity at a critical stress. Here we report the characteristics and causes of a jetting flow instability of shear banding wormlike micelle solutions in microfluidic channels with rectangular cross sections over an intermediate volumetric flow regime. Particle-tracking methods are used to measure the three-dimensional flow field in channels of differing aspect ratios, sizes, and wall materials. When jetting occurs, it is self-contained within a portion of the channel where the flow velocity is greater than the surroundings. We observe that the instability forms in channels with aspect ratio greater than 5, and that the location of the high-velocity jet appears to be sensitive to stress localizations. Jetting is not observed in a lower concentration solution without shear banding. Simulations using the Johnson-Segalman viscoelastic model show a qualitatively similar behavior to the experimental observations and indicate that compressive normal stresses in the cross-stream directions support the development of the jetting flow. Our results show that nonuniform flow of shear thinning fluids can develop across the wide dimension in rectangular microfluidic channels, with implications for microfluidic rheometry.

  8. Particle acceleration in rotating and shearing jets from AGN

    NASA Astrophysics Data System (ADS)

    Rieger, F. M.; Mannheim, K.

    2002-12-01

    We model the acceleration of energetic particles due to shear and centrifugal effects in rotating astrophysical jets. The appropriate equation describing the diffusive transport of energetic particles in a collisionless, rotating background flow is derived and analytical steady state solutions are discussed. In particular, by considering velocity profiles from rigid, over flat to Keplerian rotation, the effects of centrifugal and shear acceleration of particles scattered by magnetic inhomogeneities are distinguished. In the case where shear acceleration dominates, it is confirmed that power law particle momentum solutions f(p) ~ p-(3+alpha ) exist, if the mean scattering time tauc ~ palpha is an increasing function of momentum. We show that for a more complex interplay between shear and centrifugal acceleration, the recovered power law momentum spectra might be significantly steeper but flatten with increasing azimuthal velocity due to the increasing centrifugal effects. The possible relevance of shear and centrifugal acceleration for the observed extended emission in AGN is demonstrated for the case of the jet in the quasar 3C273.

  9. 1st ACT global trajectory optimisation competition: Results found at the Jet Propulsion Laboratory

    NASA Astrophysics Data System (ADS)

    Petropoulos, Anastassios E.; Kowalkowski, Theresa D.; Vavrina, Matthew A.; Parcher, Daniel W.; Finlayson, Paul A.; Whiffen, Gregory J.; Sims, Jon A.

    2007-11-01

    Results obtained at the Jet Propulsion Laboratory for the 1st ACT global trajectory optimisation competition are presented and the methods used to obtain them are described. The search for the globally optimal, low-thrust, gravity-assist trajectory for maximally deflecting an asteroid is performed in two steps. The first step involves a rough global search of the global search space, which has, however, been somewhat bounded based on prior mission-design experience, intuition, and energy arguments. A shape-based method is used to represent the low-thrust arcs, while the ballistic portions are searched almost exhaustively. The second step involves local optimisation of trajectories which stand out from the rough global search. The low-thrust optimisation problem is turned into a parameter optimisation problem by approximating the continuous thrusting as a series of impulsive manoeuvres. Of the many trajectories found, three optimal trajectories are reported and compared, including the one submitted for the competition. The best one employed a double-Venus, quadruple-Earth, Jupiter Saturn Jupiter gravity-assist sequence. The trajectory submitted for the competition used one less Venus flyby and one less Earth flyby.

  10. A Computational and Experimental Investigation of Shear Coaxial Jet Atomization

    NASA Technical Reports Server (NTRS)

    Ibrahim, Essam A.; Kenny, R. Jeremy; Walker, Nathan B.

    2006-01-01

    The instability and subsequent atomization of a viscous liquid jet emanated into a high-pressure gaseous surrounding is studied both computationally and experimentally. Liquid water issued into nitrogen gas at elevated pressures is used to simulate the flow conditions in a coaxial shear injector element relevant to liquid propellant rocket engines. The theoretical analysis is based on a simplified mathematical formulation of the continuity and momentum equations in their conservative form. Numerical solutions of the governing equations subject to appropriate initial and boundary conditions are obtained via a robust finite difference scheme. The computations yield real-time evolution and subsequent breakup characteristics of the liquid jet. The experimental investigation utilizes a digital imaging technique to measure resultant drop sizes. Data were collected for liquid Reynolds number between 2,500 and 25,000, aerodynamic Weber number range of 50-500 and ambient gas pressures from 150 to 1200 psia. Comparison of the model predictions and experimental data for drop sizes at gas pressures of 150 and 300 psia reveal satisfactory agreement particularly for lower values of investigated Weber number. The present model is intended as a component of a practical tool to facilitate design and optimization of coaxial shear atomizers.

  11. A Single Parameter to Characterize Wall Shear Stress Developed from an Underexpanded Axisymmetric Impinging Jet

    NASA Astrophysics Data System (ADS)

    Fillingham, Patrick; Murali, Harikrishnan

    2016-11-01

    Wall shear stress is characterized for underexpanded axisymmetric impinging jets for the application of aerodynamic particle resuspension from a surface. Analysis of the flow field and the wall shear stress resulted from normally impinging axisymmetric jets is conducted using Computational Fluid Dynamics. A normally impinging jet is modeled with a constant area nozzle, while varying height to diameter ratio (H/D) and inlet pressures. Schlieren photography is used to visualize the density gradient of the flow field for validation of the CFD. The Dimensionless Jet Parameter (DJP) is developed to describe flow regimes and characterize the shear stress. The DJP is defined as being proportional to the jet pressure ratio divided by the H/D ratio squared. Maximum wall shear stress is examined as a function of DJP with three distinct regimes: (i) subsonic impingement (DJP<1), (ii) transitional (12). Due to the jet energy dissipation in shock structures, which become a dominant dissipation mechanism in the supersonic impingement regime, wall shear stress is limited to a finite value. Additionally, formation of shock structures in the wall flow were observed for DJP>2 resulting in difficulties with dimensionless analysis. In the subsonic impingement and transitional regimes equations as a function of the DJP are obtained for the maximum wall shear stress magnitude, maximum shear stress location, and shear stress decay. Using these relationships wall shear stress can be predicted at all locations along the impingement surface.

  12. Performance and control of optimized shear discharges in JET

    NASA Astrophysics Data System (ADS)

    Bécoulet, A.; Eriksson, L.-G.; Baranov, Yu. F.; Borba, D. N.; Challis, C. D.; Conway, G. D.; Fuchs, V.; Gormezano, C.; Gowers, C. W.; Hawkes, N. C.; Hender, T. C.; Huysmans, G. T. A.; Joffrin, E.; Litaudon, X.; Lomas, P. J.; Maas, A.; Mayoral, M. L.; Parail, V. V.; Rimini, F. G.; Rochard, F.; Sarazin, Y.; Sips, A. C. C.; Söldner, F. X.; Zastrow, K.-D.; Zwingman, W. P.

    2000-06-01

    High performance discharges are routinely obtained on JET with low or reversed magnetic shear (s = (r/q)dq/dr), and the potential for steady state operation of such discharges is under investigation. With the use of the proper heating and fuelling, these `optimized shear' (OS) discharges exhibit an internal transport barrier (ITB), resulting in a strong peaking of the pressure profile, and thus in high fusion performance. These regimes have been extensively studied during the last (DD and DT) JET campaigns in order to promote this type of scenario as the basis for `advanced tokamak' operation. A review is given of the highest performance achieved on JET OS discharges during the last experimental campaigns, in both DD (up to 5.6 × 1016neutrons/s) and DT operation (fusion power up to 8.2 MW, ni0Ti0τE up to 1021 m-3 keV s). The role of the plasma edge is pointed out, as the power required to trigger an ITB is often higher than the H mode power threshold, leading to double barrier regimes. The presence of an H mode pedestal both modifies the ITB and induces edge bootstrap and ELM activity, which should be controlled to prolong such discharges. The operational procedure of optimization is then discussed, addressing the problems of ITB formation (power threshold, timing of the main heating phase, i.e. optimization of the target q profile, influence of the heating scheme, electron versus ion ITBs), ITB evolution (expansion of the ITB footpoint, H mode formation) and ITB termination (disruptive and/or `soft' MHD limits). Finally, the crucial problem of the route to steady state for such OS discharges is addressed, both in terms of ITB sustainment and control within the stability domain and in terms of edge pedestal control by means of impurity injection. The impurity behaviour is found, and examples of high performance discharges sustained for several energy confinement times are given (βN = 1.95, H89 = 2.3, Pfusioneq~10 MW, QDTeq~0.4 sustained for ~3 s). Extrapolation

  13. Estimation of turbulent shear stress in free jets: application to valvular regurgitation.

    PubMed

    Winoto, S H; Shah, D A; Liu, H

    1996-01-01

    In an attempt to better assess the severity of valvular regurgitation, an in-vitro experiment has been conducted to estimate turbulent shear stress levels within free jets issuing from different orifice shapes and sizes by means of hot-wire anemometry. On the basis of the measured mean velocities and the jet profiles, the distributions of the normalized kinematic turbulent shear stress (uv/Um2) were estimated for different jets by using an equation available for self-preserving circular jet. The results indicate that the equation can estimate the distributions of uv/Um2 independent of the orifice shape and Reynolds number of the jet. For the range of Reynolds numbers considered, the estimation of maximum turbulent shear stress inferred from these distributions suggests that the critical shear stress level of approximately 200 N/m2, corresponding to destruction of blood cells, is exceeded for typical blood flow velocity of 5 m/s at the valvular lesion.

  14. Minimisation of the wall shear stress gradients in bypass grafts anastomoses using meshless CFD and genetic algorithms optimisation.

    PubMed

    El Zahab, Zaher; Divo, Eduardo; Kassab, Alain

    2010-02-01

    The wall shear stress (WSS) spatial and temporal gradients are two hemodynamics parameters correlated with endothelial damage. Those two gradients become well pronounced in a bypass graft anastomosis geometry where the blood flow patterns are quite disturbed. The WSS gradient minimisation on the host artery floor can be achieved by optimising the anastomosis shape and hence may lead to an improved long-term post-surgical performance of the graft. The anastomosis shape optimisation can be executed via an integrated computational tool comprised of a meshless computational fluid dynamics (CFD) solver and a genetic algorithm (GA) shape optimiser. The meshless CFD solver serves to evaluate the WSS gradients and the GA optimiser serves to search for the end-to-side distal anastomosis (ETSDA) optimal shape that best minimises those gradients. We utilise a meshless CFD method to resolve hemodynamics and a GA for the purpose of optimisation. We consider three different anastomotic models: the conventional ETSDA, the Miller Cuff ETSDA and the hood ETSDA. The results reported herein demonstrate that the graft calibre should always be maximised whether a conventional or Miller Cuff ETSDA model is utilised. Also, it was noted that the Miller Cuff height should be minimised. The choice of an optimal anastomotic angle should be optimised to achieve a compromise between the concurrent minimisations of both the spatial WSS gradient and the temporal WSS gradient.

  15. A Study of the Unstable Modes in High Mach Number Gaseous Jets and Shear Layers

    NASA Astrophysics Data System (ADS)

    Bassett, Gene Marcel

    1993-01-01

    Instabilities affecting the propagation of supersonic gaseous jets have been studied using high resolution computer simulations with the Piecewise-Parabolic-Method (PPM). These results are discussed in relation to jets from galactic nuclei. These studies involve a detailed treatment of a single section of a very long jet, approximating the dynamics by using periodic boundary conditions. Shear layer simulations have explored the effects of shear layers on the growth of nonlinear instabilities. Convergence of the numerical approximations has been tested by comparing jet simulations with different grid resolutions. The effects of initial conditions and geometry on the dominant disruptive instabilities have also been explored. Simulations of shear layers with a variety of thicknesses, Mach numbers and densities perturbed by incident sound waves imply that the time for the excited kink modes to grow large in amplitude and disrupt the shear layer is taug = (546 +/- 24) (M/4)^{1.7 } (Apert/0.02) ^{-0.4} delta/c, where M is the jet Mach number, delta is the half-width of the shear layer, and A_ {pert} is the perturbation amplitude. For simulations of periodic jets, the initial velocity perturbations set up zig-zag shock patterns inside the jet. In each case a single zig-zag shock pattern (an odd mode) or a double zig-zag shock pattern (an even mode) grows to dominate the flow. The dominant kink instability responsible for these shock patterns moves approximately at the linear resonance velocity, nu_ {mode} = cextnu_ {relative}/(cjet + c_ {ext}). For high resolution simulations (those with 150 or more computational zones across the jet width), the even mode dominates if the even penetration is higher in amplitude initially than the odd perturbation. For low resolution simulations, the odd mode dominates even for a stronger even mode perturbation. In high resolution simulations the jet boundary rolls up and large amounts of external gas are entrained into the jet. In low

  16. The near field interaction between a sound pulse and a jet shear layer

    NASA Technical Reports Server (NTRS)

    Bayliss, A.; Maestrello, L.

    1980-01-01

    The in-flow and near field of a jet which is excited by an axial mass source located in the potential core is simulated numerically, taking due account of the jet spreading, and experimentally, using a shock-tube driver. Comparison is made for both excited and unexcited jets. It is shown that many of the features observed experimentally are consequences of the instability of the mean flow profile and not of turbulence. This instability is shown to be a significant amplifier of low frequency sound. The terms responsible for this amplification are those describing action between the fluctuating velocities and the gradient of the mean flow, which were identified by Ribner as the shear noise terms. The results demonstrate that a primary component of the observed shear noise in jets is generated by the mean profile instability.

  17. Passive control of wall shear stress and mass transfer generated by submerged lobed impinging jet

    NASA Astrophysics Data System (ADS)

    Sodjavi, Kodjovi; Montagné, Brice; Meslem, Amina; Byrne, Paul; Serres, Laurent; Sobolik, Vaclav

    2016-05-01

    Particle image velocimetry was used to investigate the flow field in an impinging lobed daisy hemispherical nozzle jet in comparison to its counterpart round jet, at a Reynolds number of 5620 based on the exit velocity and the equivalent diameter D e of the nozzle. The limitations of the PIV technique in the vicinity of the target wall due to the laser scattering were addressed by using the electrodiffusion (ED) technique to determine the wall shear rate distribution. The distribution of the mass transfer coefficient is also obtained using the ED technique. The target wall is placed at a distance H = 2 D e from the plane tangent to the nozzle, at the center of the orifice. The entrainment of ambient fluid in the free jet region, which is larger in the lobed jet compared to the round jet, feeds in turn the wall jet region. The maximum wall shear rate was found significantly higher in the daisy jet, with an excess of 93 % compared to the reference round jet. The maximum mass transfer is 35 % higher in the former compared to the latter. Therefore, the hemispherical daisy nozzle is an excellent candidate in passive strategies to enhance local skin-friction and the subsequent local mass transfer at a constant exit Reynolds number.

  18. Measurements in the annular shear layer of high subsonic and under-expanded round jets

    NASA Astrophysics Data System (ADS)

    Feng, Tong; McGuirk, James J.

    2016-01-01

    An experimental study has been undertaken to document compressibility effects in the annular shear layers of axisymmetric jets. Comparison is made of the measured flow development with the well-documented influence of compressibility in planar mixing layers. High Reynolds number (~106) and high Mach number jets issuing from a convergent nozzle at nozzle pressure ratios (NPRs) from 1.28 to 3.0 were measured using laser Doppler anemometry instrumentation. Detailed radial profile data are reported, particularly within the potential core region, for mean velocity, turbulence rms, and turbulence shear stress. For supercritical NPRs the presence of the pressure waves in the inviscid shock cell region as the jet expanded back to ambient pressure was found to exert a noticeable effect on shear layer location, causing this to shift radially outwards at high supercritical NPR conditions. After a boundary layer to free shear layer transition zone, the turbulence development displayed a short region of similarity before adjustment to near-field merged jet behaviour. Peak turbulence rms reduction due to compressibility was similar to that observed in planar layers with radial rms suppression much stronger than axial. Comparison of the compressibility-modified annular shear layer growth rate with planar shear layer data on the basis of the convective Mach number ( M C) showed notable differences; in the annular shear layer, compressibility effects began at lower M C and displayed a stronger reduction in growth. For high Mach number aerospace propulsion applications involving round jets, the current measurements represent a new data set for the calibration/validation of compressibility-affected turbulence models.

  19. Shear Layer Interactions in the Helical Hydrodynamic Structures of Swirling, Reacting Jets

    NASA Astrophysics Data System (ADS)

    Smith, Travis; Manoharan, Kiran; Emerson, Benjamin; Hemchandra, Santosh; Lieuwen, Tim

    2016-11-01

    Swirling jets with density stratification are a canonical combustor flow field. This work consisted of coupled experimental and theoretical analysis of the spatial structure of the most amplified modes in an annular jet, with a specific focus on the radial mode shapes of the shear layer disturbances, which we characterize as inner shear layer (ISL) motion relative to outer shear layer (OSL) motion. The stability analysis identifies spatial structures dominated by ISL motion, modes dominated by OSL motion, and modes with mixed ISL and OSL motion. These mixed modes are further classified as sinuous or varicose radial structures, depending on the relative motions of the two shear layers. The presence and spatial dependencies of these spatial modes are demonstrated experimentally with a 5 kHz stereo PIV measurement of a reacting swirling jet. In the experiment, we demonstrate that external excitations of various spatial configurations can be used to elicit hydrodynamic responses of axisymmetric and helical motions in either the ISL, the OSL, or the sinuous or varicose radial modes.

  20. Jet transport performance in thunderstorm wind shear conditions

    NASA Technical Reports Server (NTRS)

    Mccarthy, J.; Blick, E. F.; Bensch, R. R.

    1979-01-01

    Several hours of three dimensional wind data were collected in the thunderstorm approach-to-landing environment, using an instrumented Queen Air airplane. These data were used as input to a numerical simulation of aircraft response, concentrating on fixed-stick assumptions, while the aircraft simulated an instrument landing systems approach. Output included airspeed, vertical displacement, pitch angle, and a special approach deterioration parameter. Theory and the results of approximately 1000 simulations indicated that about 20 percent of the cases contained serious wind shear conditions capable of causing a critical deterioration of the approach. In particular, the presence of high energy at the airplane's phugoid frequency was found to have a deleterious effect on approach quality. Oscillations of the horizontal wind at the phugoid frequency were found to have a more serious effect than vertical wind. A simulation of Eastern flight 66, which crashed at JFK in 1975, served to illustrate the points of the research. A concept of a real-time wind shear detector was outlined utilizing these results.

  1. Lear jet boundary layer/shear layer laser propagation experiments

    NASA Technical Reports Server (NTRS)

    Gilbert, K.

    1980-01-01

    Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.

  2. Characteristic modes and evolution processes of shear-layer vortices in an elevated transverse jet

    NASA Astrophysics Data System (ADS)

    Huang, Rong F.; Lan, Jen

    2005-03-01

    Characteristics and evolution processes of the traveling coherent flow structure in the shear layer of an elevated round jet in crossflow are studied experimentally in an open-loop wind tunnel. Streak pictures of the smoke flow patterns illuminated by the laser-light sheet in the median and horizontal planes are recorded with a high speed digital camera. Time histories of the instantaneous velocity of the vortical flows in the shear layer are digitized by a hot-wire anemometer through a high-speed data acquisition system. By analyzing the streak pictures of the smoke flow visualization, five characteristic flow structures, mixing-layer type vortices, backward-rolling vortices, forward-rolling vortices, swing-induced mushroom vortices, and jet-type vortices, are identified in the shear layer evolving from the up-wind edge of the jet exit. The behaviors and mechanisms of the vortical flow structure in the bent shear layer are prominently distinct in different flow regimes. The frequency characteristics, Strouhal number, power-spectrum density functions, autocorrelation coefficient, as well as the time and length scales of the coherent structure and the Lagrangian integral scales are obtained by processing the measured instantaneous velocity data. The Strouhal number is found to decay exponentially with the increase of the jet-to-crossflow momentum flux ratio. The autocorrelation coefficients provide the information for calculating the statistical time scales of the coherent structure and the integral time scales of turbulence fluctuations. The corresponding length scales of the vortical structure and the integral length scales of turbulence in the shear layer are therefore obtained and discussed.

  3. Microturbulence and Flow Shear in High-performance JET ITB Plasma

    SciTech Connect

    R.V. Budny; A. Andre; A. Bicoulet; C. Challis; G.D. Conway; W. Dorland; D.R. Ernst; T.S. Hahm; T.C. Hender; D. McCune; G. Rewoldt; S.E. Sharapov

    2001-12-05

    The transport, flow shear, and linear growth rates of microturbulence are studied for a Joint European Torus (JET) plasma with high central q in which an internal transport barrier (ITB) forms and grows to a large radius. The linear microturbulence growth rates of the fastest growing (most unstable) toroidal modes with high toroidal mode number are calculated using the GS2 and FULL gyrokinetic codes. These linear growth rates, gamma (subscript lin) are large, but the flow-shearing rates, gamma (subscript ExB) (dominated by the toroidal rotation contribution) are also comparably large when and where the ITB exists.

  4. On the interaction of a sound pulse with the shear layer of an axisymmetric jet

    NASA Technical Reports Server (NTRS)

    Maestrello, L.; Bayliss, A.; Turkel, E.

    1981-01-01

    The behavior of a sound pulse from a simulated source in a jet is investigated both experimentally and numerically. Both approaches show that in the low and medium frequencies the far field acoustic power exhibits and marked amplification as the flow velocity increases. Experimentally this changes to an attenuation at the higher frequencies which cannot be computed by the numerical model. This amplification is traced to shear noise terms which trigger the instability waves that are inherent within the flow.

  5. Shear flow control of cold and heated rectangular jets by mechanical tabs. Volume 2: Tabulated data

    NASA Technical Reports Server (NTRS)

    Brown, W. H.; Ahuja, K. K.

    1989-01-01

    The effects of mechanical protrusions on the jet mixing characteristics of rectangular nozzles for heated and unheated subsonic and supersonic jet plumes were studied. The characteristics of a rectangular nozzle of aspect ratio 4 without the mechanical protrusions were first investigated. Intrusive probes were used to make the flow measurements. Possible errors introduced by intrusive probes in making shear flow measurements were also examined. Several scaled sizes of mechanical tabs were then tested, configured around the perimeter of the rectangular jet. Both the number and the location of the tabs were varied. From this, the best configuration was selected. This volume contains tabulated data for each of the data runs cited in Volume 1. Baseline characteristics, mixing modifications (subsonic and supersonic, heated and unheated) and miscellaneous charts are included.

  6. Shear flow control of cold and heated rectangular jets by mechanical tabs. Volume 1: Results and discussion

    NASA Technical Reports Server (NTRS)

    Brown, W. H.; Ahuja, K. K.

    1989-01-01

    The effects of mechanical protrusions on the jet mixing characteristics of rectangular nozzles for heated and unheated subsonic and supersonic jet plumes were studied. The characteristics of a rectangular nozzle of aspect ratio 4 without the mechanical protrusions were first investigated. Intrusive probes were used to make the flow measurements. Possible errors introduced by intrusive probes in making shear flow measurements were also examined. Several scaled sizes of mechanical tabs were then tested, configured around the perimeter of the rectangular jet. Both the number and the location of the tabs were varied. From this, the best configuration was selected. The conclusions derived were: (1) intrusive probes can produce significant errors in the measurements of the velocity of jets if they are large in diameter and penetrate beyond the jet center; (2) rectangular jets without tabs, compared to circular jets of the same exit area, provide faster jet mixing; and (3) further mixing enhancement is possible by using mechanical tabs.

  7. The effect of a shear boundary layer on the stability of a capillary jet

    NASA Astrophysics Data System (ADS)

    Ganan-Calvo, Alfonso; Montanero, Jose M.; Herrada, Miguel A.

    2014-11-01

    The generic stabilization effect of a shear boundary layer over the free surface of a capillary jet is here studied from analytical (asymptotic), numerical and experimental approaches. In first place, we show the consistency of the proposed asymptotic analysis by a linear stability (numerical) analysis of the Navier-Stokes equations for a finite boundary layer thickness. We show how the convective-to-absolute instability transition departs drastically from the flat velocity profile case as the axial coordinate becomes closer to the origin of the boundary layer development. For large enough axial distances from that origin, Rayleigh's dispersion relation is recovered. A collection of experimental observations is analyzed from the perspective provided by these results. We propose a systematic framework to the dynamics of capillary jets issued from a nozzle, either by direct injection into a quiescent atmosphere or in a co-flow (e.g. gas flow-focused jets), which exhibit peculiarities now definitely attributable in first order to the formation of shear boundary layers. Partial support from the Ministry of Economy and Competitiveness, Junta de Extremadura, and Junta de Andalucia (Spain) through Grant Nos. DPI2010-21103, GR10047, P08-TEP-04128, and TEP-7465, respectively, is gratefully acknowledged.

  8. Breakup dynamics and dripping-to-jetting transition in a Newtonian/shear-thinning multiphase microsystem.

    PubMed

    Ren, Yong; Liu, Zhou; Shum, Ho Cheung

    2015-01-07

    The breakup dynamics in non-Newtonian multiphase microsystems is associated with a variety of industrial applications such as food production and biomedical engineering. In this study, we numerically and experimentally characterize the dripping-to-jetting transition under various flow conditions in a Newtonian/shear-thinning multiphase microsystem. Our work can help to predict the formation of undesirable satellite droplets, which is one of the challenges in dispensing non-Newtonian fluids. We also demonstrate the variations in breakup dynamics between shear-thinning and Newtonian fluids under the same flow conditions. For shear-thinning fluids, the droplet size increases when the capillary number is smaller than a critical value, while it decreases when the capillary number is beyond the critical value. The variations highlight the importance of rheological effects in flows with a non-Newtonian fluid. The viscosity of shear-thinning fluids significantly affects the control over the droplet size, therefore necessitating the manipulation of the shear rate through adjusting the flow rate and the dimensions of the nozzle. Consequently, the droplet size can be tuned in a controlled manner. Our findings can guide the design of novel microdevices for generating droplets of shear-thinning fluids with a predetermined droplet size. This enhances the ability to fabricate functional particles using an emulsion-templated approach. Moreover, elastic effects are also investigated experimentally using a model shear-thinning fluid that also exhibits elastic behaviors: droplets are increasingly deformed with increasing elasticity of the continuous phase. The overall understanding in the model multiphase microsystem will facilitate the use of a droplet-based approach for non-Newtonian multiphase applications ranging from energy to biomedical sciences.

  9. Understanding High Recession Rates of Carbon Ablators Seen in Shear Tests in an Arc Jet

    NASA Technical Reports Server (NTRS)

    Driver, David M.; Olson, Michael W.; Barnhardt, Michael D.; MacLean, Matthew

    2010-01-01

    High rates of recession in arc jet shear tests of Phenolic Impregnated Carbon Ablator (PICA) inspired a series of tests and analysis on FiberForm (a carbon preform used in the fabrication of PICA). Arc jet tests were performed on FiberForm in both air and pure nitrogen for stagnation and shear configurations. The nitrogen tests showed little or no recession, while the air tests of FiberForm showed recession rates similar to that of PICA (when adjusted for the difference in density). While mechanical erosion can not be ruled out, this is the first step in doing so. Analysis using a carbon oxidation boundary condition within DPLR was used to predict the recession rate of FiberForm. The analysis indicates that much of the anomalous recession behavior seen in shear tests may simply be an artifact of the non-flight like test configuration (copper upstream of the test article) a result of dissimilar enthalpy and oxygen concentration profiles on the copper. Shape change effects were also investigated and shown to be relatively small.

  10. Experimental Optimisation of the Thermal Performance of Impinging Synthetic Jet Heat Sinks

    NASA Astrophysics Data System (ADS)

    Marron, Craig; Persoons, Tim

    2014-07-01

    Zero-net-mass flow synthetic jet devices offer a potential solution for energy- efficient cooling of medium power density electronic components. There remains an incomplete understanding of the interaction of these flows with extended surfaces, which prevents the wider implementation of these devices in the field. This study examines the effect of the main operating parameters on the heat transfer rate and electrical power consumption for a synthetic jet cooled heat sink. Three different heat sink geometries are tested. The results find that a modified sink with a 14 × 14 pin array with the central 6 × 6 pins removed provides superior cooling to either a fully pinned sink or flat plate. Furthermore each heat sink is found to have its own optimum jet orifice-to-sink spacing for heat transfer independent of flow conditions. The optimum heat transfer for the modified sink is H = 34 jet diameters. The effect of frequency on heat transfer is also studied. It is shown that heat transfer increases superlinearly with frequency at higher stroke lengths. The orientation of the impingement surface with respect to gravity has no effect on the heat transfer capabilities of the tested device. These tests are the starting point for further investigation into enhanced synthetic jet impingement surfaces. The equivalent axial fan cooled pinned heat sink (Malico Inc. MFP40- 18) has a thermal resistance of 1.93K/W at a fan power consumption of 0.12W. With the modified pinned heat sink, a synthetic jet at Re = 911, L0/D = 10, H/D = 30 provides a thermal resistance of 2.5K/W at the same power consumption.

  11. The Applicability of Jet-Shear-Layer Mixing and Effervescent Atomization for Low-NO(x) Combustors

    NASA Technical Reports Server (NTRS)

    Colantonio, R. O.

    1998-01-01

    An investigation has been conducted to develop appropriate technologies for a low-NO(x), liquid-fueled combustor. The combustor incorporates an effervescent atomizer used to inject fuel into a premixing duct. Only a fraction of the combustion air is used in the premixing process. This fuel-rich mixture is introduced into the remaining combustion air by a rapid jet-shear-layer mixing process involving radial fuel-air jets impinging on axial air jets in the primary combustion zone. Computational modeling was used as a tool to facilitate a parametric analysis appropriate to the design of an optimum low-NO(x) combustor. A number of combustor configurations were studied to assess the key combustor technologies and to validate the three-dimensional modeling code. The results from the experimental testing and computational analysis indicate a low-NO(x) potential for the jet-shear-layer combustor. Key features found to affect NOx emissions are the primary combustion zone fuel-air ratio, the number of axial and radial jets, the aspect ratio and radial location of the axial air jets, and the radial jet inlet hole diameter. Each of these key parameters exhibits a low-NO(x) point from which an optimized combustor was developed Also demonstrated was the feasibility of utilizing an effervescent atomizer for combustor application. Further developments in the jet-shear-layer mixing scheme and effervescent atomizer design promise even lower NO(x) with high combustion efficiency.

  12. PLIF Imaging of Capsule RCS Jets, Shear Layers, and Simulated Forebody Ablation

    NASA Technical Reports Server (NTRS)

    Inman, Jennifer A.; Danehy, Paul M.; Alderfer, David W.; Buck, Gregory M.; McCrea, Andrew

    2008-01-01

    Planar laser-induced fluorescence (PLIF) has been used to investigate hypersonic flows associated with capsule reentry vehicles. These flows included reaction control system (RCS) jets, shear layer flow, and simulated forebody heatshield ablation. Pitch, roll, and yaw RCS jets were studied. PLIF obtained planar slices in these flowfields. These slices could be viewed individually or they could be combined using computer visualization techniques to reconstruct the three dimensional shape of the flow. The tests described herein were conducted in the 31-Inch Mach 10 Air Tunnel at NASA Langley Research Center. Improvements to many facets of the imaging system increased the efficiency and quality of both data acquisition, in addition to increasing the overall robustness of the system.

  13. Refraction of Sound Emitted Near Solid Boundaries from a Sheared Jet

    NASA Technical Reports Server (NTRS)

    Dill, Loren H.; Oyedrian, Ayo A.; Krejsa, Eugene A.

    1998-01-01

    A mathematical model is developed to describe the sound emitted from an arbitrary point within a turbulent flow near solid boundaries. A unidirectional, transversely sheared mean flow is assumed, and the cross-section of the cold jet is of arbitrary shape. The analysis begins with Lilley's formulation of aerodynamic noise and, depending upon the specific model of turbulence used, leads via Fourier analysis to an expression for the spectral density of the intensity of the far-field sound emitted from a unit volume of turbulence. The expressions require solution of a reduced Green's function of Lilley's equation as well as certain moving axis velocity correlations of the turbulence. Integration over the entire flow field is required in order to predict the sound emitted by the complete flow. Calculations are presented for sound emitted from a plugflow jet exiting a semi-infinite flat duct. Polar plots of the far-field directivity show the dependence upon frequency and source position within the duct. Certain model problems are suggested to investigate the effect of duct termination, duct geometry, and mean flow shear upon the far-field sound.

  14. Studies of wall shear and mass transfer in a large scale model of neonatal high-frequency jet ventilation.

    PubMed

    Muller, W J; Gerjarusek, S; Scherer, P W

    1990-01-01

    The problem of endotracheal erosion associated with neonatal high-frequency jet ventilation (HFJV) is investigated through measurement of air velocity profiles in a scaled up model of the system. Fluid mechanical scaling principles are applied in order to construct a model within which velocity profiles are measured by hot-wire anemometry. The effects of two different jet geometries are investigated. Velocity gradients measured near the tracheal wall are used to measure the shear stresses caused by the jet flow on the wall. The Chilton-Colburn analogy between the transport of momentum and mass is applied to investigate tracheal drying caused by the high shear flow. Shear forces are seen to be more than two times higher for jets located near the endotracheal tube wall than for those located axisymmetrically in the center of the tube. Since water vapor fluxes are dependent on these shears, they are also higher for the asymmetric case. Fluxes are shown to be greatly dependent on the temperature and relative humidity of the inspired gas. Water from the tracheal surface may be depleted within one second if inspired gases are inadequately heated and humidified. It is recommended that the design of neonatal HFJV devices include delivery of heated (near body temperature), humidified (as close to 100% humidity as possible) gases through an axisymmetric jet to best avoid the problem of endotracheal erosion.

  15. Assessing the Impacts of Low Level Jets' Negative Wind Shear over Wind Turbines

    NASA Astrophysics Data System (ADS)

    Gutierrez, Walter; Ruiz-Columbie, Arquimedes; Tutkun, Murat; Castillo, Luciano

    2016-11-01

    Nocturnal Low Level Jets (LLJs) are defined as relative maxima in the vertical profile of the horizontal wind speed at the top of the stable boundary layer. Such peaks constitute major power resources, since they are observed at altitudes within the heights of commercial-size wind turbines. However, a wind speed maximum implies a transition from a positive wind shear below the maximum height to a negative one above. The effect that such transition inflicts on wind turbines has not been thoroughly studied. Here we focused on the impacts that the LLJ negative wind shears have over commercial size wind turbines. Using actual atmospheric LLJ data of high frequency as input for the NREL aeroelastic simulator FAST, different scenarios were created varying the LLJ maximum height with respect to the wind turbine hub height. We found only slight changes in the deflection and load averages for those scenarios, whereas the corresponding variances appear to decrease when a larger portion of the wind turbine sweeping area is affected by the negative shear. The exception was observed in the junction between the tower top and the nacelle, where a deflection maximum was detected that might reveal a critical structural point. The authors gratefully acknowledge the following Grants for this research: NSFCBET #1157246, NSFCMMI #1100948, NSFOISE1243482.

  16. Fluid Mechanics Optimising Organic Synthesis

    NASA Astrophysics Data System (ADS)

    Leivadarou, Evgenia; Dalziel, Stuart

    2015-11-01

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

  17. Studies on Impingement Effects of Low Density Jets on Surfaces — Determination of Shear Stress and Normal Pressure

    NASA Astrophysics Data System (ADS)

    Sathian, Sarith. P.; Kurian, Job

    2005-05-01

    This paper presents the results of the Laser Reflection Method (LRM) for the determination of shear stress due to impingement of low-density free jets on flat plate. For thin oil film moving under the action of aerodynamic boundary layer the shear stress at the air-oil interface is equal to the shear stress between the surface and air. A direct and dynamic measurement of the oil film slope is measured using a position sensing detector (PSD). The thinning rate of oil film is directly measured which is the major advantage of the LRM over LISF method. From the oil film slope history, direct calculation of the shear stress is done using a three-point formula. For the full range of experiment conditions Knudsen numbers varied till the continuum limit of the transition regime. The shear stress values for low-density flows in the transition regime are thus obtained using LRM and the measured values of shear show fair agreement with those obtained by other methods. Results of the normal pressure measurements on a flat plate in low-density jets by using thermistors as pressure sensors are also presented in the paper. The normal pressure profiles obtained show the characteristic features of Newtonian impact theory for hypersonic flows.

  18. Droplet Combustion and Non-Reactive Shear-Coaxial Jets with Transverse Acoustic Excitation

    DTIC Science & Technology

    2012-06-01

    Excitation of Coaxial Jets The earliest investigations of the effect of ambient pressure oscillations on free jets in- cludes those by Miesse [51], Newman [52...less effective in breaking up the jet than at lower chamber pressure. A majority of the studies done on acoustically excited coaxial jets involve in...outer jet on the near-field dynamics of the inner jet with axial excitation of each jet independently for 0.55 < R < 1.45. Axial forcing of the outer jet

  19. Noise measurements in a free-jet, flight simulation facility - Shear layer refraction and facility-to-flight corrections

    NASA Technical Reports Server (NTRS)

    Morfey, C. L.; Tester, B. J.

    1976-01-01

    The conversion of free-jet facility into equivalent flyover results is discussed. The essential problem is to 'calibrate out' the acoustic influence of the outer free-jet shear layer on the measurement, since this is absent in the flight case. Results are presented which illustrate the differences between current simplified models (vortex-sheet and geometric acoustics), and a more complete model based on the Lilley equation. Finally, the use of geometric acoustics for facility-to-flight data conversion is discussed.

  20. Noise measurements in a free-jet, flight simulation facility - Shear layer refraction and facility-to-flight corrections

    NASA Technical Reports Server (NTRS)

    Morfey, C. L.; Tester, B. J.

    1976-01-01

    The conversion of free-jet facility into equivalent flyover results is discussed. The essential problem is to 'calibrate out' the acoustic influence of the outer free-jet shear layer on the measurement, since this is absent in the flight case. Results are presented which illustrate the differences between current simplified models (vortex-sheet and geometric acoustics), and a more complete model based on the Lilley equation. Finally, the use of geometric acoustics for facility-to-flight data conversion is discussed.

  1. On the interaction of a sound pulse with the shear layer of an axisymmetric jet. II - Heated jets

    NASA Technical Reports Server (NTRS)

    Bayliss, A.; Maestrello, L.

    1983-01-01

    The fluctuating field of a heated jet excited by a sound pulse is simulated numerically. The fluctuations in both the flow field and the far field are studied. The flow field results depend crucially on the stability properties of the heated jet. The altered stability properties due to the heating cause a reduction in the overall fluctuations and a shift of the instability waves into lower frequencies. These changes cause a similar downward shift in the far field spectrum and a reduction in the total far field noise. The results provide a partial explanation in terms of stability theory of experimentally observed properties of the noise of heated jets.

  2. Modeling Acoustic Effects on shear-Coaxial Jet Flow Utilizing Molecular Dynamic Simulation

    DTIC Science & Technology

    2007-03-01

    two models. Model A is a second order equation while Model B is a simpler first order equation with a general slip coefficient , b, included in the...Acceleration Ai Inner jet area Ao Outer jet area b General slip coefficient c Propagation speed Di Inner jet diameter Do Outer jet...injectors exhausting parallel to the main flow field operating closely enough so their mixing zones interfere (Schetz, 1980:137). The second definition

  3. Jetting Activity and Thermal Emission across the South Polar Terrain of Enceladus: Observations and Comparisons with Shear-Heating Models

    NASA Astrophysics Data System (ADS)

    Porco, C.; DiNino, D.; Nimmo, F.; Ingersoll, A. P.; Helfenstein, P.; Roatsch, T.; Mitchell, C. J.

    2011-12-01

    Introduction: Cassini ISS Enceladus images reveal a forest of jets of fine icy particles erupting from the moon's south polar terrain (SPT) and feeding a giant plume that extends thousands of kilometers into space [1] eventually forming Saturn's E ring. Cassini infrared spectrometer (CIRS) observations have also shown the SPT to be anomalously warm [2], and the comparison of high resolution images of the SPT with the highest resolution thermal measurements has shown a coincidence between the hottest measured temperatures in the SPT and the "tiger stripe" fractures which straddle the region [1,2]. The most plausible mechanism for heat production on the fractures is tidally driven frictional heating along faults due to cyclical shearing. The time-averaged absolute shear stress on each fracture segment can be calculated [3] and will be affected by location and orientation, and proportional to the local frictional heat production rate (assuming a constant coefficient of friction). Initial triangulation measurements of the jets seen in ISS images spanning 1.3 years (from late 2005 to early 2007) and taken over a broad range of image scales (1 to 14 km/pixel), phase angles (148° to 178°), and viewing directions with respect to the surface revealed the source locations for the 8 most prominent jets [4]. All 8 fell, within 2σ measurement uncertainties, on the fractures, and about half of these sources were found to be coincident, within uncertainties, with the CIRS hot spots initially reported in 2006. Moreover, ISS jet locations were used to successfully predict the discovery of additional hot spots [4]: eg, the prominent hot spot on Baghdad Sulcus near Jet #I. Results: We have taken new, more precise jet positional measurements in the 62 highest resolution images (down to 40 m/pixel spatial scale) taken from late 2005 to early 2011 at phase angles of 130° to 165°. We now find over 80 distinct, measureable jets. Nearly all of them fall on one of the four main

  4. Effects of mean shear and scalar initial length scale on three-scalar mixing in turbulent coaxial jets

    NASA Astrophysics Data System (ADS)

    Tong, Chenning; Li, Wei; Yuan, Mengyuan; Carter, Campbell

    2016-11-01

    We investigate three-scalar mixing in a turbulent coaxial jet, in which a center jet and an annular flow, consisting of acetone-doped air and ethylene respectively, are mixed with the co-flow air. We investigate the effects of the velocity and length scale ratios of the annular flow to the center jet. Planar laser-induced fluorescence and Rayleigh scattering are employed to image the scalars. The results show that the velocity ratio alters the relative mean shear rates in the mixing layers between the center jet and the annular flow and between the annular flow and the co-flow, modifying the scalar fields through mean-flow advection, turbulent transport, and small-scale mixing. The length scale ratio determines the degree of separation between the center jet and the co-flow. The results show that while varying the velocity ratio can alter the mixing characteristics qualitatively, varying the annulus width only has quantitative effects. The evolution of the mean scalar profiles are dominated by the mean-flow advection, while the shape of the joint probability density function is largely determined by the turbulent transport and molecular diffusion. The results in the present study have implications for understanding and modeling multiscalar mixing in turbulent reactive flows. Supported by NSF.

  5. Application of Shear Plate Interferometry to Jet Diffusion Flame Temperature Measurements

    NASA Technical Reports Server (NTRS)

    VanDerWege, Brad A.; OBrien, Chris J.; Hochgreb, Simone

    1997-01-01

    The recent ban on the production of bromotrifluoromethane (CF3Br) because of its high stratospheric ozone depletion potential has led to interest in finding alternative agents for fire extinguishing applications. Some of the promising alternatives are fluorinated hydrocarbons. A clear understanding of the effects of CF3Br and alternative chemical suppressants on diffusion flames is therefore necessary in the selection of alternative suppressants for use in normal and microgravity. The flame inhibition effects of halogen compounds have been studied extensively in premixed systems. The effect of addition of halocarbons (carbon-halogen compounds) to diffusion flames has been studied experimentally in coflow configurations and in counterflow gaseous and liquid-pool flames. Halogenated compounds are believed to inhibit combustion by scavenging hydrogen radicals to form the relatively unreactive compound HF, or through a catalytic recombination cycle involving HBr to form H2. Comparisons between halogens show that bromine inhibition is significantly more effective than chlorine or fluorine. Although fluorinated compounds are only slightly more effective inhibitors on a mass basis than nitrogen, they are more effective on a volume basis and are easily stored in liquid form. The objectives of this study are (a) to determine the stability limits of laminar jet diffusion flames with respect to inhibitor concentration in both normal and microgravity, and (b) to investigate the structure of halocarbon-inhibited flames. In the initial phase of this project, visual diagnostics were used to observe the structure and behavior of normal and microgravity flames. The initial observations showed significant changes in the structure of the flames with the addition of halocarbons to the surrounding environment, as discussed below. Furthermore, the study established that the flames are more stable relative to the addition of halocarbons in microgravity than in normal gravity. Visual

  6. Application of Shear Plate Interferometry to Jet Diffusion Flame Temperature Measurements

    NASA Technical Reports Server (NTRS)

    VanDerWege, Brad A.; OBrien, Chris J.; Hochgreb, Simone

    1997-01-01

    The recent ban on the production of bromotrifluoromethane (CF3Br) because of its high stratospheric ozone depletion potential has led to interest in finding alternative agents for fire extinguishing applications. Some of the promising alternatives are fluorinated hydrocarbons. A clear understanding of the effects of CF3Br and alternative chemical suppressants on diffusion flames is therefore necessary in the selection of alternative suppressants for use in normal and microgravity. The flame inhibition effects of halogen compounds have been studied extensively in premixed systems. The effect of addition of halocarbons (carbon-halogen compounds) to diffusion flames has been studied experimentally in coflow configurations and in counterflow gaseous and liquid-pool flames. Halogenated compounds are believed to inhibit combustion by scavenging hydrogen radicals to form the relatively unreactive compound HF, or through a catalytic recombination cycle involving HBr to form H2. Comparisons between halogens show that bromine inhibition is significantly more effective than chlorine or fluorine. Although fluorinated compounds are only slightly more effective inhibitors on a mass basis than nitrogen, they are more effective on a volume basis and are easily stored in liquid form. The objectives of this study are (a) to determine the stability limits of laminar jet diffusion flames with respect to inhibitor concentration in both normal and microgravity, and (b) to investigate the structure of halocarbon-inhibited flames. In the initial phase of this project, visual diagnostics were used to observe the structure and behavior of normal and microgravity flames. The initial observations showed significant changes in the structure of the flames with the addition of halocarbons to the surrounding environment, as discussed below. Furthermore, the study established that the flames are more stable relative to the addition of halocarbons in microgravity than in normal gravity. Visual

  7. Effect of large-scale intermittency and mean shear on scaling-range exponents in a turbulent jet.

    PubMed

    Mi, J; Antonia, R A

    2001-08-01

    The present study investigates the combined impact of the intermittency associated with the turbulent-nonturbulent interface and the mean shear rate in an axisymmetric jet on the structure of turbulence in the scaling range, where the spectrum exhibits a power-law behavior. Second-order structure functions, autocorrelations of the dissipation rate, and spectra of both the longitudinal velocity fluctuation and the passive temperature fluctuation are measured at a distance of 40 diameter downstream from the nozzle exit. All the scaling range exponents are influenced by the large-scale intermittency and the mean shear. The scalar fluctuation is much more sensitive to the variation in large-scale intermittency than the velocity fluctuation.

  8. Critical shear stress measurement of cohesive soils in streams: identifying device-dependent variability using an in-situ jet test device and conduit flume

    NASA Astrophysics Data System (ADS)

    Mahalder, B.; Schwartz, J. S.; Palomino, A.; Papanicolaou, T.

    2016-12-01

    Cohesive soil erodibility and threshold shear stress for stream bed and bank are dependent on both soil physical and geochemical properties in association with the channel vegetative conditions. These properties can be spatially variable therefore making critical shear stress measurement in cohesive soil challenging and leads to a need for a more comprehensive understanding of the erosional processes in streams. Several in-situ and flume-type test devices for estimating critical shear stress have been introduced by different researchers; however reported shear stress estimates per device vary widely in orders of magnitude. Advantages and disadvantages exist between these devices. Development of in-situ test devices leave the bed and/or bank material relatively undisturbed and can capture the variable nature of field soil conditions. However, laboratory flumes provide a means to control environmental conditions that can be quantify and tested. This study was conducted to observe differences in critical shear stress using jet tester and a well-controlled conduit flume. Soil samples were collected from the jet test locations and tested in a pressurized flume following standard operational procedure to calculate the critical shear stress. The results were compared using statistical data analysis (mean-separation ANOVA procedure) to identify possible differences. In addition to the device comparison, the mini jet device was used to measure critical shear stress across geologically diverse regions of Tennessee, USA. Statistical correlation between critical shear stress and the soil physical, and geochemical properties were completed identifying that geological origin plays a significant role in critical shear stress prediction for cohesive soils. Finally, the critical shear stress prediction equations using the jet test data were examined with possible suggestions to modify based on the flume test results.

  9. An optimisation approach for culturing shear-sensitive dinoflagellate microalgae in bench-scale bubble column photobioreactors.

    PubMed

    López-Rosales, L; García-Camacho, F; Sánchez-Mirón, A; Contreras-Gómez, A; Molina-Grima, E

    2015-12-01

    The dinoflagellate Karlodinium veneficum was grown in bubble column photobioreactors and a genetic algorithm-based stochastic search strategy used to find optimal values for the culture parameters gas flow rate, culture height, and nozzle sparger diameter. Cell production, concentration of reactive oxygen species (ROS), membrane fluidity and photosynthetic efficiency were studied throughout the culture period. Gas-flow rates below 0.26Lmin(-1), culture heights over 1.25m and a nozzle diameter of 1.5mm were found to provide the optimal conditions for cell growth, with an increase of 60% in cell production with respect to the control culture. Non-optimal conditions produced a sufficiently high shear stress to negatively affect cell growth and even produce cell death. Cell physiology was also severely affected in stressed cultures. The production of ROS increased by up to 200%, whereas cell membrane fluidity decreased by 60% relative to control cultures. Photosynthetic efficiency decreased concomitantly with membrane fluidity.

  10. Geometry Effects on Steady and Acoustically Forced Shear-Coaxial Jet Sprays

    DTIC Science & Technology

    2012-09-01

    ORGANIZATION REPORT NO. Air Force Research Laboratory (AFMC) AFRL/RQRC 10 E. Saturn Blvd. Edwards AFB CA 93524-7680 9. SPONSORING...Pressure Antinode • Pressure antinode ( PAN ) – condition of maximum pressure perturbation in the acoustic field • Piezo-sirens forced in-phase...Superposition of quasi-1D acoustic waves traveling in opposite directions PAN at the jet location (geometric center of test section) Coaxial Jet

  11. Cryogenic High-Pressure Shear-Coaxial Jets Exposed to Transverse Acoustic Forcing

    DTIC Science & Technology

    2011-12-13

    measure the inner and outer jet flow rates, which were controlled via metering valves . The jets issued into the test section (Figure 1) of the inner...chamber halfway between the two piezo -sirens located at opposite ends of the chamber. Each piezo -siren was fitted with a waveguide that transitioned from a...circular cross-section to a rectangular one. The inner chamber was used to maximize the amplitude of acoustic oscillations gen- erated by the piezo

  12. Geometry Effects on Steady and Acoustically Forced Shear-Coaxial Jet Sprays

    DTIC Science & Technology

    2012-04-15

    meters (123-DKASVDAA) were used to measure the inner and outer jet flow rates, which were controlled via metering valves . The jets issued into the test...section (Fig. 1) of the inner chamber halfway between the two piezo -sirens located at opposite ends of the chamber. Each piezo -siren was fitted with...oscillations generated by the piezo -sirens. However, both the inner and main chambers were maintained at the same static pressure, which was measured with

  13. Vortex dynamics and wall shear stress behaviour associated with an elliptic jet impinging upon a flat plate

    NASA Astrophysics Data System (ADS)

    Long, J.; New, T. H.

    2016-07-01

    Vortical structures and dynamics of a Re h = 2100 elliptic jet impinging upon a flat plate were studied at H/ d h = 1, 2 and 4 jet-to-plate separation distances. Flow investigations were conducted along both its major and minor planes using laser-induced fluorescence and digital particle image velocimetry techniques. Results show that the impingement process along the major plane largely consists of primary jet ring-vortex and wall-separated secondary vortex formations, where they subsequently separate from the flat plate at smaller H/ d h = 1 and 2 separation distances. Key vortex formation locations occur closer to the impingement point as the separation distance increases. Interestingly, braid vortices and rib structures begin to take part in the impingement process at H/ d h = 4 and wave instabilities dominate the flow field. In contrast, significantly more coherent primary and secondary vortices with physically larger vortex core sizes and higher vortex strengths are observed along the minor plane, with no signs of braid vortices and rib structures. Lastly, influences of these different flow dynamics on the major and minor plane instantaneous and mean skin friction coefficient levels are investigated to shed light on the effects of separation distance on the wall shear stress distributions.

  14. Droplet Combustion and Non-Reactive Shear-Coaxial Jets with and without Transverse Acoustic Excitation

    DTIC Science & Technology

    2012-01-01

    et al. [34], Perrault-Joncas and Maslowe [49]). Sevilla et al. [34] investigate the effect of outer to inner jet diameter ratio as well as S on the...Jets with and without Transverse Acoustic Excitation 5a. CONTRACT NUMBER In-House 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR( S ) 5d...PROJECT NUMBER Sophonias Teshome 5e. TASK NUMBER 5f. WORK UNIT NUMBER 23080533 7. PERFORMING ORGANIZATION NAME( S ) AND ADDRESS(ES) 8. PERFORMING

  15. Application of jet-shear-layer mixing and effervescent atomization to the development of a low-NO(x) combustor. Ph.D. Thesis - Purdue Univ.

    NASA Technical Reports Server (NTRS)

    Colantonio, Renato Olaf

    1993-01-01

    An investigation was conducted to develop appropriate technologies for a low-NO(x), liquid-fueled combustor. The combustor incorporates an effervescent atomizer used to inject fuel into a premixing duct. Only a fraction of the combustion air is used in the premixing process to avoid autoignition and flashback problems. This fuel-rich mixture is introduced into the remaining combustion air by a rapid jet-shear-layer-mixing process involving radial fuel-air jets impinging on axial air jets in the primary combustion zone. Computational analysis was used to provide a better understanding of the fluid dynamics that occur in jet-shear-layer mixing and to facilitate a parametric analysis appropriate to the design of an optimum low-NO(x) combustor. A number of combustor configurations were studied to assess the key combustor technologies and to validate the modeling code. The results from the experimental testing and computational analysis indicate a low-NO(x) potential for the jet-shear-layer combustor. Key parameters found to affect NO(x) emissions are the primary combustion zone fuel-air ratio, the number of axial and radial jets, the aspect ratio and radial location of the axial air jets, and the radial jet inlet hole diameter. Each of these key parameters exhibits a low-NO(x) point from which an optimized combustor was developed. Using the parametric analysis, NO(x) emissions were reduced by a factor of 3 as compared with the emissions from conventional, liquid-fueled combustors operating at cruise conditions. Further development promises even lower NO(x) with high combustion efficiency.

  16. High-shear, jet-cooking, and alkali treatment of corn distillers' dried grains to obtain products with enhanced protein, oil and phenolic antioxidants.

    PubMed

    Inglett, G E; Chen, D; Rose, D J; Berhow, M

    2010-08-01

    Distillers dried grains (DDG) have potential to be a nutritionally important source of protein, oil and phenolic antioxidants. DDG was subjected to high-shear and jet-cooking, with or without alkaline pH adjustment and autoclaving. Soluble and insoluble fractions were analyzed for protein, oil and ash. Extracts were analyzed for phenolic acids and antioxidant activity. Protein contents were significantly elevated in the insoluble fractions after treatment and the oil content was drastically increased in the insoluble fraction after high-shear and jet-cooking without pH adjustment. Alkaline pH adjustment resulted in a soluble fraction that was highest in phenolic acids, but not antioxidant activity. The highest antioxidant activity was found in the 50% ethanol extract from DDG that had been subjected to high-shear and jet-cooking. These results suggest that high-shear and jet-cooking may be useful processing treatments to increase the value of DDG by producing fractions high in protein, oil and extractable phenolic acids with high antioxidant activity. The DDG fractions and extracts described herein may be useful as food and nutraceutical ingredients, and, if used for these applications, will increase the value of DDG and ease economic burdens on ethanol producers, allowing them to compete in the bio-fuel marketplace.

  17. Jets.

    PubMed

    Rhines, Peter B.

    1994-06-01

    This is a discussion of concentrated large-scale flows in planetary atmospheres and oceans, argued from the viewpoint of basic geophysical fluid dynamics. We give several elementary examples in which these flows form jets on rotating spheres. Jet formation occurs under a variety of circumstances: when flows driven by external stress have a rigid boundary which can balance the Coriolis force, and at which further concentration can be caused by the beta effect; when there are singular lines like the line of vanishing windstress or windstress-curl, or the Equator; when compact sources of momentum, heat or mass radiate jet-like beta plumes along latitude circles; when random external stirring of the fluid becomes organized by the beta effect into jets; when internal instability of the mass field generates zonal flow which then is concentrated into jets; when bottom topographic obstacles radiate jets, and when frontogenesis leads to shallow jet formation. Essential to the process of jet formation in stratified fluids is the baroclinic life cycle described in geostrophic turbulence studies; there, conversion from potential to kinetic energy generates eddy motions, and these convert to quasibarotropic motions which then radiate and induce jet-like large-scale circulation. Ideas of potential vorticity stirring by eddies generalize the notion of Rossby-wave radiation, showing how jets embedded in an ambient potential vorticity gradient (typically due to the spherical geometry of the rotating planet) gain eastward momentum while promoting broader, weaker westward circulation. Homogenization of potential vorticity is an important limit point, which many geophysical circulations achieve. This well-mixed state is found in subdomains of the terrestrial midlatitude oceans, the high-latitude circumpolar ocean, and episodically in the middle atmosphere. Homogenization expels potential vorticity gradients vertically to the top and bottom of the fluid, and sideways to the edges of

  18. Effects of external intermittency and mean shear on the spectral inertial-range exponent in a turbulent square jet.

    PubMed

    Zhang, J; Xu, M; Pollard, A; Mi, J

    2013-05-01

    This study investigates by experiment the dependence of the inertial-range exponent m of the streamwise velocity spectrum on the external intermittency factor γ (≡ the fraction of time the flow is fully turbulent) and the mean shear S in a turbulent square jet. Velocity measurements were made using hot-wire anemometry in the jet at 15 < x/D(e) < 40, where D(e) denotes the exit equivalent diameter, and for an exit Reynolds number of Re = 50,000. The Taylor microscale Reynolds number R(λ) varies from about 70 to 450 in the present study. The TERA (turbulent energy recognition algorithm) method proposed by Falco and Gendrich [in Near-Wall Turbulence: 1988 Zoran Zariç Memorial Conference, edited by S. J. Kline and N. H. Afgan (Hemisphere Publishing Corp., Washington, DC, 1990), pp. 911-931] is discussed and applied to estimate the intermittency factor from velocity signals. It is shown that m depends strongly on γ but negligibly on S. More specifically, m varies with γ following m=m(t)+(lnγ(-0.0173))(1/2), where m(t) denotes the spectral exponent found in fully turbulent regions.

  19. Effects of external intermittency and mean shear on the spectral inertial-range exponent in a turbulent square jet

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Xu, M.; Pollard, A.; Mi, J.

    2013-05-01

    This study investigates by experiment the dependence of the inertial-range exponent m of the streamwise velocity spectrum on the external intermittency factor γ (≡ the fraction of time the flow is fully turbulent) and the mean shear S in a turbulent square jet. Velocity measurements were made using hot-wire anemometry in the jet at 15 < x/De < 40, where De denotes the exit equivalent diameter, and for an exit Reynolds number of Re = 50 000. The Taylor microscale Reynolds number Rλ varies from about 70 to 450 in the present study. The TERA (turbulent energy recognition algorithm) method proposed by Falco and Gendrich [in Near-Wall Turbulence: 1988 Zoran Zariç Memorial Conference, edited by S. J. Kline and N. H. Afgan (Hemisphere Publishing Corp., Washington, DC, 1990), pp. 911-931] is discussed and applied to estimate the intermittency factor from velocity signals. It is shown that m depends strongly on γ but negligibly on S. More specifically, m varies with γ following m=mt+(lnγ-0.0173)1/2, where mt denotes the spectral exponent found in fully turbulent regions.

  20. Non-Reactive Shear-Coaxial Jets with and without Transverse Acoustic Forcing

    DTIC Science & Technology

    2012-04-23

    Force Research Laboratory (AFMC) AFRL/RQRC 10 E. Saturn Blvd. Edwards AFB CA 93524-7680 9. SPONSORING / MONITORING AGENCY NAME(S) AND...Acoustic Field Set-Up: Pressure Antinode • Pressure antinode ( PAN ) – condition of maximum pressure perturbation in the acoustic field • Piezo-sirens...forced in-phase • Superposition of quasi-1D acoustic waves traveling in opposite directions PAN at the jet location (geometric center of test section

  1. Long Distance Coupling of Lower Hybrid Waves in ITER Relevant Edge Conditions in JET Reversed Shear Plasmas

    NASA Astrophysics Data System (ADS)

    Ekedahl, A.; Granucci, G.; Mailloux, J.; Petrzilka, V.; Rantamäki, K.; Baranov, Y.; Erents, K.; Goniche, M.; Joffrin, E.; Lomas, P. J.; Mantsinen, M.; McDonald, D.; Noterdaeme, J.-M.; Pericoli, V.; Sartori, R.; Silva, C.; Stamp, M.; Tuccillo, A. A.; Efda-Jet Contributors

    2003-12-01

    A significant step towards demonstrating the feasibility of coupling Lower Hybrid (LH) waves in ITER has been achieved in the latest LH current drive experiments in JET. The local electron density in front of the LH launcher was increased by injecting gas (D2 or CD4) from a dedicated gas injection module magnetically connected to the launcher. PLHCD=3MW was coupled with an average reflection coefficient of 5%, at a distance between the last closed flux surface and the launcher of 10cm, in plasmas with an internal transport barrier (ITB) and H-mode edge, with type I and type III ELMs. Following a modification of the gas injection system, in order to optimise the gas localisation with respect to the LH launcher, injection of D2 proved to be more efficient than CD4. A D2 flux of 5-8×1021el/s provided good coupling conditions at a clearance of 10cm, while when using CD4, a flux of 12×1021el/s was required at 9cm. The plasma performance (neutron rate, H-factor, ion temperature) was similar with D2 and CD4. An additional advantage with D2 injection was found, as it reduced the amplitude of the ELMs, which further facilitated the LH coupling. Furthermore, preliminary results of the study of the behaviour of electron density profile in the scrape-off layer during injection of C2H6 and C3H8 are reported. Finally, the appearance of hot spots, resulting from parasitic absorption of LHCD power in front of the launcher mouth, was studied in the long distance discharges with near gas injection.

  2. Shear layer structure of a low speed jet. Ph.D. Thesis. Final Report, 28 Jun. 1974 - 31 Dec. 1975; [measurements of field pressure and turbulent velocity functions

    NASA Technical Reports Server (NTRS)

    Petersen, R. A.

    1976-01-01

    A series of measurements of near field pressures and turbulent velocity fluctuations were made in a low speed jet with a Reynolds number near 50,000 in order to investigate more quantitatively the character and behavior of the large scale structures and their interactions with each other. The near field measurements were modelled according to the vortex pairing hypothesis to deduce the distribution of pairings along the jet axis and the variances about the mean locations. The hodograph plane description of turbulence was explored in some detail, and a complex correlation quantity was synthesized which has useful properties for turbulence in the presence of mean shear.

  3. On the vertical wind shear of Saturn's Equatorial Jet at cloud level

    NASA Astrophysics Data System (ADS)

    Sánchez-Lavega, A.; Pérez-Hoyos, S.

    2005-08-01

    With the aim of retrieving the altitude of cloud features used as zonal wind tracers in Saturn's atmosphere, we have reanalyzed three different sets of photometric and calibrated data corresponding to the Voyager epoch 1979-1981 (ground-based in 1979, Voyager 2 PPS and ISS observations in 1981), and we have analyze a new set of Hubble Space Telescope images for 2004. This analysis is put in the perspective of our previous HST study for 1994-2003 (Pérez-Hoyos et al., Icarus, 176, 155. 2005). A common result is found that the individual cloud tracers are embedded within a variable tropospheric haze. According to our models, the Voyager 2 ISS images locate the cloud tracers moving with zonal velocities of 455 to 465 (± 2) m/s at a pressure level of 360 ± 140 mbar. For HST observations, the cloud tracers moving with zonal wind speeds of 280 ± 10 m/s, locate at a pressure level of about 50 ± 10 mbar. All these values are calculated in the latitude 3 deg North. The speed difference, if interpreted as a vertical wind shear (Porco et al., Science, 307, 1226. 2005), requires a change of 90 m/s per scale height, two times greater than that estimated from Cassini CIRS data (Flasar et al., Science, 307, 1247, 2005). We also perform an initial guess on Cassini ISS vertical sounding levels, retrieving values compatible with the HST ones but not with Voyager wind measurements. We conclude that the wind speed velocity differences measured between 1979-81 and 2004 in the upper troposphere cannot be solely explained as a wind shear effect and demand dynamical processes. We discuss the possible action of Rossby waves or an intrinsic circulation change in the ammonia cloud layer and above, following a large period of equatorial storm activity. Acknowledgments: This work was supported by MCYT AYA2003-03216, FEDER, and Grupos UPV 15946/2004. S.P.-H. acknowledges a PhD fellowship from the Spanish MEC and R. H. a post-doc contract from Gobierno Vasco.

  4. The role of axisymmetric reconnection events in JET discharges with extreme shear reversal

    NASA Astrophysics Data System (ADS)

    Stratton, B. C.; Breslau, J. A.; Budny, R. V.; Jardin, S. C.; Park, W.; Strauss, H. R.; Zakharov, L. E.; Alper, B.; Drozdov, V.; Hawkes, N. C.; Reyes-Cortes, S.; EFDA-JET Workprogramme, contributors to the

    2002-07-01

    Injection of lower hybrid heating and current drive into the current ramp-up phase of JET discharges can produce extremely reversed q-profiles characterized by a core region of very small or zero current density (within motional Stark effect diagnostic measurement errors) and qmin>1. Te-profiles show sawtooth-like collapses and the presence of an internal transport barrier. Accurate equilibrium reconstructions of these discharges are obtained using the ESC code, which was recently extended to allow equilibrium reconstructions in which a free boundary solver determines the plasma boundary and a fixed boundary solver provides the magnetic geometry and current density profile. The core current density does not appear to go negative, although current diffusion calculations indicate that sufficient non-inductive current drive to cause this is present. This is explained by nonlinear resistive MHD simulations in toroidal geometry which predict that these discharges undergo n = 0 reconnection events (axisymmetric sawteeth) that redistribute the current to hold the core current density near zero.

  5. The formation and evolution of extreme shear reversal in JET and its influence on local thermal transport

    NASA Astrophysics Data System (ADS)

    Hawkes, N. C.; Andrew, Y.; Challis, C. D.; DeAngelis, R.; Drozdov, V.; Hobirk, J.; Joffrin, E.; Lotte, P.; Mazon, D.; Rachlew, E.; Reyes-Cortes, S.; Sattin, F.; Solano, E.; Stratton, B. C.; Tala, T.; Valisa, M.; EFDA-JET workprogramme, contributors to the

    2002-07-01

    In JET discharges where lower hybrid heating and current drive (LHCD) is applied early during the current ramp, a region of the plasma with zero current density is formed near the axis. At the boundary of this region the current density is large and Bθ increases rapidly over a small distance. In the central region the safety factor, q, is effectively infinite, but this falls steeply in the boundary region. Outside the boundary region q reaches a minimum, where the magnetic shear s≡r/q (dq/dr) becomes zero. The formation of this region of zero current is dependent on both the heating and the current drive effects of the LHCD. When LHCD is switched off the current profile begins to relax towards the resistive peaked current distribution of fully inductive tokamak operation. If LHCD is not used in the current rise then these current profiles are not established. Although the physical mechanism exists to drive the central plasma current below zero, in most cases it appears to be prevented from going negative. At least one MHD mechanism has been identified which could be responsible for this. The presence of the zero central current is closely linked to the periodic relaxation events seen in these discharges. In these discharges, internal transport barriers have been observed with additional heating powers substantially below the values required to obtain barriers in monotonic q profile cases.

  6. On the behavior of a shear-coaxial jet, spanning sub- to supercritical pressures, with and without an externally imposed transverse acoustic field

    NASA Astrophysics Data System (ADS)

    Davis, Dustin Wayne

    In the past, liquid rocket engines (LRE) have experienced high-frequency combustion instability, which impose an acoustic field in the combustion chamber. The acoustic field interacts with the fluid jets issuing from the injectors, thus altering the behavior of the jet compared to that of stable operation of the LRE. It is possible that this interaction could be a substantial feed back mechanism driving the combustion instability. In order to understand the problem of combustion instability, it is necessary to understand the interaction of the jet with the acoustic waves. From past combustion instability studies of the liquid oxygen and hydrogen propellant combination in a shear-coaxial injector configuration, a design guideline of outer-to-inner jet velocity ratio greater than about ten was proposed in order to avoid high-frequency acoustic combustion instability problems. However, no satisfactory physical explanation was provided. To promote this understanding, a cold-flow experimental investigation of a shear-coaxial jet interacting with a high-amplitude non-linear acoustic field was undertaken under chamber pressures extending into the supercritical regime. Liquid nitrogen (LN2) flowed from the inner tube of a coaxial injector while gaseous nitrogen (GN2) issued from its annular region. The injector fluids were directed into a chamber pressurized with gaseous nitrogen. The acoustic excitation was provided by an external driver capable of delivering acoustic field amplitudes up to 165 dB. The resonant modes of the chamber governed the two frequencies studied here, with the first two modes being about 3 and 5.2 kHz. High-speed images of the jet were taken with a Phantom CMOS camera. The so-called "dark core" of the jet is among the most salient features in the acquired images, and therefore, was defined and measured. The core length was found to decrease with increasing velocity and momentum flux ratio. Because of the ability of the camera to capture thousands of

  7. Fixed-base simulation study of decoupled longitudinal controls during approach and landing of a medium jet transport in the presence of wind shear

    NASA Technical Reports Server (NTRS)

    Miller, G. K., Jr.

    1979-01-01

    The use of decoupled longitudinal controls during the approach and landing of a typical twin-engine jet transport in the presence of wind shear was studied. The simulation included use of a localizer and flight director to capture and maintain a 3 deg glide slope. The pilot then completed the landing by using visual cues provided below an altitude of 200 m by closed-circuit television and a terrain model. The decoupled controls used constant prefilter and feedback gains to provide steady state decoupling of flight path angle, pitch angle, and forward velocity. The use of the decoupled control system improved pilot performance during the approach and at touchdown in the presence of wind shears. The pilots preferred the decoupled controls and rated the task 1 to 3 increments better on a pilot rating scale, depending on wind conditions, than was the case when conventional controls were used.

  8. On the Behavior of a Shear-Coaxial Jet, Spanning Sub- to Supercritical Pressures, with and without an Externally Imposed Transverse Acoustic Field

    DTIC Science & Technology

    2006-05-01

    Motivation Combustion instability in liquid rocket engines was the problem in mind at the onset of this study , and the motivation starts there. Culick...of vehicle and payload, or worse, to a loss of human life. A great deal of research primarily in the 2 1950’s and 1960’s during the space race [2...something can be learned from a cold-flow study of a shear-coaxial jet, in which similar conditions to those in liquid rocket engines during a

  9. Optimising endorphins.

    PubMed

    Kirkham, Mavis; Jowitt, Margaret

    2012-11-01

    The interactions of the hormones of pregnancy, labour and birth are complex and subtle and their effects are far reaching. Within these complex interactions beta endorphin (beta-end) has a key balancing function, being a hormone of relationship and a stress hormone. As well as helping the mother cope with labour, beta-end enhances relationships with the newborn and the initiation of breastfeeding. Both too much endorphin and too little can create problems in labour. Optimising endorphin levels is therefore more complex than simply enhancing them and calls for midwifery skills to relieve fear so that women feel safe.

  10. Numeric and experimental investigation of the sound generating mechanisms of a starting jet in volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Sesterhenn, Joern; Pena Fernandez, Juan Jose

    2015-04-01

    Every volcanic eruption generates in its very first stage an impulsively starting free jet, and while continuous free jets have been investigated and optimised during the last 60 years, the impulsively started jet is still relatively unexplored. Its sound structure is qualitatively different from the sound generated by a continuously blowing jet. We focus here upon the very first stage of a supersonic free round jet, when the flow is only few diameters long and the vortex ring generated by the sudden expansion interacts with the shock-waves and the shear layer. Direct numerical simulations with more than 2 x 109 grid points are carried out, discretising the compressible Navier-Stokes equations to compute both the fluid flow and the noise radiated by the interaction of the shear layer, the shock-waves and the vortex ring in a compressible free round jet. The first acoustic wave radiated due to the strong expansion at the nozzle in the first stage is also computed. As a result of the mentioned interaction, a sound level of 111[dB] at a distance of 100 diameters from the jet axis has been computed. The acoustic signal of more than 2000 eruptions has been recorded with synchronised microphones at Stromboli and Mount Etna in order to identify the sound generating mechanisms and to compare with the numerical simulations. An interaction between the shear layer, the shock-waves and the vortex ring has been investigated using numerical methods in an impulsively started supersonic free round jet and noise levels of order of the loudest acoustic phenomenon in the continuous jet have been identified and quantified. Numerous short volcanic eruptions were recorded at Stromboli and Etna covering a range of very short to medium length eruptions. Statistical and modal analysis are performed on the different eruptions and compared to the numerical computations to identify the different sound source mechanisms in the signals, which are observed in the computations.

  11. Evaluation of Aortic Stenosis Severity using 4D Flow Jet Shear Layer Detection for the Measurement of Valve Effective Orifice Area

    PubMed Central

    Garcia, Julio; Markl, Michael; Schnell, Susanne; Allen, Bradley; Entezari, Pegah; Mahadevia, Riti; Malaisrie, S Chris; Pibarot, Philippe; Carr, James; Barker, Alex J

    2014-01-01

    Aims The objective of this study was to evaluate the potential of 4D flow MRI to assess valve effective orifice area (EOA) in patients with aortic stenosis as determined by the jet shear layer detection (JSLD) method. Methods and Results An in-vitro stenosis phantom was used for validation and in-vivo imaging was performed in 10 healthy controls and 40 patients with aortic stenosis. EOA was calculated by the JSLD method using standard 2D phase contrast MRI (PC-MRI) and 4D flow MRI measurements (EOAJSLD-2D and EOAJSLD-4D, respectively). As a reference standard, the continuity equation was used to calculate EOA (EOACE) with the 2D PC-MRI velocity field and compared to the EOAJSLD measurements. The in-vitro results exhibited excellent agreement between flow theory (EOA=0.78 cm2) and experimental measurement (EOAJSLD-4D=0.78±0.01 cm2) for peak velocities ranging from 0.9 to 3.7 m/s. In-vivo results showed good correlation and agreement between EOAJSLD-2D and EOACE (r=0.91, p<0.001; bias: −0.01±0.38cm2; agreement limits: 0.75 to −0.77cm2), and between EOAJSLD-4D and EOACE (r=0.95, p<0.001; bias: −0.09±0.26cm2; limits: 0.43 to −0.62cm2). Conclusion This study demonstrates the feasibility of measuring EOAJSLD using 4D flow MRI. The technique allows for optimization of the EOA measurement position by visualizing the 3D vena contracta, and avoids potential sources of EOACE measurement variability. PMID:24865143

  12. Dichotomy of Solar Coronal Jets: Standard Jets and Blowout Jets

    NASA Astrophysics Data System (ADS)

    Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.; Falconer, David A.

    2010-09-01

    By examining many X-ray jets in Hinode/X-Ray Telescope coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop Hα macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major coronal mass ejections. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 Å snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T ~ 104 - 105 K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

  13. DICHOTOMY OF SOLAR CORONAL JETS: STANDARD JETS AND BLOWOUT JETS

    SciTech Connect

    Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.; Falconer, David A.

    2010-09-01

    By examining many X-ray jets in Hinode/X-Ray Telescope coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop H{alpha} macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major coronal mass ejections. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 A snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T {approx} 10{sup 4} - 10{sup 5} K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

  14. Dichotomy of Solar Coronal Jets: Standard Jets and Blowout Jets

    NASA Technical Reports Server (NTRS)

    Moore, R. L.; Cirtain, J. W.; Sterling, A. C.; Falconer, D. A.

    2010-01-01

    By examining many X-ray jets in Hinode/XRT coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop H alpha macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major CMEs. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 Angstrom snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T 10(exp 4) - 10(exp 5) K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

  15. The jet in crossflowa)

    NASA Astrophysics Data System (ADS)

    Karagozian, Ann R.

    2014-10-01

    The jet in crossflow, or transverse jet, is a flowfield that has relevance to a wide range of energy and propulsion systems. Over the years, our group's studies on this canonical flowfield have focused on the dynamics of the vorticity associated with equidensity and variable density jets in crossflow, including the stability characteristics of the jet's upstream shear layer, as a means of explaining jet response to altered types of excitation. The jet's upstream shear layer is demonstrated to exhibit convectively unstable behavior at high jet-to-crossflow momentum flux ratios, transitioning to absolutely unstable behavior at low momentum flux and/or density ratios, with attendant differences in shear layer vorticity evolution and rollup. These differences in stability characteristics are shown to have a significant effect on how one optimally employs external excitation to control jet penetration and spread, depending on the flow regime and specific engineering application. Yet recent unexpected observations on altered transverse jet structure under different flow conditions introduce a host of unanswered questions, primarily but not exclusively associated with the nature of molecular mixing, that make this canonical flowfield one that is of great interest for more extensive exploration.

  16. Control of jet noise

    NASA Technical Reports Server (NTRS)

    Schreck, Stefan

    1993-01-01

    This reports describes experiments conducted at the High-Speed Jet Facility at the University of Southern California on supersonic jets. The goal of the study was to develop methods for controlling the noise emitted from supersonic jets by passive and/or active means. Work by Seiner et al (1991) indicates that eddy Mach wave radiation is the dominant noise source in a heated high speed jet. Eddy Mach radiation is caused by turbulent eddies traveling at supersonic speed in the shear layer of the jet. The convection velocity of the eddies decays with increasing distance from the nozzle exit due to the mixing of the jet stream with the ambient fluid. Once the convection speed reaches subsonic velocities, eddy Mach wave radiation ceases. To control noise, a rapid decay of the convection velocity is desired. This may be accomplished by enhanced mixing in the jet. In this study, small aspect ratio rectangular jet nozzles were tested. A flapping mode was noticed in the jets. By amplifying screech components of the jets and destabilizing the jet columns with a collar device, the flapping mode was excited. The result was a rapid decay of the jet velocity. A reduction in eddy Mach radiation in rectangular supersonic jets may be achieved with this device.

  17. Jet mixer noise suppressor using acoustic feedback

    NASA Technical Reports Server (NTRS)

    Rice, Edward J. (Inventor)

    1995-01-01

    The present invention generally relates to providing an improved jet mixer noise suppressor for high speed jets that rapidly mixes high speed air flow with a lower speed air flow, and more particularly, relates to an improved jet mixer noise suppressor that uses feedback of acoustic waves produced by the interaction of shear flow instability waves with an obstacle downstream of the jet nozzle.

  18. Optimising X-point target plates

    NASA Astrophysics Data System (ADS)

    Pick, M. A.; Deksnis, E.; Dietz, K. J.; Lowry, C.; Parsons, W.; Tivey, R.

    1992-12-01

    Prior to the 1992 JET experimental campaign new X-point energy dump plates were installed at both top and bottom of the JET vessel. The active areas of the lower plates were covered with beryllium tiles whilst the upper plates were covered with carbon fibre reinforced graphite tiles. This paper describes the design and geometry of the dump plate tile assemblies and how they were modified to optimise the poer handling capability of the system and reducing the probability of producing "hot spots" leading to carbon or beryllium blooms. The design principles can be generalized to apply to other components such as limiters and divertor target plates. The new JET divertor target plates are described as an example.

  19. Dynamics of High Pressure Reacting Shear Flows

    DTIC Science & Technology

    2013-12-17

    and supercritical acoustic-jet interactions to reacting flow in a canonical coaxial shear flow configuration – Emphasis on the flame holding region...unlimited. PA#13554 11 Coaxial Jets Initial...PA#13554 12 Forced Coaxial Jets 1. Transverse Acoustic mode from chamber

  20. Measuring soil erodibility using a laboratory "mini" JET

    USDA-ARS?s Scientific Manuscript database

    Typically the erosion rate of cohesive soils is quantified using an excess shear stress equation, dependent on two major soil parameters: the critical shear stress and the erodibility coefficient. A submerged jet test (JETJet Erosion Test) is one method that has been developed for measuring the...

  1. Twin Jet

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda; Bozak, Rick

    2010-01-01

    Many subsonic and supersonic vehicles in the current fleet have multiple engines mounted near one another. Some future vehicle concepts may use innovative propulsion systems such as distributed propulsion which will result in multiple jets mounted in close proximity. Engine configurations with multiple jets have the ability to exploit jet-by-jet shielding which may significantly reduce noise. Jet-by-jet shielding is the ability of one jet to shield noise that is emitted by another jet. The sensitivity of jet-by-jet shielding to jet spacing and simulated flight stream Mach number are not well understood. The current experiment investigates the impact of jet spacing, jet operating condition, and flight stream Mach number on the noise radiated from subsonic and supersonic twin jets.

  2. Optimisation in fluoroscopy

    PubMed Central

    Axelsson, B

    2007-01-01

    Optimisation of radiation protection in fluoroscopy is important since the procedure could lead to relatively high absorbed doses both in patients and personnel resulting in acute radiation injury. Optimisation procedures include adjustment of the fluoroscopy equipment such as exposure factors as well as proper use of automatic brightness control and pulsed fluoroscopy. It is also important to gain the benefits of image processing and the higher sensitivity of flat panel detectors as compared to image intensifier-TV systems. Proper positioning of the patient with respect to detector and X-ray tube is of fundamental importance to image quality and radiation dose to the patient. Both image quality and radiation dose are also affected by the methodology used with parameters such as magnification factor, increased filtration, use of last-image-hold and the use of a grid. There is a direct relation between patient dose and the absorbed dose to the personnel since this is mostly due to scattered radiation from the patient. If the correct methodology and the correct radiation protection devices are used, the absorbed dose to the personnel could be minimised to acceptable levels even for those working with complex procedures. In order to have an organised review of all aspects of optimisation, it is recommendable to have an active quality system at the department. This system should define responsibilities and tasks for persons involved. PMID:21614280

  3. Shear Acceleration in Expanding Flows

    NASA Astrophysics Data System (ADS)

    Rieger, F. M.; Duffy, P.

    2016-12-01

    Shear flows are naturally expected to occur in astrophysical environments and potential sites of continuous non-thermal Fermi-type particle acceleration. Here we investigate the efficiency of expanding relativistic outflows to facilitate the acceleration of energetic charged particles to higher energies. To this end, the gradual shear acceleration coefficient is derived based on an analytical treatment. The results are applied to the context of the relativistic jets from active galactic nuclei. The inferred acceleration timescale is investigated for a variety of conical flow profiles (i.e., power law, Gaussian, Fermi-Dirac) and compared to the relevant radiative and non-radiative loss timescales. The results exemplify that relativistic shear flows are capable of boosting cosmic-rays to extreme energies. Efficient electron acceleration, on the other hand, requires weak magnetic fields and may thus be accompanied by a delayed onset of particle energization and affect the overall jet appearance (e.g., core, ridge line, and limb-brightening).

  4. Coherent motion in excited free shear flows

    NASA Technical Reports Server (NTRS)

    Wygnanski, Israel J.; Petersen, Robert A.

    1987-01-01

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

  5. Jet shielding of jet noise

    NASA Technical Reports Server (NTRS)

    Simonich, J. C.; Amiet, R. K.; Schlinker, R. H.

    1986-01-01

    An experimental and theoretical study was conducted to develop a validated first principle analysis for predicting the jet noise reduction achieved by shielding one jet exhaust flow with a second, closely spaced, identical jet flow. A generalized fuel jet noise analytical model was formulated in which the acoustic radiation from a source jet propagates through the velocity and temperature discontinuity of the adjacent shielding jet. Input variables to the prediction procedure include jet Mach number, spacing, temperature, diameter, and source frequency. Refraction, diffraction, and reflection effects, which control the dual jet directivity pattern, are incorporated in the theory. The analysis calculates the difference in sound pressure level between the dual jet configuration and the radiation field based on superimposing two independent jet noise directivity patterns. Jet shielding was found experimentally to reduce noise levels in the common plane of the dual jet system relative to the noise generated by two independent jets.

  6. Optimising medical elastomer performance.

    PubMed

    Woo, Lecon

    2004-04-01

    The ability of DSC to detect and quantify the degree of cure is a major tool for optimising the property and processing of elastomer components. The rapid and information-rich OIT measurements can be applied in numerous ways to monitor and develop antioxidant packages. In addition, through some less applied tests, subtle differences between ionising radiation sources for sterilisation can be quantified and put to use in an advantageous way, for example, with reduction in surface tack and maintenance of mechanical strength in a surgical glove.

  7. Perioperative Haemodynamic Optimisation.

    PubMed

    Aya, Hollmann D; Cecconi, Maurizio; Rhodes, Andrew

    2014-04-01

    During the latest years, a number of studies have confirmed the benefits of perioperative haemodynamic optimisation on surgical mortality and postoperative complication rate. This process requires the use of advanced haemodynamic monitoring with the purpose of guiding therapies to reach predefined goals. This review aim to present recent evidence on perioperative goal directed therapy (GDT), with an emphasis in some aspects that may merit further investigation. In order to maximise the benefits on outcomes, GDT must be implemented as early as possible; intravascular volume optimisation should be in accordance with the response of the preload-reserve, goals should be individualised and adequacy of the intervention must be also assessed; non-invasive or minimally invasive monitoring should be used and, finally, side effects of every therapy should be taken into account in order to avoid undesired complications. New drugs and technologies, particularly those exploring the venous side of the circulation, may improve in the future the effectiveness and facilitate the implementation of this group of therapeutic interventions.

  8. Hypersonic Induced Interactions of Plasma and Non-Plasma Jets

    DTIC Science & Technology

    2006-06-12

    optimised . A preliminary assessment of the effects of plasma actuators on jet and jet in crossflow was conducted. NOMENCLATURE C Chapman-Rubesin...highly adaptable so as to allow for efficient changeover between the use of different geometries . The model was a zero incidence flat plate with a...Final Report: FA8655-07-1-3032 / Kontis, K Figure 7: Schematic of flat plate geometry Table 1 Pressure tappings. The non-plasma air jet was

  9. Jetting tool

    SciTech Connect

    Szarka, D.D.; Schwegman, S.L.

    1991-07-09

    This patent describes an apparatus for hydraulically jetting a well tool disposed in a well, the well tool having a sliding member. It comprises positioner means for operably engaging the sliding member of the well tool; and a jetting means, connected at a rotatable connection to the positioner means so that the jetting means is rotatable relative to the positioner means and the well tool, for hydraulically jetting the well tool as the jetting means is rotated relative thereto.

  10. Subsampling for dataset optimisation

    NASA Astrophysics Data System (ADS)

    Ließ, Mareike

    2017-04-01

    Soil-landscapes have formed by the interaction of soil-forming factors and pedogenic processes. In modelling these landscapes in their pedodiversity and the underlying processes, a representative unbiased dataset is required. This concerns model input as well as output data. However, very often big datasets are available which are highly heterogeneous and were gathered for various purposes, but not to model a particular process or data space. As a first step, the overall data space and/or landscape section to be modelled needs to be identified including considerations regarding scale and resolution. Then the available dataset needs to be optimised via subsampling to well represent this n-dimensional data space. A couple of well-known sampling designs may be adapted to suit this purpose. The overall approach follows three main strategies: (1) the data space may be condensed and de-correlated by a factor analysis to facilitate the subsampling process. (2) Different methods of pattern recognition serve to structure the n-dimensional data space to be modelled into units which then form the basis for the optimisation of an existing dataset through a sensible selection of samples. Along the way, data units for which there is currently insufficient soil data available may be identified. And (3) random samples from the n-dimensional data space may be replaced by similar samples from the available dataset. While being a presupposition to develop data-driven statistical models, this approach may also help to develop universal process models and identify limitations in existing models.

  11. Deriving parameters of a fundamental detachment model for cohesive soils from flume and jet erosion tests

    USDA-ARS?s Scientific Manuscript database

    The erosion rate of cohesive soils is commonly quantified using the excess shear stress equation, dependent on two major soil parameters: the critical shear stress and the erodibility coefficient. A submerged jet test (JETJet Erosion Test) is one method that has been developed for measuring thes...

  12. Comparison with Analytical Solution: Generation and Radiation of Acoustic Waves from a 2-D Shear Layer

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.

    2000-01-01

    An acoustic source inside of a 2-D jet excites an instability wave in the shear layer resulting in sound radiating away from the shear layer. Solve the linearized Euler equations to predict the sound radiation outside of the jet. The jet static pressure is assumed to be constant. The jet flow is parallel and symmetric about the x-axis. Use a symmetry boundary condition along the x-axis.

  13. Mixing augmentation of transverse hydrogen jet by injection of micro air jets in supersonic crossflow

    NASA Astrophysics Data System (ADS)

    Anazadehsayed, A.; Barzegar Gerdroodbary, M.; Amini, Y.; Moradi, R.

    2017-08-01

    In this study, the influences of the micro air jet on the mixing of the sonic transverse hydrogen through micro-jets subjected to a supersonic crossflow are investigated. A three-dimensional numerical study has been performed to reveal the affects of micro air jet on mixing of the hydrogen jet in a Mach 4.0 crossflow with a global equivalence ratio of 0.5. Parametric studies were conducted on the various air jet conditions by using the Reynolds-averaged Navier-Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. Complex jet interactions were found in the downstream region with a variety of flow features depending upon the angle of micro air jet. These flow features were found to have subtle effects on the mixing of hydrogen jets. Results indicate a different flow structure as air jet is presented in the downstream of the fuel jet. According to the results, without air, mixing occurs at a low rate. When the air jet is presented in the downstream of fuel jet, significant increase (up to 300%) occurs in the mixing performance of the hydrogen jet at downstream. In multi fuel jets, the mixing performance of the fuel jet is increased more than 200% when the micro air jet is injected. Consequently, an enhanced mixing zone occurs downstream of the injection slots which leads to flame-holding.

  14. MOPTOP: a multi-colour optimised optical polarimeter

    NASA Astrophysics Data System (ADS)

    Jermak, Helen; Steele, Iain A.; Smith, Robert J.

    2016-08-01

    We present the design and science case for the Liverpool Telescope's fourth-generation polarimeter; MOPTOP: a Multicolour OPTimised Optical Polarimeter which is optimised for sensitivity and bi-colour observations. We introduce an optimised polarimeter which is as far as possible limited only by the photon counting efficiency of the detectors. Using a combination of CMOS cameras, a continuously rotating half-wave plate and a wire grid polarising beamsplitter, we predict we can accurately measure the polarisation of sources to 1% at 19th magnitude in 10 minutes on a 2 metre telescope. For brighter sources we anticipate much low systematics (< 0.1%) than our current polarimeter. The design also gives the ability to measure polarization and photometric variability on timescales as short as a few seconds. Overall the instrument will allow accurate measurements of the intra-nightly variability of the polarisation of sources such as gamma-ray bursts and blazars (AGN orientated with the jet pointing toward the observer), allowing the constraint of magnetic field models revealing more information about the formation, ejection and collimation of jets.

  15. Turbulent Mixing in Exponential Transverse Jets

    DTIC Science & Technology

    1990-09-30

    1989 MIT; Seminar, April 7, 1989 University of Michigan; AFOSR Contractors Meeting, June 19-21, 1989 Rocketdyne Div.; Consulting Boeing Aerospace...which entrainment of the cros-flow tentially applicable to numerous free shear flow prob- fluid into the jet relies heavily on the ring vortices lems ...8217nonsteadiness’ is brought into the prob- injection region of a free jet, for example, engulfs both lem by introducing this jet into a cross-flow as illus- the

  16. Mixing in Shear Coaxial Jets (Briefing Charts)

    DTIC Science & Technology

    2013-08-01

    currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) July 2013 2. REPORT TYPE...Distribution Unlimited Four geometric configurations studied SAR-thick LAR-thick SAR-thin LAR-thin Injector D1 D2 D3 D4 t/D1 Ao/Ai l /D1 LAR-thick 0.51 1.59...Distribution A: Approved for Public Release; Distribution Unlimited Dark-core length measurement L • First raw grayscale images were converted to

  17. Medicines optimisation: priorities and challenges.

    PubMed

    Kaufman, Gerri

    2016-03-23

    Medicines optimisation is promoted in a guideline published in 2015 by the National Institute for Health and Care Excellence. Four guiding principles underpin medicines optimisation: aim to understand the patient's experience; ensure evidence-based choice of medicines; ensure medicines use is as safe as possible; and make medicines optimisation part of routine practice. Understanding the patient experience is important to improve adherence to medication regimens. This involves communication, shared decision making and respect for patient preferences. Evidence-based choice of medicines is important for clinical and cost effectiveness. Systems and processes for the reporting of medicines-related safety incidents have to be improved if medicines use is to be as safe as possible. Ensuring safe practice in medicines use when patients are transferred between organisations, and managing the complexities of polypharmacy are imperative. A medicines use review can help to ensure that medicines optimisation forms part of routine practice.

  18. Fuzzy jets

    NASA Astrophysics Data System (ADS)

    Mackey, Lester; Nachman, Benjamin; Schwartzman, Ariel; Stansbury, Conrad

    2016-06-01

    Collimated streams of particles produced in high energy physics experiments are organized using clustering algorithms to form jets. To construct jets, the experimental collaborations based at the Large Hadron Collider (LHC) primarily use agglomerative hierarchical clustering schemes known as sequential recombination. We propose a new class of algorithms for clustering jets that use infrared and collinear safe mixture models. These new algorithms, known as fuzzy jets, are clustered using maximum likelihood techniques and can dynamically determine various properties of jets like their size. We show that the fuzzy jet size adds additional information to conventional jet tagging variables in boosted topologies. Furthermore, we study the impact of pileup and show that with some slight modifications to the algorithm, fuzzy jets can be stable up to high pileup interaction multiplicities.

  19. Fuzzy jets

    DOE PAGES

    Mackey, Lester; Nachman, Benjamin; Schwartzman, Ariel; ...

    2016-06-01

    Collimated streams of particles produced in high energy physics experiments are organized using clustering algorithms to form jets . To construct jets, the experimental collaborations based at the Large Hadron Collider (LHC) primarily use agglomerative hierarchical clustering schemes known as sequential recombination. We propose a new class of algorithms for clustering jets that use infrared and collinear safe mixture models. These new algorithms, known as fuzzy jets , are clustered using maximum likelihood techniques and can dynamically determine various properties of jets like their size. We show that the fuzzy jet size adds additional information to conventional jet tagging variablesmore » in boosted topologies. Furthermore, we study the impact of pileup and show that with some slight modifications to the algorithm, fuzzy jets can be stable up to high pileup interaction multiplicities.« less

  20. Fuzzy jets

    SciTech Connect

    Mackey, Lester; Nachman, Benjamin; Schwartzman, Ariel; Stansbury, Conrad

    2016-06-01

    Collimated streams of particles produced in high energy physics experiments are organized using clustering algorithms to form jets . To construct jets, the experimental collaborations based at the Large Hadron Collider (LHC) primarily use agglomerative hierarchical clustering schemes known as sequential recombination. We propose a new class of algorithms for clustering jets that use infrared and collinear safe mixture models. These new algorithms, known as fuzzy jets , are clustered using maximum likelihood techniques and can dynamically determine various properties of jets like their size. We show that the fuzzy jet size adds additional information to conventional jet tagging variables in boosted topologies. Furthermore, we study the impact of pileup and show that with some slight modifications to the algorithm, fuzzy jets can be stable up to high pileup interaction multiplicities.

  1. Shock structure in non-circular jets

    NASA Technical Reports Server (NTRS)

    Morris, Philip J.; Bhat, Thonse R. S.

    1989-01-01

    The shock-cell structure of supersonic jets with non-circular exit geometry is modeled using a linearized analysis. The model takes into account the finite thickness of the jet shear layer using realistic velocity and density profiles. The effects of the shear layer turbulence are included by incorporating eddy-viscosity terms. A finite-difference numerical method is used to solve the steady linearized equations of motion. A body-fitted coordinate system is used to describe the shear layer. The variation of the pressure fluctuation with downstream distance is given for circular jets and for an elliptic jet of aspect ratio 2.0. Comparisons with experimental data are made. Difficulties with the numerical technique are also discussed.

  2. Muscle injuries: optimising recovery.

    PubMed

    Järvinen, Tero A H; Järvinen, Teppo L N; Kääriäinen, Minna; Aärimaa, Ville; Vaittinen, Samuli; Kalimo, Hannu; Järvinen, Markku

    2007-04-01

    Muscle injuries are one of the most common traumas occurring in sports. Despite their clinical importance, there are only a few clinical studies on the treatment of muscle injuries. Lack of clinical studies is most probably attributable to the fact that there is not only a high heterogeneity in the severity of injuries, but also the injuries take place in different muscles, making it very demanding to carry out clinical trials. Accordingly, the current treatment principles of muscle injuries have either been derived from experimental studies or been tested empirically only. Clinically, first aid for muscle injuries follows the RICE (Rest, Ice, Compression and Elevation) principle. The objective of RICE is to stop the injury-induced bleeding into the muscle tissue and thereby minimise the extent of the injury. Clinical examination should be carried out immediately after the injury and 5-7 days after the initial trauma, at which point the severity of the injury can be assessed more reliably. At that time, a more detailed characterisation of the injury can be made using imaging diagnostic modalities (ultrasound or MRI) if desired. The treatment of injured skeletal muscle should be carried out by immediate immobilisation of the injured muscle (clinically, relative immobility/avoidance of muscle contractions). However, the duration of immobilisation should be limited to a period sufficient to produce a scar of sufficient strength to bear the forces induced by remobilisation without re-rupture and the return to activity (mobilisation) should then be started gradually within the limits of pain. Early return to activity is needed to optimise the regeneration of healing muscle and recovery of the flexibility and strength of the injured skeletal muscle to pre-injury levels. The rehabilitation programme should be built around progressive agility and trunk stabilisation exercises, as these exercises seem to yield better outcome for injured skeletal muscle than programmes based

  3. Vaccine strategies: Optimising outcomes.

    PubMed

    Hardt, Karin; Bonanni, Paolo; King, Susan; Santos, Jose Ignacio; El-Hodhod, Mostafa; Zimet, Gregory D; Preiss, Scott

    2016-12-20

    factors that encourage success, which often include strong support from government and healthcare organisations, as well as tailored, culturally-appropriate local approaches to optimise outcomes. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

  4. A Visual Study of Vortex Generator Jets

    NASA Astrophysics Data System (ADS)

    Compton, Debora A.; Stadnicki, John

    1997-11-01

    A jet which issues from a small hole in a flow surface, pitched and skewed relative to the crossflow, creates a single streamwise vortex which resembles the flow downstream of a half-delta-wing vortex generator. The term ``vortex generator jet'' (VGJ) has been used to describe such a flow. Investigators of jet-generated vortices have recognized their applicability to active control and their flexibility in terms of being activated and deactivated. We have installed a spanwise array of VGJ's in a turbulent boundary layer in the zero-pressure-gradient test section of the 12" × 36" boundary layer wind tunnel at Boston University. The Reynolds number based on jet diameter is in the range 4000 < Re < 10000. Our experimental investigations include flow visualization of a single pitched and skewed jet in crossflow, as well as wall shear stress measurements downstream of the array of jets. To capture still images of a cross-section of the jet flow, a light sheet formed by a pulsed Nd:YAG laser is used to illuminate smoke-tagged jet fluid. The wall shear stress measurements are made using an oil-film interferometry technique. Parameters varied include jet velocity and angles of jet pitch and skew.

  5. Turbulent wall jet in a coflowing stream

    NASA Technical Reports Server (NTRS)

    Campbell, J. F.

    1975-01-01

    A theoretical investigation was undertaken to develop a relatively simple model of a two-dimensional, turbulent wall jet in a coflowing stream. The incompressible jet flow was modeled by using an integral method which includes turbulent shear stress, entrainment, and heat transfer. The method solves the conservation equations for the average jet flow properties and uses the velocity profile suggested by Escudier and Nicoll to obtain detailed characteristics of the jet on a flat plate. The analytical results compare favorably with experimental data for a range of injection velocities, which demonstrates the usefulness of the theory for estimating jet growth, velocity decay, and wall skin friction. The theory, which was applied to a Coanda jet on a circular cylinder, provided estimates of suction pressures aft of the jet exit that were in close agreement with experimental values.

  6. Supersonic Jet Mixing Enhancement due to Natural and Induced Screech

    NASA Technical Reports Server (NTRS)

    Rice, E. J.; Raman, G.

    1999-01-01

    Outline of presentation are: (1) Review of experimental apparatus. (2) Effect of natural screech of jet mixing; converging nozzle, underexpanded jet and converging-diverging nozzle, design pressure.(3) Effect of induced screech on jet mixing: produced by paddles in shear layers, similar to edge tones, and converging-diverging nozzle, design pressure. (4) Effect of paddles on near-field jet noise. and (5) Concluding remarks.

  7. Noise from Supersonic Coaxial Jets. Part 3; Inverted Velocity Profile

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Morris, Philip J.

    1997-01-01

    The instability wave noise generation model is used to study the instability waves in the two shear layers of an inverted velocity profile, supersonic, coaxial jet and the noise radiated from the dominant wave. The inverted velocity profile jet has a high speed outer stream surrounding a low speed inner stream and the outer shear layer is always larger than the inner shear layer. The jet mean flows are calculated numerically. The operating conditions are chosen to exemplify the effect of the coaxial jet outer shear layer initial spreading rates. Calculations are made for the stability characteristics in the coaxial jet shear layers and the noise radiated from the instability waves for different operating conditions with the same total thrust, mass flow and exit area as a single reference jet. Results for inverted velocity profile jets indicate that relative maximum instability wave amplitudes and far field peak noise levels can be reduced from that of the reference jet by having higher spreading rates for the outer shear layer, low velocity ratios, and outer streams hotter than the inner stream.

  8. Time accurate simulations of compressible shear flows

    NASA Technical Reports Server (NTRS)

    Givi, Peyman; Steinberger, Craig J.; Vidoni, Thomas J.; Madnia, Cyrus K.

    1993-01-01

    The objectives of this research are to employ direct numerical simulation (DNS) to study the phenomenon of mixing (or lack thereof) in compressible free shear flows and to suggest new means of enhancing mixing in such flows. The shear flow configurations under investigation are those of parallel mixing layers and planar jets under both non-reacting and reacting nonpremixed conditions. During the three-years of this research program, several important issues regarding mixing and chemical reactions in compressible shear flows were investigated.

  9. Interaction between a surface quasi-geostrophic buoyancy anomaly jet and internal vortices

    NASA Astrophysics Data System (ADS)

    Reinaud, J. N.; Dritschel, D. G.; Carton, X.

    2017-08-01

    This paper addresses the dynamical coupling of the ocean's surface and the ocean's interior. In particular, we investigate the dynamics of an oceanic surface jet and its interaction with vortices at depth. The jet is induced by buoyancy (density) anomalies at the surface. We first focus on the jet alone. The linear stability indicates there are two modes of instability: the sinuous and the varicose modes. When a vortex in present below the jet, it interacts with it. The velocity field induced by the vortex perturbs the jet and triggers its destabilisation. The jet also influences the vortex by pushing it under a region of co-operative shear. Strong jets may also partially shear out the vortex. We also investigate the interaction between a surface jet and a vortex dipole in the interior. Again, strong jets may partially shear out the vortex structure. The jet also modifies the trajectory of the dipole. Dipoles travelling towards the jet at shallow incidence angles may be reflected by the jet. Vortices travelling at moderate incidence angles normally cross below the jet. This is related to the displacement of the two vortices of the dipole by the shear induced by the jet. Intense jets may also destabilise early and form streets of billows. These billows can pair with the vortices and separate the dipole.

  10. Turbulence measurements in curved wall jets

    NASA Astrophysics Data System (ADS)

    Rodman, L. C.; Wood, N. J.; Roberts, L.

    1987-01-01

    Accurate turbulence measurements taken in wall jet flows are difficult to obtain, due to high intensity turbulence and problems in achieving two-dimensionality. The problem is compounded when streamwise curvature of the flow is introduced, since the jet entrainment and turbulence levels are greatly increased over the equivalent planar values. In this experiment, two-dimensional plane and curved wall jet flows are simulated by having a jet blow axially over a cylinder. In the plane case the cylinder has constant transverse radius, and in the curved cases the cylinder has a varying transverse radius. Although the wall jet in these cases is axisymmetric, adequate 'two-dimensional' flow can be obtained as long as the ratio of the jet width to the cylinder radius is small. The annular wall jet has several advantages over wall jets issuing from finite rectangular slots. Since the slot has no ends, three-dimensional effects caused by the finite length of the slot and side wall interference are eliminated. Also, the transverse curvature of the wall allows close optical access to the surface using a Laser Doppler Velocimetry (LDV) system. Hot wire measurements and some LDV measurements are presented for plane and curved wall jet flows. An integral analysis is used to assess the effects of transverse curvature on the turbulent shear stress. The analysis and the data show that the effects of transverse curvature on both the mean flow and the shear stress are small enough for two-dimensional flow to be approximately satisfactorily.

  11. Coupling dynamic of twin supersonic jets

    NASA Astrophysics Data System (ADS)

    Kuo, Ching-Wen; Cluts, Jordan; Samimy, Mo

    2015-11-01

    In a supersonic shock-containing jet, the interaction of large-scale structures in the jet's shear layer with the shock waves generates acoustic waves. The waves propagate upstream, excite the jet initial shear layer instability, establish a feedback loop at certain conditions, and generate screech noise. The screech normally contains different modes of various strengths. Similarly, twin-jet plumes contain screech tones. If the dynamics of the two jet plumes are synchronized, the screech amplitude could be significantly amplified. There is a proposed analytical model in the literature for screech synchronization in twin rectangular jets. This model shows that with no phase difference in acoustic waves arriving at neighboring nozzle lips, twin-jet plumes feature a strong coupling with a significant level of screech tones. In this work the maximum nozzle separation distance for sustained screech synchronization and strong coupling is analytically derived. This model is used with our round twin-jet experiments and the predicted coupling level agrees well with the experimental results. Near-field microphone measurements and schlieren visualization along with the analytical model are used to investigate the coupling mechanisms of twin supersonic jets. Supported by ONR.

  12. Cosmic jets

    NASA Technical Reports Server (NTRS)

    Rees, M. J.

    1986-01-01

    The evidence that active galactic nuclei produce collimated plasma jets is summarised. The strongest radio galaxies are probably energised by relativistic plasma jets generated by spinning black holes interacting with magnetic fields attached to infalling matter. Such objects can produce e(+)-e(-) plasma, and may be relevant to the acceleration of the highest-energy cosmic ray primaries. Small-scale counterparts of the jet phenomenon within our own galaxy are briefly reviewed.

  13. Water Jetting

    NASA Technical Reports Server (NTRS)

    1985-01-01

    Hi-Tech Inc., a company which manufactures water jetting equipment, needed a high pressure rotating swivel, but found that available hardware for the system was unsatisfactory. They were assisted by Marshall, which had developed water jetting technology to clean the Space Shuttles. The result was a completely automatic water jetting system which cuts rock and granite and removes concrete. Labor costs have been reduced; dust is suppressed and production has been increased.

  14. LHCD experiments in high performance plasmas in JET

    NASA Astrophysics Data System (ADS)

    Ekedahl, A.; Baranov, Y.; Dobbing, J. A.; Fischer, B.; Goniche, M.; Gormezano, C.; Romero, J. A.; Schild, P.; Söldner, F. X.; Challis, C. D.; Sips, A. C. C.; Tubbing, B.

    1997-04-01

    Lower Hybrid Current Drive (LHCD) has been used for current profile shaping in the shear optimisation experiments in 1996/97 in JET. PLH≲3MW has been applied in the initial current ramp-up in order to control the internal inductance. An internal transport barrier with improved central electron confinement has been produced in this phase with LHCD alone. This has resulted in a peaking of the electron temperature profile and Te0 above 10keV at ne0⩽1.5×1019 m-3. The profile of the LH driven current, as determined by hard X-ray mesurements, is peaked at approximately mid-radius in these conditions. Good coupling of the LH waves has been obtained by the use of a near gas feed. This method reduces the risk of plasma-launcher interaction, since the launcher can be positioned in the shadow of the poloidal limiters. A reflection coefficient of 5% has been maintained at a plasma-launcher distance of 8 cm and PLH=5 MW has been coupled to divertor plasmas in L-mode with this method.

  15. Shear layer excitation, experiment versus theory

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.; Stahl, B.

    1984-01-01

    The acoustical excitation of shear layers is investigated. Acoustical excitation causes the so-called orderly structures in shear layers and jets. Also, the deviations in the spreading rate between different shear layer experiments are due to the same excitation mechanism. Measurements in the linear interaction region close to the edge from which the shear layer is shed are examined. Two sets of experiments (Houston 1981 and Berlin 1983/84) are discussed. The measurements were carried out with shear layers in air using hot wire anemometers and microphones. The agreement between these measurements and the theory is good. Even details of the fluctuating flow field correspond to theoretical predictions, such as the local occurrence of negative phase speeds.

  16. The flow feature of transverse hydrogen jet in presence of micro air jets in supersonic flow

    NASA Astrophysics Data System (ADS)

    Barzegar Gerdroodbary, M.; Amini, Younes; Ganji, D. D.; Takam, ​M. Rahimi

    2017-03-01

    Scramjet is found to be the efficient method for the space shuttle. In this paper, numerical simulation is performed to investigate the fundamental flow physics of the interaction between an array of fuel jets and multi air jets in a supersonic transverse flow. Hydrogen as a fuel is released with a global equivalence ratio of 0.5 in presence of micro air jets on a flat plate into a Mach 4 crossflow. The fuel and air are injected through streamwise-aligned flush circular portholes. The hydrogen is injected through 4 holes with 7dj space when the air is injected in the interval of the hydrogen jets. The numerical simulation is performed by using the Reynolds-averaged Navier-Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. Both the number of air jets and jet-to-freestream total pressure ratio are varied in a parametric study. The interaction of the fuel and air jet in the supersonic flow present extremely complex feature of fuel and air jet. The results present various flow features depending upon the number and mass flow rate of micro air jets. These flow features were found to have significant effects on the penetration of hydrogen jets. A variation of the number of air jets, along with the jet-to-freestream total pressure ratio, induced a variety of flow structure in the downstream of the fuel jets.

  17. Plasma confinement at JET

    NASA Astrophysics Data System (ADS)

    Nunes, I.; JET Contributors

    2016-01-01

    Operation with a Be/W wall at JET (JET-ILW) has an impact on scenario development and energy confinement with respect to the carbon wall (JET-C). The main differences observed were (1) strong accumulation of W in the plasma core and (2) the need to mitigate the divertor target temperature to avoid W sputtering by Be and other low Z impurities and (3) a decrease of plasma energy confinement. A major difference is observed on the pedestal pressure, namely a reduction of the pedestal temperature which, due to profile stiffness the plasma core temperature is also reduced leading to a degradation of the global confinement. This effect is more pronounced in low β N scenarios. At high β N, the impact of the wall on the plasma energy confinement is mitigated by the weaker plasma energy degradation with power relative to the IPB98(y, 2) scaling calculated empirically for a CFC first wall. The smaller tolerable impurity concentration for tungsten (<10-5) compared to that of carbon requires the use of electron heating methods to prevent W accumulation in the plasma core region as well as gas puffing to avoid W entering the plasma core by ELM flushing and reduction of the W source by decreasing the target temperature. W source and the target temperature can also be controlled by impurity seeding. Nitrogen and Neon have been used and with both gases the reduction of the W source and the target temperature is observed. Whilst more experiments with Neon are necessary to assess its impact on energy confinement, a partial increase of plasma energy confinement is observed with Nitrogen, through the increase of edge temperature. The challenge for scenario development at JET is to extend the pulse length curtailed by its transient behavior (W accumulation or MHD), but more importantly by the divertor target temperature limits. Re-optimisation of the scenarios to mitigate the effect of the change of wall materials maintaining high global energy confinement similar to JET-C is

  18. Optimisation of solar synoptic observations

    NASA Astrophysics Data System (ADS)

    Klvaña, Miroslav; Sobotka, Michal; Švanda, Michal

    2012-09-01

    The development of instrumental and computer technologies is connected with steadily increasing needs for archiving of large data volumes. The current trend to meet this requirement includes the data compression and growth of storage capacities. This approach, however, has technical and practical limits. A further reduction of the archived data volume can be achieved by means of an optimisation of the archiving that consists in data selection without losing the useful information. We describe a method of optimised archiving of solar images, based on the selection of images that contain a new information. The new information content is evaluated by means of the analysis of changes detected in the images. We present characteristics of different kinds of image changes and divide them into fictitious changes with a disturbing effect and real changes that provide a new information. In block diagrams describing the selection and archiving, we demonstrate the influence of clouds, the recording of images during an active event on the Sun, including a period before the event onset, and the archiving of long-term history of solar activity. The described optimisation technique is not suitable for helioseismology, because it does not conserve the uniform time step in the archived sequence and removes the information about solar oscillations. In case of long-term synoptic observations, the optimised archiving can save a large amount of storage capacities. The actual capacity saving will depend on the setting of the change-detection sensitivity and on the capability to exclude the fictitious changes.

  19. Metallurgical examination of recovered copper jet particles

    SciTech Connect

    Lassila, D.H.; Nikkel, D.J. Jr.; Kershaw, R.P.; Walters, W.P.

    1995-11-30

    A shaped charge (81 mm, 42{degrees}, OFHC copper cone) was fired into a ``soft` recovery bunker to allow metallurgical examination of recovered jet particles and the slug. The initial weight of the copper liner was 245 gm, of which 184 gm was recovered. The number of jet particles recovered was 37 (approximately 63% of the particles formed by the charge). Extensive metallurgical analyses were performed on the recovered slug and jet particles. The microstructural features associated with voids, e.g. dendritic grain growth, clearly indicate that the regions in the vicinity of the centerline of the slug and jet particles were melted. In this work we present calculations of jet temperature as a function of constitutive behavior. In order to predict melt in the center region of the jet we find it necessary to scale flow stress with a pressure dependent shear modulus.

  20. Minimum cut and shear bands

    NASA Astrophysics Data System (ADS)

    Tordesillas, Antoinette; Cramer, Andrew; Walker, David M.

    2013-06-01

    We explore the efficacy of network optimisation theory for minimum cut to quantify the evolution of granular fabric and its functionality as a transmission medium in deforming dense granular media. Our focus here is on force transmission in a sheared assembly of polydisperse particles, in a biaxial compression test under constant confining pressure. The granular fabric is examined with respect to the material's force-bearing contact network over that regime when the material has reached its residual strength, and is deforming under a near constant volume in the presence of a fully developed shear band. The structural evolution of the fabric is quantitatively characterized using a representative weighted-directed network that is similarly evolving as the sample deforms. The edges or links, representing the interparticle contacts, are each weighted by the capacity of the contact to transmit force: a scalar that depends solely on the relative motion of the contacting grains. In the large strain failure regime, the minimum cut which represents the bottleneck in force transmission is found to lie in the persistent shear band. This study paves the way for the future analysis of flows and force transmission through an evolving contact network and, in turn, the characterisation of the relationship between the material's contact topology and its capacity to transmit forces through its contact network.

  1. Streamline curvature in supersonic shear layers

    NASA Technical Reports Server (NTRS)

    Kibens, V.

    1992-01-01

    Results of an experimental investigation in which a curved shear layer was generated between supersonic flow from a rectangular converging/diverging nozzle and the freestream in a series of open channels with varying radii of curvature are reported. The shear layers exhibit unsteady large-scale activity at supersonic pressure ratios, indicating increased mixing efficiency. This effect contrasts with supersonic flow in a straight channel, for which no large-scale vortical structure development occurs. Curvature must exceed a minimum level before it begins to affect the dynamics of the supersonic shear layer appreciably. The curved channel flows are compared with reference flows consisting of a free jet, a straight channel, and wall jets without sidewalls on a flat and a curved plate.

  2. Streamline curvature in supersonic shear layers

    NASA Technical Reports Server (NTRS)

    Kibens, V.

    1992-01-01

    Results of an experimental investigation in which a curved shear layer was generated between supersonic flow from a rectangular converging/diverging nozzle and the freestream in a series of open channels with varying radii of curvature are reported. The shear layers exhibit unsteady large-scale activity at supersonic pressure ratios, indicating increased mixing efficiency. This effect contrasts with supersonic flow in a straight channel, for which no large-scale vortical structure development occurs. Curvature must exceed a minimum level before it begins to affect the dynamics of the supersonic shear layer appreciably. The curved channel flows are compared with reference flows consisting of a free jet, a straight channel, and wall jets without sidewalls on a flat and a curved plate.

  3. Bouncing Jets

    NASA Astrophysics Data System (ADS)

    Wadhwa, Navish; Vlachos, Pavlos; Jung, Sunghwan

    2011-11-01

    Contrary to common intuition, free jets of fluid can ``bounce'' off each other on collision in mid-air, through the effect of a lubricating air film that separates the jets. We have developed a simple experimental setup to stably demonstrate and study the non-coalescence of jets on collision. We present the results of an experimental investigation of oblique collision between two silicone oil jets, supported by a simple analytical explanation. Our focus is on elucidating the role of various physical forces at play such as viscous stresses, capillary force and inertia. A parametric study conducted by varying the nozzle diameter, jet velocity, angle of inclination and fluid viscosity reveals the scaling laws for the quantities involved such as contact time. We observed a transition from bouncing to coalescence with an increase in jet velocity and inclination angle. We propose that a balance between the contact time of jets and the time required for drainage of the trapped air film can provide a criterion for transition from non-coalescence to coalescence.

  4. Bifurcating Jets at High Reynolds Numbers

    DTIC Science & Technology

    1988-12-07

    its natural state to some desired state. Due to the Kelvin- Helmholtz instability, the shear layer of a jet naturally rolls up into distinct vortex... Hermann 1982, Ho & Huerre 1984, Gaster et al. 1985, Samet & Petersen 1987, and Monkewitz 1988). These features include amplification of disturbances...downstream from the jet exit (Michalke & Hermann 1982). The velocity ratio of a mixing layer is typically defined as (U1 - U2 )/(U 1 + U2), where U1 and U2

  5. Measurement of surface shear stress vector distribution using shear-sensitive liquid crystal coatings

    NASA Astrophysics Data System (ADS)

    Zhao, Ji-Song; Scholz, Peter; Gu, Liang-Xian

    2012-10-01

    The global wall shear stress measurement technique using shear-sensitive liquid crystal (SSLC) is extended to wind tunnel measurements. Simple and common everyday equipment is used in the measurement; in particular a tungsten-halogen light bulb provides illumination and a saturation of SSLC coating color change with time is found. Spatial wall shear stress distributions of several typical flows are obtained using this technique, including wall-jet flow, vortex flow generated by a delta wing and junction flow behind a thin cylinder, although the magnitudes are not fully calibrated. The results demonstrate that SSLC technique can be extended to wind tunnel measurements with no complicated facilities used.

  6. Supersonic Jet Noise Reductions Predicted With Increased Jet Spreading Rate

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Morris, Philip J.

    1998-01-01

    In this paper, predictions are made of noise radiation from single, supersonic, axisymmetric jets. We examine the effects of changes in operating conditions and the effects of simulated enhanced mixing that would increase the spreading rate of jet shear layer on radiated noise levels. The radiated noise in the downstream direction is dominated by mixing noise and, at higher speeds, it is well described by the instability wave noise radiation model. Further analysis with the model shows a relationship between changes in spreading rate due to enhanced mixing and changes in the far field radiated peak noise levels. The calculations predict that enhanced jet spreading results in a reduction of the radiated peak noise level.

  7. Supersonic jet noise reductions predicted with increased jet spreading rate

    NASA Astrophysics Data System (ADS)

    Dahl, Milo D.; Morris, Philip J.

    1995-03-01

    In this paper, predictions are made of noise radiation from single, supersonic, axisymmetric jets. We examine the effects of changes in operating conditions and the effects of simulated enhanced mixing that would increase the spreading rate of the jet shear layer on radiated noise levels. The radiated noise in the downstream direction is dominated by mixing noise and it is well described by the instability wave noise radiation analysis. A numerical prediction scheme is used for the mean flow providing an efficient method to obtain the mean flow development for various operating conditions and to simulate the enhanced mixing. Using far field radiated noise measurements as a reference, the calculations predict that enhanced jet spreading results in a reduction of radiated noise.

  8. Supersonic Jet Noise Reductions Predicted with Increased Jet Spreading Rate

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Morris, Philip J.

    1995-01-01

    In this paper, predictions are made of noise radiation from single, supersonic, axisymmetric jets. We examine the effects of changes in operating conditions and the effects of simulated enhanced mixing that would increase the spreading rate of the jet shear layer on radiated noise levels. The radiated noise in the downstream direction is dominated by mixing noise and it is well described by the instability wave noise radiation analysis. A numerical prediction scheme is used for the mean flow providing an efficient method to obtain the mean flow development for various operating conditions and to simulate the enhanced mixing. Using far field radiated noise measurements as a reference, the calculations predict that enhanced jet spreading results in a reduction of radiated noise.

  9. Site-scale variability of streambank fluvial erodibility parameters as measured with a jet erosion test

    USDA-ARS?s Scientific Manuscript database

    The erosion rate of cohesive streambanks is typically modeled using the excess shear stress equation, dependent on two erodibility parameters: critical shear stress and erodibility coefficient. The Jet Erosion Test (JET) has become the most common method for estimating these erodibility parameters ...

  10. Coronal Jet Collimation by Nonlinear Induced Flows

    NASA Astrophysics Data System (ADS)

    Vasheghani Farahani, S.; Hejazi, S. M.

    2017-08-01

    Our objective is to study the collimation of solar jets by nonlinear forces corresponding to torsional Alfvén waves together with external forces. We consider a straight, initially non-rotating, untwisted magnetic cylinder embedded in a plasma with a straight magnetic field, where a shear between the internal and external flows exists. By implementing magnetohydrodynamic theory and taking into account the second-order thin flux tube approximation, the balance between the internal nonlinear forces is visualized. The nonlinear differential equation containing the ponderomotive, magnetic tension, and centrifugal forces in the presence of the shear flow is obtained. The solution presents the scale of influence of the propagating torsional Alfvén wave on compressive perturbations. Explicit expressions for the compressive perturbations caused by the forces connected to the torsional Alfvén wave show that, in the presence of a shear flow, the magnetic tension and centrifugal forces do not cancel each other’s effects as they did in its absence. This shear flow plays in favor of the magnetic tension force, resulting in a more efficient collimation. Regarding the ponderomotive force, the shear flow has no effect. The phase relations highlight the interplay of the shear flow and the plasma-β. As the shear flow and plasma-β increase, compressive perturbation amplitudes emerge. We conclude that the jet collimation due to the torsional Alfvén wave highly depends on the location of the jet. The shear flow tightens the collimation as the jet elevates up to the solar corona.

  11. TEM turbulence optimisation in stellarators

    NASA Astrophysics Data System (ADS)

    Proll, J. H. E.; Mynick, H. E.; Xanthopoulos, P.; Lazerson, S. A.; Faber, B. J.

    2016-01-01

    With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has been achieved via shaping of the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence is addressed in the present paper. Recent analytical and numerical findings suggest TEMs are stabilised when a large fraction of trapped particles experiences favourable bounce-averaged curvature. This is the case for example in Wendelstein 7-X (Beidler et al 1990 Fusion Technol. 17 148) and other Helias-type stellarators. Using this knowledge, a proxy function was designed to estimate the TEM dynamics, allowing optimal configurations for TEM stability to be determined with the STELLOPT (Spong et al 2001 Nucl. Fusion 41 711) code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stellarator experiment HSX (Anderson et al 1995 Fusion Technol. 27 273) is presented for which a reduction of the linear growth rates is achieved over a broad range of the operational parameter space. As an important consequence of this property, the turbulent heat flux levels are reduced compared with the initial configuration.

  12. Blowout Jets: Hinode X-Ray Jets that Don't Fit the Standard Model

    NASA Technical Reports Server (NTRS)

    Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.; Falconer, David A.

    2010-01-01

    Nearly half of all H-alpha macrospicules in polar coronal holes appear to be miniature filament eruptions. This suggests that there is a large class of X-ray jets in which the jet-base magnetic arcade undergoes a blowout eruption as in a CME, instead of remaining static as in most solar X-ray jets, the standard jets that fit the model advocated by Shibata. Along with a cartoon depicting the standard model, we present a cartoon depicting the signatures expected of blowout jets in coronal X-ray images. From Hinode/XRT movies and STEREO/EUVI snapshots in polar coronal holes, we present examples of (1) X-ray jets that fit the standard model, and (2) X-ray jets that do not fit the standard model but do have features appropriate for blowout jets. These features are (1) a flare arcade inside the jet-base arcade in addition to the small flare arcade (bright point) outside that standard jets have, (2) a filament of cool (T is approximately 80,000K) plasma that erupts from the core of the jetbase arcade, and (3) an extra jet strand that should not be made by the reconnection for standard jets but could be made by reconnection between the ambient unipolar open field and the opposite-polarity leg of the filament-carrying flux-rope core field of the erupting jet-base arcade. We therefore infer that these non-standard jets are blowout jets, jets made by miniature versions of the sheared-core-arcade eruptions that make CMEs

  13. JET helps prepare for ITER operation

    NASA Astrophysics Data System (ADS)

    Watkins, Michael

    2005-10-01

    The main focus of the JET programme (2006-10) in preparation of ITER operation is a new ITER-like ICRH antenna (total RF power increased to ˜15MW), a new ITER-like first wall (beryllium in the main chamber, tungsten in the divertor, and possibly CFC at the strike points), upgraded NB power (to 35MW/20s or 17.5MW/10s), and an improved diagnostic and control capability. Mass flows for ITER Scenarios with the ITER-like first wall will be optimised, particularly to minimise in-vessel tritium inventory, since this must be controlled strictly in ITER and has been shown on JET with a carbon first wall to depend sensitively on plasma conditions. Higher power will allow confinement scalings to be resolved for normalised parameters closer to ITER (beta dependence of ELMy H-modes, confinement of improved H-modes at low ρ*) and offers the prospect of high beta operation at high current and density, and new fully non-inductive, high performance, ITB discharges sustained to long pulse by real time current and pressure profile control, particularly in bootstrap current dominated regimes. Together, the first wall and increased heating power place strict constraints on the optimisation of ITER scenarios for long pulse operation with low melt damage. Large ELMs (in excess of 1MJ; marginally accessible on JET at present) and disruptions could cause melt severe damage which must be studied and controlled. The testing and optimisation of techniques for ELM mitigation (impurity seeding, demonstrated on JET; use of a new high frequency pellet injector (10-60Hz) to prevent large ELMs, demonstrated on ASDEX Upgrade) and disruption mitigation (fast gas injection from a new disruption mitigation valve, demonstrated on DIII-D) will be even more relevant under the ITER-like edge plasma conditions accessible with the increased power. Acknowledgement : Contributors to EFDA-JET Workprogramme

  14. Jet flow in steadily swimming adult squid.

    PubMed

    Anderson, Erik J; Grosenbaugh, Mark A

    2005-03-01

    Although various hydrodynamic models have been used in past analyses of squid jet propulsion, no previous investigations have definitively determined the fluid structure of the jets of steadily swimming squid. In addition, few accurate measurements of jet velocity and other jet parameters in squid have been reported. We used digital particle imaging velocimetry (DPIV) to visualize the jet flow of adult long-finned squid Loligo pealei (mantle length, L(m)=27.1+/-3.0 cm, mean +/-S.D.) swimming in a flume over a wide range of speeds (10.1-59.3 cm s(-1), i.e. 0.33-2.06 L(m) s(-1)). Qualitatively, squid jets were periodic, steady, and prolonged emissions of fluid that exhibited an elongated core of high speed flow. The development of a leading vortex ring common to jets emitted from pipes into still water often appeared to be diminished and delayed. We were able to mimic this effect in jets produced by a piston and pipe arrangement aligned with a uniform background flow. As in continuous jets, squid jets showed evidence of the growth of instability waves in the jet shear layer followed by the breakup of the jet into packets of vorticity of varying degrees of coherence. These ranged from apparent chains of short-lived vortex rings to turbulent plumes. There was some evidence of the complete roll-up of a handful of shorter jets into single vortex rings, but steady propulsion by individual vortex ring puffs was never observed. Quantitatively, the length of the jet structure in the visualized field of view, L(j), was observed to be 7.2-25.6 cm, and jet plug lengths, L, were estimated to be 4.4-49.4 cm using average jet velocity and jet period. These lengths and an average jet orifice diameter, D, of 0.8 cm were used to calculate the ratios L(j)/D and L/D, which ranged from 9.0 to 32.0 and 5.5 to 61.8, respectively. Jets emitted from pipes in the presence of a background flow suggested that the ratio between the background flow velocity and the jet velocity was more

  15. Business Jet

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The Citation Jet, developed by Cessna Aircraft Company, Wichita, KS, is the first business jet to employ Langley Research Center's natural laminar flow (NLF) technology. NLF reduces drag and therefore saves fuel by using only the shape of the wing to keep the airflow smooth, or laminar. This reduces friction between the air and wing, and therefore, reduces drag. NASA's Central Industrial Applications Center, Rural Enterprises, Inc., Durant, OK, its Kansas affiliate, and Wichita State University assisted in the technology transfer.

  16. Emerging jets

    NASA Astrophysics Data System (ADS)

    Schwaller, Pedro; Stolarski, Daniel; Weiler, Andreas

    2015-05-01

    In this work, we propose a novel search strategy for new physics at the LHC that utilizes calorimeter jets that (i) are composed dominantly of displaced tracks and (ii) have many different vertices within the jet cone. Such emerging jet signatures are smoking guns for models with a composite dark sector where a parton shower in the dark sector is followed by displaced decays of dark pions back to SM jets. No current LHC searches are sensitive to this type of phenomenology. We perform a detailed simulation for a benchmark signal with two regular and two emerging jets, and present and implement strategies to suppress QCD backgrounds by up to six orders of magnitude. At the 14 TeV LHC, this signature can be probed with mediator masses as large as 1.5 TeV for a range of dark pion lifetimes, and the reach is increased further at the high-luminosity LHC. The emerging jet search is also sensitive to a broad class of long-lived phenomena, and we show this for a supersymmetric model with R-parity violation. Possibilities for discovery at LHCb are also discussed.

  17. Linear properties of eddies in a Jovian troposphere forced by deep jets

    NASA Astrophysics Data System (ADS)

    Orsolini, Y.; Leovy, C. B.

    1989-11-01

    A linear quasi-geostrophic beta-plane model is used to study large-scale instabilities of the Jovian upper troposphere forced from below by zonal jets. The jets are presumed to be barotropically stable in the isentropic deep interior, but barotropically unstable in the statically stable upper troposphere. The effect on this barotropic instability of weak vertical shear causing the jets to decay with height is examined. It is found that eastward jets are stabilized by weaker shear than westward jets, the most unstable eddies are strongly confined by the shear, and eddy fluxes contribute to vertical decay of the jets. The lower residual mean meridional circulation cells exhibit rising motion in regions of anticyclonic shear, but these are overlain by reverse cells.

  18. Development of the mean velocity distribution in rectangular jets

    NASA Technical Reports Server (NTRS)

    Morrison, G. L.; Swan, D. H.; Deotte, R. E., Jr.

    1992-01-01

    The mean flowfield of 1 x 2 and 1 x 4 aspect ratio rectangular jets has been measured using a laser Doppler anemometer system. The development of the downstream velocity distribution is analyzed with respect to centerline velocity decay, shear layer growth, axis switching, and velocity profile development. Comparisons are made with axisymmetric, planar, and other rectangular jets.

  19. Robust optimisation of railway crossing geometry

    NASA Astrophysics Data System (ADS)

    Wan, Chang; Markine, Valeri; Dollevoet, Rolf

    2016-05-01

    This paper presents a methodology for improving the crossing (frog) geometry through the robust optimisation approach, wherein the variability of the design parameters within a prescribed tolerance is included in the optimisation problem. Here, the crossing geometry is defined by parameterising the B-spline represented cross-sectional shape and the longitudinal height profile of the nose rail. The dynamic performance of the crossing is evaluated considering the variation of wheel profiles and track alignment. A multipoint approximation method (MAM) is applied in solving the optimisation problem of minimising the contact pressure during the wheel-rail contact and constraining the location of wheel transition at the crossing. To clarify the difference between the robust optimisation and the normal deterministic optimisation approaches, the optimisation problems are solved in both approaches. The results show that the deterministic optimum fails under slight change of the design variables; the robust optimum, however, has improved and robust performance.

  20. Periodic Excitation for Jet Vectoring and Enhanced Spreading

    NASA Technical Reports Server (NTRS)

    Pack, LaTunia G.; Seifert, Avi

    1999-01-01

    The effects of periodic excitation on the evolution of a turbulent jet were studied experimentally. A short, wide-angle diffuser was attached to the jet exit and excitation was introduced at the junction between the jet exit and the diffuser inlet. The introduction of high amplitude periodic excitation at the jet exit enhances the mixing and promotes attachment of the jet shear-layer to the diffuser wall. Vectoring is achieved by applying the excitation over a fraction of the circumference of the circular jet, enhancing its spreading rate on the excited side and its tendency to reattach to that side. Static deflection studies demonstrate that the presence of the wide-angle diffuser increases the effectiveness of the added periodic momentum due to a favorable interaction between the excitation, the jet shear-layer and the diffuser wall. This point was further demonstrated by the evolution of a wave packet that was excited in the jet shear-layer. Strong amplification of the wave packet was measured with a diffuser attached to the jet exit. The turbulent jet responds quickly (10-20 msec) to step changes in the level of the excitation input. The response scales with the jet exit velocity and is independent of the Reynolds number. Jet deflection angles were found to be highly sensitive to the relative direction between the excitation and the jet flow and less sensitive to the excitation frequency. The higher jet deflection angles were obtained for a diffuser length of about two diameters and for diffusers with half-angles greater than 15 degrees.

  1. Propagation of sound through a sheared flow

    NASA Technical Reports Server (NTRS)

    Woolley, J. P.; Smith, C. A.; Karamcheti, K.

    1978-01-01

    Sound generated in a moving fluid must propagate through a shear layer in order to be measured by a fixed instrument. These propagation effects were evaluated for noise sources typically associated with single and co-flowing subsonic jets and for subcritical flow over airfoils in such jets. The techniques for describing acoustic propagation fall into two categories: geometric acoustics and wave acoustics. Geometric acoustics is most convenient and accurate for high frequency sound. In the frequency range of interest to the present study (greater than 150 Hz), the geometric acoustics approach was determined to be most useful and practical.

  2. Influence of jet-cooking corn bran on its antioxidant activities, phenolic contents and viscoelastic properties

    USDA-ARS?s Scientific Manuscript database

    Corn bran was subjected to high-shear and jet-cooking with or without alkaline treatment. The highest antioxidant activity was found in the soluble solids from jet-cooked corn bran without alkaline treatment. Jet-cooking under alkaline conditions resulted in a soluble fraction having the highest phe...

  3. Noise from Supersonic Coaxial Jets. Part 2; Normal Velocity Profile

    NASA Technical Reports Server (NTRS)

    Dahl, M. D.; Morris, P. J.

    1997-01-01

    Instability waves have been established as noise generators in supersonic jets. Recent analysis of these slowly diverging jets has shown that these instability waves radiate noise to the far field when the waves have components with phase velocities that are supersonic relative to the ambient speed of sound. This instability wave noise generation model has been applied to supersonic jets with a single shear layer and is now applied to supersonic coaxial jets with two initial shear layers. In this paper the case of coaxial jets with normal velocity profiles is considered, where the inner jet stream velocity is higher than the outer jet stream velocity. To provide mean flow profiles at all axial locations, a numerical scheme is used to calculate the mean flow properties. Calculations are made for the stability characteristics in the coaxial jet shear layers and the noise radiated from the instability waves for different operating conditions with the same total thrust, mass flow and exit area as a single reference jet. The effects of changes in the velocity ratio, the density ratio and the area ratio are each considered independently.

  4. NASA Jet Noise Research

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda

    2016-01-01

    The presentation highlights NASA's jet noise research for 2016. Jet-noise modeling efforts, jet-surface interactions results, acoustic characteristics of multi-stream jets, and N+2 Supersonic Aircraft system studies are presented.

  5. [Jet lag].

    PubMed

    Lagarde, D; Doireau, P

    1997-01-01

    Desynchronization of circadian rhythmicity resulting from rapid travel through at least four time zones leads to symptoms known in everyday English as jet-lag. The most detrimental effect of jet-lag is fatigue with poor alertness and psychomotor performance. Severity is subject to individual variation in susceptibility (morning/evening typology, age,...) and environmental factors (direction of travel, number of time zones crossed, psychosocial environment...). Many measures used to prevent or reduce jet lag are inappropriate or ineffective and some may even be dangerous, such as use of melatonin. One of the most reliable preventive techniques consists of reinforcing social synchronizers by maintaining exposure to sunlight and social activity. Only two drugs currently available on the market can be recommended, i.e. non-benzodiazepinic hypnotics which induce high quality sleep to allow quick recovery and a new time-release caffeine agent which has been shown to prolong psychomotor performance.

  6. Supersonic Coaxial Jets: Noise Predictions and Measurements

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Papamoschou, Dimitri; Hixon, Ray

    1998-01-01

    The noise from perfectly expanded coaxial jets was measured in an anechoic chamber for different operating conditions with the same total thrust, mass flow, and exit area. The shape of the measured noise spectrum at different angles to the jet axis was found to agree with spectral shapes for single, axisymmetric jets. Based on these spectra, the sound was characterized as being generated by large turbulent structures or fine-scale turbulence. Modeling the large scale structures as instability waves, a stability analysis was conducted for the coaxial jets to identify the growing and decaying instability waves in each shear layer and predict their noise radiation pattern outside the jet. When compared to measured directivity, the analysis identified the region downstream of the outer potential core, where the two shear layers were merging, as the source of the peak radiated noise where instability waves, with their origin in the inner shear layer, reach their maximum amplitude. Numerical computations were also performed using a linearized Euler equation solver. Those results were compared to both the results from the instability wave analysis and to measured data.

  7. Optimising resource management in neurorehabilitation.

    PubMed

    Wood, Richard M; Griffiths, Jeff D; Williams, Janet E; Brouwers, Jakko

    2014-01-01

    To date, little research has been published regarding the effective and efficient management of resources (beds and staff) in neurorehabilitation, despite being an expensive service in limited supply. To demonstrate how mathematical modelling can be used to optimise service delivery, by way of a case study at a major 21 bed neurorehabilitation unit in the UK. An automated computer program for assigning weekly treatment sessions is developed. Queue modelling is used to construct a mathematical model of the hospital in terms of referral submissions to a waiting list, admission and treatment, and ultimately discharge. This is used to analyse the impact of hypothetical strategic decisions on a variety of performance measures and costs. The project culminates in a hybridised model of these two approaches, since a relationship is found between the number of therapy hours received each week (scheduling output) and length of stay (queuing model input). The introduction of the treatment scheduling program has substantially improved timetable quality (meaning a better and fairer service to patients) and has reduced employee time expended in its creation by approximately six hours each week (freeing up time for clinical work). The queuing model has been used to assess the effect of potential strategies, such as increasing the number of beds or employing more therapists. The use of mathematical modelling has not only optimised resources in the short term, but has allowed the optimality of longer term strategic decisions to be assessed.

  8. The free jet as a simulator of forward velocity effects on jet noise

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Tester, B. J.; Tanna, H. K.

    1978-01-01

    A thorough theoretical and experimental study of the effects of the free-jet shear layer on the transmission of sound from a model jet placed within the free jet to the far-field receiver located outside the free-jet flow was conducted. The validity and accuracy of the free-jet flight simulation technique for forward velocity effects on jet noise was evaluated. Transformation charts and a systematic computational procedure for converting measurements from a free-jet simulation to the corresponding results from a wind-tunnel simulation, and, finally, to the flight case were provided. The effects of simulated forward flight on jet mixing noise, internal noise and shock-associated noise from model-scale unheated and heated jets were established experimentally in a free-jet facility. It was illustrated that the existing anomalies between full-scale flight data and model-scale flight simulation data projected to the flight case, could well be due to the contamination of flight data by engine internal noise.

  9. An integral turbulent kinetic energy analysis of free shear flows

    NASA Technical Reports Server (NTRS)

    Peters, C. E.; Phares, W. J.

    1973-01-01

    Mixing of coaxial streams is analyzed by application of integral techniques. An integrated turbulent kinetic energy (TKE) equation is solved simultaneously with the integral equations for the mean flow. Normalized TKE profile shapes are obtained from incompressible jet and shear layer experiments and are assumed to be applicable to all free turbulent flows. The shear stress at the midpoint of the mixing zone is assumed to be directly proportional to the local TKE, and dissipation is treated with a generalization of the model developed for isotropic turbulence. Although the analysis was developed for ducted flows, constant-pressure flows were approximated with the duct much larger than the jet. The axisymmetric flows under consideration were predicted with reasonable accuracy. Fairly good results were also obtained for the fully developed two-dimensional shear layers, which were computed as thin layers at the boundary of a large circular jet.

  10. Design Optimisation of Coronary Artery Stent Systems.

    PubMed

    Bressloff, Neil W; Ragkousis, Giorgos; Curzen, Nick

    2016-02-01

    In recent years, advances in computing power and computational methods have made it possible to perform detailed simulations of the coronary artery stenting procedure and of related virtual tests of performance (including fatigue resistance, corrosion and haemodynamic disturbance). Simultaneously, there has been a growth in systematic computational optimisation studies, largely exploiting the suitability of surrogate modelling methods to time-consuming simulations. To date, systematic optimisation has focussed on stent shape optimisation and has re-affirmed the complexity of the multi-disciplinary, multi-objective problem at hand. Also, surrogate modelling has predominantly involved the method of Kriging. Interestingly, though, optimisation tools, particularly those associated with Kriging, haven't been used as efficiently as they could have been. This has especially been the case with the way that Kriging predictor functions have been updated during the search for optimal designs. Nonetheless, the potential for future, carefully posed, optimisation strategies has been suitably demonstrated, as described in this review.

  11. Refinement of Catalyst hypotheses using simplex optimisation

    NASA Astrophysics Data System (ADS)

    Norinder, Ulf

    2000-08-01

    The program HypoOpt in combination with the MSI program citest has been used to optimise and expand 3D QSAR Catalyst hypotheses using simplex optimisation coupled with cross-validation. Three data sets related to angiotensin converting enzyme inhibition, squalene epoxidase inhibition and HIV protease inhibition were used to investigate the outcome of hypothesis optimisation. Simplex optimisation using leave-one-out cross-validation during the hypothesis refinement resulted in improved models with respect to predictivity of an external test set. Furthermore, the utilisation of the geometry of the active site for the HIV protease inhibitors, represented by Catalyst `excluded volume' features, resulted in an optimised hypothesis with improved predictivity compared with the corresponding hypothesis derived without receptor information.

  12. Evolutionary programming for neutron instrument optimisation

    NASA Astrophysics Data System (ADS)

    Bentley, Phillip M.; Pappas, Catherine; Habicht, Klaus; Lelièvre-Berna, Eddy

    2006-11-01

    Virtual instruments based on Monte-Carlo techniques are now integral part of novel instrumentation development and the existing codes (McSTAS and Vitess) are extensively used to define and optimise novel instrumental concepts. Neutron spectrometers, however, involve a large number of parameters and their optimisation is often a complex and tedious procedure. Artificial intelligence algorithms are proving increasingly useful in such situations. Here, we present an automatic, reliable and scalable numerical optimisation concept based on the canonical genetic algorithm (GA). The algorithm was used to optimise the 3D magnetic field profile of the NSE spectrometer SPAN, at the HMI. We discuss the potential of the GA which combined with the existing Monte-Carlo codes (Vitess, McSTAS, etc.) leads to a very powerful tool for automated global optimisation of a general neutron scattering instrument, avoiding local optimum configurations.

  13. Enhancing shear thickening

    NASA Astrophysics Data System (ADS)

    Madraki, Yasaman; Hormozi, Sarah; Ovarlez, Guillaume; Guazzelli, Élisabeth; Pouliquen, Olivier

    2017-03-01

    A cornstarch suspension is the quintessential particulate system that exhibits shear thickening. By adding large non-Brownian spheres to a cornstarch suspension, we show that shear thickening can be significantly enhanced. More precisely, the shear-thickening transition is found to be increasingly shifted to lower critical shear rates. This influence of the large particles on the discontinuous shear-thickening transition is shown to be more dramatic than that on the viscosity or the yield stress of the suspension.

  14. Gas Jets

    NASA Technical Reports Server (NTRS)

    Chaplygin, S.

    1944-01-01

    A brief summary of the contents of this paper is presented here. In part I the differential equations of the problem of a gas flow in two dimensions is derived and the particular integrals by which the problem on jets is solved are given. Use is made of the same independent variables as Molenbroek used, but it is found to be more suitable to consider other functions. The stream function and velocity potential corresponding to the problem are given in the form of series. The investigation on the convergence of these series in connection with certain properties of the functions entering them forms the subject of part II. In part III the problem of the outflow of a gas from an infinite vessel with plane walls is solved. In part IV the impact of a gas jet on a plate is considered and the limiting case where the jet expands to infinity changing into a gas flow is taken up in more detail. This also solved the equivalent problem of the resistance of a gaseous medium to the motion of a plate. Finally, in part V, an approximate method is presented that permits a simpler solution of the problem of jet flows in the case where the velocities of the gas (velocities of the particles in the gas) are not very large.

  15. Characterization of needle-assisted jet injections.

    PubMed

    Li, Xinxin; Ruddy, Bryan; Taberner, Andrew

    2016-12-10

    than those used in NFJI, yet still maintain the high-speed nature of jet injection by achieving a delivery rate of 2.25mL/s. The lower pressures required in needle-assisted drug delivery can lead to reduced device size and cost, as well as reduced shear stresses during jet injection and can therefore minimise the potentially adverse effect of shear on the structural integrity of proteins, vaccines and DNA.

  16. Reconnection and Spire Drift in Coronal Jets

    NASA Astrophysics Data System (ADS)

    Moore, Ronald; Sterling, Alphonse; Falconer, David

    2015-04-01

    It is observed that there are two morphologically-different kinds of X-ray/EUV jets in coronal holes: standard jets and blowout jets. In both kinds: (1) in the base of the jet there is closed magnetic field that has one foot in flux of polarity opposite that of the ambient open field of the coronal hole, and (2) in coronal X-ray/EUV images of the jet there is typically a bright nodule at the edge of the base. In the conventional scenario for jets of either kind, the bright nodule is a compact flare arcade, the downward product of interchange reconnection of closed field in the base with impacted ambient open field, and the upper product of this reconnection is the jet-outflow spire. It is also observed that in most jets of either kind the spire drifts sideways away from the bright nodule. We present the observed bright nodule and spire drift in an example standard jet and in two example blowout jets. With cartoons of the magnetic field and its reconnection in jets, we point out: (1) if the bright nodule is a compact flare arcade made by interchange reconnection, then the spire should drift toward the bright nodule, and (2) if the bright nodule is instead a compact flare arcade made, as in a filament-eruption flare, by internal reconnection of the legs of the erupting sheared-field core of a lobe of the closed field in the base, then the spire, made by the interchange reconnection that is driven on the outside of that lobe by the lobe’s internal convulsion, should drift away from the bright nodule. Therefore, from the observation that the spire usually drifts away from the bright nodule, we infer: (1) in X-ray/EUV jets of either kind in coronal holes the interchange reconnection that generates the jet-outflow spire usually does not make the bright nodule; instead, the bright nodule is made by reconnection inside erupting closed field in the base, as in a filament eruption, the eruption being either a confined eruption for a standard jet or a blowout eruption (as

  17. A novel method for upper tropospheric jet stream detection

    NASA Astrophysics Data System (ADS)

    Spengler, Thomas; Spensberger, Clemens

    2014-05-01

    There are several methods to detect upper tropospheric jet streams. These schemes are often based on a threshold-criterion for the wind speed, while others utilise gradients in vorticity or the refractive index for Rossby waves. Most of these schemes diagnose an area or volume, which is identified as the jet stream. For some applications, however, it is of higher value to identify the actual axis of the jet stream. For example, cyclonic and anticyclonic Rossby wave breaking occurs preferentially on the cyclonically and anticyclonically sheared side of the jet stream, respectively, where the jet axis marks the transition between the two types of shear. Furthermore, the definition of an axis allows for the analysis of relative distance between collocated jet streams, allowing for an assessment of potential interaction. We propose a new method to detect jet axes based on deformation and the relative angle of the axis of dilatation. The detection performs equally well for instantaneous data as well as for monthly or even longer time averages of the wind field. We present climatologies of jet axis positions and pinpoint new insights revealed by our method. Furthermore, we present composites for different phases of common climate indices such as the NAO and PNA. We also present jet axis composites for different phases of the MJO supporting earlier findings and highlighting the interaction of the MJO with the Pacific jet stream.

  18. Fast ion JET diagnostics: confinement and losses

    SciTech Connect

    Kiptily, V. G.; Pinches, S. D.; Sharapov, S. E.; Syme, D. B.; Cecconello, M.; Darrow, D.; Hill, K.; Goloborod'ko, V.; Yavorskij, V.; Johnson, T.; Murari, A.; Reich, M.; Gorini, G.; Zoita, V.

    2008-03-12

    A study of magnetically confined fast ions in tokamaks plays an important role in burning plasma research. To reach ignition and steady burning of a reactor plasma an adequate confinement of energetic ions produced by NBI heating, accelerated with ICRF and born in fusion reactions is essential to provide efficient heating of the bulk plasma. Thus, investigation of the fast ion behaviour is an immediate task for present-day large machines, such as JET, in order to understand the main mechanisms of slowing down, redistribution and losses, and to develop optimal plasma scenarios. Today's JET has an enhanced suite of fast ion diagnostics both of confined and lost ions that enable to significantly contribute to this important area of research. Fast ion populations of p, d, t, {sup 3}He and {sup 4}He, made with ICRF, NBI, and fusion reactions have been investigated in experiments on JET with sophisticated diagnostics in conventional and shear-reversed plasmas, exploring a wide range of effects. This paper will introduce to the JET fast-ion diagnostic techniques and will give an overview of recent observations. A synergy of the unique diagnostic set was utilised in JET, and studies of the response of fast ions to MHD modes (e.g. tornado modes, sawtooth crashes), fast {sup 3}He-ions behaviour in shear-reversed plasmas are impressive examples of that. Some results on fast ion losses in JET experiments with various levels of the toroidal field ripple will be demonstrated.

  19. Multiple Mode Actuation of a Turbulent Jet

    NASA Technical Reports Server (NTRS)

    Pack, LaTunia G.; Seifert, Avi

    2001-01-01

    The effects of multiple mode periodic excitation on the evolution of a circular turbulent jet were studied experimentally. A short, wide-angle diffuser was attached to the jet exit. Streamwise and cross-stream excitations were introduced at the junction between the jet exit and the diffuser inlet on opposing sides of the jet. The introduction of high amplitude, periodic excitation in the streamwise direction enhances the mixing and promotes attachment of the jet shear-layer to the diffuser wall. Cross-stream excitation applied over a fraction of the jet circumference can deflect the jet away from the excitation slot. The two modes of excitation were combined using identical frequencies and varying the relative phase between the two actuators in search of an optimal response. It is shown that, for low and moderate periodic momentum input levels, the jet deflection angles depend strongly on the relative phase between the two actuators. Optimum performance is achieved when the phase difference is pi +/- pi/6. The lower effectiveness of the equal phase excitation is attributed to the generation of an azimuthally symmetric mode that does not produce the required non-axisymmetric vectoring. For high excitation levels, identical phase becomes more effective, while phase sensitivity decreases. An important finding was that with proper phase tuning, two unsteady actuators can be combined to obtain a non-linear response greater than the superposition of the individual effects.

  20. Optimising code generation with haggies

    NASA Astrophysics Data System (ADS)

    Reiter, T.

    2010-07-01

    This article describes haggies, a program for the generation of optimised programs for the efficient numerical evaluation of mathematical expressions. It uses a multivariate Horner-scheme and Common Subexpression Elimination to reduce the overall number of operations. The package can serve as a back-end for virtually any general purpose computer algebra program. Built-in type inference that allows to deal with non-standard data types in strongly typed languages and a very flexible, pattern-based output specification ensure that haggies can produce code for a large variety of programming languages. We currently use haggies as part of an automated package for the calculation of one-loop scattering amplitudes in quantum field theories. The examples in this articles, however, demonstrate that its use is not restricted to the field of high energy physics. Program summaryProgram title: haggies Catalogue identifier: AEGF_v1_0 Program summary: URL: http://cpc.cs.qub.ac.uk/summaries/AEGF_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU GPL v3 No. of lines in distributed program, including test data, etc.: 56 220 No. of bytes in distributed program, including test data, etc.: 579 010 Distribution format: tar.gz Programming language: Java, JavaCC Computer: Any system that runs the Java Virtual Machine Operating system: Any system that runs the Java Virtual Machine RAM: Determined by the size of the problem Classification: 4.14, 5, 6.2, 6.5, 11.1 Nature of problem: Generation of optimised programs for the evaluation of possibly large algebraic expressions Solution method: Java implementation Running time: Determined by the size of the problem

  1. A jet-driven dynamo (JEDD) from jet-inflated bubbles in cooling flows

    NASA Astrophysics Data System (ADS)

    Soker, Noam

    2017-04-01

    I suggest that the main process that amplifies magnetic fields in cooling flows in clusters and group of galaxies is a jet-driven dynamo (JEDD). The main processes that are behind the JEDD is the turbulence that is formed by the many vortices formed in the inflation processes of bubbles, and the large scale shear formed by the propagating jet. It is sufficient that a strong turbulence exits in the vicinity of the jets and bubbles, just where the shear is large. The typical amplification time of magnetic fields by the JEDD near the jets and bubbles is approximately hundred million years. The amplification time in the entire cooling flow region is somewhat longer. The vortices that create the turbulence are those that also transfer energy from the jets to the intra-cluster medium, by mixing shocked jet gas with the intra-cluster medium gas, and by exciting sound waves. The JEDD model adds magnetic fields to the cyclical behaviour of energy and mass in the jet-feedback mechanism in cooling flows.

  2. A jet-driven dynamo (JEDD) from jets-inflated bubbles in cooling flows

    NASA Astrophysics Data System (ADS)

    Soker, Noam

    2017-01-01

    I suggest that the main process that amplifies magnetic fields in cooling flows in clusters and group of galaxies is a jet-driven dynamo (JEDD). The main processes that are behind the JEDD is the turbulence that is formed by the many vortices formed in the inflation processes of bubbles, and the large scale shear formed by the propagating jet. It is sufficient that a strong turbulence exits in the vicinity of the jets and bubbles, just where the shear is large. The typical amplification time of magnetic fields by the JEDD near the jets and bubbles is approximately hundred million years. The amplification time in the entire cooling flow region is somewhat longer. The vortices that create the turbulence are those that also transfer energy from the jets to the intra-cluster medium, by mixing shocked jet gas with the intra-cluster medium gas, and by exciting sound waves. The JEDD model adds magnetic fields to the cyclical behavior of energy and mass in the jet-feedback mechanism (JFM) in cooling flows.

  3. Characteristics of transverse hydrogen jet in presence of multi air jets within scramjet combustor

    NASA Astrophysics Data System (ADS)

    Barzegar Gerdroodbary, M.; Fallah, Keivan; Pourmirzaagha, H.

    2017-03-01

    In this article, three-dimensional simulation is performed to investigate the effects of micro air jets on mixing performances of cascaded hydrogen jets within a scramjet combustor. In order to compare the efficiency of this technique, constant total fuel rate is injected through one, four, eight and sixteen arrays of portholes in a Mach 4.0 crossflow with a fuel global equivalence ratio of 0.5. In this method, micro air jets are released within fuel portholes to augment the penetration in upward direction. Extensive studies were performed by using the Reynolds-averaged Navier-Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. Numerical studies on various air and fuel arrangements are done and the mixing rate and penetration are comprehensively investigated. Also, the flow feature of the fuel and air jets for different configuration is revealed. According to the obtained results, the influence of the micro air jets is significant and the presence of micro air jets increases the mixing rate about 116%, 77%, 56% and 41% for single, 4, 8 and 16 multi fuel jets, respectively. The maximum mixing rate of the hydrogen jet is obtained when the air jets are injected within the sixteen multi fuel jets. According to the circulation analysis of the flow for different air and fuel arrangements, it was found that the effects of air jets on flow structure are varied in various conditions and the presence of the micro jet highly intensifies the circulation in the case of 8 and 16 multi fuel jets.

  4. VLBA AND CHANDRA OBSERVATIONS OF JETS IN FRI RADIO GALAXIES: CONSTRAINTS ON JET EVOLUTION

    SciTech Connect

    Kharb, P.; O'Dea, C. P.; Tilak, A.; Baum, S. A.; Haynes, E.; Noel-Storr, J.; Fallon, C.; Christiansen, K.

    2012-07-20

    We present here the results from new Very Long Baseline Array (VLBA) observations at 1.6 and 5 GHz of 19 galaxies of a complete sample of 21 Uppasala General Catalog (UGC) Fanaroff-Riley type I (FRI) radio galaxies. New Chandra data of two sources, viz., UGC 00408 and UGC 08433, are combined with the Chandra archival data of 13 sources. The 5 GHz observations of 10 'core-jet' sources are polarization-sensitive, while the 1.6 GHz observations constitute second-epoch total intensity observations of nine 'core-only' sources. Polarized emission is detected in the jets of seven sources at 5 GHz, but the cores are essentially unpolarized, except in M87. Polarization is detected at the jet edges in several sources, and the inferred magnetic field is primarily aligned with the jet direction. This could be indicative of magnetic field 'shearing' due to jet-medium interaction, or the presence of helical magnetic fields. The jet peak intensity I{sub {nu}} falls with distance d from the core, following the relation, I{sub {nu}}{proportional_to}d{sup a} , where a is typically {approx} - 1.5. Assuming that adiabatic expansion losses are primarily responsible for the jet intensity 'dimming,' two limiting cases are considered: (1) the jet has a constant speed on parsec scales and is expanding gradually such that the jet radius r{proportional_to}d 0{sup .4}; this expansion is, however, unobservable in the laterally unresolved jets at 5 GHz, and (2) the jet is cylindrical and is accelerating on parsec scales. Accelerating parsec-scale jets are consistent with the phenomenon of 'magnetic driving' in Poynting-flux-dominated jets. While slow jet expansion as predicted by case (1) is indeed observed in a few sources from the literature that are resolved laterally, on scales of tens or hundreds of parsecs, case (2) cannot be ruled out in the present data, provided the jets become conical on scales larger than those probed by VLBA. Chandra observations of 15 UGC FRIs detect X-ray jets in

  5. Stability of Shallow Jovian Atmospheric Zonal Jets

    NASA Astrophysics Data System (ADS)

    Sayanagi, Kunio M.; Dowling, T. E.; Showman, A. P.

    2007-10-01

    Jupiter's cloud-level zonal jets are remarkably steady in time despite their sharp curvature (i.e., second latitudinal derivative of the zonal wind profile). The stable jets must be supported by a proper sub-cloud wind and thermal structure; however, the large-scale deep structure of the zonal jets and temperature remain a major unknown in the gas-giant planet atmospheres. Past studies suggest two end-point scenarios of deep wind structures that allow stable cloud-level jets. The first shows that the jets are stable if they penetrate through the molecular hydrogen layer (Ingersoll and Pollard, 1982), although they do not address how the deep flow may be coupled to the cloud-level wind. Many other studies, though they may not directly address the shear instabilities, support this "deep jet” scenario (e.g. Heimpel and Aurnou, 2007); however, they do not rule out the possibility that the jets are shallow. Gierasch (2004) introduced a notable alternative to this "deep” picture. Through linear stability analysis, he showed that an isolated eastward jet that reaches a point of zero motion at 100-bar level, with Jupiter-like speeds and widths at the top, can be stable under certain conditions. However, his analysis contained several untested assumptions, and whether such flows are actually stable in a more realistic setting remains an open question. The possibility of stable shallow zonal jets on Jupiter remains largely unexplored, and this possibility deserves a thorough consideration. We present full-3D nonlinear simulations that test the stability of shallow zonal jets. We use Richardson number as a measure of vertical flow scale, and aim to show whether shallow jets are consistent with the observed jets and place theoretical constraints on the sub-cloud wind structure. Our study uses the EPIC model (Dowling et al., 1998, 2006). The research has been supported by NASA Planetary Atmosphere grants to APS and TED.

  6. Overview of JET results

    NASA Astrophysics Data System (ADS)

    Paméla, J.; Solano, Emilia R.; EFDA Contributors, JET

    2003-12-01

    Scientific and technical activities on JET focus on the issues likely to affect the ITER design and operation. Our understanding of the ITER reference mode of operation, the ELMy H-mode, has progressed significantly. The extrapolation of ELM size to ITER has been re-evaluated. Neoclassical tearing modes have been shown to be meta-stable in JET, and their beta limits can be raised by destabilization (modification) of sawteeth by ion cyclotron radio frequency heating (ICRH). Alpha simulation experiments with ICRH accelerated injected 4He beam ions provide a new tool for fast particle and magnetohydrodynamic studies, with up to 80-90% of plasma heating by fast 4He ions. With or without impurity seeding, a quasi-steady-state high confinement (H98 = 1), high density (ne/nGW = 0.9-1) and high bgr (bgrN = 2) ELMy H-mode has been achieved by operating near the ITER triangularity (dgr~ 0.40-0.5) and safety factor (q95~ 3), at Zeff~ 1.5-2. In advanced tokamak (AT) scenarios, internal transport barriers (ITBs) are now characterized in real time with a new criterion, \\rho^*_T . Tailoring of the current profile with lower hybrid current drive provides reliable access to a variety of q profiles, lowering access power for barrier formation. Rational q surfaces appear to be associated with ITB formation. Alfvén cascades were observed in reversed shear plasmas, providing identification of q profile evolution. Plasmas with 'current holes' were observed and modelled. Transient high confinement AT regimes with H89 = 3.3, bgrN = 2.4 and ITER-relevant q < 5 were achieved with reversed magnetic shear. Quasi-stationary ITBs are developed with full non-inductive current drive, including ~50% bootstrap current. A record duration of ITBs was achieved, up to 11 s, approaching the resistive time. For the first time, pressure and current profiles of AT regimes are controlled by a real-time feedback system, in separate experiments. Erosion and co-deposition studies with a quartz micro

  7. Jet lag.

    PubMed

    Herxheimer, Andrew

    2008-12-04

    Jet lag affects most air travellers crossing five or more time zones; it tends to be worse on eastward than on westward flights. We conducted a systematic review and aimed to answer the following clinical question: What are the effects of interventions to prevent or minimise jet lag? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2008 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). We found five systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. In this systematic review we present information relating to the effectiveness and safety of the following interventions: hypnotics, melatonin, and lifestyle and environmental adaptations.

  8. Filament Channel Formation, Eruption, and Jet Generation

    NASA Astrophysics Data System (ADS)

    DeVore, C. Richard; Antiochos, Spiro K.; Karpen, Judith T.

    2017-08-01

    The mechanism behind filament-channel formation is a longstanding mystery, while that underlying the initiation of coronal mass ejections and jets has been studied intensively but is not yet firmly established. In previous work, we and collaborators have investigated separately the consequences of magnetic-helicity condensation (Antiochos 2013) for forming filament channels (Zhao et al. 2015; Knizhnik et al. 2015, 2017a,b) and of the embedded-bipole model (Antiochos 1996) for generating reconnection-driven jets (Pariat et al. 2009, 2010, 2015, 2016; Wyper et al. 2016, 2017). Now we have taken a first step toward synthesizing these two lines of investigation. Our recent study (Karpen et al. 2017) of coronal-hole jets with gravity and wind employed an ad hoc, large-scale shear flow at the surface to introduce magnetic free energy and form the filament channel. In this effort, we replace the shear flow with an ensemble of local rotation cells, to emulate the Sun’s ever-changing granules and supergranules. As in our previous studies, we find that reconnection between twisted flux tubes within the closed-field region concentrates magnetic shear and free energy near the polarity inversion line, forming the filament channel. Onset of reconnection between this field and the external, unsheared, open field releases stored energy to drive the impulsive jet. We discuss the results of our new simulations with implications for understanding solar activity and space weather.

  9. Reduced shear power spectrum

    SciTech Connect

    Dodelson, Scott; Shapiro, Charles; White, Martin J.; /UC, Berkeley, Astron. Dept. /UC, Berkeley

    2005-08-01

    Measurements of ellipticities of background galaxies are sensitive to the reduced shear, the cosmic shear divided by (1-{kappa}) where {kappa} is the projected density field. They compute the difference between shear and reduced shear both analytically and with simulations. The difference becomes more important an smaller scales, and will impact cosmological parameter estimation from upcoming experiments. A simple recipe is presented to carry out the required correction.

  10. Optimising uncertainty in physical sample preparation.

    PubMed

    Lyn, Jennifer A; Ramsey, Michael H; Damant, Andrew P; Wood, Roger

    2005-11-01

    Uncertainty associated with the result of a measurement can be dominated by the physical sample preparation stage of the measurement process. In view of this, the Optimised Uncertainty (OU) methodology has been further developed to allow the optimisation of the uncertainty from this source, in addition to that from the primary sampling and the subsequent chemical analysis. This new methodology for the optimisation of physical sample preparation uncertainty (u(prep), estimated as s(prep)) is applied for the first time, to a case study of myclobutanil in retail strawberries. An increase in expenditure (+7865%) on the preparatory process was advised in order to reduce the s(prep) by the 69% recommended. This reduction is desirable given the predicted overall saving, under optimised conditions, of 33,000 pounds Sterling per batch. This new methodology has been shown to provide guidance on the appropriate distribution of resources between the three principle stages of a measurement process, including physical sample preparation.

  11. An optimisation method for complex product design

    NASA Astrophysics Data System (ADS)

    Li, Ni; Yi, Wenqing; Bi, Zhuming; Kong, Haipeng; Gong, Guanghong

    2013-11-01

    Designing a complex product such as an aircraft usually requires both qualitative and quantitative data and reasoning. To assist the design process, a critical issue is how to represent qualitative data and utilise it in the optimisation. In this study, a new method is proposed for the optimal design of complex products: to make the full use of available data, information and knowledge, qualitative reasoning is integrated into the optimisation process. The transformation and fusion of qualitative and qualitative data are achieved via the fuzzy sets theory and a cloud model. To shorten the design process, parallel computing is implemented to solve the formulated optimisation problems. A parallel adaptive hybrid algorithm (PAHA) has been proposed. The performance of the new algorithm has been verified by a comparison with the results from PAHA and two other existing algorithms. Further, PAHA has been applied to determine the shape parameters of an aircraft model for aerodynamic optimisation purpose.

  12. Nature-Inspired Chemical Reaction Optimisation Algorithms.

    PubMed

    Siddique, Nazmul; Adeli, Hojjat

    2017-01-01

    Nature-inspired meta-heuristic algorithms have dominated the scientific literature in the areas of machine learning and cognitive computing paradigm in the last three decades. Chemical reaction optimisation (CRO) is a population-based meta-heuristic algorithm based on the principles of chemical reaction. A chemical reaction is seen as a process of transforming the reactants (or molecules) through a sequence of reactions into products. This process of transformation is implemented in the CRO algorithm to solve optimisation problems. This article starts with an overview of the chemical reactions and how it is applied to the optimisation problem. A review of CRO and its variants is presented in the paper. Guidelines from the literature on the effective choice of CRO parameters for solution of optimisation problems are summarised.

  13. Rotatable shear plate interferometer

    DOEpatents

    Duffus, Richard C.

    1988-01-01

    A rotatable shear plate interferometer comprises a transparent shear plate mounted obliquely in a tubular supporting member at 45.degree. with respect to its horizontal center axis. This tubular supporting member is supported rotatably around its center axis and a collimated laser beam is made incident on the shear plate along this center axis such that defocus in different directions can be easily measured.

  14. Free turbulent shear flows. Volume 2: Summary of data

    NASA Technical Reports Server (NTRS)

    Birch, S. F.

    1973-01-01

    The proceedings of a conference on free turbulent shear flows are presented. Objectives of the conference are as follows: (1) collect and process data for a variety of free mixing problems, (2) assess present theoretical capability for predicting mean velocity, concentration, and temperature distributions in free turbulent flows, (3) identify and recommend experimental studies to advance knowledge of free shear flows, and (4) increase understanding of basic turbulent mixing process for application to free shear flows. Examples of specific cases of jet flow are included.

  15. Mx Magnetometry Optimisation in Unshielded Environments

    NASA Astrophysics Data System (ADS)

    Ingleby, Stuart; Griffin, Paul; Arnold, Aidan; Riis, Erling; Hunter, Dominic

    2016-05-01

    Optically pumped magnetometry in unshielded environments is potentially of great advantage in a wide range of surveying and security applications. Optimisation of OPM modulation schemes and feedback in the Mx scheme offers enhanced sensitivity through noise cancellation and decoherence suppression. The work presented demonstrates capability for software-controlled optimisation of OPM performance in ambient fields in the 0 . 5 G range. Effects on magnetometer bandwidth and sensitivity are discussed. Supported by UK National Quantum Technologies Programme.

  16. Optimising costs in WLCG operations

    NASA Astrophysics Data System (ADS)

    Alandes Pradillo, María; Dimou, Maria; Flix, Josep; Forti, Alessandra; Sciabà, Andrea

    2015-12-01

    The Worldwide LHC Computing Grid project (WLCG) provides the computing and storage resources required by the LHC collaborations to store, process and analyse the 50 Petabytes of data annually generated by the LHC. The WLCG operations are coordinated by a distributed team of managers and experts and performed by people at all participating sites and from all the experiments. Several improvements in the WLCG infrastructure have been implemented during the first long LHC shutdown to prepare for the increasing needs of the experiments during Run2 and beyond. However, constraints in funding will affect not only the computing resources but also the available effort for operations. This paper presents the results of a detailed investigation on the allocation of the effort in the different areas of WLCG operations, identifies the most important sources of inefficiency and proposes viable strategies for optimising the operational cost, taking into account the current trends in the evolution of the computing infrastructure and the computing models of the experiments.

  17. Effects of shear coupling on shear properties of wood

    Treesearch

    Jen Y. Liu

    2000-01-01

    Under pure shear loading, an off-axis element of orthotropic material such as pure wood undergoes both shear and normal deformations. The ratio of the shear strain to a normal strain is defined as the shear coupling coefficient associated with the direction of the normal strain. The effects of shear coupling on shear properties of wood as predicted by the orthotropic...

  18. MAGNETIC FIELD GENERATION AND PARTICLE ENERGIZATION AT RELATIVISTIC SHEAR BOUNDARIES IN COLLISIONLESS ELECTRON-POSITRON PLASMAS

    SciTech Connect

    Liang, Edison; Smith, Ian; Boettcher, Markus E-mail: iansmith@rice.edu

    2013-04-01

    Using particle-in-cell simulations, we study the kinetic physics of relativistic shear flow in collisionless electron-positron (e+e-) plasmas. We find efficient magnetic field generation and particle energization at the shear boundary, driven by streaming instabilities across the shear interface and sustained by the shear flow. Nonthermal, anisotropic high-energy particles are accelerated across field lines to produce a power-law tail turning over just below the shear Lorentz factor. These results have important implications for the dissipation and radiation of jets in blazars and gamma-ray bursts.

  19. Analysis of ``soft`` recovered shaped charge jet particles

    SciTech Connect

    Lassila, D.H.; Nikkel, D.J. Jr.; Kershaw, R.P.; Walters, W.P.

    1996-04-01

    A shaped charge with an 81 mm diameter, 42{degree} apex angle oxygen-free high-conductivity (OFHC) copper conical liner was fired into a ``soft`` recovery bunker to allow metallurgical examination of recovered jet particles and the slug. The initial weight of the copper liner was 245 g, of which 184 g was recovered. The number of jet particles recovered was 37 (approximately 63% of the particles formed by the charge). Extensive metallurgical analyses were performed on the recovered slug and jet particles. The microstructural features associated with voids, e.g., dendritic grain growth, clearly indicate that the regions in the vicinity of the centerline of the slug and jet particles were melted. In this work the authors present calculations of jet temperature as a function of constitutive behavior. In order to predict melt in the center region of the jet they find it necessary to scale flow stress with a pressure dependent shear modulus.

  20. A NUMERICAL MODEL OF STANDARD TO BLOWOUT JETS

    SciTech Connect

    Archontis, V.; Hood, A. W.

    2013-06-01

    We report on three-dimensional (3D) MHD simulations of the formation of jets produced during the emergence and eruption of solar magnetic fields. The interaction between an emerging and an ambient magnetic field in the solar atmosphere leads to (external) reconnection and the formation of ''standard'' jets with an inverse Y-shaped configuration. Eventually, low-atmosphere (internal) reconnection of sheared fieldlines in the emerging flux region produces an erupting magnetic flux rope and a reconnection jet underneath it. The erupting plasma blows out the ambient field and, moreover, it unwinds as it is ejected into the outer solar atmosphere. The fast emission of the cool material that erupts together with the hot outflows due to external/internal reconnection form a wider ''blowout'' jet. We show the transition from ''standard'' to ''blowout'' jets and report on their 3D structure. The physical plasma properties of the jets are consistent with observational studies.

  1. Vorticity Dynamics in Single and Multiple Swirling Reacting Jets

    NASA Astrophysics Data System (ADS)

    Smith, Travis; Aguilar, Michael; Emerson, Benjamin; Noble, David; Lieuwen, Tim

    2015-11-01

    This presentation describes an analysis of the unsteady flow structures in two multinozzle swirling jet configurations. This work is motivated by the problem of combustion instabilities in premixed flames, a major concern in the development of modern low NOx combustors. The objective is to compare the unsteady flow structures in these two configurations for two separate geometries and determine how certain parameters, primarily distance between jets, influence the flow dynamics. The analysis aims to differentiate between the flow dynamics of single nozzle and triple nozzle configurations. This study looks at how the vorticity in the shear layers of one reacting swirling jet can affect the dynamics of a nearby similar jet. The distance between the swirling jets is found to have an effect on the flow field in determining where swirling jets merge and on the dynamics upstream of the merging location. Graduate Student, School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA.

  2. Enhancement of wall jet transport properties

    DOEpatents

    Claunch, S.D.; Farrington, R.B.

    1997-02-04

    By enhancing the natural instabilities in the boundary layer and in the free shear layer of a wall jet, the boundary is minimized thereby increasing the transport of heat and mass. Enhancing the natural instabilities is accomplished by pulsing the flow of air that creates the wall jet. Such pulsing of the flow of air can be accomplished by sequentially occluding and opening a duct that confines and directs the flow of air, such as by rotating a disk on an axis transverse to the flow of air in the duct. 17 figs.

  3. Enhancement of wall jet transport properties

    DOEpatents

    Claunch, Scott D.; Farrington, Robert B.

    1997-01-01

    By enhancing the natural instabilities in the boundary layer and in the free shear layer of a wall jet, the boundary is minimized thereby increasing the transport of heat and mass. Enhancing the natural instabilities is accomplished by pulsing the flow of air that creates the wall jet. Such pulsing of the flow of air can be accomplished by sequentially occluding and opening a duct that confines and directs the flow of air, such as by rotating a disk on an axis transverse to the flow of air in the duct.

  4. X-ray Radiography Measurements of Shear Coaxial Rocket Injectors

    DTIC Science & Technology

    2013-05-07

    These injectors rely on the shear between an outer lower-density, high-velocity annulus and a higher-density, low-velocity inner jet to atomize and...velocities and the distance between radial points – Large uncertainty given the small distances, high velocities, and limited number of points

  5. Refraction and scattering of sound by a shear layer

    NASA Technical Reports Server (NTRS)

    Schlinker, R. H.; Amiet, R. K.

    1980-01-01

    The angle and amplitude changes for acoustic waves refracted by a circular open jet shear layer were determined. The generalized refraction theory was assessed experimentally for on axis and off axis acoustic source locations as source frequency varied from 1 kHz to 10 kHz and free stream Mach number varied from 0.1 to 0.4. Angle and amplitude changes across the shear layer show good agreement with theory. Experiments confirm that the refraction theory is independent of shear layer thickness, acoustic source frequency, and source type. A generalized theory is, thus, available for correcting far field noise data acquired in open jet test facilities. The effect of discrete tone scattering by the open jet turbulent shear layer was also studied. Scattering effects were investigated over the same Mach number range as frequency varied from 5 kHz to 15 kHz. Attenuation of discrete tone amplitude and tone broadening were measured as a function of acoustic source position and radiation angle. Scattering was found to be stronger at angles close to the open jet axis than at 90 deg, and becomes stronger as the acoustic source position shifts downstream. A scattering analysis provided an estimate of the onset of discrete tone scattering.

  6. PIV measurements of isothermal plane turbulent impinging jets at moderate Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Khayrullina, A.; van Hooff, T.; Blocken, B.; van Heijst, G. J. F.

    2017-04-01

    This paper contains a detailed experimental analysis of an isothermal plane turbulent impinging jet (PTIJ) for two jet widths at moderate Reynolds numbers (7200-13,500) issued on a horizontal plane at fixed relative distances equal to 22.5 and 45 jet widths. The available literature on such flows is scarce. Previous studies on plane turbulent jets mainly focused on free jets, while most studies on impinging jets focused on the heat transfer between the jet and an impingement plane, disregarding jet development. The present study focuses on isothermal PTIJs at moderate Reynolds numbers characteristic of air curtains. Flow visualisations with fluorescent dye and 2D particle image velocimetry (PIV) measurements have been performed. A comparison is made with previous studies of isothermal free turbulent jets at moderate Reynolds numbers. Mean and instantaneous velocity and vorticity, turbulence intensity, and Reynolds shear stress are analysed. The jet issued from the nozzle with higher aspect ratio shows more intensive entrainment and a faster decay of the centreline velocity compared to the jet of lower aspect ratio for the same value of jet Reynolds number. The profiles of centreline and cross-jet velocity and turbulence intensity show that the PTIJs behave as a free plane turbulent jet until 70-75% of the total jet height. Alongside the information obtained on the jet dynamics, the data will be useful for the validation of numerical simulations.

  7. Jet lag

    PubMed Central

    2008-01-01

    Introduction Jet lag is a syndrome caused by disruption of the "body clock", and affects most air travellers crossing five or more time zones; it tends to be worse on eastward than on westward flights. Methods and outcomes We conducted a systematic review and aimed to answer the following clinical question: What are the effects of interventions to prevent or minimise jet lag? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2008 (Clinical Evidence reviews are updated periodically; please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). Results We found five systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. Conclusions In this systematic review we present information relating to the effectiveness and safety of the following interventions: hypnotics, lifestyle and environmental adaptations, and melatonin. PMID:19445780

  8. F Ring Mini-Jets

    NASA Astrophysics Data System (ADS)

    Attree, N.; Murray, C.; Cooper, N. J.; Williams, G.

    2012-12-01

    Mini-jets are small, (~50 km) linear features observed in Cassini images to be emanating from Saturn's F ring; they are believed to be produced by collisions with a local population of moonlets. An analysis of one such feature, observed over the course of a ~7.5 h sequence as its length changed from ~75 km to ~250 km while it simultaneously appeared to collapse back into the core, supports the collisional theory of their origin [1]. Orbit determination suggests that this mini-jet consisted of ring material displaced by a ~1 m/s collision with a nearby object, resulting in paths relative to the core that are due to a combination of keplerian shear and epicyclic motion. The colliding object itself is likely to be too small to resolve in these images but represents just one member of a population of F ring moonlets. Such a population has been investigated by UVIS occultations [2], and other methods, but generally remains unresolved in Cassini images. Collisional features such as this mini-jet therefore provide an additional tracer for the region's moonlet population. In this talk we will present the results of recent work in measuring and describing a subset of ~350 catalogued mini-jets, applying knowledge gained from the original mini-jet feature. Their distribution in space and time, proximity to Prometheus and evolution are all examined in an effort to place constraints on the properties of the underlying population of colliding objects. References [1] N. O. Attree, C. D. Murray, N. J. Cooper, and G. A. Williams. Detection of low velocity collisions in Saturn's F ring. Ap. J. Lett. (In press). [1] B. K. Meinke, L. W. Esposito, N. Albers, and M. Sremevi. Classification of F ring features observed in cassini UVIS occultations. Icarus, 218(1):545 - 554, 2012.

  9. Inclusive Jets in PHP

    NASA Astrophysics Data System (ADS)

    Roloff, P.

    Differential inclusive-jet cross sections have been measured in photoproduction for boson virtualities Q^2 < 1 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 300 pb^-1. Jets were identified in the laboratory frame using the k_T, anti-k_T or SIScone jet algorithms. Cross sections are presented as functions of the jet pseudorapidity, eta(jet), and the jet transverse energy, E_T(jet). Next-to-leading-order QCD calculations give a good description of the measurements, except for jets with low E_T(jet) and high eta(jet). The cross sections have the potential to improve the determination of the PDFs in future QCD fits. Values of alpha_s(M_Z) have been extracted from the measurements based on different jet algorithms. In addition, the energy-scale dependence of the strong coupling was determined.

  10. On Unified Mode in Grid Mounted Round Jets

    NASA Astrophysics Data System (ADS)

    Parimalanathan, Senthil Kumar; T, Sundararajan; v, Raghavan

    2015-11-01

    The turbulence evolution in a free round jet is strongly affected by its initial conditions. Since the transition to turbulence is moderated by instability modes, the initial conditions seem to play a major role in altering the dynamics of these modes. In the present investigation, grids of different configurations are placed at the jet nozzle exit and the flow field characterization is carried out using a bi-component hot-wire anemometer. The instability modes has been obtained by analyzing the velocity spectral data. Free jets are characterized by the presence of two instability modes, viz., the preferred mode and the shear mode. The preferred mode corresponds to the most amplified oscillations along the jet centerline, while the shear modes are due to the dynamic evolution of vortical structures in the jet shear layer. The presence of grid clearly alters the jet structure, and plays a major role in altering the shear layer mode in particular. In fact, it is observed that close to the nozzle exit, the presence of grids deviate the streamlines inwards around the edge due to the momentum difference between the jet central core and the boundary layer region near the wall. This result in a single unified mode, where there is no distinct preferred or shear mode. This phenomena is more dominant in case of the grids having higher blockage ratio with small grid opening. In the present study, investigation of the physics behind the evolution of unified mode and how the grids affect the overall turbulent flow field evolution has been reported. Experimental Fluid Mechanics.

  11. Visualizing interior and exterior jet aircraft noise

    NASA Astrophysics Data System (ADS)

    Moondra, Manmohan S.

    In today's competitive aerospace industry, the quest for quiet has drawn significant attention to both the interior and exterior design of an airplane. Understanding the noise generation mechanisms of a jet aircraft is a crucial first step toward developing the most cost-effective noise and vibrations abatement methods. In this investigation, the Helmholtz Equation Least Squares (HELS) based nearfield acoustic holography will be used to understand noise transmission caused by jet engine and turbulence into the fuselage of a jet aircraft cruising at 30,000 ft. Modern propulsive jet engines produce exterior noise sources with a high amplitude noise field and complicated characteristics, which makes them very difficult to characterize. In particular, there are turbulent eddies that are moving through the jet at high speeds along the jet boundary. These turbulent eddies in the shear layer produce a directional and frequency dependent noise. The original HELS approach assumes a spherical source at the origin and computes the acoustic field based on spherical emission from this source. This assumption of one source at the origin is not sufficient to characterize a complex source like a jet. As such, a modified HELS approach is introduced that will help improve the source characterization as it is not dependent on a single source at the origin but a number of virtual sources throughout the space. Custom microphones are created to take acoustic pressure measurements around the jet engine. These measured acoustic pressures are then taken as input to the modified HELS algorithm to visualize the noise pattern of a subsonic jet engine.

  12. Mixing in plasma and low density jets

    NASA Astrophysics Data System (ADS)

    Russ, S.; Strykowski, P. J.; Pfender, E.

    1994-04-01

    This study was undertaken to examine the mechanisms which produce the large entrainment measured near the exit of thermal plasma torches. A research facility was constructed to examine low density jet behavior under similar dimensionless conditions as those produced by thermal plasma spray torches; the Reynolds number based on jet diameter and average properties was 1000, and the ratio of jet to ambient density was 0.07. This very low density jet produced organized vortex structures which were partially responsible for the rapid entrainment of external air. The formation of these organized structures could be disrupted by introducing turbulence, but the rapid entrainment process was not significantly affected. The structure of the jet produced by a commercial plasma torch was examined and compared to the low density research jet. At low gas flow rates the plasma jet also displayed the formation of coherent vortex structures, the passage frequency of which compared favorably with that measured in the low density research jet. At higher gas flow rates the shear layer of the plasma jet rapidly broke down producing relatively small scale turbulence. Visualizations of the hot plasma core were compared against measurements of the torch voltage fluctuations caused by arc instabilities. At low flow rates the arc voltage fluctuations were quite low and the plume was very steady. At higher flow rates the arc voltage fluctuations increased and produced “surging” and “whipping” in the hot potential core. It is believed that this low frequency unsteadiness is partially responsible for the rapid entrainment measured in plasma torches.

  13. Analysis of a dusty wall jet

    NASA Technical Reports Server (NTRS)

    Lim, Hock-Bin; Roberts, Leonard

    1991-01-01

    An analysis is given for the entrainment of dust into a turbulent radial wall jet. Equations are solved based on incompressible flow of a radial wall jet into which dust is entrained from the wall and transported by turbulent diffusion and convection throughout the flow. It is shown that the resulting concentration of dust particles in the flow depends on the difference between the applied shear stress at the surface and the maximum level of shear stress that the surface can withstand (varies as rho(sub d)a(sub g)D) i.e., the pressure due to the weight of a single layer of dust. The analysis is expected to have application to the downflow that results from helicopter and VTOL aircraft.

  14. Splitting of Forced Elliptic Jets and Flames

    NASA Technical Reports Server (NTRS)

    Hertzberg, J.; Carlton, J.; Schwieterman, M.; Davis, E.; Bradley, E.; Linne, M.

    1997-01-01

    The objective of this work is to understand the fluid dynamics in the interaction of large scale, three-dimensional vortex structures and transitional diffusion flames in a microgravity environment. The vortex structures are used to provide a known perturbation of the type used in passive and active shear layer control techniques. 'Passive techniques' refers to manipulation of the system geometry to influence the three dimensional dynamics of vortex structures, and 'active' refers to any technique which adds energy (acoustic or kinetic) to the flow to influence the shear layer vortex dynamics. In this work the passive forcing is provided by an elliptic jet cross-section, and the active forcing is incorporated by perturbing the jet velocity using a loudspeaker in the plenum section.

  15. Corporate Jet

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Gulfstream Aerospace Corporation, Savannah, GA, used a version of a NASA program called WIBCO to design a wing for the Gulfstream IV (G-IV) which will help to reduce transonic drag (created by shock waves that develop as an airplane approaches the speed of sound). The G-IV cruises at 88 percent of the speed of sound, and holds the international record in its class for round-the-world flight. They also used the STANS5 and Profile programs in the design. They will use the NASA program GASP to help determine the gross weight, range, speed, payload and optimum wing area of an intercontinental supersonic business jet being developed in cooperation with Sukhoi Design Bureau, a Soviet organization.

  16. Numerical Study on Cryogenic Coflowing Jets under Transcritical Conditions

    NASA Astrophysics Data System (ADS)

    Tani, Hiroumi; Teramoto, Susumu; Okamoto, Koji; Yamanishi, Nobuhiro

    2012-11-01

    A numerical and experimental study is presented on cryogenic coflowing jets under transcritical conditions for a better understanding of the propellant mixing in supercritical-pressure rocket engines. The major concerns are dominant flow structures in the mixing of cryogenic coflowing jets under transcritical conditions. Experimentally, in advance of detailed numerical simulations, cryogenic nitrogen/gaseous nitrogen coaxial jets were visualized by the backlighting photography technique. It was observed that a dense nitrogen core has a shear-layer instability near the injector exit and eventually breaks up into large lumps which dissolve and fade away downstream. In numerical simulations, LES technique was employed for more detailed discussion on the flow structures. LES of a cryogenic nitrogen/gaseous nitrogen coflowing plane jet was conducted with the same density and velocity ratios of inner/outer jets as the experiments. As observed in the experiments, the shear-layer instability in the inner mixing layers is predominant near the injector exit. After roll-up and paring, the shear-layer instability waves become large-scale vortices. They cause coherent vortex structures which become dominant in the downstream and break the dense core into lumps. Strouhal numbers of the shear-layer instability and the dense lump shedding in the numerical simulations were comparable to those measured in the experiments, respectively.

  17. Jet inclusive cross sections

    SciTech Connect

    Del Duca, V.

    1992-11-01

    Minijet production in jet inclusive cross sections at hadron colliders, with large rapidity intervals between the tagged jets, is evaluated by using the BFKL pomeron. We describe the jet inclusive cross section for an arbitrary number of tagged jets, and show that it behaves like a system of coupled pomerons.

  18. Coaxial Jets Subjected to External Acoustics

    DTIC Science & Technology

    2011-10-20

    pressures with respect to the propellants • Need to understand mixing and combustion beyond liquid, gas states • Shear coaxial injectors are a...Charts 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Coaxial Jets Subjected to External Acoustics 5b. GRANT NUMBER 5c...Modern rockets operate at supercritical pressures with respect to propellants . There is a need to understand mixing and combustion beyond liquid and

  19. Shearing stability of lubricants

    NASA Technical Reports Server (NTRS)

    Shiba, Y.; Gijyutsu, G.

    1984-01-01

    Shearing stabilities of lubricating oils containing a high mol. wt. polymer as a viscosity index improver were studied by use of ultrasound. The oils were degraded by cavitation and the degradation generally followed first order kinetics with the rate of degradation increasing with the intensity of the ultrasonic irradiation and the cumulative energy applied. The shear stability was mainly affected by the mol. wt. of the polymer additive and could be determined in a short time by mechanical shearing with ultrasound.

  20. Multi-objective optimisation for musculoskeletal modelling: application to a planar elbow model.

    PubMed

    Dumas, Raphaël; Moissenet, Florent; Lafon, Yoann; Cheze, Laurence

    2014-10-01

    One of the open issues in musculoskeletal modelling remains the choice of the objective function that is used to solve the muscular redundancy problem. Some authors have recently proposed to introduce joint reaction forces in the objective function, and the question of the weights associated with musculo-tendon forces and joint reaction forces arose. This question typically deals with a multi-objective optimisation problem. The aim of this study is to illustrate, on a planar elbow model, the ensemble of optimal solutions (i.e. Pareto front) and the solution of a global objective method that represent different compromises between musculo-tendon forces, joint compression force, and joint shear force. The solutions of the global objective method, based either on the minimisation of the sum of the squared musculo-tendon forces alone or on the minimisation of the squared joint compression force and shear force together, are in the same range. Minimising either the squared joint compression force or shear force alone leads to extreme force values. The exploration of the compromises between these forces illustrates the existence of major interactions between the muscular and joint structures. Indeed, the joint reaction forces relate to the projection of the sum of the musculo-tendon forces. An illustration of these interactions, due to the projection relation, is that the Pareto front is not a large surface, like in a typical three-objective optimisation, but almost a curve. These interactions, and the possibility to take them into account by a multi-objective optimisation, seem essential for the application of musculoskeletal modelling to joint pathologies. © IMechE 2014.

  1. Flow and acoustic characteristics of non-axisymmetric jets at subsonic conditions

    NASA Astrophysics Data System (ADS)

    Upadhyay, Puja; Valentich, Griffin; Kumar, Rajan; Alvi, Farrukh

    2017-05-01

    Flow and acoustic behavior of two asymmetric, rectangular (AR = 4) and elliptic (AR = 2.5), jets are studied and compared to an equivalent area round jet. The jets are operated at a Mach number of 0.9 and temperature ratio of 1. Time-averaged flow field measurements are carried out using planar and stereoscopic particle image velocimetry. In addition, far-field microphone measurements are performed to compare jet acoustics. Mean flow field results demonstrate that for the given Mach number and aspect ratios, rectangular and elliptic jet properties are somewhat modified compared to the round jet. The elliptic jet exhibits properties that are intermediate between two geometric extremes. Moderately enhanced mixing in asymmetric jets as a result of weak streamwise vortices is evidenced by overall shorter potential core, faster centerline velocity decay, and higher shear layer growth rates. Centerline turbulence levels and transverse shear stress distribution also show enhanced fluctuations for non-circular jets. Compared to their major axis planes, relatively higher turbulence levels are measured in the minor axis planes for both rectangular and elliptic jets. Far-field acoustic measurements reveal the asymmetric nature of the sound field. Compared to the round jet, major axis orientation for asymmetric jets is observed to provide moderate acoustic benefit in the downstream direction. However, enhanced fluctuations in the minor axis plane result in a marginal noise augmentation at moderate to high frequencies in this plane for downstream polar angles.

  2. Enhancing Shear Thickening

    NASA Astrophysics Data System (ADS)

    Madraki, Fatemeh; Hormozi, Sarah; Ovarlez, Guillaume; Guazzelli, Elisabeth; Pouliquen, Olivier

    2016-11-01

    A cornstarch suspension is the quintessential particulate system that exhibits shear thickening. By adding large non-Brownian spheres to a cornstarch suspension, we show that shear thickening can be significantly enhanced. More precisely, the shear thickening transition is found to be increasingly shifted to lower critical shear rates. This enhancement is found to be mainly controlled by the concentration of the large particles. ANR(ANR-13-IS09-0005-01), ANR(ANR-11-LABX-0092), MIDEX (ANR-11-IDEX-0001-02), NSF (CBET-1554044-CAREER).

  3. Shear Thinning in Xenon

    NASA Technical Reports Server (NTRS)

    Bergm Robert F.; Moldover, Michael R.; Yao, Minwu; Zimmerli, Gregory A.

    2009-01-01

    We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids such as molten plastics or ketchup, near the critical point of xenon. The data span a wide range of dimensionless shear rate: the product of the shear rate and the relaxation time of critical fluctuations was greater than 0.001 and was less than 700. As predicted by theory, shear thinning occurred when this product was greater than 1. The measurements were conducted aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity.

  4. Filament Eruptions, Jets, and Space Weather

    NASA Technical Reports Server (NTRS)

    Moore, Ronald; Sterling, Alphonse; Robe, Nick; Falconer, David; Cirtain, Jonathan

    2013-01-01

    Previously, from chromospheric H alpha and coronal X-ray movies of the Sun's polar coronal holes, it was found that nearly all coronal jets (greater than 90%) are one or the other of two roughly equally common different kinds, different in how they erupt: standard jets and blowout jets (Yamauchi et al 2004, Apl, 605, 5ll: Moore et all 2010, Apj, 720, 757). Here, from inspection of SDO/AIA He II 304 A movies of 54 polar x-ray jets observed in Hinode/XRT movies, we report, as Moore et al (2010) anticipated, that (1) most standard x-ray jets (greater than 80%) show no ejected plasma that is cool enough (T is less than or approximately 10(exp 5K) to be seen in the He II 304 A movies; (2) nearly all blownout X-ray jets (greater than 90%) show obvious ejection of such cool plasma; (3) whereas when cool plasma is ejected in standard X-ray jets, it shows no lateral expansion, the cool plasma ejected in blowout X-ray jets shows strong lateral expansion; and (4) in many blowout X-ray jets, the cool plasma ejection displays the erupting-magnetic-rope form of clasic filament eruptions and is thereby seen to be a miniature filament eruption. The XRT movies also showed most blowout X-ray jets to be larger and brighter, and hence to apparently have more energy, than most standard X-ray jets. These observations (1) confirm the dichotomy of coronal jets, (2) agree with the Shibata model for standard jets, and (3) support the conclusion of Moore et al (2010) that in blowout jets the magnetic-arch base of the jet erupts in the manner of the much larger magnetic arcades in which the core field, the field rooted along the arcade's polarity inversion line, is sheared and twisted (sigmoid), often carries a cool-plasma filament, and erupts to blowout the arcade, producing a CME. From Hinode/SOT Ca II movies of the polar limb, Sterling et al (2010, ApJ, 714, L1) found that chromospheric Type-II spicules show a dichotomy of eruption dynamics similar to that found here for the cool

  5. Optimisation techniques in vaginal cuff brachytherapy.

    PubMed

    Tuncel, N; Garipagaoglu, M; Kizildag, A U; Andic, F; Toy, A

    2009-11-01

    The aim of this study was to explore whether an in-house dosimetry protocol and optimisation method are able to produce a homogeneous dose distribution in the target volume, and how often optimisation is required in vaginal cuff brachytherapy. Treatment planning was carried out for 109 fractions in 33 patients who underwent high dose rate iridium-192 (Ir(192)) brachytherapy using Fletcher ovoids. Dose prescription and normalisation were performed to catheter-oriented lateral dose points (dps) within a range of 90-110% of the prescribed dose. The in-house vaginal apex point (Vk), alternative vaginal apex point (Vk'), International Commission on Radiation Units and Measurements (ICRU) rectal point (Rg) and bladder point (Bl) doses were calculated. Time-position optimisations were made considering dps, Vk and Rg doses. Keeping the Vk dose higher than 95% and the Rg dose less than 85% of the prescribed dose was intended. Target dose homogeneity, optimisation frequency and the relationship between prescribed dose, Vk, Vk', Rg and ovoid diameter were investigated. The mean target dose was 99+/-7.4% of the prescription dose. Optimisation was required in 92 out of 109 (83%) fractions. Ovoid diameter had a significant effect on Rg (p = 0.002), Vk (p = 0.018), Vk' (p = 0.034), minimum dps (p = 0.021) and maximum dps (p<0.001). Rg, Vk and Vk' doses with 2.5 cm diameter ovoids were significantly higher than with 2 cm and 1.5 cm ovoids. Catheter-oriented dose point normalisation provided a homogeneous dose distribution with a 99+/-7.4% mean dose within the target volume, requiring time-position optimisation.

  6. Stability characteristics of jets in linearly-stratified, rotating fluids

    NASA Astrophysics Data System (ADS)

    Chen, Rui-Rong; Boyer, Don L.; Tao, Lijun

    A series of laboratory experiments are conducted concerning an azimuthal jet of a linearly stratified rotating fluid in a cylindrical geometry. The jet is characterized by vertical and horizontal shear and the question of the stability of the flow is considered experimentally. The jet is driven by a source-sink method characterized by a volume flow rate of strength Q. BecauseQ has no direct geophysical significance a combined external set of dimensionless parameters is introduced. These include the Rossby, Richardson and Ekman numbers, the jet aspect ratio and two geometrical parameters. A RossbyRo against RichardsonRi number flow regime diagram is presented which shows that the wave mode of the instability generally decreases with increasingRo andRi, for fixedRi andRo, respectively. In accordance with Killworth's (1980) linear stability analysis, the wave mode for smallRi (Ri ⪉ 15) depends principally onRi with the instability being largely a baroclinic one. For largerRi(Ri ⪉ 100), again as predicted by Killworth's theory, the wave mode depends primarily onRo, the instability being a barotropic one. The regime diagram can be used to estimate the wave-length of jet instabilities in the atmosphere and oceans. These estimates suggest that the wave-lengths decrease with increasing jet velocity, decreasing jet width (equivalent to increasing horizontal shear) and increasing vertical shear, other parameters being fixed. An azimuthal topography aligned along the jet has the tendency to stabilize the jet in the sense that the amplitude of the instability is shown to be dramatically smaller in the presence of the topography, other parameters being fixed. The topography also tends to increase the wave-length of the instability. A scaling analysis is advanced, and supporting experimental data presented, relating the external and internal parameters utilized.

  7. [Process optimisation: from theory to practical implementation].

    PubMed

    Töpfer, Armin

    2010-01-01

    Today process optimisation is an indispensable approach to mastering the current challenges of modern health care management. The objective is to design business processes free of defects and free of waste as well as their monitoring and controlling with meaningful test statistics. Based on the identification of essential key performance indicators, key success factors and value cash generators two basic approaches to process optimisation, which are well-established and widely used in the industry, are now being implemented in the health care sector as well: Lean Management and Six Sigma.

  8. Optimised simulated annealing for Ising spin glasses

    NASA Astrophysics Data System (ADS)

    Isakov, S. V.; Zintchenko, I. N.; Rønnow, T. F.; Troyer, M.

    2015-07-01

    We present several efficient implementations of the simulated annealing algorithm for Ising spin glasses on sparse graphs. In particular, we provide a generic code for any choice of couplings, an optimised code for bipartite graphs, and highly optimised implementations using multi-spin coding for graphs with small maximum degree and discrete couplings with a finite range. The latter codes achieve up to 50 spin flips per nanosecond on modern Intel CPUs. We also compare the performance of the codes to that of the special purpose D-Wave devices built for solving such Ising spin glass problems.

  9. Shear Stress Sensing with Elastic Microfence Structures

    NASA Technical Reports Server (NTRS)

    Cisotto, Alexxandra; Palmieri, Frank L.; Saini, Aditya; Lin, Yi; Thurman, Christopher S; Kim, Jinwook; Kim, Taeyang; Connell, John W.; Zhu, Yong; Gopalarathnam, Ashok; hide

    2015-01-01

    In this work, elastic microfences were generated for the purpose of measuring shear forces acting on a wind tunnel model. The microfences were fabricated in a two part process involving laser ablation patterning to generate a template in a polymer film followed by soft lithography with a two-part silicone. Incorporation of a fluorescent dye was demonstrated as a method to enhance contrast between the sensing elements and the substrate. Sensing elements consisted of multiple microfences prepared at different orientations to enable determination of both shear force and directionality. Microfence arrays were integrated into an optical microscope with sub-micrometer resolution. Initial experiments were conducted on a flat plate wind tunnel model. Both image stabilization algorithms and digital image correlation were utilized to determine the amount of fence deflection as a result of airflow. Initial free jet experiments indicated that the microfences could be readily displaced and this displacement was recorded through the microscope.

  10. Anisotropic Particle Acceleration in Relativistic Shear Layers

    NASA Astrophysics Data System (ADS)

    Boettcher, Markus; Liang, Edison P.; Fu, Wen

    2017-08-01

    We present results of Particle in Cell (PIC) simulations of relativistic shear layers as relevant to the relativistic jets of acive galactic nuclei and gamma-ray bursts. We study the self-generation of electro-magnetic fields and particle acceleration for various different plasma compositions (electron-ion vs. electron-positron pair vs. hybrid). Special emphasis is placed on the angular distribution of accelerated particles. We find that electron-ion shear layers lead to highly anisotropic particle distributions in the frame of the fast-moving inner spine. The beaming pattern of the highest-energy particles is much narrower than the characteristic beaming angle of 1/Gamma resulting from relativistic aberration of a co-moving isotropic distribution. This may pose a possible solution to the Lorentz-Factor crisis in blazars and explain very hard X-ray / soft gamma-ray spectra of some gamma-ray bursts.

  11. Microbursts as an aviation wind shear hazard

    NASA Technical Reports Server (NTRS)

    Fujita, T. T.

    1981-01-01

    The downburst-related accidents or near-misses of jet aircraft have been occurring at the rate of once or twice a year since 1975. A microburst with its field comparable to the length of runways can induce a wind shear which endangers landing or liftoff aircraft; the latest near miss landing of a 727 aircraft at Atlanta, Ga. in 1979 indicated that some microbursts are too small to trigger the warning device of the anemometer network at major U.S. airports. The nature of microbursts and their possible detection by Doppler radar are discussed, along with proposed studies of small-scale microbursts.

  12. Igniter jet dynamics in solid fuel ramjets

    NASA Astrophysics Data System (ADS)

    Tahsini, A. M.; Farshchi, M.

    2009-01-01

    The dynamics of a two dimensional plane jet injected at the base of a step, parallel to the wall, in backward facing step flow geometry is numerically studied. The objective of this work is to gain insight into the dynamics of the igniter flow field in solid fuel ramjet motors. Solid fuel ramjets operate by ingestion of air and subsequent combustion with a solid fuel grain such as polyethylene. The system of governing equations is solved with a finite volume approach using a structured grid in which the AUSM + scheme is used to calculate the convective fluxes. The Spalart and Allmaras turbulence model is used in these simulations. Experimental data have been used to validate the flow solver and turbulence model simulation results. The comparison of the numerical results and experimental data has validated the use of the adopted turbulence model for the study of this type of problem. A special attention is paid to the igniter jet exit location. It is shown that the wall jet igniter, issuing from the base of the step, drastically changes the structure of recirculating region of backward facing step flow and produces large and damaging shear stress on the fuel surface. Moving the igniter jet exit location to the top of the backward facing step changes the flow field favorably, by reducing the fuel surface shear stress by an order of magnitude and maintaining the recirculating region behind the step, which can provide proper residence time for the fuel-air mixture chemical reactions.

  13. Flight effects on jet mixing noise - Scaling laws predicted for single jets from flight simulation data

    NASA Astrophysics Data System (ADS)

    Buckley, R.; Morfey, C. L.

    1983-04-01

    The geometric acoustics model of static jet mixing noise of Szewczyk, Morfey and Tester (1978) is successfully generalized to jets in flight using flight simulation data. The analysis is limited to unheated jets. The reduction leads to a master spectrum of the shear layer quadrupole turbulence that is proportional at all Strouhal numbers to (1 - lambda) to the 5th power, where lambda is the ratio of the flight speed to the jet speed. Of the three scaling parameters used in describing the turbulent eddies, the transverse size is found to be dependent on compressibility at higher Mach numbers and to increase somewhat as lambda increases. Even though corresponding compressibility and lambda dependences for the axial size and convection speed are clearly present, they have not yet been reduced satisfactorily to quantitative form. The turbulent mixing process in the primary jet shear layer is modeled by an equivalent source distribution that includes convection, noncompactness, and directivity and involves for these purposes a set of velocity parameters describing the eddies.

  14. Modeling of Turbulent Free Shear Flows

    NASA Technical Reports Server (NTRS)

    Yoder, Dennis A.; DeBonis, James R.; Georgiadis, Nicolas J.

    2013-01-01

    The modeling of turbulent free shear flows is crucial to the simulation of many aerospace applications, yet often receives less attention than the modeling of wall boundary layers. Thus, while turbulence model development in general has proceeded very slowly in the past twenty years, progress for free shear flows has been even more so. This paper highlights some of the fundamental issues in modeling free shear flows for propulsion applications, presents a review of past modeling efforts, and identifies areas where further research is needed. Among the topics discussed are differences between planar and axisymmetric flows, development versus self-similar regions, the effect of compressibility and the evolution of compressibility corrections, the effect of temperature on jets, and the significance of turbulent Prandtl and Schmidt numbers for reacting shear flows. Large eddy simulation greatly reduces the amount of empiricism in the physical modeling, but is sensitive to a number of numerical issues. This paper includes an overview of the importance of numerical scheme, mesh resolution, boundary treatment, sub-grid modeling, and filtering in conducting a successful simulation.

  15. Absolute and Convective Instability of a Liquid Jet

    NASA Technical Reports Server (NTRS)

    Lin, S. P.; Hudman, M.; Chen, J. N.

    1999-01-01

    The existence of absolute instability in a liquid jet has been predicted for some time. The disturbance grows in time and propagates both upstream and downstream in an absolutely unstable liquid jet. The image of absolute instability is captured in the NASA 2.2 sec drop tower and reported here. The transition from convective to absolute instability is observed experimentally. The experimental results are compared with the theoretical predictions on the transition Weber number as functions of the Reynolds number. The role of interfacial shear relative to all other relevant forces which cause the onset of jet breakup is explained.

  16. Spectra and Diffusion in a Round Turbulent Jet

    NASA Technical Reports Server (NTRS)

    Corrsin, Stanley; Uberoi, Mahinder S

    1951-01-01

    In a round turbulent jet at room temperature, measurement of the shear correlation coefficient as a function of frequency (through band-pass filters) has given a rather direct verification of Kolmogoroff's local-isotropy hypothesis. One-dimensional power spectra of velocity and temperature fluctuations, measured in unheated and heated jets, respectively, have been contrasted. Under the same conditions, the two corresponding transverse correlation functions have been measured and compared. Finally, measurements have been made of the mean thermal wakes behind local (line) heat sources in the unheated turbulent jet, and the order of magnitude of the temperature fluctuations has been determined.

  17. Penetration Characteristics of Air, Carbon Dioxide and Helium Transverse Sonic Jets in Mach 5 Cross Flow

    PubMed Central

    Erdem, Erinc; Kontis, Konstantinos; Saravanan, Selvaraj

    2014-01-01

    An experimental investigation of sonic air, CO2 and Helium transverse jets in Mach 5 cross flow was carried out over a flat plate. The jet to freestream momentum flux ratio, J, was kept the same for all gases. The unsteady flow topology was examined using high speed schlieren visualisation and PIV. Schlieren visualisation provided information regarding oscillating jet shear layer structures and bow shock, Mach disc and barrel shocks. Two-component PIV measurements at the centreline, provided information regarding jet penetration trajectories. Barrel shocks and Mach disc forming the jet boundary were visualised/quantified also jet penetration boundaries were determined. Even though J is kept the same for all gases, the penetration patterns were found to be remarkably different both at the nearfield and the farfield. Air and CO2 jet resulted similar nearfield and farfield penetration pattern whereas Helium jet spread minimal in the nearfield. PMID:25494348

  18. Shear flexibility for structures

    NASA Technical Reports Server (NTRS)

    Stangeland, Maynard L. (Inventor)

    1976-01-01

    This device comprises a flexible sheet member having cross convolutions oriented 45.degree. to the shear vector with spherical reliefs at the convolution junctions. The spherical reliefs are essential to the shear flexibility by interrupting the principal stress lines that act along the ridges of the convolutions. The spherical reliefs provide convolutions in both directions in the plane of the cross-convolution ridges.

  19. Shear flexibility for structures

    NASA Technical Reports Server (NTRS)

    Stangeland, Maynard L. (Inventor)

    1977-01-01

    This device comprises a flexible sheet member having cross convolutions oriented 45.degree. to the shear vector with spherical reliefs at the convolution junctions. The spherical reliefs are essential to the shear flexibility by interrupting the principal stress lines that act along the ridges of the convolutions. The spherical reliefs provide convolutions in both directions in the plane of the cross-convolution ridges.

  20. Mean flow and turbulence measurements in a Mach 5 shear layer.

    NASA Technical Reports Server (NTRS)

    Morrisette, E. L.; Birch, S. F.; Wagner, R. D.

    1973-01-01

    Hot-wire study of turbulent mixing in the near field of a Mach 5 jet with extension of the results into the hypersonic range. Mean and fluctuating measurement data are given for the free shear layer of the 10.6-cm diameter jet which was contained in a 61-by-61 cm vacuum chamber and exhausted into a diffuser 44 cm downstream of the jet exit. An auxiliary air supply was used to equalize the static pressures in the chamber and the nozzle. The nozzle wall boundary layer was turbulent at the jet exit, providing measurement data at higher Reynolds numbers, which are also included.

  1. Stretched Inertial Jets

    NASA Astrophysics Data System (ADS)

    Ghabache, Elisabeth; Antkowiak, Arnaud; Seon, Thomas; Villermaux, Emmanuel

    2015-11-01

    Liquid jets often arise as short-lived bursting liquid flows. Cavitation or impact-driven jets, bursting champagne bubbles, shaped-charge jets, ballistospores or drop-on-demand inkjet printing are a few examples where liquid jets are suddenly released. The trademark of all these discharge jets is the property of being stretched, due to the quenching injection. the present theoretical and experimental investigation, the structure of the jet flow field will be unraveled experimentally for a few emblematic occurrences of discharge jets. Though the injection markedly depends on each flow configuration, the jet velocity field will be shown to be systematically and rapidly attracted to the universal stretching flow z/t. The emergence of this inertial attractor actually only relies on simple kinematic ingredients, and as such is fairly generic. The universality of the jet velocity structure will be discussed.

  2. Investigating the Dynamics of Canonical Flux Tubes in Jet Geometry

    NASA Astrophysics Data System (ADS)

    Lavine, Eric; You, Setthivoine

    2014-10-01

    Highly collimated plasma jets are frequently observed at galactic, stellar, and laboratory scales. Some models suppose these jets are magnetohydrodynamically-driven magnetic flux tubes filled with flowing plasma, but they do not agree on a collimation process. Some evidence supporting a universal MHD pumping mechanism has been obtained from planar electrode experiments with aspect ratios of ~10:1 however, these jets are subject to kink instabilities beyond a certain length and are unable to replicate the remarkable aspect ratios (10-1000:1) seen in astrophysical systems. Other models suppose these jets are flowing Z-pinch plasmas and experiments that use stabilizing shear flows have achieved aspect ratios of ~30:1, but are line tied at both ends. Can both collimation and stabilization mechanisms work together to produce long jets without kink instabilities and only one end tied to the central object? This question is evaluated from the point of view of canonical flux tubes and canonical helicity transport, indicating that jets can become long and collimated due to a combination of strong helical shear flows and conversion of magnetic helicity into kinetic helicity. The MOCHI LabJet experiment is designed to study this in the laboratory. Supported by US DoE Early Career Grant DE-SC0010340.

  3. Analysis of the stability and sensitivity of jets in crossflow

    NASA Astrophysics Data System (ADS)

    Regan, Marc; Mahesh, Krishnan

    2016-11-01

    Jets in crossflow (transverse jets) are a canonical fluid flow in which a jet of fluid is injected normal to a crossflow. A high-fidelity, unstructured, incompressible, DNS solver is shown (Iyer & Mahesh 2016) to reproduce the complex shear layer instability seen in low-speed jets in crossflow experiments. Vertical velocity spectra taken along the shear layer show good agreement between simulation and experiment. An analogy to countercurrent mixing layers has been proposed to explain the transition from absolute to convective stability with increasing jet to crossflow ratios. Global linear stability and adjoint sensitivity techniques are developed within the unstructured DNS solver in an effort to further understand the stability and sensitivity of jets in crossflow. An Arnoldi iterative approach is used to solve for the most unstable eigenvalues and their associated eigenmodes for the direct and adjoint formulations. Frequencies from the direct and adjoint modal analyses show good agreement with simulation and experiment. Development, validation, and results for the transverse jet will be presented. Supported by AFOSR.

  4. 3D printed fluidics with embedded analytic functionality for automated reaction optimisation

    PubMed Central

    Capel, Andrew J; Wright, Andrew; Harding, Matthew J; Weaver, George W; Li, Yuqi; Harris, Russell A; Edmondson, Steve; Goodridge, Ruth D

    2017-01-01

    Additive manufacturing or ‘3D printing’ is being developed as a novel manufacturing process for the production of bespoke micro- and milliscale fluidic devices. When coupled with online monitoring and optimisation software, this offers an advanced, customised method for performing automated chemical synthesis. This paper reports the use of two additive manufacturing processes, stereolithography and selective laser melting, to create multifunctional fluidic devices with embedded reaction monitoring capability. The selectively laser melted parts are the first published examples of multifunctional 3D printed metal fluidic devices. These devices allow high temperature and pressure chemistry to be performed in solvent systems destructive to the majority of devices manufactured via stereolithography, polymer jetting and fused deposition modelling processes previously utilised for this application. These devices were integrated with commercially available flow chemistry, chromatographic and spectroscopic analysis equipment, allowing automated online and inline optimisation of the reaction medium. This set-up allowed the optimisation of two reactions, a ketone functional group interconversion and a fused polycyclic heterocycle formation, via spectroscopic and chromatographic analysis. PMID:28228852

  5. An efficient and flexible web services-based multidisciplinary design optimisation framework for complex engineering systems

    NASA Astrophysics Data System (ADS)

    Li, Liansheng; Liu, Jihong

    2012-08-01

    Multidisciplinary design optimisation (MDO) involves multiple disciplines, multiple coupled relationships and multiple processes, which is implemented by different specialists dispersed geographically on heterogeneous platforms with different analysis and optimisation tools. The product design data integration and data sharing among the participants hampers the development and applications of MDO in enterprises seriously. Therefore, a multi-hierarchical integrated product design data model (MH-iPDM) supporting the MDO in the web environment and a web services-based multidisciplinary design optimisation (Web-MDO) framework are proposed in this article. Based on the enabling technologies including web services, ontology, workflow, agent, XML and evidence theory, the proposed framework enables the designers geographically dispersed to work collaboratively in the MDO environment. The ontology-based workflow enables the logical reasoning of MDO to be processed dynamically. The evidence theory-based uncertainty reasoning and analysis supports the quantification, aggregation and analysis of the conflicting epistemic uncertainty from multiple sources, which improves the quality of product. Finally, a proof-of-concept prototype system is developed using J2EE and an example of supersonic business jet is demonstrated to verify the autonomous execution of MDO strategies and the effectiveness of the proposed approach.

  6. 3D printed fluidics with embedded analytic functionality for automated reaction optimisation.

    PubMed

    Capel, Andrew J; Wright, Andrew; Harding, Matthew J; Weaver, George W; Li, Yuqi; Harris, Russell A; Edmondson, Steve; Goodridge, Ruth D; Christie, Steven D R

    2017-01-01

    Additive manufacturing or '3D printing' is being developed as a novel manufacturing process for the production of bespoke micro- and milliscale fluidic devices. When coupled with online monitoring and optimisation software, this offers an advanced, customised method for performing automated chemical synthesis. This paper reports the use of two additive manufacturing processes, stereolithography and selective laser melting, to create multifunctional fluidic devices with embedded reaction monitoring capability. The selectively laser melted parts are the first published examples of multifunctional 3D printed metal fluidic devices. These devices allow high temperature and pressure chemistry to be performed in solvent systems destructive to the majority of devices manufactured via stereolithography, polymer jetting and fused deposition modelling processes previously utilised for this application. These devices were integrated with commercially available flow chemistry, chromatographic and spectroscopic analysis equipment, allowing automated online and inline optimisation of the reaction medium. This set-up allowed the optimisation of two reactions, a ketone functional group interconversion and a fused polycyclic heterocycle formation, via spectroscopic and chromatographic analysis.

  7. Optimised system configuration for stent manufacturing.

    PubMed

    Rekowski, Ron

    2008-01-01

    Optimising the major components of a laser stent machining platform will lead to improved part quality and machine throughput. Mechanical, control and software elements are reviewed here. Trends in stent design are also discussed together with their implications on these machine design elements.

  8. On Optimal Development and Becoming an Optimiser

    ERIC Educational Resources Information Center

    de Ruyter, Doret J.

    2012-01-01

    The article aims to provide a justification for the claim that optimal development and becoming an optimiser are educational ideals that parents should pursue in raising their children. Optimal development is conceptualised as enabling children to grow into flourishing persons, that is persons who have developed (and are still developing) their…

  9. Optimising fuel treatments over time and space

    Treesearch

    Woodam Chung; Greg Jones; Kurt Krueger; Jody Bramel; Marco Contreras

    2013-01-01

    Fuel treatments have been widely used as a tool to reduce catastrophic wildland fire risks in many forests around the world. However, it is a challenging task for forest managers to prioritise where, when and how to implement fuel treatments across a large forest landscape. In this study, an optimisation model was developed for long-term fuel management decisions at a...

  10. Structure and Mixing Characterization of Variable Density Transverse Jet Flows

    NASA Astrophysics Data System (ADS)

    Gevorkyan, Levon

    This dissertation describes an experimental study of the structural and mixing characteristics of transverse jets, or jets in crossfiow (JICF). Hot-wire anemometry, stereo particle image velocimetry (PIV), and acetone planar laser-induced fiuorescence (PLIF) measurements were utilized to illuminate and quantify the wind-ward (upstream) jet shear layer instability characteristics and their relationship to the velocity field evolution, as well as the effect of the overall velocity field on the scalar field distribution and resulting mixing characteristics. Transverse jets of various jet-to-crossfiow momentum flux ratios in the range 41 ≥ J ≥ 2, and jet-to-crossfiow density ratios in the range 1.00 ≥ S ≥ 0.35, were generated using mixtures of helium and nitrogen in the jet fluid. Jets were injected from one of three different injectors explored: a convergent nozzle with circular geometry which was mounted flush with the wind tunnel floor, another convergent nozzle with circular geometry whose exit plane lies above the crossfiow boundary layer, and a flush-mounted straight pipe injector with a circular orifice. Jet Reynolds number was kept constant for the majority of the mixing and structural exploration experiments at Rej = 1900, except when the effect of Reynolds number on cross-sectional jet structure was explored. Previous hot-wire based measurements at UCLA suggest that the upstream jet shear layer transitions from convective instability to absolute instability, giving rise to self-excited nonlinear states, as either the momentum flux ratio is lowered below J ≈10, or the density ratio is lowered below S ≈ 0.45 for the JICF injected from the flush nozzle injector. A similar transition to absolute instability when lowering momentum flux ratio was found in this work for the flush-mounted pipe injector. Cross-sectional PLIF measurements in the present studies suggested clear correspondence between the formation of a symmetric counter-rotating vortex pair

  11. Control of jet noise

    NASA Technical Reports Server (NTRS)

    Schreck, Stefan

    1992-01-01

    To investigate the possibility of active control of jet noise, knowledge of the noise generation mechanisms in natural jets is essential. Once these mechanisms are determined, active control can be used to manipulate the noise production processes. We investigated the evolution of the flow fields and the acoustic fields of rectangular and circular jets. A predominant flapping mode was found in the supersonic rectangular jets. We hope to increase the spreading of supersonic jets by active control of the flapping mode found in rectangular supersonic jets.

  12. Understanding jet noise.

    PubMed

    Karabasov, S A

    2010-08-13

    Jets are one of the most fascinating topics in fluid mechanics. For aeronautics, turbulent jet-noise modelling is particularly challenging, not only because of the poor understanding of high Reynolds number turbulence, but also because of the extremely low acoustic efficiency of high-speed jets. Turbulent jet-noise models starting from the classical Lighthill acoustic analogy to state-of-the art models were considered. No attempt was made to present any complete overview of jet-noise theories. Instead, the aim was to emphasize the importance of sound generation and mean-flow propagation effects, as well as their interference, for the understanding and prediction of jet noise.

  13. Modern developments in shear flow control with swirl

    NASA Technical Reports Server (NTRS)

    Farokhi, Saeed; Taghavi, R.

    1990-01-01

    Passive and active control of swirling turbulent jets is experimentally investigated. Initial swirl distribution is shown to dominate the free jet evolution in the passive mode. Vortex breakdown, a manifestation of high intensity swirl, was achieved at below critical swirl number (S = 0.48) by reducing the vortex core diameter. The response of a swirling turbulent jet to single frequency, plane wave acoustic excitation was shown to depend strongly on the swirl number, excitation Strouhal number, amplitude of the excitation wave, and core turbulence in a low speed cold jet. A 10 percent reduction of the mean centerline velocity at x/D = 9.0 (and a corresponding increase in the shear layer momentum thickness) was achieved by large amplitude internal plane wave acoustic excitation. Helical instability waves of negative azimuthal wave numbers exhibit larger amplification rates than the plane waves in swirling free jets, according to hydrodynamic stability theory. Consequently, an active swirling shear layer control is proposed to include the generation of helical instability waves of arbitrary helicity and the promotion of modal interaction, through multifrequency forcing.

  14. Experimental assessment of theory for refraction of sound by a shear layer

    NASA Technical Reports Server (NTRS)

    Schlinker, R. H.; Amiet, R. K.

    1978-01-01

    The refraction angle and amplitude changes associated with sound transmission through a circular, open-jet shear layer were studied in a 0.91 m diameter open jet acoustic research tunnel. Free stream Mach number was varied from 0.1 to 0.4. Good agreement between refraction angle correction theory and experiment was obtained over the test Mach number, frequency and angle measurement range for all on-axis acoustic source locations. For off-axis source positions, good agreement was obtained at a source-to-shear layer separation distance greater than the jet radius. Measureable differences between theory and experiment occurred at a source-to-shear layer separation distance less than one jet radius. A shear layer turbulence scattering experiment was conducted at 90 deg to the open jet axis for the same free stream Mach numbers and axial source locations used in the refraction study. Significant discrete tone spectrum broadening and tone amplitude changes were observed at open jet Mach numbers above 0.2 and at acoustic source frequencies greater than 5 kHz. More severe turbulence scattering was observed for downstream source locations.

  15. Fighting wind shear

    NASA Astrophysics Data System (ADS)

    A “coherent and sustained program” of improved radar detection of weather, pilot training, and better communication between pilots and air controllers can greatly reduce the risk of wind shear to airplanes landing or taking off, according to a National Research Council (NRC) committee.Wind shear, characterized by winds rapidly changing direction and speed, has caused several serious accidents in recent years; among the most notable is the July 8, 1982, crash of a Pan American World Airlines jetliner at the New Orleans International Airport, which killed 153 persons. Following the accident, Congress directed the Federal Aviation Administration (FAA) to contract with the NRC to study wind shear.

  16. Angular shear plate

    DOEpatents

    Ruda, Mitchell C [Tucson, AZ; Greynolds, Alan W [Tucson, AZ; Stuhlinger, Tilman W [Tucson, AZ

    2009-07-14

    One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative rotation of the plates and by the use of an appropriate polynomial function for the thickness of the shear plate, light passing therethrough can be focused at variable positions.

  17. On vortex pairing in several free shear layer containing high Reynolds number flows

    NASA Astrophysics Data System (ADS)

    Samimy, Mo; Crawley, Michael

    2015-11-01

    There are several free shear flows with-well known Kevin Helmholtz instability, which contain an additional instability mechanism. For example, a jet has shear layer and jet column instabilities, a stalled airfoil has shear layer and wake instabilities, and a cavity flow has a shear layer instability and Rossiter modes. The shear layer's most amplified frequency is normally several times larger than that of the other instability. Typically, the structures associated with the lower frequency instability are observed in the experiments. There is not much information in the literature, especially in high Reynolds number flows, on whether these structures are generated directly or by multiple merging of smaller structures generated by the shear layer instability. Single or multiple merging has been shown in the literature in only low Reynolds number flows (e.g. in jets). Our recent experimental results in high Reynolds number flows excited by plasma actuators seem to show the occurrence of multiple merging events before the observation of lower frequency large-scale coherent structures. The experimental PIV images obtained in jets using reconstructed flow and in stalled airfoils obtained using phase averaging. Supported by AFOSR, ARO, AFRL.

  18. Jupiter's unearthly jets: a new idealised model

    NASA Astrophysics Data System (ADS)

    Thomson, S. I.; McIntyre, M. E.

    2013-09-01

    A longstanding mystery about Jupiter has been the straightness of real Jovian jets, quite unlike terrestrial strong jets with their characteristic long-wavelength meandering. The problem is addressed in two steps. The first is to take seriously the classic Ingersoll-Cuong [4], Dowling-Ingersoll [1] and Stamp-Dowling [12] scenarios, with deep zonal jets in the convection layer underlying the weather layer, recognising moreover the relevance of Arnol'd's second shear-stability criterion ('A2 stability') and hence the possibility of stable upper jets even with reversed upper potential-vorticity (PV) gradients (e.g. [12, 2, 3]). The second step is to improve the realism of the small-scale forcing used to represent the effects of Jupiter's moist convection in physical space, albeit within an idealised, 1½-layer setting. The real moist convection is likely to generate cyclonic as well as anticyclonic PV anomalies but with unequal strengths ('PV-biased forcing'), and to occur preferentially where the interface to the deep flow is coldest (e.g. [5]). The resulting model appears to have promise as a way of explaining the jet straightness and of constraining possible values of the Rossby deformation length LD for the real planet, as well as suggesting new guidelines for general circulation model studies.

  19. Lateral jet injection into typical combustor flowfields

    NASA Technical Reports Server (NTRS)

    Lilley, D. G.

    1986-01-01

    The experimental problem of lateral jet injection into typical flow fields in the absence of combustion was studied. All flow fields being investigated have no expansion of the crossflow (the test section to swirler diameter ratio D/d = 1), after its passage through an optional swirler (with swirl vane angle phi = 0 (swirler removed), 45, and 70 degree). The lateral jet(s) is(are) located one test-section diameter downstream of the test-section inlet (x/D = 1). The lateral jets have round-sectioned nozzles, each of which has an area of 1/100th of the cross sectional area of the crossflow (A sub j/A sub c = 1/100). Jet-to-crossflow velocity ratios of R = v sub j/u sub o = 2, 4, and 6 were investigated. Helium-bubble low visualization, five-hole pitot probe time-mean velocity measurements, and single-wire time-mean velocity and normal and shear stress turbulence data were obtained in the research program.

  20. Glottal jet inertance

    NASA Astrophysics Data System (ADS)

    Mphail, Michael; Krane, Michael

    2016-11-01

    Estimates of an inertive contribution of the glottal jet to glottal aerodynamic resistance is presented. Given that inertance of the flow in a constriction can be expressed in terms of the kinetic energy of the flow, and that a jet is a maximum kinetic energy flow pattern, it is argued that the glottal jet possesses its own inertance which is at least as large as that of the vocal tract. These arguments are supported by estimates of inertance obtained from simulations of an unsteady flow through an axisymmetric orifice, and of a compliant constriction with the approximate shape and mechanical properties of the vocal folds. It is further shown that the inertive effect of the glottal jet depends on the jet path and jet mixing, with a slowly diffusing, symmetric jet showing higher inertance than an asymmetric jet which rapidly mixes with supraglottal air. Acknowledge support of NIH Grant 2R01DC005642-10A1.

  1. Flow field topology of submerged jets with fractal generated turbulence

    NASA Astrophysics Data System (ADS)

    Cafiero, Gioacchino; Discetti, Stefano; Astarita, Tommaso

    2015-11-01

    Fractal grids (FGs) have been recently an object of numerous investigations due to the interesting capability of generating turbulence at multiple scales, thus paving the way to tune mixing and scalar transport. The flow field topology of a turbulent air jet equipped with a square FG is investigated by means of planar and volumetric particle image velocimetry. The comparison with the well-known features of a round jet without turbulence generators is also presented. The Reynolds number based on the nozzle exit section diameter for all the experiments is set to about 15 000. It is demonstrated that the presence of the grid enhances the entrainment rate and, as a consequence, the scalar transfer of the jet. Moreover, due to the effect of the jet external shear layer on the wake shed by the grid bars, the turbulence production region past the grid is significantly shortened with respect to the documented behavior of fractal grids in free-shear conditions. The organization of the large coherent structures in the FG case is also analyzed and discussed. Differently from the well-known generation of toroidal vortices due to the growth of azimuthal disturbances within the jet shear layer, the fractal grid introduces cross-wise disturbs which produce streamwise vortices; these structures, although characterized by a lower energy content, have a deeper streamwise penetration than the ring vortices, thus enhancing the entrainment process.

  2. Turbulence Model Comparisons for Shear Layers and Axisymmetric Jets.

    DTIC Science & Technology

    1979-10-01

    ieatr p)Cifeet at tills, amxal location. Ihle kf2 model prediction show., s a reduced eClocii\\ cor pa red %kithI c ’peinelnt indicating that mnixing is...It\\ OftI hie’\\() ()I rectioI.A lil aC amlounlt Of hecat if od tced 11 rm mnu te tClifIilIt tIeC oll reetalI It". Com pa I solns \\kere Iltadc for thle...STREAMLINE y=y*(2) Figure A-2. Plane mixing layer fluid element (top half). 99 * - l~lgN aw G PA = a ma DIJ iOn flhlD -T x+ P6(x) max + 2 sine Z pdy y

  3. Fountain-Jet Turbulence.

    DTIC Science & Technology

    1980-09-01

    and 3 times higher than expected from free- jet results. Hill et al., (Reference 6) in work with foun- tain jets impacting fuselage models, detected ...delineate the origins of the turbulent anomalies associated with fountain jets by extending the previous studies. The results are presented herein...jet velocities were detected with a Thermal Systems Inc. Model 1050 dual-channel constant-temperature anemometer equipped with a Thermal Systems Inc

  4. Jets of incipient liquids

    NASA Astrophysics Data System (ADS)

    Reshetnikov, A. V.; Mazheiko, N. A.; Skripov, V. P.

    2000-05-01

    Jets of incipient water escaping into the atmosphere through a short channel are photographed. In some experiments. complete disintegration of the jet is observed. The relationship of this phenomenon with intense volume incipience is considered. The role of the Coanda effect upon complete opening of the jet is revealed. Measurement results of the recoil force R of the jets of incipient liquids are presented. Cases of negative thrust caused by the Coanda effect are noted. Generalization of experimental data is proposed.

  5. NASA Jet Noise Research

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda

    2012-01-01

    The presentation highlights jet-noise research conducted in the Subsonic Fixed Wing, Supersonics, and Environmentally Responsible Aviation Projects in the Fundamental Aeronautics Program at NASA. The research efforts discussed include NASA's updated Aircraft NOise Prediction Program (ANOPP2), acoustic-analogy-based prediction tools, jet-surface-interaction studies, plasma-actuator investigations, N+2 Supersonics Validation studies, rectangular-jet experiments, twin-jet experiments, and Hybrid Wind Body (HWB) activities.

  6. Magnetic Field Generation in Core-sheath Jets via the Kinetic Kelvin-Helmholtz Instability

    NASA Astrophysics Data System (ADS)

    Nishikawa, K.-I.; Hardee, P. E.; Duţan, I.; Niemiec, J.; Medvedev, M.; Mizuno, Y.; Meli, A.; Sol, H.; Zhang, B.; Pohl, M.; Hartmann, D. H.

    2014-09-01

    We have investigated magnetic field generation in velocity shears via the kinetic Kelvin-Helmholtz instability (kKHI) using a relativistic plasma jet core and stationary plasma sheath. Our three-dimensional particle-in-cell simulations consider plasma jet cores with Lorentz factors of 1.5, 5, and 15 for both electron-proton and electron-positron plasmas. For electron-proton plasmas, we find generation of strong large-scale DC currents and magnetic fields that extend over the entire shear surface and reach thicknesses of a few tens of electron skin depths. For electron-positron plasmas, we find generation of alternating currents and magnetic fields. Jet and sheath plasmas are accelerated across the shear surface in the strong magnetic fields generated by the kKHI. The mixing of jet and sheath plasmas generates a transverse structure similar to that produced by the Weibel instability.

  7. Shear coaxial injector instability mechanisms

    NASA Technical Reports Server (NTRS)

    Puissant, C.; Kaltz, T.; Glogowski, M.; Micci, M.

    1994-01-01

    There is no definitive knowledge of which of several concurrent processes ultimately results in unstable combustion within liquid rocket chambers employing shear coaxial injectors. Possible explanations are a detrimental change in the atomization characteristics due to a decrease in the gas-to-liquid velocity ratio, a change in the gas side injector pressure drop allowing acoustic coupling to the propellant feed system or the disappearance of a stabilizing recirculation region at the base of the LOX post. The aim of this research effort is to investigate these proposed mechanisms under conditions comparable to actual engine operation. Spray characterization was accomplished with flash photography and planar laser imaging to examine the overall spray morphology and liquid jet breakup processes and with a PDPA to quantify the spatial distribution of droplet size and mean axial velocity. A simplified stability model based on the Rayleigh criterion was constructed for the flow dynamics occurring within the chamber and injector to evaluate the potential coupling between the chamber and injector acoustic modes and was supported by high frequency measurements of chamber and injector pressure oscillations. To examine recirculation within the LOX post recess, velocity measurements were performed in the recess region by means of LDV. Present experiments were performed under noncombusting conditions using LOX/GH2 stimulants at pressures up to 4 MPa.

  8. Optimising a vortex fluidic device for controlling chemical reactivity and selectivity

    NASA Astrophysics Data System (ADS)

    Yasmin, Lyzu; Chen, Xianjue; Stubbs, Keith A.; Raston, Colin L.

    2013-07-01

    A vortex fluidic device (VFD) involving a rapidly rotating tube open at one end forms dynamic thin films at high rotational speed for finite sub-millilitre volumes of liquid, with shear within the films depending on the speed and orientation of the tube. Continuous flow operation of the VFD where jet feeds of solutions are directed to the closed end of the tube provide additional tuneable shear from the viscous drag as the liquid whirls along the tube. The versatility of this simple, low cost microfluidic device, which can operate under confined mode or continuous flow is demonstrated in accelerating organic reactions, for model Diels-Alder dimerization of cyclopentadienes, and sequential aldol and Michael addition reactions, in accessing unusual 2,4,6-triarylpyridines. Residence times are controllable for continuous flow processing with the viscous drag dominating the shear for flow rates >0.1 mL/min in a 10 mm diameter tube rotating at >2000 rpm.

  9. Bacterial trapping in shear

    NASA Astrophysics Data System (ADS)

    Rusconi, Roberto; Guasto, Jeffrey S.; Stocker, Roman

    2012-11-01

    Bacteria are ubiquitously exposed to flow, both in natural environments and artificial devices (e.g., catheters), where confining surfaces create non-uniform shear. While the effects of shear on passive particles are well understood, little is known about the consequences of shear on motile bacteria. We exposed bacteria having different motility strategies (e.g., run-and-tumble, run-and-reverse) to microfluidic Poiseuille flows and quantified the swimming kinematics and cell distribution in the channel using video-microscopy. We discovered that the coupling of motility and a spatially varying shear results in a dramatic trapping of motile cells in high-shear regions, and conversely a strong depletion in the low-shear portion of the channel. We demonstrate experimentally that this trapping process is robust across species such as Bacillus subtilis and Pseudomonas aeruginosa, and can have far-reaching consequences on bacterial transport, by (i) counteracting bacterial chemotactic responses; and (ii) enhancing surface attachment and thus biofilm formation by trapping cells near walls. More generally, this work shows that-despite the low Reynolds number-the coupling of flow and self-propulsion can be nonlinear and not simply a superposition of the two effects.

  10. Large-eddy simulation of turbulent circular jet flows

    SciTech Connect

    Jones, S. C.; Sotiropoulos, F.; Sale, M. J.

    2002-07-01

    This report presents a numerical method for carrying out large-eddy simulations (LES) of turbulent free shear flows and an application of a method to simulate the flow generated by a nozzle discharging into a stagnant reservoir. The objective of the study was to elucidate the complex features of the instantaneous flow field to help interpret the results of recent biological experiments in which live fish were exposed to the jet shear zone. The fish-jet experiments were conducted at the Pacific Northwest National Laboratory (PNNL) under the auspices of the U.S. Department of Energy’s Advanced Hydropower Turbine Systems program. The experiments were designed to establish critical thresholds of shear and turbulence-induced loads to guide the development of innovative, fish-friendly hydropower turbine designs.

  11. Buckling optimisation of sandwich cylindrical panels

    NASA Astrophysics Data System (ADS)

    Abouhamzeh, M.; Sadighi, M.

    2016-06-01

    In this paper, the buckling load optimisation is performed on sandwich cylindrical panels. A finite element program is developed in MATLAB to solve the governing differential equations of the global buckling of the structure. In order to find the optimal solution, the genetic algorithm Toolbox in MATLAB is implemented. Verifications are made for both the buckling finite element code and also the results from the genetic algorithm by comparisons to the results available in literature. Sandwich cylindrical panels are optimised for the buckling strength with isotropic or orthotropic cores with different boundary conditions. Results are presented in terms of stacking sequence of fibers in the face sheets and core to face sheet thickness ratio.

  12. Acoustic Resonator Optimisation for Airborne Particle Manipulation

    NASA Astrophysics Data System (ADS)

    Devendran, Citsabehsan; Billson, Duncan R.; Hutchins, David A.; Alan, Tuncay; Neild, Adrian

    Advances in micro-electromechanical systems (MEMS) technology and biomedical research necessitate micro-machined manipulators to capture, handle and position delicate micron-sized particles. To this end, a parallel plate acoustic resonator system has been investigated for the purposes of manipulation and entrapment of micron sized particles in air. Numerical and finite element modelling was performed to optimise the design of the layered acoustic resonator. To obtain an optimised resonator design, careful considerations of the effect of thickness and material properties are required. Furthermore, the effect of acoustic attenuation which is dependent on frequency is also considered within this study, leading to an optimum operational frequency range. Finally, experimental results demonstrated good particle levitation and capture of various particle properties and sizes ranging to as small as 14.8 μm.

  13. Pre-operative optimisation of lung function

    PubMed Central

    Azhar, Naheed

    2015-01-01

    The anaesthetic management of patients with pre-existing pulmonary disease is a challenging task. It is associated with increased morbidity in the form of post-operative pulmonary complications. Pre-operative optimisation of lung function helps in reducing these complications. Patients are advised to stop smoking for a period of 4–6 weeks. This reduces airway reactivity, improves mucociliary function and decreases carboxy-haemoglobin. The widely used incentive spirometry may be useful only when combined with other respiratory muscle exercises. Volume-based inspiratory devices have the best results. Pharmacotherapy of asthma and chronic obstructive pulmonary disease must be optimised before considering the patient for elective surgery. Beta 2 agonists, inhaled corticosteroids and systemic corticosteroids, are the main drugs used for this and several drugs play an adjunctive role in medical therapy. A graded approach has been suggested to manage these patients for elective surgery with an aim to achieve optimal pulmonary function. PMID:26556913

  14. Effect of Gravity on the Near Field Flow Structure of Helium Jet in Air

    NASA Technical Reports Server (NTRS)

    Agrawal, Ajay K.; Parthasarathy, Ramkumar; Griffin, DeVon

    2002-01-01

    Experiments have shown that a low-density jet injected into a high-density surrounding medium undergoes periodic oscillations in the near field. Although the flow oscillations in these jets at Richardson numbers about unity are attributed to the buoyancy, the direct physical evidence has not been acquired in the experiments. If the instability were indeed caused by buoyancy, the near-field flow structure would undergo drastic changes upon removal of gravity in the microgravity environment. The present study was conducted to investigate this effect by simulating microgravity environment in the 2.2-second drop tower at the NASA Glenn Research Center. The non-intrusive, rainbow schlieren deflectometry technique was used for quantitative measurements of helium concentrations in buoyant and non-buoyant jets. Results in a steady jet show that the radial growth of the jet shear layer in Earth gravity is hindered by the buoyant acceleration. The jet in microgravity was 30 to 70 percent wider than that in Earth gravity. The microgravity jet showed typical growth of a constant density jet shear layer. In case of a self-excited helium jet in Earth gravity, the flow oscillations continued as the jet flow adjusted to microgravity conditions in the drop tower. The flow oscillations were however not present at the end of the drop when steady microgravity conditions were reached.

  15. Treatment planning optimisation in proton therapy

    PubMed Central

    McGowan, S E; Burnet, N G; Lomax, A J

    2013-01-01

    ABSTRACT. The goal of radiotherapy is to achieve uniform target coverage while sparing normal tissue. In proton therapy, the same sources of geometric uncertainty are present as in conventional radiotherapy. However, an important and fundamental difference in proton therapy is that protons have a finite range, highly dependent on the electron density of the material they are traversing, resulting in a steep dose gradient at the distal edge of the Bragg peak. Therefore, an accurate knowledge of the sources and magnitudes of the uncertainties affecting the proton range is essential for producing plans which are robust to these uncertainties. This review describes the current knowledge of the geometric uncertainties and discusses their impact on proton dose plans. The need for patient-specific validation is essential and in cases of complex intensity-modulated proton therapy plans the use of a planning target volume (PTV) may fail to ensure coverage of the target. In cases where a PTV cannot be used, other methods of quantifying plan quality have been investigated. A promising option is to incorporate uncertainties directly into the optimisation algorithm. A further development is the inclusion of robustness into a multicriteria optimisation framework, allowing a multi-objective Pareto optimisation function to balance robustness and conformity. The question remains as to whether adaptive therapy can become an integral part of a proton therapy, to allow re-optimisation during the course of a patient's treatment. The challenge of ensuring that plans are robust to range uncertainties in proton therapy remains, although these methods can provide practical solutions. PMID:23255545

  16. Crosscut shearing of roundwood bolts.

    Treesearch

    Rodger A. Arola

    1971-01-01

    Discusses results of study on crosscut shearing of aspen, basswood, spruce, hard maple, and yellow birch with numerous shear blade and anvil designs. Also includes effect of temperature, coated shear blades, dulling, wood properties, and very thin shear blades on force and splitting damage.

  17. A local eddy viscosity model for turbulent shear flow

    NASA Technical Reports Server (NTRS)

    Ortwerth, P. J.; Rabe, D. C.; Mcerlean, D. P.

    1973-01-01

    In the model described, the eddy viscosity is assumed to be a fluid property dependent on the state of the fluid locally, namely the local density, turbulent kinetic energy, turbulence scale, and Mach number. An empirical law was found which related eddy viscosity to these properties satisfactorily for free jets. This law is used without modification for a set of test cases in free shear layers, free-jet decay, coaxial mixing, and wakes. The scale of turbulence is taken as a constant at any axial location equal to the width of the shear layer. By utilizing the boundary-layer order-of-magnitude analysis, a coupled set of fluid dynamic equations is formulated, which of necessity includes the equation for the production of turbulent kinetic energy.

  18. Structural and mixing characteristics in actively controlled transverse jets

    NASA Astrophysics Data System (ADS)

    Shoji, Takeshi; Besnard, Andrea; Harris, Elijah; M'closkey, Robert; Karagozian, Ann; Cortelezzi, Luca

    2016-11-01

    These experiments explore the effect of external excitation on gaseous transverse jet (TJ) structural and mixing characteristics, emphasizing axisymmetric jet forcing. Sinusoidal as well as single and multiple square wave pulses, the latter with variable amplitudes, are explored for a range of jet-to-crossflow momentum flux ratios J, spanning regimes of absolutely unstable upstream shear layers (J < 10) and convectively unstable shear layers (J > 10). The studies utilize acetone PLIF imaging of the jet, as done for unforced jets. Axisymmetric forcing, irrespective of the waveform, can enhance cross-sectional symmetry of the TJ for convectively unstable conditions, but generally disrupts the usually symmetric counter-rotating vortex pair (CVP) observed for the absolutely unstable TJ. Conditions producing deeply penetrating, periodic vortical structures, such as square wave forcing at critical stroke ratios, increase jet spread, but do not always optimize molecular mixing. Creating multiple vortex structures of different strengths via multiple square pulses leads to enhanced interactions and accelerated vortex breakdown, potentially increasing mixing. Supported by NSF (CBET-1437014) & AFOSR (FA9550-15-1-0261).

  19. Preliminary analysis of tone-excited two-stream jet velocity decay

    NASA Technical Reports Server (NTRS)

    Vonglahn, U. H.

    1985-01-01

    Acoustic research related to jet flows has established that sound, by amplifying the naturally occuring large-scale structures in turbulent shear layers, can cause a more rapidly decay of the jet plume velocity and temperature and an increase in jet spreading rate. One possible application of this sound-flow interaction phenomenon is to future STOL aircraft that may require modified jet plume characteristics in order to reduce the loads and temperatures on the deflected flaps during take-off and landing operations. The tone-excitation effect on the velocity decay of model-scale, two-stream jet plumes is analyzed. Measured data are correlated in terms of parameters that include excitation sound level and outer-to-inner stream velocity ratio. The effect of plume tone-excitation on far-field jet noise is examined and its implication for large-scale two-stream jets is discussed.

  20. Jet Noise Reduction

    NASA Technical Reports Server (NTRS)

    Kenny, Patrick

    2004-01-01

    The Acoustics Branch is responsible for reducing noise levels for jet and fan components on aircraft engines. To do this, data must be measured and calibrated accurately to ensure validity of test results. This noise reduction is accomplished by modifications to hardware such as jet nozzles, and by the use of other experimental hardware such as fluidic chevrons, elliptic cores, and fluidic shields. To insure validity of data calibration, a variety of software is used. This software adjusts the sound amplitude and frequency to be consistent with data taken on another day. Both the software and the hardware help make noise reduction possible. work properly. These software programs were designed to make corrections for atmosphere, shear, attenuation, electronic, and background noise. All data can be converted to a one-foot lossless condition, using the proper software corrections, making a reading independent of weather and distance. Also, data can be transformed from model scale to full scale for noise predictions of a real flight. Other programs included calculations of Over All Sound Pressure Level (OASPL), Effective Perceived Noise Level (EPNL). OASPL is the integration of sound with respect to frequency, and EPNL is weighted for a human s response to different sound frequencies and integrated with respect to time. With the proper software correction, data taken in the NATR are useful in determining ways to reduce noise. display any difference between two or more data files. Using this program and graphs of the data, the actual and predicted data can be compared. This software was tested on data collected at the Aero Acoustic Propulsion Laboratory (AAPL) using a variety of window types and overlaps. Similarly, short scripts were written to test each individual program in the software suite for verification. Each graph displays both the original points and the adjusted points connected with lines. During this summer, data points were taken during a live experiment

  1. Active vibration reduction of a flexible structure bonded with optimised piezoelectric pairs using half and quarter chromosomes in genetic algorithms

    NASA Astrophysics Data System (ADS)

    Daraji, A. H.; Hale, J. M.

    2012-08-01

    The optimal placement of sensors and actuators in active vibration control is limited by the number of candidates in the search space. The search space of a small structure discretized to one hundred elements for optimising the location of ten actuators gives 1.73 × 1013 possible solutions, one of which is the global optimum. In this work, a new quarter and half chromosome technique based on symmetry is developed, by which the search space for optimisation of sensor/actuator locations in active vibration control of flexible structures may be greatly reduced. The technique is applied to the optimisation for eight and ten actuators located on a 500×500mm square plate, in which the search space is reduced by up to 99.99%. This technique helps for updating genetic algorithm program by updating natural frequencies and mode shapes in each generation to find the global optimal solution in a greatly reduced number of generations. An isotropic plate with piezoelectric sensor/actuator pairs bonded to its surface was investigated using the finite element method and Hamilton's principle based on first order shear deformation theory. The placement and feedback gain of ten and eight sensor/actuator pairs was optimised for a cantilever and clamped-clamped plate to attenuate the first six modes of vibration, using minimization of linear quadratic index as an objective function.

  2. Improved parallel preconditioners for multidisciplinary topology optimisations

    NASA Astrophysics Data System (ADS)

    Akay, H. U.; Oktay, E.; Manguoglu, M.; Sivas, A. A.

    2016-04-01

    Two commonly used preconditioners were evaluated for parallel solution of linear systems of equations with high condition numbers. The test cases were derived from topology optimisation applications in multiple disciplines, where the material distribution finite element methods were used. Because in this optimisation method, the equations rapidly become ill-conditioned due to disappearance of large number of elements from the design space as the optimisations progresses, it is shown that the choice for a suitable preconditioner becomes very crucial. In an earlier work the conjugate gradient (CG) method with a Block-Jacobi preconditioner was used, in which the number of CG iterations increased rapidly with the increasing number processors. Consequently, the parallel scalability of the method deteriorated fast due to the increasing loss of interprocessor information among the increased number of processors. By replacing the Block-Jacobi preconditioner with a sparse approximate inverse preconditioner, it is shown that the number of iterations to converge became independent of the number of processors. Therefore, the parallel scalability is improved.

  3. In-vivo turbulent stresses of bileaflet prosthesis leakage jets.

    PubMed

    Travis, Brandon R; Christensen, Thomas D; Smerup, Morten; Olsen, Morten S; Hasenkam, J Michael; Nygaard, Hans

    2005-09-01

    Previous studies of leakage jet turbulence have been carried out in vitro, using a Newtonian fluid to simulate blood and large, rigid approximations to the chambers of the heart. The study aim was to apply an in-vivo method of quantifying leakage jet turbulence to a variety of bileaflet mechanical heart valves, and thereafter to determine the effects of exercise and valve design on turbulent shear stresses within leakage flow. Bileaflet prostheses sewn to a manual traversing device were implanted in the mitral position of 29 pigs of body weight ca. 90 kg. Pulsed Doppler ultrasound was used to acquire velocity measurements within the leakage jets detected 1 mm upstream of the housing. Analytical techniques were used to estimate peak velocities and maximum turbulent shear stresses from these velocity measurements. Maximum turbulent shear stress was found to rise with increasing ventricular pressure. No leakage turbulence was found from a valve with relatively small leakage gap widths. The Medtronic Parallel valve was found to have considerable significant leakage flow disturbance, even under low ventricular pressure conditions. Similar maximum turbulent shear stress magnitudes were estimated in the leakage jets of the St. Jude Medical, CarboMedics and Sorin Bicarbon valves at medium ventricular pressure conditions. The maximum turbulent shear stresses estimated in these experiments were lower than those found in previous in-vitro measurements. Exercise raises the turbulent shear stresses of leakage flow substantially. Hinge design and leakage gap width also affect the magnitudes of these stresses. Leakage flow turbulence may be less damaging to the blood than was previously thought, and is considerably less damaging than forward-flow turbulence.

  4. Flow field and noise characteristics of a supersonic impinging jet

    NASA Astrophysics Data System (ADS)

    Krothapalli, A.; Rajkuperan, E.; Alvi, F.; Lourenco, L.

    1999-08-01

    This paper describes the results of a study examining the flow and acoustic characteristics of an axisymmetric supersonic jet issuing from a sonic and a Mach 1.5 converging diverging (C D) nozzle and impinging on a ground plane. Emphasis is placed on the Mach 1.5 nozzle with the sonic nozzle used mainly for comparison. A large-diameter circular plate was attached at the nozzle exit to measure the forces generated on the plate owing to jet impingement. The experimental results described in this paper include lift loss, particle image velocimetry (PIV) and acoustic measurements. Suckdown forces as high as 60% of the primary jet thrust were measured when the ground plane was very close to the jet exit. The PIV measurements were used to explain the increase in suckdown forces due to high entrainment velocities. The self-sustained oscillatory frequencies of the impinging jet were predicted using a feedback loop that uses the measured convection velocities of the large-scale coherent vortical structures in the jet shear layer. Nearfield acoustic measurements indicate that the presence of the ground plane increases the overall sound pressure levels (OASPL) by approximately 8 dB relative to a corresponding free jet. For moderately underexpanded jets, the influence of the shock cells on the important flow features was found to be negligible except for close proximity of the ground plane.

  5. The Breakout Model for Coronal Jets with Filaments

    NASA Astrophysics Data System (ADS)

    Wyper, Peter; DeVore, C. Richard; Antiochos, Spiro K.

    2016-05-01

    Coronal jets are impulsive, collimated plasma outflows originating low in the solar corona. Many of these events exhibit broad, curtain-like morphologies with helical structure and motions. Recently, Sterling et al. (2015) [doi:10.1038/nature14556] reported that such jets are associated with the eruption of small filaments and, therefore, are miniature versions of corona mass ejections (CMEs). This account differs from the traditional picture of jets, in that internal flare reconnection, rather than interchange reconnection with the external ambient magnetic field, creates the bright loops observed at the jet base. We present 3D simulations, performed with the Adaptively Refined MHD Solver (ARMS), which demonstrate how the magnetic breakout mechanism generates mini-CME-type jets in a compact bipolar region energized by simple footpoint motions. Our numerical model captures the formation of the strongly sheared pre-jet filament structure, the post-jet flare-like loops and ribbons, and the curtain-like untwisting dynamics observed higher in the corona. We will discuss the significance of our new results for understanding solar EUV and X-ray jets and CMEs in general. NASA supported this research by awards to the NASA Postdoctoral Program (P.F.W.) and the LWS TR&T and H-SR programs (C.R.D. & S.K.A.).

  6. Effect of Turbulence Modeling on an Excited Jet

    NASA Technical Reports Server (NTRS)

    Brown, Clifford A.; Hixon, Ray

    2010-01-01

    The flow dynamics in a high-speed jet are dominated by unsteady turbulent flow structures in the plume. Jet excitation seeks to control these flow structures through the natural instabilities present in the initial shear layer of the jet. Understanding and optimizing the excitation input, for jet noise reduction or plume mixing enhancement, requires many trials that may be done experimentally or computationally at a significant cost savings. Numerical simulations, which model various parts of the unsteady dynamics to reduce the computational expense of the simulation, must adequately capture the unsteady flow dynamics in the excited jet for the results are to be used. Four CFD methods are considered for use in an excited jet problem, including two turbulence models with an Unsteady Reynolds Averaged Navier-Stokes (URANS) solver, one Large Eddy Simulation (LES) solver, and one URANS/LES hybrid method. Each method is used to simulate a simplified excited jet and the results are evaluated based on the flow data, computation time, and numerical stability. The knowledge gained about the effect of turbulence modeling and CFD methods from these basic simulations will guide and assist future three-dimensional (3-D) simulations that will be used to understand and optimize a realistic excited jet for a particular application.

  7. Reductions in Multi-Component Jet Noise by Water Injection

    NASA Technical Reports Server (NTRS)

    Norum, Thomas D.

    2004-01-01

    An experimental investigation was performed in the NASA Langley Low Speed Aeroacoustics Wind Tunnel to determine the extent of jet exhaust noise reduction that can be obtained using water injection in a hot jet environment. The effects of water parameters such as mass flow rate, injection location, and spray patterns on suppression of dominant noise sources in both subsonic and supersonic jets were determined, and extrapolations to full-scale engine noise reduction were made. Water jets and sprays were injected in to the shear layers of cold and hot circular jets operating at both subsonic and supersonic exhaust conditions. Use of convergent-divergent and convergent nozzles (2.7in. D) allowed for simulations of all major jet noise sources. The experimental results show that water injection clearly disrupts shock noise sources within the jet plume, with large reductions in radiated shock noise. There are smaller reductions in jet mixing noise, resulting in only a small decrease in effective perceived noise level when projections are made to full scale. The fact that the measured noise reduction in the direction upstream of the nozzle was consistently larger than in the noisier downstream direction contributed to keeping effective perceived noise reductions small. Variations in the operation of the water injection system clearly show that injection at the nozzle exit rather than further downstream is required for the largest noise reduction. Noise reduction increased with water pressure as well as with its mass flow, although the type of injector had little effect.

  8. Noise from Supersonic Coaxial Jets. Part 1; Mean Flow Predictions

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.; Morris, Philip J.

    1997-01-01

    Recent theories for supersonic jet noise have used an instability wave noise generation model to predict radiated noise. This model requires a known mean flow that has typically been described by simple analytic functions for single jet mean flows. The mean flow of supersonic coaxial jets is not described easily in terms of analytic functions. To provide these profiles at all axial locations, a numerical scheme is developed to calculate the mean flow properties of a coaxial jet. The Reynolds-averaged, compressible, parabolic boundary layer equations are solved using a mixing length turbulence model. Empirical correlations are developed to account for the effects of velocity and temperature ratios and Mach number on the shear layer spreading. Both normal velocity profile and inverted velocity profile coaxial jets are considered. The mixing length model is modified in each case to obtain reasonable results when the two stream jet merges into a single fully developed jet. The mean flow calculations show both good qualitative and quantitative agreement with measurements in single and coaxial jet flows.

  9. Diagnosing particle acceleration in relativistic jets

    NASA Astrophysics Data System (ADS)

    Böttcher, Markus; Baring, Matthew G.; Liang, Edison P.; Summerlin, Errol J.; Fu, Wen; Smith, Ian A.; Roustazadeh, Parisa

    2015-03-01

    The high-energy emission from blazars and other relativistic jet sources indicates that electrons are accelerated to ultra-relativistic (GeV - TeV) energies in these systems. This paper summarizes recent results from numerical studies of two fundamentally different particle acceleration mechanisms potentially at work in relativistic jets: Magnetic-field generation and relativistic particle acceleration in relativistic shear layers, which are likely to be present in relativistic jets, is studied via Particle-in-Cell (PIC) simulations. Diffusive shock acceleration at relativistic shocks is investigated using Monte-Carlo simulations. The resulting magnetic-field configurations and thermal + non-thermal particle distributions are then used to predict multi-wavelength radiative (synchrotron + Compton) signatures of both acceleration scenarios. In particular, we address how anisotropic shear-layer acceleration may be able to circumvent the well-known Lorentz-factor crisis, and how the self-consistent evaluation of thermal + non-thermal particle populations in diffusive shock acceleration simulations provides tests of the bulk Comptonization model for the Big Blue Bump observed in the SEDs of several blazars.

  10. Iterated Stretching of Viscoelastic Jets

    NASA Technical Reports Server (NTRS)

    Chang, Hsueh-Chia; Demekhin, Evgeny A.; Kalaidin, Evgeny

    1999-01-01

    We examine, with asymptotic analysis and numerical simulation, the iterated stretching dynamics of FENE and Oldroyd-B jets of initial radius r(sub 0), shear viscosity nu, Weissenberg number We, retardation number S, and capillary number Ca. The usual Rayleigh instability stretches the local uniaxial extensional flow region near a minimum in jet radius into a primary filament of radius [Ca(1 - S)/ We](sup 1/2)r(sub 0) between two beads. The strain-rate within the filament remains constant while its radius (elastic stress) decreases (increases) exponentially in time with a long elastic relaxation time 3We(r(sup 2, sub 0)/nu). Instabilities convected from the bead relieve the tension at the necks during this slow elastic drainage and trigger a filament recoil. Secondary filaments then form at the necks from the resulting stretching. This iterated stretching is predicted to occur successively to generate high-generation filaments of radius r(sub n), (r(sub n)/r(sub 0)) = square root of 2[r(sub n-1)/r(sub 0)](sup 3/2) until finite-extensibility effects set in.

  11. Natural instability of free shear layers

    NASA Technical Reports Server (NTRS)

    Husain, Z. D.; Hussain, A. K. M. F.

    1983-01-01

    Under controlled small-amplitude excitation, an initially laminar free shear layer experiences maximum growth rate at a Strouhal number St(theta) of 0.017 (consistent with theory) and maximum growth at St(theta) = 0.011, while the natural instability frequency St(theta-n) (of an unexcited shear layer) is found to have an intermediate value. Investigations in both axisymmetric and plane shear layers in a number of independent facilities reveal that the St(theta-n) value falls in the range 0.0125-0.0155, depending on the exit boundary-layer fluctuation level and the spanwise radius of curvature. The St(theta-n) value decreases with increasing jet diameter or exit boundary-layer fluctuation level, but is not a direct function of the exit momentum thickness Reynolds number. For a given facility, the instability details are found to be independent of whether the entrainment at the lip is parallel to the stream or orthogonal (due to the addition of an end plate). The steamwise evolutions of the amplitudes at the fundamental frequency and its harmonics and subharmonics are unique functions of the downstream distance nondimensionalized by the exit momentum thickness, but their details remain functions of the flow geometry (i.e., axisymmetric or plane).

  12. Large bouncing jets

    NASA Astrophysics Data System (ADS)

    Cardin, Karl; Weislogel, Mark

    2016-11-01

    We experimentally investigate the phenomena of large jet rebound (bounce), a mode of fluid transfer following oblique jet impacts on hydrophobic surfaces. We initially seek to describe the regimes of such jet bounce in tests conducted in the weightless environment of a drop tower. A parametric study reveals the dependence of the rebound mode on the relevant dimensionless groups such as Weber number We⊥ defined on the velocity component perpendicular to the surface. We show that significantly larger diameter jets behave similarly as much smaller jets demonstrated during previous terrestrial investigations when We⊥ 1 . For We⊥ > 1 , large jet impacts create fishbone-like structures. We also explore rebounds from nonplanar substrates. Improving our understanding of such jet rebound opens avenues for unique transport capabilities. NASA Cooperative Agreement NNX12A047A.

  13. Hydroacoustic pulsating jet generator

    NASA Astrophysics Data System (ADS)

    Unrau, A.; Meier, G. E. A.

    1987-04-01

    A high pressure turbulent jet generator connected to a low pressure hydraulic tube is studied to investigate water hammer in tubes with fast flow variations, generating high pressure pulsating water jets. The pulsating jet generator consists of a tube, a hydraulic valve, a spring, and a water container. The jet is the effect of the combination of turbulent pipe flow with a valve for flow nozzle. The jet pressure depends on specific oscillation impedance and flow velocity variations. For inlet pressure of 0.5 to 2 bar the pressure rises to 40 bar. The described pulsating jet generator is more effective than the earlier model. A piezoelectric pressure controller is used to register pressure signals and high speed photos are made of the jet. Test results are consistent with theoretical calculation.

  14. Impinging Jets and the Erodibility of Cohesive Sediment

    NASA Astrophysics Data System (ADS)

    Karamigolbaghi, M.; Bennett, S. J.; Ghaneeizad, S. M.; Atkinson, J. F.

    2016-12-01

    Defining the erodibility of cohesive sediment remains a critical challenge in Earth surface systems. The primary geomorphic law used in such applications relates erosion rate to an erodibility coefficient and an excess shear stress term. To assess erodibility, an inverse modeling approach can be adopted, wherein a known stress is applied to the cohesive sediment, and the erodibility parameters can be deduced through observation of erosion as a function of time. An impinging jet, as used in the jet erosion test, would appear to be an ideal flow (stress) source for erosion assessment. Recent work, however, has demonstrated that jet hydrodynamics can depart significantly from ideal flow conditions when employed for in situ erosion assessment. Here we will review jet theory and the use of jets for assessing the erodibility of cohesive sediment. Our results show that (1) flow confinement and the generation of secondary circulation can significantly change bed shear stress near and downstream of impingement, (2) the evolving scour hole shape, as conditioned by material characteristics and the erosion process, can significantly alter jet hydrodynamics and bed shear stress magnitudes and distributions near and downstream of impingement, and (3) incidental variations in material characteristics in carefully-executed, long-lived experiments can produce markedly different scour hole shapes and derived erodibility indices. Examples from experimental, numerical, and field observations will be used to illustrate these hydrodynamic and material effects on observed and predicted erosion rates. Because such effects are difficult to anticipate, the uncertainty of in situ cohesive sediment assessments using impinging jets can be quite large.

  15. PHOTOSPHERIC EMISSION FROM STRATIFIED JETS

    SciTech Connect

    Ito, Hirotaka; Nagataki, Shigehiro; Ono, Masaomi; Lee, Shiu-Hang; Mao, Jirong; Yamada, Shoichi; Pe'er, Asaf; Mizuta, Akira; Harikae, Seiji

    2013-11-01

    We explore photospheric emissions from stratified two-component jets, wherein a highly relativistic spine outflow is surrounded by a wider and less relativistic sheath outflow. Thermal photons are injected in regions of high optical depth and propagated until the photons escape at the photosphere. Because of the presence of shear in velocity (Lorentz factor) at the boundary of the spine and sheath region, a fraction of the injected photons are accelerated using a Fermi-like acceleration mechanism such that a high-energy power-law tail is formed in the resultant spectrum. We show, in particular, that if a velocity shear with a considerable variance in the bulk Lorentz factor is present, the high-energy part of observed gamma-ray bursts (GRBs) photon spectrum can be explained by this photon acceleration mechanism. We also show that the accelerated photons might also account for the origin of the extra-hard power-law component above the bump of the thermal-like peak seen in some peculiar bursts (e.g., GRB 090510, 090902B, 090926A). We demonstrate that time-integrated spectra can also reproduce the low-energy spectrum of GRBs consistently using a multi-temperature effect when time evolution of the outflow is considered. Last, we show that the empirical E{sub p}-L{sub p} relation can be explained by differences in the outflow properties of individual sources.

  16. Railway vehicle performance optimisation using virtual homologation

    NASA Astrophysics Data System (ADS)

    Magalhães, H.; Madeira, J. F. A.; Ambrósio, J.; Pombo, J.

    2016-09-01

    Unlike regular automotive vehicles, which are designed to travel in different types of roads, railway vehicles travel mostly in the same route during their life cycle. To accept the operation of a railway vehicle in a particular network, a homologation process is required according to local standard regulations. In Europe, the standards EN 14363 and UIC 518, which are used for railway vehicle acceptance, require on-track tests and/or numerical simulations. An important advantage of using virtual homologation is the reduction of the high costs associated with on-track tests by studying the railway vehicle performance in different operation conditions. This work proposes a methodology for the improvement of railway vehicle design with the objective of its operation in selected railway tracks by using optimisation. The analyses required for the vehicle improvement are performed under control of the optimisation method global and local optimisation using direct search. To quantify the performance of the vehicle, a new objective function is proposed, which includes: a Dynamic Performance Index, defined as a weighted sum of the indices obtained from the virtual homologation process; the non-compensated acceleration, which is related to the operational velocity; and a penalty associated with cases where the vehicle presents an unacceptable dynamic behaviour according to the standards. Thus, the optimisation process intends not only to improve the quality of the vehicle in terms of running safety and ride quality, but also to increase the vehicle availability via the reduction of the time for a journey while ensuring its operational acceptance under the standards. The design variables include the suspension characteristics and the operational velocity of the vehicle, which are allowed to vary in an acceptable range of variation. The results of the optimisation lead to a global minimum of the objective function in which the suspensions characteristics of the vehicle are

  17. The Prediction of Broadband Shock-Associated Noise from Dualstream and Rectangular Jets Using RANS CFD

    NASA Technical Reports Server (NTRS)

    Miller, Steven A.; Morris, Philip J.

    2010-01-01

    Supersonic jets operating off-design produce broadband shock-associated noise. Broadband shock-associated noise is characterized by multiple broadband peaks in the far-field and is often the dominant source of noise towards the sideline and upstream direction relative to the jet axis. It is due to large scale coherent turbulence structures in the jet shear layers interacting with the shock cell structure. A broadband shock-associated noise model recently developed by the authors predicts this noise component from solutions to the Reynolds averaged Navier-Stokes equations using a two-equation turbulence model. The broadband shock-associated noise model is applied to dualstream and rectangular nozzles operating supersonically, heated, and off-design. The dualstream jet broadband shock-associated noise predictions are conducted for cases when the core jet is supersonic and the fan jet is subsonic, the core jet is subsonic and the fan jet is supersonic, and when both jet streams operate supersonically. Rectangular jet predictions are shown for a convergent-divergent nozzle operating both over- and under-expanded for cold and heated conditions. The original model implementation has been heavily modified to make accurate predictions for the dualstream jets. It is also argued that for over-expanded jets the oblique shock wave attached to the nozzle lip contributes little to broadband shock-associated noise. All predictions are compared with experiments.

  18. Virtual topological optimisation of scaffolds for rapid prototyping.

    PubMed

    Almeida, Henrique de Amorim; Bártolo, Paulo Jorge da Silva

    2010-09-01

    Advanced additive techniques are now being developed to fabricate scaffolds with controlled architecture for tissue engineering. These techniques combine computer-aided design (CAD) with computer-aided manufacturing (CAM) tools to produce three-dimensional structures layer by layer in a multitude of materials. Actual prediction of the effective mechanical properties of scaffolds produced by additive technologies, is very important for tissue engineering applications. A novel computer based technique for scaffold design is topological optimisation. Topological optimisation is a form of "shape" optimisation, usually referred to as "layout" optimisation. The goal of topological optimisation is to find the best use of material for a body that is subjected to either a single load or a multiple load distribution. This paper proposes a topological optimisation scheme in order to obtain the ideal topological architectures of scaffolds, maximising its mechanical behaviour. 2010 IPEM. Published by Elsevier Ltd. All rights reserved.

  19. Second order modeling of boundary-free turbulent shear flows

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  20. Shear strength of metals under uniaxial deformation and pure shear

    NASA Astrophysics Data System (ADS)

    Latypov, F. T.; Mayer, A. E.

    2015-11-01

    In this paper, we investigate the dynamic shear strength of perfect monocrystalline metals using the molecular dynamics simulation. Three types of deformation (single shear, uniaxial compression and tension) are investigated for five metals of different crystallographic systems (fcc, bcc and hcp). A strong dependence of the calculated shear strength on the deformation type is observed. In the case of bcc (iron) and hcp (titanium) metals, the maximal shear strength is achieved at the uniaxial compression, while the minimal shear strength is observed at the uniaxial tension. In the case of fcc metals (aluminum, copper, nickel) the largest strength is achieved at the pure shear, the lowest strength is obtained at the uniaxial compression.

  1. Jet Substructure Without Trees

    SciTech Connect

    Jankowiak, Martin; Larkoski, Andrew J.; /SLAC /Stanford U., ITP

    2011-08-19

    We present an alternative approach to identifying and characterizing jet substructure. An angular correlation function is introduced that can be used to extract angular and mass scales within a jet without reference to a clustering algorithm. This procedure gives rise to a number of useful jet observables. As an application, we construct a top quark tagging algorithm that is competitive with existing methods. In preparation for the LHC, the past several years have seen extensive work on various aspects of collider searches. With the excellent resolution of the ATLAS and CMS detectors as a catalyst, one area that has undergone significant development is jet substructure physics. The use of jet substructure techniques, which probe the fine-grained details of how energy is distributed in jets, has two broad goals. First, measuring more than just the bulk properties of jets allows for additional probes of QCD. For example, jet substructure measurements can be compared against precision perturbative QCD calculations or used to tune Monte Carlo event generators. Second, jet substructure allows for additional handles in event discrimination. These handles could play an important role at the LHC in discriminating between signal and background events in a wide variety of particle searches. For example, Monte Carlo studies indicate that jet substructure techniques allow for efficient reconstruction of boosted heavy objects such as the W{sup {+-}} and Z{sup 0} gauge bosons, the top quark, and the Higgs boson.

  2. Ultrasonic shear wave couplant

    DOEpatents

    Kupperman, David S.; Lanham, Ronald N.

    1985-01-01

    Ultrasonically testing of an article at high temperatures is accomplished by the use of a compact layer of a dry ceramic powder as a couplant in a method which involves providing an ultrasonic transducer as a probe capable of transmitting shear waves, coupling the probe to the article through a thin compact layer of a dry ceramic powder, propagating a shear wave from the probe through the ceramic powder and into the article to develop echo signals, and analyzing the echo signals to determine at least one physical characteristic of the article.

  3. Ultrasonic shear wave couplant

    DOEpatents

    Kupperman, D.S.; Lanham, R.N.

    1984-04-11

    Ultrasonically testing of an article at high temperatures is accomplished by the use of a compact layer of a dry ceramic powder as a couplant in a method which involves providing an ultrasonic transducer as a probe capable of transmitting shear waves, coupling the probe to the article through a thin compact layer of a dry ceramic powder, propagating a shear wave from the probe through the ceramic powder and into the article to develop echo signals, and analyzing the echo signals to determine at least one physical characteristic of the article.

  4. On the asymmetric distribution of shear-relative typhoon rainfall

    NASA Astrophysics Data System (ADS)

    Gao, Si; Zhai, Shunan; Li, Tim; Chen, Zhifan

    2017-01-01

    The Tropical Rainfall Measuring Mission (TRMM) 3B42 precipitation, the National Centers for Environmental Prediction (NCEP) Final analysis and the Regional Specialized Meteorological Center (RSMC) Tokyo best-track data during 2000-2015 are used to compare spatial rainfall distribution associated with Northwest Pacific tropical cyclones (TCs) with different vertical wind shear directions and investigate possible mechanisms. Results show that the maximum TC rainfall are all located in the downshear left quadrant regardless of shear direction, and TCs with easterly shear have greater magnitudes of rainfall than those with westerly shear, consistent with previous studies. Rainfall amount of a TC is related to its relative position and proximity from the western Pacific subtropical high (WPSH) and the intensity of water vapor transport, and low-level jet is favorable for water vapor transport. The maximum of vertically integrated moisture flux convergence (MFC) are located on the downshear side regardless of shear direction, and the contribution of wind convergence to the total MFC is far larger than that of moisture advection. The cyclonic displacement of the maximum rainfall relative to the maximum MFC is possibly due to advection of hydrometeors by low- and middle-level cyclonic circulation of TCs. The relationship between TC rainfall and the WPSH through water vapor transport and vertical wind shear implies that TC rainfall may be highly predictable given the high predictability of the WPSH.

  5. Shear wave transmissivity measurement by color Doppler shear wave imaging

    NASA Astrophysics Data System (ADS)

    Yamakoshi, Yoshiki; Yamazaki, Mayuko; Kasahara, Toshihiro; Sunaguchi, Naoki; Yuminaka, Yasushi

    2016-07-01

    Shear wave elastography is a useful method for evaluating tissue stiffness. We have proposed a novel shear wave imaging method (color Doppler shear wave imaging: CD SWI), which utilizes a signal processing unit in ultrasound color flow imaging in order to detect the shear wave wavefront in real time. Shear wave velocity is adopted to characterize tissue stiffness; however, it is difficult to measure tissue stiffness with high spatial resolution because of the artifact produced by shear wave diffraction. Spatial average processing in the image reconstruction method also degrades the spatial resolution. In this paper, we propose a novel measurement method for the shear wave transmissivity of a tissue boundary. Shear wave wavefront maps are acquired by changing the displacement amplitude of the shear wave and the transmissivity of the shear wave, which gives the difference in shear wave velocity between two mediums separated by the boundary, is measured from the ratio of two threshold voltages required to form the shear wave wavefronts in the two mediums. From this method, a high-resolution shear wave amplitude imaging method that reconstructs a tissue boundary is proposed.

  6. Shear and extensional rheology of hydroxypropyl cellulose melt using capillary rheometry.

    PubMed

    Paradkar, Anant; Kelly, Adrian; Coates, Phil; York, Peter

    2009-02-20

    With increasing interest in hot melt extrusion for preparing polymer-drug systems, knowledge of the shear and extensional rheology of polymers is required for the formulation and process design. Shear and extensional rheology of three commercial grades of hydroxypropyl cellulose (HPC) was examined at 140, 145 and 150 degrees C using twin bore capillary rheometry at range of processing rates. The power law model fitted for shear flow behaviour up to shear strain rates of approximately 1000s(-1), above which measured shear viscosities deviated from the power law and surface instabilities were observed in the extrudate, particularly for higher molecular weight grades. Shear thinning index was found to be relatively independent of temperature and molecular weight, whilst the consistency index, indicative of zero shear viscosity increased exponentially with increase in molecular weight. Extensional viscosity of all grades studied was found to decrease with increasing temperature and increasing processing rate. Foaming of the extrudate occurred especially at low temperatures and with the high molecular weight grade. An understanding of the relationships between shear and extensional flows with temperature, processing rate and molecular weight is a useful tool for process design; optimisation and troubleshooting of Hot melt extrusion (HME) of pharmaceutical formulations.

  7. Behaviour of Lyapunov's function for different strategies of circuit optimisation

    NASA Astrophysics Data System (ADS)

    Zemliak, Alexander; Markina, Tatiana

    2015-04-01

    The process of analogue circuit optimisation is mathematically defined as a controllable dynamic system. In this context the minimisation of the processor time of designing can be formulated as a problem of time minimisation for transitional process of dynamic system. In order to analyse the properties of such a system, it is proposed to use the concept of Lyapunov function of dynamic system. Using this function and its time derivative, the special functions have been built that allow us to predict the total processor time for circuit optimisation by analysing the initial interval of the optimisation process. Numerical results indicate the possibility of predicting the processor time of different strategies for circuit optimisation.

  8. Modeling of Turbulence Generated Noise in Jets

    NASA Technical Reports Server (NTRS)

    Khavaran, Abbas; Bridges, James

    2004-01-01

    A numerically calculated Green's function is used to predict jet noise spectrum and its far-field directivity. A linearized form of Lilley's equation governs the non-causal Green s function of interest, with the non-linear terms on the right hand side identified as the source. In this paper, contributions from the so-called self- and shear-noise source terms will be discussed. A Reynolds-averaged Navier-Stokes solution yields the required mean flow as well as time- and length scales of a noise-generating turbulent eddy. A non-compact source, with exponential temporal and spatial functions, is used to describe the turbulence velocity correlation tensors. It is shown that while an exact non-causal Green's function accurately predicts the observed shift in the location of the spectrum peak with angle as well as the angularity of sound at moderate Mach numbers, at high subsonic and supersonic acoustic Mach numbers the polar directivity of radiated sound is not entirely captured by this Green's function. Results presented for Mach 0.5 and 0.9 isothermal jets, as well as a Mach 0.8 hot jet conclude that near the peak radiation angle a different source/Green's function convolution integral may be required in order to capture the peak observed directivity of jet noise.

  9. Coiling and Folding of Viscoelastic Jets

    NASA Astrophysics Data System (ADS)

    Majmudar, Trushant; Varagnat, Matthieu; McKinley, Gareth

    2007-11-01

    The study of fluid jets impacting on a flat surface has industrial applications in many areas, including processing of foods and consumer goods, bottle filling, and polymer melt processing. Previous studies have focused primarily on purely viscous, Newtonian fluids, which exhibit a number of different dynamical regimes including dripping, steady jetting, folding, and steady coiling. Here we add another dimension to the problem by focusing on mobile (low viscosity) viscoelastic fluids, with the study of two wormlike-micellar fluids, a cetylpyridinum-salicylic acid salt (CPyCl/NaSal) solution, and an industrially relevant shampoo base. We investigate the effects of viscosity and elasticity on the dynamics of axi-symmetric jets. The viscoelasticity of the fluids is systematically controlled by varying the concentration of salt counterions. Experimental methods include shear and extensional rheology measurements to characterize the fluids, and high-speed digital video imaging. In addition to the regimes observed in purely viscous systems, we also find a novel regime in which the elastic jet buckles and folds on itself, and alternates between coiling and folding behavior. We suggest phase diagrams and scaling laws for the coiling and folding frequencies through a systematic exploration of the experimental parameter space (height of fall, imposed flow rate, elasticity of the solution).

  10. On the preferred mode of jet instability

    NASA Technical Reports Server (NTRS)

    Petersen, R. A.; Samet, M. M.

    1988-01-01

    The preferred mode of instability was investigated in an axisymmetric air jet of moderate Reynolds number. Natural instabilities are shown to scale with local shear-layer thickness and the preferred mode is shown to be a shear-layer instability. The spatial evolution of the preferred mode was examined by exciting the flow acoustically and then mapping the phase-locked velocity fluctuations. Throughout the potential core region the phase-locked profiles are shown to agree with the eigensolutions of the Orr-Sommerfeld stability equations provided the calculations are based on measured, mean velocity profiles. The excitation intensity was varied from low levels, where the flow was merely tagged, to high levels where the mean flow was substantially distorted, and over that range of excitation there was no apparent deterioration in the agreement with stability predictions.

  11. Haemodynamic optimisation: are we dynamic enough?

    PubMed

    Parker, Sophie J; Boyd, Owen

    2011-01-01

    Perioperative haemodynamic optimisation of high-risk surgical patients has long been documented to improve both short-term and long-term outcomes, as well as to reduce the rate of postoperative complications. Based on the evidence, cardiac output monitoring and fluid resuscitation, combined with the use of inotropes, would seem to be the gold standard of care for these difficult surgical cases. However, clinicians do not universally apply these techniques and principles in their everyday practice. By exploring the reasons why this is so, perhaps we could move forward in the standardisation of care and the application of evidence-based practice.

  12. Pillar III--optimisation of anaemia tolerance.

    PubMed

    Meier, Jens; Gombotz, Hans

    2013-03-01

    In the case of acute bleeding, the use of the anaemia tolerance of a patient enables the physician to either avoid blood transfusions or delay them after bleeding has ceased. This concept is the cornerstone of the third pillar of modern patient blood management programmes. Its efficacy depends on the degree of utilisation of anaemia tolerance, which is not constant but depends on the compensatory capacity of the individual patient in a given situation. Fortunately, the specifications of anaemia tolerance can be influenced by the anaesthesiologist. This article presents the concept of anaemia tolerance and highlights the options for how anaemia tolerance can be optimised in the pre-, intra-, and postoperative periods.

  13. Genetic algorithms for modelling and optimisation

    NASA Astrophysics Data System (ADS)

    McCall, John

    2005-12-01

    Genetic algorithms (GAs) are a heuristic search and optimisation technique inspired by natural evolution. They have been successfully applied to a wide range of real-world problems of significant complexity. This paper is intended as an introduction to GAs aimed at immunologists and mathematicians interested in immunology. We describe how to construct a GA and the main strands of GA theory before speculatively identifying possible applications of GAs to the study of immunology. An illustrative example of using a GA for a medical optimal control problem is provided. The paper also includes a brief account of the related area of artificial immune systems.

  14. Cost optimisation studies of high power accelerators

    SciTech Connect

    McAdams, R.; Nightingale, M.P.S.; Godden, D.

    1995-10-01

    Cost optimisation studies are carried out for an accelerator based neutron source consisting of a series of linear accelerators. The characteristics of the lowest cost design for a given beam current and energy machine such as power and length are found to depend on the lifetime envisaged for it. For a fixed neutron yield it is preferable to have a low current, high energy machine. The benefits of superconducting technology are also investigated. A Separated Orbit Cyclotron (SOC) has the potential to reduce capital and operating costs and intial estimates for the transverse and longitudinal current limits of such machines are made.

  15. Optimising Terpene Synthesis with Flow Biocatalysis

    PubMed Central

    Tang, Xiaoping

    2017-01-01

    Sesquiterpenes are an important family of natural products, many of which exhibit important pharmaceutical and agricultural properties. They are biosynthesised from farnesyl diphosphate in sesquiterpene synthase catalysed reactions. Here, we report the development of a highly efficient segmented flow system for the enzyme‐catalysed continuous flow production of sesquiterpenes. Design of experiment (DoE) methods were used to optimise the performance of the flow biocatalysis, and quantitative yields were achieved by using an operationally simple but highly effective segmented flow system. PMID:28286413

  16. Study of the Low Level Wind Shear using AMDAR reports

    NASA Astrophysics Data System (ADS)

    Urlea, Ana-Denisa; Pietrisi, Mirela

    2015-04-01

    The aim of this work is the study of the effects of the wind shear on aircraft flights, in particularly when it appears on path of take-off or landing phase which is the most troublesome phase. This phenomenon has a lot of generating sources as: convection, frontal surfaces, strong surface wind coupled with local topography, breezes (either sea or mountain originated), mountain waves or low level temperature inversions. Low Level Jet is also a most frequent cause of Low Level Wind Shear. It has a lot of generating causes, but in Romania the most encountered is the presence of a Mediterranean low in southeastern part of Europe mainly in winter, sometimes in the first days of spring or the last days of autumn. It generates Low Level Wind Shear between surface and up to 600m, affecting approaching, landing or take-off phases of an aircraft flight. Diagnosis of meteorological general and local conditions and presence of Low Level Jet- generating Low Level Wind Shear is made using Meteo-France ARPEGE products model and ALARO high resolution model dedicated to Romanian area. The study is focused on use of real-time and in situ data as AMDAR (Aircraft Meteorological Data Relay) registrations with verification of a mobile Doppler SODAR registrations-("SOnic Detection And Ranging" system -PCS.2000- Metek manufactured by Meteorologische Messtechnik GMBH) in the processes of estimation of the quantitative and qualitative manifestation of Low Level Wind Shear. The results will be used to improve the timing and the accuracy of the Low Level Wind Shear forecasting for the aerodrome area.

  17. Measuring the reduced shear

    NASA Astrophysics Data System (ADS)

    Zhang, Jun

    2011-11-01

    Neglecting the second order corrections in weak lensing measurements can lead to a few percent uncertainties on cosmic shears, and becomes more important for cluster lensing mass reconstructions. Existing methods which claim to measure the reduced shears are not necessarily accurate to the second order when a point spread function (PSF) is present. We show that the method of Zhang (2008) exactly measures the reduced shears at the second order level in the presence of PSF. A simple theorem is provided for further confirming our calculation, and for judging the accuracy of any shear measurement method at the second order based on its properties at the first order. The method of Zhang (2008) is well defined mathematically. It does not require assumptions on the morphologies of galaxies and the PSF. To reach a sub-percent level accuracy, the CCD pixel size is required to be not larger than 1/3 of the Full Width at Half Maximum (FWHM) of the PSF, regardless of whether the PSF has a power-law or exponential profile at large distances. Using a large ensemble (gtrsim107) of mock galaxies of unrestricted morphologies, we study the shear recovery accuracy under different noise conditions. We find that contaminations to the shear signals from the noise of background photons can be removed in a well defined way because they are not correlated with the source shapes. The residual shear measurement errors due to background noise are consistent with zero at the sub-percent level even when the amplitude of such noise reaches about 1/10 of the source flux within the half-light radius of the source. This limit can in principle be extended further with a larger galaxy ensemble in our simulations. On the other hand, the source Poisson noise remains to be a cause of systematic errors. For a sub-percent level accuracy, our method requires the amplitude of the source Poisson noise to be less than 1/80 ~ 1/100 of the source flux within the half-light radius of the source, corresponding to

  18. Measuring the reduced shear

    SciTech Connect

    Zhang, Jun

    2011-11-01

    Neglecting the second order corrections in weak lensing measurements can lead to a few percent uncertainties on cosmic shears, and becomes more important for cluster lensing mass reconstructions. Existing methods which claim to measure the reduced shears are not necessarily accurate to the second order when a point spread function (PSF) is present. We show that the method of Zhang (2008) exactly measures the reduced shears at the second order level in the presence of PSF. A simple theorem is provided for further confirming our calculation, and for judging the accuracy of any shear measurement method at the second order based on its properties at the first order. The method of Zhang (2008) is well defined mathematically. It does not require assumptions on the morphologies of galaxies and the PSF. To reach a sub-percent level accuracy, the CCD pixel size is required to be not larger than 1/3 of the Full Width at Half Maximum (FWHM) of the PSF, regardless of whether the PSF has a power-law or exponential profile at large distances. Using a large ensemble (∼>10{sup 7}) of mock galaxies of unrestricted morphologies, we study the shear recovery accuracy under different noise conditions. We find that contaminations to the shear signals from the noise of background photons can be removed in a well defined way because they are not correlated with the source shapes. The residual shear measurement errors due to background noise are consistent with zero at the sub-percent level even when the amplitude of such noise reaches about 1/10 of the source flux within the half-light radius of the source. This limit can in principle be extended further with a larger galaxy ensemble in our simulations. On the other hand, the source Poisson noise remains to be a cause of systematic errors. For a sub-percent level accuracy, our method requires the amplitude of the source Poisson noise to be less than 1/80 ∼ 1/100 of the source flux within the half-light radius of the source

  19. Interpretation of extragalactic jets

    SciTech Connect

    Norman, M.L.

    1985-01-01

    The nature of extragalatic radio jets is modeled. The basic hypothesis of these models is that extragalatic jets are outflows of matter which can be described within the framework of fluid dynamics and that the outflows are essentially continuous. The discussion is limited to the interpretation of large-scale (i.e., kiloparsec-scale) jets. The central problem is to infer the physical parameters of the jets from observed distributions of total and polarized intensity and angle of polarization as a function of frequency. 60 refs., 6 figs.

  20. The remarkable AGN jets

    NASA Astrophysics Data System (ADS)

    Komissarov, Serguei

    The jets from active galactic nuclei exhibit stability which seems to be far superior compared to that of terrestrial and laboratory jets. They manage to propagate over distances up to a billion of initial jet radii. Yet this may not be an indication of some exotic physics but mainly a reflection of the specific environment these jets propagate through. The key property of this environment is a rapid decline of density and pressure along the jet, which promotes its rapid expansion. Such an expansion can suppress global instabilities, which require communication across the jet, and hence ensure its survival over huge distances. At kpc scales, some AGN jets do show signs of strong instabilities and even turn into plumes. This could be a result of the flattening of the external pressure distribution in their host galaxies or inside the radio lobes. In this regard, we discuss the possible connection between the stability issue and the Fanaroff-Riley classification of extragalactic radio sources. The observations of AGN jets on sub-kpc scale do not seem to support their supposed lack of causal connectivity. When interpreted using simple kinematic models, they reveal a rather perplexing picture with more questions than answers on the jets dynamics.

  1. Towards the optimisation and adaptation of dry powder inhalers.

    PubMed

    Cui, Y; Schmalfuß, S; Zellnitz, S; Sommerfeld, M; Urbanetz, N

    2014-08-15

    Pulmonary drug delivery by dry powder inhalers is becoming more and more popular. Such an inhalation device must insure that during the inhalation process the drug powder is detached from the carrier due to fluid flow stresses. The goal of the project is the development of a drug powder detachment model to be used in numerical computations (CFD, computational fluid dynamics) of fluid flow and carrier particle motion through the inhaler and the resulting efficiency of drug delivery. This programme will be the basis for the optimisation of inhaler geometry and dry powder inhaler formulation. For this purpose a multi-scale approach is adopted. First the flow field through the inhaler is numerically calculated with OpenFOAM(®) and the flow stresses experienced by the carrier particles are recorded. This information is used for micro-scale simulations using the Lattice-Boltzmann method where only one carrier particle covered with drug powder is placed in cubic flow domain and exposed to the relevant flow situations, e.g. plug and shear flow with different Reynolds numbers. Therefrom the fluid forces on the drug particles are obtained. In order to allow the determination of the drug particle detachment possibility by lift-off, sliding or rolling, also measurements by AFM (atomic force microscope) were conducted for different carrier particle surface structures. The contact properties, such as van der Waals force, friction coefficient and adhesion surface energy were used to determine, from a force or moment balance (fluid forces versus contact forces), the detachment probability by the three mechanisms as a function of carrier particle Reynolds number. These results will be used for deriving the drug powder detachment model.

  2. Shear Thinning of Noncolloidal Suspensions

    NASA Astrophysics Data System (ADS)

    Vázquez-Quesada, Adolfo; Tanner, Roger I.; Ellero, Marco

    2016-09-01

    Shear thinning—a reduction in suspension viscosity with increasing shear rates—is understood to arise in colloidal systems from a decrease in the relative contribution of entropic forces. The shear-thinning phenomenon has also been often reported in experiments with noncolloidal systems at high volume fractions. However its origin is an open theoretical question and the behavior is difficult to reproduce in numerical simulations where shear thickening is typically observed instead. In this letter we propose a non-Newtonian model of interparticle lubrication forces to explain shear thinning in noncolloidal suspensions. We show that hidden shear-thinning effects of the suspending medium, which occur at shear rates orders of magnitude larger than the range investigated experimentally, lead to significant shear thinning of the overall suspension at much smaller shear rates. At high particle volume fractions the local shear rates experienced by the fluid situated in the narrow gaps between particles are much larger than the averaged shear rate of the whole suspension. This allows the suspending medium to probe its high-shear non-Newtonian regime and it means that the matrix fluid rheology must be considered over a wide range of shear rates.

  3. Shear Thinning of Noncolloidal Suspensions.

    PubMed

    Vázquez-Quesada, Adolfo; Tanner, Roger I; Ellero, Marco

    2016-09-02

    Shear thinning-a reduction in suspension viscosity with increasing shear rates-is understood to arise in colloidal systems from a decrease in the relative contribution of entropic forces. The shear-thinning phenomenon has also been often reported in experiments with noncolloidal systems at high volume fractions. However its origin is an open theoretical question and the behavior is difficult to reproduce in numerical simulations where shear thickening is typically observed instead. In this letter we propose a non-Newtonian model of interparticle lubrication forces to explain shear thinning in noncolloidal suspensions. We show that hidden shear-thinning effects of the suspending medium, which occur at shear rates orders of magnitude larger than the range investigated experimentally, lead to significant shear thinning of the overall suspension at much smaller shear rates. At high particle volume fractions the local shear rates experienced by the fluid situated in the narrow gaps between particles are much larger than the averaged shear rate of the whole suspension. This allows the suspending medium to probe its high-shear non-Newtonian regime and it means that the matrix fluid rheology must be considered over a wide range of shear rates.

  4. Effects of excitation around jet preferred mode Strouhal number in high-speed jets

    NASA Astrophysics Data System (ADS)

    Kuo, Ching-Wen; Cluts, Jordan; Samimy, Mo

    2017-04-01

    It has been widely reported in the literature that the jet preferred mode Strouhal number varies over a large range of 0.2-0.6, depending upon the facility where the measurement is made as well as the measurement techniques and the location in the jet plume where the measurement is taken. This study investigates this wide variation and potential explanations for it. Active flow control is used to show that the jet is receptive to excitation over a large range of Strouhal numbers and azimuthal modes. The wide variation in the preferred mode Strouhal number is shown to be tightly linked to the evolution, spacing, and scale of the coherent flow structures, which dominate the jet shear layer's development. The low-end of the range is determined by the minimum Strouhal number at which structures begin to interact with one another in the jet plume. Below this range, structures have no significant effect on the plume's statistical properties. For Strouhal numbers at the high-end of the range, the development of coherent flow structures shifts upstream toward the nozzle exit and the structures disintegrate earlier in the jet plume. The earlier development and disintegration prevent these structures from strongly impacting the entire flowfield. The results imply that upstream perturbations in the flow present in various facilities could be responsible for the variations in the measured jet preferred mode Strouhal number. Experimental results from schlieren imaging and near- and far-field microphone measurements are used to investigate the preferred mode Strouhal number across this range.

  5. On the axisymmetric stability of heated supersonic round jets

    PubMed Central

    2016-01-01

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

  6. Deformation of a Thin Film by a Wall Jet

    NASA Astrophysics Data System (ADS)

    Hammoud, Naima; Al-Housseiny, Talal; Stone, Howard

    2012-11-01

    A variety of industrial processes such as jet stripping or jet wiping involve a high speed stream of gas flowing over a liquid film. In this work, we model this kind of situation by considering a thin viscous liquid film, over which a high Reynolds number laminar wall jet (or Glauert jet) is flowing. We study the shape of the thin liquid film, which is deformed due to the shear stress induced by a jet of a low-viscosity fluid. The mechanics of the jet, which is modeled by boundary-layer theory, is coupled to the mechanics of the thin film, which includes the influence of surface tension and buoyancy. We describe the unsteady shape of the film using the lubrication description to derive a nonlinear PDE that is coupled to the Glauert jet via interfacial stresses. For the steady state, we obtain analytical solutions in different asymptotic regimes. We compare our theoretical findings to numerical simulations conducted with the finite volume solver FLUENT.

  7. Effect of Free Jet on Refraction and Noise

    NASA Technical Reports Server (NTRS)

    Khavaran, Abbas; Georgiadis, Nicholas J.; Bridges, James E.; Dippold, Vance F., III

    2005-01-01

    This article investigates the role of a free jet on the sound radiated from a jet. In particular, the role of an infinite wind tunnel, which simulates the forward flight condition, is compared to that of a finite wind tunnel. The second configuration is usually used in experiments, where the microphones are located in a static ambient medium far outside the free jet. To study the effect of the free jet on noise, both propagation and source strength need to be addressed. In this work, the exact Green's function in a locally parallel flow is derived for a simulated flight case. Numerical examples are presented that show a reduction in the magnitude of the Green's function in the aft arc and an increase in the forward arc for the simulated flight condition. The effect of finite wind tunnel on refraction is sensitive to the source location and is most pronounced in the aft arc. A Reynolds-averaged Navier-Stokes solution (RANS) yields the required mean flow and turbulence scales that are used in the jet mixing noise spectrum calculations. In addition to the sound/flow interaction, the separate effect of source strength and elongation of the noise-generating region of the jet in a forward flight is studied. Comparisons are made with experiments for the static and finite tunnel cases. Finally, the standard free-jet shear corrections that convert the finite wind tunnel measurements to an ideal wind tunnel arrangement are evaluated.

  8. Three-Dimensional Modeling of Quasi-Homologous Solar Jets

    NASA Technical Reports Server (NTRS)

    Pariat, E.; Antiochos, S. K.; DeVore, C. R.

    2010-01-01

    Recent solar observations (e.g., obtained with Hinode and STEREO) have revealed that coronal jets are a more frequent phenomenon than previously believed. This higher frequency results, in part, from the fact that jets exhibit a homologous behavior: successive jets recur at the same location with similar morphological features. We present the results of three-dimensional (31)) numerical simulations of our model for coronal jets. This study demonstrates the ability of the model to generate recurrent 3D untwisting quasi-homologous jets when a stress is constantly applied at the photospheric boundary. The homology results from the property of the 3D null-point system to relax to a state topologically similar to its initial configuration. In addition, we find two distinct regimes of reconnection in the simulations: an impulsive 3D mode involving a helical rotating current sheet that generates the jet, and a quasi-steady mode that occurs in a 2D-like current sheet located along the fan between the sheared spines. We argue that these different regimes can explain the observed link between jets and plumes.

  9. Integrated numerical prediction of atomization process of liquid hydrogen jet

    NASA Astrophysics Data System (ADS)

    Ishimoto, Jun; Ohira, Katsuhide; Okabayashi, Kazuki; Chitose, Keiko

    2008-05-01

    The 3-D structure of the liquid atomization behavior of an LH jet flow through a pinhole nozzle is numerically investigated and visualized by a new type of integrated simulation technique. The present computational fluid dynamics (CFD) analysis focuses on the thermodynamic effect on the consecutive breakup of a cryogenic liquid column, the formation of a liquid film, and the generation of droplets in the outlet section of the pinhole nozzle. Utilizing the governing equations for a high-speed turbulent cryogenic jet flow through a pinhole nozzle based on the thermal nonequilibrium LES-VOF model in conjunction with the CSF model, an integrated parallel computation is performed to clarify the detailed atomization process of a high-speed LH2 jet flow through a pinhole nozzle and to acquire data, which is difficult to confirm by experiment, such as atomization length, liquid core shape, droplet-size distribution, spray angle, droplet velocity profiles, and thermal field surrounding the atomizing jet flow. According to the present computation, the cryogenic atomization rate and the LH2 droplets-gas two-phase flow characteristics are found to be controlled by the turbulence perturbation upstream of the pinhole nozzle, hydrodynamic instabilities at the gas-liquid interface and shear stress between the liquid core and the periphery of the LH2 jet. Furthermore, calculation of the effect of cryogenic atomization on the jet thermal field shows that such atomization extensively enhances the thermal diffusion surrounding the LH2 jet flow.

  10. Estimation of aerodynamic noise generated by forced compressible round jets

    NASA Astrophysics Data System (ADS)

    Maidi, Mohamed

    2006-05-01

    An acoustic numerical code based on Ligthill's analogy is combined with large-eddy simulations techniques in order to evaluate the noise emitted by subsonic (M=0.7) and supersonic (M=1.4) round jets. We show first that, for centerline Mach number M=0.9 and Reynolds number Re=3.6×10, acoustic intensities compare satisfactorily with experimental data of the literature in terms of levels and directivity. Afterwards, high Reynolds number (Re=3.6×10) free and forced jets at Mach 0.7 and 1.4 are studied. Numerical results show that the jet noise intensity depends on the nature of the upstream mixing layer. Indeed, the subsonic jet is 4 dB quieter than the free jet when acting on this shear layer by superposing inlet varicose and flapping perturbations at preferred and first subharmonic frequency, respectively. The maximal acoustic level of the supersonic jet is, on the other hand, 3 dB lower than the free one with a flapping upstream perturbation at the second subharmonic. The results reported in this paper confirm previous works presented in the literature demonstrating that jet noise may be modified according to the inlet conditions. To cite this article: M. Maidi, C. R. Mecanique 334 (2006).

  11. ON A CORONAL BLOWOUT JET: THE FIRST OBSERVATION OF A SIMULTANEOUSLY PRODUCED BUBBLE-LIKE CME AND A JET-LIKE CME IN A SOLAR EVENT

    SciTech Connect

    Shen Yuandeng; Liu Yu

    2012-02-01

    The coronal blowout jet is a peculiar category among various jet phenomena, in which the sheared base arch, often carrying a small filament, experiences a miniature version of blowout eruption that produces large-scale coronal mass ejection (CME). In this paper, we report such a coronal blowout jet with high-resolution multi-wavelength and multi-angle observations taken from Solar Dynamics Observatory, Solar Terrestrial Relations Observatory, and Big Bear Solar Observatory. For the first time, we find that simultaneous bubble-like and jet-like CMEs were dynamically related to the blowout jet that showed cool and hot components next to each other. Our observational results indicate that (1) the cool component resulted from the eruption of the filament contained within the jet's base arch, and it further caused the bubble-like CME; (2) the jet-like CME was associated with the hot component, which was the outward moving heated plasma generated by the reconnection of the base arch and its ambient open field lines. On the other hand, bifurcation of the jet's cool component was also observed, which resulted from the uncoupling of the erupting filament's two legs that were highly twisted at the very beginning. Based on these results, we propose a model to interpret the coronal blowout jet, in which the external reconnection not only produces the jet-like CME, but also leads to the rising of the filament. Subsequently, internal reconnection starts underneath the rising filament and thereby causes the bubble-like CME.

  12. Spray Formation of Herschel-Bulkley Fluids using Impinging Jets

    NASA Astrophysics Data System (ADS)

    Rodrigues, Neil; Gao, Jian; Chen, Jun; Sojka, Paul E.

    2015-11-01

    The impinging jet spray formation of two non-Newtonian, shear-thinning, Herschel-Bulkley fluids was investigated in this work. The water-based gelled solutions used were 1.0 wt.-% agar and 1.0 wt.-% kappa carrageenan. A rotational rheometer and a capillary viscometer were used to measure the strain-rate dependency of viscosity and the Herschel-Bulkley Extended (HBE) rheological model was used to characterize the shear-thinning behavior. A generalized HBE jet Reynolds number Rej , gen - HBE was used as the primary parameter to characterize the spray formation. A like-on-like impinging jet doublet was used to produce atomization. Shadowgraphs were captured in the plane of the sheet formed by the two jets using a CCD camera with an Nd:YAG laser beam providing the back-illumination. Typical behavior for impinging jet atomization using Newtonian liquids was not generally observed due to the non-Newtonian, viscous properties of the agar and kappa carrageenan gels. Instead various spray patterns were observed depending on Rej , gen - HBE. Spray characteristics of maximum instability wavelength and sheet breakup length were extracted from the shadowgraphs. Multi-University Research Initiative Grant Number W911NF-08-1-0171.

  13. An experimental study of planar heterogeneous supersonic confined jets

    NASA Astrophysics Data System (ADS)

    Tanis, Frederick J., Jr.

    1994-12-01

    The effects of varying the exit pressure of a supersonic helium jet exhausting coaxially with two parallel supersonic air streams into a constant area duct were investigated. The method used to evaluate the mass entrainment rate was to measure helium molar concentration profiles and mass flux across the duct using a binary gas probe then calculate the mass entrainment into the helium jet. In order to conduct this study a novel binary gas probe was developed which allowed helium concentration and mass flux data to be obtained during continuous traverses across the supersonic flowfield. High exit pressure ratio (EPR) led to improved overall mixing compared to the baseline case with an EPR near unity. The high EPR caused low mass entrainment along the jet shear layers due to high convective Mach numbers and velocity ratios, but the high EPR caused oblique shocks to form which reflected off the duct walls and intersected with the helium jet several times causing significant mass entrainment due to numerous shock-shear layer interactions (SSLI's). A correlation between the vorticity generated during a SSLI and the mass entrainment into the jet was developed.

  14. Mass and Momentum Turbulent Transport Experiments with Confined Coaxial Jets

    NASA Technical Reports Server (NTRS)

    Johnson, B. V.; Bennett, J. C.

    1981-01-01

    Downstream mixing of coaxial jets discharging in an expanded duct was studied to obtain data for the evaluation and improvement of turbulent transport models currently used in a variety of computational procedures throughout the propulsion community for combustor flow modeling. Flow visualization studies showed four major shear regions occurring; a wake region immediately downstream of the inlet jet inlet duct; a shear region further downstream between the inner and annular jets; a recirculation zone; and a reattachment zone. A combination of turbulent momentum transport rate and two velocity component data were obtained from simultaneous measurements with a two color laser velocimeter (LV) system. Axial, radial and azimuthal velocities and turbulent momentum transport rate measurements in the r-z and r-theta planes were used to determine the mean value, second central moment (or rms fluctuation from mean), skewness and kurtosis for each data set probability density function (p.d.f.). A combination of turbulent mass transport rate, concentration and velocity data were obtained system. Velocity and mass transport in all three directions as well as concentration distributions were used to obtain the mean, second central moments, skewness and kurtosis for each p.d.f. These LV/LIF measurements also exposed the existence of a large region of countergradient turbulent axial mass transport in the region where the annular jet fluid was accelerating the inner jet fluid.

  15. Blowout Jets: Evidence from Hinode/XRT for X-Ray Jets Made by Blowout Eruption of the Emerging Bipole

    NASA Technical Reports Server (NTRS)

    Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.

    2009-01-01

    Yamauchi et al (2004, ApJ, 605, 511) found that there are two structurally and dynamically distinct types of H macrospicules in polar coronal holes: single-column jet macrospicules and erupting-loop macrospicules. The structure and motion of the single-column jet macrospicules fit the standard Shibata reconnection picture for solar X-ray jets (Shibata et al 1992, PASJ, 44, L173). The form and motion of the erupting-loop macrospicules is reminiscent of the ejective eruption of the sheared-core-field flux rope in the filament-eruption birth of a bubble-type coronal mass ejection (CME). That roughly half of all polar H macrospicules were observed to be erupting-loop macrospicules suggests that there should be a corresponding large class of X-ray jets in which the emerging bipole at the base of the jet undergoes a blowout eruption as in a bubble-type CME, instead of staying closed as in the standard picture for X-ray jets. Along with a cartoon of the standard picture, we present a cartoon depicting the signatures to be expected of a blowout jet in high-resolution coronal X-ray movies such as from Hinode/XRT. From Hinode/XRT movies in polar coronal holes, we show: (1) examples of X-ray jets that fit the standard picture very well, and (2) other examples that do not fit the standard picture but do show signatures appropriate for blowout jets. These signatures are (1) a flare arcade inside the emerging bipole in addition to the flare arcade produced between the emerging bipole and the ambient high-reaching unipolar field by reconnection of these two fields as in the standard picture, and (2) in addition to the jet prong expected from the standard reconnection, a second jet prong or strand, one that could not be produced by the standard reconnection but could be produced by reconnection between the ambient unipolar field and one leg of an erupting core-field flux rope that has blown out the emerging bipole. We therefore infer that these "two pronged" jets are made by

  16. Blowout Jets: Evidence from Hinode/XRT for X-Ray Jets Made by Blowout Eruption of the Emerging Bipole

    NASA Technical Reports Server (NTRS)

    Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.

    2009-01-01

    Yamauchi et al (2004, ApJ, 605, 511) found that there are two structurally and dynamically distinct types of H macrospicules in polar coronal holes: single-column jet macrospicules and erupting-loop macrospicules. The structure and motion of the single-column jet macrospicules fit the standard Shibata reconnection picture for solar X-ray jets (Shibata et al 1992, PASJ, 44, L173). The form and motion of the erupting-loop macrospicules is reminiscent of the ejective eruption of the sheared-core-field flux rope in the filament-eruption birth of a bubble-type coronal mass ejection (CME). That roughly half of all polar H macrospicules were observed to be erupting-loop macrospicules suggests that there should be a corresponding large class of X-ray jets in which the emerging bipole at the base of the jet undergoes a blowout eruption as in a bubble-type CME, instead of staying closed as in the standard picture for X-ray jets. Along with a cartoon of the standard picture, we present a cartoon depicting the signatures to be expected of a blowout jet in high-resolution coronal X-ray movies such as from Hinode/XRT. From Hinode/XRT movies in polar coronal holes, we show: (1) examples of X-ray jets that fit the standard picture very well, and (2) other examples that do not fit the standard picture but do show signatures appropriate for blowout jets. These signatures are (1) a flare arcade inside the emerging bipole in addition to the flare arcade produced between the emerging bipole and the ambient high-reaching unipolar field by reconnection of these two fields as in the standard picture, and (2) in addition to the jet prong expected from the standard reconnection, a second jet prong or strand, one that could not be produced by the standard reconnection but could be produced by reconnection between the ambient unipolar field and one leg of an erupting core-field flux rope that has blown out the emerging bipole. We therefore infer that these "two pronged" jets are made by

  17. Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow

    NASA Technical Reports Server (NTRS)

    Simon, Frederick F.; Ciancone, Michael L.

    1987-01-01

    A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configurations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.

  18. Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow

    NASA Technical Reports Server (NTRS)

    Simon, F. F.; Ciancone, M. L.

    1985-01-01

    A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configutations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.

  19. Response of multi-panel assembly to noise from a jet in forward motion

    NASA Technical Reports Server (NTRS)

    Bayliss, A.; Maestrello, L.; Mcgreevy, J. L.; Fenno, C. C., Jr.

    1995-01-01

    A model of the interaction of the noise from a spreading subsonic jet with a 4 panel assembly is studied numerically in two dimensions. The effect of forward motion of the jet is accounted for by considering a uniform flow field superimposed on a mean jet exit profile. The jet is initially excited by a pulse-like source inserted into the flow field. The pulse triggers instabilities associated with the inviscid instability of the jet shear layer. These instabilities generate sound which in turn serves to excite the panels. We compare the sound from the jet, the responses of the panels and the resulting acoustic radiation for the static jet and the jet in forward motion. The far field acoustic radiation, the panel response and sound radiated from the panels are all computed and compared to computations of a static jet. The results demonstrate that for a jet in forward motion there is a reduction in sound in downstream directions and an increase in sound in upstream directions in agreement with experiments. Furthermore, the panel response and radiation for a jet in forward motion exhibits a downstream attenuation as compared with the static case.

  20. Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow

    NASA Technical Reports Server (NTRS)

    Simon, Frederick F.; Ciancone, Michael L.

    1987-01-01

    A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configurations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.

  1. Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow

    NASA Astrophysics Data System (ADS)

    Simon, Frederick F.; Ciancone, Michael L.

    A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configurations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.

  2. Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow

    NASA Astrophysics Data System (ADS)

    Simon, F. F.; Ciancone, M. L.

    A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configutations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.

  3. Optimal recovery from microburst wind shear

    NASA Technical Reports Server (NTRS)

    Mulgund, Sandeep S.

    1993-01-01

    Severe low-altitude wind variability represents an infrequent but significant hazard to aircraft taking off or landing. During the period from 1964 to 1985, microburst wind shear was a contributing factor in at least 26 civil aviation accidents involving nearly 500 fatalities and over 200 injuries. A microburst is a strong localized downdraft that strikes the ground, creating winds that diverge radially from the impact point. The physics of microbursts have only been recently understood in detail, and it has been found that effective recovery from inadvertent encounters may require piloting techniques that are counter-intuitive to flight crews. The goal of this work was to optimize the flight path of a twin-jet transport aircraft encountering a microburst during approach to landing. The objective was to execute an escape maneuver that maintained safe ground clearance and an adequate stall margin during the climb-out portion of the trajectory.

  4. Optimising Antibiotic Usage to Treat Bacterial Infections

    PubMed Central

    Paterson, Iona K.; Hoyle, Andy; Ochoa, Gabriela; Baker-Austin, Craig; Taylor, Nick G. H.

    2016-01-01

    The increase in antibiotic resistant bacteria poses a threat to the continued use of antibiotics to treat bacterial infections. The overuse and misuse of antibiotics has been identified as a significant driver in the emergence of resistance. Finding optimal treatment regimens is therefore critical in ensuring the prolonged effectiveness of these antibiotics. This study uses mathematical modelling to analyse the effect traditional treatment regimens have on the dynamics of a bacterial infection. Using a novel approach, a genetic algorithm, the study then identifies improved treatment regimens. Using a single antibiotic the genetic algorithm identifies regimens which minimise the amount of antibiotic used while maximising bacterial eradication. Although exact treatments are highly dependent on parameter values and initial bacterial load, a significant common trend is identified throughout the results. A treatment regimen consisting of a high initial dose followed by an extended tapering of doses is found to optimise the use of antibiotics. This consistently improves the success of eradicating infections, uses less antibiotic than traditional regimens and reduces the time to eradication. The use of genetic algorithms to optimise treatment regimens enables an extensive search of possible regimens, with previous regimens directing the search into regions of better performance. PMID:27892497

  5. Optimising Antibiotic Usage to Treat Bacterial Infections

    NASA Astrophysics Data System (ADS)

    Paterson, Iona K.; Hoyle, Andy; Ochoa, Gabriela; Baker-Austin, Craig; Taylor, Nick G. H.

    2016-11-01

    The increase in antibiotic resistant bacteria poses a threat to the continued use of antibiotics to treat bacterial infections. The overuse and misuse of antibiotics has been identified as a significant driver in the emergence of resistance. Finding optimal treatment regimens is therefore critical in ensuring the prolonged effectiveness of these antibiotics. This study uses mathematical modelling to analyse the effect traditional treatment regimens have on the dynamics of a bacterial infection. Using a novel approach, a genetic algorithm, the study then identifies improved treatment regimens. Using a single antibiotic the genetic algorithm identifies regimens which minimise the amount of antibiotic used while maximising bacterial eradication. Although exact treatments are highly dependent on parameter values and initial bacterial load, a significant common trend is identified throughout the results. A treatment regimen consisting of a high initial dose followed by an extended tapering of doses is found to optimise the use of antibiotics. This consistently improves the success of eradicating infections, uses less antibiotic than traditional regimens and reduces the time to eradication. The use of genetic algorithms to optimise treatment regimens enables an extensive search of possible regimens, with previous regimens directing the search into regions of better performance.

  6. Visual parameter optimisation for biomedical image processing.

    PubMed

    Pretorius, A J; Zhou, Y; Ruddle, R A

    2015-01-01

    Biomedical image processing methods require users to optimise input parameters to ensure high-quality output. This presents two challenges. First, it is difficult to optimise multiple input parameters for multiple input images. Second, it is difficult to achieve an understanding of underlying algorithms, in particular, relationships between input and output. We present a visualisation method that transforms users' ability to understand algorithm behaviour by integrating input and output, and by supporting exploration of their relationships. We discuss its application to a colour deconvolution technique for stained histology images and show how it enabled a domain expert to identify suitable parameter values for the deconvolution of two types of images, and metrics to quantify deconvolution performance. It also enabled a breakthrough in understanding by invalidating an underlying assumption about the algorithm. The visualisation method presented here provides analysis capability for multiple inputs and outputs in biomedical image processing that is not supported by previous analysis software. The analysis supported by our method is not feasible with conventional trial-and-error approaches.

  7. Visual parameter optimisation for biomedical image processing

    PubMed Central

    2015-01-01

    Background Biomedical image processing methods require users to optimise input parameters to ensure high-quality output. This presents two challenges. First, it is difficult to optimise multiple input parameters for multiple input images. Second, it is difficult to achieve an understanding of underlying algorithms, in particular, relationships between input and output. Results We present a visualisation method that transforms users' ability to understand algorithm behaviour by integrating input and output, and by supporting exploration of their relationships. We discuss its application to a colour deconvolution technique for stained histology images and show how it enabled a domain expert to identify suitable parameter values for the deconvolution of two types of images, and metrics to quantify deconvolution performance. It also enabled a breakthrough in understanding by invalidating an underlying assumption about the algorithm. Conclusions The visualisation method presented here provides analysis capability for multiple inputs and outputs in biomedical image processing that is not supported by previous analysis software. The analysis supported by our method is not feasible with conventional trial-and-error approaches. PMID:26329538

  8. Critical assessment of jet erosion test methodologies for cohesive soil and sediment

    NASA Astrophysics Data System (ADS)

    Karamigolbaghi, Maliheh; Ghaneeizad, Seyed Mohammad; Atkinson, Joseph F.; Bennett, Sean J.; Wells, Robert R.

    2017-10-01

    The submerged Jet Erosion Test (JET) is a commonly used technique to assess the erodibility of cohesive soil. Employing a linear excess shear stress equation and impinging jet theory, simple numerical methods have been developed to analyze data collected using a JET to determine the critical shear stress and erodibility coefficient of soil. These include the Blaisdell, Iterative, and Scour Depth Methods, and all have been organized into easy to use spreadsheet routines. The analytical framework of the JET and its associated methods, however, are based on many assumptions that may not be satisfied in field and laboratory settings. The main objective of this study is to critically assess this analytical framework and these methodologies. Part of this assessment is to include the effect of flow confinement on the JET. The possible relationship between the derived erodibility coefficient and critical shear stress, a practical tool in soil erosion assessment, is examined, and a review of the deficiencies in the JET methodology also is presented. Using a large database of JET results from the United States and data from literature, it is shown that each method can generate an acceptable curve fit through the scour depth measurements as a function of time. The analysis shows, however, that the Scour Depth and Iterative Methods may result in physically unrealistic values for the erosion parameters. The effect of flow confinement of the impinging jet increases the derived critical shear stress and decreases the erodibility coefficient by a factor of 2.4 relative to unconfined flow assumption. For a given critical shear stress, the length of time over which scour depth data are collected also affects the calculation of erosion parameters. In general, there is a lack of consensus relating the derived soil erodibility coefficient to the derived critical shear stress. Although empirical relationships are statistically significant, the calculated erodibility coefficient for a

  9. Evidence of melt in {open_quotes}soft{close_quotes} recovered copper jets

    SciTech Connect

    Lassila, D.H.; Nikkel, D.J. Jr.; Kershaw, R.P.

    1995-08-01

    A shaped charge (81 mm, 42{degrees}, OFHC copper cone) was fired into a {open_quotes}soft{close_quotes} recovery bunker to allow metallurgical examination of recovered jet particles and the slug. The initial weight of the copper liner was 245 gm, of which 184 gm was recovered. The number of jet particles recovered was 37 (approximately 63% of the particles formed by the charge). Extensive metallurgical analyses were performed on the recovered slug and jet particles. The microstructural features associated with voids, e.g. dendritic grain growth, clearly indicate that the regions in the vicinity of the centerline of the slug and jet particles were melted. In this work we present calculations of jet temperature as a function of constitutive behavior. In order to predict melt in the center region of the jet we find it necessary to scale flow stress with a pressure dependent shear modulus.

  10. RECURRENT SOLAR JETS INDUCED BY A SATELLITE SPOT AND MOVING MAGNETIC FEATURES

    SciTech Connect

    Chen, Jie; Su, Jiangtao; Yin, Zhiqiang; Priya, T. G.; Zhang, Hongqi; Xu, Haiqing; Yu, Sijie; Liu, Jihong

    2015-12-10

    Recurrent and homologous jets were observed to the west edge of active region NOAA 11513 at the boundary of a coronal hole. We find two kinds of cancellations between opposite polarity magnetic fluxes, inducing the generation of recurrent jets. First, a satellite spot continuously collides with a pre-existing opposite polarity magnetic field and causes recurrent solar jets. Second, moving magnetic features, which emerge near the sunspot penumbra, pass through the ambient plasma and eventually collide with the opposite polarity magnetic field. Among these recurrent jets, a blowout jet that occurred around 21:10 UT is investigated. The rotation of the pre-existing magnetic field and the shear motion of the satellite spot accumulate magnetic energy, which creates the possibility for the jet to experience blowout right from the standard.

  11. The AGN Jet Model of the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Guo, Fulai

    2017-01-01

    The nature and origin of the Fermi bubbles detected in the inner Galaxy remain elusive. In this paper, we briefly discuss some recent theoretical and observational developments, with a focus on the AGN jet model. Analogous to radio lobes observed in massive galaxies, the Fermi bubbles could be naturally produced by a pair of opposing jets emanating nearly along the Galaxy's rotation axis from the Galactic center. Our two-fluid hydrodynamic simulations reproduce quite well the bubble location and shape, and interface instabilities at the bubble surface could be effectively suppressed by shear viscosity. We briefly comment on some potential issues related to our model, which may lead to future progress.

  12. CAT LIDAR wind shear studies

    NASA Technical Reports Server (NTRS)

    Goff, R. W.

    1978-01-01

    The studies considered the major meteorological factors producing wind shear, methods to define and classify wind shear in terms significant from an aircraft perturbation standpoint, the significance of sensor location and scan geometry on the detection and measurement of wind shear, and the tradeoffs involved in sensor performance such as range/velocity resolution, update frequency and data averaging interval.

  13. An analytical study of the longitudinal response of airplanes to positive wind shear

    NASA Technical Reports Server (NTRS)

    Sherman, W. L.

    1981-01-01

    The longitudinal response of jet transport aircraft to vertical variation of the horizontal winds is analyzed. Specific reference is given to the role of the speed (u) stability derivatives in the interaction of the airplane and its environment. The relative importance of the u stability derivatives is determined. The wind shear tolerance factor is found which can be used to determine, in a qualitative manner, the stability (tolerance) of an airplane to wind shear. A further study of the control problem shows that the criteria for good control could be reduced from two to one automatic control systems. Only a speed control system is necessary for good control in wind shear.

  14. Jet lag modification.

    PubMed

    Simmons, Emily; McGrane, Owen; Wedmore, Ian

    2015-01-01

    Athletes often are required to travel for sports participation, both for practice and competition. A number of those crossing multiple time zones will develop jet lag disorder with possible negative consequences on their performance. This review will discuss the etiology of jet lag disorder and the techniques that are available to shorten or minimize its effects. This includes both pharmacological and nonpharmacological approaches.

  15. Jet measurements in ATLAS

    NASA Astrophysics Data System (ADS)

    Loch, Peter; ATLAS Collaboration

    2011-11-01

    The reconstruction of jets generated in the proton-proton collisions at the Large Hadron Collider (LHC) at a center of mass energy of TeV with the ATLAS detector is discussed. Beginning with a brief review of the calorimeter signal definitions relevant for jet finding, and the use of reconstructed charged particle tracks, the jet reconstruction strategy is described in some detail. Emphasis is put on the jet energy scale (JES) calibration strategy applied for first data, which is based on a short sequence of data driven and simulation based calibrations and corrections to restore the measured jet energy to particle level. The level of understanding of the signal patterns entering the JES corrections is shown for selected variables in comparisons to simulations. The present systematic uncertainties on the JES, which can be as low as 2% for central jets, are presented and analyzed with respect to the individual fractional contributions entering their determination. Some characteristic jet reconstruction performance and selected results from the first year of jet physics with ATLAS in a newly accessible kinematic domain are shown in conclusion.

  16. Jet lag prevention

    MedlinePlus

    ... be harder to adjust to because you lose time. Jet lag can make you feel like going to bed ... such as trying to adjust to the new time zone before you arrive. Images Jet lag prevention References Berry RB, Wagner MH. Patients with ...

  17. Shear bands in concentrated bacterial suspensions under oscillatory shear

    NASA Astrophysics Data System (ADS)

    Cheng, Xiang; Samanta, Devranjan; Xu, Xinliang

    2016-11-01

    Bacterial suspensions show interesting rheological behaviors such as a remarkable "superfluidic" state with vanishing viscosity. Although the bulk rheology of bacterial suspensions has been experimentally studied, shear profiles within bacterial suspensions have not been systematically explored so far. Here, by combining confocal rheometry with PIV, we investigated the flow behaviors of concentrated E. coli suspensions under planar oscillatory shear. We found that concentrated bacterial suspensions exhibit strong non-homogeneous flow profiles at low shear rates, where shear rates vanish away from the moving shear plate. We characterized the shape of the nonlinear shear profiles at different applied shear rates and bacterial concentrations and activities. The shear profiles follow a simple scaling relation with the applied shear rates and the enstrophy of suspensions, unexpected from the current hydrodynamic models of active fluids. We demonstrated that this scaling relation can be quantitatively understood by considering the power output of bacteria at different orientations with respect to shear flows. Our experiments reveal a profound influence of shear flows on the locomotion of bacteria and provide new insights into the dynamics of active fluids. The research is funded by ACS Petroleum Research Fund (54168-DNI9) and by the David & Lucile Packard Foundation. X. X. acknowledges support by the National Natural Science Foundation of China No. 11575020.

  18. Shear Yielding and Shear Jamming of Dense Hard Sphere Glasses

    NASA Astrophysics Data System (ADS)

    Urbani, Pierfrancesco; Zamponi, Francesco

    2017-01-01

    We investigate the response of dense hard sphere glasses to a shear strain in a wide range of pressures ranging from the glass transition to the infinite-pressure jamming point. The phase diagram in the density-shear strain plane is calculated analytically using the mean-field infinite-dimensional solution. We find that just above the glass transition, the glass generically yields at a finite shear strain. The yielding transition in the mean-field picture is a spinodal point in presence of disorder. At higher densities, instead, we find that the glass generically jams at a finite shear strain: the jamming transition prevents yielding. The shear yielding and shear jamming lines merge in a critical point, close to which the system yields at extremely large shear stress. Around this point, highly nontrivial yielding dynamics, characterized by system-spanning disordered fractures, is expected.

  19. Boundary element based multiresolution shape optimisation in electrostatics

    NASA Astrophysics Data System (ADS)

    Bandara, Kosala; Cirak, Fehmi; Of, Günther; Steinbach, Olaf; Zapletal, Jan

    2015-09-01

    We consider the shape optimisation of high-voltage devices subject to electrostatic field equations by combining fast boundary elements with multiresolution subdivision surfaces. The geometry of the domain is described with subdivision surfaces and different resolutions of the same geometry are used for optimisation and analysis. The primal and adjoint problems are discretised with the boundary element method using a sufficiently fine control mesh. For shape optimisation the geometry is updated starting from the coarsest control mesh with increasingly finer control meshes. The multiresolution approach effectively prevents the appearance of non-physical geometry oscillations in the optimised shapes. Moreover, there is no need for mesh regeneration or smoothing during the optimisation due to the absence of a volume mesh. We present several numerical experiments and one industrial application to demonstrate the robustness and versatility of the developed approach.

  20. Particle removal from smooth and rough surfaces by turbulent jet impingement

    NASA Astrophysics Data System (ADS)

    Liebner, Thomas; Settles, Gary

    2006-11-01

    Recent experiments, e.g. Phares, Smedley & Flagan, J. Aerosol Sci. 31(11) 1335, 2000, have characterized monodisperse particle removal as a function of the theoretical wall shear stress induced by a free turbulent jet impinging upon a smooth surface. These experiments were done with variable jet impingement angle, duration, pressure, standoff distance, etc. The current research expands upon this theme through the experimental investigation of particle removal at larger standoff distances and correspondingly lower wall shear stress levels. We determine particle removal efficiency ratings as a function of the induced wall shear stress for particles of varying size and composition. Finally, we address the complications that arise in particle removal by turbulent jets if the impingement surface is no longer smooth (e.g. a fabric surface). This work has application to such problems as contamination control and the sampling of chemical traces from common surfaces.

  1. Shear-thinning Fluid

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Whipped cream and the filling for pumpkin pie are two familiar materials that exhibit the shear-thinning effect seen in a range of industrial applications. It is thick enough to stand on its own atop a piece of pie, yet flows readily when pushed through a tube. This demonstrates the shear-thinning effect that was studied with the Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002. CVX observed the behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. The principal investigator was Dr. Robert Berg of the National Institutes of Standards and Technology in Gaithersburg, MD.

  2. Shear-thinning Fluid

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Whipped cream and the filling for pumpkin pie are two familiar materials that exhibit the shear-thinning effect seen in a range of industrial applications. It is thick enough to stand on its own atop a piece of pie, yet flows readily when pushed through a tube. This demonstrates the shear-thinning effect that was studied with the Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002. CVX observed the behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. The principal investigator was Dr. Robert Berg of the National Institutes of Standards and Technology in Gaithersburg, MD.

  3. Gelation under shear

    SciTech Connect

    Butler, B.D.; Hanley, H.J.M.; Straty, G.C.; Muzny, C.D.

    1995-12-31

    An experimental small angle neutron scattering (SANS) study of dense silica gels, prepared from suspensions of 24 nm colloidal silica particles at several volume fractions {theta} is discussed. Provided that {theta}{approx_lt}0.18, the scattered intensity at small wave vectors q increases as the gelation proceeds, and the structure factor S(q, t {yields} {infinity}) of the gel exhibits apparent power law behavior. Power law behavior is also observed, even for samples with {theta}>0.18, when the gel is formed under an applied shear. Shear also enhances the diffraction maximum corresponding to the inter-particle contact distance of the gel. Difficulties encountered when trying to interpret SANS data from these dense systems are outlined. Results of computer simulations intended to mimic gel formation, including computations of S(q, t), are discussed. Comments on a method to extract a fractal dimension characterizing the gel are included.

  4. Multiple jet study

    NASA Technical Reports Server (NTRS)

    Walker, R. E.; Kors, D. L.

    1973-01-01

    Test data is presented which allows determination of jet penetration and mixing of multiple cold air jets into a ducted subsonic heated mainstream flow. Jet-to-mainstream momentum flux ratios ranged from 6 to 60. Temperature profile data is presented at various duct locations up to 24 orifice diameters downstream of the plane of jet injection. Except for two configurations, all geometries investigated had a single row of constant diameter orifices located transverse to the main flow direction. Orifice size and spacing between orifices were varied. Both of these were found to have a significant effect on jet penetration and mixing. The best mixing of the hot and cold streams was achieved with duct height.

  5. Instability of rectangular jets

    NASA Technical Reports Server (NTRS)

    Tam, Christopher K. W.; Thies, Andrew T.

    1992-01-01

    The instability of rectangular jets is investigated using a vortex sheet model. It is shown that such jets support four linearly independent families of instability waves. Within each family there are infinitely many modes. A way to classify these modes according to the characteristics of their mode shapes or eigenfunctions is proposed. A parametric study of the instability wave characteristics has been carried out. A sample of the numerical results is reported here. It is found that the first and third modes of each instability wave family are corner modes. The pressure fluctuations associated with these instability waves are localized near the corners of the jet. The second mode, however, is a center mode with maximum fluctuations concentrated in the central portion of the jet flow. The center mode has the largest spatial growth rate. It is anticipated that as the instability waves propagate downstream the center mode would emerge as the dominant instability of the jet.

  6. Description of Jet Breakup

    NASA Technical Reports Server (NTRS)

    Papageorgiou, Demetrios T.

    1996-01-01

    In this article we review recent results on the breakup of cylindrical jets of a Newtonian fluid. Capillary forces provide the main driving mechanism and our interest is in the description of the flow as the jet pinches to form drops. The approach is to describe such topological singularities by constructing local (in time and space) similarity solutions from the governing equations. This is described for breakup according to the Euler, Stokes or Navier-Stokes equations. It is found that slender jet theories can be applied when viscosity is present, but for inviscid jets the local shape of the jet at breakup is most likely of a non-slender geometry. Systems of one-dimensional models of the governing equations are solved numerically in order to illustrate these differences.

  7. Relativistic Jets and Collapsars

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Woosley, S. E.

    2001-05-01

    In order to study the relativistic jets from collapsars, we have developed a special relativistic multiple-dimensional hydrodynamics code similar to the GENESIS code (Aloy et al., ApJS, 122, 151). The code is based on the PPM interpolation algorithm and Marquina's Riemann solver. Using this code, we have simulated the propagation of axisymmetric jets along the rotational axis of collapsed rotating stars (collapsars). Using the progenitors of MacFadyen, Woosley, and Heger, a relativistic jet is injected at a given inner boundary radius. This radius, the opening angle of the jet, its Lorentz factor, and its total energy are parameters of the problem. A highly collimated, relativistic outflow is observed at the surface of the star several seconds later. We will discuss the hydrodynamical focusing of the jet, it's break out properties, time evolution, and sensitivity to the adopted parameters.

  8. Jet Lag in Athletes

    PubMed Central

    Lee, Aaron; Galvez, Juan Carlos

    2012-01-01

    Context: Prolonged transmeridian air travel can impart a physical and emotional burden on athletes in jet lag and travel fatigue. Jet lag may negatively affect the performance of athletes. Study Type: Descriptive review. Evidence Acquisition: A Medline search for articles relating to jet lag was performed (1990-present), as was a search relating to jet lag and athletes (1983-January, 2012). The results were reviewed for relevance. Eighty-nine sources were included in this descriptive review. Results: Behavioral strategies are recommended over pharmacological strategies when traveling with athletes; pharmacological aides may be used on an individual basis. Strategic sleeping, timed exposure to bright light, and the use of melatonin are encouraged. Conclusions: There is strong evidence that mood and cognition are adversely affected by jet lag. Some measures of individual and team performance are adversely affected as well. PMID:23016089

  9. Instability of rectangular jets

    NASA Technical Reports Server (NTRS)

    Tam, Christopher K. W.; Thies, Andrew T.

    1992-01-01

    The instability of rectangular jets is investigated using a vortex sheet model. It is shown that such jets support four linearly independent families of instability waves. Within each family there are infinitely many modes. A way to classify these modes according to the characteristics of their mode shapes or eigenfunctions is proposed. A parametric study of the instability wave characteristics has been carried out. A sample of the numerical results is reported here. It is found that the first and third modes of each instability wave family are corner modes. The pressure fluctuations associated with these instability waves are localized near the corners of the jet. The second mode, however, is a center mode with maximum fluctuations concentrated in the central portion of the jet flow. The center mode has the largest spatial growth rate. It is anticipated that as the instability waves propagate downstream the center mode would emerge as the dominant instability of the jet.

  10. Jet physics at CDF

    SciTech Connect

    Melese, P.

    1997-05-01

    We present high E{sub T} jet measurements from CDF at the Fermilab Tevatron Collider. The incfilusive jet cross section at {radical}s = 1800 GeV with {approximately} 5 times more data is compared to the published CDF results, preliminary D0 results, and next-to-leading order QCD predictions. The {summation}E{sub T} cross section is also compared to QCD predictions and the dijet angular distribution is used to place a limit on quark compositeness. The inclusive jet cross section at {radical}s = 630 GeV is compared with that at 1800 GeV to test the QCD predictions for the scaling of jet cross sections with {radical}s. Finally, we present momentum distributions of charged particles in jets and compare them to Modified Leading Log Approximation predictions.

  11. Bolt Shear Force Sensor

    DTIC Science & Technology

    2015-03-12

    Attorney Docket No. 102587 7 August 15 The below identified patent application is available for licensing. Requests for...of any royalties thereon or therefor. CROSS REFERENCE TO OTHER PATENT APPLICATIONS [0002] None. BACKGROUND OF THE INVENTION (1) Field of the...shearing forces. [0010] In the known art, Slack (United States Patent No. 4,870,866) describes an ultrasonic method for measuring contact Attorney

  12. Shear Roll Mill Reactivation

    DTIC Science & Technology

    2012-09-13

    pneumatically operated paste dumper and belt conveyor system, the loss in weight feeder system, the hydraulically operated shear roll mill, the pellet...out feed belt conveyor , and the pack out system comprised of the metal detector, scale, and pack out empty and full drum roller conveyors . Page | 4...feed hopper and conveyor supplying the loss in weight feeder were turned on, and it was verified that these items functioned as designed. The

  13. Micromechanics of shear banding

    SciTech Connect

    Gilman, J.J.

    1992-08-01

    Shear-banding is one of many instabilities observed during the plastic flow of solids. It is a consequence of the dislocation mechanism which makes plastic flow fundamentally inhomogeneous, and is exacerbated by local adiabatic heating. Dislocation lines tend to be clustered on sets of neighboring glide planes because they are heterogeneously generated; especially through the Koehler multiple-cross-glide mechanism. Factors that influence their mobilities also play a role. Strain-hardening decreases the mobilities within shear bands thereby tending to spread (delocalize) them. Strain-softening has the inverse effect. This paper reviews the micro-mechanisms of these phenomena. It will be shown that heat production is also a consequence of the heterogeneous nature of the microscopic flow, and that dislocation dipoles play an important role. They are often not directly observable, but their presence may be inferred from changes in thermal conductivity. It is argued that after deformation at low temperatures dipoles are distributed a la Pareto so there are many more small than large ones. Instability at upper yield point, the shapes of shear-band fronts, and mechanism of heat generation are also considered. It is shown that strain-rate acceleration plays a more important role than strain-rate itself in adiabatic instability.

  14. Micromechanics of shear banding

    SciTech Connect

    Gilman, J.J.

    1992-08-01

    Shear-banding is one of many instabilities observed during the plastic flow of solids. It is a consequence of the dislocation mechanism which makes plastic flow fundamentally inhomogeneous, and is exacerbated by local adiabatic heating. Dislocation lines tend to be clustered on sets of neighboring glide planes because they are heterogeneously generated; especially through the Koehler multiple-cross-glide mechanism. Factors that influence their mobilities also play a role. Strain-hardening decreases the mobilities within shear bands thereby tending to spread (delocalize) them. Strain-softening has the inverse effect. This paper reviews the micro-mechanisms of these phenomena. It will be shown that heat production is also a consequence of the heterogeneous nature of the microscopic flow, and that dislocation dipoles play an important role. They are often not directly observable, but their presence may be inferred from changes in thermal conductivity. It is argued that after deformation at low temperatures dipoles are distributed a la Pareto so there are many more small than large ones. Instability at upper yield point, the shapes of shear-band fronts, and mechanism of heat generation are also considered. It is shown that strain-rate acceleration plays a more important role than strain-rate itself in adiabatic instability.

  15. Control of jet flow mixing and stabilization

    NASA Astrophysics Data System (ADS)

    Yuan, Chih-Chung

    This dissertation examines the effect of feedback controllers on mixing and stabilization of unstable two-dimensional jet flows. The mixing enhancement control law uses a pair of actuators at the jet nozzle exit acting on the shear layers near the corners by blowing and subtracting fluid in an anti-symmetric fashion with a zero net mass flux. The sensor measures the pressure difference across the nozzle diameter and is either located at downstream or at the nozzle exit with time delay. If the length/time scale is long enough and the feedback gain is sufficiently large, this control strategy will provide a constant vortex generation pattern that successfully improves mixing. The evolution of a passive scalar and mixing of particles with mass in jet flows are visualized and quantified. Probability Density Functions based on the particle/scalar distribution are constructed as measures of mixing. The stabilization control law employs filaments with distributed sensors and actuators in the jet flow. The sensors measure the local pressure difference across nozzle diameter and the actuators act as a reaction body force in the normal direction. The instability is damped with sufficiently large feedback gain. The Reynolds numbers of jet flows studied are 100 and 150 that are in the transient range. The results are obtained by means of Direct Numerical Simulation. The Navier-Stokes equations are spatially discretized by second order finite-difference method and advanced in time using a fractional step technique with a hybrid Runge-Kutta/Crank-Nicolson time discretization. This hybrid technique is developed to gain a larger time step while numerical stability is maintained. Stretched and staggered grids are used in both stream-wise and normal directions. The simulation results are validated by comparison with previous works and through self-similar analysis.

  16. Global optimisation methods for poroelastic material characterisation using a clamped sample in a Kundt tube setup

    NASA Astrophysics Data System (ADS)

    Vanhuyse, Johan; Deckers, Elke; Jonckheere, Stijn; Pluymers, Bert; Desmet, Wim

    2016-02-01

    The Biot theory is commonly used for the simulation of the vibro-acoustic behaviour of poroelastic materials. However, it relies on a number of material parameters. These can be hard to characterize and require dedicated measurement setups, yielding a time-consuming and costly characterisation. This paper presents a characterisation method which is able to identify all material parameters using only an impedance tube. The method relies on the assumption that the sample is clamped within the tube, that the shear wave is excited and that the acoustic field is no longer one-dimensional. This paper numerically shows the potential of the developed method. It therefore performs a sensitivity analysis of the quantification parameters, i.e. reflection coefficients and relative pressures, and a parameter estimation using global optimisation methods. A 3-step procedure is developed and validated. It is shown that even in the presence of numerically simulated noise this procedure leads to a robust parameter estimation.

  17. Simulation study to evaluate a constant-groundspeed approach method in moderate and severe wind shears

    NASA Technical Reports Server (NTRS)

    Kelley, W. W.

    1979-01-01

    The use of a constant-groundspeed procedure for flying final approaches in moderate and severe wind shear environments was investigated. Performance was compared to results of simulated constant-airspeed approaches in identical wind profiles. The simulation model was a medium twin-jet transport equipped with an autothrottle for maintaining constant groundspeed or constant airspeed. For both moderate and severe wind shears, the constant-groundspeed approach method was shown to provide a way to more safely negotiate the shears while also providing predictable and acceptable touchdown performance. Results showed airspeeds on final approach to be considerably higher using the constant-groundspeed method, which supplied the additional stall margin needed when tail-wind shears were encountered. Throttle movements were noticeably reduced in all wind profiles when constant-groundspeed approaches were flown. Touchdown conditions were practically identical for both approach methods in moderate wind shear.

  18. Optimal Jet Finder

    NASA Astrophysics Data System (ADS)

    Grigoriev, D. Yu.; Jankowski, E.; Tkachov, F. V.

    2003-09-01

    We describe a FORTRAN 77 implementation of the optimal jet definition for identification of jets in hadronic final states of particle collisions. We discuss details of the implementation, explain interface subroutines and provide a usage example. The source code is available from http://www.inr.ac.ru/~ftkachov/projects/jets/. Program summaryTitle of program: Optimal Jet Finder (OJF_014) Catalogue identifier: ADSB Program Summary URL:http://cpc.cs.qub.ac.uk/summaries/ADSB Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: Any computer with the FORTRAN 77 compiler Tested with: g77/Linux on Intel, Alpha and Sparc; Sun f77/Solaris (thwgs.cern.ch); xlf/AIX (rsplus.cern.ch); MS Fortran PowerStation 4.0/Win98 Programming language used: FORTRAN 77 Memory required: ˜1 MB (or more, depending on the settings) Number of bytes in distributed program, including examples and test data: 251 463 Distribution format: tar gzip file Keywords: Hadronic jets, jet finding algorithms Nature of physical problem: Analysis of hadronic final states in high energy particle collision experiments often involves identification of hadronic jets. A large number of hadrons detected in the calorimeter is reduced to a few jets by means of a jet finding algorithm. The jets are used in further analysis which would be difficult or impossible when applied directly to the hadrons. Grigoriev et al. [ hep-ph/0301185] provide a brief introduction to the subject of jet finding algorithms and a general review of the physics of jets can be found in [Rep. Prog. Phys. 36 (1993) 1067]. Method of solution: The software we provide is an implementation of the so-called optimal jet definition ( OJD). The theory of OJD was developed by Tkachov [Phys. Rev. Lett. 73 (1994) 2405; 74 (1995) 2618; Int. J. Mod. Phys. A 12 (1997) 5411; 17 (2002) 2783]. The desired jet configuration is obtained as the one that minimizes Ω R, a certain function of the input particles and jet

  19. Simulations of Solar Jets

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-02-01

    Formation of a coronal jet from twisted field lines that have reconnected with the ambient field. The colors show the radial velocity of the plasma. [Adapted from Szente et al. 2017]How do jets emitted from the Suns surface contribute to its corona and to the solar wind? In a recent study, a team of scientists performed complex three-dimensional simulations of coronal jets to answer these questions.Small ExplosionsCoronal jets are relatively small eruptions from the Suns surface, with heights of roughly 100 to 10,000 km, speeds of 10 to 1,000 km/s, and lifetimes of a few minutes to around ten hours. These jets are constantly present theyre emitted even from the quiet Sun, when activity is otherwise low and weve observed them with a fleet of Sun-watching space telescopes spanning the visible, extreme ultraviolet (EUV), and X-ray wavelength bands.A comparison of simulated observations based on the authors model (left panels) to actual EUV and X-ray observations of jets (right panels). [Szente et al. 2017]Due to their ubiquity, we speculate that these jets might contribute to heating the global solar corona (which is significantly hotter than the surface below it, a curiosity known as the coronal heating problem). We can also wonder what role these jets might play in driving the overall solar wind.Launching a JetLed by Judit Szente (University of Michigan), a team of scientists has explored the impact of coronal jets on the global corona and solar wind with a series of numerical simulations. Szente and collaborators used three-dimensional, magnetohydrodynamic simulations that provide realistic treatment of the solar atmosphere, the solar wind acceleration, and the complexities of heat transfer throughout the corona.In the authors simulations, a jet is initiated as a magnetic dipole rotates at the solar surface, winding up field lines. Magnetic reconnection between the twisted lines and the background field then launches the jet from the dense and hot solar

  20. Paediatric CT protocol optimisation: a design of experiments to support the modelling and optimisation process.

    PubMed

    Rani, K; Jahnen, A; Noel, A; Wolf, D

    2015-07-01

    In the last decade, several studies have emphasised the need to understand and optimise the computed tomography (CT) procedures in order to reduce the radiation dose applied to paediatric patients. To evaluate the influence of the technical parameters on the radiation dose and the image quality, a statistical model has been developed using the design of experiments (DOE) method that has been successfully used in various fields (industry, biology and finance) applied to CT procedures for the abdomen of paediatric patients. A Box-Behnken DOE was used in this study. Three mathematical models (contrast-to-noise ratio, noise and CTDI vol) depending on three factors (tube current, tube voltage and level of iterative reconstruction) were developed and validated. They will serve as a basis for the development of a CT protocol optimisation model.

  1. Generating and controlling homogeneous air turbulence using random jet arrays

    NASA Astrophysics Data System (ADS)

    Carter, Douglas; Petersen, Alec; Amili, Omid; Coletti, Filippo

    2016-12-01

    The use of random jet arrays, already employed in water tank facilities to generate zero-mean-flow homogeneous turbulence, is extended to air as a working fluid. A novel facility is introduced that uses two facing arrays of individually controlled jets (256 in total) to force steady homogeneous turbulence with negligible mean flow, shear, and strain. Quasi-synthetic jet pumps are created by expanding pressurized air through small straight nozzles and are actuated by fast-response low-voltage solenoid valves. Velocity fields, two-point correlations, energy spectra, and second-order structure functions are obtained from 2D PIV and are used to characterize the turbulence from the integral-to-the Kolmogorov scales. Several metrics are defined to quantify how well zero-mean-flow homogeneous turbulence is approximated for a wide range of forcing and geometric parameters. With increasing jet firing time duration, both the velocity fluctuations and the integral length scales are augmented and therefore the Reynolds number is increased. We reach a Taylor-microscale Reynolds number of 470, a large-scale Reynolds number of 74,000, and an integral-to-Kolmogorov length scale ratio of 680. The volume of the present homogeneous turbulence, the largest reported to date in a zero-mean-flow facility, is much larger than the integral length scale, allowing for the natural development of the energy cascade. The turbulence is found to be anisotropic irrespective of the distance between the jet arrays. Fine grids placed in front of the jets are effective at modulating the turbulence, reducing both velocity fluctuations and integral scales. Varying the jet-to-jet spacing within each array has no effect on the integral length scale, suggesting that this is dictated by the length scale of the jets.

  2. Instabilities in shear and simple shear deformations of gold crystals

    NASA Astrophysics Data System (ADS)

    Pacheco, A. A.; Batra, R. C.

    We use the tight-binding potential and molecular mechanics simulations to study local and global instabilities in shear and simple shear deformations of three initially defect-free finite cubes of gold single crystal containing 3480, 7813, and 58,825 atoms. Displacements on all bounding surfaces are prescribed while studying simple shear deformations, but displacements on only two opposite surfaces are assigned during simulations of shear deformations with the remaining four surfaces kept free of external forces. The criteria used to delineate local instabilities in the system include the following: (i) a component of the second-order spatial gradients of the displacement field having large values relative to its average value in the body, (ii) the minimum eigenvalue of the Hessian of the energy of an atom becoming non-positive, and (iii) structural changes represented by a high value of the common neighborhood parameter. It is found that these criteria are met essentially simultaneously at the same atomic position. Effects of free surfaces are evidenced by different deformation patterns for the same specimen deformed in shear and simple shear. The shear strength of a specimen deformed in simple shear is more than three times that of the same specimen deformed in shear. It is found that for each cubic specimen deformed in simple shear the evolution with the shear strain of the average shear stress, prior to the onset of instabilities, is almost identical to that in an equivalent hyperelastic material with strain energy density derived from the tight-binding potential and the assumption that it obeys the Cauchy-Born rule. Even though the material response of the hyperelastic body predicted from the strain energy density is stable over the range of the shear strain simulated in this work, the molecular mechanics simulations predict local and global instabilities in the three specimens.

  3. Automatic optimisation of gamma dose rate sensor networks: The DETECT Optimisation Tool

    NASA Astrophysics Data System (ADS)

    Helle, K. B.; Müller, T. O.; Astrup, P.; Dyve, J. E.

    2014-05-01

    Fast delivery of comprehensive information on the radiological situation is essential for decision-making in nuclear emergencies. Most national radiological agencies in Europe employ gamma dose rate sensor networks to monitor radioactive pollution of the atmosphere. Sensor locations were often chosen using regular grids or according to administrative constraints. Nowadays, however, the choice can be based on more realistic risk assessment, as it is possible to simulate potential radioactive plumes. To support sensor planning, we developed the DETECT Optimisation Tool (DOT) within the scope of the EU FP 7 project DETECT. It evaluates the gamma dose rates that a proposed set of sensors might measure in an emergency and uses this information to optimise the sensor locations. The gamma dose rates are taken from a comprehensive library of simulations of atmospheric radioactive plumes from 64 source locations. These simulations cover the whole European Union, so the DOT allows evaluation and optimisation of sensor networks for all EU countries, as well as evaluation of fencing sensors around possible sources. Users can choose from seven cost functions to evaluate the capability of a given monitoring network for early detection of radioactive plumes or for the creation of dose maps. The DOT is implemented as a stand-alone easy-to-use JAVA-based application with a graphical user interface and an R backend. Users can run evaluations and optimisations, and display, store and download the results. The DOT runs on a server and can be accessed via common web browsers; it can also be installed locally.

  4. Liquid jets injected into non-uniform crossflow

    NASA Astrophysics Data System (ADS)

    Tambe, Samir

    An experimental study has been conducted with liquid jets injected transversely into a crossflow to study the effect of non-uniformities in the crossflow velocity distribution to the jet behavior. Two different non-uniform crossflows were created during this work, a shear-laden crossflow and a swirling crossflow. The shear-laden crossflow was generated by merging two independent, co-directional, parallel airstreams creating a shear mixing layer at the interface between them. The crossflow exhibited a quasi-linear velocity gradient across the height of the test chamber. By varying the velocities of the two airstreams, the sense and the slope of the crossflow velocity gradient could be changed. Particle Image Velocimetry (PIV) studies were conducted to characterize the crossflow. The parameter, UR, is defined as the ratio of the velocities of the two streams and governs the velocity gradient. A positive velocity gradient was observed for UR > 1 and a negative velocity gradient for UR < 1. PIV and Phase Doppler Particle Anemometry (PDPA) studies were conducted to study the penetration and atomization of 0.5 mm diameter water jets injected into this crossflow. The crossflow velocity gradient was observed to have a significant effect on jet penetration as well as the post breakup spray. For high UR (> 1), jet penetration increased and the Sauter Mean Diameter (SMD) distribution became more uniform. For low UR (< 1), low penetration, higher droplet velocities and better atomization were observed. The second crossflow tested was a swirling flow generated using in-house designed axial swirlers. Three swirlers were used, with vane exit angles of 30°, 45° and 60°. Laser Doppler Velocimetry (LDV) was used to study the crossflow velocities. The axial (Ux) and the tangential (Utheta) components of the crossflow velocity were observed to decrease with increasing radial distance away from the centerbody. The flow angle of the crossflow was smaller than the vane exit angle

  5. Common mode chokes and optimisation aspects

    NASA Astrophysics Data System (ADS)

    Kut, T.; Lücken, A.; Dickmann, S.; Schulz, D.

    2014-11-01

    Due to the increasing electrification of modern aircraft, as a result of the More Electric Aircraft concept, new strategies and approaches are required to fulfil the strict EMC aircraft standards (DO-160/ED-14-Sec. 20). Common mode chokes are a key component of electromagnetic filters and often oversized because of the unknown impedance of the surrounding power electronic system. This oversizing results in an increase of weight and volume. It has to be avoided as far as possible for mobile applications. In this context, an advanced method is presented to measure these impedances under operating conditions. Furthermore, the different parameters of the inductance design is explained and an optimisation for weight and volume is introduced.

  6. Optimising Impact in Astronomy for Development Projects

    NASA Astrophysics Data System (ADS)

    Grant, Eli

    2015-08-01

    Positive outcomes in the fields of science education and international development are notoriously difficult to achieve. Among the challenges facing projects that use astronomy to improve education and socio-economic development is how to optimise project design in order to achieve the greatest possible benefits. Over the past century, medical scientists along with statisticians and economists have progressed an increasingly sophisticated and scientific approach to designing, testing and improving social intervention and public health education strategies. This talk offers a brief review of the history and current state of `intervention science'. A similar framework is then proposed for astronomy outreach and education projects, with applied examples given of how existing evidence can be used to inform project design, predict and estimate cost-effectiveness, minimise the risk of unintended negative consequences and increase the likelihood of target outcomes being achieved.

  7. The effect of jet shape on jet injection.

    PubMed

    Park, Geehoon; Modak, Ashin; Hogan, N Catherine; Hunter, Ian W

    2015-01-01

    The effects of the dispersion pattern of a needle-free jet injector are explored. The shape of the jets were compared using a high-speed video camera and jet injections of collimated and dispersed fluid jets with a Lorentz-force actuated jet injector were made into acrylamide gel and post-mortem porcine tissue. A custom-built high-speed X-ray imaging system was used in order to observe the dynamics of the dispersion mechanism for each injection in real time. We show that a collimated jet stream results in greater tissue penetration than a dispersed jet stream.

  8. Directional control of a jet using synthetic jets

    NASA Astrophysics Data System (ADS)

    Frunzulica, Florin; Macovei, Alexandru Cǎtǎlin; Dumitrache, Alexandru; Crunteanu, Daniel

    2017-07-01

    The paper presents an application of synthetic jets in the flow control of a jet. The synthetic jet actuator consists of an oscillating membrane operating at high frequency and separating two cavities with exit slots of different geometries. The synthetic jets work as an alternating push-pull system and the generated vortical structure changes the flow direction of the main jet (jet vectoring). The numerical investigations are performed using a RANS solver with an adequate turbulence model and demonstrates a changing of a jet direction.

  9. Controlling laser-induced jet formation for bioprinting mesenchymal stem cells with high viability and high resolution.

    PubMed

    Ali, Muhammad; Pages, Emeline; Ducom, Alexandre; Fontaine, Aurelien; Guillemot, Fabien

    2014-09-12

    Laser-assisted bioprinting is a versatile, non-contact, nozzle-free printing technique which has demonstrated high potential for cell printing with high resolution. Improving cell viability requires determining printing conditions which minimize shear stress for cells within the jet and cell impact at droplet landing. In this context, this study deals with laser-induced jet dynamics to determine conditions from which jets arise with minimum kinetic energies. The transition from a sub-threshold regime to jetting regime has been associated with a geometrical parameter (vertex angle) which can be harnessed to print mesenchymal stem cells with high viability using slow jet conditions. Finally, hydrodynamic jet stability is also studied for higher laser pulse energies which give rise to supersonic but turbulent jets.

  10. Jet noise suppression

    NASA Astrophysics Data System (ADS)

    Gliebe, P. R.; Brausch, J. F.; Majjigi, R. K.; Lee, R.

    1991-08-01

    The objectives of this chapter are to review and summarize the jet noise suppression technology, to provide a physical and theoretical model to explain the measured jet noise suppression characteristics of different concepts, and to provide a set of guidelines for evolving jet noise suppression designs. The underlying principle for all jet noise suppression devices is to enhance rapid mixing (i.e., diffusion) of the jet plume by geometric and aerothermodynamic means. In the case of supersonic jets, the shock-cell broadband noise reduction is effectively accomplished by the elimination or mitigation of the shock-cell structure. So far, the diffusion concepts have predominantly concentrated on jet momentum and energy (kinetic and thermal) diffusion, in that order, and have yielded better noise reduction than the simple conical nozzles. A critical technology issue that needs resolution is the effect of flight on the noise suppression potential of mechanical suppressor nozzles. A more thorough investigation of this mechanism is necessary for the successful development and design of an acceptable noise suppression device for future high-speed civil transports.

  11. Synthetic Fence Jets

    NASA Astrophysics Data System (ADS)

    Sigurdson, Lorenz; Apps, Christopher

    2000-11-01

    "Synthetic Jets" have previously been produced where an oscillating flow with zero net mass flux acts on the edges of an orifice. The resulting flow is similar to a normal jet. We have proposed and verified that another type of jet called a "Synthetic Fence Jet" (SFJ or "fe-je") can also be created. We introduced a fence perpendicular to both a wall and an oscillating velocity field. Under certain conditions a jet was formed by vortices of alternating sign. The vortices were shed from the fence and they induced each other away from it. This phenomenon could be used as a method of flow control. The objective of this project was to use flow visualization to prove the existence of and characterize this jet. A test rig was used which incorporates smoke-wire flow visualization; independent oscillation level and frequency control; and computer- controlled data acquisition. It has been discovered that the jet direction can be vectored by altering the forcing waveform shape. To explain this a theory was developed that is based on the Biot-Savart law of vortex dynamics.

  12. Jet Noise Suppression

    NASA Technical Reports Server (NTRS)

    Gliebe, P. R.; Brausch, J. F.; Majjigi, R. K.; Lee, R.

    1991-01-01

    The objectives of this chapter are to review and summarize the jet noise suppression technology, to provide a physical and theoretical model to explain the measured jet noise suppression characteristics of different concepts, and to provide a set of guidelines for evolving jet noise suppression designs. The underlying principle for all jet noise suppression devices is to enhance rapid mixing (i.e., diffusion) of the jet plume by geometric and aerothermodynamic means. In the case of supersonic jets, the shock-cell broadband noise reduction is effectively accomplished by the elimination or mitigation of the shock-cell structure. So far, the diffusion concepts have predominantly concentrated on jet momentum and energy (kinetic and thermal) diffusion, in that order, and have yielded better noise reduction than the simple conical nozzles. A critical technology issue that needs resolution is the effect of flight on the noise suppression potential of mechanical suppressor nozzles. A more thorough investigation of this mechanism is necessary for the successful development and design of an acceptable noise suppression device for future high-speed civil transports.

  13. Solar coronal jets

    NASA Astrophysics Data System (ADS)

    Dobrzyck, D.

    The solar jets were first observed by SOHO instruments (EIT, LASCO, UVCS) during the previous solar minimum. They were small, fast ejections originating from flaring UV bright points within large polar coronal holes. The obtained data provided us with estimates of the jet plasma conditions, dynamics, evolution of the electron temperature and heating rate required to reproduce the observed ionization state. To follow the polar jets through the solar cycle a special SOHO Joint Observing Program (JOP 155) was designed. It involves a number of SOHO instruments (EIT, CDS, UVCS, LASCO) as well as TRACE. The coordinated observations have been carried out since April 2002. The data enabled to identify counterparts of the 1996-1998 solar minimum jets. Their frequency of several events per day appear comparable to the frequency from the previous solar minimum. The jets are believed to be triggered by field line reconnection between emerging magnetic dipole and pre-existing unipolar field. Existing models predict that the hot jet is formed together with another jet of a cool material. The particular goal of the coordinated SOHO and TRACE observations was to look for possible association of the hot and cool plasma ejections. Currently there is observational evidence that supports these models.

  14. Planning, optimisation and evaluation of hyperthermia treatments.

    PubMed

    Kok, H P; Kotte, A N T J; Crezee, J

    2017-09-01

    Hyperthermia treatment planning using dedicated simulations of power and temperature distributions is very useful to assist in hyperthermia applications. This paper describes an advanced treatment planning software package for a wide variety of applications. The in-house developed C++ software package Plan2Heat runs on a Linux operating system. Modules are available to perform electric field and temperature calculations for many heating techniques. The package also contains optimisation routines, post-treatment evaluation tools and a sophisticated thermal model enabling to account for 3D vasculature based on an angiogram or generated artificially using a vessel generation algorithm. The use of the software is illustrated by a simulation of a locoregional hyperthermia treatment for a pancreatic cancer patient and a spherical tumour model heated by interstitial hyperthermia, with detailed 3D vasculature included. The module-based set-up makes the software flexible and easy to use. The first example demonstrates that treatment planning can help to focus the heating to the tumour. After optimisation, the simulated absorbed power in the tumour increased with 50%. The second example demonstrates the impact of accurately modelling discrete vasculature. Blood at body core temperature entering the heated volume causes relatively cold tracks in the heated volume, where the temperature remains below 40 °C. A flexible software package for hyperthermia treatment planning has been developed, which can be very useful in many hyperthermia applications. The object-oriented structure of the source code allows relatively easy extension of the software package with additional tools when necessary for future applications.

  15. A Theoretical Basis for the Scaling Law of Broadband Shock Noise Intensity in Supersonic Jets

    NASA Technical Reports Server (NTRS)

    Kandula, Max

    2011-01-01

    A theoretical basis for the scaling of broadband shock noise intensity In supersonic jets was formulated considering linear shock-shear wave interaction. Modeling of broadband shock noise with the aid of shock-turbulence interaction with special reference to linear theories is briefly reviewed. An hypothesis has been postulated that the peak angle of incidence (closer to the critical angle) for the shear wave primarily governs the generation of sound in the interaction process with the noise generation contribution from off-peak incident angles being relatively unimportant. The proposed hypothesis satisfactorily explains the well-known scaling law for the broadband shock-associated noise in supersonic jets.

  16. On the Scaling Law for Broadband Shock Noise Intensity in Supersonic Jets

    NASA Technical Reports Server (NTRS)

    Kanudula, Max

    2009-01-01

    A theoretical model for the scaling of broadband shock noise intensity in supersonic jets was formulated on the basis of linear shock-shear wave interaction. An hypothesis has been postulated that the peak angle of incidence (closer to the critical angle) for the shear wave primarily governs the generation of sound in the interaction process rather than the noise generation contribution from off-peak incident angles. The proposed theory satisfactorily explains the well-known scaling law for the broadband shock -associated noise in supersonic jets.

  17. Free surface effects on the statistical properties of a submerged rectangular jet

    NASA Astrophysics Data System (ADS)

    Tay, Godwin F. K.; Mishra, Anuvrat; Kuhn, David C. S.; Tachie, Mark F.

    2017-02-01

    The results of an experimental investigation of turbulent rectangular jets offset from a free surface are presented. Two rectangular jets of aspect ratio 2 and 4 were examined and the results were compared to a square jet at the same offset height ratio of h/De ≈ 2.7, where De is the circle-equivalent diameter of the nozzle. A particle image velocimetry (PIV) was used to measure the mean flow and turbulent characteristics at a Reynolds number of 7900 and a Froude number of 1.29. The results indicate significant enhancements in the jet spreading rate and mean streamwise velocity decay rate for the larger aspect ratio nozzles. The results reveal that the jet-free surface interaction had a greater impact on the mean surface-normal velocity than the mean streamwise velocity. The values of the turbulence intensities, Reynolds shear stress and structure parameter were found to be nearly independent of the nozzle aspect ratio. Surface mean velocity and turbulence intensities were also measured to characterize the influence of the shear layer on the free surface. The results indicate a damping of the surface-normal turbulence intensities compared to the streamwise turbulence intensity. The influence of the free surface was felt as an enhancement in streamwise fluctuating velocity two-point correlation and a suppression of the surface-normal fluctuating velocity two-point correlation. The free surface also increased the structure inclination angle in the upper shear layer compared to that in the lower shear layer.

  18. Unsteady Shear Layers.

    DTIC Science & Technology

    1985-10-29

    plunging airfoils, elliptic jets with mass entrainment and impinging ’ j ets. Additionally, the 3-D vortical flow over a backward facing step was...reattachment length is only about 4 step depths which is much shorter than that in a 2-D J . .1 r r*~ % 4,V rq ~ 4 case. The reattachment line shows a ...Boundary Layers", R.F. Blackwelder and J.H. Haritonidis, J . Fluid Mech., 132, 87, 1983. 2. "Breakdown of Streamwise Vortices near a Wall", J.D

  19. Coherent structures - Reality and myth. [in turbulent shear flow

    NASA Technical Reports Server (NTRS)

    Hussain, A. K. M. F.

    1983-01-01

    Large-scale coherent structures (CS) in turbulent shear flows are characterized, reviewing recent theoretical and experimental investigations. The use of computers as a research tool and the flow-visualization experimental technique are introduced, CS are defined, the history of their discovery is traced, and their main characteristics are listed. Topics discussed and illustrated include the initial condition of the free shear layer, triple and double decomposition, topological features of CS, detection and eduction of CS, phase alignment via cross correlation, induced versus natural structures, the bursting phenomenon, turbulent spot, streaks, bursting frequency, the axisymmetric mixing layer, vortex pairing in an axisymmetric jet, CS and jet noise, broadband noise amplification via pure-tone excitation, CS interaction in a plane-jet near field, the Taylor hypothesis applied to CS, negative production, and the validity of the Reynolds-number similarity hypothesis. It is found that the coherent Reynolds stress, vorticity, and production are not much greater than the time-averaged values for fully developed flows with significant incoherent turbulence, suggesting that the importance of CS may have been exaggerated in some recent studies.

  20. Interaction between plasma synthetic jet and subsonic turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Zong, Haohua; Kotsonis, Marios

    2017-04-01

    exhibits a prominent spatiotemporal behaviour. The residence time of the CVP is estimated as the jet duration time, while the maximum extent of the affected flow in the three coordinate directions (x, y, and z) is approximately 32D, 8.5D, and 10D, respectively. An extremely high level of turbulent kinetic energy production is shown in the jet shear-layer, front vortex ring, and CVP, of which the contribution of the streamwise Reynolds normal stress is dominant. Finally, a conceptual model of the interaction between the PSJ and the TBL is proposed.

  1. Driving Flows in Laboratory Astrophysical Plasma Jets: The Mochi.LabJet Experiment

    NASA Astrophysics Data System (ADS)

    Carroll, Evan G.

    Mochi.Labjet is a new experiment at the University of Washington developed to investigate the interaction of shear flows in plasma jets with boundary conditions similar to an accretion disc system. This thesis details the engineering design and first plasmas of the Mochi.Labjet experiment. The experiment required construction of a new three electrode plasma gun with azimuthal symmetric gas injection, two optically-isolated pulsed power supplies for generating and sustaining plasma, and one optically-isolated pulsed power supply for generating a background magnetic field. Optical isolation is achieved with four custom circuits: the TTL-optical transmitter, optical-TTL receiver, optical-relay, and optical-tachometer circuits. First plasmas, during the commissioning phase of the apparatus, show evidence of flared jet structures with significant azimuthal symmetry.

  2. Jet Physics at CDF

    SciTech Connect

    Sally Seidel

    2004-06-28

    Jets have been studied by the CDF Collaboration [1] as a means of searching for new particles and interactions, testing a variety of perturbative QCD predictions, and providing input for the global parton distribution function (PDF) fits. Unless otherwise indicated below, the jets were reconstructed using a cone algorithm [2] with cone radius R = 0.7 from data taken at the Fermilab Tevatron collider in Run 2, 2001-2003, with {radical}s = 1.96 TeV. Central jets, in the pseudorapidity range relative to fixed detector coordinates 0.1 < |{eta}| < 0.7, are used.

  3. Angular Scaling In Jets

    SciTech Connect

    Jankowiak, Martin; Larkoski, Andrew J.; /SLAC

    2012-02-17

    We introduce a jet shape observable defined for an ensemble of jets in terms of two-particle angular correlations and a resolution parameter R. This quantity is infrared and collinear safe and can be interpreted as a scaling exponent for the angular distribution of mass inside the jet. For small R it is close to the value 2 as a consequence of the approximately scale invariant QCD dynamics. For large R it is sensitive to non-perturbative effects. We describe the use of this correlation function for tests of QCD, for studying underlying event and pile-up effects, and for tuning Monte Carlo event generators.

  4. Validation of the Small Hot Jet Acoustic Rig for Jet Noise Research

    NASA Technical Reports Server (NTRS)

    Bridges, James; Brown, Clifford A.

    2005-01-01

    The development and acoustic validation of the Small Hot Jet Aeroacoustic Rig (SHJAR) is documented. Originally conceived to support fundamental research in jet noise, the rig has been designed and developed using the best practices of the industry. While validating the rig for acoustic work, a method of characterizing all extraneous rig noise was developed. With this in hand, the researcher can know when the jet data being measured is being contaminated and design the experiment around this limitation. Also considered is the question of uncertainty, where it is shown that there is a fundamental uncertainty of 0.5dB or so to the best experiments, confirmed by repeatability studies. One area not generally accounted for in the uncertainty analysis is the variation which can result from differences in initial condition of the nozzle shear layer. This initial condition was modified and the differences in both flow and sound were documented. The bottom line is that extreme caution must be applied when working on small jet rigs, but that highly accurate results can be made independent of scale.

  5. A Thermodynamic, kinematic and microphysical analysis of a jet and gigantic jet-producing Florida thunderstorm

    NASA Astrophysics Data System (ADS)

    Lazarus, S. M.; Splitt, M. E.; Brownlee, James; Spiva, Nicholas; Liu, Ningyu

    2015-08-01

    This paper presents a meteorological analysis of a storm that produced two jets, four gigantic jets (GJ), and a starter, which were observed by two radars as well as the Kennedy Space Center 4-Dimensional Lightning Surveillance System on 3 August 2013 in Central Florida. The work is the first application of dual polarization data to a jet-producing storm and is the fifth case related to a tropical disturbance. The storm environment is consistent with the moist tropical paradigm that characterizes about three quarters of the surface and aircraft observed jet and GJ events. The most unstable (MU) convective available potential energy is not unusual for Florida summer convection and is below the climatological mean for these events. An unusual speed shear layer is located near the storm equilibrium level (EL) and the storm exhibits a tilted structure with CGs displaced upshear. The turbulence, as measured by the eddy dissipation rate, is extreme near the storm top during the event window, consistent with the GJ mixing hypothesis. The individual events are collocated with, and track along, the center axis of the divergent outflow at the EL and occur within the region of the coldest GOES IR temperatures—placing the events within the overshoot. The dual polarization data indicate a deep graupel column, extending above the mixed phase layer, to a 13 km altitude.

  6. Multiobjective evolutionary optimisation for surface-enhanced Raman scattering.

    PubMed

    Jarvis, Roger M; Rowe, William; Yaffe, Nicola R; O'Connor, Richard; Knowles, Joshua D; Blanch, Ewan W; Goodacre, Royston

    2010-07-01

    In most optimisation experiments, a single parameter is first optimised before a second and then third one are subsequently modified to give the best result. By contrast, we believe that simultaneous multiobjective optimisation is more powerful; therefore, an optimisation of the experimental conditions for the colloidal SERS detection of L-cysteine was carried out. Six aggregating agents and three different colloids (citrate, borohydride and hydroxylamine reduced silver) were tested over a wide range of concentrations for the enhancement and the reproducibility of the spectra produced. The optimisation was carried out using two methods, a full factorial design (FF, a standard method from the experimental design literature) and, for the first time, a multiobjective evolutionary algorithm (MOEA), a method more usually applied to optimisation problems in computer science. Simulation results suggest that the evolutionary approach significantly out-performs random sampling. Real experiments applying the evolutionary method to the SERS optimisation problem led to a 32% improvement in enhancement and reproducibility compared with the FF method, using far fewer evaluations.

  7. Using Optimisation Techniques to Granulise Rough Set Partitions

    SciTech Connect

    Crossingham, Bodie; Marwala, Tshilidzi

    2007-11-02

    This paper presents an approach to optimise rough set partition sizes using various optimisation techniques. Three optimisation techniques are implemented to perform the granularisation process, namely, genetic algorithm (GA), hill climbing (HC) and simulated annealing (SA). These optimisation methods maximise the classification accuracy of the rough sets. The proposed rough set partition method is tested on a set of demographic properties of individuals obtained from the South African antenatal survey. The three techniques are compared in terms of their computational time, accuracy and number of rules produced when applied to the Human Immunodeficiency Virus (HIV) data set. The optimised methods results are compared to a well known non-optimised discretisation method, equal-width-bin partitioning (EWB). The accuracies achieved after optimising the partitions using GA, HC and SA are 66.89%, 65.84% and 65.48% respectively, compared to the accuracy of EWB of 59.86%. In addition to rough sets providing the plausabilities of the estimated HIV status, they also provide the linguistic rules describing how the demographic parameters drive the risk of HIV.

  8. Using Optimisation Techniques to Granulise Rough Set Partitions

    NASA Astrophysics Data System (ADS)

    Crossingham, Bodie; Marwala, Tshilidzi

    2007-11-01

    This paper presents an approach to optimise rough set partition sizes using various optimisation techniques. Three optimisation techniques are implemented to perform the granularisation process, namely, genetic algorithm (GA), hill climbing (HC) and simulated annealing (SA). These optimisation methods maximise the classification accuracy of the rough sets. The proposed rough set partition method is tested on a set of demographic properties of individuals obtained from the South African antenatal survey. The three techniques are compared in terms of their computational time, accuracy and number of rules produced when applied to the Human Immunodeficiency Virus (HIV) data set. The optimised methods results are compared to a well known non-optimised discretisation method, equal-width-bin partitioning (EWB). The accuracies achieved after optimising the partitions using GA, HC and SA are 66.89%, 65.84% and 65.48% respectively, compared to the accuracy of EWB of 59.86%. In addition to rough sets providing the plausabilities of the estimated HIV status, they also provide the linguistic rules describing how the demographic parameters drive the risk of HIV.

  9. The effects of initial jet exit conditions on plume resonance

    NASA Technical Reports Server (NTRS)

    Ponton, Michael K.; Seiner, John M.

    1989-01-01

    The acoustic emission and boundary layer of a cold jet issuing from an underexpanded sonic nozzle have been measured for lip thicknesses of the nozzle exit varying from 0.015-0.625 nozzle diameters. Near-field acoustic data demonstrate that the amplitude and frequency of certain modes of screech and the dominant mode of instability which exists in the shear layer are dependent on nozzle lip thickness. Changes in momentum thickness due to variations in the nozzle exit were also quantified.

  10. Analysis of Kelvin Helmholtz Instabilities of Plasma Jets

    NASA Technical Reports Server (NTRS)

    Friedman, Mark J.; Hollingsworth, Blane J.

    1999-01-01

    Ulysses data indicates density fluctuations which axe theorized to be the result of shear between a solar jet and its ambient. The MHD Kelvin-Helmholtz ("KH") instability causes such fluctuations as observed by Ulysses. A new dispersion relationship which accounts for this KH instability is derived via the linearization of the MHD equations. This generalizes an earlier result by Hardee. This dispersion relationship has the form of eight non-linear equations with nine unknowns.

  11. Analysis of Kelvin Helmholtz Instabilities of Plasma Jets

    NASA Technical Reports Server (NTRS)

    Friedman, Mark J.; Hollingsworth, Blane J.

    1999-01-01

    Ulysses data indicates density fluctuations which are theorized to be the result of shear between a solar jet and its ambient. The MHD Kelvin-Helmholtz ("KH") instability causes such fluctuations as observed by Ulysses. A new dispersion relationship which accounts for this KH instability is derived via the linearization of the MHD equations. This generalizes an earlier result by Hardee. This dispersion relationship has the form of eight non-linear equations with nine unknowns.

  12. X-Point Reconnection from Shear Driving in Kinetic Simulations

    NASA Astrophysics Data System (ADS)

    Black, C.; Antiochos, S. K.; DeVore, C. R.; Germaschewski, K.; Bessho, N.; Karpen, J. T.

    2014-12-01

    The explosive energy release in solar eruptive phenomena such as CMEs/eruptive flares and coronal jets is believed to be due to magnetic reconnection. Magnetic free energy builds up slowly in the corona due to footpoint stressing by the photospheric motions. Along with the free energy, current sheets build up at coronal nulls, which eventually triggers fast reconnection and explosive energy release. This basic scenario has been modeled extensively by MHD simulations and applied to both CMEs/eruptive flares and jets, but the reconnection itself is well-known to be due to kinetic processes. Consequently, it is imperative that shear-driven X-point reconnection be modeled in a fully kinetic system so as to test and guide the MHD results. In MHD simulations, the application of a magnetic-field shear at the system boundary is a trivial matter, but this is definitely not the case for a kinetic system, because the electric currents need to be fully consistent with all the mass motions. We present the first results of reconnection in a 2D X-Point geometry due to a velocity shear driver perpendicular to the plane of reconnection. We compare the results to high-resolution MHD simulations and discuss the implications for coronal activity.

  13. Dynamics of laminar circular jet impingement upon convex cylinders

    NASA Astrophysics Data System (ADS)

    New, T. H.; Long, J.

    2015-02-01

    Flow dynamics associated with a laminar circular jet impinging upon a convex cylinder has been investigated by laser-induced fluorescence and digital particle-image velocimetry techniques. Cylinder-to-jet diameter ratios of 1, 2, and 4 were investigated, while the jet-to-cylinder separation distance was kept at four jet diameters throughout. Flow visualization and λ2 criterion results show that once the jet ring-vortices impinge upon the cylindrical surface, they move away from the impingement point by wrapping themselves partially around the surface. As the cylinder diameter increases, wall boundary layer separation, vortex dipole formation, and separation locations are initiated earlier along the cylindrical surface, producing significantly larger wakes. Along the cylinder straight-edges, ring-vortex cores are significantly smaller after impingement. This is due to accentuated vortex-stretching caused by partial wrapping around the cylindrical surface by the ring-vortices, on top of their movement away from the impingement point. Interestingly, vortex dipoles demonstrate a strong tendency to travel upstream and interact with other upstream vortex dipoles, instead of moving downstream gradually seen for flat-surface jet-impingements. Wall shear stress results are also presented to quantify the effects of cylinder diameter-ratio on surface skin friction distribution. Finally, these preceding observations are corroborated and explained in a three-dimensional flow dynamics model presented here.

  14. The Triggering Mechanism of coronal jets and CMEs: Flux Cancelation

    NASA Technical Reports Server (NTRS)

    Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

    2017-01-01

    Recent investigations show that coronal jets are driven by the eruption of a small-scale filament (10,000 - 20,000 km long, called a minifilament) following magnetic flux cancelation at the neutral line underneath the minifilament. Minifilament eruptions appear to be analogous to larger-scale solar filament eruptions: they both reside, before the eruption, in the highly sheared field between the adjacent opposite-polarity magnetic flux patches (neutral line); jet-producing minifilament and larger-scale solar filament first show a slow-rise, followed by a fast-rise as they erupt; during the jet-producing minifilament eruption a jet bright point (JBP) appears at the location where the minifilament was rooted before the eruption, analogous to the situation with CME-producing larger-scale filament eruptions where a solar flare arcade forms during the filament eruption along the neutral line along which the filament resided prior to its eruption. In the present study we investigate the triggering mechanism of CME-producing large solar filament eruptions, and find that enduring flux cancelation at the neutral line of the filaments often triggers their eruptions. This corresponds to the finding that persistent flux cancelation at the neutral is the cause of jet-producing minifilament eruptions. Thus our observations support coronal jets being miniature version of CMEs.

  15. Shear mode grinding

    SciTech Connect

    Brown, N.J.; Fuchs, B.A.

    1989-04-24

    The thesis of this paper is that shear mode grinding of glass (1) occurs with abrasive particle sizes less than 1/mu/m, (2) that it is the mechanical limit of the the more common mechanical-chemical glass polishing, and (3) that the debris is insufficient in size to perform the function of eroding the binder in the grinding wheel and thus necessitates the addition of an abrasive and/or chemical additions to the coolant to effect wheel-dressing. 13 refs.

  16. Diffeomorphic registration using geodesic shooting and Gauss–Newton optimisation

    PubMed Central

    Ashburner, John; Friston, Karl J.

    2011-01-01

    This paper presents a nonlinear image registration algorithm based on the setting of Large Deformation Diffeomorphic Metric Mapping (LDDMM), but with a more efficient optimisation scheme — both in terms of memory required and the number of iterations required to reach convergence. Rather than perform a variational optimisation on a series of velocity fields, the algorithm is formulated to use a geodesic shooting procedure, so that only an initial velocity is estimated. A Gauss–Newton optimisation strategy is used to achieve faster convergence. The algorithm was evaluated using freely available manually labelled datasets, and found to compare favourably with other inter-subject registration algorithms evaluated using the same data. PMID:21216294

  17. Measurement of jet activity in top quark events using the eμ final state with two b-tagged jets in pp collisions at $$\\sqrt{s}=8 $$ TeV with the ATLAS detector

    DOE PAGES

    Aaboud, M.; Aad, G.; Abbott, B.; ...

    2016-09-13

    Measurements of the jet activity in tt¯ events produced in proton-proton collisions at √s=8 TeV are presented, using 20.3 fb–1 of data collected by the ATLAS experiment at the Large Hadron Collider. The events were selected in the dilepton eμ decay channel with two identified b-jets. The numbers of additional jets for various jet transverse momentum (pT) thresholds, and the normalised differential cross-sections as a function of pT for the five highest-pT additional jets, were measured in the jet pseudo-rapidity range |η| < 4.5. The gap fraction, the fraction of events which do not contain an additional jet in amore » central rapidity region, was measured for several rapidity intervals as a function of the minimum pT of a single jet or the scalar sum of pT of all additional jets. These fractions were also measured in different intervals of the invariant mass of the eμbb¯ system. All measurements were corrected for detector effects, and found to be mostly well-described by predictions from next-to-leading-order and leading-order tt¯ event generators with appropriate parameter choices. Lastly, the results can be used to further optimise the parameters used in such generators.« less

  18. Measurement of jet activity in top quark events using the eμ final state with two b-tagged jets in pp collisions at $\\sqrt{s}=8 $ TeV with the ATLAS detector

    SciTech Connect

    Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Abeloos, B.; Aben, R.; AbouZeid, O. S.; Abraham, N. L.; Abramowicz, H.; Abreu, H.; Abreu, R.; Abulaiti, Y.; Acharya, B. S.; Adamczyk, L.; Adams, D. L.; Adelman, J.; Adomeit, S.; Adye, T.; Affolder, A. A.; Agatonovic-Jovin, T.; Agricola, J.; Aguilar-Saavedra, J. A.; Ahlen, S. P.; Ahmadov, F.; Aielli, G.; Akerstedt, H.; Åkesson, T. P. A.; Akimov, A. V.; Alberghi, G. L.; Albert, J.; Albrand, S.; Alconada Verzini, M. J.; Aleksa, M.; Aleksandrov, I. N.; Alexa, C.; Alexander, G.; Alexopoulos, T.; Alhroob, M.; Ali, B.; Aliev, M.; Alimonti, G.; Alison, J.; Alkire, S. P.; Allbrooke, B. M. M.; Allen, B. W.; Allport, P. P.; Aloisio, A.; Alonso, A.; Alonso, F.; Alpigiani, C.; Alstaty, M.; Alvarez Gonzalez, B.; Álvarez Piqueras, D.; Alviggi, M. G.; Amadio, B. T.; Amako, K.; Amaral Coutinho, Y.; Amelung, C.; Amidei, D.; Amor Dos Santos, S. P.; Amorim, A.; Amoroso, S.; Amundsen, G.; Anastopoulos, C.; Ancu, L. S.; Andari, N.; Andeen, T.; Anders, C. F.; Anders, G.; Anders, J. K.; Anderson, K. J.; Andreazza, A.; Andrei, V.; Angelidakis, S.; Angelozzi, I.; Anger, P.; Angerami, A.; Anghinolfi, F.; Anisenkov, A. V.; Anjos, N.; Annovi, A.; Antel, C.; Antonelli, M.; Antonov, A.; Anulli, F.; Aoki, M.; Aperio Bella, L.; Arabidze, G.; Arai, Y.; Araque, J. P.; Arce, A. T. H.; Arduh, F. A.; Arguin, J-F.; Argyropoulos, S.; Arik, M.; Armbruster, A. J.; Armitage, L. J.; Arnaez, O.; Arnold, H.; Arratia, M.; Arslan, O.; Artamonov, A.; Artoni, G.; Artz, S.; Asai, S.; Asbah, N.; Ashkenazi, A.; Åsman, B.; Asquith, L.; Assamagan, K.; Astalos, R.; Atkinson, M.; Atlay, N. B.; Augsten, K.; Avolio, G.; Axen, B.; Ayoub, M. K.; Azuelos, G.; Baak, M. A.; Baas, A. E.; Baca, M. J.; Bachacou, H.; Bachas, K.; Backes, M.; Backhaus, M.; Bagiacchi, P.; Bagnaia, P.; Bai, Y.; Baines, J. T.; Baker, O. K.; Baldin, E. M.; Balek, P.; Balestri, T.; Balli, F.; Balunas, W. K.; Banas, E.; Banerjee, Sw.; Bannoura, A. A. E.; Barak, L.; Barberio, E. L.; Barberis, D.; Barbero, M.; Barillari, T.; Barisits, M-S; Barklow, T.; Barlow, N.; Barnes, S. L.; Barnett, B. M.; Barnett, R. M.; Barnovska, Z.; Baroncelli, A.; Barone, G.; Barr, A. J.; Barranco Navarro, L.; Barreiro, F.; Barreiro Guimarães da Costa, J.; Bartoldus, R.; Barton, A. E.; Bartos, P.; Basalaev, A.; Bassalat, A.; Bates, R. L.; Batista, S. J.; Batley, J. R.; Battaglia, M.; Bauce, M.; Bauer, F.; Bawa, H. S.; Beacham, J. B.; Beattie, M. D.; Beau, T.; Beauchemin, P. H.; Bechtle, P.; Beck, H. P.; Becker, K.; Becker, M.; Beckingham, M.; Becot, C.; Beddall, A. J.; Beddall, A.; Bednyakov, V. A.; Bedognetti, M.; Bee, C. P.; Beemster, L. J.; Beermann, T. A.; Begel, M.; Behr, J. K.; Belanger-Champagne, C.; Bell, A. S.; Bella, G.; Bellagamba, L.; Bellerive, A.; Bellomo, M.; Belotskiy, K.; Beltramello, O.; Belyaev, N. L.; Benary, O.; Benchekroun, D.; Bender, M.; Bendtz, K.; Benekos, N.; Benhammou, Y.; Benhar Noccioli, E.; Benitez, J.; Benjamin, D. P.; Bensinger, J. R.; Bentvelsen, S.; Beresford, L.; Beretta, M.; Berge, D.; Bergeaas Kuutmann, E.; Berger, N.; Beringer, J.; Berlendis, S.; Bernard, N. R.; Bernius, C.; Bernlochner, F. U.; Berry, T.; Berta, P.; Bertella, C.; Bertoli, G.; Bertolucci, F.; Bertram, I. A.; Bertsche, C.; Bertsche, D.; Besjes, G. J.; Bessidskaia Bylund, O.; Bessner, M.; Besson, N.; Betancourt, C.; Bethke, S.; Bevan, A. J.; Bianchi, R. M.; Bianchini, L.; Bianco, M.; Biebel, O.; Biedermann, D.; Bielski, R.; Biesuz, N. V.; Biglietti, M.; Bilbao De Mendizabal, J.; Billoud, T. R. V.; Bilokon, H.; Bindi, M.; Binet, S.; Bingul, A.; Bini, C.; Biondi, S.; Bjergaard, D. M.; Black, C. W.; Black, J. E.; Black, K. M.; Blackburn, D.; Blair, R. E.; Blanchard, J. -B.; Blanco, J. E.; Blazek, T.; Bloch, I.; Blocker, C.; Blum, W.; Blumenschein, U.; Blunier, S.; Bobbink, G. J.; Bobrovnikov, V. S.; Bocchetta, S. S.; Bocci, A.; Bock, C.; Boehler, M.; Boerner, D.; Bogaerts, J. A.; Bogavac, D.; Bogdanchikov, A. G.; Bohm, C.; Boisvert, V.; Bokan, P.; Bold, T.; Boldyrev, A. S.; Bomben, M.; Bona, M.; Boonekamp, M.; Borisov, A.; Borissov, G.; Bortfeldt, J.; Bortoletto, D.; Bortolotto, V.; Bos, K.; Boscherini, D.; Bosman, M.; Bossio Sola, J. D.; Boudreau, J.; Bouffard, J.; Bouhova-Thacker, E. V.; Boumediene, D.; Bourdarios, C.; Boutle, S. K.; Boveia, A.; Boyd, J.; Boyko, I. R.; Bracinik, J.; Brandt, A.; Brandt, G.; Brandt, O.; Bratzler, U.; Brau, B.; Brau, J. E.; Braun, H. M.; Breaden Madden, W. D.; Brendlinger, K.; Brennan, A. J.; Brenner, L.; Brenner, R.; Bressler, S.; Bristow, T. M.; Britton, D.; Britzger, D.; Brochu, F. M.; Brock, I.; Brock, R.; Brooijmans, G.; Brooks, T.; Brooks, W. K.; Brosamer, J.; Brost, E.; Broughton, J. H.; Bruckman de Renstrom, P. A.; Bruncko, D.; Bruneliere, R.; Bruni, A.; Bruni, G.; Bruni, L. S.; Brunt, BH; Bruschi, M.; Bruscino, N.; Bryant, P.; Bryngemark, L.; Buanes, T.; Buat, Q.; Buchholz, P.; Buckley, A. G.; Budagov, I. A.; Buehrer, F.; Bugge, M. K.; Bulekov, O.; Bullock, D.; Burckhart, H.; Burdin, S.; Burgard, C. D.; Burghgrave, B.; Burka, K.; Burke, S.; Burmeister, I.; Burr, J. T. P.; Busato, E.; Büscher, D.; Büscher, V.; Bussey, P.; Butler, J. M.; Buttar, C. M.; Butterworth, J. M.; Butti, P.; Buttinger, W.; Buzatu, A.; Buzykaev, A. R.; Cabrera Urbán, S.; Caforio, D.; Cairo, V. M.; Cakir, O.; Calace, N.; Calafiura, P.; Calandri, A.; Calderini, G.; Calfayan, P.; Callea, G.; Caloba, L. P.; Calvente Lopez, S.; Calvet, D.; Calvet, S.; Calvet, T. P.; Camacho Toro, R.; Camarda, S.; Camarri, P.; Cameron, D.; Caminal Armadans, R.; Camincher, C.; Campana, S.; Campanelli, M.; Camplani, A.; Campoverde, A.; Canale, V.; Canepa, A.; Cano Bret, M.; Cantero, J.; Cantrill, R.; Cao, T.; Capeans Garrido, M. D. M.; Caprini, I.; Caprini, M.; Capua, M.; Caputo, R.; Carbone, R. M.; Cardarelli, R.; Cardillo, F.; Carli, I.; Carli, T.; Carlino, G.; Carminati, L.; Caron, S.; Carquin, E.; Carrillo-Montoya, G. D.; Carter, J. R.; Carvalho, J.; Casadei, D.; Casado, M. P.; Casolino, M.; Casper, D. W.; Castaneda-Miranda, E.; Castelijn, R.; Castelli, A.; Castillo Gimenez, V.; Castro, N. F.; Catinaccio, A.; Catmore, J. R.; Cattai, A.; Caudron, J.; Cavaliere, V.; Cavallaro, E.; Cavalli, D.; Cavalli-Sforza, M.; Cavasinni, V.; Ceradini, F.; Cerda Alberich, L.; Cerio, B. C.; Cerqueira, A. S.; Cerri, A.; Cerrito, L.; Cerutti, F.; Cerv, M.; Cervelli, A.; Cetin, S. A.; Chafaq, A.; Chakraborty, D.; Chan, S. K.; Chan, Y. L.; Chang, P.; Chapman, J. D.; Charlton, D. G.; Chatterjee, A.; Chau, C. C.; Chavez Barajas, C. A.; Che, S.; Cheatham, S.; Chegwidden, A.; Chekanov, S.; Chekulaev, S. V.; Chelkov, G. A.; Chelstowska, M. A.; Chen, C.; Chen, H.; Chen, K.; Chen, S.; Chen, S.; Chen, X.; Chen, Y.; Cheng, H. C.; Cheng, H. J.; Cheng, Y.; Cheplakov, A.; Cheremushkina, E.; Cherkaoui El Moursli, R.; Chernyatin, V.; Cheu, E.; Chevalier, L.; Chiarella, V.; Chiarelli, G.; Chiodini, G.; Chisholm, A. S.; Chitan, A.; Chizhov, M. V.; Choi, K.; Chomont, A. R.; Chouridou, S.; Chow, B. K. B.; Christodoulou, V.; Chromek-Burckhart, D.; Chudoba, J.; Chuinard, A. J.; Chwastowski, J. J.; Chytka, L.; Ciapetti, G.; Ciftci, A. K.; Cinca, D.; Cindro, V.; Cioara, I. A.; Ciocca, C.; Ciocio, A.; Cirotto, F.; Citron, Z. H.; Citterio, M.; Ciubancan, M.; Clark, A.; Clark, B. L.; Clark, M. R.; Clark, P. J.; Clarke, R. N.; Clement, C.; Coadou, Y.; Cobal, M.; Coccaro, A.; Cochran, J.; Coffey, L.; Colasurdo, L.; Cole, B.; Colijn, A. P.; Collot, J.; Colombo, T.; Compostella, G.; Conde Muiño, P.; Coniavitis, E.; Connell, S. H.; Connelly, I. A.; Consorti, V.; Constantinescu, S.; Conti, G.; Conventi, F.; Cooke, M.; Cooper, B. D.; Cooper-Sarkar, A. M.; Cormier, K. J. R.; Cornelissen, T.; Corradi, M.; Corriveau, F.; Corso-Radu, A.; Cortes-Gonzalez, A.; Cortiana, G.; Costa, G.; Costa, M. J.; Costanzo, D.; Cottin, G.; Cowan, G.; Cox, B. E.; Cranmer, K.; Crawley, S. J.; Cree, G.; Crépé-Renaudin, S.; Crescioli, F.; Cribbs, W. A.; Crispin Ortuzar, M.; Cristinziani, M.; Croft, V.; Crosetti, G.; Cueto, A.; Cuhadar Donszelmann, T.; Cummings, J.; Curatolo, M.; Cúth, J.; Cuthbert, C.; Czirr, H.; Czodrowski, P.; D’amen, G.; D’Auria, S.; D’Onofrio, M.; Da Cunha Sargedas De Sousa, M. J.; Da Via, C.; Dabrowski, W.; Dado, T.; Dai, T.; Dale, O.; Dallaire, F.; Dallapiccola, C.; Dam, M.; Dandoy, J. R.; Dang, N. P.; Daniells, A. C.; Dann, N. S.; Danninger, M.; Dano Hoffmann, M.; Dao, V.; Darbo, G.; Darmora, S.; Dassoulas, J.; Dattagupta, A.; Davey, W.; David, C.; Davidek, T.; Davies, M.; Davison, P.; Dawe, E.; Dawson, I.; Daya-Ishmukhametova, R. K.; De, K.; de Asmundis, R.; De Benedetti, A.; De Castro, S.; De Cecco, S.; De Groot, N.; de Jong, P.; De la Torre, H.; De Lorenzi, F.; De Maria, A.; De Pedis, D.; De Salvo, A.; De Sanctis, U.; De Santo, A.; De Vivie De Regie, J. B.; Dearnaley, W. J.; Debbe, R.; Debenedetti, C.; Dedovich, D. V.; Dehghanian, N.; Deigaard, I.; Del Gaudio, M.; Del Peso, J.; Del Prete, T.; Delgove, D.; Deliot, F.; Delitzsch, C. M.; Deliyergiyev, M.; Dell’Acqua, A.; Dell’Asta, L.; Dell’Orso, M.; Della Pietra, M.; della Volpe, D.; Delmastro, M.; Delsart, P. A.; DeMarco, D. A.; Demers, S.; Demichev, M.; Demilly, A.; Denisov, S. P.; Denysiuk, D.; Derendarz, D.; Derkaoui, J. E.; Derue, F.; Dervan, P.; Desch, K.; Deterre, C.; Dette, K.; Deviveiros, P. O.; Dewhurst, A.; Dhaliwal, S.; Di Ciaccio, A.; Di Ciaccio, L.; Di Clemente, W. K.; Di Donato, C.; Di Girolamo, A.; Di Girolamo, B.; Di Micco, B.; Di Nardo, R.; Di Simone, A.; Di Sipio, R.; Di Valentino, D.; Diaconu, C.; Diamond, M.; Dias, F. A.; Diaz, M. A.; Diehl, E. B.; Dietrich, J.; Diglio, S.; Dimitrievska, A.; Dingfelder, J.; Dita, P.; Dita, S.; Dittus, F.; Djama, F.; Djobava, T.; Djuvsland, J. I.; do Vale, M. A. B.; Dobos, D.; Dobre, M.; Doglioni, C.; Dohmae, T.; Dolejsi, J.; Dolezal, Z.; Dolgoshein, B. A.; Donadelli, M.; Donati, S.; Dondero, P.; Donini, J.; Dopke, J.; Doria, A.; Dova, M. T.; Doyle, A. T.; Drechsler, E.; Dris, M.; Du, Y.; Duarte-Campderros, J.; Duchovni, E.; Duckeck, G.; Ducu, O. A.; Duda, D.; Dudarev, A.; Duffield, E. M.; Duflot, L.; Duguid, L.; Dührssen, M.; Dumancic, M.; Dunford, M.; Duran Yildiz, H.; Düren, M.; Durglishvili, A.; Duschinger, D.; Dutta, B.; Dyndal, M.; Eckardt, C.; Ecker, K. M.; Edgar, R. C.; Edwards, N. C.; Eifert, T.; Eigen, G.; Einsweiler, K.; Ekelof, T.; El Kacimi, M.; Ellajosyula, V.; Ellert, M.; Elles, S.; Ellinghaus, F.; Elliot, A. A.; Ellis, N.; Elmsheuser, J.; Elsing, M.; Emeliyanov, D.; Enari, Y.; Endner, O. C.; Endo, M.; Ennis, J. S.; Erdmann, J.; Ereditato, A.; Ernis, G.; Ernst, J.; Ernst, M.; Errede, S.; Ertel, E.; Escalier, M.; Esch, H.; Escobar, C.; Esposito, B.; Etienvre, A. I.; Etzion, E.; Evans, H.; Ezhilov, A.; Fabbri, F.; Fabbri, L.; Facini, G.; Fakhrutdinov, R. M.; Falciano, S.; Falla, R. J.; Faltova, J.; Fang, Y.; Fanti, M.; Farbin, A.; Farilla, A.; Farina, C.; Farina, E. M.; Farooque, T.; Farrell, S.; Farrington, S. M.; Farthouat, P.; Fassi, F.; Fassnacht, P.; Fassouliotis, D.; Faucci Giannelli, M.; Favareto, A.; Fawcett, W. J.; Fayard, L.; Fedin, O. L.; Fedorko, W.; Feigl, S.; Feligioni, L.; Feng, C.; Feng, E. J.; Feng, H.; Fenyuk, A. B.; Feremenga, L.; Fernandez Martinez, P.; Fernandez Perez, S.; Ferrando, J.; Ferrari, A.; Ferrari, P.; Ferrari, R.; Ferreira de Lima, D. E.; Ferrer, A.; Ferrere, D.; Ferretti, C.; Ferretto Parodi, A.; Fiedler, F.; Filipčič, A.; Filipuzzi, M.; Filthaut, F.; Fincke-Keeler, M.; Finelli, K. D.; Fiolhais, M. C. N.; Fiorini, L.; Firan, A.; Fischer, A.; Fischer, C.; Fischer, J.; Fisher, W. C.; Flaschel, N.; Fleck, I.; Fleischmann, P.; Fletcher, G. T.; Fletcher, R. R. M.; Flick, T.; Floderus, A.; Flores Castillo, L. R.; Flowerdew, M. J.; Forcolin, G. T.; Formica, A.; Forti, A.; Foster, A. 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C.; Sannino, M.; Sansoni, A.; Santoni, C.; Santonico, R.; Santos, H.; Santoyo Castillo, I.; Sapp, K.; Sapronov, A.; Saraiva, J. G.; Sarrazin, B.; Sasaki, O.; Sasaki, Y.; Sato, K.; Sauvage, G.; Sauvan, E.; Savage, G.; Savard, P.; Sawyer, C.; Sawyer, L.; Saxon, J.; Sbarra, C.; Sbrizzi, A.; Scanlon, T.; Scannicchio, D. A.; Scarcella, M.; Scarfone, V.; Schaarschmidt, J.; Schacht, P.; Schachtner, B. M.; Schaefer, D.; Schaefer, R.; Schaeffer, J.; Schaepe, S.; Schaetzel, S.; Schäfer, U.; Schaffer, A. C.; Schaile, D.; Schamberger, R. D.; Scharf, V.; Schegelsky, V. A.; Scheirich, D.; Schernau, M.; Schiavi, C.; Schier, S.; Schillo, C.; Schioppa, M.; Schlenker, S.; Schmidt-Sommerfeld, K. R.; Schmieden, K.; Schmitt, C.; Schmitt, S.; Schmitz, S.; Schneider, B.; Schnoor, U.; Schoeffel, L.; Schoening, A.; Schoenrock, B. D.; Schopf, E.; Schott, M.; Schovancova, J.; Schramm, S.; Schreyer, M.; Schuh, N.; Schulte, A.; Schultens, M. J.; Schultz-Coulon, H. -C.; Schulz, H.; Schumacher, M.; Schumm, B. A.; Schune, Ph.; Schwartzman, A.; Schwarz, T. A.; Schwegler, Ph.; Schweiger, H.; Schwemling, Ph.; Schwienhorst, R.; Schwindling, J.; Schwindt, T.; Sciolla, G.; Scuri, F.; Scutti, F.; Searcy, J.; Seema, P.; Seidel, S. C.; Seiden, A.; Seifert, F.; Seixas, J. M.; Sekhniaidze, G.; Sekhon, K.; Sekula, S. J.; Seliverstov, D. M.; Semprini-Cesari, N.; Serfon, C.; Serin, L.; Serkin, L.; Sessa, M.; Seuster, R.; Severini, H.; Sfiligoj, T.; Sforza, F.; Sfyrla, A.; Shabalina, E.; Shaikh, N. W.; Shan, L. Y.; Shang, R.; Shank, J. T.; Shapiro, M.; Shatalov, P. B.; Shaw, K.; Shaw, S. M.; Shcherbakova, A.; Shehu, C. Y.; Sherwood, P.; Shi, L.; Shimizu, S.; Shimmin, C. O.; Shimojima, M.; Shiyakova, M.; Shmeleva, A.; Shoaleh Saadi, D.; Shochet, M. J.; Shojaii, S.; Shrestha, S.; Shulga, E.; Shupe, M. A.; Sicho, P.; Sickles, A. M.; Sidebo, P. E.; Sidiropoulou, O.; Sidorov, D.; Sidoti, A.; Siegert, F.; Sijacki, Dj.; Silva, J.; Silverstein, S. B.; Simak, V.; Simard, O.; Simic, Lj.; Simion, S.; Simioni, E.; Simmons, B.; Simon, D.; Simon, M.; Sinervo, P.; Sinev, N. B.; Sioli, M.; Siragusa, G.; Sivoklokov, S. Yu.; Sjölin, J.; Skinner, M. B.; Skottowe, H. P.; Skubic, P.; Slater, M.; Slavicek, T.; Slawinska, M.; Sliwa, K.; Slovak, R.; Smakhtin, V.; Smart, B. H.; Smestad, L.; Smiesko, J.; Smirnov, S. Yu.; Smirnov, Y.; Smirnova, L. N.; Smirnova, O.; Smith, M. N. K.; Smith, R. W.; Smizanska, M.; Smolek, K.; Snesarev, A. A.; Snyder, S.; Sobie, R.; Socher, F.; Soffer, A.; Soh, D. A.; Sokhrannyi, G.; Solans Sanchez, C. A.; Solar, M.; Soldatov, E. Yu.; Soldevila, U.; Solodkov, A. A.; Soloshenko, A.; Solovyanov, O. V.; Solovyev, V.; Sommer, P.; Son, H.; Song, H. Y.; Sood, A.; Sopczak, A.; Sopko, V.; Sorin, V.; Sosa, D.; Sotiropoulou, C. L.; Soualah, R.; Soukharev, A. M.; South, D.; Sowden, B. C.; Spagnolo, S.; Spalla, M.; Spangenberg, M.; Spanò, F.; Sperlich, D.; Spettel, F.; Spighi, R.; Spigo, G.; Spiller, L. A.; Spousta, M.; Denis, R. D. St.; Stabile, A.; Stamen, R.; Stamm, S.; Stanecka, E.; Stanek, R. W.; Stanescu, C.; Stanescu-Bellu, M.; Stanitzki, M. M.; Stapnes, S.; Starchenko, E. A.; Stark, G. H.; Stark, J.; Staroba, P.; Starovoitov, P.; Stärz, S.; Staszewski, R.; Steinberg, P.; Stelzer, B.; Stelzer, H. J.; Stelzer-Chilton, O.; Stenzel, H.; Stewart, G. A.; Stillings, J. A.; Stockton, M. C.; Stoebe, M.; Stoicea, G.; Stolte, P.; Stonjek, S.; Stradling, A. R.; Straessner, A.; Stramaglia, M. E.; Strandberg, J.; Strandberg, S.; Strandlie, A.; Strauss, M.; Strizenec, P.; Ströhmer, R.; Strom, D. M.; Stroynowski, R.; Strubig, A.; Stucci, S. A.; Stugu, B.; Styles, N. A.; Su, D.; Su, J.; Suchek, S.; Sugaya, Y.; Suk, M.; Sulin, V. V.; Sultansoy, S.; Sumida, T.; Sun, S.; Sun, X.; Sundermann, J. E.; Suruliz, K.; Susinno, G.; Sutton, M. 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    2016-09-13

    Measurements of the jet activity in tt¯ events produced in proton-proton collisions at √s=8 TeV are presented, using 20.3 fb–1 of data collected by the ATLAS experiment at the Large Hadron Collider. The events were selected in the dilepton eμ decay channel with two identified b-jets. The numbers of additional jets for various jet transverse momentum (pT) thresholds, and the normalised differential cross-sections as a function of pT for the five highest-pT additional jets, were measured in the jet pseudo-rapidity range |η| < 4.5. The gap fraction, the fraction of events which do not contain an additional jet in a central rapidity region, was measured for several rapidity intervals as a function of the minimum pT of a single jet or the scalar sum of pT of all additional jets. These fractions were also measured in different intervals of the invariant mass of the eμbb¯ system. All measurements were corrected for detector effects, and found to be mostly well-described by predictions from next-to-leading-order and leading-order tt¯ event generators with appropriate parameter choices. Lastly, the results can be used to further optimise the parameters used in such generators.

  19. Measurement of jet activity in top quark events using the eμ final state with two b-tagged jets in pp collisions at √{s}=8 TeV with the ATLAS detector

    NASA Astrophysics Data System (ADS)

    Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Abeloos, B.; Aben, R.; AbouZeid, O. S.; Abraham, N. L.; Abramowicz, H.; Abreu, H.; Abreu, R.; Abulaiti, Y.; Acharya, B. S.; Adamczyk, L.; Adams, D. L.; Adelman, J.; Adomeit, S.; Adye, T.; Affolder, A. A.; Agatonovic-Jovin, T.; Agricola, J.; Aguilar-Saavedra, J. A.; Ahlen, S. P.; Ahmadov, F.; Aielli, G.; Akerstedt, H.; Åkesson, T. P. A.; Akimov, A. V.; Alberghi, G. L.; Albert, J.; Albrand, S.; Alconada Verzini, M. J.; Aleksa, M.; Aleksandrov, I. N.; Alexa, C.; Alexander, G.; Alexopoulos, T.; Alhroob, M.; Ali, B.; Aliev, M.; Alimonti, G.; Alison, J.; Alkire, S. P.; Allbrooke, B. M. M.; Allen, B. W.; Allport, P. P.; Aloisio, A.; Alonso, A.; Alonso, F.; Alpigiani, C.; Alstaty, M.; Alvarez Gonzalez, B.; Álvarez Piqueras, D.; Alviggi, M. G.; Amadio, B. T.; Amako, K.; Amaral Coutinho, Y.; Amelung, C.; Amidei, D.; Amor Dos Santos, S. P.; Amorim, A.; Amoroso, S.; Amundsen, G.; Anastopoulos, C.; Ancu, L. S.; Andari, N.; Andeen, T.; Anders, C. F.; Anders, G.; Anders, J. K.; Anderson, K. J.; Andreazza, A.; Andrei, V.; Angelidakis, S.; Angelozzi, I.; Anger, P.; Angerami, A.; Anghinolfi, F.; Anisenkov, A. V.; Anjos, N.; Annovi, A.; Antel, C.; Antonelli, M.; Antonov, A.; Anulli, F.; Aoki, M.; Aperio Bella, L.; Arabidze, G.; Arai, Y.; Araque, J. P.; Arce, A. T. H.; Arduh, F. A.; Arguin, J.-F.; Argyropoulos, S.; Arik, M.; Armbruster, A. J.; Armitage, L. J.; Arnaez, O.; Arnold, H.; Arratia, M.; Arslan, O.; Artamonov, A.; Artoni, G.; Artz, S.; Asai, S.; Asbah, N.; Ashkenazi, A.; Åsman, B.; Asquith, L.; Assamagan, K.; Astalos, R.; Atkinson, M.; Atlay, N. B.; Augsten, K.; Avolio, G.; Axen, B.; Ayoub, M. K.; Azuelos, G.; Baak, M. A.; Baas, A. E.; Baca, M. J.; Bachacou, H.; Bachas, K.; Backes, M.; Backhaus, M.; Bagiacchi, P.; Bagnaia, P.; Bai, Y.; Baines, J. T.; Baker, O. K.; Baldin, E. M.; Balek, P.; Balestri, T.; Balli, F.; Balunas, W. K.; Banas, E.; Banerjee, Sw.; Bannoura, A. A. E.; Barak, L.; Barberio, E. L.; Barberis, D.; Barbero, M.; Barillari, T.; Barisits, M.-S.; Barklow, T.; Barlow, N.; Barnes, S. L.; Barnett, B. M.; Barnett, R. M.; Barnovska, Z.; Baroncelli, A.; Barone, G.; Barr, A. J.; Barranco Navarro, L.; Barreiro, F.; Barreiro Guimarães da Costa, J.; Bartoldus, R.; Barton, A. E.; Bartos, P.; Basalaev, A.; Bassalat, A.; Bates, R. L.; Batista, S. J.; Batley, J. R.; Battaglia, M.; Bauce, M.; Bauer, F.; Bawa, H. S.; Beacham, J. B.; Beattie, M. D.; Beau, T.; Beauchemin, P. H.; Bechtle, P.; Beck, H. P.; Becker, K.; Becker, M.; Beckingham, M.; Becot, C.; Beddall, A. J.; Beddall, A.; Bednyakov, V. A.; Bedognetti, M.; Bee, C. P.; Beemster, L. J.; Beermann, T. A.; Begel, M.; Behr, J. K.; Belanger-Champagne, C.; Bell, A. S.; Bella, G.; Bellagamba, L.; Bellerive, A.; Bellomo, M.; Belotskiy, K.; Beltramello, O.; Belyaev, N. L.; Benary, O.; Benchekroun, D.; Bender, M.; Bendtz, K.; Benekos, N.; Benhammou, Y.; Benhar Noccioli, E.; Benitez, J.; Benjamin, D. P.; Bensinger, J. R.; Bentvelsen, S.; Beresford, L.; Beretta, M.; Berge, D.; Bergeaas Kuutmann, E.; Berger, N.; Beringer, J.; Berlendis, S.; Bernard, N. R.; Bernius, C.; Bernlochner, F. U.; Berry, T.; Berta, P.; Bertella, C.; Bertoli, G.; Bertolucci, F.; Bertram, I. A.; Bertsche, C.; Bertsche, D.; Besjes, G. J.; Bessidskaia Bylund, O.; Bessner, M.; Besson, N.; Betancourt, C.; Bethke, S.; Bevan, A. J.; Bianchi, R. M.; Bianchini, L.; Bianco, M.; Biebel, O.; Biedermann, D.; Bielski, R.; Biesuz, N. V.; Biglietti, M.; Bilbao De Mendizabal, J.; Billoud, T. R. V.; Bilokon, H.; Bindi, M.; Binet, S.; Bingul, A.; Bini, C.; Biondi, S.; Bjergaard, D. M.; Black, C. W.; Black, J. E.; Black, K. M.; Blackburn, D.; Blair, R. E.; Blanchard, J.-B.; Blanco, J. E.; Blazek, T.; Bloch, I.; Blocker, C.; Blum, W.; Blumenschein, U.; Blunier, S.; Bobbink, G. J.; Bobrovnikov, V. S.; Bocchetta, S. S.; Bocci, A.; Bock, C.; Boehler, M.; Boerner, D.; Bogaerts, J. A.; Bogavac, D.; Bogdanchikov, A. G.; Bohm, C.; Boisvert, V.; Bokan, P.; Bold, T.; Boldyrev, A. S.; Bomben, M.; Bona, M.; Boonekamp, M.; Borisov, A.; Borissov, G.; Bortfeldt, J.; Bortoletto, D.; Bortolotto, V.; Bos, K.; Boscherini, D.; Bosman, M.; Bossio Sola, J. D.; Boudreau, J.; Bouffard, J.; Bouhova-Thacker, E. V.; Boumediene, D.; Bourdarios, C.; Boutle, S. K.; Boveia, A.; Boyd, J.; Boyko, I. R.; Bracinik, J.; Brandt, A.; Brandt, G.; Brandt, O.; Bratzler, U.; Brau, B.; Brau, J. E.; Braun, H. M.; Breaden Madden, W. D.; Brendlinger, K.; Brennan, A. J.; Brenner, L.; Brenner, R.; Bressler, S.; Bristow, T. M.; Britton, D.; Britzger, D.; Brochu, F. M.; Brock, I.; Brock, R.; Brooijmans, G.; Brooks, T.; Brooks, W. K.; Brosamer, J.; Brost, E.; Broughton, J. H.; Bruckman de Renstrom, P. A.; Bruncko, D.; Bruneliere, R.; Bruni, A.; Bruni, G.; Bruni, L. S.

    2016-09-01

    Measurements of the jet activity in toverline{t} events produced in proton-proton collisions at √{s}=8 TeV are presented, using 20.3 fb-1 of data collected by the ATLAS experiment at the Large Hadron Collider. The events were selected in the dilepton eμ decay channel with two identified b-jets. The numbers of additional jets for various jet transverse momentum ( p T) thresholds, and the normalised differential cross-sections as a function of p T for the five highest- p T additional jets, were measured in the jet pseudo-rapidity range | η| < 4 .5. The gap fraction, the fraction of events which do not contain an additional jet in a central rapidity region, was measured for several rapidity intervals as a function of the minimum p T of a single jet or the scalar sum of p T of all additional jets. These fractions were also measured in different intervals of the invariant mass of the eμ boverline{b} system. All measurements were corrected for detector effects, and found to be mostly well-described by predictions from next-to-leading-order and leading-order toverline{t} event generators with appropriate parameter choices. The results can be used to further optimise the parameters used in such generators. [Figure not available: see fulltext.

  20. Spectral and polarization properties of photospheric emission from stratified jets

    SciTech Connect

    Ito, Hirotaka; Nagataki, Shigehiro; Matsumoto, Jin; Lee, Shiu-Hang; Tolstov, Alexey; Mao, Jirong; Dainotti, Maria; Mizuta, Akira

    2014-07-10

    We explore the spectral and polarization properties of photospheric emissions from stratified jets in which multiple components, separated by sharp velocity shear regions, are distributed in lateral directions. Propagation of thermal photons injected at a high optical depth region are calculated until they escape from the photosphere. It is found that the presence of the lateral structure within the jet leads to the nonthermal feature of the spectra and significant polarization signal in the resulting emission. The deviation from thermal spectra, as well as the polarization degree, tends to be enhanced as the velocity gradient in the shear region increases. In particular, we show that emissions from multicomponent jet can reproduce the typical observed spectra of gamma-ray bursts irrespective of the position of the observer when a velocity shear region is closely spaced in various lateral (θ) positions. The degree of polarization associated with the emission is significant (>few percent) at a wide range of observer angles and can be higher than 30%.

  1. Coanda effect jet around a cylinder with an interacting adjacent surface

    NASA Astrophysics Data System (ADS)

    Churchill, Randolph Allen

    The effects of placing a plane solid surface in close proximity to a Coanda effect jet turning over a cylindrical surface are investigated to help judge the possible application of this type of jet to manufacturing line processes. The Coanda jet is proposed as a coating control mechanism for fluidic coatings on sheets or a particulate removal device. A Coanda jet placed close to a surface will develop a strong tangential flow that will shear by viscous effects and pressure gradients. A turbulent k-epsilon finite element model, developed in FIDAP, is presented that studies the effects of cylinder-sheet separation distance and jet-to-gap angular placement of the jet. It is assumed that the operation is isothermal and that the sheet speed is negligible compared to the air jet speed. Unconstrained models and cases with a distant surface were run and compared to published experimental results for an unconstrained Coanda jet to validate the modeling method and optimize the empirical constants in the k-epsilon equations. Best agreement is found if the C(sub 2) parameter in the equations is increased from 1.92 to 3.0. Maximum shear stress and pressure gradient values increased exponentially for a decreasing gap size and physical geometric constraints will be the limiting factor to efficiency. For similar initial jets this study shows that the Coanda jet develops stripping forces about 1/2 as great as the regular air-knife, but has advantages such as directed flow. The Coanda jet is seen as a viable option to air-knives for certain operations.

  2. Blinded by the Jets

    NASA Image and Video Library

    2005-07-04

    This image shows the view from NASA Deep Impact probe 30 minutes before it was pummeled by comet Tempel 1. The picture brightness has been enhanced to show the jets of dust streaming away from the comet.

  3. Counterflowing Jet Subsystem Design

    NASA Technical Reports Server (NTRS)

    Farr, Rebecca; Daso, Endwell; Pritchett, Victor; Wang, Ten-See

    2010-01-01

    A counterflowing jet design (a spacecraft and trans-atmospheric subsystem) employs centrally located, supersonic cold gas jets on the face of the vehicle, ejecting into the oncoming free stream. Depending on the supersonic free-stream conditions and the ejected mass flow rate of the counterflowing jets, the bow shock of the vehicle is moved upstream, further away from the vehicle. This results in an increasing shock standoff distance of the bow shock with a progressively weaker shock. At a critical jet mass flow rate, the bow shock becomes so weak that it is transformed into a series of compression waves spread out in a much wider region, thus significantly modifying the flow that wets the outer surfaces, with an attendant reduction in wave and skin friction drag and aerothermal loads.

  4. Astrophysics: Cosmic jet engines

    NASA Astrophysics Data System (ADS)

    Young, Andy

    2010-02-01

    In some galaxies, matter falling onto a supermassive black hole is ejected in narrow jets moving at close to the speed of light. New observations provide insight into the workings of these cosmic accelerators.

  5. Undercover Jet Exposed

    NASA Image and Video Library

    2011-04-04

    This image layout shows two views of the same baby star from NASA Spitzer Space Telescope. Spitzer view shows that this star has a second, identical jet shooting off in the opposite direction of the first.

  6. Dilution jet mixing program

    NASA Technical Reports Server (NTRS)

    Srinivasan, R.; Coleman, E.; Johnson, K.

    1984-01-01

    Parametric tests were conducted to quantify the mixing of opposed rows of jets (two-sided injection) in a confined cross flow. Results show that jet penetrations for two sided injections are less than that for single-sided injections, but the jet spreading rates are faster for a given momentum ratio and orifice plate. Flow area convergence generally enhances mixing. Mixing characteristics with asymmetric and symmetric convergence are similar. For constant momentum ratio, the optimum S/H(0) with in-line injections is one half the optimum value for single sided injections. For staggered injections, the optimum S/H(0) is twice the optimum value for single-sided injection. The correlations developed predicted the temperature distributions within first order accuracy and provide a useful tool for predicting jet trajectory and temperature profiles in the dilution zone with two-sided injections.

  7. Jet propulsion for airplanes

    NASA Technical Reports Server (NTRS)

    Buckingham, Edgar

    1924-01-01

    This report is a description of a method of propelling airplanes by the reaction of jet propulsion. Air is compressed and mixed with fuel in a combustion chamber, where the mixture burns at constant pressure. The combustion products issue through a nozzle, and the reaction of that of the motor-driven air screw. The computations are outlined and the results given by tables and curves. The relative fuel consumption and weight of machinery for the jet, decrease as the flying speed increases; but at 250 miles per hour the jet would still take about four times as much fuel per thrust horsepower-hour as the air screw, and the power plant would be heavier and much more complicated. Propulsion by the reaction of a simple jet can not compete with air screw propulsion at such flying speeds as are now in prospect.

  8. Reduction of membrane fouling by innovative method (injection of air jet).

    PubMed

    Amiraftabi, Maryam-Sadat; Mostoufi, Navid; Hosseinzadeh, Mostafa; Mehrnia, Mohammad-Reza

    2014-01-01

    One of the most important challenges about the Membrane Bio Reactors is membrane fouling. Fouling has been at the centre of a globe debate for more recent years. It leads to high operational and maintenance costs such as membrane damage and replacement of membrane. Membrane fouling is attributed to the physicochemical interactions between the bio fluid and membrane. In order to decrease the fouling in bioreactors there are common anti fouling strategies such as operation at low flux, Optimization of aeration flow-rate and Physical and chemical cleanings. However, often they are not effective. This work deal with fouling crisis by a new and innovative method in order to reduce of fouling on membrane surface by injection of parallel air jet on membrane bio reactor. This is a new idea and fundamental study about the influence of wall jet on fouling of membrane surface. This study is included both experimental and numerical investigations. In order to polarize the stream path on the surface of the membrane, four symmetric nozzles were implemented at the bottom of the membrane surface upon the sparger. The changes in the fouling resistance were experimentally measured at five various jet velocities and all of them recorded by a computer system. In addition the effect of air jet velocity and shear stress on fouling resistances was also investigated by computational fluid dynamics at the similar conditions. It was revealed that the permeate flux and resistance of fouling can be related to shear stress of air flow at the membrane surface. When the velocity of air jets increase, the permeate flux increase too. Also, results illustrate that jet injection can partially remove the cake which was formed on the surface of the membrane. Correlations were developed for estimating each resistance of the membrane surface via the shear stress. The resistances of the cake are removed by the jet velocity changes, from 20% in lower jet velocity up to 40% in higher jet velocity.

  9. Reynold stress closure in jet flows using wave models

    NASA Technical Reports Server (NTRS)

    Morris, P. J.

    1988-01-01

    Research program efforts have continued to concentrate on the development of the numerical methods that will form the computational part of the turbulence closure scheme. Studies have continued on the wave model for the two dimensional shear layer. This configuration is being used as a test case for the closure schemes. Several numerical schemes for the solution of the non-separable Rayleigh equation were developed. This solution is required for the closure scheme in more complex geometries. The most efficient method found is a Hybrid scheme that combines both pseudospectral and finite difference techniques. In addition, conformal transformation techniques were developed to transform the arbitrary geometry of the jet to a simple computational domain. The study of the shock structure in arbitrary geometry jets and multiple jets. These developments are described briefly.

  10. Velocity Statistics and Spectra in Three-Stream Jets

    NASA Technical Reports Server (NTRS)

    Ecker, Tobias; Lowe, K. Todd; Ng, Wing F.; Henderson, Brenda; Leib, Stewart

    2016-01-01

    Velocimetry measurements were obtained in three-stream jets at the NASA Glenn Research Center Nozzle Acoustics Test Rig using the time-resolved Doppler global velocimetry technique. These measurements afford exceptional frequency response, to 125 kHz bandwidth, in order to study the detailed dynamics of turbulence in developing shear flows. Mean stream-wise velocity is compared to measurements acquired using particle image velocimetry for validation. Detailed results for convective velocity distributions throughout an axisymmetric plume and the thick side of a plume with an offset third-stream duct are provided. The convective velocity results exhibit that, as expected, the eddy speeds are reduced on the thick side of the plume compared to the axisymmetric case. The results indicate that the time-resolved Doppler global velocimetry method holds promise for obtaining results valuable to the implementation and refinement of jet noise prediction methods being developed for three-stream jets.

  11. Mechanics of the turbulent-nonturbulent interface of a jet.

    PubMed

    Westerweel, J; Fukushima, C; Pedersen, J M; Hunt, J C R

    2005-10-21

    We report the results of an experimental investigation of the mechanics and transport processes at the bounding interface between the turbulent and nonturbulent regions of flow in a turbulent jet, which shows the existence of a finite jump in the tangential velocity at the interface. This is associated with small-scale eddying motion at the outward propagating interface (nibbling) by which irrotational fluid becomes turbulent, and this implies that large-scale engulfment is not the dominant entrainment process. Interpretation of the jump as a singular structure yields an essential and significant contribution to the mean shear in the jet mixing region. Finally, our observations provide a justification for Prandtl's original hypothesis of a constant eddy viscosity in the nonturbulent outer jet region.

  12. Excited waves in shear layers

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.

    1982-01-01

    The generation of instability waves in free shear layers is investigated. The model assumes an infinitesimally thin shear layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical shear layer excitation by a source further away from the plate edge in the downstream direction is very weak while upstream from the plate edge the excitation is relatively efficient. A special solution is given for the source at the plate edge. The theory is then extended to two streams on both sides of the shear layer having different velocities and densities. Furthermore, the excitation of a shear layer in a channel is calculated. A reference quantity is found for the magnitude of the excited instability waves. For a comparison with measurements, numerical computations of the velocity field outside the shear layer were carried out.

  13. Wind shear test

    NASA Astrophysics Data System (ADS)

    Techniques for forecasting and detecting a type of wind shear called microbursts are being tested this month in an operational program at Denver's Stapleton International Airport as part of an effort to reduce hazards to airplanes and passengers.Wind shear, which can be spawned by convective storms, can occur as a microburst. These downbursts of cool air are usually recognizable as a visible rain shaft beneath a thundercloud. Sometimes, however, the rain shaft evaporates before reaching the ground, leaving the downdraft invisible. Although thunderstorms are traditionally avoided by airplane pilots, these invisible downdrafts also harbor hazards in what usually appear to be safe skies. When the downdraft reaches the earth's surface, the downdraft spreads out horizontally, much like a stream of water gushing from a garden hose on a concrete surface, explained John McCarthy, director of the operational program. Airplanes can encounter trouble when the downdraft from the microburst causes sudden shifts in wind direction, which may reduce lift on the wing, an especially dangerous situation during takeoff.

  14. TUBE SHEARING VALVE

    DOEpatents

    Wilner, L.B.

    1960-05-24

    Explosive operated valves can be used to join two or more containers in fluid flow relationship, one such container being a sealed reservoir. The valve is most simply disposed by mounting it on the reservoir so thst a tube extends from the interior of the reservoir through the valve body, terminating at the bottom of the bore in a closed end; other containers may be similarly connected or may be open connected, as desired. The piston of the valve has a cutting edge at its lower end which shears off the closed tube ends and a recess above the cutting edge to provide a flow channel. Intermixing of the fluid being transferred with the explosion gases is prevented by a copper ring at the top of the piston which is force fitted into the bore at the beginning of the stroke. Although designed to avoid backing up of the piston at pressures up to 10,000 psi in the transferred fluid, proper operation is independent of piston position, once the tube ends were sheared.

  15. Adjoint based noise minimization of a round supersonic jet

    NASA Astrophysics Data System (ADS)

    Schulze, J.; Sesterhenn, J.

    2011-12-01

    Jets with complex shock-cell structures appear in numerous technological applications. The shock/shear-layer interaction emanates a broadband noise component. This may trigger the thin shear layer at the nozzle exit, forming a feedback loop which results in a discrete noise component called screech. Both components are undesirable from structural and environmental (cabin noise) points of view. Screech tones produce sound pressure levels of 160 dB and beyond. The focus of the present research project lies in the minimization of supersonic jet-noise and in particular in the minimization of jet-screech. Since screech - a phenomenon which is not yet understood in all details - seems to be affected by the presence of the jet-nozzle, a porous material will be added to the nozzle exit to suppress the feedback mechanism. Thus, to minimize the emanated noise. It is by no means clear how the shape an characteristic properties of the porous material should be. To this end, an optimization technique, based on adjoint methods will be applied to optimize the material with respect to the emanated noise.

  16. Streamwise Vorticity Generation in Laminar and Turbulent Jets

    NASA Technical Reports Server (NTRS)

    Demuren, Aodeji O.; Wilson, Robert V.

    1999-01-01

    Complex streamwise vorticity fields are observed in the evolution of non-circular jets. Generation mechanisms are investigated via Reynolds-averaged (RANS), large-eddy (LES) and direct numerical (DNS) simulations of laminar and turbulent rectangular jets. Complex vortex interactions are found in DNS of laminar jets, but axis-switching is observed only when a single instability mode is present in the incoming mixing layer. With several modes present, the structures are not coherent and no axis-switching occurs, RANS computations also produce no axis-switching. On the other hand, LES of high Reynolds number turbulent jets produce axis-switching even for cases with several instability modes in the mixing layer. Analysis of the source terms of the mean streamwise vorticity equation through post-processing of the instantaneous results shows that, complex interactions of gradients of the normal and shear Reynolds stresses are responsible for the generation of streamwise vorticity which leads to axis-switching. RANS computations confirm these results. k - epsilon turbulence model computations fail to reproduce the phenomenon, whereas algebraic Reynolds stress model (ASM) computations, in which the secondary normal and shear stresses are computed explicitly, succeeded in reproducing the phenomenon accurately.

  17. Experimental and Computational Study of Sonic and Supersonic Jet Plumes

    NASA Technical Reports Server (NTRS)

    Venkatapathy, E.; Naughton, J. W.; Fletcher, D. G.; Edwards, Thomas A. (Technical Monitor)

    1994-01-01

    Study of sonic and supersonic jet plumes are relevant to understanding such phenomenon as jet-noise, plume signatures, and rocket base-heating and radiation. Jet plumes are simple to simulate and yet, have complex flow structures such as Mach disks, triple points, shear-layers, barrel shocks, shock-shear-layer interaction, etc. Experimental and computational simulation of sonic and supersonic jet plumes have been performed for under- and over-expanded, axisymmetric plume conditions. The computational simulation compare very well with the experimental observations of schlieren pictures. Experimental data such as temperature measurements with hot-wire probes are yet to be measured and will be compared with computed values. Extensive analysis of the computational simulations presents a clear picture of how the complex flow structure develops and the conditions under which self-similar flow structures evolve. From the computations, the plume structure can be further classified into many sub-groups. In the proposed paper, detail results from the experimental and computational simulations for single, axisymmetric, under- and over-expanded, sonic and supersonic plumes will be compared and the fluid dynamic aspects of flow structures will be discussed.

  18. Radiation from Relativistic Jets

    NASA Technical Reports Server (NTRS)

    Nishikawa, K.-I.; Mizuno, Y.; Hardee, P.; Sol, H.; Medvedev, M.; Zhang, B.; Nordlund, A.; Frederiksen, J. T.; Fishman, G. J.; Preece, R.

    2008-01-01

    Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations of relativistic electron-ion (electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In the presence of relativistic jets, instabilities such as the Buneman instability, other two-streaming instability, and the Weibel (filamentation) instability create collisionless shocks, which are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The 'jitter' radiation from deflected electrons in small-scale magnetic fields has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation, a case of diffusive synchrotron radiation, may be important to understand the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

  19. Relativistic Jets from Collapsars

    NASA Astrophysics Data System (ADS)

    Aloy, M. A.; Müller, E.; Ibáñez, J. M.; Martí, J. M.; MacFadyen, A.

    2000-03-01

    Using a collapsar progenitor model of MacFadyen & Woosley, we have simulated the propagation of an axisymmetric jet through a collapsing rotating massive star with the GENESIS multidimensional relativistic hydrodynamic code. The jet forms as a consequence of an assumed (constant or variable) energy deposition in the range of 1050-1051 ergs s-1 within a 30 deg cone around the rotation axis. The jet flow is strongly beamed (approximately less than a few degrees), spatially inhomogeneous, and time dependent. The jet reaches the surface of the stellar progenitor (R*=2.98x1010 cm) intact. At breakout, the maximum Lorentz factor of the jet flow is 33. After breakout, the jet accelerates into the circumstellar medium, whose density is assumed to decrease exponentially and then become constant, ρext=10-5 g cm-3. Outside the star, the flow begins to expand laterally also (v~c), but the beam remains very well collimated. At a distance of 2.54 R*, where the simulation ends, the Lorentz factor has increased to 44.

  20. Inductive shearing of drilling pipe

    DOEpatents

    Ludtka, Gerard M.; Wilgen, John; Kisner, Roger; Mcintyre, Timothy

    2016-04-19

    Induction shearing may be used to cut a drillpipe at an undersea well. Electromagnetic rings may be built into a blow-out preventer (BOP) at the seafloor. The electromagnetic rings create a magnetic field through the drillpipe and may transfer sufficient energy to change the state of the metal drillpipe to shear the drillpipe. After shearing the drillpipe, the drillpipe may be sealed to prevent further leakage of well contents.

  1. Axisymmetric wall jet development in confined jet impingement

    NASA Astrophysics Data System (ADS)

    Guo, Tianqi; Rau, Matthew J.; Vlachos, Pavlos P.; Garimella, Suresh V.

    2017-02-01

    The flow field surrounding an axisymmetric, confined, impinging jet was investigated with a focus on the early development of the triple-layered wall jet structure. Experiments were conducted using stereo particle image velocimetry at three different confinement gap heights (2, 4, and 8 jet diameters) across Reynolds numbers ranging from 1000 to 9000. The rotating flow structures within the confinement region and their interaction with the surrounding flow were dependent on the confinement gap height and Reynolds number. The recirculation core shifted downstream as the Reynolds number increased. For the smallest confinement gap height investigated, the strong recirculation caused a disruption of the wall jet development. The radial position of the recirculation core observed at this small gap height was found to coincide with the location where the maximum wall jet velocity had decayed to 15% of the impinging jet exit velocity. After this point, the self-similarity hypothesis failed to predict the evolution of the wall jet further downstream. A reduction in confinement gap height increased the growth rates of the wall jet thickness but did not affect the decay rate of the wall jet maximum velocity. For jet Reynolds numbers above 2500, the decay rate of the maximum velocity in the developing region of the wall jet was approximately -1.1, which is close to previous results reported for the fully developed region of radial wall jets. A much higher decay rate of -1.5 was found for the wall jet formed by a laminar impinging jet at Re = 1000.

  2. Interpretation of Core Length in Shear Coaxial Rocket Injectors from X-ray Radiography Measurements (Briefing Charts)

    DTIC Science & Technology

    2014-06-01

    Shear coaxial jets can be found in a number of combustion devices – Turbofan engine exhaust, air blast furnaces, and liquid rocket engines ...case where both fluids are supercritical – Common in modern boost-class liquid rocket engines • Current focus is on two-phase coaxial jets for... rocket engine applications – Common in upper-stage engines and during throttled conditions, startup and shutdown transients of boost-class engines

  3. Shearing dynamics and jamming density

    NASA Astrophysics Data System (ADS)

    Olsson, Peter; Vâgberg, Daniel; Teitel, Stephen

    2009-03-01

    We study the effect of a shearing dynamics on the properties of a granular system, by examining how the jamming density depends on the preparation of the starting configurations. Whereas the jamming density at point J was obtained by relaxing random configurations [O'Hern et al, Phys. Rev. E 68, 011306 (2003)], we apply this method to configurations obtained after shearing the system at a certain shear rate. We find that the jamming density increases somewhat and that this effect is more pronounced for configurations produced at smaller shear rates. Different measures of the order of the jammed configurations are also discussed.

  4. Failure During Sheared Edge Stretching

    NASA Astrophysics Data System (ADS)

    Levy, B. S.; van Tyne, C. J.

    2008-12-01

    Failure during sheared edge stretching of sheet steels is a serious concern, especially in advanced high-strength steel (AHSS) grades. The shearing process produces a shear face and a zone of deformation behind the shear face, which is the shear-affected zone (SAZ). A failure during sheared edge stretching depends on prior deformation in the sheet, the shearing process, and the subsequent strain path in the SAZ during stretching. Data from laboratory hole expansion tests and hole extrusion tests for multiple lots of fourteen grades of steel were analyzed. The forming limit curve (FLC), regression equations, measurement uncertainty calculations, and difference calculations were used in the analyses. From these analyses, an assessment of the primary factors that contribute to the fracture during sheared edge stretching was made. It was found that the forming limit strain with consideration of strain path in the SAZ is a major factor that contributes to the failure of a sheared edge during stretching. Although metallurgical factors are important, they appear to play a somewhat lesser role.

  5. True Shear Parallel Plate Viscometer

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin; Kaukler, William

    2010-01-01

    This viscometer (which can also be used as a rheometer) is designed for use with liquids over a large temperature range. The device consists of horizontally disposed, similarly sized, parallel plates with a precisely known gap. The lower plate is driven laterally with a motor to apply shear to the liquid in the gap. The upper plate is freely suspended from a double-arm pendulum with a sufficiently long radius to reduce height variations during the swing to negligible levels. A sensitive load cell measures the shear force applied by the liquid to the upper plate. Viscosity is measured by taking the ratio of shear stress to shear rate.

  6. Tunable shear thickening in suspensions

    PubMed Central

    Lin, Neil Y.C.; Ness, Christopher; Cates, Michael E.; Sun, Jin; Cohen, Itai

    2016-01-01

    Shear thickening, an increase of viscosity with shear rate, is a ubiquitous phenomenon in suspended materials that has implications for broad technological applications. Controlling this thickening behavior remains a major challenge and has led to empirical strategies ranging from altering the particle surfaces and shape to modifying the solvent properties. However, none of these methods allows for tuning of flow properties during shear itself. Here, we demonstrate that by strategic imposition of a high-frequency and low-amplitude shear perturbation orthogonal to the primary shearing flow, we can largely eradicate shear thickening. The orthogonal shear effectively becomes a regulator for controlling thickening in the suspension, allowing the viscosity to be reduced by up to 2 decades on demand. In a separate setup, we show that such effects can be induced by simply agitating the sample transversely to the primary shear direction. Overall, the ability of in situ manipulation of shear thickening paves a route toward creating materials whose mechanical properties can be controlled. PMID:27621472

  7. Three-dimensional large eddy simulation for jet aeroacoustics

    NASA Astrophysics Data System (ADS)

    Uzun, Ali

    Future design of aircraft engines with low jet noise emissions undoubtedly needs a better understanding of noise generation in turbulent jets. Such an understanding, on the other hand, demands very reliable prediction tools. This study is therefore focused on developing a Computational Aeroacoustics (CAA) methodology that couples the near field unsteady flow field data computed by a 3-D Large Eddy Simulation (LES) code with various integral acoustic formulations for the far field noise prediction of turbulent jets. Turbulent jet simulations were performed at various Reynolds numbers. Comparisons of jet mean flow, turbulence statistics as well as jet aeroacoustics results with experimental data of jets at similar flow conditions were done and reasonable agreement was observed. The actual jet nozzle geometry was not included in the present simulations in order to keep the computational cost at manageable levels, therefore the jet shear layers downstream of the nozzle exit were modelled in an ad hoc fashion. As also observed by other researchers, the results obtained in the simulations were seen to be somewhat sensitive to the way the inflow forcing was done. The study of the effects of the eddy-viscosity based Smagorinsky subgrid-scale (SGS) model on noise predictions shows that the Smagorinsky model suppresses the resolved scale high-frequency noise. Simulations with filtering only suggest that treating the spatial filter as an implicit SGS model might be a good alternative. To our best knowledge, Lighthill's acoustic analogy was applied to a reasonably high Reynolds number jet for the first time in this study. A database greater than 1 Terabytes (TB) in size was post-processed using 1160 processors in parallel on a modern supercomputing platform for this purpose. It is expected that the current CAA methodology will yield better jet noise predictions when improved SGS models for both turbulence and high-frequency noise are incorporated into the LES code and when the

  8. Acoustics of dual-stream high-speed jets

    NASA Astrophysics Data System (ADS)

    Debiasi, Marco Tullio

    2000-10-01

    This work presents the results of noise measurements in high-speed, round jets whose Mach number and velocity simulate the conditions of jet engines at take-off. The Mach number of the jet potential core ranged from 1.27 to 1.77 and the velocity ranged from 550 m/s to 1010 m/s. Most of the jets were silenced with a coflow that prevented the formation of Mach waves, a dominant contribution to supersonic jet noise. This method, called Mach Wave Elimination, relies on the shielding effect of the coflow which makes the motion of the eddies subsonic with respect to the surrounding streams, thus impeding the creation of Mach waves. Schlieren photography and pitot probe surveys were used to detect the principal features and the growth rate of the jets. Microphone measurements were performed inside an anechoic chamber at many positions around the jet exit. The results were corrected for the microphone response and for the effect of human sensitivity to sound. Equal-thrust comparison of different experimental results shows that elimination of Mach waves is very effective in reducing noise in the direction of strongest emission. Except for localized shock-associated components, noise emission was found to be insensitive to nozzle exit pressure and to depend principally on the values of fully-expanded Mach number and velocity in the jet potential core. Jets with a shorter Mach wave emitting region exhibited better noise suppression. Best results were obtained with an eccentric coflow that allows the shear layer of the upper part of the jet to grow naturally while silencing the jet in the downward direction. Coflows are capable of reducing the near-field screech peaks by up to 10 dB in imperfectly-expanded jets. Scaling the experimental results to a fall-size engine shows that eccentric coflows reduce the noise perceived in the direction of peak emission by up to 11 dB. Preliminary analysis of the application of this silencing technique to engine design indicates that Mach

  9. Optimisation of lateral car dynamics taking into account parameter uncertainties

    NASA Astrophysics Data System (ADS)

    Busch, Jochen; Bestle, Dieter

    2014-02-01

    Simulation studies on an active all-wheel-steering car show that disturbance of vehicle parameters have high influence on lateral car dynamics. This motivates the need of robust design against such parameter uncertainties. A specific parametrisation is established combining deterministic, velocity-dependent steering control parameters with partly uncertain, velocity-independent vehicle parameters for simultaneous use in a numerical optimisation process. Model-based objectives are formulated and summarised in a multi-objective optimisation problem where especially the lateral steady-state behaviour is improved by an adaption strategy based on measurable uncertainties. The normally distributed uncertainties are generated by optimal Latin hypercube sampling and a response surface based strategy helps to cut down time consuming model evaluations which offers the possibility to use a genetic optimisation algorithm. Optimisation results are discussed in different criterion spaces and the achieved improvements confirm the validity of the proposed procedure.

  10. The Formation of Non-Zonal Jets over Sloped Topography

    NASA Astrophysics Data System (ADS)

    Boland, E.; Thompson, A. F.; Shuckburgh, E.; Haynes, P. H.

    2012-04-01

    We present the results of an investigation into the effect of a spatially uniform slope in bottom topography in a quasi-geostrophic, doubly periodic, two-layer model. A slope in the meridional direction results in the enhancement of the 'beta' effect, producing zonal jets, familiar from many previous studies. The novel aspect of this investigation is that the bottom slope has arbitrary orientation. Jets continue to form but they are non-zonal and tilted relative to layer-wise potential vorticity gradients. We show that these non-zonal jets follow the barotropic potential vorticity gradient, and we find that eddy energies are larger when the barotropic potential vorticity gradient is aligned with the direction of the shear in the system. The tilted jets are also demonstrated to be weaker barriers to transport than their zonal counterparts using an effective diffusivity diagnostic. These results are shown to be independent of the ratio of layer depths and to carry over to more complicated topographies containing slopes. We also interpret these results in the light of linear Rossby wave theory, showing the extent to which the jet orientation can be explained by the alteration of the linear dispersion relation by the presence of sloped topography, and the extent to which a Rhines scale can explain the separation of such jets. This work is of relevance to the many regions of the oceans where strong non-zonal jets are present, and is a significant step towards understanding the influence of topography on the dynamical properties of jets.

  11. Design of thin shear blades for crosscut shearing of wood.

    Treesearch

    Rodger A. Arola; Thomas R. Grimm

    1974-01-01

    Discusses principles and presents formulations for evaluating the elastic stability of thin plates subjected to edge loadings. Three different prestress methods to increase late stability are presented. A procedure is given to evaluate the elastic stability of thin shear blades under expected shearing loads.

  12. The role of shear in the transition from continuous shear thickening to discontinuous shear thickening

    NASA Astrophysics Data System (ADS)

    Jiang, Weifeng; Xuan, Shouhu; Gong, Xinglong

    2015-04-01

    Dense non-Brownian suspension has rich rheology and is hard to understand, especially for distinguishing continuous shear thickening (CST) from discontinuous shear thickening (DST). By studying the shear stress dependent rheology of a well-known DST suspension of cornstarch in water, we find that the transition from CST to DST could occur not only by increasing the volume fraction ϕ but also by increasing the shear stress σ. For the recovery process of jammed suspension, we observe that the shear activates the time-dependent nature of particle rearrangement. DST can then be interpreted as the consequence of shear-induced jamming. Based on the test data, we plot the schematic phase diagram in the ϕ-σ plane and find out that ϕ and σ perform almost the same effect on flow-state transition.

  13. A ray tracing study of shock leakage in a model supersonic jet

    NASA Astrophysics Data System (ADS)

    Shariff, Karim; Manning, Ted A.

    2013-07-01

    Recent work has described screech noise from a supersonic jet as being due to leakage of a wave that is otherwise trapped in the jet's interior. In that work, the simplest of many techniques used is ray tracing for a single shear-layer modeled as a row of Stuart vortices. In the present work, a lower row of vortices is added to form a plane jet. Instead of plotting ray paths, a technique of visualization analogous to streaklines is used that better corresponds to instantaneous density fields as observed, for instance, by the Schlieren method. This produces striking images that show leakage of waves at each internal reflection resulting in a row of acoustic sources as envisioned since the 1950s. However, the sources are not isotropic and each has a zone of silence in the downstream direction. Leakage creates a fold in the wave pattern internal to the jet which leads to fine scale features. Reported experiments have also observed fine scale features (described as splitting) in the shock-cell pattern; they may be related to those observed here. Internally reflected rays also undergo a diffusive process as they propagate down the jet. In particular, each successive internal reflection at an unsteady shear-layer scatters rays along a wider range of wave angle and makes them more susceptible to leakage at the next reflection. It also causes more downstream directivity for the more downstream sources. An important result is that as the Mach number Mj is varied, maxima in leakage rate and mean acoustic amplitude occur at (near) resonances between the Mach-wave and shear-layer periods. Maxima in sound pressure level versus Mj have also been reported for laboratory round jets. Finally, as the shear-layer thickness is increased, a minimum in the rate of leakage (correlated with a minimum in radiation amplitude) occurs due to the competing effects of increased shear-layer penetration versus reduced eddy passage frequency.

  14. A supportive architecture for CFD-based design optimisation

    NASA Astrophysics Data System (ADS)

    Li, Ni; Su, Zeya; Bi, Zhuming; Tian, Chao; Ren, Zhiming; Gong, Guanghong

    2014-03-01

    Multi-disciplinary design optimisation (MDO) is one of critical methodologies to the implementation of enterprise systems (ES). MDO requiring the analysis of fluid dynamics raises a special challenge due to its extremely intensive computation. The rapid development of computational fluid dynamic (CFD) technique has caused a rise of its applications in various fields. Especially for the exterior designs of vehicles, CFD has become one of the three main design tools comparable to analytical approaches and wind tunnel experiments. CFD-based design optimisation is an effective way to achieve the desired performance under the given constraints. However, due to the complexity of CFD, integrating with CFD analysis in an intelligent optimisation algorithm is not straightforward. It is a challenge to solve a CFD-based design problem, which is usually with high dimensions, and multiple objectives and constraints. It is desirable to have an integrated architecture for CFD-based design optimisation. However, our review on existing works has found that very few researchers have studied on the assistive tools to facilitate CFD-based design optimisation. In the paper, a multi-layer architecture and a general procedure are proposed to integrate different CFD toolsets with intelligent optimisation algorithms, parallel computing technique and other techniques for efficient computation. In the proposed architecture, the integration is performed either at the code level or data level to fully utilise the capabilities of different assistive tools. Two intelligent algorithms are developed and embedded with parallel computing. These algorithms, together with the supportive architecture, lay a solid foundation for various applications of CFD-based design optimisation. To illustrate the effectiveness of the proposed architecture and algorithms, the case studies on aerodynamic shape design of a hypersonic cruising vehicle are provided, and the result has shown that the proposed architecture

  15. Multiobjective optimisation of bogie suspension to boost speed on curves

    NASA Astrophysics Data System (ADS)

    Milad Mousavi-Bideleh, Seyed; Berbyuk, Viktor

    2016-01-01

    To improve safety and maximum admissible speed on different operational scenarios, multiobjective optimisation of bogie suspension components of a one-car railway vehicle model is considered. The vehicle model has 50 degrees of freedom and is developed in multibody dynamics software SIMPACK. Track shift force, running stability, and risk of derailment are selected as safety objective functions. The improved maximum admissible speeds of the vehicle on curves are determined based on the track plane accelerations up to 1.5 m/s2. To attenuate the number of design parameters for optimisation and improve the computational efficiency, a global sensitivity analysis is accomplished using the multiplicative dimensional reduction method (M-DRM). A multistep optimisation routine based on genetic algorithm (GA) and MATLAB/SIMPACK co-simulation is executed at three levels. The bogie conventional secondary and primary suspension components are chosen as the design parameters in the first two steps, respectively. In the last step semi-active suspension is in focus. The input electrical current to magnetorheological yaw dampers is optimised to guarantee an appropriate safety level. Semi-active controllers are also applied and the respective effects on bogie dynamics are explored. The safety Pareto optimised results are compared with those associated with in-service values. The global sensitivity analysis and multistep approach significantly reduced the number of design parameters and improved the computational efficiency of the optimisation. Furthermore, using the optimised values of design parameters give the possibility to run the vehicle up to 13% faster on curves while a satisfactory safety level is guaranteed. The results obtained can be used in Pareto optimisation and active bogie suspension design problems.

  16. optPBN: An Optimisation Toolbox for Probabilistic Boolean Networks

    PubMed Central

    Trairatphisan, Panuwat; Mizera, Andrzej; Pang, Jun; Tantar, Alexandru Adrian; Sauter, Thomas

    2014-01-01

    Background There exist several computational tools which allow for the optimisation and inference of biological networks using a Boolean formalism. Nevertheless, the results from such tools yield only limited quantitative insights into the complexity of biological systems because of the inherited qualitative nature of Boolean networks. Results We introduce optPBN, a Matlab-based toolbox for the optimisation of probabilistic Boolean networks (PBN) which operates under the framework of the BN/PBN toolbox. optPBN offers an easy generation of probabilistic Boolean networks from rule-based Boolean model specification and it allows for flexible measurement data integration from multiple experiments. Subsequently, optPBN generates integrated optimisation problems which can be solved by various optimisers. In term of functionalities, optPBN allows for the construction of a probabilistic Boolean network from a given set of potential constitutive Boolean networks by optimising the selection probabilities for these networks so that the resulting PBN fits experimental data. Furthermore, the optPBN pipeline can also be operated on large-scale computational platforms to solve complex optimisation problems. Apart from exemplary case studies which we correctly inferred the original network, we also successfully applied optPBN to study a large-scale Boolean model of apoptosis where it allows identifying the inverse correlation between UVB irradiation, NFκB and Caspase 3 activations, and apoptosis in primary hepatocytes quantitatively. Also, the results from optPBN help elucidating the relevancy of crosstalk interactions in the apoptotic network. Summary The optPBN toolbox provides a simple yet comprehensive pipeline for integrated optimisation problem generation in the PBN formalism that can readily be solved by various optimisers on local or grid-based computational platforms. optPBN can be further applied to various biological studies such as the inference of gene regulatory

  17. Quasi-equilibrium Dynamics of Stratified Turbulence In A Model Tropospheric Jet

    NASA Astrophysics Data System (ADS)

    Mahalov, A.; Nicolaenko, B.

    Direct numerical simulations are performed to study the dynamics of an inhomoge- neous stratified shear flow for a model atmospheric jet in the tropopause. The basic state is characterized by a jet centered at the tropopause in which the density strat- ification is vertically non-uniform. Small to moderate background stratifications are selected, a weak background rotation is imposed and simulations are conducted for a range of Reynolds and Froude numbers. A new spectral domain decomposition method that is particularly suitable for simulations of inhomogeneous stratified flows is developed to generate the desired turbulent jet, and quasi-equilibrium flow-fields are obtained after long-time integration of the governing equations. The structure of the mean flow and turbulence fields are calculated, which are interpreted using relevant length scales (Ozmidov, buoyancy, shear, Ellison and Kolmogorov) and Richardson number profiles. The ratios of the Ellison to buoyancy scales are much smaller than unity at the jet core and approach unity at the edges, confirming that mechanical tur- bulence prevails in the jet core, whereas nonlinear waves and stratification effects are significant at the edges. The jet core is found to support sustained mechanical (active) turbulence, outside of which lay a region of intermittent turbulence and non-linear gravity wave activity characterized by spatially decaying velocity fluctuations and strong temperature fluctuations. Detailed energy budgets show how energy is parti- tioned within the flow, including the transport of energy from the jet to its immediate vicinity by non-linear gravity waves.

  18. On the interaction of jet noise with a nearby flexible structure

    NASA Technical Reports Server (NTRS)

    Mcgreevy, J. L.; Bayliss, A.; Maestrello, L.

    1994-01-01

    The model of the interaction of the noise from a spreading subsonic jet with a panel-stringer assembly is studied numerically in two dimensions. The radiation resulting from this flow/acoustic/structure coupling is computed and analyzed in both the time and frequency domains. The jet is initially excited by a pulse-like source inserted into the flow field. The pulse triggers instabilities associated with the inviscid instability of the jet mean flow shear layer. These instabilities in turn generate sound which provides the primary loading for the panels. The resulting structural vibration and radiation depends strongly on their placement relative to the jet/nozzle configuration. Results are obtained for the panel responses as well as the transmitted and incident pressure. The effect of the panels is to act as a narrow filter, converting the relatively broad band forcing, heavily influenced by jet instabilities, into radiation concentrated in narrow spectral bands.

  19. Vortex structure and breakup mechanism of gaseous jet in supersonic crossflow with laminar boundary layer

    NASA Astrophysics Data System (ADS)

    Zhao, Yanhui; Liang, Jianhan; Zhao, Yuxin

    2016-11-01

    Employing nano-particle planar laser scattering and particle image velocimetry technology, underexpanded jet in supersonic crossflow with laminar boundary layer is experimental investigated in a low noise wind tunnel. Instantaneous flow structures and average velocity distribution of jet plume are captured in experimental images. Horseshoe vortex system is dominated by oscillating and coalescing regime, contributing to vortex generation of jet shear layer. The "tilting-stretching-tearing" mechanism dominating in near field raises average fractal dimension. But vortex structures generated on the windward side of jet plume scatter in jet plume and dissipate gradually, which makes the vortexes break up from outside in near field and break down into small turbulence completely in far field.

  20. A study on reynolds shear stress measurement by LDV

    NASA Astrophysics Data System (ADS)

    Munekata, Mizue; Ohba, Hideki; Matsuzaki, Kazuyoshi

    2001-03-01

    The measurement results by Laser Doppler Velocimetry (LDV) are compared with the direct numerical simulation result by Eggels et al.[1] for a cylindrical pipe flow. In the case of a pipe flow, the bias error for mean velocity is very small, because the local turbulent intensity is very small all over the pipe cross section. However the difference of the combination of u' and v' have considerable effects on Reynolds shear stress. From our investigation, it is found that the selection of coincidence time that is a necessary parameter for combination of u' and v' is more important in obtaining the accurate Reynolds shear stress. The suitable coincidence time is selected for a jet flow and the effectiveness of coincident time method or equal time interval method with coincidence data is shown.

  1. Predictability of Sheared Tropical Cyclones

    NASA Astrophysics Data System (ADS)

    Zhang, F.; Tao, D.

    2015-12-01

    Predictability of the formation, rapid intensification and eyewall replacement of sheared tropical cyclones (TCs) are explored through a series of convection-permitting ensemble simulations using the Weather Research and Forecasting (WRF) model with different environmental vertical wind shear, sea-surface temperature (SST), and ambient moisture conditions. It is found that the intrinsic predictability of the RI onset time is more limited with increasing shear magnitude until the shear magnitude is large enough to prevent the TC formation. Based on ensemble sensitivity and correlation analysis, the RI onset timing within one set is largely related to the vortex tilt magnitude, the diabatic heating distribution and the strength of the primary vortex circulation. Systematic differences amongst the ensemble members begin to arise right after the initial burst of moist convection associated with the incipient vortex. This difference from the randomness inherent in moist convection in terms of both location and intensity first changes the TC vortex structure subtly and then leads to the deviations in system scales and eventually in the development (and precession) of the TC. On average, a higher SST has a positive effect on the TC formation and reduces the uncertainty of development under all shear conditions, while a drier environment has a negative impact on the TCs development and either broadens the ensemble spread of RI onset time or prevents the storm from forming when the shear-induced tilt is large. Nevertheless, the uncertainty in environmental shear magnitudes may dominate over the effect of randomness in moist convection in terms of TC formation and predictability. A byproduct of tropical cyclones under vertical wind shear is the secondary eyewall formation (SEF). It is found that the eyewall formation is more often observed in TCs with moderate to high shear, which was inherently more unpredictable. The inward contraction/axisymmeterization of shear

  2. Vortical dissipation in two-dimensional shear flows

    NASA Technical Reports Server (NTRS)

    Horne, W. Clifton; Karamcheti, Krishnamurty

    1986-01-01

    An exact expression is derived for the viscous dissipation function of a real homogeneous and isotropic fluid, which has terms associated with the square of vorticity, wave radiation, and dilatation. The implications of the principle of maximal dissipation rate, are explored by means of this equation for a parallel channel flow and a cylindrical vortex flow. The consequences of a condition of maximum dissipation rate on the growth of disturbances in an unsteady, laminar shear layer are apparently consistent with predictions and observations of maximum growth rate of vortical disturbances. Finally, estimates of the magnitudes of several dissipative components of an unsteady vortex flow are obtained from measurements of a periodic wall jet.

  3. Refraction of sound by a shear layer - Experimental assessment

    NASA Technical Reports Server (NTRS)

    Schlinker, R. H.; Amiet, R. K.

    1979-01-01

    An experimental study was conducted to determine the refraction angle and amplitude changes associated with sound transmission through a circular, open jet shear layer. Both on-axis and off-axis acoustic source locations were used. Source frequency varied from 1 kHz to 10 kHz while freestream Mach number varied from 0.1 to 0.4. The experimental results were compared with an existing refraction theory which was extended to account for off-axis source positions. A simple experiment was also conducted to assess the importance of turbulence scattering between 1 kHz and 25 kHz.

  4. Refraction of sound by a shear layer - Experimental assessment

    NASA Technical Reports Server (NTRS)

    Schlinker, R. H.; Amiet, R. K.

    1979-01-01

    An experimental study was conducted to determine the refraction angle and amplitude changes associated with sound transmission through a circular, open jet shear layer. Both on-axis and off-axis acoustic source locations were used. Source frequency varied from 1 kHz to 10 kHz while freestream Mach number varied from 0.1 to 0.4. The experimental results were compared with an existing refraction theory which was extended to account for off-axis source positions. A simple experiment was also conducted to assess the importance of turbulence scattering between 1 kHz and 25 kHz.

  5. The importance of realism in reservoir operation optimisation

    NASA Astrophysics Data System (ADS)

    Dobson, Barnaby

    2017-04-01

    In previous work, we find that one of the most important barriers to uptake of reservoir operation optimisation methods in practice is the focus on sophisticated optimisation techniques at the expense of realism in problem formulation. Water resource management problems may be simplified to improve optimisation or even just to aid method explanation, however this does not foster faith about the applicability of its solution in real-world. We aim to make the first step towards developing a methodology to identify the trade-off between estimated performance within the optimisation model and actual performance when the 'optimal' solutions are implemented in practice. We start by robustly optimising reservoir operation policies over a wide range of inflow scenarios and confirming whether this optimal performance estimate is robust under a wider range of input forcing and model structure uncertainties. Model structure uncertainties are addressed, for example, through increased temporal resolution and inclusion of more sophisticated physical representations such as water head, losses and maintenance. Demand uncertainty will be considered in a similar manner to inflow uncertainty through use of an ensemble of synthetic demand time series. A longer-term goal and extension of this study is to investigate how to incorporate such wider uncertainties directly into the optimisation process itself.

  6. Application-tailored optimisation of photonic crystal waveguides

    NASA Astrophysics Data System (ADS)

    Billings, Sean; Schulz, Sebastian A.; Upham, Jeremy; Boyd, Robert W.

    2016-11-01

    Photonic crystal (PhC) waveguides are used for a wide range of applications with diverse performance metrics. A waveguide optimised for one application may not be suitable for others and no one-size-fits-all solution exists. Therefore each application requires a specialised waveguide design, a computationally and time intensive process. Here, we present a hybrid, multi-objective optimisation routine for PhC waveguides, to efficiently guide the device design. The algorithm can be configured to optimise for a wide range of performance metrics and applications. We demonstrate optimisations for three different applications: slow light performance, propagation loss due to fabrication disorder and delay line applications. For each optimisation target, our routine quickly finds practical waveguide designs (<48 h, on a laptop computer) that match or exceed the performance of state-of-the-art devices designed by the community over the last 10 years. This is also the first time that scattering loss from fabrication disorder has been incorporated into an optimisation algorithm, ensuring realistic predictions of a PhC waveguide design’s practical performance.

  7. Optimisation study of a vehicle bumper subsystem with fuzzy parameters

    NASA Astrophysics Data System (ADS)

    Farkas, L.; Moens, D.; Donders, S.; Vandepitte, D.

    2012-10-01

    This paper deals with the design and optimisation for crashworthiness of a vehicle bumper subsystem, which is a key scenario for vehicle component design. The automotive manufacturers and suppliers have to find optimal design solutions for such subsystems that comply with the conflicting requirements of the regulatory bodies regarding functional performance (safety and repairability) and regarding the environmental impact (mass). For the bumper design challenge, an integrated methodology for multi-attribute design engineering of mechanical structures is set up. The integrated process captures the various tasks that are usually performed manually, this way facilitating the automated design iterations for optimisation. Subsequently, an optimisation process is applied that takes the effect of parametric uncertainties into account, such that the system level of failure possibility is acceptable. This optimisation process is referred to as possibility-based design optimisation and integrates the fuzzy FE analysis applied for the uncertainty treatment in crash simulations. This process is the counterpart of the reliability-based design optimisation used in a probabilistic context with statistically defined parameters (variabilities).

  8. Principles of free jets

    SciTech Connect

    Miller, D.R.

    1995-03-01

    The principles of the free jet expansion are well established and only a brief tutorial overview of selected concepts is presented below. Almost every important theoretical and/or experimental aspect of the free jet related to molecular beam sampling has appeared in one of the 19 International Symposium on Rarefied Gas Dynamics and many detailed reviews exist. The first stage of pressure reduction in a mass spectrometer sampling system is often simply an aperture or short capillary tube across which a significant pressure ratio is maintained. When this pressure ratio between the system being sampled and the first vacuum stage exceeds about two then the gas flow reaches sonic conditions at the exit, Mach number M = 1, and the exiting flow is known as {open_quotes}choked{close_quotes} flow. It is called choked because for fixed source conditions the mass flux out of the aperture will not exceed this M = 1 condition regardless of how low the exit chamber pressure is taken, ie how much pumping is added. Beyond the exit the gas expands in a supersonic free jet expansion as it adjusts to the low pressure in the exit chamber. The expansion is called a free jet because there are no diverging nozzle walls to constrain the flow, which would lead to viscous boundary layers and a much smaller rate of expansion. Diverging nozzle walls are used in rockets to direct the exiting flows along the axis for better forward thrust, and researchers use them to slow the rate of expansion to, for example, grow clusters or study fast kinetics. Only the free jet is dealt with here. The free jet nozzle only consists of the subsonic nozzle geometry. The nozzle exit to be referred to here is then just the aperture or capillary exit, and the free jet expansion is the unconstrained subsequent supersonic flow downstream of this nozzle exit.

  9. Antimicrobial agents - optimising the ecological balance.

    PubMed

    Woon, Sze-Ann; Fisher, Dale

    2016-08-05

    There is no more challenging a group of pharmaceuticals than antimicrobials. With the antibiotic era came great optimism as countless deaths were prevented from what were previously fatal conditions. Although antimicrobial resistance was quickly identified, the abundance of antibiotics entering the market helped cement attitudes of arrogance as the "battle against pestilence appeared won". Opposite emotions soon followed as many heralded the return of the pre-antibiotic era, suggesting that the "antibiotic pipeline had dried up" and that our existing armament would soon be rendered worthless. In reality, humans overrate their ecological importance. For millions of years there has been a balance between factors promoting bacterial survival and those disturbing it. The first half century of the "antibiotic era" was characterised by a cavalier attitude disturbing the natural balance; however, recent efforts have been made through several mechanisms to respond and re-strengthen the antimicrobial armament. Such mechanisms include a variety of incentives, educational efforts and negotiations. Today, there are many more "man-made" factors that will determine a new balance or state of ecological harmony. Antibiotics are not a panacea nor will they ever be inutile. New resistance mechanisms will be identified and new antibiotics will be discovered, but most importantly, we must optimise our application of these extraordinary "biological tools"; therein lays our greatest challenge - creating a society that understands and respects the determinants of the effectiveness of antibiotics.

  10. Shape optimisation to maximise crack initiation time.

    PubMed

    Hedia, H S

    2001-01-01

    Most of machine parts, artificial joints and their components used for human body contain fillets, which connects two different diameters or widths. These fillets may cause a failure for these components. So, in this paper an optimisation method is presented which calculates and predicts optimal shape of the longitudinal profile for transition length of a tension bar, which connects two different diameters, using the ANSYS program. This method is applied to maximise the crack initiation time by minimising the fatigue notch factor Kf. A specified program has been developed to calculate the fatigue notch factor using Ansys Parametric Design Language (APDL) which is associated to the ANSYS Package. It was observed that the maximisation of crack initiation time with higher value of the statistical parameter, k, is also a minimisation of stress concentration factor, kt, at the same time.A tension bar with four different transition length, t (t/d=0.333, 0.4167, 0.5 and 0.583) is considered. The crack initiation time of the optimal shape for all cases was increased by 17%, 12%, 9% and 7%, respectively. The stress concentration factor was reduced by 20%, 17%, 15% and 12.5%, respectively.

  11. Shape optimisation of an underwater Bernoulli gripper

    NASA Astrophysics Data System (ADS)

    Flint, Tim; Sellier, Mathieu

    2015-11-01

    In this work, we are interested in maximising the suction produced by an underwater Bernoulli gripper. Bernoulli grippers work by exploiting low pressure regions caused by the acceleration of a working fluid through a narrow channel, between the gripper and a surface, to provide a suction force. This mechanism allows for non-contact adhesion to various surfaces and may be used to hold a robot to the hull of a ship while it inspects welds for example. A Bernoulli type pressure analysis was used to model the system with a Darcy friction factor approximation to include the effects of frictional losses. The analysis involved a constrained optimisation in order to avoid cavitation within the mechanism which would result in decreased performance and damage to surfaces. A sensitivity based method and gradient descent approach was used to find the optimum shape of a discretised surface. The model's accuracy has been quantified against finite volume computational fluid dynamics simulation (ANSYS CFX) using the k- ω SST turbulence model. Preliminary results indicate significant improvement in suction force when compared to a simple geometry by retaining a pressure just above that at which cavitation would occur over as much surface area as possible. Doctoral candidate in the Mechanical Engineering Department of the University of Canterbury, New Zealand.

  12. Optimising musculoskeletal care for patients with haemophilia.

    PubMed

    Carcao, Manuel; Hilliard, Pamela; Escobar, Miguel A; Solimeno, Luigi; Mahlangu, Johnny; Santagostino, Elena

    2015-12-01

    Despite recent improvements in the quality of care and treatment outcomes for haemophilia, joint disease remains a major concern for patients with and without inhibitors. Most bleeding episodes occur in the musculoskeletal system, and recurrent bleeding may result in progressive joint damage, leading to haemophilic arthropathy. Consequently, early identification and management of musculoskeletal bleeding episodes are important to prevent crippling deformities and dysfunction. Management strategies should aim at optimising joint function by reducing the frequency of, and preventing, joint bleeds. Although prophylactic factor replacement is proven to be effective in reducing bleeding frequency into joints and preserving musculoskeletal function in patients without inhibitors, the role for prophylaxis (with bypassing agents) in patients with inhibitors remains unclear. The available bypassing agents, activated prothrombin complex concentrate and recombinant activated factor VII (rFVIIa), are currently the standard of care for acute bleeding episodes in patients with high-titre inhibitors. These agents also prevent bleeding during elective orthopaedic surgery (EOS) in this patient population. This review discusses published data and uses illustrative cases to describe effective strategies for assessing joint health and maintaining optimal musculoskeletal care, focusing on the use of rFVIIa for haemostatic control in haemarthroses and when EOS is required in patients with inhibitors.

  13. Shear rotation numbers

    NASA Astrophysics Data System (ADS)

    Doeff, E.; Misiurewicz, M.

    1997-11-01

    This paper presents results on rotation numbers for orientation-preserving torus homeomorphisms homotopic to a Dehn twist. Rotation numbers and the rotation set for such homeomorphisms have been defined and initially investigated by the first author in a previous paper. Here we prove that each rotation number 0951-7715/10/6/017/img5 in the interior of the rotation set is realized by some compact invariant set, and that there is an ergodic measure on that set with mean rotation number 0951-7715/10/6/017/img5. It is also proved that the function which assigns its rotation set to such a homeomorphism is continuous. Finally, a counterexample is presented that shows that rational extremal points of the shear rotation set do not necessarily correspond to any periodic orbits.

  14. A theoretical analysis of airplane longitudinal stability and control as affected by wind shear

    NASA Technical Reports Server (NTRS)

    Sherman, W. L.

    1977-01-01

    The longitudinal equations of motion with wind shear terms were used to analyze the stability and motions of a jet transport. A positive wind shear gives a decreasing head wind or changes a head wind into a tail wind. A negative wind shear gives a decreasing tail wind or changes a tail wind into a head wind. It was found that wind shear had very little effect on the short period mode and that negative wind shear, although it affected the phugoid, did not cause stability problems. On the other hand, it was found that positive wind shear can cause the phugoid to become aperiodic and unstable. In this case, a stability boundary for the phugoid was found that is valid for most aircraft at all flight speeds. Calculations of aircraft motions confirmed the results of the stability analysis. It was found that a flight path control automatic pilot and an airspeed control system provide good control in all types of wind shear. Appendixes give equations of motion that include the effects of downdrafts and updrafts and extend the longitudinal equations of motion for shear to six degrees of freedom.

  15. REVIEW: The scientific success of JET

    NASA Astrophysics Data System (ADS)

    Keilhacker, M.; Gibson, A.; Gormezano, C.; Rebut, P. H.

    2001-12-01

    The paper highlights the JET work in physics and technology during the period of the JET Joint Undertaking (1978-1999), with special emphasis on what has been learned for extrapolation to a NEXT STEP device. - Global confinement scaling has been extended to high currents and heating powers. Dimensionless scaling experiments of ELMy H mode plasmas suggest that bulk plasma transport is gyro-Bohm and predict ignition for a device with ITER-FDR parameters. Experiments in which the plasma elongation and triangularity were varied independently show a strong increase of confinement time with elongation (τE ~ κa 0.8 +/- 0.3), thus supporting a basic design principle of ITER-FEAT. With the Pellet Enhanced Performance (PEP) mode, JET has discovered the beneficial effect of reversed magnetic shear on confinement, opening the possibility of advanced tokamak scenarios. - With a three stage programme of progressively more closed divertors, JET has demonstrated the benefits of divertor closure, in particular, of high divertor neutral pressure which facilitates helium removal. It has also shown that in detached (or semidetached) radiative divertor plasmas the average power load on the target plates of a NEXT STEP device should be tolerable but, in addition, that the transient power loads during ELMs could cause problems. - In 1991 JET has demonstrated the first ever controlled production of a megawatt of fusion power. More extensive D-T experiments in 1997 (DTE1) have established new records in fusion performance: 16 MW transient fusion power with Qin = 0.62 (i.e. close to breakeven, Qin = 1) and 4 MW steady state fusion power with Qin = 0.18 for 4 s. DTE1 has also allowed a successful test of various reactor ICRF heating schemes and a clear demonstration of alpha particle heating, consistent with classical expectations. - JET has developed and tested some of the most important technologies for a NEXT STEP and a reactor, in particular the safe handling of tritium and the remote

  16. Impulsively started incompressible turbulent jet

    SciTech Connect

    Witze, P O

    1980-10-01

    Hot-film anemometer measurements are presented for the centerline velocity of a suddenly started jet of air. The tip penetration of the jet is shown to be proportional to the square-root of time. A theoretical model is developed that assumes the transient jet can be characterized as a spherical vortex interacting with a steady-state jet. The model demonstrates that the ratio of nozzle radius to jet velocity defines a time constant that uniquely characterizes the behavior and similarity of impulsively started incompressible turbulent jets.

  17. LES of a Jet Excited by the Localized Arc Filament Plasma Actuators

    NASA Technical Reports Server (NTRS)

    Brown, Clifford A.

    2011-01-01

    The fluid dynamics of a high-speed jet are governed by the instability waves that form in the free-shear boundary layer of the jet. Jet excitation manipulates the growth and saturation of particular instability waves to control the unsteady flow structures that characterize the energy cascade in the jet.The results may include jet noise mitigation or a reduction in the infrared signature of the jet. The Localized Arc Filament Plasma Actuators (LAFPA) have demonstrated the ability to excite a high-speed jets in laboratory experiments. Extending and optimizing this excitation technology, however, is a complex process that will require many tests and trials. Computational simulations can play an important role in understanding and optimizing this actuator technology for real-world applications. Previous research has focused on developing a suitable actuator model and coupling it with the appropriate computational fluid dynamics (CFD) methods using two-dimensional spatial flow approximations. This work is now extended to three-dimensions (3-D) in space. The actuator model is adapted to a series of discrete actuators and a 3-D LES simulation of an excited jet is run. The results are used to study the fluid dynamics near the actuator and in the jet plume.

  18. Integrated Design Analysis and Optimisation of Aircraft Structures (L’Analyse Integrale de la Conception et l’Optimisation des Structures des Aeronefs)

    DTIC Science & Technology

    1992-05-01

    parameter has usually been structural weight, though cost , performance or other factors are now being considered. The parameter being optimised is...of structural optimisation to cover more extensive objective functions which include factors such as performance, cost , etc. Indeed, certain... Optimisation ofO A Aircraft Structures (LAnalyse Int6grae de la Conception et I’Optimisation des Structures des AMronefs) Th7 uteka mw an thispuabicwain *w

  19. Gravity Waves in the Presence of Shear during DEEPWAVE

    NASA Astrophysics Data System (ADS)

    Doyle, J. D.; Jiang, Q.; Reinecke, P. A.; Reynolds, C. A.; Eckermann, S. D.; Fritts, D. C.; Smith, R. B.; Taylor, M. J.; Dörnbrack, A.

    2016-12-01

    The DEEP propagating gravity WAVE program (DEEPWAVE) is a comprehensive, airborne and ground-based measurement and modeling program centered on New Zealand and focused on providing a new understanding of gravity wave dynamics and impacts from the troposphere through the mesosphere and lower thermosphere. This program employed the NSF/NCAR GV (NGV) research aircraft from a base in New Zealand in a 6-week field measurement campaign in June-July 2014. During the field phase, the NGV was equipped with new Rayleigh and sodium resonance lidars and an advanced mesospheric temperature mapper (AMTM), a microwave temperature profiler (MTP), as well as dropwindsondes and flight level instruments providing measurements spanning altitudes from immediately above the NGV flight altitude ( 13 km) to 100 km. In this study, we utilize the DEEPWAVE observations and the nonhydrostatic COAMPS configured at high resolution (2 km) with a deep domain (60-80 km) to explore the effects of horizontal wind shear on gravity wave propagation and wave characteristics. Real-data simulations have been conducted for several DEEPWAVE cases. The results suggest that horizontal shear associated with the stratospheric polar night jet refracts the gravity waves and leads to propagation of waves significantly downwind of the South Island. These waves have been referred to as "trailing gravity waves", since they are found predominantly downwind of the orography of the South Island and the wave crests rotate nearly normal to the mountain crest. Observations from the G-V, remote sensing instruments, and the AIRS satellite confirm the presence of gravity waves downwind of the orography in numerous events. The horizontal propagation in the stratosphere can be explained by group velocity arguments for gravity waves in which the wave energy is advected downwind by the component of the flow normal to the horizontal wavevector. We explore the impact of the shear on gravity wave propagation in COAMPS configured in

  20. APPARATUS FOR SHEARING TUBULAR JACKETS

    DOEpatents

    Simon, J.P.

    1962-09-01

    A machine is designed for removing the jacket from the core of a used rod-like fuel element by shearing the jacket into a spiral ribbon. Three skewed rolls move the fuel element axially and rotatively, and a tool cooperates with one of the rolls to carry out the shearing action. (AEC)

  1. Ram-jet Performance

    NASA Technical Reports Server (NTRS)

    Cervenko, A. J.; Friedman, R.

    1956-01-01

    The ram jet is basically one of the most dimple types of aircraft engine. It consists only of an inlet diffuser, a combustion system, and an exit nozzle. A typical ram-jet configuration is shown in figure 128. The engine operates on the Brayton cycle, and ideal cycle efficiency depends only on the ratio of engine to ambient pressure. The increased, engine pressures are obtained by ram action alone, and for this reason the ram jet has zero thrust at zero speed. Therefore, ram-jet-powered aircraft must be boosted to flight speeds close to a Mach number of 1.0 before appreciable thrust is generated by the engine. Since pressure increases are obtained by ram action alone, combustor-inlet pressures and temperatures are controlled by the flight speed, the ambient atmospheric condition, and by the efficiency of the inlet diffuser. These pressures and temperatures, as functions of flight speed and altitude, are shown in figure 129 for the NACA standard atmosphere and for practical values of diffuser efficiency. It can be seen that very wide ranges of combustor-inlet temperatures and pressures may be encountered over the ranges of flight velocity and altitude at which ram jets may be operated. Combustor-inlet temperatures from 500 degrees to 1500 degrees R and inlet pressures from 5 to 100 pounds per square inch absolute represent the approximate ranges of interest in current combustor development work. Since the ram jet has no moving parts in the combustor outlet, higher exhaust-gas temperatures than those used in current turbojets are permissible. Therefore, fuel-air ratios equivalent to maximum rates of air specific impulse or heat release can be used, and, for hydrocarbon fuels, this weight ratio is about 0.070. Lower fuel-air ratios down to about 0.015 may also be required to permit efficient cruise operation. This fuel-air-ratio range of 0.015 to 0.070 used in ram jets can be compared with the fuel-air ratios up to 0.025 encountered in current turbojets. Ram-jet

  2. Jet engine testing apparatus

    SciTech Connect

    Zweifel, T.L.

    1987-03-24

    An apparatus is described for testing jet engines mounted on an aircraft, the jet engines of the type having a high speed rotor and a low speed rotor, comprising: representative signal means for providing first representative signals representative of rotation rates of the low speed rotor in the jet engines and second representative signals representative of rotation rates of the high speed rotor in the jet engines; equivalent signal means coupled to receive the second representative signals for deriving equivalent signals representative of low speed rotor rotation rates of normally operating jet engines having high speed rotor rotation rates represented by the second representative signals; first difference signal means coupled to receive the first representative signals and the equivalent signals for providing first difference signals representative of differences between the first representative signals and the equivalent signals; means for providing threshold signals; first detector means coupled to the threshold signal means and the first difference signal means for comparing the threshold signals and the first difference signals to provide first detected signals representative of values of the first difference signals relative to the threshold signals; and engine failure indicator means coupled to receive the detected signals for determination of engine failures.

  3. The Twin Jet Nebula

    NASA Technical Reports Server (NTRS)

    1997-01-01

    M2-9 is a striking example of a 'butterfly' or a bipolar planetary nebula. Another more revealing name might be the 'Twin Jet Nebula.' If the nebula is sliced across the star, each side of it appears much like a pair of exhausts from jet engines. Indeed, because of the nebula's shape and the measured velocity of the gas, in excess of 200 miles per second, astronomers believe that the description as a super-super-sonic jet exhaust is quite apt. This is much the same process that takes place in a jet engine: The burning and expanding gases are deflected by the engine walls through a nozzle to form long, collimated jets of hot air at high speeds. M2-9 is 2,100 light-years away in the constellation Ophiucus. The observation was taken Aug. 2, 1997 by the Hubble telescope's Wide Field and Planetary Camera 2. In this image, neutral oxygen is shown in red, once-ionized nitrogen in green, and twice-ionized oxygen in blue.

  4. Jet propulsion without inertia

    NASA Astrophysics Data System (ADS)

    Spagnolie, Saverio E.; Lauga, Eric

    2010-08-01

    A body immersed in a highly viscous fluid can locomote by drawing in and expelling fluid through pores at its surface. We consider this mechanism of jet propulsion without inertia in the case of spheroidal bodies and derive both the swimming velocity and the hydrodynamic efficiency. Elementary examples are presented and exact axisymmetric solutions for spherical, prolate spheroidal, and oblate spheroidal body shapes are provided. In each case, entirely and partially porous (i.e., jetting) surfaces are considered and the optimal jetting flow profiles at the surface for maximizing the hydrodynamic efficiency are determined computationally. The maximal efficiency which may be achieved by a sphere using such jet propulsion is 12.5%, a significant improvement upon traditional flagella-based means of locomotion at zero Reynolds number, which corresponds to the potential flow created by a source dipole at the sphere center. Unlike other swimming mechanisms which rely on the presentation of a small cross section in the direction of motion, the efficiency of a jetting body at low Reynolds number increases as the body becomes more oblate and limits to approximately 162% in the case of a flat plate swimming along its axis of symmetry. Our results are discussed in the light of slime extrusion mechanisms occurring in many cyanobacteria.

  5. Sweeping Jet Optimization Studies

    NASA Technical Reports Server (NTRS)

    Melton, LaTunia Pack; Koklu, Mehti; Andino, Marlyn; Lin, John C.; Edelman, Louis

    2016-01-01

    Progress on experimental efforts to optimize sweeping jet actuators for active flow control (AFC) applications with large adverse pressure gradients is reported. Three sweeping jet actuator configurations, with the same orifice size but di?erent internal geometries, were installed on the flap shoulder of an unswept, NACA 0015 semi-span wing to investigate how the output produced by a sweeping jet interacts with the separated flow and the mechanisms by which the flow separation is controlled. For this experiment, the flow separation was generated by deflecting the wing's 30% chord trailing edge flap to produce an adverse pressure gradient. Steady and unsteady pressure data, Particle Image Velocimetry data, and force and moment data were acquired to assess the performance of the three actuator configurations. The actuator with the largest jet deflection angle, at the pressure ratios investigated, was the most efficient at controlling flow separation on the flap of the model. Oil flow visualization studies revealed that the flow field controlled by the sweeping jets was more three-dimensional than expected. The results presented also show that the actuator spacing was appropriate for the pressure ratios examined.

  6. B-jets and z + b-jets at CDF

    SciTech Connect

    Jeans, Daniel; /Rome U.

    2006-06-01

    The authors present CDF cross-section measurements for the inclusive production of b jets and the production of b jets in association with a Z{sup 0} boson. Both measurements are in reasonable agreement with NLO QCD predictions.

  7. The M87 Jet. "Rosetta Stone" of AGN Jets

    NASA Astrophysics Data System (ADS)

    Nakamura, Masanori; Asada, Keiichi

    2013-12-01

    We investigate the structure and dynamics of the M87 jet based on multi-frequency VLBI observations and MHD jet theories. Millimeter VLBI cores are considered as innermost jet emissions. The jet structure up to ~ 105 rs is described as a parabolic streamline, indicating the lateral expansion under a confinement by the stratified ISM. Thus, the jet collimation maintains in five orders of magnitude in the distance starting from the vicinity of the supermassive black hole (SMBH), less than 10 rs. We here examine the jet parabolic structure in order to identify the property of a bulk acceleration; observed sub-to-superluminal motions indicate an MHD acceleration from non-relativistic to relativistic regimes. We propose that the M87 jet consists of Poynting-flux dominated flows, powered by nonlinear torsional Alfvén waves. Future sub-mm VLBI observations play an important role in resolving the origin of the M87 jets.

  8. Electroosmotic shear flow in microchannels.

    PubMed

    Mampallil, Dileep; van den Ende, Dirk

    2013-01-15

    We generate and study electroosmotic shear flow in microchannels. By chemically or electrically modifying the surface potential of the channel walls a shear flow component with controllable velocity gradient can be added to the electroosmotic flow caused by double layer effects at the channel walls. Chemical modification is obtained by treating the channel wall with a cationic polymer. In case of electric modification, we used gate electrodes embedded in the channel wall. By applying a voltage to the gate electrode, the zeta potential can be varied and a controllable, uniform shear stress can be applied to the liquid in the channel. The strength of the shear stress depends on both the gate voltage and the applied field which drives the electroosmotic shear flow. Although the stress range is still limited, such a microchannel device can be used in principle as an in situ micro-rheometer for lab on a chip purposes.

  9. A Piezoelectric Shear Stress Sensor

    NASA Technical Reports Server (NTRS)

    Kim, Taeyang; Saini, Aditya; Kim, Jinwook; Gopalarathnam, Ashok; Zhu, Yong; Palmieri, Frank L.; Wohl, Christopher J.; Jiang, Xiaoning

    2016-01-01

    In this paper, a piezoelectric sensor with a floating element was developed for shear stress measurement. The piezoelectric sensor was designed to detect the pure shear stress suppressing effects of normal stress generated from the vortex lift-up by applying opposite poling vectors to the: piezoelectric elements. The sensor was first calibrated in the lab by applying shear forces and it showed high sensitivity to shear stress (=91.3 +/- 2.1 pC/Pa) due to the high piezoelectric coefficients of PMN-33%PT (d31=-1330 pC/N). The sensor also showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is 0-800 Hz. Keywords: Piezoelectric sensor, shear stress, floating element, electromechanical symmetry

  10. Aeroacoustic Experiments with Twin Jets

    NASA Technical Reports Server (NTRS)

    Bozak, Richard F.; Henderson, Brenda S.

    2012-01-01

    While the noise produced by a single jet is azimuthally symmetric, multiple jets produce azimuthally varying far-field noise. The ability of one jet to shield another reduces the noise radiated in the plane of the jets, while often increasing the noise radiated out of the plane containing the jets. The present study investigates the shielding potential of twin jet configurations over subsonic and over-expanded supersonic jet conditions with simulated forward flight. The experiments were conducted with 2 in. throat diameter nozzles at four jet spacings from 2.6d to 5.5d in center-to-center distance, where d is the nozzle throat diameter. The current study found a maximum of 3 dB reduction in overall sound pressure level relative to two incoherent jets in the peak jet noise direction in the plane containing the jets. However, an increase of 3 dB was found perpendicular to the plane containing the jets. In the sideline direction, shielding is observed for all jet spacings in this study.

  11. Parameters optimisation of a vehicle suspension system using a particle swarm optimisation algorithm

    NASA Astrophysics Data System (ADS)

    Centeno Drehmer, Luis Roberto; Paucar Casas, Walter Jesus; Martins Gomes, Herbert

    2015-04-01

    The purpose of this paper is to determine the lumped suspension parameters that minimise a multi-objective function in a vehicle model under different standard PSD road profiles. This optimisation tries to meet the rms vertical acceleration weighted limits for human sensitivity curves from ISO 2631 [ISO-2631: guide for evaluation of human exposure to whole-body vibration. Europe; 1997] at the driver's seat, the road holding capability and the suspension working space. The vehicle is modelled in the frequency domain using eight degrees of freedom under a random road profile. The particle swarm optimisation and sequential quadratic programming algorithms are used to obtain the suspension optimal parameters in different road profile and vehicle velocity conditions. A sensitivity analysis is performed using the obtained results and, in Class G road profile, the seat damping has the major influence on the minimisation of the multi-objective function. The influence of vehicle parameters in vibration attenuation is analysed and it is concluded that the front suspension stiffness should be less stiff than the rear ones when the driver's seat relative position is located forward the centre of gravity of the car body. Graphs and tables for the behaviour of suspension parameters related to road classes, used algorithms and velocities are presented to illustrate the results. In Class A road profile it was possible to find optimal parameters within the boundaries of the design variables that resulted in acceptable values for the comfort, road holding and suspension working space.

  12. Optimisation of the formulation of a bubble bath by a chemometric approach market segmentation and optimisation.

    PubMed

    Marengo, Emilio; Robotti, Elisa; Gennaro, Maria Carla; Bertetto, Mariella

    2003-03-01

    The optimisation of the formulation of a commercial bubble bath was performed by chemometric analysis of Panel Tests results. A first Panel Test was performed to choose the best essence, among four proposed to the consumers; the best essence chosen was used in the revised commercial bubble bath. Afterwards, the effect of changing the amount of four components (the amount of primary surfactant, the essence, the hydratant and the colouring agent) of the bubble bath was studied by a fractional factorial design. The segmentation of the bubble bath market was performed by a second Panel Test, in which the consumers were requested to evaluate the samples coming from the experimental design. The results were then treated by Principal Component Analysis. The market had two segments: people preferring a product with a rich formulation and people preferring a poor product. The final target, i.e. the optimisation of the formulation for each segment, was obtained by the calculation of regression models relating the subjective evaluations given by the Panel and the compositions of the samples. The regression models allowed to identify the best formulations for the two segments ofthe market.

  13. Shear jamming in highly strained granular system without shear banding

    NASA Astrophysics Data System (ADS)

    Zhao, Yiqiu; Barés, Jonathan; Zheng, Hu; Behringer, Robert

    2016-11-01

    Bi et al. have shown that, if sheared, a granular material can jam even if its packing fraction (ϕ) is lower than the critical isotropic jamming point ϕJ. They have introduced a new critical packing fraction value ϕS such that for ϕS< ϕ< ϕJ the system jams if sheared. Nevertheless, the value of ϕS as a function of the shear profile or the strain necessary to observe jamming remain poorly understood because of the experimental complexity to access high strain without shear band. We present a novel 2D periodic shear apparatus made of 21 independent, aligned and mirrored glass rings. Each ring can be moved independently which permits us to impose any desired shear profile. The circular geometry allows access to any strain value. The forces between grains are measured using reflective photoelasticity. By performing different shear profiles for different packing fractions we explored the details of jamming diagram including the location of the yield surface. This work is supported by NSF No.DMR1206351, NASA No.NNX15AD38G and W. M. Keck Foundation.

  14. Jet Formation Mechanisms in the presence of Topography

    NASA Astrophysics Data System (ADS)

    Boland, Emma; Haynes, Peter; Shuckburgh, Emily

    2013-04-01

    Despite over 35 years of discussion, there still remain a range of theories describing the formation of jets on a beta plane. One such theory, first proposed by Rhines (1975), is that jets form as a result of an inverse cascade of energy that is halted by the excitation of Rossby waves. We present the results of an investigation in which we attempt to apply this theory to the case of tilted jets forming over a uniform slope in bottom topography in a quasi-geostrophic, two-layer, doubly periodic model. The forms of the Rossby wave frequencies of this system depend on the Rossby deformation radius, and have two limits: a shortwave limit in which the two frequencies are the equivalent layer-wise frequencies, and orientated with the layer-wise PV gradients; and a longwave limit in which the two frequencies are barotropic- and baroclinic-like, and orientated with the barotropic PV gradient. Freely decaying simulations of the system show that the anisotropy of the frequencies successfully predicts the orientation of the jets that form, which are found to be decoupled and follow layer-wise PV gradients in the shortwave limit, and to be coupled and follow the barotropic PV gradient in the longwave limit. Introducing shear and bottom friction does not change the qualitative form of the Rossby wave frequencies, but due to the forcing by baroclinic instability occurring close to the deformation radius, all such quasi-equilibrated simulations are in the longwave limit and jets follow the barotropic PV gradient. However, only some simulations demonstrate the predicted inverse cascade and associated cascade barrier. Other simulations do not have a well developed inverse cascade, and yet still show jet formation. Previous studies have also shown that significant non-local transfers of energy occur in quasi-geostrophic systems with jets, which suggests a richer picture of jet formation. We thus propose that Rossby waves provide a barrier to further energy transfer, and their

  15. Numerical Investigation of the Formation and Detachment of Droplets from Pores in a Shear Flow Field

    NASA Astrophysics Data System (ADS)

    Feigl, Kathleen; Tanner, Franz X.; Windhab, Erich J.

    2010-09-01

    The formation and detachment behavior of droplets from a pore opening into a simple shear field within a channel gap is investigated using numerical simulations. The mathematical model consists of the governing equations for an incompressible two-phase flow problem with a moving contact line. These equations are numerically solved using the volume-of-fluid method implemented in the open source software OpenFOAM. A parameter study was performed to determine the effect of relevant dimensionless parameters on the formation and detachment behavior of the droplets. These dimensionless parameters involve the pore size, pore flow rate, gap shear rate, interfacial tension, and the viscosity and density of the two fluid phases. For the parameter range considered in this study, different degrees of jetting behavior were observed. Also, the sizes of the detached droplets were seen to decrease as the gap shear rate increased, and increase with the pore flow rate, with the gap shear rate having a larger effect.

  16. Renewable jet fuel.

    PubMed

    Kallio, Pauli; Pásztor, András; Akhtar, M Kalim; Jones, Patrik R

    2014-04-01

    Novel strategies for sustainable replacement of finite fossil fuels are intensely pursued in fundamental research, applied science and industry. In the case of jet fuels used in gas-turbine engine aircrafts, the production and use of synthetic bio-derived kerosenes are advancing rapidly. Microbial biotechnology could potentially also be used to complement the renewable production of jet fuel, as demonstrated by the production of bioethanol and biodiesel for piston engine vehicles. Engineered microbial biosynthesis of medium chain length alkanes, which constitute the major fraction of petroleum-based jet fuels, was recently demonstrated. Although efficiencies currently are far from that needed for commercial application, this discovery has spurred research towards future production platforms using both fermentative and direct photobiological routes.

  17. Low-altitude wind measurements from wide-body jet transports

    NASA Technical Reports Server (NTRS)

    Dunham, R. E., Jr.

    1982-01-01

    For a 2-week period in the spring of 1977, data were collected onboard wide-body jet transports for the determination of winds and wind shear during landings and take-offs. The data represent about 640 take-offs or landings at 14 airports in Europe and the United States. Analysis of the wind-shear data indicates that shears of a given value are equally likely to occur at any altitude in the lower 1400-ft section of the atmosphere. Analysis of the data indicates that low shears (plus or minus .033 knot/per ft) have a 67-percent chance of occurrence during a landing or take-off, while higher values (plus or minus 0.15 knot/per ft) have a 0.5-percent chance of occurrence. A determination of the duration of a given shear was not made.

  18. Low-order Description and Conditional Averaging in a Transitional Variable-Density Jet

    NASA Astrophysics Data System (ADS)

    Viggiano, Bianca; Dib, Tamara; Ali, Naseem; Mastin, Larry; Solovitz, Stephen; Cal, Raul Bayoan

    2016-11-01

    A vertically oriented jet is investigated using particle image velocimetry to identify characteristics of the flow that contribute to the distribution of turbulent kinetic energy and development of Reynolds shear stresses. Experiments with three different gases air, argon and helium as the jet and a range of exit velocities were performed to allow for variety of the Reynolds and Richardson numbers. Five cases are examined in total. Proper orthogonal decomposition is applied to assess the energy distribution of all cases with respect to the number of modes. Reconstruction of the Reynolds shear stresses using 50% of the total turbulent kinetic energy is performed. Quadrant analysis with respect to the Reynolds shear stress is also performed for insight into the entrainment of the jet. Reynolds shear stresses are dominant in Q1 - advancing ejections and Q3 - impeding entrainment and exhibit negligible contributions from the remaining two quadrants. POD is able to identify most dominant structures and transition effects within the basis. Via quadrant analysis, advancing ejection and impeding entrainment further describe the streamwise development of each jet. National Science Foundation.

  19. Potential applications for amylose inclusion complexes produced by steam jet cooking

    USDA-ARS?s Scientific Manuscript database

    Steam jet cooking is a commercially scalable method of thermomechanically processing starch for many applications. Previous studies at NCAUR have revealed the specific effects of heat and shear on various starch types cooked under different steam flow, pressure, and slurry flow conditions. Starch-...

  20. Control of Penetration and Mixing of an Excited Supersonic Jet Into a Supersonic Cross Stream (Postprint)

    DTIC Science & Technology

    2006-10-01

    1 identified jet- shear layer to be a primary location where combustion took place. Increasing the interracial contact would of course be beneficial...afforded by the injection scheme and de- fines the relationship between the perimeter and the area of a given contour compared to a perfect circle. A

  1. Characteristics of a horizontal square jet interacting with the free surface

    NASA Astrophysics Data System (ADS)

    Tay, Godwin F. K.; Rahman, Mohammad S.; Tachie, Mark F.

    2017-06-01

    The characteristics of a horizontal submerged square jet interacting with the free surface are investigated experimentally. A particle image velocimetry system is used to measure the mean flow and turbulent characteristics in the vertical symmetry plane of the jet at a Reynolds number of approximately 5500. It is shown that the effect of the free surface is to cancel the turbulent-nonturbulent interface and reduce the mean spanwise vorticity, Reynolds shear stress, and jet spreading rate in the upper shear layer in comparison to those measured in the lower shear layer. The results indicate that lowering of the jet offset height ratio increases the confinement effect of the free surface. Stronger confinement reduces the maximum mean streamwise velocity decay rate and mean surface velocity defect in the interaction region. The results also indicate a dramatic reduction in surface-normal turbulence intensity in the interaction region due to the damping effect of the free surface on the surface-normal velocity fluctuations. The decay of the surface-normal turbulence intensity near the free surface produces commensurate reductions in the surface-normal velocity fluctuation autocorrelation in the upper shear layer while enhancing the streamwise velocity fluctuation autocorrelation. The damping effect of the free surface on the surface-normal velocity fluctuations is found to be connected to the redistribution of the turbulent kinetic energy from the surface-normal velocity fluctuations to the streamwise velocity fluctuations.

  2. Numerical Simulations of Noise Generated by Supersonic Rectangular Jets Part 2: Frequency Band Analysis of Far-field Noise

    NASA Astrophysics Data System (ADS)

    Johnson, Ryan; Viswanath, Kamal; Kailasanath, Kazhikathra

    2015-11-01

    A method has been developed to analyze the asymmetry of far-field noise generated by rectangular jets by examining the contributions arising from different frequency bands. This method was used to analyze simulations of a supersonic jet issuing from a rectangular nozzle with aspect ratio of 2.0 at four frequency ranges for several over-expanded, cold jet scenarios. Results show that low frequency phenomenon, such as shear layer noise, contribute the most to the asymmetry of rectangular jet noise for these conditions. This method is being extended to examine the differences in asymmetry in comparable circular jets, as well as heated rectangular jets. Supported by Office of Naval Research (ONR) through the Computational Physics Task Area under the NRL 6.1 Base Program.

  3. Numerical study of an impinging jet to a turbulent channel flow in a T-Junction configuration

    NASA Astrophysics Data System (ADS)

    Georgiou, Michail; Papalexandris, Miltiadis

    2016-11-01

    In this talk we report on Large Eddy Simulations of an impinging planar jet to a turbulent channel flow in a T-Junction configuration. Due to its capacity for mixing and heat transfer enhancement, this type of flow is encountered in various industrial applications. In particular, our work is related to the emergency cooling systems of pressurized water reactors. As is well known, this type of flow is dominated by a large separation bubble downstream the jet impingement location. Secondary regions of flow separation are predicted both upstream and downstream the impinging jet. We describe how these separation regions interact with the shear layer that is formed by the injection of the jet to the crossflow, and how they affect the mixing process. In our talk we further examine the influence of the jet's velocity to characteristic quantities of the jet, such as penetration length and expansion angle, as well as to the first and second-order statistics of the flow.

  4. Impact of red giant/AGB winds on active galactic nucleus jet propagation

    NASA Astrophysics Data System (ADS)

    Perucho, M.; Bosch-Ramon, V.; Barkov, M. V.

    2017-10-01

    the mass-load of the jet and thus affect its dynamics. Shear layer mass-entrainment could be important. The interaction structure can be a source of significant non-thermal emission.

  5. Flow Field and Acoustic Predictions for Three-Stream Jets

    NASA Technical Reports Server (NTRS)

    Simmons, Shaun Patrick; Henderson, Brenda S.; Khavaran, Abbas

    2014-01-01

    Computational fluid dynamics was used to analyze a three-stream nozzle parametric design space. The study varied bypass-to-core area ratio, tertiary-to-core area ratio and jet operating conditions. The flowfield solutions from the Reynolds-Averaged Navier-Stokes (RANS) code Overflow 2.2e were used to pre-screen experimental models for a future test in the Aero-Acoustic Propulsion Laboratory (AAPL) at the NASA Glenn Research Center (GRC). Flowfield solutions were considered in conjunction with the jet-noise-prediction code JeNo to screen the design concepts. A two-stream versus three-stream computation based on equal mass flow rates showed a reduction in peak turbulent kinetic energy (TKE) for the three-stream jet relative to that for the two-stream jet which resulted in reduced acoustic emission. Additional three-stream solutions were analyzed for salient flowfield features expected to impact farfield noise. As tertiary power settings were increased there was a corresponding near nozzle increase in shear rate that resulted in an increase in high frequency noise and a reduction in peak TKE. As tertiary-to-core area ratio was increased the tertiary potential core elongated and the peak TKE was reduced. The most noticeable change occurred as secondary-to-core area ratio was increased thickening the secondary potential core, elongating the primary potential core and reducing peak TKE. As forward flight Mach number was increased the jet plume region decreased and reduced peak TKE.

  6. Hybrid RANS/LES of round impinging jets

    NASA Astrophysics Data System (ADS)

    Kubacki, Slawomir; Rokicki, Jacek; Dick, Erik

    2011-12-01

    Fluid flow and heat transfer characteristics are presented for simulations of round impinging jets at two nozzle-plate distances H/D = 2 and 10 (D is the nozzle exit diameter) and two Reynolds numbers Re = 5000 and 70,000 with hybrid RANS/LES (Reynolds-averaged Navier-Stokes/Large Eddy Simulation), dynamic Smagorinsky LES and RANS k-ω models. Three k-ω based hybrid RANS/LES models are analyzed. With the hybrid RANS/LES models, improved heat transfer results are obtained, when compared to RANS, in the impact region and in the developing wall-jet region. For accurate predictions at low nozzle-plate distance, it is necessary to sufficiently resolve the formation and development of the near-wall vortices in the jet impingement region. At high nozzle-plate distance, it is important to capture the evolution and breakup of the unsteady vortices in the shear layer of the jet, so that realistic mean and fluctuating velocity profiles are obtained in the impact jet region.

  7. Supersonic Jet Noise Reduction Using Flapping Injection and Pulsed Injection

    NASA Astrophysics Data System (ADS)

    Hafsteinsson, Haukur; Eriksson, Lars-Erik; Cuppoletti, Daniel; Gutmark, Ephraim; Department of Applied Mechanics, Chalmers University of Technology Team; Department of Aerospace Engineering, University of Cincinatti Team; Swedish Defence Material Administration, Sweden Team

    2013-11-01

    Aircraft are in general noisy and there is a high demand for reducing their noise levels. The jet exhaust is in most cases the main noise source of the aircraft, especially for low bypass ratio jet engines. Fluidic injection affecting the shear layer close to the nozzle exit is a promising noise reduction technique as it can be turned of while not needed and thus the negative effect on the engine performance will be minimized. In the presented work, LES is used to compare steady-state mass flow injection with steady-state mass flow flapping jet injection. The work is a direct continuation of a previous LES study on pulsed injection which showed that the pulsed injection induced pressure pulses in the jet which caused increased tonal noise in the downstream directions. The injection system considered in the presented work consists of eight evenly distributed injectors at the nozzle exit plane with a 90° injection angle relative to the flow direction. Flapping jet injection is believed to minimize the creation of these pressure pulses since it provides steady-state mass flow. This work is funded by Swedish Defense Material Administration (FMV).

  8. The development of an axisymmetric curved turbulent wall jet

    NASA Astrophysics Data System (ADS)

    Gregory-Smith, D. G.; Hawkins, M. J.

    1991-12-01

    An experimental study has been carried out of the low speed Coanda wall jet with both streamwise and axisymmetric curvature. A single component laser Doppler technique was used, and by taking several orientations at a given point, values of the three mean velocities and five of the six Reynolds stresses were obtained. The lateral divergence and convex streamwise curvature both enhanced the turbulence in the outer part of the jet compared with a plane two-dimensional wall jet. The inner layer exhibited a large separation of the positions of maximum velocity and zero shear stress. It was found that the streamwise mean velocity profile became established very rapidly downstream of the slot exit. The profile appeared fairly similar at later downstream positions, but the mean radial velocity and turbulence parameters showed the expected nonself preservation of the flow. Removal of the streamwise curvature resulted in a general return of the jet conditions toward those expected of a plane wall jet. The range and accuracy of the data may be used for developing turbulence models and computational techniques for this type of flow.

  9. A gyrokinetic perspective on the JET-ILW pedestal

    NASA Astrophysics Data System (ADS)

    Hatch, D. R.; Kotschenreuther, M.; Mahajan, S.; Valanju, P.; Liu, X.

    2017-03-01

    JET has been unable to recover historical confinement levels when operating with an ITER-like wall (ILW) due largely to the inaccessibility of high pedestal temperatures. Finding a path to overcome this challenge is of utmost importance for both a prospective JET DT campaign and for future ITER operation. Gyrokinetic simulations (using the Gene code) quantitatively capture experimental transport levels for a representative experimental discharge and qualitatively recover the major experimental trends. Microtearing turbulence is a major transport mechanisms for the low-temperature pedestals characteristic of unseeded JET-ILW discharges. At higher temperatures and/or lower {ρ\\ast} , we identify electrostatic ITG transport of a type that is strongly shear-suppressed on smaller machines. Consistent with observations, this transport mechanism is strongly reduced by the presence of a low-Z impurity (e.g. carbon or nitrogen at the level of {{Z}\\text{eff}}∼ 2 ), recovering the accessibility of high pedestal temperatures. Notably, simulations based on dimensionless {ρ\\ast} scans recover historical scaling behavior except in the unique JET-ILW parameter regime where ITG turbulence becomes important. Our simulations also elucidate the observed degradation of confinement caused by gas puffing, emphasizing the important role of the density pedestal structure. This study maps out important regions of parameter space, providing insights that may point to optimal physical regimes that can enable the recovery of high pedestal temperatures on JET.

  10. Round impinging jets with relatively large stand-off distance

    NASA Astrophysics Data System (ADS)

    Shademan, Mehrdad; Balachandar, Ram; Roussinova, Vesselina; Barron, Ron

    2016-07-01

    Large eddy simulation and particle image velocimetry measurements have been performed to evaluate the characteristics of a turbulent impinging jet with large nozzle height-to-diameter ratio (H/D = 20). The Reynolds number considered is approximately 28 000 based on the jet exit velocity and nozzle diameter. Mean normalized centerline velocity in both the free jet and impingement regions and pressure distribution over the plate obtained from simulations and experiments show good agreement. The ring-like vortices generated due to the Kelvin-Helmholtz instabilities at the exit of the nozzle merge, break down and transform into large scale structures while traveling towards the impingement plate. A Strouhal number of 0.63 was found for the vortices generated at the exit of the nozzle. However, this parameter is reduced along the centerline towards the impingement zone. A characteristic frequency was also determined for the large scale structures impinging on the plate. The expansion, growth, tilt, and three-dimensionality of the impinging structures cause dislocation of the impinging flow from the centerline, which is significantly larger when compared with flows having small H/D ratios. Contrary to the behavior of impinging jets with small stand-off distance, due to the loss of coherence, the large scale structures do not result in significant secondary vortices in the wall jet region and consequently less fluctuations were observed for wall shear stress.

  11. Energy Usage Optimisation in South African Mines

    NASA Astrophysics Data System (ADS)

    Hasan, Ali; Twala, Bhekisipho; Ouahada, Khmaies; Marwala, Tshilidzi

    2014-03-01

    In recent years, South Africa has encountered a critical electricity supply which necessitated the implementation of demand-side management (DSM) projects. Load shifting and energy (EE) efficiency projects were introduced in mining sector to reduce the electricity usage during day peak time. As the compressed air networks and the water pumping systems are using large amounts of the mines' electricity, possible ways were investigated and implemented to improve and optimise the energy consumption and to reduce the costs. Implementing DSM and EE in four different mines resulted in achieving the desired energy savings and load-shifting. W ostatnich latach w Południowej Afryce zanotowano pewne trudności z dostawami energii elektrycznej, co wymusiło wdrożenie działań mających na celu skuteczne zarządzanie zagadnieniami energetycznymi. Wprowadzono działania mające na celu zmianę systemu obciążeń roboczych i bardziej efektywne wykorzystanie energii tak, by obniżyć zapotrzebowanie na energię w trakcie szczytowych godzin w ciągu dnia. Sieci dostarczające sprężone powietrze oraz stacje pomp zużywają znaczne ilości energii w kopalni, przeanalizowano więc możliwe sposoby redukcji i optymalizacji zapotrzebowania na energię i tym samym obniżenia kosztów produkcji. Wdrożenie odpowiednich projektów nakierowanych na oszczędności i optymalizację w czterech kopalniach doprowadziło do oczekiwanych oszczędności energii i umożliwiło zmianę systemu obciążeń roboczych w trakcie procesu produkcji.

  12. Jet Shockwaves Produce Gamma Rays

    NASA Image and Video Library

    Theorists believe that GRB jets produce gamma rays by two processes involving shock waves. Shells of material within the jet move at different speeds and collide, generating internal shock waves th...

  13. Resolving boosted jets with XCone

    NASA Astrophysics Data System (ADS)

    Thaler, Jesse; Wilkason, Thomas F.

    2015-12-01

    We show how the recently proposed XCone jet algorithm [1] smoothly interpolates between resolved and boosted kinematics. When using standard jet algorithms to reconstruct the decays of hadronic resonances like top quarks and Higgs bosons, one typically needs separate analysis strategies to handle the resolved regime of well-separated jets and the boosted regime of fat jets with substructure. XCone, by contrast, is an exclusive cone jet algorithm that always returns a fixed number of jets, so jet regions remain resolved even when (sub)jets are overlapping in the boosted regime. In this paper, we perform three LHC case studies — dijet resonances, Higgs decays to bottom quarks, and all-hadronic top pairs — that demonstrate the physics applications of XCone over a wide kinematic range.

  14. Control of Asymmetric Jet

    DTIC Science & Technology

    1992-06-30

    with 5hciir Irycr frequencies arnd miodfy th-e preferied mode. Perforte~d steel plateCs "-leed with tempcratuze-resistatr: mnsulativ- mineral wool reduce...Insulation of the Jet facility was initially ... ovid. d 6y ibuiglass, then mineral wool and at the present there is none for health concerns. The...imerior of the jet’s anechoic chamber was also insulated with mineral wool to foitify acoustic damping, however this too has been removed due to portions

  15. Jet pump assisted artery

    NASA Technical Reports Server (NTRS)

    1975-01-01

    A procedure for priming an arterial heat pump is reported; the procedure also has a means for maintaining the pump in a primed state. This concept utilizes a capillary driven jet pump to create the necessary suction to fill the artery. Basically, the jet pump consists of a venturi or nozzle-diffuser type constriction in the vapor passage. The throat of this venturi is connected to the artery. Thus vapor, gas, liquid, or a combination of the above is pumped continuously out of the artery. As a result, the artery is always filled with liquid and an adequate supply of working fluid is provided to the evaporator of the heat pipe.

  16. 'Photonic jets' from dielectric microaxicons

    SciTech Connect

    Geints, Yu E; Zemlyanov, A A; Panina, E K

    2015-08-31

    We consider a specific spatially localised light structure, namely, a 'photonic jet' formed in the near field upon scattering of an optical wave in a dielectric micron particle. Dimensional parameters and intensity of a photonic jet from microaxicons of different spatial orientation are studied theoretically. It is found for the first time that an axicon-generated photonic jet has in this case a substantially larger length compared with the case of a jet formed on a spherical particle. (scattering of light)

  17. Cooperative Investigation of Jet Flows.

    DTIC Science & Technology

    1982-06-01

    high and low Reynolds number jets. Controlling the jet with pure tone excitation, that enhances the helical mode of its instability, resulted in a... helical modes and upstream influence appear to be key mechanisms in our findings 3.- -- - Disatributio~n/ Availit- UNCLASSIFIED 89CUMIIY CLAWIPCAT OF...and low Reynolds number*’ jets. Controlling the jet with pure tone excitation, that enhances the helical mode of its instability, resulted in a

  18. Shear Jamming in Particulate Media

    NASA Astrophysics Data System (ADS)

    Bertrand, Thibault; O'Hern, Corey S.; Shattuck, Mark D.

    2014-11-01

    More than two decades ago, Liu and Nagel introduced the concept of jamming and proposed a phase diagram for the jamming transition as a function of applied shear stress, density, and temperature. Since then, numerous computational as well as experimental studies have underscored the usefulness of this concept in systems ranging from colloidal glasses to packings of granular materials. Recently, Bi et al. presented experimental results that suggested that jamming via isotropic compression can lead to different packings than those generated via shear. To investigate fundamental aspects of shear-induced jamming, we performed numerical simulations and theoretical analyses of frictionless and frictional particulate media undergoing simple shear. We are able to predict the form of the boundaries in the shear-jamming phase diagram and determine how they change with system size. We also study the relationship between the shear-jamming phase diagram and the fluctuations in the stress versus strain for packings undergoing continuous shear in the context of geometrical families of packings.

  19. Improving Interlaminar Shear Strength

    NASA Technical Reports Server (NTRS)

    Jackson, Justin

    2015-01-01

    To achieve NASA's mission of space exploration, innovative manufacturing processes are being applied to the fabrication of complex propulsion elements.1 Use of fiber-reinforced, polymeric composite tanks are known to reduce weight while increasing performance of propulsion vehicles. Maximizing the performance of these materials is needed to reduce the hardware weight to result in increased performance in support of NASA's missions. NASA has partnered with the Mississippi State University (MSU) to utilize a unique scalable approach of locally improving the critical properties needed for composite structures. MSU is responsible for the primary development of the concept with material and engineering support provided by NASA. The all-composite tank shown in figure 1 is fabricated using a prepreg system of IM7 carbon fiber/CYCOM 5320-1 epoxy resin. This is a resin system developed for out-of-autoclave applications. This new technology is needed to support the fabrication of large, all composite structures and is currently being evaluated on a joint project with Boeing for the Space Launch System (SLS) program. In initial efforts to form an all composite pressure vessel using this prepreg system, a 60% decrease in properties was observed in scarf joint regions. Inspection of these areas identified interlaminar failure in the adjacent laminated structure as the main failure mechanism. This project seeks to improve the interlaminar shear strength (ILSS) within the prepreg layup by locally modifying the interply region shown in figure 2.2

  20. Effects of Acoustically Lined Cylindrical Ducts on Instability Waves in Confined Supersonic Jets

    NASA Technical Reports Server (NTRS)

    Dahl, Milo D.

    1997-01-01

    The pressure disturbances generated by an instability wave in the shear layer of a supersonic jet are studied for an axisymmetric jet inside a lined cylindrical duct. For the supersonic jet, locally linear stability analysis with duct wall boundary conditions is used to calculate the eigenvalues and the eigenfunctions. These values are used to determine the growth rates and phase velocities of the instability waves and the radial pressure disturbance patterns. The study is confined to the dominant Kelvin-Helmholtz instability mode and to the region just downstream of the nozzle exit where the shear layer is growing but is still small in size compared to the radius of the duct. Numerical results are used to study the effects of changes in the outer flow, growth in the shear layer thickness, wall distance, wall impedance, and frequency. Results indicate that the effects of the duct wall on shear layer growth rates diminish as the outer flow increases. Also, wall reflections cause variations in growth rates depending on wall height and Strouhal number. These variations are due to the phase relationship between the outgoing and the reflected incoming pressure disturbances at the shear layer. The growth rate variations can be reduced and the maximum growth rate minimized by keeping the imaginary part of the impedance negative.