Real Jet Research Articles

Functional Performance Analysis and Optimization for the High-Frequency Magnetic Diagnostic System in ITER — I: Overview of the Results

The measurement performance of the baseline system design for the ITER high-frequency magnetic diagnostic has been analyzed using an algorithm based on the sparse representation of signals. This algorithm, derived from the SparSpec code [S. Bourguignon et al., Astron. Astrophys., 462, 379 (2007)] has previously been extensively benchmarked on real and simulated JET data. To optimize the system design of the ITER high-frequency magnetic diagnostic, we attempt to reduce false detection of the modes and to minimize the sensitivity of the measurement with respect to noise in the data, loss of faulty sensors, and the displacement of the sensors. Using this approach, the original layout design for the ITER high-frequency magnetic diagnostic system, which uses 168 sensors, is found to be inadequate to meet the ITER measurement requirements.Based on this analysis, and taking into account the guidelines for the risk mitigation strategies that are given in the ITER management plan, various attempts at optimization of this diagnostic system have been performed. A revised proposal for its implementation has been developed, which now meets the ITER requirements for measurement performance and risk management. For toroidal mode number detection, this implementation includes two arrays of 50 to 55 sensors and two arrays of 25 to 35 unevenly spaced sensors each on the low-field side and two arrays of 25 to 35 unevenly spaced sensors each on the high-field side. For poloidal mode number detection, we propose six arrays of 25 to 40 sensors each located in nonequidistant machine sectors, not covering the divertor region and, possibly, poloidal angles in the range 75 < |θ|(deg) < 105, as this region is the most sensitive to the details of the magnetic equilibrium. In this paper we present the general summary results of this work, for which more details and an overview of our test calculations are reported in the companion paper.

The downstream impact of tropical cyclones on a developing baroclinic wave in idealized scenarios of extratropical transition

AbstractThe interaction of a tropical cyclone with a developing baroclinic wave is investigated in an idealized scenario of extratropical transition (ET). The impact of ET is examined by comparing and analyzing two numerical baroclinic‐wave experiments: a traditional experiment in which baroclinic development is excited by a localized upper‐level perturbation on a realistic jet profile and an experiment in which, additionally, a model tropical cyclone is inserted south of the jet at the initial time.ET occurs in a wavy upper‐level flow while baroclinic surface systems are still weak. The characteristic direct impact of ET on the midlatitude flow is the formation of a distinct jet streak and the amplification of a ridge–trough couplet in the adjacent downstream region. The subsequent rapid cyclogenesis downstream is a direct consequence of these upper‐level flow modifications. This faster and stronger development constitutes the amplification of the leading edge of downstream development. Both the upper‐level wave pattern and the surface development are subsequently amplified in the region further downstream.The formation of the ridge adjacent to the intensified downstream cyclone is analyzed in detail to elucidate the next stage in the downstream dispersion of the ET impact. Ridge‐building in the ET scenario exhibits characteristics distinct from those in the life‐cycle experiment. Wave breaking, feedback from the modified low‐level frontal structure and diabatic processes all contribute to the high‐amplitude wave pattern downstream of ET.The downstream impact of ET is highly sensitive to the initial storm location and intensity. The considerable amplification of the leading edge found in the reference experiment is the most widespread and rapidly propagating impact. We thus speculate that this leading edge represents an optimal location of the midlatitude circulation, where ET can lead to the most significant impact on the downstream flow. Copyright © 2010 Royal Meteorological Society

THE COMPLETE SPECTRUM OF THE NEUTRON STAR X-RAY BINARY 4U 0614+091

We observed the neutron star (NS) ultra-compact X-ray binary 4U0614+091 quasi-simultaneously in the radio band (VLA), mid-IR/IR (Spitzer/MIPS and IRAC), near-IR/optical (SMARTS), optical-UV (Swift/UVOT), soft and hard X-rays (Swift/XRT and RXTE). The source was steadily in its `hard state'. We detected the source in the whole range, for the first time in the radio band at 4.86 and 8.46 GHz and in the mid-IR at 24 um, up to 100 keV. The optically thick synchrotron spectrum of the jet is consistent with being flat from the radio to the mid-IR band. The flat jet spectrum breaks in the range (1-4)x10^(13) Hz to an optically-thin power-law synchrotron spectrum with spectral index ~-0.5. These observations allow us to estimate a lower limit on the jet radiative power of ~3x10^(32) erg/s and a total jet power Lj~10^(34) u_(0.05)^(-1) Ec^(0.53) erg/s (where Ec is the high-energy cutoff of the synchrotron spectrum in eV and u_(0.05) is the radiative efficiency in units of 0.05). The contemporaneous detection of the optically thin part of the compact jet and the X-ray tail above 30 keV allows us to assess the contribution of the jet to the hard X-ray tail by synchrotron self-Compton (SSC) processes. We conclude that, for realistic jet size, boosting, viewing angle and energy partition, the SSC emission alone, from the post-shock, accelerated, non-thermal population in the jet, is not a viable mechanism to explain the observed hard X-ray tail of the neutron star 4U0614+091.

Jet noise simulations for realistic jet nozzle geometries

This paper describes a methodology for the direct calculation of noise from realistic nozzle geometries. The focus of the paper is on the numerical approach to this problem to provide noise predictions to engineering accuracy in an efficient manner. In addition, issues related to grid generation are discussed. The methodology uses structured multiblock grids. The block surrounding the jet centerline has a Cartesian form and the surrounding grid blocks have a cylindrical polar form–at least for nearly axisymmetric jet nozzle geometries. Appropriate block interface conditions are used. In the case of military style jet nozzles the nozzles are not smooth in the azimuthal direction but have facets representative of the movable flaps in such variable area nozzles. These features must be included in the grid. To enable efficient calculations, in addition to parallel computation, a dual time-stepping approach is used. The sub-iterations in the fictitious time are accelerated using a two-level multigrid approach. A Detached Eddy Simulation (DES) approach based on the Spalart-Allmaras (S-A) one-equation turbulence model is used. Comparisons are made between flow predictions using the DES with the S-A model everywhere and with the turbulence model turned off in the jet external flow. Noise predictions are made with the permeable surface Ffowcs Williams–Hawkings (FW-H) solution. Noise predictions are presented for both a smooth convergent-divergent nozzle as well as a nozzle representative of a military aircraft engine. Comparisons are made with available experimental data.

Low-frequency sound radiated by a nonlinearly modulated wavepacket of helical modes on a subsonic circular jet

A possible fundamental physical mechanism by which instability modes generate sound waves in subsonic jets is presented in the present paper. It involves a wavepacket of a pair of helical instability modes with nearly the same frequencies but opposite azimuthal wavenumbers. As the wavepacket undergoes simultaneous spatial–temporal development in a circular jet, the mutual interaction between the helical modes generates a strong three-dimensional, slowly modulating ‘mean-flow distortion’. It is demonstrated that this ‘mean field’ radiates sound waves to the far field. The emitted sound is of very low frequency, with characteristic time and length scales being comparable with those of the envelope of the wavepacket, which acts as a non-compact source. A matched-asymptotic-expansion approach is used to determine, in a self-consistent manner, the acoustic field in terms of the envelope of the wavepacket and a transfer factor characterizing the refraction effect of the background base flow. For realistic jet spreading rates, the nonlinear development of the wavepacket is found to be influenced simultaneously by non-parallelism and non-equilibrium effects, and so a composite modulation equation including both effects is constructed in order to describe the entire growth–attenuation–decay cycle. Parametric studies pertaining to relevant experimental conditions indicate that the acoustic field is characterized by a single-lobed directivity pattern beamed at an angle about 45°–60° to the jet axis and a broadband spectrum centred at a Strouhal number St ≈ 0.07–0.2. As the nonlinear effect increases, the radiation becomes more efficient and the noise spectrum broadens, but the gross features of the acoustic field remain robust, and are broadly in agreement with experimental observations.

Numerical simulation of gaseous fuel injection: A new methodology for multi‐dimensional modelling

AbstractThe use of natural gas (instead of liquid or solid fuels) is nowadays drawing an increasing interest in many applications (gas turbines, boilers, internal combustion engines), because of the greater attention to environmental issues. To facilitate the development of these applications, computer models are being developed to simulate gaseous injection, air entrainment and the ensuing combustion.This paper introduces a new method for modelling the injection process of gaseous fuels that aims to hold down grid requirements in order to allow the simulation also of other phenomena, like combustion or valve and piston motion, in reciprocating internal combustion engines. After a short overview of existing models, the transient jet model and the evaluation of inflow conditions are described in detail. Then a basic study of the grid effects on the jet evolution is presented. The model is updated and validated by comparing numerical results with available experimental data for two different operating conditions: a subsonic and a supersonic under‐expanded case. The model demonstrates to be fast enough to be used in a multi‐dimensional code and accurate enough to follow the real gas jet evolution. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Development and validation of stereoscopic micro-PTV using match probability

A stereoscopic micro-PTV (particle tracking velocimetry) technique based on 2-frame PTV using match probability was developed. This method measures not only a two-dimensional velocity field but also the out-of-plane velocity component in micro fluid flow. A validation study of SMPTV by using a simulated flow model and a real micro jet flow was performed to verify the accuracy and feasibility of the method. The effects of different kinds of microscopes and the out-of-focus effect were also investigated. All test results were compared with the SMPIV method in order to evaluate the performance. The results showed that the SMPTV method using a CMO type microscope accurately measured the micro flow with the lowest bias error and higher spatial resolution than the SMPIV method.

LES of high pressure hydrogen jet fire

This work describes a large eddy simulation (LES) approach to model high pressure jet fires. Numerical simulations are compared against a large scale vertical, hydrogen jet fire test [Schefer, R. W., Houf, W. G., Williams, T. C., Bourne, B., & Colton, J. (2007). Characterization of high-pressure, under-expanded hydrogen-jet flames. International Journal of Hydrogen Energy, 32(12), 2081–2093], which gives experimental data for blowdown from a tank at an initial pressure of 413 bar through a 5.08 mm diameter nozzle. In this work, conditions 5 s after the start of the release have been taken to simulate a “quasi-steady” state. The work was driven by the need to develop contemporary tools for safety assessment of real scale under-expanded hydrogen jet fires and an aim was to study an LES model performance to reproduce such large scale jet fires in an industrial safety context. Detailed simulations of the flow structure in under-expanded part of the jet are avoided in this work using the notional nozzle concept. The LES combustion model is based on the mixture fraction approach and probability density function to account for flame–turbulence interaction. A flamelet library of the relationship between the instantaneous composition of the reacting mixture and the mixture fraction is calculated in advance. A comparison of experimental observations and simulation results (flame length, flame width) is discussed in view of the grid resolution required for LES and boundary conditions such as turbulence intensity and turbulent length scale at the notional nozzle.

Comparison of fusion alpha performance in JET advanced scenario and H-mode plasmas

Currently, plasmas with internal transport barriers (ITBs) appear the most likely candidates for steady-state scenarios for future fusion reactors. In such plasmas, the broad hot and dense region in the plasma core leads to high fusion gain, while the cool edge protects the integrity of the first wall. Economically desirable large bootstrap current fraction and low inductive current drive may, however, lead to degraded fast ion confinement. In this work the confinement and heating profile of fusion alphas were compared between H-mode and ITB plasmas in realistic JET geometry. The work was carried out using the Monte Carlo-based guiding-center-following code ASCOT.For the same plasma current, the ITB discharges were found to produce four to eight times more fusion power than a comparable ELMy H-mode discharge. Unfortunately, also the alpha particle losses were larger (∼16%) compared with the H-mode discharge (7%). In the H-mode discharges, alpha power was deposited to the plasma symmetrically around the magnetic axis, whereas in the current-hole discharge, the power was spread out to a larger volume in the plasma center. This was due to wider particle orbits, and the magnetic structure allowing for a broader hot region in the centre.

Numerical study of the response of the ocean to a northerly wind jet in the equatorial Eastern Pacific

Abstract. The response of the equatorial and South American coastal ocean circulation to the anomalous March 2002 wind jet extending from the Gulf of Panama to 6° S is studied in a linear ocean model. Two experiments were performed: one without continental boundaries and the other with an eastern boundary at 81° W, representing the American continent. The spatial and temporal structure of the imposed wind anomaly, represented with idealized mathematical functions, is similar to that of the real jet. The duration of the wind jet was six days where the maximum intensity occurred at the third day. The results of the experiments indicate that the wind-jet anomaly over the Gulf of Panama is another source of ocean waves that influence the western coast of South America in the form of coastal Kelvin waves (CKW).

Effect of an axial jet on vortex merging

Experiments were conducted to understand the effect of an axial jet on the merging process of a simulated flap-edge and wing-tip corotating vortex pair in the near wake. Cross-flow velocity measurements and flow visualization were performed for the three realistic jet positions on both equal and unequal strength like-signed vortices for a range of momentum coefficients. The main finding was that the initial jet position has a vastly contrasting effect on the merging process. If the jet turbulence rapidly interacts with only one of the vortices, severe diffusion of that vortex occurs which ultimately wraps around and becomes consumed by the unaffected vortex structure. The jet causes a reduction in the vortex spacing and an increase in the rotation angle; hence, merging is promoted. If the jet turbulence does not directly interact with either vortex but instead interferes with the mechanism in the outer-recirculation region that advects vorticity to a larger radius, then merging can be retarded. In this case, an increase in vortex spacing and reduction in rotation angle were observed. Increasing the momentum coefficient, hence, introducing more turbulence into the flow, has a greater effect on the merging process.

Aerodynamic Characteristics of a Gurney/Jet Flap at Low Reynolds Numbers

A low-speed wind-tunnel investigation has been undertaken to establish the effect of a Gurney flap used in conjunction with a jet flap at low Reynolds numbers. The characteristics of the combination were explored as a potential control effector for small unmanned aerial vehicles. Measurements included force balance, wake survey, and flow visualization. The results indicate that the jet flap maintains a theoretically determined dependence on the jet momentum coefficient, even at a low Reynolds number (160,000). A numerical lifting-line program was modified to allow estimate of the rolling moment that may be generated by ailerons composed of a Gumey/jet flap. The numerical data suggest that the jet flap is capable of generating significant rolling moments with realistic jet momentum coefficients.

Prediction of Flowfield and Acoustic Signature of a Coaxial Jet Using RANS-Based Methods and Large-Eddy Simulation

The feasibility of using large-eddy simulation (LES) for jet noise predictions has been discussed in several publications. The vast majority of these studies are, however, restricted to fairly simple geometries and moderate Reynolds numbers flows. Recent studies have shown that LES-based methods can be used for realistic flows and complex geometries with promising results. With continuously increased computer capacity and with the possibility to perform computations in parallel on PC-clusters, the possibility of using LES for industrial applications is increasing. However, although, the complexity of configurations for which LES may be used is approaching that of a real jet engine, due to high demands for computational power and long turn-over times LES is still not feasible for industrial use. For low-noise nozzle design, engineering tools with short turn-over time, accurate enough for prediction of noise trends are therefore needed. In the development of such methods, LES can provide data suitable for method validation. In the present work, the high-subsonic flow in an axisymmetric coaxial nozzle/jet configuration is studied. Flowfield predictions obtained using an axisymmetric RANS solver for compressible flows and predicted acoustic signature obtained using a method based on RANS and Lighthill's acoustic analogy are compared with flowfield and radiated sound predictions obtained using LES combined with Kirchhoff surface integration. In the predicted flow statistics, the most noticeable difference between RANS and LES results is that the RANS calculation gives somewhat lower levels of turbulence kinetic energy in the shear layers in the near-nozzle regions and hence the LES jet mixes somewhat faster and thus the potential core region is shorter in this simulation.

The effect of jet velocity profile on the characteristics of thickness and velocity of the liquid sheet formed by two impinging jets

In this study, the effect of jet velocity profile on the thickness and velocity of the liquid sheet formed by two low-speed impinging jets was investigated. In addition to the constant jet velocity and the Poiseuille parabolic profile, the jet velocity profile measured experimentally was considered to account for the real nonuniform jet velocity profile. For three jet velocity profiles, the distributions of the thickness and velocity of the liquid sheet were analytically predicted by solving conservation equations for mass, momentum, and energy. The predicted results were compared with the previous experimental results. The jet velocity profile affected the resulting thickness and velocity characteristics of the liquid sheet. The distributions of the thickness and velocity of the liquid sheet predicted by using the measured jet velocity profile produced more acceptable results, which agreed better with the experimental observations, than those obtained by using the constant jet velocity, which has been commonly used in previous theoretical works.

Mode-ratio bootstrapping method for PIV outlier correction

This paper proposes a new method for correcting spurious displacement vectors obtained by using particle image velocimetry. Unlike methods that generate and use statistics from neighboring vectors toward outlier identification, a bootstrapping process is employed to generate statistics for each component. The mode-ratio criterion, defined as the normalized absolute value of the difference between the mode of the generated statistics and the actual value on the field, is used to identify and tag spurious components. The bootstrapping process is repeated to generate new statistics from the untagged components. This process is then repeated multiple times. The resulting mode field is used as the correction field. Two different displacement fields, each with a different error type, are artificially generated to evaluate the performance of the method. The evaluation is done by measuring the deviation between the resulting mode field and the perfect component field. The method is then tested on a real turbulent jet flow, obtained from www.pivchallenge.org, and the effect of the spatial gradient is discussed.

A novel method for oxidative desulfurization of liquid hydrocarbon fuels based on catalytic oxidation using molecular oxygen coupled with selective adsorption

The present study explored a novel oxidative desulfurization (ODS) method of liquid hydrocarbon fuels, which combines a catalytic oxidation step of the sulfur compounds directly in the presence of molecular oxygen and an adsorption step of the oxidation-treated fuel over activated carbon. The ODS of a model jet fuel and a real jet fuel (JP-8) was conducted in a batch system at ambient conditions. It was found that the oxidation in the presence of molecular oxygen with Fe(III) salts was able to convert the thiophenic compounds in the fuel to the corresponding sulfone and/or sulfoxide compounds at 25°C. The oxidation reactivity of the sulfur compounds decreases in the order of 2-methylbenzothiophene>5-methylbenzothiophene>benzothiophene≫dibenzothiophene. The alkyl benzothiophenes with more alkyl substituents have higher oxidation reactivity. In real JP-8 fuel, 2,3-dimethylbenzothiophene was found to be the most refractory sulfur compound to be oxidized. The catalytic oxidation of the sulfur compounds to form the corresponding sulfones and/or sulfoxides improved significantly the adsorptivity of the sulfur compounds on activated carbon, because the activated carbon has higher adsorptive affinity for the sulfones and sulfoxides than thiophenic compounds due to the higher polarity of the former. The remarkable advantages of the developed ODS method are that the ODS can be run in the presence of O2 at ambient condition without using peroxides and aqueous solvent and thus without involving the biphasic oil–aqueous-solution system.

On the near-wall structure in reverse-flow and post-reattachment recovery regions of separated flow and its equivalence to the structure in wall and free-surface jets

The statistical and structural properties of two wall jets, one developing along a real wall and the other along a shear-free wall, are contrasted with the equivalent properties in the post-reattachment-recovery and reverse-flow regions of a separated backward-facing step flow, respectively. The study was motivated, principally, by the wish to isolate and understand the mechanisms responsible for the poor representation of the post-reattachment recovery returned by most RANS closures. It demonstrates a substantive commonality in the turbulent processes between, on the one hand, the real wall jet and post-reattachment recovery, and on the other hand, between the zero-wall-shear jet and the reattachment zone, as well as the reverse-flowing near-wall layer in the backward-facing-step flow. All regions under consideration are found to be characterised by an influential interaction between an outer shear layer and the wall, but an important distinction arises from the presence or absence of strong near-wall shear which introduces significant changes to the nature of this interaction: in the absence or near-absence of wall shear, the interaction is largely inviscid, associated with wall-blocking, while strong shear tends to shield the wall from the outer flow. The commonality between the two sets of flow conditions is explored by way of mean-flow properties, budgets, anisotropy maps, departures from local equilibrium, non-dimensional strain parameter, length-scale variations and structural properties. The study shows that the post-reattachment-recovery region, like the real wall jet, is far from the state of local equilibrium found in a standard boundary layer, that the recovery of the flow towards a state of equilibrium is slow, and that the near-wall region is strongly affected by turbulent diffusion associated with the migration of large-scale structures towards the wall. In statistical terms, this last process is represented by the importance of turbulent transport by third moments and pressure–velocity correlations. Within the reattachment and reverse–flow layer, near-wall shear is weak, and so is the shielding of the wall from the outer layer. In these regions, the flow shares many of the properties of the zero-wall-shear jet.

Nonlinear Stability Analysis of Thin Film Flow from a Liquid Jet Impinging on a Circular Concentric Disk

AbstractThe paper investigates the stability of thin film flow from a liquid jet impinging on a circular concentric disk using a long-wave perturbation method to solve for the generalized nonlinear kinematic equations of free film interface. To begin with a normal mode approach is employed to obtain the linear stability solution for the film flow. In the linear stability solutions only subcritical region can be resolved. In other words, no solution of supercritical region can be obtained in linear domain. Furthermore, the role that the forces of gravitation and surface tension play in the flow is nothing but to stabilize the system. To further investigate the realistic impinging jet flow stability conditions, the weak nonlinear dynamics of a film flow is studied by using the method of multiple scales. Various subcritical nonlinear behaviors expressed in terms of absolute stability, conditional stability and explosive instability can be characterized by solving the Ginzburg-Landau equation. It is found that the jet flow will become relatively unstable for an increasing Reynolds number, a relative smaller distance from the center of the impinging jet on the disk and a smaller diameter of the exit jet. It is also concluded that the flow will always stay in a subcritical instability region if the characteristic diameter of the potential core at nozzle exit is less than 0.01mm for the numerical conditions given in this paper. In such a case when the amplitude of external flow disturbance is smaller than the threshold amplitude a stable jet flow can be ensured.

Validation of Ink Media Interaction Mechanisms for Dye and Pigment-based Aqueous and Solvent Inks

In this article, the dynamics of droplet impingement, spreading, absorption, penetration, and evaporation are discussed for different ink jet ink classes. Both dye and pigment based aqueous inks are included, as well as solvent or eco-solvent inks. The fundamental physicochemical rules determining the dynamics can be very dependent from ink to ink, and are compared. After impact there is a fast spreading phase that takes into account the evolution of the kinetic energy of the droplet to forced spreading on the receiver. Later on, diffusion or capillary wicking is possible, and is depending upon the nature of the substrate. The speed of these processes can be influenced by the presence of dyes or pigments in the inks. After absorption / penetration, the carrier liquid can evaporate leading to the final equilibrium condition. For (eco)-solvent inks the evaporation is much more important compared to the other penetration/absorption processes, so that it cannot be easily separated into different independent time scales. In situ visualization of the dynamics for real size ink jet droplets is not easy, especially for the droplets of only a few pl volume. Comparison of large droplet impact dynamic studies with theory and extrapolation of the behavior to small droplet cases has some risks. Test experiments have been setup in order to simulate transient absorption phases on different receivers. Traditional microscopic evaluations have been done in order to verify whether the proposed models for describing the transient behavior are in agreement with the experimental observations for real small sized droplets.

Quasi-One-Dimsensional Model for Realistic Three-Dimensional Synthetic Jet Actuators

A systematic methodology for approximating realistic three-dimensional synthetic jet actuators by using a reduced-order model based on the time-dependent compressible quasi-one-dimensional Euler equations is presented. The following major questions are addressed: 1) which three-dimensional actuator geometries are amenable to the quasi-one-dimensional approximation; 2) which three-dimensional actuator parameters should be retained in the quasi-one-dimensional model; 3) which actuator flow regions are essentially multidimensional and are not candidates for reduced-order modeling; and 4) which geometrical features practically do not contribute to the fidelity of the actuator solution. Constraints that should be imposed on the actuator geometry and the flow parameters are discussed. The accuracy of the quasi-one-dimensional model is validated by comparing the numerical results with experimental data and full time-dependent Navier-Stokes simulation of the same realistic actuator.