Jet Configuration Research Articles

Dominant SST Mode in the Southern Hemisphere Extratropics and Its Influence on Atmospheric Circulation

The variability in the Southern Ocean (SO) sea surface temperature (SST) has drawn increased attention due to its unique physical features; therefore, the temporal characteristics of the SO SST anomalies (SSTA) and their influence on extratropical atmospheric circulation are addressed in this study. Results from empirical orthogonal function analysis show that the principal mode of the SO SSTA exhibits a dipole-like structure, suggesting a negative correlation between the SSTA in the middle and high latitudes, which is referred to as the SO Dipole (SOD) in this study. The SOD features strong zonal symmetry, and could reflect more than 50% of total zonal-mean SSTA variability. We find that stronger (weaker) Subantarctic and Antarctic polar fronts are related to the positive (negative) phases of the SOD index, as well as the primary variability of the large-scale SO SSTA meridional gradient. During December–January–February, the Ferrel cell and the polar jet shift toward the Antarctic due to changes in the SSTA that could be associated with a positive phase of the SOD, and are also accompanied by a poleward shift of the subtropical jet. During June–July–August, in association with a positive SOD, the Ferrel cell and the polar jet are strengthened, accompanied by a strengthened subtropical jet. These seasonal differences are linked to the differences in the configuration of the polar jet and the subtropical jet in the Southern Hemisphere.

Evolution and Size Distribution of Solid CO2 Particles in Supercritical CO2 Releases

CO2 transportation safety is important for the successful implementation of carbon capture and storage (CCS) projects. The formation of solid CO2 is a unique phenomenon in high-pressure CO2 release. The evolution and size distribution of dry ice particles have a significant impact on assessment of the consequences of accidental release of supercritical CO2 from a pipeline. The motivation is to investigate the particle behavior and size distribution and understand how the impact factors affect them. An experiment with various measurement methods was developed to carry out controllable CO2 release from a high-pressure vessel. The macroparameters such as jet configuration, temperature, and velocity were recorded. Meanwhile, motion of the microparticles was also analyzed. In addition, the effects of initial pressure and temperature on the particle size distribution were investigated. The results showed that the agglomeration influenced the size distribution at different positions of the jet.

Influence of Propulsion Type on the Stratified Near Wake of an Axisymmetric Self-Propelled Body

To better understand the influence of swirl on the thermally-stratified near wake of a self-propelled axisymmetric vehicle, three propulsor schemes were considered: a single propeller, contra-rotating propellers (CRP), and a zero-swirl, uniform-velocity jet. The propellers were modeled using an Actuator-Line model in an unsteady Reynolds-Averaged Navier–Stokes simulation, where the Reynolds number is R e L = 3.1 × 10 8 using the freestream velocity and body length. The authors previously showed good comparison to experimental data with this approach. Visualization of vortical structures shows the helical paths of blade-tip vortices from the single propeller as well as the complicated vortical interaction between contra-rotating blades. Comparison of instantaneous and time-averaged fields shows that temporally stationary fields emerge by half of a body length downstream. Circumferentially-averaged axial velocity profiles show similarities between the single propeller and CRP in contrast to the jet configuration. Swirl velocity of the CRP, however, was attenuated in comparison to that of the single propeller case. Mixed-patch contour maps illustrate the unique temperature distribution of each configuration as a consequence of their respective swirl profiles. Finally, kinetic and potential energy is integrated along downstream axial planes to reveal key differences between the configurations. The CRP configuration creates less potential energy by reducing swirl that would otherwise persist in the near wake of a single-propeller wake.

Coastal Upwelling Front Detection off Central Chile (36.5–37°S) and Spatio-Temporal Variability of Frontal Characteristics

In Eastern Boundary Upwelling Systems, cold coastal waters are separated from offshore by a strong cross-shore Sea Surface Temperature (SST) gradient zone. This upwelling front plays a major role for the coastal ecosystem. This paper proposes a method to automatically identify the front and define its main characteristics (position, width, and intensity) from high resolution data. The spatio-temporal variability of the front characteristics is then analyzed in a region off Central Chile (37°S), from 2003 to 2016. The front is defined on daily 1 km-resolution SST maps by isotherm T0 with T0 computed from mean SST with respect to the distance from the coast. The probability of detecting a front, as well as the front width and intensity are driven by coastal wind conditions and increased over the 2007–2016 period compared to the 2003–2006 period. The front position, highly variable, is related to the coastal jet configuration and does not depend on the atmospheric forcing. This study shows an increase by 14% in the probability of detecting a front and also an intensification by 17% of the cross-front SST difference over the last 14 years. No trend was found in the front position.

Influence of multi-perforation synthetic jet configuration on heat transfer enhancement

The multi-perforated wall of synthetic jets bas been analyzed to enhance heat transfer under laminar and turbulence cross-flow and for several dynamic configurations. To study the role of cross-flow and synthetic jet interactions, a dedicated experimental set-up was developed with convective heat transfer coefficients along the wall. Multi-perforated results were directly compared to single synthetic jet data. Sensitive parameters such as jet frequency, piston amplitude displacement and cross-flow velocity were determined. Heat transfer from the synthetic jet device can be amplified from 23 to as much as 175% depending on experimental conditions. The role of multi-perforating plate with regard to the single row configuration is clearly demonstrated. It is reinforced by continuous interaction between the main flow and synthetic jets.

Advanced CFD modelling of air and recycled flue gas staging in a waste wood-fired grate boiler for higher combustion efficiency and greater environmental benefits

Grate-fired boilers are commonly used to burn biomass/wastes for heat and power production. In spite of the recent breakthrough in integration of advanced secondary air systems in grate boilers, grate-firing technology needs to be advanced for higher efficiency and lower emissions. In this paper, innovative staging of combustion air and recycled flue gas in a 13 MWth waste wood-fired grate boiler is comprehensively studied based on a numerical model that has been previously validated. In particular, the effects of the jet momentum, position and orientation of the combustion air and recycled flue gas streams on in-furnace mixing, combustion and pollutant emissions from the boiler are examined. It is found that the optimized air and recycled flue gas jets remarkably enhance mixing and heat transfer, result in a more uniform temperature and velocity distribution, extend the residence time of the combustibles in the hot zone and improve burnout in the boiler. Optimizing the air and recycled flue gas jet configuration can reduce carbon monoxide emission from the boiler by up to 86%, from the current 41.0 ppm to 5.7 ppm. The findings of this study can serve as useful guidelines for novel design and optimization of the combustion air supply and flue gas recycling for grate boilers of this type.

Large-eddy simulation of circular jet mixing: Lip- and inner-ribbed nozzles

Jet mixing of a circular nozzle in two different configurations is extensively investigated using large-eddy simulation (LES), i.e., the lip-ribbed one with an annular rib at the nozzle exit, and the inner-ribbed one with a rib placed 1.0D upstream of the nozzle exit; the latter one is particularly selected to generate unsteady reattachment of the separated shear layer near the nozzle exit. A jet issuing from a hydrodynamically smooth pipe with fully developed turbulent flow into a larger cylindrical domain (a ‘pipe jet’) is used as the baseline configuration for comparison. The Reynolds number based on the mean (bulk) velocity in the pipe and the pipe diameter is 6000. Validation of the LES approach is performed on the baseline pipe jet using particle image velocimetry (PIV) and laser-induced fluorescence (LIF) measurements; perfect agreement is obtained in terms of the mean streamwise velocity and concentration and their fluctuation parts. The LES results show that both ribbed jet configurations exhibit higher levels of mixing than the pipe jet; the most rapid decay of the centreline concentration and the largest entrainment are observed in the inner-ribbed jet. The inner-ribbed nozzle induced high flow fluctuations behind the rib due to frequent reattachment of flow to the pipe wall that are similar to what is known as fluid flapping motion. These flapping motions give rise to the energetic large-scale structures at the pipe exit and serve as an effective control imposed on the jet. The ‘slice’ proper orthogonal decomposition analysis performed on the flow helps to identify the jet's ‘preferred modes’ by selecting the most energetic structures with a specified azimuthal wavenumber. In the lip-ribbed jet, the separated shear layer modified the frequencies of the axisymmetric mode but made a limited contribution to the energy level of the jet preferred mode. In the inner-ribbed jet, however, the jet preferred modes were extensively altered. The single- and double-helical modes (m=1 and 2) were substantially intensified, with increasing energy levels up to 58%, giving rise to the significant enhancement of jet mixing, especially in the upstream regions.

Fabrication by Laser Irradiation in a Continuous Flow Jet of Carbon Quantum Dots for Fluorescence Imaging.

Fluorescent carbon quantum dots (CQDs) are synthesized by laser irradiation of carbon glassy particles suspended in polyethylene glycol 200 by two methods, a batch and a flow jet configuration. The flow jet configuration is carried out by the simple combination of common laboratory objects to construct a home-made passage reactor of continuous flow. Despite the simplicity of the system, the laser energy is better harvested by the carbon microparticles, improving the fabrication efficiency a 15% and enhancing the fluorescence of CQDs by an order of magnitude in comparison with the conventional batch. The flow jet-synthesized CQDs have a mean size of 3 nm and are used for fluorescent imaging of transparent healthy and cancer epithelial human cells. Complete internalization is observed with a short incubation time of 10 min without using any extra additive or processing of the cell culture. The CQDs are well fixed in the organelles of the cell even after its death; hence, this is a simple manner to keep the cell information for prolonged periods of time. Moreover, the integrated photostability of the CQDs internalized in in vitro cells is measured and it remains almost constant during at least 2 h, revealing their outstanding performance as fluorescent labels.

Control of vortex-induced motion in multi-column offshore platform by near-wake jets

Vortex-induced motion (VIM) poses a serious challenge in many engineering applications such as offshore structures, floating wind turbines, and high rise buildings. In particular, significant aspects of VIM have to be considered in offshore platforms subjected to high currents. The objective of this numerical study is to investigate the VIM suppression of multi-column floating platforms by injecting steady near-wake jets at the wake side of the columns. Before proceeding to the blowing-jet based flow control method, the transverse VIM amplitude of floating platform is validated with the model test data. We perform a systematic investigation of 3D scaled model with and without prescribed jet flows for varying reduced velocity (Ur) at a fixed mass ratio m*=0.83, the damping ratio ζ=0.01 and the Reynolds number Re=20,000. The numerical investigations are carried out for different near-wake jet configurations at reduced velocity Ur=10. We assess the response characteristics and flow profile patterns to identify a suitable configuration of blowing jet along the columns. We demonstrate that the semi-submersible with elongated near-wake jet configuration is efficient in suppressing VIM in comparison to other near-wake jet configurations and the uncontrolled no-jet case. The vibration amplitudes, the force coefficients and the flow patterns of semi-submersible with the blowing-based control technique are further examined for various mass flow rate coefficients. From our studies, we observe approximately 30% reduction of forces and the amplitudes for the offshore system with the prescribed jet flow compared to the system without near-wake jets. The optimal Vjet/U is estimated to be in the range of 2.5–5, for the effective VIM suppression, where Vjet and U are the prescribed jet flow speed and the free-stream speed, respectively. To understand the underpinning of VIM suppression mechanism, the vortex dynamics and flow patterns in the near-wake region of a freely vibrating semi-submersible platform with the near-wake jet are explored. For this numerical study, we employ a stabilized finite element formulation with an explicit dynamic subgrid-scale model to simulate the fluid-structure interaction subjected to a turbulent wake flow.

Numerical and Experimental Analysis of Impinging Synthetic Jets for Cooling a Point-Like Heat Source

High power light emitting diodes (LEDs) being used for low and high beam in automotive lighting need active cooling of their heat sinks by radial or axial fans. But the moving elements of the fan cause abrasion, noise, and high energy consumption. Synthetic jets can replace conventional fans with their disadvantages and allow the directed cooling of LEDs. Therefore, in this paper, flow and heat transfer characteristics of impinging synthetic jets are investigated numerically and experimentally as an alternative to cooling LEDs with fans. It is shown that the impact plate brings forward the laminar-turbulent transition of the jets temporally and spatially. The impact plate itself should not be positioned in the region of the free jet's transition height. Increasing the frequency of the synthetic jet has a greater influence on the heat transfer compared to an increase in amplitude. The maximum cooling performance is achieved for all jet configurations with moderate distances between the orifice and the impact plate. In this case, the jet reaches its highest mass flow and impulse and its lowest temperature.

Turbulent jet simulation using high-order DG methods for aeroacoustic analysis

This work deals with the application of a high-order discontinuous Galerkin (DG) method to predict the noise generated by a subsonic free jet at high Reynolds number ReD=106, based on the nozzle diameter. The large-eddy simulation (LES) technique is used to compute the turbulent flow dynamics and acoustics in the near field. The estimation of the far-field noise is made by means of the Ffowcs Williams and Hawkings surface integral formulation. A fourth-order DG simulation of this jet configuration is presented in this paper. The DG simulation is based on the Smagorinsky model and the computational grid employed is fully tetrahedral. This DG simulation is compared to an LES computation performed in previous work by means of a second-order finite-volume (FV) solver using a similar type of grid and SGS model. The results from the DG and FV computations are also compared to the available experimental data. It appears from this study that the DG computation is able to resolve higher-frequency components close to the nozzle exit, which is related to the better match found with the experimental data in the far field.

Conceptual design of high-speed underwater jet engine using high concentration of hydrogen peroxide

The conceptual design of high-speed underwater jet engine was conducted and demonstrated using high concentration of hydrogen peroxide as a green propellant. On the basis of the principles of steam jet ejector, the central water jet configuration was applied for the engine where a central water jet was surrounded by an annular steam flow. The annular steam flow as the primary fluid was the decomposition gas of hydrogen peroxide and cold water was the secondary fluid. The catalyst pack was composed of the alumina pellets doped with manganese oxides. The performance evaluation of the engine was performed without the flow field of the secondary fluid. The demonstrator successfully generated a practical propulsive force, which could be applied for the systems of unmanned underwater vehicles. For design of experiments, the nozzle exit areas were dealt with. It should be ensured that the exit area of nozzle was sufficiently large to prevent thrust instabilities due to the disturbance in the high-speed flows. In contrast, the excessively large area of the nozzle exit might decrease the efficiency of the engine performance in that the geometry of the engine failed to encourage the heat energy transfer between the primary and the secondary fluids.

Experimental Characterization of Intrinsic Properties Associated With Air-Assisted Liquid Jet and Liquid Sheet

The present study focuses on experimental characterization of interfacial instability pertinent to liquid jet and liquid sheet in the first wind-induced zone. To accomplish this objective, the interfacial wave growth rate, critical wave number, and breakup frequency associated with air-assisted atomizer systems were extracted by utilizing high-speed flow visualization techniques. For a range of liquid to gas velocities tested, nondimensionalization with appropriate variables generates the corresponding correlation functions. These functions enable to make an effective comparison between interfacial wave developments for liquid jet and sheet configurations. It exhibits liquid sheets superiority over liquid jets in the breakup processes leading to efficient atomization.

Inverse optimization design of an impinging co-axial jet in order to achieve heat flux uniformity over the target object

In this study, co-axial impinging jet was optimized in order to obtain uniform heat flux over an isothermal heated surface by determining four design variables including geometrical and flow variables. The governing equations were solved using the finite volume method for a laminar, incompressible, and axisymmetric flow. The solution of inverse design problem was achieved by minimizing the root mean square of the difference between the local Nusselt number and the uniform design Nusselt number. A combination of pattern search and gradient-based methods was used for optimization. Also a co-axial jet with a new geometry was presented to improve the objective function and two design variables were added to the four previous variables. Optimization was performed for two jet configurations under 15 different conditions. Heat flux uniformity was obtained by these two jets with acceptable errors less than 2% for the outer jet to the target surface diameter ratios of higher than 0.6. The proposed co-axial jet showed its superiority at the small diameter ratios (0.4 and 0.3) and it reduced the error significantly (about 50%) for design Nusselt numbers of 7 and 10.

Large-Eddy simulation of an impinging heated jet for a small nozzle-to-plate distance and high Reynolds number

This paper reports on the investigation of an original impinging jet configuration through a wall-resolved large-eddy simulation. The heated jet issues from a fully developed pipe flow at temperature of 130 °C and a Reynolds number based on the bulk velocity of 60000. The impinged plate is located three diameters downstream of the pipe exit. The CFD results have been validated against a specifically-created experimental database (Grenson et al., 2016). The overall statistical fields are well retrieved by the simulation both in the free jet and the wall jet region. In particular, the secondary maximum at the radial location r/D=2 in the Nusselt number distribution is well predicted by the simulation. The underlying mechanisms from which the secondary maximum originates has been investigated. This analysis revealed that small-scale hot spots of strong convective heat transfer coefficient are responsible for the emergence of this secondary maximum. It is shown that the hot spots can be associated either to local unsteady “separation” of the flow or streaks-like structures above the impinging plate.

Numerical assessment of two phase flow modeling using plunging jet configurations

This paper presents unsteady numerical simulation of air entrainment by water plunging jet using Volume of fluid model coupled to PLIC algorithm for phase interface reconstruction and Euler–Euler model considering continuous water phase and dispersed air phase.Plunging jet simulations aim to find out the ability of each model to reproduce air entrainment phenomenon. The investigation tackled the air plume depth, air entrainment rate and velocity profiles. Further simulations were performed to highlight the influence of the free jet length on the entrainment rate and plume development below the free surface.The results show good agreement with the available experimental data particularly velocity profiles in both radial and axial directions, plume shape and development along transient intervals. The initial impact is well reproduced referring to literature and bubbles penetration depth is comparable to the empirical correlations.It is noticed that further improvements are required for interfacial forces modeling in volume of fluid model to ensure good control of bubbles migration in the plume region.Entrainment rate discrepancies in Euler–Euler model are related to the lack of information about interface location due to averaging process; hence, an appropriate interface detection function is needed.

Batch Injection Analysis‐Multiple Pulse Amperometric Fingerprint: A Simple Approach for Fast On‐site Screening of Drugs

AbstractIn this work, the association of batch injection analysis with multiple pulse amperometric detection (BIA‐MPA) is presented as a new approach to obtain drugs fingerprints. To illustrate the potential of this screening method, tablets containing sildenafil as the active substance were used. Here, a sequence of three potential pulses as a function of time (+1.3, +1.6 and +2.1 V) were applied on a boron‐doped diamond electrode while reproducible injections were performed in a BIA cell (wall jet configuration). The chemical profile of the respective drug combined three ratios among the peak currents obtained in each amperogram: R1=ipa1.6V/ipa1.3V, R2=ipa2.1V/ipa1.6V, R3=ipa2.1V/ipa1.3V. This simple protocol allowed discrimination between Viagra® (reference)/generic and two smuggled tablets, as well as pure Viagra® from Viagra® adulterated with other electroactive compounds (caffeine, dipyrone, paracetamol and tadalafil). For comparison, screening of these samples was also performed using square wave voltammetry combined with a chemometric method (principal component analysis), in which was achieved similar discrimination by one or other strategy for the most of drugs. This new BIA‐MPA fingerprinting combines desirable features in forensic science such as low cost, simplicity, high sample throughput (two drugs discerned in less than 30 s) and portability (screening at the place of the seizure).

A new method for extending solutions to the self-similar relativistic magnetohydrodynamic equations for black hole outflows

The paradigm in which magnetic fields play a crucial role in launching/collimating outflows in many astrophysical objects continues to gain support. However, semi-analytical models including the effect of magnetic fields on the dynamics and morphology of jets are still missing due to the intrinsic difficulties in integrating the equations describing a collimated, relativistic flow in the presence of gravity. Only few solutions have been found so far, due to the highly nonlinear character of the equations together with the need to blindly search for singularities. These numerical problems prevented a full exploration of the parameter space. We present a new integration scheme to solve r-self-similar, stationary, axisymmetric magnetohydrodynamics equations describing collimated, relativistic outflows crossing smoothly all the singular points (Alfven point and modified slow/fast points). For the first time, we are able to integrate from the disk mid-plane to downstream of the modified fast point. We discuss an ensemble of jet solutions, emphasising trends and features that can be compared to observables. We present, for the first time with a semi-analytical MHD model, solutions showing counter-rotation of the jet for a substantial fraction of its extent. We find diverse jet configurations with bulk Lorentz factors up to 10 and potential sites for recollimation between $10^3-10^7$ gravitational radii. Such extended coverage of the intervals of quantities, such as magnetic-to-thermal energy ratios at the base or the heights/widths of the recollimation region, makes our solutions suitable for application to many different systems where jets are launched.

Experimental study of the aeroacoustic interaction between two supersonic hot jets

The first stage of space launchers often use multiple engines. The supersonic jet noise at lift-off is a major source of vibrations for the launcher’s equipments and payloads. In parallel with the development of the Ariane 6 launcher and its launch pad ELA4, the CNES MARTEL test bench have been improved in order to study experimentally the aeroacoustic interaction between two hot supersonic jets (mach 3, 2000K). In collaboration with the PPRIME laboratory of the University of Poitiers, acoustic and PIV measurements have been made in the free jets configurations. Further test campaigns will study the interaction of jets inside the flame duct, and their impingement on the launch table.

Volume reconstruction of an impinging jet obtained from stereoscopic-PIV data using POD

Ventilation and air conditioning systems are specified by the configuration of jets which may interact with sharp edges when travelling from the nozzle. These configurations could in some cases be a source of aeraulic and acoustic discomfort. In order to solve this disadvantage, the volumetric flow dynamics involved in these configurations should be understood and controlled. The objectives of the present study is to reconstruct and analyse the volume using stereoscopic PIV measurements (SPIV). To do so, an experimental platform has been developed to generate a flow at different Reynolds numbers. The dynamics of these flows are investigated experimentally using the PIV technique. The kinematic fields of parallel planes are measured by SPIV acquisitions in order to study the corresponding fluid flow. The snapshot proper orthogonal decomposition technique (POD) is applied in order to obtain the most energetic modes of the jet. Three modes were sufficient to reconstruct each of the measured planes. A trigger signal was chosen to determine the phase of the planes which are unsynchronized. The volume is afterwards, obtained by an interpolation of the reconstructed planes. This reconstruction is highlighted in order to study the dynamics of the transverse vortices. Several vortex detection criteria have been tested to locate and analyse the vortex structures.