Primary Jet Research Articles

Design and analysis of a compact synthetic-jet-based air pump for large airflow

In this paper, a compact synthetic jet actuator comprising a primary jet actuator and a synthetic jet chamber was proposed. This synthetic jet actuator can enhance the total airflow rate by combining the primary, and secondary flows synthesized by the synthetic jet. The oscillating diaphragm and valve parts of the synthetic jet actuator were designed as a closed magnetic flux loop to enhance the magnetic flux density in the coils. The primary jet actuator was designed with a separate inlet and outlet to serve as a heat-dissipation application and prevent the re-ingesting of heated air. Thus, a dynamic model of a synthetic jet actuator was constructed, and motion equations were subsequently derived using plate theory, the Lorentz law, and magnetic flux simulation. The behavior in association with the displacement of the oscillating diaphragm, oscillation frequency, and driving current is discussed in this paper. Finally, an experimental rig was constructed to verify the correctness of the airflow simulations. The synthetic jet actuator was integrated with flow channels, and achieved an airflow rate of 9.23 L/min at a 1.5 V driving voltage.

Aeroacoustics of Three-Stream High-Speed Jets from Coaxial and Asymmetric Nozzles

The development of three-stream variable-cycle turbofan engines for tactical aircraft provides an opportunity for noise reduction by shaping the exhaust of the secondary and tertiary streams. The paper reviews an experimental study of subscale three-stream jets operating at high specific thrust and issuing from rapid-prototyped nozzles. Exhaust conditions at four set points, with variable tertiary pressure ratio and bypass ratio, were determined using thermodynamic cycle analysis. Nozzles were fabricated for each set point and featured coaxial and non-coaxial exit geometries. The operating conditions were simulated using precisely metered helium–air mixtures, and far-field noise surveys were collected using a 24-microphone array. For a low-bypass ratio, a coaxial configuration offers no significant noise benefit compared to the single-stream primary jet. Configurations with offset secondary or tertiary streams offer significant noise reduction in the direction of the thicker flow. For an overall bypass ratio around 0.5, reductions of 5.1 dB in overall sound pressure level and 4.2 dB in effective perceived noise level were attained.

Extreme ultraviolet tomography of multi-jet gas puff target for high-order harmonic generation

A volume, tomographic reconstruction of a novel, multi-jet gas puff target, developed for possible applications in high-order harmonic generation (HHG), is presented. The target, produced by pulsed injection of argon gas through nozzle in a form of linearly oriented small orifices, has been characterized in the extreme ultraviolet at 13.5 nm wavelength. Target density estimations were performed, and 3-D representation of pulsed gaseous target has been obtained by combining 2-D shadowgram images, recorded at various rotation angles. More detailed information about higher-order jets, formed as a result of collisions of primary jets, was obtained. Tomographic studies of such type of targets dedicated for HHG have been obtained to our knowledge for the first time.

Microstructure effects on shock-induced surface jetting

We investigate with large-scale molecular dynamics simulations shock-induced surface jetting from grooved Cu as regards microstructure effects, including jetting mass/velocity ratios, directionality, jetting phase diagram, secondary jetting, and underlying mechanisms. The grooves are of wedged, cylindrical, and rectangular shapes. Other microstructure features explored are half angles, crystal structure asymmetry as represented by grain boundaries, geometrical asymmetry, and deformation heterogeneity. The common fundamental mechanism is that jetting is driven by stress gradients due to transverse mass collision. For symmetrical wedged grooves, the velocity ratio (maximum jet head velocity/free surface velocity of flat surface) increases linearly with decreasing half angle, with a slope similar for different materials and at nano- to macroscales, as indicated by our simulations and previous experiments. However, the jetting factor or mass ratio reaches the maximum at certain intermediate half angle. An impact strength vs. half angle phase diagram is established for a typical case of wedged grooves, useful for predicting the critical parameters for jetting (e.g., the critical impact velocity for a given half angle, as well as deducing yield strength). Small asymmetries, including crystal structure and geometrical asymmetries as well as deformation inhomogeneities, may induce considerable deviation of the jetting direction. Wedged, cylindrical, and rectangular grooves form a geometrical hierarchy. Primary jetting can be well described with wedged grooves, and secondary jetting is a result of collision of primary jets. Rectangular grooves may yield pronounced, velocity-enhanced, secondary jetting.

The shortening of lift-off length associated with jet–wall and jet–jet interaction in a small-bore optical diesel engine

Jet–wall and jet–jet interactions are important diesel combustion phenomena that impact fuel–air mixing, flame lift-off and pollutant formation. Previous studies to visualise a wall-interacting jet in heavy-duty diesel engines suggested that the shortening of lift-off length could occur due to the recirculated hot combustion products that are entrained back into incoming diesel jet. The significance of this effect, known as re-entrainment, can be higher in small-bore engines due to shorter nozzle-to-wall distance and increased wall curvature. In this study, we performed hydroxyl chemiluminescence imaging using an intensified CCD camera and high-speed imaging of natural soot luminosity using a CMOS camera in an automotive-size optical diesel engine. To provide detailed understanding of the reacting jet under the influence of re-entrainment as well as jet–jet interaction, various jet trajectories were investigated using one and two-hole injectors coupled with a modified piston that allows (1) the identification of the shortening of lift-off length, (2) the measurements of lift-off lengths for varying degrees of jet–wall interactions and (3) the clarification on inter-jet spacing effects on the lift-off lengths. Findings from the measurements support the re-entrainment theory because the shortening of lift-off length occurs only before the end of injection when the strong jet momentum induces the ambient gas entrainment. The shortening also shows good correspondence with the penetration of the recirculated jet head back towards the centre of the combustion chamber. Simultaneous imaging of the bowl-wall-interacting jet and cylinder-liner-wall-interacting jet depicts a shorter lift-off length for the bowl-wall-interacting jet, which further supports the importance of re-entrainment on diesel combustion. Inter-jet spacing effects on the lift-off length are also studied utilising two-hole injectors with two inter-jet spacing angles (51.4° and 102.8°). A narrower spacing between the jets results in the shorter lift-off length of the primary jet due to the higher jet–jet interaction even if short injection duration is used to suppress the re-entrainment. For tested conditions of this study, the shortening of lift-off length appears to be more sensitive to jet–jet interaction than to the re-entrainment caused by the jet–wall interaction.

Parametric Effects on Internal Aerodynamics of Lobed Mixer-Ejector With Curved Mixing Duct

The internal flow characteristics inside lobed mixer-ejector with curved mixing duct and the parametric effects on the lobed mixer-ejector performance are investigated numerically and validated by experimental test. The curved mixing duct affects the development of the streamwise vortices induced by the lobed mixer. When the mixing process undergoes the transition from the straight section to the bent section, the flow inside the curved mixing duct is dominated by the impinging and centrifugal effects. In general, the pumping ratio is decreased approximately 20%–30% once the bent section is mounted on the straight duct. The mixer-ejector performance could by improved by increasing the straight section length, due to more fully momentum utilization of primary jet and weaker influence of bent section on the back pressure near nozzle exit. The mixer-ejector pumping capacity is also augmented with the increase of mixing duct area ratio until the area ratio is reached to 3.5. And the fully-utilization of primary jet momentum inside mixing duct with big area ratio needs long mixing distance. The pumping ratio is decreased as the increase of bent angle of curved mixing duct in approximately linear relationship. When the bent angle exceeds 45 deg, the thermal mixing efficiency is decreased rapidly as the increase of bent angle.

Moderate or Intense Low-Oxygen Dilution Oxy-combustion Characteristics of Light Oil and Pulverized Coal in a Pilot-Scale Furnace

This study investigates by experiment the global characteristics of both moderate or intense low-oxygen dilution (MILD) oxy-combustion and air combustion of firing light oil and pulverized coal in a pilot-scale furnace. There are three burner configurations used, i.e., (I) central straight (primary) jet + swirl (secondary) jet, (II) central straight (primary) jet + two side symmetrical (secondary) jets, and (III) central straight (primary) jet + side asymmetrical jet. The furnace centerline temperature, species concentrations, and exhaust emissions are measured and compared for the MILD and conventional combustion cases. For light oil and pulverized coal, the MILD air combustion or oxy-combustion occurs with burner II or III, while the conventional combustion takes place when using burner I. For the light oil, the MILD oxy-combustion can be reached even using pure oxygen. As the MILD combustion is reached, a fairly uniform temperature distribution and low emissions of NO and CO are obtained. Note that burner III produces the largest internal recirculation of the flue gas, lowest peak temperature, and most uniform temperature, whereas the opposite occurs for burner I. Importantly, the MILD combustion is found to reduce the NO emission much more effectively in the oxy-combustion case than in the air combustion case. Moreover, the appearance of the MILD combustion of light oil and pulverized coal differs from the invisible MILD combustion of gaseous fuels. Dark sparks from burning oil droplets or char particles are present in the MILD combustion of light oil or pulverized coal. It is also revealed that the char burnout under the MILD combustion is weaker than that under the conventional combustion.

Effects of area-ratio on the near-field flow characteristics and deflection of circular inclined coaxial jets

An experimental study was carried out on 45° and 60° inclined coaxial jets, where secondary-to-primary jet area- and velocity-ratios were 4.0 and ranged from 0.5 to 2.0 respectively. Results reveal that the use of a relatively larger area-ratio here is able to suppress self-excited jet oscillations seen earlier in comparatively smaller area-ratio jets when velocity-ratio is 1.0. Flow visualization and PIV measurements demonstrate that this is due to the physically wider annular gap associated with a larger area-ratio. This reduces the extent to which primary and secondary ring-vortices can undergo vortex-pairing and merging seen in the previous study. Near-field centerline flow characteristics clarify the impact of area-ratio upon the flow fields, as well as its relationships with velocity-ratio and incline-angle. Unlike relatively smaller area-ratio jets, the effects of the velocity-ratio are found to be insignificant in the lower cases of 0.5 and 1 examined here. Correspondingly, primary jet deflections are found to be comparatively smaller for relatively larger area-ratio jets and significant only when velocity-ratio reaches 2.0. Lastly, jet velocity profile developments reveal that within the present measurement range, the two jet-streams in relatively larger area-ratio jets do not merge as rapidly as smaller area-ratio counterparts, particularly at a velocity-ratio of 2.0.

In Situ PLIF and Particle Image Velocimetry Measurements of the Primary Entrainment Fuel Jet in a Naturally Aspirated Water Heater

The time-averaged characteristics of a fuel jet have been measured via acetone planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) in the primary mixing region of an operating gas-fired water heater. These measurements allow for experimental characterization of the cross-sectional scalar and velocity fields as well as the estimation of the mass entrainment as the flow enters the burner in a practical system. In these experiments, reasonable results were obtained when only the fuel jet was seeded with acetone or PIV particles rather than the entire flow, thus demonstrating the potential for simplified experimental configurations in some applications where controlling or seeding the entire flow may be difficult. The entrainment characteristics of the fuel jet are compared with benchmarks from literature. The commercial device exhibits a larger mass entrainment rate than is found in typical free jets that have been studied in the literature. This may be a result of the jet's low Reynolds number (9,600) in comparison with other literature studies, and a result of initial conditions.

A Survey of Performance of Fluidic Thrust Vectoring Mechanisms by Numerical and Experimental Studies

The objectives of this paper are to compare the effect of fluidic thrust vectoring (FTV) parameters on two converging-diverging nozzle models and discuss the relation of evaluation methods between thrust pitching angle and thrust pitching moment. The interaction of a secondary jet with the primary jet flow in two nozzle models is also investigated. Numerical and experimental studies of FTV were done with nozzle model 1 and nozzle model 2. The experiments are carried out with a nozzle pressure ratio (NPR) of 3-10, a secondary pressure ratio (SPR) of 1, 2 and 3, and two different secondary jet locations. Numerical simulations of the nozzle flow are performed with solving the Navier-Stokes equation, and the parameters are the same with the experimental conditions. Combinations of NPR, SPR, and secondary jet location are set to compare the performance of the two nozzle models. The thrust pitching moment and the thrust pitching angle are determined to evaluate the FTV performance. Positive inter-relation betwe...

WISE J233237.05–505643.5: A DOUBLE-PEAKED, BROAD-LINED ACTIVE GALACTIC NUCLEUS WITH A SPIRAL-SHAPED RADIO MORPHOLOGY

We present radio continuum mapping, optical imaging and spectroscopy of the newly discovered double-peaked broad-lined AGN WISE J233237.05-505643.5 at redshift z = 0.3447. This source exhibits an FR-I and FR-II hybrid-morphology, characterized by bright core, jet, and Doppler-boosted lobe structures in ATCA continuum maps at 1.5, 5.6, and 9 GHz. Unlike most FR-II objects, W2332-5056 is hosted by a disk-like galaxy. The core has a projected 5" linear radio feature that is perpendicular to the curved primary jet, hinting at unusual and complex activity within the inner 25 kpc. The multi-epoch optical-near-IR photometric measurements indicate significant variability over a 3-20 year baseline from the AGN component. Gemini-South optical data shows an unusual double-peaked emission-line features: the centroids of the broad-lined components of H-alpha and H-beta are blueshifted with respect to the narrow lines and host galaxy by ~ 3800 km/s. We examine possible cases which involve single or double supermassive black holes in the system, and discuss required future investigations to disentangle the mystery nature of this system.

Closed-form model for the analysis of W-type shaped charges

This paper presents a closed-form model for the analysis of symmetric planar W-type shaped charges (WSCs) with two V-sections, which produce two primary cores and two primary jets. If these two V-sections have proper asymmetry, these primary cores will force two primary jets into a secondary core formed on the axis of symmetry of a planar symmetric WSC. For the analysis of such a planar WSC, a complete generalized model for an asymmetric planar V-shaped charge (VSC) with any desired order of asymmetry is mandatory. In this paper, the model is applied to describe the secondary jet formation in the WSC. By presenting a closed-form analysis of the WSC, the secondary jet specifications can be easily evaluated and, thus, can be compared with respect to the jet quantities in symmetric or asymmetric VSCs. Finally, for the primary and secondary jets, the coherency conditions are investigated, and the critical parameters responsible for these conditions are determined.

A Survey of Fluidic Thrust Vectoring Nozzle by Numerical Analysis

Numerical investigations are conducted to simulate the flow field of a 2D converging-diverging nozzle, for fluidic thrust vectoring. The numerical simulation of nozzle flow is carried out with Navier-Stokes equations model. Simulations are done with different primary and secondary jet conditions. The numerical results show that the smaller of the distance between secondary jet and exit, the larger is the thrust deflection angle. As the injection pressure ratio increases, the deflection angle increases followed on the premise of not far between secondary jet port and exit. The parameters play important roles on thrust vectoring capability.

Flame pattern, temperatures and stability limits of pulverized oxy-coal combustion

The challenges in maintaining a stable oxy-coal flame have been reported in the open literature. In case of pulverized coal combustion, narrower flammable regimes arise not only of differences in the feed gas composition, but also due to changes in the flow dynamics because of reduced volume flow rate through the burners to match similar temperatures and radiative heat transfer within the furnace. The present work focuses on the study of flame structure and stability of pre-dried lignite fired by a staged feed-gas burner. Experimental runs were carried out in a 0.40MWth laboratory facility, with the objective of investigating the effects of swirl strength and feed gas distribution in the burner registers. To assess the experimental data, a numerical study of the non-reacting flow in the near burner region is performed. Predicted flow pattern and flame images show that the primary fuel jet penetrates the internal recirculation zone, forming an annular doughnut reverse flow region for both firing conditions and resembling a type-1 flame pattern. Temperature measurements indicate that the feed gas distribution among the burner registers control the flame temperature in parallel with the swirl number in both air-fired and oxy-fired environments. The oxy-fuel cases exhibite markedly reduced temperatures on the flame axis. This difference in the core arises not just from the more pronounced penetration depth of the primary jet, but also due to reaction mechanisms including pyrolysis and gasification reactions at the higher concentrations of CO2 and water vapor. Flame stabilization is shown to be strongly dependent on an appropriate distribution of the feed gas and strength of swirling flow in the burner front. The results correlated in terms of swirl number, secondary/tertiary flow ratio and secondary/primary axial momentum point to similarities in the stability limits between air-firing and oxy-firing.

Ejector Scavenging of Bearing Chambers. A Numerical and Experimental Investigation

Oil system architecture in aero engines has remained almost the same for the last 30 years. At least one oil feed pump is responsible for distributing pressurized oil into the bearing chambers, and several scavenge pumps are responsible for evacuating the bearing chambers from the oil and the air mixture. Air is used as the sealing medium in bearing chambers and is the dominant medium in terms of volume occupation and expansion phenomena. In order to simplify the oil system architecture and thus improve the system's reliability with less mechanical parts and also decrease weight, an ejector system has been designed for scavenging bearing chambers. The idea behind the ejector is to use high-pressure oil from the feed pump and use it for feeding the ejector's primary jet. Through the momentum transfer between the pressurized oil at the jet's tip and the two-phase mixture of air and oil from the bearing chamber, the mixture will be discharged into the oil tank. In order to design the ejector for aero engine applications, engine-relevant performance conditions had to be considered. The design was performed using a one-dimensional analysis tool and then considerably refined by using the numerical tool ansys cfx. In a further step, the ejector was manufactured out of pure quartz glass and was tested in a lube rig with a bearing chamber, which has evolved from a real engine application. In the bearing chamber, engine-relevant performance conditions were simulated. Through the provided instrumentation for pressures, temperatures, and air/oil flows, the performance characteristics of the ejector were assessed and were compared to the analytic and numerical results. A high-speed camera was used to record the two-phase flow downstream of the bearing chamber in the scavenge pipe. This work is part of the European Union-funded research program Engine LUBrication System TechnologieS (ELUBSYS) within the 7th EU Frame Programme for Aeronautics and Transport (AAT.2008.4.2.3).

Boiling flow simulations on adaptive octree grids

Boiling flow simulations are conducted on adaptive octree grids. A phase change model consistent with the mixture formulation, in conjunction with the Volume-of-Fluid (VOF) model, is used to track the liquid–vapor interface. Test cases including Rayleigh Taylor instability and bubble growth in a uniform superheat are conducted to validate the phase change model on adaptive grids. The validated model is then used to conduct film boiling simulations on both two-dimensional and three-dimensional adaptive grids. The average wall Nusselt number agrees well with the widely accepted correlations of Berenson (1961) and Klimenko (1981) and Klimenko and Shelepen (1982) for film boiling on a horizontal surface. For the test cases presented, the efficiency of the adaptive technique, as measured by the adaptive mesh refinement (AMR) efficiency, is mostly in the range of 50–80%. Although this efficiency is a function of the nature and dimensionality of the problem, this range of efficiency is comparable to those obtained in the simulations of primary jet atomization conducted by Fuster et al. (2009). This work opens the prospect of conducting more realistic (three-dimensional) multi-modal boiling flow simulations, and problems of similar complexity, in an efficient manner.

Sensitivity analysis of LES–CMC predictions of piloted jet flames

The sensitivity of Large Eddy Simulation with Conditional Moment Closure (LES–CMC) simulations of the Sandia piloted jet Flames D and F to various parameters have been investigated. It was found that while an LES grid may sufficiently resolve velocity fields, the conditional scalar dissipation rate obtained may still be affected by grid size due to the calculation of sub-grid scalar dissipation rate, and this can affect the degree of localised extinction predicted. A study of the relative size of the terms in the CMC equation during an extinction/reignition event showed that transport, including in the cross stream direction, plays a key role. The results are sensitive to the choice of inlet boundary conditions as extinction is only observed when the inert-mixing distributions in mixture fraction space are used as inlet conditions for the CMC equation in the primary jet and air jets.

Active Control of Methane-Air Coaxial Jet Mixing and Combustion with Arrayed Miniature Jet Actuators

Large-scale vortical structures and associated mixing in a methane-air coaxial jet are actively controlled by manipulating the initial jet shear layer with miniature jet actuators installed on the inner surface of the annular nozzle. The periodic radial miniature jet injections are realized by using a rapid-response pneumatic servovalve, and sinusoidal/pulsed flowing are employed in the present study. The spatio-temporal primary jet structures are investigated through phase-locked 2C-PIV (2 Component Particle Image Velocimetry) and Stereoscopic-PIV. In the pulsed configuration, it is found that intense vortex rings are produced in phase with the periodic control input regardless of the valve-driven frequency fv examined. When the Strouhal number Stv, which is defined with fv, is larger than unity, the vortex rings are densely-shed and thus methane/air mixing is prompted with low periodic fluctuation. The diameter of the vortices becomes small as Stv is increased, so that the transport range of the inner methane and outer air fluids can be controlled by changing Stv. In addition, the evolution of counter-rotating streamwise vortex pair is also confirmed. These streamwise vortices are formed as a result of the radial injection of the miniature jet, which leads to entrainment of the ambient fluid near the primary jet shear layer. They contribute the mixing enhancement in the downstream, where the vortex rings are broken down. Moreover, it is demonstrated that the coaxial jet flame characteristics such as flame holding are drastically improved by the present jet control scheme.

S052033 プラズマアクチュエータを用いた噴流拡散制御の研究 : 同心円型アクチュエータによる間欠制御([S052-03]プラズマアクチュエータ(3))

In this study, the concentric DBD plasma actuator was applied the diffusion control of the round jet. The induced flow by the plasma actuator was used as a secondary flow that controls a round jet. It was examined the change of the induced flow and the change of the jet structures by the continuous operating the intermittent operating of the plasma actuator. When it is continuously operated the plasma actuator, the induced flow was annular flow the circumference of the circular jet. And the velocity of the primary jet was increasing by the contraction effect of the induced flow. But, when it is intermittent operated, the induced flow becomes half velocity in the case of continuous operating, and the diffusion of the jet was suppressed.

Experimental and Numerical Research of a Novel Combustion Chamber for Small Gas Turbine Engines

New combustion chamber concept (based on burner JETIS-JET Induced Swirl) for small gas turbine engine (up to 200kW) is presented in this article. The combustion chamber concept is based on the flame stabilization by the generated swirl swirl generated by two opposite tangentially arranged jet tubes in the intermediate zone, this arrangement replaces air swirler, which is very complicated and expensive part in the scope of small gas turbines with annular combustion chamber. The mixing primary jets are oriented partially opposite to the main exhaust gasses flow, this enhances hot product recirculation and fuel-air mixing necessary for low NOx production and flame stability. To evaluate the designed concept a JETIS burner demonstrator (methane fuel) was manufactured and atmospheric experimental measurements of CO, NOx for various fuel nozzles and jet tubes the configuration were done. Results of these experiments and comparison with CFD simulation are presented here. Practical application of the new chamber concept in small gas turbine liquid fuel combustor was evaluated (verified) on 3 nozzles planar combustor sector test rig at atmospheric conditions results of the experiment and numerical simulation are also presented.