Pulsed Jet Research Articles

Tomographic optical emission spectroscopy of an atmospheric pressure plasma jet and surface ionization waves on planar and structured surfaces

In this paper, an approach for 3D plasma structure diagnostics using tomographic optical emission spectroscopy (Tomo-OES) of a nanosecond pulsed atmospheric pressure plasma jet (APPJ) is presented. In contrast to the well-known Abel inversion, Tomo-OES does not require cylindrical symmetry to recover 3D distributions of plasma light emission. Instead, many 2D angular projections are measured with intensified cameras and the multiplicative algebraic reconstruction technique is used to recover the 3D distribution of light emission. This approach solves the line-of-sight integration problem inherent to optical diagnostics, allowing recovery of localized OES information within the plasma that can be used to better infer plasma parameters within complex plasma structures. Here, Tomo-OES was applied to investigate an APPJ operated with helium in ambient air and impinging on planar and structured dielectric surfaces. Surface charging caused the guided streamer from the APPJ to transition to a surface ionization wave (SIW) that propagated along the surface. The SIW experienced variable geometrical and electrical material properties as it propagated, leading to 3D configurations that were non-symmetric and spatially complex. Light emission from He, N, and N2 were imaged at ten angular projections and the respective time-resolved 3D emission distributions in the plasma were then reconstructed. The spatial resolution of each tomographic reconstruction was 7.4 µm and the temporal resolution was 5 ns, sufficient to observe the guided streamer and the effects of the structured surface on the SIW. Emission from He showed the core of the jet and emission from N and N2 indicated effects of entrainment of ambient air. Penning ionization of N2 created a ring or outer layer of N that spatially converged to form the ‘plasma bullet’ or spatially diverged across a surface as part of a SIW. The SIW entered trenches of size 150 µm, leading to decreases in plasma light emission in regions above the trenches. The plasma light emission was higher in some regions with trenches, possibly due to effects of field enhancement.

Experimental and numerical investigation of an S-shaped duct using pulsed jet actuators with multiple angles

The complexity and twistiness of the ultra-compact S-shaped ducts with high curvature aggravate the internal flow separation, which affects the intake efficiency. An advanced flow control technology, pulsed jet actuators (PJAs), was implemented to improve the flow condition in the S-shaped duct at a Mach number of 0.4. Based on the considerable control effect obtained from the experimental studies, the influence of the pulsed jet angles on the S-shaped duct was further investigated by utilizing the unsteady Reynolds-averaged Navier–Stokes equations (URANS). The jet angles as a research parameter were set to 15°, 30°, 45°, 60° and 75°, respectively. Moreover, steady jet schemes were adopted to reveal the unsteady flow control mechanism of the pulsed jet. The results showed that the overall performance of the S-shaped duct with the pulsed jet was improved, mainly attributed to the additional kinetic energy and dispersion. The total pressure loss coefficient and distortion index at the aerodynamic interface plane (AIP) were decreased by 7 % and 2.9 % when the pulsed jet angle was 30°. Furthermore, the temperature distortion was significantly improved, with a maximum temperature rise rate of −87.59 K/s. It is concluded that the suitable penetration of the mainstream is the prerequisite for achieving the best flow control effect.

N → π* Interaction Enabling Transient Inversion of Chirality.

This study reports the observation and characterization of two isomers of the acrolein dimer by using high-resolution rotational spectroscopy in pulsed jets. The first isomer is stabilized by two hydrogen bonds, adopting a planar configuration, and is energetically favored over the second isomer, which exhibits a dominant n → π* interaction in a nearly orthogonal arrangement. Surprisingly, the n → π* interaction was revealed to enable a concerted tunneling motion of two moieties along the carbonyl group. This motion leads to the inversion of transient chirality associated with the exchange of donor-acceptor roles, as revealed by the spectral feature of quadruplets. Inversion of transient chirality is a fundamental phenomenon in quantum mechanics and commonly observed for only inversional motions of protons. It is the first discovery, to the best of our knowledge, that such heavy moieties can also undergo chirality inversion.

Nanosecond pulsed cold atmospheric plasma jet suppresses proliferation and migration of human glioblastoma cells via apoptosis promotion and EMT inhibition

Glioblastoma (GBM) is one of the most aggressive and challenging cancers to treat. Despite extensive research on dozens of cancer cells, including GBM, the effect of cold atmospheric plasma (CAP) on the invasive migration of GBM cells has received limited attention, and the underlying mechanisms remain poorly understood. This study aims to investigate the potential molecular mechanism of ns-CAPJ in inhibiting the invasive migration of human GBM cells. The findings indicate that ns-CAPJ significantly reduces GBM cell invasion and migration, and induces apoptosis in GBM cells. Further mechanistic studies demonstrate a direct correlation between the suppression of the epithelial-mesenchymal transition (EMT) signaling pathway and ns-CAPJ’s inhibitory effect on GBM cell invasion and migration. Additionally, combined with the N-acetyl cysteine (NAC, a ROS inhibitor) assay, we found that the ROS stimulated by the ns-CAPJ plays an important role in suppressing the EMT process. This work is expected to provide new insight into understanding the molecular mechanisms of how ns-CAPJ inhibits the proliferation and migration of human GBM cells.

Multi-Objective Parameter Optimized Design of Self-Oscillating Cavitation Jet Nozzles

Self-oscillating cavitation jet technology has become a research hotspot of scholars in various fields. However, existing research lacks a summary of the rules of the influence of various factors on the cavitation performance, such that efficient and stable extensive engineering applications are impossible to achieve. This paper aims at optimizing the design of the self-oscillating cavitation jet nozzle (SOCJN) as the objective; this is carried out by the experimental design, optimal Latin hypercube method, and response surface method in (design of experiment) DOE methods on the basis of the ISIGHT optimization method. In addition, taking the vapor volume fraction and cavitation number as a research objective, the obtained optimal structural parameters of the nozzles are applied under the condition of clear water to establish the function mapping relationship between the external geometric characteristics and the vapor volume fraction and cavitation number; then, this is compared with the experiment. The results indicate that the second-order response surface approximate model is suitable for the SOCJN and there is an error smaller than 8% between the approximate model results and the calculated results of the nozzle response. When the diameter of the upper nozzle is D1 = 4.7 mm, the ratio of the upper nozzle’s diameter to the lower’s diameter (D1/D2) is 2.6 and the ratio of the chamber length to the chamber diameter (L/D) is 0.63; pulse jets from the SOCJN have the best pitting effect on the sample at the monitoring point when the convergence angle of collision wall α is 120°. When the structural parameters of the nozzle are optimal structural parameters, the cavitation performance is the best at the initial pressure of 4.8 MPa. This research provides a reference for the optimized design of the SOCJN for industrial applications.

Spectra of Rg-water dimers in the region of the D2O ν3 asymmetric stretch (Rg = Ar, Kr, Xe)

Spectra of rare gas (Rg) – D2O dimers (Rg = Ar, Kr, Xe) are studied in the region of the D2O ν3 asymmetric stretch (≈2800 cm−1), using a rapid-scan tunable infrared optical parametric oscillator source to probe a pulsed supersonic slit jet expansion. Three bands are observed in each case, labelled according to the D2O rotational transition with which they correlate as: Σ(101) ← Σ(000), Π(101) ← Σ(000), and Σ(000) ← Σ(101). The Ar-D2O bands exhibit various perturbations and line broadening effects. For Kr-D2O, the Π(101) ← Σ(000) and Σ(000) ← Σ(101) bands are simple and relatively unperturbed with almost no resolved Kr isotope structure, while the Σ(101) ← Σ(000) band is highly perturbed and shows large isotope splittings. This latter perturbation is analyzed in detail with good results. For Xe-D2O, the experimental spectra are unfortunately weaker. Analysis of the Π(101) ← Σ(000) and Σ(000) ← Σ(101) bands is again relatively straightforward, but the Σ(101) ← Σ(000) band is even more perturbed than for Kr-D2O and its analysis proves impossible. Line broadening (for Ar-D2O) and vibrational frequency shift effects are described.

Study on Mechanism and Regularity of Rock Breaking by Pulsed Water Injection with Particles

In recent years, the drilling technology applied to deep and ultra-deep formations has developed rapidly, but the drilling speed for hard formations is low. Therefore, it is very important to study the drilling methods for deep and hard strata. Particle pulsed jet drilling is a new drilling method based on particle jet impact drilling technology and high-pressure pulsed water jet impact drilling technology. In this paper, the mathematical models of the shear layer amplification coefficient and wave velocity are established based on a similar network theory, and the motion equations of a single particle and particle swarm are established according to the motion of particles in a pulsed jet environment. Then, based on the self-designed particle jet impact rock-breaking experimental platform, the numerical simulation results are compared, analyzed, and verified. The results show that the rock-breaking efficiency increases with the increase in the average velocity of the particle pulsed jet. When the average speed exceeds 160 m/s, the rock-breaking efficiency increases significantly. With the increase in the particle concentration, the rock-breaking efficiency of the particle pulsed jet also increases, but there is an optimal value. When the concentration is too high, the impact of particles on the rock is affected by the collision between particles, and the wear of the drill intensifies. This research is helpful for understanding deep-well drilling-speed-increasing technology and promotes the development and engineering applications of particle jet impact drilling theory.

Nectophore coordination and kinematics by physonect siphonophores.

Siphonophores are ubiquitous and often highly abundant members of pelagic ecosystems throughout the open ocean. They are unique among animal taxa in that many species use multiple jets for propulsion. Little is known about the kinematics of the individual jets produced by nectophores (the swimming bells of siphonophores) or whether the jets are coordinated during normal swimming behavior. Using remotely operated vehicles and SCUBA, we video recorded the swimming behavior of several physonect species in their natural environment. The pulsed kinematics of the individual nectophores that comprise the siphonophore nectosome were quantified and, based on these kinematics, we examined the coordination of adjacent nectophores. We found that, for the five species considered, nectophores located along the same side of the nectosomal axis (i.e. axially aligned) were coordinated and their timing was offset such that they pulsed metachronally. However, this level of coordination did not extend across the nectosome and no coordination was evident between nectophores on opposite sides of the nectosomal axis. For most species, the metachronal contraction waves of nectophores were initiated by the apical nectophores and traveled dorsally. However, the metachronal wave of Apolemia rubriversa traveled in the opposite direction. Although nectophore groups on opposite sides of the nectosome were not coordinated, they pulsed with similar frequencies. This enabled siphonophores to maintain relatively linear trajectories during swimming. The timing and characteristics of the metachronal coordination of pulsed jets affects how the jet wakes interact and may provide important insight into how interacting jets may be optimized for efficient propulsion.

Effect of CF4 concentration on the discharge dynamics and reactive species distribution of atmospheric nanosecond pulsed He plasma jet

Based on a two dimensional self-consistent model, the effect of different CF4 concentrations on the discharge dynamics characteristics, F-containing species distribution and the distribution of the axial and radial ionization rates of He atmospheric pressure plasma jet (APPJ) has been investigated. In addition, the accuracy of the simulation is verified by comparing the experimental results. The ionization rate of He APPJ enhances with the increase of CF4 from 0% to 2% because of the Penning ionization of CF4 with metastable He while decreases in the case of 3% CF4 owing to the electronegativity and the electron excitation energy loss of CF4. The increase of CF4 concentration and the decrease of the electron density leads to the decrease of CF4 + density at 3% CF4. CF3 + density is determined by the Penning ionization rate of CF4 and the reaction rate of He+ + CF4 → CF3 + + F + He. As CF4 concentration increases from 2% to 3%, the decrease of metastable He and He+ concentration results in the significant decrease of CF3 + density. The densities of CF3 − and F− keep increasing from 1% to 3% CF4 due to the effect of the electron attachment reaction of CF4. With the addition of CF4, the ionization reaction of CF4 is gradually playing the major role in the streamer head, the Penning ionization of CF4 is the main source of electron ionization inside the jet and dominates in the formation of ionization wave tail. As the concentration of CF4 increases from 0% to 2%, the electron impact ionization rates of He and CF4 near the axis increase, resulting in the more uniform radial ionization rate distribution of He + 2% CF4 APPJ.

Composition and Textural Characteristics of Char Powders Produced by Thermomechanical Processing of Sunflower Seed Husks

The paper presents the results of experimental studies on the production of fine char powder from sunflower seed husks by a novel method of thermomechanical treatment with pulsed shock waves and supersonic jets of the mixture of ultra-superheated (above 2000 °C) steam and carbon dioxide, as well as the results of examination of the produced char powder in terms of its chemical, phase, and granulometric composition and structural, morphological, and texture characteristics. The objective of the research is to explore the possibility of using the resulting char powder as a sorption-active material for organic substances. It is shown that the obtained char particles and their agglomerates have an average size of 20–30 nm and 12–24 µm, respectively, have the shape of disks and ellipsoids, consist mainly of amorphous carbon (up to 56 wt%) and oxygen (up to 42 wt%), and have a specific surface area of 1.1–1.7 m2/g. It is concluded that such a char powder can be used as an absorbent for organic substances when dried and deagglomerated.

Manipulating the propagation of ionization wave by pulsed electrical potential in atmospheric plasma jet

A noninvasive method was developed to measure the electrical potential in an atmospheric pressure plasma jet. The spatiotemporal evolution of electrical potential was measured by a wire electrode in experiment and simulated by a two-dimensional self-consistent numerical model, which demonstrates that the electrical potential along with the traveling ionization wave outside the discharge tube in ambient air plays a significant role on the propagation of ionization wave. It furtherly shows that the enhancement and restriction of ionization wave propagation are dependent on the amplitude of electrical potential on the auxiliary electrode, which proposes the way to manipulate the propagation of ionization wave in atmospheric pulsed discharge plasma jet.

Review on research progress in liquid jet in crossflow

Liquid jet in crossflow (LJIC) is an important subject of fluid mechanics, which is considered as an effective method of fuel atomization in aircraft and widely used in gas turbine engine, sub combustion ramjet, and scramjet. The atomization of liquid jet directly affects the subsequent fuel combustion, which is one of the most important processes in the engine propulsion system. Therefore, how to recognize the evolution of LJIC, and how to promote two-phase mixing determine the combustion efficiency of the engine directly. A lot of researches on LJIC have been done and provide impetus for the development of scramjet. Based on the recent researches, subsonic LJIC is reviewed from breakup model and surface wave, influence of crossflow on atomization, and factors affecting atomization. And supersonic LJIC is reviewed from two-phase mixing and flow field characteristics, jet breakup and surface wave, and factors affecting atomization. At the same time, the shortcomings of current research and the prospect of future research are put forward, especially in the selection of the jet medium, the determination of the experimental conditions, the application of the numerical method, the vortex, the pulsed jet, and the atomization enhancement by multiple means.

Experiment and simulation of electron density distribution in discharge plasma at hypersonic speed

Pulsed discharge can generate high density and high dynamic plasma, which has promising application prospects in the field of stealth technology for high-speed aircraft. To study the evolution process of pulsed discharge plasma jet in a hypersonic flow field, the pulsed discharge experiment was performed in a hypersonic wind tunnel with 8 M in this paper. The plasma evolution process and electron density were measured by a high-speed schlieren device and spectrum acquisition system. A shock wave appeared after the blast wave generated by the discharge interacted with the external flow field. In the region below the shock wave, the plasma jet flowed downstream and produced a plasma layer. The electron density of the jet increases with the injected energy, and the peak density reaches 5.28 × 1015 cm−3. Due to the limitations of experimental measurements, based on the Navier–Stokes equations and the air dissociation and ionization model, including 11 components and 20 chemical reactions, a simulation for the experimental process was performed. At the injected energy of 495 and 880 mJ, the difference between the simulated electron density and the experimental value is 16.09% and 15.34%, respectively. The thickness of the plasma layer initially increases and then decreases over time, with higher injected energy leading to a thicker layer. Specifically, when 880 mJ of energy is injected, the plasma layer can reach a maximum thickness of 6.69 cm. The collision frequency fluctuates around 1 GHz, and the collision frequency at the upper edge of the plasma layer is large.

Application of Shadow Visualization to Study the Drag of Toroidal Bubbles

In this work, the ascent of a toroidal bubble created by the injection of a pulsed air jet into water vertically upwards is studied by the shadow method. When using the shadow method, the bubble border on the image is darkened, and the contrast in comparison with the background is increased, which makes it possible to use software processing algorithms to determine the parameters of the ring on each frame. There are experimental results indicating that, in addition to the buoyancy force, the drag force also acts on the toroidal bubble. In this paper, the experimental data on the change in the torus radius as a function of time are compared with a theoretical model constructed with and without taking into account the drag force. It is shown that taking into account the drag force leads to a much better agreement between theory and experiment. The drag force is concluded to act on toroidal bubbles, but its influence decreases with time, i.e., as the bubble rises. The drag coefficient used in the calculations is determined empirically and assumed to be constant.

Numerical modeling of turbulent puffs evolution

The results of numerical simulation of the formation and motion of turbulent puffs resulting from the blowing of pulsed jets with different initial velocities and durations are presented. A model of an axisymmetric turbulent flow described by non-stationary Reynolds equations is adopted. It is shown that, regardless of the initial conditions, after the same dimensionless time interval from the instant the jet outflow begins, a vortex cloud appears, which has a spherical shape of vortex. The vortex-induced flow in the rest of the space is close to potential. It has been established that the velocity profiles in vortices in the axial and transverse directions are close to self-similar and are similar for different conditions of the outflow of pulsed jets. Time dependences of the geometric and kinematic characteristics of puffs are presented and analyzed: the position of the cloud center (points with maximum velocity) and the radius of a sphere equivalent in volume to a puff, as well as maximum and average velocities. For the studied jet outflow conditions, the characteristics of puffs turn out to be similar.

Numerical study on the design of multi-staged, opposing pulsed-jet cleaning (M-OPJC) for pleated filter cartridges

Opposing pulsed-jet cleaning (OPJC) has recently been proposed as a method to improve the filtration media regeneration of pleated filter cartridges, specifically addressing the patchy cleaning issue typically encountered in conventional pulsed jet cleaning. In this study, we first investigate the effect of pressure ratio (PR, the ratio of pressures at the opposing nozzles) on the OPJC performance in terms of cleaning intensity, uniformity, comprehensive pressure, and cleaning efficiency for pleated filter cartridges. A new OPJC strategy, named multi-staged, opposing pulsed-jet cleaning (M-OPJC), is proposed to enable the movement of a high-pressure region (formed by the collision of the pulsed-jet airflows introduced from opposing nozzles) within the core of a filter cartridge during the cleaning. The M-OPJC divides one cleaning jet cycle into four jetting stages with different PR values. Among all the evaluated cases, the M-OPJC with PR = [1.00, 1.00, 1.33, 2.00] offers the best cleaning performance for a pleated filter cartridge. Compared to conventional pulsed-jet cleaning (i.e., M-OPJC with PR = [0, 0, 0, 0]), the M-OPJC method increased the peak pressure at the cartridge’s upper part by 325.93%, comprehensive pressure by 171.10%, and cleaning efficiency by 48.85%.

Improved Pulsed-Jet Cleaning of Cone Filter Cartridges Using an Annular-Slit Nozzle

There is a problem with the insufficient cleaning of the dust filter cartridge by the pulsed-jet cleaning method. This paper examines the improvement in the pulse-jet performance of cone filter cartridges achieved by using an annular-slit nozzle. Off-line pulse jet experiments were conducted to study the influence of initial compressed air pressure, jet distance, and Venturi tube on injection pressure. This paper compared the filtration performance of conventional nozzles versus slit nozzles by conducting an online dust filtration-cleaning experiment and investigating the effect of a Venturi tube. The results demonstrated that the jet produced by the slit nozzle had a bigger surface area in contact with the surrounding air, enhancing the entrainment effect, boosting the overall pulsed-jet pressure, and significantly elevating the pressure in the upper and middle section of the cartridge, particularly in the upper section. In both common nozzle and slit nozzle cases, the pulsed-jet intensity initially increased and then decreased with the jet distance. The corresponding optimal jet distances were 500 mm and 400 mm, respectively. The slit nozzle provoked an increment of 16% and 44% in the pulsed-jet intensity and uniformity (to 619 Pa and 0.19), respectively. And there was an 8% reduction in residual pressure drop, a 6% improvement in fallen dust mass, and a 7% improvement in comprehensive filtration performance. The fallen dust mass produced by a single cleaning of the slit nozzle was 0.64 kg and the comprehensive filtration performance was 0.18. While the addition of a Venturi tube improved the cleaning of the filter cartridge, it also led to a higher filtration pressure drop in the dust collector and reduced comprehensive filtration performance.

Numerical and Experimental Study of an Aircraft Igniter Plasma Jet Discharge

The spark discharge of an aircraft plasma jet igniter is studied using high-fidelity numerical simulations and X-ray radiography measurements. The target problem here features the thermal expansion of hot gas introduced by the electric spark within a confined igniter cavity, which eventually evolves into a pulsed jet of a high-temperature kernel. A comprehensive set of models adapted from existing strategies for internal combustion engine spark plug discharge is extended to the target problem, including the modeling of energy deposition, plasma reactions, thermodynamic properties, and heat losses. A series of validation and parameter studies are performed and presented. The kernel size is found to be sensitive to heat losses arising from radiation and hot gas remained within the discharge cavity, rather than heat conduction to the wall in the discharge cavity. Depending on the enforced shape of the post-breakdown electric arc, the spark kernel can be off-centered, tilted, and considerably asymmetric. These features have been previously not considered when studying such igniter configurations and may have a first-order impact on the ignition process. Provided a proper setup of the heat loss models and electric arc shape, the numerical results are quantitatively comparable to the experimental results in terms of the kernel size, shape, and velocity throughout different stages after the spark discharge.

Study on dynamic characteristics of transient high-speed water jet impacting into and out water

This research investigates the physical mechanism and dynamic characteristics of morphological evolution of transient high-speed water jet impacting target plates above and below the water layer. Two experimental systems were used to measure the jet velocity and wall pressure, capture the jet morphology under different conditions, and obtain the influence relationship between the water layer and the transient high speed water jet. A numerical method based on VOF was used to observe the morphological change process of the jet tip at the central section. When the jet does not pass through the water layer and impinges upward on the target plate in the air, the mushroom-shaped annular ligament and obvious tip are formed at the front of the jet. When the jet impinges on the target plate in the air through the water layer, a transient pulsed high-speed water jet is formed. When the jet impinges on the target plate under the water layer through the still air, the front end of the jet forms a tip with elevated curvature and short length. With the shift of the thickness of the water layer and the quality of the explosion, single-layer or multilayer tower tips, different forms of cavitation bubble groups and bullet impact ligament and other physical phenomena can be observed in the tip formation region. It is concluded that the water layer plays a crucial role in the dynamic characteristics of transient high-speed water jet.

Influence of Hydraulic Parameters on Multi-Stage Pulse Characteristics of Pressurized Pulsed Water Jet

The multi-stage pulse competition of pressurized pulsed water jet becomes the initial pulse at the head tip, and hydraulic parameters are the key parameters that affect the characteristics of multiple pulses. Based on the ultra-high-speed imaging system, a pressurized pulsed water jet flow field capture system was constructed, and the effects of initial pressure and driving pressure of the pressurized chamber on the characteristics of multi-stage pulses were studied. The experimental results show that as the initial pressure of the booster chamber increases, the jet changes from a discontinuous state to a continuous state, and the multi-level pulse simultaneously changes from dominant multi-pulse to implicit multi-pulse; as the driving pressure increases, the initial spacing between the first pulse and the second pulse increases, and the peak velocity of the initial pulse gradually increases. At the same time, the location of the peak velocity also shifts away from the nozzle as the driving pressure increases. In addition, the peak velocity of the initial pulse is relatively close to the theoretical velocity of the continuous jet under driving pressure conditions.