Pulsed Jet Research Articles

Simulation and Experiment on Elimination for the Bottom-Sitting Adsorption Effect of a Submersible Based on a Submerged Jet

When a submersible is sitting on a seabed, it could lose buoyancy because of the bottom-sitting adsorption effect. In this article, a numerical calculation model and experimental scheme for eliminating the bottom-sitting adsorption effect of under-sea equipment were established. An analysis of the hydrostatic pressure variation on a submersible’s bottom was carried out, and a submerged water jet which was based on the method of soil liquefaction was proposed to solve the problem of reducing hydrostatic pressure. It was shown that a water jet could liquefy soil to restore hydrostatic pressure on the submersible’s bottom, and there was an optimal jet velocity to form the largest liquefied soil thickness. A rectangular pulsed jet was the best way to liquefy soil in terms of efficiency and the liquefaction degree, which can be seen from the calculation of the two-dimensional two-phase flow. Through the calculation of the three-dimensional two-phase flow, it was found that the soil liquefaction developed from the periphery to the center, and a variation in jet liquefaction with the top wall constraint was obtained. Finally, an experiment was carried out to prove that a submerged water jet could eliminate the bottom-sitting adsorption effect of a submersible. The results showed that the submerged jet was an efficient way to liquefy soil, and a submersible could quickly recover hydrostatic pressure on the bottom and refloat up independently.

Ultrashort Ne+ ion pulses for use in pump–probe experiments: numerical simulations

A time resolved experiment to investigate the ultrafast dynamics following an ion impact onto a solid surface requires an ultrashort ion pump pulse in combination with a properly synchronized and time resolved probe. In order to realize such an experiment, we have investigated a strategy to use femtosecond laser photoionization of atoms entrained in a pulsed supersonic jet for the production of sufficiently short ion pulses. While the generation of Arq+ ions was targeted in previous work, it has in the meantime been demonstrated that argon is not suitable due to extensive cluster formation in the supersonic expansion. Here, we therefore present numerical simulations investigating the use of neon as a precursor gas and show the feasibility of pulses containing up to ∼1000 Ne+ ions at keV energies and picosecond duration. In the process, we demonstrate that space charge broadening can be significantly reduced by detuning the flight time focusing conditions of an ion bunching system. Moreover, the results show that a controlled variation of the buncher geometry and potentials permits the generation of picosecond pulses at variable ion energy between 1 and 5 keV.

Numerical Study of a Pulsed Jet Flow of an Inhomogeneous Gas-Dispersed Mixture

Numerical Study of a Pulsed Jet Flow of an Inhomogeneous Gas-Dispersed Mixture

A numerical investigation into thermo-fluid characteristics of pulsating jet impingement on a dimpled surface

A two-dimensional axisymmetric numerical model is employed to study the flow and heat transfer attributes of the pulsating air jet impingement on a dimpled surface. The results are compared with the steady jet impingement. The results are examined at a fixed Reynolds number of 5000, over a Strouhal number range of 0.1–0.5, and pulsation amplitude of 15% and 25% for three different nozzle-to-surface separations (z/d = 2, 6, and 10). The pulsation amplitude of 15% has a minor effect on heat transfer from the dimpled surface. However, at 25% pulsation amplitude, significant improvements in the heat transfer rates are obtained in many combinations of jet Strouhal number and jet surface spacing. The value of the optimum Strouhal number provides conditions for the maximum heat transfer rate, which varied with nozzle-to-surface separation distances. Combinations of higher separations and lower Strouhal numbers (and vice versa) produced optimum heat transfer among the cases considered in the present study. The maximum improvement (17.41%) in the average heat transfer over the steady jet was found at z/d = 10 for pulsation at St = 0.1, while at z/d = 6, St = 0.2 provides the highest heat transfer rate. It is urged that the vortices formed in pulse jet close to the natural frequency of vortex formation provide a conducive environment for the vortex growth and their existence, significantly affecting the jet entrainment, mixing, and jet spread, which eventually play the decisive factor in determining the overall heat transfer rates on the dimpled surface.

Proof of concept study on a self-driven pulsed jet on a compressor stator blade by numerical simulation

This study presents a new concept of self-driven pulsed jet flow control on a compressor stator blade. This passive unsteady flow control method has the advantage that neither external flow nor electrical source is needed. This study’s preliminary proof-of-concept study on a low-speed compressor stator blade is performed using numerical simulation. When the pulsed jet frequency is 100 Hz, the optimum control performance and control efficiency are reached, and the total pressure loss coefficient is reduced by 8.9%. As the valve’s rotational speed increases, the pulsed jet’s momentum coefficient decreases gradually. The analysis of the unsteady characteristics of the self-driven pulsed jet shows that the jet velocity is close to a periodic square wave signal, and the typical reduced jet velocity ranges from approximately 0.15 to 0.8. Moreover, the time-averaged driving torque on the valve depends on the rotational speed and is relevant to the self-starting and self-driven characteristics of this passive flow control method. Under different bearing resistance torque, the self-driven valve behaves differently in three cases that can self-start and be self-driven, cannot self-start but can be self-driven, and cannot self-start nor be self-driven.

Experimental Investigations of the Detachment of Different Particle Structures from a Magnetizable Fiber in the Gas Phase

A current subject of research is the application of magnetic effects for the detachment of accumulated particles of fibrous collectors in gas particle separation. Initial studies have already shown the magnetically induced detachment behavior of a compact particle structure after a single deflection from a single fiber. In this study, the detachment behavior of particle structures with different morphologies from a single fiber is investigated as a function of the particle loading stage on the fiber, the external magnetic flux density, the inflow velocity and the number of regenerations of the fiber for a certain parameter range. Diffusive and more compact particle structures with non-magnetic properties are deposited on the magnetizable single fiber. By applying an external magnetic field, the fiber is magnetized and experiences a torsional moment. The deposited particle structures on the fiber are detached by the acceleration forces. The detachment of the particle structures is observed using a high-speed camera and the image sequences are analyzed. By determining the projection area before and after the fiber deflection, a degree of regeneration is calculated. With magnetic-induced regeneration, high degrees of regeneration close to 100% can be achieved. Repetitive fiber deflections improve the detachment of the particle structures. The magnetic-induced regeneration is suitable for applications where flow reversal is not possible and can be performed either online or offline. Due to the gentle regeneration, fewer emissions are produced on the clean gas side than, for example, with jet pulse cleaning. It makes it easier to achieve emission limits and simplifies product recovery.

Experimental Investigation on Flow Control over a Circular Cylinder Using Antiphase Pulsed Jets

To investigate the flow control characteristics of antiphase pulsed jet technology and explore a more efficient method to control unsteady flow with minimal impact on flow turbulence, wind tunnel experiments were conducted. The aim was to address the issue of flow separation control on the surface of a cylindrical model. The model had a diameter of 100 mm, and an experimental setup utilizing an antiphase pulsed jet excitation was developed. The optimisation of unsteady jet control involved adjusting parameters such as jet momentum coefficient, slot position, and excitation frequency. The flow separation control effect on the cylinder surface was compared between in-phase and antiphase pulsed jet using a particle image velocimetry (PIV) technique. The mechanisms of flow control for these two methods were analysed. The results showed that in still air, increasing the jet momentum led to a gradual decrease in the high-velocity region, which also moved away from the wall. Under incoming flow conditions, positioning the slot closer to the separation point resulted in better flow separation control, particularly when the excitation frequency matched the main flow frequency. Both in-phase and antiphase pulsed jet excitations effectively suppressed flow separation. In the near-wall region within the symmetric plane between the two slots, the antiphase excitation reduced the root mean square of velocity fluctuations by approximately 1.9% and increased the average velocity by approximately 15.5% compared to in-phase pulsed jet excitation. In-phase pulsed jets exhibited low-frequency, high-velocity characteristics near the separation point, while antiphase pulsed jets, due to the alternating discharge of the two jets, had a lesser impact on the flow field turbulence.

C···S Tetrel Bond Favored in the Phenyl Isothiocyanate-CO2 Complex: A Rotational Study.

The rotational spectrum of the phenyl isothiocyanate-CO2 complex was investigated by pulsed-jet Fourier transform microwave spectroscopy complemented by quantum chemical calculations. Only one isomer, with CO2 almost in the plane of phenyl isothiocyanate, has been detected in the pulsed jet, of which the spectrum displays a quadrupole coupling hyperfine structure due to the presence of a 14N nucleus (I = 1). This structure is nearly equal to the lowest energy geometry obtained by B3LYP-D3(BJ)/6-311++G(d,p), which has been dominated by a C···S tetrel bond (n → π* interaction) and one secondary C-H···O hydrogen bond (n → σ* interaction). Molecular electrostatic potential and natural bond orbital analysis were used to characterize the noncovalent interactions of the complex. The results from this study would lay the groundwork for the design and advancement of materials that exhibit high efficiency in capturing CO2.

Quantitative evaluation of the low-temperature pulsed plasma-wound interaction based on splint model

An atmospheric pressure low-temperature plasma jet has a promising application prospect in biomedical fields due to its low operating temperature and its ability to act in open space. In this paper, a mouse excisional wound splinting (MEWS) model is developed using a BALB/c strain of mice. A pulsed low-temperature plasma jet close to the human temperature is generated to treat the wound of the mouse skin. We have demonstrated that the pulsed low-temperature plasma jet can effectively promote wound healing. The large number of active particles contained in the plasma, such as reactive oxygen species, reactive nitrogen species, etc., may be responsible for its ability to increase the wound healing rate and promote skin tissue regeneration. The MEWS model adopted in this experiment reduces the interference in the evaluation of the wound healing effect caused by skin contraction and wound dressing, and thus is closer to the healing process of human wounds, and the method of wound area acquisition and calculation based on image processing reduces human interference and is more standardized, which can be used to evaluate the effect of the pulsed low-temperature plasma jet on promoting wound healing.

Study on combustion characteristics of sinusoidal hydrogen pulsed jet with different frequencies in supersonic flows

Pulsed jets can effectively improve mixing and combustion efficiencies, while sinusoidal pulsed jets have the advantages of good performance and simple setup. Therefore, the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations and Shear Stress Transfer k-omega model (SST) are utilized to study the combustion characteristics of sinusoidal pulsed jets with three different frequencies and steady jet in order to obtain an approach to improve the combustion performance in the supersonic flow. In the current study, the combustion performances of the steady jet and the pulsed jets with an equal average momentum flux ratio to the steady jet are compared and analyzed, and the instantaneous combustion characteristics of four different time points in one cycle of the pulsed jets are analyzed in detail. The obtained results show that the pulsed jet can obviously improve the combustion efficiency, although the total pressure loss is slightly larger than that of the steady jet. On the whole, the pulsed jets have a good impact on the combustion performance of the combustor, and the combustion performance of the f = 20 kHz pulsed jet case is the best in this study.

Study on the rock-breaking characteristics of high-energy pulsed plasma jet for granite

Plasma jet rock-breaking technology, characterized by its high rock-breaking efficiency, low specific energy, and absence of mechanical wear, is one of the most promising methods for efficiently fracturing hard rock formations such as hot dry rock (HDR). This study designed a novel high-energy pulsed plasma power supply and pulsed gas supply system to achieve rock fracturing through the instantaneous high-temperature and thermal stress impact of the high-energy pulsed plasma jet on the rock surface. This paper conducted comparative experiments with a traditional constant plasma jet. The impact of crucial electrical parameters (peak current, valley current, frequency, and duty cycle) and rock initial temperature on the damage and fracturing patterns of granite was extensively investigated. Comprehensive evaluation criteria, including removal mass, diameter, depth, rate of penetration, and specific energy, were employed to study the effects meticulously. The results indicate that the pulsed plasma jet significantly enhances energy utilization, effectively reducing the occurrence of thermal melting. The specific energy decreased significantly by 54.74%, while the rate of penetration increased by 17.81%. Additionally, electrode wear was reduced by 50.06%, extending the lifespan of the plasma bit. Parametric analysis revealed that the peak current is the primary factor influencing the rock-breaking performance and efficiency. The valley current has minimal impact on hole morphology but significantly affects specific energy. Frequency and duty cycle can be adjusted to optimize the single-pulse energy, achieving the best specific energy and efficiency. Additionally, the rock temperature has a great influence on the breaking effect. The fracturing characteristics of granite were also analyzed from a microscopic level. Based on the experimental results, recommended parameters of pulsed plasma jet are provided for breaking granite. These findings offer guidance for high-energy pulsed plasma jet drilling of HDR.

Penetration of a Pulsed Guided Streamer Discharge into Micrometer-Sized Capillary Tubes

The penetration and propagation of streamers in capillary tubes is critical for applications involving the plasma-enabled disinfection of medical devices like catheters and plasma catalysis. In this study, a guided streamer is generated in a pulsed plasma jet operating in helium and impinged downstream onto a capillary tube with an inner diameter between 75 and 500 µm. The threshold voltage required to start the penetration of the guided streamer into the capillary was determined for both positive and negative polarities, and we observed a time delay between the streamer striking the top of the capillary and its penetration, which was found to be larger for the positive than the negative streamer. The observed differences can be explained by the need to sustain an electric field large enough to generate a sufficient seed electron density in the capillary to launch the streamer. The reported results suggest that the electric field at the capillary inlet is likely reduced by the formation of strong surface ionization waves for positive streamers. Nonetheless, in the case of positive streamers, the formation of surface streamers along the outside of the capillary wall can enhance streamer penetration into the capillary and the streamer propagation speed.

Analysis of Macroscopic Cavitation Characteristics of a Self-Excited Oscillating Cavitation Jet Nozzle

The self-excited oscillating cavitation jet nozzle (SEOCJN) serves as a crucial component for converting hydrostatic energy into dynamic pressure energy and ensuring optimal hydraulic and cavitation performance of cavitating jets. Thus, it is of crucial significance to understand the cavitation characteristics and the influence law of SEOCJN for its extensive industrial applications. This paper utilizes numerical simulation methods to analyze the dynamic process of cavitation initiation, development, and outlet cavitation performance of SEOCJN. It explores the effects of inlet pressure and flow rate on the frequency characteristics of SEOCJN, and establishes a mathematical relationship between self-excited oscillation frequency and outlet flow frequency. The results indicate that the self-excited oscillation nozzle has an inlet diameter (D1) of 4.7 mm, an outlet diameter (D2) of 12.2 mm, a length (L) of 52 mm, a chamber diameter (D) of 83 mm, an oscillation angle of 120°, and an inlet pressure (Pin) of 4.8 MPa. At these parameters, the frequency of the pulse jet reaches 830.01 Hz, with an internal flow period of approximately 0.0024 s. The maximum vapor volume fraction is found to be located 0.28 m from the outlet of the SEOCJN. Furthermore, the frequency of self-excited oscillation pulse increases with an increase in inlet pressure. These findings provide a theoretical basis for the industrial application of self-excited oscillation cavitation jet nozzles.

On the concrete breakage by pulsed water jet impact: Fracture characteristic, stress and damage evolution laws

To reveal the dynamic response characteristic and damage-fracture evolution laws of concrete under pulse water jet impact, the numerical simulations on pulse water jets impinging concrete for different operating parameters were established based on SPH-FEM coupling algorithm and verified in this paper. The concrete-breaking effects of pulse water jet and continuous water jet were compared, and the effects of key jet parameters and concrete strength on the damage-fracture characteristics of concrete were investigated. And the damage and stress evolution laws inner concrete were revealed. The results show that there is a better concrete-breaking effect for pulse water jet by repeatedly utilizing the extremely high water-hammer pressure and effectively weakening the water-cushion effect, compared with continuous water jet. The broken pit area and the total length of main cracks decrease with the increase of pulse length, and there is an optimal pulse spacing for pulse water jet to improve the concrete-breaking effect. The broken pit area and the total length of main cracks both linearly increase with the increasing jet velocity and exponentially increase with the increasing jet diameter. As the concrete strength increases, the broken pit area shows an S-shaped curve decreasing trend and the total length of main cracks exponentially decreases. The broken pit width first rapidly increases and tends to stabilize with the increase of jet velocity and concrete strength, and changes linearly with jet diameter and is less affected by pulse length and spacing. The farther away from the jet impact center, the longer the damage cumulative period of concrete due to the jet impact energy attenuation. In horizontal direction, concrete breakage range is approximately 4–5 times of jet diameter; in vertical direction, the previous pulses will cause concrete to be destroyed or damaged, and the subsequent pulses will make the damaged concrete suffer greater stress, causing more serve damage. And the induced stress peak decreases in form of Power function with the increasing distance. The research results could provide theoretical guidance for the parameters selection of pulse water jet efficiently breaking concrete.

Large-Eddy simulations on interaction flow structures of pulsed jets in a crossflow

Numerical investigations of pulsed jets in a crossflow are carried out using large-eddy simulation. The flow mechanism and coherent structure evolution of pulsed jets with different frequencies (f = 20 Hz, 50 Hz, and 100 Hz) are analyzed and compared with the steady-state jet. The proper orthogonal decomposition (POD) method is used to analyze the effect of different vortex structures in the flow field, which further elaborates the influence mechanism of frequency on pulse jets in the crossflow. The results show that under the same velocity ratio, the normal penetration depth of pulsed jets to the crossflow are greater than that of the steady-state jet. Due to the pulsating effect, the pulsed jets will form a large-scale shear layer vortex, which strengthens the turbulence pulsation and promotes the mixing between jets and the crossflow. As the pulse frequency increases, the scale of the vortex rings in the downstream shear layer will become smaller but the number will increase, and fine vortex clusters will be formed around them. At f = 50 Hz, the counter-rotating vortex pair (CVP) and the jet front shear layer vortex have a greater influence in the flow field, followed by the downstream shear layer vortex, and the wake vortex has the least influence in the flow field. At f = 20 Hz and 100 Hz, the wake vortex has a greater influence in the flow field than that at f = 50 Hz.

Comparative study on the water droplet erosion behavior between stretched and casted aeronautical PMMA

Rain droplet erosion is a potential threat in aviation, especially for forward-facing components such as windshields of aircraft. To comprehend and mitigate such hazards, a comparative study was conducted on two kinds of commonly used aeronautical PMMA materials: casted and biaxially stretched. The study aimed to investigate the water droplet erosion (WDE) behavior and the underlying damage mechanism. A modified pulsed water jet erosion facility was constructed to mimic the impact of successive water droplets. The influence of impact velocity on the WDE behavior was explored and quantitative evaluations of volume loss, surface entrance area, and erosion depth were conducted. Results revealed that the increase in impact velocity leads to faster damage initiation and a larger erosion rate. Compared with the stretched sample, the casted sample exhibits higher erosion resistance. The stretched sample exhibits a funnel-shaped cavity with a flat bottom, while the casted sample shows a tapered crater with shallow depth. The cavity shape can influence the subsequent flow fields and stress distribution, thereby affecting the development of erosion entrance and depth. Microscopic analysis of the erosion cavities revealed different damage mechanisms at each stage of erosion. The stretched sample exhibited exfoliation of fine flakes and denudation of large pieces due to stress waves and lateral jet-induced shear, whereas hydraulic penetration had a more pronounced effect on the casted sample. The cushioning effect of the water film was also studied, noting a gradual reduction in its effectiveness with increasing impact velocity.

Investigation on the influence of the frequency of pulsed water jet on the rock-breaking effect

Frequency plays a pivotal role in determining the rock-breaking effect of self-excited oscillating pulsed water jet. Experiments were conducted to investigate the relationship between frequency and rock-breaking effectiveness. A relationship between frequency and chamber length was established. An explanation was provided for the varying rock-breaking effects resulting from changes in frequency using the resonance effect theory, thereby revealing the mechanism through which frequency characteristics impact rock-breaking. Our findings demonstrate that the resonance effect significantly influences the rock-breaking effectiveness of the pulsed water jet. The closer the frequency ratio is to 1, the better the rock-breaking results. Notably, the pulse frequency of Helmholtz nozzles closely approximates the frequency of stress waves generated in the rock mass, and both decrease as the chamber length increases.

Pressurization Characteristics and Proppants Transport of Pulse Jet Fracturing with CFD-DEM Coupling Method

Pressurization Characteristics and Proppants Transport of Pulse Jet Fracturing with CFD-DEM Coupling Method

Numerical simulation of the pressure characteristics of the pulsed jet actuator

AbstractA compressible large eddy simulation (LES) is performed to study a pulsed jet actuator that is used to control a turbulent axisymmetric bluff body wake. The actuator is driven at low-frequency ( $f = 200$ Hz, $S{t_\theta } = 0.029$ ) and high amplitude ( ${C_\mu } = 0.034$ ). The numerical scheme and a suitable boundary condition for the pulsed jet are validated, showing good agreement with experimental results. A comparison of the velocity boundary condition and the moving boundary condition shows that, in the vicinity of the orifice/slot and in the downstream region, the results from these two methods are identical, while the fluid behaviour inside the cavity shows difference. An analysis of the pulsed jet actuator shows that the phase lag of the cavity pressure is determined by the integration of the diaphragm motion and the pulsed jet. The mean total pressure distribution shows that the total pressure loss is concentrated in the vicinity of the slot. Dynamic mode decomposition (DMD) on the pressure field is used to extract coherent structures which oscillate with the same frequency as that of the diaphragm motion. Some small-scale high-frequency structures are also apparent.

Impact frequency variation of self-excited oscillation pulsed supercritical carbon dioxide jets

In order to obtain the impact frequency of resonant coal breaking by self-excited oscillation pulsed supercritical carbon dioxide (SC-CO2) jet, large eddy simulation was used to analyze the formation and development process of self-excited oscillation pulsed SC-CO2 jet, the variation of jet impact frequency in the nozzle and the free flow field, and the variation of jet impact frequency at different positions in the jet axis and under different cavity lengths. The test device of jet impact frequency was developed, and experiments were performed to verify the conclusions of the numerical simulations. The results show that the frequency of the self-excited oscillation pulsed SC-CO2 jet is different in the nozzle and the free flow field. In the nozzle, the frequency generated by the fluid disturbance is the same, and the jet frequency at the exit of the nozzle is consistent with that inside the nozzle. In the free flow field, due to the compressibility of CO2, the pressure, velocity and other parameters of SC-CO2 jets have obvious fluctuation patterns. This feature causes the impact frequency of the self-excited oscillation pulsed SC-CO2 jet to decrease gradually in the axis. Changing the cavity length allows the adjustment of the jet impact frequency in the free flow field by affecting the disturbance frequency of the self-excited oscillation pulsed SC-CO2 jet inside the nozzle.