Pulsed Jet Research Articles

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.

Pulsed Impinging Jets for Heat Transfer: A Short Review

Abstract Because of their effectiveness and adaptability, impinging jets have found their way into a host of applications ranging from cooling turbine blades, to heat management of electronic systems. With constantly increasing demand for efficient and compact cooling systems in certain industries, such as the aerospace or electronics industries, variations on the textbook-setup of an impinging jet have been studied over the years. One such variation introduces a periodic disturbance into the jet that can have an effect on both the structure of flow and the thermal boundary layer at the target surface. In what follows is a short overview of studies having used pulsed jets, often in tandem with other modifications, to try and improve heat transfer. Special attention was also given to the methods by which the periodic disturbance can be produced since they involve setups of different levels of complexity and having different implementation costs.

Flow Control in Serpentine Inlet Duct Using Vortex Generator Jets

The objective of the present research is to study the effectiveness of steady and pulsed vortex generator jets in reducing inlet flow distortion and in improving pressure recovery by effective secondary flow control in uniform inflow serpentine duct diffuser. The measurements were carried out at a test Reynolds number of 6.5 x 105 based on the diffuser inlet width. Serpentine duct diffuser consisted of two main portions, namely, a square to circular constant area transition duct followed by a circular diffusing duct. Investigations show that the flow in the serpentine diffusing duct suffers from stall on the inner wall and consequently the outflow at AIP has considerable flow distortion due to the combined effect of secondary flow and the inner wall stall. It is observed that the use of vortex generator jets, both in steady and pulsed modes, improve the performance substantially. The number of jets, location of jets, velocity ratios and the pulse frequency are some of the variables that are studied. The results obtained so far suggest that use of pulsed jet not only gives better performance but also reduces the amount of air that is needed to be injected through the jets in comparison to steady jets for similar velocity ratios.

Effects of an unsteady end-wall pulsed jet on a highly loaded compressor cascade at different incidence angles

We report work done to investigate the adaptability of the end wall unsteady pulsed jet (UPJ) at different incidence angles. In this research, the influence of the UPJ on the cascade aerodynamic performance at different incidence angles was systematically studied using validated numerical simulation methods. A comparative analysis using a traditional steady constant jet (SCJ) was also carried out. The numerical results show that the control effect of the UPJ is significantly superior to that of the SCJ for the design incidence angle, and the same for the time-averaged jet flow. When the time-averaged jet flow ratio ms = 0.28% and the actuation frequency F+ = 0.80, a maximum total-pressure-loss coefficient reduction of 28.66% and a static-pressure-rise coefficient increment of 13.17% are obtained. Compared with the SCJ, the loss for a cascade with the UPJ is decreased by 25.65%, and the static-pressure-rise coefficient is increased by 10.54%. For variable incidence angle, the UPJ can diminish the cascade loss for the range of incidence angle i from −8° to +4° and can improve the cascade aerodynamic performance to the greatest extent near i = 0°. The SCJ shows excellent adaptability when the incidence angle is negative, but worsens the cascade performance at large positive incidence angles.

Mode‐Selective Vibrational‐Tunneling Dynamics in theN=2 Triad of the Hydrogen‐Bonded (HF)2Cluster

AbstractRovibrationally resolved spectra of theNj=22,Ka=0←1 transition and of theNj=23,Ka=0←0 andKa=1←0 transitions of the hydrogen‐bonded (HF)2have been measured in the near infrared range near 1.3 μm by cw‐diode laser cavity ring‐down spectroscopy in a pulsed supersonic slit jet expansion. The spectroscopic assignment and analysis provided an insight into the dynamics of these highly‐excited vibrational states, in particular concerning the predissociation of the hydrogen bond and the tunneling process of the hydrogen bond switching. Together with our previously analyzed spectra of theNj=21andNj=22components, the mode‐specific dynamics in all three components of this triad can now be compared. In theN=2 triad, the HF‐stretching vibration is excited by two quanta with similar excitation energy, but the quanta are distributed in three different ways, which has a distinct influence on the dynamics. The observed band centers and tunneling splittings are in agreement with our recent calculations on the (HF)2potential energy hypersurface SO‐3, resolving the long‐standing discussion about the symmetry ordering of polyad levels in this overtone region. The results are also discussed in relation to the general questions of non‐statistical reaction dynamics of polyatomic molecules and clusters and in relation to quasi‐adiabatic channel above barrier tunneling.

Laboratory Rotational Spectrum and Radio-Astronomical Search of Acetoin.

The rotational spectrum of acetoin (3-hydroxy-2-butanone) was measured by using Fourier transform microwave spectroscopy with the aid of quantum chemical calculations. Only one conformer of acetoin was detected in the pulsed jet, whose spectrum featured the splittings raised from the internal rotation of the methyl top linking to the C═O group. Based on the spectroscopic result, radio-astronomical searches for acetoin were carried out toward the massive star-forming region Sgr B2(N) using the Shanghai Tianma 65 m and IRAM 30 m radio telescopes. No lines belonging to acetoin were detected toward Sgr B2(N). Its upper limit of column density was calculated.

Numerical Investigation of a Pulsed Jet Actuator Having Non-Negligible Switching Time

An internal unsteady compressible flowfield of a pulsed jet actuator (PJA) is simulated by unsteady Reynolds-averaged Navier–Stokes (URANS) and large-eddy simulation (LES) frameworks. The PJA’s feedback loops are short enough to have non-negligible jet switching time compared to the oscillation period. The results show that within a range of inlet pressure (which is the only control parameter) where the jet goes from subsonic to supersonic regime, the oscillation frequencies and the exit velocity waveform predicted by LES are in better agreement with the measured data than those predicted by URANS. Although URANS is able to capture the flowfield inside the feedback loops, it fails to predict the exit jet dynamics, unlike LES. This indicates the importance of a proper resolution of turbulence in the interaction region where jet switching occurs. Using LES data, it is found that the total jet switching time remains constant as the inlet pressure changes. It is also found that only the part of the jet switching period that ends at the first moment when the jet attaches to the opposite wall is involved in the oscillation period. Therefore, a new lumped model is proposed to estimate the oscillation frequency, which also explains the trend observed for the low inlet pressure values.

Study on the development law of self-oscillating pulsed SC-CO2 jet vortex structure and its effect on frequency

The self-oscillating pulsed supercritical (SC)-CO2 jet technology has higher pulse pressure and the resonant rock-breaking effect, which can improve the drilling efficiency of the development of unconventional gas sources. The jet impact frequency is the key to resonance in coal rock mass; however, the relationship between frequency variation and flow field remain unknown. This study investigates the vortex change law and the effect on frequency of self-oscillating pulsed SC-CO2 jets. Large eddy simulations are used to analyze the variation characteristics of vortex structure and frequency at different locations of the jet. The results show that the variation of the vortex size in the oscillating cavity leads to the change of the jet velocity. Large-scale vortex is generated at the downstream nozzle exit and is accompanied by a high-speed zone of the jet, vortex development produces energy dissipation, which decreases the velocity in the high-speed zone. The jet frequency in the oscillating cavity is the same as the vortex ring size variation law; the vortex passing frequency in the free flow field is the same as the jet frequency, and the vortex ring energy dissipation causes the jet velocity to decrease, resulting in a lower frequency.

Impact of jet velocity profile on the propulsive performance and vortex ring formation of pulsed jet propulsion

A squid-inspired jet propulsion system that indudes a deformable body and a nozzle exit attached to it is numerically studied. By prescribing the body deformation during a single discharge, we examine the impact of jet speed profiles on the vortex ring formation and propulsion performance of the system. Our results show that a secondary vortex ring following the leading vortex ring can be produced by the reverse cosine jet speed pattern at a given maximum stroke ratio, and for the other profiles (i.e., constant, cosine, reverse cosine, half cosine and rever half cosine styles) only distributed vortices are seen behind the leading vortex ring. The constant jet speed produces the largest time-averaged thrust due to jet momentum flux related thrust associated with its large jet speed. Except for the constant speed style, the largest mean thrust production and propulsion factor are obtained by the reverse cosine profile among the other four styles attributed to the formation of the secondary vortex ring. Nevertheless, this secondary vortex ring would not be produced at a small maximum stroke ratio for the reverse cosine speed fashion. We also find that the mean thrust production can reach a maximum under a specific maximum stroke ratio (Γm = 7.60) when two vortex rings are produced. This work may provide insight into the mechanical and control design of jet-based biomimetic propellers and robots.

Study on the optimal target distance of self-oscillation pulsed SC-CO2 jet based on resonant effect

The SC-CO2 jet has broad application prospects in drilling engineering, but its promotion and application are limited by the high threshold pressure of coal breaking and system energy consumption. The high pulse pressure and resonance effects of the self-oscillation pulsed SC-CO2 jet can effectively reduce the threshold pressure of coal breaking and significantly improve the coal breaking efficiency. To fully utilize the resonance effect, based on the nozzle structure of the self-oscillation pulsed SC-CO2 jet, two nozzles with different pulse characteristics are used to study the comprehensive effect of pulse frequency and pressure amplitude at different target distances. The large eddy simulation was used to analyze the flow field structure of the jet, and the variation laws of the pulse frequency and pressure amplitude in the axial direction of the flow field were clarified. The effect of the target distance on the impact frequency and impact pressure of the jet was studied by the pulse characteristics test experiment, and the comprehensive effect of pulse characteristics on coal breaking was studied by coal breaking experiments. The results show that the pulse frequency and pulse pressure amplitude of the self-oscillation pulsed SC-CO2 jet do not remain constant in the axial direction of the jet, and they gradually decrease with the increasing target distance. Considering only the pulse frequency cannot maximize the resonance effect, and it is necessary to comprehensively consider the influence of pulse frequency and pressure amplitude on the resonance effect. Using displacement response amplitude to characterize the resonance effect can reflect the comprehensive influence of frequency and amplitude on resonance. When the target distance is small, from 0 mm to 13 mm, the main influencing factor of the displacement response amplitude is the pulse pressure amplitude; when the target distance is large, from 13 mm to 26 mm, the main influencing factor changes to the pulse frequency. In addition, reducing the pulse frequency and increasing the pressure amplitude can effectively improve the displacement response amplitude. Under the conditions of nozzle structure with different pulse characteristics, the transition positions of the main influencing factors of displacement response amplitude are different, and the optimal target distance is also not the same. Both nozzles achieve the best coal breaking effect at the maximum displacement response amplitude, which indicates that the displacement response amplitude can be used as the criterion to judge the optimal target distance. In this paper, the dimensionless optimal target distances of nozzle a and nozzle b are 7 and 9 respectively.

Low Barrier Methyl Internal Rotations and 14N Quadrupole Coupling in the Microwave Spectrum of 2,4-Dimethylthiazole.

The microwave spectrum of 2,4-dimethylthiazole was recorded using a pulsed molecular jet Fourier-transform microwave spectrometer operating in the frequency range from 2.0 to 26.5 GHz. Torsional splittings into quintets were observed for all rotational transitions due to internal rotations of two inequivalent methyl groups. Hyperfine structures arising from the nuclear quadrupole coupling of the 14N nucleus were fully resolved. The microwave spectra were analyzed using the modified version of the XIAM code and the BELGI-Cs-2Tops-hyperfine code. The barriers to methyl internal rotation of the 4- and 2-methyl groups were determined to be 396.707(25) cm-1 and 19.070(58) cm-1, respectively. The very low barrier hindering the 2-methyl torsion was a challenge for the spectral analysis and modeling, and separately fitting the five torsional species together with combination difference loops was the key for a successful assignment. The methyl torsional barriers were compared with those of other thiazole derivatives, showing the influence of the methyl group position on the barrier height. The experimental results were supported by quantum chemical calculations.

Laboratory rotational spectroscopy and astronomical search for 2-ethylacrolein

The rotational spectrum of 2-ethylacrolein was investigated by pulsed jet Fourier transform microwave spectroscopy complementary with quantum chemical calculations. The rotational spectra of both conformers cis and gauche and their all mono-substituted 13C and 18O isotopologues were measured and assigned in natural abundance, allowing the accurate structural determinations on their heavy-atom skeletons. The relative population ratio of cis to gauche in pulsed jets was estimated to be ≈ 3:1. With the accurate rotational transition frequencies, radio astronomical searches toward the massive star-forming region Sgr B2(N) were carried out by using the Shanghai Tianma 65 m radio telescope. No transition lines belonging to 2-ethylacrolein were detected, the upper limits of column densities for cis and gauche were derived to be 7.52 × 1013 cm−2 and 1.29 × 1015 cm−2, respectively.

Analysis of Corneal Biomechanical Properties in Different Keratotopographic Patterns of Keratoconus.

To analyze the frequency of main keratotopographic patterns at the 1st, 2nd, and 3rd stages of keratoconus and investigate corneal biomechanical properties across different patterns. The study comprised two stages. The first stage was computational-experimental, where we utilized COMSOL Multiphysics® software (COMSOL AB, Stockholm, Sweden) to mathematically model corneal mechanical behavior under intraocular pressure and pulsed air jet action in both normal and keratoconic conditions. The second stage was the clinical phase, during which we retrospectively analyzed the examination results of both healthy subjects and patients with keratoconus. In total, the study included 256 eyes (256 subjects). Among them, 174 eyes (174 healthy individuals) had normal corneas with different refractions, and 82 eyes (82 individuals) had stages 1, 2, and 3 of keratoconus based on Amsler-Krumeich classification. The keratotopographic characteristics of the participants were assessed using Sirius (Schwind, Germany) and Pentacam AXL (OCULUS Optikgeräte GmbH, Germany) keratotomographs, while the corneal biomechanical properties were studied using noncontact tonometry with the Corvis ST device (OCULUS Optikgeräte GmbH, Germany). The study focused on evaluating corneal stiffness index values in the central optical zone under various keratotopographic patterns. In addition, it compared the elastic coefficient values c1, c2, and c3 for the model of hyperelastic behavior of corneal material outside the keratoconus zone. Furthermore, the study examined the values of reduced stiffness zone characteristics, including the stiffness reduction factor ψmax, effective radius Rk, and the ratio of maximum and minimum strain intensity in keratoconus of different stages. The mean age of the patients in the study was 30.16 ± 8.31 years, with 166 men and 90 women participating. The study revealed typical keratotopographic patterns in the examined keratoconus stages, as well as their occurrence frequency. In the 1st stage of keratoconus, the pattern of asymmetric astigmatism was noted more frequently (in 75% of cases). In the 2nd stage, the pattern with an ectasia zone in the lower cornea was observed in 80% of cases, and in the 3rd stage, a centrally located keratotopographic ectasia pattern was found in 42% of cases. Comparative analysis showed that the greatest decrease in stiffness parameter (SpA1) and stress-strain index occurred in the central pattern (by 64% and 46%, respectively), while the least decrease was observed in local corneal radius reduction in the lower cornea (by 42% and 33%, respectively). The decrease in strength properties in keratoconus occurs in a local area, the size and degree of which are determined by the disease stage. The indicated biomechanical parameters are consistent regardless of the shape and localization of keratotopographic patterns but are relevant to diagnostic specifications using the Corvis ST pneumotonometer, which assesses corneal properties in the apical zone.

An active mixing enhancement technique in supersonic ejectors using pulsed streamwise injections

The current study numerically investigates an active mixing enhancement technique for a supersonic ejector with a constant area mixing chamber operating under the critical regime. Streamwise control jet injections are alternatively pulsed at the top and bottom sides of the mixing chamber entrance. The induced oscillation of the primary jet enhances the bulk mixing between the primary and secondary streams. The secondary stream penetrates the primary core flow much upstream with the control strategy compared to the no-injection case, improving the onset of mixing by 65.36%. A higher spread of the primary jet along the mixing chamber height is observed with the control strategy indicating an enhanced mixing between the two streams. Dynamic mode decomposition analysis of the fluctuations of the velocity magnitude revealed that the dominant dynamic structures are determined by the pulsation frequency and a dominant flapping mode can be observed. The frequency spectrum of the primary jet oscillation revealed that the dominant frequency of oscillation is dictated by the pulsation frequency of the injection. With an increase in the control jet pulsation frequency, the amplitude of primary jet oscillation reduces near the entrance region of the mixing chamber, whereas the amplitude of oscillation far downstream reaches nearly the same value for all the cases. The power spectral analysis of the unsteady pressure fluctuations along the mixing chamber wall revealed that the wall pressure oscillations are contributed by the control jet pulsation frequency as well as the shock wave reflections produced by the supersonic jet–jet interaction within the mixing chamber.

Design and implementation of a novel dust collector controller for powder production industry

Industries those work with powder either in production or processing always left a portion of industrial dust in the air. By releasing this air directly in the surrounding environment of the industry pollution occurs. Therefore air filtration system is mandatory in these industries and usually bag filter dust collector controller is used. To control and maintain the proper functionality of the bag filtration system PLC based control system or a modular control board is used. In this paper, a novel dust collector controller is designed which can be installed by any user without having any programming knowledge. The main control keys of the control board are the pulse duration and pulse interval which drive the solenoid valves to release air pressure on the filter bags sequentially. Pulse duration can be controlled in the range of 0.01-0.9 seconds and pulse interval can be varied in the range of 1-99 seconds to control 10 rows of pulse jet simultaneously connected with the solenoid valve. The Number of rows can be adjusted and expanded if required. Moreover, noiseless switching provides silent operational functionalities and switching durability as well as the addition of surge controller ensures a complete protection from any sudden high electrical surge. The finally developed prototype was tested in different industries and provides maximum operational efficiency, which can effectively control online bag filter dust collector to separate micro dust particles from the polluted air.

Impact of progressive pulse cleaning pressure on polyester filter media performance using pulse jet filtration test rig

Impact of progressive pulse cleaning pressure on polyester filter media performance using pulse jet filtration test rig

Effect of Jet Speed on the Microstructure and Performances of Ni-TiN Nanocomposites Prepared via Jet Pulse Electrodeposition

Effect of Jet Speed on the Microstructure and Performances of Ni-TiN Nanocomposites Prepared via Jet Pulse Electrodeposition

Design, Modeling, and Control of an Aurelia-Inspired Robot Based on SMA Artificial Muscles.

This paper presented a flexible and easily fabricated untethered underwater robot inspired by Aurelia, which is named "Au-robot". The Au-robot is actuated by six radial fins made of shape memory alloy (SMA) artificial muscle modules, which can realize pulse jet propulsion motion. The thrust model of the Au-robot's underwater motion is developed and analyzed. To achieve a multimodal and smooth swimming transition for the Au-robot, a control method integrating a central pattern generator (CPG) and an adaptive regulation (AR) heating strategy is provided. The experimental results demonstrate that the Au-robot, with good bionic properties in structure and movement mode, can achieve a smooth transition from low-frequency swimming to high-frequency swimming with an average maximum instantaneous velocity of 12.61 cm/s. It shows that a robot designed and fabricated with artificial muscle can imitate biological structures and movement traits more realistically and has better motor performance.

Relaxation Fluidic Oscillators: Design Parameters, New Operating Modes, and Characteristics of Their Internal and External Flows

AbstractFluidic oscillators are no-moving-part actuators that can be used to produce pulsating jets. The characteristics of these devices and of the flow fields they produce are of particular interest in the field of heat transfer, as pulsating impinging jets have been shown to improve heat transfer compared to steady jets. In this study, special focus is given to these characteristics as a preparation for a subsequent thermal study that will evaluate the performance of these pulsed jets against steady jets. The functioning of the device in response to different operating and design parameters is first considered. It was shown that a transition between different operating modes is possible, depending on both the inlet mass flowrate and the width of the feedback channel of the device. This was followed by a study of the velocity fields of the pulsed jets produced by the device. More specifically, attention is given to the developing characteristics and flow structures of the pulsating free jets of air which are then compared to equivalent steady jets. Finally, by taking advantage of the periodic aspect of the flow, the phase-averaged velocity field was reconstructed. Vortex dipoles were detected, tracked and their convection velocity computed from the same data and compared to a theoretical value from the literature. A proper orthogonal decomposition (POD) of the synchronized raw data was then performed to further highlight the presence of these vortex structures and other flow instabilities.