Pulsed Jet Research Articles

Stepwise hydrations of anhydride tuned by hydrogen bonds: rotational study on maleic anhydride-(H2O)1-3.

The rotational spectra of maleic anhydride-(H2O)1-3 have been investigated for the first time by using pulsed jet Fourier transform microwave spectroscopy with complementary computational analyses. The experimental evidence points out that water tends to self-aggregate with hydrogen bonds and form homodromic cycles. Differences in bond lengths and charge distribution between the two carbonyl sites have been observed upon stepwise hydrations, which might further introduce a selectivity on the nucleophilic attack sites of hydrolysis. This study provides an important insight into the incipient solvation process (microsolvation) of maleic anhydride in water by understanding the cooperation and rearrangement of intermolecular hydrogen bonds in its stepwise hydrates.

Лазерный двигатель на основе абляционно-реактивного эффекта в пленках

The operation principle and design of a solid-fuel laser pulse jet engine are proposed. An experimental confirmation of the proposed operation principle of the laser engine has been obtained.

Development of Ultrasonic Pulsed Plasma Jet Source for Remote Surface Treatment

We have developed a supersonic pulsed plasma jet device capable of long-distance and high-speed processing, and investigated its basic characteristics for surface treatment applications, mainly in the material and medical fields. The developed apparatus is equipped with a mechanism to transport active species in the plasma to the object to be treated by jetting the generated high-density plasma outward with supersonic pulse jets, which allows the gas flow velocity to increase significantly during pulse jetting compared with plasma generation. This enables the active species in the plasma to reach the treatment target before deactivation, thereby realizing surface treatment at a distance. Measurements using the Schlieren method revealed that the velocity of the jet flow reached Mach 1.7.

Ultrasonic coupled abrasive jet polishing (UC-AJP) of glass-based micro-channel for micro-fluidic chip

The efficiency of abrasive jet polishing (AJP) is relatively low for glass-based micro-channels, and an ultrasonic coupled AJP (UC-AJP) approach was thus proposed. The fluid mechanic model of the UC-AJP was established to reveal the ultrasonic enhancement law and the optimal design parameters. The calculation results indicated that ultrasonic vibration could help significantly improve the turbulent kinetic energy and impact erosion that had an important role in jet stability and polishing efficiency. High-speed photograph and polishing experiments with different amplitudes were then performed to explore the performance of the proposed UC-AJP method. It was found that for glass-based micro-channel UC-AJP produced a smoother surface and higher polishing efficiency than AJP. There is an optimal amplitude range in the UC-AJP process, which can maximize the polishing efficiency for the micro-channel. Such improvements were ascribed to the synergistic effect of the pulse and cavitation as a result of the formation of pulsed abrasive jet.

Investigation on frequency influence on the transverse pulsed jet in a supersonic crossflow

AbstractThe pulsed jet is a novel and effective active mixing enhancement approach. For the transverse pulsed jet in the supersonic crossflow, the frequency influence is investigated using the three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations coupled with the SST k-ω turbulence model. The averaged flow field properties of the pulsed jet are better than those of the steady jet when considering mixing efficiency and jet penetration depth, especially for the case with the pulsed frequency being 50kHz. The flow field structures of the pulsed jet are connected with the time, with periodic wave structures generating in the flow field and moving downstream. The size of the wave structures and its distance are related to the frequency, namely the size and flow distance are relatively small at 50kHz, and it takes some time for the pulsed jet to establish its influence in the full flow field. At low frequencies, the flow field produces large fluctuations, and this may be detrimental to the stable operation of the engine.

How Water Interacts with the NOH Group: The Rotational Spectrum of the 1:1 N,N-diethylhydroxylamine·Water Complex

The rotational spectrum of the 1:1 N,N-diethylhydroxylamine-water complex has been investigated using pulsed jet Fourier transform microwave spectroscopy in the 6.5-18.5 GHz frequency region. The most stable conformer has been detected as well as the 13C monosubstituted isotopologues in natural abundance and the 18O enriched water species, allowing to determine the nitrogen nuclear quadrupole coupling constants and the molecular structure in the vibrational ground state. The molecule has a Cs symmetry and the water lies in the bc symmetry plane forming two hydrogen bonds with the NOH frame with length: dHOH·NOH = 1.974 Å and dH2O·HON = 2.096 Å. From symmetry-adapted perturbation theory calculations coupled to atoms in molecule approach, the corresponding interaction energy values are estimated to be 24 and 13 kJ·mol-1, respectively. The great strength of the intermolecular interaction involving the nitrogen atom is in agreement with the high reactivity of hydroxylamine compounds at the nitrogen site.

Spectroscopic detection of the stannylidene (H2C=Sn and D2C=Sn) molecule in the gas phase.

The H2CSn and D2CSn molecules have been detected for the first time by laser-induced fluorescence (LIF) and emission spectroscopic techniques through the B̃1B2-X̃1A1 electronic transition in the 425-400nm region. These reactive species were prepared in a pulsed electric discharge jet using (CH3)4Sn or (CD3)4Sn diluted in high-pressure argon. Transitions to the electronic excited state of the jet-cooled molecules were probed with LIF, and the ground state and low-lying Ã1A2 state energy levels were measured from single vibronic level emission spectra. We supported the experimental studies by a variety of ab initio calculations that predicted the energies, geometries, and vibrational frequencies of the ground and lower excited electronic states. The spectroscopy of stannylidene (H2CSn) is in many aspects similar to that of silylidene (H2CSi) and germylidene (H2CGe).

Spectra of CO2-Rg2 and CO2-Rg-He trimers (Rg = Ne, Ar, Kr, and Xe): Intermolecular CO2 rock, vibrational shifts and three-body effects.

Weakly bound CO2-Rg2 trimers are studied by high-resolution (0.002cm-1) infrared spectroscopy in the region of the CO2 ν3 fundamental band (≈2350cm-1), using a tunable optical parametric oscillator to probe a pulsed supersonic slit jet expansion with an effective rotational temperature of about 2K. CO2-Ar2 spectra have been reported previously, but they are extended here to include Rg = Ne, Kr, and Xe as well as new combination and hot bands. For Kr and Xe, a unified scaled parameter scheme is used to account for the many possible isotopic species. Vibrational shifts of CO2-Rg2 trimers are compared to those of CO2-Rg dimers, and in all cases the trimer shifts are slightly more positive (blue-shifted) than expected on the basis of linear extrapolation from the dimer. Combination bands directly measure an intermolecular vibrational mode (the CO2 rock) and give values of about 32.2, 33.8, and 34.7cm-1 for CO2-Ar2, -Kr2, and -Xe2. Structural parameters derived for CO2-Rg2 trimers are compared with those of CO2-Rg and Rg2 dimers. Spectra of the mixed trimers CO2-Rg-He are also reported.

Modal analysis of compressor cascades with sweeping jet actuator and pulsed jet for active flow control based on large Eddy simulation

This study utilized large eddy simulation (LES) to explore the mitigation effects of endwall pulsed jet (PJ) and suction-surface sweeping jet actuator (SJA) controls on corner separation. Two modal analysis methods, proper orthogonal decomposition (POD) and dynamic modal decomposition (DMD), were applied to extract the main structures in the flow field and to analyze the mechanism of the effect of an unsteady jet on flow separation. First, LES was first performed in a linear cascade to capture the pulsating information in the flow field. The spectral analysis shows the dominance of the shedding vortex dynamic feature in the measured position of the original scheme. Furthermore, the dominant flow pattern in the flow field was obtained using POD. Both unsteady jet schemes made the energy distribution in the decomposed reconstructed flow field of the POD more dispersed than that in the origin. However, POD loses the actual physical meaning of the eigenvalues and corresponding modes of that order when finding the optimal orthogonal basis. Therefore, this study used DMD to retain information reflecting the time-evolution process. The magnitude of each order of energy corresponded to the characteristic frequency of the flow field. The highest energy modal frequency was consistent with the jet frequency for both jet schemes. The results of the modal analysis showed that the PJ and its induced small-scale flow structures dominate most of the higher energy modes. These small-scale flow structures inhibit the development of transverse secondary flows at the endwall. In comparison, the dominant flow-field structure using the SJA is a large-scale streamwise vortex. The sweeping jet accelerates the corner low-energy fluid over a broader area by the induced streamwise vortex itself, thus controlling the corner separation.

Synergistic effect of hydrodynamic cavitation characteristics of self-excited oscillation cavity for degradation of dye wastewater

Dye wastewater in production process of the textile industry will cause serious environmental problems. Hydrodynamic cavitation includes many structures, such as a venturi tube, orifice, and pulsed jet. Self-excited oscillation cavitation is a kind of pulsed jet. In this paper, hydrodynamic cavitation is realized by self-excited oscillation cavitation. In this research, to study the hydrodynamic cavitation (HC) characteristics of the self-excited oscillation cavity and the degradation effect of dye wastewater, several experimental studies were carried out by selecting methylene blue as the colorant pollutant. During the experiment, the effects of experimental operating condition (including system pressure and initial solution concentration) on the degradation of methylene blue were studied, and its optimal operating conditions were obtained. And then the effects of the combination method of HC and oxidizing additives (hydrogen peroxide and ozone) on methylene blue degradation were analyzed. The results show that under the optimal system pressure of 1.4 MPa and solution concentration of 5.6 mg/L, the maximum extent of degradation is 24.90%, and the degradation rate is 2.3 × 10−3 min−1. The degradation effects of the combination methods of HC + Hydrogen peroxide and HC + Ozone can be greatly improved compared to only HC. The extent of methylene blue degradation of HC + Hydrogen peroxide is 83.70%, the degradation rate is 14.9 × 10−3 min−1, and the synergy index is 3.63; the extent of degradation of HC + Ozone is 92.62%, the degradation rate is 37.7 × 10−3 min−1, and the synergy index is 5.80. The lowest cost of the HC + Ozone combination method is 9.797 USD/m3, thereby the comparison of cavitation yield and energy consumption cost shows that HC + Ozone is the preferential combination treatment method. This study will not only play a significantly guiding role on the optimization of process parameters of SEOC for AOPs to obtain the preferable cavitation effect, but also provide support for the development of hybrid AOPs for wastewater treatment in the direction of large-scale application.

Heat transfer enhancement in turbulent boundary layers with a pulsed slot jet in crossflow

The convective heat transfer enhancement in a turbulent boundary layer (TBL) employing a pulsed, slot jet in crossflow is investigated experimentally. A parametric study on actuation frequencies and duty cycles is performed. The actuator is a flush-mounted slot jet that injects fluid into a well-behaved zero-pressure-gradient TBL over a flat plate. A heated-thin-foil sensor measures the time-averaged convective heat transfer coefficient downstream of the actuator location and the flow field is characterised by means of Particle Image Velocimetry. The results show that both the jet penetration in the streamwise direction and the overall Nusselt number increase with increasing duty cycle. The frequency at which the Nusselt number is maximised is independent of the duty cycle. The flow topology is considerably altered by the jet pulsation. A wall-attached jet rises from the slot accompanied by a pair of counter-rotating vortices that promote flow entrainment and mixing. Eventually, a simplified model is proposed which decouples the effect of pulsation frequency and duty cycle in the overall heat transfer enhancement, with a good agreement with experimental data. The cost of actuation is also quantified in terms of the amount of injected fluid during the actuation, leading to conclude that the lowest duty cycle is the most efficient for heat transfer enhancement.

Spatio-temporal profile of atomic oxygen in a 1 kHz repetition atmospheric-pressure plasma jet in He–O2–H2O mixture

Atomic oxygen (O) is one of the essential reactive species in plasma oxidation processes. We investigated the behavior of atomic oxygen in a 1 kHz-repetition pulsed plasma jet in atmospheric-pressure He/O2/H2O mixture. By two-photon absorption laser-induced fluorescence, the spatio-temporal profiles of O density were measured under various conditions. In the dry ([H2O] 100 ppm) condition, the rate of O production did not depend on the [O2] fraction in the range of [O2] = 275–8600 ppm. The analysis of the O-production rate indicates that the atomic oxygen in this plasma jet arises from electron-impact dissociation and quenching of O(1 D), similar to the O-production mechanism in radio-frequency plasma jet. The dependence of O-production in each discharge pulse (Δ[O]) on the discharge energy and [O2] in the plasma region at dry condition is formulated as . The decay rate of atomic oxygen was not explained by self-recombination or ozone-generation reactions; it was consistent with the reaction rate of O + OH O2 + H at [OH] = cm−3. This result suggests that the small amount of [OH] with 1013 cm−3 density is more responsible for O behavior than [O2] with large fraction of 1015 cm−3. We conducted a chemical reaction simulation considering the measured results of [O] and [OH] production, resulting in good agreement with the spatial distribution of [O]. Chemical reaction analysis revealed that the cyclic reproduction of OH via chain reaction with O and O2 is important, therefore a small amount of OH catalytically consumes atomic oxygen with two-order higher density.

Nozzle resonance mechanism and cooperative optimization of self-excited oscillating pulse cavitation jet

The peak value and pulsation amplitude of the self-excited oscillating pulse cavitation jet nozzle are essential indices to evaluate the jet performance. We established a simulation model of the jet process of the nozzle to investigate the evolution mechanism of the inner and outer flow fields. We used the chamber fillet, chamber diameter, chamber length, and outlet-tube diameter as the design variables, and the peak value of the striking force and the amplitude of the pulsation of the striking force as the target variables. The collaborative optimization design method of the nozzle was determined by combining the orthogonal test method, the back propagation neural network, and the nondominated sorting genetic algorithm. As indicated by the results, when the inlet pressure was 3 MPa, the factors ranked as follows in terms of their effects on the jet performance of the nozzle: the chamber fillet, the outlet-tube diameter, chamber diameter, and the chamber length. To verify the feasibility of the collaborative optimization method, the nozzle was fabricated via 3D printing, and the simulation model was verified by testing. This study provides support to the development of design theory for self-oscillating pulsed cavitation jet nozzles.

Piezo Actuator-Driven Pulsed Water Jet for Neurosurgery: Laboratory Evaluation with the Swine Model and Implications of Mechanical Properties.

Object Pulsed water jet is an emerging surgical instrumentation intended to achieve both maximal lesion resection and functional maintenance through preservation of fine vessels and minimal damage to the surrounding tissue. The piezo actuator-driven pulsed water jet (ADPJ) is a new technology that can deliver a precisely controlled uniform and efficient pulsed water jet with minimum water flow. The present study evaluated the ADPJ system in preclinical animal studies in the swine brain, and investigated breaking strength, one of the parameters for mechanical properties, to elucidate the mechanism of tissue selectivity for tissue dissection by the water jet. Methods This system consisted of a pump chamber driven by a piezo actuator, a stainless steel tube, and a nozzle (internal diameter: 0.15 mm). The water was supplied at 6 ml/min. The relationship between input voltage (3-25 V at 400 Hz) and peak pressure was measured using a pressure sensor through a sensing hole. Temporal profile of dissection depth during moving application was evaluated using gelatin brain phantom and swine brain. The dissected specimens were evaluated histologically. The mechanical property (breaking strength) of swine brain was measured by a compact table-top universal tester. Results Peak pressure increased linearly with increase in the input voltage, which reflected dissection depth in both the gelatin brain phantom and swine brain. Small arteries were preserved, and minimum damage to surrounding tissues occurred. The breaking strength of arachnoid membrane (0.12 ± 0.014 MPa) was significantly higher compared to gray matter (0.030 ± 0.010 MPa) and white matter (0.056 ± 0.009 MPa) (p < 0.05). The breaking strength of gray matter corresponded to that of 3 wt% gelatin, and that of white matter corresponded to a value between those of 3.5 and 4 wt% gelatin, and the dissection depth seemed to be estimated by 3-4 wt% gelatin. Conclusion The present study suggests that the ADPJ system has the potential to achieve accurate tissue dissection with preservation of blood vessels in neurosurgery. The difference in breaking strength may explain the tissue selectivity between brain parenchyma and tissue protected by the arachnoid membrane.

The Review and Development of Devices with an Increasing Rate of Penetration (ROP) in Deep Formation Drilling Based on Drill String Vibration

The oil and gas resources stored in deep strata are an important replacement field of the petroleum industry. Accelerating the exploration and development of deep oil and gas is of great significance to the security of energy strategy. Drilling is the primary link and necessary means of deep oil and gas exploration and development. Slow drilling speed is one of the key problems restricting the exploration and development of deep oil and gas. The research and development of down-hole equipment with an increasing ROP provides a technical means for increasing the ROP. However, the energy of existing down-hole equipment with an increasing ROP comes from the drilling circulation medium, and the ROP increase effect of such equipment is relatively obvious in shallow and middle formations. However, with the increase in well depth, energy in the circulation medium increasingly struggles to reach deeper formations, and the ROP increase effect is not good at the later stage of drilling. In the drilling process, drill string vibration is a frequently encountered complex situation, but it also contains sufficient energy, and the energy of drill string vibration will increase with an increase in the well depth, which can meet the energy demand of increasing the ROP in deep oil and gas exploration. This paper analyzes the characteristics of drill string vibration, and introduces six kinds of devices that take drill string vibration as energy and realize drill string vibration reduction, bottom-hole pressurization, and high-pressure pulse jet, providing a new idea for the development of deep down-hole speed-increasing devices.

Resuspension of trace explosive particle residues by planar impinging jet: Effects of exposure duration and wall shear stress

Aerodynamic particle resuspension is important in many practical applications, such as surface cleaning, understanding particle fate in the environment, and surface sampling. In practical application, the probability of particle resuspension from the surface depends on several parameters, such as particle size, morphology, chemical composition, surface properties, environmental and flow conditions. The wall shear stress (τw) links fluid motion and forces acting on the particle and can be used to characterize particle resuspension. The literature reports that the resuspension rates decay as 1/t at long exposure times; however, the effect of very short exposures to aerodynamic forces on the resuspension of irregular microparticles has not been characterized. This work examines the effect of τw and exposure duration utilizing planar jet pulses. We evaluated resuspension silica spheres and irregular Trimethylenetrinitramine (RDX) microparticles from a smooth glass surface with a 10–100 ms pulse duration and extended exposure (60 s) for the same wall shear stresses. Reducing the jet duration shows that the removal rate is inversely proportional to exposure time; the trend is more visible at lower τw. At higher shear stresses, up to 80% of particles are removed in the first 10 ms of exposure to aerodynamic force.

Combined experimental and numerical studies on soot characteristics of diesel sprays with split injection strategies

Experimental and numerical studies on the soot characteristics of Spray A flames were conducted with a focus on the effects of different split injection strategies in high-pressure high-temperature vessels within the engine combustion network. Three high-speed imaging techniques were used to obtain the transient information of flame evolution. Schlieren was applied to identify the spray boundaries and spray penetration. Moreover, a combined extinction and radiation technique was applied to quantify the spatial soot and temperature fields simultaneously. Finally, high-speed OH* chemiluminescence was applied at the baseline condition to measure the temporal high-temperature flame evolution. To substantiate the analysis, the experimental results were compared with the computational fluid dynamics (CFD) predictions from a Reynolds-averaged Navier Stokes approach with Unsteady Flamelet Progress Variable combustion and a two-equation soot-in-flamelet models, which qualitatively reproduced the experimental results.According to the chosen split injection strategy, dwell and first-injection pulse durations were varied. For all cases, the ignition delay (ID) and soot production of the second-injection pulse were shorter and higher than those of the first one, respectively. A slight change in the experimental soot production was observed when the dwell time was changed. The CFD calculations revealed a small reduction in the ID of the second pulse with long dwell times, which was due to variations in the interaction between the newly injected fuel and combustion recession. However, the effect of dwell variation was extremely small to produce significant differences in the evolution of the second pulse, neither in combustion nor in soot production. With regard to the duration of the first injection, no effect on the experimental soot production of the second pulse was observed despite noticeable differences due to the first pulse. The CFD results indicated that because of the quasi-steady flow and combustion process near the nozzle along the first injection, the evolution of the spray in the region close to the nozzle was identical in all first-pulse-duration cases, with differences only occurring at the tip of the first pulse jet. Thus, the second pulse evolution occurred under identical conditions for ignition and soot production. Although the sensitivity to both dwell and first-pulse durations was low, the CFD analysis highlighted the important effects of both end-of-injection wave propagation and combustion recession on the ignition and soot production of the second pulse.

Deep reinforcement learning for active control of a three-dimensional bluff body wake

The application of deep reinforcement learning (DRL) to train an agent capable of learning control laws for pulsed jets to manipulate the wake of a bluff body is presented and discussed. The work has been performed experimentally at a value of the Reynolds number Re∼105 adopting a single-step approach for the training of the agent. Two main aspects are targeted: first, the dimension of the state, allowing us to draw conclusions on its effect on the training of the neural network; second, the capability of the agent to learn optimal strategies aimed at maximizing more complex tasks identified with the reward. The agent is trained to learn strategies that minimize drag only or minimize drag while maximizing the power budget of the fluidic system. The results show that independently on the definition of the reward, the DRL learns forcing conditions that yield values of drag reduction that are as large as 10% when the reward is based on the drag minimization only. On the other hand, when also the power budget is accounted for, the agent learns forcing configurations that yield lower drag reduction (5%) but characterized by large values of the efficiency. A comparison between the natural and the forced conditions is carried out in terms of the pressure distribution across the model's base. The different structure of the wake that is obtained depending on the training of the agent suggests that the possible forcing configuration yielding similar values of the reward is local minima for the problem. This represents, to the authors' knowledge, the first application of a single-step DRL in an experimental framework at large values of the Reynolds number to control the wake of a three-dimensional bluff body.

The effect of nozzle geometry on the flow and heat transfer of pulsed impinging jet on the concave surface

The main aim of this paper is to investigate the effect of nozzle geometry on the flow and heat transfer from a pulsed jet into a concave surface. Experiments have been carried out for pulsed circular jet and numerical simulations were done for circular, elliptical, rectangular and square geometries. Numerical solution was performed for the frequency ranges of 25Hz to 100Hz, the jet Reynolds number of 7000, the dimensionless nozzle distance to concave surfaces of 2 and 5. Numerical results show a consistent agreement with experimental results and previous works. Accordingly, the geometry of nozzle directly affects the air entrainment ratio. In addition, with the increase of aspect ratio of the nozzle, average Nusselt number (Nuave) decreases. By pulsating the inlet jet with pulse frequency of 100Hz, the average Nu number for circular/square and elliptical/rectangular jets increases 22% and 15%, respectively. Generally, the pulsation causes a reduction and an increase of the Nuave at low and high frequencies, respectively, compared to that of the steady jet. At low frequencies, the Nuave of circular jet decreases significantly in comparison to that of the square and elliptical jets. However, at high frequencies, circular jet shows higher Nuave compared to other ones. As the distance between the jet and the concave surface increases, the effect of the nozzle shape on Nuave decreases.

Effect of pulsation on flow and thermal characteristics of a wall jet

In the current investigation, a computational analysis of the thermal and dynamic characteristics of a pulsed incompressible laminar wall jet is performed under a forced convection regime. The considered wall is isothermal with a temperature dissimilar from that of the surrounding fluid. The nozzle outlet is marked by a periodic and parabolic profile of the longitudinal velocity as well as a uniform temperature. The dimensionless transport equations governing the heat and momentum transfer phenomenon are solved using the finite difference method with irregular mesh. Our results are validated against those which emanate from the non-pulsed jet in its different regions. The spatial and temporal evolution of the wall jet characteristics such as the velocities, the friction coefficient, the jet spreading, and the Nusselt number are presented and analyzed. It was revealed that the inclusion of pulsation leads to the spreading of the jet and the curtailment of the potential core length relative to a steady jet. Moreover, the pulsation strengthens the entrainment and mixing of the ambient fluid and therefore improves the heat transfer in the potential cone area.