Increase of efficiency of cavitation processes in liquids and melts is reached by gas cavities saturation with the sizes not exceeding the resonant sizes of cavitation germs. Gas saturation of liquids and melts raises...Increase of efficiency of cavitation processes in liquids and melts is reached by gas cavities saturation with the sizes not exceeding the resonant sizes of cavitation germs. Gas saturation of liquids and melts raises level of cavitation pressure upon 20% - 25% that intensifies US processing: cleaning, soldering and metallization.展开更多
Intensity of cavitation is significant in ultrasonic wastewater treatment,but is complicated to measure.A time difference based method of ultrasonic cavitation measurement is proposed.The time differences at different...Intensity of cavitation is significant in ultrasonic wastewater treatment,but is complicated to measure.A time difference based method of ultrasonic cavitation measurement is proposed.The time differences at different powers of 495 kHz ultrasonic are measured in experiment in comparison with conductimetric method.Simulation results show that time difference and electrical conductivity are both approximately positive proportional to the ultrasonic power.The degradation of PNP solution verifies the availability in wastewater treatment by using ultrasonic.展开更多
Gold ores in the Jiaozhou region of China are characterized by their abundant reserves,low grade,fine dissemination,and chal-lenges in upgrading.Froth flotation,with xanthate as the collector,is a commonly employed me...Gold ores in the Jiaozhou region of China are characterized by their abundant reserves,low grade,fine dissemination,and chal-lenges in upgrading.Froth flotation,with xanthate as the collector,is a commonly employed method for enriching auriferous pyrite from these ores.This study aimed to develop a more efficient flotation process by utilizing cavitation nanobubbles for a low-grade gold ore.Batch flotation tests demonstrated that nanobubbles significantly enhanced the flotation performance of auriferous pyrite,as evidenced by improved concentrate S and Au grades and their recoveries.The mechanisms underlying this enhancement were explored by investigat-ing surface nanobubble(SNB)formation,bulk nanobubble(BNB)attachment to hydrophobic pyrite surfaces,and nanobubble-induced agglomeration using atomic force microscopy(AFM)and focused beam reflectance measurement(FBRM).The results revealed that nan-obubble coverage on the pyrite surface is a critical factor influencing surface hydrophobicity and agglomeration.SNBs exhibited higher coverage on pyrite surfaces with increased surface hydrophobicity,flow rate,and cavitation time.Similarly,BNB attachment on pyrite surfaces was significantly increased with surface hydrophobicity and cavitation time.Enhanced surface hydrophobicity,along with higher flow rates and cavitation times,promoted pyrite particle agglomeration owing to the increased nanobubble coverage,ultimately leading to improved flotation performance.展开更多
This paper aims to numerically explore the characteristics of unsteady cavitating flow around a NACA0015 hydrofoil,with a focus on vorticity attributes.The simulation utilizes a homogeneous mixture model coupled with ...This paper aims to numerically explore the characteristics of unsteady cavitating flow around a NACA0015 hydrofoil,with a focus on vorticity attributes.The simulation utilizes a homogeneous mixture model coupled with a filter-based density correction turbulence model and a modified Zwart cavitation model.The study investigates the dynamic cavitation features of the thermal fluid around the hydrofoil at various incoming flow velocities.It systematically elucidates the evolution of cavitation and vortex dynamics corresponding to each velocity condition.The results indicate that with increasing incoming flow velocity,distinct cavitation processes take place in the flow field.展开更多
Cavitation is an unavoidable phenomenon in the operation of centrifugal pumps.Prolonged cavitation can cause significant damage to the components of the flow channel,and in severe cases,it may even interfere with the ...Cavitation is an unavoidable phenomenon in the operation of centrifugal pumps.Prolonged cavitation can cause significant damage to the components of the flow channel,and in severe cases,it may even interfere with the normal energy exchange processes within the pump.Therefore,effective monitoring of cavitation in centrifugal pumps is crucial.This article presents a study that approaches the issue from an acoustic perspective,using experimental methods to gather and analyze acoustic data at the inlet and outlet of centrifugal pumps across various flow rates,with hydrophones as the primary measuring instruments.Results show that flow rate significantly affects noise levels in both non-cavitation and mild cavitation stages,with noise increasing as the flow rate rises.As the cavitation margin(NPSHa)decreases,inlet and outlet noise trends diverge:inlet noise drops sharply,while outlet noise initially increases before sharply decreasing.Both exhibit a distinct zone of abrupt change,where NPSHa values offer earlier cavitation detection than traditional methods.The noise at the pump’s inlet and outlet primarily consists of discrete and broadband noise,with most energy concentrated at discrete frequencies—shaft frequency(24 Hz),blade frequency(144 Hz),and their harmonics.As NPSHa decreases,the inlet’s discrete and broadband noise frequencies decline,while they increase at the outlet.Monitoring changes in these spectrum characteristics provides an additional means of predicting cavitation onset.展开更多
Cavitation and cavitation erosion are prevalent phenomena in hydraulic machinery.In the present paper,a multiscale Eulerian-Lagrangian method in OpenFOAM is used to simulate cavitating flow in a Venturi tube.Additiona...Cavitation and cavitation erosion are prevalent phenomena in hydraulic machinery.In the present paper,a multiscale Eulerian-Lagrangian method in OpenFOAM is used to simulate cavitating flow in a Venturi tube.Additionally,a novel erosion prediction model is proposed,incorporating material hardening behavior under impact loads caused by asymmetric bubble collapse near walls.The model couples detailed bubble dynamics with the nonlinear plastic response of materials,enabling direct calculation of erosion pit depth.Simulation results show strong agreement with experimental erosion patterns,confirming the feasibility of this new method.The proposed method is pivotal for further studying how various materials respond to cavitation wear.展开更多
Hydrodynamic cavitation,as an efficient technique applied in many physical and chemical treatment methods,has been widely used by various industries and in several technological fields.Relevant generators,designed wit...Hydrodynamic cavitation,as an efficient technique applied in many physical and chemical treatment methods,has been widely used by various industries and in several technological fields.Relevant generators,designed with specific structures and parameters,can produce cavitation effects,thereby enabling effective treatment and reasonable transformation of substances.This paper reviews the design principles,performance,and practical applications associated with different types of cavitation generators,aiming to provide theoretical support for the optimization of these systems.It systematically analyzes the underpinning mechanisms and the various factors influencing the cavitation phenomena,also conducting a comparative analysis of the performance of different types of generators.Specific applications dealing with wastewater treatment,chemical reaction acceleration,and other fields are discussed together with the advantages,disadvantages,and applicability of each type of cavitation generator.We also explore research progress in areas such as cavitation stability,energy efficiency,and equipment design upgrades.The study concludes by forecasting the application prospects of intelligent design and computational fluid dynamics(CFD)in optimizing and advancing cavitation generators.It proposes new ideas for the further development of cavitation technology and highlights directions for its widespread future application.展开更多
Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets(SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets(AFESOPWs) exhibit a higher surge pressure throug...Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets(SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets(AFESOPWs) exhibit a higher surge pressure through self-priming. However, their pressure frequency and cavitation characteristics remain unclear, resulting in an inability to fully utilize resonance and cavitation erosion to break coal and rock. In this study, high-frequency pressure testing, high-speed photography, and large eddy simulation(LES) are used to investigate the distribution of the pressure frequency band, evolution law of the cavitation cloud, and its regulation mechanism of a continuous waterjet, SOPW, and AFESOPW. The results indicated that the excitation of the plunger pump, shearing layer vortex, and bubble collapse corresponded to the three high-amplitude frequency bands of the waterjet pressure. AFESOPWs have an additional self-priming frequency that can produce a larger amplitude under a synergistic effect with the second high-amplitude frequency band. A better cavitation effect was produced after self-priming the annulus fluid, and the shedding frequency of the cavitation clouds of the three types of waterjets was linearly related to the cavitation number. The peak pressure of the waterjet and cavitation erosion effect can be improved by modulating the waterjet pressure oscillation frequency and cavitation shedding frequency.展开更多
The synergetic technology of hydrodynamic cavitation(HC)and peroxydisulfate(PDS)has been adopted for the treatment of organic pollutants,while the rationale behind the thermal-activation of PDS in this process remains...The synergetic technology of hydrodynamic cavitation(HC)and peroxydisulfate(PDS)has been adopted for the treatment of organic pollutants,while the rationale behind the thermal-activation of PDS in this process remains lacking.This paper presented investigation on the degradation of tetracycline under two types of operating conditions,including“internal reaction conditions”(pH value and TC/PDS molar ratio)and“external physical conditions”(hole shape,solution temperature and inlet pressure).Special emphasis was paid on the analysis of thermal effects through a robust modeling approach.The results showed that a synergy index of 6.26 and a degradation rate of 56.71%could be obtained by the HC-PDS process,respectively,when the reaction conditions were optimized.Quenching experiment revealed that·OH and·SO_(4)^(-)were the predominant free radicals and their contribution to the degradation was 75.4%and 24.6%respectively,since a part of·SO_(4)^(-)was transformed into·OH in the solution.The thermal activation of PDS mainly occurred near the hole where the fitting temperature was around 340 K,while·OH was generated in the bubble collapse region downstream the hole,where the temperature was much higher and favorable for the cleavage of water molecular.The average temperature under different external physical conditions was in good consistence with the degradation rates.This research developed a useful method to effectively evaluate the activation extent of PDS by HC and could provide reliable guidance for further development of cavitational reactors to treat organic pollutants based on this hybrid approach.展开更多
During strong unsteady flow processes such as cavitation initiation and collapse,the volume changes generated by the materials transformation of cavitation phase transition seriously lag behind the volume evolution fo...During strong unsteady flow processes such as cavitation initiation and collapse,the volume changes generated by the materials transformation of cavitation phase transition seriously lag behind the volume evolution formed by the flow process.The phase transition and hydrodynamics are in a non-equilibrium state.A cavitation model that can describe such non-equilibrium phenomena is needed in numerical simulations of cavitation flow.The paper starts from the molecular dynamics’principle of phase change of matter,and based on the Maxwell velocity distribution form of molecular thermal motion,elaborates on the formation process of Hertz Knudsen formula for material exchange at the interface between liquid and vapor.On this basis,using the evolution equation of gas nucleus number density in water and the compressible state equation of vapor,a non-equilibrium cavitation model for phase transition and hydrodynamics is established.The simulation results of a vapor bubble collapse process in the non-equilibrium cavitation model show different behavior from the simulation results of the equilibrium cavitation model.The simulation results of the equilibrium cavitation model show that the vapor bubble collapses once and completely disappear,while the simulation results of the non-equilibrium cavitation model show multiple collapses and rebound,which is agreement with the experimental results of the vapor bubble collapse.展开更多
Understanding the behaviour of composite marine propellers during operating conditions is a need of the present era since they emerge as a potential replacement for conventional propeller materials such as metals or a...Understanding the behaviour of composite marine propellers during operating conditions is a need of the present era since they emerge as a potential replacement for conventional propeller materials such as metals or alloys.They offer several benefits,such as high specific strength,low corrosion,delayed cavitation,improved dynamic stability,reduced noise levels,and overall energy efficiency.In addition,composite materials undergo passive deformation,termed as“bend-twist effect”,under hydrodynamic loads due to their inherent flexibility and anisotropy.Although performance analysis methods were developed in the past for marine propellers,there is a significant lack of literature on composite propellers.This article discusses the recent advancements in experimental and numerical modelling,state-of-the-art computational technologies,and mutated mathematical models that aid in designing,analysing,and optimising composite marine propellers.In the initial sections,performance evaluation methods and challenges with the existing propeller materials are discussed.Thereafter,the benefits of composite propellers are critically reviewed.Numerical and experimental FSI coupling methods,cavitation performance,the effect of stacking sequence,and acoustic measurements are some critical areas discussed in detail.A two-way FSI-coupled simulation was conducted in a non-cavitating regime for four advanced ratios and compared with the literature results.Finally,the scope for future improvements and conclusions are mentioned.展开更多
Bulb-type hydro turbines are commonly used in small-to medium-scale hydropower stations due to their compact design and adaptability to low-head conditions.However,long-termoperation often results in wear at the runne...Bulb-type hydro turbines are commonly used in small-to medium-scale hydropower stations due to their compact design and adaptability to low-head conditions.However,long-termoperation often results in wear at the runner rim,increasing tip clearance and triggering leakage flow and cavitation.These effects reduce hydraulic efficiency and accelerate blade surface erosion,posing serious risks to unit safety and operational stability.This study investigates the influence of tip clearance on cavitation performance in a 24 MW prototype bulb turbine.A three-dimensional numericalmodel is developed to simulate various operating conditions with different tip clearance values(3.0,4.5,and 6.0 mm)and cavitation numbers(σ=1.20–1.33).Internal flow characteristics—including pressure distribution,velocity fields,hydraulic efficiency,and pressure pulsation—are analyzed to elucidate the impact of tip clearance on cavitation development.Results show that underσ=1.2 and a 4.5 mm tip clearance,the pressure pulsation amplitude at the blade tip reaches 4870 Pa—approximately 1.5 times higher than that near the hub.At partial flowconditions,turbine efficiency decreases by up to 6.8%compared to the rated condition.Increasing the tip clearance from 1.5 to 6.0 mm expands the low-pressure area near the blade tip by around 32%,significantly intensifying cavitation.Frequency domain analysis reveals dominant pulsation frequencies between 10–20Hz,characterized by blade-passing features and a wave-clipping effect.These findings provide theoretical insight and quantitative evidence to support the optimization of tip clearance design and cavitation mitigation strategies in bulb turbines,aiming to improve both efficiency and operational stability.展开更多
Bubbles play crucial roles in various fields,including naval and ocean engineering,chemical engineering,and biochemical engineering.Numerous theoretical analyses,numerical simulations,and experimental studies have bee...Bubbles play crucial roles in various fields,including naval and ocean engineering,chemical engineering,and biochemical engineering.Numerous theoretical analyses,numerical simulations,and experimental studies have been conducted to reveal the mysteries of bubble motion and its mechanisms.These efforts have significantly advanced research in bubble dynamics,where theoretical study is an efficient method for bubble motion prediction.Since Lord Rayleigh introduced the theoretical model of single-bubble motion in incompressible fluid in 1917,theoretical studies have been pivotal in understanding bubble dynamics.This study provides a comprehensive review of the development and applicability of theoretical studies in bubble dynamics using typical theoretical bubble models across different periods as a focal point and an overview of bubble theory applications in underwater explosion,marine cavitation,and seismic exploration.This study aims to serve as a reference and catalyst for further advancements in theoretical analysis and practical applications of bubble theory across marine fields.展开更多
Soil aggregate stability is a fundamental measure for evaluating soil structure.While numerous tests exist for assessing soil aggregate stability,ultrasonic agitation(UA)is widely recognized for its effectiveness.None...Soil aggregate stability is a fundamental measure for evaluating soil structure.While numerous tests exist for assessing soil aggregate stability,ultrasonic agitation(UA)is widely recognized for its effectiveness.Nonetheless,a significant limitation of UA is the lack of standardized methodologies and stability assessment criteria,resulting in inconsistency and incomparability across studies.Several critical factors influence the assessment of soil aggregate stability,including sample preparation(e.g.,drying,sieving,and settling duration),initial and final aggregate size classes,the definition of final energy form and its calculation,variations in instrumentation and laboratory procedures,and the absence of standardized criteria.Unlike some stability methods,UA produces a broad range of results,with dispersion energy varying significantly(0.5–13440 J g^(-1))across different soil and aggregate types due to divergent procedural settings.These settings encompass factors such as initial power and amplitude,temperature fluctuation,soil/water ratio,probe specification(diameter and insertion depth),and the choice of liquid used during the process.Furthermore,UA faces challenges related to limited reproducibility,raising doubts about its status as a standard stability assessment method.To address these issues,standardization through predefined procedures and stability criteria has the potential to transform UA into a precise and widely accepted method for both qualitative and quantitative assessments of soil stability.In this comprehensive review,we outline the challenges in standardizing UA,elucidate the factors contributing to dispersion energy variation,and offer practical recommendations to establish standardized protocols for UA in soil aggregate stability assessments.展开更多
Verification and validation(V&V)is a helpful tool for evaluating simulation errors,but its application in unsteady cavitating flow remains a challenging issue due to the difficulty in meeting the requirement of an...Verification and validation(V&V)is a helpful tool for evaluating simulation errors,but its application in unsteady cavitating flow remains a challenging issue due to the difficulty in meeting the requirement of an asymptotic range.Hence,a new V&V approach for large eddy simulation(LES)is proposed.This approach offers a viable solution for the error estimation of simulation data that are unable to satisfy the asymptotic range.The simulation errors of cavitating flow around a projectile near the free surface are assessed using the new V&V method.The evident error values are primarily dispersed around the cavity region and free surface.The increasingly intense cavitating flow increases the error magnitudes.In addition,the modeling error magnitudes of the Dynamic Smagorinsky-Lilly model are substantially smaller than that of the Smagorinsky-Lilly model.The present V&V method can capture the decrease in the modeling errors due to model enhancements,further exhibiting its applicability in cavitating flow simulations.Moreover,the monitoring points where the simulation data are beyond the asymptotic range are primarily dispersed near the cavity region,and the number of such points grows as the cavitating flow intensifies.The simulation outcomes also suggest that the re-entrant jet and shedding cavity collapse are the chief sources of vorticity motions,which remarkably affect the simulation accuracy.The results of this study provide a valuable reference for V&V research.展开更多
The underwater launch of an axisymmetric body involves complex cavity-structure interactions.Studying the evolution of cavity pressure around an axisymmetric body is crucial for researching its motion stability.In thi...The underwater launch of an axisymmetric body involves complex cavity-structure interactions.Studying the evolution of cavity pressure around an axisymmetric body is crucial for researching its motion stability.In this work,we propose a deep neural network model for cavity pressure distribution recovery,called CPDR-net.This model can reconstruct the full-domain distribution of surface pressure based solely on the local pressure distribution.The CPDR-net model was trained using numerical simulation data with different launch depths and initial velocities,and subsequently tested on two simulation datasets under new conditions.Both training and testing datasets are obtained from the ventilated cavitating flow over an underwater axisymmetric vehicle.Results demonstrated that CPDR-net can accurately predict the pressure distribution along each longitudinal line of the axisymmetric body and provide the pressure evolution over time for each point on the surface.Thus,we can obtain the evolution of surface pressure distribution throughout the entire voyage process based on the CPDR-net model.The findings from this study may provide a valuable reference for subsequent research on underwater launches.展开更多
The behaviors of unsteady flow structures and corresponding hydrodynamics for a pitching hydrofoil are investigated numerically and theoretically in the present paper.The aims are to derive the total lift by finite-do...The behaviors of unsteady flow structures and corresponding hydrodynamics for a pitching hydrofoil are investigated numerically and theoretically in the present paper.The aims are to derive the total lift by finite-domain impulse theory for subcavitating flow(σ=8.0)and cavitating flow(σ=3.0),and to quantify the distinct impact of individual vortex structures on the transient lift to appreciate the interplay among cavitation,flow structures,and vortex dynamics.The motion of the hydrofoil is set to pitch up clockwise with an almost constant rate from 0°to 15°and then back to 0°,for the Reynolds number,7.5×105,and the frequency,0.2 Hz,respectively.The results reveal that the presence of cavities delays the migration of the laminar separation bubble(LSB)from the trailing edge(TE)to the leading edge(LE),consequently postponing the hysteresis in the inflection of lift coefficients.The eventual stall under the sub-cavitation regime is the result of LSB bursting.While the instabilities within the leading-edge LSB induce the convection of cavitation-dominated vortices under the cavitation regime instead.Having validated the lift coefficients on the hydrofoil through the finite-domain impulse theory using the standard force expression,the Lamb vector integral emerges as the main contribution to the generation of unsteady lift.Moreover,the typical vortices’contributions to the transient lift during dynamic stall are accurately quantified.The analysis indicates that the clockwise leading-edge vortex(−LEV)contributes positively,while the counterclockwise trailing-edge vortex(+TEV)contributes negatively.The negative influence becomes particularly pronounced after reaching the peak of total lift,as the shedding of the concentrated wake vortex precipitates a sharp decline due to a predominant negative lift contribution from the TEV region.Generally,the vortices’contribution is relatively modest in sub-cavitating flow,but it is notably more significant in the context of incipient cavitating flow.展开更多
Polymer microfluidic chips are a common tool in biomedical research,and the production of mold inserts with microscale structures represents a crucial step in the precise molding of these chips.Electrical discharge ma...Polymer microfluidic chips are a common tool in biomedical research,and the production of mold inserts with microscale structures represents a crucial step in the precise molding of these chips.Electrical discharge machining(EDM)can achieve high-quality machining of microstructures on high-hardness mold steel inserts.This can reduce the manufacturing cost of microfluidic chip molds and extend the service life of molds.However,the EDM process is susceptible to the formation of poor-quality surfaces due to the occurrence of abnormal discharges.To address this issue,this paper presents in-depth research on a novel ultrasonic cavitation-assisted electrical discharge machining method.An ultrasonic transducer is placed in an electrical discharge working fluid to promote the removal of electrical corrosion products through the cavitation effect of the liquid.This can also reduce the occurrence of poor discharge,thereby improving the machining surface quality.The aluminum foil corrosion method is employed to investigate the distribution of ultrasonic action in the electric discharge working fluid.The attenuation law of ultrasonic action in the electric discharge working fluid is also investigated.The range of ultrasonic action is determined,providing a reference for subsequent ultrasonic vibration electric discharge working fluid processing experiments.The results of the aluminum foil tests are used to inform the selection of NAK80 mold steel as the experimental object.The effects of cavitation at three ultrasonic frequencies on the surface microstructure are investigated.The experimental results indicate that ultrasonic cavitation can facilitate the movement of corrosion products in electrical machining,reduce the occurrence of abnormal discharges caused by carbon deposition or the secondary re-melting of metals,and thereby enhance the machining surface quality.展开更多
Bubbles within an elastic shell,which undergo ultrasound-driven oscillation to treat tumors and soft tissues,are frequently treated as viscoelastic media.Therefore,studying the dynamic behavior of bubbles wrapped in a...Bubbles within an elastic shell,which undergo ultrasound-driven oscillation to treat tumors and soft tissues,are frequently treated as viscoelastic media.Therefore,studying the dynamic behavior of bubbles wrapped in a viscoelastic medium while considering an elastic shell can provide theoretical support for ultrasound biotherapy.Bubbles are always in the form of clusters.Therefore,a model of spherical bubble clusters in a liquid cavity wrapped by an elastic shell was constructed,the coupled oscillation equations of bubbles were obtained by taking into account the dynamic effects of the elastic shell and the viscoelastic media outside the cavity,and the oscillation behaviors of the bubbles were analyzed.Acoustic waves at 1.5 MHz could cause bubbles with a radius of 1μm to resonate.Increasing the number of bubbles increased the suppressing effect of bubble oscillation caused by bubble interaction.The bubble cluster oscillation caused the elastic shell to oscillate and be stressed,and the stress trend was the inverse of the bubble oscillation trend with maximal tensile and compressive stresses.Bubbles with an equilibrium radius of 2μm exhibited the lowest inertial cavitation threshold,making inertial cavitation more likely under high-frequency acoustic excitation.The inertial cavitation threshold of bubbles was heavily influenced by the acoustic wave frequency,bubble number density,and bubble cluster radius.The nonspherical oscillation stability of bubbles was primarily affected by the driving acoustic pressure amplitude and frequency,bubble initial radius,bubble number density,and bubble cluster radius.The acoustic frequency and amplitude exhibited a synergistic effect,with a minimum unstable driving acoustic pressure threshold of approximately 0.13 MPa.The initial radius within the elastic shell affected the minimum unstable driving acoustic pressure threshold.展开更多
Addressing the issue of excessive cavitation pressure fluctuation on the propeller behind a catamaran,numerical simulation is conducted to assess the quality of the wake flow and to numerically predict the pressure fl...Addressing the issue of excessive cavitation pressure fluctuation on the propeller behind a catamaran,numerical simulation is conducted to assess the quality of the wake flow and to numerically predict the pressure fluctuation induced by the propeller cavitation.Additionally,the interaction between the wake vortex field and the propeller is investigated,revealing the presence of propeller-hull vortex.To improve the propeller's inflow quality,the impact of vortex generators on the wake flow and pressure fluctuation is numerically simulated.Then,numerical simulations are conducted to compare the cavitation pressure fluctuation of optimized propeller design,evaluating the effects of vortex generators at different spatial locations and angles of attack,to determine the optimal vortex generator scheme.A more comprehensive integrated control plan for the wake flow and the cavitation pressure fluctuation of the propeller behind the catamaran is finally formed.展开更多
文摘Increase of efficiency of cavitation processes in liquids and melts is reached by gas cavities saturation with the sizes not exceeding the resonant sizes of cavitation germs. Gas saturation of liquids and melts raises level of cavitation pressure upon 20% - 25% that intensifies US processing: cleaning, soldering and metallization.
基金Supported by the National Natural Science Foundation of China(No.11274092,11274091,11304026)the Fundamental Research Funds for the Central Universities(No.14B10128)
文摘Intensity of cavitation is significant in ultrasonic wastewater treatment,but is complicated to measure.A time difference based method of ultrasonic cavitation measurement is proposed.The time differences at different powers of 495 kHz ultrasonic are measured in experiment in comparison with conductimetric method.Simulation results show that time difference and electrical conductivity are both approximately positive proportional to the ultrasonic power.The degradation of PNP solution verifies the availability in wastewater treatment by using ultrasonic.
基金support from the National Natural Science Foundation of China(No.52204274)the Shandong Provincial Natural Science Foundation,China(No.ZR2021QE122)+1 种基金Shandong Provincial Department of Science and Technology Key Project,China(No.2023TZXD021)Shandong Provincial Department of Science and Technology,China(No.ZTYJY-KY-2033-11).
文摘Gold ores in the Jiaozhou region of China are characterized by their abundant reserves,low grade,fine dissemination,and chal-lenges in upgrading.Froth flotation,with xanthate as the collector,is a commonly employed method for enriching auriferous pyrite from these ores.This study aimed to develop a more efficient flotation process by utilizing cavitation nanobubbles for a low-grade gold ore.Batch flotation tests demonstrated that nanobubbles significantly enhanced the flotation performance of auriferous pyrite,as evidenced by improved concentrate S and Au grades and their recoveries.The mechanisms underlying this enhancement were explored by investigat-ing surface nanobubble(SNB)formation,bulk nanobubble(BNB)attachment to hydrophobic pyrite surfaces,and nanobubble-induced agglomeration using atomic force microscopy(AFM)and focused beam reflectance measurement(FBRM).The results revealed that nan-obubble coverage on the pyrite surface is a critical factor influencing surface hydrophobicity and agglomeration.SNBs exhibited higher coverage on pyrite surfaces with increased surface hydrophobicity,flow rate,and cavitation time.Similarly,BNB attachment on pyrite surfaces was significantly increased with surface hydrophobicity and cavitation time.Enhanced surface hydrophobicity,along with higher flow rates and cavitation times,promoted pyrite particle agglomeration owing to the increased nanobubble coverage,ultimately leading to improved flotation performance.
文摘This paper aims to numerically explore the characteristics of unsteady cavitating flow around a NACA0015 hydrofoil,with a focus on vorticity attributes.The simulation utilizes a homogeneous mixture model coupled with a filter-based density correction turbulence model and a modified Zwart cavitation model.The study investigates the dynamic cavitation features of the thermal fluid around the hydrofoil at various incoming flow velocities.It systematically elucidates the evolution of cavitation and vortex dynamics corresponding to each velocity condition.The results indicate that with increasing incoming flow velocity,distinct cavitation processes take place in the flow field.
基金supported by the National Natural Science Foundation of China(Research Project No.52169018).
文摘Cavitation is an unavoidable phenomenon in the operation of centrifugal pumps.Prolonged cavitation can cause significant damage to the components of the flow channel,and in severe cases,it may even interfere with the normal energy exchange processes within the pump.Therefore,effective monitoring of cavitation in centrifugal pumps is crucial.This article presents a study that approaches the issue from an acoustic perspective,using experimental methods to gather and analyze acoustic data at the inlet and outlet of centrifugal pumps across various flow rates,with hydrophones as the primary measuring instruments.Results show that flow rate significantly affects noise levels in both non-cavitation and mild cavitation stages,with noise increasing as the flow rate rises.As the cavitation margin(NPSHa)decreases,inlet and outlet noise trends diverge:inlet noise drops sharply,while outlet noise initially increases before sharply decreasing.Both exhibit a distinct zone of abrupt change,where NPSHa values offer earlier cavitation detection than traditional methods.The noise at the pump’s inlet and outlet primarily consists of discrete and broadband noise,with most energy concentrated at discrete frequencies—shaft frequency(24 Hz),blade frequency(144 Hz),and their harmonics.As NPSHa decreases,the inlet’s discrete and broadband noise frequencies decline,while they increase at the outlet.Monitoring changes in these spectrum characteristics provides an additional means of predicting cavitation onset.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52479085,12472245)supported by the Hubei Provincial Natural Science Foundation of China(Grant No.2023AFB826)。
文摘Cavitation and cavitation erosion are prevalent phenomena in hydraulic machinery.In the present paper,a multiscale Eulerian-Lagrangian method in OpenFOAM is used to simulate cavitating flow in a Venturi tube.Additionally,a novel erosion prediction model is proposed,incorporating material hardening behavior under impact loads caused by asymmetric bubble collapse near walls.The model couples detailed bubble dynamics with the nonlinear plastic response of materials,enabling direct calculation of erosion pit depth.Simulation results show strong agreement with experimental erosion patterns,confirming the feasibility of this new method.The proposed method is pivotal for further studying how various materials respond to cavitation wear.
文摘Hydrodynamic cavitation,as an efficient technique applied in many physical and chemical treatment methods,has been widely used by various industries and in several technological fields.Relevant generators,designed with specific structures and parameters,can produce cavitation effects,thereby enabling effective treatment and reasonable transformation of substances.This paper reviews the design principles,performance,and practical applications associated with different types of cavitation generators,aiming to provide theoretical support for the optimization of these systems.It systematically analyzes the underpinning mechanisms and the various factors influencing the cavitation phenomena,also conducting a comparative analysis of the performance of different types of generators.Specific applications dealing with wastewater treatment,chemical reaction acceleration,and other fields are discussed together with the advantages,disadvantages,and applicability of each type of cavitation generator.We also explore research progress in areas such as cavitation stability,energy efficiency,and equipment design upgrades.The study concludes by forecasting the application prospects of intelligent design and computational fluid dynamics(CFD)in optimizing and advancing cavitation generators.It proposes new ideas for the further development of cavitation technology and highlights directions for its widespread future application.
基金supported by the program for National Natural Science Foundation of China (Nos. 52174173, 52274188, and 52104190)the Joint Funds of the National Natural Science Foundation of China (No. U24A2091)+1 种基金The Natural Science Foundation of Henan Polytechnic University (No. B2021-2)Double FirstClass Initiative of Safety and Energy Engineering (Henan Polytechnic University) (Nos. AQ20240703 and AQ20230304)。
文摘Under submerged conditions, compared with traditional self-excited oscillating pulsed waterjets(SOPWs), annular fluid-enhanced self-excited oscillating pulsed waterjets(AFESOPWs) exhibit a higher surge pressure through self-priming. However, their pressure frequency and cavitation characteristics remain unclear, resulting in an inability to fully utilize resonance and cavitation erosion to break coal and rock. In this study, high-frequency pressure testing, high-speed photography, and large eddy simulation(LES) are used to investigate the distribution of the pressure frequency band, evolution law of the cavitation cloud, and its regulation mechanism of a continuous waterjet, SOPW, and AFESOPW. The results indicated that the excitation of the plunger pump, shearing layer vortex, and bubble collapse corresponded to the three high-amplitude frequency bands of the waterjet pressure. AFESOPWs have an additional self-priming frequency that can produce a larger amplitude under a synergistic effect with the second high-amplitude frequency band. A better cavitation effect was produced after self-priming the annulus fluid, and the shedding frequency of the cavitation clouds of the three types of waterjets was linearly related to the cavitation number. The peak pressure of the waterjet and cavitation erosion effect can be improved by modulating the waterjet pressure oscillation frequency and cavitation shedding frequency.
基金supported by the National Natural Science Foundation of China(Nos.22136003 and 21972073)the Opening foundation of the Engineering Research Center of Ecoenvironment in Three Gorges Reservoir Region,Ministry of Education(No.KF2023-01)the Natural Science Foundation of Yichang City(No.A22-3-005)。
文摘The synergetic technology of hydrodynamic cavitation(HC)and peroxydisulfate(PDS)has been adopted for the treatment of organic pollutants,while the rationale behind the thermal-activation of PDS in this process remains lacking.This paper presented investigation on the degradation of tetracycline under two types of operating conditions,including“internal reaction conditions”(pH value and TC/PDS molar ratio)and“external physical conditions”(hole shape,solution temperature and inlet pressure).Special emphasis was paid on the analysis of thermal effects through a robust modeling approach.The results showed that a synergy index of 6.26 and a degradation rate of 56.71%could be obtained by the HC-PDS process,respectively,when the reaction conditions were optimized.Quenching experiment revealed that·OH and·SO_(4)^(-)were the predominant free radicals and their contribution to the degradation was 75.4%and 24.6%respectively,since a part of·SO_(4)^(-)was transformed into·OH in the solution.The thermal activation of PDS mainly occurred near the hole where the fitting temperature was around 340 K,while·OH was generated in the bubble collapse region downstream the hole,where the temperature was much higher and favorable for the cleavage of water molecular.The average temperature under different external physical conditions was in good consistence with the degradation rates.This research developed a useful method to effectively evaluate the activation extent of PDS by HC and could provide reliable guidance for further development of cavitational reactors to treat organic pollutants based on this hybrid approach.
文摘During strong unsteady flow processes such as cavitation initiation and collapse,the volume changes generated by the materials transformation of cavitation phase transition seriously lag behind the volume evolution formed by the flow process.The phase transition and hydrodynamics are in a non-equilibrium state.A cavitation model that can describe such non-equilibrium phenomena is needed in numerical simulations of cavitation flow.The paper starts from the molecular dynamics’principle of phase change of matter,and based on the Maxwell velocity distribution form of molecular thermal motion,elaborates on the formation process of Hertz Knudsen formula for material exchange at the interface between liquid and vapor.On this basis,using the evolution equation of gas nucleus number density in water and the compressible state equation of vapor,a non-equilibrium cavitation model for phase transition and hydrodynamics is established.The simulation results of a vapor bubble collapse process in the non-equilibrium cavitation model show different behavior from the simulation results of the equilibrium cavitation model.The simulation results of the equilibrium cavitation model show that the vapor bubble collapses once and completely disappear,while the simulation results of the non-equilibrium cavitation model show multiple collapses and rebound,which is agreement with the experimental results of the vapor bubble collapse.
基金Supporting by the project‘FILE NO.CRG/2022/001718’.
文摘Understanding the behaviour of composite marine propellers during operating conditions is a need of the present era since they emerge as a potential replacement for conventional propeller materials such as metals or alloys.They offer several benefits,such as high specific strength,low corrosion,delayed cavitation,improved dynamic stability,reduced noise levels,and overall energy efficiency.In addition,composite materials undergo passive deformation,termed as“bend-twist effect”,under hydrodynamic loads due to their inherent flexibility and anisotropy.Although performance analysis methods were developed in the past for marine propellers,there is a significant lack of literature on composite propellers.This article discusses the recent advancements in experimental and numerical modelling,state-of-the-art computational technologies,and mutated mathematical models that aid in designing,analysing,and optimising composite marine propellers.In the initial sections,performance evaluation methods and challenges with the existing propeller materials are discussed.Thereafter,the benefits of composite propellers are critically reviewed.Numerical and experimental FSI coupling methods,cavitation performance,the effect of stacking sequence,and acoustic measurements are some critical areas discussed in detail.A two-way FSI-coupled simulation was conducted in a non-cavitating regime for four advanced ratios and compared with the literature results.Finally,the scope for future improvements and conclusions are mentioned.
基金Funded by the National Natural Science Foundation of China(52066011)Jiuquan Science and Technology Plan Project University-Level Key Project(2024XJKXM03)Foundation of Key Laboratory of Solar Power System(Grant No.2024SPKL03).
文摘Bulb-type hydro turbines are commonly used in small-to medium-scale hydropower stations due to their compact design and adaptability to low-head conditions.However,long-termoperation often results in wear at the runner rim,increasing tip clearance and triggering leakage flow and cavitation.These effects reduce hydraulic efficiency and accelerate blade surface erosion,posing serious risks to unit safety and operational stability.This study investigates the influence of tip clearance on cavitation performance in a 24 MW prototype bulb turbine.A three-dimensional numericalmodel is developed to simulate various operating conditions with different tip clearance values(3.0,4.5,and 6.0 mm)and cavitation numbers(σ=1.20–1.33).Internal flow characteristics—including pressure distribution,velocity fields,hydraulic efficiency,and pressure pulsation—are analyzed to elucidate the impact of tip clearance on cavitation development.Results show that underσ=1.2 and a 4.5 mm tip clearance,the pressure pulsation amplitude at the blade tip reaches 4870 Pa—approximately 1.5 times higher than that near the hub.At partial flowconditions,turbine efficiency decreases by up to 6.8%compared to the rated condition.Increasing the tip clearance from 1.5 to 6.0 mm expands the low-pressure area near the blade tip by around 32%,significantly intensifying cavitation.Frequency domain analysis reveals dominant pulsation frequencies between 10–20Hz,characterized by blade-passing features and a wave-clipping effect.These findings provide theoretical insight and quantitative evidence to support the optimization of tip clearance design and cavitation mitigation strategies in bulb turbines,aiming to improve both efficiency and operational stability.
文摘Bubbles play crucial roles in various fields,including naval and ocean engineering,chemical engineering,and biochemical engineering.Numerous theoretical analyses,numerical simulations,and experimental studies have been conducted to reveal the mysteries of bubble motion and its mechanisms.These efforts have significantly advanced research in bubble dynamics,where theoretical study is an efficient method for bubble motion prediction.Since Lord Rayleigh introduced the theoretical model of single-bubble motion in incompressible fluid in 1917,theoretical studies have been pivotal in understanding bubble dynamics.This study provides a comprehensive review of the development and applicability of theoretical studies in bubble dynamics using typical theoretical bubble models across different periods as a focal point and an overview of bubble theory applications in underwater explosion,marine cavitation,and seismic exploration.This study aims to serve as a reference and catalyst for further advancements in theoretical analysis and practical applications of bubble theory across marine fields.
基金support from the National Natural Science Foundation of China(No.42177299)the Guangdong Province Key Areas Research and Development Plan Project,China—Key Preparation Technology and Application of Green and Efficient Agricultural Input Controlled-Release Materials(No.2023B0202080002)。
文摘Soil aggregate stability is a fundamental measure for evaluating soil structure.While numerous tests exist for assessing soil aggregate stability,ultrasonic agitation(UA)is widely recognized for its effectiveness.Nonetheless,a significant limitation of UA is the lack of standardized methodologies and stability assessment criteria,resulting in inconsistency and incomparability across studies.Several critical factors influence the assessment of soil aggregate stability,including sample preparation(e.g.,drying,sieving,and settling duration),initial and final aggregate size classes,the definition of final energy form and its calculation,variations in instrumentation and laboratory procedures,and the absence of standardized criteria.Unlike some stability methods,UA produces a broad range of results,with dispersion energy varying significantly(0.5–13440 J g^(-1))across different soil and aggregate types due to divergent procedural settings.These settings encompass factors such as initial power and amplitude,temperature fluctuation,soil/water ratio,probe specification(diameter and insertion depth),and the choice of liquid used during the process.Furthermore,UA faces challenges related to limited reproducibility,raising doubts about its status as a standard stability assessment method.To address these issues,standardization through predefined procedures and stability criteria has the potential to transform UA into a precise and widely accepted method for both qualitative and quantitative assessments of soil stability.In this comprehensive review,we outline the challenges in standardizing UA,elucidate the factors contributing to dispersion energy variation,and offer practical recommendations to establish standardized protocols for UA in soil aggregate stability assessments.
基金Supported by the National Key R&D Program of China(2022YFB3303501)the National Natural Science Foundation of China(Project Nos.52176041 and 12102308)the Fundamental Research Funds for the Central Universities(Project Nos.2042023kf0208 and 2042023kf0159).
文摘Verification and validation(V&V)is a helpful tool for evaluating simulation errors,but its application in unsteady cavitating flow remains a challenging issue due to the difficulty in meeting the requirement of an asymptotic range.Hence,a new V&V approach for large eddy simulation(LES)is proposed.This approach offers a viable solution for the error estimation of simulation data that are unable to satisfy the asymptotic range.The simulation errors of cavitating flow around a projectile near the free surface are assessed using the new V&V method.The evident error values are primarily dispersed around the cavity region and free surface.The increasingly intense cavitating flow increases the error magnitudes.In addition,the modeling error magnitudes of the Dynamic Smagorinsky-Lilly model are substantially smaller than that of the Smagorinsky-Lilly model.The present V&V method can capture the decrease in the modeling errors due to model enhancements,further exhibiting its applicability in cavitating flow simulations.Moreover,the monitoring points where the simulation data are beyond the asymptotic range are primarily dispersed near the cavity region,and the number of such points grows as the cavitating flow intensifies.The simulation outcomes also suggest that the re-entrant jet and shedding cavity collapse are the chief sources of vorticity motions,which remarkably affect the simulation accuracy.The results of this study provide a valuable reference for V&V research.
基金supported by the Leading Talent Project for Scientific and Technological Innovation in Zhejiang Province(Grant No.2023R5220).
文摘The underwater launch of an axisymmetric body involves complex cavity-structure interactions.Studying the evolution of cavity pressure around an axisymmetric body is crucial for researching its motion stability.In this work,we propose a deep neural network model for cavity pressure distribution recovery,called CPDR-net.This model can reconstruct the full-domain distribution of surface pressure based solely on the local pressure distribution.The CPDR-net model was trained using numerical simulation data with different launch depths and initial velocities,and subsequently tested on two simulation datasets under new conditions.Both training and testing datasets are obtained from the ventilated cavitating flow over an underwater axisymmetric vehicle.Results demonstrated that CPDR-net can accurately predict the pressure distribution along each longitudinal line of the axisymmetric body and provide the pressure evolution over time for each point on the surface.Thus,we can obtain the evolution of surface pressure distribution throughout the entire voyage process based on the CPDR-net model.The findings from this study may provide a valuable reference for subsequent research on underwater launches.
基金supported by the National Science Foundation of China (Grant Nos.52279081,and 51839001).
文摘The behaviors of unsteady flow structures and corresponding hydrodynamics for a pitching hydrofoil are investigated numerically and theoretically in the present paper.The aims are to derive the total lift by finite-domain impulse theory for subcavitating flow(σ=8.0)and cavitating flow(σ=3.0),and to quantify the distinct impact of individual vortex structures on the transient lift to appreciate the interplay among cavitation,flow structures,and vortex dynamics.The motion of the hydrofoil is set to pitch up clockwise with an almost constant rate from 0°to 15°and then back to 0°,for the Reynolds number,7.5×105,and the frequency,0.2 Hz,respectively.The results reveal that the presence of cavities delays the migration of the laminar separation bubble(LSB)from the trailing edge(TE)to the leading edge(LE),consequently postponing the hysteresis in the inflection of lift coefficients.The eventual stall under the sub-cavitation regime is the result of LSB bursting.While the instabilities within the leading-edge LSB induce the convection of cavitation-dominated vortices under the cavitation regime instead.Having validated the lift coefficients on the hydrofoil through the finite-domain impulse theory using the standard force expression,the Lamb vector integral emerges as the main contribution to the generation of unsteady lift.Moreover,the typical vortices’contributions to the transient lift during dynamic stall are accurately quantified.The analysis indicates that the clockwise leading-edge vortex(−LEV)contributes positively,while the counterclockwise trailing-edge vortex(+TEV)contributes negatively.The negative influence becomes particularly pronounced after reaching the peak of total lift,as the shedding of the concentrated wake vortex precipitates a sharp decline due to a predominant negative lift contribution from the TEV region.Generally,the vortices’contribution is relatively modest in sub-cavitating flow,but it is notably more significant in the context of incipient cavitating flow.
基金supported by the Higher Education Science and Technology Innovation Project of Shanxi Province(No.2022L706)Natural Science Foundation of Jiangsu Province(No.BK20210755).
文摘Polymer microfluidic chips are a common tool in biomedical research,and the production of mold inserts with microscale structures represents a crucial step in the precise molding of these chips.Electrical discharge machining(EDM)can achieve high-quality machining of microstructures on high-hardness mold steel inserts.This can reduce the manufacturing cost of microfluidic chip molds and extend the service life of molds.However,the EDM process is susceptible to the formation of poor-quality surfaces due to the occurrence of abnormal discharges.To address this issue,this paper presents in-depth research on a novel ultrasonic cavitation-assisted electrical discharge machining method.An ultrasonic transducer is placed in an electrical discharge working fluid to promote the removal of electrical corrosion products through the cavitation effect of the liquid.This can also reduce the occurrence of poor discharge,thereby improving the machining surface quality.The aluminum foil corrosion method is employed to investigate the distribution of ultrasonic action in the electric discharge working fluid.The attenuation law of ultrasonic action in the electric discharge working fluid is also investigated.The range of ultrasonic action is determined,providing a reference for subsequent ultrasonic vibration electric discharge working fluid processing experiments.The results of the aluminum foil tests are used to inform the selection of NAK80 mold steel as the experimental object.The effects of cavitation at three ultrasonic frequencies on the surface microstructure are investigated.The experimental results indicate that ultrasonic cavitation can facilitate the movement of corrosion products in electrical machining,reduce the occurrence of abnormal discharges caused by carbon deposition or the secondary re-melting of metals,and thereby enhance the machining surface quality.
基金supported by the National Natural Science Foundation of China(Grant No.12374441)。
文摘Bubbles within an elastic shell,which undergo ultrasound-driven oscillation to treat tumors and soft tissues,are frequently treated as viscoelastic media.Therefore,studying the dynamic behavior of bubbles wrapped in a viscoelastic medium while considering an elastic shell can provide theoretical support for ultrasound biotherapy.Bubbles are always in the form of clusters.Therefore,a model of spherical bubble clusters in a liquid cavity wrapped by an elastic shell was constructed,the coupled oscillation equations of bubbles were obtained by taking into account the dynamic effects of the elastic shell and the viscoelastic media outside the cavity,and the oscillation behaviors of the bubbles were analyzed.Acoustic waves at 1.5 MHz could cause bubbles with a radius of 1μm to resonate.Increasing the number of bubbles increased the suppressing effect of bubble oscillation caused by bubble interaction.The bubble cluster oscillation caused the elastic shell to oscillate and be stressed,and the stress trend was the inverse of the bubble oscillation trend with maximal tensile and compressive stresses.Bubbles with an equilibrium radius of 2μm exhibited the lowest inertial cavitation threshold,making inertial cavitation more likely under high-frequency acoustic excitation.The inertial cavitation threshold of bubbles was heavily influenced by the acoustic wave frequency,bubble number density,and bubble cluster radius.The nonspherical oscillation stability of bubbles was primarily affected by the driving acoustic pressure amplitude and frequency,bubble initial radius,bubble number density,and bubble cluster radius.The acoustic frequency and amplitude exhibited a synergistic effect,with a minimum unstable driving acoustic pressure threshold of approximately 0.13 MPa.The initial radius within the elastic shell affected the minimum unstable driving acoustic pressure threshold.
文摘Addressing the issue of excessive cavitation pressure fluctuation on the propeller behind a catamaran,numerical simulation is conducted to assess the quality of the wake flow and to numerically predict the pressure fluctuation induced by the propeller cavitation.Additionally,the interaction between the wake vortex field and the propeller is investigated,revealing the presence of propeller-hull vortex.To improve the propeller's inflow quality,the impact of vortex generators on the wake flow and pressure fluctuation is numerically simulated.Then,numerical simulations are conducted to compare the cavitation pressure fluctuation of optimized propeller design,evaluating the effects of vortex generators at different spatial locations and angles of attack,to determine the optimal vortex generator scheme.A more comprehensive integrated control plan for the wake flow and the cavitation pressure fluctuation of the propeller behind the catamaran is finally formed.
