Cavitation Field Research Articles

Experimental study on attenuation effect of liquid viscosity on shockwaves of cavitation bubbles collapse

How to precisely control and efficiently utilize the physical processes such as high temperature, high pressure, and shockwaves during the collapse of cavitation bubbles is a focal concern in the field of cavitation applications. The viscosity change of the liquid will affect the bubble dynamics in turn, and further affect the precise control of intensity of cavitation field. This study used high-speed photography technology and schlieren optical path system to observe the spatiotemporal evolution of shockwaves in liquid with different viscosities. It was found that as the viscosity of the liquid increased, the wave front of the collapse shockwave of the cavitation bubble gradually thickened. Furthermore, a high-frequency pressure testing system was used to quantitatively analyze the influence of viscosity on the intensity of the shockwave. It was found that the pressure peak of the shockwave in different viscous liquid was proportional to Lb (L represented the distance between the center of bubble and the sensor measuring point), and the larger the viscosity was, the smaller the value of b was. Through in-depth analysis, it was found that as the viscosity of the liquid increased, the proportion of the shockwave energy of first bubble collapse to the maximal mechanical energy of bubble gradually decreased. The proportion of the mechanical energy of rebounding bubble to the maximal mechanical energy of bubble gradually increased. These new findings have an important theoretical significance for the efficient utilization of ultrasonic cavitation.

Cavitation Characteristics in Ultrasonic Soldering and the Erosion Effect

In this work, the cavitation characteristics of the solder sonocapillary action during ultrasonic soldering were studied by a high-speed camera. The effects of ultrasonic power and time on the acoustic pressure, cavitation characteristics, and erosion effects were also investigated. Results showed that cavitation occurred throughout the entire sonocapillary action. Two kinds of bubble structures were observed. The steady bubbles had large sizes and long life periods. The transient bubbles had small sizes and short life periods. The steady bubbles preferentially appeared at the primary filling stage, while the transient bubbles dominated the entire cavitation field. The sonocapillary action was divided into the primary filling stage, the intermediate filling stage, and the completion filling stage. The primary filling stage had low acoustic pressure but high bubble density because the air content in the solder was high and some additional air entered the solder through the triple interface caused by ultrasonic vibration. Higher ultrasonic power resulted in stronger cavitation and, thus, better erosion effect on the substrate.

Theoretical study on the movements of bubbles

The radial and translational motions of multiple interacting spherical bubbles are obtained using classical Newton mechanics. It is seen that bubbles not only move in straight line, but also in circular motion. The tracks of the bubbles show that the interactions among them include attractive, repulsive and dynamic equilibrium. There are three types of straight line corresponding to attraction, coexistence of attraction and repulsion and dynamic equilibrium, and two types of circular movement corresponding to attraction and dynamic equilibrium. The results can provide an explanation for cavitation chain and profile in cavitation field.

Analysis on the evolution of cavitation and flow field of vehicles entering water vertically at high speed

A numerical method is developed to consider the effects of fluid force and structural deformation on the flow field. The accuracy of the method is verified by experiments. The cavity evolution process are studied, and the characteristics of the velocity and vortex in the calculated flow field region are analyzed. The motion process of the dynamic wall of the cavity around the vehicle is simulated, and the phenomena of vortex distribution in the wake of the vehicle, instability in the wake of the cavity, and multistage closure of the cavity wall are obtained. It is revealed that the closing of the cavity will cause the velocity of the flow field inside the cavity to be reduced, and the return jet generated by the closing of the cavity will hit the vehicle and cause its attitude to be deflected. The peak velocity of the cavity wall appears at the position of cavity closure and the position of head cavity generation. The vortex scale around the vehicle gradually increases from the head of the body towards the top of the water surface. The research in this paper provides reference for the design of water entry vehicle.

Investigation of Valve Seat Cone Angle on Small Opening Direct-Acting Relief Valve Cavitation Noise

Direct-acting relief valves are important pressure-control components in hydraulic systems; however, noise problems are now common. This study aimed to reduce and numerically analyze the valve cavitation and noise using the Zwart–Gerber–Belamri (ZBG) model with the Ffowcs Williams and Hawkings (FW–H) model to optimize the design based on the sound field perspective. First, a direct-acting relief valve flow field model was established to determine the relationship between the seat structure and the degree of cavitation through a CFD (Computational Fluid Dynamics) simulation. Second, sound field analysis was conducted based on the cavitation and non-cavitation flow fields, respectively, and the resulting noise levels were compared. Finally, prototypes of the relief valve were manufactured, and noise levels between the original and optimized valves were compared. The results revealed that cavitation within the relief valve generated noise while optimizing the valve seat cone angle suppressed this phenomenon, thereby reducing the noise emitted by the optimized valve by 18.2 dB compared to the original valve. These findings can serve as a guide for designing and optimizing direct-acting relief valves.

Study of the Influence of Cavitation and Magnetic Field on the Change of Water Properties and its Purification in a Vibrating Machine with Determination of Drive Modes

Study of the Influence of Cavitation and Magnetic Field on the Change of Water Properties and its Purification in a Vibrating Machine with Determination of Drive Modes

High-speed photography and particle image velocimetry of cavitation in a Venturi tube

This article details the construction of an experimental visualization platform for observing cavitation. The platform uses high-speed photography and particle image velocimetry (PIV) techniques to conduct experimental research into the flow pattern and vortex field of cavitation in Venturi tubes. Dynamic mode decomposition is employed to extract the energy distribution characteristics of the cavitation flow field. Cavitation occurs at an exit-to-inlet pressure ratio of 0.595, and the length of the cavitation zone increases as this ratio decreases. When the pressure ratio reaches 0.280, the flow rate remains almost constant and the flow becomes chocked. The cavitation shape evolves periodically in the chocking flow, and the cavitation zone can be divided into three parts: an initiation and development area, a fusion area, and a collapse area. The fusion area exhibits periodic changes in the form of contraction, expansion, and re-contraction. Near the wall, the collapse area exhibits complex boundary conditions, with re-entrant jet causing bubble aggregation, rolling, and shedding. PIV and energy extraction reveal that vortices primarily appear near the wall, where they undergo a periodic process of fragmentation and fusion. The strength of the vortices exhibits a small–large–small pattern that is related to the cloud aggregation, rolling, and shedding caused by the re-entrant jet.

Efficient degradation of organics by ultrasonic piezoelectric effect on CuO-BTO/AFC composite

The recombination of photoexcited electron–hole pairs greatly limits the degradation performance of photocatalysts. Ultrasonic cavitation and internal electric field induced by the piezoelectric effect are helpful for the separation of electron–hole pairs and degradation efficiency. The activated foam carbon (AFC) owing to its high surface area is often used as the substrate to grow catalysts to provide more reactive active sites. In this work, CuO@BaTiO3 (CuO@BTO) heterostructure is prepared by hydrothermal method on the surface of AFC to investigate the ultrasonic piezoelectric catalysis effect. X-ray diffraction (XRD), Raman spectroscopy, energy dispersive x-ray spectroscopy (EDS) and scanning electron microscopy (SEM) were used to analyze the structure and morphology of CuO-BTO/AFC composite. It is found that the CuO-BTO/AFC composite exhibits excellent piezo-catalytic performance for the degradation of organics promoted by ultrasonic vibration. The CuO-BTO/AFC composite can decompose methyl orange and methylene blue with degradation efficiency as high as 93.9% and 97.6% within 25 min, respectively. The mechanism of piezoelectricity enhanced ultrasound supported catalysis effect of system CuO-BTO/AFC is discussed. The formed heterojunction structure between BTO and CuO promotes the separation of positive and negative charges caused by the piezoelectric effect.

Visual experimental study on cavitation performance of double-suction centrifugal pump

In this paper, the cavitation test results of double-suction centrifugal pump are further “visualized” and verified by using high-speed photography technology to photograph the development process and flow field of impeller inlet cavitation. By optimizing the impeller inlet parameters, the key geometric factors affecting the cavitation performance of the double suction pump were determined. The experimental results show that by optimizing the inlet parameters of the double-suction pump and combining the visualization test verification of cavitation, on the basis of ensuring the wide and efficient efficiency of the double-suction centrifugal pump, the optimization scheme of the experimental design greatly improves its cavitation performance, and provides a new design idea and reference for guiding the development and design of products with high cavitation performance.

Estimation of 2D pressure and cavitation fields from sparse pseudo-pressure sensor point data using super-resolution machine learning

Estimation of 2D pressure and cavitation fields from sparse pseudo-pressure sensor point data using super-resolution machine learning

Structural stability analysis of spherical bubble clusters in acoustic cavitation fields

The upwelling growth and evolution of spherical bubble clusters appearing at one-quarter wavelength from the water surface in ultrasonic cavitation fields at frequencies of 28 kHz and 40 kHz are studied by high-speed photography. Due to the interactions among bubbles, the stable bubble aggregation occurs throughout the rise of the bubble cluster, whose vertical pressure difference leads to a more significant spreading in the upper part of the cluster in the standing-wave field. At 28 kHz, the rising speed is about 0.6 m/s, controlled by the primary acoustic field. After a violent collapse of the bubble clusters, the aggregating structure begins to hover near the water surface. The size and stability of the structure are affected by the frequency and pressure of the primary acoustic field. If two clusters are close to each other, the clusters deviate from the spherical shape, even trailing off, and eventually merge into a single bubble cluster. By considering the influence of water-air boundary, based on the mirror principle, a spherical bubble cluster model is developed to explore the structure stability of the clusters, and the modified dynamics equations are obtained. The effects of driving acoustic pressure amplitude, bubble number density, water depth, and bubble equilibrium radius on the optimal stable radius of the spherical bubble cluster are numerically analyzed by using the equivalent potentials at 28 kHz and 40 kHz. The results show that the optimal stabilizing radius of spherical bubble cluster is in a range of 1–2 mm, and it tends to decrease slightly with the increase of the driving acoustic pressure and bubble number density. It is worth noting that the nonlinearity is enhanced by increasing acoustic pressure, which may promote the stability of the cluster structure. The smaller the unstable equilibrium radius, the easier it is to grow, and the stable size at 40 kHz is slightly smaller than that at 28 kHz. Generally, spherical clusters first appear in a high-pressure region and then move to a low-pressure region. If the acoustic pressure drops below a certain critical value, bubble clusters disappear. The theoretical analysis is in good agreement with the experimental observation. The analysis of the growth and structural stability of spherical bubble cluster is helpful in understanding the behavioral modulation of bubbles.

ІНТЕНСИФІКАЦІЯ ОКИСНОЇ ДЕСТРУКЦІЇ БЕНЗЕНУ НАТРІЮ ГІПОХЛОРИТОМ ПІД ДІЄЮ УЛЬТРАЗВУКОВОГО ВИПРОМІНЮВАННЯ

The process of the interaction of benzene with sodium hypochlorite in a model environment under the action of ultrasonic radiation of different power and under the metered supply of an oxidant solution was investigated. The course of the process was evaluated by the change in the value of the redox potential of the medium over time. By the method of spectrophotometric analysis, it was established that as a result of interaction with sodium hypochlorite in cavitation fields, almost complete mineralization of benzene occurs. It is shown that the oxidative destruction of benzene mainly occurs due to the products of sonolysis of water.

Unsteady Cavitation Analysis of the Centrifugal Pump Based on Entropy Production and Pressure Fluctuation

A numerical method using combined detached-eddy simulation (DES) and a cavitation model considering the rotation effect is used for unsteady cavitation flow field of the centrifugal pump. A closed-type pump test system was established to obtain the pump performance and pressure pulsation characteristics under different flow rates and cavitation condition, which provide boundary conditions and verification of calculations. Based on the calculation results of the unsteady flow field of the centrifugal pump cavitation, the entropy generation analysis of the flow field and an analysis of the pressure fluctuation characteristics were carried out. Then, we tried to reveal the relationship between cavitation and the deterioration of the centrifugal pump performance and the generation of the unstable operation excitation force. The internal energy loss is mainly concentrated in the impeller, volute, and pump cavity area, which accounts for more than 85% of the total entropy generation. The characteristic frequency of a Strouhal number of about 0.333 appears at the volute tongue due to the cavitation flow spread downstream.

Experimental study on influence of particle shape on shockwave from collapse of cavitation bubble

The bubble dynamics under the influence of particles is an unavoidable issue in many cavitation applications, with a fundamental aspect being the shockwave affected by particles during bubble collapse. In our experiments, the method of spark-induced bubbles was used, while a high-speed camera and a piezoresistive pressure sensor were utilized to investigate how particle shape affects the evolution of shockwaves. Through the high-speed photography, we found that the presence of the particle altered the consistency of the liquid medium around the bubble, which result in the emitting of water hammer shockwave and implosion shockwave respectively during the collapse of the bubble. This stratification effect was closely related to the bubble-particle relative distance φ and particle shape δ. Specifically, when the bubble-particle relative distance φ < 1.34 e-0.10δ, particles disrupted the medium consistency around the bubbles and led to a nonspherical collapse and the consequent stratification of the shockwave. By measuring the stratified shockwave intensity affected by different particle shapes, we found that the stratified shockwave intensity experienced varying degrees of attenuation. Furthermore, as the particle shape δ increased, the attenuation of the particle on shockwave intensity gradually reduced. These new findings hold significant theoretical implications for elucidating cavitation erosion mechanisms in liquid–solid two-phase flows and applications and prevention strategies in liquid–solid two-phase cavitation fields.

The relevance of bubble dynamics in ultrasonic/sonochemical processes

Acoustic cavitation bubble dynamics has been extensively studied by physicists and mathematicians. Process intensification is primarily studied by chemical engineers. Chemists tend to focus on bubble dynamics in a multibubble field to optimize the physical and chemical forces generated during acoustic cavitation with an intention to maximise/intensify chemical processes. To achieve process intensification successfully a multidisciplinary approach is required. Our early work on multibubble cavitation unveiled various factors that contribute to process optimization. For example, while single bubble dynamics can estimate the maximum bubble temperatures, they may not be relevant to achieving higher chemical yield, which in turn depends on varus other factors such as average bubble temperatures, number of active cavitation bubbles, etc. Other factors critical for process intensification include the generation of a homogeneous cavitation field, control over mass transfer effects caused by bubble oscillations, reactor design, etc. The presentation will provide an overview on the relevance of single and multibubble bubble dynamics in ultrasonic/sonochemical processes.

Deep learning, numerical, and experimental methods to reveal hydrodynamics performance and cavitation development in centrifugal pump

The hydrodynamic performance and cavitation development in centrifugal pump have a decisive impact on its energy conversion and performance. However, there are still bottlenecks when using current experimental methods and simulation algorithms in the real-time measurement and visual display of flow fields, and the high experimental and computational cost cannot be ignored. Here, we integrated computational fluid dynamics (CFD) and experimental platform with our customized framework based on a multi-attribute point cloud dataset and advanced deep learning network. This combination is made possible by our workflow to generate simulated data of flow characteristics of cavitation in the pump as the training/ test dataset, complete the deep learning algorithm process and check the consistency with the experimental results. Deep learning models the multiphase flow system of centrifugal pump and completes the mapping from the structure of pump and working conditions to the cavitation, pressure, and velocity field. The statistical analysis shows that predictions results are in agreement with the CFD method, but the calculation time is greatly reduced. Compared to the prevalent methods, the proposed deep learning framework shows superior performance in accuracy, computational cost, visual display and has the potential of generality to model the interaction between different fluids and impellers.

Numerical study on the effects of viscous heating and random rough surface on cavitating flow in fuel injection nozzles

A transient numerical model was developed to investigate cavitating flow in fuel injection nozzles, incorporating the effects of viscous heating and latent heat of phase change. A three-dimensional Gaussian rough surface generated by Monte Carlo simulation was compared to a wall function correction-based roughness model to assess the impact of surface roughness on both flow and thermal fields. Results demonstrated that viscous heating increased fuel temperature significantly near the nozzle wall, whereas latent heat had minimal effect due to the diesel fuel's low thermal sensitivity. The random rough surface performed better than the wall function correction-based model in inducing local cavitation, reflecting sub-micron scale roughness, and revealing significant randomness in velocity, temperature, and cavitation fields. Roughness height and correlation length were found to be critical factors characterizing surface roughness, where an increase in roughness height and a decrease in correlation length predicted a rougher surface and enhanced effect of viscous heating. The ratio of these two parameters showed a clear linear relationship with temperature rise. Geometric and localized cavitation were observed, leading to temperature increases caused by cavity evolution and collapse. These insights are valuable for improving fuel atomization and combustion efficiency.

Extensive investigation of geometric effects in sonoreactors: Analysis by luminol mapping and comparison with numerical predictions.

This investigation focuses on the influence of geometric factors on cavitational activity within a 20kHz sonoreactor containing water. Three vessels with different shapes were used, and the transducer immersion depth and liquid height were varied, resulting in a total of 126 experiments conducted under constant driving current. For each one, the dissipated power was quantified using calorimetry, while luminol mapping was employed to identify the shape and location of cavitation zones. The raw images of blueish light emission were transformed into false colors and corrected to compensate for refraction by the water–glass and glass-air interfaces. Additionally, all configurations were simulated using a sonoreactor model that incorporates a nonlinear propagation of acoustic waves in cavitating liquids. A systematic visual comparison between luminol maps and color-plots displaying the computed bubble collapse temperature in bubbly regions was conducted. The calorimetric power exhibited a nearly constant yield of approximately 70% across all experiments, thus validating the transducer command strategy. However, the numerical predictions consistently overestimated the electrical and calorimetric powers by a factor of roughly 2, indicating an overestimation of dissipation in the cavitating liquid model. Geometric variations revealed non-monotonic relationships between transducer immersion depth and dissipated power, emphasizing the importance of geometric effects in sonoreactor. Complex features were revealed by luminol maps, exhibiting appearance, disappearance, and merging of different luminol zones. In certain parametric regions, the luminol bright regions are reminiscent of linear eigenmodes of the water/vessel system. In the complementary parametric space, these structures either combine with, or are obliterated by typical elongated axial structures. The latter were found to coincide with an increased calorimetric power, and are conjectured to result from a strong cavitation field beneath the transducer producing acoustic streaming. Similar methods were applied to an additional set of 57 experiments conducted under constant geometry but with varying current, and suggested that the transition to elongated structures occurs above some amplitude threshold. While the model partially reproduced some experimental observations, further refinement is required to accurately account for the intricate acoustic phenomena involved.

Ultrasonics and sonochemistry: Editors’ perspective

Ultrasonic waves can induce physical and chemical changes in liquid media via acoustic cavitation. Various applications have benefitted from utilizing these effects, including but not limited to the synthesis of functional materials, emulsification, cleaning, and processing. Several books and review articles in the public domain cover both fundamental and applied aspects of ultrasonics and sonochemistry. The Editors of the Ultrasonics Sonochemistry journal possess diverse expertise in this field, from theoretical and experimental aspects of acoustic cavitation to materials synthesis, environmental remediation, and sonoprocessing. This article provides Editors’ perspectives on various aspects of ultrasonics and sonochemistry that may benefit students and early career researchers.

Stabilized formulation for phase-transforming flows with special emphasis on cavitation inception

Despite significant advancement in the field of cavitation, the inception of vapor bubbles from pure liquid is still not well understood. In this paper, we propose a numerical algorithm to solve the Navier–Stokes–Korteweg equations, which are phase-field equations that govern the dynamics of multiphase compressible flows. These equations can predict cavitation inception without phenomenological assumptions about mass transfer. We present a modification to the bulk free energy of the fluid that can help us simulate cavitation at much larger length scales than previously possible. We propose a numerical scheme based on a Taylor–Galerkin discretization, a residual-based discontinuity capturing operator and a spatial filtering scheme. Our numerical method can be used for high speed flows with large pressure gradients, which are distinctive features of flows where we observe cavitation inception. We present numerical examples that show the accuracy, stability and robustness of our scheme. Finally, we use the proposed numerical scheme to study benchmark problems in the field of cavitation inception such as flow past a wedge and flow past a bluff body. The proposed numerical scheme opens opportunities to understand different aspects of cavitation in general and inception in particular, in much more detail.