Water Cavitation Research Articles

Observation of Superposition of Cavitation Instability in Liquid Rocket Inducer by Multi-point Pressure Measurement

Abstract The purpose of this study is to investigate the relationship between the growth and contraction processes of each blade cavity and cavitation instability, and to conduct multi-point pressure measurement tests. The experiments will be conducted using cavitation water flow tunnels installed at the Kakuda Space Center of the Japan Aerospace Exploration Agency (JAXA). In the multi-point pressure measurement experiment, a number of pressure sensors are installed in the inducer casing, and the cavity area can be estimated and the cavity length can be obtained by creating a pressure distribution between the blades during the depressurization experiments. This method makes it possible to continuously determine cavity length variation during inducer experiments and to investigate the cavity growth process. In addition, cavity length variation can be obtained with higher time resolution than in visualization experiment, allowing more detailed investigation of the unsteady cavity behaviour during cavitation instability. And two types of superposition cavitation instability were found in this study: one is Super-S R.C. and C.S., the other is Sync R.C. and C.S..

Analysis of the flow field characterization on the cavitation water jet applied to planar and curved surfaces

Analysis of the flow field characterization on the cavitation water jet applied to planar and curved surfaces

Experimental study on the unsteady behavior and frequency characteristics of high-speed submerged cavitating water jets

The frequency characteristics of cavitation fluctuations in high-speed cavitating jets are intricate due to the coupling mechanisms of unsteady behaviors. This study employs high-speed photography to experimentally investigate the relationship between frequency characteristics and the unsteady behavior of cavitating jets with various cavitation numbers. Temporal evolution patterns of the cavitating jets are analyzed through spatiotemporal (s-t) diagrams. The spatial distribution and temporal evolution of cavitation fluctuation frequencies are examined using fast Fourier transform (FFT) and continuous wavelet transform (CWT), respectively. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are employed to identify coherent structures and their corresponding frequencies. In results, the s-t diagrams reveal the distinct regions influenced by cavitation shedding and collapse. FFT results indicate that upstream of the jet trajectory, spectral energy is concentrated in the shedding band, shifting toward lower frequencies with increasing axial distance. The CWT spectrum exhibits a single peak in the upstream, identifying it as the shedding frequency. POD modes associated with shedding dominate the energy contribution at higher cavitation numbers, while they become less prominent at lower cavitation numbers. DMD extracts and identifies coherent structures associated with shedding through frequency-specific decomposition.

Cavitation as a zero-waste circular economy process to convert citrus processing waste into biopolymers in high demand

Cavitation in water only, no matter whether hydrodynamic or acoustic, is a zero-waste circular economy process to convert industrial citrus processing waste into high-performance polysaccharides in high demand in a single-step at room temperature and ambient pressure using a modest amount of electricity as the only energy input. Following previous reports in which we used hydrodynamic cavitation, we now use an industrial acoustic sonicator to demonstrate the general viability of cavitation to convert biowaste residue of the industrial squeezing of pigmented sweet orange (Citrus sinensis) into highly bioactive “IntegroPectin” pectin and micronized cellulose “CytroCell”. From biomedicine through advanced composite membranes, said biomaterials hold great applicative potential. We conclude discussing the economic and technical feasibility of industrial implementation of the “CytroCav” process.

Feasibility study on the micro-forming of novel metal foil arrays based on submerged cavitating water-jet impingement

With the increasing demand for metal foil parts with micro-array structures in micro-electromechanical systems (MEMS), it is urgent to explore a novel array micro-forming technology with high efficiency, low cost, and high flexibility. The cavitation water jet uses the high-energy shock wave generated by the collapse of the cavitation bubble group as the loading force. It has the characteristics of large range of action, uniform pressure distribution, and can realize large-area array micro-forming processing. To verify the feasibility of cavitating water jet array micro-forming, this paper performs cavitating water jet array micro-forming on 304 stainless steel foil with a thickness of 80 μm, and analyzes the variation of cavitation bubbles collapse impact zone with target distance. The effects of target distance and impact time on the forming quality of metal foil array micro-holes were studied from the aspects of forming depth, surface roughness, and thickness thinning rate. The results show that the forming depth and uniformity of the array micro-holes located in the cavitation collapse area increase with time. However, with the increase of target distance, the forming depth increases first and then decreases. When the target distance is L = 120 mm, the forming depth reaches the maximum. The surface roughness ( Ra) of the array micro hole is Ra = 1.54 μm. The thickness thinning rate of the micro-forming parts is between 2% and 10%, and the maximum thickness thinning rate in the die fillet area is 13.5%. This paper provides a novel processing method for manufacturing metal foil parts with micro array structure.

Quantitative evaluation on the cavitation damage energy of metals via multiscale approaches

In-situ experimental observation cannot be an effective method in the impact process of metal cavitation erosion, and the impact damage energy prediction theory has not been established based on a detailed mathematical and physical model. Research has shown that the metal material can be regarded as a sensor to reflect the impact parameters. Soft metal materials such as industrial pure copper with a single α-phase microstructure can be a suitable sensor to detect cavitation erosion effects, revealing the impact behaviors of the cavitation jet through the depth, width and spatial distribution of cavitation pits on the surface. In this scenario, volume loss of cavitation pits on a macro/mesoscale are obtained by three-dimensional surface measurement. A coupled fluid-solid simulation model calculating the impact damage energy on a macro/mesoscale is established based on the Smoothed Particle Hydrodynamics (SPH) and the Crystal Plasticity Finite Element Method (CPFEM). Python programming is used to set the trajectory of SPH particles to determine the macro cavitation flow field. IFEM methods were used to construct the prediction theory of cavitation impact energy in a relatively simple exponential equation, establishing the quantitative relationship between cavitation impact damage energy and measured volume of cavitation pits. Compared with conventional measurement and simulation, the present multiscale approaches are assumed as a further step advancement towards calculating the impact damage energy of cavitation water jet.

Discovery of delayed gas production after implantation of a continuous-flow left ventricular assist device and a preliminary exploration of the mechanisms of its occurrence.

To characterize the gas production phenomenon in the animal model of left ventricular assist device (LVAD), and study its mechanism. An in vitro bubble precipitation experiment was conducted, and the blood samples of Parma spp. animals were divided into ordinary group and oxygen-enriched group according to whether they were oxygenated or not at the time of blood collection, and a static control group was set up respectively. Blood gases were drawn and analyzed before and after the experiment. Activate the pump, and the number of air bubbles in the loop was measured by ultrasound at different rotational speeds; CFD was applied to simulate the flow field in the blood pump, and pressure, fluid velocity vector and shear force diagrams were plotted, and a thrombus model was constructed and the flow field was simulated and plotted as a cloud diagram. There was a statistical difference in the number of bubbles in the inflow and outflow tubes of the blood pump (P values of 0.04 and 0.023, respectively), and the number of bubbles in the outflow tubes of both groups was significantly higher than the number of bubbles in the inflow tubes. The number of bubbles in the tubes of both the oxygen-enriched and normal groups was significantly higher than that in the inflow group. In both the normal and oxygen-enriched groups, more gas was produced at higher speeds than at lower speeds. Blood gas analysis showed that the reduced gas composition in the blood was mainly oxygen. Flow field simulation results: the high rotation speed group had lower central pressure and greater scalar shear. The thrombus simulation group was more prone to turbulence, sudden pressure changes, and greater shear than the normal group. Blood gas production is associated with higher partial pressures of blood oxygen, higher rotation speed, and intrapump thrombosis, and the mechanism of pump gas production is degassing of dissolved gases rather than cavitation of water, and the gas released is most likely to have oxygen. The degassing phenomenon is an warning factor for pump thrombosis.

Shedding of Cavitation Clouds in an Orifice Nozzle

Focused on the unsteady property of a cavitating water jet issuing from an orifice nozzle in a submerged condition, this paper presents a fundamental investigation of the periodicity of cloud shedding and the mechanism of cavitation cloud formation and release by combining the use of high-speed camera observation and flow simulation methods. The pattern of cavitation cloud shedding is evaluated by analyzing sequence images from a high-speed camera, and the mechanism of cloud formation and release is further examined by comparing the results of flow visualization and numerical simulation. It is revealed that one pair of ring-like clouds consisting of a leading cloud and a subsequent cloud is successively shed downstream, and this process is periodically repeated. The leading cloud is principally split by a shear vortex flow along the nozzle exit wall, and the subsequent cloud is detached by a re-entrant jet generated while a fully extended cavity breaks off. The subsequent cavitation cloud catches the leading one, and they coalesce over the range of x/d≈1.8~2.5. Cavitation clouds shed downstream from the nozzle at two dominant frequencies. The Strouhal number of the leading cavitation cloud shedding varies from 0.21 to 0.29, corresponding to the injection pressure. The mass flow rate coefficient fluctuates within the range of 0.59~0.66 at the same frequency as the leading cloud shedding under the effect of cavitation.

Water hammer stress on water transmission line

ABSTRACT The present work investigated the pressure changes caused by water hammer through the georeferenced model to investigate the stress impact on water transmission lines. The results of the hydraulic analysis of the research showed that the sudden stop of the pumps in the transmission line 1,600 m in length caused negative pressures of −5 to −10 (bar). In pressure values close to −10 (bar), the water vaporization, cavitation, and separation of the column happened. The maximum pressure in the transmission line was calculated to be 43 (mH2O) and the minimum pressure in the transmission line was 10 (mH2O). The relative vacuum mentioned in the transmission line as a destructive factor caused two columns of steam and water to collide. The collision of two columns caused a great pressure that had the potential to destroy the transmission line. The research results showed that the maximum amount of elastic strain was equal to 16772E-7 mm/m. The equivalent stress beneath the pipe Q4 varied from 0.000 to 7E-2 m and the maximum stress value was 3.3535E7 (Pascal). The maximum amount of deformation or change in the shape and size of the pipe due to the applied stress (0.000–7E-2 m) was equivalent to 1.9287E5 m.

A Study of Cavitation Erosion in Artificial Submerged Water Jets

The artificially submerged cavitation water jet is effectively utilized by ejecting a high-pressure water stream into a low-pressure water stream through concentric nozzles and utilizing the cavitation phenomenon generated by the shear layer formed between the two streams. In this study, we investigated the cavitation characteristics of artificially submerged cavitation water jets by combining numerical simulations and erosion experiments. The results indicate that an appropriate standoff distance can generate more cavitation clouds on the workpiece surface, and the erosion characteristics of the artificially submerged cavitation water jet are most pronounced at a dimensionless standoff distance of SD = 30. The shear effect formed between the two jets plays a crucial role in generating initial cavitation bubbles within the flow field of the artificially submerged cavitation water jet. Moreover, increasing the convergent angle between the two jets can significantly enhance the cavitation effect between them and lead to a more substantial cavitation effect. Simultaneously, increasing the pressure of the high-pressure inner nozzle also contributes to enhancing the cavitation effect of the artificially submerged cavitation water jet.

Mechanical mechanism of shear cavitating water jet dissociation of flake graphite

Abstract To obtain the mechanical mechanism of shear-type cavitation water jet dissociating flake graphite to improve the grinding technology of flake graphite, the motion state of flake graphite particles in shear-type cavitation water jet, the micro-jet impact process, the high-pressure elastic potential energy pressure release process, and the water wedge stretching process have been analyzed using the theory of hydraulic transport of liquid-solid two-phase, the theory of jets, the cavitation primordial principle, the principle of capacity conversion, and the water wedge action. The primary mechanical mechanism of shear cavitation water jet dissociation of flake graphite is collision friction effect, micro-jet impact, pressure release, and water wedge stretching effect, under these four kinds of loads individually or jointly, to achieve the purpose of removing the surface of flake graphite particles of the veinstone minerals to realize the dissociation of flake graphite. Moreover, the collision friction, pressure release, and water wedge stretching effects destroy the material under tensile stress to remove the veinstone minerals, and the micro-jet impact effect is the destruction of the material under compressive stress to remove the veinstone minerals.

Multibubble sonoluminescence in supercooled water.

Cavitation in supercooled water has been induced by the short ultrasound pulses of an ultrasonic horn driven at 20kHz. The cavitation during the ultrasonic pulses and occasionally the crystallization events thereafter have been imaged by a high-speed camera. The probability of ice crystallization in dependence on the pulse duration and temperature showed a high chance for the water to remain liquid if sufficiently short bursts of moderate acoustic power were applied. This regime has been used for the assessment of sonoluminescence (SL) from the generated cavitation bubbles in the supercooled liquid state. To this end, light emitting events were summed up over a number of ultrasonic pulses by an image intensifier. SL appeared mostly directly under the tip of the ultrasonic horn and sometimes also a few millimeters below the tip. The intensity of SL events showed a slight rise for a decrease in temperature, i.e., for an increase in supercooling. This behavior is in accord with the SL dependence on temperature above the freezing point and might be attributed to a further lowering of vapor pressure. An increase in the bubble collapse peak temperature for increased supercooling is calculated on the basis of spherical bubble model calculations, which supports the findings. The simulations predict further that the peak temperature will fall off again beyond a certain supercooling level.

Experimental study on cavitation water jet cleaning of marine fouling

The accumulation of marine fouling on a ship’s hull can increase its fuel consumption, necessitating removal. The use of a cavitation water jet as an efficient method for cleaning marine fouling has been widely adopted. In the research, experiments are conducted on water jet cleaning of marine fouling to investigate the influence of water jet parameters on cleaning efficiency. The findings reveal that the surface damage to specimens was minimized when maintaining an erosion pressure of 16 MPa, employing a 25 mm standoff distance, and applying a 90° incidence angle. This research can provide theoretical guidance for subsequent optimization of cavitation water jet cleaning parameters.

Evolution of cavitation clouds under cavitation impinging jets based on three-view high-speed visualization

Cavitation cloud is an important index for evaluating the unsteady behaviour of cavitation water jets. However, when cavitation jets are applied in a restricted space, the optimal standoff distance is not applied. To study the evolution and collapse mechanisms of cavitation clouds at small standoff distances, this study conducted visualization research on the behaviour of submerged cavitation water jet impacting the target surface at three standoff distances from three-view using a high-speed visualization system. The effect of the optimal standoff distance and the small standoff distance on the morphology of cavitation clouds was explored by observing their shedding behaviour and evolution on the target surface, obtaining a pattern for the morphological evolution of cavitation clouds. The evolution of cavitation clouds under impact flow conditions can be divided into stages: incipient cavitation, ring vortex cavitation, spindle-shaped cavitation cloud, mushroom-type cavitation cloud, cavitation ring, ring vortex cavitation, and collapse. The periodicity of cavitation clouds on the target surface was confirmed by monitoring the grayscale change at the center of the target. Furthermore, the changing of cavitation jet structures is illustrated through Proper Order Decomposition (POD) analysis, showing that the frequency of cavitation clouds increased with the decrease of standoff distance within a certain range. The behaviour of cavitation flow impinging on the target surface at optimal standoff distance and small standoff distance was simulated using the Large Eddy Simulation (LES) turbulence model combined with the Zwart-Gerber-Belamri (ZGB) cavitation model. The results show that the numerical simulation can capture the high-pressure zone generated when the cavitation cloud collapses, and the area of the high-pressure zone increases with the standoff distance within a certain range, the concentration of cavitation bubbles on the target surface did not represent the intensity of erosion. The transient vortex structures of the flow field at different standoff distances were investigated based on the Q-criterion. The findings of this study not only provide critical technical support for the application of cavitation jets in confined spaces, but also contribute to a broader understanding of the erosion mechanism of cavitation jets.

Study on Dynamic Evolution and Erosion Characteristics of Cavitation Clouds in Submerged Cavitating Water Jets

The dynamic evolution behavior of submerged water jet cavitation clouds was studied by combining experiments and simulation. The formation, development, shedding, and collapsing process of a void cloud was analyzed by high-speed camera technology, and the influence of jet pressure was studied. Cavitation water jet erosion experiments were carried out on AL6061 specimens with standard cylindrical nozzles, and the correlation between cavitation cloud evolution and material erosion was studied by surface analysis. The results showed that the evolution of a cavitation cloud has obvious periodicity, that one period is about 0.8 ms, and its action region can be divided according to the attenuation rate of the jet velocity of the nozzle axis. The attenuation rate of the jet velocity at the nozzle axis in the central jet action zone is less than or equal to 82.5%, in the mixed action zone greater than 82.5% and less than 96%, and in the cavitation action zone greater than or equal to 96%. The erosion damage characteristics in different regions of the mixed action zone are significantly different.

Experimental study of cavitation development in liquid in pulsed non-uniform electric field under the action of ponderomotive forces

In this paper, the Rayleigh scattering method is used to study the formation of cavitation in water in a pulsed inhomogeneous electric field when a nanosecond high voltage pulse is applied to a needlelike electrode. The observational results confirm the theoretical picture of cavitation development under the action of electrostrictive ponderomotive forces. The values of the negative pressure, the average size of the cavitation nanovoids, and their concentration were obtained from these measurements, which are in agreement with theoretical estimates.

An Experimental and Numerical Study on the Cavitation and Spray Characteristics of Micro-Orifice Injectors under Low-Pressure Conditions

A fuel injector plays a crucial role in an internal combustion engine, and the occurrence of cavitation inside the injector may affect the engine’s spray, atomization, and combustion efficiency. In this study, a micro-turbojet engine equipped with a micro-orifice fuel injector was developed that operated under low injection pressure (Pinj), that is, at a low Reynolds number (Re). Given the paucity of cavitation studies conducted under such conditions, the current study experimentally and numerically investigated the cavitation and spray characteristics of water and kerosene in a micro-orifice injector with a diameter of 0.3 mm. The results indicated that the water and kerosene exhibited no cavitation, cavitation, supercavitation, and hydraulic flip. However, the discharged jet was unaffected by internal flows, and the jet angles remained nearly constant, indicating that the cavitation in micro-orifice injectors at a low Re is less important than that at a high Re. Because cavitation in micro-orifice injectors under a low Re has no positive effects on the atomization and spray, determining the geometry of a micro-injector is essential. The injector with a length-to-diameter (L/D) ratio of 3 exhibited an approximately 25% higher discharge coefficient (Cd) than those of injectors with L/D ratios of 6 and 8 and, thus, is recommended for injectors in micro-turbojet engines.

Numerical implementation and verification of the Zwart-Gerber-Belamri cavitation model with the consideration of thermodynamic effect

In the world of pumps, turbopumps, and industrial applications, the absorption and release of latent heat in high-temperature zones play a pivotal role in the cavitation process. This phenomenon exerts a profound influence on system performance, especially when handling hot and cryogenic fluids, which are particularly susceptible to thermodynamic influences. The pressing need arises for a robust computational approach to address the intricacies of thermodynamic effects on cryogenic cavitation. The study at hand introduces a modification to the Zwart-Gerber-Belamri cavitation model, incorporating thermodynamic considerations to simulate quasi-steady cavitating flow around a NACA0015 hydrofoil. The SST k-ε turbulence model and homogeneous mass transfer cavitation model are employed to account for thermal effects, while the Clausius-Clapeyron equation is utilized to adjust the saturated vapor pressure within the cavitation model. Comparing the results with experimental data from Cervone et al. [1], especially in the thermal domain, reveals congruence in the estimated pressure and temperature drop (ΔT) within the cavity under varying free stream temperature conditions. Notably, thermodynamic effects exert a significant influence on cavitation dynamics during the phase-change process, potentially hindering or delaying cavitation in hot and cryogenic fluids. This enhanced cavitation model offers a marginally improved prediction of cavitation in water.

Design of a high-speed cavitation hydrodynamics test system

Due to the high sediment content in rivers in China and the relatively high concentration of “gas core” in water, cavitation of hydraulic machinery is likely to occur at high speeds, leading to a series of problems such as reduced efficiency of hydraulic machinery, intensified vibration and material erosion. To carry out the study of cavitation erosion, a test system (hereinafter referred to as the cavitation water tunnel) suitable for the basic study of cavitation dynamics at high velocity is designed in this paper. The whole system includes a circulating loop structure, which mainly consists of a suction chamber, contraction rectifier, and test section. The test section is convenient for observing different types of cavitation flow fields inside and the highest test velocity in the test section can exceed 35 m/s. A water-gas separation chamber is designed to collect bubbles over 100 microns to ensure that the inlet of the test section is not affected by cavitation. The functions of the test system include basic experiments such as flow field characteristics, cavitation dynamics, acoustic characteristics, and cavitation erosion characteristics around hydrofoils/blades, which can provide test conditions for the study of high-speed hydrodynamic characteristics such as pumps/turbines, propellers and underwater vehicles.

Structure Design Of ROV-Based MOPU Platform Pin Hole Spin Cleaning Device

The pile legs of the MOPU platform have been submerged in seawater for a long time, and there are a large number of Marine organisms on the surface, which has a negative impact on the stability of the platform and needs to be cleaned regularly. Most of the existing jacket cleaning technologies are aimed at cleaning the outer surface, and there are few studies on cleaning the Marine organisms attached to the pin holes of the pile legs of MOPU platform. In order to solve the above problems, this paper firstly designs a spin-type pin hole cleaning device based on underwater wall-climbing robot by drawing lessons from domestic and foreign experience. At the same time, the Fluent simulation of three commonly used cavitation water jet nozzles is carried out, and the most suitable nozzle type for pin hole cleaning is selected from the organ pipe type, shear type and corner cavitation nozzles. In the actual operation, the water temperature and depth around the ROV are changing, so the simulation needs to consider the influence of temperature and depth changes. In this paper, a reasonable point is put forward for the structural design of the spin cavitation cleaning device. The simulation results show that the corner cavitation nozzle should be selected in the pinhole cleaning operation.