Cavitating Water Jet Research Articles

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.

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.

Experimental study on concrete-breaking by self-excited oscillating cavitation waterjet in a submerged environment

Experimental study on concrete-breaking by self-excited oscillating cavitation waterjet in a submerged environment

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.

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.

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.

A comprehensive investigation of uncertainties in cavitating waterjet experiments

This paper systematically examines the sources of uncertainty in cavitating waterjet test setups and provides illustrative case studies to conduct thorough uncertainty analyses for erosion tests using cavitating waterjet method. Within this study, utilizing examples of uncertainty analysis presented by the International Towing Tank Conference (ITTC) for various testing techniques, a novel uncertainty analysis implementation suitable for cavitating waterjet tests has been conducted. Firstly, cavitation erosion experiments were carried out on samples aluminum (Al 6063) material under cavitation number conditions (σ = 0.02 to σ = 0.033 range) as part of the validation study. Subsequently, within the scope of uncertainty analysis calculations, five erosion tests were conducted for each of the two different cavitation numbers (σ = 0.03 and σ = 0.05). The study aims to examine the bias and precision uncertainty components separately for the test results of erosion rate and establish a reliable and repeatable procedure for predicting the uncertainty level of cavitating waterjet tests. For the first time in the literature, the uncertainty components of cavitating waterjet tests were investigated in detail and the uncertainty level in cavitating waterjet tests, including bias and precision errors, was predicted in accordance with specific ITTC guidelines and procedures. Based on the results, the primary bias error source was identified as the pressure inside the cavitation chamber, with the nozzle pressure being the second most significant bias error source. Consequently, it is recommended to perform the bias error prediction based on the ratio of these two, known as the cavitation number. Precision error, crucial for uncertainty, was estimated using five sets of erosion rate values, emphasizing its importance in cavitating waterjet tests. It is anticipated that the suggested methodology will serve as a benchmark for predicting uncertainty levels in cavitating waterjet tests.

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.

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.

Fluid–solid coupling analysis of submerged water jet cavitation micro-forming

Submerged cavitating waterjet micro-forming is a novel jetting technology. Existing detection devices cannot accurately detect bubble distribution in still water domains and target workpiece processing areas. To investigate bubble generation and distribution in still water domains and their influence on target micro-forming, a submerged cavitating waterjet micro-forming fluid–solid coupling numerical model was established in this paper. The distribution of submerged cavitating waterjet cavitation effects and the hammering of micro waterjets on metal plates under the action of cavitation bubbles, as well as the coupled forces, were analyzed. The results show that bubble distribution in still water domains is closely related to turbulence, vortices, and pressure distributions. The collapse of cavitation bubbles generates enormous pressure, and the pressure generated by the collapse of cavitation bubbles causes the micro waterjet hammers to produce annular deformation zones on the metal plates. The bubble distribution laws and theoretical basis of cavitation micro-forming technology in submerged waterjets are provided in this study, which has very important engineering application significance.

Cavitation cloud of waterjet under double excitation

This study experimentally explores the interplay of active and passive excitation on double-excited cavitating waterjet clouds. High-speed imaging and high-frequency pressure sensors are used to characterize the impact of piezoelectric transducers for active excitation and nozzle lip geometries for strong, moderate, and weak passive excitation conditions. The analysis of pressure fluctuations revealed that under active excitation, the waterjet exhibited forced oscillations characterized by an amplitude amplification exceeding that of single passive excitation by an order of magnitude. High-speed imaging, combined with proper orthogonal decomposition, allowed us to observe an expansion in the volume, size, and effective standoff distance of cavitation clouds upon introducing active excitation across all passive excitation scenarios. The synergy between strong passive excitation and harmonized frequency with active excitation resulted in the most robust cavitation cloud development, characterized by the highest intensity.

Experimental study on ice breaking by a cavitating water jet in a Venturi structure

Ice breaking by a cavitating water jet based on Venturi structure is studied experimentally. Systematic researches of cavitating water jet interacting with ice are carried out by doing indoor experiments, where the cavitating jet is generated by a tailor-made device through Venturi nozzle and the circular fresh-water ice plates are made of boiled water in a cryostat. The whole evolution of cavitating jets and ice plates is recorded by two high-speed cameras from two views simultaneously. Pressure loads on the rigid wall of cavitating water jet is compared with that of conventional non-cavitating water jet and the change is analyzed. Among two typical structural parameters of Venturi cavitating nozzles selected in this paper, the ratios of throat length to diameter ε (1; 1.5; 2) and the diverging angles α (8°; 10°; 12°), the nozzle withε = 1 andα = 12° is found to be the best in terms of loads on wall. On this basis, the responses of ice plate, including crack generation, crack development and fracture, are studied under the cavitating jet loads, mainly involving the compressible pressure P1 and cavitation pressure Pc. According to the main cause and propagation sequence of cracks, the failure mechanisms of ice under Venturi cavitating jet can mainly be divided into three types: shock waves failure, overall strength failure and local strength failure, along with six damage patterns roughly. Furthermore, the effects of ice plate thickness, cavitating water jet strength and boundary conditions are also investigated.

Experimental and numerical simulations to examine the mechanism of nozzle geometry affecting cavitation water jets

The geometry of the cavitation nozzle is the major determinant of the cavitation process and cleaning effect. To better service the cleaning industry, it is necessary to understand the process by which nozzle geometry impacts cavitation. This research uses experimental flow visualization and large eddy simulation (LES) to study the cavitation effects of three different nozzle configurations (Cylindrical, organ-pipe and converging–diverging nozzles). The shedding frequency of the cavitation cloud was determined through power spectrum analysis (PSD). The collapse range of the cavitation cloud produced was measured using the frame difference technique (FDM). A cleaning experiment was carried out to remove the tube scale with the aim of assessing the performance of the nozzle. The findings indicate that under the impact of the re-entrant jet, the cavitation cloud was distorted and fractured, and large shear stresses were produced at the fracture sites. The cylindrical nozzle creates a flow field with more vapour, velocity, and Reynolds stress than the other two nozzles. The findings from the cleaning experiments indicate that the utilization of appropriate nozzle geometry and an optimal standoff distance can significantly enhance the efficiency of tube descaling. This paper can help choose the right nozzle geometry and standoff distance for the cavitation water jet cleaning process, offer crucial technical support for the efficient cleaning within tubes.

Effect of Cavitation Water Jet Peening on Properties of AlCoCrFeNi High-Entropy Alloy Coating

High-entropy alloys have been widely used in engineering manufacturing due to their hardness, good wear resistance, excellent corrosion resistance, and high-temperature oxidation resistance. However, it is inevitable that metallurgical defects, such as micro cracks and micro pores, are produced when preparing the coating, which affects the overall performance of the alloy to a certain extent. In view of this situation, cavitation water jet peening (CWJP) was used to strengthen the AlCoCrFeNi high-entropy alloy coating. The effect of CWJP impact time on the microstructure and mechanical properties of CWJP were investigated. The results show that CWJP can form an effective hardening layer on the surface layer of the AlCoCrFeNi high-entropy alloy. When the CWJP impact time was 4 h, the microhardness of the surface layer of the specimen was harder than that of 2 h and 6 h, and the CWJP impact time had little effect on the thickness of the hardening layer. Observing the surface of the untreated and CWJP-treated specimens using the EBSD test, it was evident that the microstructure was significantly homogenized, the grains were refined, and the proportion of small-angle grain boundaries increased. The system reveals the grain refinement mechanism of the AlCoCrFeNi high-entropy alloy coating during plastic deformation. This study aims to provide a new surface strengthening method for obtaining high-performance AlCoCrFeNi high-entropy alloy coatings.

Precise peening of Cr–Mo steel using energy-intensive multifunction cavitation in conjunction with a narrow nozzle and positron irradiation

A new metalworking technique referred to as positron and laser assisted magnetic energy intensive multifunction cavitation (PLMEI-MFC) using a narrow nozzle was developed and applied to SCM440 Cr–Mo steel. The effects of varying the laser wavelength and power were initially assessed without positron irradiation. In this system, water jet cavitation (WJC) bubbles were subjected to ultrasonication in a magnetic field and the resulting cavitation clouds were irradiated with laser beams having wavelengths of 450 or 405 nm and with ultraviolet light. Exposure to a broad range of ultraviolet light having a peak at 365 nm was found not to contribute to the generation of residual stress in the metal. Because the narrow nozzle produced small WJC bubbles, high compressive residual stress and significant hardness were imparted to an insulated thin specimen having a low heat capacity. The flow rate of the narrow nozzle was also shown to greatly affect the processing rate. In this system, electrons and positrons in the bubbles evidently underwent annihilation to generate γ-rays and other forms of energy such that energy was concentrated in the bubbles. This PLMEI-MFC processing dramatically improved the surface strength of Cr–Mo steel specimens. Employing this peening apparatus with positron irradiation provided a stress increase of 1160 MPa based on converting tensile residual stress into compressive residual stress. This PLMEI-MFC system using a narrow nozzle allows compressive residual stress to be applied to the surface of steel without generating peening marks.

Investigation of hydroxyl-terminated polybutadiene propellant breaking characteristics and mechanism impacted by submerged cavitation water jet

A submerged cavitation water jet (SCWJ) is an effective method to recycle solid propellant from obsolete solid engines by the breaking method. Solid propellant’s breaking modes and mechanical process under SCWJ impact are unclear. This study aims to understand those impact breaking mechanisms. The hydroxyl-terminated polybutadiene (HTPB) propellant was chosen as the research material, and a self-designed test system was used to conduct impact tests at four different working pressures. The high-speed camera characterized crack propagation, and the DIC method calculated strain change during the impact process. Besides, micro and macro fracture morphologies were characterized by scanning electron microscope (SEM) and computed tomography (CT) scanning. The results reveal that the compressive strain concentration region locates right below the nozzle, and the shear strain region distributes symmetrically with the jet axis, which increases to 4% at first 16th ms, the compressive strain rises to 2% and 6% in the axial and transverse direction, respectively. The two tensile cracks formed first at the compression strain concentrate region, and there generate many shear cracks around the tensile cracks, and those shear cracks that develop and aggregate cause the cracks to become wider and cut through the tensile cracks, forming the tensile-shear cracks and the impact parts eventually fail. The HTPB propellant forms a breaking hole shaped conical after impact 10 s. The mass loss increases by 17 times at maximum, with the working pressure increasing by three times. Meanwhile, the damage value of the breaking hole remaining on the surface increases by 7.8 times while 2.9 times in the depth of the breaking hole. The breaking efficiency is closely affected by working pressures. The failure modes of HTPB impacted by SCWJ are classified as tensile crack-dominated and tensile-shear crack-dominated damage mechanisms.