Submerged Water Jet Research Articles

Experimental and numerical investigation on the cavitation erosion effect and resonance effect of submerged water jets

ABSTRACT To analyse the cavitation erosion effect and resonance effect of submerged water jets generated by organ-pipe nozzles, experimental and numerical research is conducted in the nozzles with five different diffuser angles. The cavitation erosion intensity and the flow characteristics of submerged jets are obtained by the erosion test, high-speed photography and Large Eddy Simulation. The experimental and numerical results illustrate that the nozzle with a 60° diffuser angle is capable of producing a strong cavitation erosion effect. Compared to the fully developed submerged jet, the axial pressure oscillation of axially confined submerged jets is stronger, indicating that it has a strong resonance effect. The stress wave generated by cavitation modulates the jets after reflection from the impact wall. This modulation results in the excitation of the original main frequency oscillation of organ-pipe nozzle jets, which then gives rise to multiple frequency oscillations, thereby forming the strong resonance effect.

Numerical simulation study on ice breaking by a submerged water jet

Numerical simulation study on ice breaking by a submerged water jet

Study on the mechanism of soil erosion by submerged water jet vertical scouring in cohesive soils

The water jet trenching technique is widely used in the burial of submarine pipelines. However, its application in cohesive soils often leads to complexity in trench morphology and challenges in predicting trench dimensions due to unclear soil erosion mechanisms. These issues significantly impact pipeline burials. To investigate the soil erosion mechanism of water jet trenching in cohesive soils, two-dimensional physical simulation experiments of submerged vertical water jet erosion were conducted. The influence of jet pressure, impingement height, and nozzle diameter on the shape of the scour hole was analyzed. The erosion damage patterns of water jets on cohesive soils were studied, and a theoretical model for the development of scour holes was established. The study revealed that when the jet velocity reaches 1000 m/s and the nozzle diameter reaches 1 mm, a contracted neck forms at the upper part of the scour hole. The appearance of the contracted neck is due to excessive jet impact energy causing impact shear failure in the soil. The effective height and width of the contracted neck increase with jet pressure and nozzle diameter and decrease with impingement height. Based on Prandtl's bearing capacity model, a model for predicting impact shear failure in cohesive soils was established, and a predictive formula for the effective height and diameter of the neck was proposed. Experimental validation confirmed the accuracy of the predictive formula. These findings provide theoretical support for the application of water jet trenching techniques in cohesive seabed soils.

An Assessment Of Event-Based Imaging Velocimetry For Dimensionality Reduction In Turbulent Flows

"This study investigates the feasibility of using neuromorphic event-based vision (EBV) camera for low-order modelling, a key enabler for real-time flow control. A synchronized experiment with simultaneous Event Based Image Velocimetry (EBIV) and Particle Image Velocimetry (PIV) is performed on a submerged water jet flow at Re = 2600. Flow statistics, spectral content, and reduced-order modeling capabilities using Proper Orthogonal Decomposition (POD) are assessed. Velocity fields are computed via standard PIV processing and compared after interpolation onto a common grid. The analysis reveals good agreement in jet flow statistics and spectra between EBIV and conventional PIV, with differences observed in the power spectral density (PSD) for high frequencies (St>1.5) due to higher noise levels in EBIV data. Nonetheless, most of the spectral content is correctly captured by the EBIV. EBIV successfully identifies dominant flow structures and spectral distribution of energy. The correct identification of temporal modes confirms EBIV's potential for flow control applications based on reduced order models. Despite minor discrepancies downstream of the jet in the Low Order Reconstruction (LOR) analysis, attributed to EBIV's challenge in accurately reconstructing broad-spectrum turbulent regions, the technology proves promising for real-time imaging-based flow control."

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.

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.

Optimization of Composite Cavitation Nozzle Parameters Based on the Response Surface Methodology

Cavitation is typically observed when high-pressure submerged water jets are used. A composite nozzle, based on an organ pipe, can increase shear stress on the incoming flow, significantly enhancing cavitation performance by stacking Helmholtz cavities in series. In the present work, the flow field of the composite nozzle was numerically simulated using Large Eddy Simulation and was paired with the response surface method for global optimizing the crucial parameters of the composite nozzle to examine their effect on cavitation behavior. Utilizing peak gas-phase volume percent as the dependent variable and the runner diameter, Helmholtz chamber diameter, and Helmholtz chamber length as independent variables, a mathematical model was constructed to determine the ideal parameters of the composite nozzle through response surface methodology. The optimized nozzle prediction had an error of only 2.04% compared to the simulation results, confirming the accuracy of the model. To learn more about the cavitation cloud properties, an experimental setup for high-pressure cavitation jets was also constructed. Impact force measurements and high-speed photography tests were among the experiments conducted. The simulated evolution period of cavitation cloud characteristics is highly consistent with the experimental period. In the impact force measurement experiment, the simulated impact force oscillates between 256 and 297 N, and the measured impact force oscillates between 260 N and 289 N, with an error between 1.5% and 2.7%. The simulation model was verified by experimental results. This study provides new insights for the development of cavitation jet nozzle design theory.

On unsteady cavitation flow of a high-speed submerged water jet based on data-driven modal decomposition

Harnessing the destructive effect of cavitation, high-speed submerged cavitating water jets have a wide range of engineering applications. However, the characteristics of complex unsteady flow patterns due to turbulence and super-cavitation are still unclear. This paper employs the data-driven modal decomposition to study the mechanism of the unsteady turbulent cavitation flow. The simulation is based on the stress-blended eddy simulation (SBES) turbulence model coupled with the Schnerr-Sauer cavitation model. The internal evolution and frequency characteristics of cavitation flow are analyzed. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are utilized to identify the flow pattern of turbulent cavitation flow, including the vapor and the velocity fields. In results, the upstream part of the cavitating jet is characterized by growth and shedding behaviors, while the downstream part by decay and collapse behaviors. POD modes extract the most energetic structures within the flow field, with low-order modes capturing the majority of the energy. The vapor-based POD Mode 2 and Mode 3 reveal the behavior pattern of cavitation cloud shedding. While DMD identifies the shedding behavior and collapse behavior of cavitation through the decoupling of frequency domain.

Development of a Cavitation Generator Mimicking Pistol Shrimp.

Pistol shrimp generate cavitation bubbles. Cavitation impacts due to bubble collapses are harmful phenomena, as they cause severe damage to hydraulic machinery such as pumps and valves. However, cavitation impacts can be utilized for mechanical surface treatment to improve the fatigue strength of metallic materials, which is called "cavitation peening". Through conventional cavitation peening, cavitation is generated by a submerged water jet, i.e., a cavitating jet or a pulsed laser. The fatigue strength of magnesium alloy when treated by the pulsed laser is larger than that of the jet. In order to drastically increase the processing efficiency of cavitation peening, the mechanism of pistol shrimp (specifically when used to create a cavitation bubble), i.e., Alpheus randalli, was quantitatively investigated. It was found that a pulsed water jet generates a cavitation bubble when a shrimp snaps its claws. Furthermore, two types of cavitation generators were developed, namely, one that uses a pulsed laser and one that uses a piezo actuator, and this was achieved by mimicking a pistol shrimp. The generation of cavitation bubbles was demonstrated by using both types of cavitation generators: the pulsed laser and the piezo actuator.

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.

Simulation and Experiment on Elimination for the Bottom-Sitting Adsorption Effect of a Submersible Based on a Submerged Jet

When a submersible is sitting on a seabed, it could lose buoyancy because of the bottom-sitting adsorption effect. In this article, a numerical calculation model and experimental scheme for eliminating the bottom-sitting adsorption effect of under-sea equipment were established. An analysis of the hydrostatic pressure variation on a submersible’s bottom was carried out, and a submerged water jet which was based on the method of soil liquefaction was proposed to solve the problem of reducing hydrostatic pressure. It was shown that a water jet could liquefy soil to restore hydrostatic pressure on the submersible’s bottom, and there was an optimal jet velocity to form the largest liquefied soil thickness. A rectangular pulsed jet was the best way to liquefy soil in terms of efficiency and the liquefaction degree, which can be seen from the calculation of the two-dimensional two-phase flow. Through the calculation of the three-dimensional two-phase flow, it was found that the soil liquefaction developed from the periphery to the center, and a variation in jet liquefaction with the top wall constraint was obtained. Finally, an experiment was carried out to prove that a submerged water jet could eliminate the bottom-sitting adsorption effect of a submersible. The results showed that the submerged jet was an efficient way to liquefy soil, and a submersible could quickly recover hydrostatic pressure on the bottom and refloat up independently.

Numerical simulations of cavitating water jet by an improved cavitation model of compressible mixture flow with an emphasis on phase change effects

Focusing on cavitation phenomena caused by high-speed submerged water jets, this paper presents an improved cavitation model for a compressible fluid mixture based on a concise estimation of fluid compressibility that considers phase change effects. The homogeneous two-phase flow assumption is adopted, and the gas phase is assumed to consist of vapor and non-condensable components. Equations of state for a pure liquid and an ideal gas are employed to evaluate the compressibility of the liquid and non-condensable components, and the compressibility of the vapor is treated semi-empirically as a constant. The model is embedded in an unsteady Reynolds-averaged Navier–Stokes solver, with the realizable k-ε model employed to evaluate the eddy viscosity. The turbulent cavitating flow caused by an impulsively started submerged water jet is treated. The pattern of periodic cavitation cloud shedding is acceptably captured, and the mass flow rate coefficient and its fluctuation frequency evaluated by simulations agree with the experimental results well. The validity of the proposed method is confirmed. The results reveal that cavitation occurs when pin/Pin reaches 0.65 and fluid flow begins to pulsate. In the well-developed stage, the leading cavitation cloud and a subsequent cloud are successively shed downstream, and this process is repeated. The subsequent cloud catches the leading cloud, and they coalesce in the range x/d≈ 2–3. The pressure fluctuations concentrate in the range of x/d≈2–5 corresponding to the periodic shedding of cavitation clouds. The mass flow rate coefficient pulsates from 0.59–0.66 under the effect of cavitation.

Design and parameter optimization of a submerged water jet scallop skirt cleaning device

Design and parameter optimization of a submerged water jet scallop skirt cleaning device

Forming analysis of T2 copper foil processed by submerged water jet cavitation

Forming analysis of T2 copper foil processed by submerged water jet cavitation

Experimental investigation on submerged water jet wrapped in an annular gas jet

To reduce the energy dissipation of the submerged water jet, a series of experiments of the submerged water jet wrapped in an annular gas jet are performed under different gas ventilation rates, annular sizes, water jet nozzle diameters, and water jet velocities in a transparent water tank. In the experiments, a ventilated cavity is created by the annular gas jet that encloses the submerged water jet. The submerged water jet is separated from the surrounding water within a certain distance after leaving the nozzle exit by the ventilated cavity, which contributes to the effective working length of the submerged water jet significantly increasing, referring to the energy dissipation decrease. Furthermore, the geometry of the ventilated cavity changes periodically, i.e., the cavity length and diameter decrease after increasing to the peak values in each cycle. Moreover, the ventilated cavity development process can be mainly divided into formation, collapse, and intermission stages. The maximum cavity length of the ventilated cavity decrease with the per unit time momentum ratio between the water jet and the gas jet. Namely, the per unit time momentum ratio between the water jet and the gas jet is the dominating parameter of the cavity geometry.

Experimental investigation of two-phase flow evolution in a high-speed submerged water jet with air ventilation

In order to improve the submerged cutting performance of water abrasive suspension jet an experimental investigation on the two-phase flow structure of submerged water jet with semi-coaxial air ventilation is conducted by the method of high-speed camera observation under the condition of flow dynamic similarity, and its unsteady behavior under different conditions is evaluated by analyzing of sequence images. Experiment results show that the flow pattern of air-ventilated jet depends upon the ventilation flow rate. It may be classified into bubbly flow surrounded jet, continuous air-layer covered jet and cavity-bubble flow surrounded jet. In the case of non-ventilation, high-speed water jet into water is accompanied by intensive cavitation and the flow field appears to be a narrow jet surrounded by cavitation bubble clouds. By ventilating to the cavitating jet, air-bubbles become bigger gradually and a cavity area is formed at the exit of nozzle head. When the ventilation flow ratio reaches to the level of 5 a large cavity covering the jet is formed and a continuous air-layer covered jet is then generated. Image analysis demonstrates that the continuous air-layer covering the liquid jet pulsates and sheds downstream periodically. The Strouhal number defined by the dominant frequency of jet pulsation decreases quickly with the increase of ventilation flow rate in the range of Cq ≤ 5. At a suitable ventilation flow ratio (Cq ≈ 6 ~ 8) a relative long stable continuous air-layer covering the jet is generated at high time ratio, which will dramatically enhance the processing ability of submerged water jets. Cutting tests demonstrates that the cutting ability of air ventilated jet depends on the ventilation flow ratio. The relation of processing ability with the flow structure of air ventilated jet is clarified.

Engineering application of submerged water jets for sediment removal in a tidal riverbed

Sediment deposition problems have attracted the interest of engineers and researchers. Several experimental studies have been conducted on scour depth using turbulent jets. However, field observation and monitoring have rarely been reported. This study aimed to eliminate sediments on a tidal riverbed using a prototype device, which consisted of a set of submerged vertical water nozzles and submerged horizontal air nozzles. The effectiveness of the water jet in sediment removal during spring and neap tides was evaluated. The quantitative relationships of dimensionless parameters, such as (1) the relative sediment scour volume versus the number of flows from the jet exit, (2) the relative sediment scour volume versus the relative scour depth, and (3) the relative scour size versus the relative jet intensity, were analyzed. The results showed that the freshwater flowing to the sea affected the sediment scour volume during the falling cycle of spring tides. In contrast, the rising cycle of spring tides retarded the freshwater flow, resulting in a decrease in the sediment scour volume. A steep water surface slope accelerated the river flow and further influenced the cross-flow current around the study area. As a result, a highly diffusive turbulent flow was produced, causing suspended sediments to be rapidly removed from the scour hole center. An increase in the number of flows from the jets led to intensified diffusion of turbulent energy into the flow. The rapidly varying water depth caused jet energy to be dissipated before approaching the riverbed, and it significantly affected the scour process during the spring-tide period. The proposed equations can be used to estimate the scour volume, scour size, and re-suspended sediments in tidal rivers within defined ranges of parameters.

A Numerical Study of a Submerged Water Jet Impinging on a Stationary Wall

The impinging jet is a classical flow model with relatively simple geometric boundary conditions, and it is widely used in marine engineering. In recent years, scholars have conducted more and more fundamental studies on impact jets, but most of the classical turbulence models are used in numerical simulations, and the accuracy of their calculation results is still a problem in regions with large changes in velocity gradients such as the impact zone. In order to study the complex flow characteristics of the water flow under the condition of a submerged jet impacting a stationary wall, the Wray–Agarwal turbulence model was chosen for the Computational Fluid Dynamics (CFD) numerical simulation study of the impacting jet. Continuous jets with different Reynolds numbers and different impact heights H/D were used to impact the stationary wall, and the results show that the jet flow structure depends on the impact height and is relatively independent of the Reynolds number. With the increase in the impact height, the diffusion of the jet reaching the impact area gradually increases, and its velocity gradually decreases. As the impact height increases, the maximum pressure coefficient decreases and the rate of decrease increases gradually, and the dimensionless pressure distribution is almost constant. In this paper, the flow field structure and pressure characteristics of a continuous submerged jet impacting a stationary wall are explored in depth, which is of great guidance to engineering practice.

Experimental Study on the Effect of the Inclination Angle on the Scouring Efficiency of Submerged Water Jets

The effects of oblique submerged scouring jets on sand beds with various particle sizes have been studied experimentally. In particular, a total of 25 experiments have been carried out to explore the influences of the jet angle and application time on the considered submerged sand beds. Test results conducted with a specially-designed device have shown that the scouring efficiency attains a maximum when the inclination angle is in the range between 15° and 20° and then it decreases when the inclination angle becomes higher.

Experiments and numerical analysis of rebounding behaviors of a laser-induced cloud cavitation

It is well known that a high-speed submerged water jet generates a cloud of cavitation bubbles experiencing a collective unsteady behavior that repeats growth and collapse. In particular, it is considered that a high-pressure shock wave may be emitted associated with the collapse of the cloud. However, its mechanism has not been enough clarified and hence it is required to be explored both from the experimental and numerical analyses. In this study, we fist make an observation of such a unsteady behavior of the cloud cavitation that is generated by a pulsed Ho:YAG laser-induced liquid jet using a high-speed video camera. Then, a two-dimensional numerical analysis based on the SPH method is examined to simulate the unsteady behavior of the cloud, in which the mixture model of liquids and gas bubbles is employed. Finally, the validity of our numerical analysis is illustrated by showing that the unsteady behavior of the cloud from its inception, growth, shrink, collapse to rebound is realized in qualitative agreement with the experimental data.