Cavitation Erosion Intensity Research Articles

Effects of jet impact angle on cavitation erosion intensity and cavitation cloud dynamics

Cavitation water jet technology has been widely used in industrial production, but the effects of cavitation cloud evolution and erosion patterns at different impact angles remain to be determined. To study the erosive effects of cavitation jets at different impact angles, this study conducted erosion experiments with different impact angles. The flow conditions are varied at 45°, 60°, 75°, and 90°, four different jet impact angles on the target surface at the optimal standoff distance. The influence of impact angle on the erosion effect was explored by erosion morphology and erosion quality. Larger mass loss occur under erosion conditions at larger impact angles (75° and 90°), while relatively less mass loss occurs at smaller impact angles (45° and 60°). Furthermore, the evolution of cavitation clouds at different impact angles is illustrated through high-speed visualization experiments. The changing of cavitation jet structures is investigated by Proper Order Decomposition(POD) analysis. The smaller the impact angle, the closer the position of the re-entrant jet is to the nozzle, which leads to an increase in the frequency of cavitation cloud shedding. Meanwhile, cavitation bubbles don't have enough time to develop, resulting in reduced erosion capacity. The behaviour of the cavitation jet impinging on the target at different impact angles is simulated by the Large Eddy Simulation (LES) turbulence model. As the angle decreases, the pressure fluctuation caused by the cavitation cloud on the target surface decreases, and the duration also decreases accordingly. The results of this study provide technical support for the application of cavitation jets under different impact angle conditions and also help to understand the cavitation erosion mechanism under different impact angles.

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.

Experimental study on the effect of dissolved CO2 on cavitation erosion intensity by submerged waterjet

Gas content has an important influence on the intensity of cavitation erosion, affecting the formation and collapse of cavitation nuclei. Previous studies have primarily focused on the influence of dissolved oxygen and nitrogen on cavitation erosion. Studying the effect of other gases on cavitation erosion can promote a better understanding of cavitation. This study first analysed the erosion morphology with various standoff distances under the same cavitation number. Subsequently, a typical erosion profile at a set distance was selected to study the effect of dissolved CO2 on submerged self-resonating waterjet cavitation erosion. The mass loss, maximum erosion height difference, and average roughness were used as indicators of cavitation erosion intensity. These three indicators show a similar trend with the change in cavitation erosion intensity. When the CO2 content was small, the dissolved CO2 primarily affected the cavitation intensity by affecting the pH of the water. With a further increase in air content, the inhibitory effect of gas content on the cavitation erosion intensity became apparent.

Research on Cavitation Characteristics of Two-Throat Nozzle Submerged Jet

Ship fouling not only increases ship resistance and fuel consumption but is equally a type of biological invasion, which causes severe ecological damage. Submerged cavitation jet cleaning is an environmentally friendly, high-efficiency, and energy-saving cleaning method. The nozzle structure has an essential influence on the cleaning effect. Thus, a two-throat nozzle was designed for application in submerged cavitation jet cleaning. To investigate the cavitation characteristics of the two-throat nozzle, a high-speed photographic visualization experiment and an erosion experiment concerning the submerged cavitation jet were carried out in this study. The frame-difference method (FDM) was used to analyze the dynamic changes in the cavitation cloud in a single period. The dynamic changes in the cavitation cloud and the characteristics of the submerged cavitation jet were investigated under different inlet pressures. The sample mass loss and the macroscopic and microscopic changes in surface morphology were used to evaluate the cavitation intensity of the two-throat nozzle submerged jet. The experimental results demonstrate that the two-throat nozzle has a good cavitation effect, and the cavitation cloud of the submerged jet has obvious periodicity. With the increase in inlet pressure, the length, width, and area of the cavitation cloud continue to increase, and the shedding frequency of the cavitation cloud continues to decrease. The intensity of cavitation erosion is related to target distance and impact time. There is an appropriate target distance by which to achieve the optimal cavitation effect. The collapse of cavitation bubbles near the sample surface is related to the erosion distribution on the sample surface. Moreover, the magnitude of the absolute values of the root-mean-square surface roughness and surface skewness increase with cavitation intensity. The results in this paper are helpful for a better understanding of the cavitation characteristics of the two-throat nozzle submerged jet.

Quantitative evaluation of the microjet velocity and cavitation erosion on a copper plate produced by a spherical cavity focused transducer at the high hydrostatic pressure

Cavitation erosion at the high hydrostatic pressure causes the equipment to operate abnormally for the huge economic losses. Few methods can quantitatively evaluate the cavitation erosion intensity. In order to solve this problem, the cavitation erosion on a copper plate was carried out in a spherical cavity focused transducer system at the hydrostatic pressure of 3, 6, and 10 MPa. Meanwhile, the corresponding cavitation threshold, the initial bubble radius, and the microjet velocity in the ultrasonic field are theoretically analyzed to determine the dimension and velocity of microjet based on the following hypotheses: (1) the influence of the coalescence on the bubble collapse is ignored; (2) the dimension of the microjet is equal to the largest bubble size without the influence of gravity and buoyancy. Using the Westervelt equation for the nonlinear wave propagation and the Johnson-Cook material constitutive model for the high strain rate, a microjet impact model of the multi-bubble cavitation was constructed. In addition, through the analogy with the indentation test, an inversion model was proposed to calculate the microjet velocity and the cavitation erosion intensity. The microjet geometric model was constructed from the dimension and velocity of the microjet. The continuous microjet impact was proposed according to the equivalent impact momentum and solved by the finite element method. The relative errors of the pit depth are 4.02%, 3.34%, and 1.84% at the hydrostatic pressure of 3, 6, and 10 MPa, respectively, and the relative error in the evolution of pit morphology is 7.33% at 10 MPa, which verified the reliability of the proposed models. Experimental and simulation results show that the higher the hydrostatic pressure, the greater the pit depth, pit diameter, the pit-to-microjet diameter ratio, and the cavitation erosion intensity, but the smaller the pit diameter-to-depth ratio. The cavitation erosion intensity becomes significant with the ongoing ultrasonic exposure. In addition, a comparison of the cavitation pit morphology in the microjet pulsed and continuous impact modes shows that the continuous impact mode is effective without the elastic deformation caused by the residual stress. Using the cavitation pit morphology at the different hydrostatic pressures, the microjet velocity can be estimated successfully and accurately in a certain range, whose corresponding errors at the lower and upper limit are 5.98% and 0.11% at 3 MPa, 6.62% and 9.14% at 6 MPa, 6.54% and 5.42% at 10 MPa, respectively. Our proposed models are valid only when the cavitation pit diameter-to-depth ratio is close to 1. Altogether, the cavitation erosion induced by multi-bubble collapses in the focal region of a focused transducer could be evaluated both experimentally and numerically. Using the cavitation pit morphology and the inversion model, the microjet velocity in a certain range could be estimated successfully with satisfactory accuracy.

Numerical prediction of cavitation erosion to investigate the effect of wake on marine propellers

This paper presents validation studies to simulate performance, cavitation and cavitation erosion properties of the King's College (KCD) KCD-193 model propeller. The simulations are performed to investigate the effect of wake on the cavitation formation and the cavitation erosion intensity. The numerical (CFD) study is achieved by using unsteady Reynolds Averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) techniques with SST (Menter) k-ω turbulence model. The Schnerr-Sauer cavitation model and Eulerian approach with the Volume of Fluid (VOF) multiphase model are used to model a two-phase cavitation flow. The sliding mesh technique is applied to simulate the rotation of the propeller, and particular mesh refinement is performed on the regions where cavitation development is observed. Erosion intensity values on the propeller surface are obtained by Erosive Power Method (EPM) approach, and erosion formation on the blades is illustrated by utilizing the erosion intensity dataset. Numerical comparison for the erosion intensity values using RANS and DES models is carried out to evaluate the effect of wake in behind condition. Numerical results are evaluated against cavitation tunnel measurements at the Emerson Cavitation Tunnel (ECT) of Newcastle University. The main objectives of the study are to obtain the cavitation and cavitation erosion formation on the propeller in good agreement with experimental data obtained in ECT and to investigate the characteristics of the erosion intensity subject to cavitation conditions. In view of the flow conditions investigated, the RANS model is also found appropriate and required less computing efforts to predict the erosion intensity than the DES model. The results confirm the EPM method is to be compatible in predicting the erosion intensity. The results of the simulations indicate that a decrease in cavitation number does not necessarily cause an increase in the erosion intensity, requiring further investigation.

O-008. Influence of Hypertension in Pregnancy on Hematological Phenotypes of Preterm Infants with Gestational Age Inferior to 32 Weeks

This paper presents validation studies to simulate performance, cavitation and cavitation erosion properties of the King's College (KCD) KCD-193 model propeller. The simulations are performed to investigate the effect of wake on the cavitation formation and the cavitation erosion intensity. The numerical (CFD) study is achieved by using unsteady Reynolds Averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) techniques with SST (Menter) k-ω turbulence model. The Schnerr-Sauer cavitation model and Eulerian approach with the Volume of Fluid (VOF) multiphase model are used to model a two-phase cavitation flow. The sliding mesh technique is applied to simulate the rotation of the propeller, and particular mesh refinement is performed on the regions where cavitation development is observed. Erosion intensity values on the propeller surface are obtained by Erosive Power Method (EPM) approach, and erosion formation on the blades is illustrated by utilizing the erosion intensity dataset. Numerical comparison for the erosion intensity values using RANS and DES models is carried out to evaluate the effect of wake in behind condition. Numerical results are evaluated against cavitation tunnel measurements at the Emerson Cavitation Tunnel (ECT) of Newcastle University. The main objectives of the study are to obtain the cavitation and cavitation erosion formation on the propeller in good agreement with experimental data obtained in ECT and to investigate the characteristics of the erosion intensity subject to cavitation conditions. In view of the flow conditions investigated, the RANS model is also found appropriate and required less computing efforts to predict the erosion intensity than the DES model. The results confirm the EPM method is to be compatible in predicting the erosion intensity. The results of the simulations indicate that a decrease in cavitation number does not necessarily cause an increase in the erosion intensity, requiring further investigation.

Resistance of curved surfaces to the cavitation erosion produced through high-pressure submerged waterjet

The aim of the present study is to reveal fundamental cavitation erosion characteristics of the curved surface. The submerged waterjet was used to produce cavitation. An experimental work was performed on a standard cavitation erosion test rig. The Al 5083 specimens with three curvature radii, 7.0, 9.0 and 10.0 mm, were selected as the target specimens. The flat surfaces were tested for comparison. The mass loss of the eroded specimens was measured. The cumulative erosion rate was calculated. Morphology of the eroded surfaces was observed using techniques of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The root mean square (RMS) surface roughness of the eroded specimen was obtained. The results indicate that the curvature radius has a significant effect on the cavitation erosion intensity. The surface with the largest radius of curvature exhibits the weakest resistance to the cavitation erosion. No explicit relevance is recognized between the curvature radius and the extent of the cavitation erosion. In the early stage of the cavitation erosion, the central region of the target surface is less eroded. As the cavitation erosion progresses, the mass removal in the central area manifests a layer-by-layer pattern. Large erosion pits are evidenced in such a region. The specimen of R = 9.0 mm, with the highest resistance to the cavitation erosion, is featured by a sharp decline of the skewness of surface height distribution in the early stage of the cavitation erosion.

Pressure fluctuation and surface morphology induced by the high-pressure submerged waterjet confined in a square duct

Driven by high pressures, the submerged waterjet is featured by high velocity and cavitation, which arouse unsteady flow signals. To elucidate the temporal and spatial characteristics of the high-pressure submerged waterjet, an experimental work was carried out with the waterjet submerged in a square duct and jet pressures varied from 50 to 320 MPa. Three nozzles with different throat-segment diameters were considered. Under non-impingement condition, pressure fluctuations near the waterjet stream were acquired with miniature dynamic pressure transducers. For the jet impingement cases, microhardness, surface morphology and mass removal rate of the impinged specimens were measured. The results show that drastic change of pressure in ambient water is caused by the waterjet. As the jet pressure rises, high-frequency components are excited and the effect of cavitation is significant. In streamwise direction, the gap between the first, second and third highest frequencies is progressively narrowed. The maximum pressure amplitude increases as waterjet develops, irrespective of the jet pressure and the nozzle diameter. High jet pressures lead to high microhardness of the target surface. Surface morphology serves as an indicator of the synthetic effect of jet impingement and cavitation. Erosion patterns associated with the three nozzles are considerably different; cavitation erosion intensity declines with the increase in the nozzle diameter.

Studies of Erosion Resistance of Protective Coats on the Surfaces of Machine Elements Washed with Fluids

Abstract This article indicated at erosion as one of the causes of degradation of surfaces washed by fluids and conditions of its occurrence. Corrosive – erosive theory of metal surface degradation has been discussed linking it with an instance of destructive processes taking place in cylinder liner blocks of combustion engines. Physics and conditions influencing processes on liquid – washed operational surface phase boundary have been justified. Out of the contemporary hypotheses explaining the physics of cavitation erosion, the bubble theory has been considered. A mathematical model of erosion has been presented in the context of cavitation implosion energy determining crash interactions of liquid cumulative fluxes on the washed surface. Occurring plastic deformations have been graphically explained linking them with the occurrence of fatigue micro-cracks and later with erosive pits. Influence of initial steel hardness on intensity of cavitation erosion has been checked. Discussion of ways to increase metal surface resistance to cavitation erosion has been carried out.

The Impact of Static Pressure on the Intensity of Ultrasonic Cavitation in Aqueous Media

Physical processes occurring after placing the filter diaphragm in cavitation medium created by ultrasonic wave, the intensity of which exceeds the threshold of cavitation conditions have been studied. The behavior of cavitation bubble and pollutant particle in ultrasonic field are analyzed making it possible to build a mathematical model of the water filtration process in ultrasonic medium. The impact of different factors on the cavitation intensity was also studied. Experiments were conducted to investigate the impact of static pressure on the intensity of cavitation erosion by using the erosion test method. Aluminum foil was used as a test material. Experiments were conducted in the cavitation chamber at the low and increased values of static pressure with respect to its atmospheric value.

Joint experiments of cavitation jet: High-speed visualization and erosion test

Cavitation is a ubiquitous phenomenon in ocean engineering. In order to figure out the relationship between cavitation cloud and cavitation erosion, high-speed visualization and erosion test of cavitation jet were simultaneously performed. The temporal and spatial distributions of cavitation cloud was analyzed using Proper Orthogonal Decomposition (POD) and the morphology of eroded specimen was analyzed from both macroscopic and microcosmic perspectives. The results show that POD modes of side view images are able to estimate the maximum radial distribution of cavitation pits, while the energy fraction of the first POD mode can serve as an indicator of specimen mass loss. The intensity of cavitation erosion is decided by both the bubble concentration and collapse intensity at specimen surface. At a medium standoff distance, where collapse intensity and bubble concentration are well compromised, maximum cavitation erosion is achieved. The aggravation of cavitation erosion is the combined consequences of the growth of single cavitation pits and the connection of adjacent pits. These results suggest that the collapse of cavitation bubbles is a necessary, but not sufficient, condition for severe cavitation erosion. The findings are expected to improve the physical understanding of the relationship between cavitation phenomenon and cavitation damage.

Experimental study on the effects of feeding pipe diameter on the cavitation erosion performance of self-resonating cavitating waterjet

Self-resonating cavitating waterjet (SRCW) combines the advantages of pulsed waterjets and cavitating waterjets, and is thus much superior to a plain waterjet in many applications. In order to further improve the erosion performance of SRCW, the effects of feeding pipe diameter were studied as a pioneering effort. A preliminarily theoretical exploration of the relations between feeding pipe diameter and the cavitation capability of SRCW was performed with respect to wave propagation and damping. Organ-pipe nozzles were used to produce SRCWs under pump pressures of 10, 15, 20, and 25MPa. Numerous cavitation erosion tests were conducted with the use of three feeding pipes of diameters of 6, 13, and 25mm. Cavitation erosion intensity evaluated by mass loss and erosion area, erosion rate, and specific energy consumption were used to characterize the performance of SRCWs influenced by feeding pipe diameter. Results show that feeding pipe diameter dramatically affects the cavitation erosion performance of SRCWs, especially at high pump pressures. By comparing with conventional cavitating waterjets issuing from a conical nozzle, it is expected that feeding pipe diameter mainly influences the hydroacoustic waves and the self-resonance, which are the basis for generating SRCWs. Moreover, feeding pipe of diameter of 13mm is always the one for achieving the best cavitation erosion performance of SRCWs under the experimental conditions. Feeding pipe with a diameter of 6mm is better than that with a diameter of 25mm in improving the cavitation erosion intensity and rate only under pump pressures of 10 and 15MPa. And at pump pressures of 20 and 25MPa, the roles of these two pipes are reversed. Although such an approach is empirical and qualitative in nature, this procedure generates information of value in guiding future theoretical and experimental work on exploring the relationships between feeding pipe and the self-resonating nozzle.

Cavitation Erosion of P110 Steel in Different Drilling Muds

Abstract The P110 steel specimens were subjected to ultrasonic cavitation erosion in different compositions of drilling muds and surfactant additive. The test procedure was based on ASTM-G-32 standard recommendations. API 5CT-P110 steel is used for pipes in oil and gas industry. The harsh environment and high velocity of flows poses corrosive and erosive threat on materials used there. The composition of drilling fluid influences its rheological properties and thus intensity of cavitation erosion. The erosion curves based on weight loss were measured.

Effects of nozzle inner surface roughness on the cavitation erosion characteristics of high speed submerged jets

Cavitating jet is now being widely used in a variety of situations due to its strong aggressive erosion ability. In order to push the erosion capability to a maximum, the effects of nozzle inner surface roughness on the cavitation erosion characteristics of submerged cavitating jets were experimentally investigated for the first time with respect to aggressive erosion intensity and efficiency. By impinging the submerged jets on specimens of pure aluminum (1070A) using six organ-pipe cavitating nozzles of different surface roughness values (0.8μm , 1.6μm, 3.2μm, 6.3μm, 12.5μm, and 25μm), the mass loss and specific energy consumption at various inlet pressures and standoff distances were measured and analyzed. And the macroscopic appearances of eroded specimens at optimum standoff distances corresponding to each inlet pressure were displayed and analyzed. Results show that surface roughness can have great effects on cavitation erosion intensity at standoff distances around the optimum and on erosion efficiency at standoff distances exceeding the optimum. The influence of surface roughness on cavitation erosion, adverse or advantageous, depends largely on the inlet pressure which determines the viscous sublayer thickness. More specifically, at inlet pressure of 10MPa and 15MPa, surface roughness value of 12.5μm is the best for achieving the strongest erosion intensity and maximum efficiency at standoff distance around 50mm; while at inlet pressure of 20MPa and 25MPa, roughness value of 6.3μm replaces 12.5μm to be the best one with the optimum standoff distance increased to 60mm. After standoff distance exceeds the optimum value, the specific energy consumption greatly increases, especially at relative lower inlet pressures, indicating a dramatic decrease of erosion efficiency. It can be concluded that excessive smooth surface is not conducive to the formation of cavitation bubbles, leading to an attenuated intensity of cavitation erosion; while excessive rough surface causes much energy dissipation and leads to divergent jets, resulting in a significant reduction of erosion intensity. According to the experimental results, there exists an optimum inner surface roughness value to achieve the strongest aggressive cavitation erosion capability for submerged cavitating jets.

Cavitation erosion of the calcium carbonate deposits

The paper presents the research of erosion effects caused by acoustic cavitation on metallic and enamelled specimens coated with calcium carbonate - scale. The deposition of calcium carbonate was performed under controlled laboratory conditions. The deposition took place at the same integral conditions to the specimens of different surface roughness. Cavitation as a cause of erosion was generated in a vessel with ultrasonic excitation. Simultaneously with the monitoring of cavitation above the specimens, the destruction of scale on the surface of specimens was analysed. The results of experiments indicate a characteristic effect of cavitation intensity on the destruction of scale surface layer. The intensity of cavitation erosion is proportional to the voltage on the sonotrode or the intensity of pressure fluctuations, and depends on the roughness of the surface of specimens, on which the scales were deposited.

Numerical Prediction of Cavitation Erosion Intensity in Cavitating Flows around a Clark Y 11.7% Hydrofoil

A numerical prediction method of cavitation erosion is proposed. In this method, the analysis of bubbles in cavitating flows is performed and the intensity of cavitation erosion is evaluated by the impact pressure induced by spherical bubble collapse. In the present study, two-dimensional cavitating flow around the Clark Y 11.7 % hydrofoil is used to examine the proposed numerical prediction method. The proposed numerical method predicts that the intensities of cavitation erosion in noncavitating, attached cavitating and pseudo-supercavitating flows are far weaker than the intensity of cavitation erosion in a transient cavitating flow, and the intensity in the vicinity of the sheet cavity termination is high. These results correspond well to experimental results, and it is confirmed that systematic erosion characteristics are generally captured by this method. Furthermore, the velocity dependence of cavitation erosion is examined, and it is found that the exponent n in the relation between the intensity I and main flow velocity Uin (I ∝ Uinn) becomes large when the bubble radius is large and ranges between 4.3 and 7.0 in the present study. According to the bubble dynamics, the ambient pressure and the rate of increases in pressure increase as the main flow velocity, and the maximum internal pressure increase. Therefore, it is thought that smaller bubbles cause cavitation erosion when the main flow velocity is large.

0406 壁面近傍での非球状気泡崩壊挙動に関する一考察(OS4-2 キャビテーションおよびマイクロバブル効果とその応用技術,オーガナイズドセッション)

Collapsing bubble near wall boundary is numerically analyzed to clarify the mechanism of cavitation bubble collapse and develop numerical prediction method of cavitation erosion. 2D axisymmetric and 3D plane-symmetric calculations using a locally homogeneous model of gas-liquid two-phase medium are performed until the second bubble collapse. It is confirmed that microjet generation, propagation of induced pressure wave and collapse of torus bubble can be realized and that the second collapse is responsible for the intensity of cavitation erosion. It is also found that the collapse of slightly asymmetric bubble from spherical bubble causes the different distribution of maximum impact pressure.

Estimation of cavitation intensity from the time taken for bubbles to develop

In order to estimate the cavitation erosion rate, the time taken for cavitation bubbles to develop and the cavitation erosion intensity were investigated. The cavitation intensity was found to be proportional to the 7th power of the time taken for bubbles to develop. This is a similar dependency to the effect of scaling on cavitation erosion, which shows how the cavitation erosion rate increases with cavitating length.

Prediction of Cavitation Erosion

The objective of this study is to develop a procedure of predicting the cavitation erosion intensity. To this end, it is necessary to estimate impulsive forces caused by collapse of cavity bubbles. In the first report the authors measured cumulative events of impulsive forces by collapse of cavity bubbles on a two-dimensional foil with a piezoelectric sensor. In this paper the authors measured the cumulative events again with three sensors of different kind to verify the results reported in the first report. The measurements by the three different sensors agreed well with each other. Among these sensors, the PVDF sensor was practical and suitable for the authors' purpose. In addition, collapse of cavitation bubble clusters was observed with a digital high-speed video camera synchronized with the signal of impulsive force sensors. Duration of collapse was the order of 100 microseconds, which was far slower than that of an impulsive force that was around 5 microseconds. According to theoretical calculations the impulsive pressure is generated when the whole cloud cavity collapses completely. But in this observation the peaks of impulsive force did not meet the instant of final collapse, but occurred some 10 to some 100 microseconds earlier than the final collapse. These results suggest that an impulsive force may not be caused by the global collapse of a bubble cluster but by the collapse of a part of cloud cavity.