Prediction Of Cavitation Erosion Research Articles

Numerical Prediction of Cavitation Erosion Risk Based on a New Erosion Indicator

ABSTRACTCavitation erosion would degrade the performance of the fluid machinery. To improve the reliability and prolong the life span of fluid machinery, it is necessary to study the mechanism of cavitation erosion and predict the possibility of erosion. Since the erosion power to be measured and calculated is closer to the actual state of cavitation, a new cavitation erosion indicator epp model based on erosion power is proposed, which can reflect the size and region of the erosion generated by cavitation more precisely. Concerning the cases of the axisymmetric nozzle and venturi tube, the prediction of cavitation erosion based on the newly proposed indicator is illustrated. It is found that cavitation erosion mainly occurs near the maximum margin of the cavitation region. This research indicates the possible erosion state of fluid machinery in a cavitation environment and provides a new approach to estimate the state of cavitation erosion.

Obtaining the Synthetic Fuels from Waste Plastic and Their Effect on Cavitation Formation in a Common-Rail Diesel Injector

The presented paper addresses two significant issues of the present time. In general, the studies of the effect of synthetic fuels on cavitation formation and cavitation erosion prediction in the nozzle tip of common-rail diesel injectors were addressed. The first problem is plastic waste, which can have a significant negative environmental impact if not treated properly. Most plastic waste has high energy value, so it represents valuable material that can be used in resource recovery to produce various materials. One possible product is synthetic fuel, which can be produced using thermal and catalytic pyrolysis processes. The first issue addressed in the presented paper is the determination of fuel properties since they highly influence the fuel injection process, spray development, combustion, etc. The second is the prediction of cavitation development and cavitation erosion in a common-rail diesel injector when using pyrolytic oils from waste plastic. At first, pyrolytic oils from waste high- and low-density polyethylene were obtained using thermal and catalytic pyrolysis processes. Then, the obtained oils were further characterised. Finally, the properties of the obtained oils were implemented in the ANSYS FLUENT computational program and used in the study of the cavitation phenomena inside an injection nozzle hole. The cavitating flow in FLUENT was calculated using the Mixture Model and Zwart-Gerber-Belamri cavitation model. For the modelling of turbulence, a realisable k–ε model with Enhanced Wall Treatment was used, and an erosion risk indicator was chosen to compare predicted locations of cavitation erosion. The results indicate that the properties of the obtained pyrolytic oils have slightly lower density, surface tension and kinematic viscosity compared to conventional diesel fuel, but these minor differences influence the cavitation phenomenon inside the injection hole. The occurrence of cavitation is advanced when pyrolytic oils are used, and the length of cavitation structures is greater. This further influences the shift of the area of cavitation erosion prediction closer to the nozzle exit and increases its magnitude up to 26% compared to diesel fuel. All these differences have the potential to further influence the spray break-up process, combustion process and emission formation inside the combustion chamber.

Numerical assessment of cavitation erosion risk on the Delft twisted hydrofoil using a hybrid Eulerian-Lagrangian strategy

Cavitation damage is a major threat to the life span of fluid machinery and has been a hot research issue in engineering for a long time. The current work aims to show the ability to assess cavitation erosion risk on the twisted hydrofoil using a hybrid Eulerian-Lagrangian solver. The volume of fluid method is used for the liquid-vapor interface of resolved vapor structures, while the discrete bubble model is utilized to track micro-scale unresolvable bubbles. A two-way coupling approach is introduced to enable the transition between resolved cavities and bubbles based on their volume, relative location, and shape. A Lagrangian erosion model considering the effect of asymmetric bubble collapse is proposed to predict cavitation erosion risk. Compared with the experimental result, the current model can accurately identify the high erosion risk regions on the hydrofoil surface. The distribution and intensity of the high impact pressures emitted from bubbles is quantitatively evaluated. In addition, the erosion sensitive zones at different stages of the one cloud cavitation cycle are determined and the hydrodynamic mechanisms of aggressive collapse events are analyzed in detail. The results reveal that the potential erosion risk is highest in areas where primary shedding occurs, which causes the macroscopic cavity to roll up. Bubbles with high impact pressures are mainly focused around the edges of the shedding cavity. The secondary shedding contributes to erosive structure in a limited middle angle of attack area, such that when the primary shedding U-shaped structure evolves and begins to collapse, it becomes less erosive, and only isolated points of erosion is found. Further investigation demonstrates that this is due to a transformation from U-shaped vortex to O-shaped vortex, moving the bubbles gradually away from the hydrofoil surface, thereby reducing the cavitation erosion risk.

Cavitation erosion risk assessment on a full-scale steerable thruster

Propeller cavitation erosion prediction at an early design stage is becoming more and more important since it is one of the key constraints in the search for maximum propeller efficiency. Despite the experience from model tests, cavitation erosion research on actual ship scale is very limited. In this study, an attempt is made to assess the erosion risk on the blades of a full-scale steerable thruster of a tug boat. Pressure side cavitation was detected on board for three different propeller designs. For the first time, a cavitation erosion analysis is performed on ship-scale, using a rigorous potential energy approach, which accounts for the focusing of the potential energy at the collapse center during the cavity collapse. A full sensitivity study has been performed for the blade surface accumulated energy. The erosion model shows the erosion risk for different propeller designs applied on the vessel, and different operating conditions, by looking at the surface specific energy on the blade. The erosion analysis shows locations of high erosion risk that show a good resemblance with the actual damage locations on the real blades.

Cavitation Erosion Modelling on a Radial Divergent Test Section Using RANS

Cavitation is the phenomenon of fluid evaporation in hydraulic systems, which occurs due to a pressure drop below the value of the vapor pressure. For numerical modeling of this generally undesirable phenomenon, which is often associated with material damage (erosion), there are various mathematical vapor transfer models that have been validated in the past. There are different approaches to predicting cavitation erosion, which have mostly been experimental in the past. Recently various numerical models have been developed with the development of numerical simulations. They describe the phenomenon of cavitation erosion based on different theoretical considerations, such as Pressure wave hypothesis, Microjet hypothesis, or a combination of both. In the present paper, an analysis of the Schnerr-Sauer transport cavitation model was used, upgraded with an erosive potential energy model based on pressure wave hypothesis for cavitation erosion prediction. The extended numerical model has been applied to the case of a radial divergent test section in three different mathematical formulations. The results of simulation were compared and validated to experimental work performed by other authors. The study shows that the distribution of surface accumulated energy agrees with the experimental results, although certain differences exist between formulations. The applied method appears to be appropriate for further use, and to be extended to materials response modeling in the future.

Prediction of cavitation erosion with different erosion risk indicators

This present work devoted to simulate the unsteady cavitating flow around a hydrofoil and assess its erosion power predicted by different erosion risk indicators. For that, the behavior of unsteady cloud cavity is numerically reproduced using density corrected Shear Stress Transport (SST) k-ω turbulence model and the mass transfer between vapor and water phases is modelled with the Schnerr-Sauer cavitation model. The definitions of different erosion risk indicators are mathematically derived and their performance on predicting erosion power is compared systematically. The results demonstrate that indicator, defined only with the rapid temporal variations of the pressure, is unable to distinguish the erosion area caused by cavity collapse. And the erosion risk indicator defined by time derivative of flow properties is unable to capture the main erosion occurred on the cavity closure region because the high erosion power on such area is mainly contributed by the advection term. In addition, it is founded that the full form of erosion power definition, defined by material derivative, is the best erosion indicator which can well predict the most eroded area and thus is recommended to be applied in the industrial and practical applications.

Assessment of Cavitation Erosion in a Water-Jet Pump Based on the Erosive Power Method.

Cavitation affects the performance of water-jet pumps. Cavitation erosion will appear on the surface of the blade under long-duration cavitation conditions. The cavitation evolution under specific working conditions was simulated and analyzed. The erosive power method based on the theory of macroscopic cavitation was used to predict cavitation erosion. The result shows that the head of the water-jet pump calculated using the DCM-SST turbulence model is 12.48 m. The simulation error of the rated head is 3.8%. The cavitation structure of tip leakage vortex was better captured. With the decrease of the net positive suction head, the position where the severe cavitation appears in the impeller domain gradually moves from the tip to the root. The erosion region obtained by the cavitation simulation based on the erosive power method is similar to the practical erosion profile in engineering. As the net positive suction head decreases, the erodible area becomes larger, and the erosion intensity increases.

Prediction of Cavitation Evolution and Cavitation Erosion on Centrifugal Pump Blades by the DCM-RNG Method.

Cavitation can reduce the efficiency and service life of the centrifugal pumps, and a long-term operation under cavitation conditions will cause cavitation damage on the surface of material. The external characteristic test of the IS65-50-174 single-stage centrifugal pump was carried out. Moreover, the cavitation mechanism under specific conditions was analyzed by numerical simulation. Considering the macroscopic cavitation flow structure in the centrifugal pump, three different cavitation erosion prediction methods were used to predict the erodible areas. The results show that the calculation results obtained by the density correction method (DCM) can well match the flow characteristics of the centrifugal pump under the rated conditions. When the centrifugal pump head drops by 3%, cavitation mainly occurs on the suction surface, and the cavity on the pressure surface is mainly concentrated near the front cover. The cavitation prediction method based on the time derivation of pressure change is not suitable for centrifugal pumps, while the prediction result of the erosive power method is more reasonable than the others. At time 0.493114 s, the maximum erosive power appears on the blade near the volute tongue, and its value is 1.46e − 04 W.

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.

Cavitation Erosion Prediction at Vibrating Walls by Coupling Computational Fluid Dynamics and Multi-body-Dynamic Solutions

Cavitation Erosion Prediction at Vibrating Walls by Coupling Computational Fluid Dynamics and Multi-body-Dynamic Solutions

Анализ современных исследований по кавитационной эрозии

Object and purpose of research. This paper discusses cavitation erosion on propeller blades. The purpose of this work is to review and analyse modern studies on cavitation erosion, as well as to apply these research results for better under-standing of cavitation damage risk on full-scale propellers. Materials and methods. The paper reviews recent studies on cavitation erosion, as well as the author’s own findings in cavitation erosion on full-scale steel propellers, analyzing the energy needed to create cavitation damage of recorded size. This energy was calculated as per the model based on the results of metallurgical studies discussing the effect of shot blasting upon steel properties. Comparison of these results with those obtained as per classic formulae for the collapse energy of cavita-tion bubble made it possible to estimate the conditions of cavitation erosion on propeller blades. Main results. The review of recent studies on cavitation erosion has shown that current progress in the technologies of experimental studies and computer-based simulations made it possible to considerably improve the knowledge about cavitation erosion process as compared to the level of the 20th century. This review shows that cavitation erosion studies followed three practically independent paths: experimental studies and computer-based simulation of flow around propeller blades with locali-zation of peaks for one or several criteria reflecting the intensity of cavitation energy fluctuations; the studies intended to esti-mate the pressure exerted by collapsing cavitation bubbles and emerging cumulative jets; and finally, the studies on the proper-ties of materials affected by cumulative jets and collapsing bubbles. At this point, it would be practicable to merge these three paths using the results of full-scale cavitation erosion analysis for propellers. KSRC findings in cavitation damage of full-scale steel propeller has shown that cavitation damage recorded in these studies might occur due to a certain combination between the required energy, bubble-blade interaction pressure and the size of affect-ed area on steel blade surface, and this combination, in its turn, might take place when cavitation bubbles consisting of vapour fraction with partial air content hit the blade surface and collapse. Conclusion. This paper shows the capabilities of modern research methods in obtaining new data on the inception mecha-nism of cavitation erosion. Still, to develop the methods for prediction of cavitation erosion (in particular, on propellers), it is necessary to merge the results obtained in different branches of cavitation studies. The basis for this merging could become a power-based analysis of cavitation processes, with help of the cavitation erosion model suggested in this paper and based on the similarity between cavitation erosion and shot-blasting.

Modelling and prediction of cavitation erosion in GDi injectors operated with E100 fuel

Ethanol (E100) can be utilised in spark ignition engines for passenger car vehicles. This brings a challenge to the durability of the fuel injection system components since its use can result in corrosion, further enhanced by cavitation-induced erosion. This work reports computational fluid dynamics (CFD) predictions for both the flow development and the locations prone to cavitation erosion in multi-hole gasoline direct injection (GDi) injectors operated with E100. The compressible form of the Navier–Stokes equations is solved numerically considering the motion of the injector’s needle valve. Thermodynamic and mechanical equilibrium is assumed between the liquid, vapour and non-condensable gas; E100 liquid and vapour are considered as a barotropic fluids where the corresponding variation in density with pressure and the speed of sound are estimated via a relevant equation of state; an additional transport equation is solved for simulating the non-condensable air entrainment into the injector during the dwell time between successive injections. Turbulence is modelled using both large eddy simulation (LES) and Unsteady Reynolds-averaged Navier–Stokes (URANS) considering a sector and the full nozzle geometry, respectively. Various cavitation erosion indices reported in the literature are evaluated against new durability tests of surface erosion damage obtained after 400 M injection cycles. The relevant nozzle wall erosion images are found to correlate well with the accumulated erosive power predicted from the computational model.

Numerical Prediction of Various Cavitation Erosion Mechanisms

Abstract Numerical prediction of cavitation erosion is a great scientific and technological challenge. In the past, many attempts were made—many successful. One of the issues when a comparison between a simulation and erosion experiments is made, is the great difference in time scale. In this work, we do not attempt to obtain quantitatively accurate predictions of erosion process but concentrate qualitatively on cavitation mechanisms with quantitative prediction of pressure pulses which lead to erosion. This is possible, because of our recent experimental work on simultaneous observation of cavitating flow and cavitation erosion by high speed cameras. In this study, the numerical simulation was used to predict details of the cavitation process during the vapor collapse phase. The fully compressible, cavitating flow simulations were performed to resolve the formation of the pressure waves at cavitation collapse. We tried to visualize the mechanisms and dynamics of vapor structures during collapse phase at the Venturi geometry. The obtained results show that unsteady Reynolds-averaged Navier–Stokes (URANS) simulation of cavitation is capable of reproducing four out of five mechanisms of cavitation erosion, found during experimental work.

An axisymmetric solid SPH solver with consistent treatment of particles close to the symmetry axis

A meshless smoothed particle hydrodynamics solid solver is developed in order to study fluid–structure interactions and to predict cavitation erosion. The solid solver is developed in-house in an axisymmetric configuration. The existing SPH methods dedicated to solid materials do not allow a consistent treatment of particles close to the symmetry axis, so a density correction scheme is proposed here to derive new density and momentum equations for solid mechanics in axisymmetric SPH formulation. The new SPH equations are coded in the solver, and the SPH solid solver is then validated against FEM results, which shows excellent agreement.

Cavitation erosion prediction based on a multi-scale method

In hydraulic turbines, cavitation has unwanted consequences such as vibrations, noise, or material degradation. Thus, developping a method which can anticipate this phenomenon with good accuracy is vital from the designer’s perspective.This work aims at predicting two aspects of cavitation erosion: determining areas most endangered, and quantifying cavitation erosion in a relative way.

Systematic investigation of coating application methods and soft paint types to detect cavitation erosion on marine propellers

Cavitation erosion is perhaps the most detrimental result of the cavitation on propellers, which results in an increase in noise and vibration characteristics, loss of propeller performance as well as high maintenance costs.In this paper, some types of coatings and application techniques used in marine propellers have been tested by conducting series of cavitation erosion tests in the Emerson Cavitation Tunnel of Newcastle University. Therefore, this paper investigates the cavitation erosion phenomenon by conducting a systematic investigation of different paint-like coatings that were applied in different procedures on propeller blades. The blades were exposed to cavitation in a cavitation tunnel and erosion patterns were macroscopically analysed. The propeller blades were coated with off-the shelf commercial stencil inks, as well as S1 (a soft coating) which was largely preferred by major testing facilities but has recently been stopped to be produced. Within this framework, this paper aims to evaluate and establish a soft paint application method for cavitation erosion prediction by carrying out an extensive experimental test process. To achieve this aim, a series of propeller cavitation tests were performed in search of a promising detailed guidance for coating application for the erosion detection. In conclusion, promising coating application and improving preparation methods are outlined. Resulting pitting formations are correlated with the observed cavitation patterns and types. Amongst the tested alternatives of the coating application methods to apply soft paints, dipping appeared to be the most promising technique providing a uniform soft surface over the blades.

On the Applicability of Cavitation Erosion Risk Models With a URANS Solver

In the maritime industry, cavitation erosion prediction becomes more and more critical, as the requirements for more efficient propellers increase. Model testing is yet the most typical way a propeller designer can, nowadays, get an estimation of the erosion risk on the propeller blades. However, cavitation erosion prediction using computational fluid dynamics (CFD) can possibly provide more information than a model test. In the present work, we review erosion risk models that can be used in conjunction with a multiphase unsteady Reynolds‐averaged Navier–Stokes (URANS) solver. Three different approaches have been evaluated, and we conclude that the energy balance approach, where it is assumed that the potential energy contained in a vapor structure is proportional to the volume of the structure, and the pressure difference between the surrounding pressure and the pressure within the structure, provides the best framework for erosion risk assessment. Based on this framework, the model used in this study is tested on the Delft Twist 11 hydrofoil, using a URANS method, and is validated against experimental observations. The predicted impact distribution agrees well with the damage pattern obtained from paint test. The model shows great potential for future use. Nevertheless, it should further be validated against full scale data, followed by an extended investigation on the effect of the driving pressure that leads to the collapse.

Isothermal compressible flow solver for prediction of cavitation erosion

Cavitation erosion can be observed on hydraulic mechanical devices and has long been studied as a challenging research topic. In this paper, a practical method to predict cavitation erosion was developed. To simulate cavitating flows using computational fluid dynamics (CFD), an isothermal compressible cavitating flow solver was developed using the OpenFOAM toolkit. A cavitation erosion coefficient was proposed as a function of the cavitation and Reynolds numbers. From the simulations, the cavitation erosion coefficients were calculated using metamodeling methods. Finally, the developed practical method of cavitation erosion was applied to a marine propeller. As observed in experiments, cavitation erosion was predicted near the propeller tip.

Calculated and experimental determination of erosion zones in the flow part of the vane type pump

The results of numerical and experimental investigations aimed at creating a methodology for predicting the erosion characteristics of vane pumps were conducted in this paper. This methodology especially relevant in the case of pumping liquids with physical properties different from water. The methods of computational fluid dynamics (CFD) well predict the operation failure due to cavitation and allow us to determine the areas of possible cavitation erosion. The conditions for the absence of cavitation erosion also could be predicted with the help of CFD methods. In order to verify the numerical prediction of cavitation erosion, test bench working on water was created, which allows to verify methods of experimental investigations of cavitation erosion with the help of express analysis based on paint coatings.

Numerical prediction of cavitation erosion on a ship propeller in model- and full-scale

The cavitating flow around a ship propeller was simulated with an implicit RANS based flow solver using the Volume of Fluid (VoF) method to model the interface between the two phases. The sliding interface method was applied to simulate the rotation of the propeller, comprising a rotor and a stator region. Erosion was predicted with a numerical model based on the microjet hypothesis, using the information from the flow solution. Simulations of a propeller under non-cavitating and cavitating conditions were compared to experimental measurements, thereby demonstrating the ability of the presented numerical method to qualitatively predict cavitation erosion for a ship propeller.