Cavitating Liquid Jet Research Articles

Cavitation erosion behaviors and damage mechanism of Ti-Ni alloy impacted by water jet with different standoff distances

The cavitation erosion of Ti-Ni alloy is explored on a cavitating liquid jet with different standoff distances. The cavitation erosion characteristics of Ti-Ni alloy specimens are analyzed, and the influences that different standoff distances of the water jet have on cavitation erosion are explored. The results of cavitation erosion outcomes under different standoff distances of 6 mm, 8 mm, 10 mm, 12 mm, 14 mm and 16 mm show slight deformation, grain boundary cracking and formation of initial micro-pits, pits of maximum depth around 50 μm, more pits of maximum depth around 80 μm with micro-cracks, obvious plastic deformation traces with some pits, bulges and slip bands, respectively. When the Ti-Ni alloy is impacted by water jet with a standoff distance of 12 mm for 4 hrs, the surface microstructure undergoes substructural evolution and new fine grains form, with obvious stress concentration and dislocation accumulation appearing on the subsurface.

Numerical prediction of erosion due to a cavitating jet

We numerically investigate the erosion potential of a cavitating liquid jet by means of high-resolution finite volume simulations. As thermodynamic model, we employ a barotropic equilibrium cavitation approach, embedded into a homogeneous mixture model. To resolve the effects of collapsing vapor structures and to estimate the erosion potential, full compressibility is considered. Two different operating points featuring different cavitation intensities are investigated and their erosion potential is estimated and compared. Different methods are used for this purpose, including collapse detection (Mihatsch et al., 2015), maximum pressure distribution on the wall, and a new method of generating numerical pit equivalents. The data of numerical pit equivalents is analyzed in detail and compared with experimental data from the literature. Furthermore, a comprehensive grid study for both operating points is presented.

Cavitation Erosion Behaviour of Martensitic Stainless Steels SUS 420J2 and SUS440C by High Pressure Liquid Jet

The high-pressure cavitation erosion (CE) behavior of SUS420J2 and SUS440C were studied by a high pressure cavitating liquid jet experiment apparatus, according to ASTM Standard G134-95. The microstructures were investigated by X-ray diffraction and scanning electron microscopy to determine the phases and precipitates. The mass loss vs. exposure time relations indicated that SUS440C had longer incubation time and a decreasing erosion rate. The eroded topographical evolution was investigated, indicating that the initiation of cavitation erosion was accumulated from grain boundaries for SUS420J2, and from M3C precipitates or ferric oxide inclusions for SUS440C. The dominant factors that influenced CE behaviors changed in different cavitation stages. Micro-pitting and initial damage induced by grain boundaries or precipitates were the dominant erosion forms during the incubation stage; however, the matrix hardness started to prevail as the dominant factor after the precipitates had been torn off, or grain boundaries damage disappeared.

Experimental Study of the Influence of Test Chamber Dimensions on Aggressive Intensity of the Cavitating Jet

Abstract The ASTM G134 standard, Standard Test Method for Erosion of Solid Materials by Cavitating Liquid Jet, provides specifications for assessing the material resistance to the cavitation erosion caused by submerged cavitating jet. Nevertheless, the influence of test chamber dimensions on cavitation erosion is not considered in such an international standard. To fill in the gap, nine test chambers with different chamber lengths and diameters were devised to facilitate a comparative investigation of the cavitation aggressive intensity. The cavitation number was fixed at 0.014. Aluminum (JIS A1070) and stainless steel (JIS SUS316L) specimens were used in the experiment. The results show that at the distance of 19 mm between the nozzle outlet section and the specimen surface, the most severe erosion is accomplished, which is shared by the nine test chambers. Both the mass loss and the erosion rate vary with the test chamber length and diameter. A long test chamber is associated with a low erosion rate. The coefficient of variation on the cumulative erosion rate is 12 %. As the chamber length equals the chamber diameter, the coefficient of variation is 3 %. At the test chamber length of 30 mm and diameter of 40 mm, the maximum erosion rate is higher than its counterparts. The present study provides important data for the ASTM G134 standard to decide the operation parameters and test chamber dimensions.

Numerical simulation of cavitation for liquid injection in non-condensable gas

Modern internal combustion engines rely on a high pressure fuel injection system to deliver the fuel inside the engine. This high pressure fuel injection also results in additional complexities, one of which is the cavitation occurring due to large pressure drops inside the injector. The generation of cavitation pockets inside the injector is known to increase the turbulence locally, affecting the external jet formation. To capture this effect, a specific procedure is needed to study the effect of in-nozzle cavitation on the external jet. In this study, we propose and validate a method to study cavitation as well as the external jet formation using a consistent numerical framework based on interface capturing techniques. This formalism allows the representation of three phases : liquid, air and vapor. Numerical simulations of a cavitating liquid jet for two types of cavitation regimes are presented, namely developing cavitation and super cavitation. Numerical results are compared quantitatively, with the existing experimental measurements from the literature of the velocity field inside the injector, and qualitatively, by comparing the liquid and vapor structures obtained in the experiment and the simulation.

Nonlinear Evolution and Breakup of the Cavitating Liquid Jet Surrounded by the Rotary Compressible Air.

A nonlinear dispersion relationship has been established to study the surface evolution and breakup of the cavitating liquid jet with cavitation bubbles surrounded by the rotary air, and the built dispersion relationship and its solution are validated by comparing with the results in the reference. The effects of air rotation, fluid compressibility, and bubble volume fraction on jet morphology are investigated mainly. Air rotation changes the dominant mode of perturbation wave on the jet surface, and more uneven corrugated flows are formed at the interface with the increase of gas rotational strength. The fluid compressibility has little impact on jet morphology in the circumferential direction, while it has some impacts on the axial morphology, especially on the arrangement of droplets. Cavitation bubbles will affect the jet morphology, while the effect is smaller than gas rotation. Both swirling gas and fluid compressibility promote the jet breakup, while the influence of compressibility on jet breakup is obviously greater than gas rotation. In addition, the bubble volume fraction will promote the breakup of the cavitating liquid jet; however, this kind of promoting impact decreases with the increase of the cavitation bubble volume fraction.

Recommended Procedures to Test the Resistance of Materials to Cavitation Erosion

Abstract Predicting cavitation erosion under full-scale operating conditions is difficult and relies on laboratory testing using accelerated methods such as ASTM G32-09, Standard Test Method for Cavitation Erosion Using Vibratory Apparatus, and ASTM G134-95, Standard Test Method for Erosion of Solid Materials by a Cavitating Liquid Jet. The main difficulty is that full-scale cavitation intensity is often unknown, and correlating cavitation field characteristics of the accelerated method and the full scale is not obvious. The problem is more acute for compliant polymeric coatings, used for protection or repair of parts subject to cavitation. Extensive testing of such materials shows that, unlike metallic surfaces, they are highly resistant to low-intensity cavitation but fail catastrophically when the intensity exceeds a certain threshold. Such behavior creates the risk of accepting a candidate coating for its resistance to cavitation if the coating was tested at a low cavitation intensity not representative of the application field conditions. This highlights the need to conduct tests with a range of cavitation intensities rather than a single intensity. This article uses results from extensive tests under various forms of cavitation to propose a generalized definition of cavitation intensity. It then presents data on the response of both metals and polymeric coatings to various levels of accelerated cavitation. A new method to test the coatings at varying cavitation intensities is then presented. Such tests provide maps of material resistance to different levels of cavitation and are helpful to make an informed decision. The tests also show that during cavitation exposure, the coatings are subjected not only to mechanical stress but also to significant heating, which dynamically modifies their properties during the exposure. Temperature rise in the coating when exposed to cavitation is directly connected to the cavitation intensity to which it is exposed, and this interaction needs to be considered.

Jet Cavitation Erosion in Chamfered and Tapered Cylindrical Passages: Comparison with Visualization and Simulation

Abstract In hydraulic equipment, a jet cavitation occurs frequently at points wherein oil flows through an orifice and a gap that is due to a high pressure and large pressure difference. These jets typically erode equipment surfaces when the cavitation bubbles collapse. Although the erosion characteristics have been studied for cases wherein jets impinge on surfaces at normal or oblique angles, cavitation erosion has not been studied in cases wherein jets flow parallel to the wall surfaces. This study uses the method outlined in ASTM G134-17, Standard Test Method for Erosion of Solid Materials by Cavitating Liquid Jet, to perform 8-hour-long erosion tests on aluminum specimens and to visualize cavitation jets in transparent acrylic specimens. We test specimens with chamfers and tapers in different orientations and compare the results with numerical simulations to better understand the mechanisms behind cavitation erosion. The inner walls of the chamfered specimens were partially eroded near the downstream chamfered edge, regardless of the chamfer location. During the testing time, the chamfered surfaces and outer surfaces on both ends were not eroded. Erosion pits were visible locally along the convergent and straight paths in the tapered specimen, but the pits did not appear in the divergent-tapered specimen. Visualization and numerical results offer some insights into the pressure dynamics that explain why divergent tapers seem to be effective countermeasures against cavitation erosion in hydraulic equipment.

Experimental Study of Jet Cavitation Erosion Applicable to Oil and Water-Hydraulic Equipment

Abstract Hydraulic components, such as valves, pumps, and actuators, include many narrow passages in the form of nozzles, orifices, and gaps. Cavitation can occur when jets flow from high to low pressure through such sections, making it unavoidable for jets containing cavitation bubbles to impinge on the inner walls of hydraulic components. This report summarizes a series of experiments involving erosion tests, flow visualization, and pressure measurements with hydraulic oils and municipal water. For the erosion tests, the ASTM G134, Standard Test Method for Erosion of Solid Materials by a Cavitating Liquid Jet, method of jet cavitation erosion is used to evaluate the eroded mass loss and the specimen’s surface damage. The experimental apparatus consists of a stainless steel cylindrical chamber, a high-pressure hydraulic pump, and auxiliary hydraulic components. The main test parameters are the standoff distance, cavitation number, nozzle outlet geometry, specimen surface shape, and liquid type. The specimen mass is measured, and the eroded surfaces are recorded at specific intervals. For the visualization tests, an acrylic chamber and a digital video camera are used. Video frames are extracted as pictures and are processed by superposition. For the pressure measurements, pressure-sensitive films are used to estimate the pressure distributions on the impinged surfaces. The films are bonded on the specimen surface beforehand, exposed to the cavitating jets for a short period, and then analyzed using an image analysis system. Overall, by comparing the mass loss, surface damage, visualization pictures, and pressure mapping, the effects of the experimental parameters on the erosion characteristics are examined. Moreover, design approaches that are applicable to both oil and water-hydraulic components are proposed in order to reduce erosion by cavitating jets.

Cavitation erosion of low-density polyethylene coatings for pipe liners

The relationship between mechanical properties and the erosion rate was examined for chloroprene rubber and a number of polyethylene materials produced by different methods. As electric power plants are in operation over long periods of time, the effect of aging was also examined by testing material intended for use in pipes in electric power plants. Cavitation erosion tests were carried out by using a flowing apparatus as specified in the American Society for Testing Materials G134-95 standard. A flow velocity of 150 m/s and a test time of 24hours, were the experimental conditions used for a cavitating liquid jet test on polyethylene. The maximum depth of erosion rate (MaxDER) of polyethylene was found to decrease with the increase in hardness. Among all the tested materials, the relatively high molecular weight polyethylene with low density (m-LLDPE-H), showed the best resistance to cavitation erosion in terms of MaxDER. The effect of aging on the erosion rate of polyethylene was limited.

Simulating cavitating liquid jets using a compressible and equilibrium two-phase flow solver

In internal combustion engines the injection of high-pressure liquid fuel into a low-pressure gas through a nozzle passage is an important process to atomize the liquid and achieve optimal fuel–air mixing. A Computational Fluid Dynamics (CFD) model is developed in the present work to simulate the internal- and external-nozzle flow fields in an integrated way. The model assumes that the flow within and near the nozzle is continuous, and an Eulerian flow solver is developed using the general conservation laws of fluid dynamics. Differences in the thermodynamic states of the liquid and gas phases are modeled with a Stiffened Gas Equation of State (EOS). A practical phase equilibrium solver is developed, and is implemented into the Eulerian flow solver to predict phase changes in the flows – in particular, cavitation of the liquid within the injector nozzle passage. The combined equilibrium solver is applied to single-component and two component flows with one component being non-condensable air. A number of test problems are simulated to verify the numerical methods and validate the proposed models. These include two-phase shock tube problems, a converging–diverging nozzle flow problem, a submerged liquid jet problem, and a cavitating liquid jet problem.

Cavitation Inception and Erosion in Flowing System of Water and Liquid Metal

The cavitation erosion in liquid metals is important for the safety and reliability of nuclear reactors and industrial machinery. However, an evaluation method of cavitation erosion in liquid metal has so far not been established. This study clarifies the incipient condition of cavitation in a liquid metal. A cavitating liquid jet test apparatus in a liquid metal was developed. A cavitating liquid jet was issued from an orifice nozzle with a hole of 0.6mm diameter. PbBi-68 was used as liquid metal. The tests were carried out in water using various nozzles with different shapes to obtain the nozzle shape effect on the incipient number and the erosion rate. It was found that the incipient cavitation number in tap water and PbBi-68 is almost the same regardless of the flow velocity. When the cavitation number is defined by an equation as 2(pd-pv)/ρv2 (pd: downstream pressure, pv: vapor pressure, ρ: density, v: throat velocity), the incipient cavitation number becomes a constant regardless of the nozzle shape. Cavitation erosion tests were carried out with different nozzle shapes. It was concluded that the erosion rate can be qualitatively estimated by the output voltage of an acceleration sensor.

Experimental comparison of cavitation erosion rates of different steels used in hydraulic turbines

The prediction of cavitation erosion rates has an important role in order to evaluate the exact life of components in fluid machineries. Hydro-Québec has studied this phenomenon for several years, in particular in hydraulic turbine runners, to try to understand the different degradation mechanisms related to this phenomenon. This paper presents part of this work. In this study, we carried out experimental erosion tests to compare different steels used in actual hydraulic turbine runners (carbon steels, austenitic and martensitic stainless steels) to high strength steels in terms of cavitation erosion resistance. The results for these different classes of steels are presented. The tests have been performed in a cavitating liquid jet apparatus according to the ASTM G134-95 standard to simulate the flow conditions. The mass loss has been followed during the exposure time. The maximum depth of erosion, the mean depth of erosion, and the mean depth erosion rate are determined. As a result we found that ASTM-A514 high strength steels present excellent cavitation erosion resistance properties. The cavitation eroded surface is followed by optical profilometry technique. Determination of mechanical properties and examinations of the eroded surfaces of the samples have also been carried out in order to identify the erosion mechanisms involved in the degradation of these kinds of materials.

Prediction method for cavitation erosion based on measurement of bubble collapse impact loads

The prediction of cavitation erosion rates is important in order to evaluate the approximate life of components in fluid machinery. The measurement of impact loads in bubble collapses helps us to predict the life under cavitation erosion. In this study, we carried out the erosion tests and measured impact loads in bubble collapses with a cavitating liquid jet apparatus which complies with the ASTM G134-95 standard. The bubble collapse impact loads were measured by a piezo ceramic transducer in a cavitating liquid jet apparatus. To produce various cavitation conditions, the flow velocity was changed from 184 down to 80 m/s. We evaluated the incubation period based on a cumulative damage rule by measuring the impact loads of cavitation acting on the specimen surface and using the “constant impact load – number of impact curve” similar to the modified Miner's rule which is employed for fatigue life prediction. We found that the parameter ∑(Fiα×ni) (Fi: impact load, ni: number of impacts and α: constant) is suitable for the evaluation of the erosion life. After the constant α has been obtained under two different cavitation conditions, we can predict the incubation period with the cavitating liquid jet method under yet another condition, provided that the bubble collapse impact loads are measured.

Cavitation erosion resistance of stellite alloy weld overlays

Stellite alloys have excellent cavitation erosion resistance and are often used for liquid machinery, but the erosion properties of various stellite alloys have not been evaluated by a standard method. In this study, we evaluate the erosion resistance for various stellite alloy weld overlays of ST6 and ST21 in a vibrating method and in a cavitating liquid jet method. The grain size of the Co matrix affects the cavitation erosion resistance of stellite alloy weld overlays of ST6. The erosion rate of the maximum rate stage of stellite weld overlay alloys of ST6-1, ST6-2 and ST6-3 were found to be about 1/13 to 1/7 times that of SUS304. Moreover, we clarified the cavitation erosion mechanism of SUS304 and ST6 by scanning electron microscopy. Furthermore, by comparing the erosion behavior in a cavitating liquid jet method with that in a vibratory method, it was found that the erosion rate of the cavitating jet method and the vibratory method have a good correlation.

Formation and progression of cavitation erosion surface for long exposure

Cavitation erosion often causes the leakage of water in piping systems of industrial plants. Cavitation erosion tests were carried out for S15C carbon steel equivalent to pipe steel STPG370 in a stationary specimen test method using a vibratory apparatus specified by ASTM G32-03. Another test was performed using a cavitating liquid jet method according to ASTM G134-95 to simulate the flow condition. It was found that the maximum depth of erosion (MaxDE) increases with exposure time with a power of about 0.5 which is different from the ordinary power of 1.0. The distribution of the maximum depth of erosion pits was obtained by the extreme value analysis (Gumbel distribution) at every exposure time.

Detection of Incipient Cavitationin Cavitating Liquid Jet Apparatus with an Accelerometer and Its Application to Orifice Cavitation

In general, cavitation is an undesirable phenomenon in many cases. In order to prevent from cavitation which produces great damage in the valves and piping system of power plants, it is necessary to detect the occurrence of cavitation. In order to determine the initial stage of cavitation process, an accelerometer was used to establish the technique of estimating the incipient cavitation number by impact signals. On the other hand, in many cases, cavitation number in orifice part is defined with the average flow velocity, however, the definition with upstream and downstream pressure of flow is more useful. Therefore, the incipient cavitation number defined in general way by using a cavitating jet method was clarified and was extended to regular orifice cavitation.

Formation and Progression of Cavitation Erosion Surface for Long Exposure

Cavitation erosion often causes a leak of water in piping systems of industrial plants. Cavitation erosion tests were carried out for the S 15 C carbon steel equivalent to pipe steel STPG 370 under the condition of the stationary specimen test using the vibratory apparatus specified by ASTM G 32-03. Another test was performed using the cavitating liquid jet method by ASTM G 134-95 to simulate a flow condition. It was found that the maximum depth increases with erosion time with a power of about 0.5 and the erosion pit was formed locally with time by statistical analysis made on a Gumbel probability paper.

Effects of materials and solution temperatures on cavitation erosion of pure titanium and titanium alloy in seawater

Cavitation erosion was studied for various pure titanium and titanium alloy samples using a rotating disk method in seawater at 303, 318, and 333 K. Their respective erosion resistances were evaluated in terms of Vickers hardness (HV). The resistance increased in order with increasing hardness: pure titanium samples of first, second, and third types, and titanium alloy (Ti–6Al–4V). The relative temperature was defined as 273 K for freezing temperature and 373 K for boiling temperature under pressurized water. The volume loss rate of test specimens increased with rising seawater temperature of 289–316 K of the relative temperature, as well as in cases using cavitating liquid jet and vibratory apparatuses.

Influence of temperature on erosion by a cavitating liquid jet

The influence of water temperature on cavitation erosion has previously been studied using a vibratory apparatus, but no researches have been conducted at a constant cavitation number in flow condition. This study deals with the influence of the water temperature on cavitation erosion using a cavitating jet apparatus. The optimum stand-off distance at 25 °C was 11, 15, 21 and 25 mm at cavitation number of σ = 0.03, 0.025, 0.02 and 0.015, respectively, and was almost the same as that of a guideline in the ASTM G134 standard. The optimum stand-off distance at 75 °C is similar to that at 25 °C. The erosion rate increases with the liquid temperature and reaches a peak, followed by a decrease. The relative temperature was defined as 0 °C for freezing temperature and 100 °C for boiling temperature of pressurized water. The peak appears at the approximate average of freezing and boiling relative temperatures. The erosion rate increases by 1%/ °C between 5 and 45 °C of relative temperatures, and decreases by 2%/ °C between 45 and 80 °C.