Cavitation Rate Research Articles

Study on cavitation erosion mechanism of UHMWPE and PTFE

Polymer materials possess low density, high strength, corrosion resistance, and excellent cavitation erosion resistance. As a result, they are widely used in marine, water conservancy, and other engineering equipment as replacements for metal materials. However, polymer friction pairs working in a water environment for an extended period are easily damaged by cavitation erosion. In this work, the cavitation behavior of polytetrafluoroethylene (PTFE) and ultra-high molecular weight polyethylene (UHMWPE) in deionized water and seawater is investigated through experiments and computational fluid dynamics (CFD) simulations. The results indicate that the cavitation erosion resistance of UHMWPE is significantly better than that of PTFE, and the UHMWPE has four cavitation process stages, while the PTFE has only three cavitation stages. 316L counterparts in the seawater corrosion and cavitation coupling effect of a large number of metal particles off and wash polymer material surface, so that the cavitation erosion of PTFE and UHMWPE is more serious in seawater environment. CFD simulation demonstrates that the cavitation erosion zone under the radiator shows a semicircular distribution. Meanwhile, the formation of ring-shaped cavitation pit is related to the distribution of bubbles on the surface of the radiator. The cavitation rate of PTFE and UHMWPE is slowed down by the “water cushion effect”.

Cavitation mitigation via curvilinear barriers in centrifugal pump

Cavitation is a significant problem in hydraulic machinery that leads to the deterioration of hydraulic performance, material damage, and flow instability. While current methods partially address cavitation instability, there is a lack of comprehensive understanding of the control mechanisms. This study focuses on controlling cavitation flow instability in a centrifugal pump by proposing an active method using obstacles on the blade's surface. A low-specific speed centrifugal pump was chosen as the research object, and a three-dimensional unsteady full-flow channel numerical simulation was conducted. The findings indicate that in the absence of cavitation, the wake vortex induced by obstacles increases energy loss in the centrifugal pump, resulting in a slight drop in efficiency. However, when cavitation occurs, the obstacles effectively improve the flow field, reduce the vortex strength near the back of the blade in the flow channel, and significantly reduce the growth rate of cavitation volume. This reduction is observed in both the cavitation volume and its first derivative. Thus, the obstacles optimize the flow structure, reduce vortex strength, and slow the growth rate of cavitation. The main control mechanism involves inducing high-pressure waves to collapse cavities and improving flow transition characteristics. To solve the inverse problem of cavitation control with obstacles inside a centrifugal pump, dimensionless geometric parameters are studied to determine better suppression effects.

Analysis of turbulent cavitation effects on water-lubricated bearing in single screw compressors

PurposeTo guide the stable radius clearance choice of water-lubricated bearings for single screw compressors, this paper aims to analyze the effects of turbulence and cavitation on bearing performance under two conditions of specified external load and radius clearance.Design/methodology/approachA modified Reynolds equation considering turbulence and cavitation is adopted, based on the Jakobsson–Floberg–Olsson boundary condition, Ng–Pan model and turbulent factors. The equation is solved using the finite difference method and successive over-relaxation method to investigate the bearing performance.FindingsThe turbulent effect can increase the hydrodynamic pressure and cavitation. In addition, the turbulent effect can lead to an increase in the equilibrium radius clearance. The turbulent region exhibits a higher load capacity and cavitation rate. However, the increased cavitation negatively impacts the frictional coefficient and end flow rate. The impact of turbulence increases as the radius clearance decreases. As the rotating speed increases, the turbulence effect has a greater impact on the bearing characteristics.Originality/valueThe research can provide theoretical support for the design of water-lubricated journal bearings used in high-speed water-lubricated single screw compressors.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2024-0029/

Cross-influence of cavitation and flow rate on pressure pulsation of a volute mixed flow pump

Mixed-flow pump is a general purpose hydraulic machinery in many fields of fluid transport for its advantages of wide efficient operation flow rate range, but its operation stability is restricted by cavitation. To obtain the cross effect of cavitation and flow rate on its pressure pulsation, a high-precision experimental system was first established to monitor the pressure signals at four key positions, obtaining their time domain; second, based on this tested results, time frequency domain analysis technique based on continuous wavelet transform was adopted to capture the temporal evolution; third, wavelet coherence value analysis was further adopted to diagnose the cavitation development speed at different spatial positions. Primary findings are as follows: (1) the secondary peaks induced by cavitation generated the discrete disturbance in low-frequency range, and the amplitudes at shaft frequency and blade passing frequency were both increased, with a worse time continuity. (2) Under 1.0 QBEP, the mixed flow pump had a best anti-cavitation performance. Under 0.8 QBEP, its internal flow pattern was easily to be disturbed by cavitation flow, while that under 1.2 QBEP had the fastest cavitation development speed. (3) Under the action of unstable potential flow, within the flow field near the rotor–static interface and the downstream, a close flow exchange was established between the cavitation bubbles and mainstream; thus, the pressure pulsation inside the volute became more sensitive to the cavitation development.

Experimental and Numerical Investigation of Cavitation Assessment for Runner Blades in a Francis Turbine

Cavitation in hydro turbines causes component deterioration that requires continuous and costly maintenance in the hydroelectric power generation stations. The Tarbela Dam Hydel Project (TDHP) in Pakistan is facing a cavitation problem in the Francis Turbine components, such as the runner and draft tube. Simulation work has been performed to examine and quantify the cavitation rate as a function of the suction head (SH) and flow velocity (FV) by utilizing a homogeneous cavitation model. The result shows that pressure fluctuation is maximum for overcrowded conditions and minimum for rated load conditions. Moreover, a higher cavitation rate is found for the part and overcrowded conditions compared to the rated load condition. Additionally, the cavitation rate becomes 50% higher when the SH increases from 5.54 to 12.34 m. Moreover, SEM results have verified the CFD results that higher FV and SH enhance the cavitation rate. Furthermore, the numerical work is validated by simplified hydrofoil geometry. The computational fluid dynamics results presented a good arrangement with the experimental data.

Numerical research on the hydrodynamic effect on the leakage of two-phase refrigerant-oil mixture in the flank gaps of compressors

This paper investigates the two-phase leakage of the flank gap in rotary compressors by using the coupled models of compressible Reynolds equation and refrigerant-oil pair solubility. The models are verified by both the classical analytical model and the published results in the static and dynamic situations. Moreover, results also firstly show how the hydrodynamic pressure, cavitation, and leakage mass flow rate can be influenced by the motion of the roller in the rotary compressor. Compared to the static situation, the pressurized zone in the high-pressure side due to the hydrodynamic effect can potentially increase the leakage mass flow rate of the mixture.

Cavitation resistance of laser-sintered MS1 steel

This study focuses on the determination of cavitation rate for samples produced by Direct Metal Laser Sintering (DMLS) of MS1 maraging steel powder without any post-processing thermal or mechanical treatment (as-built). The test samples, fabricated using an EOSINT M280 machine in a nitrogen atmosphere, were evaluated for their cavitation resistance using the ultrasonic vibration method as proposed by the ASTM G32 standard. Surface characterization to determine the duration of the experiment, as well as during and after the experiment to analyze changes in surface characteristics, was conducted using Scanning Electron Microscopy (SEM). Additionally, chemical analysis was performed using the Energy Dispersive X-ray Spectroscopy (EDS) method before and after the experiment to identify any changes and locations of significant surface damage. The mass loss of the samples over time was measured to calculate the cavitation rate. The goal of this research was to explore the potential applications of laser-sintered MS1 steel powder for manufacturing machine components and parts that are subject to cavitation erosion, due to the numerous benefits of additive manufacturing over traditional conventional technologies.

Cavitation erosion of samples based on cordierite-talc ceramics

In the paper, the cavitation resistance of cordierite samples with the addition of 10%, 15% and 20% talc, sintered at 1200?C, was investigated. The ultrasonic vibration method with a stationary sample according to the ASTM G32 standard was applied. The formation and development of damage to the surface of the samples was monitored using a scanning electron microscope and the level of damage to the surface of the samples was quantified using image analysis. The change in the mass of the samples as a function of the cavitation time was monitored to determine the cavitation rate. By measuring the mass loss and morphological analysis of the pits formed on the surface of the sintered samples of the cordierite-talc ceramics, the mechanism of degradation and resistance to the effect of cavitation was monitored. The obtained results were compared with the results of earlier tests of cavitation resistance of sintered cordierite samples. The addition of talc in the mixture with cordierite significantly improved cavitation resistance of the sintered material compared to sintered pure cordierite. The tests were done to see the potential application of this material in hydrodynamic conditions, especially because of the strong corrosion resistance of these refractory materials.

Influence of pressure disturbance wave on dynamic response characteristics of liquid film seal for multiphase pump

Slug flow or high GVF (Gas Volume Fraction) conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps, endangering the safety of multiphase pump units. The mechanical seal model is simplified by using periodic boundary conditions and numerical calculations are carried out based on the Zwart-Gerber-Belamri cavitation model. UDF (User Define Function) programs such as structural dynamics equations, alternating load equations, and pressure disturbance equations are embedded in numerical calculations, and the dynamic response characteristics of mechanical seal are studied using layered dynamic mesh technology. The results show that when the pressure disturbance occurs at the inlet, as the amplitude and period of the disturbance increase, the film thickness gradually decreases. And the fundamental reason for the hysteresis of the film thickness change is that the pressure in the high-pressure area cannot be restored in a timely manner. The maximum value of leakage and the minimum value of axial velocity are independent of the disturbance period and determined by the disturbance amplitude. The mutual interference between enhanced waves does not have a significant impact on the film thickness, while the front wave in the attenuated wave has a promoting effect on the subsequent film thickness changes, and the fluctuation of the liquid film cavitation rate and axial velocity under the attenuated wave condition deviates from the initial values. Compared with pressure disturbance conditions, alternating load conditions have a more significant impact on film thickness and leakage. During actual operation, it is necessary to avoid alternating load conditions in multiphase pump mechanical seals.

Structural selection of liquid hydrogen lubricated herringbone spiral-grooved thrust bearing considering viscous dissipative heat

Spiral-grooved thrust bearing (SGTB) is one of the important kinds of supporting component in high-speed rotating devices. The high shearing rate of SGTB can produce a large amount of viscous dissipative heat, which causes a temperature rise. Dynamic pressure effect induces pressure variation in the herringbone SGTB (HSGTB). When liquid hydrogen (LH2) is used as a lubricant, cavitation caused by lower pressure and higher temperature can result in lubrication failure. Especially, the cavitation of LH2 is more prone to occur because of its small temperature difference between the triple point and critical point, and the smaller supercooling degree. The influence of thermal properties on the phase transition process of LH2 is more significant. In this paper, the thermal and mechanical performance of three different structures of LH2 lubricated SGTB is compared by considering viscous dissipative heat. Herringbone SGTB is proposed for better performance and feasibility of its application in LH2 lubrication. The static performances of HSGTB such as load capacity, friction torque, cavitation rate, average temperature, and heat flux have been evaluated numerically by introducing the cryogenic cavitation model. The orthogonal sampling method and range analysis are used to optimize the HSGTB structure. Compared with the original HSGTB, cavitation rate and temperature rise are significantly suppressed in the optimized HSGTB. In addition, the load capacity is also improved effectively at high rotational speed, which is expected to be applied to high-speed centrifugal pumps.

Effect of Shielding Gas Arc Welding Process on Cavitation Resistance of Welded Joints of AlMg4.5Mn Alloy.

The effect of the shielding gas arc welding process on the cavitation resistance of the three-component aluminum alloy AlMg4.5Mn and its welded joints was investigated. Welding was performed using the GTAW and GMAW processes in a shielded atmosphere of pure argon. After the welding, metallographic tests were performed, and the hardness distribution in the welded joints was determined. The ultrasonic vibration method was used to evaluate the base metal's and weld metal's resistance to cavitation. The change in mass was monitored to determine the cavitation rates. The morphology of the surface damage of the base metal and weld metal due to cavitation was monitored using scanning electron microscopy to explain the effect of the shielding gas arc welding process on their resistance to cavitation.

Identification of cavitation state of centrifugal pump based on current signal

Centrifugal pump, which is widely used in water conservancy, electric power, petrochemical, ship, aerospace, and other technical fields, is the core equipment used to ensure all kinds of energy transfer. Cavitation not only affects the service life of the centrifugal pump but also seriously impacts the reliability of the process flow or device system. Due to the influence of the life, position and number of vibration sensors, the existing cavitation fault feature identification accuracy is not enough. The state analysis and characteristic recognition of the current signal under the cavitation state of the centrifugal pump are conducted in this paper based on soft sensing technology, and the signal component and judgment threshold representing the cavitation state are obtained. The following results are presented. Under different critical cavitation numbers, a small number of bubbles appeared near the suction surface of the inlet edge of the impeller, which verified the reliability of criterion for the critical cavitation number when the head coefficient decreased by 3%. The overall accuracy of binary classification cavitation recognition based on the current signal is 12.9% higher than that of three classification cavitation recognition. The recognition rate of VMD decomposition under different working conditions is higher than that of EMD, in design conditions, for example, overall accuracy improved by 7.3%, which also indicates that the obtained cavitation information of each component by VMD decomposition is richer than that obtained by EMD decomposition. Comparing different working conditions, a large flow rate easily leads to cavitation and high recognition current rate, compared with the flow of 0.75 Q and 1.25 Q, the overall accuracy is improved by 9.6%.

A Deep Potential model for liquid-vapor equilibrium and cavitation rates of water.

Computational studies of liquid water and its phase transition into vapor have traditionally been performed using classical water models. Here, we utilize the Deep Potential methodology-a machine learning approach-to study this ubiquitous phase transition, starting from the phase diagram in the liquid-vapor coexistence regime. The machine learning model is trained on abinitio energies and forces based on the SCAN density functional, which has been previously shown to reproduce solid phases and other properties of water. Here, we compute the surface tension, saturation pressure, and enthalpy of vaporization for a range of temperatures spanning from 300 to 600K and evaluate the Deep Potential model performance against experimental results and the semiempirical TIP4P/2005 classical model. Moreover, by employing the seeding technique, we evaluate the free energy barrier and nucleation rate at negative pressures for the isotherm of 296.4K. We find that the nucleation rates obtained from the Deep Potential model deviate from those computed for the TIP4P/2005 water model due to an underestimation in the surface tension from the Deep Potential model. From analysis of the seeding simulations, we also evaluate the Tolman length for the Deep Potential water model, which is (0.091 ± 0.008) nm at 296.4K. Finally, we identify that water molecules display a preferential orientation in the liquid-vapor interface, in which H atoms tend to point toward the vapor phase to maximize the enthalpic gain of interfacial molecules. We find that this behavior is more pronounced for planar interfaces than for the curved interfaces in bubbles. This work represents the first application of Deep Potential models to the study of liquid-vapor coexistence and water cavitation.

Numerical simulation of cavitation performance in a scaled-up bath-type sonoreactor considering inhomogeneous bubble cloud

The bath-type sonoreactor holds great potential in industrial applications of process intensification. However, the scale-up of this bath-type sonoreactor is limited by a lack of investigation into sonoreactor design. In this work, we employed linearized wave equation considering inhomogeneous bubble distribution for simulation of scale-up bath-type sonoreactor design. Comprehensive validation experiments were conducted to verify simulation accuracy. This model predicts abnormal attenuation phenomenon during sound waves transmission that pose challenges for optimal design of sonoreactors. The result implies that increasing driving pressure cannot constantly increase conversion rate of cavitation energy. For example, as driving pressure increases, cavitation rate become stabilized to be a constant value of 0.4 and average cavitation pressure tends to be 1.1 times of driving pressure. Reactor width determines cavitation area and a width of 350 mm generates most cavitation volume under a liquid level of 100 mm. Regardless of the liquid level, increasing the driving pressure causes sound pressure in the near-field decrease due to abnormal attenuation. Once sound wave has travelled to a distance of 60–80 mm, cavitation will not make a noticeable difference.

Ultrasound assisted extraction: A relook at solvent to material ratio, its effects on process efficiency and how it can be exploited for different uses

AbstractUltrasound assisted extraction (UAE) is one of the preferred green extraction techniques widely used for the extraction of bioactive compounds from plant materials. It has attracted much attention and many studies have been done to understand its mechanism, effects and efficiency. However, no study has discovered and given enough attention to the superior role solvent‐to‐material ratio (SMR) plays in moderating UAE efficiency. This study therefore emphasizes the importance of SMR as the main determinant of UAE efficiency and further proves its mechanistic effects with ultrasound physics. It discusses SMR effects on extraction medium density, acoustic energy transfer, cavitation rate, power intensity attenuation and free hydroxyl radical generation during water‐based UAE. This understanding is needed to assist researchers in the design of their extraction experiments and optimizations. Without this insight, even optimization processes will be limited in giving the true conditions needed for the highest UAE efficiency. The study shows that low SMR increases acoustic energy scattering and absorption and attenuates ultrasound power intensity and vice versa. SMR can be controlled to either preserve bioactivity of compounds or produce free radicals for microbial inactivation and elimination and oxidative degradation of natural pigments in aqueous media.Practical applicationA comprehensive understanding of the mechanism and physics behind the effects of solvent‐to‐material ratio (SMR) during ultrasound assisted extraction (UAE) of bioactive compounds helps in fine‐tuning SMR purposely to ensure that ultrasound power attenuation is minimized. Ultrasound power defines UAE efficiency by virtue of acoustic cavitation. Due to the fact that UAE in aqueous media generates free hydroxyl radicals (*OH) from water autolysis, SMR can be deliberately tuned to induce controlled power attenuation to limit this phenomenon. This becomes a strategy to protect bioactive compounds that are prone to oxidative degradation. As ultrasound power is linked to energy consumption, fine‐tuning SMR to minimize power attenuation can significantly improve process efficiency and reduce treatment time, saving energy and enhancing profitability, especially during large scale industrial treatments.

The water cavitation line as predicted by the TIP4P/2005 model.

The formation of vapor bubbles in a metastable liquid, cavitation, is an activated process due to the free energy cost of having both phases at contact. Such an energetic penalty enables the existence of the liquid beyond its thermodynamic borders. Establishing the stability limits of a liquid as ubiquitous as water has important practical implications and has thereby attracted a lot of attention. Different experimental strategies and theoretical analyses have been employed to measure and predict the cavitation line, or the pressure-temperature kinetic stability border of liquid water. Understanding the location of the cavitation line requires knowing the cavitation rate dependence on pressure and temperature. Such dependency is difficult to obtain in experiments, and we use molecular simulations with the TIP4P/2005 model to fill this gap. By deeply overstretching liquid water below the saturation pressure, we are able to observe and quantify spontaneous cavitation. To deal with a lower overstretching regime, we resort to the Seeding technique, which consists of analyzing simulations of a liquid containing a vapor bubble under the theoretical framework of Classical Nucleation Theory. Combining spontaneous cavitation with Seeding, we get a wide overview of the cavitation rate. We study two different temperatures (450 and 550K) and complement our perspective with the results previously obtained at 296.4K [Menzl et al., Proc. Natl. Acad. Sci. 113, 13582 (2016)] to establish a broad simulation-experiment comparison. We find a good agreement between simulations and both isobaric heating and isochoric cooling experiments using quartz inclusions. We are, however, unable to reconcile simulations with other experimental techniques. Our results predict a decrease in the solid-liquid interfacial free energy as the liquid becomes increasingly overstretched with a temperature independent Tolman length of 0.1nm. Therefore, the capillarity approximation underestimates the nucleation rate. Nonetheless, it provides a fair indication of the location of the cavitation line given the steep rate vs pressure dependence. Overall, our work provides a comprehensive view of the water cavitation phenomenon and sets an efficient strategy to investigate it with molecular simulations.

Estimation of bubble cavitation rates in a symmetrical Lennard-Jones mixture by NVT seeding simulations.

The liquid-vapor transition starts with the formation of a sufficiently large bubble in the metastable liquid to trigger the phase transition. Understanding this process is of fundamental and practical interest, but its study is challenging because it occurs over timescales that are too short for experiments but too long for simulations. The seeding method estimates cavitation rates by simulating a liquid in which a bubble is inserted, thus avoiding the long times needed for its formation. In one-component systems, in the NpT ensemble, the bubble grows or redissolves depending on whether its size is larger or smaller than the critical size, whereas in the NVT ensemble (i.e., at constant number of particles, volume, and temperature), the critical bubble can remain in equilibrium. Provided that a good criterion is used to determine the bubble size, this method, combined with the Classical Nucleation Theory (CNT), gives cavitation rates consistent with those obtained by methods independent of the CNT. In this work, the applicability of NVT seeding to homogeneous cavitation in mixtures is demonstrated, focusing on a partially miscible symmetrical binary Lennard-Jones (LJ) liquid at a temperature within the mixing regime. At the same stretching pressure, cavitation rates are higher in the binary mixture than in the pure liquid due to the lower interfacial free energy of the mixture. Curiously, the cost of creating a bubble is similar in the pure and binary LJ liquids at the same metastability, Δμ/Δμspin, with Δμ being the difference in chemical potential between the metastable liquid and coexistence, and Δμspin between the spinodal and coexistence.

Vibration and cavitation in high-speed gears caused by faults

In high-speed gear transmission, cavitation occurs easily due to vibration. When gear has pitting or crack fault, the cavitation will be more violent due to stronger vibration, causing potential safety hazards. However, researches on gear cavitation mechanism considering pitting and crack are limited. For studying the cavitation mechanism of faulty gear, a model combined computational fluid dynamics and faulty gear dynamics has been proposed, being regarded as the innovation of this paper. The dynamic characteristics of the faulty gear is obtained by solving the gear finite element model, and the results will be applied to the analysis of lubricating oil flow characteristics as boundary conditions. For proving the validity of the proposed model, the simulation results are compared with the available experimental results. Moreover, the novelty of this paper is to consider the influence of gear failures on cavitation, factors such as rotational speed, pitting depth and crack depth are discussed, tooth profile changes are also considered. The results indicate that gear faults have greater impact on cavitation at high speeds. At 10,000 rpm, with the deepening of pitting, the cavitation intensity will increase firstly and then decrease. When the pitting depth increases from 0.2 mm to 0.3 mm, the root mean square value of average vapour volume fraction decreases from 0.0752 to 0.0724. For cracked gears, the crack depth will affect the cavitation enhancement rate. The increase rate of cavitation decreases from 17.4 to 1.1% when crack depth increases from 1 to 4.5 mm. This study provides an effective tool for gear cavitation suppression and high reliability.

Numerical Modeling of Cavitation Rates and Noise Acoustics of Marine Propellers

The study numerically investigated the noise dissipation, cavitation, output power, and energy produced by marine propellers. A Ffowcs Williams–Hawkings (FW–H) model was used to determine the effects of three different marine propellers with three to five blades and a fixed advancing ratio. The large-eddy Simulations model best predicted the turbulent structures’ spatial and temporal variation, which would better illustrate the flow physics. It was found that a high angle of incidence between the blade’s leading edge and the water flow direction typically causes the hub vortex to cavitate. The roll-up of the cavitating tip vortex was closely related to propeller noise. The five-blade propeller was quieter under the same dynamic conditions, such as the advancing ratio, compared to three- or four-blade propellers.

Investigation of cavitating vortex rope instabilities and its suppression inside a Francis turbine model with Thoma number variation

Cavitating vortex rope at part load (PL) condition at lower values of the Thoma number (σ) induces severe pressure fluctuation and efficiency reduction in a Francis turbine, which ultimately hinders continuous energy production. Installation of fins at draft tube (DT) can mitigate these instabilities and can safeguard the turbine operation with lower maintenance costs. The effect of fins on hydraulic performance and internal flow physics at PL condition with the variation of σ is examined in the present numerical investigation. For the two extreme opposite values of σ, the flow characteristics are predicted accurately for the turbine with and without fins by conducting transient simulations using ANSYS-CFX. The numerical findings on the structured and unstructured grid points are validated with the experimental results. The turbine's performance remains constant for higher values of Thoma numbers, and as the value decreases, the performance declines. The cavitation vortex rope formation inside the DT with fins is mitigated significantly at the minimum σ, while at the maximum value, the vortex rope with bubble generation is restricted. Compared to the without fin case, the swirl intensity is minimized remarkably (68%) with the presence of fins at the lowest σ. The maximum cavitation rate is manifested by the DT without fins, which is about 60% higher than the DT with fins. At minimum σ, extreme pressure pulsations are induced inside the DT without fins, which are reduced by 43% in the finned draft tube. Therefore, stable energy production is maximized with the installation of fins at both Thoma numbers.