Cavitation Formation Research Articles

Effect of leading edge tubercles bionic blade of high speed pump jet propulsor on cavitation suppression

The occurrence of cavitation in hydraulic machinery is a matter of significant concern, as it presents a substantial risk to the reliable functioning of pump jet propulsors. The point of this study is to find out how well bionic blades with different kinds of leading edge (LE) tubercles distribution stop cavitation in high-speed pump jet propulsors. Furthermore, it examines their performance in various cavitation scenarios. The study conducts a thorough evaluation of the function of bionic blades in mitigating cavitation and maintaining performance by analyzing head, efficiency, cavitation shape, pressure distribution, entropy production, vortex flow, and pressure pulsations. In the absence of reaching the cavitation critical point, the bionic blade 1 (BB1) model exhibited a head that was 2.65% greater than that of the original blade (OB) model. Additionally, it had the highest level of effectiveness among the three bionic blades in preventing cavitation, causing a 5%–8% delay. Furthermore, the LE tubercles not only successfully inhibited cavitation but to some degree stimulated the formation of both tip clearance cavitation and tip leakage cavitation. The BB1 model did a better job of controlling entropy production and vortex flow during the inception to collapse of cavitation. This led to lower losses, more consistent flow properties, and higher efficiency compared to the OB model. Analysis of the pressure pulsations shows that BB1 exhibits a reduction in pulsation intensity across all cavitation numbers, indicating excellent dynamic stability.

Large eddy simulation of micro vortex generator-controlled cavitation across multiple stages

Micro vortex generators (mVGs) control cavitation by altering the boundary layer flow structure. This study employs the wall-adapting local eddy-viscosity large eddy simulation (WALE-LES) turbulence model combined with the Zwart–Gerber–Belamri cavitation model to conduct transient numerical simulations on the National Advisory Committee for Aeronautics 0015 baseline hydrofoil and the hydrofoil equipped with mVGs under various cavitation numbers. The proper orthogonal decomposition method and experiments verify the accuracy and consistency of these simulations regarding cavity scale. The study elucidates mechanisms by which mVGs suppress cloud cavitation at low cavitation numbers and induce vortex cavitation at high cavitation numbers. Results indicate that mVGs maintain sheet cavitation characteristics at low cavitation numbers, reducing wall pressure fluctuations and enhancing flow stability. During cavitation inception, mVG-induced vortex cavitation leads to early cavitation formation. In the sheet cavitation phase, modal energy distribution is more dispersed, while in the inception phase, energy is concentrated with significant dominant modes. Moreover, the counter-rotating vortices generated by mVGs mitigate flow separation, enhance leading-edge flow attachment stability, and reduce high-frequency vibrations caused by bubble shedding. This study significantly advances the understanding of cavitation control by accurately simulating and revealing the cavitation control mechanisms of mVGs across different stages using the WALE-LES model. The findings demonstrate that mVGs can effectively stabilize cavity structures at low cavitation numbers, reducing flow instabilities and enhancing overall hydrofoil performance. These insights will have a significant impact on the design of hydrofoils and the development of cavitation control strategies.

Investigation of numerical solution approaches for the cavitating flow analysis of twisted hydrofoils

In this study, geometrical parameters such as twist, section thickness, and angle of attack are numerically investigated for their influence on lift and drag coefficients, as well as cavitation development. The Delft 11 Hydrofoil, a twisted version of the NACA0009 foil with a −2° angle of attack, is used as the benchmark geometry for validation studies under both non-cavitating and cavitating flow conditions. After the validation studies, the geometries of the NACA0009 and NACA0015 hydrofoils were redesigned as half-twisted and twisted. These redesigned hydrofoils, along with the original no-twist versions, were analyzed under cavitating flow conditions within an angle of attack range of −2<AoA<5°. In the study, three-dimensional, unsteady, cavitating flow is modelled by two different solution approaches, RANS and DES, with the SST Menter k-omega turbulence model. The Schnerr-Sauer cavitation model is employed to obtain cavitation formation. The same physical conditions with RANS simulations are performed using a refined mesh with the DES method, focusing particularly on accurately and precisely obtaining cavitation development, especially cavitation cycles. Additionally, DES analyses were performed for various time step values, demonstrating the specific influence of the time step on cavitation cycles. The results show that while the RANS method effectively predicts the lift and drag forces of the hydrofoil, the DES method is crucial for capturing cavitation dynamics with greater precision, particularly for obtaining cavitation cycles. The results also indicate that twisted hydrofoil geometries produce more lift and drag force than half-twisted and no-twist geometries for both NACA0009 and NACA0015 hydrofoils. In addition, the cavitation formation around the hydrofoil generally increases with the twistiness.

Study on the formation and characteristics of unstable sheet cavitation on hydrofoils

Hydrofoils, as fundamental components of hydraulic machinery, directly influence the performance of such machinery. This study conducted an analysis of the cavitation characteristics of hydrofoils at a + 4° angle of attack under various cavitation numbers using numerical simulation and experimental research methods. The focus of the research was to explore the phenomenon of unstable sheet cavitation and its causes, as well as to reveal the characteristics of the re-entrant jet. The large eddy simulation method was employed to calculate the cavitation morphology under three different cavitation numbers. The method is highly consistent with the experimental results in simulating the small-scale detachment at the tail of unstable sheet cavitation and the large-scale shedding of cloud cavitation. The study found that the detachment of unstable sheet cavitation is closely related to the re-entrant jet, which exhibits transient and abrupt characteristics during the unstable sheet cavitation phase. Furthermore, by applying FFT processing to the distribution of maximum reverse velocity and the spatiotemporal changes of Ux on characteristic lines, eigenfrequency of the detachment of unstable sheet cavitation were identified. The research results indicate that cavitation mainly show as sheet cavitation when the cavitation closure point does not exceed the zero-slope point. Beyond this point, it transitions to cloud cavitation. This study provides new insights into the cavitation phenomenon of hydrofoils and offers quantitative research on the phenomenon of unstable sheet cavitation.

The effect of a textured surface in the form of triangular prisms on the occurrence and development of cavitation behind the cylinder in microchannels

Cavitation flow in a microchannel behind a cylinder with a smooth and textured surface is investigated using mathematical modeling methods. The textured cylinder has 72 triangular prisms on its surface. The height of the prism, normal to the surface of the bluff body, was 100 nm. Profiles of the flow velocity and volume fraction of vapor are constructed. The monitoring of the velocity and pressure at five points behind both the smooth and the textured cylinder was carried out, while the inlet pressure changed up to 30 bars. It is shown that there is no restructuring of the vortex street to a symmetrical form at quite high-pressure values at the inlet to the channel for a rough cylinder. Namely, roughness prevents the flow stabilization. A pressure jump in the microchannel is observed when a cavity appears with a uniform increase in the flow rate. Two pulsation frequencies are determined for each of the flow modes. The first pulsation frequency ranges from 480 to 2200 Hz and is associated with the formation of cavitation. The second pulsation frequency is associated with the hydrodynamic flow around the cylinder and its values range from 26 to 95 kHz. An increase in surface roughness leads to a growth of the cavitation pulsation frequency and intensifies cavitation. At that, the velocity pulsations in the flow before the onset of cavitation increase, and the frequency of hydrodynamic pulsations after its onset decrease. The paper provides an analysis of the drag coefficient of a hydraulic section with rough and smooth cylindrical bluff bodies. The effect of roughness on the change in the hydrodynamic characteristics of the flow is described.

Severe necrotizing tracheobronchitis caused by influenza B and methicillin-resistant Staphylococcus aureus co-infection in an immunocompetent patient

Purpose and methodNecrotizing tracheobronchitis is a rare clinical entity presented as a necrotic inflammation involving the mainstem trachea and distal bronchi. We reported a case of severe necrotizing tracheobronchitis caused by influenza B and methicillin-resistant Staphylococcus aureus (MRSA) co-infection in an immunocompetent patient.Case presentationWe described a 36-year-old man with initial symptoms of cough, rigors, muscle soreness and fever. His status rapidly deteriorated two days later and he was intubated. Bronchoscopy demonstrated severe necrotizing tracheobronchitis, and CT imaging demonstrated multiple patchy and cavitation formation in both lungs. Next-generation sequencing (NGS) and bronchoalveolar lavage fluid (BALF) culture supported the co-infection of influenza B and MRSA. We also found T lymphocyte and NK lymphocyte functions were extremely suppressed during illness exacerbation. The patient was treated with antivirals and antibiotics including vancomycin. Subsequent bronchoscopy and CT scans revealed significant improvement of the airway and pulmonary lesions, and the lymphocyte functions were restored. Finally, this patient was discharged successfully.ConclusionNecrotizing tracheobronchitis should be suspected in patients with rapid deterioration after influenza B infection. The timely diagnosis of co-infection and accurate antibiotics are important to effective treatment.

Experimental and numerical studies on the partial cavitation in a Venturi

Abstract To effectively control the adverse effects of cavitation, it is crucial to understand the mechanism behind the formation of cloud cavitation. The transition from sheet to cloud cavitation, or cavitation shedding, can be caused by two mechanisms: re-entrant jet and condensation shock. This study investigated the shedding mechanism of partial cavitation in a Venturi using high-speed photography and Large-Eddy Simulation. The Rankine-Hugoniot equation was used to verify that the cavitation shedding mechanism: the condensation shock at σ = 0.37 and the re-entrant jet mechanism at σ = 0.98. Both operating conditions exhibit backflow, which can cause variations in image grayscale values. The relation between backflowing velocity and grayscale variation was identified in different shedding mechanisms. When the adverse pressure gradient is constant, the shock velocity is inversely proportional to the image grayscale variation, while the re-entrant jet velocity is proportional to it. These findings may contribute to a better understanding of cavitation shedding mechanism.

Study of Hydrofoil Unstable Partial Cavitation Emphasizing Unstable Sheet Cavitation Phenomenon

Abstract Unstable partial cavitation phenomenon often occurs during the operation of axial flow pumps. In this paper, the hydrofoil of an axial flow pump is taken as the research object, and the cavitation morphology at the design angle of attack is obtained by high-speed photography. And the flow characteristics under the transformation cavitation number of sheet cloud cavitation are studied by SBES turbulence model. The hydrofoil has hydrodynamic phenomena such as unstable sheet cavitation and multistage cloud cavitation. The high pressure propagating upstream from the trailing edge may be the cause of secondary cloud shedding, and the closer to the hydrofoil wall surface, the greater the intensity of this pressure. The frequency of unstable sheet cavitation shedding is 166.6 Hz. The instable closure of cavitation and the hydrofoil wall may be the main cause of unstable sheet cavitation formation. The generated quasi-periodic re-entrant jet will have a greater impact on the flow in the rear of the hydrofoil. This study provides reference for the design and operation of axial flow pumps and prevention of cavitation damage.

Characterisation of the creep cavitation process on grain boundaries in a polycrystalline nickel-base alloy 247

ABSTRACT Hot gas components such as gas turbine blades are loaded with constant centrifugal stress at high temperatures and thus the formation of creep cavitation on grain boundaries is expedited. Conventionally cast polycrystalline Nickel-base superalloys used as blade materials are prone to creep cavitation as unfavourably orientated grain boundaries exist. This research presents a diffusion-based probabilistic creep model which describes the creep cavitation process on grain boundaries. It includes the three mechanisms: pore nucleation, growth, and coalescence. The calibration of the model has been carried out by analysing Alloy 247 as-received specimens and specimens with pre-strain. For the evaluation of the pore numbers and sizes, a deep learning model for pore detection was trained on light microscopic and scanning electron microscopy images. Electron backscatter diffraction images are analysed for further investigations regarding grain orientations and grain boundary angles to the loading direction. The calibrated model allows predictions of pore size distributions over time.

Study on dynamic characteristics of cavitation in underwater explosion with large charge

Underwater explosions (UNDEX) generate shock waves that interact with the air–water interface and structures, leading to the occurrence of rarefaction waves and inducing cavitation phenomena. In deep-water explosions, complex coupling relationships exist between shock wave propagation, bubble motion, and cavitation evolution. The shock wave initiates the formation of cavitation, and their growth and collapse are influenced by the pressure field. The collapsing bubbles generate additional shock waves and fluid motion, affecting subsequent shock wave propagation and bubble behavior. This intricate interaction significantly impacts the hydrodynamic characteristics of deep-water explosions, including pressure distribution, density, and phase changes in the surrounding fluid. In this paper, we utilize a two-fluid phase transition model to capture the evolution of cavitation in deep-water explosions. Our numerical results demonstrate that the introduction of a two-phase vapor–liquid phase change model is necessary to accurately capture scenarios involving prominent evaporation or condensation phenomena. Furthermore, we find that the cavitation produced by the same charge under different explosion depths exhibits significant differences, as does the peak value of cavitation collapse pressure. Similarly, the cavitation produced by different charge quantities under the same explosion depth varies, and the relationship between cavitation volume and charge quantity is not a simple linear increase. The research methods and results presented in this paper provide an important reference for studying the dynamic characteristics of deep-water explosions.

Experimental study of cavitation development in liquid in pulsed non-uniform electric field under the action of ponderomotive forces

In this paper, the Rayleigh scattering method is used to study the formation of cavitation in water in a pulsed inhomogeneous electric field when a nanosecond high voltage pulse is applied to a needlelike electrode. The observational results confirm the theoretical picture of cavitation development under the action of electrostrictive ponderomotive forces. The values of the negative pressure, the average size of the cavitation nanovoids, and their concentration were obtained from these measurements, which are in agreement with theoretical estimates.

Abstract WP130: Prevalence and Predictors of Hemorrhagic Foci on Long-Term Follow-Up MRI of Recent Single Subcortical Infarcts

Background: Hemorrhagic foci surrounding the lacune in the long-term evolution of recent single subcortical infarcts (RSSIs) remains largely unexplored. We aimed to determine the prevalence, characteristics, and predictors of hemorrhagic foci in patients with RSSI. Methods: From a prospective, longitudinal study of RSSIs, we recruited patients who underwent multimodal MRI assessments at baseline and approximately one year after stroke onset. Hemorrhagic foci were identified using susceptibility-weighted imaging (SWI). Results: Among 72 patients with RSSI, nearly half (n = 35, 48.6%) had hemorrhagic foci within the index RSSI lesions on follow-up SWI. RSSIs with hemorrhagic foci formation were associated with a longer time to follow-up imaging (median 484 versus 425 days, P = 0.008) and higher likelihood of being located in the anterior circulation compared to those without hemorrhagic foci (100.0% versus 75.7%, P = 0.001). Hemorrhagic foci were also associated with larger lesion size (P &lt; 0.001), higher proportion of cavitation formation (P = 0.042), and poorer functional outcome (P = 0.036). In the subset of RSSIs in the LSA territory, after adjustment for covariates, larger initial lesion volume (OR 1.63, 95% CI 1.06-2.53; P = 0.027) and greater reduction in LSA total length (OR 0.60, 95% CI 0.37-0.97; P = 0.035) were independently associated with hemorrhagic foci formation. Conclusion: Half of RSSI patients developed hemorrhagic foci within the lacunes during follow-up SWI. This hemorrhagic feature might represent hemosiderin deposits from a previously thrombosed perforating artery. The pathophysiologic mechanism and clinical implications remain to be determined.

Investigation of influence of geometry of jet orifice of throttling device on formation of cavitation

Throttling devices are used in hydraulic systems both as regulating valves and to provide protective functions, which determines the relevance of developing such a design that will ensure their cavitation-free operation. The aim of the study is to investigate cavitation phenomena in single-stage throttling devices with different geometry of the jet orifices in order to identify the geometric shape capable of minimizing cavitation. The paper presents a study of the effect of different geometric shapes of the orifices of single-stage throttling devices on cavitation formation in the low-pressure areas. In addition, the objective of the study is to investigate the influence of physical quantities (velocity and pressure) on cavitation formation and to carry out a comparative analysis by means of which the influence of the correlation between the geometrical shape of the orifice of the jets, the velocity of the working medium and the pressure in the area of the orifice of the jets on the formation of cavitation zones in the areas of reduced pressure is clearly demonstrated. The computational experiment was conducted using Ansys CFX software and was based on the Rayleigh-Plesset mathematical model of cavitation. The study investigated the possibility of cavitation phenomena in single-stage throttling devices, and identified the geometric shape of the jet orifice that promotes cavitation-free operation of the single-stage throttling device. Thus, the results of the study show that the jet with a conical orifice minimizes the volume fraction of vapor, arising during cavitation processes, in single-stage throttling devices. The conducted research has practical significance and can increase the service life of single-stage throttling devices by minimizing the formation of cavitation zones in areas of low pressure.

Stabilize cloud cavitation with an obstacle near hydrofoil's trailing edge and conduct local entropy production analysis

Cloud cavitation always causes severe damage to the efficiency and stability of the hydraulic machinery, resulting in extra energy losses in the system. We have observed an effective and simple way to prevent cloud cavitation formation by placing an obstacle near the hydrofoil's trailing edge. Cavitating flows around four different types of hydrofoils were simulated using the stress-blended eddy simulation turbulence model: the National Advisory Committee for Aeronautics (NACA) 66 hydrofoil and the NACA 66 hydrofoil with a 1 ×1 mm2 obstacle at 0.3c, 0.5c, or 0.7c. Sheet cavitation is the predominant mode of cavity flow when the obstruction is positioned at 0.7c. To find out why the cloud cavitation growth can be stopped when the obstruction is positioned at 0.7c, the velocity field, vorticity in the Z direction, and vortex structure of the Q-criterion were computed. To study the energy loss of the cavity flow and comprehend how obstacles affect it, the local entropy production rate was computed. It was discovered that the vorticity downstream of the obstacle, positioned at 0.7c, is restructured, which helps manage the flow separation upstream of the obstacle. Consequently, the hydrofoil's suction surface vorticity nearly rotates in the same direction as the obstacle at 0.7c, and the direction of Vx upstream of the obstacle is in the positive direction of the X axis, indicating that the reentrant flow has been controlled upstream of the 0.7c obstacle. Furthermore, cavitation shedding and the entropy production rate are strongly correlated, and regulating cloud cavitation growth is advantageous for energy conservation.

The evolution of carbides during long-term creep/aging of nickel based superalloy K444

In K444 alloy, the evolution of carbides during stress aging (creep) and stress-free aging at 900 °C for 5000 h, and interrupted at 3000 h were investigated, combining microstructure characterization and quantitative statistics method. After stress-free aging for 5000 h, the volume fraction of intragranular MC and M6C carbides decrease from 0.48 % to 0.66 %–0.26 % and 0.48 %, respectively, while that of M23C6 carbides increase to 0.28 %. The two degradation behaviors can be concluded as MC + γ → M6C + M23C6 + γ′ and M6C + γ → M23C6 + γ′ respectively. The former controlled by the diffusion of Ti occurred earlier, while the latter determined by the diffusion of W and Mo mainly happened later. The applied stress did not change degradation reactions while accelerate the degradation rate slightly. During stress-free aging, the morphology of grain boundaries (GBs) changed from discrete distribution to semi-continuous and then to continuous chain, and the content of MC and M6C carbides decreases while that of M23C6 carbides increases. The applied stress markedly promotes above behaviors. Especially, the completed continuous chain formed before 3000 h. Moreover, the applied stress induced the formation of cavitation on the GBs, which is attributed to the following reasons. First, it can accelerate the degradation of GBs and decline the GBs strength. What's more, dislocations pile up on the GBs and cause a high level of stress concentration. Finally, the new generated phase interfaces have a greater deviation with its adjacent carbides, weakening the binding force of GBs.

Cavitation cloud formation and surface damage of a model stone in a high-intensity focused ultrasound field

This work investigates the fundamental role of cavitation bubble clouds in stone comminution by focused ultrasound. The fragmentation of stones by ultrasound has applications in medical lithotripsy for the comminution of kidney stones or gall stones, where their fragmentation is believed to result from the high acoustic wave energy as well as the formation of cavitation. Cavitation is known to contribute to erosion and to cause damage away from the target, yet the exact contribution and mechanisms of cavitation remain currently unclear. Based on in situ experimental observations, post-exposure microtomography and acoustic simulations, the present work sheds light on the fundamental role of cavitation bubbles in the stone surface fragmentation by correlating the detected damage to the observed bubble activity. Our results show that not all clouds erode the stone, but only those located in preferential nucleation sites whose locations are herein examined. Furthermore, quantitative characterizations of the bubble clouds and their trajectories within the ultrasonic field are discussed. These include experiments with and without the presence of a model stone in the acoustic path length. Finally, the optimal stone-to-source distance maximizing the cavitation-induced surface damage area has been determined. Assuming the pressure magnitude within the focal region to exceed the cavitation pressure threshold, this location does not correspond to the acoustic focus, where the pressure is maximal, but rather to the region where the acoustic beam and thereby the acoustic cavitation activity near the stone surface is the widest.

The effect of three-type Vortex Generators (VGs) on NACA-0015 hydrofoil cavitation formation at different angles of attack

Cavitation, the formation of vapor bubbles on hydrofoil surfaces, poses a significant challenge to the performance and durability of marine vessels utilizing hydrofoils. Vortex generators, small structures embedded on the hydrofoil surface, have emerged as a potential solution for mitigating cavitation, but the optimal shape of vortex generators for achieving maximum cavitation resistance remains an open question. This study aims to address this challenge by systematically investigating the impact of rectangular, triangular, and circular vortex generators on the cavitation characteristics of a NACA-0015 hydrofoil. Utilizing computational fluid dynamics (CFD) simulations, the influence of these vortex generator shapes on cavitation inception and critical cavitation numbers will be evaluated under varying angles of attack and flow velocities. The findings of this study will provide valuable insights into the design and optimization of vortex generators for hydrofoil applications. Despite the effectiveness of vortex generators in mitigating cavitation, the optimal vortex generator shape for specific hydrofoil designs and operating conditions remains unclear. The precise mechanisms by which vortex generators suppress cavitation are not fully understood, requiring further investigation to optimize their design and placement. The durability and long-term performance of vortex generators under various environmental conditions, including turbulence and corrosion, warrant further evaluation. By addressing these unsolved challenges, this study will contribute to the advancement of vortex generator technology and its practical application in hydrofoil systems, leading to more efficient and reliable marine vessels.

Prevalence and Predictors of Hemorrhagic Foci on Long-term Follow-up MRI of Recent Single Subcortical Infarcts

AbstractHemorrhagic foci surrounding the lacune in the long-term evolution of recent single subcortical infarcts (RSSIs) remains largely unexplored. We aimed to determine the prevalence, characteristics, and predictors of hemorrhagic foci in patients with RSSI. From a prospective, longitudinal study of RSSIs, we recruited patients who underwent multimodal MRI assessments both at baseline and approximately one year after the stroke onset. Hemorrhagic foci were identified using susceptibility-weighted imaging (SWI). Among 101 patients with RSSI, nearly half (n = 45, 44.6%) had hemorrhagic foci within the index RSSI lesions on follow-up SWI. RSSIs with hemorrhagic foci formation were associated with a longer time to follow-up imaging (median 449 versus 401 days, P = 0.005) and higher likelihood of being located in the anterior circulation compared to those without hemorrhagic foci (88.9% versus 64.3%, P = 0.003). Hemorrhagic foci were also associated with larger lesion size (P &lt; 0.001), a higher proportion of cavitation formation (P = 0.003), higher baseline NIHSS scores (P = 0.004), and poorer functional outcomes (P = 0.001). In the subset of RSSIs in the lenticulostriate artery (LSA) territory, after adjustment for covariates, larger initial lesion volume (OR 1.80, 95% CI 1.13–2.87; P = 0.014) and greater decreases in LSA total length (OR 0.59, 95% CI 0.36–0.96; P = 0.035) were independently associated with hemorrhagic foci formation. The extent of ischemia in the initial infarct is predictive of the presence of hemorrhagic residues. Our findings contribute to the current understanding of the mechanisms underlying the evolution of RSSIs.

Effects of flow conditions on the cavitation characteristics of viscous oil around a hydrofoil

Viscous oils, which are media commonly used for fluid power transmission, are characterized by high velocities, temperatures, and pressures when working in fluid components and mechanics. The transient nature of viscous oil makes it susceptible to complex operating conditions, which result in cavitation phenomena and can threaten the normal operation and safety of machinery and components. In this study, a three-dimensional computational fluid dynamics model that accounts for cavitation was developed to study the cavitation characteristics, formation conditions, and development of cavitating flow in viscous oil around a hydrofoil under various flow conditions. Moreover, a visual experimental system in which viscous oil flowed around the hydrofoil was proposed and developed to investigate the cavitation properties with regard to various flow conditions. Both numerical results and experimental data indicated that cavitation occurred on the suction surface of the hydrofoil head, and the cavitation characteristics in viscous oil are significantly influenced by the flow conditions. The maximum vapor volume change rate for the degree of effects on cavitation in viscous oil by flow conditions was calculated to be 1.78 cm3/(m/s), −130.66 cm3/MPa, 0.16 cm3/°C, and 4.52 cm3/°, respectively. Low velocities, high pressures, low temperatures, and small impact angles were proved to be able to suppress cavitation. This study provides a research method, an experimental mean, and data support for cavitation flow of viscous fluids, especially oil. It has significant engineering application significance for the development of fluid machinery.

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.