Abstract
The polar ships are often in bollard pull condition, which is prone to induce propeller cavitation and cause thrust reduction, weakening the ship’s ice-breaking ability. Based on the model ...tests and numerical simulations, this paper aims to investigate the propeller thrust reduction in the bollard pull condition. Firstly, the test of a self-designed ice class propeller under different cavitation numbers is carried out. The thrust reduction phenomenon is successfully captured and the hydrodynamic characteristics are obtained. Subsequently, the simulation based on Star-CCM+ is performed. It is found that the propeller thrust decreases almost linearly after the cavitation number reaches a certain threshold. When the cavitation number is equal to 0.25, the thrust decreases to 38.1% of that in the open water condition. By analyzing the mechanism of thrust reduction, the main reason is recognized that the average pressure of the blade face decreases greatly due to the influence of the cavitation on the blade back.
The cavitation development process in regulating valve under different inlet pressures is investigated experimentally and numerically in our paper. The influence of inlet pressure P
in
on cavitation ...location, shape, area and intensity is studied in axial and radial directions, and the axial and radial pressure distributions are also analyzed. The cavitation is generally annular in shape radially and irregular polygon in shape axially. Cavitation bubbles occur at the throat entrance when the inlet pressure increases. The bubbles then accumulate, and a bubble ring is formed. The cavitation development process under different inlet pressures is separated into three stages, no-cavitation, initial cavitation and steady-cavitation stages. During the no-cavitation stage, no bubbles exist. During the initial cavitation stage, bubbles occur and the area and intensity of cavitation increase in the radial and axial directions with increasing inlet pressure. During the steady-cavitation stage, the calculation area and intensity of bubble rings reach their maximum values and then remain stable. The cavitation bubbles extend downstream, and the area of cavitation ring and cavitation intensity increase with increasing inlet pressure. A slit exists between the upper and lower parts of bubbles in the cavitation process, both parts touch each other forming a whole.
A completely nickel-aluminum-copper (Ni-Al-Cu) layer was obtained through thermal diffusion process on a nickel-aluminum-bronze (NAB) substrate. The cumulative mass loss of the NAB alloy during the ...cavitation erosion tests was about 6.4 times and 5.5 times as large as that of the Ni-Al-Cu layer in distilled water and 3.5 wt% sodium chloride (NaCl), respectively. Electrochemical measurements under quiescence and cavitation erosion conditions were conducted to investigate the synergistic effects of cavitation erosion and corrosion. The results showed that the synergism had measurable effect on the cavitation erosion-corrosion process for both the NAB alloy and the Ni-Al-Cu layer. The total contribution of the cavitation erosion component including WE and WCIE was more than 80% and WE occupied the largest percentage. Thus, the improved cavitation erosion resistance of the Ni-Al-Cu layer was mainly due to mechanical factors, which implied a homogeneous and refined microstructure and the formation of hardened Ni3Al phase.
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•Surface modification with Ni-Al-Cu layer was obtained through thermal diffusion.•Mechanical properties of Ni-Al-Cu layer was improved compared to NAB substrate.•The better properties was due to the refined and harden intermetallic particles.•Cavitation erosion-corrosion resistance was about 5.5 times compared to NAB alloy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Resistance to cavitation is a major determinant of plant survival under severe drought and can be used to quantify species adaptive potential. Interspecific variation in this key trait is well ...defined in woody species, but intraspecific variation (level and structure) resulting from standing genetic variation and phenotypic plasticity has never been determined.
Combining for the first time in situ characterization of natural populations and two reciprocal common gardens in dry and wet sites, we estimated variance components (phenotypic, genetic, environmental, and genetic 9 environmental) of cavitation resistance based on 513 genotypes of a Mediterranean pine, Pinus pinaster.
Despite the selected populations being climatically contrasted, phenotypic plasticity in resistance to cavitation remained low and was essentially attributed to family level. Between-population variation in cavitation resistance for both phenotypic and genetic variation was limited.
These results strongly suggest that cavitation resistance is buffered against genetic and to a lesser extent environmental variation (canalization) in maritime pine. Consequently, in a drier world, the increasing drought tolerance of Pinus species might be severely constrained by the low level of cavitation resistance variation, resulting in a large-scale loss of productivity.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Zusammenfassung In hydrodynamischen Gleitlagern kann im Schmierfilm unter gewissen Betriebsbedingungen Flüssigkeitskavitation auftreten. Die Flüssigkeitskavitation lässt sich in drei ...Kavitationsformen unterscheiden: Pseudo-, Gas- und Dampfkavitation. Lediglich Dampfkavitation kann in Verbindung mit Werkstoffkavitation zum Schaden und später zum Ausfall eines Gleitlagers führen. Eine mögliche Ursache zur Entstehung von Dampfkavitation liegt in der Dynamik der Spaltweitenänderung einer Wellenverlagerungsbahn begründet. Die Autoren haben den erstmaligen Nachweis von implodierenden Dampfblasen im Schmierfilm eines Gleitlagers in Folge einer transienten Spaltweitenänderung vollumfänglich erbracht. Zum Erzeugen der schadensrelevanten Dampfkavitation muss eine kritische Spaltweitenänderungsgeschwindigkeit in Verbindung mit einer kritischen Exzentrizität erreicht werden. Für diese Untersuchungen steht ein Gleitlager-Modellexperiment zur Verfügung, welches kontinuierlich erweitert wurde und so dem Stand der Forschung entspricht. Es ist somit möglich, kavitierende Schmierspaltströmungen sowohl qualitativ als auch quantitativ zu untersuchen. Das Modellexperiment verfügt über eine Aktorik, die eine gezielte Steuerung der Spaltweitenänderungsgeschwindigkeit zulässt und so die Kavitationsbereiche einer realen Wellenverlagerungsbahn abbildet. Das Experiment beinhaltet ein speziell entwickeltes Fluid, dass die Reynolds- und Kavitationsähnlichkeit erfüllt. Bei der Untersuchung von Flüssigkeitskavitation muss sowohl das Verdampfen der Flüssigkeit (Dampfkavitation), das Ausgasen von Luft (Gaskavitation) sowie das Vorhandensein kleinster Luftblasen (Pseudokavitation) experimentell abgebildet werden. Dies wird u. a. durch die Verwendung von konditionierten Flüssigkeiten realisiert. Abhängig vom Betriebspunkt des Gleitlagers, treten die drei Kavitationsformen separat als auch in Verbindung miteinander auf. Das gleichzeitige Auftreten reduziert, je nach Anteil der Kavitationsformen, die Kavitationserosion, indem sie die schädigungsrelevante Dampfkavitation dämpft. Das übergeordnete Forschungsziel ist es einen Parameterbereich zu definieren, in dem eine kritische Spaltweitenänderung mit einer kritischen Exzentrizität zur „reinen“ Dampfkavitation führt. Damit soll der schadenskritische Parameterbereich eingegrenzt werden. Dies soll zukünftig bei der Auslegung und Parametrisierung von hydrodynamischen Gleitlagern helfen. Die gezeigten experimentellen Ergebnisse umfassen Hochgeschwindigkeitsaufnahmen, die eine detaillierte Analyse der Blasenbildung mit einer Geschwindigkeit von 10.000 Bildern pro Sekunde (fps) ermöglichen. Es lässt sich zusammenfassen, dass die Arbeit ein tieferes Verständnis für den Kavitationsprozess in dynamisch belasteten Gleitlagern erbringt. Das Forschungsvorhaben wurde gefördert durch die Deutsche Forschungsgemeinschaft (DFG) unter der Projektnummer 462581008.
A simplified test case of a centrifugal pump blade, a hydrofoil with circular leading edge, is investigated. Cloud cavitation as a particularly aggressive type of cavitation is studied using a ...compressible 3D flow solver with barotropic cavitation model. The results are compared to measurement data for different Reynolds and cavitation numbers. The shedding frequency is well predicted. A statistical evaluation of a multitude of single collapsing voids is performed. Collapse frequency and magnitude of the pressure peaks are evaluated to obtain wall load collectives. Material damage on the hydrofoil suction surface obtained in erosion measurements is compared to the local flow aggressiveness distribution in the simulation. Erosion sensitive wall zones are identified in good agreement with measurement data. A relationship between cloud cavitation structures and erosion sensitive wall zones is demonstrated that enables a simple and approximate erosion assessment by 3D flow simulation.
•Compressible CFD solution is successfully validated for hydrofoil flow.•Flow aggressiveness is predicted by statistical evaluation of void collapses.•Erosion sensitive wall zones are well predicted.•A relationship between cavitation structures and erosion is demonstrated.•CFD-based engineering tool for simple and approximate erosion assessment is proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Surface ultrasonic rolling process (SURP) is a prior self-nano-technology of surface strengthening to improve the cavitation resistance of metal materials. In the paper, the 304 stainless steel ...(304SS) specimens were processed into 5 times, 10 times, 15 times and 20 times by SURP, then were cut into pieces along the SURP surface. In order to investigate impact of SURP on cavitation erosion behavior of 304SS, microstructure, mechanical properties and phase distribution of 304SS with difference SURP times were characterized firstly. Subsequently, ultrasonic cavitation erosion process and electrochemical measurements was experimented respectively: the specimens with different SURP times were subjected to 3 h in ore pulp solution (The mass fraction of 3.5% NaCl and 5% plumbum-zinc) by ultrasonic cavitation erosion process (UCEP), meanwhile, the electrochemical behaviors of the 304SS specimens with difference SURP times, such as open circuit potential (OCP), polarization curves and electrochemical impedance spectroscopy (EIS) were measured successively. Finally, the influences of the mechanical properties and corrosion characteristics of the 304SS with different microstructures after SURP on cavitation corrosion resistance were discussed in details, in the meantime, the microscopic mechanisms of the cavitation resistance for 304SS with different SURP times were investigated. The result shows that SURP is significantly beneficial to protect 304SS from the cavitation erosion behavior via introduction of deformation layers, transformation between martensite and austenitic, formation of passivation film, grain refinement and the surface hardness as well as residual stress of the 304SS were enhanced accordingly. However, the energy transfer of SURP is not only used to surface hardening, grain refinement, slip bands establishment but also defects formation, overmuch energy transfer plays the opposite role. Therefore SURP 10 times is a suitable SURP times that makes 304SS achieved optimal cavitation resistance.
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•304SS specimens were processed by surface ultrasonic rolling process (SURP).•Microstructure, mechanical properties and phase of SURP specimens were characterized.•Ultrasonic cavitation process and electrochemical measurement were test respectively.•SURP is significantly beneficial to protect 304SS from cavitation erosion behavior.•SURP 10 times is the proper time makes 304SS achieved optimal cavitation resistance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Application of hydrodynamic and acoustic cavitation to oxidation of organic pollutants.•Design of cavitation devices for effluent treatment.•Comparison of efficiency of oxidation of ...organic pollutants in the cavitation processes.
Hydrodynamic and acoustic cavitation combined with advanced oxidation processes (AOPs), including, among others, the Fenton process, is a promising alternative to the technologies of wastewater treatment technologies in use today. The present review discusses processes based on cavitation combined with AOPs and evaluates their effectiveness in oxidation of organic contaminants. Complete degradation of, among others, p-nitrotoluene, p-aminophenol, 1,4-dioxane, alachlor, chloroform, trichloroethylene, sodium pentachlorophenate and carbon tetrachloride was achieved by using hydrodynamic cavitation or acoustic cavitation alone. Cavitation is also an effective method of disinfection of water. Complete oxidation of hardly degradable organic contaminants, including pharmaceuticals, organic dyes, insecticides, phenol and its derivatives was observed when using hybrid processes: hydrodynamic or acoustic cavitation combined with the Fenton process, ozonation, hydrogen peroxide, UV irradiation, catalysts and persulfates. The review also discusses the cavitational reactors used in the wastewater treatment and the effect of process parameters (including pH, temperature, concentration and kind of contaminants) on the effectiveness of oxidation. The oxidation effectiveness for individual treatment methods is compared and their advantages and limitations discussed. The analysis of economics of the treatment processes performed to evaluate the possibility of scaling up reveals that the only economical processes should be based on hydrodynamic cavitation (mainly due to low cost of reactors and low consumption of electrical energy compared with ultrasonic reactors).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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•PHZ coatings were synthesized by addition of ZIF-8 NPs with various sizes.•The PHZ coatings exhibit excellent hydrophobic, mechanical and thermal properties.•Coatings’ thermal and ...mechanical properties are inversely proportional to ZIF-8 size.•The PHZ1 coating shows the optimal antifouling and anti-cavitation performance.
Biofouling and cavitation erosion are the key important factors causing the degradation and fatigue failure of metal materials in seawater. Herein, a series of polyurethane (PU) /ZIF-8 (PHZ) composite coatings were successfully synthesized with different sizes of ZIF-8 nanoparticles (NPs) for antifouling property combined with cavitation erosion resistance. The morphology and structure of the PHZ composite coatings were characterized by XRD, ATR-FTIR, SEM and AFM. The static water contact angle, dynamic mechanical analysis and thermo gravimetric tests further confirmed that the ZIF-8 NPs could improve the hydrophobic, mechanical and thermal properties of the PU coatings. Importantly, the effect of the ZIF-8 NPs with different sizes on the performance of the PHZ coatings was also investigated. The PHZ1 coating with the ZIF-8 NPs (~50 nm) displayed the highest static water contact angle (105°), the largest tensile strength (6.78 MPa) and the best thermal stability among these PHZ coatings. The antifouling properties of the PHZ coatings were also tested against marine diatom (Nitzschia closterium). Especially, the biofouling attachment rate of the PHZ1 coating was 0.51%, which was far less than that of pure PU coating (92%). Moreover, the mass loss of the PHZ1 coating was only 8.9 mg after cavitation test for 24 h. Notably, both antifouling and anti-cavitation properties of the PHZ coatings were inversely proportional to the particle size of the ZIF-8 NPs. The present study offers a simple and green coating technology that combines the antifouling and anti-cavitation to promote the development of ZIF/PU nanocomposite systems for practical applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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