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1

Computational evaluation of the limiting thrust of the peripheral thruster taking into account the propeller blade yield stress and the thrust breakdown due to cavitation

Kraskowski Marek, Dymarski Paweł, Dymarski Czesław, Hebel Włodzimierz, Łuniewski Paweł

Polish Maritime Research

|

2025

|

nr 2

106--114

EN

The work presented in this article is related to the performance of an alternative design for the side thruster for ships, referred to as a peripheral thruster. Unlike the standard side thruster design, which uses the tunnel across the hull structure, the peripheral thruster consists of two separate devices mounted on two sides of the hull, with retracTable ducted propellers. The computational analyses presented here focus on evaluation of the maximum thrust achievable by this alternative design for the side thruster for a specified propeller diameter of 250 mm. Two limiting factors were considered: the strength of the propeller material, and the drop in thrust due to excessive cavitation. The analyses were carried out using STAR-CCM+ solver, and involved both a flow model (RANS FVM) and a solid stress model (FEM). The article focuses on the sensitivity of the results to the settings of the computational models, which is a key issue for this type of analysis due to its complexity.

2

Effect of mesh density and grid type on cavitation cloud volume

Jasionowski Robert, Kostrzewa Waldemar

Zeszyty Naukowe Politechniki Morskiej w Szczecinie

|

2024

|

nr 80 (152)

23--31

EN

This work is devoted to determining the effect of mesh density and mesh type on cavitation cloud volume generated during the flow of water through the cavitation tunnel. The numerical analysis was carried out on a water model based on a cavitation tunnel located at the Institute of Water Problems of the Bulgarian Academy of Sciences in Sofia, used to test the resistance of construction materials to cavitation erosion. A numerical analysis is performed for four different types of grids: polyhedra, poly-hexcore, hexcore, and tetrahedral. These grids have five different maximum cell sizes: 0.0025, 0.0020, 0.0015, 0.0010, and 0.0005 m. A numerical analysis is performed using commercial CFD software ‒ i.e., Ansys Fluent 2023 R1. The Schnerr and Sauer cavitation model and the k-omega viscous model for shear stress transport (SST) are used. This paper analyzes the qualitative parameters of the quality of the grid, distribution of velocity, pressure, average cell volume, and volume of cavitation cloud consisting of 90% volume vapor fraction. Based on the numerical analyses, it is shown that the basis for obtaining accurate results of the CFD simulations is not only the qualitative parameters of the grid but also its density.

3

Erosion of Tubular Heat Exchangers

Krupicz Bazyli, Zastocki Piotr, Krupicz Paweł

Tribologia

|

2024

|

nr 1

79--88

EN

This paper presents the results of an erosion study of a tubular heat exchanger operating on a railroad sleeper saturation processing line. The object of the study is a DN 800 oil condenser cooling the creosote oil vapors flowing through the condenser tubes, fixed in the sieve plates located in top head and bottom head of the condenser. Subject to the erosion are the upper part of the tubes and the weld connecting the tubes to the upper sieve plate. This resulted in unsealing of the connection, which led to the contamination of the cooling medium. The key problem, therefore, is to protect the entire top head of the condenser from erosion. Since only the central part of the surface of the top sieve plate was eroded, the conclusion is that the velocity of the vapor stream over the inlet to the condenser tubes in the central part and beyond is varied. This thesis was confirmed by the correspondence of the actual eroded area with the cavitation area resulting from a simulated flow in Autodesk CFD 2019 Ultimate software after increasing the height of top head of the condenser, placing a stream dispersing element between the liquid vapor inlet to the condenser and the upper sieve plate, and after applying a protective sieve plate. Flow simulation studies for each of these variants, or a combination of them, made it possible to evaluate the tested solutions in terms of protection against erosion, including cavitation erosion, of the upper sieve plate of the condenser.

PL

W pracy przeprowadzono analizę erozji kawitacyjnej rurowego wymiennika ciepła pracującego na linii technologicznej nasycania drewna. Obiektem badań jest kondensator oleju DN 800 schładzający pary oleju kreozotowego przepływające przez rurki kondensatora zamocowane w płycie sitowej dennicy górnej i dolnej. Intensywną erozją kawitacyjną była objęta powierzchnia górnej płyty sitowej znajdującej się bezpośrednio nad wlotem par cieczy do kondensatora. Erozji ulega górna część rurek oraz spaw łączący rurki z górną płytą sitową. W efekcie powstawało rozszczelnienie połączenia, którego następstwem było skażenia czynnika schładzającego. Kluczowym problemem jest więc ochrona przed kawitacją całej dennicy kondensatora. Ponieważ erozji podlegała tylko część centralna powierzchni górnej płyty sitowej, stąd wniosek, że prędkość strumienia pary nad wlotem do rurek kondensatora w części centralnej i poza nią jest zróżnicowana. Potwierdzeniem tej tezy była zgodność rzeczywistego obszaru objętego erozją z miejscem kawitacji wynikającym z symulacyjnego przepływu w programie Autodesk CFD 2019 Ultimate. W tym programie zbadano również, jak zmienia się ciśnienie i prędkość przepływu par cieczy w dennicy górnej po modernizacji dennicy górnej w kilku wariantach, polegających na: podwyższeniu wysokości dennicy górnej, umieszczeniu elementu rozpraszającego strugę między wlotem par cieczy do kondensatora i górną płytą sitową, zastosowanie ochronnej płyty sitowej. Badania symulacyjne przepływu dla każdego z tych wariantów lub ich połączenie pozwalają ocenić badane rozwiązania pod kątem ochrony przed erozją kawitacyjną górnej płyty sitowej kondensatora.

4

Bilge and oily water treatment during operation of vessel

Malakhov O. V., Palagin O. M., Naydyonov A. I., Lykhoglyad K. A., Bondarenko A. V.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2024

|

Vol. 18 No. 2

433--445

EN

Bilge and oily water (BOW) during vessel’s operation are the most large-tonnage type of waste and for their treatment all ships, in accordance with regulatory requirements [14], have to be equipped with special equipment – oily water separators. Under conditions of sea vessel operation BOW are process effluents that occur in the engine room, in cargo holds, as well as during the operation of the different equipment and deck machinery. At sea vessel’s operating conditions three main directions of BOW cleaning are now used: physical, chemical and biological. In most technological cases, they are used in combination with each other. The analysis of BOW separation methods based on these three directions has shown that they all could be characterized by one common drawback - unidirectional cleaning. During separation the final product – water is only one component of multiphase flow. It is very difficult to obtain secondary petrochemical products when modern methods of purification are used on the sea vessel during separation. Because of this reason in the research, a new method for BOW separation was developed. It is based on the use of a hydrodynamic process of supercavitation with artificial ventilation of the cavitational cavern. With local origin in the flow of a supercavitating cavern, there will always be saturated water vapor inside of it. The process of permanent water vapor selection from the cavern will ultimately contribute to the production of highly concentrated mixture of those petroleum products that form the initial mixture of BOW. In research, an assessment of the spatial stability of the cavitational cavern in the range of various cavitation numbers was done. During the study of BOW separation process it was found that decreasing of the working pressure inside the working chamber of the cavitation separator have to be always compensated by an increase in the temperature of the processed multiphase flow.

5

Neutralization of acidic condensate obtained after combustion of natural gas using the hydrodynamic cavitation method. Features and efficiency of the process

Nedbailo Anna, Ivanitsky Georgiy, Tselen Bogdan, Obodovych Oleksandr, Radchenko Nataliya, Gozhenko Liubov

Journal of New Technologies in Environmental Science

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2024

|

Vol. 8, nr 1

12--17

EN

This paper examines the question of the efficiency of neutralization of acidic liquid media by the method of hydrodynamic cavitation. This method was proposed for the neutralization of acidic condensate obtained as a result of the combustion of natural gas at thermal power plants and allows to significantly reduce the acidity of the solution without adding chemical reagents with moderate energy consumption due to the removal of dissolved gases. If we consider acidic condensate, then it contains up to 70 mg/l of CO2, when the solubility of this gas at normal temperature in water reaches 0.47 mg/l. The majority of this gas is present in the form of bubbles with a radius of less than 5 μm. Their removal leads to a change in the balance of carbonic acid in the system, which affects the acidity of the solution. To evaluate the effectiveness of removing soluble gases from a liquid by the method of hydrodynamic cavitation, studies of the effectiveness of degassing of a model substance (CO2 solution in distilled water) were conducted. The rotor-pulsation apparatus was chosen as the cavitation device in the installation. As a result of theoretical studies, the minimum size of the CO2 bubble was determined, that can be removed from the liquid with the applied processing parameters, and the total volume of carbon dioxide removed during processing and the dynamics of changes in the volume of gas during storage over time were determined.

6

Influence of Ultrasonic Cavitation on Botryococcus Braunii Growth

Salaeh Asleena

Archives of Acoustics

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2024

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Vol. 49, nr 3

439--445

EN

This study investigates ultrasonic energy’s impact on enhancing the growth of Botryococcus braunii (B. braunii) microalgae. Microalgae, known for their advantages in greenhouse gas mitigation and biomass conversion, were subjected to various stressors, including ultrasonic waves, to optimize productivity. Ultrasonic waves induce acoustic cavitation, increasing membrane permeability and substrate conversion. The study examined the impact of energy and maximum pressure resulting from bubble collapse on the relative specific growth rate of B. braunii microalgae. It was observed that reproduction showed a promotive trend until the energy surpassed 30 kJ. However, when ultrasonic energy reached 18.2 kJ, reproduction was inhibited due to the maximum pressure generated during bubble bursting, which reached 5.7 μN/μm^2, leading to the suppression of reproduction upon encountering bubble collapse events. Under specific ultrasonic conditions (15.1 kJ energy, maximum pressure of 45.5 × 10^5 Pa), a maximum specific growth rate of 0.329 ± 0.020 day^−1 in a two-day interval boosted B. braunii microalgae biomass productivity. These findings advance our understanding of ultrasonic wave effects on microalgae reproduction and underscore the potential for optimizing ultrasonic parameters to enhance biomass production

7

Study of the Influence of Cavitation and Magnetic Field on the Change of Water Properties and its Purification in a Vibrating Machine with Determination of Drive Modes

Hordieiev Anatoly, Kalda Galyna, Pashechko Mykhaylo, Hanzyuk Andriy, Tkachuk Vitaliy, Kostiuk Nazar

Advances in Science and Technology. Research Journal

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2024

|

Vol. 18, no. 3

234--245

EN

The paper presents the results of research into the influence of low-frequency sound and magnetic fields on the change in the properties of water and its purification in a vibrating machine with an eccentric drive, which allows obtaining a constant amplitude of oscillation when the frequency of oscillations of the drive is changed. A method and construction of a vibrating machine for changing the properties of water and cleaning is proposed. Thanks to its reciprocating movement, and in the pulsation chamber and the nozzle, appropriate reactions take place. At certain oscillation frequencies, a cavitation cavity appears in the nozzle and the pulsation chamber, in which the process of splitting water molecules into active radicals takes place. At the same time, during the reciprocating movement of water through a non-magnetic nozzle, which is covered by permanent magnets, an additional effect of a variable magnetic field direction is exerted on water, which strengthens the breaking of hydrogen bonds in water molecules. Visualization of the hydrocavitation process during operation of a vibrating machine with a transparent nozzle was studied. During the experiment, changes in water parameters were studied, i.e. changes in pH, changes in the oxidation-reduction potential of treatment ORP and the total content of mineralization according to the TDS index with treatment time. The total concentration of dissolved salts decreases from 400 to 300 units, which also indicates an improvement in water quality. The rational frequency limits of the vibration drive of the machine are in the range from 18 to 23 Hz with an amplitude of oscillations of 0.002 m, and the ratio of its design parameters is determined: with a piston diameter of 0.1 m, it is recommended to use a diameter of the hole in the piston from 0.006 to 0.008 m.

8

Numerical analysis of the volume of cavitation cloud in a cavitation tunnel using multiphase computational fluid dynamics simulations

Jasionowski Robert, Kostrzewa Waldemar

Zeszyty Naukowe Politechniki Morskiej w Szczecinie

|

2023

|

nr 76 (148)

48--56

EN

This work is devoted to a computational investigation of the position and volume of the cavitation cloud in a cavitation tunnel. The position of the cavitation cloud and its volume in the cavitation tunnel, determined by numerical analysis with respect to the inlet velocity, allows for the determination of the lower or higher intensity of cavitation erosion within the tunnel of the sample material. A numerical analysis is carried out on a model of a typical cavitation tunnel used to investigate the resistance of structural materials to cavitation erosion. The tunnel under study consists of barricade (upper) and counter-barricade (lower) systems. The numerical analysis is carried out with the following five different values of the velocity in the tunnel inlet: 6 m/s, 9 m/s, 12 m/s, 15 m/s, and 18 m/s in the commercial CFD software – Ansys Fluent 2019 R3. The Schnerr and Sauer cavitation model and shear stress transport (SST) viscous model k-omega are used. The paper analyzes the distribution of velocity, pressure, and volume of the cavitation cloud. On the basis of the performed numerical analyses, the optimal velocity at the inlet to the tunnel of 15 m/s is determined, for which the volume of the cavitation cloud is the largest and the phenomenon of cavitation is the most intense. The determination of the position and maximum volume of the cavitation cloud relative to the inlet velocity to the tunnel will, in future, allow us to shorten the resistance tests for cavitation erosion of different materials under real fluid flow conditions.

9

Effect of Cavitation Phenomenon on the Quality of High-Pressure Aluminium Alloy Castings

Brzeziński Marcin, Wiśniowski Jakub

Journal of Casting & Materials Engineering

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2023

|

Vol. 7, no. 3

27--30

EN

This article presents an analysis of the effect of cavitation on the erosion of pressure moulds intended for the HPDC casting mould manufacturing process. Changes in the surface area of the eroded areas were investigated via photographs of castings at the beginning of the mould life as well as at 30%. The individual process variables were described and their influence verified via the cavitation potential module of the Flow3D simulation programme. The results are presented graphically with a description of the relationships and observations. The summary provides an explanation of the results and the dependencies that occurred.

10

Removal of Fouling from Steel Plate Surfaces Based on Multi-Frequency Eco-Friendly Ultrasonic Guided Wave Technology

Huang Mingkun, Jin Shuo, Nie Gaoqian, Wang Xiaopeng, Zhang Quanpeng, An Yang, Qu Zhigang, Yin Wuliang

Archives of Acoustics

|

2023

|

Vol. 48, No. 4

593--601

EN

Fouling is inevitable on the surfaces of industrial equipment, especially on heat-exchanging surfaces in contact with fluids, which causes water pollution and destroys the ecological environment. In this paper, a novel fouling-removal methodology for plate structure based on cavitation by multi-frequency ultrasonic guided waves is proposed, which can remove fouling on stainless steel plates. A numerical simulation method has been developed to study the acoustic pressure distribution on a steel plate. According to the simulation results, the distribution of sound pressure on the plate under triple-frequency excitation is denser and more prone to cavitation than in single-frequency cases and dual-frequency cases, which improves fouling removal rate. The stainless steel plate is immersed in water for the descaling experiment, and the results show that the fouling removal rates of three water-loaded stainless steel plates under different single-frequency excitation seem unsatisfactory. However, the multi-frequency excitation improves the descaling performance and the removal rate of fouling reaches 80%. This new method can be applied to the surface descaling of large equipment plates, which is of great significance for purifying water quality and protecting the ecological environment.

11

Experimental Diagnostic of Cavitation Flow in the Centrifugal Pump Under Various Impeller Speeds Based on Acoustic Analysis Method

Al-Obaidi Ahmed Ramadhan

Archives of Acoustics

|

2023

|

Vol. 48, No. 2

159--170

EN

Condition monitoring in a centrifugal pump is a significant field of study in industry. The acoustic method offers a robust approach to detect cavitations in different pumps. As a result, an acoustic-based technique is used in this experiment to predict cavitation. By using an acoustic technique, detailed information on outcomes can be obtained for cavitation detection under a variety of conditions. In addition, various features are used in this work to analyze signals in the time domain using the acoustic technique. A signal in the frequency domain is also investigated using the fast Fourier method. This method has shown to be an effective tool for predicting future events. In addition, this experimental investigation attempts to establish a good correlation between noise characteristics and cavitation detection in a pump by using an acoustic approach. Likewise, it aims to find a good method for estimating cavitation levels in a pump based on comparing and evaluating different systems.

12

An Application of Orifice Hydrodynamic Cavitation Reactor for Tertiary Treatment of Wastewater Treatment Plant Effluents

Szaja Aleksandra, Montusiewicz Agnieszka, Lebiocka Magdalena, Skrzypiec Jan

Advances in Science and Technology. Research Journal

|

2023

|

Vol. 17, no. 6

98--107

EN

In this paper, a multi-orifice hydrodynamic cavitator (HC) has been applied as an effective device for water reclamation. Municipal wastewater after mechanical and biological treatment has been applied as a medium. The effectiveness of using this device has been evaluated on the basis on the microbiological indicators. Moreover, optimization of operating parameters was evaluated. Two experiments with different inlet pressure of 0.4 and 0.6 MPa were performed. The samples for analyses were taken at the following time intervals: 0, 15, 30, 60 and 90 min. The application of HC reactor provided the effective destruction of microorganisms, thus allowing for subsequent use of reclaimed water. With regard to Escherichia coli and Coliform bacteria destruction, the longest time of 90 min and higher pressure of 0.6 MPa might be considered as the most advantageous conditions to perform cavitation. In both cases, the microbes were deactivated in over 50%. In the case of Enterococci, Pseudomonas aeruginosa and colony count, more beneficial results were found at lower pressure of 0.4 MPa and 90 min. Therein, the high level of microorganisms destruction was achieved varied between 81 and 92%. The applied HC allowed for selecting optimal operating parameters and process control through the application of gauge system.

13

Phenomenological model of cavitation erosion of nitrogen ion implanted HIPed Stellite 6

Szala Mirosław

Advances in Materials Science

|

2023

|

Vol. 23, nr 1(75)

98--109

EN

Stellites are a group of Co-Cr-C-W/Mo-containing alloys showing outstanding behavior under cavitation erosion (CE) operational conditions. The process of ion implantation can improve the CE resistance of metal alloys. This work presents the elaborated original phenomenological model of CE of nitrogen ion implanted HIP-consolidated (Hot Isostatically Pressed) cobalt alloy grade Stellite 6. The ultrasonic vibratory test rig was used for CE testing. The nitrogen ion implantation with 120 keV and fluence of 5 × 1016 N+/cm−2 improves HIPed Stellite 6 cavitation erosion resistance two times. Ion-implanted HIPed Stellite 6 has more than ten times higher CE resistance than the reference AISI 304 stainless steel sample. Comparative analysis of AFM, SEM and XRD results done at different test intervals reveals the kinetic of CE process. The model includes the surface roughness development and clarifies the meaning of cobalt-based matrix phase transformations under the nitrogen ion implantation and cavitation loads. Ion implantation modifies the cavitation erosion mechanisms of HIPed Stellite 6. The CE of unimplanted alloy starts on material loss initiated at the carbides/matrix interfaces. Deterioration starts with cobalt matrix plastic deformation, weakening the carbides restraint in the metallic matrix. Then, the cobalt-based matrix and further hard carbides are removed. Finally, a deformed cobalt matrix undergoes cracking, accelerating material removal and formation of pits and craters' growth. The nitrogen ion implantation facilitates ɛ (hcp—hexagonal close-packed)) → γ (fcc—face-centered cubic) phase transformation, which further is reversed due to cavitation loads, i.e., CE induces the γ → ɛ martensitic phase transformation of the cobalt-based matrix. This phenomenon successfully limits carbide removal by consuming the cavitation loads for martensitic transformation at the initial stages of erosion. The CE incubation stage for ion implanted HIPed Stellite 6 lasts longer than for unimplanted due to the higher initial content of γ phase. Moreover, this phase slows the erosion rate by restraining carbides in cobalt-based matrix, facilitating strain-induced martensitic transformation and preventing the surface from severe material loss.

14

Wykorzystanie widma szumu kawitacyjnego do badania wodnego roztworu wielkocząsteczkowego polimeru

Redzicki Romuald, Szulc Piotr, Sitka Andrzej, Tietze Tomasz, Smykowski Daniel

Rynek Energii

|

2022

|

Nr 6

60--65

PL

W artykule przedstawiono badania eksperymentalne na podstawie, których uzyskano charakterystyki widmowe dla różnych natężeń ultradźwięków dla wody oraz wodnego roztworu PAA WF1 (-CH2-CHCONH2-CH2-)n n=30 tys.÷50 tys., (masa cząsteczkowa 4,4106 g/mol) o stężeniach 0,25% i 0,1%. Eksperyment miał na celu zbadanie zależności intensywności kawitacji i obszaru największych zmian w charakterystykach widma szumu kawitacyjnego od natężenia ultradźwięków. Również przeprowadzono badania polegające na nadźwiękawianiu badanego roztworu ze stałym natężeniem ultradźwięków. Celem tych badań była obserwacja zmian zachodzących w obłokach kawitacyjnych oraz zmian charakterystyk widma szumu kawitacyjnego wraz ze zmianą właściwości roztworu poddanego ciągłemu działaniu fali ultradźwiękowej.

EN

he article presents experimental studies on the basis of which spectral characteristics were obtained for various ultrasound intensities for water and the aqueous PAA WF1 solution (-CH2-CHCONH2-CH2-)n n = 30000 ÷ 50000, (molecular weight 4,4106 g/mol) at concentrations of 0.25% and 0.1%. The aim of the experiment was to investigate the dependence of the cavitation intensity and the area of the greatest changes in the characteristics of the cavitation noise spectrum on the intensity of ultrasound. Also, tests were carried out involving the sonication of the test solution with a constant intensity of ultrasound. The aim of these studies was to observe the changes taking place in the cavitation clouds and changes in the characteristics of the cavitation noise spectrum along with the change in the properties of the solution subjected to continuous ultrasound wave action.

15

Prospects for the use of cavitation mechanisms in order to reduce the consumption of natural water in municipal energy

Tselen Bogdan, Ivanitsky Georgiy, Nedbaylo Anna, Radchenko Nataliya

Journal of New Technologies in Environmental Science

|

2022

|

Vol. 6, nr 2

53--58

EN

The paper discusses the existing methods of neutralizing condensate among which the most effective method of hydrodynamic cavitation is determined. To implement the effects of hydrodynamic cavitation, it is proposed to use the way of discrete - pulsed energy input, which allows neutralization by degassing condensate of natural gas combustion products. Based on the created universal mathematical models of the dynamics of single steam-gas bubbles and the ensemble of bubble dynamics, numerical modeling of the growth of steam-gas bubbles in condensate was carried out. Within the framework of the mathematical model of the dynamics of the ensemble of bubbles, an analytical study of the evolution of the unit of steam-gas bubbles to achieve a critical value of the gas content in them was carried out. It has been experimentally proven, the effectiveness of the proposed method, in particular, has been established that the main amount of carbonic acid from both flue gas condensate and model liquid is removed within two minutes of processing. The obtained data prove that an increase in the pH of the treated condensate corresponds to the pH of distillate, which indicates the complete removal of carbonic acid. The implementation of the proposed method of neutralizing condensate will create conditions for improving the environment. This is achieved by reducing the amount of effluent and rational use of water resources by reducing the need for natural water.

16

Simulation study of hydrodynamic cavitation in the orifice flow

Pietrykowski Konrad, Karpiński Paweł

Applied Computer Science

|

2022

|

Vol. 18, no. 3

31--41

EN

Hydrodynamic cavitation is a phenomenon that can be used in the water treatment process. For this purpose, venturis or orifices varying in geometry are used. Studying this phenomenon under experimental conditions is challenging due to its high dynamics and difficulties in measuring and observing the phase transition of the liquid. For this reason, the CFD method was used to study the phenomenon of hydrodynamic cavitation occurring in water flow through the orifice and then analyze flow parameters for different boundary conditions. The research was performed for four different orifice geometries and two defined fluid pressure values at the inlet, based on a computational 2D model of the research object created in Ansys Fluent software. As a result of the numerical simulation, the distribution of fluid velocity and pressure and volume fraction of the gas phase were obtained. A qualitative and quantitative analysis of the phenomenon of hydrodynamic cavitation under the considered flow conditions was conducted for the defined orifice geometries. The largest cavitation zone and thus the largest volume fraction of the gas phase was obtained for the orifice diameter of 2 mm with a sharp increase in diameter. However, the geometry with a linear change in diameter provided the largest volume fraction of the gas phase per power unit.

17

Blade cup method for cavitation reduction in marine propellers

Samsul M. Burak

Polish Maritime Research

|

2021

|

nr 2

54--62

EN

Energy efficiency has become more important in every industry and daily life. Designing and building a more efficient marine vehicle can lead to lower fuel consumption and a longer lifetime for the components of the vehicle. Erosion caused by cavitation reduces the service life of the propeller and the related components in the propulsion and maneuvering system. Reducing cavitation leads to a longer life for these components. This paper aims to explain and investigate propeller blade cup as a cavitation reduction method for marine propellers. A cavitating no-cup propeller is created and analyzed then the cupped version of this propeller is generated and analyzed to compare with the no-cup propeller. Cavitation results of these propellers are investigated. In addition, the thrust, torque, and efficiency of the propellers are compared.

18

Effects of a water hammer and cavitation on vibration transients in a reservoir-pipe-valve system

Miao Yang, Qiu Zaihui, Zhang Xiaolu, Jiang Yuncheng, Pan Jun, Liu Yi, Zhang Li, Li Kun

Journal of Theoretical and Applied Mechanics

|

2021

|

Vol. 59 nr 4

611--622

EN

An extraordinary phenomenon with violent oscillation, accompanied by an abnormal “click” sound is observed during the valve closing in a fuel feeding pipe system. A fluctuation model with flow cavitation, in which time-varying stiffness, time-varying damping coefficients and flow cavitation are comprehensively considered, is proposed. On this basis, a dynamic vibration equation is established and an expression of flow pressure at the valve port is derived. The critical displacement of the flow cavitation system is defined. When the vibration amplitude reaches the critical displacement, cavitation occurs. Based on this model, simulation of vibration displacement and flow pressure is given. The simulated transient process shows the phenomena of vibration fluctuation with cavitation. The results are compared with the experimental data measured by a pressure sensor. Under our experimental conditions, the critical displacement of vibration is 1.41mm, and the average relative pressure peak error is 0.022. The comparison between the simulation and experimental results shows that they are in an acceptable agreement.

19

Projekt stanowiska dydaktycznego do wyznaczania charakterystyk pomp wirowych

Ochał Norbert

Journal of Polish CIMEEAC

|

2021

|

Vol. 16, no 1

79--87

PL

W artykule przedstawiono projekt oraz gotowe stanowisko do wyznaczenia charakterystyk przepływowych pomp wirowych w pracy indywidualnej oraz w wybranych wariantach współpracy szeregowej jak i równoległej. Obserwację parametrów kontrolnych pomp wirowych w różnych stanach pracy: dławienie przepływu, zmiana prędkości obrotowej. Dużą zaletą stanowiska jest wymuszanie obserwację zjawiska kawitacji.

20

The non-unicity of the film thickness in the hydrodynamic lubrication: novel approach generating equivalent micro-grooves and roughness

El Gadari M., Hajjam M.

International Journal of Applied Mechanics and Engineering

|

2021

|

Vol. 26, no. 3

44--61

EN

Since the 1960s, all studies have assumed that a film thickness “h” provides a unique pressure field “p” by resolving the Reynolds equation. However, it is relevant to investigate the film thickness unicity under a given hydrodynamic pressure within the inverse theory. This paper presents a new approach to deduce from an initial film thickness a widespread number of thicknesses providing the same hydrodynamic pressure under a specific condition of gradient pressure. For this purpose, three steps were presented: 1) computing the hydrodynamic pressure from an initial film thickness by resolving the Reynolds equation with Gümbel’s cavitation model, 2) using a new algorithm to generate a second film thickness, 3) comparing and validating the hydrodynamic pressure produced by both thicknesses with the modified Reynolds equation. Throughout three surface finishes: the macro-shaped, micro-textured, and rough surfaces, it has been demonstrated that under a specific hydrodynamic pressure gradient, several film thicknesses could generate the same pressure field with a slight difference by considering cavitation. Besides, this paper confirms also that with different ratios of the averaged film thickness to the root mean square (RMS) similar hydrodynamic pressure could be generated, thereby the deficiency of this ratio to define the lubrication regime as commonly known from Patir and Cheng theory.