Cavitation Length Research Articles

Characterization of ventilated supercavitation regimes using Bayesian optimized Random Forest models

Ventilated supercavitation, a complex two-phase flow, has mostly been explored through experiments and simulations, with machine learning yet to emerge as a complementary research approach. This study combines experiments, numerical simulations, and machine learning models to explore the characteristics of ventilated supercavitation and the different cavitating regimes behind a disk-shaped cavitator. The experimental data were used to validate the simulation models. Subsequently, an optimized Random Forest model, enhanced using the Bayesian Optimization Algorithm (BOA-RF), was trained on the simulation results to predict cavitation length, cavitation number, and classify the cavitation regime type. The BOA-RF model exhibited high accuracy when compared with both experimental and numerical results. The results indicate that the supercavity length increases with the ventilation coefficient (CQ). However, at the formation ventilation coefficient (CQf), the cavity length undergoes a significant and rapid increase. Moreover, as the ventilation coefficient (CQ) increases, the cavitation regime evolves from foamy cavitation to a continuous transparent and asymmetric cavity, and when CQ ≥ CQf, it transitions to clean supercavity. Additionally, the results indicate that as the Froude number increases, the CQf initially increases and then decreases.

Comparative investigation of cavitating and non-cavitating flows around a two-dimensional hydrofoil using particle image velocimetry

This study presents a thorough comparative analysis of non-cavitating and cavitating flows around a two-dimensional National Advisory Committee for Aeronautics airfoil (NACA) 0012 hydrofoil, focusing on flow behavior at different cavitation numbers while maintaining a constant Reynolds number. The experiments, conducted at Chungnam National University's cavitation tunnel, employ Particle Image Velocimetry to capture and analyze the flow dynamics under both regimes. The Reynolds number ranges from 5.8 × 105 to 7.2 × 105, with cavitation numbers (σ) ranging from 4.2 to 3.1 under cavitating conditions and 8.4 to 6.6 under non-cavitating conditions. The results indicated that cavitation substantially influences flow structures, forming re-entrant jets, intensifying shear zones, and increasing vortex shedding. As the cavitation length expands from 0.05 C to 0.4 C with decreasing σ, regions of heightened shear strain are observed between 0.2 and 0.65 C. The flow under non-cavitating conditions demonstrates smoother, more consistent behavior, with vortices concentrated near the trailing edge beyond 0.5 C. Detailed analyses of vector tracking, Q-criterion, and vorticity further clarify the complex interactions between cavitation and vortex dynamics, providing a comprehensive understanding of cavitating flows' turbulent behaviors and instabilities. This research offers new insights into the impact of cavitation on hydrofoil performance by maintaining a constant velocity while varying cavitation numbers. It contributes to a more profound understanding of cavitation phenomena and their implications for design and performance optimization in marine and industrial applications. These findings are essential for advancing mitigation strategies and enhancing the efficiency of hydrofoil-based systems in environments prone to cavitation.

Experimental study on spatiotemporal distribution characteristics of different cavitation stages based on the flow deviation method

Cavitation may quickly damage the surfaces of the valve core and valve seat, causing noise, and vibration problems. Different cavitation stages will affect the regulating valve's flow characteristics to different degrees. Flow rate is one of the basic parameters in a hydraulic system, which is innovatively used to evaluate the cavitation flow. By analyzing the deviation ratio K between actual and theoretical flow rate, cavitation flows are divided into four stages, and the dynamic behavior in different stages is discussed using a high-speed camera and image processing technology. When K is zero, it is defined as the no-cavitation stage. A slight increase in K is the incipient cavitation stage, whose K is within 2%. A rapid decrease in K is the critical cavitation stage, while a significant increase in K is the severe cavitation stage. In the incipient cavitation stage, bubbles are adhered to the valve orifice forming attached cavities. In the critical cavitation stage, attached cavities develop along the throat wall, with some bubbles detaching to form free cavities. This process is accompanied by high-frequency shedding and collapses, with a dominant frequency of 4266 Hz. In the severe cavitation stage, larger attached cavities are located at the throat, whose front edge of cavitation will fracture into large-scale cavitation clouds. Furthermore, this study proposed the cavitation intensity to elucidate the spatial distribution and density of cavitation flow, the cavitation change rate to highlight the disturbances and nonuniformities caused by cavitation bubbles, and the cavitation coefficient to evaluate the severity of cavitation. Additionally, there is a strong correlation between the growth rate of cavitation length L and the growth rate of flow rate Q in the regulating valve. Both the growth rate of L and Q increase in the critical cavitation stage and decrease in the severe cavitation stage.

Cavitation in viscoelastic dilute polymer solutions through a Venturi nozzle

This research experimentally examines the influence of viscoelastic dilute water solutions of polyethylene oxide on Venturi cavitation. Variations in solutions are engineered to manipulate the viscoelastic properties that in turn affect cavitation patterns and attributes. The consequences of viscoelasticity and flow conditions on cavitation are quantified using dimensionless numbers, including the elasticity number (El), the Reynolds number (Re), and the pressure ratio (κ). The experiment identifies three distinct cavitation patterns in the solutions, with their transitions being impacted by alterations in El and κ. As El amplifies, the cavitation bubbles expand and get smoother, and the reentrant jet thickens and amplifies. The behavior of cavitation aligns with the model proposed by Zhang et al. [Phys. Fluids 31, 097107 (2019)], suggesting the critical role of the reentrant jet in the shedding of the cavity cluster. The study also substantiates that the reentrant jet intensifies with ascending El or Re. The collective influence of El, Re, and κ is discovered to shape the cavitation length and shedding frequency of cavity clusters. An increased El or a decreased Re reinforces the vorticity and the reentrant jet, which inevitably leads to a reduction in cavitation lengths and an uptick in the shedding frequency. Conversely, a larger El results in a more gradual response of the bubble to pressure alterations and pronounced rebounds, extending the cavitation length.

Experiment investigation on cavitation bubble and mechanism of anti-cavitation performance in the bionic pressure relief valve

The anti-cavitation ability of the bionic pressure relief valve is investigated, the void fraction λ is employed to quantitatively analyze the gas-phase volume fraction experimentally. The results show that the void fraction is positively correlated with the gas volume fraction. The higher the void fraction, the higher the cavitation strength. Cavitation length and area with the bionic valve core are decreased significantly because of the non-smooth bionic surface. Compared with the traditional valve with a smooth surface, the maximum cavitation length of the bionic valve is reduced by 31.48%, and the maximum cavitation area is reduced by 22.75%. Furthermore, the cavitation inhibition efficiency is proposed to assess the cavitation suppression behavior of the bionic valve. The maximum cavitation inhibition efficiency varies from 63.25% to 72.66% when the flow velocity is in the extent of 42.13–52.66 L/min. Due to the non-smooth bionic surface, the flow field could be effectively perturbed to generate an anti-vortex, the cavitation suppression performance is significantly improved.

Characterization of cavitation zone in cavitating venturi flows: Challenges and road ahead

Dynamic features of a cavitating venturi have been a topic of investigation for the past few decades. This review presents state-of-the-art of experimental and numerical studies in cavitating venturi to address the challenges in understanding flow behavior and developing reliable numerical models. Many experimental studies have shown that two strongly coupled mechanisms, namely, Re-entrant Jet and the bubbly shock influence the cavitation zone behavior. We provide pointers from the past and recent studies to the influence of geometry and operating conditions, introducing changes in cavity oscillation. From an operational viewpoint, the modeling studies need to predict four crucial parameters related to its steady and dynamic operation: choked mass flow rate, operating pressure ratio range, cavitation length, and frequency of cavity oscillations. In this paper, we discuss the possible ways to properly configure a one-dimensional (1D) model, which can be a handy tool for extracting the key integral parameters. Realistic predictions require direct numerical simulations, which is not always an economically viable option. Recent three-dimensional (3D) simulations with compressible formulations for flow field and a cavitation model coupled with large eddy simulations to handle turbulence have achieved some success in predictions. Many simplified approaches have been popular. In this paper, we systematically bring out the predictability limits of popularly used mixture models coupled with cavitation and turbulence in more commonly studied two-dimensional (2D) and fewer three-dimensional geometries. Two-fluid models could provide answers, but further studies are required to mitigate the modeling challenges and to enable realistic predictions of the steady and dynamic features of this elegant flow control device for a chosen application.

Numerical and experimental analysis of cavitation characteristics in safety valves of the nuclear power second circuit using a modified cavitation model

Cavitation frequently arises in the safety valve of nuclear power plants’ secondary circuits operating under high pressure conditions. This study integrates valve flow characteristics and velocity strain rate corrections into the Zwart-Gerber-Belamri model to accurately simulate cavitation inside the valve, reducing the impact of physical empirical coefficient variations on cavitation length prediction. Subsequently, a visualisation test rig is developed to validate the accuracy of the numerical model, and experimental cavitation results are obtained using the grayscale detection method. The evaporation/condensation coefficients are optimised using the AES-MSI model and GA based on the experimental results. The accuracy of the constructed model is validated by comparing it with experimental results obtained under various operating conditions. Finally, the high-fidelity numerical model is employed to investigate the effects of pressure drop and valve openings on cavitation, elucidating the underlying mechanisms governing cavitation variations resulting from pressure drops. Furthermore, a comprehensive equation is derived to determine the effective flow area, aiding in the identification of cavitation locations and offering insights into the relationship between cavitation behaviour and valve openings. The modified cavitation model proposed in this study can be readily extended to investigate cavitation prediction in other valves or throttle elements.

ORIFICE WALL CAVITATION AND SINGLE STRING CAVITATION IN FUEL INJECTORS

It has been pointed out that cavitation inside a fuel injector plays an important role in the fuel spray characteristics, which affects the thermal efficiency and exhaust gas emissions. Recently, it was pointed out that when needle lift is low, not only orifice wall cavitation but also single string cav-itation may occur in the mini-sac and valve-covered orifice (VCO) nozzles, which increases largely the spray cone angle. However, the mechanism and condition of the appearance of single string cav-itation have not been clarified yet. In this study we carry out high-speed visualization of orifice wall cavitation and single string cavitation in various transparent injectors with a single orifice and a simple rectangular sac, whose gap <i>Z</i>, sac width <i>W</i>, orifice diameter <i>D</i>, liquid kinematic viscosity ν, and mean liquid velocity <i>V</i> in the orifice are varied, to investigate the governing dimensionless parameters and to examine whether we can quantitatively predict the formation criteria of single string cavitation or not. Moreover, particle image velocimetry (PIV) analysis is conducted to measure the velocity distribution, to clarify the flow structure, and to quantify the circulation in the sac. As a result, we conclude that regardless of the shape and size of the fuel injectors, the length of cavitation in an orifice can be predicted by using the modified cavitation number σ<sub>c</sub>. The appearance of single string cavitation and circulation in the sac are possible to be predicted quantitatively by using a dimensionless Re<sub>1</sub> proposed in this study, which is the ratio among the inertial and viscous forces.

Flow field characteristics analysis of Venturi tube with cavity

Venturi tube flow is prone to cavitation at high flow rate. In this paper, based on the study of the cavitation flow field in Venturi tube, the authors improve the throat structure of Venturi tube with cavity and carry out analysis of numerical simulation Flow field characteristics by Large eddy simulation (LES), analyze the pressure pulsation in Venturi tube to explore the change of pressure and velocity in different positions, study on the change of cavitation volume fraction, explore the changes of cavitation number and cavitation length under different pressure ratios. Through the previous research and analysis, the flow field characteristics of Venturi tube with cavity are understood, which lays the foundation for cavitation application of Venturi tube.

Combined suppression effects on hydrodynamic cavitation performance in Venturi-type reactor for process intensification

Hydrodynamic cavitation is an emerging intensification technology in water treatment or chemical processing, and Venturi-type cavitation reactors exhibit advantages for industrial-scale production. The effects of temperature on hydrodynamic cavitating flows are investigated to find the optimum reaction conditions enhancing cavitating treatment intensity. Results show that the cavitation performance, including the cavitation intensity and cavitation unsteady behavior, is influenced by (1) cavitation number σ (the pressure difference affecting the vaporization process), (2) Reynolds number Re (the inertial/viscous ratio affecting the bubble size and liquid–vapor interface area), and (3) thermodynamic parameter Σ (the thermal effect affecting the temperature drop). With increasing temperature, the cavitation length first increases and then decreases, with a cavitation intensity peak at the transition temperature of 58 °C. With the growth of cavitation extent, the cavity-shedding regimes tend to transition from the attached sheet cavity to the periodic cloud cavity, and the vapor volume fluctuating frequency decreases accordingly. A combined suppression parameter (CSP) is provided to predict that, with increasing CSP value, the cavitation intensity can be decreased. Recommendations are given that working under the low-CSP range (55–60 °C) could enhance the intensification of the cavitation process.

Hydrodynamic characteristics and optimization design of a bio-inspired anti-erosion structure for a regulating valve core

Cavitation is the main failure mode of coal liquefaction regulating valve, which seriously limits the service life of the regulating valve. In order to restrain cavitation in the regulating valve, a bio-inspired anti-cavitation structure inspired by the red willow of valve core is proposed. Distributions of pressure, velocity and vapor volume fraction in the bionic valve under different openings (30%, 40%, 50%, and 60%) and inlet pressures (2.0MPa, 3.0MPa, 4.0MPa, and 5.0MPa) are discussed. In addition, the parameters of bionic valve structure are optimized using NSGA-II algorithm, the field synergy principle is applied to evaluate the flow field optimization in the bionic valve. The results show that the cavitation area and cavitation length in these bionic structures are reduced significantly compared with the traditional smooth structure. And the anti-cavitation performance of the trench structure is the best, when the inlet pressure is 3 MPa and the opening is 30%, the vapor volume is 0.10 mm3, the vapor volume is reduced by 98.07% compared with traditional smooth structure. Convex hull structure is the second. When the inlet pressure is 5.0 MPa, the vapor volume of the traditional smooth structure is as high as 148 mm3, and the vapor volume of the convex hull structure is 35 mm3, the vapor volume of the trench structure is 19 mm3. Through the field synergy theory to evaluate the internal flow field, it is found that the effective viscosity coefficient in the traditional smooth structure regulating valve varies from 0.7 to 1.2, that of the bionic trench valve changes from 0.1 to 0.5, both the flow resistance and energy consumption in the trench structure valve are reduced. It is proved that the bionic trench structure of the valve core can effectively improve anti cavitation performance and optimize the internal flow resistance of the flow field, which is of great significance to the optimal design of the control valve.

Experimental and numerical analysis on vortex cavitation morphological characteristics in u-shape notch spool valve and the vortex cavitation coupled choked flow conditions

The u-shape notch of spool valve is usually combined with the other typical throttling notches to achieve proportional flowrate adjustments in practical hydraulic control applications. Due to the vacuum-suction nozzle-structural effect, u-shape notch is more likely for cavitation arising. Traditionally, notch throttling is based on the continuity and Bernoulli equation to explain the Harvey nuclei bubble flow from development to collapse, which is not entirely agreed with present proliferated large vapor vortex cavitation researches. In this paper, experimental and numerical analysis discuss the morphological characteristics of u-shape notch vortex cavitation and the choked flow issues caused by vortex cavitation. The large vapor vortex cavitation morphological reproduced by the Large Eddy Simulation (LES) model associated with the multi-phase cavitation model is very close to experimental observations. Further, based on the clear cavity entity obtained by simulation, it could be found that, as notch opening increases, the cavity starting position moves back and the cavity moves upward. And as pressure difference increases, the cavity length increases smoothly until critical pressure value, after which the length increases sharply and maintains in long length level. In addition, it seems that the normalized measurement manner of cavitation length could be proposed, if using local cavitation number dividing incipient cavitation as abscissa to measure the cavity length. Moreover, the cavitating flowrate equation is proposed considering the cavitation-induced serious choked flow problem. The vortex cavitation, especially its length, is assumed to represent intense enough notch vortex flow friction loss. Based on the added flow loss term, the classical flowrate equation is revised, according to which the cavitating flowrate could be predicted within the accuracy of 0.5–2.0%.

Intensity and regimes changing of hydrodynamic cavitation considering temperature effects

Venturi-type cavitation reactors still appear as the most promising candidates for industrial-scale production due to their cheapness and ease of construction, scaling, and replicability. The effects of temperature on hydrodynamic cavitating flows in a Venturi section are investigated to find the optimum reacting conditions enhancing cavitating treatment intensity. The flow conditions are varied with 4 different flow rates and a wide range of temperatures between 28 ℃ to 63 ℃. Results show that both the cavitation length and the transition between sheet and cloud cavitation regimes are influenced by a combination of the pressure drop (indicated by the cavitation number σ), the inertial/viscous effects (controlled by the Reynolds number Re), and the thermal effect (indicated by the thermodynamic parameter Σ). As the temperature is elevated, both the cavitation length and thickness increase first, and then decrease. The cavitation intensity peaks at a transition temperature of 58 ℃. With the increase of cavitation length and thickness, the regimes tend to switch earlier from the attached sheet cavity to periodical cloud shedding, and the shedding frequency decreases accordingly. When the temperature is progressively increased, the changing of cavitating flow structures is illustrated through Proper Order Decomposition analysis. This study allows us to understand the instability, size evolution, shedding regime transition of partial cavities considering thermodynamic effects. Recommendations are provided to beer-brewing, biodiesel production, or water treatment industries that working under a 55 ℃ to 60 ℃ temperature range will attain the highest cavitation intensity.

Experimental Study on the Relationship Between Cavitation and Lift Fluctuations of S-Shaped Hydrofoil

In order to study the energy loss of bi-directional hydraulic machinery under cavitation conditions, this paper uses high-speed photography combined with six-axis force and torque sensors to collect cavitating flow images and lift signals of S-shaped hydrofoils simultaneously in a cavitation tunnel. The experimental results show that the stall angle of attack of the S-shaped hydrofoil is at ±12° and that the lift characteristics are almost symmetrical about +1°. Choosingα= +6° andα= −4° with almost equal average lift for comparison, it was found that both cavitation inception and cloud cavitation inception were earlier atα= −4° than atα= +6°, and that the cavitation length atα= −4° grew significantly faster than atα= +6°. Whenα= +6°, the cavity around the S-shaped hydrofoil undergoes a typical cavitation stage as the cavitation number decreases: from incipient cavitation to sheet cavitation to cloud cavitation. However, whenα= −4°, as the cavitation number decreases, the cavitation phase goes through a developmental process from incipient cavitation to sheet cavitation to cloud cavitation to sheet cavitation to cloud cavitation, mainly because the shape of the S-shaped hydrofoil at the negative angle of attack affects the flow of the cavity tails, which is not sufficient to form re-entrant jets that cuts off the sheet cavitation. The formation mechanism of cloud cavitation at the two different angles of attack (α = +6°、−4°) is the same, both being due to the movement of the re-entrant jet leading to the unstable shedding of sheet cavity. The fast Fourier analysis reveals that the fluctuations of the lift signals under cloud cavitation are significantly higher than those under non-cavitation, and the main frequencies of the lift signals under cloud cavitation were all twice the frequency of the cloud cavitation shedding.

Effect of Leading Edge Profile on Cavitation Performance of Mixed Flow Impeller

Cavitation inception on a pump impeller blade is affected by the blade profile around the leading edge. Even if the difference of the blade profile is limited around the local leading edge area, such as, different elliptical ratios of the leading edge, pressure limitation of cavitation inception differs drastically. This leads to the difference of cavitation erosion speed, and it is important to understand the mechanism and quantitative effect of leading edge shape on cavitation inception, to avoid troubles related to cavitation erosion. In this study, CFD and experimental investigation were carried out to clarify the effect of leading edge shape on cavitation inception. The tested pump was a mixed flow pump, which is widely used as a circulating water pump for power plants. Various leading edge shape were calculated and tested with keeping the blade camber line. Only elliptical ratio of the leading edge on the suction side was changed. As for CFD, isolated impeller, single phase analysis was carried out for 90, 100 and 110% design flow rates, blade surface area on which pressure is less than the vapour pressure was evaluated for each cases. In the experiment, 5 bladed mixed flow pump model was used, and the cavitation length was measured. Both experimental and calculated results were compared and considered. As a result, it was clarified that the optimized value of elliptical ratio is around 2 to 6, which changes depending on the flow rate. Additionally, when the elliptical ratio is 4, was almost half of the one with elliptical ratio 1. Cavity length and cavitation intensity has positive correlation, and estimated erosion speed when the elliptical ratio is4 is almost an eighth of baseline.

Analysis of Bulb Turbine Hydrofoil Cavitation

The influence of a bulb runner blade hydrofoil shape on flow characteristics around the blade was studied. Experimental work was performed on a bulb turbine measuring station and a single hydrofoil in a cavitating tunnel. In the cavitation tunnel, flow visualization was performed on the hydrofoil’s suction side. Cavitation structures were observed for several cavitation numbers. Cavitation was less intense on the modified hydrofoil than on the original hydrofoil, delaying the cavitation onset by several tenths in cavitation number. The results of the visualization in the cavitation tunnel show that modifying the existing hydrofoil design parameters played a key role in reducing the cavitation inception and development, as well as the size of the cavitation structures. A regression model was produced for cavitation cloud length. The results of the regression model show that cavitation length is dependent on Reynolds’s number and the cavitation number. The coefficients of determination for both the existing and modified hydrofoils were reasonably high, with R2 values above 0.95. The results of the cavitation length regression model also confirm that the modified hydrofoil exhibits improved the cavitation properties.

Cavitation dynamics and thermodynamic effects at elevated temperatures in a small Venturi channel

The effects of temperature on hydraulic cavitation dynamics are investigated under various operating conditions, in a close loop cavitation tunnel with a small-scale venturi type section. A systematic study is performed with temperatures varying between 24°C and 85°C, using a high-speed visualization system to observe the cavitating flow. The image processing methods provided in the paper present a quantitative comparison of the cavitation dynamics and structure development. The results show that the increase of the fluid temperature induces the growth of the cavitation volume up to about 55°C, thereafter an additional increase in temperature has the opposite effect. This evolution is interpreted as a competition between a Reynolds effect and the well-known thermal effect. Cavitation is more closely investigated within the temperature range 50°C - 65°C, to analyze the changes in the structure and the cavitation dynamics. For the prediction of thermal suppression head, the thermal effect parameter Σ which can be used empirically, is derived at the maximum cavitation length. This fluid thermodynamic parameter Σ(Ttrans) at the transition peak can be referred to to avoid the maximum cavitation aggressiveness induced vibration or erosion for thermos-fluids around the thermal transition temperature. Finally, the factors influencing cavitation length and shedding frequency are presented and analyzed.

Determination of the shedding frequency of cavitation cloud in a submerged cavitation jet based on high-speed photography images

To accurately determine the shedding frequency of the cavitation cloud in a submerged cavitation jet, the spectral analysis and the proper orthogonal decomposition (POD) for high-speed photography images are performed. The spectrums of 6 different kinds of image signals (the area-averaged gray level, the line-averaged gray level, the point gray level, the cavitation length, width, and area) are calculated and compared. The line-averaged gray level is found to be optimal in determining the shedding frequency but an accurate frequency can only be obtained in the stable-frequency zone where the cavitation cloud sheds. In repeated experiments, the plateau-shape distribution of the main frequency is established with a deviation of 10.8%. A revised Reynolds number Re′ is defined and the shedding frequency can be correlated to Re′ by a power law when the cavitation number is less than 0.02. This relationship is validated by the experimental data in literature. The first mode of the POD characterizes the ensemble-average of the cavitation cloud while the second mode is the major part of the cavitation cloud transient components. The modes 2–5 are organized in pairs, which confirms the periodic feature of the cavitation cloud in the submerged cavitation jet. Near the nozzle exit, the modes 2–5 are symmetrically distributed in the jet shear layer. The shedding frequency of the cloud cavitation can also be precisely determined by performing the spectral analysis of the weighting coefficients of the mode 2. This paper shows that the two parameters, namely, the line-averaged gray level and the weighting coefficients of the mode 2, can be confidently used to calculate the shedding frequency of the cavitation cloud in a submerged cavitation jet.

Study on Cavitating Flow Inside Orifice and Spray Angle Near Nozzle Tip According to the Position of Needle Using Enlarged Transparent Acrylic Nozzle

This study aims to analyze effect of needle position inside nozzle on the internal and external flow characteristics. To visualize cavitating flow inside nozzle, the transparent acrylic nozzle was used. We tested five needle positions that simulated the needle movement of injector. The cross-section of test nozzle is rectangular with a very narrow width instead of circular shaped for a better visualization of cavitating flow. The inside of the nozzle was visualized by the shadowgraphic visualization using a high-speed camera and a metal-halide lamp. From the experiments, development of the cavitating flow according to the needle positions depends on the flow velocity and the cavitation number. The cavitation length, cavitation width, and spray angle are relatively symmetrically shown when the needle was at the center. However, they were asymmetrical when the needle position was biased. When the needle positions were in the same on the vertical line, the minimum cavitation length, minimum cavitation width, and minimum spray angle were larger when the upper level. The needle position affects the development timing and cavitation growth. When the needle position was located at the upper level, the hydraulic flip occurred at a higher injection pressure than the lower level.

Experimental and numerical studies on the cavitation in an advanced rotational hydrodynamic cavitation reactor for water treatment

Hydrodynamic cavitation (HC) has emerged as one of the most potential technologies for industrial-scale water treatment. The advanced rotational hydrodynamic cavitation reactors (ARHCRs) that appeared recently have shown their high effectiveness and economical efficiency compared with conventional devices. For the interaction-type ARHCRs where cavitation is generated from the interaction between the cavitation generation units (CGUs) located on the rotor and the stator, their flow field, cavitation generation mechanism, and interaction process are still not well defined. The present study experimentally and numerically investigated the cavitation flow characteristics in a representative interaction-type ARHCR which has been proposed in the past. The cavitation generation mechanism and development process, which was categorized into “coinciding”, “leaving”, and “approaching” stages, were analyzed explicitly with experimental flow visualization and computational fluid dynamics (CFD) simulations. The changes in the cavitation pattern, area ratio, and sheet cavitation length showed high periodicity with a period of 0.5 ms/cycle at a rotational speed of 3,600 rpm in the flow visualization. The experimental and CFD results indicated that sheet cavitation can be generated on the downstream sides of both the moving and the static CGUs. The sheet cavitation was induced and continuously enlarged in the “leaving” and “approaching” stages and was crushed after the moving CGUs coincided with the static CGUs. In addition, vortex cavitation was formed in the vortex center of each CGU due to high-speed rotating fluid motion. The shape and size of the vortex cavitation were determined by the compression effect produced by the interaction. The findings of this work are important for the fundamental understanding, design, and application of the ARHCRs in water treatment.