Cavitation Mechanism Research Articles

Cavitation characteristics in rectangular flow restriction microchannel seals

The shaft seal of the primary pump relies on microchannel flow to prevent coolant leakage, but cavitation increases resistance, reduces efficiency, and damages equipment, affecting safety. Therefore, studying microchannel cavitation is crucial for optimizing seal performance and equipment reliability. This study explores the cavitation flow characteristics within a 0.1 mm rectangular flow restriction microchannel seal through experimental methods and numerical simulations. First, using a microfluidic experimental platform and visualization techniques, we directly observed the cavitation phenomena in the microchannel and quantified the evolution of cavitation bubbles under different conditions. Second, by establishing a numerical model of the microchannel, we analyzed the formation mechanisms of cavitation and its impact on flow characteristics under various conditions. The results show that lower cavitation numbers significantly increase the length of cavitation jets and the distribution range of cavitation bubbles, intensifying the cavitation phenomena within the microchannel. Additionally, microchannels with closely spaced double flow restriction structures are more effective at inhibiting cavitation than channels with a single flow restriction structure. These findings offer valuable insights into the mechanisms of microchannel cavitation and provide scientific guidance for the design and optimization of shaft seals.

Experimental Study on Preparation of Nano ZnO by Hydrodynamic Cavitation-Enhanced Carbonization Method and Response Surface Optimization

The carbonization method for preparing Nano ZnO is characterized by its simplicity, ease of reaction control, high product purity, environmental friendliness, and potential for CO2 recycling. However, traditional carbonization processes suffer from poor heat and mass transfer, leading to in situ growth and agglomeration, resulting in low carbonization efficiency, small specific surface area, and inferior product performance. To enhance micro-mixing and mass transfer efficiency, ZnO derived from zinc ash calcination was used as the raw material, and hydrodynamic cavitation technology was employed to intensify the carbonization reaction process. The reaction mechanism of hydrodynamic cavitation was analyzed, and a single-factor experimental study investigated the effects of reaction time, reaction temperature, solid–liquid ratio, calcination temperature, incident angle, cavitation number, and position height on the specific surface area and carbonization rate of Nano ZnO. The response surface method was utilized to explore the significance of the three most influential factors—solid–liquid ratio, cavitation number, and position height—on the carbonization rate and specific surface area. The products were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), laser particle size analysis, and specific surface area analysis. The results showed that the optimal process parameters were a reaction temperature of 80 °C, a reaction time of 120 min, a solid–liquid ratio of 5.011:100, a calcination temperature of 500 °C for 1 h, an incident angle of 60°, a cavitation number of 0.366, and a position height of 301.128 mm. The interaction between solid–liquid ratio and position height significantly influenced the process parameter variations. Under these conditions, the specific surface area and carbonization rate were 63.190 m2/g and 94.623%, respectively. The carbonized product was flaky Nano ZnO with good dispersion and small particle size. Compared to traditional mechanical stirring and bubbling methods, the specific surface area increased by 1.5 times, the carbonization rate improved by 10%, and the particle size decreased by half, significantly enhancing the product performance.

Mechanism of multiscale cavitation induced pressure pulses on a propeller

Mechanism of multiscale cavitation induced pressure pulses on a propeller

Solid–Liquid Diffusion Stresses Leading to Voiding

AbstractThis paper discusses cavitation within a two-phase solid–liquid enclosed system due to interdiffusion. This mechanism is discussed within the context of solid–liquid interdiffusion bonding for metal systems and the voids which are caused by this mechanism. A case study composed of liquid (Sn), Ni3Sn4, and (Ni) phases was used. The mechanical tension and bubble volume resulting from the mechanically enclosed system during isothermal solidification at 250 °C were calculated using a fitted 1D growth model coupled with thermodynamics. Thermodynamic energy calculations showed that it becomes favorable for cavitation after 6 seconds for a starting liquid pocket of 5 µm3. The critical pressure for this cavitation was − 0.029 GPa. The volumetric change for the reaction was determined to be − 12.3 vol pct by a partial molar volume balance. While the volumetric change determined by the thermodynamics found − 7.2 vol pct. The likely presence of unwettable inclusions in non-pure liquids would circumvent this cavitation mechanism, even though cavitation conditions are present. Meaning cavitation for these systems can only be expected when the liquid metal purity is sufficient. Lastly, the bubble growth is attributed to a combination of thermodynamic bubble growth and Kirkendall vacancies.

Study on the characteristics of cavitation and COD removal of an addendum rotational hydrodynamic cavitation reactors

AbstractThis paper presented an addendum rotational hydrodynamic cavitation reactors (ARHCR) that enabled circumferential shear cavitation, axial cavitation, and the Venturi effect, thus increasing cavitation efficiency. The experiments on hydroxyl (·OH) release and chemical oxygen demand (COD) removal demonstrate the feasibility of cavitation performance characterization and COD removal rate. The findings indicate that the COD removal rate can reach a maximum value of 28% or 30% with an increase in flow rate or rotating speed, respectively. Specifically, the maximum values were achieved at a rotation speed of 2,500 rpm or a flow rate of 1.0 m3·h−1. Based on the mechanism of the addendum cavitation, the wedge angles, and the crucial structural parameters, were examined for optimizing cavitation performance. The results revealed that the cavitation number and cavitation bubble were significantly influenced by wedge angles, as well as the efficiency of cavitation energy. The mechanical shear of fluid was enhanced by wedge angles, resulting in constant compression and release of fluid with increased kinetic energy. This led to stronger effects on bulge blocks, and the formation of vortexes that rebounded constantly, resulting in lower pressure areas and expanded regions of cavitation. Among the wedge angles tested, the wedge angle of 15° exhibited the highest cavitation bubbles with a maximum value of 46%. This was 31% higher than the grooves‐type cavitator reported. Furthermore, the cavitation performance was extremely improved with a wedge angle of 15°, as corresponding with the maximum efficiency of cavitation energy. These explorations provide references for the removal of COD in industrial and agricultural wastewater, as well as the development of novel reactors for wastewater treatment.

Research on Rapid Detection Method of Cavitation State of Water jet Propulsion Pump Based on Multi-source and Multi-feature of Acoustic Emission Signal and Bayesian Network

Abstract Cavitation prevents the conversion of internal dynamic and pressure energy in a water jet propulsion pump and causes erosion of flow passage components. Acoustic emission is a non-destructive test method for instability signals. Based on the incipient mechanism and development process of cavitation, three acoustic emission signal feature parameters (ring counting rate, energy release rate, Hurst index) are proposed to define the cavitation state utilizing the waveform pattern and signal self-similarity. The multi-source and multi-feature cavitation identification model of acoustic emission signals is established through cavitation simulation, multi-monitoring point acoustic emission signal testing, and feature parameter extraction, and a large number of probabilistic trainings are carried out using Bayesian network, resulting in a fast cavitation state identification method based on acoustic emission signals. The research results have important practical engineering application significance for the prediction of cavitation resistance, real-time dynamic monitoring of cavitation phenomenon and prevention of cavitation damage.

Multiscale modeling of cavitation around high-speed object based on Euler-Lagrange model and overset mesh

Abstract Cavitation is a common phenomenon, which usually occurs inside the high-speed liquid or at the liquid-solid interface. The unsteady behaviors of cavitating flow, such as shedding and collapse, can cause intense pressure fluctuations and reduce the stability of devices such as under-water high-speed vehicles. In addition, cavitating flow changes the dynamic characteristics of the liquid and causes vibration of the structure as well, making it extremely difficult in achieving precise control. Using OpenFOAM, the present work employs the large eddy simulation (LES) approach to investigate the characteristics of the unsteady cavitating flow around a high-speed under-water object with using the overset mesh technology. The volume of fluid (VOF) approach jointed with the Lagrangian discreate bubble model (DBM) is used for capturing the multiscale cavitation features. The Schnerr & Sauer model is applied for the mass transfer between water and vapor in macroscale, while the Reynolds-Pel equation is incorporated for the growing and collapsing of microscale bubbles. Due to the difficulty in incorporating the multi-scale method into the problems with mesh motion, the present work employs the overset mesh method. Compared with the published small-scale water tank experiment, the LES simulation results fit well with the experimental phenomena, and the DBM can capture the small bubbles accurately. On the basis of model verification, the mechanisms of cavitation forming and collapsing is investigated and the effect of cavitation shedding on the motion of the object is also studied. Moreover, the nucleation, growth, collapse of bubbles, and the interaction between discrete bubbles and large cavities can be well revealed. Further, the multi-scale Euler-Lagrange model is also applied in the rotating propeller, the generation of tip vortex cavitation which is hard to be captured by traditional models is well presented.

A Method of Images to Study Plate-Impact-Induced Cavitation in Aluminum through Molecular Dynamics Simulation

The tensile stress generated by the superposition of two reflection waves in the target plays a critical role in explaining plate-impact-induced spalling. A method of images is proposed to simulate the physical process of wave superposition and this method is applied in order to study the cavitation mechanism in single-crystal Al through molecular dynamics simulation. The critical impact-load velocity for the cavitation obtained by this method is as small as 400 m/s, which is much lower than the result (650 m/s) obtained by the conventional piston-load method. The new cavitation mechanism found is distinctively different from the conventional dislocation-entanglement-induced cavitation under high-velocity impact. The new mechanism involves two key events: firstly, a crack-like defect is formed and its relevant atomic bonds are broken under high tensile stress, resulting in a great momentum of related atoms; and secondly, previous high-momentum atoms collide with the atoms in their running way, resulting in the destruction of the original FCC structure locally and nanovoids or penny-shaped voids being formed. Additionally, the cavitation region, the number of voids, and delamination surfaces increases with the impact-load rate.

2D spatiotemporal passive cavitation imaging and evaluation during ultrasound thrombolysis based on diagnostic ultrasound platform

Acoustic cavitation plays a critical role in various biomedical applications. However, uncontrolled cavitation can lead to undesired damage to healthy tissues. Therefore, real-time monitoring and quantitative evaluation of cavitation dynamics is essential for understanding underlying mechanisms and optimizing ultrasound treatment efficiency and safety. The current research addressed the limitations of traditionally used cavitation detection methods by developing introduced an adaptive time-division multiplexing passive cavitation imaging (PCI) system integrated into a commercial diagnostic ultrasound platform. This new method combined real-time cavitation monitoring with B-mode imaging, allowing for simultaneous visualization of treatment progress and 2D quantitative evaluation of cavitation dosage within targeted area. An improved delay-and-sum (DAS) algorithm, optimized with a minimum variance (MV) beamformer, is utilized to minimize the side lobe effect and improve the axial resolution typically associated with PCI. In additional to visualize and quantitatively assess the cavitation activities generated under varied acoustic pressures and microbubble concentrations, this system was specifically applied to perform 2D cavitation evaluation for ultrasound thrombolysis mediated by different solutions, e.g., saline, nanodiamond (ND) and nitrogen-annealed nanodiamond (N-AND). This research aims to bridge the gap between laboratory-based research systems and real-time spatiotemporal cavitation evaluation demands in practical uses. Results indicate that this improved 2D cavitation monitoring and evaluation system could offer a useful tool for comprehensive evaluating cavitation-mediated effects (e.g., ultrasound thrombolysis), providing valuable insights into in-depth understanding of cavitation mechanisms and optimization of cavitation applications.

Sound-vortex conversion on droplets: A surface curvature oscillation engine for cavitation

Cavitation, a confusing yet essential natural process, remains the target of intensive scientific research. Discovered through propeller cavitation nearly a century ago, initial theories suggest that bubble collapse initiates cavitation. The mechanism of bubble collapse in cavitation remains unclear, especially in modern cavitation scenarios like sonodynamic tumor therapy or aerodynamic noise without natural bubbles. Therefore, a comprehensive visualization-based cavitation mechanism is vital to comprehend and investigate various cavitation phenomena, from historical propeller cavitation to modern in vivo tumor treatment. This study introduces and discusses the direct conversion between two fundamental motions, sound and vortex, and its application as a universal cavitation mechanism to initiate and sustain tailored long-life cavitation from droplets. The results demonstrate a special acoustic phenomenon and its potential technological applications for harnessing sound with customized acoustics cavitation devoid of bubbles.

Study on ultrasound-enhanced molecular transport in articular cartilage.

Local intra-articular administration with minimal side effects and rapid efficacy is a promising strategy for treating osteoarthritis(OA). Most drugs are rapidly cleared from the joint space by capillaries and lymphatic vessels before free diffusion into cartilage. Ultrasound, as a non-invasive therapy, enhances molecular transport within cartilage through the mechanisms of microbubble cavitation and thermal effects. This study investigated the mass transfer behavior of solute molecules with different molecular weights (479 Da, 40 kDa, 150 kDa) within porcine articular cartilage under low-frequency ultrasound conditions of 40 kHz and ultrasound intensities of 0.189 W/cm2 and 0.359 W/cm2. The results revealed that under the conditions of 0.189 W/cm2 ultrasound intensity, the mass transfer concentration of solute molecules were higher compared to passive diffusion, and with an increase in ultrasound intensity to 0.359 W/cm2, the mass transfer effect within the cartilage was further enhanced. Ultrasound promotes molecular transport in different layers of cartilage. Under static conditions, after 2 h of mass transfer, the concentration of small molecules in the superficial layer is lower than that in the middle layer. After applying ultrasound at 0.189 W/cm2, the molecular concentration in the superficial layer significantly increases. Under conditions of 0.359 W/cm2, after 12 h of mass transfer, the concentration of medium and large molecules in the deep layer region increased by more than two times. In addition, this study conducted an assessment of damage to porcine articular cartilage under ultrasound exposure, revealing the significant potential of low-frequency, low-intensity ultrasound in drug delivery and treatment of OA.

A rheological study on nano-bubble assisted flotation of phosphate fine particles

ABSTRACT The application of ultrafine bubbles a.k.a. nano-bubbles (NBs) in upgrading the flotation recovery of fine particles has been extensively investigated from various perspectives over the last two decades. However, their rheological aspect has not been studied yet, which is presented for the first time in this paper. To this end, the current study addresses the effect of six crucial variables including solid content (5%, 15%, and 25% (w/w)), presence and absence of NBs, inner diameter of a Venturi tube (1.5 and 2.2 mm), pH of pulp (4.5–11) and frother dosage (3, 13, and 33 mg/L) on the variation of rheological parameters i.e. shear stress, shear tension, and viscosity. Ultrafine bubbles were generated in a conditioning tank through the hydrodynamic cavitation mechanism using a fatty-acid-based frother (Flo-Y-S), while the rheological responses were continuously monitored and measured by a rheometer and parallel plate spindle (for pulp) and a double gap spindle (for NBs). Flotation tests were conducted on a high-grade phosphate ore (d80 = 37 µm) using a mechanically agitated Denver®-type (D12) flotation cell. The experimental results revealed that fluid behavior without NBs using 13 mg/L frother was in the range of shear rates less than 1 s−1 non-Newtonian and close to the shear thinning state, while it became completely Newtonian in the range of 1 to 1500 s−1. However, the presence of NBs at the same frother content changed this tendency to non-Newtonian and Newtonian fluids at shear rates of <30 s−1 and >30 s−1, respectively. It was also found that either in acidic (5.5) or strong alkaline (11) domains, the pulp viscosity trends were almost close to each other and varied from 0.002−10 to 0.002−4 Pa.s, respectively. On the other hand, on the same trend, the amount was lowered to three times in the neutral range (7.5) and weak alkalinities (9). Diminishing the inner diameter of the Venturi tube from 2.2 mm to 1.5 mm led to an increment of shear stress and viscosity about twice at the shear rates <100 s−1. The results of evaluating frother dosage showed that an increase in the amount of frother dosage, which reduced bubble dimensions, exceeded the viscosity and the amount of shear stress. Finally, we concluded that the rheological properties significantly impacted the selective separation of NB-assisted flotation processes and need further investigations in the future.

A new insight into the mechanism of MNB-assisted flotation of copper: A link between chalcopyrite and its-bearing bulk ore

The present study systematically explores the relationship between chalcopyrite mono-mineral and copper-bearing ore flotation in the presence and absence of micro- and nano-bubbles (MNBs). Ultrafine bubbles were generated through a cavitation mechanism, and their stability, size, and zeta potential were monitored over a period of 0–25 days. Micro-flotation and batch rougher kinetic flotation experiments were carried out with and without ultrafine bubbles using a modified Hallimond tube and 2.5 L Denver® flotation cell, respectively. The results showed that the presence of MNBs improved the recovery of chalcopyrite mono-mineral and its ore by 24.5 % and 7 %, respectively. Furthermore, the adsorption behavior of sodium isopropyl xanthate (SIPX) collector at various concentrations was analyzed in the presence and absence of stable MNBs using UV–visible spectroscopy, FTIR analysis and kinetic models. The adsorption studies supported the micro-flotation findings, demonstrating that the presence of MNBs not only boosted collector adsorption on the chalcopyrite surface (by an average of 73.8 %) but also improved the adsorption kinetics (by 69.44 %). The sorption kinetics followed the pseudo 2nd order model in the presence of MNBs, while in the absence of MNBs, both pseudo 1st order and pseudo 2nd order models were observed. The sorption of SIPX onto chalcopyrite was identified as a chemisorption process in the presence of MNBs, whereas it was a physicochemical sorption in the absence of MNBs.

Study on cavitation and pulsation characteristics of a novel rotor-radial groove hydrodynamic cavitation reactor

Abstract Hydrodynamic cavitation is widely used in many fields such as water treatment, impact rock breaking, and food preparation. The performance of hydrodynamic cavitation is closely related to its internal flow field. In the present study, cavitation flow field was analyzed by computational fluid dynamics in the reactor. The cavitation performance of the rotor is evaluated under different operating conditions. The time frequency distribution of pressure pulsation is studied. The pressure increases at the connection point between the local low-pressure area and the mainstream low-pressure area. Cavitation bubbles collapsed at the tail end of the cavity to form a local void area. The blade frequency amplitude of pressure pulsation shows the significant periodic change. The blade frequency amplitude decreases along the flow direction. The effect of the fluid outlet led to the increase in the second-order harmonic frequency amplitude. The research results could provide theoretical support for the research of cavitation mechanism of cavitation equipment.

Dual frequency ultrasonic liquid phase exfoliation method for the production of few layer graphene in green solvents

In this work, we implement a dual frequency (24 kHz and 1174 kHz) ultrasonic assisted liquid phase exfoliation (ULPE) technique in deionized water (DIW) and other eco-friendly solvents, to produce a variety of high-quality few-layer graphene (FLG) solutions under controlled ultrasonication conditions. The resulting FLG dispersions of variable sizes (∼0.2–1.5 μm2) confirmed by characterisation techniques comprising UV–Vis spectroscopy, Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM). For the first time we demonstrate that high yield of FLG flakes with minimal defects, stable for 6 + months in a solution (stability ∼ 70 %), can be obtained in less than 1-hour of treatment in either water/ethanol (DIW:EtOH) or water/isopropyl alcohol (DIW:IPA) eco-friendly mixtures.We also scrutinized the underlying mechanisms of cavitation using high-speed imaging synchronized with acoustic pressure measurements. The addition of ethanol or IPA to deionized water is proposed to play a central role in exfoliation as it regulates the extend of the cavitation zone, the intensity of the ultrasonic field and, thus, the cavitation effectiveness. Our study revealed that lateral sizes of the obtained FLG depend on the choice of exfoliating media and the diameter of a sonotrode used. This variability offers flexibility in producing FLG of different sizes, applicable in a wide spectrum of size-specific applications.

Modal decomposition of the shedding mechanism of partial cavitation in a Venturi Tube

Abstract The present paper studies the shedding mechanism of partial cavitation in a Venturi Tube, dominated by re-entrant jet and bubbly shock mechanisms, by using two data-driven modal decomposition methods: proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD). According to the snapshot data series obtained by high-speed photography, the modal decomposition and reconstruction of the grey image are carried out. The POD results indicate that the main frequency of the re-entrant jet is higher than that of the shock under the sixth-order mode, and the energy amplitude of the latter is about 20 times that of the former. Furthermore, as the cavitation number increases, the condensation shock mechanism eventually replaces the re-entrant jet mechanism. The DMD results show that the shock behaves obvious traveling wave mode, because the frequency is higher and the phase of the spatial distribution changes evenly under the fourth-order mode. POD and DMD can help to understand the shedding mechanism of partial cavitation.

Carbon-dot/attapulgite composite sonocatalytic towards efficient indigo-containing wastewater degradation based on the cavitation mechanism

Catalytic degradation is an effective method to treat indigo carmine (IC) in wastewater, while high-performance catalyst materials need to be explored. Herein, a facile “spot-heating” synthesis method was employed, whereby the carbon dots (CDs) sonosensitizer was loaded onto the surface of attapulgite (ATP) with ultrasonic cavitation effect, resulting in a composite sonosensitizer ec-CDs/ATP (where ec-CDs represent CDs prepared from ethanol (e) and citric acid (c)). ATP served as a good carrier promotes uniform dispersion of CDs. Benefiting from the large specific surface area, more active sites on the surface of ec-CDs/ATP were exposed, which promotes efficient degradation performance for IC, with a 20 % improvement in performance compared to the reported pure CDs or composite CDs photocatalysts (Bi2O3/dots, Cl-dots). The selective deactivation reactions and relative characterizations further verify that the catalytic process is compatible with the sonocatalytic mechanism originating from the fracture of surface oxygen-containing groups. Importantly, ec-CDs/ATP with a small mass of CDs loading achieves the same catalytic performance as a large mass of pure CDs. This research innovatively presents a simple synthesis method of a composite CDs sonosensitizer and explores its mechanism of degradation, thus pointing the way to the design of multifunctional sonocatalysts for the degradation of IC in wastewater.

Modeling high‐intensity ultrasound to enhance shrimp (Penaeus vannamei) brining without compromising crucial purchase attributes

AbstractTraditional brining methods, such as immersion, are time‐consuming and affect the quality of the food product. Thus, high‐intensity ultrasound (HIUS) has been studied as a brining‐assisted non‐thermal technology. However, this approach to shrimp and the assessment of the individual and combined effects of HIUS parameters, for example, time (t), power (P), and salt concentration (SC), is a knowledge gap. This study aimed to model HIUS‐brining for improving salt diffusion and water properties while maintaining relevant purchase attributes closer to fresh shrimp (Penaeus vannamei) quality. Our findings suggest HIUS improves salt diffusion, decreasing Aw and enhancing water‐holding capacity (WHC). Instead, the increased P reduced hardness and enhanced whiteness. HIUS‐brining (22.02 min/267.89 W/6.68%) maximized Na+ (2.58%) and WHC (86.31%), minimized Aw (.92), and retained hardness (71.07 N) and whiteness (55.14) close to freshness. Therefore, it is possible to employ HIUS in the shrimp brine to improve salt diffusion without damaging physicochemical attributes.Practical applicationsDespite traditional methods for seafood brining being considered effective, they are time‐consuming, taking hours to reach the desirable moisture value. High‐intensity ultrasound (HIUS) is an emerging non‐thermal technology recently explored as a brining technology for animal‐origin food, such as meat. The cavitation induced by HIUS generates gas microbubbles. The implosion increases local temperature and pressure and generates microjets, facilitating the mass transfer (sponge effect) and salt diffusion in the muscle tissues. However, the cavitation mechanism also releases free radicals, resulting in physicochemical alterations during processing, such as damage to color and texture. The present research contributes to providing a better understanding of the application and optimization of HIUS to accelerate the shrimp brining process. The findings herein are promising for the industrial utilization of sonication to obtain brined products without damaging the quality attributes of shrimp.

Internal flow field changes and cavitation characteristics research of the high-pressure axial plunger pump

High pressure axial piston pumps have the characteristics of high power density, small volume and high integration degree and are used in coal machinery, construction machinery and other industrial fields. However, the cavitation impact of the oil flow field inside the pump directly affects the performance and stability of the plunger pump. Once the fault occurs, it will cause the equipment to stop, threatening the life of the current personnel. Taking the axial piston pump as the research object, this paper conducts a numerical simulation analysis of part of the basin model in the piston pump, discusses the fluid characteristics and cavitation mechanism in the piston pump, and provides a theoretical reference for the design and application of high pressure pumps.

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.