Initial Cavitation Research Articles

Enamel caries lesions, with and without initial cavitation, in relation to anatomical areas of the proximal surface in deciduous molars

Objectiveproximal enamel caries lesions (PEC) are believed to initiate and progress to cavitation below the proximal contact area (PCA), but no evidence exists on the location of initial carious cavitation on the proximal surface with functional PCA. This study aimed to test the association of anatomical areas of the proximal surface with the severity of PEC and the frequency of cavitation in PEC in primary molars Designlaboratory, observational, transversal study. Exfoliated primary molars (n = 33) with functional PCA (biofilm-free PCA surrounded by biofilm) had their proximal surfaces (one/tooth) divided anatomically into up to nine areas: 3 areas based on the occlusal/cervical PCA boundaries (areas I, II, and III; occluso-cervically) and 3 areas based on the bucco/lingual PCA boundaries (A, B, and C), with area IIB representing the PCA and area IIIB as the sub-PCA (below the PCA). PEC (ICDAS scores 1 and 2–3) and cavitation in PEC were quantified in all areas using stereomicroscopy and microCT. PEC volume was quantified in areas IIB and IIIB under microCT ResultsPEC severity increased occluso-cervically. PCA and sub-PCA presented different PEC severities (higher in sub-PCA) and similar PCE volumes, but the odds of carious cavitation were much higher (Odds ratio = 197.4; 95 % CI: 8.7/4480.7) in the PCA than in the sub-PCA (no cavitation). ConclusionPCA presented lower PEC severity and similar PEC volume compared to sub-PCA, but PCA concentrated all cavitations in PEC, supporting a new model for the pathogenesis of PEC.

Experimental Flow Performance Investigation of Francis Turbines from Model to Prototype

Investigating the flow performance of Francis turbines from model to prototype is a complex but essential process for ensuring reliable and efficient turbine operation in hydropower plants. It ensures that Francis turbine designs operate efficiently under various operating conditions, extending from laboratory reduced-scale models to full-scale prototype installations. In this investigation, a Francis turbine model was tested under different operating conditions, and its properties were measured, including torque, hydraulic efficiency, power output, cavitation coefficient, rotational speed, flow rate, and pressure pulsations. The results of the Francis turbine model test indicate that it achieved the maximum torque with the designed discharge and designed head. The cavitation coefficient consistently remained higher than the critical cavitation coefficient. The initial cavitation bubbles were observed at 50% partial load but disappeared at full load. Pressure pulsations under different operating conditions showed the maximum peak-to-peak amplitude appearing at the turbine inlet domain and the minimum amplitude occurring at the draft tube elbow. A hill chart shows that the model’s best efficiency was 93.66%, and the estimated best efficiency of the prototype was 95.03% at the design head. The conclusions and methodology of this study can be generalized to other similar hydraulic turbines, especially prototype Francis turbines that lack experimental results.

A cavitation performance prediction method for pumps PART3 feasible for axial-flow reactor coolant pump

This study introduces a novel method to enhance the prediction of cavitation performance in axial flow reactor coolant pumps. Utilizing computational fluid dynamics (CFD), the paper examines the internal flow characteristics and establishes a relationship between minimum pressure, low-pressure isosurface area, and net positive suction head (NPSH). A key finding is that the pressure isosurface area ratio to blade area (Rs) is crucial for cavitation prediction. The study’s method was validated under design conditions with an initial cavitation prediction hypothesis. It was determined that at a flow rate of 0.2912 m3/s and a rotational speed of 1485r/min, the pump’s critical cavitaion performance NPSHc is 4.52 m, with a corresponding low-pressure isosurface pressure of 57117.6 Pa. The current low-pressure isosurface area is 0.00581849 m2, and the blade area is 0.13452 m2, yielding an Rs of 4.325 %. The study reveals a linear relationship between the pressure isosurface area and NPSHa when NPSHa is below a certain threshold, suggesting that this area can predict cavitation performance. This method is significant for optimizing the design and cavitation performance of axial flow reactor coolant pumps.

A Study of Cavitation Erosion in Artificial Submerged Water Jets

The artificially submerged cavitation water jet is effectively utilized by ejecting a high-pressure water stream into a low-pressure water stream through concentric nozzles and utilizing the cavitation phenomenon generated by the shear layer formed between the two streams. In this study, we investigated the cavitation characteristics of artificially submerged cavitation water jets by combining numerical simulations and erosion experiments. The results indicate that an appropriate standoff distance can generate more cavitation clouds on the workpiece surface, and the erosion characteristics of the artificially submerged cavitation water jet are most pronounced at a dimensionless standoff distance of SD = 30. The shear effect formed between the two jets plays a crucial role in generating initial cavitation bubbles within the flow field of the artificially submerged cavitation water jet. Moreover, increasing the convergent angle between the two jets can significantly enhance the cavitation effect between them and lead to a more substantial cavitation effect. Simultaneously, increasing the pressure of the high-pressure inner nozzle also contributes to enhancing the cavitation effect of the artificially submerged cavitation water jet.

Research on the multiphase flow interference and motion characteristics of vehicles during an underwater salvo

A cavitation flow can greatly impact a vehicle's attitude and stability when leaving water. This paper adopts an improved delayed detached eddy turbulence model and Schnerr–Sauer cavitation model as well as the volume-of-fluid method and an overlapping grid technique to investigate this effect. The simulation method used for the cavitation model is validated. The interference effects of a transient multiphase flow, collapse loads, and the motion instability of vehicles during an underwater salvo are studied. The results show multiple obvious pressure peaks during the process of cavity collapse, which do not overlap significantly. Instead, they are sequentially arranged from the top to the end of the bubble, and the synchronous collapse pressure peak is much stronger than the other pressure peaks. The synchronous collapse pressure has a high peak and a short pulse width, and its action position is at the bottom of the shoulder cavity. The salvo time interval is zero, the launch depth is equal to the length of the vehicle, the initial cavitation number is 0.233, and the lateral launch spacing is varied from 2 times the diameter to 5 times the diameter. When the lateral spacing is in the range of 4 times the diameter to 5 times the diameter, the effect of flow interference on the underwater travel and water exit stages disappears.

CT findings as predictive factors for treatment failure in Mycobacterium abscessus complex lung disease: a retrospective cohort study

PurposeMycobacterium abscessus complex (MABC) commonly causes lung disease (LD) and has a high treatment failure rate of around 50%. In this study, our objective is to investigate specific CT patterns for predicting treatment prognosis and monitoring treatment response, thus providing valuable insights for clinical physicians in the management of MABC-LD treatment.MethodsWe retrospectively assessed 34 patients with MABC-LD treated between January 2015 and December 2020. CT scores for bronchiectasis, cellular bronchiolitis, consolidation, cavities, and nodules were measured at initiation and after treatment. The ability of the CT scores to predict treatment outcomes was analyzed in logistic regression analyses.ResultsThe CT scoring system had excellent inter-reader agreement (all intraclass correlation coefficients, > 0.82). The treatment failure (TF) group (17/34; 50%) had higher cavitation diameter (p = 0.049) and extension (p = 0.041) at initial CT and higher cavitation diameter (p = 0.049) and extension (p =0 .045), consolidation (p = 0.022), and total (p = 0.013) scores at follow-up CT than the treatment success (TS) group. The changes of total score and consolidation score (p = 0.049 and 0.024, respectively) increased in the TF group more than the TS group between the initial and follow-up CT. Multivariable logistic regression analysis showed initial cavitation extension, follow-up consolidation extension, and change in consolidation extension (adjusted odds ratio: 2.512, 2.495, and 9.094, respectively, per 1-point increase; all p < 0.05) were significant predictors of treatment failure.ConclusionsA high pre-treatment cavitation extension score and an increase in the consolidation extension score during treatment on CT could be alarm signs of treatment failure requiring tailor the treatment of MABC-LD carefully.

Numerical study of the evolution of unsteady cavitation flow around hydrofoils with leading-edge tubercles

Humpback leading-edge (LE) tubercles are applied to the cavitation control of hydrofoils, and the effect of LE tubercles on hydrofoil cavitation characteristics under different cavitation numbers (σ) is discussed. The results show that LE tubercles can promote hydrofoil initial cavitation, with cavitation appearing first in the groove. This is because the separation effect of LE tubercles induces flow from peak to trough, resulting in an accelerated flow rate and a local low-pressure area. The quasiperiodic properties of the cloud-cavitation stage are not improved, but LE tubercles considerably reduced hydrofoil cavitation, resulting in a cavitation volume reduction of roughly 16.5%–20.4% and maximum cavitation volume reduction of roughly 10.5%–21.8%. The flow field at the tubercle was analyzed, and it was found that vortex cavitation was induced by the spiral vortex. The pressure pulsation on the hydrofoil is highly related to the cavitating evolution. The dominant frequency of the pressure pulsation increases with the decrease of σ and is not affected by the LE tubercles. Finally, LE tubercles are observed to facilitate the transformation of laminar flow to turbulent flow, hence increasing wake disturbance and facilitating the disintegration of the wake vortex structure.

A numerical study on bubble dynamics in hydrodynamic cavitation

This study examines the dynamic interactions of single and double bubbles in infinite liquid domains within hydrodynamic cavitation systems notably within a single-hole orifice-plate reactor. Critical parameters such as cavitation radius and implosion time are analyzed by solving the Rayleigh-Plesset and Keller-Miksis models for compressible fluids. This analysis is extended to multiple oscillations after the initial cavitation implosion has occurred. Furthermore, a numerical solution of both the Rayleigh-Plesset and Keller-Miksis models is employed to demonstrate the influence of key factors, including the polytropic index in single bubble systems and inter-bubble distances, along with secondary Bjerknes forces in double-bubble interactions. The findings highlight the significant impact of one bubble on the oscillations of neighbouring bubbles, resulting in substantial variations in the overall dynamics of the system.

Study on noise induced by cavitation flow in orifice plates

In water supply pipelines, the installation of multiple orifice plates as throttling components can lead to significant noise generation, caused by the cavitation flow downstream, which in turn, can negatively impact the stealth performance of ships and human health. This study aims to investigate the noise reduction characteristics of orifice plates used for throttling. For this purpose, a test rig was established to measure the noise generated by cavitation flow through orifice plates with varying porosity rates, along with the corresponding pressure losses. Additionally, Large Eddy Simulation (LES) and the Zwart-Gerber-Belamri (ZGB) cavitation model were used to numerically simulate the cavitation flow through orifice plates with a porosity rate of β = 0.4. The results show that the pressure loss coefficient is approximately inversely proportional to the porosity rate and follows a power function with the Reynolds number, with the exponent closely related to the porosity rate. During the cavitation stage, the sound pressure level significantly increases in the high-frequency range of 500–8000 Hz, exhibiting broad-spectrum characteristics. During the initial cavitation, bubbles are mainly confined to the surface of the orifice wall. Nevertheless, under conditions of intense cavitation, the generation of bubbles in the shear layer and trail-flowing region is induced by vortex cavitation. Moreover, cavities form at the intersection of the jet and shear layer, which extend towards the orifice plate. To optimize the noise reduction performance of orifice plate throttling components, it is advisable to maintain the porosity rate within the range of 0.40–0.49.

Near-Wall Cavitation Effect: A Molecular Dynamics Study.

Cavitation has been the subject of abundant studies, but the internal mechanism of cavitation is less well known. In this article, a microlevel near-wall model was established by using LAMMPS to present the process of cavitation effect. The results of molecular dynamics simulation revealed the fluctuation process of the liquid near the wall with the change in pressure. Molecular dynamics was also used to evaluate the void volume fraction and density distribution of the system. The results exhibited that the cavitation process can be divided into two stages: the initial cavitation stage and the rapid growth stage. Based on these results, the effects of wettability and initial system temperature on the near-wall cavitation effect were demonstrated. The results indicated that the hydrophobic near-wall forms a gas layer to weaken the density fluctuation, while the hydrophilic wall is opposite. Increasing the temperature could positively affect molecular motion and cavitation. This work provides a theoretical basis for further exploration of the cavitation effect.

Study on pump mode cavitation characteristic of variable speed pump turbine

The continuous variable speed technology is a key technology in the development of pumped storage units. When the operating range of the rotation speed is widened, the unit's stable and safe operation range will be constrained by conditions, such as cavitation, hump, and power limit. This paper uses a traditional fixed-speed pumped storage station as the research object. Based on the complete characteristic curves of the unit, the modification hypothesis after the application of variable speed technology is carried out, and the preferred operation curve of the pump working condition is obtained. The improvement of the cavitation characteristics of the fixed speed unit by the variable speed technology is studied in this paper, and the problems in the prediction of cavitation of prototypes based on model tests are also analyzed. In this paper, the cavitation characteristics of the model and prototype of a pump turbine are analyzed using computational fluid dynamics simulation, with the initial cavitation coefficient as the basis for judging the cavitation. This paper points out that there is a deviation in the direct prediction of the cavitation characteristics of the prototype through the model test and provides a more accurate method to predict the cavitation limit range of variable speed units, which provides a reference for practical engineering.

Enhancing the cavitation erosion resistance of AISI 420-type stainless steel with quenching and partitioning

Stainless steels are commonly used in hydraulic components where they may be susceptible to cavitation erosion. In this study the cavitation erosion resistance of AISI 420-type stainless steel is examined after quenching and partitioning (Q&P) heat treatment. Q&P-samples were prepared with varying heat treatment parameters, and their initial properties were examined with X-ray diffraction and hardness measurements. Reference samples were also prepared with quenching and tempering and quenching without partitioning. The samples were eroded for 6 h with an ultrasonic cavitation erosion device, and their mass losses were measured. The eroded areas were examined with scanning electron microscopy, optical profilometry, and magnetic induction measurements. The results suggest that the cavitation erosion resistance of the examined stainless steel can be significantly enhanced with Q&P. This enhancement of cavitation erosion resistance results from high initial hardness and retained austenite fraction of the steel. During cavitation erosion the retained austenite can absorb cavitation bubble collapse energy by transforming into strain induced martensite, which increases the hardness of the steel and generates expansion of the lattice. This expansion additionally hinders crack propagation at grain boundaries, which reduces the formation of initial cavitation damage.

Behavior and mechanism of cyanide loss in ultrasound-assisted gold leaching process

The potential effect of ultrasound was investigated, which could lead to cyanide loss or decomposition during gold leaching. The variations of cyanide concentration during gold leaching with and without ultrasound were compared. The influence of initial cyanide concentration, pH, temperature, atmosphere, natural loss, hydrolysis, and cavitation effect on the loss of cyanide was examined. The results showed that the loss of cyanide was mainly caused by hydrolysis, oxidation, and reaction with CO2 in the traditional gold leaching process. With the introduction of ultrasound, the oxidative •OH slightly increased the loss of cyanide. Comparing the concentration variations of total cyanide and free cyanide proved that ultrasound (120 W) exhibited a non-detrimental effect on the loss of cyanide in gold leaching process.

Experimental and Numerical Investigation on the Transient Cavitating Flows in a Mixed Flow Pump With Different Number of Blades at Startup

Abstract The objective of this paper is to experimentally and numerically investigate the transient cavitation flow during the startup process of mixed flow pump with emphasis on studying the influence of blade numbers. The transient cavitation simulation was studied based on the improved SST k–ω turbulence model and the Zwart cavitation model. Firstly, in order to obtain the relationship between transient flow rate and the variation of rotational speed at startup, a theoretical analysis based on the fast transients of centrifugal pump was first applied to mixed flow pump and was verified by the current experiment study. Subsequently, the influence of blade number on the cavitation flow in the startup was studied. It is found that the transient cavitation could be classified into four stages regardless of the number of blades: no cavitation stage, the cavitation growth stage, the cavitation reduction stage and the cavitation stabilization stage. However, the blade number does have an impact on the spatial-temporal evolution of cavitation. More specifically, when the blade number increases, the initial cavitation appeared lately, the coverage area of the triangular cavitation cloud and sheet cavitation both decreased, and the increase in blade number has a better inhibitory effect on the sheet cavitation at the cavitation growth stage, and can make sheet cavitation disappear more quickly at the cavitation reduction stage.

Deteksi kavitasi menggunakan linear discriminant analysis pada pompa sentrifugal

Cavitation is a phenomenon that often occurs in the centrifugal pumps. The impact of cavitation is a decrease in pump performance which will affect the ongoing production process in the industries. It is important to have a method to detect the phenomenon of cavitation early. The vibration signal is a parameter that is often used in detecting cavitation or other faulty components. One of the methods is based on the pattern recognition i.e. machine learning. Linear Discriminant Analysis (LDA) is a machine learning algorithm that has the advantage of reducing the parameters used into low dimensions without reducing the accuracy of their classification. The study proposes LDA to classify normal conditions, initial cavitation, intermediate cavitation and severe cavitation. The recording of the vibration signal is taken using the an accelerometer mounted on the inlet of the centrifugal pump. The vibration signal is then extracted using 10 statistic parameters of time domain as the LDA feature selection, namely mean, RMS, standard deviation, kurtosis, skewness, crest factor, clearance factor, shape factor, variance and peak value. The results shows that the LDA classifier can detect and classify cavitation conditions with an accuracy rate of 98.8% on training and 99.6% on testing. The shape factor, kurtosis, skewness and RMS parameters are a combination of parameters that have a large contribution to the classifier to detect and classify cavitation conditions.Keywords: Linear Discriminant Analysis (LDA), cavitation, centrifugal pump, statistical parameter

Cavitation streamlining of a round cylinder in the critical range

The paper presents experimental results on the transverse cavitation streamlining of a circular cylinder by a turbulent water flow in the critical range of Reynolds numbers determined on diameter. Using the PIV method, averaged velocity fields are obtained. Their vector patterns serve to determine the lengths of the reverse flow and the distance between vortices in the near wake behind the cylinder. The presence of a minimum of spatial characteristics of the vortex zone for the initial cavitation modes is shown. Initial cavitation, transient modes, and developed cavitation are determined for different flow rates. The beginning of cavitation is found to depend on the Reynolds number. With smooth decrease in static pressure in front of the cylinder, critical anomalous phenomena, probably related to the rearrangement of cavitation modes, are detected in very narrow range. Vortex shedding from the cylinder surface is found to occur quasi-periodically despite the possibility of simultaneous shedding and breakdown of vortices.

Rational collaborative ablation of bacterial biofilms ignited by physical cavitation and concurrent deep antibiotic release

Bacteria biofilm has extracellular polymeric substances to protect bacteria from external threats, which is a stubborn problem for human health. Herein, a kind of gasifiable nanodroplet is fabricated to ablate Staphylococcus aureus (S. aureus) biofilm. Upon NIR pulsed laser irradiation, the nanodroplets can gasify to generate destructive gas shockwave, which further potentiates initial acoustic cavitation effect, thus synergistically disrupting the protective biofilm and killing resident bacteria. More importantly, the gasification can further promote antibiotic release in deep biofilm for residual bacteria eradication. The nanodroplets not only exhibit deep biofilm penetration capacity and high potency to ablate biofilms, but also good biocompatibility without detectable side effects. In vivo mouse implant model indicates that the nanodroplets can accumulate at the S. aureus infected implant sites. Upon pulsed laser treatment, the nanodroplets efficiently eradicate bacteria biofilm in implanted catheter by synergistic contribution of gas shockwave-enhanced cavitation and deep antibiotic release. Current phase changeable nanodroplets with synergistic physical and chemical therapeutic modalities are promising to combat complex bacterial biofilms with drug resistance, which provides an alternative visual angle for biofilm inhibition in biomedicine.

Effects of immersion depth on the dynamics of cavitation bubbles generated during ns laser ablation of submerged targets

On laser shock peening and underwater laser micromachining, previous studies have shown that the immersion depth of the sample significantly affects laser ablation of submerged targets; however, the underlying mechanisms are still obscure. In this work, we observe and study the formation, growth, and collapse of cavitation bubbles generated during nanosecond laser ablation of submerged titanium targets that are exposed at various immersion depths utilizing a stroboscopic shadowgraphy system. Our results show that the initial laser absorption and cavitation bubble formation after the laser incidence are not affected by the immersion depth. Nevertheless, when the immersion depth is less than the maximum radius of the generated cavitation bubble, the bubble shrinks asymmetrically during the collapse stage. Thus, the cavitation bubble is not fully compressed at the maximum implosion, and phenomena related to the violent implosive collapse, e.g., the second etching effect and the emission of strong shockwaves, are absent. We also propose a strategy to estimate the maximum radius of the laser-induced cavitation bubble, which helps to determine the optimal liquid depth for related engineering applications. Our results provide succinct explanations for the effects of immersion depth on pulsed laser ablation of submerged targets, which are important steps toward a deeper understanding of laser-materials’ interactions in liquid environments.

Study on the influence of the specific area of balance hole on cavitation performance of high- speed centrifugal pump

In this paper, the influence of the specific area of balancing hole on the cavitation performance of high-speed centrifugal pump is studied by numerical method. The results show that in the initial cavitation stage, with the increase of the specific area, the head and efficiency of the pump decreases, and the shaft power increases in a small range. The specific area of the balance hole can change the magnitude and direction of the rotor axial force. With the increase of the specific area, the anti-cavitation performance of the pump is weakened, especially when the specific area reaches a certain value, the vortex flow appears in the balance hole, which causes serious distortion of the flow condition at the inlet of the centrifugal impeller. Meanwhile, cavitation also occurs in the balance chamber and is mainly concentrated near the hub of the centrifugal impeller.

Degradation of chitosan with self-resonating cavitation

For the degradation of chitosan, a novel physical method of self-resonating cavitation with strong cavitation effects was investigated in this paper. The effects of initial concentration, pH, temperature, inlet pressure and cavitation time on the degradation efficiency of chitosan were evaluated. It was found that the degradation efficiency was positively correlated with temperature and cavitation time, but was negatively correlated with the solution concentration. The degradation efficiency was maximized at pH of 4.4 and inlet pressure of 0.4 MPa. Under the experimental conditions, the intrinsic viscosity of chitosan solution was reduced by 92.2%, which was twice as high as the degradation efficiency where a Venturi tube cavitator was used. The viscosity-average molecular weights of initial and degraded chitosan were 651 and 104 kD, respectively. The deacetylation degree of chitosan slightly decreased from 89.34% to 88.05%. Structures and polydispersity of initial and degraded chitosan were measured by Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance hydrogen spectroscopy (1H NMR), X-ray diffraction (XRD) and gel permeation chromatography (GPC). The results showed that the degradation process did not change the natural structure of chitosan. XRD peaks of the original chitosan were observed at 2θ of 9.59° and 20.00°, and the one at 2θ of 20.00° was obviously weakened after the degradation process, which indicated that the crystallinity of chitosan decreased significantly after the degradation. The polydispersity index of chitosan samples decreased from 3.17 to 2.75, indicating that the molecular-weight distribution of products after the degradation was more concentrated. The results proved that self-resonating cavitation prompted the degradation of chitosan and could reduce the polydispersity of the products for the production of oligochitosan with homogeneous molecular weights.