Different Types Of Cavitation Research Articles

Study on the pump cavitation characteristic through novel independent rotation of inducer and centrifugal impeller in co-rotation and counter-rotation modes

The influence of counter-rotation between the inducer and impeller, along with a newly introduced system for their independent rotation on the pump cavitation characteristics, has been studied experimentally. Remarkably, this pump allows users to select between co-rotation and counter-rotation modes, providing significant operational adaptability. The high-speed camera is used to analyze vaporization structures and closely monitor the stability of the head pressure delivered by the pump during the cavitation testing phase. For both co-rotation and counter-rotation modes, different types of cavitation within the inducer and between the inducer and the impeller at three varied flow rates have been studied using image analysis. The results reveal improved cavitation performance and comparable efficiency at consistent pressure–flowrate combinations, emphasizing the advantages of counter-rotation across the three tested flow rates. In counter-rotation mode, the tangential velocity of the flow at the output of the inducer is opposite to that of the co-rotation mode. Consequently, the tangential velocity of the flow entering the impeller is reduced, leading to enhanced flow stability and increased pump pressure. The findings from image analysis demonstrate that the structure of cavitation varies between co-rotation and counter-rotation modes. Reversing the rotation direction of the inducer not only improves the pump cavitation characteristics but also changes the vapor structure due to changes in the flow pattern.

Effect of ultrasound on mass transfer during vacuum impregnation of low-porous food materials on the example of potato (Solanum Tuberosum L.)

Vacuum impregnation (VI) is a process that allows modification or enrichment of porous food products with vitamins, minerals, functional ingredients, etc. There are many factors that hamper mass transfer during VI, e.g. low porosity, composition of the matrix, processing pressure and time, etc. The objective of this study was to evaluate the effect of starch on blocking mass transport during VI, and the potential of ultrasound as a factor enhancing mass transfer. The effectiveness of VI was evaluated on the basis of the ascorbic acid content (AAC), a marker compound introduced from the solution. It was found that starch can hinder the mass transfer but ultrasound intensifies the flow of the impregnating solution (16–67% increase in AAC). The quantitative effects, however, depended on the application stage. This may be explained by the different types of cavitation (stable or transient) dominant at different pressures. Importantly, the negative effects of VI on the analyzed quality parameters analyzed (e.g., color, texture, structure-forming compound content) were not stated. The results indicated that the effectiveness of VI in low-porous and starch-rich materials may be increased by applying ultrasound, but more research is required to analyze the stability of the compound introduced during preservation processes.

Empirical mode decomposition of ship hull pressure fluctuation induced by cavitating propeller

We report for the first time a cavitation-induced pressure fluctuation decomposition developed from empirical mode decomposition (EMD) [Huang et al., Proc. R. Soc. London, Ser. A 454, 903–995 (1998)]. The idea is to decompose the nonlinear and non-stationary time series data into a finite and usually small number of “intrinsic mode functions” based on the local properties of the signal, which admit a well-behaved Fourier transform. With this transform, we can obtain frequency characteristics that give sharp identifications of imbedded structures. The cavitation evolution and excited pressure fluctuation around a cavitating propeller in the nonuniform wake are investigated using high-speed imaging and pressure sensors. By the EMD method, we separate the pressure fluctuations induced by different types of cavitation. The high frequency components of the pressure fluctuations are mainly caused by the collapse of sheet cavitation, followed by the shrinking and growth of sheet cavitation. Furthermore, the tip vortex cavitation leads to higher frequency but contributes less to pressure fluctuations. The periodical motion of the propeller contributes to the first blade frequency, and the pressure fluctuations induced by cavitation are superimposed on it.

Control of the dynamics of a boiling vapour bubble using pressure-modulated high intensity focused ultrasound without the shock scattering effect: A first proof-of-concept study

Boiling histotripsy is a promising High-Intensity Focused Ultrasound (HIFU) technique that can be used to induce mechanical tissue fractionation at the HIFU focus via cavitation. Two different types of cavitation produced during boiling histotripsy exposure can contribute towards mechanical tissue destruction: (1) a boiling vapour bubble at the HIFU focus and (2) cavitation clouds in between the boiling bubble and the HIFU source. Control of the extent and degree of mechanical damage produced by boiling histotripsy is necessary when treating a solid tumour adjacent to normal tissue or major blood vessels. This is, however, difficult to achieve with boiling histotripsy due to the stochastic formation of the shock scattering-induced inertial cavitation clouds. In the present study, a new histotripsy method termed pressure-modulated shockwave histotripsy is proposed as an alternative to or in addition to boiling histotripsy without inducing the shock scattering effect. The proposed concept is (a) to generate a boiling vapour bubble via localised shockwave heating and (b) subsequently control its extent and lifetime through manipulating peak pressure magnitudes and a HIFU pulse length. To demonstrate the feasibility of the proposed method, bubble dynamics induced at the HIFU focus in an optically transparent liver tissue phantom were investigated using a high speed camera and a passive cavitation detection systems under a single 10, 50 or 100 ms-long 2, 3.5 or 5 MHz pressure-modulated HIFU pulse with varying peak positive and negative pressure amplitudes from 5 to 89 MPa and −3.7 to −14.6 MPa at the focus. Furthermore, a numerical simulation of 2D nonlinear wave propagation with the presence of a boiling bubble at the focus of a HIFU field was conducted by numerically solving the generalised Westervelt equation. The high speed camera experimental results showed that, with the proposed pressure-modulated shockwave histotripsy, boiling bubbles generated by shockwave heating merged together, forming a larger bubble (of the order of a few hundred micron) at the HIFU focus. This coalesced boiling bubble then persisted and maintained within the HIFU focal zone until the end of the exposure (10, 50, or 100 ms). Furthermore, and most importantly, no violent cavitation clouds which typically appear in boiling histotripsy occurred during the proposed histotripsy excitation (i.e. no shock scattering effect). This was likely because that the peak negative pressure magnitude of the backscattered acoustic field by the boiling bubble was below the cavitation cloud intrinsic threshold. The size of the coalesced boiling bubble gradually increased with the peak pressure magnitudes. In addition, with the proposed method, an oval shaped lesion with a length of 0.6 mm and a width of 0.1 mm appeared at the HIFU focus in the tissue phantom, whereas a larger lesion in the form of a tadpole (length: 2.7 mm, width: 0.3 mm) was produced by boiling histotripsy. Taken together, these results suggest that the proposed pressure-modulated shockwave histotripsy could potentially be used to induce a more spatially localised tissue destruction with a desired degree of mechanical damage through controlling the size and lifetime of a boiling bubble without the shock scattering effect.

Cavitation in high density polyethylene/Al2O3 nanocomposites

In the paper the cavitation phenomenon during tensile deformation of high density polyethylene/Al2O3 nanocomposites was analyzed. The influence of solidification process, filler content and diameter of its particles on the structure of HDPE/Al2O3 nanocomposites was described. Two different types of cavitation, i.e.: interlamellar cavitation of polymer matrix and cavitation around filler particles (by debonding), were identified. In the case of fast solidified nanocomposites interlamellar cavitation was suppressed. High intensity of the cavitation by debonding was related to the numerosity of small particles, as compared to the cavitation by large particles at similar weight concentration. Finally, the influence of different cavitation types on the intensity of fragmentation of lamellar crystals was presented.

A CFD Study on the Mechanisms Which Cause Cavitation in Positive Displacement Reciprocating Pumps

A transient multiphase CFD model was set up to investigate the main causes which lead to cavitation in positive displacement (PD) reciprocating pumps. Many authors such as Karsten Opitz [1] agree on distinguishing two different types of cavitation affecting PD pumps: flow induced cavitation and cavitation due to expansion. The flow induced cavitation affects the zones of high fluid velocity and consequent low static pressure e.g. the valve-seat volume gap while the cavitation due to expansion can be detected in zones where the decompression effects are important e.g. in the vicinity of the plunger. This second factor is a distinctive feature of PD pumps since other devices such as centrifugal pumps are only affected by the flow induced type. Unlike what has been published in the technical literature to date, where analysis of positive displacement pumps are based exclusively on experimental or analytic methods, the work presented in this paper is based entirely on a CFD approach, it discusses the appearance and the dynamics of these two phenomena throughout an entire pumping cycle pointing out the potential of CFD techniques in studying the causes of cavitation and assessing the consequent loss of performance in positive displacement pumps.

Multi-resolution analysis of passive cavitation detector signals

Passive cavitation detectors are widely used for measuring acoustic emissions from cavitating bubbles. Acoustic emissions related to the dynamics of oscillating bubbles contain complex time and frequency domain information. Signal processing techniques traditionally used to analyse transient and stationary signals may be of limited value when analysing such acoustic emissions. This paper describes a multi-resolution approach developed for processing acoustic emissions data. The technique consists of the combination of a discrete wavelet transform and of the statistical and spectral analysis to extract cavitation features. These features include broadband emissions and harmonic, sub-harmonic and ultra-harmonic information. The implementation of the technique on experimental datasets demonstrates that this approach provides detailed information about key features of the acoustic signal, especially in complex situations where different types of cavitation occur simultaneously. Furthermore, statistical metrics used in this technique can provide a quantitative means for classifying signatures of cavitation, particularly the broadband segment of the spectrum created by inertial cavitation, which constitutes novel work.

Measurements of void fraction distribution in cavitating pipe flow using x-ray CT

Measuring the void fraction distribution is still one of the greatest challenges in cavitation research. In this paper, a measurement technique for the quantitative void fraction characterization in a cavitating pipe flow is presented. While it is almost impossible to visualize the inside of the cavitation region with visible light, it is shown that with x-ray computed tomography (CT) it is possible to capture the time-averaged void fraction distribution in a quasi-steady pipe flow. Different types of cavitation have been investigated including cloud-like cavitation, bubble cavitation and film cavitation at very high flow rates. A specially designed nozzle was employed to induce very stable quasi-steady cavitation. The obtained results demonstrate the advantages of the measurement technique compared to other ones; for example, structures were observed inside the cavitation region that could not be visualized by photographic images. Furthermore, photographic images and pressure measurements were used to allow comparisons to be made and to prove the superiority of the CT measurement technique.

Experimental Investigations on Cavitation in a Kaplan Turbine

An experimental investigation has been carried out in order to evaluate the detection of cavitation in Kaplan turbine. The methodology is based on the analysis of structural vibrations and sound level measured in the turbine. The proposed techniques have been checked in horizontal dispositioned Kaplan turbine suffering from different types of cavitation. Although cavitation within pumps has been the subject of extensive research up to now, as demonstrated by the works from [1], [2], [3], [4] and others, it must be noted that few studies have been published related to cavitation within hydropower turbines. Because of that, the current paper is mainly focused in detection of cavitation in kaplan turbines. First, different causes of vibration in the Kaplan turbine model which has been selected for the experiment are discussed. The work presented here is focused on the most important ones which are the leading edge cavitation due to its erosive power, the bubble cavitation because it affects the machine performance and the draft tube swirl that limits the operation stability and vortex cavitation which is the dominating type of cavitation in Kaplan turbine. Cavitation detection is based on the previous understanding of the cavity dynamics and its location inside the machine. The main techniques are the study of the high frequency spectral content of the signals and of their amplitude demodulation for a given frequency band. Moreover, low frequency spectral content can also be used in certain cases. The results obtained for the various load conditions and speed found in the selected machine are presented and discussed in detail in the paper. Conclusions are drawn about the best sensor, measuring location, signal processing and analysis for each type of cavitation, which serve to validate and to improve the detection techniques.

Microemboli in aortic valve replacement

Microembolic signals (MES) can be detected in many recipients of mechanical aortic valve prostheses by transcranial Doppler ultrasound. The nature and etiology of these MES have remained unclear for a long time. The solid and gaseous nature of MES are discussed, as well as whether or not MES may reflect artifacts. Recently, the gaseous nature of these MES has been widely established. To understand the physics of bubble formation related to mechanical heart valve prostheses, it is necessary to discuss the different types of cavitation occurring at the prostheses and the conditions leading to the degassing of blood. We describe the history of transcranial Doppler ultrasound-techniques and the current techniques in the measurement of these signals. Furthermore, the possible clinical impact of MES, as well as strategies for the design of new prostheses and surgical alternatives to diminish their load are discussed.

Detection of cavitation in hydraulic turbines

An experimental investigation has been carried out in order to evaluate the detection of cavitation in actual hydraulic turbines. The methodology is based on the analysis of structural vibrations, acoustic emissions and hydrodynamic pressures measured in the machine. The proposed techniques have been checked in real prototypes suffering from different types of cavitation. In particular, one Kaplan, two Francis and one Pump-Turbine have been investigated in the field. Additionally, one Francis located in a laboratory has also been tested. First, a brief description of the general features of cavitation phenomenon is given as well as of the main types of cavitation occurring in hydraulic turbines. The work presented here is focused on the most important ones which are the leading edge cavitation due to its erosive power, the bubble cavitation because it affects the machine performance and the draft tube swirl that limits the operation stability. Cavitation detection is based on the previous understanding of the cavity dynamics and its location inside the machine. This knowledge has been gained from flow visualisations and measurements in laboratory devices such as a high-speed cavitation tunnel and a reduced scale turbine test rig. The main techniques are the study of the high frequency spectral content of the signals and of their amplitude demodulation for a given frequency band. Moreover, low frequency spectral content can also be used in certain cases. The results obtained for the various types of cavitation found in the selected machines are presented and discussed in detail in the paper. Conclusions are drawn about the best sensor, measuring location, signal processing and analysis for each type of cavitation, which serve to validate and to improve the detection techniques.

Sonoluminescence Emission from Aqueous Solutions of Organic Monomers

The quenching of multibubble sonoluminescence, MBSL, by seven organic monomers in aqueous solution using ultrasound at two frequencies is reported. The results at 515 kHz closely parallel those reported for other simple organic compounds in solution. However, at 20 kHz, significant differences from those at the higher frequency were observed with lower degrees of quenching. In some cases, enhancement of the MBSL was observed. These effects are accounted for in terms of a model where monomer adsorbs to the bubble/solution interface and different types of cavitation can be observed at the two frequencies. The implication of the results for polymerization of these monomers is discussed.

Ultrasonically initiated free radical-catalyzed emulsion polymerization of methyl methacrylate (i)

The emulsion polymerization of methyl methacrylate initiated by ultrasound has been studied at ambient temperature using sodium lauryl sulfate as the surfactant. The investigation includes the: (1) nature and source of the free radical for the initiation process; (2) effects of different types of cavitation; and (3) dependence of the polymerization rate, polymer particle number generated, and the polymer molecular weight on acoustic intensity, argon gas flow rate, surfactant concentration, and initial monomer concentration. It was found that the polymerization could be initiated by ultrasound in the emulsion systems containing methyl methacrylate, water, and sodium lauryl sulfate at ambient temperature in the absence of a conventional initiator. The source of the free radical for the initiation process was found to come from the degradation of the sodium lauryl sulfate, presumably in the aqueous phase. The weight average molecular weight of the poly(methyl methacrylate) obtained varied from 2,500,000 to 3,500,000 g mol−1, and the conversion for polymerization was up to 70%. Deviations from the Smith–Ewart kinetics were observed. The polymerization rate was found to be proportional to the acoustic intensity to the 0.98 power; to the argon gas flow rate to the 0.086 power; to the surfactant concentration to the 0.08 power, with the 0.035M–0.139M surfactant concentration range; and to the surfactant concentration to the 0.58 power, with the 0.139M–0.243M surfactant concentration range. The polymerization rate was found to increase with increasing initial monomer concentration up to a point where it became independent of initial monomer concentration. The polymer particle number generated per milliliter of water was found to be proportional to the acoustic intensity to the 1.23 power; to the argon gas flow rate to the 0.16 power; to the surfactant concentration to the 0.3 power, with the 0.035M–0.139M surfactant concentration range; and to the surfactant concentration to the 1.87 power, with the 0.139M–0.243M surfactant concentration range. The polymer weight average molecular weight was found to be proportional to the acoustic intensity to the 0.21 power, and to the argon gas flow rate to the 0.02 power. It was found to be inversely proportional to the surfactant concentration to the 0.12 and 0.34 power, with the 0.035M–0.139M and the 0.139M–0.243M surfactant concentration ranges, respectively. The polymer yield and polymerization rate were found to be much larger than those obtained from an ultrasonically initiated bulk polymerization method. The polymerization rates obtained at ambient temperature were found to be similar to or higher than those obtained from the conventional higher temperature thermal emulsion polymerization method. This investigation demonstrated the capability of ultrasound to both initiate and accelerate polymerization in the emulsion system, and to do this at a lower temperature that could offer substantial energy savings. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 797–825, 1999

Influence of the Nuclei on the Cavitation Inception for Different Types of Cavitation on Ship Propellers

In order to relate nuclei size distributions with inception cavitation in cavitation facilities, a test program was conducted at the Grand Tunnel Hydrodynamique (GTH) of the Bassin d’Essais des Care`nes. The GTH, which has a complete air control system including dissolved gas and nuclei (microbubbles) control, offers the opportunity to answer this question. The tests were conducted on the three 34 mm diameter propellers used by Kuiper (1981), each of these propellers being characterized by a different cavitation type: bubble, sheet and vortex cavitation. The water nuclei content correspond to strong degassed water (maximum tension), low injection of medium size nuclei (medium tension-low content), large injection of medium size nuclei (medium tension-high content) and large injection of large nuclei (minimum tension). By injecting medium size nuclei for a low content and a high content, we can examine the influence of the number of nuclei on the cavitation inception characteristic. During all the tests, the dissolved air content was kept constant. The GTH online Cavitation Nuclei Counter (Centerbody Venturi) was used to measure both the water nuclei distribution and the liquid tension. Comparisons are made with the calibrated Centerbody Venturi, a Phases Doppler Particles Analyzer (PDPA) and Holographic measurements.

Cavitation Nuclei and Cavitation Inception of Marine Propellers: State of the Art at the Dawn of the 21st Century.

The important role of nuclei on cavitation inception and cavitation development is now well known. Several recent studies have allowed a precise correlation between cavitation inception for different types of cavitation on marine propellers and nuclei distributions(20th ITTC report). In a standard cavitation facility the nuclei distribution will depend on the hydrodynamic operating conditions, and can change during whole cavitation tests. Then, to be able to transpose the model results to full-scale, it is necessary to determine precisely the nuclei distribution corresponding to each cavitation operating point. An illustration is given by analyzing the influence of the operating conditions on a complete cavitation inception <<bucket>>. Moreover, as nuclei govern the whole cavitation process, nuclei measurements are also conducted at sea. The main purpose of all these studies is the accurate prediction of full-scale cavitation behavior from precise transposition laws. This is possible only when nuclei distributions are determined.

Velocity of cavitation bubbles in uniform flowfield high and low Reynolds number

AGASEOUS bubble caused by the tip cavitation of a propeller blade operating in a uniform flowfield environment experiences a drag force in relation to its angular velocity and a thrust force in the axial direction. In this paper, a mathematical model is presented that studies propagation of the gaseous bubble at low and high Reynolds number cases. The temporal and the spatial profile velocity variations are presented. The time constants involved in both regimes are obtained. The velocity variations are shown to be exponential for the low Reynolds number case and algebraic for the high Reynolds number case. Contents When a propeller operates in an underwater environment at high revolutions, cavitation will occur. Three different types of cavitation can occur: 1) hub cavitation, 2) blade cavitation, and 3) tip cavitation. In this paper, tip cavitation will be considered. Tip cavitation produces tip vortices of entrained gases that propagate downstream in a helical motion. The rate at which the cavitation gases propagate downstream is a function of propeller geometry, flowfield, and the geometry of the cavitation gases. The three different types of cavitation that can exist are 1) individual spherical bubbles of equal size, 2) individual bubbles of different sizes, and 3) train of gas shaped in cylindrical form. In this paper, it will be assumed that the cavitation bubbles are spherical and the shape does not change as a function of time. The motion of air bubbles in a fluid has been investigated by a variety of authors with numerous articles being presented by Lauterborn.1 Individual gaseous bubbles will be assumed to be moving in a flowfield, and interactions between successive bubbles will be neglected. The bubble is assumed to move with velocity V, whereas the flowfield has a velocity U. The effect of the added mass and the mass of the displaced fluid have to be considered in the general governing equation. The governing equation of motion is the conservation of momentum equation as given by Newman2 dV dV

Comparison of erosion mechanisms in different types of cavitation

A new cavitation erosion device producing vortex cavitation has been extensively used. A comparative study between various cavitation erosion situations was carried out to verify the ability of this vortex cavitation generator to produce realistic cavitation erosion with respect to that observed in hydraulic machinery. For this purpose, specimens of indium and α + β brass were subjected to different cavitation erosion situations in a Francis turbine model, a cavitation water tunnel, a vibratory cavitation device and our vortex cavitation generator. The surface deformation and the development of damage in exposed specimens were examined using scanning electron microscopy. In all cases, except for the vibratory cavitation device, the damage starts with the formation of isolated hollows and craters of similar morphologies and sizes, produced by collapse impingements. The accumulation of isolated damage distributed statistically over the specimens results in erosion. Meanwhile, for vibratory cavitation the damage is initially scattered uniformly over the specimen surface and develops progressively. In spite of this, the topographies of severely eroded surfaces in various types of cavitation did not present noticeable differences. However, transmission electron microscopy observations of subsurface microstructures in eroded specimens indicate the same arrangements of dislocations and the appearance of largescale deformation twins. Hardened superficial layers in specimens exposed to flow cavitation are thicker than those in vibratory cavitation, which leads to higher erosion rates.

Cavitation Observation in a Jet-flow Gate-valve

As a step for clarification of the mechanism of cavitation erosion as well as noises at a jet-flow gate-valve, the cavitation-aspects and the associated sound-pressures were simultaneously observed systematically by means of high-speed-photography and sensitive pressure-detection through a hydrophone, in a 1/10-scale model-valve for various openings. We found the following three different types of cavitation, i.e. stringlike vortex cavitation (Type I), bubbly cavitation (Type II) in the jet shear layer, and induced cavitation (Type III). Each of them has its own desinent cavitation number as well as zone where cavities occur, and emits an impulsive pressure of special wave form. Especially for a narrower opening, the bubbly cavitation develops dominantly there emitting very high impulsive pressures, and the free jet is remarkably deflected downwards in the settling chamber, often touching the bottom, so that the valve will be heavily eroded.

Cavitation Characteristics and Infinite-Aspect-Ratio Characteristics of a Hydrofoil Section

Abstract This paper describes “two-dimensional” tests in a water tunnel of a profile identical to the 4412 airfoil section of the National Advisory Committee for Aeronautics. The tests included photographic observations of the inception and growth of cavitation as influenced by velocity, pressure (submergence), and angle of attack, and measurements, during cavitation-free operation, of the hydrodynamic forces and moments as functions of Reynolds number and angle of attack. The relation between the angle of attack and the value of the cavitation parameter at which inception occurs is shown for each face of the hydrofoil. The effect of profile geometry in causing cavitation, and the significance of distinctly different types of cavitation obtained with change in variables are discussed. Convenient curves are given showing the submergence required to avoid cavitation for different velocities and angles of attack. The measured hydrodynamic characteristics are presented in graphical form and are also compared with previously existing data from wind-tunnel tests of a finite-aspect-ratio span. The experimental procedure and its reliability in indicating true infinite-aspect-ratio characteristics are discussed.