Cavitation In Fluid Research Articles

Analysis of multi-frequency ultrasound effect on acoustic microcavitations in [formula omitted]-dimensional fluid

Acoustic microcavitation and associated mechanical effects, such as stress and strain, are significant in decreasing cavitation thresholds and improving cavitation effects at multiple (i.e., single, dual, and triple) frequencies. Ultrasonic excitation and the introduction of microbubbles as cavitation nuclei are both extremely successful techniques. Besides, the enhancing effects brought on by a dual and triple frequency approach, the cavitation dynamics of microbubbles in viscoelastic tissues under the influence of dual and triple frequency excitation are poorly known. This work deals with the modelling and numerical investigation of acoustic cavitation in N-dimensional fluid based on the multifrequency of ultrasound fields. The mathematical model of ultrasonic microcavitation bubble dynamics is formulated by continuity and Navier-Stokes equations in N-dimensions and the equation of pressure due to acoustic multifield. The proposed model is solved and investigated numerically based on the hybrid-B-Spline method. The numerical results illustrate that the behaviour of the microcavitation bubble dynamics increases with a decrease of the value of the N-dimensional fluid. Moreover, the results of the numerical simulation show the importance of the effect of different multifrequency on the behaviour of the microbubble dynamics, as the results obtained showed that in the case of a single frequency, the radius of the microbubbles is higher than in the cases of dual and triple frequency. Additionally, at different initial radii values for cavitation microbubbles, the growth and departure rates for microcavitation dynamics were examined. Finally, in the proposed model, numerical solutions are studied, their stability is verified, and they are compared with previous theoretical works.

Simulation of dynamic process of double bubble coupled acoustic cavitation

In order to simulate the acoustic cavitation process of double-bubble coupling, based on the fluid dynamics governing equation and fluid volume fraction model, this paper proposes a three-dimensional finite element simulation model of double-bubble coupled ultrasonic cavitation in Fluent software, and numerically simulates the dynamic process of double-bubble coupled acoustic cavitation in fluid driven by ultrasonic wave. The nonlinear dynamic characteristics of coupled acoustic cavitation with double bubbles are studied by evaluating the variation of the acoustic field around the cavitation bubble. The results indicate that under the ultrasonic drive, the spherical bubbles gradually widen first to the maximal radius, then shrink swiftly, and finally collapse. There is an interaction force between the paired double bubbles, which inhibits the expansion of cavitation bubbles and increases the bubble contraction time. The ability of the cavitation bubble to converse the energy is strengthened in the contraction stage. Compared with the acoustic cavitation of the single bubble, the pressure inside the bubble is expanded when the coupled double bubble collapses. The analysis results in this paper will provide the reference for the dynamic process simulation of the ultrasonic cavitation bubbles.

Non-Lethal Blasts can Generate Cavitation in Cerebrospinal Fluid While Severe Helmeted Impacts Cannot: A Novel Mechanism for Blast Brain Injury.

Cerebrospinal fluid (CSF) cavitation is a likely physical mechanism for producing traumatic brain injury (TBI) under mechanical loading. In this study, we investigated CSF cavitation under blasts and helmeted impacts which represented loadings in battlefield and road traffic/sports collisions. We first predicted the human head response under the blasts and impacts using computational modelling and found that the blasts can produce much lower negative pressure at the contrecoup CSF region than the impacts. Further analysis showed that the pressure waves transmitting through the skull and soft tissue are responsible for producing the negative pressure at the contrecoup region. Based on this mechanism, we hypothesised that blast, and not impact, can produce CSF cavitation. To test this hypothesis, we developed a one-dimensional simplified surrogate model of the head and exposed it to both blasts and impacts. The test results confirmed the hypothesis and computational modelling of the tests validated the proposed mechanism. These findings have important implications for prevention and diagnosis of blast TBI.

Mechanisms of tensile failure of cerebrospinal fluid in blast traumatic brain injury

Mechanisms of blast-induced Traumatic Brain Injury (BTBI), particularly those linked to the primary pressure wave, are still not fully understood. One possible BTBI mechanism is cavitation in the cerebrospinal fluid (CSF) caused by CSF tensile failure, which is likely to increase strain and strain rate in the brain tissue near the CSF. Blast loading of the head can generate rarefaction (expansion) waves and rapid head motion, which both can produce tensile forces in the CSF. However, it is not clear which of these mechanisms is more likely to cause CSF tensile failure. In this study, we used a high-fidelity 3-dimensional computational model of the human head to test whether the CSF tensile failure increases brain deformation near the brain/CSF boundary and to determine the key failure mechanisms. We exposed the head model to a frontal blast wave and predicted strain and strain rate distribution in the cortex. We found that CSF tensile failure significantly increased strain and strain rate in the cortex. We then studied whether the rapid head motion or the rarefaction wave causes strain and strain rate concentration in cortex. We isolated these two effects by conducting simulations with pure head motion loading (i.e. prescribing the skull velocity but eliminating the pressure wave) and pure blast wave loading (i.e. eliminating head motion by fixing the skull base). Our results showed that the strain increase in the cortex was mainly caused by head motion. In contrast, strain rate increase was caused by both rapid head motion and rarefaction waves, but head motion had a stronger effect on elevating strain rate. Our results show that rapid motion of the head produced by blast wave is the key mechanism for CSF tensile failure and subsequent concentration of strain and strain rate in cortex. This finding suggests that mitigation of rapid head motion caused by blast loading needs to be addressed in the design of protective equipment in order to prevent the tensile failure of CSF.

Hydrodynamic cavitation in Stokes flow of anisotropic fluids

Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. Here, by combining liquid crystal microfluidic experiments, nonequilibrium molecular dynamics simulations and theoretical arguments, we report flow-induced cavitation in an anisotropic fluid. The cavitation domain nucleates due to sudden pressure drop upon flow past a cylindrical obstacle within a microchannel. For an anisotropic fluid, the inception and growth of the cavitation domain ensued in the Stokes regime, while no cavitation was observed in isotropic liquids flowing under similar hydrodynamic parameters. Using simulations we identify a critical value of the Reynolds number for cavitation inception that scales inversely with the order parameter of the fluid. Strikingly, the critical Reynolds number for anisotropic fluids can be 50% lower than that of isotropic fluids.

Gaseous bubble oscillations in anisotropic non-Newtonian fluids under influence of high-frequency acoustic field

Progress of technology and medicine dictates the ever-increasing requirements (heat resistance, corrosion resistance, strength properties, impregnating ability, etc.) for non-Newtonian fluids and materials produced on their basis (epoxy resin, coating materials, liquid crystals, etc.). Materials with improved properties obtaining is possible by modification of their physicochemical structure. One of the most promising approaches to the restructuring of non-Newtonian fluids is cavitation generated by high-frequency acoustic vibrations. The efficiency of cavitation in non-Newtonian fluid is determined by dynamics of gaseous bubble. Today, bubble dynamics in isotropic non-Newtonian fluids, in which cavitation bubble shape remains spherical, is most full investigated, because the problem reduces to ordinary differential equation for spherical bubble radius. However, gaseous bubble in anisotropic fluids which are most wide kind of non-Newtonian fluids (due to orientation of macromolecules) deviates from spherical shape due to viscosity dependence on shear rate direction. Therefore, the paper presents the mathematical model of gaseous bubble dynamics in anisotropic non-Newtonian fluids. The model is based on general equations for anisotropic non-Newtonian fluid flow. The equations are solved by asymptotic decomposition of fluid flow parameters. It allowed evaluating bubble size and shape evolution depending on rheological properties of liquid and acoustic field characteristics.

On the possibility of shock-induced cavitation in submerged cylindrical shell systems

A circular cylindrical shell loaded by one or two fluids and responding to an external shock wave is analyzed in the context of the possible inception of shock-induced cavitation. Several scenarios of fluid contact are considered including a submerged evacuated shell and a submerged fluid-filled shell for three different combinations of the parameters of the internal and external fluids. A semi-analytical shell-shock interaction model is employed in order to predict the regions of the fluids where cavitation is likely to occur, and the respective cavitation development is hypothesized about. The most interesting and practically important finding is that when fluid is present both inside and outside the shell, there exist conditions when cavitation is expected to occur in both the internal and external fluid, resulting in a particularly complex and violent structural re-loading occurring upon the collapse of the respective cavitation regions. The inception of cavitation in the internal fluid alone and in the external fluid alone is also possible. The findings are summarized in a manner that is suitable for use at the pre-design stage as a guide for preliminary assessment of the possibility of shock-induced cavitation in fluid-interacting industrial systems.

Cavitation in dielectric fluid in inhomogeneous pulsed electric field

This paper proposes a method for studying the early stages of the cavitation development in arbitrary, non-stationary conditions. This method is based on the comparison of the results of calculations in the framework of a theoretical model of the liquid dielectrics motion in a strong non-uniform electric field and experiments with controlled parameters. This approach allows us to find the critical negative pressure, at which cavitation begins to develop, and to determine the values of the constants in the classical models of cavitation.

The motion and acoustic radiation characteristics for cavitation in the compressible vortex fluid

Based on the compressible fluid theory, the boundary integral equation is used to solve the motion law of cavitation in vortex flow within different surface pressure models. The time-domain sound pressure characteristics induced by cavitation in vortex field are obtained by the moving surface Kirchhoff formulation. With the surface discretion and coordinate transformation, the cavitation surfaces are treated as the moving deformable boundary and the acoustic source directly. The influence of vortex field parameters on motion and radiation of cavitation is analyzed. Results show that with the consideration of compression, the amplitude of cavitation's pulsation as well as the sound pressure will be decreased. In the vortex fluid, cavitation will be extended, necked and splitted, and may generate a jet in sub-bubbles. While the pressure is reduced in the fluid field, the maximum radius and length before splitting of the cavitation will be enlarged. The number of sub-bubbles will increase when the pressure is small in the fluid field. The directive property of cavitation is weak. And the splitting of cavitation will generate a great peak value of sound pressure. With the increase in vortex flux or the decrease in the cavity number, the period of the cavitation oscillation and its radiation sound pressure are elongated, and the peak of sound pressure is retarded and reduced. The results in this paper could be used as the reference data for the research about the motion and sound radiation characteristics of cavitation in vortex fluid.

Water entry of flexible wedges: Some issues on the FSI phenomena

Deformable bodies entering the water can face unexpected fluid–structure interaction (FSI) phenomena introduced by the mutual interaction between the fluid motion and the structural deformations. This brief communication presents some preliminary results on the FSI phenomena involved with the water entry of deformable wedges. Wedges with various deadrise angle and flexibility impact the water at different velocities. Two different kinds of FSI are found: (i) a repetition of impacts and separations in the fluid jet and (ii) a tendency to cavitation in the underwater fluid–structure interface. These experimental findings are important since large deformations are found to introduce clearly visible FSI phenomena commonly neglected or ignored, but crucial to correctly predict the hydrodynamic load.

Numerical calculation of thermal effect on cavitation in cryogenic fluids

A key design issue related to the turbopump of the rocket engine is that cavitation occurs in cryogenic fluids when the fluid pressure is lower than the vapor pressure at a local thermodynamic state. Cavitation in cryogenic fluids generates substantial thermal effects and strong variations in fluid properties, which in turn alter the cavity characteristics. To date, fewer investigate the thermal effect on cavitation in cryogenic fluids clearly by the numerical methods due to the difficulty of the heat transfer in the phase change process. In order to study the thermal effect on cavitation in cryogenic fluid, computations are conducted around a 2D quarter caliber hydrofoil in liquid nitrogen and hydrogen respectively by implementing modified Merkle cavitation model, which accounts for the energy balance and variable thermodynamic properties of the fluid. The numerical results show that with the thermal effect, the vapour content in constant location decreases, the cavity becomes more porous and the interface becomes less distinct which shows increased spreading while getting shorter in length. In the cavity region, the temperature around the cavity depresses due to absorb the evaporation latent heat and the saturation pressure drops. When the vapour volume fraction is higher, the temperature depression and pressure depression becomes larger. It is also observed that a slight temperature rise is found above the reference fluid temperature at the cavity rear end attributed to the release of latent heat during the condensation process. When the fluid is operating close to its critical temperature, thermal effects on cavitation are more obviously in both the liquid nitrogen and hydrogen. The thermal effect on cavitation in liquid hydrogen is more distinctly compared with that in liquid nitrogen due to the density ratio, vapour pressure and other variable properties of the fluid. The investigation provides aid for the design of the cryogenic pump of the liquid rocket.

Monte Carlo Simulation of Cavitation in Pores with Nonwetting Defects

We investigate the onset of cavitation in a metastable fluid confined to nanoscale pores with nonwetting defects present. Using grand canonical and gauge cell mesocanonical Monte Carlo simulations, we study the degree of metastability (relative vapor pressure), at which the critical bubble forms in a spherical pore with a circular nonwetting defect. It is shown that an increase of the defect size leads to a transition from homogeneous to heterogeneous nucleation of critical bubbles formed at the defect site. In this case, the desorption process may be initiated at larger relative vapor pressures than those predicted by the theories of homogeneous cavitation.

Flow instability due to cryogenic cavitation in the downstream of orifice

Flow instability in LRE (liquid rocket engine) occurs due to various reasons such as flow interactions with valve, orifice and venturi, etc. The inception of cavitation, especially in the propellant feeding system, is the primary cause of mass and pressure oscillations because of the cyclic formation and depletion of cavitation. Meanwhile, the main propellant in a liquid rocket engine is the cryogenic fluid, which properties are very sensitive to temperature variation. And the change of propellant properties to temperature variation by thermodynamic effect needs to be properly taken into account in the flow analysis in order to understand basic mechanisms for cryogenic cavitation. The present study focuses on the formation of cryogenic cavitation by using the IDM model suggested by Shyy and coworkers. The flow instability was also numerically investigated in the downstream of orifice with a developed numerical code. Calculation results show that cryogenic cavitation can be a primary source of flow instability, leading to mass fluctuations accompanied by pressure oscillations. The prediction of cavitation in cryogenic fluid is of vital importance in designing a feeding system of an LRE.

Submerged fluid-filled cylindrical shell subjected to a shock wave: Fluid–structure interaction effects

Abstract A submerged fluid-filled circular cylindrical shell subjected to a shock wave propagating in the external fluid is considered. The study focuses on a number of acoustic and structural effects taking place during the interaction. Specifically, the influence of the acoustic phenomena in the fluid on the stress–strain state of the shell is analysed using two different visualization techniques. The effect that the parameters of the shell have on the internal acoustic field is addressed as well, and the ‘shock transparency’ of various shells is discussed. Special attention is paid to the analysis of the contribution of the terms in the shell equations representing bending stiffness, and the limits of applicability of the membrane theory of thin shells are discussed in the fluid–structure interaction context. The possibility of cavitation in the internal fluid is investigated, and the effect that cavitation could have on the structural dynamics of the shell is discussed. The present paper is a follow-up of the author's earlier study of the interaction between fluid-filled cylindrical shells and external shock waves.

Erratum to ‘A spectral‐element method for modelling cavitation in transient fluid–structure interaction’ (Int. J. Numer. Meth. Eng. 2004; 60:2467–2499)

International Journal for Numerical Methods in EngineeringVolume 61, Issue 11 p. 1976-1976 ErratumFree Access Erratum to ‘A spectral-element method for modelling cavitation in transient fluid–structure interaction’ (Int. J. Numer. Meth. Eng. 2004; 60:2467–2499) M. A. Sprague, Corresponding Author M. A. Sprague [email protected] Mechanical Engineering, University of Colorado, Boulder, CO 80309-0427, U.S.A.Applied Mathematics, University of Colorado, Boulder, CO 80309-0526, U.S.A.Search for more papers by this authorT. L. Geers, T. L. Geers Mechanical Engineering, University of Colorado, Boulder, CO 80309-0427, U.S.A.Search for more papers by this author M. A. Sprague, Corresponding Author M. A. Sprague [email protected] Mechanical Engineering, University of Colorado, Boulder, CO 80309-0427, U.S.A.Applied Mathematics, University of Colorado, Boulder, CO 80309-0526, U.S.A.Search for more papers by this authorT. L. Geers, T. L. Geers Mechanical Engineering, University of Colorado, Boulder, CO 80309-0427, U.S.A.Search for more papers by this author First published: 02 November 2004 https://doi.org/10.1002/nme.1200AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume61, Issue1121 November 2004Pages 1976-1976 RelatedInformation

Generation of vacancies in high-speed plastic deformation

In a recent experiment, crystalline metals were subjected to high-speed plastic deformation, and subsequently a number of vacancy clusters were observed without any trace of dislocations. In an effort to explain this result, in the present study fluid-like behavior of solid in ultra-high-speed deformation is considered, and the possibility of spontaneous generation of vacancies analogous to cavitation in high-speed fluid flow is discussed. Similar to a large velocity gradient that induces turbulence in a high-speed fluid flow, large shear stress induced in a solid material during the course of high-speed deformation may generate vacancies instead of dislocations, if the dislocations cannot follow the deformation speed. In this paper, similarities between dislocation in solid and vortex in a fluid discussed, along with similarities between vacancy in a solid and cavitation in fluid, and a mechanism of vacancy production under high-speed plastic deformation of crystalline materials is proposed.

Effect of increased ambient pressure on lithotripsy-induced cavitation in bulk fluid and at solid surfaces

By reducing cell damage but maintaining stone comminution, overpressure (OP)—increased hydrostatic pressure—offers the promise of safer more effective shock wave lithotripsy (SWL) [Delius, UMB 23, 611–617]. A current hypothesis is that stones offer cavitation sites—sites of violent bubble activity—when the cavitation nuclei in a free field have been dissolved into the fluid by overpressure. Cavitation around solid bodies and in a free field with and without overpressure is investigated. High-speed photography and dual passive cavitation detection (PCD) were used to measure the temporal and spatial extent of cavitation in a 10-cm3 plastic chamber that minimally altered the shock wave. In a free field at OP=0 atm, cavitation bubbles formed and collapsed in 280±20 μs. The time of collapse tc was halved at OP=1 atm, and cavitation activity was not detectable at OP=3 atm. With a stone present, a bubble ∼10 times larger than free-field bubbles grew on the surface of the stone and collapsed after 440±50 μs. With overpressure tc shortened cavitation was still measurable (tc=80±12 μs at OP=3 atm). Results were similar with human kidney stones, artificial cement stones, and an aluminum plate, and support the caviation hypothesis. [Work supported by NIH DK43881, FIRCA, and CRDF.]

Thermal nucleation and cavitation in helium-3 fluids

We have investigated droplet nucleation and bubble cavitation in the quantum fluid helium-3 based on a nonlocal density-functional approach. A marked effect of droplet (or bubble) curvature on the rate of droplet nucleation or cavitation has been found. Without considering this curvature effect (as in the classical theory of nucleation) the droplet nucleation rate for helium-3 could be underestimated (i.e., near 1 K) or overestimated (i.e., near 2.5 K) by orders of magnitude, respectively; for bubble cavitation, the rate could be underestimated by more than twenty orders of magnitude (near 1 K).

Acoustic emission from leaking values

The acoustic emission associated with leakage through air, steam, hydraulic, and water valves has been investigated. Experiments were performed to determine what characteristics of the acoustic emission may be related to leak rate with the hope that instrumentation could be developed to acoustically detect and measure leakage. The spectral and temporal characteristics of leakage‐associated signals taken from externally mounted detectors or valves indicate that average acoustic amplitude in selected frequency ranges provide a useful measure of valve leakage for most styles of air, steam, hydraulic, and water valves. The existence of cavitation in water and hydraulic fluid complicates leakage measurement and, for hydraulic fluid, the sum of event amplitudes multiplied by their rate of occurrence results in a value which increases with increasing leak rate. The data collection and analysis used to support the conclusions are discussed.