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Sample records for cavitation mechanics

  1. Cell mechanics in biomedical cavitation

    PubMed Central

    Wang, Qianxi; Manmi, Kawa; Liu, Kuo-Kang

    2015-01-01

    Studies on the deformation behaviours of cellular entities, such as coated microbubbles and liposomes subject to a cavitation flow, become increasingly important for the advancement of ultrasonic imaging and drug delivery. Numerical simulations for bubble dynamics of ultrasound contrast agents based on the boundary integral method are presented in this work. The effects of the encapsulating shell are estimated by adapting Hoff's model used for thin-shell contrast agents. The viscosity effects are estimated by including the normal viscous stress in the boundary condition. In parallel, mechanical models of cell membranes and liposomes as well as state-of-the-art techniques for quantitative measurement of viscoelasticity for a single cell or coated microbubbles are reviewed. The future developments regarding modelling and measurement of the material properties of the cellular entities for cutting-edge biomedical applications are also discussed. PMID:26442142

  2. Analogy between fluid cavitation and fracture mechanics

    NASA Technical Reports Server (NTRS)

    Hendricks, R. C.; Mullen, R. L.; Braun, M. J.

    1983-01-01

    When the stresses imposed on a fluid are sufficiently large, rupture or cavitation can occur. Such conditions can exist in many two-phase flow applications, such as the choked flows, which can occur in seals and bearings. Nonspherical bubbles with large aspect ratios have been observed in fluids under rapid acceleration and high shear fields. These bubbles are geometrically similar to fracture surface patterns (Griffith crack model) existing in solids. Analogies between crack growth in solid and fluid cavitation are proposed and supported by analysis and observation (photographs). Healing phenomena (void condensation), well accepted in fluid mechanics, have been observed in some polymers and hypothesized in solid mechanics. By drawing on the strengths of the theories of solid mechanics and cavitation, a more complete unified theory can be developed.

  3. Cavitation dynamics of mechanical heart valve prostheses.

    PubMed

    Lee, C S; Chandran, K B; Chen, L D

    1994-10-01

    Nine different mechanical mitral heart valves were chosen in order to study cavitation dynamics in detail in an in vitro flow system simulating a single event of mitral valve closure. The transvalvular pressure (ventricular minus atrial pressure) rise rate averaged during the valve closing period was used as an index of the loading rate. A series of photographs in the vicinity of the inflow surface of the valve were attempted during the bubble appearance period using a stroboscopic visualization technique. The in vitro study revealed three sources of cavitation initiation in the design of the mechanical heart valves tested: stop (seat stop or seating lip), inflow strut, and clearance (gap formed between the occluder and the housing or between the two occluders in the closed position). Among these, the occluder stop design was the most critical to cavitation since all valves having the stop at the edge of the major orifice area showed a higher intensity of cavitation and threshold loading rates below the estimated normal physiological value. The analysis of bubble locations and dynamics led us to propose that the fluid squeezing effect between the occluder and the stop in the housing and the streamline contraction effect along the clearance are factors responsible for cavitation incipience.

  4. On instationary mechanisms in cavitating micro throttles

    NASA Astrophysics Data System (ADS)

    Beban, B.; Legat, S.; Schmidt, S. J.; Adams, N. A.

    2015-12-01

    The current investigation presents numerical simulations of cavitating flows in a simplified model of a mushroom valve chamber of a piezo common rail injection system. Two discharge throttles with different step diameters are investigated. The developed models are able to predict relevant features of cavitating flow in fuel injectors. Special attention is put on the investigation of wave dynamics and related instationary mechanisms in the discharge throttle and the valve chamber. To this respect, a compressible flow solver with a homogeneous mixture model and barotropic description of the diesel-like-fluid is utilized. Highly unsteady phenomena are observed in both investigated designs. The structure of the cavitating flow is further analyzed with an emphasis on the interaction between collapsing vapor clouds in the throttle step and reentrant motion in the discharge throttle. Furthermore, numerical simulations reveal significant influence of the throttle step diameter on the cavity dynamics.

  5. Mechanisms of thrombolysis acceleration by cavitation

    NASA Astrophysics Data System (ADS)

    Weiss, Hope; Selvaraj, Prashanth; Ahadi, Golnaz; Voie, Arne; Hoelscher, Thilo; Okita, Kohei; Matsumoto, Yoichiro; Szeri, Andrew

    2012-11-01

    Recent studies, in vitro and in vivo, have shown that High Intensity Focused Ultrasound (HIFU) accelerates thrombolysis, the dissolution of blood clots, for ischemic stroke. Although the mechanisms are not fully understood, cavitation is thought to play an important role in sonothrombolysis. The damage to a blood clot's fibrin fiber network from cavitation in a HIFU field is studied using two independent approaches for an embedded bubble. One method is extended to the more important scenario of a bubble outside a blood clot that collapses asymmetrically creating a jet towards the clot. There is significantly more damage potential from a bubble undergoing cavitation collapse outside the clot compared to a rapidly expanding bubble embedded within the clot structure. Also, the effects of the physical properties of skull bone when a HIFU wave propagates through it are examined by use of computer simulation. The dynamics of a test bubble placed at the focus is used in understanding of the pressure field. All other things being equal, the analysis suggests that skull thickness can alter the wave at the focus, which in turn can change the nature of cavitation bubble dynamics and the amount of energy available for clot damage. Now at MSOE.

  6. Photoacoustic cavitation for theranostics: mechanism, current progress and applications

    NASA Astrophysics Data System (ADS)

    Feng, Y.; Qin, D.; Wan, M.

    2015-12-01

    As an emerging cavitation technology, photoacoustic cavitation (PAC) means the formation of bubbles in liquids using focused laser and pre-established ultrasound synchronously. Its significant advantages include the decreased threshold of each modality and the precise location of cavitation determined by the focused laser. In this paper, a brief review of PAC is presented, including the physical mechanism description, the classic experimental technology, the representative results in variety of media, and its applications in biomedical imaging and therapy. Moreover, some preliminary results of PAC in perfluoropentane (PFP) liquid and PFP droplets investigated by passive cavitation detection (PCD) in our group are also presented.

  7. Cavitation damage of pyrolytic carbon in mechanical heart valves.

    PubMed

    Kafesjian, R; Howanec, M; Ward, G D; Diep, L; Wagstaff, L S; Rhee, R

    1994-04-01

    A summary of the observations of cavitation-related damage is presented for over a hundred mechanical heart valves (MHV) containing pyrolytic carbon components. Valves were obtained from several types of simulators, animal studies and clinical explantations, and were primarily of the bileaflet type. Damage on these valves was documented as to location, type, and severity. This report focuses on the damage location where cavitation bubbles have been observed in vitro. Pitting and microcracking are the forms of damage observed that can be associated with cavitation. The pitting is primarily of a focal nature and is thought to be due to cavitation bubble collapse or, possibly, initiation. Certain features of the deposited material appear to be important relative to cavitation damage resistance and the so-called cavitation threshold of a MHV. A highly polished surface with few micropores provides few nucleation sites for cavitation bubbles and will better withstand cavitation forces. Attributing certain observations of in vivo damage to cavitation is done by inference from; 1. the similarity of the damage features observed on explants to those produced by cavitation in vitro, and 2. the identity of the location of this damage with the location of cavitation as observed by high speed video (HSV). In addition, confirmation was obtained in a number of instances by in vitro observation of cavitation coinciding with a specific damage location on the same explanted MHV. In most of the fractures, a focal pit was usually present on the fracture line at or near the fracture origin, indicating pitting as a primary damage mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

  8. Cavitation Damage Mechanisms: Review of Literature.

    DTIC Science & Technology

    1980-02-01

    34 (The Damping of Oscillations in Oil Hydraulic Lines), VDI-Forschungsheft 575, 1976, 48 pages. 1.12 Kobayashi, R., "Effect of Cavitation on the...Continue on revmers aide If necesom and identify by block umbw) Cavitation Hydraulic Activator Hydraulic Control Systems Dissolved and Free Gas Spool...Capability of hydraulic fluid to contain and release gas........................ 21 C. Effect of dissolved and free gas on cavitation ..... 23 D

  9. Mechanical heart valve cavitation in patients with bileaflet valves.

    PubMed

    Johansen, Peter; Andersen, Tina S; Hasenkam, J Michael; Nygaard, Hans; Paulsen, Peter K

    2014-01-01

    Today, the quality of mechanical heart valves is quite high, and implantation has become a routine clinical procedure with a low operative mortality (< 5%). However, patients still face the risks of blood cell damage, thromboembolic events, and material failure of the prosthetic device. One mechanism found to be a possible contributor to these adverse effects is cavitation. In vitro, cavitation has been directly demonstrated by visualization and indirectly in vivo by registering of high frequency pressure fluctuations (HFPF). Tilting disc valves are thought of having higher cavitation potential than bileaflet valves due to higher closing velocities. However, the thromboembolic potential seems to be the same. Further studies are therefore needed to investigate the cavitation potential of bileaflet valves in vivo. The post processing of HFPF have shown difficulties when applied on bileaflet vavles due to asynchronous closure of the two leaflets. The aim of this study was therefore to isolate the pressure signature from each leaflet closure and perform cavitation analyses on each component. Six patients were included in the study (St. Jude Medical (n=3) and CarboMedics (n=3); all aortic bileaflet mechanical heart valves). HFPFs were recorded intraoperatively through a hydrophone at the aortic root. The pressure signature relating to the first and second leaflet closure was isolated and cavitation parameters were calculated (RMS after 50 kHz highpass filtering and signal energy). Data were averaged over 30 heart cycles. For all patients both the RMS value and signal energy of the second leaflet closure were higher than for the first leaflet closure. This indicates that the second leaflet closure is most prone to cause cavitation. Therefore, quantifying cavitation based on the HFPF related to the second leaflet closure may suggest that the cavitation potential for bileaflet valves in vivo may be higher than previous studies have suggested.

  10. Statistical characteristics of mechanical heart valve cavitation in accelerated testing.

    PubMed

    Wu, Changfu; Hwang, Ned H C; Lin, Yu-Kweng M

    2004-07-01

    Cavitation damage has been observed on mechanical heart valves (MHVs) undergoing accelerated testing. Cavitation itself can be modeled as a stochastic process, as it varies from beat to beat of the testing machine. This in-vitro study was undertaken to investigate the statistical characteristics of MHV cavitation. A 25-mm St. Jude Medical bileaflet MHV (SJM 25) was tested in an accelerated tester at various pulse rates, ranging from 300 to 1,000 bpm, with stepwise increments of 100 bpm. A miniature pressure transducer was placed near a leaflet tip on the inflow side of the valve, to monitor regional transient pressure fluctuations at instants of valve closure. The pressure trace associated with each beat was passed through a 70 kHz high-pass digital filter to extract the high-frequency oscillation (HFO) components resulting from the collapse of cavitation bubbles. Three intensity-related measures were calculated for each HFO burst: its time span; its local root-mean-square (LRMS) value; and the area enveloped by the absolute value of the HFO pressure trace and the time axis, referred to as cavitation impulse. These were treated as stochastic processes, of which the first-order probability density functions (PDFs) were estimated for each test rate. Both the LRMS value and cavitation impulse were log-normal distributed, and the time span was normal distributed. These distribution laws were consistent at different test rates. The present investigation was directed at understanding MHV cavitation as a stochastic process. The results provide a basis for establishing further the statistical relationship between cavitation intensity and time-evolving cavitation damage on MHV surfaces. These data are required to assess and compare the performance of MHVs of different designs.

  11. Transient pressure signals in mechanical heart valve cavitation.

    PubMed

    Wu, Z J; Slonin, J H; Hwang, N H

    1996-01-01

    The purpose of this investigation was to establish a correlation between mechanical heart valve (MHV) cavitation and transient pressure (TP) signals at MHV closure. This correlation may suggest a possible method to detect in vivo MHV cavitation. In a pulsatile mock flow loop, a study was performed to measure TP and observe cavitation bubble inception at MHV closure under simulated physiologic ventricular and aortic pressures at heart rates of 70, 90, 120, and 140 beats/min with corresponding cardiac outputs of 5.0, 6.0, 7.5, and 8.5 L/min, respectively. The experimental study included two bileaflet MHV prostheses: 1) St. Jude Medical 31 mm and 2) Carbomedics 31 mm. High fidelity piezo-electric pressure transducers were used to measure TP immediately before and after the valve leaflet/housing impact. A stroboscopic lighting imaging technique was developed to capture cavitation bubbles on the MHV inflow surfaces at selected time delays ranging from 25 microseconds to 1 ms after the leaflet/housing impact. The TP traces measured 10 mm away from the valve leaflet tip showed a large pressure reduction peak at the leaflet/housing impact, and subsequent high frequency pressure oscillations (HPOs) while the cavitation bubbles were observed. The occurrence of cavitation bubbles and HPO bursts were found to be random on a beat by beat basis. However, the amplitude of the TP reduction, the intensity of the cavitation bubble (size and number), and the intensity of HPO were found to increase with the test heart rate. A correlation between the MHV cavitation bubbles and the HPO burst was positively established. Power spectrum analysis of the TP signals further showed that the frequency of the HPO (cavitation bubble collapse pressures) ranged from 100 to 450 kHz.

  12. Cavitation mechanisms during tensile creep of an advanced silicon nitride

    SciTech Connect

    Lofaj, F.; Okada, A.; Usami, H.

    1996-12-31

    Creep cavitation was investigated by electron microscopic methods after tensile creep tests of a self-reinforced silicon nitride conducted at temperatures ranging from 1250 to 1400{degrees}C. Fast and intensive cavitation in the amorphous secondary phase and slow growth of cavities inside the large silicon nitride grains were observed. Two basic types of cavities in glassy boundary phase were found; rounded cavities on the facets of large grains and irregular cavities in pockets among the matrix grains. A driving force for cavitation in boundary phase on large grain facets is concluded to be local tensile stress on local irregularities of facets produced on the interfaces between large grains and finer matrix grains during grain boundary sliding (GBS). Dilatant hydrostatic tensile stresses generated in a matrix due to GBS were thought to be responsible for cavitation in multigrain junctions. Small cavities formed on the facets and large cavities penetrating through the whole large grains of silicon nitride were found after long-term tests. The stresses transferred from matrix to large grains are suggested as a driving force for slow growth of small cavities on the facets and their later penetration inside the large silicon nitride grains. Basic cavitation mechanisms in amorphous phase are thought to be GBS and viscous flow while solution-precipitation is responsible for cavity growth in large silicon nitride grains.

  13. Molecular mechanism for cavitation in water under tension.

    PubMed

    Menzl, Georg; Gonzalez, Miguel A; Geiger, Philipp; Caupin, Frédéric; Abascal, José L F; Valeriani, Chantal; Dellago, Christoph

    2016-11-29

    Despite its relevance in biology and engineering, the molecular mechanism driving cavitation in water remains unknown. Using computer simulations, we investigate the structure and dynamics of vapor bubbles emerging from metastable water at negative pressures. We find that in the early stages of cavitation, bubbles are irregularly shaped and become more spherical as they grow. Nevertheless, the free energy of bubble formation can be perfectly reproduced in the framework of classical nucleation theory (CNT) if the curvature dependence of the surface tension is taken into account. Comparison of the observed bubble dynamics to the predictions of the macroscopic Rayleigh-Plesset (RP) equation, augmented with thermal fluctuations, demonstrates that the growth of nanoscale bubbles is governed by viscous forces. Combining the dynamical prefactor determined from the RP equation with CNT based on the Kramers formalism yields an analytical expression for the cavitation rate that reproduces the simulation results very well over a wide range of pressures. Furthermore, our theoretical predictions are in excellent agreement with cavitation rates obtained from inclusion experiments. This suggests that homogeneous nucleation is observed in inclusions, whereas only heterogeneous nucleation on impurities or defects occurs in other experiments.

  14. Molecular mechanism for cavitation in water under tension

    PubMed Central

    Menzl, Georg; Gonzalez, Miguel A.; Geiger, Philipp; Caupin, Frédéric; Abascal, José L. F.; Dellago, Christoph

    2016-01-01

    Despite its relevance in biology and engineering, the molecular mechanism driving cavitation in water remains unknown. Using computer simulations, we investigate the structure and dynamics of vapor bubbles emerging from metastable water at negative pressures. We find that in the early stages of cavitation, bubbles are irregularly shaped and become more spherical as they grow. Nevertheless, the free energy of bubble formation can be perfectly reproduced in the framework of classical nucleation theory (CNT) if the curvature dependence of the surface tension is taken into account. Comparison of the observed bubble dynamics to the predictions of the macroscopic Rayleigh–Plesset (RP) equation, augmented with thermal fluctuations, demonstrates that the growth of nanoscale bubbles is governed by viscous forces. Combining the dynamical prefactor determined from the RP equation with CNT based on the Kramers formalism yields an analytical expression for the cavitation rate that reproduces the simulation results very well over a wide range of pressures. Furthermore, our theoretical predictions are in excellent agreement with cavitation rates obtained from inclusion experiments. This suggests that homogeneous nucleation is observed in inclusions, whereas only heterogeneous nucleation on impurities or defects occurs in other experiments. PMID:27803329

  15. Damage mechanisms for ultrasound-induced cavitation in tissue

    NASA Astrophysics Data System (ADS)

    Warnez, M.; Vlaisavljevich, E.; Xu, Z.; Johnsen, E.

    2017-03-01

    In a variety of biomedical applications, cavitation occurs in soft tissue. Although significant amounts of research have been performed on cavitation in water, bubble dynamics, and related bioeffects remain poorly understood. We use numerical simulations of spherical bubble dynamics in soft tissue to assess the extent to which viscoelasticity affects "known" and introduces "new" damage mechanisms. We find that deviatoric stresses - although not an important damage mechanism in water - are significantly enhanced and could be an important bioeffect mechanism in tissue. Both the viscoelastic properties and the nonlinear, large-collapse radius contribute to stress amplification in the surroundings. In addition, temperatures in the surrounding medium increase more in the Zener tissue than in water, due to viscous heating.

  16. Acoustic and visual characteristics of cavitation induced by mechanical heart valves.

    PubMed

    Sohn, Kwanghyun; Manning, Keefe B; Fontaine, Arnold A; Tarbell, John M; Deutsch, Steven

    2005-07-01

    A sudden pressure drop and recovery can induce cavitation in liquids. Mechanical heart valves (MHVs) generate such a pressure drop at closure, and cavitation generation around MHVs has been demonstrated many times. Cavitation is suspected as being a cause of blood and valve material damage. In this in-vitro experiment, visual images and acoustic signals associated with MHV cavitation were studied to reveal cavitation characteristics. Björk-Shiley Convex-Concave valves, one with a pyrolytic carbon occluder and one with a Delrin occluder, were installed in a single-shot valve chamber. Cavitation intensity was controlled by load (dP/dt) and air content of water. The acoustic signal was measured using a hydrophone and visual images recorded with a high-speed digital camera system. Cavitation images showed that 10 ppm water rarely developed cavitation, unlike the 16 ppm water. A distinct peak pressure was observed at cavitation collapse that was a good indicator of MHV cavitation intensity. The average of the peak pressures revealed that cavitation intensity increased faster with increasing load for the 16 ppm water. The use of the peak pressure may be the preferred method for correlating cavitation intensity in structures for which the separation of valve closure noise and cavitation signal is difficult, as for the valves studied here.

  17. The fern cavitation catapult: mechanism and design principles.

    PubMed

    Llorens, C; Argentina, M; Rojas, N; Westbrook, J; Dumais, J; Noblin, X

    2016-01-01

    Leptosporangiate ferns have evolved an ingenious cavitation catapult to disperse their spores. The mechanism relies almost entirely on the annulus, a row of 12-25 cells, which successively: (i) stores energy by evaporation of the cells' content, (ii) triggers the catapult by internal cavitation, and (iii) controls the time scales of energy release to ensure efficient spore ejection. The confluence of these three biomechanical functions within the confines of a single structure suggests a level of sophistication that goes beyond most man-made devices where specific structures or parts rarely serve more than one function. Here, we study in detail the three phases of spore ejection in the sporangia of the fern Polypodium aureum. For each of these phases, we have written the governing equations and measured the key parameters. For the opening of the sporangium, we show that the structural design of the annulus is particularly well suited to inducing bending deformations in response to osmotic volume changes. Moreover, the measured parameters for the osmoelastic design lead to a near-optimal speed of spore ejection (approx. 10 m s(-1)). Our analysis of the trigger mechanism by cavitation points to a critical cavitation pressure of approximately -100 ± 14 bar, a value that matches the most negative pressures recorded in the xylem of plants. Finally, using high-speed imaging, we elucidated the physics leading to the sharp separation of time scales (30 versus 5000 µs) in the closing dynamics. Our results highlight the importance of the precise tuning of the parameters without which the function of the leptosporangium as a catapult would be severely compromised.

  18. The fern cavitation catapult: mechanism and design principles

    PubMed Central

    Llorens, C.; Argentina, M.; Rojas, N.; Westbrook, J.; Dumais, J.; Noblin, X.

    2016-01-01

    Leptosporangiate ferns have evolved an ingenious cavitation catapult to disperse their spores. The mechanism relies almost entirely on the annulus, a row of 12–25 cells, which successively: (i) stores energy by evaporation of the cells’ content, (ii) triggers the catapult by internal cavitation, and (iii) controls the time scales of energy release to ensure efficient spore ejection. The confluence of these three biomechanical functions within the confines of a single structure suggests a level of sophistication that goes beyond most man-made devices where specific structures or parts rarely serve more than one function. Here, we study in detail the three phases of spore ejection in the sporangia of the fern Polypodium aureum. For each of these phases, we have written the governing equations and measured the key parameters. For the opening of the sporangium, we show that the structural design of the annulus is particularly well suited to inducing bending deformations in response to osmotic volume changes. Moreover, the measured parameters for the osmoelastic design lead to a near-optimal speed of spore ejection (approx. 10 m s–1). Our analysis of the trigger mechanism by cavitation points to a critical cavitation pressure of approximately −100 ± 14 bar, a value that matches the most negative pressures recorded in the xylem of plants. Finally, using high-speed imaging, we elucidated the physics leading to the sharp separation of time scales (30 versus 5000 µs) in the closing dynamics. Our results highlight the importance of the precise tuning of the parameters without which the function of the leptosporangium as a catapult would be severely compromised. PMID:26763327

  19. Mechanisms of cavitation erosion of TiAl-based titanium aluminide intermetallic alloys

    SciTech Connect

    Howard, R.L.; Ball, A.

    1996-08-01

    The modes and controlling mechanisms of cavitation erosion of plasma arc-melted TiAl-based titanium aluminide intermetallic alloys, Ti-52Al (at.%) and Ti-48Al-2Mn-2Nb (at.%) were studied and compared to those of the Ti{sub 3}Al-based alloy, Ti-25Al-10Nb-3V-1Mo (at.%) and other comparative materials. The accumulation of cavitation damage during the initial stages of cavitation erosion was monitored and the work hardening produced in steady state erosion conditions was measured on 5{degree} taper sections. The cavitation erosion resistance of the titanium cavitation erosion resistance of the TiAl-based titanium aluminide alloys compared to Ti-25Al-10Nb-3V-1Mo (at.%) is ascribed to their ability to twin and their greater work hardening ability during cavitation erosion.

  20. Characteristics of mechanical heart valve cavitation in a pneumatic ventricular assist device.

    PubMed

    Lee, Hwansung; Taenaka, Yoshiyuki

    2008-06-01

    In previous studies, we investigated the mechanism of mechanical heart valve (MHV) cavitation and cavitation intensity with a nonsynchronized experiment system. Our group is currently developing a pneumatic ventricular assist device (PVAD), and in this study we investigated MHV cavitation intensity in the PVAD using a synchronized analysis of the cavitation images and the acoustic signal of cavitation bubbles. A 23-mm Medtronic Hall valve with an opening angle of 70 degrees was mounted in the mitral position of the PVAD after removing the sewing ring. A function generator provided a square signal, which used the trigger signal of the electrocardiogram R wave (ECG-R) mode of the control-drive console for circulatory support. This square signal was delayed by a delay circuit and was then used as the trigger signal for a pressure sensor and a high-speed video camera. The data were stored using a digital oscilloscope at a 1-MHz sampling rate, and then the pressure signal was band-pass filtered between 35 and 200 kHz using a digital filter. The band-pass filtered root mean squared (RMS) pressure and cavitation cycle duration were used as an index of cavitation intensity. The cavitation bubbles were concentrated at the valve stop, and the cavitation cycle duration and RMS pressure increased as the heart rate and driving pressure increased. At the low valve-closing velocity, bubble cavitation was observed near the valve stop. However, at the fast valve-closing velocity, cloud cavitation was observed. A high-frequency signal wave was generated when the bubbles collapsed. The cavitation cycle duration and RMS pressure increased as the valve-closing velocity increased linearly.

  1. Experimental investigation on dynamic characteristics and strengthening mechanism of laser-induced cavitation bubbles.

    PubMed

    Ren, X D; He, H; Tong, Y Q; Ren, Y P; Yuan, S Q; Liu, R; Zuo, C Y; Wu, K; Sui, S; Wang, D S

    2016-09-01

    The dynamic features of nanosecond laser-induced cavitation bubbles near the light alloy boundary were investigated with the high-speed photography. The shock-waves and the dynamic characteristics of the cavitation bubbles generated by the laser were detected using the hydrophone. The dynamic features and strengthening mechanism of cavitation bubbles were studied. The strengthening mechanisms of cavitation bubble were discussed when the relative distance parameter γ was within the range of 0.5-2.5. It showed that the strengthening mechanisms caused by liquid jet or shock-waves depended on γ much. The research results provided a new strengthening method based on laser-induced cavitation shotless peening (CSP).

  2. A Study on the Mechanism for Cavitation in the Mechanical Heart Valves with an Electrohydraulic Total Artificial Heart

    NASA Astrophysics Data System (ADS)

    Lee, Hwansung; Tsukiya, Tomonori; Homma, Akihiko; Kamimura, Tadayuki; Tatsumi, Eisuke; Taenaka, Yoshiyuki; Kitamura, Soichiro

    It has been conceived that the mechanical heart valves mounted in an artificial heart close much faster than in vivo use, resulting in cavitation bubbles formation. In this study, the mechanisms for cavitation in mechanical heart valves (MHVs) is investigated with monoleaflet and bileaflet valves in the mitral position with an electrohydraulic total artificial heart (EHTAH). The valve-closing velocity and pressure-drop through the valve were done, and a high-speed video camera was employed to investigate the mechanism for MHVs cavitation. The valve-closing velocity and pressure-drop of the bileaflet valves were less than that of the monoleaflet valves. Most of the cavitation bubbles in the monoleaflet valves were observed next to the edge of the valve stop and the inner side of the leaflet. With the bileaflet valves, cavitation bubbles were concentrated along the leaflet tip. Also, the number density of cavitation bubbles in the bileaflet valves was less than that of the monoleaflet valves. The number density of cavitation bubbles increased with an increase in the valve-closing velocity and the valve stop area. It is established that squeeze flow holds the key to cavitation in the mechanical heart valve. In a viewpoint of squeeze flow, the bileaflet valve with slow valve-closing velocity and small valve stop area, is safer to prevent of blood cell damage than the monoleaflet valves.

  3. Time-frequency analysis of transient pressure signals for a mechanical heart valve cavitation study.

    PubMed

    Yu, A A; White, J A; Hwang, N H

    1998-01-01

    A series of transient pressure signals (TPSs) can be measured using a miniature pressure transducer mounted near the tip of the inflow side of a mechanical heart valve (MHV) occluder during closure. A relationship appears to exist between the intensity and pattern of the TPS and the cavitation potential of a MHV. To study the relationship between MHV cavitation and the TPSs, we installed an MHV in a valve testing chamber of a digitally controlled burst test loop. A charge coupled device (CCD) camera and a personal computer based image grabbing program was used to visualize cavitation bubbles appearing on or near the occluder surface. One bileaflet MHV was used as the model for this study. Cavitation bubbles were observed within 300 microsec of the leaflet/housing impact. The valve was tested at various driving pressures between 100 and 1,300 mmHg. MHV cavitation bubble intensities were qualitatively classified into three categories: 1) strong, 2) weak, and 3) none. Digital images of the MHV occluder inflow surface were recorded simultaneously with the TPSs. TPSs were studied by the time-frequency analysis method (spectrogram) and correlated to MHV cavitation potential. The intensity of the cavitation bubbles was found to be associated with burst test loop driving pressures during leaflet closure.

  4. Cavitation behavior observed in three monoleaflet mechanical heart valves under accelerated testing conditions.

    PubMed

    Lo, Chi-Wen; Liu, Jia-Shing; Li, Chi-Pei; Lu, Po-Chien; Hwang, Ned H

    2008-01-01

    Accelerated testing provides a substantial amount of data on mechanical heart valve durability in a short period of time, but such conditions may not accurately reflect in vivo performance. Cavitation, which occurs during mechanical heart valve closure when local flow field pressure decreases below vapor pressure, is thought to play a role in valve damage under accelerated conditions. The underlying flow dynamics and mechanisms behind cavitation bubble formation are poorly understood. Under physiologic conditions, random perivalvular cavitation is difficult to capture. We applied accelerated testing at a pulse rate of 600 bpm and transvalvular pressure of 120 mm Hg, with synchronized videographs and high-frequency pressure measurements, to study cavitation of the Medtronic Hall Standard (MHS), Medtronic Hall D-16 (MHD), and Omni Carbon (OC) valves. Results showed cavitation bubbles between 340 and 360 micros after leaflet/housing impact of the MHS, MHD, and OC valves, intensified by significant leaflet rebound. Squeeze flow, Venturi, and water hammer effects each contributed to cavitation, depending on valve design.

  5. New Insights into the Mechanisms of Water-Stress-Induced Cavitation in Conifers

    PubMed Central

    Cochard, Hervé; Hölttä, Teemu; Herbette, Stéphane; Delzon, Sylvain; Mencuccini, Maurizio

    2009-01-01

    Cavitation resistance is a key parameter to understand tree drought tolerance but little is known about the mechanisms of air entry into xylem conduits. For conifers three mechanisms have been proposed: (1) a rupture of pit margo microfibrils, (2) a displacement of the pit torus from its normal sealing position over the pit aperture, and (3) a rupture of an air-water menisci in a pore of the pit margo. In this article, we report experimental results on three coniferous species suggesting additional mechanisms. First, when xylem segments were injected with a fluid at a pressure sufficient to aspirate pit tori and well above the pressure for cavitation induction we failed to detect the increase in sample conductance that should have been caused by torus displacement from blocking the pit aperture or by membrane rupture. Second, by injecting xylem samples with different surfactant solutions, we found a linear relation between sample vulnerability to cavitation and fluid surface tension. This suggests that cavitation in conifers could also be provoked by the capillary failure of an air-water meniscus in coherence with the prediction of Young-Laplace's equation. Within the bordered pit membrane, the exact position of this capillary seeding is unknown. The possible Achilles' heel could be the seal between tori and pit walls or holes in the torus. The mechanism of water-stress-induced cavitation in conifers could then be relatively similar to the one currently proposed for angiosperms. PMID:19641033

  6. Cavitation erosion mechanism of titanium alloy radiation rods in aluminum melt.

    PubMed

    Dong, Fang; Li, Xiaoqian; Zhang, Lihua; Ma, Liyong; Li, Ruiqing

    2016-07-01

    Ultrasound radiation rods play a key role in introducing ultrasonic to the grain refinement of large-size cast aluminum ingots (with diameter over 800 mm), but the severe cavitation corrosion of radiation rods limit the wide application of ultrasonic in the metallurgy field. In this paper, the cavitation erosion of Ti alloy radiation rod (TARR) in the semi-continuous direct-chill casting of 7050 Al alloy was investigated using a 20 kHz ultrasonic vibrator. The macro/micro characterization of Ti alloy was performed using an optical digital microscopy and a scanning electron microscopy, respectively. The results indicated that the cavitation erosion and the chemical reaction play different roles throughout different corrosion periods. Meanwhile, the relationship between mass-loss and time during cavitation erosion was measured and analyzed. According to the rate of mass-loss to time, the whole cavitation erosion process was divided into four individual periods and the mechanism in each period was studied accordingly. Copyright © 2015 Elsevier B.V. All rights reserved.

  7. Mechanism of low-threshold hypersonic cavitation stimulated by broadband laser pump.

    PubMed

    Bunkin, N F; Lobeyev, A V; Lyakhov, G A; Ninham, B W

    1999-08-01

    A low threshold acoustic cavitation regime was observed for the excitation of hypersonic waves due to a stimulated Brillouin scattering (SBS) mechanism, when the optical pump lies within the uv frequency range. Cavitation occurs if the optical pump bandwidth Delta(+)>Omega(0), where Omega(0) is the Stokes frequency shift (the hypersonic frequency). In the opposite case (Delta(+)cavitation does not occur despite the fact that the hypersonic wave intensity is much higher. The effect is associated with the stimulation of a broad frequency spectrum of hypersonic pressure in a field provided by the broadband optical pump. In contrast, for a monochromatic optical pump, the hypersonic wave is of single-frequency character. Induction of cavitation at the low intensities of acoustic pressure is attributed to nanobubbles of fixed size that occur in the liquid. The resonant frequency of the nanobubbles coincides with the frequency of some spectral component of hypersound present in the broadband SBS process. That conclusion is reinforced by the further observation that at the same intensity of broadband pumping the cavitation vanishes after degassing the liquid. In parallel experiments on four-photon polarization Rayleigh wing spectroscopy, it was also demonstrated that spectral lines exist in ordinary (not degassed) water, which can be ascribed to resonances of radial vibrations of nanobubbles. Those lines are absent in the degassed water spectrum.

  8. Mechanism of low-threshold hypersonic cavitation stimulated by broadband laser pump

    NASA Astrophysics Data System (ADS)

    Bunkin, N. F.; Lobeyev, A. V.; Lyakhov, G. A.; Ninham, B. W.

    1999-08-01

    A low threshold acoustic cavitation regime was observed for the excitation of hypersonic waves due to a stimulated Brillouin scattering (SBS) mechanism, when the optical pump lies within the uv frequency range. Cavitation occurs if the optical pump bandwidth Δ+>>Ω0, where Ω0 is the Stokes frequency shift (the hypersonic frequency). In the opposite case (Δ+<<Ω0), cavitation does not occur despite the fact that the hypersonic wave intensity is much higher. The effect is associated with the stimulation of a broad frequency spectrum of hypersonic pressure in a field provided by the broadband optical pump. In contrast, for a monochromatic optical pump, the hypersonic wave is of single-frequency character. Induction of cavitation at the low intensities of acoustic pressure is attributed to nanobubbles of fixed size that occur in the liquid. The resonant frequency of the nanobubbles coincides with the frequency of some spectral component of hypersound present in the broadband SBS process. That conclusion is reinforced by the further observation that at the same intensity of broadband pumping the cavitation vanishes after degassing the liquid. In parallel experiments on four-photon polarization Rayleigh wing spectroscopy, it was also demonstrated that spectral lines exist in ordinary (not degassed) water, which can be ascribed to resonances of radial vibrations of nanobubbles. Those lines are absent in the degassed water spectrum.

  9. The mechanism of erosion of metallic materials under cavitation attack

    NASA Technical Reports Server (NTRS)

    Rao, B. C. S.; Buckley, D. H.

    1985-01-01

    The mean depth of penetration rates (MDPRs) of eight polycrystalline metallic materials, Al 6061-T6, Cu, brass, phosphor bronze, Ni, Fe, Mo, and Ti-5Al-2.5Sn exposed to cavitation attack in a viscous mineral oil with a 20 kHz ultrasonic oscillator vibrating at 50 micron amplitude are reported. The titanium alloy followed by molybdenum have large incubation periods and small MDPRs. The incubation periods correlate linearly with the inverse of hardness and the average MDPRs correlate linearly with the inverse of tensile strength of materials. The linear relationships yield better statistical parameters than geometric and exponential relationships. The surface roughness and the ratio of pit depth to pit width (h/a) increase with the duration of cavitation attack. The ratio h/a varies from 0.1 to 0.8 for different materials. Recent investigations (20) using scanning electron microscopy to study deformation and pit formation features are briefly reviewed. Investigations with single crystals indicate that the geometry of pits and erosion are dependent on their orientation.

  10. Histotripsy-Induced Cavitation Cloud Initiation Thresholds in Tissues of Different Mechanical Properties

    PubMed Central

    Vlaisavljevich, Eli; Maxwell, Adam; Warnez, Matthew; Johnsen, Eric; Cain, Charles A.; Xu, Zhen

    2014-01-01

    Histotripsy is an ultrasound ablation method that depends on the initiation and maintenance of a cavitation bubble cloud to fractionate soft tissue. This paper studies how tissue properties impact the pressure threshold to initiate the cavitation bubble cloud. Our previous study showed that shock scattering off one or more initial bubbles, expanded to sufficient size in the focus, plays an important role in initiating a dense cavitation cloud. In this process, the shock scattering causes the positive pressure phase to be inverted, resulting in a scattered wave that has the opposite polarity of the incident shock. The inverted shock is superimposed on the incident negative pressure phase to form extremely high negative pressures, resulting in a dense cavitation cloud growing toward the transducer. We hypothesize that increased tissue stiffness impedes the expansion of initial bubbles, reducing the scattered tensile pressure, and thus requiring higher initial intensities for cloud initiation. To test this hypothesis, 5-cycle histotripsy pulses at pulse repetition frequencies (PRFs) of 10, 100, or 1000 Hz were applied by a 1-MHz transducer focused inside mechanically tunable tissue-mimicking agarose phantoms and various ex vivo porcine tissues covering a range of Young’s moduli. The threshold to initiate a cavitation cloud and resulting bubble expansion were recorded using acoustic backscatter detection and optical imaging. In both phantoms and ex vivo tissue, results demonstrated a higher cavitation cloud initiation threshold for tissues of higher Young’s modulus. Results also demonstrated a decrease in bubble expansion in phantoms of higher Young’s modulus. These results support our hypothesis, improve our understanding of the effect of histotripsy in tissues with different mechanical properties, and provide a rational basis to tailor acoustic parameters for fractionation of specific tissues. PMID:24474139

  11. Detection of acoustic cavitation in the heart with microbubble contrast agents in vivo: a mechanism for ultrasound-induced arrhythmias.

    PubMed

    Rota, Claudio; Raeman, Carol H; Child, Sally Z; Dalecki, Diane

    2006-11-01

    Ultrasound fields can produce premature cardiac contractions under appropriate exposure conditions. The pressure threshold for ultrasound-induced premature contractions is significantly lowered when microbubble contrast agents are present in the vasculature. The objective of this study was to measure directly ultrasound-induced cavitation in the murine heart in vivo and correlate the occurrence of cavitation with the production of premature cardiac contractions. A passive cavitation detection technique was used to quantify cavitation activity in the heart. Experiments were performed with anesthetized, adult mice given intravenous injections of either a contrast agent (Optison) or saline. Murine hearts were exposed to ultrasound pulses (200 kHz, 1 ms, 0.1-0.25 MPa). Premature beats were produced in mice injected with Optison and the likelihood of producing a premature beat increased with increasing pressure amplitude. Similarly, cavitation was detected in mice injected with Optison and the amplitude of the passive cavitation detector signal increased with increasing exposure amplitude. Furthermore, there was a direct correlation between the extent of cavitation and the likelihood of ultrasound producing a premature beat. Neither premature beats nor cavitation activity were observed in animals injected with saline and exposed to ultrasound. These results are consistent with acoustic cavitation as a mechanism for this bioeffect.

  12. Statistical correlation between transient pressure drop and cavitation at closure of a mechanical heart valve.

    PubMed

    Wu, Changfu; Liu, Jia-Shing; Hwang, Ned H C; Lin, Yu-Kweng M

    2005-01-01

    Cavitation on a mechanical heart valve (MHV) is attributable to transient regional pressure drop at the instant of valve closure. As a cavitation bubble collapses, it emits shock waves, which have the characteristics of high frequency oscillations (HFO) on a pressure time trace. The potential for such HFO bursts to cause material damage on an MHV can be measured by the cavitation impulse I, which is defined as the area under the trace of the HFO bursts. In the present study, experiments were conducted on a bileaflet MHV in a durability tester, operated at pulse rates from 300-1,000 bpm. In each case, the transient pressure near an occluder was monitored for 60,000 beats via a transducer. The peak pressure drop Pm and the corresponding cavitation impulse I obtained for the 60,000 beat sequence are found to resemble sample records of two stationary stochastic processes, each of which follows a log normal distribution. Their first order probability density functions are estimated from the records. The correlation is investigated between I and Pm associated with each beat, which is found to be of statistical significance.

  13. Observation and quantification of cavitation on a mechanical heart valve with an electro-hydraulic total artificial heart.

    PubMed

    Lee, H; Taenaka, Y

    2006-03-01

    In previous studies, we investigated the cavitation phenomenon in a mechanical heart valve using an electro-hydraulic total artificial heart. With this system, a 50% glycerin solution kept at 37 degrees C was used as the working fluid. We reported that most of the cavitation bubbles were observed near the valve stop and were caused by the squeeze flow. However, in these studies, the effect of the partial pressure of CO(2) on the mechanical heart valve cavitation was neglected. In this study, in order to investigate the effect of the partial pressure of CO(2) on mechanical heart valve cavitation using an electro-hydraulic total artificial heart, we controlled the partial pressure of the CO(2) in vitro. A 25-mm Medtronic Hall valve was installed in the mitral position of an electro-hydraulic total artificial heart. In order to quantify the mechanical heart valve cavitation, we used a high-speed camera. Even though cavitation intensity slightly increased with increases in the PCO(2) at heart rates of 60, 70 and 100 bpm, throughout the experiment, there was no significant difference between the PCO(2) and cavitation intensity.

  14. Histotripsy in focused ultrasound surgery: Mechanical ablation of tissue using controlled acoustic cavitation

    NASA Astrophysics Data System (ADS)

    Parsons, Jessica Erin

    This research has investigated non-invasive tissue ablation techniques in ultrasonic surgery that are mediated primarily by the mechanical effects of controlled acoustic cavitation, thereby de-emphasizing the role of thermal coagulation during treatment of diseased tissues. This approach is referred to as "histotripsy," in which soft tissues are broken apart by mechanical agitation, in analogy to established lithotripsy procedures whereby renal stones are similarly comminuted. During histotripsy, cavitation microbubbles are formed endogenously in the treatment volume due to the intense rarefactional pressures (> 20 MPa) incurred. The actions of these microbubbles can impart severe yet highly localized mechanical damage to surrounding cellular architecture. The primary goal of this research was to investigate acoustic methods to control these powerful cavitation effects in order to produce therapeutic soft tissue lesions with minimal thermal invasiveness to surrounding collateral structures. Toward this end, an acoustic pulsing scheme was developed to actively sustain cavitation activity through the use of short-duration (e.g., 15 mus), high-intensity (e.g., 40 kW/cm2 ISPPA) pulses delivered at low repetition frequencies (e.g., 0.17 kHz). This approach maintained the microbubble population during treatment without producing significant temperature elevations (e.g., DeltaT = 5°C). Cavitation-mediated damage morphology in porcine myocardium and renal parenchyma consisted of well-circumscribed, 0.5-1 cm3 voids containing homogenized tissue slurry. Standard histological staining revealed extremely fine pulverization that often bisected single cells. This type of damage morphology offers particular advantages over thermal ablation in applications where diseased or impeding tissue must be physically removed, not merely treated and left in situ. In general, the ability to sustain effective cavitation during histotripsy was strongly influenced by acoustic pulse conditions

  15. Intramembrane Cavitation as a Predictive Bio-Piezoelectric Mechanism for Ultrasonic Brain Stimulation

    NASA Astrophysics Data System (ADS)

    Plaksin, Michael; Shoham, Shy; Kimmel, Eitan

    2014-01-01

    Low-intensity ultrasonic waves can remotely and nondestructively excite central nervous system (CNS) neurons. While diverse applications for this effect are already emerging, the biophysical transduction mechanism underlying this excitation remains unclear. Recently, we suggested that ultrasound-induced intramembrane cavitation within the bilayer membrane could underlie the biomechanics of a range of observed acoustic bioeffects. In this paper, we show that, in CNS neurons, ultrasound-induced cavitation of these nanometric bilayer sonophores can induce a complex mechanoelectrical interplay leading to excitation, primarily through the effect of currents induced by membrane capacitance changes. Our model explains the basic features of CNS acoustostimulation and predicts how the experimentally observed efficacy of mouse motor cortical ultrasonic stimulation depends on stimulation parameters. These results support the hypothesis that neuronal intramembrane piezoelectricity underlies ultrasound-induced neurostimulation, and suggest that other interactions between the nervous system and pressure waves or perturbations could be explained by this new mode of biological piezoelectric transduction.

  16. Interaction mechanisms of cavitation bubbles induced by spatially and temporally separated fs-laser pulses.

    PubMed

    Tinne, Nadine; Kaune, Brigitte; Krüger, Alexander; Ripken, Tammo

    2014-01-01

    The emerging use of femtosecond lasers with high repetition rates in the MHz regime together with limited scan speed implies possible mutual optical and dynamical interaction effects of the individual cutting spots. In order to get more insight into the dynamics a time-resolved photographic analysis of the interaction of cavitation bubbles is presented. Particularly, we investigated the influence of fs-laser pulses and their resulting bubble dynamics with various spatial as well as temporal separations. Different time courses of characteristic interaction effects between the cavitation bubbles were observed depending on pulse energy and spatio-temporal pulse separation. These ranged from merely no interaction to the phenomena of strong water jet formation. Afterwards, the mechanisms are discussed regarding their impact on the medical application of effective tissue cutting lateral to the laser beam direction with best possible axial precision: the mechanical forces of photodisruption as well as the occurring water jet should have low axial extend and a preferably lateral priority. Furthermore, the overall efficiency of energy conversion into controlled mechanical impact should be maximized compared to the transmitted pulse energy and unwanted long range mechanical side effects, e.g. shock waves, axial jet components. In conclusion, these experimental results are of great importance for the prospective optimization of the ophthalmic surgical process with high-repetition rate fs-lasers.

  17. Interaction Mechanisms of Cavitation Bubbles Induced by Spatially and Temporally Separated fs-Laser Pulses

    PubMed Central

    Tinne, Nadine; Kaune, Brigitte; Krüger, Alexander; Ripken, Tammo

    2014-01-01

    The emerging use of femtosecond lasers with high repetition rates in the MHz regime together with limited scan speed implies possible mutual optical and dynamical interaction effects of the individual cutting spots. In order to get more insight into the dynamics a time-resolved photographic analysis of the interaction of cavitation bubbles is presented. Particularly, we investigated the influence of fs-laser pulses and their resulting bubble dynamics with various spatial as well as temporal separations. Different time courses of characteristic interaction effects between the cavitation bubbles were observed depending on pulse energy and spatio-temporal pulse separation. These ranged from merely no interaction to the phenomena of strong water jet formation. Afterwards, the mechanisms are discussed regarding their impact on the medical application of effective tissue cutting lateral to the laser beam direction with best possible axial precision: the mechanical forces of photodisruption as well as the occurring water jet should have low axial extend and a preferably lateral priority. Furthermore, the overall efficiency of energy conversion into controlled mechanical impact should be maximized compared to the transmitted pulse energy and unwanted long range mechanical side effects, e.g. shock waves, axial jet components. In conclusion, these experimental results are of great importance for the prospective optimization of the ophthalmic surgical process with high-repetition rate fs-lasers. PMID:25502697

  18. Extracorporeal shock waves stimulate frog sciatic nerves indirectly via a cavitation-mediated mechanism.

    PubMed Central

    Schelling, G.; Delius, M.; Gschwender, M.; Grafe, P.; Gambihler, S.

    1994-01-01

    Shock waves (SWs) are single pressure pulses with amplitudes up to over 100 MPa, a rise time of only a few nanoseconds, and a short duration of approximately 2 microseconds. Their clinical application for stone destruction causes pain, indicating nerve stimulation by SWs. To examine this phenomenon, sciatic nerves of frogs were exposed to SWs in an organ bath. The SWs were generated with an experimental Dornier lithotripter model XL1 at an operating voltage of 15 kV. The nerves were mounted in a chamber which allowed electrical nerve stimulation and the registration of electrically and SW-induced compound action potentials (SWCAPs). The chamber was filled with frog Ringer's solution. In a standardized protocol. The first experiment established that 95.0 +/- 4.7% of administered SWs induced action potentials which were lower in amplitude (1.45 +/- 1.14 versus 1.95 +/- 0.95 mV, p = 0.004) but similar in shape to electrically induced compound action potentials. In a second experiment, it was shown that the site of origin of the SWCAPs could be correctly determined by simultaneous recording of action potentials at both ends of the nerve. The mechanism of shock wave stimulation was examined by experiments 3 and 4. In experiment 3, in contrast to the previous experiments, SW exposure of the nerves was performed 6 cm outside the shock wave focus. This resulted in a mean probability of inducing a SWCAP of only 4%. After gas bubble administration, this probability increased to 86% for the first SW released immediately after bubble application and declined to 56% for the second, 21% for the third, to 0 for the 10th SW after fluid injection. This indicates that cavitation, the interaction between shock waves and gas bubbles in fluid or tissues, was involved in SWCAP generation. In experiment 4, nerves were again exposed in the focus, however, the Ringer's solution surrounding the nerve was replaced by polyvinyl alcohol (PVA). PVA is a solution with low cavitation activity

  19. Modelling the mechanical behaviour of pit membranes in bordered pits with respect to cavitation resistance in angiosperms.

    PubMed

    Tixier, Aude; Herbette, Stephane; Jansen, Steven; Capron, Marie; Tordjeman, Philippe; Cochard, Hervé; Badel, Eric

    2014-08-01

    Various correlations have been identified between anatomical features of bordered pits in angiosperm xylem and vulnerability to cavitation, suggesting that the mechanical behaviour of the pits may play a role. Theoretical modelling of the membrane behaviour has been undertaken, but it requires input of parameters at the nanoscale level. However, to date, no experimental data have indicated clearly that pit membranes experience strain at high levels during cavitation events. Transmission electron microscopy (TEM) was used in order to quantify the pit micromorphology of four tree species that show contrasting differences in vulnerability to cavitation, namely Sorbus aria, Carpinus betulus, Fagus sylvatica and Populus tremula. This allowed anatomical characters to be included in a mechanical model that was based on the Kirchhoff-Love thin plate theory. A mechanistic model was developed that included the geometric features of the pits that could be measured, with the purpose of evaluating the pit membrane strain that results from a pressure difference being applied across the membrane. This approach allowed an assessment to be made of the impact of the geometry of a pit on its mechanical behaviour, and provided an estimate of the impact on air-seeding resistance. The TEM observations showed evidence of residual strains on the pit membranes, thus demonstrating that this membrane may experience a large degree of strain during cavitation. The mechanical modelling revealed the interspecific variability of the strains experienced by the pit membrane, which varied according to the pit geometry and the pressure experienced. The modelling output combined with the TEM observations suggests that cavitation occurs after the pit membrane has been deflected against the pit border. Interspecific variability of the strains experienced was correlated with vulnerability to cavitation. Assuming that air-seeding occurs at a given pit membrane strain, the pressure predicted by the model

  20. Cavitation bioeffects.

    PubMed

    Kimmel, Eitan

    2006-01-01

    Acoustic cavitation takes place when tiny gas bubbles oscillate, grow, and collapse in liquid under the influence of ultrasonic field. This study reviews cavitation bioeffects that are found both in vivo and in vitro when exposed to either low- or high-power acoustics. Proposed mechanisms are discussed here as well based on theoretical studies, simulations and test bench experiments. Bioeffects are induced in living tissue once the gas bubble is, for instance, within a blood vessel in close vicinity to the endothelium or to the red blood cells. Conditions for inducing various bioeffects are discussed - from severe damage, such as cell necrosis, to delicate alterations, such as increased permeability of cell membrane. Present and potential applications for therapeutic purpose from stone pulverization and tissue ablation to gene transfection and transdermal delivery are reviewed including the growing use of artificial microbubbles.

  1. Effects of Laser Shock Processing on Morphologies and Mechanical Properties of ANSI 304 Stainless Steel Weldments Subjected to Cavitation Erosion

    PubMed Central

    Zhang, Lei; Lu, Jin-Zhong; Zhang, Yong-Kang; Ma, Hai-Le; Luo, Kai-Yu; Dai, Feng-Ze

    2017-01-01

    Effects of laser shock processing (LSP) on the cavitation erosion resistance of laser weldments were investigated by optical microscope (OM), scanning electron microscope (SEM) observations, roughness tester, micro hardness tester, and X-ray diffraction (XRD) technology. The morphological microstructures were characterized. Cumulative mass loss, incubation period, erosion rate, and damaged surface areas were monitored during cavitation erosion. Surface roughness, micro-hardness, and residual stress were measured in different zones. Results showed that LSP could improve the damage of morphological microstructures and mechanical properties after cavitation erosion. The compressive residual stresses were generated during the process of LSP, which was an effective guarantee for the improvement of the above mentioned properties. PMID:28772652

  2. Intramembrane cavitation as a unifying mechanism for ultrasound-induced bioeffects.

    PubMed

    Krasovitski, Boris; Frenkel, Victor; Shoham, Shy; Kimmel, Eitan

    2011-02-22

    The purpose of this study was to develop a unified model capable of explaining the mechanisms of interaction of ultrasound and biological tissue at both the diagnostic nonthermal, noncavitational (<100 mW · cm(-2)) and therapeutic, potentially cavitational (>100 mW · cm(-2)) spatial peak temporal average intensity levels. The cellular-level model (termed "bilayer sonophore") combines the physics of bubble dynamics with cell biomechanics to determine the dynamic behavior of the two lipid bilayer membrane leaflets. The existence of such a unified model could potentially pave the way to a number of controlled ultrasound-assisted applications, including CNS modulation and blood-brain barrier permeabilization. The model predicts that the cellular membrane is intrinsically capable of absorbing mechanical energy from the ultrasound field and transforming it into expansions and contractions of the intramembrane space. It further predicts that the maximum area strain is proportional to the acoustic pressure amplitude and inversely proportional to the square root of the frequency (ε A,max ∝ P(A)(0.8f - 0.5) and is intensified by proximity to free surfaces, the presence of nearby microbubbles in free medium, and the flexibility of the surrounding tissue. Model predictions were experimentally supported using transmission electron microscopy (TEM) of multilayered live-cell goldfish epidermis exposed in vivo to continuous wave (CW) ultrasound at cavitational (1 MHz) and noncavitational (3 MHz) conditions. Our results support the hypothesis that ultrasonically induced bilayer membrane motion, which does not require preexistence of air voids in the tissue, may account for a variety of bioeffects and could elucidate mechanisms of ultrasound interaction with biological tissue that are currently not fully understood.

  3. Correlation between cavitation erosion resistance and cyclic mechanical properties of different metallic materials

    NASA Astrophysics Data System (ADS)

    Kaufhold, Corinna; Pöhl, Fabian; Theisen, Werner

    2017-05-01

    Machine components in contact with flowing fluids are especially prone to cavitation erosion, where plastic deformation and material loss occur due to the repeated implosion of cavitation bubbles in the vicinity of a solid surface. Identifying a correlation between experimentally derivable material properties and resistance against cavitation erosion could help improve the lifetime of cavitation-affected components. Cavitation erosion is a predominantly fatigue-driven phenomenon. In this investigation, we conducted nanoindentation experiments to examine cyclic micromechanical material properties in response to an increasing number of cycles. The experiments were performed on pure iron and different steel grades, i.e., austenitic stainless CrMnCN steels, interstitially alloyed with carbon and nitrogen. We confirmed the view, also proposed in literature, that indentation hardness is inappropriate for ordering the investigated materials by incubation period or maximum erosion rate. We found that the percentage increase of nanoindentation contact stiffness, after an increasing number of cycles, is a promising indicator in terms of the overall ranking of cavitation erosion resistance among the considered materials. Although a single cavitation impact is associated with a significantly higher strain rate than nanoindentation experiments, it is shown that the plastically deformed area around each indent exhibits indications of deformation, such as the formation of slip lines that are also observable after cavitation-induced impacts.

  4. Cavitation distribution within large phantom vessel and mechanical damage formed on surrounding vessel wall.

    PubMed

    Qiao, Yangzi; Yin, Hui; Li, Zhaopeng; Wan, Mingxi

    2013-11-01

    Blood vessel is one of the most important targets encountered during focused ultrasound (FU) therapy. The lasting high temperature caused by continuous FU can result in structural modification of small vessel. For the vessel with a diameter larger than 2mm, convective cooling can significantly weaken the thermal effect of FU. Meanwhile, the continued presence of ultrasound will cause repetitive cavitation and acoustic microstreaming, making comprehension of continuous wave induced cavitation effect in large vessels necessary. The Sonoluminescence (SL) method, mechanical damage observation and high-speed camera were used in this study to investigate the combination effect of ultrasound contrast agents (UCAs) and continuous FU in large phantom vessels with a diameter of 10mm without consideration of thermal effect. When the focus was positioned at the proximal wall, cylindrical hole along the acoustic axis opposite the ultrasound wave propagation direction was observed at the input power equal to or greater than 50 W. When the focus was located at the distal wall, only small tunnels can be found. The place where the cylindrical hole formed was corresponding to where bubbles gathered and emitted brilliant light near the wall. Without UCAs neither such bright SL nor cylindrical hole can be found. However, the UCAs concentration had little influence on the SL distribution and the length of cylindrical hole. The SL intensity near the proximal vessel wall and the length of the cylindrical hole both increased with the input power. It is suggested that these findings need to be considered in the large vessel therapy and UCAs usage.

  5. Acoustic cavitation as an enhancing mechanism of low-frequency sonophoresis for transdermal drug delivery.

    PubMed

    Ueda, Hideo; Mutoh, Mizue; Seki, Toshinobu; Kobayashi, Daisuke; Morimoto, Yasunori

    2009-05-01

    We investigated the role of acoustic cavitation on sonophoretic skin permeation of calcein, a model permeant, across excised hairless rat skin. Three different frequencies (41, 158, 445 kHz) and various intensities (60 to 300 mW/cm(2)) of ultrasound were applied. Cavitation generation in degassed and undegassed (normal) water was monitored using a commercially available cavitation meter, then compared with skin permeability from calcein solution consistent of them. In addition, the penetration of a fluorescent dye, rhodamine B, into gelatin gel as a skin alternative was observed to estimate the role of cavitation collapse in the solution at or near the skin surface. Cavitation generation in the undegassed water was dependent on the ultrasound frequency, and the rank order of the cavitation was 41 kHz>158 kHz>445 kHz. At 41 kHz, cavitation generation in degassed water was clearly lower than that in undegassed water. Calcein permeability during ultrasound application correlated well with the cavitation generation in the medium, suggesting the important role of the indirect actions of cavitation collapse which occurred in the applied solution rather than the direct action in the skin. When ultrasound (41 or 158 kHz) was applied to the gelatin gels covered with rhodamine B solution, alteration in the surface configuration, like spots, and the coincident penetration of the dye were observed only at 41 kHz, while no alteration in the surface configuration was evident at 158 kHz. These results suggest that cavitation collapses in the vicinity of the skin surface might be more important for solute penetration in addition to skin permeabilization.

  6. Characterizing cryogenic propellant flow behavior through a cavitating venturi in comparison to alternative flow control mechanisms

    NASA Astrophysics Data System (ADS)

    Ingle, Marjorie Adele

    The work detailed is an investigation of the use of a cavitating venturi as both a flow control and metering device. This was achieved through the combination of actual experimentation and numerical modeling of the fluid behavior of both liquid water and liquid methane as it passes through the test article designed, developed, and validated here within this study. The discharge coefficient of the cavitating venturi was determined through weigh flow calibration testing to determine an average mass flow rate. Turbine flow meter flow rate readings were used as a point of comparison and the discharge coefficient was computed. The discharge coefficient was then implemented into the Bernoulli Equation along with experimental pressure and temperature data to again calculate mass flow rate through the cavitating venturi. The agreement of the venturi flow rate data to that of the turbine flow meter effectively established its applicability as a passive flow control and metering feature. A preliminary CFD cavitation model was developed and validated for cavitating water flow regimes using ANSYS FLUENT. Agreement between mass flow rates obtained from the model to experimental data for cavitating water flow indicates that deviations in results for liquid methane analysis from experimental results could simply be the result of insufficiently defined fluid characteristics in the ANSYS FLUENT materials database. SEM surface roughness analysis of a secondary test article indicated that the default average surface roughness for steel in ANSYS FLUENT was reasonable. In addition, the methodology could be further applied to future duty life studies for the cavitating venturi flow meter.

  7. Cavitation as a Mechanism to Enhance Wetting in a Mercury Thermal Convection Loop

    SciTech Connect

    Pawel, SJ

    2001-07-17

    Type 316L stainless steel was statically tested under cavitation conditions via an ultrasonic transducer externally mounted on a tube filled with ambient mercury. During the preliminary exposure (24 h, 20 kHz, 1.5 MPa), cavitation resulted in apparent wetting of the specimens by mercury as well as general surface roughening and wastage similar to erosion damage. Subsequently, a thermal convection loop identical to those used previously to study thermal gradient mass transfer was modified to include an externally-mounted donut-shaped transducer in order to similarly produce cavitation and wetting at temperatures prototypic of those expected in the SNS target. However, a series of attempts to develop cavitation and wetting on 316L specimens in the thermal convection loop was unsuccessful.

  8. Mechanism of water-stress induced cavitation in conifers: bordered pit structure and function support the hypothesis of seal capillary-seeding

    PubMed Central

    DELZON, SYLVAIN; DOUTHE, CYRIL; SALA, ANNA; COCHARD, HERVE

    2010-01-01

    Resistance to water-stress induced cavitation is an important indicator of drought tolerance in woody species and is known to be intimately linked to the anatomy of the xylem. However, the actual mechanical properties of the pit membrane are not well known and the exact mode of air-seeding by which cavitation occurs is still uncertain. We examined the relationship between cavitation resistance and bordered pit structure and function in 40 coniferous species. Xylem pressure inducing 50% loss of hydraulic conductance (P50, a proxy for cavitation resistance) varied widely among species, from −2.9 to −11.3 MPa. The valve effect of the pit membrane, measured as a function of margo flexibility and torus overlap, explained more variation in cavitation-resistance than simple anatomical traits such as pit membrane, pit aperture or torus size. Highly cavitation resistant species exhibited both a high flexibility of the margo and a large overlap between the torus and the pit aperture, allowing the torus to tightly seal the pit aperture. Our results support the hypothesis of seal capillary-seeding as the most likely mode of air-seeding, and suggest that the adhesion of the torus to the pit border may be the main determinant of cavitation resistance in conifers. PMID:20636490

  9. An investigation of cavitation in a mechanically alloyed 15 vol % SiCp/IN9021 aluminum composite

    SciTech Connect

    Higashi, K.; Okada, T.; Mukai, T.; Tanimura, S.; Nieh, T.G.; Wadsworth, J.

    1993-07-01

    A mechanically alloyed 15 vol % SiCp/IN9021 aluminum composite exhibited a maximum elongation of 610 % at a very high strain of 5 s{sup {minus}1} at 823 K. Nonetheless, the maximum elongation was obtained at a lower strain rate than that where the maximum m value (about 0.5) was obtained. This discrepancy between the optimum superplastic strain rate for the largest elongation and the strain rate for the maximum m value was believed to be associated with the cavitation behavior. Cavitation behavior of the SiCp/IN9021 aluminum composite was, therefore, carried out. It was found that cavities initiated at ends of particulate reinforcements and parallel to the applied stress direction within initial small strains, and their subsequent growth and coalescence invariably leads to premature failure. Experimental results indicated that cavity growth is plasticity controlled and can be described by a model proposed by Stowell.

  10. Cavitation During Superplastic Forming

    PubMed Central

    Campbell, John

    2011-01-01

    Cavitation is the opening of pores during superplastic forming, typically at grain boundary triple points or on second phase grain boundary particles during slip of grain boundaries. Theories for the initiation of cavitation are reviewed. It seems that cavitation is unlikely to occur by processes intrinsic to metals such as dislocation mechanisms or point defect condensation. It is proposed that cavitation can only occur at non-bonded interfaces such as those introduced extrinsically (i.e., from the outside) during the original casting of the metal. These defects, known as oxide bifilms, are naturally introduced during pouring of the liquid metal, and are frozen into the solid, often pushed by dendritic growth into grain boundaries where they are difficult to detect because of their extreme thinness, often measured in nanometres. Their unbonded central interface acts as a crack and can initiate cavitation. Second phase precipitates probably do not nucleate and grow on grain boundaries but grow on bifilms in the boundaries, explaining the apparent association between boundaries, second phase particles and failure initiation. Improved melting and casting techniques can provide metal with reduced or zero bifilm population for which cavitation would not be possible, promising significant improvements in superplastic behaviour. PMID:28824142

  11. Experimental Investigation of Cavitation as a Possible Damage Mechanism in Blast-Induced Traumatic Brain Injury in Post-Mortem Human Subject Heads.

    PubMed

    Salzar, Robert S; Treichler, Derrick; Wardlaw, Andrew; Weiss, Greg; Goeller, Jacques

    2017-01-13

    The potential of blast-induced traumatic brain injury from the mechanism of localized cavitation of the cerebrospinal fluid (CSF) is investigated. While the mechanism and criteria for non-impact blast-induced traumatic brain injury is still unknown, this study demonstrates that local cavitation in the CSF layer of the cranial volume could contribute to these injuries. The cranial contents of three post-mortem human subject (PMHS) heads were replaced with both a normal saline solution and a ballistic gel mixture with a simulated CSF layer. Each were instrumented with multiple pressure transducers and placed inside identical shock tubes at two different research facilities. Sensor data indicates that cavitation may have occurred in the PMHS models at pressure levels below those for a 50% risk of blast lung injury. This study points to skull flexion, the result of the shock wave on the front of the skull leading to a negative pressure in the contrecoup, as a possible mechanism that contributes to the onset of cavitation. Based on observation of intracranial pressure transducer data from the PMHS model, cavitation onset is thought to occur from approximately a 140 kPa head-on incident blast.

  12. Memory Effect and Redistribution of Cavitation Nuclei

    NASA Astrophysics Data System (ADS)

    Lixin, Bai; Weijun, Lin; Jingjun, Deng; Chao, Li; Delong, Xu; Pengfei, Wu

    Temporal evolution and spatial distribution of acoustic cavitation structures (evolving complicated patterns with clear boundary) in a very thin liquid layer were investigated experimentally with high-speed photography. The inception and disappearance processes of cavitation bubble cloud are revealed that the metastable cavitaton structures formed in the thin liquid layer cause a long-term "memory effect". The mechanism and effect factors of memory effect are analysed. The redistribution of cavitation nuclei was investigated by changing the temporal decay of the memory effect. The thin-liquid-layer-cavitation method is useful for the investigation of cavitation nuclei because of the two-dimensional nature of thin liquid layer.

  13. Dynamics and mechanism of cavitation erosion on perspex and epoxy resins tested in a rotating disk device

    NASA Technical Reports Server (NTRS)

    Rao, P. V.; Rao, N. S. L.; Rao, B. C. S.

    1982-01-01

    The cavitation erosion behavior including the initiation, dynamics and mechanism of damage process on perspex and epoxy resin specimens tested in a rotating disk device were discussed with respect to exposure time. The inception of erosion always took place at the location nearest to the center of rotation of the disk. Subsequently, as exposure time increased, erosion initiated at other locations as well. Light optical photographs and scanning electron micrographs clearly indicate that most of the material loss appears to occur form the networks of cracks due to their interaction and pits indicate particle debris. The optical degradation (loss of transmittance) on perspex was observed to be more on the rear side than on the front side.

  14. Focused Ultrasound-Induced Blood-Brain Barrier Opening: Association with Mechanical Index and Cavitation Index Analyzed by Dynamic Contrast-Enhanced Magnetic-Resonance Imaging

    PubMed Central

    Chu, Po-Chun; Chai, Wen-Yen; Tsai, Chih-Hung; Kang, Shih-Tsung; Yeh, Chih-Kuang; Liu, Hao-Li

    2016-01-01

    Focused ultrasound (FUS) with microbubbles can temporally open the blood-brain barrier (BBB), and the cavitation activities of microbubbles play a key role in the BBB-opening process. Previous attempts used contrast-enhanced magnetic resonance imaging (CE-MRI) to correlate the mechanical index (MI) with the scale of BBB-opening, but MI only partially gauged acoustic activities, and CE-MRI did not fully explore correlations of pharmacodynamic/pharmacokinetic behaviors. Recently, the cavitation index (CI) has been derived to serve as an indicator of microbubble-ultrasound stable cavitation, and may also serve as a valid indicator to gauge the level of FUS-induced BBB opening. This study investigates the feasibility of gauging FUS-induced BBB opened level via the two indexes, MI and CI, through dynamic contrast-enhanced (DCE)-MRI analysis as well as passive cavitation detection (PCD) analysis. Pharmacodynamic/pharmacokinetic parameters derived from DCE-MRI were characterized to identify the scale of FUS-induced BBB opening. Our results demonstrated that DCE-MRI can successfully access pharmacodynamic/pharmacokinetic BBB-opened behavior, and was highly correlated both with MI and CI, implying the feasibility in using these two indices to gauge the scale of FUS-induced BBB opening. The proposed finding may facilitate the design toward using focused ultrasound as a safe and reliable noninvasive CNS drug delivery. PMID:27630037

  15. Focused Ultrasound-Induced Blood-Brain Barrier Opening: Association with Mechanical Index and Cavitation Index Analyzed by Dynamic Contrast-Enhanced Magnetic-Resonance Imaging

    NASA Astrophysics Data System (ADS)

    Chu, Po-Chun; Chai, Wen-Yen; Tsai, Chih-Hung; Kang, Shih-Tsung; Yeh, Chih-Kuang; Liu, Hao-Li

    2016-09-01

    Focused ultrasound (FUS) with microbubbles can temporally open the blood-brain barrier (BBB), and the cavitation activities of microbubbles play a key role in the BBB-opening process. Previous attempts used contrast-enhanced magnetic resonance imaging (CE-MRI) to correlate the mechanical index (MI) with the scale of BBB-opening, but MI only partially gauged acoustic activities, and CE-MRI did not fully explore correlations of pharmacodynamic/pharmacokinetic behaviors. Recently, the cavitation index (CI) has been derived to serve as an indicator of microbubble-ultrasound stable cavitation, and may also serve as a valid indicator to gauge the level of FUS-induced BBB opening. This study investigates the feasibility of gauging FUS-induced BBB opened level via the two indexes, MI and CI, through dynamic contrast-enhanced (DCE)-MRI analysis as well as passive cavitation detection (PCD) analysis. Pharmacodynamic/pharmacokinetic parameters derived from DCE-MRI were characterized to identify the scale of FUS-induced BBB opening. Our results demonstrated that DCE-MRI can successfully access pharmacodynamic/pharmacokinetic BBB-opened behavior, and was highly correlated both with MI and CI, implying the feasibility in using these two indices to gauge the scale of FUS-induced BBB opening. The proposed finding may facilitate the design toward using focused ultrasound as a safe and reliable noninvasive CNS drug delivery.

  16. Focused Ultrasound-Induced Blood-Brain Barrier Opening: Association with Mechanical Index and Cavitation Index Analyzed by Dynamic Contrast-Enhanced Magnetic-Resonance Imaging.

    PubMed

    Chu, Po-Chun; Chai, Wen-Yen; Tsai, Chih-Hung; Kang, Shih-Tsung; Yeh, Chih-Kuang; Liu, Hao-Li

    2016-09-15

    Focused ultrasound (FUS) with microbubbles can temporally open the blood-brain barrier (BBB), and the cavitation activities of microbubbles play a key role in the BBB-opening process. Previous attempts used contrast-enhanced magnetic resonance imaging (CE-MRI) to correlate the mechanical index (MI) with the scale of BBB-opening, but MI only partially gauged acoustic activities, and CE-MRI did not fully explore correlations of pharmacodynamic/pharmacokinetic behaviors. Recently, the cavitation index (CI) has been derived to serve as an indicator of microbubble-ultrasound stable cavitation, and may also serve as a valid indicator to gauge the level of FUS-induced BBB opening. This study investigates the feasibility of gauging FUS-induced BBB opened level via the two indexes, MI and CI, through dynamic contrast-enhanced (DCE)-MRI analysis as well as passive cavitation detection (PCD) analysis. Pharmacodynamic/pharmacokinetic parameters derived from DCE-MRI were characterized to identify the scale of FUS-induced BBB opening. Our results demonstrated that DCE-MRI can successfully access pharmacodynamic/pharmacokinetic BBB-opened behavior, and was highly correlated both with MI and CI, implying the feasibility in using these two indices to gauge the scale of FUS-induced BBB opening. The proposed finding may facilitate the design toward using focused ultrasound as a safe and reliable noninvasive CNS drug delivery.

  17. Cavitating ultrasound hydrogenation of water-soluble olefins employing inert dopants: Studies of activity, selectivity and reaction mechanisms

    SciTech Connect

    Disselkamp, Robert S.; Chajkowski, Sarah M.; Boyles, Kelly R.; Hart, Todd R.; Peden, Charles HF

    2006-12-07

    Here we discuss results obtained as part of a three-year investigation at Pacific Northwest National Laboratory of ultrasound processing to effect selectivity and activity in the hydrogenation of water-soluble olefins on transition metal catalysts. We have shown previously that of the two regimes for ultrasound processing, high-power cavitating and high-power non-cavitating, only the former can effect product selectivity dramatically (> 1000%) whereas the selectivity of the latter was comparable with those obtained in stirred/silent control experiments [R.S. Disselkamp, Y.-H. Chin, C.H.F. Peden, J. Catal., 227, 552 (2005)]. As a means of ensuring the benefits of cavitating ultrasound processing, we introduced the concept of employing inert dopants into the reacting solution. These inert dopants do not partake in solution chemistry but enable a more facile transition from high-power non-cavitating to cavitating conditions during sonication treatment. With cavitation processing conditions ensured, we discuss here results of isotopic H/D substitution for a variety of substrates and illustrate how such isotope dependent chemistries during substrate hydrogenation elucidate detailed mechanistic information about these reaction systems.

  18. Cavitations Development In a Liquid Behind Strong Acoustic Waves

    NASA Astrophysics Data System (ADS)

    Voronin, D. V.; Teslenko, V. S.

    2008-06-01

    The generation of bubbles behind an acoustic pulse is theoretically and experimentally investigated in the paper. It was found out that at growth of the amplitude of falling wave two different modes of cavitations development occur: "chain" mechanism of duplication of cavitations germs is replaced by mechanism of "real" liquid cavitations, when the liquid is initially filled with a set of cavitations nuclei and apparent bubble occurrence is caused by different periods of nucleus growth from them.

  19. Bacterial Sterilization Using Cavitating Jet

    NASA Astrophysics Data System (ADS)

    Azuma, Yohei; Kato, Hiroharu; Usami, Ron; Fukushima, Tadamasa

    In this paper, a new sterilization method using cavitating flow is presented. Water with bacteria was pressurized up to 105 MPa and flushed out through two very small nozzles 0.1-0.31 mm in diameter, where a cavitating jet was generated containing bubbles that collapsed downstream. First, the effects of jet velocity and cavitation number on the sterilization rate of Escherichia coli JCM1649T (E. coli) were examined. The sterilization rate increased with jet velocity. The rate was proportional to the 3rd power of the velocity. All the E. coli cells were killed by three successive treatments at V=355.7 m/s and cavitation number σ=0.154. The sterilization rate has a peak depending on cavitation number at the low-jet-velocity region of less than 300 m/s. An experiment was also performed to compare two types of bacteria, E. coli, as typical Gram-negative bacteria and Bacillus subtilis JCM1465T (B. subtilis), as typical Gram-positive bacteria. Additional tests were performed using Pseudomonas putida JCM13063T, Gram-negative bacteria and Bacillus halodurans JCTM9153, Gram-positive bacteria. The sterilization rate of the Gram-positive bacteria was much lower than that of the Gram-negative bacteria under the same experimental conditions. Gram-positive bacteria have a thicker peptidoglycan layer than Gram-negative bacteria. This may be the reason why B. subtilis is more resistant to the mechanical stress caused by cavitating flow.

  20. Cavitation resonance in the draft tube of a turbine

    SciTech Connect

    Pei she yi

    1995-12-31

    This paper presents a further analysis of {open_quotes}An Experimental Investigation on The Cavitation Pressure Pulsations in The Draft Tube of A Turbine{close_quotes}. The emphasis is put on the effect of the cavitation resonance. The mechanism of formation and the characteristics of the pressure pulsation of die cavitation resonance are discussed based on the statistical analysis in the paper.

  1. On the mechanism of explosive eruption of mount erebus volcano: the dynamics of the rupture structure in a cavitating layer

    NASA Astrophysics Data System (ADS)

    Bol'shakova, E. S.; Kedrinskiy, V. K.

    2016-10-01

    This paper presents the results of an experimental simulation of rupture development in heavily cavitating magma melt flow in volcanic conduits and its effect on the structure of explosive volcanic eruptions. The dynamics of the state of a layer of distilled water (similar in the density of cavitation nuclei to magma melt) under shock-wave loading was studied. The experiments were performed using electromagnetic hydrodynamic shock tubes (EM HST) with maximum capacitor bank energy of up to 100 J and 5 kJ. It was found that the topology of the rupture formed on the membrane surface did not change during its development. Empirical estimates were obtained for the proportion of the capacitor bank energy expended in the development of the rupture and the characteristic time of its existence. The study revealed a number of fundamentally new physical effects in the cavity dynamics in a cavitating medium: a cavitation “boundary layer” is formed on the surface of the quasi-empty rupture, which is transformed into a cluster of high energy density upon closure of the flow.

  2. Microbubble cavitation imaging.

    PubMed

    Vignon, Francois; Shi, William T; Powers, Jeffry E; Everbach, E Carr; Liu, Jinjin; Gao, Shunji; Xie, Feng; Porter, Thomas R

    2013-04-01

    Ultrasound cavitation of microbubble contrast agents has a potential for therapeutic applications such as sonothrombolysis (STL) in acute ischemic stroke. For safety, efficacy, and reproducibility of treatment, it is critical to evaluate the cavitation state (moderate oscillations, stable cavitation, and inertial cavitation) and activity level in and around a treatment area. Acoustic passive cavitation detectors (PCDs) have been used to this end but do not provide spatial information. This paper presents a prototype of a 2-D cavitation imager capable of producing images of the dominant cavitation state and activity level in a region of interest. Similar to PCDs, the cavitation imaging described here is based on the spectral analysis of the acoustic signal radiated by the cavitating microbubbles: ultraharmonics of the excitation frequency indicate stable cavitation, whereas elevated noise bands indicate inertial cavitation; the absence of both indicates moderate oscillations. The prototype system is a modified commercially available ultrasound scanner with a sector imaging probe. The lateral resolution of the system is 1.5 mm at a focal depth of 3 cm, and the axial resolution is 3 cm for a therapy pulse length of 20 μs. The maximum frame rate of the prototype is 2 Hz. The system has been used for assessing and mapping the relative importance of the different cavitation states of a microbubble contrast agent. In vitro (tissue-mimicking flow phantom) and in vivo (heart, liver, and brain of two swine) results for cavitation states and their changes as a function of acoustic amplitude are presented.

  3. Overview of Rotating Cavitation and Cavitation Surge in the Fastrac Engine LOX Turbopump

    NASA Technical Reports Server (NTRS)

    Zoladz, Thomas; Turner, Jim (Technical Monitor)

    2001-01-01

    Observations regarding rotating cavitation and cavitation surge experienced during the development of the Fastrac 60 Klbf engine turbopump are discussed. Detailed observations from the analysis of both water flow and liquid oxygen test data are offered. Scaling and general comparison of rotating cavitation between water flow and liquid oxygen testing are discussed. Complex data features linking the localized rotating cavitation mechanism of the inducer to system surge components are described in detail. Finally a description of a simple lumped-parameter hydraulic system model developed to better understand observed data is given.

  4. Observations on Rotating Cavitation and Cavitation Surge from the Development of the Fastrac Engine Turbopump

    NASA Technical Reports Server (NTRS)

    Zoladz, Thomas F.

    2000-01-01

    Observations regarding rotating cavitation and cavitation surge experienced during the development of the Fastrac engine turbopump are discussed. Detailed observations acquired from the analysis of both water flow and liquid oxygen test data are offered in this paper. Scaling and general comparison of rotating cavitation between water flow and liquid oxygen testing are discussed. Complex data features linking the localized rotating cavitation mechanism of the inducer to system surge components are described in detail. Finally a description of a lumped-parameter hydraulic system model developed to better understand observed data is given.

  5. Study of cavitating inducer instabilities

    NASA Technical Reports Server (NTRS)

    Young, W. E.; Murphy, R.; Reddecliff, J. M.

    1972-01-01

    An analytic and experimental investigation into the causes and mechanisms of cavitating inducer instabilities was conducted. Hydrofoil cascade tests were performed, during which cavity sizes were measured. The measured data were used, along with inducer data and potential flow predictions, to refine an analysis for the prediction of inducer blade suction surface cavitation cavity volume. Cavity volume predictions were incorporated into a linearized system model, and instability predictions for an inducer water test loop were generated. Inducer tests were conducted and instability predictions correlated favorably with measured instability data.

  6. Observation of cavitation during shock wave lithotripsy

    NASA Astrophysics Data System (ADS)

    Bailey, Michael R.; Crum, Lawrence A.; Pishchalnikov, Yuri A.; McAteer, James A.; Pishchalnikova, Irina V.; Evan, Andrew P.; Sapozhnikov, Oleg A.; Cleveland, Robin O.

    2005-04-01

    A system was built to detect cavitation in pig kidney during shock wave lithotripsy (SWL) with a Dornier HM3 lithotripter. Active detection, using echo on B-mode ultrasound, and passive cavitation detection (PCD), using coincident signals on confocal, orthogonal receivers, were equally sensitive and were used to interrogate the renal collecting system (urine) and the kidney parenchyma (tissue). Cavitation was detected in urine immediately upon SW administration in urine or urine plus X-ray contrast agent, but in tissue, cavitation required hundreds of SWs to initiate. Localization of cavitation was confirmed by fluoroscopy, sonography, and by thermally marking the kidney using the PCD receivers as high intensity focused ultrasound sources. Cavitation collapse times in tissue and native urine were about the same but less than in urine after injection of X-ray contrast agent. Cavitation, especially in the urine space, was observed to evolve from a sparse field to a dense field with strong acoustic collapse emissions to a very dense field that no longer produced detectable collapse. The finding that cavitation occurs in kidney tissue is a critical step toward determining the mechanisms of tissue injury in SWL. [Work sup ported by NIH (DK43881, DK55674, FIRCA), ONRIFO, CRDF and NSBRI SMS00203.

  7. Role of vortices in cavitation formation in the flow at the closure of a bileaflet mitral mechanical heart valve.

    PubMed

    Li, Chi-Pei; Chen, Sheng-Fu; Lo, Chi-Wen; Lu, Po-Chien

    2012-03-01

    Bubble cavitation occurs in the flow field when local pressure drops below vapor pressure. One hypothesis states that low-pressure regions in vortices created by instantaneous valve closure and occluder rebound promote bubble formation. To quantitatively analyze the role of vortices in cavitation, we applied particle image velocimetry (PIV) to reduce the instantaneous fields into plane flow that contains information about vortex core radius, maximum tangential velocity, circulation strength, and pressure drop. Assuming symmetrical flow along the center of the St. Jude Medical 25-mm valve, flow fields downstream of the closing valve were measured using PIV in the mitral position of a circulatory mock loop. Flow measurements were made during successive time phases immediately following the impact of the occluder with the housing (O/H impact) at valve closing. The velocity profile near the vortex core clearly shows a typical Rankine vortex. The vortex strength reaches maximum immediately after closure and rapidly decreases at about 10 ms, indicating viscous dissipation; vortex strength also intensifies with rising pulse rate. The maximum pressure drop at the vortex center is approximately 20 mmHg, an insignificant drop relative to atmospheric vapor pressures, which implies vortices play a minor role in cavitation formation.

  8. Experimental investigation of cavitation behavior in valveless micropumps

    NASA Astrophysics Data System (ADS)

    Chandrasekaran, Arvind; Packirisamy, Muthukumaran

    2012-12-01

    Recently, there have been several reports on the observation of cavitation in microfluidics and in micropumps. Though cavitation is a common occurrence in micropumping, this is one of the least understood of all micropumping phenomena, and very limited progress has been made to study the behavior of cavitation in micropumps. Hence, a dedicated study on cavitation in micropumps and its effects on the performance of the micropump would be very useful. This work presents an experimental study on the behavior of cavitation in valveless micropump. The mechanism of cavitation occurrence in valveless micropumps has been explained by applying macroscale pumping principles to suit micropumping. The different stages of micropump cavitation have been defined through suitably conducted experiments and the results have been presented.

  9. Review on Lithotripsy and Cavitation in Urinary Stone Therapy.

    PubMed

    Ghorbani, Morteza; Oral, Ozlem; Ekici, Sinan; Gozuacik, Devrim; Kosar, Ali

    2016-01-01

    Cavitation is the sudden formation of vapor bubbles or voids in liquid media and occurs after rapid changes in pressure as a consequence of mechanical forces. It is mostly an undesirable phenomenon. Although the elimination of cavitation is a major topic in the study of fluid dynamics, its destructive nature could be exploited for therapeutic applications. Ultrasonic and hydrodynamic sources are two main origins for generating cavitation. The purpose of this review is to give the reader a general idea about the formation of cavitation phenomenon and existing biomedical applications of ultrasonic and hydrodynamic cavitation. Because of the high number of the studies on ultrasound cavitation in the literature, the main focus of this review is placed on the lithotripsy techniques, which have been widely used for the treatment of urinary stones. Accordingly, cavitation phenomenon and its basic concepts are presented in Section II. The significance of the ultrasound cavitation in the urinary stone treatment is discussed in Section III in detail and hydrodynamic cavitation as an important alternative for the ultrasound cavitation is included in Section IV. Finally, side effects of using both ultrasound and hydrodynamic cavitation in biomedical applications are presented in Section V.

  10. Numerical analysis of the interactions of sheet cavitation and cloud cavitation around a hydrofoil

    NASA Astrophysics Data System (ADS)

    Pan, D. Z.; Zhang, D. S.; Wang, H. Y.; Shi, W. D.; Shi, L.

    2015-01-01

    Partial cavitation and cloud cavitation on NACA66(MOD) was studied based on PANS turbulence model combined with the Zwart cavitation model. The results agree well with the data from the experimental results. The existence of a kind of unsteady characteristics of cloud cavitation is analysed in details. The reasons for the inhibition mechanism of the sheet cavitation are discussed. Pressure shock wave occurs near the tailing edge of the hydrofoil when the collapse of cloud is so large leading to great influence on the cavity closed to the leading edge. The evolution of the pressure peak and its propagation toward the leading edge were investigated through the study of the time domain signal of the monitor points along the streamline of flow. Finally, the propagation of the pressure wave on the suction side was further investigated through analysing the spatial-time history of wall pressure.

  11. FOREWORD: International Symposium of Cavitation and Multiphase Flow (ISCM 2014)

    NASA Astrophysics Data System (ADS)

    Wu, Yulin

    2015-01-01

    The International Symposium on Cavitation and Multiphase Flow (ISCM 2014) was held in Beijing, China during 18th-21st October, 2014, which was jointly organized by Tsinghua University, Beijing, China and Jiangsu University, Zhenjiang, China. The co-organizer was the State Key Laboratory of Hydroscience and Engineering, Beijing, China. Cavitation and multiphase flow is one of paramount topics of fluid mechanics with many engineering applications covering a broad range of topics, e.g. hydraulic machinery, biomedical engineering, chemical and process industry. In order to improve the performances of engineering facilities (e.g. hydraulic turbines) and to accelerate the development of techniques for medical treatment of serious diseases (e.g. tumors), it is essential to improve our understanding of cavitation and Multiphase Flow. For example, the present development towards the advanced hydrodynamic systems (e.g. space engine, propeller, hydraulic machinery system) often requires that the systems run under cavitating conditions and the risk of cavitation erosion needs to be controlled. The purpose of the ISCM 2014 was to discuss the state-of-the-art cavitation and multiphase flow research and their up-to-date applications, and to foster discussion and exchange of knowledge, and to provide an opportunity for the researchers, engineers and graduate students to report their latest outputs in these fields. Furthermore, the participants were also encouraged to present their work in progress with short lead time and discuss the encountered problems. ISCM 2014 covers all aspects of cavitation and Multiphase Flow, e.g. both fundamental and applied research with a focus on physical insights, numerical modelling and applications in engineering. Some specific topics are: Cavitating and Multiphase Flow in hydroturbines, pumps, propellers etc. Numerical simulation techniques Cavitation and multiphase flow erosion and anti-erosion techniques Measurement techniques for cavitation and

  12. Stability of cavitation structures in a thin liquid layer.

    PubMed

    Wu, Pengfei; Bai, Lixin; Lin, Weijun; Yan, Jiuchun

    2017-09-01

    The inception and evolution of acoustic cavitation structures in thin liquid layers under different conditions and perturbations are investigated experimentally with high speed photography. The stability and characterization of cavitation structures are quantified by image analysis methods. It is found that cavitation structures (shape of bubble cloud and number of bubbles) are stable under unaltered experimental conditions, and the cavitation bubble cloud will return to the original structure and remain stable even in the face of large perturbations. When the experimental conditions are altered (for example, acoustic intensity, cavitation nuclei, boundary), the cavitation structures will vary correspondingly. Further analysis implies that the stability of cavitation structures is closely related to the number of bubbles in the cavitation bubble cloud. There are two mechanisms acting simultaneously in the cavitation bubble cloud evolution, one "bubble production" and the other "bubble disappearance". We propose that the two mechanisms acting together constitute the most likely explanation for the stability of cavitation structures and their transformation. Copyright © 2017 Elsevier B.V. All rights reserved.

  13. A finite element model on effects of impact load and cavitation on fatigue crack propagation in mechanical bileaflet aortic heart valve.

    PubMed

    Mohammadi, H; Klassen, R J; Wan, W-K

    2008-10-01

    Pyrolytic carbon mechanical heart valves (MHVs) are widely used to replace dysfunctional and failed heart valves. As the human heart beats around 40 million times per year, fatigue is the prime mechanism of mechanical failure. In this study, a finite element approach is implemented to develop a model for fatigue analysis of MHVs due to the impact force between the leaflet and the stent and cavitation in the aortic position. A two-step method to predict crack propagation in the leaflets of MHVs has been developed. Stress intensity factors (SIFs) are computed at a small initiated crack located on the leaflet edge (the worst case) using the boundary element method (BEM). Static analysis of the crack is performed to analyse the stress distribution around the front crack zone when the crack is opened; this is followed by a dynamic crack analysis to consider crack propagation using the finite element approach. Two factors are taken into account in the calculation of the SIFs: first, the effect of microjet formation due to cavitation in the vicinity of leaflets, resulting in water hammer pressure; second, the effect of the impact force between the leaflet and the stent of the MHVs, both in the closing phase. The critical initial crack length, the SIFs, the water hammer pressure, and the maximum jet velocity due to cavitation have been calculated. With an initial crack length of 35 microm, the fatigue life of the heart valve is greater than 60 years (i.e. about 2.2 x 10(9) cycles) and, with an initial crack length of 170 microm, the fatigue life of the heart valve would be around 2.5 years (i.e. about 9.1 x 10(7) cycles). For an initial crack length greater than 170 microm, there is catastrophic failure and fatigue cracking no longer occurs. A finite element model of fatigue analysis using Patran command language (PCL custom code) in MSC software can be used to evaluate the useful lifespan of MHVs. Similar methodologies can be extended to other medical devices under cyclic

  14. The Role of Cavitation in Liposome Formation

    PubMed Central

    Richardson, Eric S.; Pitt, William G.; Woodbury, Dixon J.

    2007-01-01

    Liposome size is a vital parameter of many quantitative biophysical studies. Sonication, or exposure to ultrasound, is used widely to manufacture artificial liposomes, yet little is known about the mechanism by which liposomes are affected by ultrasound. Cavitation, or the oscillation of small gas bubbles in a pressure-varying field, has been shown to be responsible for many biophysical effects of ultrasound on cells. In this study, we correlate the presence and type of cavitation with a decrease in liposome size. Aqueous lipid suspensions surrounding a hydrophone were exposed to various intensities of ultrasound and hydrostatic pressures before measuring their size distribution with dynamic light scattering. As expected, increasing ultrasound intensity at atmospheric pressure decreased the average liposome diameter. The presence of collapse cavitation was manifested in the acoustic spectrum at high ultrasonic intensities. Increasing hydrostatic pressure was shown to inhibit the presence of collapse cavitation. Collapse cavitation, however, did not correlate with decreases in liposome size, as changes in size still occurred when collapse cavitation was inhibited either by lowering ultrasound intensity or by increasing static pressure. We propose a mechanism whereby stable cavitation, another type of cavitation present in sound fields, causes fluid shearing of liposomes and reduction of liposome size. A mathematical model was developed based on the Rayleigh-Plesset equation of bubble dynamics and principles of acoustic microstreaming to estimate the shear field magnitude around an oscillating bubble. This model predicts the ultrasound intensities and pressures needed to create shear fields sufficient to cause liposome size change, and correlates well with our experimental data. PMID:17766335

  15. Observations of the cavitating jet in a narrow watercourse

    SciTech Connect

    Soyama, H.; Ikohagi, T.; Oba, R.

    1994-12-31

    Highspeed submerged water-jets ar very often successfully applied for peening and cleaning. And such a jet-working-capacity closely depends on the shedding of cavitation clouds. In order to make clear the shedding mechanism of the clouds, the authors systematically observe the aspects of a two-dimensional jet in a 0.35mm-thin narrow watercourse, ejecting from the nozzle whose throat is 4mm long and 1mm wide. The cavitating jet is carefully observed by means of a highspeed photography and a digital image processing technique. The cavitating jet is very rapidly changing with time, and the clouds associated with the highly erosive cavitation are periodically shedding, whose frequency is about 800 Hz. The vortex cavitation around the jet is also shedding in 3kHz. The acceleration levels associated with high cavitation-erosion-energy are also measured.

  16. Can Cavitation Be Anticipated?

    SciTech Connect

    Allgood, G.O.; Dress, W.B.; Hylton, J.O.; Kercel, S.W.

    1999-04-25

    The major problem with cavitation in pumps and hydraulic systems is that there is no effective (conventional) method for detecting or predicting its inception. The traditional method of recognizing cavitation in a pump is to declare the event occurring when the total head drops by some arbitrary value (typically 3%) in response to a pressure reduction at the pump inlet. However, the device is already seriously cavitating when this happens. What is actually needed is a practical method to detect impending rather than incipient cavitation. Whereas the detection of incipient cavitation requires the detection of features just after cavitation starts, the anticipation of cavitation requires the detection and identification of precursor features just before it begins. Two recent advances that make this detection possible. The first is acoustic sensors with a bandwidth of 1 MHz and a dynamic range of 80 dB that preserve the fine details of the features when subjected to coarse vibrations. The second is the application of Bayesian parameter estimation which makes it possible to separate weak signals, such as those present in cavitation precursors, from strong signals, such as pump vibration. Bayesian parameter estimation derives a model based on cavitation hydrodynamics and produces a figure of merit of how well it fits the acquired data. Applying this model to an anticipatory engine should lead to a reliable method of anticipating cavitation before it occurs. This paper reports the findings of precursor features using high-performance sensors and Bayesian analysis of weak acoustic emissions in the 100-1000kHz band from an experimental flow loop.

  17. Experimental characterization of aviation-fuel cavitation

    NASA Astrophysics Data System (ADS)

    Dunn, Patrick F.; Thomas, Flint O.; Davis, Michael P.; Dorofeeva, Irina E.

    2010-11-01

    The results of an experimental investigation of the gaseous cavitation of JP-8 aviation fuel in a converging-diverging nozzle are presented. Fuel cavitation is experimentally characterized by high-speed digital imaging, static pressure distributions, and nonintrusive void fraction and bubble velocity measurements. For comparative purposes, experiments were performed using distilled water and dodecane for the same nozzle and nozzle pressure ratios. Dodecane, the largest component of JP-8 by weight, served as its single-component surrogate. For each working fluid, the experiments examined two different flow regimes: an initially single-phase liquid flow in which no cavitation occurred and another that evolved into two-phase cavitating flow. Additional experiments were performed to study the effect of air bubbles injected into either water or JP-8 at the nozzle inlet. For a sufficiently low range of imposed back pressures, gaseous cavitation led to choked flow for each working fluid. The character of the cavitation in the three fluids was different. These differences are highlighted and plausible mechanisms responsible for the observed behavior are discussed.

  18. Cavitation in flowing superfluid helium

    NASA Technical Reports Server (NTRS)

    Daney, D. E.

    1988-01-01

    Flowing superfluid helium cavitates much more readily than normal liquid helium, and there is a marked difference in the cavitation behavior of the two fluids as the lambda point is traversed. Examples of cavitation in a turbine meter and centrifugal pump are given, together with measurements of the cavitation strength of flowing superfluid helium. The unusual cavitation behavior of superfluid helium is attributed to its immense thermal conductivity .

  19. A cavitation model for computations of unsteady cavitating flows

    NASA Astrophysics Data System (ADS)

    Zhao, Yu; Wang, Guoyu; Huang, Biao

    2016-04-01

    A local vortical cavitation (LVC) model for the computation of unsteady cavitation is proposed. The model is derived from the Rayleigh-Plesset equations, and takes into account the relations between the cavitation bubble radius and local vortical effects. Calculations of unsteady cloud cavitating flows around a Clark-Y hydrofoil are performed to assess the predictive capability of the LVC model using well-documented experimental data. Compared with the conventional Zwart's model, better agreement is observed between the predictions of the LVC model and experimental data, including measurements of time-averaged flow structures, instantaneous cavity shapes and the frequency of the cloud cavity shedding process. Based on the predictions of the LVC model, it is demonstrated that the evaporation process largely concentrates in the core region of the leading edge vorticity in accordance with the growth in the attached cavity, and the condensation process concentrates in the core region of the trailing edge vorticity, which corresponds to the spread of the rear component of the attached cavity. When the attached cavity breaks up and moves downstream, the condensation area fully transports to the wake region, which is in accordance with the dissipation of the detached cavity. Furthermore, using vorticity transport equations, we also find that the periodic formation, breakup, and shedding of the sheet/cloud cavities, along with the associated baroclinic torque, are important mechanisms for vorticity production and modification. When the attached cavity grows, the liquid-vapour interface that moves towards the trailing edge enhances the vorticity in the attached cavity closure region. As the re-entrant jet moves upstream, the wavy/bubbly cavity interface enhances the vorticity near the trailing edge. At the end of the cycle, the break-up of the stable attached cavity is the main reason for the vorticity enhancement near the suction surface.

  20. Examples of oil cavitation erosion in positive displacement pumps

    NASA Technical Reports Server (NTRS)

    Halat, J. A.; Ellis, G. O.

    1974-01-01

    The effects of cavitation flow on piston type, positive displacement, hydraulic pumps are discussed. The operating principles of the pump and the components which are most subject to erosion effects are described. The mechanisms of cavitation phenomena are identified from photographic records. Curves are developed to show the solubility of air in water, oil-water emulsion, and industrial hydraulic oil.

  1. Examples of oil cavitation erosion in positive displacement pumps

    NASA Technical Reports Server (NTRS)

    Halat, J. A.; Ellis, G. O.

    1974-01-01

    The effects of cavitation flow on piston type, positive displacement, hydraulic pumps are discussed. The operating principles of the pump and the components which are most subject to erosion effects are described. The mechanisms of cavitation phenomena are identified from photographic records. Curves are developed to show the solubility of air in water, oil-water emulsion, and industrial hydraulic oil.

  2. Alternative approach for cavitation damage study utilizing repetitive laser pulses

    SciTech Connect

    Ren, Fei; Wang, Jy-An John; Wang, Hong

    2010-01-01

    Cavitation is a common phenomenon in fluid systems that can lead to dramatic degradation of solid materials surface in contact with the cavitating media. Study of cavitation damage has great significance in many engineering fields. Current techniques for cavitation damage study either require large scale equipments or tend to introduce damages from other mechanisms. In this project, we utilized the cavitation phenomenon induced by laser optical breakdown and developed a prototype apparatus for cavitation damage study. In our approach, cavitation was generated by the repetitive pressure waves induced by high-power laser pulses. As proof of principal study, stainless steel and aluminum samples were tested using the novel apparatus. Surface characterization via scanning electron microscopy revealed damages such as indentation and surface pitting, which were similar to those reported in literature using other state-of-the-art techniques. These preliminary results demonstrated the new device was capable of generating cavitation damages and could be used as an alternative method for cavitation damage study.

  3. Temperature measurements in cavitation bubbles

    NASA Astrophysics Data System (ADS)

    Coutier-Delgosha, Olivier

    2016-11-01

    Cavitation is usually a nearly isothermal process in the liquid phase, but in some specific flow conditions like hot water or cryogenic fluids, significant temperature variations are detected. In addition, a large temperature increase happens inside the cavitation bubbles at the very end of their collapse, due to the fast compression of the gas at the bubble core, which is almost adiabatic. This process is of primary interest in various biomedical and pharmaceutical applications, where the mechanisms of bubble collapse plays a major role. To investigate the amplitude and the spatial distribution of these temperature variations inside and outside the cavitation bubbles, a system based on cold wires has been developed. They have been tested in a configuration of a single bubble obtained by submitting a small air bubble to a large amplitude pressure wave. Some promising results have been obtained after the initial validation tests. This work is funded by the Office of Naval Research Global under Grant N62909-16-1-2116, Dr. Salahuddin Ahmed & Ki-Han Kim program managers.

  4. Numerical simulation on the cavitation of waterjet propulsion pump

    NASA Astrophysics Data System (ADS)

    Xia, C. Z.; Cheng, L.; Shang, Y. N.; Zhou, J. R.; Yang, F.; Jin, Y.

    2016-05-01

    Waterjet propulsion system is widely used in high speed vessels with advantages of simple transmission mechanism, low noise underwater and good manoeuvrability. Compared with the propeller, waterjet propulsion can be used flow stamping to increasing cavitation resistance at high speed. But under certain conditions, such as low ship speed or high ship speed, cavitation problem still exists. If water-jet propulsion pump is run in cavitation condition for a long time, then the cavitation will cause a great deal of noise CFD is applied to analysis and predict the process of production and development of cavitation in waterjet propulsion pump. Based on the cavitation model of Zwart-Gerber-Belamri and a mixture of homogeneous flow model, commercial CFD software CFX was taken for characteristics of cavitation under the three operating conditions. Commercial software ANSYS 14.0 is used to build entity model, mesh and numerical simulation. The grid independence analysis determine the grid number of mixed flow pump model is about 1.6 million and the grid number of water-jet pump system unit is about 2.7 million. The cavitation characteristics of waterjet pump under three operating conditions are studied. The results show that the cavitation development trend is similar design and small rate of flow condition .Under the design conditions Cavitation bubbles are mainly gathered in suction surface of blade near the inlet side of the hub under the primary stage, and gradually extended to the water side in the direction of the rim with the loss of the inlet total pressure. Cavitation appears in hub before the blade rim, but the maximum value of gas content in blade rim is bigger than that in hub. Under large flow conditions, bubble along the direction of wheel hub extends to the rim gradually. Cavitation is found in the pressure surface of blade near the hub region under the critical point of cavitation nearby. When NPSHa is lower than critical point, the area covering by bubbles

  5. Research on 3D reconstruction measurement and parameter of cavitation bubble based on stereo vision

    NASA Astrophysics Data System (ADS)

    Li, Shengyong; Ai, Xiaochuan; Wu, Ronghua; Cao, Jing

    2017-02-01

    The problems caused by the cavitation bubble and caused many adverse effects on the ship propeller, hydraulic machinery and equipment. In order to research the production mechanism of cavitation bubble under different conditions, cavitation bubble zone parameter fine measurement and analysis technology is indispensable, this paper adopts a non-contact measurement method of optical autonomous construction of binocular stereo vision measurement system according to the characteristics of cavitation bubble, the texture features are not clear, transparent and difficult to obtain, 3D imaging measurement of cavitation bubble using composite dynamic lighting, and 3D reconstruction of cavitation bubble region and obtained the characteristics of more accurate parameters, test results show that the cavitation bubble characteristics of the fine technology can obtain and analyze cavitation bubble region and instability.

  6. Acoustic Cavitation Studies

    DTIC Science & Technology

    1981-09-01

    34 Rayleigh - Plesset -Noltingk-Neppiras- Poritsky equation " that has been used extensively in cavitation research. We present measurements of the pulsation...general equations of cavitation nucleation. / / PRECEDING PAGE BLANK 4 They also were unable to give a quantitative explanation of the thresh- old...in Tissue by Rectified Diffusion," submitted to Physics in Medicine and Biology. 4. "Generalized Equations of Rectified Diffusion," submitted to

  7. Low frequency cavitation erosion

    NASA Astrophysics Data System (ADS)

    Pardue, Sally J.; Chandekar, Gautam

    2002-11-01

    Damage of diesel engine piston sleeve liners due to cavitation of the coolant fluid can be severe. Coolant fluid additives are used to inhibit cavitation damage, and are evaluated by industry suppliers using ASTM G32-98 Standard Test Method for Cavitation Erosion Using Vibratory Apparatus. The ASTM G32-98 test procedure uses an ultrasonic horn at 20 kHz to vibrate a test button in the coolant. The test button mass loss and surface appearance are studied to sort the performance of new coolant additives. Mismatch between good lab performers and actual engine test runs has raised concerns over the current lab test. The frequency range of the current test has been targeted for investigation. A low frequency, less than 2000 Hz, test rig was built to explore the cavitation damage. The test system did produce cavitation on the surface of the test button for a period of 36 h, with minimal mass loss. The test rig experienced cyclic fatigue when test times were extended. The work is now focusing on designing a better test rig for long duration tests and on developing numerical models in order to explore the effects of cavitation excitation frequency on surface erosion.

  8. Experimental evidence for heat plume-induced cavitation and xylem deformation as a mechanism of rapid post-fire tree mortality.

    PubMed

    West, Adam G; Nel, Jacques A; Bond, William J; Midgley, Jeremy J

    2016-08-01

    Recent work suggests that hydraulic mechanisms, rather than cambium necrosis, may account for rapid post-fire tree mortality. We experimentally tested for xylem cavitation, as a result of exposure to high-vapour-deficit (D) heat plumes, and permanent xylem deformation, as a result of thermal softening of lignin, in two tree species differing in fire tolerance. We measured percentage loss of conductance (PLC) in distal branches that had been exposed to high-D heat plumes or immersed in hot water baths (high temperature, but not D). Results were compared with predictions from a parameterized hydraulic model. Physical damage to the xylem was examined microscopically. Both species suffered c. 80% PLC when exposed to a 100°C plume. However, at 70°C, the fire-sensitive Kiggelaria africana suffered lower PLC (49%) than the fire-resistant Eucalytpus cladocalyx (80%). Model simulations suggested that differences in PLC between species were a result of greater hydraulic segmentation in E. cladocalyx. Kiggelaria africana suffered considerable PLC (59%), as a result of heat-induced xylem deformation, in the water bath treatments, but E. cladocalyx did not. We suggest that a suite of 'pyrohydraulic' traits, including hydraulic segmentation and heat sensitivity of the xylem, may help to explain why some tree species experience rapid post-fire mortality after low-intensity fires and others do not.

  9. Cavitation guide for control valves

    SciTech Connect

    Tullis, J.P.

    1993-04-01

    This guide teaches the basic fundamentals of cavitation to provide the reader with an understanding of what causes cavitation, when it occurs, and the potential problems cavitation can cause to a valve and piping system. The document provides guidelines for understanding how to reduce the cavitation and/or select control valves for a cavitating system. The guide provides a method for predicting the cavitation intensity of control valves, and how the effect of cavitation on a system will vary with valve type, valve function, valve size, operating pressure, duration of operation and details of the piping installation. The guide defines six cavitation limits identifying cavitation intensities ranging from inception to the maximum intensity possible. The intensity of the cavitation at each limit Is described, including a brief discussion of how each level of cavitation influences the valve and system. Examples are included to demonstrate how to apply the method, including making both size and pressure scale effects corrections. Methods of controlling cavitation are discussed providing information on various techniques which can be used to design a new system or modify an existing one so it can operate at a desired level of cavitation.

  10. Cavitation in medicine.

    PubMed

    Brennen, Christopher Earls

    2015-10-06

    We generally think of bubbles as benign and harmless and yet they can manifest the most remarkable range of physical effects. Some of those effects are the stuff of our everyday experience as in the tinkling of a brook or the sounds of breaking waves at the beach. But even these mundane effects are examples of the ability of bubbles to gather, focus and radiate energy (acoustic energy in the above examples). In other contexts that focusing of energy can lead to serious technological problems as when cavitation bubbles eat great holes through ships' propeller blades or cause a threat to the integrity of the spillways at the Hoover Dam. In liquid-propelled rocket engines, bubbles pose a danger to the stability of the propulsion system, and in artificial heart valves they can cause serious damage to the red blood cells. In perhaps the most extraordinary example of energy focusing, collapsing cavitation bubbles can emit not only sound, but also light with black body radiation temperatures equal to that of the sun (Brennen 1995 Cavitation and bubble dynamics). But, harnessed carefully, this almost unique ability to focus energy can also be put to remarkably constructive use. Cavitation bubbles are now used in a remarkable range of surgical and medical procedures, for example to emulsify tissue (most commonly in cataract surgery or in lithotripsy procedures for the reduction of kidney and gall stones) or to manipulate the DNA in individual cells. By creating cavitation bubbles non-invasively thereby depositing and focusing energy non-intrusively, one can generate minute incisions or target cancer cells. This paper will begin by briefly reviewing the history of cavitation phenomena and will end with a vision of the new horizons for the amazing cavitation bubble.

  11. Cavitation in medicine

    PubMed Central

    Brennen, Christopher Earls

    2015-01-01

    We generally think of bubbles as benign and harmless and yet they can manifest the most remarkable range of physical effects. Some of those effects are the stuff of our everyday experience as in the tinkling of a brook or the sounds of breaking waves at the beach. But even these mundane effects are examples of the ability of bubbles to gather, focus and radiate energy (acoustic energy in the above examples). In other contexts that focusing of energy can lead to serious technological problems as when cavitation bubbles eat great holes through ships' propeller blades or cause a threat to the integrity of the spillways at the Hoover Dam. In liquid-propelled rocket engines, bubbles pose a danger to the stability of the propulsion system, and in artificial heart valves they can cause serious damage to the red blood cells. In perhaps the most extraordinary example of energy focusing, collapsing cavitation bubbles can emit not only sound, but also light with black body radiation temperatures equal to that of the sun (Brennen 1995 Cavitation and bubble dynamics). But, harnessed carefully, this almost unique ability to focus energy can also be put to remarkably constructive use. Cavitation bubbles are now used in a remarkable range of surgical and medical procedures, for example to emulsify tissue (most commonly in cataract surgery or in lithotripsy procedures for the reduction of kidney and gall stones) or to manipulate the DNA in individual cells. By creating cavitation bubbles non-invasively thereby depositing and focusing energy non-intrusively, one can generate minute incisions or target cancer cells. This paper will begin by briefly reviewing the history of cavitation phenomena and will end with a vision of the new horizons for the amazing cavitation bubble. PMID:26442145

  12. Secondary cavitation in a rigid tube

    NASA Astrophysics Data System (ADS)

    Ji, Chen; Li, Bo; Zou, Jun

    2017-08-01

    The oscillation of a single spark-generated bubble in a rigid tube is studied experimentally, with the help of a high-speed camera and a hydrophone. The non-dimensional collapse position XF is divided into three regimes, according to the various phenomena after the first oscillation period T1. In an asymmetric regime, secondary cavitation is observed. Both the axial position and the oscillation period of the secondary cavitation show a linear correlation with the first bubble. The period ratio k is independent of the relative bubble size L1* but is affected by the tube diameter Dt. In a symmetric regime, the secondary cavitation is much weaker and unrepeatable. The rebound bubble is strengthened in this regime, and the rebound ratio kr is independent of both L1* and Dt. A mechanism of reflected rarefaction wave is proposed to explain the position relation between the first and secondary cavities, and the energy partition in different regimes is discussed.

  13. Detecting Cavitation Pitting Without Disassembly

    NASA Technical Reports Server (NTRS)

    Barkhoudarian, S.

    1986-01-01

    Technique for detecting cavitation pitting in pumps, turbines, and other machinery uses low-level nuclear irradiation. Isotopes concentrated below surface emit gamma radiation, a portion of which is attenuated by overlying material. Where there are cavitation pits, output of gamma-ray detector fluctuates as detector is scanned near pits. Important to detect cavitation pits because nozzle, turbine blade, or other pump component weakened by cavitation could fail catastrophically and cause machine to explode.

  14. Prediction of pump cavitation performance

    NASA Technical Reports Server (NTRS)

    Moore, R. D.

    1974-01-01

    A method for predicting pump cavitation performance with various liquids, liquid temperatures, and rotative speeds is presented. Use of the method requires that two sets of test data be available for the pump of interest. Good agreement between predicted and experimental results of cavitation performance was obtained for several pumps operated in liquids which exhibit a wide range of properties. Two cavitation parameters which qualitatively evaluate pump cavitation performance are also presented.

  15. Do Xylem Fibers Affect Vessel Cavitation Resistance?1

    PubMed Central

    Jacobsen, Anna L.; Ewers, Frank W.; Pratt, R. Brandon; Paddock, William A.; Davis, Stephen D.

    2005-01-01

    Possible mechanical and hydraulic costs to increased cavitation resistance were examined among six co-occurring species of chaparral shrubs in southern California. We measured cavitation resistance (xylem pressure at 50% loss of hydraulic conductivity), seasonal low pressure potential (Pmin), xylem conductive efficiency (specific conductivity), mechanical strength of stems (modulus of elasticity and modulus of rupture), and xylem density. At the cellular level, we measured vessel and fiber wall thickness and lumen diameter, transverse fiber wall and total lumen area, and estimated vessel implosion resistance using (t/b)h2, where t is the thickness of adjoining vessel walls and b is the vessel lumen diameter. Increased cavitation resistance was correlated with increased mechanical strength (r2 = 0.74 and 0.76 for modulus of elasticity and modulus of rupture, respectively), xylem density (r2 = 0.88), and Pmin (r2 = 0.96). In contrast, cavitation resistance and Pmin were not correlated with decreased specific conductivity, suggesting no tradeoff between these traits. At the cellular level, increased cavitation resistance was correlated with increased (t/b)h2 (r2 = 0.95), increased transverse fiber wall area (r2 = 0.89), and decreased fiber lumen area (r2 = 0.76). To our knowledge, the correlation between cavitation resistance and fiber wall area has not been shown previously and suggests a mechanical role for fibers in cavitation resistance. Fiber efficacy in prevention of vessel implosion, defined as inward bending or collapse of vessels, is discussed. PMID:16100359

  16. Dynamics of cavitating cascades

    NASA Technical Reports Server (NTRS)

    Acosta, A. J.; Brennen, C.; Kim, J. H.

    1972-01-01

    Brief accounts of the theoretical research conducted on the unsteady cavitation characteristics of liquid rocket engine turbopumps are reported. The objective is to produce estimates of the cavitation compliance and other unsteady characteristics which could then be used in analysis of the pogo instability. Blade cavitation is the particular pheonomenon which is investigated and line arized free streamline methods were employed in both quasistatic and complete dynamic cascade analyses of the unsteady flow. The simpler quasistatic analysis was applied to particular turbopumps but yielded values of compliances significantly smaller than those indirectly obtained from experiments. Reasons for this discrepancy are discussed. The complete dynamic analysis presents a new problem in fundamental hydrodynamics and, though the basic solution is presented, numerical results have not as yet been obtained.

  17. Promoting inertial cavitation by nonlinear frequency mixing in a bifrequency focused ultrasound beam.

    PubMed

    Saletes, Izella; Gilles, Bruno; Bera, Jean-Christophe

    2011-01-01

    Enhancing cavitation activity with minimal acoustic intensities could be interesting in a variety of therapeutic applications where mechanical effects of cavitation are needed with minimal heating of surrounding tissues. The present work focuses on the relative efficiency of a signal combining two neighbouring frequencies and a one-frequency signal for initiating ultrasound inertial cavitation. Experiments were carried out in a water tank, using a 550kHz piezoelectric composite spherical transducer focused on targets with 46μm roughness. The acoustic signal scattered, either by the target or by the cavitation bubbles, is filtered using a spectral and cepstral-like method to obtain an inertial cavitation activity measurement. The ultrasound excitations consist of 1.8ms single bursts of single frequency f(0)=550kHz excitation, in the monofrequency case, and of dual frequency f(1)=535kHz and f(2)=565kHz excitation, in the bifrequency case. It is shown that depending on the value of the monofrequency cavitation threshold intensity the bifrequency excitation can increase or reduce the cavitation threshold. The analysis of the thresholds indicates that the mechanisms involved are nonlinear. The progress of the cavitation activity beyond the cavitation threshold is also studied. The slope of the cavitation activity considered as a function of the acoustic intensity is always steeper in the case of the bifrequency excitation. This means that the delimitation of the region where cavitation occurs should be cleaner than with a classical monofrequency excitation.

  18. Numerical modeling of natural and ventilated cavitating flows

    NASA Astrophysics Data System (ADS)

    Qin, Qiao

    Cavitation is a phenomenon that frequently occurs in fluid-handling machinery, ranging from all types of pumps, turbines, and propellers to various piping systems and hydraulic structures. Cavitation research has been pursued for over a century and an enormous quantity of literature on cavitation has been generated. Cavitation modeling is challenging and is still in the development stage due to its inherent complexity of the physics involved. There are basically three objectives in this thesis work. First, an existing virtual single-phase natural cavitation model is used to extensively explore the unsteadiness of sheet/cloud cavitation on two hydrofoils (NACA 0015 and CAV2003). Five discrete vortex shedding mechanisms are identified in this research. Second, this existing virtual single-phase natural cavitation model is further modified to take into account the effect of incondensable gas that comes out of solution due to the cavitation evaporation process. This was motivated by the observation that the computed mean velocity distribution in the wake of a cavitating hydrofoil, without the effect of incondensable gas, agrees well with experimental data close to the trailing edge but deviates systematically further downstream. This revision shows a significant improvement on the computed mean velocity distribution in the wake compared to that without the incondensable gas effect and the results are in agreement with those from experiments. These are two new findings that are absent in literature. Third, a two-phase, fully compressible flow model based on Large Eddy Simulation (LES) for ventilated cavitating flows is developed and is successfully implemented in the simulation of an axisymmetric underwater body.

  19. Characterization of Axial Inducer Cavitation Instabilities via High Speed Video Recordings

    NASA Technical Reports Server (NTRS)

    Arellano, Patrick; Peneda, Marinelle; Ferguson, Thomas; Zoladz, Thomas

    2011-01-01

    Sub-scale water tests were undertaken to assess the viability of utilizing high resolution, high frame-rate digital video recordings of a liquid rocket engine turbopump axial inducer to characterize cavitation instabilities. These high speed video (HSV) images of various cavitation phenomena, including higher order cavitation, rotating cavitation, alternating blade cavitation, and asymmetric cavitation, as well as non-cavitating flows for comparison, were recorded from various orientations through an acrylic tunnel using one and two cameras at digital recording rates ranging from 6,000 to 15,700 frames per second. The physical characteristics of these cavitation forms, including the mechanisms that define the cavitation frequency, were identified. Additionally, these images showed how the cavitation forms changed and transitioned from one type (tip vortex) to another (sheet cavitation) as the inducer boundary conditions (inlet pressures) were changed. Image processing techniques were developed which tracked the formation and collapse of cavitating fluid in a specified target area, both in the temporal and frequency domains, in order to characterize the cavitation instability frequency. The accuracy of the analysis techniques was found to be very dependent on target size for higher order cavitation, but much less so for the other phenomena. Tunnel-mounted piezoelectric, dynamic pressure transducers were present throughout these tests and were used as references in correlating the results obtained by image processing. Results showed good agreement between image processing and dynamic pressure spectral data. The test set-up, test program, and test results including H-Q and suction performance, dynamic environment and cavitation characterization, and image processing techniques and results will be discussed.

  20. A Study of Cavitation Erosion

    SciTech Connect

    Hiromu Isaka; Masatsugu Tsutsumi; Tadashi Shiraishi; Hiroyuki Kobayashi

    2002-07-01

    The authors performed experimental study for the purpose of the following two items from a viewpoint of cavitation erosion of a cylindrical orifice in view of a problem at the letdown orifice in PWR (Pressurized Water Reactor). 1. To get the critical cavitation parameter of the cylindrical orifice to establish the design criteria for prevention of cavitation erosion, and 2. to ascertain the erosion rate in such an eventuality that the cavitation erosion occurs with the orifice made of stainless steel with precipitation hardening (17-4-Cu hardening type stainless steel), so that we confirm the appropriateness of the design criteria. Regarding the 1. item, we carried out the cavitation tests to get the critical cavitation parameters inside and downstream of the orifice. The test results showed that the cavitation parameter at inception is independent of the length or the diameter of the orifice. Moreover, the design criteria of cavitation erosion of cylindrical orifices have been established. Regarding the 2. item, we tested the erosion rate under high-pressure conditions. The cavitation erosion actually occurred in the cylindrical orifice at the tests that was strongly resemble to the erosion occurred at the plant. It will be seldom to reproduce resemble cavitation erosion in a cylindrical orifice with the hard material used at plants. We could establish the criteria for preventing the cavitation erosion from the test results. (authors)

  1. Ultrafast cavitation induced by an X-ray laser in water drops

    NASA Astrophysics Data System (ADS)

    Stan, Claudiu; Willmott, Philip; Stone, Howard; Koglin, Jason; Liang, Mengning; Aquila, Andrew; Robinson, Joseph; Gumerlock, Karl; Blaj, Gabriel; Sierra, Raymond; Boutet, Sebastien; Guillet, Serge; Curtis, Robin; Vetter, Sharon; Loos, Henrik; Turner, James; Decker, Franz-Josef

    2016-11-01

    Cavitation in pure water is determined by an intrinsic heterogeneous cavitation mechanism, which prevents in general the experimental generation of large tensions (negative pressures) in bulk liquid water. We developed an ultrafast decompression technique, based on the reflection of shock waves generated by an X-ray laser inside liquid drops, to stretch liquids to large negative pressures in a few nanoseconds. Using this method, we observed cavitation in liquid water at pressures below -100 MPa. These large tensions exceed significantly those achieved previously, mainly due to the ultrafast decompression. The decompression induced by shock waves generated by an X-ray laser is rapid enough to continue to stretch the liquid phase after the heterogeneous cavitation occurs in water, despite the rapid growth of cavitation nanobubbles. We developed a nucleation-and-growth hydrodynamic cavitation model that explains our results and estimates the concentration of heterogeneous cavitation nuclei in water.

  2. Interactions of inertial cavitation bubbles with stratum corneum lipid bilayers during low-frequency sonophoresis.

    PubMed

    Tezel, Ahmet; Mitragotri, Samir

    2003-12-01

    Interactions of acoustic cavitation bubbles with biological tissues play an important role in biomedical applications of ultrasound. Acoustic cavitation plays a particularly important role in enhancing transdermal transport of macromolecules, thereby offering a noninvasive mode of drug delivery (sonophoresis). Ultrasound-enhanced transdermal transport is mediated by inertial cavitation, where collapses of cavitation bubbles microscopically disrupt the lipid bilayers of the stratum corneum. In this study, we describe a theoretical analysis of the interactions of cavitation bubbles with the stratum corneum lipid bilayers. Three modes of bubble-stratum corneum interactions including shock wave emission, microjet penetration into the stratum corneum, and impact of microjet on the stratum corneum are considered. By relating the mechanical effects of these events on the stratum corneum structure, the relationship between the number of cavitation events and collapse pressures with experimentally measured increase in skin permeability was established. Theoretical predictions were compared to experimentally measured parameters of cavitation events.

  3. The effect of the aortic valve orientation on cavitation.

    PubMed

    Johansen, Peter; Travis, Brandon R; Smerup, Morten; Decker Christensen, Thomas; Funder, Jonas; Nyboe, Camilla; Nygaard, Hans; Hasenkam, J Michael

    2016-08-01

    When implanting a mechanical aortic valve the annulus orientation is important with respect to turbulence. However, the effect on cavitation has not yet been investigated. The aim of this study was to investigate how cavitation is influenced hereof in vivo. Three pigs were included in the study. An Omnicarbon 21mm valve equipped with a rotating mechanism enabling controlled rotation of the valve was implanted in aortic position. Under stable hemodynamic conditions, measurements were performed using a hydrophone positioned at the aortic root. The valve was rotated from 0-360° in increments of 30°. From the pressure fluctuations recorded by the hydrophone the root mean square of the 50 kHz high pass filtered signal as well as the non-deterministic signal energy was calculated as indirect measures of cavitation. Various degrees of cavitation were measured but no relationship was found between either of the two cavitation measures and the valve orientation. Hemodynamics varied during the experiments for all pigs (3.9-5.7 l/min; 5.0-7.2 l/min; 3.1-7.5 l/min). Changes in cavitation quantities seemed to be caused by changes in hemodynamics rather than valve angular position. In conclusion, these results do not favor any position over another in terms of cavitation potential.

  4. Use of hydrodynamic cavitation in (waste)water treatment.

    PubMed

    Dular, Matevž; Griessler-Bulc, Tjaša; Gutierrez-Aguirre, Ion; Heath, Ester; Kosjek, Tina; Krivograd Klemenčič, Aleksandra; Oder, Martina; Petkovšek, Martin; Rački, Nejc; Ravnikar, Maja; Šarc, Andrej; Širok, Brane; Zupanc, Mojca; Žitnik, Miha; Kompare, Boris

    2016-03-01

    The use of acoustic cavitation for water and wastewater treatment (cleaning) is a well known procedure. Yet, the use of hydrodynamic cavitation as a sole technique or in combination with other techniques such as ultrasound has only recently been suggested and employed. In the first part of this paper a general overview of techniques that employ hydrodynamic cavitation for cleaning of water and wastewater is presented. In the second part of the paper the focus is on our own most recent work using hydrodynamic cavitation for removal of pharmaceuticals (clofibric acid, ibuprofen, ketoprofen, naproxen, diclofenac, carbamazepine), toxic cyanobacteria (Microcystis aeruginosa), green microalgae (Chlorella vulgaris), bacteria (Legionella pneumophila) and viruses (Rotavirus) from water and wastewater. As will be shown, hydrodynamic cavitation, like acoustic, can manifest itself in many different forms each having its own distinctive properties and mechanisms. This was until now neglected, which eventually led to poor performance of the technique. We will show that a different type of hydrodynamic cavitation (different removal mechanism) is required for successful removal of different pollutants. The path to use hydrodynamic cavitation as a routine water cleaning method is still long, but recent results have already shown great potential for optimisation, which could lead to a low energy tool for water and wastewater cleaning. Copyright © 2015 Elsevier B.V. All rights reserved.

  5. Ozone and Cavitation Combination

    NASA Astrophysics Data System (ADS)

    Carreon, Ernestina; Traversoni, Leonardo

    2009-09-01

    From laboratory measurements it is well known that the addition of ozone and cavitation enhances the properties of both, understanding for that the ones related to disinfection and carbon removal from waste water. This paper shows modeling of such phenomena that gives some light to the understanding of it and also provides the opportunity to improve the effectiveness of the current procedures.

  6. Cavitation during wire brushing

    NASA Astrophysics Data System (ADS)

    Li, Bo; Zou, Jun; Ji, Chen

    2016-11-01

    In our daily life, brush is often used to scrub the surface of objects, for example, teeth, pots, shoes, pool, etc. And cleaning rust and stripping paint are accomplished using wire brush. Wire brushes also can be used to clean the teeth for large animals, such as horses, crocodiles. By observing brushing process in water, we capture the cavitation phenomenon on the track of moving brush wire. It shows that the cavitation also can affect the surface. In order to take clear and entire pictures of cavity, a simplified model of one stainless steel wire brushing a boss is adopted in our experiment. A transparent organic tank filled with deionized water is used as a view box. And a high speed video camera is used to record the sequences. In experiment, ambient pressure is atmospheric pressure and deionized water temperature is kept at home temperature. An obvious beautiful flabellate cavity zone appears behind the moving steel wire. The fluctuation of pressure near cavity is recorded by a hydrophone. More movies and pictures are used to show the behaviors of cavitation bubble following a restoring wire. Beautiful tracking cavitation bubble cluster is captured and recorded to show.

  7. Cavitational hydrothermal oxidation: A new remediation process. 1998 annual progress report

    SciTech Connect

    Suslick, K.S.

    1998-06-01

    'The primary goal is to develop a quantitative understanding of cavitation phenomena in aqueous media and the development of applications of cavitation to remediation processes. Efforts have focused on three separate areas: sonoluminescence as a probe of conditions created during cavitational collapse in aqueous media, the use of cavitation for remediation of contaminated water, and an addition of the use of ultrasound in the synthesis of novel heterogeneous catalysts for hydrodehalogenation of halocarbons under mild conditions. This report summarizes work after one year of a three year project. In order to gain further understanding of the conditions present during cavitation, the author has continued his studies of sonoluminescence. He has made recent breakthroughs in the use of emission spectroscopy for temperature and pressure measurement of cavitation events, which he expects to publish shortly. He has been able to measure for the first time the temperature of cavitation in water during multi-bubble cavitation in the presence of aromatic hydrocarbons. The emission from excited states of C{sub 2} in water gives temperatures that are consistent with adiabatic compressional heating, with maximum temperatures of 4,300 K. Prior measurements of cavitation temperatures in low vapor pressure nonaqueous media gave somewhat higher temperatures of 5,000 K. This work lays permanently to rest exotic mechanisms for cavitational chemistry, at least for cavitation fields.'

  8. Cavitational hydrothermal oxidation: A new remediation process. Annual progress report, September 1996--August 1997

    SciTech Connect

    Suslick, K.S.

    1997-11-21

    'During the past year, the authors have continued to make substantial scientific progress on the understanding of cavitation phenomena in aqueous media and applications of cavitation to remediation processes. The efforts have focused on three separate areas: sonoluminescence as a probe of conditions created during cavitational collapse in aqueous media, the use of cavitation for remediation of contaminated water, and an addition of the use of ultrasound in the synthesis of novel heterogeneous catalysts for hydrodehalogenation of halocarbons under mild conditions. In order to gain further understanding of the conditions present during cavitation, the author has continued his studies of sonoluminescence. He has made recent breakthroughs in the use of emission spectroscopy for temperature and pressure measurement of cavitation events, which he expects to publish shortly. He has been able to measure for the first time the temperature of cavitation in water during multi-bubble cavitation in the presence of aromatic hydrocarbons. The emission from excited states of C{sub 2} in water gives temperatures that are consistent with adiabatic compressional heating, with maximum temperatures of 4,300 K. Prior measurements of cavitation temperatures in low vapor pressure nonaqueous media gave somewhat higher temperatures of 5,000 K. This work lays permanently to rest exotic mechanisms for cavitational chemistry, at least for cavitation fields.'

  9. Cell death activation during cavitation of embryoid bodies is mediated by hydrogen peroxide.

    PubMed

    Hernández-García, David; Castro-Obregón, Susana; Gómez-López, Sandra; Valencia, Concepción; Covarrubias, Luis

    2008-06-10

    The formation of the proamniotic cavity is the first indication of programmed cell death associated to a morphogenetic process in mammals. Although some growth factors have been implicated in proamniotic cavitation, very little is known about the intracellular mechanisms that control the cell death process itself. Reactive oxygen species (ROS) are potent activators of cell death, thus, in the present work we evaluated the role of ROS during the cavitation of embryoid bodies (EBs), a common model to study proamniotic cavitation. During cavitation, ROS concentration increases in the inner cells of EBs, and this ROS accumulation appears to be associated with the mitochondrial respiratory activity. In agreement with a role of ROS in cavitation, EBs derived from ES cells that overproduce catalase, an enzyme that specifically degrades hydrogen peroxide, do not cavitate, and caspase activation and cell death is markedly decreased. Notably, cell death, but not the rise in ROS, during EB cavitation is caspase-dependent. The apoptosis-inducing factor (Aif) is released from the mitochondria during cavitation, but EBs derived from Aif(-/y) ES cells cavitate and ROS levels in the inner cells remain high. We conclude that hydrogen peroxide is a cell death activating signal essential for EB cavitation, suggesting that cell death during proamniotic cavitation is mediated by ROS.

  10. Experimental and Theoretical Investigations of Cavitation in Water

    NASA Technical Reports Server (NTRS)

    Ackeret, J.

    1945-01-01

    The cavitation in nozzles on airfoils of various shape and on a sphere are experimentally investigated. The limits of cavitation and the extension of the zone of the bubbles in different stages of cavitation are photographically established. The pressure in the bubble area is constant and very low, jumping to high values at the end of the area. The analogy with the gas compression shock is adduced and discussed. The collapse of the bubbles under compression shock produces very high pressures internally, which must be contributory factors to corrosion. The pressure required for purely mechanical corrosion is also discussed.

  11. Detecting cavitation in vivo from shock-wave therapy devices

    NASA Astrophysics Data System (ADS)

    Matula, Thomas J.; Yu, Jinfei; Bailey, Michael R.

    2005-04-01

    Extracorporeal shock-wave therapy (ESWT) has been used as a treatment for plantar faciitis, lateral epicondylitis, shoulder tendonitis, non-unions, and other indications where conservative treatments have been unsuccessful. However, in many areas, the efficacy of SW treatment has not been well established, and the mechanism of action, particularly the role of cavitation, is not well understood. Research indicates cavitation plays an important role in other ultrasound therapies, such as lithotripsy and focused ultrasound surgery, and in some instances, cavitation has been used as a means to monitor or detect a biological effect. Although ESWT can generate cavitation easily in vitro, it is unknown whether or not cavitation is a significant factor in vivo. The purpose of this investigation is to use diagnostic ultrasound to detect and monitor cavitation generated by ESWT devices in vivo. Diagnostic images are collected at various times during and after treatment. The images are then post-processed with image-processing algorithms to enhance the contrast between bubbles and surrounding tissue. The ultimate goal of this research is to utilize cavitation as a means for optimizing shock wave parameters such as amplitude and pulse repetition frequency. [Work supported by APL internal funds and NIH DK43881 and DK55674.

  12. The effect of static pressure on the inertial cavitation threshold.

    PubMed

    Bader, Kenneth B; Raymond, Jason L; Mobley, Joel; Church, Charles C; Felipe Gaitan, D

    2012-08-01

    The amplitude of the acoustic pressure required to nucleate a gas or vapor bubble in a fluid, and to have that bubble undergo an inertial collapse, is termed the inertial cavitation threshold. The magnitude of the inertial cavitation threshold is typically limited by mechanisms other than homogeneous nucleation such that the theoretical maximum is never achieved. However, the onset of inertial cavitation can be suppressed by increasing the static pressure of the fluid. The inertial cavitation threshold was measured in ultrapure water at static pressures up to 30 MPa (300 bars) by exciting a radially symmetric standing wave field in a spherical resonator driven at a resonant frequency of 25.5 kHz. The threshold was found to increase linearly with the static pressure; an exponentially decaying temperature dependence was also found. The nature and properties of the nucleating mechanisms were investigated by comparing the measured thresholds to an independent analysis of the particulate content and available models for nucleation.

  13. Tip vortex cavitation suppression via mass injection

    NASA Astrophysics Data System (ADS)

    Ganesh, Harish; Chang, Natasha; Yakushiji, Ryo; Ceccio, Steven

    2009-11-01

    Tip vortex cavitation (TVC) suppression by mass injection in the core of the vortex was studied with an elliptical plan-form hydrofoil NACA-66 modified in a re-circulating water tunnel of known nuclei distribution. The chord based Re was O(106) for all experiments. Water and Polyox WSR 301 solution for a range of concentrations (10 to 500pmm) and relative flow rates (Qjet / Qcore of 0.033 to 0.27) were injected. Also, different injection port size and angle of attack were studied. It was found that the TVC suppression effect was different for inception and desinence. The baseline (no injection) inception cavitation number was more than the average negative pressure coefficient, -Cp of the vortex, while mass addition reduced the inception cavitation number to approximately the --Cp value. TVC desinence for the baseline case was found to match the estimated --Cp value and polymer injection provided some cavitation suppression. Flow measurements were made to understand the underlying physics of TVC. The mechanisms and scalability that lead to TVC suppression by mass injection are discussed.

  14. Cavitation of a Physically Associating Gel

    NASA Astrophysics Data System (ADS)

    Mishra, Satish; Kundu, Santanu

    Self-assembly of block copolymers in selective solvents form ordered structures such as micelles, vesicles, and physically crosslinked gels due to difference in their interaction with solvents. These gels have wide range of applications in tissue engineering, food science and biomedical field due to their tunable properties and responsiveness with changing environmental conditions. Pressurization of a defect inside a physically associating gel can lead to elastic instability (cavitation) leading to failure of the gel. The failure behavior involves dissociation of physical networks. A thermoreversible, physically associating gel with different volume fractions of a triblock copolymer, poly (methyl methacrylate)-poly (n-butyl acrylate)-poly (methyl methacrylate) [PMMA-PnBA-PMMA] in 2-ethyl 1-hexanol, a midblock selective solvent, is considered here. Mechanical properties were investigated using shear rheology and cavitation experiments. The experimental data is fitted with a constitutive model that captures the stiffening behavior followed by softening behavior of a physical gel. Finite element analysis has been performed on cavitation rheology geometry to capture the failure behavior and to calculate energy release rate during cavitation experiments.

  15. Cavitation Generation and Usage Without Ultrasound: Hydrodynamic Cavitation

    NASA Astrophysics Data System (ADS)

    Gogate, Parag R.; Pandit, Aniruddha B.

    Hydrodynamic Cavitation, which was and is still looked upon as an unavoidable nuisance in the flow systems, can be a serious contender as an alternative to acoustic cavitation for harnessing the spectacular effects of cavitation in physical and chemical processing. The present chapter covers the basics of hydrodynamic cavitation including the considerations for the bubble dynamics analysis, reactor designs and recommendations for optimum operating parameters. An overview of applications in different areas of physical, chemical and biological processing on scales ranging from few grams to several hundred kilograms has also been presented. Since hydrodynamic cavitation was initially proposed as an alternative to acoustic cavitation, it is necessary to compare the efficacy of both these modes of cavitations for a variety of applications and hence comparisons have been discussed either on the basis of energy efficiency or based on the scale of operation. Overall it appears that hydrodynamic cavitation results in conditions similar to those generated using acoustic cavitation but at comparatively much larger scale of operation and with better energy efficiencies.

  16. Numerical investigation of tip clearance cavitation in Kaplan runners

    NASA Astrophysics Data System (ADS)

    Nikiforova, K.; Semenov, G.; Kuznetsov, I.; Spiridonov, E.

    2016-11-01

    There is a gap between the Kaplan runner blade and the shroud that makes for a special kind of cavitation: cavitation in the tip leakage flow. Two types of cavitation caused by the presence of clearance gap are known: tip vortex cavitation that appears at the core of the rolled up vortex on the blade suction side and tip clearance cavitation that appears precisely in the gap between the blade tip edge and the shroud. In the context of this work numerical investigation of the model Kaplan runner has been performed taking into account variable tip clearance for several cavitation regimes. The focus is put on investigation of structure and origination of mechanism of cavitation in the tip leakage flow. Calculations have been performed with the help of 3-D unsteady numerical model for two-phase medium. Modeling of turbulent flow in this work has been carried out using full equations of Navier-Stokes averaged by Reynolds with correction for streamline curvature and system rotation. For description of this medium (liquid-vapor) simplification of Euler approach is used; it is based on the model of interpenetrating continuums, within the bounds of this two- phase medium considered as a quasi-homogeneous mixture with the common velocity field and continuous distribution of density for both phases. As a result, engineering techniques for calculation of cavitation conditioned by existence of tip clearance in model turbine runner have been developed. The detailed visualization of the flow was carried out and vortex structure on the suction side of the blade was reproduced. The range of frequency with maximum value of pulsation was assigned and maximum energy frequency was defined; it is based on spectral analysis of the obtained data. Comparison between numerical computation results and experimental data has been also performed. The location of cavitation zone has a good agreement with experiment for all analyzed regimes.

  17. Controlled multibubble surface cavitation.

    PubMed

    Bremond, Nicolas; Arora, Manish; Ohl, Claus-Dieter; Lohse, Detlef

    2006-06-09

    Heterogeneous bubble nucleation at surfaces has been notorious because of its irreproducibility. Here controlled multibubble surface cavitation is achieved by using a hydrophobic surface patterned with microcavities. The expansion of the nuclei in the microcavities is triggered by a fast lowering of the liquid pressure. The procedure allows us to control and fix the bubble distance within the bubble cluster. We observe a perfect quantitative reproducibility of the cavitation events where the inner bubbles in the two-dimensional cluster are shielded by the outer ones, reflected by their later expansion and their delayed collapse. Apart from the final bubble collapse phase (when jetting flows directed towards the cluster's center develop), the bubble dynamics can be quantitatively described by an extended Rayleigh-Plesset equation, taking pressure modification through the surrounding bubbles into account.

  18. Controlled Multibubble Surface Cavitation

    NASA Astrophysics Data System (ADS)

    Bremond, Nicolas; Arora, Manish; Ohl, Claus-Dieter; Lohse, Detlef

    2006-06-01

    Heterogeneous bubble nucleation at surfaces has been notorious because of its irreproducibility. Here controlled multibubble surface cavitation is achieved by using a hydrophobic surface patterned with microcavities. The expansion of the nuclei in the microcavities is triggered by a fast lowering of the liquid pressure. The procedure allows us to control and fix the bubble distance within the bubble cluster. We observe a perfect quantitative reproducibility of the cavitation events where the inner bubbles in the two-dimensional cluster are shielded by the outer ones, reflected by their later expansion and their delayed collapse. Apart from the final bubble collapse phase (when jetting flows directed towards the cluster’s center develop), the bubble dynamics can be quantitatively described by an extended Rayleigh-Plesset equation, taking pressure modification through the surrounding bubbles into account.

  19. Shock Induced Cavitation

    DTIC Science & Technology

    1991-02-01

    Rehak, Margareta L, Frank L. DiMaggio and Ivan S. Sandler, "Interactive Ap- proximations for a Cavitating Fluid around a Floating Structure...INC ATTN: LIBRARY ATTN: R FRANK DEPARTMENT OF THE AIR FORCE BDM INTERNATIONAL INC ATTN: E DORCHAK AIR FORCE INSTITUTE OF TECHNOLOGY/EN ATTN: COMMANDER...F SHELTON ATTN: LIBRARY B KINSLOW SCIENCE APPLICATIONS INTL CORP ATTN: J R BRITT KAMAN SCIENCES CORP ATTN: DASIAC SRI INTERNATIONAL ATTN: E CONRAD

  20. Role of cavitation in high-speed droplet impact problems

    NASA Astrophysics Data System (ADS)

    Kondo, Tomoki; Ando, Keita

    2014-11-01

    High-speed droplet impact is found in physical cleaning using liquid jets, but its mechanisms for particle removal from target surfaces are yet unclear. In this study, we explore the possibility of having cavitation inside the droplet. The pressure evolution within a droplet colliding with a flat surface of deformable materials is determined by multicomponent Euler equations. Dynamics of cavitation bubbles heterogeneously nucleated from preexisting nuclei are determined from Rayleigh-Plesset calculations according to the pressure evolution within the droplet in one-way-coupling manner. The simulation shows that cavitation indeed occurs due to tension that arises from the water hammer shock reflection at the droplet interface. The role of cavitation including pressure emission from its collapse is to be discussed based on the one-way-coupling computations.

  1. Cavitation studies in microgravity

    NASA Astrophysics Data System (ADS)

    Kobel, Philippe; Obreschkow, Danail; Farhat, Mohamed; Dorsaz, Nicolas; de Bosset, Aurele

    The hydrodynamic cavitation phenomenon is a major source of erosion for many industrial systems such as cryogenic pumps for rocket propulsion, fast ship propellers, hydraulic pipelines and turbines. Erosive processes are associated with liquid jets and shockwaves emission fol-lowing the cavity collapse. Yet, fundamental understanding of these processes requires further cavitation studies inside various geometries of liquid volumes, as the bubble dynamics strongly depends the surrounding pressure field. To this end, microgravity represents a unique platform to produce spherical fluid geometries and remove the hydrostatic pressure gradient induced by gravity. The goal of our first experiment (flown on ESA's parabolic flight campaigns 2005 and 2006) was to study single bubble dynamics inside large spherical water drops (having a radius between 8 and 13 mm) produced in microgravity. The water drops were created by a micro-pump that smoothly expelled the liquid through a custom-designed injector tube. Then, the cavitation bubble was generated through a fast electrical discharge between two electrodes immersed in the liquid from above. High-speed imaging allowed to analyze the implications of isolated finite volumes and spherical free surfaces on bubble evolution, liquid jets formation and shock wave dynamics. Of particular interest are the following results: (A) Bubble lifetimes are shorter than in extended liquid volumes, which could be explain by deriving novel corrective terms to the Rayleigh-Plesset equation. (B) Transient crowds of micro-bubbles (smaller than 1mm) appeared at the instants of shockwaves emission. A comparison between high-speed visualizations and 3D N-particle simulations of a shock front inside a liquid sphere reveals that focus zones within the drop lead to a significantly increased density of induced cavitation. Considering shock wave crossing and focusing may hence prove crucially useful to understand the important process of cavitation erosion

  2. Cavitation onset caused by acceleration

    PubMed Central

    Pan, Zhao; Kiyama, Akihito; Tagawa, Yoshiyuki; Daily, David J.; Thomson, Scott L.; Hurd, Randy

    2017-01-01

    Striking the top of a liquid-filled bottle can shatter the bottom. An intuitive interpretation of this event might label an impulsive force as the culprit in this fracturing phenomenon. However, high-speed photography reveals the formation and collapse of tiny bubbles near the bottom before fracture. This observation indicates that the damaging phenomenon of cavitation is at fault. Cavitation is well known for causing damage in various applications including pipes and ship propellers, making accurate prediction of cavitation onset vital in several industries. However, the conventional cavitation number as a function of velocity incorrectly predicts the cavitation onset caused by acceleration. This unexplained discrepancy leads to the derivation of an alternative dimensionless term from the equation of motion, predicting cavitation as a function of acceleration and fluid depth rather than velocity. Two independent research groups in different countries have tested this theory; separate series of experiments confirm that an alternative cavitation number, presented in this paper, defines the universal criteria for the onset of acceleration-induced cavitation. PMID:28739956

  3. Enhancement of cavitation erosion resistance of 316 L stainless steel by adding molybdenum.

    PubMed

    Li, D G; Chen, D R; Liang, P

    2017-03-01

    The influence of Mo on ultrasonic cavitation erosion of 316 L stainless steel in 3.5% NaCl solution were investigated using an ultrasonic cavitation erosion (CE) facility. The morphologies of specimen after cavitation erosion were observed by scanning electron microscopy (SEM). The results showed that the addition of Mo can sharply decrease the mean depth of erosion (MDE) of 316 L SS, implying the increased resistance of cavitation erosion. In order to better understanding the influence of Mo on the cavitation erosion of 316 L SS, the semi-conductive property of passive films on 316 L SS containing different concentrations of Mo were studied by Mott-Schottky plot. Based on Mott-Schottky results and semiconductor physics, a physical model was proposed to explain the effect mechanism of Mo on cavitation erosion of 316 L SS. Copyright © 2016 Elsevier B.V. All rights reserved.

  4. Creep Cavitation in Lower Crustal Shear Zones

    NASA Astrophysics Data System (ADS)

    Menegon, L. M.; Fusseis, F.; Stunitz, H. H.

    2014-12-01

    Shear zones channelize fluid flow in the Earth's crust. A number of mechanisms have been suggested to control fluid migration pathways in upper- and mid-crustal shear zones, amongst them creep cavitation, which is well-known from deforming metals and ceramics. However, little is known on deep crustal fluid migration and on how fluids are channelized and distributed in actively deforming lower crustal shear zones.This study investigates the deformation mechanisms, fluid-rock interaction, and development of porosity in a monzonite ultramylonite from Lofoten, northern Norway. The rock was deformed under lower crustal conditions (T=700-730° C, P=0.65-0.8 GPa). The ultramylonite consists of feldspathic layers and of domains of amphibole + quartz + calcite, which represent the products of hydration reactions of magmatic clinopyroxene. The average grain size in both domains is <25 μm. Microstructural observations and EBSD analysis are consistent with diffusion creep as the dominant deformation mechanism in both domains. In feldspathic layers, isolated quartz grains without a crystallographic preferred orientation occur along C'-type shear bands. All microstructures suggest that quartz precipitated in cavities. The orientation of such quartz bands overlaps with the preferred orientation of pores in the ultramylonites, as evidenced from synchrotron X-ray microtomography. Such C'-type shear bands are interpreted as high-strain cavitation bands resulting from diffusion creep deformation associated with grain boundary sliding. Mass-balance calculation indicates a 2% volume increase during the protolith-ultramylonite transformation. The volume increase is consistent with a synkinematic formation of cavities. Thus, this study presents clear evidence that high-strain cavitation bands may control deep crustal porosity and fluid flow. Nucleation of new phases in cavitation bands inhibits grain growth and enhances the activity of grain-size sensitive creep, thereby maintaining

  5. Study on cavitation influence for pump head in an axial flow pump

    NASA Astrophysics Data System (ADS)

    Hosono, K.; Kajie, Y.; Saito, S.; Miyagawa, K.

    2015-12-01

    The size of axial flow pumps used in drainage pump stations has recently decreased, and their rotation speeds have increased, causing an increase in the risk of cavitation. Therefore, to provide highly reliable pumps, it is important to understand the internal flow of pumps under cavitating conditions. In this study, high-speed camera measurements and computational fluid dynamics analysis were performed to understand the cavitation performance of an axial flow pump. The mechanism that causes the head to change as a result of cavitation under low net positive suction head values is shown to be the balance between the increasing angular momentum and the loss indicated by the changing streamlines.

  6. Physical facets of ultrasonic cavitational synthesis of zinc ferrite particles.

    PubMed

    Reddy, Bhaskar Rao; Sivasankar, Thirugnanasambandam; Sivakumar, Manickam; Moholkar, Vijayanand S

    2010-02-01

    This paper addresses the physical features of the ultrasonic cavitational synthesis of zinc ferrite particles and tries to establish the relationship between cavitation physics and sonochemistry of the zinc ferrite synthesis. A dual approach of coupling experimental results with simulations of radial motion of cavitation bubbles has been adopted. The precursors for the zinc ferrite, viz. ZnO and Fe(3)O(4) are produced in situ by the hydrolysis of Zn and Fe(II) acetates stimulated by (*)OH radicals produced from the transient collapse of the cavitation bubbles. Experiments performed under different conditions create significant variation in the production of (*)OH radicals, and hence, the rate of acetate hydrolysis. Correlation of the results of experiments and simulations sheds light on the important facets of the physical mechanism of ultrasonic cavitational zinc ferrite synthesis. It is revealed that too much or too little rate of acetate hydrolysis results in smaller particle size of zinc ferrite. The first effect of a higher rate of hydrolysis leads to excessively large growth of particles, due to which they become susceptible to the disruptive action of cavitation bubbles. Whereas, the second effect of too small rate of hydrolysis of Zn and Fe(II) acetates restricts the growth of particles. It has been observed that the initial reactant concentration does not influence the mean particle size or the size distribution of zinc ferrite particles. The present investigation clearly confirms that the rate-controlling step of zinc ferrite synthesis through ultrasonic cavitational route is the rate of formation of (*)OH radicals from cavitation bubbles.

  7. Cavitation-resistant inducer

    DOEpatents

    Dunn, Charlton; Subbaraman, Maria R.

    1989-01-01

    An improvement in an inducer for a pump wherein the inducer includes a hub, a plurality of radially extending substantially helical blades and a wall member extending about and encompassing an outer periphery of the blades. The improvement comprises forming adjacent pairs of blades and the hub to provide a substantially rectangular cross-sectional flow area which cross-sectional flow area decreases from the inlet end of the inducer to a discharge end of the inducer, resulting in increased inducer efficiency improved suction performance, reduced susceptibility to cavitation, reduced susceptibility to hub separation and reduced fabrication costs.

  8. Cavitation-resistant inducer

    DOEpatents

    Dunn, C.; Subbaraman, M.R.

    1989-06-13

    An improvement in an inducer for a pump is disclosed wherein the inducer includes a hub, a plurality of radially extending substantially helical blades and a wall member extending about and encompassing an outer periphery of the blades. The improvement comprises forming adjacent pairs of blades and the hub to provide a substantially rectangular cross-sectional flow area which cross-sectional flow area decreases from the inlet end of the inducer to a discharge end of the inducer, resulting in increased inducer efficiency improved suction performance, reduced susceptibility to cavitation, reduced susceptibility to hub separation and reduced fabrication costs. 11 figs.

  9. Surface tension and quasi-emulsion of cavitation bubble cloud.

    PubMed

    Bai, Lixin; Chen, Xiaoguang; Zhu, Gang; Xu, Weilin; Lin, Weijun; Wu, Pengfei; Li, Chao; Xu, Delong; Yan, Jiuchun

    2017-03-01

    A quasi-emulsion phenomenon of cavitation structure in a thin liquid layer (the thin liquid layer is trapped between a radiating surface and a hard reflector) is investigated experimentally with high-speed photography. The transformation from cloud-in-water (c/w) emulsion to water-in-cloud (w/c) emulsion is related to the increase of cavitation bubble cloud. The acoustic field in the thin liquid layer is analyzed. It is found that the liquid region has higher acoustic pressure than the cloud region. The bubbles are pushed from liquid region to cloud region by the primary Bjerknes forces. The rate of change of CSF increased with the increase of CSF. The cavitation bubbles on the surface of cavitation cloud are attracted by the cavitation bubbles inside the cloud due to secondary Bjerknes forces. The existence of surface tension on the interface of liquid region and cloud region is proved. The formation mechanism of disc-shaped liquid region and cloud region are analysed by surface tension and incompressibility of cavitation bubble cloud.

  10. Cavitation Bubble Streaming in Ultrasonic-Standing-Wave Field

    NASA Astrophysics Data System (ADS)

    Nomura, Shinfuku; Mukasa, Shinobu; Kuroiwa, Masaya; Okada, Yasuyuki; Murakami, Koichi

    2005-05-01

    The mechanism of cavitation bubble streaming by ultrasonic vibration in a water tank was experimentally investigated. A standard ultrasonic cleaner unit with a resonant frequency of 40 kHz was used as an ultrasonic generator. The behavior of the streaming was visualized by the schlieren method and sonochemical luminescence, and the velocity of the streaming was measured by laser Doppler velocity measurement equipment (LDV). The cavitation bubble streaming has two structures. A cavitation cloud, which consists of many cavitation bubbles, is shaped like a facing pair of bowls with a diameter of approximately 1/3 the wavelength of the standing wave, and moves inside the standing-wave field with a velocity of 30 to 60 mm/s. The cavitation bubbles move intensely in the cloud with a velocity of 5 m/s at an ultrasonic output power of 75 W. The streaming is completely different from conventional acoustic streaming. Also the cavitation bubble is generated neither at the pressure node nor at the antinode.

  11. Cavitation erosion resistance of microarc oxidation coating on aluminium alloy

    NASA Astrophysics Data System (ADS)

    Cheng, Feng; Jiang, Shuyun; Liang, Jun

    2013-09-01

    Two ceramic coatings are prepared on 2124 aluminum alloy by microarc oxidation (MAO) technology. To explore the cavitation erosion resistance of the MAO coating, cavitation tests were performed by using a rotating-disk test rig. The mass losses, surface morphologies, chemical compositions and the phase constituents of the samples after cavitation tests were examined by using digital balance, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The results indicate that the MAO coatings can extend the incubation period of aluminum alloy, and thus enhance the cavitation erosion resistance as compared to the untreated aluminum alloy samples. After duration of 63 h cavitation test, a lot of erosion pits and the particles in various shapes can be observed on the surfaces of the aluminum alloy samples, while only a few erosion pits are observed on the MAO coatings. Moreover, the mean depths of erosion on the MAO coatings are lower in the first 30 h and are independent on erosion time. The results show that the cavitation erosion of MAO coating is governed by water mechanical impaction, resulting from the effects of brittle fracture of the MAO coating.

  12. Numerical Study on the Inhibition of Cavitation in Piping Systems

    NASA Astrophysics Data System (ADS)

    Byeon, Sun Seok; Lee, Sang Jun; Kim, Youn-Jea

    Abrupt closing valve in piping systems is sometimes resulted in cavitation due to the occurrence of high pressure difference. The bubbles generating by cavitation influence operating pressure and then those generate shock wave and vibration. These phenomena can consequentially cause to corrosion and erosion. So, the cavitation is the important factor to consider reliability of piping systems and mechanical lifetime. This paper investigated the various inhibition methods of cavitation in piping systems in which butterfly valves are installed. To prevent cavitation occurrence, it is desirable to analyze its characteristics between the upstream and downstream of process valve. Results show that the fluid velocity is fast when a working fluid passed through butterfly valve. The pressure of these areas was not only under saturation vapor pressure of water, but also cavitation was continuously occurred. We confirmed that the effect of existence of inserted orifice and influence to break condition under saturation vapor pressure of water. Results were graphically depicted by pressure distribution, velocity distribution, and vapor volume fraction.

  13. Researches upon the cavitation erosion behaviour of austenite steels

    NASA Astrophysics Data System (ADS)

    Bordeasu, I.; Popoviciu, M. O.; Mitelea, I.; Salcianu, L. C.; Bordeasu, D.; Duma, S. T.; Iosif, A.

    2016-02-01

    Paper analyzes the cavitation erosion behavior of two stainless steels with 100% austenitic structure but differing by the chemical composition and the values of mechanical properties. The research is based on the MDE(t) and MDER(t) characteristic curves. We studied supplementary the aspect of the eroded areas by other to different means: observations with performing optical microscopes and roughness measurements. The tests were done in the T2 vibratory facility in the Cavitation Laboratory of the Timisoara Polytechnic University. The principal purpose of the study is the identification of the elements influencing significantly the cavitation erosion resistance. It was established the effect of the principal chemical components (determining the proportion of the structural components in conformity the Schaffler diagram) upon the cavitation erosion resistance. The results of the researches present the influence of the proportion of unstable austenite upon cavitation erosion resistance. The stainless steel with the great proportion of unstable austenite has the best behavior. The obtained conclusion are important for the metallurgists which realizes the stainless steels used for manufacturing the runners of hydraulic machineries (turbines and pumps) with increased resistance to cavitation attack.

  14. Physics associated with cavitation induced material damage

    NASA Technical Reports Server (NTRS)

    Peterson, F. B.

    1974-01-01

    The role of cavitation in mechanical failure is discussed. Some of the most common types of material damage associated with the presence of cavitation are surface material removal, delamination and structural vibration. This occurs in external flows such as on propellers, hydrofoils, and high speed non-lifting surfaces. In internal flows, pipe bends, inlets, constructions, pumps and turbines are typical. Nominally nonflowing liquids are also susceptible in, for example, strong acoustic fields and high energy particle detectors. For flowing systems, Bernoulli's equation shows how a local pressure is reduced as the fluid's velocity is increased. At sufficiently high velocities, a tension can actually develop and this has, in fact, been demonstrated experimentally. Once the pressure is reduced below the fluid vapor pressure a vapor cavity can be nucleated. Various aspects of this process are simply shown by considering the flow over a lifting surface.

  15. Preparation of graphene by jet cavitation.

    PubMed

    Shen, Zhigang; Li, Jinzhi; Yi, Min; Zhang, Xiaojing; Ma, Shulin

    2011-09-07

    Despite its bright prospects, graphene faces challenges including issues concerning mass production. Here we present a totally green approach whereby common crystal graphite can be exfoliated into graphene sheets in aqueous solution by jet cavitation. This is possible mainly because the tensile stress caused by graphite-solution interfacial reflection of compressive waves acts an intensive 'suction disk' on the graphite flakes. We confirm the presence of graphene sheets by diverse characterizations. The graphene yield by our method is estimated as ∼ 4 wt%, which could potentially be improved by further processing. The method, of a mechanical nature, is powerful compared to the traditional low-throughput micromechanical cleavage. Our work here illustrates jet cavitation as a facile, low cost, timesaving and laborsaving route, which can potentially be scaled up to mass production of graphene.

  16. Preparation of graphene by jet cavitation

    NASA Astrophysics Data System (ADS)

    Shen, Zhigang; Li, Jinzhi; Yi, Min; Zhang, Xiaojing; Ma, Shulin

    2011-09-01

    Despite its bright prospects, graphene faces challenges including issues concerning mass production. Here we present a totally green approach whereby common crystal graphite can be exfoliated into graphene sheets in aqueous solution by jet cavitation. This is possible mainly because the tensile stress caused by graphite-solution interfacial reflection of compressive waves acts an intensive 'suction disk' on the graphite flakes. We confirm the presence of graphene sheets by diverse characterizations. The graphene yield by our method is estimated as ~ 4 wt%, which could potentially be improved by further processing. The method, of a mechanical nature, is powerful compared to the traditional low-throughput micromechanical cleavage. Our work here illustrates jet cavitation as a facile, low cost, timesaving and laborsaving route, which can potentially be scaled up to mass production of graphene.

  17. Physics associated with cavitation induced material damage

    NASA Technical Reports Server (NTRS)

    Peterson, F. B.

    1974-01-01

    The role of cavitation in mechanical failure is discussed. Some of the most common types of material damage associated with the presence of cavitation are surface material removal, delamination and structural vibration. This occurs in external flows such as on propellers, hydrofoils, and high speed non-lifting surfaces. In internal flows, pipe bends, inlets, constructions, pumps and turbines are typical. Nominally nonflowing liquids are also susceptible in, for example, strong acoustic fields and high energy particle detectors. For flowing systems, Bernoulli's equation shows how a local pressure is reduced as the fluid's velocity is increased. At sufficiently high velocities, a tension can actually develop and this has, in fact, been demonstrated experimentally. Once the pressure is reduced below the fluid vapor pressure a vapor cavity can be nucleated. Various aspects of this process are simply shown by considering the flow over a lifting surface.

  18. Anticipatory model of cavitation

    NASA Astrophysics Data System (ADS)

    Kercel, Stephen W.; Allgood, Glenn O.; Dress, William B.; Hylton, James O.

    1999-03-01

    The Anticipatory System (AS) formalism developed by Robert Rosen provides some insight into the problem of embedding intelligent behavior in machines. AS emulates the anticipatory behavior of biological systems. AS bases its behavior on its expectations about the near future and those expectations are modified as the system gains experience. The expectation is based on an internal model that is drawn from an appeal to physical reality. To be adaptive, the model must be able to update itself. To be practical, the model must run faster than real-time. The need for a physical model and the requirement that the model execute at extreme speeds, has held back the application of AS to practical problems. Two recent advances make it possible to consider the use of AS for practical intelligent sensors. First, advances in transducer technology make it possible to obtain previously unavailable data from which a model can be derived. For example, acoustic emissions (AE) can be fed into a Bayesian system identifier that enables the separation of a weak characterizing signal, such as the signature of pump cavitation precursors, from a strong masking signal, such as a pump vibration feature. The second advance is the development of extremely fast, but inexpensive, digital signal processing hardware on which it is possible to run an adaptive Bayesian-derived model faster than real-time. This paper reports the investigation of an AS using a model of cavitation based on hydrodynamic principles and Bayesian analysis of data from high-performance AE sensors.

  19. Current Status in Cavitation Modeling

    NASA Technical Reports Server (NTRS)

    Singhal, Ashok K.; Avva, Ram K.

    1993-01-01

    Cavitation is a common problem for many engineering devices in which the main working fluid is in liquid state. In turbomachinery applications, cavitation generally occurs on the inlet side of pumps. The deleterious effects of cavitation include: lowered performance, load asymmetry, erosion and pitting of blade surfaces, vibration and noise, and reduction of the overall machine life. Cavitation models in use today range from rather crude approximations to sophisticated bubble dynamics models. Details about bubble inception, growth and collapse are relevant to the prediction of blade erosion, but are not necessary to predict the performance of pumps. An engineering model of cavitation is proposed to predict the extent of cavitation and performance. The vapor volume fraction is used as an indicator variable to quantify cavitation. A two-phase flow approach is employed with the assumption of the thermal equilibrium between liquid and vapor. At present velocity slip between the two phases is selected. Preliminary analyses of 2D flows shows qualitatively correct results.

  20. Nuclei and propeller cavitation inception

    SciTech Connect

    Gindroz, B.; Billet, M.L.

    1994-12-31

    Propeller cavitation inception tests were conducted in the Grand Tunnel Hydrodynamique (GTH) of the Bassin d`Essaid des Carenes. Both acoustic and visual cavitation inception were determined for leading-edge sheet, travelling bubble, and tip vortex. These data were obtained for specific water quality conditions. The water quality was determined from cavitation susceptibility meter measurements for degassed water (maximum liquid tension, few nuclei), low injection rate of microbubbles (medium liquid tension, low nuclei concentration), medium injection rate of microbubbles (medium liquid tension, high nuclei concentration) and high injection rate of microbubbles (minimum liquid tension, high nuclei concentration). Results clearly demonstrate a different influence of water quality for each type of cavitation. Little variation in cavitation inception index for a significant increase in liquid tension and microbubble size distribution was found for leading-edge sheet; however, tip vortex cavitation inception index decreased significantly for an increase in liquid tension. In addition, a dependency on event rate was determined for tip vortex cavitation inception.

  1. Experimental investigation on cavitating flow shedding over an axisymmetric blunt body

    NASA Astrophysics Data System (ADS)

    Hu, Changli; Wang, Guoyu; Huang, Biao

    2015-03-01

    Nowadays, most researchers focus on the cavity shedding mechanisms of unsteady cavitating flows over different objects, such as 2D/3D hydrofoils, venturi-type section, axisymmetric bodies with different headforms, and so on. But few of them pay attention to the differences of cavity shedding modality under different cavitation numbers in unsteady cavitating flows over the same object. In the present study, two kinds of shedding patterns are investigated experimentally. A high speed camera system is used to observe the cavitating flows over an axisymmetric blunt body and the velocity fields are measured by a particle image velocimetry (PIV) technique in a water tunnel for different cavitation conditions. The U-type cavitating vortex shedding is observed in unsteady cavitating flows. When the cavitation number is 0.7, there is a large scale cavity rolling up and shedding, which cause the instability and dramatic fluctuation of the flows, while at cavitation number of 0.6, the detached cavities can be conjunct with the attached part to induce the break-off behavior again at the tail of the attached cavity, as a result, the final shedding is in the form of small scale cavity and keeps a relatively steady flow field. It is also found that the interaction between the re-entrant flow and the attached cavity plays an important role in the unsteady cavity shedding modality. When the attached cavity scale is insufficient to overcome the re-entrant flow, it deserves the large cavity rolling up and shedding just as that at cavitation number of 0.7. Otherwise, the re-entrant flow is defeated by large enough cavity to induce the cavity-combined process and small scale cavity vortexes shedding just as that of the cavitation number of 0.6. This research shows the details of two different cavity shedding modalities which is worthful and meaningful for the further study of unsteady cavitation.

  2. Effect of a cavitation treatment of coals on their physicochemical properties and ability for thermal dissolution

    SciTech Connect

    Yu. F. Patrakov; N.I. Fedorova; S.A. Semenova

    2007-08-15

    It was found that the cavitation treatment of low-metamorphized coals from the Kuznetsk Basin resulted in not only their mechanical degradation but also changes in the chemical composition of the surface layers of coal particles due to the occurrence of oxidation-hydrolysis reactions with water in a supercritical state under cavitation conditions.

  3. Dynamic response of cavitating turbomachines

    NASA Technical Reports Server (NTRS)

    Ng, S. L.

    1976-01-01

    Stimulated by the pogo instability encountered in many liquid propellant rockets, the dynamic behavior of cavitating inducers is discussed. An experimental facility where the upstream and downstream flows of a cavitating inducer could be perturbed was constructed and tested. The upstream and downstream pressure and mass flow fluctuations were measured. Matrices representing the transfer functions across the inducer pump were calculated from these measurements and from the hydraulic system characteristics for two impellers in various states of cavitation. The transfer matrices when plotted against the perturbing frequency showed significant departure from steady state or quasi-steady predictions especially at higher frequencies.

  4. Hydrodynamic cavitation as a novel approach for delignification of wheat straw for paper manufacturing.

    PubMed

    Badve, Mandar P; Gogate, Parag R; Pandit, Aniruddha B; Csoka, Levente

    2014-01-01

    The present work deals with application of hydrodynamic cavitation for intensification of delignification of wheat straw as an essential step in the paper manufacturing process. Wheat straw was first treated with potassium hydroxide (KOH) for 48 h and subsequently alkali treated wheat straw was subjected to hydrodynamic cavitation. Hydrodynamic cavitation reactor used in the work is basically a stator and rotor assembly, where the rotor is provided with indentations and cavitational events are expected to occur on the surface of rotor as well as within the indentations. It has been observed that treatment of alkali treated wheat straw in hydrodynamic cavitation reactor for 10-15 min increases the tensile index of the synthesized paper sheets to about 50-55%, which is sufficient for paper board manufacture. The final mechanical properties of the paper can be effectively managed by controlling the processing parameters as well as the cavitational parameters. It has also been established that hydrodynamic cavitation proves to be an effective method over other standard digestion techniques of delignification in terms of electrical energy requirements as well as the required time for processing. Overall, the work is first of its kind application of hydrodynamic cavitation for enhancing the effectiveness of delignification and presents novel results of significant interest to the paper and pulp industry opening an entirely new area of application of cavitational reactors.

  5. Vortex cavitation and oscillation in a double-suction volute pump

    NASA Astrophysics Data System (ADS)

    Sato, T.; Nagahara, T.; Tanaka, K.; Fuchiwaki, M.; Shimizu, F.

    2010-08-01

    In recent years, Computational Fluid Dynamics (CFD) codes have been utilized actively in the early part of the product development cycle. Numerical analysis models have also been developed rapidly and have added cavitation flow analysis functions peculiar to hydraulic machines, in which the flow analysis has been developed remarkably with high-precision and high-reliability. On the other hand, it is well known that three kinds of cavitation, such as vortex cavitation, reverse flow cavitation and cloud cavitation appear in a double-suction volute pump. We have much interest in a relationship among the cavitating flows, pump oscillation and noise. In this study, full 3D numerical simulations have been performed using a commercial code inside the pump from the inlet of suction duct to the outlet of delivery duct. The numerical model is based on a combination of multiphase flow equations with the truncated version of the Rayleigh-Plesset model predicting the complicated growth and collapse process of cavity bubbles. This study highlights especially the mechanism of vortex cavitation occurrence from the end of the suction duct in the pump and pump oscillation which causes cavitation noise from the pump. The experimental investigations have also been performed on the cavitating flow with flow visualization to evaluate the numerical results.

  6. An Experimental Study of Cavitation Detection in a Centrifugal Pump Using Envelope Analysis

    NASA Astrophysics Data System (ADS)

    Tan, Chek Zin; Leong, M. Salman

    Cavitation represents one of the most common faults in pumps and could potentially lead to a series of failure in mechanical seal, impeller, bearing, shaft, motor, etc. In this work, an experimental rig was setup to investigate cavitation detection using vibration envelope analysis method, and measured parameters included sound, pressure and flow rate for feasibility of cavitation detection. The experiment testing included 3 operating points of the centrifugal pump (B.E.P, 90% of B.E.P and 80% of B.E.P). Suction pressure of the centrifugal pump was decreased gradually until the inception point of cavitation. Vibration measurements were undertaken at various locations including casing, bearing, suction and discharge flange of the centrifugal pump. Comparisons of envelope spectrums under cavitating and non-cavitating conditions were presented. Envelope analysis was proven useful in detecting cavitation over the 3 testing conditions. During the normal operating condition, vibration peak synchronous to rotational speed was more pronounced. It was however during cavitation condition, the half order sub-harmonic vibration component was clearly evident in the envelope spectrums undertaken at all measurement locations except at the pump bearing. The possible explanation of the strong sub-harmonic (½ of BPF) during cavitation existence in the centrifugal pump was due to insufficient time for the bubbles to collapse completely before the end of the single cycle.

  7. Dynamics of Isolated Tip Vortex Cavitation

    NASA Astrophysics Data System (ADS)

    Pennings, Pepijn; Bosschers, Johan; van Terwisga, Tom

    2014-11-01

    Performance of ship propellers and comfort levels in the surroundings are limited by various forms of cavitation. Amongst these forms tip vortex cavitation is one of the first appearing forms and is expected to be mainly responsible for the emission of broadband pressure fluctuations typically occurring between the 4th to the 7th blade passing frequency (approx. 40--70 Hz). These radiated pressure pulses are likely to excite parts of the hull structure resulting in a design compromise between efficiency and comfort. Insight is needed in the mechanism of acoustic emission from the oscillations by a tip vortex cavity. In the current experimental study the tip vortex cavity from a blade with an elliptic planform and sections based on NACA 662 - 415 with meanline a = 0 . 8 is observed using high speed shadowgraphy in combination with blade force and acoustic measurements. An analytic model describing three main cavity deformation modes is verified and used to explain the origin of a cavity eigenfrequency or ``vortex singing'' phenomenon observed by Maines and Arndt (1997) on the tip vortex cavity originating from the same blade. As no hydrodynamic sound originating from the tip vortex cavity was observed it is posed that a tip flow instability is essential for ``vortex singing.'' This research was funded by the Lloyd's Register Foundation as part of the International Institute for Cavitation Research.

  8. Megasonic cleaning, cavitation, and substrate damage: an atomistic approach

    NASA Astrophysics Data System (ADS)

    Kapila, Vivek; Deymier, Pierre A.; Shende, Hrishikesh; Pandit, Viraj; Raghavan, Srini; Eschbach, Florence O.

    2006-05-01

    Megasonic cleaning has been a traditional approach for the cleaning of photomasks. Its feasibility as a damage free approach to sub 50 nm particulate removal is under investigation for the cleaning of optical and EUV photomasks. Two major mechanisms are active in a megasonic system, namely, acoustic streaming and acoustic cavitation. Acoustic streaming is instrumental in contaminant removal via application of drag force and rolling of particles, while cavitation may dislodge particles by the release of large energy during cavity implosion or by acting as a secondary source of microstreaming. Often times, the structures (substrates with or without patterns) subjected to megasonic cleaning show evidence of damage. This is one of the impediments in the implementation of megasonic technology for 45 nm and future technology nodes. Prior work suggests that acoustic streaming does not lead to sufficiently strong forces to cause damage to the substrates or patterns. However, current knowledge of the effects of cavitation on cleaning and damage can be described, at best, as speculative. Recent experiments suggest existence of a cavity size and energy distributions in megasonic systems that may be responsible for cleaning and damage. In the current work, we develop a two-dimensional atomistic model to study such multibubble cavitation phenomena. The model consists of a Lennard-Jones liquid which is subjected to sinusoidal pressure changes leading to the formation of cavitation bubbles. The current work reports on the effects of pressure amplitude (megasonic power) and frequency on cavity size distributions in vaporous and gaseous cavitation. The findings of the work highlight the role of multibubble cavitation as cleaning and damage mechanism in megasonic cleaning.

  9. Microleakage of Cavit, CavitW, CavitG and IRM by impedance spectroscopy.

    PubMed

    Jacquot, B M; Panighi, M M; Steinmetz, P; G'Sell, C

    1996-07-01

    The aim of this study was to quantify the sealing ability of four temporary filling materials over 9 days using a new electrochemical technique. Fifty-two extracted human maxillary bicuspids were selected and prepared for the measurements. They were divided into four groups of 12 teeth each, in addition to two positive and two negative controls. After preparation of the endodontic access cavity the sealing ability was registered. After a randomization procedure one group was obturated with IRM, another group with Cavit, a third group with CavitW and the last group with CavitG. The sealability was measured just after obturation (time 0) and after days 1, 2, 3, 4, 7 and 9. The results showed that the IRM group was significantly more watertight than the different Cavit formulations. Throughout the experiment no significant difference was noticed between the Cavit and CavitW groups (P > 0.05). The CavitG group was significantly less watertight throughout the measurements (P < 0.05).

  10. Cavitation-controlled ultrasonic agitator

    SciTech Connect

    Sheen, S.H.; Lawrence, W.P.; Raptis, A.C.

    1989-10-01

    High-intensity ultrasound generally produces nonlinear acoustic cavitation and streaming in liquids. The ultrasonic energy required to cause cavitation and streaming in a liquid depends on the physical properties of the liquid, e.g., surface tension, viscosity, and entrained gases. Both cavitation and streaming generate acoustic noise whose signatures may be used to distinguish the stage of agitation and thus allow the process to be controlled. An ultrasonic agitator has been designed for application in a confined area with a high-temperature, high-pressure, and corrosive environment. Control of this agitator is based on the detection of noise levels and subharmonics produced during cavitation and streaming. Noise signatures of agitation in different liquids and in liquids with particles have been determined, and discussed. 6 refs., 6 figs.

  11. Cavitating vortex generation by a submerged jet

    SciTech Connect

    Belyakov, G. V.; Filippov, A. N.

    2006-05-15

    The surface geometry of a cavitating vortex is determined in the limit of inviscid incompressible flow. The limit surface is an ovaloid of revolution with an axis ratio of 5: 3. It is shown that a cavitating vortex ring cannot develop if the cavitation number is lower than a certain critical value. Experiments conducted at various liquid pressures and several jet exit velocities confirm the existence of a critical cavitation number close to 3. At cavitation numbers higher than the critical one, the cavitating vortex ring does not develop. At substantially lower cavitation numbers (k {<=} 0.1), an elongated asymmetric cavitation bubble is generated, with an axial reentrant jet whose length can exceed the initial jet length by several times. This flow structure is called an asymmetric cavitating vortex, even though steady motion of this structure has not been observed.

  12. Cavitation performance evaluation for a condensate pump

    NASA Astrophysics Data System (ADS)

    Yu, A.; Yu, W. P.; Pan, Z. B.; Luo, X. W.; Ji, B.; Y Xu, H.

    2013-12-01

    Cavitation in a condensate pump with specific speed of 95 m·m3s-1·min-1 was treated in this study. Cavitation performance for the pump was tested experimentally, and the steady state cavitating flows in the pump impeller were simulated by RANS method as well as a homogeneous cavitation model. It is noted that cavitating flow simulation reasonably depicted cavitation development in the pump. Compared to the tested results, the numerical simulation basically predicted later performance drops due to cavitation. Unfortunately, the cavitation simulation at the operation condition of 50% best efficiency point could not predict the head drop up to 3%. By applying the concept of relative cavity length cavitation performance evaluation is achieved. For better application, future study is necessary to establish the relation between relative cavity length and performance drop.

  13. Current research in cavitating fluid films

    NASA Technical Reports Server (NTRS)

    Brewe, D. E. (Editor); Ball, J. H. (Editor); Khonsari, M. M. (Editor)

    1990-01-01

    A review of the current research of cavitation in fluid films is presented. Phenomena and experimental observations include gaseous cavitation, vapor cavitation, and gas entrainment. Cavitation in flooded, starved, and dynamically loaded journal bearings, as well as squeeze films are reviewed. Observations of cavitation damage in bearings and the possibility of cavitation between parallel plates with microasperities were discussed. The transcavity fluid transport process, meniscus motion and geometry or form of the film during rupture, and reformation were summarized. Performance effects were related to heat transfer models in the cavitated region and hysteresis influence on rotor dynamics coefficients. A number of cavitation algorithms was presented together with solution procedures using the finite difference and finite element methods. Although Newtonian fluids were assumed in most of the discussions, the effect of non-Newtonian fluids on cavitation was also discussed.

  14. A metallurgical approach to improved cavitation-erosion resistance

    SciTech Connect

    Richman, R.H.; McNaughton, W.P.

    1997-10-01

    Although cavitation erosion in hydraulic systems is an old problem, the damage mechanism that culminates in material loss was not known with certainty until recently. An investigation is described that aimed at clarifying the damage mechanism in cavitation erosion and applying that knowledge to make hydraulic equipment more resistant to cavitation. Strong correlations were established between cyclic deformation (fatigue) parameters and cavitation-erosion rates. This identification facilitated the search for more resistant materials. Finite element modeling confirmed that localized impacts on metal surfaces produce fatigue like deformations and damage accumulation. Among available materials, near-equiatomic alloys of nickel and titanium are anomalously resistant to low-cycle fatigue and thus should be very resistant to cavitation erosion. Experiments confirmed the expected erosion resistance. Building large machines entirely out of NiTi is impractical, however, and a way of selectively cladding common constructional materials is required. Because NiTi has not been fusion welded successfully to other alloys, explosive bonding of thin NiTi plates to structural steel was investigated. Excellent welds were achieved, and the erosion resistance of the resulting clads has been demonstrated. Comparisons are made to other erosion processes and to other erosion-resistant materials, and some applications to hydraulic devices are suggested.

  15. Cavitation in shock wave lithotripsy

    NASA Astrophysics Data System (ADS)

    Bailey, Michael R.; Crum, Lawrence A.; Sapozhnikov, Oleg A.; Evan, Andrew P.; McAteer, James A.; Colonius, Tim; Cleveland, Robin O.

    2003-10-01

    A case is presented for the important role of cavitation in stone comminution and tissue injury in shock wave lithotripsy (SWL). Confocal hydrophones and a coincidence algorithm were used to detect cavitation in kidney parenchyma. Elevated hydrostatic pressure dissolved cavitation nuclei and suppressed cell injury and stone comminution in vitro. A low-insertion-loss, thin, mylar film nearly eliminated stone erosion and crack formation only when in direct contact with the stone. This result indicates not only that cavitation is important in both cracking and erosion but also that bubbles act at the surface. Time inversion of the shock wave by use of a pressure-release reflector reduced the calculated pressure at bubble collapse and the measured depth of bubble-induced pits in aluminum. Correspondingly tissue injury in vivo was nearly eliminated. Cavitation was localized and intensified by the use of synchronously triggered, facing lithotripters. This dual pulse lithotripter enhanced comminution at its focus and reduced lysis in surrounding blood samples. The enhancement of comminution was lost when stones were placed in glycerol, which retarded bubble implosion. Thus, cavitation is important in comminution and injury and can be controlled to optimize efficacy and safety. [Work supported by NIH DK43381, DK55674, and FIRCA.

  16. Numerical estimation of cavitation intensity

    NASA Astrophysics Data System (ADS)

    Krumenacker, L.; Fortes-Patella, R.; Archer, A.

    2014-03-01

    Cavitation may appear in turbomachinery and in hydraulic orifices, venturis or valves, leading to performance losses, vibrations and material erosion. This study propose a new method to predict the cavitation intensity of the flow, based on a post-processing of unsteady CFD calculations. The paper presents the analyses of cavitating structures' evolution at two different scales: • A macroscopic one in which the growth of cavitating structures is calculated using an URANS software based on a homogeneous model. Simulations of cavitating flows are computed using a barotropic law considering presence of air and interfacial tension, and Reboud's correction on the turbulence model. • Then a small one where a Rayleigh-Plesset software calculates the acoustic energy generated by the implosion of the vapor/gas bubbles with input parameters from macroscopic scale. The volume damage rate of the material during incubation time is supposed to be a part of the cumulated acoustic energy received by the solid wall. The proposed analysis method is applied to calculations on hydrofoil and orifice geometries. Comparisons between model results and experimental works concerning flow characteristic (size of cavity, pressure,velocity) as well as pitting (erosion area, relative cavitation intensity) are presented.

  17. Effect of geometrical parameters on submerged cavitation jet discharged from profiled central-body nozzle

    NASA Astrophysics Data System (ADS)

    Yang, Minguan; Xiao, Shengnan; Kang, Can; Wang, Yuli

    2013-05-01

    The flow characteristics of cavitation jets are essential issues among relevant studies. The physical properties of the jet are largely determined by the geometrical parameters of the nozzle. The structure and cavitation jets characteristics of the angular-nozzle and the self-resonating cavitation nozzle have been extensively studied, but little research is conducted in the central-body cavitation nozzle mainly because of its hard processing and the cavitation jet effect not satisfactory. In this paper, a novel central-body nozzle (a non-plunger central-body nozzle with square outlet) is studied to solve above problems. Submerged jets discharged from the novel central-body nozzle are simulated, employing the full cavitation model. The impact of nozzle configuration on jet properties is analyzed. The analysis results indicate that when central-body relative diameter keeps constant, there is an optimal contraction degree of nozzle's outlet, which can induce intense cavitation in the jet. The central-body relative diameter also affects jet profiles. In the case of large central-body relative diameter, most of the bubbles settle in the jet core. On the contrary, a smaller relative diameter makes bubbles concentrate in the interface between the jet and its surrounding fluid. Moreover, the shorter outlet part allows the cavitation zone further extend in both the axial and racial directions. The research results further consummate the study on the central-body nozzles and the correlation between cavitation jet and the structure, and elementarily reveal the mechanism of cavitation jet produced in a non-plunger novel central-body nozzle and the effect of the structure parameters on the cavitation jet, moreover, provide the theoretical basis for the optimal design of the nozzle.

  18. Cavitation assisted delignification of wheat straw: a review.

    PubMed

    Iskalieva, Asylzat; Yimmou, Bob Mbouyem; Gogate, Parag R; Horvath, Miklos; Horvath, Peter G; Csoka, Levente

    2012-09-01

    Wheat is grown in most of the Indian and Chinese regions and after harvesting, the remaining straw offers considerable promise as a renewable source most suitable for papermaking and as a pulping resource. Delignification of wheat straw offers ample scope for energy conservation by way of the application of the process intensification principles. The present work reviews the pretreatment techniques available for improving the effectiveness of the conventional approach for polysaccharide component separation, softening and delignification. A detailed overview of the cavitation assisted delignification process has been presented based on the earlier literature illustrations and important operational guidelines have been presented for overall low-cost and amenable energy utilization in the processes. The effectiveness of the methods has been evaluated according to yield and properties of the isolated fibers in comparison to the conventional treatment. Also the experimental results of one such non-conventional treatment scheme based on the use of hydrodynamic cavitation have been presented for the pulping of wheat straw. The effect of hydrodynamically induced cavitation on cell wall matrix and its components have been characterized using FT-IR analysis with an objective of understanding the cavitation assisted digestion mechanism on straws. It has been observed that the use of hydrodynamic cavitation does not degrade the fibrillar structure of cellulose but causes relocalisation and partial removal of lignin. Overall it appears that considerable improvement can be obtained due to the use of pretreatment or alternate techniques for delignification, which is an energy intensive step in the paper making industries.

  19. Gauging the likelihood of stable cavitation from ultrasound contrast agents

    NASA Astrophysics Data System (ADS)

    Bader, Kenneth B.; Holland, Christy K.

    2013-01-01

    The mechanical index (MI) was formulated to gauge the likelihood of adverse bioeffects from inertial cavitation. However, the MI formulation did not consider bubble activity from stable cavitation. This type of bubble activity can be readily nucleated from ultrasound contrast agents (UCAs) and has the potential to promote beneficial bioeffects. Here, the presence of stable cavitation is determined numerically by tracking the onset of subharmonic oscillations within a population of bubbles for frequencies up to 7 MHz and peak rarefactional pressures up to 3 MPa. In addition, the acoustic pressure rupture threshold of an UCA population was determined using the Marmottant model. The threshold for subharmonic emissions of optimally sized bubbles was found to be lower than the inertial cavitation threshold for all frequencies studied. The rupture thresholds of optimally sized UCAs were found to be lower than the threshold for subharmonic emissions for either single cycle or steady state acoustic excitations. Because the thresholds of both subharmonic emissions and UCA rupture are linearly dependent on frequency, an index of the form ICAV = Pr/f (where Pr is the peak rarefactional pressure in MPa and f is the frequency in MHz) was derived to gauge the likelihood of subharmonic emissions due to stable cavitation activity nucleated from UCAs.

  20. Gauging the likelihood of stable cavitation from ultrasound contrast agents.

    PubMed

    Bader, Kenneth B; Holland, Christy K

    2013-01-07

    The mechanical index (MI) was formulated to gauge the likelihood of adverse bioeffects from inertial cavitation. However, the MI formulation did not consider bubble activity from stable cavitation. This type of bubble activity can be readily nucleated from ultrasound contrast agents (UCAs) and has the potential to promote beneficial bioeffects. Here, the presence of stable cavitation is determined numerically by tracking the onset of subharmonic oscillations within a population of bubbles for frequencies up to 7 MHz and peak rarefactional pressures up to 3 MPa. In addition, the acoustic pressure rupture threshold of an UCA population was determined using the Marmottant model. The threshold for subharmonic emissions of optimally sized bubbles was found to be lower than the inertial cavitation threshold for all frequencies studied. The rupture thresholds of optimally sized UCAs were found to be lower than the threshold for subharmonic emissions for either single cycle or steady state acoustic excitations. Because the thresholds of both subharmonic emissions and UCA rupture are linearly dependent on frequency, an index of the form I(CAV) = P(r)/f (where P(r) is the peak rarefactional pressure in MPa and f is the frequency in MHz) was derived to gauge the likelihood of subharmonic emissions due to stable cavitation activity nucleated from UCAs.

  1. Experimental and simulation investigations of acoustic cavitation in megasonic cleaning

    NASA Astrophysics Data System (ADS)

    Muralidharan, Krishna; Keswani, Manish; Shende, Hrishikesh; Deymier, Pierre; Raghavan, Srini; Eschbach, Florence; Sengupta, Archita

    2007-03-01

    Extreme ultra-violet (EUV) lithography has become the technique of choice to print the ever-shrinking nanoscale features on the silicon wafer. For successful transfer of patterns on to the wafer, the EUV photomask cannot contain defects greater than 30 nm. Megasonic cleaning is a very successful cleaning technique for removal of particles on photomasks, but also causes a relatively high amount of damage to the fragile EUV photomasks thin film structures. Though it is believed that acoustic cavitation is the primary phenomenon responsible for cleaning as well as pattern damage, a fundamental picture of the acoustic cavitation mechanisms in play during megasonic cleaning has not yet clearly emerged. In this study, we characterize the role of acoustic cavitation in megasonic cleaning by examining the effects of acoustic power densities, cleaning solution properties, and dissolved gas content on cavitation via experiments and molecular dynamics (MD) simulations. MD is an atomistic computation technique capable of modeling atomic-level and nanoscale processes accurately making it well suited to study the effect of cavitation on nano-sized particles and patterns.

  2. Cavitation induced by a surfactant leads to a transient release of water stress and subsequent 'run away' embolism in Scots pine (Pinus sylvestris) seedlings.

    PubMed

    Hölttä, Teemu; Juurola, Eija; Lindfors, Lauri; Porcar-Castell, Albert

    2012-01-01

    Cavitation decreases the hydraulic conductance of the xylem and has, therefore, detrimental effects on plant water balance. However, cavitation is also hypothesized to relieve water stress temporarily by releasing water from embolizing conduits to the transpiration stream. Stomatal closure in response to decreasing water potentials in order to avoid excessive cavitation has been well documented in numerous previous studies. However, it has remained unclear whether the stomata sense cavitation events themselves or whether they act in response to a decrease in leaf water potential to a level at which cavitation is initiated. The effects of massive cavitation on leaf water potential, transpiration, and stomatal behaviour were studied by feeding a surfactant into the transpiration stream of Scots pine (Pinus sylvestris) seedlings. The stomatal response to cavitation in connection with the capacitive effect was also studied. A major transient increase in leaf water potential was found due to cavitation in the seedlings. As cavitation was induced by lowering the surface tension, the two mechanisms could be uncoupled, as the usual relation between xylem water potential and the onset of cavitation did not hold. Our results indicate that the seedlings responded more to leaf water potential and less to cavitation itself, as stomatal closure was insufficient to prevent the seedlings from being driven to 'run-away' cavitation in a manner of hours.

  3. Methods of Experimental Investigation of Cavitation in a Convergent - Divergent Nozzle of Rectangular Cross Section

    NASA Astrophysics Data System (ADS)

    Jablonská, Jana; Kozubková, Milada; Himr, Daniel; Weisz, Michal

    2016-08-01

    Cavitation is a phenomenon with both positive and negative effects and with dynamic manifestations in hydraulic, food, chemical and other machinery. This article deals with the detection and dynamic behavior of cavitation clouds in water flows through a rectangular cross-section convergent-divergent nozzle. Cavitation was measured by methods applicable in engineering practice. Pressure, flow rate, noise, vibration, and amount of air dissolved in the liquid were measured and cavitation region was recorded with a high-speed camera. Evaluation of acquired images in connection with measured pressure pulsations and mechanical vibrations was performed with the use of the FFT method. In certain cases, dimensionless parameters were used to generalize the measurements. The results will be used to specify multiphase mathematical cavitation model parameters.

  4. Study of Cavitation in Wakes of Circular Cylinders and Symmetric Wedges Using X-ray Densitometry

    NASA Astrophysics Data System (ADS)

    Koot, Joachim; Wu, Juliana; Ganesh, Harish; Ceccio, Steven

    2016-11-01

    Cavitation in wakes behind canonical objects can exhibit variation in Strouhal number with a reduction in cavitation number. Circular cylinders of two diameters and symmetric wedges with a wedge angle of 15, 30, and 60 degrees are used to study cavitation in their wakes using X-ray densitometry. Using high speed video and X-ray densitometry, the nature of cavitation is studied in near-wake and a part of the far-wake region. In addition, acoustic measurements are also carried out to understand the spectral content of such wake cavities. Based on void fraction flow field and high-speed video measurements, the effect of cavitation on the Kármán vortex street spacing in the far wake region is studied. The results are the interpreted to explain the physical mechanisms responsible for the observed change in Strouhal number. Office of Naval Research.

  5. Study on the Effect of Inlet Fluctuation on Cavitation in a Cone Flow Channel.

    PubMed

    Hai, Liu; Shuping, Cao; Xiaohui, Luo

    2015-05-01

    A mathematical method was conducted to investigate the mechanism of formation of cavitation cloud, while the inlet stream contains a fluctuating flow. Based on the Rayleigh-Plesset equation and the static pressure distribution in a cone flow channel, parameters related to cavitation cloud are estimated, and the collapse pressure of the cavitation cloud is obtained by solving the equation of Mørch's model. Moreover, the effect of the amplitude and frequency of inlet fluctuation on cavitation is studied. Results revealed that the smaller the amplitude, the smaller the cloud and the lower the collapse pressure. And frequency of fluctuating stream was found to have a relative great effect on frequency of peak pressure but not so significant on peak collapse pressure and size of cloud. It is concluded that limiting the inlet fluctuation reduces the erosion and noise generated by cavitation collapse.

  6. Influence of Ultrasound Treatment on Cavitation Erosion Resistance of AlSi7 Alloy

    PubMed Central

    Pola, Annalisa; Montesano, Lorenzo; Tocci, Marialaura; La Vecchia, Giovina Marina

    2017-01-01

    Ultrasound treatment of liquid aluminum alloys is known to improve mechanical properties of castings. Aluminum foundry alloys are frequently used for production of parts that undergo severe cavitation erosion phenomena during service. In this paper, the effect of the ultrasound treatment on cavitation erosion resistance of AlSi7 alloy was assessed and compared to that of conventionally cast samples. Cavitation erosion tests were performed according to ASTM G32 standard on as-cast and heat treated castings. The response of the alloy in each condition was investigated by measuring the mass loss as a function of cavitation time and by analyzing the damaged surfaces by means of optical and scanning electron microscope. It was pointed out that the ultrasound treatment increases the cavitation erosion resistance of the alloy, as a consequence of the higher chemical and microstructural homogeneity, the finer grains and primary particles and the refined structure of the eutectic induced by the treatment itself. PMID:28772617

  7. Influence of Ultrasound Treatment on Cavitation Erosion Resistance of AlSi7 Alloy.

    PubMed

    Pola, Annalisa; Montesano, Lorenzo; Tocci, Marialaura; La Vecchia, Giovina Marina

    2017-03-03

    Ultrasound treatment of liquid aluminum alloys is known to improve mechanical properties of castings. Aluminum foundry alloys are frequently used for production of parts that undergo severe cavitation erosion phenomena during service. In this paper, the effect of the ultrasound treatment on cavitation erosion resistance of AlSi7 alloy was assessed and compared to that of conventionally cast samples. Cavitation erosion tests were performed according to ASTM G32 standard on as-cast and heat treated castings. The response of the alloy in each condition was investigated by measuring the mass loss as a function of cavitation time and by analyzing the damaged surfaces by means of optical and scanning electron microscope. It was pointed out that the ultrasound treatment increases the cavitation erosion resistance of the alloy, as a consequence of the higher chemical and microstructural homogeneity, the finer grains and primary particles and the refined structure of the eutectic induced by the treatment itself.

  8. Comparative cavitation erosion test on steels produced by ESR and AOD refining

    NASA Astrophysics Data System (ADS)

    Dojčinović, M.

    2011-09-01

    Cavitation erosion studies of steels produced by Electroslag Refining (ESR) and Argon Oxygen Decarburization (AOD refining) have been carried out. The experiments were conducted using the modified ultrasonically induced cavitation test method. Erosion rates were measured and the morphology of damages under cavitation action was studied by scanning electron microscopy and optical microscopy techniques. The present work is aimed at understanding the cavitation erosion behaviour of electroslag refined steel (ESR) compared with the steel produced by Argon Oxygen Decarburization (AOD refining), commonly used in the production of hydraulic machinery parts (Pelton blades). The results exhibited lower cavitation rate of ESR steel compared with AOD steel, as a consequence of its better mechanical properties and homogeneous and fine-grained microstructure.

  9. Nonlinear Elasticity and Cavitation of a Triblock Copolymer Gel

    NASA Astrophysics Data System (ADS)

    Kundu, Santanu; Hashemnejad, Seyed Meysam; Zabet, Mahla; Mishra, Satish

    2015-03-01

    Polymer gels are subjected to large-strain deformation during their applications. The gel deformation at large-strain is non-linear and can often lead to failure of the material. Here, we report the large-strain deformation behavior of a physically cross-linked, swollen polymer gel, which displays unique strain-stiffening response at large-strain. Investigations were performed using large amplitude oscillatory shear (LAOS) and custom developed cavitation rheology techniques. Gent constitutive model, which considers finite extensibility of midblock, was fitted with the LAOS data, therefore, linking the estimated parameters from LAOS analysis to the structure of the gel. Cavitation experiments were conducted as a function of temperature. Both analytical method and finite-element based modeling have been implemented to capture the pressure response in cavitation experiments. Our results provide a critical understanding of gel failure mechanism at large-strain.

  10. Compressible Turbulent Flow Numerical Simulations of Tip Vortex Cavitation

    NASA Astrophysics Data System (ADS)

    Khatami, F.; van der Weide, E.; Hoeijmakers, H.

    2015-12-01

    For an elliptic Arndt's hydrofoil numerical simulations of vortex cavitation are presented. An equilibrium cavitation model is employed. This single-fluid model assumes local thermodynamic and mechanical equilibrium in the mixture region of the flow, is employed. Furthermore, for characterizing the thermodynamic state of the system, precomputed multiphase thermodynamic tables containing data for the appropriate equations of state for each of the phases are used and a fast, accurate, and efficient look-up approach is employed for interpolating the data. The numerical simulations are carried out using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations for compressible flow. The URANS equations of motion are discretized using an finite volume method for unstructured grids. The numerical simulations clearly show the formation of the tip vortex cavitation in the flow about the elliptic hydrofoil.

  11. Complete Inhibition Of Ultrasound Induced Cytolysis In The Presence Of Inertial Cavitation

    NASA Astrophysics Data System (ADS)

    Sostaric, Joe Z.; Miyoshi, Norio; Riesz, Peter; De Graff, William G.; Mitchell, James B.

    2006-05-01

    The investigation of ultrasound for biotechnological applications including non-invasive surgery (HIFU), drug/gene delivery to cells (sonoporation) or through the skin (sonophoresis) and ultrasound assisted bioreactors has focused mainly on the physical effects of ultrasound. The beneficial effects of ultrasound rely on a number of application-dependent mechanisms, and may include tissue heating, acoustic streaming or cavitation. Although acoustic cavitation is necessary in some systems, cavitation bubbles simultaneously result in uncontrollable cell damage and cytolysis. Thus, the development of a number of biotechnological uses of ultrasound has been hampered by the necessity to constrain exposure parameters in order to prevent the occurrence of acoustic cavitation or to at least limit the detrimental effects of cavitation. The current study shows that non-toxic concentrations of specific n-alkyl solutes completely inhibit ultrasound induced cytolysis of in vitro suspensions of human leukemia cells (HL-60). Protection of the whole cell population from cytolysis is achieved even under extreme ultrasound exposure conditions that result in cytolysis of 100 % of the cell population in the absence of the n-alkyl solutes. Furthermore, the n-alkyl solutes did not hinder the process of inertial cavitation. This method may allow utilization of beneficial effects of ultrasound and cavitation while protecting cells from cavitation induced cytolysis and thereby presents new possibilities for ultrasound in medicine and biology.

  12. Sonoluminescence and acoustic cavitation

    NASA Astrophysics Data System (ADS)

    Choi, Pak-Kon

    2017-07-01

    Sonoluminescence (SL) is light emission under high-temperature and high-pressure conditions of a cavitating bubble under intense ultrasound in liquid. In this review, the fundamentals of the interactions between the sound field and the bubble, and between bubbles are explained. Experimental results on high-speed shadowgraphy of bubble dynamics and multibubble SL are shown, demonstrating that the SL intensity is closely related to the bubble dynamics. SL studies of alkali-metal atom (Na and K) emission are summarized. The spectral measurements in solutions with different noble-gas dissolutions and in surfactant solutions, and the results of spatiotemporal separation of SL distribution strongly suggested that the site of alkali-metal atom emission is the gas phase inside bubbles. The spectral studies indicated that alkali-metal atom lines are composed of two kinds of lines: a component that is broadened and shifted from the original D lines arises from van der Waals molecules formed between alkali-metal atoms and noble-gas atoms under extreme conditions at bubble collapse. The other spectral component exhibiting no broadening and no shift was suggested to originate from higher temperature bubbles than those producing the broadened component.

  13. Synergistic damage mechanism of corrosion and cavitation-erosion for plasma ion nitrided 18Cr-8Ni-1.1Mn-0.43C stainless steel in seawater

    NASA Astrophysics Data System (ADS)

    Chong, Sang-Ok; Kim, Seong-Jong

    2017-01-01

    In this work, it was investigated that resistance of combination damages of electrochemical corrosion and cavitation-erosion for plasma ion nitrided 18Cr-8Ni-1.1Mn-0.43C stainless steel at various process temperatures under cavitation environment in seawater. The plasma ion nitriding treatment was performed with a gas mixture ratio of 25% N2 and 75% H2 at a temperature of 623, 673, 723, and 773 K for 10 h, at a chamber pressure of 250 Pa. Expanded austenite (γN) was produced at whole plasma ion nitriding temperatures and especially phases of CrN and γ‧ were observed at 773 K in X-ray diffraction (XRD) analysis. In Tafel analysis, the highest corrosion potential and corrosion current density were analyzed on the untreated (non-cavitation) specimen among specimens under the cavitation condition. Under cavitation environment, the highest corrosion potential and the lowest corrosion current density presented at 673 K. As a result of observation of surface morphologies after anodic polarization experiment under cavitation environment, uniform corrosion was observed on the untreated specimen and plasma ion nitrided specimens, while localized corrosion was shown on the untreated substrate under non-cavitation environment. Furthermore, greater damage depth and severe morphologies were observed at plasma ion nitrided specimens than untreated substrate, whereas the greatest weight loss at 723 K was indicated due to the high pitting corrosion potential and wide passivity potential region.

  14. The role of positive and negative pressure on cavitation nucleation in nanodroplet-mediated histotripsy.

    PubMed

    Vlaisavljevich, Eli; Aydin, Omer; Lin, Kuang-Wei; Durmaz, Yasemin Yuksel; Fowlkes, Brian; ElSayed, Mohamed; Xu, Zhen

    2016-01-21

    Nanodroplet-mediated histotripsy (NMH) is an ultrasound ablation technique combining histotripsy with acoustically sensitive perfluorocarbon (PFC) nanodroplets that can be selectively delivered to tumor cells for targeted tumor ablation. NMH takes advantage of the significantly reduced cavitation threshold of the nanodroplets, allowing for cavitation to be selectively generated only in regions containing nanodroplets. Understanding the physical mechanisms underlying the nanodroplet cavitation process is essential to the development of NMH. In this study, we hypothesize that cavitation nucleation is caused by the negative pressure (p-) exposed to the PFC, and the NMH cavitation threshold is therefore determined by the incident p-  of the single-cycle pulses commonly used in NMH. This paper reports the first study that separately investigates the effects of negative and positive pressure on the NMH cavitation threshold using near half-cycle ultrasound pulses with dominant negative (negative-polarity pulses) or positive (positive-polarity pulses) pressure phases. Tissue phantoms containing perfluorohexane (PFH) nanodroplets were exposed to negative-polarity and positive-polarity pulses generated by a frequency compounding transducer recently developed in our lab, and the probability of generating cavitation was measured as a function of peak negative (p-) and peak positive (p+) pressure. The results showed close agreement in the p- cavitation threshold for PFH phantoms exposed to negative-polarity (11.4 ± 0.1 MPa) and positive-polarity (11.7 ± 0.2 MPa) pulses. The p+ at the cavitation threshold, in contrast, was measured to be sign ficantly different for the negative-polarity (4.0 ± 0.1 MPa) and positive-polarity (42.6 ± 0.2 MPa) pulses. In the final part of this study, the experimental results were compared to the cavitation threshold predicted by classical nucleation theory (CNT), with results showing close agreement between simulations and experiments

  15. Cavitation instability in bulk metallic glasses

    NASA Astrophysics Data System (ADS)

    Dai, L. H.; Huang, X.; Ling, Z.

    2015-09-01

    Recent experiments have shown that fracture surfaces of bulk metallic glasses (BMGs) usually exhibit an intriguing nanoscale corrugation like fractographic feature mediated by nanoscale void formation. We attribute the onset of this nanoscale corrugation to TTZs (tension transformation zones) mediated cavitation. In our recent study, the spall experiments of Zr-based BMG using a single-stage light gas gun were performed. To uncover the mechanisms of the spallation damage nucleation and evolution, the samples were designed to be subjected to dynamic tensile loadings of identical amplitude but with different durations by making use of the multi-stress pulse and the double-flyer techniques. It is clearly revealed that the macroscopic spall fracture in BMGs originates from the nucleation, growth and coalescence of micro-voids. Then, a microvoid nucleation model of BMGs based on free volume theory is proposed, which indicates that the nucleation of microvoids at the early stage of spallation in BMGs is resulted from diffusion and coalescence of free volume. Furthermore, a theoretical model of void growth in BMGs undergoing remote dynamic hydrostatic tension is developed. The critical condition of cavitation instability is obtained. It is found that dynamic void growth in BMGs can be well controlled by a dimensionless inertial number characterizing the competition between intrinsic and extrinsic time scales. To unveil the atomic-level mechanism of cavitation, a systematic molecular dynamics (MD) simulation of spallation behaviour of a binary metallic glass with different impact velocities was performed. It is found that micro-void nucleation is determined TTZs while the growth is controlled by shear transformation zones (STZs) at atomic scale.

  16. Cavitation erosion size scale effects

    NASA Technical Reports Server (NTRS)

    Rao, P. V.; Buckley, D. H.

    1984-01-01

    Size scaling in cavitation erosion is a major problem confronting the design engineers of modern high speed machinery. An overview and erosion data analysis presented in this paper indicate that the size scale exponent n in the erosion rate relationship as a function of the size or diameter can vary from 1.7 to 4.9 depending on the type of device used. There is, however, a general agreement as to the values of n if the correlations are made with constant cavitation number.

  17. Acoustic and Cavitation Fields of Shock Wave Therapy Devices

    NASA Astrophysics Data System (ADS)

    Chitnis, Parag V.; Cleveland, Robin O.

    2006-05-01

    Extracorporeal shock wave therapy (ESWT) is considered a viable treatment modality for orthopedic ailments. Despite increasing clinical use, the mechanisms by which ESWT devices generate a therapeutic effect are not yet understood. The mechanistic differences in various devices and their efficacies might be dependent on their acoustic and cavitation outputs. We report acoustic and cavitation measurements of a number of different shock wave therapy devices. Two devices were electrohydraulic: one had a large reflector (HMT Ossatron) and the other was a hand-held source (HMT Evotron); the other device was a pneumatically driven device (EMS Swiss DolorClast Vet). Acoustic measurements were made using a fiber-optic probe hydrophone and a PVDF hydrophone. A dual passive cavitation detection system was used to monitor cavitation activity. Qualitative differences between these devices were also highlighted using a high-speed camera. We found that the Ossatron generated focused shock waves with a peak positive pressure around 40 MPa. The Evotron produced peak positive pressure around 20 MPa, however, its acoustic output appeared to be independent of the power setting of the device. The peak positive pressure from the DolorClast was about 5 MPa without a clear shock front. The DolorClast did not generate a focused acoustic field. Shadowgraph images show that the wave propagating from the DolorClast is planar and not focused in the vicinity of the hand-piece. All three devices produced measurable cavitation with a characteristic time (cavitation inception to bubble collapse) that varied between 95 and 209 μs for the Ossatron, between 59 and 283 μs for the Evotron, and between 195 and 431 μs for the DolorClast. The high-speed camera images show that the cavitation activity for the DolorClast is primarily restricted to the contact surface of the hand-piece. These data indicate that the devices studied here vary in acoustic and cavitation output, which may imply that the

  18. Trans-Stent B-Mode Ultrasound and Passive Cavitation Imaging.

    PubMed

    Haworth, Kevin J; Raymond, Jason L; Radhakrishnan, Kirthi; Moody, Melanie R; Huang, Shao-Ling; Peng, Tao; Shekhar, Himanshu; Klegerman, Melvin E; Kim, Hyunggun; McPherson, David D; Holland, Christy K

    2016-02-01

    Angioplasty and stenting of a stenosed artery enable acute restoration of blood flow. However, restenosis or a lack of re-endothelization can subsequently occur depending on the stent type. Cavitation-mediated drug delivery is a potential therapy for these conditions, but requires that particular types of cavitation be induced by ultrasound insonation. Because of the heterogeneity of tissue and stochastic nature of cavitation, feedback mechanisms are needed to determine whether the sustained bubble activity is induced. The objective of this study was to determine the feasibility of passive cavitation imaging through a metal stent in a flow phantom and an animal model. In this study, an endovascular stent was deployed in a flow phantom and in porcine femoral arteries. Fluorophore-labeled echogenic liposomes, a theragnostic ultrasound contrast agent, were injected proximal to the stent. Cavitation images were obtained by passively recording and beamforming the acoustic emissions from echogenic liposomes insonified with a low-frequency (500 kHz) transducer. In vitro experiments revealed that the signal-to-noise ratio for detecting stable cavitation activity through the stent was greater than 8 dB. The stent did not significantly reduce the signal-to-noise ratio. Trans-stent cavitation activity was also detected in vivo via passive cavitation imaging when echogenic liposomes were insonified by the 500-kHz transducer. When stable cavitation was detected, delivery of the fluorophore into the arterial wall was observed. Increased echogenicity within the stent was also observed when echogenic liposomes were administered. Thus, both B-mode ultrasound imaging and cavitation imaging are feasible in the presence of an endovascular stent in vivo. Demonstration of this capability supports future studies to monitor restenosis with contrast-enhanced ultrasound and pursue image-guided ultrasound-mediated drug delivery to inhibit restenosis.

  19. Generation and control of acoustic cavitation structure.

    PubMed

    Bai, Lixin; Xu, Weilin; Deng, Jingjun; Li, Chao; Xu, Delong; Gao, Yandong

    2014-09-01

    The generation and control of acoustic cavitation structure are a prerequisite for application of cavitation in the field of ultrasonic sonochemistry and ultrasonic cleaning. The generation and control of several typical acoustic cavitation structures (conical bubble structure, smoker, acoustic Lichtenberg figure, tailing bubble structure, jet-induced bubble structures) in a 20-50 kHz ultrasonic field are investigated. Cavitation bubbles tend to move along the direction of pressure drop in the region in front of radiating surface, which are the premise and the foundation of some strong acoustic cavitation structure formation. The nuclei source of above-mentioned acoustic cavitation structures is analyzed. The relationship and mutual transformation of these acoustic cavitation structures are discussed.

  20. A study of pump cavitation damage

    NASA Astrophysics Data System (ADS)

    Brophy, M. C.; Stinebring, D. R.; Billet, M. L.

    1983-11-01

    The cavitation assessment for the space shuttle main engine high pressure oxidizer turbopump is documented. A model of the flow through the pump was developed. Initially, a computational procedure was used to analyze the flow through the inlet casing including the prediction of wakes downstream of the casing vanes. From these flow calculations, cavitation patterns on the inducer blades were approximated and the damage rate estimated. The model correlates the heavy damage on the housing and over the inducer with unsteady blade surface cavitation. The unsteady blade surface cavitation is due to the large incidence changes caused by the wakes of the upstream vanes. Very high cavitation damage rates are associated with this type of cavitation. Design recommendations for reducing the unsteady cavitation include removing the set of vanes closest to the inducer and modifying the remaining vanes.

  1. Air emission into a water shear layer through porous media. Part 2: Cavitation induced pressure attenuation

    SciTech Connect

    Myer, E.C.; Marboe, R.C.

    1994-12-31

    Cavitation near the casing of a hydroturbine can lead to damage through both cavitation erosion and mechanical vibration of the casing and the associated piping. Cavitation erosion results from the collapse of cavitation bubbles on or near a surface such as the casing wall. Mechanical vibrations transmitted to the casing directly through the collapse of bubbles on the casing wall indirectly through a coupling of the acoustic pressure pulse due to a nearby collapse on the turbine blade. Air emission along the casing can reduce the intensity of the tip vortex and the gap cavitation through ventilation of the cavity. Reduction in the machinery vibration is obtained by reduction of the intensity of cavitation bubble collapse and attenuation and scattering of the radiated acoustic pressure. This requires a bubble layer which may be introduced in the vicinity of the turbine blade tips. This layer remains for some distance downstream of the blades and is effective for attenuation of tip vortex induced noise and blade surface cavitation noise. For the purpose of characterizing this bubble layer within a water pipe, the authors spanned a pipe with a two dimensional hydrofoil and emitted air through porous media (20 and 100 micron porosity sintered stainless steel) into the shear flow over the hydrofoil. This paper is limited to an investigation of the attenuation of acoustic pressure propagating to the casing rather than the reduction in acoustic source level due to collapse cushioning effects.

  2. Stochastic-field cavitation model

    SciTech Connect

    Dumond, J.; Magagnato, F.; Class, A.

    2013-07-15

    Nonlinear phenomena can often be well described using probability density functions (pdf) and pdf transport models. Traditionally, the simulation of pdf transport requires Monte-Carlo codes based on Lagrangian “particles” or prescribed pdf assumptions including binning techniques. Recently, in the field of combustion, a novel formulation called the stochastic-field method solving pdf transport based on Eulerian fields has been proposed which eliminates the necessity to mix Eulerian and Lagrangian techniques or prescribed pdf assumptions. In the present work, for the first time the stochastic-field method is applied to multi-phase flow and, in particular, to cavitating flow. To validate the proposed stochastic-field cavitation model, two applications are considered. First, sheet cavitation is simulated in a Venturi-type nozzle. The second application is an innovative fluidic diode which exhibits coolant flashing. Agreement with experimental results is obtained for both applications with a fixed set of model constants. The stochastic-field cavitation model captures the wide range of pdf shapes present at different locations.

  3. Cavitation inception from bubble nuclei.

    PubMed

    Mørch, K A

    2015-10-06

    The tensile strength of ordinary water such as tap water or seawater is typically well below 1 bar. It is governed by cavitation nuclei in the water, not by the tensile strength of the water itself, which is extremely high. Different models of the nuclei have been suggested over the years, and experimental investigations of bubbles and cavitation inception have been presented. These results suggest that cavitation nuclei in equilibrium are gaseous voids in the water, stabilized by a skin which allows diffusion balance between gas inside the void and gas in solution in the surrounding liquid. The cavitation nuclei may be free gas bubbles in the bulk of water, or interfacial gaseous voids located on the surface of particles in the water, or on bounding walls. The tensile strength of these nuclei depends not only on the water quality but also on the pressure-time history of the water. A recent model and associated experiments throw new light on the effects of transient pressures on the tensile strength of water, which may be notably reduced or increased by such pressure changes.

  4. Cavitation inception from bubble nuclei

    PubMed Central

    Mørch, K. A.

    2015-01-01

    The tensile strength of ordinary water such as tap water or seawater is typically well below 1 bar. It is governed by cavitation nuclei in the water, not by the tensile strength of the water itself, which is extremely high. Different models of the nuclei have been suggested over the years, and experimental investigations of bubbles and cavitation inception have been presented. These results suggest that cavitation nuclei in equilibrium are gaseous voids in the water, stabilized by a skin which allows diffusion balance between gas inside the void and gas in solution in the surrounding liquid. The cavitation nuclei may be free gas bubbles in the bulk of water, or interfacial gaseous voids located on the surface of particles in the water, or on bounding walls. The tensile strength of these nuclei depends not only on the water quality but also on the pressure–time history of the water. A recent model and associated experiments throw new light on the effects of transient pressures on the tensile strength of water, which may be notably reduced or increased by such pressure changes. PMID:26442138

  5. Acoustic Cavitation and Bubble Dynamics.

    DTIC Science & Technology

    1985-06-15

    study, they irradiated a liquid containing luminol , a light enhancing chemical, and observed light emission indicative of chemiluminescence for acoustic...liquid was water containing luminol and saturated with argon. 1-31. Variation of the cavitation threshold of water containing luminol with duty cycle

  6. Vortex cavitation: A progress report

    SciTech Connect

    Arndt, R.E.A.; Maines, B.H.

    1994-12-31

    Cavitation in vortical flows is a significant problem. An important aspect is the need for a better understanding of the physics of cavitation in the vortices tailing from lifting surfaces such as propellers and hydrofoils. This is a review of experimental and numerical research that has been recently carried out with a series of hydrofoils. This is a review of experimental and numerical research that has been recently carried out with a series of hydrofoils. This research was aimed at investigating the interrelated effects of vortex structure, including the details of the vortex roll-up process close to the tip, dissolved gas content, and water quality as it related to the amount of tension that can be sustained in the vortex before cavitation occurs. The experimental phase includes lift and drag measurements, oil flow visualization of the boundary layer flow on the lifting surfaces, and observation of both cavitation inception and desinence in strong and weak water. An improved photographic technique has been developed to study the complex bubble dynamics inherent in the inception process. Preliminary results indicate that the bubble growth process is strongly dependent on the size and number of nuclei in the free stream. Numerical simulations indicate that the minimum pressure in the vortex is very close to the tip of the lifting surface, in agreement with the observation that the inception process also occurs very close to the tip under most conditions.

  7. Suppression of cavitation inception by gas bubble injection: a numerical study focusing on bubble-bubble interaction.

    PubMed

    Ida, Masato; Naoe, Takashi; Futakawa, Masatoshi

    2007-10-01

    The dynamic behavior of cavitation and gas bubbles under negative pressure has been studied numerically to evaluate the effect of gas bubble injection into a liquid on the suppression of cavitation inception. In our previous studies, it was demonstrated by direct observation that cavitation occurs in liquid mercury when mechanical impacts are imposed, and this will cause cavitation damage in spallation neutron sources, in which liquid mercury is bombarded by a high-power proton beam. In the present paper, we describe numerical investigations of the dynamics of cavitation bubbles in liquid mercury using a multibubble model that takes into account the interaction of a cavitation bubble with preexisting gas bubbles through bubble-radiated pressure waves. The numerical results suggest that, if the mercury includes gas bubbles whose equilibrium radius is much larger than that of the cavitation bubble, the explosive expansion of the cavitation bubble (i.e., cavitation inception) is suppressed by the positive-pressure wave radiated by the injected bubbles, which decreases the magnitude of the negative pressure in the mercury.

  8. Relations between acoustic cavitation and skin resistance during intermediate- and high-frequency sonophoresis.

    PubMed

    Rich, Kyle T; Hoerig, Cameron L; Rao, Marepalli B; Mast, T Douglas

    2014-11-28

    Enhanced skin permeability is known to be achieved during sonophoresis due to ultrasound-induced cavitation. However, the mechanistic role of cavitation during sonophoresis has been extensively investigated only for low-frequency (LFS, <100 kHz) applications. Here, mechanisms of permeability-enhancing stable and inertial cavitation were investigated by passively monitoring subharmonic and broadband emissions arising from cavitation isolated within or external to porcine skin in vitro during intermediate- (IFS, 100-700 kHz) and high-frequency sonophoresis (HFS, >1 MHz). The electrical resistance of skin, a surrogate measure of the permeability of skin to a variety of compounds, was measured to quantify the reduction and subsequent recovery of the skin barrier during and after exposure to pulsed (1 second pulse, 20% duty cycle) 0.41 and 2.0 MHz ultrasound over a range of acoustic powers (0-21.7 W) for 30 min. During IFS, significant skin resistance reductions and acoustic emissions from cavitation were measured exclusively when cavitation was isolated outside of the skin. Time-dependent skin resistance reductions measured during IFS correlated significantly with subharmonic and broadband emission levels. During HFS, significant skin resistance reductions were accompanied by significant acoustic emissions from cavitation measured during trials that isolated cavitation activity either outside of skin or within skin. Time-dependent skin resistance reductions measured during HFS correlated significantly greater with subharmonic than with broadband emission levels. The reduction of the skin barrier due to sonophoresis was reversible in all trials; however, effects incurred during IFS recovered more slowly and persisted over a longer period of time than HFS. These results quantitatively demonstrate the significance of cavitation during sonophoresis and suggest that the mechanisms and post-treatment longevity of permeability enhancement due to IFS and HFS treatments are

  9. Cavitation and pore blocking in nanoporous glasses.

    PubMed

    Reichenbach, C; Kalies, G; Enke, D; Klank, D

    2011-09-06

    In gas adsorption studies, porous glasses are frequently referred to as model materials for highly disordered mesopore systems. Numerous works suggest that an accurate interpretation of physisorption isotherms requires a complete understanding of network effects upon adsorption and desorption, respectively. The present article deals with nitrogen and argon adsorption at different temperatures (77 and 87 K) performed on a series of novel nanoporous glasses (NPG) with different mean pore widths. NPG samples contain smaller mesopores and significantly higher microporosity than porous Vycor glass or controlled pore glass. Since the mean pore width of NPG can be tuned sensitively, the evolution of adsorption characteristics with respect to a broadening pore network can be investigated starting from the narrowest nanopore width. With an increasing mean pore width, a H2-type hysteresis develops gradually which finally transforms into a H1-type. In this connection, a transition from a cavitation-induced desorption toward desorption controlled by pore blocking can be observed. Furthermore, we find concrete hints for a pore size dependence of the relative pressure of cavitation in highly disordered pore systems. By comparing nitrogen and argon adsorption, a comprehensive insight into adsorption mechanisms in novel disordered materials is provided.

  10. Transient cavitation in high-quality-factor resonators at high static pressures.

    PubMed

    Gaitan, D Felipe; Tessien, Ross A; Hiller, Robert A; Gutierrez, Joel; Scott, Corey; Tardif, Henry; Callahan, Brant; Matula, Thomas J; Crum, Lawrence A; Holt, R Glynn; Church, Charles C; Raymond, Jason L

    2010-06-01

    It is well known that cavitation collapse can generate intense concentrations of mechanical energy, sufficient to erode even the hardest metals and to generate light emissions visible to the naked eye [sonoluminescence (SL)]. Considerable attention has been devoted to the phenomenon of "single bubble sonoluminescence" (SBSL) in which a single stable cavitation bubble radiates light flashes each and every acoustic cycle. Most of these studies involve acoustic resonators in which the ambient pressure is near 0.1 MPa (1 bar), and with acoustic driving pressures on the order of 0.1 MPa. This study describes a high-quality factor, spherical resonator capable of achieving acoustic cavitation at ambient pressures in excess of 30 MPa (300 bars). This system generates bursts of violent inertial cavitation events lasting only a few milliseconds (hundreds of acoustic cycles), in contrast with the repetitive cavitation events (lasting several minutes) observed in SBSL; accordingly, these events are described as "inertial transient cavitation." Cavitation observed in this high pressure resonator is characterized by flashes of light with intensities up to 1000 times brighter than SBSL flashes, as well as spherical shock waves with amplitudes exceeding 30 MPa at the resonator wall. Both SL and shock amplitudes increase with static pressure.

  11. Cavitation damage in blood clots under HIFU

    NASA Astrophysics Data System (ADS)

    Weiss, Hope; Ahadi, Golnaz; Hoelscher, Thilo; Szeri, Andrew

    2010-11-01

    High Intensity Focused Ultrasound (HIFU) has been shown to accelerate thrombolysis, the dissolution of blood clots, in vitro and in vivo, for treatment of ischemic stroke. Cavitation in sonothrombolysis is thought to play an important role, although the mechanisms are not fully understood. The damage to a blood clot associated with bubble collapses in a HIFU field is studied. The region of damage caused by a bubble collapse on the fibrin network of the blood clot exposed to HIFU is estimated, and compared with experimental assessment of the damage. The mechanical damage to the network caused by a bubble is probed using two independent approaches, a strain based method and an energy based method. Immunoflourescent fibrin staining is used to assess the region of damage experimentally.

  12. Ablation of benign prostatic hyperplasia using microbubble-mediated ultrasound cavitation.

    PubMed

    Li, Tao; Liu, Zheng

    2010-04-01

    Benign prostatic hyperplasia (BPH) is a world-wide common disease in elderly male patients. A number of invasive physiotherapies have been used to replace prostatectomy. In this article we report our hypothesis of using microbubbles-mediated ultrasound cavitation effects to ablate prostatic tissues. Microbubble ultrasound contrast agent is widely used contrast media in ultrasonography, yet it is also found to act as cavitation nuclei or enhancer. Once excited by a high peak pressure ultrasound pulse, the mechanical effects, like shock wave and microstream, released from cavitation could produce a series of bioeffects, contributing to sonoporation, microvascular rupture and hematoma. BPH is known to have hyperplastic neovasculature and this make it possible to be disrupted by the physical effects of cavitation under existing microbubbles in circulation. Mechanical ablation of prostatic capillary or small vessels could result in pathological alterations such as thrombosis, micro-circulation blockage, prostatic necrosis and atrophia. Thereupon it could effectively treat BPH by nontraumatic ways.

  13. Prediction of cryogenic cavitation around hydrofoil by an extensional Schnerr-Sauer cavitation model

    NASA Astrophysics Data System (ADS)

    Sun, T. Z.; Wei, Y. J.; Wang, C.

    2015-12-01

    Developing a robust computational strategy to address the rich physics characteristic involved in the thermodynamic effects on the cryogenic cavitation remains a challenging problem. The objective of this present study is to model the numerical methodology to simulate the cryogenic cavitation by implanting the thermodynamic effects to the Schnerr-Sauer cavitation model, and coupling the energy equation considered the latent heat. For this purpose, cavitating flows are investigated over a three dimensional hydrofoil in liquid hydrogen and nitrogen. Experimental measurements of pressure and temperature are utilized to validate the extensional Schnerr-Sauer cavitation model. Specifically, the further analysis of the cavitation solution with respect to the thermodynamic term is conducted. The results show that the extensional Schnerr-Sauer cavitation model predicts better accuracy to the quasi-steady cavitation over hydrofoil in the two cryogenic fluids.

  14. Study on a liquid jet with cavitation bubbles

    NASA Astrophysics Data System (ADS)

    Kiyama, Akihito; Tagawa, Yoshiyuki

    2014-11-01

    A focused liquid jet is important in medical applications such as needle-free drug injection systems. A method for generating a liquid jet by laser-induced shock wave is proposed. However, there are some problems. Hence we examine another method for generating a focused liquid jet. We drop a liquid filled test tube on the rigid plate, leading to the emergence of a jet. Within certain experimental conditions, the jet velocity in our experiment agrees well with the semiempirical relation proposed by Tagawa et al. (2012, Phys. Rev. X) and Peters et al. (2013, J. Fluid Mech.). In other conditions, we find that the jet velocity remarkably increases. In order to understand the jet velocity increment, we use two high-speed cameras: One records motion of a jet. Another films cavitation bubbles inside a liquid bath. We categorize jets into three types based on their shape and the existence of cavitation bubbles. We find that the jet with cavitation bubbles is much faster than that without cavitation bubbles. For elucidating the mechanism of jet velocity increment, we discuss the effect of pressure wave, which propagates in a liquid bath. We propose a model for describing these phenomena and verify it experimentally. JSPS KAKENHI 26709007.

  15. Reversible Leaf Xylem Collapse: A Potential "Circuit Breaker" against Cavitation.

    PubMed

    Zhang, Yong-Jiang; Rockwell, Fulton E; Graham, Adam C; Alexander, Teressa; Holbrook, N Michele

    2016-12-01

    We report a novel form of xylem dysfunction in angiosperms: reversible collapse of the xylem conduits of the smallest vein orders that demarcate and intrusively irrigate the areoles of red oak (Quercus rubra) leaves. Cryo-scanning electron microscopy revealed gradual increases in collapse from approximately -2 MPa down to -3 MPa, saturating thereafter (to -4 MPa). Over this range, cavitation remained negligible in these veins. Imaging of rehydration experiments showed spatially variable recovery from collapse within 20 s and complete recovery after 2 min. More broadly, the patterns of deformation induced by desiccation in both mesophyll and xylem suggest that cell wall collapse is unlikely to depend solely on individual wall properties, as mechanical constraints imposed by neighbors appear to be important. From the perspective of equilibrium leaf water potentials, petioles, whose vessels extend into the major veins, showed a vulnerability to cavitation that overlapped in the water potential domain with both minor vein collapse and buckling (turgor loss) of the living cells. However, models of transpiration transients showed that minor vein collapse and mesophyll capacitance could effectively buffer major veins from cavitation over time scales relevant to the rectification of stomatal wrong-way responses. We suggest that, for angiosperms, whose subsidiary cells give up large volumes to allow large stomatal apertures at the cost of potentially large wrong-way responses, vein collapse could make an important contribution to these plants' ability to transpire near the brink of cavitation-inducing water potentials. © 2016 American Society of Plant Biologists. All Rights Reserved.

  16. Study of Cavitation Shedding Dynamics on a NACA0015 Hydrofoil Using X-Ray Densitometry

    NASA Astrophysics Data System (ADS)

    Ganesh, Harish; Wu, Juliana; Ceccio, Steven

    2016-11-01

    Cavitation dynamics on the NACA0015 hydrofoil at several attack angles are found to be spectrally rich, being multi-modal with abrupt changes in Strouhal number with change in cavitation number. Present study focusses on identifying the physical mechanisms responsible for the change in cavitation dynamics on a NACA0015 hydrofoil in a re-circulating water tunnel using time resolved X-ray densitometry. Time-resolved void fraction flow fields obtained using X-ray densitometry, synchronized with acoustic noise measurements using a hydrophone, are used to identify different flow features and mechanisms that are responsible for the change in the observed spectral behavior. It is shown that under higher cavitation numbers, the shedding mechanism is predominantly re-entrant liquid flow based, but as the cavitation number drops many different processes are at play. At lower cavitation numbers, the shed cavity cloud collapse arrests cavity growth and this results in altered cycle dynamics and hence the Strouhal number. In addition, propagation bubbly shock waves are also found to be a dominant mechanism of shedding for certain conditions. The multi-modal nature of the acoustic pressure signature is explained by presence of different flow features, which could be concurrent or alternating. Office of Naval Research.

  17. Application of signal analysis to cavitation

    NASA Technical Reports Server (NTRS)

    Martin, C. S.; Veerabhadra Rao, P.

    1984-01-01

    The diagnostic facilities of the cross power spectrum and the coherence function have been employed to enhance the identification of not only the inception of cavitation, but also its level. Two piezoelectric pressure transducers placed in the downstream chamber of a model spool valve undergoing various levels of cavitation allowed for the use of both functions - the phase angle of the complex cross spectrum and the dimensionless coherence function - to sense clearly the difference between noise levels associated with a noncavitating jet from those once cavitation inception is attained. The cavitation noise within the chamber exhibited quite a regular character in terms of the phase difference between instruments for limited cavitation. Varying cavitation levels clearly illustrated the effect of bubble size on the attendant frequency range for which there was an extremely high coherence or nearly perfect causality.

  18. Cavitation study of a pump-turbine at turbine mode with critical cavitation coefficient condition

    NASA Astrophysics Data System (ADS)

    Wang, J.; Yang, D.; Xu, J. W.; Liu, J. T.; Jiao, L.

    2016-05-01

    To study the cavitation phenomenon of a pump-turbine at turbine mode when it ran at the critical cavitation coefficient condition, a high-head model pump-turbine was disperse using hexahedron grid. Three dimensional, steady cavitating flow was numerically studied using SST k-ω model. It is confirmed that ZGB cavitation model and SST k-ω model are useful ways to study the two-phase cavitation flow in pump-turbine. Mass flow inlet and pressure outlet were specified at the casing inlet and draft tube outlet, respectively. The static pressure was set according to the cavitation coefficient. The steady cavitating flows at critical cavitation coefficient condition were analysed. The cavitation area in the runner was investigated. It was found that the pressure of the suction on the blade surface was decreasing gradually with the decrease of the cavitation coefficient. In addition, the vortex flow in the draft tube was observed at the critical cavitation coefficient. It was found that the vortex flow appeared at the center of the draft tube inlet with the decreasing of the cavitation coefficient. Compared with the experimental data, the simulation results show reasonable agreement with the experimental data.

  19. Modeling of Cavitating Flow through Waterjet Propulsors

    DTIC Science & Technology

    2015-02-18

    OCT-11 -31-DEC-14 To) 4. TITLE AND SUBTITLE Modeling of Cavitating Flow through Waterjet Propulsors 5a. CONTRACT NUMBER 5b. GRANT NUMBER N00014-12...239-18 Modeling of Cavitating Flow through Waterjet Propulsors Jules W. Lindau The Pennsylvania State University, Applied Research Laboratory, State...flow nature, waterjets are expected to maintain resistance to cavitation , are amenable to ad- vanced concepts such as thrust vectoring, should

  20. Measuring Dynamic Transfer Functions of Cavitating Pumps

    NASA Technical Reports Server (NTRS)

    Baun, Daniel

    2007-01-01

    A water-flow test facility has been built to enable measurement of dynamic transfer functions (DTFs) of cavitating pumps and of inducers in such pumps. Originally, the facility was intended for use in an investigation of the effects of cavitation in a rocket-engine low-pressure oxygen turbopump. The facility can also be used to measure DTFs of cavitating pumps in general

  1. Experimental modeling of cavitation occurring at vibration

    NASA Astrophysics Data System (ADS)

    Gaynutdinova, D. F.; Modorskii, V. Ya.; Shevelev, N. A.

    2016-10-01

    The article investigates the problem of effects in two-stage centrifugal pumps due to hydro-gas-dynamic processes resulting from vibrations of design elements which are difficult to forecast. Numerical and experimental simulation of this problem was conducted. The experiment discovered cavitation effects brought about by the vibrations. The area of cavitations was plotted. Dependence of cavitation bubble concentration on amplitude and frequency of the vibrations was found.

  2. Computation and analysis of cavitating flow in Francis-class hydraulic turbines

    NASA Astrophysics Data System (ADS)

    Leonard, Daniel J.

    can occur more abruptly in the model than the prototype, due to lack of Froude similitude between the two. When severe cavitation occurs, clear differences are observed in vapor content between the scales. A stage-by-stage performance decomposition is conducted to analyze the losses within individual components of each scale of the machine. As cavitation becomes more severe, the losses in the draft tube account for an increasing amount of the total losses in the machine. More losses occur in the model draft tube as cavitation formation in the prototype draft tube is prevented by the larger hydrostatic pressure gradient across the machine. Additionally, unsteady Detached Eddy Simulations of the fully-coupled cavitating hydroturbine are performed for both scales. Both mesh and temporal convergence studies are provided. The temporal and spectral content of fluctuations in torque and pressure are monitored and compared between single-phase, cavitating, model, and prototype cases. A shallow draft tube induced runner imbalance results in an asymmetric vapor distribution about the runner, leading to more extensive growth and collapse of vapor on any individual blade as it undergoes a revolution. Unique frequency components manifest and persist through the entire machine only when cavitation is present in the hub vortex. Large maximum pressure spikes, which result from vapor collapse, are observed on the blade surfaces in the multiphase simulations, and these may be a potential source of cavitation damage and erosion. Multiphase CFD is shown to be an accurate and effective technique for simulating and analyzing cavitating flow in Francis-class hydraulic turbines. It is recommended that it be used as an industrial tool to supplement model cavitation experiments for all types of hydraulic turbines. Moreover, multiphase CFD can be equally effective as a research tool, to investigate mechanisms of cavitating hydraulic turbines that are not understood, and to uncover unique new

  3. Cavitation dynamics on the nanoscale

    SciTech Connect

    Kotaidis, Vassilios; Plech, Anton

    2005-11-21

    The ultrafast excitation of gold nanoparticle sols causes a strong nonequilibrium heating of the particle lattice and subsequently of the water shell close to the particle surface. Above a threshold in laser fluence, which is defined by the onset of homogeneous nucleation, nanoscale vapor bubbles develop around the particles, expand and collapse again within the first nanosecond after excitation. We show the existence of cavitation on the nanometer and subnanosecond time scale, described within the framework of continuum thermodynamics.

  4. Breaking beer bottles with cavitation

    NASA Astrophysics Data System (ADS)

    Jung, Sunny; Fontana, Jake; Palffy-Muhoray, Peter; Shelley, Michael

    2009-03-01

    Hitting the top of a beer bottle, nearly full of water, with an open hand can cause the bottle to break, with the bottom separating from upper section. We have studied this phenomenon using a high-speed camera, and observed the formation, coalescence and collapse of bubbles. The breaking of glass is due to cavitation, typically occurring near the bottom edge. We make numerical estimates of the relevant physical parameters, and compare these with experimental observations.

  5. Stalking cavitation in the lab

    SciTech Connect

    March, P.A.; Jones, R.K.

    1993-10-01

    This article describes laboratory equipment for acoustic monitoring of cavitation in hydraulic turbines. The system uses acoustic transducers. The signals from the transducers are filtered and amplified, then analyzed and recorded with a computer using an 8-bit analog-to-digital waveform acquisition board. The signal are also provided to a wideband converter chip. The chip produces an directly related to the power of the signal. Erosion rates are determined from the signal output.

  6. Cavitation-Resistant Sonar Array

    DTIC Science & Technology

    1998-09-17

    between adjacent transducers can produce 19 cavitation due to acoustic effects alone. Low-frequency Class IV 20 flextensional transducers are often...resistant sonar array having specific acoustic 3 impedance matching that of water between the adjacent surfaces of 4 class IV flextensional transducers by...preferred embodiment, class IV flextensional 20 transducers are attached to transducer mount 14. 21 As shown in FIG. 2, the rho-c material 16 is a

  7. Cavitation dynamics on the nanoscale

    NASA Astrophysics Data System (ADS)

    Kotaidis, Vassilios; Plech, Anton

    2005-11-01

    The ultrafast excitation of gold nanoparticle sols causes a strong nonequilibrium heating of the particle lattice and subsequently of the water shell close to the particle surface. Above a threshold in laser fluence, which is defined by the onset of homogeneous nucleation, nanoscale vapor bubbles develop around the particles, expand and collapse again within the first nanosecond after excitation. We show the existence of cavitation on the nanometer and subnanosecond time scale, described within the framework of continuum thermodynamics.

  8. Cavitation on hydrofoils with sinusoidal leading edge

    NASA Astrophysics Data System (ADS)

    Johari, H.

    2015-12-01

    Cavitation characteristics of hydrofoils with sinusoidal leading edge were examined experimentally at a Reynolds number of 7.2 × 105. The hydrofoils had an underlying NACA 634-021 profile and an aspect ratio of 4.3. The sinusoidal leading edge geometries included three amplitudes of 2.5%, 5%, and 12% and two wavelengths of 25% and 50% of the mean chord length. Results revealed that cavitation on the leading edge-modified hydrofoils existed in pockets behind the troughs whereas the baseline hydrofoil produced cavitation along its entire span. Moreover, cavitation on the modified hydrofoils appeared at consistently lower angles of attack than on the baseline hydrofoil.

  9. Cavitation flow through a rotating pipe

    NASA Astrophysics Data System (ADS)

    Szumowski, A.; Laake, A.; Meier, G. E. A.

    1986-07-01

    A one-dimensional cavitation flow (without Coriolis accelaration) in a rotating pipe was investigated with a view to cooling of gas turbine blades and compressors. This flow becomes unsteady and oscillates. Thereby, and unsteady cavitation domain is produced, separating the two partial water columns. At increasing rotation speed the oscillation frequency decreases and the extension of the cavitation domain increases. Above a critical rotation speed the water column is pressed out of the pipe, and the cavitation domain disappears. The flow computation was performed using the Runge-Kutta method for an incompressible model, and the characteristics method for a compressible model. The results of the calculations are supported by experimental results.

  10. Dynamics of cavitating cascades and inducer pumps

    NASA Technical Reports Server (NTRS)

    Brennen, C. E.; Acosta, A. J.

    1981-01-01

    Report chronicles advances in understanding and predicting unsteady dynamic characteristics of cavitating cascades and inducer pumps. It includes bibliography of 19 papers authored between 1972 and 1980.

  11. Experimental and analytical study of rotating cavitation

    SciTech Connect

    Kamijo, Kenjiro; Shimura, Takashi; Tsujimoto, Yoshinobu

    1994-12-31

    This paper describes experimental and analytical results of rotating cavitation. There are four major sections in this paper. The first section presents the main characteristics of rotating cavitation which was found in the inducer test using a water tunnel. The second section describes the rotating cavitation which occurred in the development test of an LE-7 liquid oxygen pump for the H-II rocket. Also described in this section is how the rotating cavitation was suppressed. The rotating cavitation was the cause of both super synchronous shaft vibration and an unstable head coefficient curve. The third section presents how the theory of rotating cavitation was developed. The final section shows the measured cavitation compliance and mass flow gain factor of the LE-7 pump inducer for comparison of the experimental and analytical results of the rotating cavitation of the LE-7 pump inducer. Almost all the information presented in this paper has already been reported by Kamijo et al. (1977, 1980, 1993, 1993) and by Shimura (1993). In the present paper, the authors attempt to combine and give a clear overview of the experimental and analytical results described in the previous papers to systematically show their experience and findings on rotating cavitation.

  12. Modeling Unsteady Cavitation and Dynamic Loads in Turbopumps

    NASA Technical Reports Server (NTRS)

    Hosangadi, Ashvin; Ahuja, Vineet; Ungewitter, Ronald; Dash, Sanford M.

    2009-01-01

    A computational fluid dynamics (CFD) model that includes representations of effects of unsteady cavitation and associated dynamic loads has been developed to increase the accuracy of simulations of the performances of turbopumps. Although the model was originally intended to serve as a means of analyzing preliminary designs of turbopumps that supply cryogenic propellant liquids to rocket engines, the model could also be applied to turbopumping of other liquids: this can be considered to have been already demonstrated, in that the validation of the model was performed by comparing results of simulations performed by use of the model with results of sub-scale experiments in water. The need for this or a similar model arises as follows: Cavitation instabilities in a turbopump are generated as inlet pressure drops and vapor cavities grow on inducer blades, eventually becoming unsteady. The unsteady vapor cavities lead to rotation cavitation, in which the cavities detach from the blades and become part of a fluid mass that rotates relative to the inducer, thereby generating a fluctuating load. Other instabilities (e.g., surge instabilities) can couple with cavitation instabilities, thereby compounding the deleterious effects of unsteadiness on other components of the fluid-handling system of which the turbopump is a part and thereby, further, adversely affecting the mechanical integrity and safety of the system. Therefore, an ability to predict cavitation- instability-induced dynamic pressure loads on the blades, the shaft, and other pump parts would be valuable in helping to quantify safe margins of inducer operation and in contributing to understanding of design compromises. Prior CFD models do not afford this ability. Heretofore, the primary parameter used in quantifying cavitation performance of a turbopump inducer has been the critical suction specific speed at which head breakdown occurs. This parameter is a mean quantity calculated on the basis of assumed steady

  13. Sugars from woody tissue photosynthesis reduce xylem vulnerability to cavitation.

    PubMed

    De Baerdemaeker, Niels J F; Salomón, Roberto Luis; De Roo, Linus; Steppe, Kathy

    2017-09-18

    Reassimilation of internal CO2 via woody tissue photosynthesis has a substantial effect on tree carbon income and wood production. However, little is known about its role in xylem vulnerability to cavitation and its implications in drought-driven tree mortality. Young trees of Populus nigra were subjected to light exclusion at the branch and stem levels. After 40 d, measurements of xylem water potential, diameter variation and acoustic emission (AE) were performed in detached branches to obtain acoustic vulnerability curves to cavitation following bench-top dehydration. Acoustic vulnerability curves and derived AE50 values (i.e. water potential at which 50% of cavitation-related acoustic emissions occur) differed significantly between light-excluded and control branches (AE50,light-excluded  = -1.00 ± 0.13 MPa; AE50,control  = -1.45 ± 0.09 MPa; P = 0.007) denoting higher vulnerability to cavitation in light-excluded trees. Woody tissue photosynthesis represents an alternative and immediate source of nonstructural carbohydrates (NSC) that confers lower xylem vulnerability to cavitation via sugar-mediated mechanisms. Embolism repair and xylem structural changes could not explain this observation as the amount of cumulative AE and basic wood density did not differ between treatments. We suggest that woody tissue assimilates might play a role in the synthesis of xylem surfactants for nanobubble stabilization under tension. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

  14. Experimental analysis of the onset and development of cavitation in a centrifugal pump

    NASA Astrophysics Data System (ADS)

    Mousmoulis, G.; Karlsen-Davies, N.; Aggidis, G.; Anagnostopoulos, J.; Papantonis, D.

    2017-04-01

    Centrifugal pumps are considered as machines of high importance in a wide range of industries, hence several strategies and methods have been developed in order to ensure their optimum performance under different operating conditions. An important mechanism that can affect pump’s steady and dynamic operation is cavitation, which appears in the low static pressure zone at the inlet of the impeller. Several researchers have studied experimentally the physics of the phenomenon in order to develop different methodologies for its safe detection. The aim of this paper is to study the onset and evolution of cavitation in a centrifugal pump with unshrouded impeller by performing of flow visualization and acoustic emission measurements. The results showed that the acoustic emission technique is able to detect the onset of cavitation, while the leakage backflow through the clearance affects the development of cavitation between the impeller blades.

  15. Gold nanoparticle targeted photoacoustic cavitation for potential deep tissue imaging and therapy

    PubMed Central

    Ju, Hengyi; Roy, Ronald A.; Murray, Todd W.

    2012-01-01

    The laser generation of vapor bubbles around plasmonic nanoparticles can be enhanced through the application of an ultrasound field; a technique referred to as photoacoustic cavitation. The combination of light and ultrasound allows for bubble formation at lower laser fluence and peak negative ultrasound pressure than can be achieved using either modality alone. The growth and collapse of these bubbles leads to local mechanical disruption and acoustic emission, and can potentially be used to induce and monitor tissue therapy. Photoacoustic cavitation is investigated for a broad range of ultrasound pressures and nanoparticle concentrations for gold nanorods and nanospheres. The cavitation threshold fluences for both nanoparticle types are found to drastically reduce in the presence of an ultrasound field. The results indicate that photoacoustic cavitation can potentially be produced at depth in biological tissue without exceeding the safety limits for ultrasound or laser radiation at the tissue surface. PMID:23304648

  16. Numerical and Experimental Investigation of Cavitating Characteristics in Centrifugal Pump with Gap Impeller

    NASA Astrophysics Data System (ADS)

    Zhu, Bing; Chen, Hongxun; Wei, Qun

    2014-06-01

    This paper is to study the cavitating characteristics in a low specific speed centrifugal pump with gap structure impeller experimentally and numerically. A scalable DES numerical method is proposed and developed by introducing the von Karman scale instead of the local grid scale, which can switch at the RANS and LES region interface smoothly and reasonably. The SDES method can detect and grasp unsteady scale flow structures, which were proved by the flow around a triangular prism and the cavitation flow in a centrifugal pump. Through numerical and experimental research, it's shown that the simulated results match qualitatively with tested cavitation performances and visualization patterns, and we can conclude that the gap structure impeller has a superior feature of cavitation suppression. Its mechanism may be the guiding flow feature of the small vice blade and the pressure auto-balance effect of the gap tunnel.

  17. Processing and Microstructure Characteristics of As-Cast A356 Alloys Manufactured via Ultrasonic Cavitation during Solidification

    NASA Astrophysics Data System (ADS)

    Xuan, Yang; Jia, Shian; Nastac, Laurentiu

    2017-04-01

    Recent studies have showed that the microstructure and mechanical properties of A356 alloy can be significantly improved when ultrasonic cavitation and solidification processing is used. This is because during the fabrication of A356 castings, ultrasonic cavitation processing plays an important role in degassing and refining the as-cast microstructure. In the present study, A356 alloy and Al2O3/SiC nanoparticles are used as the matrix alloy and the reinforcements, respectively. Nanoparticles are injected into the molten alloy and dispersed by ultrasonic cavitation. Ultrasonic cavitation was also applied during solidification of these nanocomposites. The microstructure and nanoparticle distribution of the cast samples have been investigated in detail. The current experimental results indicated that ultrasonic cavitation during solidification will greatly improve the microstructure of the samples. Al2O3 and SiC nanoparticle reinforced nanocomposites have different nanoparticle distributions in the matrix.

  18. Microscopic investigation of cavitation erosion damage in metals

    NASA Technical Reports Server (NTRS)

    Hackworh, J. V.; Adler, W. F.

    1974-01-01

    The results of research to identify the cavitation erosion damage mechanisms at the microscopic level for three metals (aluminum, stainless steel, and titanium) representing a range of properties and microstructure are presented. The metals were exposed to cavitation generated in distilled water by a 20-kHz ultrasonic facility operating at a vibration amplitude of 2 mils. Representative properties of the metals and experimental details are summarized. Replicas of the eroded surfaces of the specimens obtained periodically during exposure were examined with a transmission electron microscope to follow progression of the erosion damage and identify dominant erosion mechanisms as a function of exposure time. Eroded surfaces of selected specimens were also examined with a scanning electron microscope to assist in the interpretation.

  19. Variations of bubble cavitation and temperature elevation during acculysis

    NASA Astrophysics Data System (ADS)

    Zhou, Yufeng; Gao, Xiaobin Wilson

    2017-03-01

    High-intensity focused ultrasound (HIFU) is effective in both thermal ablations and soft-tissue fragmentation. Mechanical and thermal effects depend on the operating parameters and vary with the progress of therapy. Different types of lesions could be produced with the pulse duration of 5-30 ms, much longer than histotripsy burst but shorter than the time for tissue boiling, and pulse repetition frequency (PRF) of 0.2-5 Hz. Meanwhile, bubble cavitation and temperature elevation in the focal region were measured by passive cavitation detection (PCD) and thermocouples, respectively. Temperature in the pre-focal region is always higher than those at the focal and post-focal position in all tests. Overall, it is suggested that appropriate synergy and monitoring of mechanical and thermal effects would broaden the HIFU application and enhance its efficiency as well as safety.

  20. Cavitation instabilities of an inducer in a cryogenic pump

    NASA Astrophysics Data System (ADS)

    Kim, Dae-Jin; Sung, Hyung Jin; Choi, Chang-Ho; Kim, Jin-Sun

    2017-03-01

    Inducers assist cryogenic pumps to operate safely under cavitation conditions by increasing the pressure of the impeller inlet, but create cavitation instabilities. The use of cryogenic fluids requires special attention because of safety and handling concerns. To examine the cavitation instabilities of a cryogenic pump, two kinds of working fluids, water and liquid oxygen, were employed. The cavitation instabilities were measured with an accelerometer installed on the pump casing. The flow coefficient and the head slightly decrease with decreases in the cavitation number before the cavitation breakdown. These trends are true of both fluids. Several cavitation instabilities were identified with the accelerometer. At lower flow coefficients, super-synchronous rotating cavitation was found in a similar cavitation number range for both fluids. At higher flow coefficients, the cavitation numbers of the cavitation instabilities in the liquid oxygen test are smaller than those of the water test.

  1. A physical model of the extreme mantis shrimp strike: kinematics and cavitation of Ninjabot.

    PubMed

    Cox, S M; Schmidt, D; Modarres-Sadeghi, Y; Patek, S N

    2014-03-01

    To study the mechanical principles and fluid dynamics of ultrafast power-amplified systems, we built Ninjabot, a physical model of the extremely fast mantis shrimp (Stomatopoda). Ninjabot rotates a to-scale appendage within the environmental conditions and close to the kinematic range of mantis shrimp's rotating strike. Ninjabot is an adjustable mechanism that can repeatedly vary independent properties relevant to fast aquatic motions to help isolate their individual effects. Despite exceeding the kinematics of previously published biomimetic jumpers and reaching speeds in excess of 25 m s(-1) at accelerations of 3.2 × 10(4) m s(-2), Ninjabot can still be outstripped by the fastest mantis shrimp, Gonodactylus smithii, measured for the first time in this study. G. smithii reached 30 m s(-1) at accelerations of 1.5 × 10(5) m s(-2). While mantis shrimp produce cavitation upon impact with their prey, they do not cavitate during the forward portion of their strike despite their extreme speeds. In order to determine how closely to match Ninjabot and mantis shrimp kinematics to capture this cavitation behavior, we used Ninjabot to produce strikes of varying kinematics and to measure cavitation presence or absence. Using Akaike Information Criterion to compare statistical models that correlated cavitation with a variety of kinematic properties, we found that in rotating and accelerating biological conditions, cavitation inception is best explained only by maximum linear velocity.

  2. Cavitation Fatigue. Embolism and Refilling Cycles Can Weaken the Cavitation Resistance of Xylem1

    PubMed Central

    Hacke, Uwe G.; Stiller, Volker; Sperry, John S.; Pittermann, Jarmila; McCulloh, Katherine A.

    2001-01-01

    Although cavitation and refilling cycles could be common in plants, it is unknown whether these cycles weaken the cavitation resistance of xylem. Stem or petiole segments were tested for cavitation resistance before and after a controlled cavitation-refilling cycle. Cavitation was induced by centrifugation, air drying of shoots, or soil drought. Except for droughted plants, material was not significantly water stressed prior to collection. Cavitation resistance was determined from “vulnerability curves” showing the percentage loss of conductivity versus xylem pressure. Two responses were observed. “Resilient” xylem (Acer negundo and Alnus incana stems) showed no change in cavitation resistance after a cavitation-refilling cycle. In contrast, “weakened” xylem (Populus angustifolia, P. tremuloides, Helianthus annuus stems, and Aesculus hippocastanum petioles) showed considerable reduction in cavitation resistance. Weakening was observed whether cavitation was induced by centrifugation, air dehydration, or soil drought. Observations from H. annuus showed that weakening was proportional to the embolism induced by stress. Air injection experiments indicated that the weakened response was a result of an increase in the leakiness of the vascular system to air seeding. The increased air permeability in weakened xylem could result from rupture or loosening of the cellulosic mesh of interconduit pit membranes during the water stress and cavitation treatment. PMID:11161035

  3. Transient cavitating vortical flows around a hydrofoil using k-ω partially averaged Navier-Stokes model

    NASA Astrophysics Data System (ADS)

    Luo, Xianwu; Huang, Renfang; Ji, Bin

    2016-01-01

    For accurate simulations of wall-bounded turbulent cavitating flows, the present paper proposed a partially averaged Navier-Stokes (PANS) method derived from the k-ω turbulence model. Transient cavitating vortical flows around a NACA66 hydrofoil were simulated by using the k-ω PANS model with various filter parameters (fk = 0.2, 0.5 and 1, while fω = 1/fk) and a mass transfer cavitation model based on the Rayleigh-Plesset equation. Compared with the available experimental data, the k-ω PANS model with fk = 0.2 can accurately reproduce the cavitation evolution with more complicated structures due to the reduction in the predicted eddy viscosity. Further analyses, using the vorticity transport equation, indicate that the transition of cavitation structure from two dimension to three dimension is associated with strong vortex-cavitation interaction, where vortex stretching and dilation may play a major role. Therefore, the k-ω PANS model with the filter parameter of fk = 0.2 is an effective method to numerically predict the transient cavitating vortical flows around hydrofoils. The results obtained in this paper are helpful to provide a physical insight into the mechanisms of cavitation shedding dynamics.

  4. Cavitation: Cavitation flow. Citations from the NTIS data base

    NASA Astrophysics Data System (ADS)

    Habercom, G. E., Jr.

    1980-05-01

    Reports on general aspects of cavitating flow are included. A wide range of theoretical, analytical, and experimental information is presented involving mathematical analysis, computer programs, and testing. Topics include marine engineering, hydrodynamic and aerodynamic configurations, symmetric and nonaxisymmetric shapes, and measuring technology. Data is given on surface piercing struts, helical inducers, pumps, liquid metal systems, and venturi tubes. Applications include dam outlets and spillways, vertical conduits, deep rock drilling, heat pipe stability, water entry, and liquid cryogenic systems. Discussions are made of flow characteristics, noise, nucleate boiling, perturbation problems, and allied subjects. This updated bibliography contains 253 abstracts.

  5. Noise from Tip Vortex and Bubble Cavitation

    DTIC Science & Technology

    1990-03-01

    composantes spectrales. la directivit6 et la forme d’onde des sons dans le champ lointain en conditions correspondant essentiellement an champ libre, jusqu...disappeared completely, leaving only bubble cavitation. A small amount of huil , vortex cavitation also was present at speeds above 1300 rpm. The final

  6. Cavitation in liquid cryogens. 1: Venturi

    NASA Technical Reports Server (NTRS)

    Hord, J.; Anderson, L. M.; Hall, W. J.

    1972-01-01

    The results of continuing cavitation studies are reported. The cavitation characteristics of liquid hydrogen and liquid nitrogen flowing in a transparent plastic Venturi are discussed. Thermodynamic data, consisting of pressure and temperature measurements within fully developed hydrogen cavities, are reported. Details concerning test apparatus, test procedure, and data correlation techniques are given.

  7. Vapor Cavitation in Dynamically Loaded Journal Bearings

    NASA Technical Reports Server (NTRS)

    Jacobson, B. O.; Hamrock, B. J.

    1983-01-01

    High speed motion camera experiments were performed on dynamically loaded journal bearings. The length to diameter ratio of the bearing, the speed of the roller and the tube, the surface material of the roller, and the static and dynamic eccentricity of the bearing were varied. One hundred and thirty-four cases were filmed. The occurrence of vapor cavitation was clearly evident in the films and figures presented. Vapor cavitation was found to occur when the tensile stress applied to the oil exceeded the tensile strength of the oil or the binding of the oil to the surface. The physical situation in which vapor cavitation occurs is during the squeezing and sliding motion within a bearing. Besides being able to accurately capture the vapor cavitation on film, an analysis of the formation and collapse of the cavitation bubbles and characteristics of the bubble content are presented.

  8. Radial Shock Wave Devices Generate Cavitation

    PubMed Central

    Császár, Nikolaus B. M.; Angstman, Nicholas B.; Milz, Stefan; Sprecher, Christoph M.; Kobel, Philippe; Farhat, Mohamed; Furia, John P.; Schmitz, Christoph

    2015-01-01

    Background Conflicting reports in the literature have raised the question whether radial extracorporeal shock wave therapy (rESWT) devices and vibrating massage devices have similar energy signatures and, hence, cause similar bioeffects in treated tissues. Methods and Findings We used laser fiber optic probe hydrophone (FOPH) measurements, high-speed imaging and x-ray film analysis to compare fundamental elements of the energy signatures of two rESWT devices (Swiss DolorClast; Electro Medical Systems, Nyon, Switzerland; D-Actor 200; Storz Medical, Tägerwillen, Switzerland) and a vibrating massage device (Vibracare; G5/General Physiotherapy, Inc., Earth City, MO, USA). To assert potential bioeffects of these treatment modalities we investigated the influence of rESWT and vibrating massage devices on locomotion ability of Caenorhabditis elegans (C. elegans) worms. Results FOPH measurements demonstrated that both rESWT devices generated acoustic waves with comparable pressure and energy flux density. Furthermore, both rESWT devices generated cavitation as evidenced by high-speed imaging and caused mechanical damage on the surface of x-ray film. The vibrating massage device did not show any of these characteristics. Moreover, locomotion ability of C. elegans was statistically significantly impaired after exposure to radial extracorporeal shock waves but was unaffected after exposure of worms to the vibrating massage device. Conclusions The results of the present study indicate that both energy signature and bioeffects of rESWT devices are fundamentally different from those of vibrating massage devices. Clinical Relevance Prior ESWT studies have shown that tissues treated with sufficient quantities of acoustic sound waves undergo cavitation build-up, mechanotransduction, and ultimately, a biological alteration that “kick-starts” the healing response. Due to their different treatment indications and contra-indications rESWT devices cannot be equated to vibrating

  9. Superplasticity and cavitation in an aluminum-magnesium alloy

    NASA Astrophysics Data System (ADS)

    Bae, Donghyun

    2000-10-01

    Fundamental issues related to the forming performance of superplastic metals include the mechanisms of flow and cavitation occurring during the forming process. Cavitation beyond a critical amount is damaging to the mechanical behavior of fabricated parts. Therefore, the role of process parameters which influence cavitation must be precisely documented and understood. In this study, (1) the mechanism of deformation, (2) cavity formation and growth, and (3) the effect of forming parameters on cavitation are systematically investigated in a fine grain Al-4.7%Mg-0.8%Mn-0.4%Cu alloy. The mechanical flow response of the alloy is characterized by a new type of step strain-rate test which preserves the initial microstructure of the alloy. Under isostructural condition, sigmoidal log s vs. log 3˙ relationship is determined and then analyzed by using a grain-mantle based quantitative model1 for superplastic flow. The activation energies in both grain-mantle creep and core creep are analyzed, and the overall controlling mechanism is found to be dislocation glide and climb. Grain-mantle creep rate in the low strain-rate region is found to be enhanced many times due to a high concentration of vacancies near grain boundaries. Cavitation caused by superplastic straining under uniaxial tension is evaluated by the SEM (for < 0.5mum size) and the number and size of cavities are monitored by image analysis through optical microscopy. Growth of pre-existing cavities and nucleation and growth of new cavities at grain boundary particles are monitored with increasing strain. Cavity nucleation and growth occur in two stages: crack-like growth along the particle-matrix interface by a constrained growth process, and beyond complete debonding growth via plastic deformation of the matrix which is modeled here. Stresses and strain-rates near the void are intensified due to the perturbed flow field near the void, and not relaxed during the time frame associated with superplastic deformation

  10. J-2X Turbopump Cavitation Diagnostics

    NASA Technical Reports Server (NTRS)

    Santi, I. Michael; Butas, John P.; Tyler, Thomas R., Jr.; Aguilar, Robert; Sowers, T. Shane

    2010-01-01

    The J-2X is the upper stage engine currently being designed by Pratt & Whitney Rocketdyne (PWR) for the Ares I Crew Launch Vehicle (CLV). Propellant supply requirements for the J-2X are defined by the Ares Upper Stage to J-2X Interface Control Document (ICD). Supply conditions outside ICD defined start or run boxes can induce turbopump cavitation leading to interruption of J-2X propellant flow during hot fire operation. In severe cases, cavitation can lead to uncontained engine failure with the potential to cause a vehicle catastrophic event. Turbopump and engine system performance models supported by system design information and test data are required to predict existence, severity, and consequences of a cavitation event. A cavitation model for each of the J-2X fuel and oxidizer turbopumps was developed using data from pump water flow test facilities at Pratt & Whitney Rocketdyne (PWR) and Marshall Space Flight Center (MSFC) together with data from Powerpack 1A testing at Stennis Space Center (SSC) and from heritage systems. These component models were implemented within the PWR J-2X Real Time Model (RTM) to provide a foundation for predicting system level effects following turbopump cavitation. The RTM serves as a general failure simulation platform supporting estimation of J-2X redline system effectiveness. A study to compare cavitation induced conditions with component level structural limit thresholds throughout the engine was performed using the RTM. Results provided insight into system level turbopump cavitation effects and redline system effectiveness in preventing structural limit violations. A need to better understand structural limits and redline system failure mitigation potential in the event of fuel side cavitation was indicated. This paper examines study results, efforts to mature J-2X turbopump cavitation models and structural limits, and issues with engine redline detection of cavitation and the use of vehicle-side abort triggers to augment the

  11. Inertial cavitation in theranostic nanoemulsions with simultaneous pulsed laser and low frequency ultrasound excitation

    NASA Astrophysics Data System (ADS)

    Arnal, Bastien; Wei, Chen-Wei; Xia, Jinjun; Pelivanov, Ivan M.; Lombardo, Michael; Perez, Camilo; Matula, Thomas J.; Pozzo, Danilo; O'Donnell, Matthew

    2014-03-01

    Ultrasound-induced inertial cavitation is a mechanical process used for site-localized therapies such as non-invasive surgery. Initiating cavitation in tissue requires very high intensity focused ultrasound (HIFU) and low-frequencies. Hence, some applications like thrombolysis require targeted contrast agents to reduce peak intensities and the potential for secondary effects. A new type of theranostic nanoemulsion has been developed as a combined ultrasound (US)/photoacoustic(PA) agent for molecular imaging and therapy. It includes a nanoscale emulsion core encapsulated with a layer of gold nanospheres at the water/ oil interface. Its optical absorption exhibits a spectrum broadened up to 1100 nm, opening the possibility that 1064 nm light can excite cavitation nuclei. If optically-excited nuclei are produced at the same time that a low-frequency US wave is at peak negative pressure, then highly localized therapies based on acoustic cavitation may be enabled at very low US pressures. We have demonstrated this concept using a low-cost, low energy, portable 1064 nm fiber laser in conjunction with a 1.24 MHz US transducer for simultaneous laser/US excitation of nanoemulsions. Active cavitation detection from backscattered signals indicated that cavitation can be initiated at very low acoustic pressures (less than 1 MPa) when laser excitation coincides with the rarefaction phase of the acoustic wave, and that no cavitation is produced when light is delivered during the compressive phase. US can sustain cavitation activity during long acoustic bursts and stimulate diffusion of the emulsion, thus increasing treatment speed. An in vitro clot model has been used to demonstrate combined US and laser excitation of the nanoemulsion for efficient thrombolysis.

  12. Physics and Control of Cavitation

    DTIC Science & Technology

    2006-03-01

    Rayleigh - Plesset equation . This equation is presented below together with a few typical behaviours...to illustrate the importance of dynamics in cavitation. 3.1 Rayleigh - Plesset Equation The objective is to determine the unsteady response of a...interface (12) finally gives the famous Rayleigh - Plesset equation : [ ] R R4 R S2 R Rp)t(ppR 2 3RR 3 0 0gv 2 µρ γ −−   +−=    + ∞

  13. Dependence of pulsed focused ultrasound induced thrombolysis on duty cycle and cavitation bubble size distribution.

    PubMed

    Xu, Shanshan; Zong, Yujin; Feng, Yi; Liu, Runna; Liu, Xiaodong; Hu, Yaxin; Han, Shimin; Wan, Mingxi

    2015-01-01

    In this study, we investigated the relationship between the efficiency of pulsed, focused ultrasound (FUS)-induced thrombolysis, the duty cycle (2.3%, 9%, and 18%) and the size distribution of cavitation bubbles. The efficiency of thrombolysis was evaluated through the degree of mechanical fragmentation, namely the number, mass, and size of clot debris particles. First, we found that the total number and mass of clot debris particles were highest when a duty cycle of 9% was used and that the mean diameter of clot debris particles was smallest. Second, we found that the size distribution of cavitation bubbles was mainly centered around the linear resonance radius (2.5μm) of the emission frequency (1.2MHz) of the FUS transducer when a 9% duty cycle was used, while the majority of cavitation bubbles became smaller or larger than the linear resonance radius when a 2.3% or 18% duty cycle was used. In addition, the inertial cavitation dose from the treatment performed at 9% duty cycle was much higher than the dose obtained with the other two duty cycles. The data presented here suggest that there is an optimal duty cycle at which the thrombolysis efficiency and cavitation activity are strongest. They further indicate that using a pulsed FUS may help control the size distribution of cavitation nuclei within an active size range, which we found to be near the linear resonance radius of the emission frequency of the FUS transducer.

  14. Improvement in cavitation erosion resistance of AISI 316L stainless steel by friction stir processing

    NASA Astrophysics Data System (ADS)

    Hajian, M.; Abdollah-zadeh, A.; Rezaei-Nejad, S. S.; Assadi, H.; Hadavi, S. M. M.; Chung, K.; Shokouhimehr, M.

    2014-07-01

    Commercial AISI 316L plates with the initial grain size of 14.8 μm were friction stir processed (FSP) with different processing parameters, resulting in two fine-grained microstructures with the grain sizes of 4.6 and 1.7 μm. The cavitation erosion behavior, before and after FSP, was evaluated in terms of incubation time, cumulative mass loss and mean depth of erosion. A separate cavitation erosion test was performed on the transverse cross section of a FSP sample to reveal the effect of grain structure. It was observed that FSP samples, depending on their grain size, are at least 3-6 times more resistant than the base material against cavitation erosion. The improvement in cavitation erosion resistance is attributed to smaller grain structure, lower fraction of twin boundaries, and favorable crystallographic orientation of grains in FSP samples. The finer the grain size, the more cavitation erosion resistance was achieved. Moreover, the microstructures of eroded surfaces were studied using a scanning electron microscope equipped with EBSD, and an atomic force microscope. The mechanisms controlling the cavitation erosion damage in friction stir processed AISI 316L are also discussed.

  15. A tissue phantom for visualization and measurement of ultrasound-induced cavitation damage

    PubMed Central

    Maxwell, Adam D.; Wang, Tzu-Yin; Yuan, Lingqian; Duryea, Alexander P.; Xu, Zhen; Cain, Charles A.

    2010-01-01

    Many ultrasound studies involve the use of tissue-mimicking materials to research phenomena in-vitro and predict in-vivo bioeffects. We have developed a tissue phantom to study cavitation-induced damage to tissue. The phantom consists of red blood cells suspended in an agarose hydrogel. The acoustic and mechanical properties of the gel phantom were found to be similar to soft tissue properties. The phantom’s response to cavitation was evaluated using histotripsy. Histotripsy causes breakdown of tissue structures by generation of controlled cavitation using short, focused, high-intensity ultrasound pulses. Histotripsy lesions were generated in the phantom and kidney tissue using a spherically focused 1-MHz transducer generating 15 cycle pulses at a pulse repetition frequency of 100 Hz with a peak negative pressure of 14 MPa. Damage appeared clearly as increased optical transparency of the phantom due to rupture of individual red blood cells. The morphology of lesions generated in the phantom was very similar to that generated in kidney tissue, at both macroscopic and cellular levels. Additionally, lesions in the phantom could be visualized as hypoechoic regions on a B-Mode ultrasound image, similar to histotripsy lesions in tissue. High speed imaging of the optically-transparent phantom was used to show that damage coincides with the presence of cavitation. These results indicate that the phantom can accurately mimic the response of soft tissue to cavitation and provide a useful tool for studying damage induced by acoustic cavitation. PMID:21030142

  16. Post-fire Tree Mortality: Heating Increases Vulnerability to Cavitation in Longleaf Pine Branches

    NASA Astrophysics Data System (ADS)

    Lodge, A.; Kavanagh, K.; Dickinson, M. B.

    2016-12-01

    Tree mortality following wild and prescribed fires is of interest to both researchers and land managers. While some models exist that can predict mortality following fires, process-based models that incorporate physiological mechanisms of mortality are still being developed and improved. Delayed post-fire tree mortality has recently received increased attention, in part due to an increased use of prescribed fire as a restoration and management tool. One hypothesized mechanism of delayed mortality in trees is disruption of water transport in xylem due to exposure to the heat plume of a fire. This heat plume rapidly increases the vapor pressure deficit in the tree canopy, quickly increasing the tension on the water held in the xylem and leaves, potentially leading to cavitation. Cavitated xylem conduits can no longer transport water, eventually leading to tree death. We conducted a laboratory experiment examining whether heating stems increases their vulnerability to cavitation. We placed longleaf pine (Pinus palustris) branches in a water bath at sub-lethal temperatures (<60°C) and applied pressure in a cavitation chamber to simulate a range of xylem tension levels that may occur during fire. Percent loss of conductivity was measured following cavitation induced by various levels of applied pressure. When we compared the resulting vulnerability curves of heated branches to those of branches pressurized at room temperature, we observed increased vulnerability to cavitation in the heated samples especially at lower pressures. P50, or the pressure at which 50% of conductivity has been lost, decreased by 18% on branches heated to approximately 54°C. This suggests that stems heated during fires may be more vulnerable to cavitation, and provides some support for hydraulic disruption as a mechanism for post-fire tree mortality. Continued advancement in understanding of the mechanisms leading to delayed mortality will improve models predicting tree mortality.

  17. Super-Cavitating Flow Around Two-Dimensional Conical, Spherical, Disc and Stepped Disc Cavitators

    NASA Astrophysics Data System (ADS)

    Sooraj, S.; Chandrasekharan, Vaishakh; Robson, Rony S.; Bhanu Prakash, S.

    2017-08-01

    A super-cavitating object is a high speed submerged object that is designed to initiate a cavitation bubble at the nose which extends past the aft end of the object, substantially reducing the skin friction drag that would be present if the sides of the object were in contact with the liquid in which the object is submerged. By reducing the drag force the thermal energy consumption to move faster can also be minimised. The super-cavitation behavioural changes with respect to Cavitators of various geometries have been studied by varying the inlet velocity. Two-dimensional computational fluid dynamics analysis has been carried out by applying k-ε turbulence model. The variation of drag coefficient, cavity length with respect to cavitation number and inlet velocity are analyzed. Results showed conical Cavitator with wedge angle of 30° has lesser drag coefficient and cavity length when compared to conical Cavitators with wedge angles 45° and 60°, spherical, disc and stepped disc Cavitators. Conical cavitator 60° and disc cavitator have the maximum cavity length but with higher drag coefficient. Also there is significant variation of supercavitation effect observed between inlet velocities of 32 m/s to 40 m/s.

  18. CAVITATION SOUNDS DURING CERVICOTHORACIC SPINAL MANIPULATION

    PubMed Central

    Mourad, Firas; Zingoni, Andrea; Iorio, Raffaele; Perreault, Thomas; Zacharko, Noah; de las Peñas, César Fernández; Butts, Raymond; Cleland, Joshua A.

    2017-01-01

    Background No study has previously investigated the side, duration or number of audible cavitation sounds during high-velocity low-amplitude (HVLA) thrust manipulation to the cervicothoracic spine. Purpose The primary purpose was to determine which side of the spine cavitates during cervicothoracic junction (CTJ) HVLA thrust manipulation. Secondary aims were to calculate the average number of cavitations, the duration of cervicothoracic thrust manipulation, and the duration of a single cavitation. Study Design Quasi-experimental study Methods Thirty-two patients with upper trapezius myalgia received two cervicothoracic HVLA thrust manipulations targeting the right and left T1-2 articulation, respectively. Two high sampling rate accelerometers were secured bilaterally 25 mm lateral to midline of the T1-2 interspace. For each manipulation, two audio signals were extracted using Short-Time Fourier Transformation (STFT) and singularly processed via spectrogram calculation in order to evaluate the frequency content and number of instantaneous energy bursts of both signals over time for each side of the CTJ. Result Unilateral cavitation sounds were detected in 53 (91.4%) of 58 cervicothoracic HVLA thrust manipulations and bilateral cavitation sounds were detected in just five (8.6%) of the 58 thrust manipulations; that is, cavitation was significantly (p<0.001) more likely to occur unilaterally than bilaterally. In addition, cavitation was significantly (p<0.0001) more likely to occur on the side contralateral to the clinician's short-lever applicator. The mean number of audible cavitations per manipulation was 4.35 (95% CI 2.88, 5.76). The mean duration of a single manipulation was 60.77 ms (95% CI 28.25, 97.42) and the mean duration of a single audible cavitation was 4.13 ms (95% CI 0.82, 7.46). In addition to single-peak and multi-peak energy bursts, spectrogram analysis also demonstrated high frequency sounds, low frequency sounds, and sounds of multiple

  19. CAVITATION SOUNDS DURING CERVICOTHORACIC SPINAL MANIPULATION.

    PubMed

    Dunning, James; Mourad, Firas; Zingoni, Andrea; Iorio, Raffaele; Perreault, Thomas; Zacharko, Noah; de Las Peñas, César Fernández; Butts, Raymond; Cleland, Joshua A

    2017-08-01

    No study has previously investigated the side, duration or number of audible cavitation sounds during high-velocity low-amplitude (HVLA) thrust manipulation to the cervicothoracic spine. The primary purpose was to determine which side of the spine cavitates during cervicothoracic junction (CTJ) HVLA thrust manipulation. Secondary aims were to calculate the average number of cavitations, the duration of cervicothoracic thrust manipulation, and the duration of a single cavitation. Quasi-experimental study. Thirty-two patients with upper trapezius myalgia received two cervicothoracic HVLA thrust manipulations targeting the right and left T1-2 articulation, respectively. Two high sampling rate accelerometers were secured bilaterally 25 mm lateral to midline of the T1-2 interspace. For each manipulation, two audio signals were extracted using Short-Time Fourier Transformation (STFT) and singularly processed via spectrogram calculation in order to evaluate the frequency content and number of instantaneous energy bursts of both signals over time for each side of the CTJ. Unilateral cavitation sounds were detected in 53 (91.4%) of 58 cervicothoracic HVLA thrust manipulations and bilateral cavitation sounds were detected in just five (8.6%) of the 58 thrust manipulations; that is, cavitation was significantly (p<0.001) more likely to occur unilaterally than bilaterally. In addition, cavitation was significantly (p<0.0001) more likely to occur on the side contralateral to the clinician's short-lever applicator. The mean number of audible cavitations per manipulation was 4.35 (95% CI 2.88, 5.76). The mean duration of a single manipulation was 60.77 ms (95% CI 28.25, 97.42) and the mean duration of a single audible cavitation was 4.13 ms (95% CI 0.82, 7.46). In addition to single-peak and multi-peak energy bursts, spectrogram analysis also demonstrated high frequency sounds, low frequency sounds, and sounds of multiple frequencies for all 58 manipulations. Cavitation was

  20. Cavitation clouds created by shock scattering from bubbles during histotripsy.

    PubMed

    Maxwell, Adam D; Wang, Tzu-Yin; Cain, Charles A; Fowlkes, J Brian; Sapozhnikov, Oleg A; Bailey, Michael R; Xu, Zhen

    2011-10-01

    Histotripsy is a therapy that focuses short-duration, high-amplitude pulses of ultrasound to incite a localized cavitation cloud that mechanically breaks down tissue. To investigate the mechanism of cloud formation, high-speed photography was used to observe clouds generated during single histotripsy pulses. Pulses of 5-20 cycles duration were applied to a transparent tissue phantom by a 1-MHz spherically focused transducer. Clouds initiated from single cavitation bubbles that formed during the initial cycles of the pulse, and grew along the acoustic axis opposite the propagation direction. Based on these observations, we hypothesized that clouds form as a result of large negative pressure generated by the backscattering of shockwaves from a single bubble. The positive-pressure phase of the wave inverts upon scattering and superimposes on the incident negative-pressure phase to create this negative pressure and cavitation. The process repeats with each cycle of the incident wave, and the bubble cloud elongates toward the transducer. Finite-amplitude propagation distorts the incident wave such that the peak-positive pressure is much greater than the peak-negative pressure, which exaggerates the effect. The hypothesis was tested with two modified incident waves that maintained negative pressure but reduced the positive pressure amplitude. These waves suppressed cloud formation which supported the hypothesis. © 2011 Acoustical Society of America

  1. Cavitation clouds created by shock scattering from bubbles during histotripsy

    PubMed Central

    Maxwell, Adam D.; Wang, Tzu-Yin; Cain, Charles A.; Fowlkes, J. Brian; Sapozhnikov, Oleg A.; Bailey, Michael R.; Xu, Zhen

    2011-01-01

    Histotripsy is a therapy that focuses short-duration, high-amplitude pulses of ultrasound to incite a localized cavitation cloud that mechanically breaks down tissue. To investigate the mechanism of cloud formation, high-speed photography was used to observe clouds generated during single histotripsy pulses. Pulses of 5−20 cycles duration were applied to a transparent tissue phantom by a 1-MHz spherically focused transducer. Clouds initiated from single cavitation bubbles that formed during the initial cycles of the pulse, and grew along the acoustic axis opposite the propagation direction. Based on these observations, we hypothesized that clouds form as a result of large negative pressure generated by the backscattering of shockwaves from a single bubble. The positive-pressure phase of the wave inverts upon scattering and superimposes on the incident negative-pressure phase to create this negative pressure and cavitation. The process repeats with each cycle of the incident wave, and the bubble cloud elongates toward the transducer. Finite-amplitude propagation distorts the incident wave such that the peak-positive pressure is much greater than the peak-negative pressure, which exaggerates the effect. The hypothesis was tested with two modified incident waves that maintained negative pressure but reduced the positive pressure amplitude. These waves suppressed cloud formation which supported the hypothesis. PMID:21973343

  2. Detection of cavitation vortex in hydraulic turbines using acoustic techniques

    NASA Astrophysics Data System (ADS)

    Candel, I.; Bunea, F.; Dunca, G.; Bucur, D. M.; Ioana, C.; Reeb, B.; Ciocan, G. D.

    2014-03-01

    Cavitation phenomena are known for their destructive capacity in hydraulic machineries and are caused by the pressure decrease followed by an implosion when the cavitation bubbles find an adverse pressure gradient. A helical vortex appears in the turbine diffuser cone at partial flow rate operation and can be cavitating in its core. Cavity volumes and vortex frequencies vary with the under-pressure level. If the vortex frequency comes close to one of the eigen frequencies of the turbine, a resonance phenomenon may occur, the unsteady fluctuations can be amplified and lead to important turbine and hydraulic circuit damage. Conventional cavitation vortex detection techniques are based on passive devices (pressure sensors or accelerometers). Limited sensor bandwidths and low frequency response limit the vortex detection and characterization information provided by the passive techniques. In order to go beyond these techniques and develop a new active one that will remove these drawbacks, previous work in the field has shown that techniques based on acoustic signals using adapted signal content to a particular hydraulic situation, can be more robust and accurate. The cavitation vortex effects in the water flow profile downstream hydraulic turbines runner are responsible for signal content modifications. Basic signal techniques use narrow band signals traveling inside the flow from an emitting transducer to a receiving one (active sensors). Emissions of wide band signals in the flow during the apparition and development of the vortex embeds changes in the received signals. Signal processing methods are used to estimate the cavitation apparition and evolution. Tests done in a reduced scale facility showed that due to the increasing flow rate, the signal -- vortex interaction is seen as modifications on the received signal's high order statistics and bandwidth. Wide band acoustic transducers have a higher dynamic range over mechanical elements; the system's reaction time

  3. Preparation of SiC based Aluminium metal matrix nano composites by high intensity ultrasonic cavitation process and evaluation of mechanical and tribological properties

    NASA Astrophysics Data System (ADS)

    Murthy, N. V.; Prasad Reddy, A.; Selvaraj, N.; Rao, C. S. P.

    2016-09-01

    Request augments on a worldwide scale for the new materials. The metal matrix nano composites can be used in numerous applications of helicopter structural parts, gas turbine exit guide vane's, space shuttle, and other structural applications. The key mailman to ameliorate performance of composite matrix in aluminium alloy metal reinforces nano particles in the matrix of alloy uniformly, which ameliorates composite properties without affecting limit of ductility. The ultrasonic assisted stir casting helped agitation was successfully used to fabricate Al 2219 metal matrix of alloy reinforced with (0.5, 1, 1.5 and 2) wt.% of nano silicon carbide (SiC) particles of different sizes 50nm and 150nm. The micrographs of scanning electron microscopy of nano composite were investigated it reveals that the uniform dispersion of nano particles silicon carbide in aluminium alloy 2219 matrix and with the low porosity. How the specific wear rate was vary with increasing weight percentage of nano particles at constant load and speed as shown in results and discussions. And the mechanical properties showed that the ultimate tensile strength and hardness of metal matrix nano composite AA 2219 / nano SiC of 50nm and 150nm lean to augment with increase weight percentage of silicon carbide content in the matrix alloy.

  4. Simulations of Cavitating Cryogenic Inducers

    NASA Technical Reports Server (NTRS)

    Dorney, Dan (Technical Monitor); Hosangadi, Ashvin; Ahuja, Vineet; Ungewitter, Ronald J.

    2004-01-01

    Simulations of cavitating turbopump inducers at their design flow rate are presented. Results over a broad range of Nss, numbers extending from single-phase flow conditions through the critical head break down point are discussed. The flow characteristics and performance of a subscale geometry designed for water testing are compared with the fullscale configuration that employs LOX. In particular, thermal depression effects arising from cavitation in cryogenic fluids are identified and their impact on the suction performance of the inducer quantified. The simulations have been performed using the CRUNCH CFD[R] code that has a generalized multi-element unstructured framework suitable for turbomachinery applications. An advanced multi-phase formulation for cryogenic fluids that models temperature depression and real fluid property variations is employed. The formulation has been extensively validated for both liquid nitrogen and liquid hydrogen by simulating the experiments of Hord on hydrofoils; excellent estimates of the leading edge temperature and pressure depression were obtained while the comparisons in the cavity closure region were reasonable.

  5. An Anticipatory Model of Cavitation

    SciTech Connect

    Allgood, G.O.; Dress, W.B., Jr.; Hylton, J.O.; Kercel, S.W.

    1999-04-05

    The Anticipatory System (AS) formalism developed by Robert Rosen provides some insight into the problem of embedding intelligent behavior in machines. AS emulates the anticipatory behavior of biological systems. AS bases its behavior on its expectations about the near future and those expectations are modified as the system gains experience. The expectation is based on an internal model that is drawn from an appeal to physical reality. To be adaptive, the model must be able to update itself. To be practical, the model must run faster than real-time. The need for a physical model and the requirement that the model execute at extreme speeds, has held back the application of AS to practical problems. Two recent advances make it possible to consider the use of AS for practical intelligent sensors. First, advances in transducer technology make it possible to obtain previously unavailable data from which a model can be derived. For example, acoustic emissions (AE) can be fed into a Bayesian system identifier that enables the separation of a weak characterizing signal, such as the signature of pump cavitation precursors, from a strong masking signal, such as a pump vibration feature. The second advance is the development of extremely fast, but inexpensive, digital signal processing hardware on which it is possible to run an adaptive Bayesian-derived model faster than real-time. This paper reports the investigation of an AS using a model of cavitation based on hydrodynamic principles and Bayesian analysis of data from high-performance AE sensors.

  6. Simulation and Experimental Study on Cavitating Water Jet Nozzle

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; He, Kai; Cai, Jiannan; Hu, Shaojie; Li, Jiuhua; Du, Ruxu

    2017-01-01

    Cavitating water jet technology is a new kind of water jet technology with many advantages, such as energy-saving, efficient, environmentally-friendly and so on. Based on the numerical simulation and experimental verification in this paper, the research on cavitating nozzle has been carried out, which includes comparison of the cleaning ability of the cavitating jet and the ordinary jet, and comparison of cavitation effects of different structures of cavitating nozzles.

  7. LBM study of flow-induced cavitation

    NASA Astrophysics Data System (ADS)

    Gonnella, Giuseppe; Kaehler, Goetz; Bonelli, Francesco; Lamura, Antonio

    2014-11-01

    This work deals with the investigation of homogeneous cavitation, induced by a fast flow past a sack wall, by using the lattice Boltzmann method (LBM). Cavitation occurs, in a liquid, because of a pressure drop, which falls below a certain threshold, with the consequent formation of vapor bubbles. The aim is to study the inception of cavitation by using LBM without any ``ad hoc'' cavitation model. A LBM with a body force term and redefined equilibrium distribution functions is employed for describing the continuity and Navier-Stokes equations for a fluid locally satisfying the van der Waals equation of state. In such a way, cavitation is directly described by the solution of the LB equation. The numerical study shows the formation of a depletion zone just under the obstacle, near its left edge, where the pressure reaches a minimum value. Cavitation occurs only when the pressure of this depletion zone reaches a value lower than the spinodal of the liquid branch, thus not confirming the Joseph's maximum tension criterion. A detailed study of the flow field, of the Reynolds number effects, and of the developed cavitation regime are presented.

  8. Cavitation passive control on immersed bodies

    NASA Astrophysics Data System (ADS)

    Javadi, Khodayar; Dorostkar, Mohammad Mortezazadeh; Katal, Ali

    2017-03-01

    This paper introduces a new idea of controlling cavitation around a hydrofoil through a passive cavitation controller called artificial cavitation bubble generator (ACG). Cyclic processes, namely, growth and implosion of bubbles around an immersed body, are the main reasons for the destruction and erosion of the said body. This paper aims to create a condition in which the cavitation bubbles reach a steady-state situation and prevent the occurrence of the cyclic processes. For this purpose, the ACG is placed on the surface of an immersed body, in particular, the suction surface of a 2D hydrofoil. A simulation was performed with an implicit finite volume scheme based on a SIMPLE algorithm associated with the multiphase and cavitation model. The modified k-ɛ RNG turbulence model equipped with a modification of the turbulent viscosity was applied to overcome the turbulence closure problem. Numerical simulation of water flow over the hydrofoil equipped with the ACG shows that a low-pressure recirculation area is produced behind the ACG and artificially generates stationary cavitation bubbles. The location, shape, and size of this ACG are the crucial parameters in creating a proper control. Results show that the cavitation bubble is controlled well with a well-designed ACG.

  9. Released air during vapor and air cavitation

    SciTech Connect

    Jablonská, Jana Kozubková, Milada

    2016-06-30

    Cavitation today is a very important problem that is solved by means of experimental and mathematical methods. The article deals with the generation of cavitation in convergent divergent nozzle of rectangular cross section. Measurement of pressure, flow rate, temperature, amount of dissolved air in the liquid and visualization of cavitation area using high-speed camera was performed for different flow rates. The measurement results were generalized by dimensionless analysis, which allows easy detection of cavitation in the nozzle. For numerical simulation the multiphase mathematical model of cavitation consisting of water and vapor was created. During verification the disagreement with the measurements for higher flow rates was proved, therefore the model was extended to multiphase mathematical model (water, vapor and air), due to release of dissolved air. For the mathematical modeling the multiphase turbulence RNG k-ε model for low Reynolds number flow with vapor and air cavitation was used. Subsequently the sizes of the cavitation area were verified. In article the inlet pressure and loss coefficient depending on the amount of air added to the mathematical model are evaluated. On the basis of the approach it may be create a methodology to estimate the amount of released air added at the inlet to the modeled area.

  10. Cavitation passive control on immersed bodies

    NASA Astrophysics Data System (ADS)

    Javadi, Khodayar; Dorostkar, Mohammad Mortezazadeh; Katal, Ali

    2017-01-01

    This paper introduces a new idea of controlling cavitation around a hydrofoil through a passive cavitation controller called artificial cavitation bubble generator (ACG). Cyclic processes, namely, growth and implosion of bubbles around an immersed body, are the main reasons for the destruction and erosion of the said body. This paper aims to create a condition in which the cavitation bubbles reach a steady-state situation and prevent the occurrence of the cyclic processes. For this purpose, the ACG is placed on the surface of an immersed body, in particular, the suction surface of a 2D hydrofoil. A simulation was performed with an implicit finite volume scheme based on a SIMPLE algorithm associated with the multiphase and cavitation model. The modified k-ɛ RNG turbulence model equipped with a modification of the turbulent viscosity was applied to overcome the turbulence closure problem. Numerical simulation of water flow over the hydrofoil equipped with the ACG shows that a low-pressure recirculation area is produced behind the ACG and artificially generates stationary cavitation bubbles. The location, shape, and size of this ACG are the crucial parameters in creating a proper control. Results show that the cavitation bubble is controlled well with a well-designed ACG.

  11. RANS computations of tip vortex cavitation

    NASA Astrophysics Data System (ADS)

    Decaix, Jean; Balarac, Guillaume; Dreyer, Matthieu; Farhat, Mohamed; Münch, Cécile

    2015-12-01

    The present study is related to the development of the tip vortex cavitation in Kaplan turbines. The investigation is carried out on a simplified test case consisting of a NACA0009 blade with a gap between the blade tip and the side wall. Computations with and without cavitation are performed using a R ANS modelling and a transport equation for the liquid volume fraction. Compared with experimental data, the R ANS computations turn out to be able to capture accurately the development of the tip vortex. The simulations have also highlighted the influence of cavitation on the tip vortex trajectory.

  12. Cavitation behavior of liquid rocket pumps

    SciTech Connect

    Gupta, N.K.

    1994-12-31

    Liquid rocket pumps were released and tested for obtaining the cavitation and non-cavitation performance. Two pumps, one each for fuel and oxidizer were tested for obtaining the critical Net Positive Suction Head for ensuring the cavitation free operation of these pumps in flight. The experimentally obtained values of NPSH have been compared with the theoretical values obtained using the model developed by Stripling (1962). Based on this comparison it is possible to predict the propellant tank pressure in advance with some confidence. The final value of tank pressure can be revised later when more comprehensive experimental values are available.

  13. A real-time measure of cavitation induced tissue disruption by ultrasound imaging backscatter reduction.

    PubMed

    Hall, Timothy L; Fowlkes, J Brian; Cain, Charles A

    2007-03-01

    A feedback method for obtaining real-time information on the mechanical disruption of tissue through ultrasound cavitation is presented. This method is based on a substantial reduction in ultrasound imaging backscatter from the target volume as the tissue structure is broken down. Ex-vivo samples of porcine liver were exposed to successive high-intensity ultrasound pulses at a low duty cycle to induce mechanical disruption of tissue parenchyma through cavitation (referred to as histotripsy). At the conclusion of treatment, B-scan imaging backscatter was observed to have decreased by 22.4 +/- 2.3 dB in the target location. Treated samples of tissue were found to contain disrupted tissue corresponding to the imaged hypoechoic volume with no remaining discernable structure and a sharp boundary. The observed, substantial backscatter reduction may be an effective feedback mechanism for assessing treatment efficacy in ultrasound surgery using pulsed ultrasound to create cavitation.

  14. Research on the noise induced by cavitation under the asymmetric cavitation condition in a centrifugal pump

    NASA Astrophysics Data System (ADS)

    Lu, J. X.; Yuan, S. Q.; Yuan, J. P.; Ren, X. D.; Pei, J.; Si, Q. R.

    2015-12-01

    An experimental investigation has been carried out to research the noise induced by cavitation under the asymmetric cavitation (AC) condition in a centrifugal pump. The acoustic pressure signals at the pump inlet and outlet were measured respectively during the development of cavitation in a closed hydraulic test rig. It could be found that both the pump inlet and outlet acoustic pressures changed obviously with the development of cavitation. The time domain and the power spectrum density of the pump inlet and outlet acoustic pressure pulsations were analyzed. The broadband pulses of the acoustic pressure pulsations were found and the reasons for the phenomenon were given.

  15. A Study of Cavitation-Ignition Bubble Combustion

    NASA Technical Reports Server (NTRS)

    Nguyen, Quang-Viet; Jacqmin, David A.

    2005-01-01

    We present the results of an experimental and computational study of the physics and chemistry of cavitation-ignition bubble combustion (CIBC), a process that occurs when combustible gaseous mixtures are ignited by the high temperatures found inside a rapidly collapsing bubble. The CIBC process was modeled using a time-dependent compressible fluid-dynamics code that includes finite-rate chemistry. The model predicts that gas-phase reactions within the bubble produce CO and other gaseous by-products of combustion. In addition, heat and mechanical energy release through a bubble volume-expansion phase are also predicted by the model. We experimentally demonstrate the CIBC process using an ultrasonically excited cavitation flow reactor with various hydrocarbon-air mixtures in liquid water. Low concentrations (< 160 ppm) of carbon monoxide (CO) emissions from the ultrasonic reactor were measured, and found to be proportional to the acoustic excitation power. The results of the model were consistent with the measured experimental results. Based on the experimental findings, the computational model, and previous reports of the "micro-diesel effect" in industrial hydraulic systems, we conclude that CIBC is indeed possible and exists in ultrasonically- and hydrodynamically-induced cavitation. Finally, estimates of the utility of CIBC process as a means of powering an idealized heat engine are also presented.

  16. Nanobubbles, cavitation, shock waves and traumatic brain injury.

    PubMed

    Adhikari, Upendra; Goliaei, Ardeshir; Berkowitz, Max L

    2016-12-07

    Collapse of bubbles, microscopic or nanoscopic, due to their interaction with the impinging pressure wave produces a jet of particles moving in the direction of the wave. If there is a surface nearby, the high-speed jet particles hit it, and as a result damage to the surface is produced. This cavitation effect is well known and intensely studied in case of microscopic sized bubbles. It can be quite damaging to materials, including biological tissues, but it can also be beneficial when controlled, like in case of sonoporation of biological membranes for the purpose of drug delivery. Here we consider recent simulation work performed to study collapse of nanobubbles exposed to shock waves, in order to understand the detailed mechanism of the cavitation induced damage to soft materials, such as biological membranes. We also discuss the connection of the cavitation effect with the traumatic brain injury caused by blasts. Specifically, we consider possible damage to model membranes containing lipid bilayers, bilayers with embedded ion channel proteins like the ones found in neural cells and also protein assemblies found in the tight junction of the blood brain barrier.

  17. Elimination of cavitation-related attenuation in shock wave lithotripsy

    NASA Astrophysics Data System (ADS)

    Sankin, G. N.; Lautz, J. M.; Simmons, W. N.; Zhong, P.; Frank, S. T.; Szeri, A. J.

    2017-03-01

    In shock wave lithotripsy (SWL), acoustic pulses with a leading compression wave followed by a tensile wave are delivered into the patient's body using a water-filled coupling cushion. Cavitation-related acoustic energy loss in the coupling unit depends critically on water conditions, e.g. dissolved gas concentration and exchange flow rate. We have systematically investigated the attenuation mechanism in the coupling water via pressure measurements and cavitation characterization. In non-degassed water the bubble cluster became progressively dense (i.e., proliferated because of gas diffusion into bubbles and splitting of bubbles into many daughter bubbles) in shock waves delivered at 1 Hz leading to reduction in the tensile wave duration from a nominal value of 4.6 to 1.8 µs. To reduce cavitation in the coupling water along the beam path, we have used a continuous jet flow to remove residual daughter bubbles between consecutive shocks. As a result, stone fragmentation efficiency was increased from 16±4% to 30±5% (p = 0.002) after 250 shocks. Such a hydrodynamic approach for tensile wave attenuation in the coupling water may be used to provide a flexible means for a novel treatment strategy with tissue protection.

  18. Transient cavitation and acoustic emission produced by different laser lithotripters.

    PubMed

    Zhong, P; Tong, H L; Cocks, F H; Pearle, M S; Preminger, G M

    1998-08-01

    Transient cavitation and shockwave generation produced by pulsed-dye and holmium:YAG laser lithotripters were studied using high-speed photography and acoustic emission measurements. In addition, stone phantoms were used to compare the fragmentation efficiency of various laser and electrohydraulic lithotripters. The pulsed-dye laser, with a wavelength (504 nm) strongly absorbed by most stone materials but not by water, and a short pulse duration of approximately 1 microsec, induces plasma formation on the surface of the target calculi. Subsequently, the rapid expansion of the plasma forms a cavitation bubble, which expands spherically to a maximum size and then collapses violently, leading to strong shockwave generation and microjet impingement, which comprises the primary mechanism for stone fragmentation with short-pulse lasers. In contrast, the holmium laser, with a wavelength (2100 nm) most strongly absorbed by water as well as by all stone materials and a long pulse duration of 250 to 350 microsec, produces an elongated, pear-shaped cavitation bubble at the tip of the optical fiber that forms a vapor channel to conduct the ensuing laser energy to the target stone (Moss effect). The expansion and subsequent collapse of the elongated bubble is asymmetric, resulting in weak shockwave generation and microjet impingement. Thus, stone fragmentation in holmium laser lithotripsy is caused primarily by thermal ablation (drilling effect).

  19. Cavitation in confined water: ultra-fast bubble dynamics

    NASA Astrophysics Data System (ADS)

    Vincent, Olivier; Marmottant, Philippe

    2012-02-01

    In the hydraulic vessels of trees, water can be found at negative pressure. This metastable state, corresponding to mechanical tension, is achieved by evaporation through a porous medium. It can be relaxed by cavitation, i.e. the sudden nucleation of vapor bubbles. Harmful for the tree due to the subsequent emboli of sap vessels, cavitation is on the contrary used by ferns to eject spores very swiftly. We will focus here on the dynamics of the cavitation bubble, which is of primary importance to explain the previously cited natural phenomena. We use the recently developed method of artificial tress, using transparent hydrogels as the porous medium. Our experiments, on water confined in micrometric hydrogel cavities, show an extremely fast dynamics: bubbles are nucleated at the microsecond timescale. For cavities larger than 100 microns, the bubble ``rings'' with damped oscillations at MHz frequencies, whereas for smaller cavities the oscillations become overdamped. This rich dynamics can be accounted for by a model we developed, leading to a modified Rayleigh-Plesset equation. Interestingly, this model predicts the impossibility to nucleate bubbles above a critical confinement that depends on liquid negative pressure and corresponds to approximately 100 nm for 20 MPa tensions.

  20. Integrated ultrasound and magnetic resonance imaging for simultaneous temperature and cavitation monitoring during focused ultrasound therapies.

    PubMed

    Arvanitis, Costas D; McDannold, Nathan

    2013-11-01

    Ultrasound can be used to noninvasively produce different bioeffects via viscous heating, acoustic cavitation, or their combination, and these effects can be exploited to develop a wide range of therapies for cancer and other disorders. In order to accurately localize and control these different effects, imaging methods are desired that can map both temperature changes and cavitation activity. To address these needs, the authors integrated an ultrasound imaging array into an MRI-guided focused ultrasound (MRgFUS) system to simultaneously visualize thermal and mechanical effects via passive acoustic mapping (PAM) and MR temperature imaging (MRTI), respectively. The system was tested with an MRgFUS system developed for transcranial sonication for brain tumor ablation in experiments with a tissue mimicking phantom and a phantom-filled ex vivo macaque skull. In experiments on cavitation-enhanced heating, 10 s continuous wave sonications were applied at increasing power levels (30-110 W) until broadband acoustic emissions (a signature for inertial cavitation) were evident. The presence or lack of signal in the PAM, as well as its magnitude and location, were compared to the focal heating in the MRTI. Additional experiments compared PAM with standard B-mode ultrasound imaging and tested the feasibility of the system to map cavitation activity produced during low-power (5 W) burst sonications in a channel filled with a microbubble ultrasound contrast agent. When inertial cavitation was evident, localized activity was present in PAM and a marked increase in heating was observed in MRTI. The location of the cavitation activity and heating agreed on average after registration of the two imaging modalities; the distance between the maximum cavitation activity and focal heating was -3.4 ± 2.1 mm and -0.1 ± 3.3 mm in the axial and transverse ultrasound array directions, respectively. Distortions and other MRI issues introduced small uncertainties in the PAM

  1. Integrated ultrasound and magnetic resonance imaging for simultaneous temperature and cavitation monitoring during focused ultrasound therapies

    PubMed Central

    Arvanitis, Costas D.; McDannold, Nathan

    2013-01-01

    Purpose: Ultrasound can be used to noninvasively produce different bioeffects via viscous heating, acoustic cavitation, or their combination, and these effects can be exploited to develop a wide range of therapies for cancer and other disorders. In order to accurately localize and control these different effects, imaging methods are desired that can map both temperature changes and cavitation activity. To address these needs, the authors integrated an ultrasound imaging array into an MRI-guided focused ultrasound (MRgFUS) system to simultaneously visualize thermal and mechanical effects via passive acoustic mapping (PAM) and MR temperature imaging (MRTI), respectively. Methods: The system was tested with an MRgFUS system developed for transcranial sonication for brain tumor ablation in experiments with a tissue mimicking phantom and a phantom-filled ex vivo macaque skull. In experiments on cavitation-enhanced heating, 10 s continuous wave sonications were applied at increasing power levels (30–110 W) until broadband acoustic emissions (a signature for inertial cavitation) were evident. The presence or lack of signal in the PAM, as well as its magnitude and location, were compared to the focal heating in the MRTI. Additional experiments compared PAM with standard B-mode ultrasound imaging and tested the feasibility of the system to map cavitation activity produced during low-power (5 W) burst sonications in a channel filled with a microbubble ultrasound contrast agent. Results: When inertial cavitation was evident, localized activity was present in PAM and a marked increase in heating was observed in MRTI. The location of the cavitation activity and heating agreed on average after registration of the two imaging modalities; the distance between the maximum cavitation activity and focal heating was −3.4 ± 2.1 mm and −0.1 ± 3.3 mm in the axial and transverse ultrasound array directions, respectively. Distortions and other MRI issues introduced small

  2. Cavitation and bubble dynamics: the Kelvin impulse and its applications

    PubMed Central

    Blake, John R.; Leppinen, David M.; Wang, Qianxi

    2015-01-01

    Cavitation and bubble dynamics have a wide range of practical applications in a range of disciplines, including hydraulic, mechanical and naval engineering, oil exploration, clinical medicine and sonochemistry. However, this paper focuses on how a fundamental concept, the Kelvin impulse, can provide practical insights into engineering and industrial design problems. The pathway is provided through physical insight, idealized experiments and enhancing the accuracy and interpretation of the computation. In 1966, Benjamin and Ellis made a number of important statements relating to the use of the Kelvin impulse in cavitation and bubble dynamics, one of these being ‘One should always reason in terms of the Kelvin impulse, not in terms of the fluid momentum…’. We revisit part of this paper, developing the Kelvin impulse from first principles, using it, not only as a check on advanced computations (for which it was first used!), but also to provide greater physical insights into cavitation bubble dynamics near boundaries (rigid, potential free surface, two-fluid interface, flexible surface and axisymmetric stagnation point flow) and to provide predictions on different types of bubble collapse behaviour, later compared against experiments. The paper concludes with two recent studies involving (i) the direction of the jet formation in a cavitation bubble close to a rigid boundary in the presence of high-intensity ultrasound propagated parallel to the surface and (ii) the study of a ‘paradigm bubble model’ for the collapse of a translating spherical bubble, sometimes leading to a constant velocity high-speed jet, known as the Longuet-Higgins jet. PMID:26442141

  3. Extreme impact and cavitation forces of a biological hammer: strike forces of the peacock mantis shrimp Odontodactylus scyllarus.

    PubMed

    Patek, S N; Caldwell, R L

    2005-10-01

    Mantis shrimp are renowned for their unusual method of breaking shells with brief, powerful strikes of their raptorial appendages. Due to the extreme speeds of these strikes underwater, cavitation occurs between their appendages and hard-shelled prey. Here we examine the magnitude and relative contribution of the impact and cavitation forces generated by the peacock mantis shrimp Odontodactylus scyllarus. We present the surprising finding that each strike generates two brief, high-amplitude force peaks, typically 390-480 micros apart. Based on high-speed imaging, force measurements and acoustic analyses, it is evident that the first force peak is caused by the limb's impact and the second force peak is due to the collapse of cavitation bubbles. Peak limb impact forces range from 400 to 1501 N and peak cavitation forces reach 504 N. Despite their small size, O. scyllarus can generate impact forces thousands of times their body weight. Furthermore, on average, cavitation peak forces are 50% of the limb's impact force, although cavitation forces may exceed the limb impact forces by up to 280%. The rapid succession of high peak forces used by mantis shrimp suggests that mantis shrimp use a potent combination of cavitation forces and extraordinarily high impact forces to fracture shells. The stomatopod's hammer is fundamentally different from typical shell-crushing mechanisms such as fish jaws and lobster claws, and may have played an important and as yet unexamined role in the evolution of shell form.

  4. Thermodynamic effects on developed cavitation

    NASA Technical Reports Server (NTRS)

    Holl, J. W.; Billet, M. L.; Weir, D. S.

    1975-01-01

    The results of an investigation of thermodynamic effects are presented. Distributions of temperature and pressure in a developed cavity were measured for zero- and quarter-caliber ogives. A semiempirical entrainment theory was developed to correlate the measured temperature depression in the cavity. This theory correlates the maximum temperature depression expressed in dimensionless form as the Jakob number in terms of the dimensionless numbers of Nusselt, Reynolds, Froude, and Peclet, and dimensionless cavity length, L/D. The results show that in general, the temperature depression increases with L/D and temperature and the cavitation number based on measured cavity pressure is a function of L/D for a given model contour, independent of the thermodynamic effect.

  5. Sonoporation from Jetting Cavitation Bubbles

    PubMed Central

    Ohl, Claus-Dieter; Arora, Manish; Ikink, Roy; de Jong, Nico; Versluis, Michel; Delius, Michael; Lohse, Detlef

    2006-01-01

    The fluid dynamic interaction of cavitation bubbles with adherent cells on a substrate is experimentally investigated. We find that the nonspherical collapse of bubbles near to the boundary is responsible for cell detachment. High-speed photography reveals that a wall bounded flow leads to the detachment of cells. Cells at the edge of the circular area of detachment are found to be permanently porated, whereas cells at some distance from the detachment area undergo viable cell membrane poration (sonoporation). The wall flow field leading to cell detachment is modeled with a self-similar solution for a wall jet, together with a kinetic ansatz of adhesive bond rupture. The self-similar solution for the δ-type wall jet compares very well with the full solution of the Navier-Stokes equation for a jet of finite thickness. Apart from annular sites of sonoporation we also find more homogenous patterns of molecule delivery with no cell detachment. PMID:16950843

  6. Numerical calculation for cavitation flow of inducer

    NASA Astrophysics Data System (ADS)

    Ning, C.; Wang, Y.; Zhu, Z. T.; Xie, S. F.; Zhao, L. F.; Liu, Z. C.

    2015-01-01

    Inducer has significant effect on improving the cavitation characteristic of centrifugal pump. Several inducers were designed and modeled by Pro/E software. The mesh of flow field was done by ICEM and then was imported to ANSYS CFX to analyze the inducer's cavitation characteristic. Effects of the blade number on the performance of an inducer are investigated in the present paper. The inducers were designed on the basis of identical design flow rate and identical pressure elevation at nominal flow rate. The study focuses on the steady behavior of the inducers in cavitating conditions. Evolutions of performance, torque, mass flow rate, and amplitude of radial forces on the shaft according to the inlet pressure are considered. Furthermore, cavitation instabilities are analyzed in the study. The purpose of the present study is to investigate the pressure distribution and vapour volume fraction distribution through numerical simulations using the Navier-stokes solver with computational fluid dynamics (CFD) code.

  7. Cavitation for improved sludge conversion into biogas

    NASA Astrophysics Data System (ADS)

    Stoop, A. H.; Bakker, T. W.; Kramer, H. J. M.

    2015-12-01

    In several studies the beneficial influence of pre-treatment of waste activated sludge with cavitation on the biogas production was demonstrated. It is however, still not fully certain whether this effect should be mainly contributed to an increase in conversion rate of organics into biogas by anaerobic bacteria, and how much cavitation increases the total biogas yield. An increase in yield is only the case if cavitation can further disrupt otherwise inaccessible cell membrane structures and long chain organic molecules. In this study the influence of hydrodynamic cavitation on sludge that was already digested for 30 days was investigated. The total biogas yield could indeed be increased. The effect of the backpressure behind the venturi tube on the yield could not yet be established.

  8. Cavitation propagation in water under tension

    NASA Astrophysics Data System (ADS)

    Noblin, Xavier; Yip Cheung Sang, Yann; Pellegrin, Mathieu; Materials and Complex Fluids Team

    2012-11-01

    Cavitation appears when pressure decreases below vapor pressure, generating vapor bubbles. It can be obtain in dynamical ways (acoustic, hydraulic) but also in quasi-static conditions. This later case is often observed in nature, in trees, or during the ejection of ferns spores. We study the cavitation bubbles nucleation dynamics and its propagation in a confined microfabricated media. This later is an ordered array of microcavities made in hydrogel filled with water. When the system is put into dry air, it dehydrates, water leaves the cavities and tension (negative pressure) builds in the cavities. This can be sustained up to a critical pressure (of order -20 MPa), then cavitation bubbles appear. We follow the dynamics using ultra high speed imaging. Events with several bubbles cavitating in a few microseconds could be observed along neighboring cells, showing a propagation phenomenon that we discuss. ANR CAVISOFT 2010-JCJC-0407 01.

  9. CAVITATION DAMAGE STUDY VIA A NOVEL REPETITIVE PRESSURE PULSE APPROACH

    SciTech Connect

    Wang, Jy-An John; Ren, Fei; Wang, Hong

    2010-01-01

    Cavitation damage can significantly affect system performance. Thus, there is great interest in characterizing cavitation damage and improving materials resistance to cavitation damage. In this paper, we present a novel methodology to simulate cavitation environment. A pulsed laser is utilized to induce optical breakdown in the cavitation media, with the emission of shock wave and the generation of bubbles. The pressure waves induced by the optical breakdown fluctuate/propagate within the media, which enables the cavitation to occur and to further develop cavitation damage at the solid boundary. Using the repetitive pulsed-pressure apparatus developed in the current study, cavitation damage in water media was verified on stainless steel and aluminum samples. Characteristic cavitation damages such as pitting and indentation are observed on sample surfaces using scanning electron microscopy.

  10. Cavitation in block copolymer modified epoxy

    NASA Astrophysics Data System (ADS)

    Declet-Perez, Carmelo; Francis, Lorraine; Bates, Frank

    2013-03-01

    Today, brittleness in epoxy networks limits most commercial applications. Significant toughness can be imparted by adding small amounts of micelle forming block copolymers (BCP) without compromising critical properties such as high use temperature and modulus. Curing the network locks in the self-assembled BCP micellar structures formed in the monomer resin providing control of the resulting morphology. Despite significant research over the last decade, a complete description of the parameters influencing toughness in block copolymer modified epoxies is still lacking. In this presentation we compare the ultimate mechanical behavior of epoxies modified with spherical micelle forming BCP's containing rubbery and glassy cores using real-time in-situ small-angle X-ray scattering (SAXS) performed during tensile deformation. Striking differences in the 2D SAXS patterns were documented for epoxies modified with rubbery (PEP) versus glassy (PS) micelle cores. Rubbery cores dilate by 100% in volume upon specimen yielding, while the glassy micelle cores deform at approximately constant volume. These results provide direct evidence of a cavitation mediated mechanism for toughness in block copolymer modified epoxies. We further interpret characteristic butterfly features in the 2D SAXS patterns in terms of epoxy network deformation. Support was provided by the NSF sponsored MRSEC at the University of Minnesota

  11. Solvent cavitation under solvophobic confinement

    NASA Astrophysics Data System (ADS)

    Ashbaugh, Henry S.

    2013-08-01

    The stability of liquids under solvophobic confinement can tip in favor of the vapor phase, nucleating a liquid-to-vapor phase transition that induces attractive forces between confining surfaces. In the case of water adjacent to hydrophobic surfaces, experimental and theoretical evidence support confinement-mediated evaporation stabilization of biomolecular and colloidal assemblies. The macroscopic thermodynamic theory of cavitation under confinement establishes the connection between the size of the confining surfaces, interfacial free energies, and bulk solvent pressure with the critical evaporation separation and interfacial forces. While molecular simulations have confirmed the broad theoretical trends, a quantitative comparison based on independent measurements of the interfacial free energies and liquid-vapor coexistence properties has, to the best of our knowledge, not yet been performed. To overcome the challenges of simulating a large number of systems to validate scaling predictions for a three-dimensional fluid, we simulate both the forces and liquid-vapor coexistence properties of a two-dimensional Lennard-Jones fluid confined between solvophobic plates over a range of plate sizes and reservoir pressures. Our simulations quantitatively agree with theoretical predictions for solvent-mediated forces and critical evaporation separations once the length dependence of the solvation free energy of an individual confining plate is taken into account. The effective solid-liquid line tension length dependence results from molecular scale correlations for solvating microscopic plates and asymptotically decays to the macroscopic value for plates longer than 150 solvent diameters. The success of the macroscopic thermodynamic theory at describing two-dimensional liquids suggests application to surfactant monolayers to experimentally confirm confinement-mediated cavitation.

  12. Initial observations of cavitation-induced erosion of liquid metal spallation target vessels at the Spallation Neutron Source

    SciTech Connect

    McClintock, David A; Riemer, Bernie; Ferguson, Phillip D; Carroll, Adam J; Dayton, Michael J

    2012-01-01

    During operation of the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory the mechanical properties of the AISI 316L target module are altered by high-energy neutron and proton radiation. The interior surfaces of the target vessel are also damaged by cavitation-induced erosion, which results from repetitive rapid heating of the liquid mercury by high-energy proton beam pulses. Until recently no observations of cavitation-induced erosion were possible for conditions prototypical to the SNS. Post irradiation examination (PIE) of the first and second operational SNS targets was performed to gain insight into the radiation-induced changes in mechanical properties of the 316L target material and the extent of cavitation-induced erosion to the target vessel inner surfaces. Observations of cavitation-induced erosion of the first and second operational SNS target modules are presented here, including images of the target vessel interiors and specimens removed from the target beam-entrance regions.

  13. Cavitation milling of natural cellulose to nanofibrils.

    PubMed

    Pinjari, Dipak Vitthal; Pandit, Aniruddha B

    2010-06-01

    Cavitation holds the promise of a new and exciting approach to fabricate both top down and bottom up nanostructures. Cavitation bubbles are created when a liquid boils under less than atmospheric pressure. The collapse process occurs supersonically and generates a host of physical and chemical effects. We have made an attempt to fabricate natural cellulose material using hydrodynamic as well as acoustic cavitation. The cellulose material having initial size of 63 micron was used for the experiments. 1% (w/v) slurry of cellulose sample was circulated through the hydrodynamic cavitation device or devices (orifice) for 6h. The average velocity of the fluid through the device was 10.81m/s while average pressure applied was 7.8 kg/cm(2). Cavitation number was found to be 2.61. The average particle size obtained after treatment was 1.36 micron. This hydrodynamically processed sample was sonicated for 1h 50 min. The average size of ultrasonically processed particles was found to be 301 nm. Further, the cellulose particles were characterized with X-ray diffraction (XRD) and differential scanning calorimetry (DSC) to see the effect of cavitation on crystallinity (X(c)) as well as on melting temperature (T(m)). Cellulose structures consist of amorphous as well as crystalline regions. The initial raw sample was 86.56% crystalline but due to the effect of cavitation, the crystallinity reduced to 37.76%. Also the melting temperature (T(m)) was found to be reduced from 101.78 degrees C of the original to 60.13 degrees C of the processed sample. SEM images for the cellulose (processed and unprocessed) shows the status and fiber-fiber alignment and its orientation with each other. Finally cavitation has proved to be very efficient tool for reduction in size from millimeter to nano scale for highly crystalline materials.

  14. Current Research in Cavitating Fluid Films

    DTIC Science & Technology

    1989-01-01

    and C.P. Ku ................... The Influence of Cavitation on Journal-Bearing By Rotordynamic Characteristics ...... ................... 52 Di.. ibtio...model. 51 THE INFLUENCE OF CAVITATION ON JOURNAL-BEARING ROTORDYNAMIC CHARACTERISTICS M.L. ADAMS" Even under the smoothest running conditions, where...damping coeffici- ents for the journal bearing, i.e., a 2 by 2 stiff- ness matrix and a 2 by 2 damping matrix. These rotordynamic coefficients for

  15. Synchronized passive imaging of single cavitation events

    NASA Astrophysics Data System (ADS)

    Gateau, Jérôme; Aubry, Jean-François; Pernot, Mathieu; Chauvet, Daurian; Boch, Anne-Laure; Fink, Mathias; Tanter, Mickaël

    2011-09-01

    Passive cavitation detection techniques are usually of relatively low sensitivity to single cavitation events. Moreover, a single-element transducer is generally used, so that the spatial localization of these cavitation events is not possible, or is limited to the probing volume. To both detect and localize single cavitation events over an extended volume, the following experimental set-up has been used and validated: cavitation is induced with a focused single-element transducer (mean frequency 660 kHz, f♯ = 1) driven by a high power (up to 5 kW) electric burst of a few cycles, and the acoustic emission of the bubbles is recorded on a standard linear array (4-7 MHz), mounted on the side of the single element to probe its focal spot. Both the frequencies and the geometry used are appropriate to in vivo implementation. The recording of ultrasonic radio-frequency (RF) data was performed simultaneously on 64 channels of the array and was synchronized with the pulsed excitation. A single cavitation event results in a high frequency and coherent wave front on the RF data. Thanks to synchronization, these RF data are beam-formed to localize the event with a axial resolution of 0.3 mm. A small number of discrete events could also be separated with this method. Besides, B-mode images obtained with the linear array prior to passive detection allowed the positioning of the events within the tissue structure. This technique has been used first ex vivo on freshly harve pig and sheep thigh muscle: with a two cycle excitation, a 9 MPa cavitation threshold was found. Cavitation detection was also achieved in vivo with a five cycle burst excitation in sheep thigh muscle for a peak acoustic pressure of 11MPa. This technique could provide useful information in order to better understand, control and monitor the initiation phase of the histotripsy process.

  16. Cavitation-Resistant Coatings for Hydropower Turbines

    DTIC Science & Technology

    2011-06-01

    and collapse of va- por pockets in a flowing liquid in regions of very low pressure ) in the tur- bine area. The level of cavitation typically destroys...power output. Unfortunately, this frequently results in cavitation (the rapid formation and collapse of vapor pockets in a flowing liquid in regions...of very low pressure ) in the turbine area. The level of ca- vitation typically destroys organic coatings in a relatively short time. Tra- ditional

  17. Numerical approach to reproduce instabilities of partial cavitation in a Venturi 8° geometry

    NASA Astrophysics Data System (ADS)

    Charriere, Boris; Goncalves, Eric

    2016-11-01

    Unsteady partial cavitation is mainly formed by an attached cavity which present periodic oscillations. Under certain conditions, the instabilities are characterized by the formation of vapour clouds, convected downstream the cavity and which collapse in higher pressure region. In order to gain a better understanding of the complex physics involved, many experimental and numerical studies have been carried out. These identified two main mechanisms responsible for the break-off cycles. The development of a liquid re-entrant jet is the most common type of instabilities, but more recently, the role of pressure waves created by the cloud collapses has been highlighted. This paper presents a one-fluid compressible Reynolds- Averaged NavierStokes (RANS) solver closed by two different equations of state (EOS) for the mixture. Based on experimental data, we investigate the ability for our simulations to reproduce the instablities of a self-sustained oscillating cavitation pocket. Two cavitation models are firstly compared. The importance of considering a non-equilibrium state for the vapour phase is also exhibited. To finish, the role played by the added transport equation to compute void ratio is emphasised. In case of partially cavitating flows with detached cavitation clouds, the reproduction of convective mechanisms is clearly improved.

  18. Cavitation on Hydrofoils with Leading Edge Protuberances

    NASA Astrophysics Data System (ADS)

    Custodio, Derrick; Henoch, Charles; Johari, Hamid; Office of Naval Research Collaboration

    2012-11-01

    The effects of spanwise-uniform sinusoidal leading edge protuberances on the flow characteristics and forces of finite-span hydrofoils under vaporous cavitation conditions were examined experimentally over angles of attack ranging from -9° α <= 27°. Two planforms were studied, rectangular and swept, at a Reynolds number of ~ 720,000. Two protuberance wavelengths, λ = 0.25 c and 0.50 c, and three amplitudes, A = 0.025 c, 0.05 c, and 0.12 c, were examined as they resemble the humpback whale flipper morphology. All hydrofoils retain a mean NACA 634-021 profile. The forces and moments were measured at a freestream velocity of 7.2 m/s, and high-speed digital photography was used to capture flow field images at several angles of attack. The cavitation number corresponding to incipient leading edge cavitation was also calculated. As far as forces and cavitation number are concerned, results show that the baseline hydrofoil tends to have nearly equal or improved performance over the modified hydrofoils at most angles of attack tested. Flow images reveal that it is possible that the extent of sheet and tip vortex cavitation can be reduced with the introduction of leading edge protuberances. The forces and cavitation characteristics will be presented. Sponsored by the ONR-ULI program.

  19. Research on cavitation characteristic of inducer

    NASA Astrophysics Data System (ADS)

    Qiu, N.; Wang, L. Q.; Y Kong, F.; Wu, D. Z.

    2013-12-01

    The inducer has significant effect on improving the cavitation characteristic of a centrifugal pump. The fact which can not be neglected is that the inducer itself is a kind of axial pump. Research on inducer's cavitation characteristic is very important. Several inducers were designed and modeled by Pro/E software. The mesh of flow field was done by ICEM and imported to ANSYS CFX to analyze the inducer's cavitation characteristic. The relationship between cavity length and head breakdown was discussed. With the decrease of NPSH, there is a slight increase in the head just prior to the decrease associated with head breakdown. This conclusion coincides with experimental results. The influence of backflow eddy on the inducer's cavitation characteristic was analyzed, and the change of backflow eddy in the process of cavitation was illustrated. It can be concluded that the correlation between the inducer head breakdown and the relative cavity length is very close which agrees well with the theoretical and experimental results. As the inlet pressure is decreased, inception almost always occurs in the tip vortex generated by the corner where the leading edge meets the tip. And backflow vortex gradually disappears in the process of cavitation.

  20. Reactor internal pump behavior during cavitation

    SciTech Connect

    Komita, Hideo; Usuki, Shouji; Fukuda, Shinichi )

    1989-11-01

    The characteristics of reactor internal pumps (RIPs) under cavitation conditions were experimentally evaluated in full scale with different water temperature parameters. The hydraulic performance and vibration behavior under cavitation conditions were clarified. An advanced boiling water reactor is equipped with RIPs for coolant recirculation. The RIP is a vertical, single-stage, mixed-flow pump that is mounted in the annular downcomer of the reactor pressure vessel. In general, when a pump operates under cavitation conditions, the pump total head decreases, and the appearance and collapse of vapor bubbles induce vibration and noise, causing damage to components. Various reports have been made on centrifugal pump behavior in cold water, but very few have discussed the characteristics of a mixed-flow pump like the RIP in hot water. Very few have measured impeller vibration in hot water, which is significantly influenced by cavitation. Therefore, it is difficult to precisely determine RIP behavior under cavitation conditions. Hydraulic performance and vibration behavior under cavitation conditions are experimentally clarified in this paper.

  1. Evaluation of inertial cavitation activity in tissue through measurement of oxidative stress.

    PubMed

    Prieur, Fabrice; Pialoux, Vincent; Mestas, Jean-Louis; Mury, Pauline; Skinner, Sarah; Lafon, Cyril

    2015-09-01

    Ultrasound cavitation is an essential mechanism involved in the therapeutic local enhancement of drug delivery by ultrasound for cancer treatment. Inertial cavitation also triggers chemical reactions that generate free radicals and subsequent oxidative stress in the tissue. The aim of this study was to measure the oxidative stress induced by inertial cavitation in ex vivo tissue and to test the association between the exposure conditions and the oxidative stress. A confocal ultrasound setup was used to sonicate and create inertial cavitation in freshly excised adipose pig tissue. The ex vivo tissue samples were then processed to measure the quantity of malondialdehyde (MDA), an end-product of polyunsaturated free fatty acid oxidation. The creation of hydroxyterephthalic acid (HTA) from the reaction of terephthalic acid (TA) with free radicals in water was also quantified in vitro. Samples were sonicated for different durations using various amplitudes for the applied pressure. The results showed a minimum 2-fold increase in the amount of detected MDA in the sonicated tissue samples compared to baseline clearly suggesting the generation of free radicals by inertial cavitation. The method exhibited a moderate dependence of MDA generated upon the duration of exposure (R(2)=057,p<0.0001). The average increase in MDA concentration was approximately 2-fold, 5-fold, 6-fold, and 9-fold for exposure durations per unit of volume of 0.13, 0.17, 0.25, and 0.50s/mm(3), respectively. The results showed no statistically significant dependence on the amplitude of the pressure within the used range. Both pressure amplitude and exposure duration, however, influenced the HTA concentration (R(2)>0.95,p<0.0001). This biochemical method can be used on ex vivo tissue to detect the generation of free radicals induced by inertial cavitation. In large enough sample populations, the cavitation activity is linked to the exposure conditions of the sonication.

  2. Incubation pit analysis and calculation of the hydrodynamic impact pressure from the implosion of an acoustic cavitation bubble.

    PubMed

    Tzanakis, I; Eskin, D G; Georgoulas, A; Fytanidis, D K

    2014-03-01

    An experimental study to evaluate cavitation bubble dynamics is conducted. The aim is to predict the magnitude and statistical distribution of hydrodynamic impact pressure generated from the implosion of various individual acoustic cavitation bubbles near to a rigid boundary, considering geometrical features of the pitted area. A steel sample was subjected to cavitation impacts by an ultrasonic transducer with a 5mm diameter probe. The pitted surface was then examined using high-precision 3D optical interferometer techniques. Only the incubation period where surface is plastically deformed without material loss is taken into account. The exposure time was adjusted in the range of 3-60 s to avoid pit overlapping and a special procedure for pit analysis and characterisation was then followed. Moreover, a high-speed camera device was deployed to capture the implosion mechanisms of cavitation bubbles near to the surface. The geometrical characteristics of single incubation pits as well as pit clusters were studied and their deformation patterns were compared. Consequently, a reverse engineering approach was applied in order the hydrodynamic impact pressure from the implosion of an individual cavitation bubble to be determined. The characteristic parameters of the cavitation implosion process such as hydrodynamic impact pressure and liquid micro-jet impact velocity as well as the hydrodynamic severity of the cavitation impacts were quantified. It was found that the length of the hypotenuse of the orthographic projections from the center of the pit, which basically represents the deformed area of the pit, increases with the hydrodynamic impact aggressiveness in a linear rate. Majority of the hydrodynamic impacts were in the range of 0.4-1 GPa while the corresponding micro-jet velocities were found to be in the range of 200-700 m/s. Outcomes of this study, contribute to further understanding the cavitation intensity from the implosion of acoustically generated bubbles and

  3. Identifying the Inertial Cavitation Pressure Threshold and Skull Effects in a Vessel Phantom Using Focused Ultrasound and Microbubbles

    NASA Astrophysics Data System (ADS)

    Tung, Yao-Sheng; Choi, James J.; Konofagou, Elisa E.

    2010-03-01

    Using Focused Ultrasound (FUS) and microbubbles to open the blood-brain barrier (BBB) has been shown promising for brain drug delivery. However, the exact mechanism behind the opening remains unknown. Here, the effects of the murine skull on the threshold of inertial cavitation were investigated. In order to investigate the pressure threshold for inertial cavitation of preformed microbubbles during sonication, passive cavitation detection in conjunction with B-mode imaging was used. A cylindrical vessel with a 610-μm diameter inside a polyacrylamide gel was generated within a polyacrylamide gel to simulate large blood vessels. Definity® (Lantheus Medical Imaging, MA, USA) microbubbles with a 1.1-3.3 μm in diameter at 2.5×107 bubbles/mL were injected into the channel before sonication (frequency: 1.525 MHz; pulse length: 100 cycles; PRF: 10 Hz; sonication duration: 2 s) through an excised mouse skull. A cylindrically focused hydrophone, confocal with the FUS transducer, acted as a passive cavitation detector (PCD) to identify the threshold. A 7.5 MHz linear array with the field-of-view perpendicular to the axial length of the FUS beam was also used to image the occurrence of bubble fragmentation. The broadband spectral response acquired at the passive cavitation detector (PCD) and the B-mode images identified the occurrence and location of the inertial cavitation, respectively. Findings indicated that the peak-rarefactional pressure threshold was approximately equal to 0.45 MPa at the presence or the absence of the skull. However, the skull induced 10-50% lower inertial cavitation dose. Mouse skulls did not affect the pressure threshold of inertial cavitation but resulted in a lower inertial cavitation dose. The broadband response could be captured through the murine skull, so the same PCD setup can be used in future in vivo applications.

  4. Observations on Rotating Cavitation and Cavitation Surge From The Development of the Fastrac Engine Turbopump

    NASA Technical Reports Server (NTRS)

    Zoladz, Thomas F.; Turner, James E. (Technical Monitor)

    2000-01-01

    The effects of rotating cavitation and cavitation surges on the Fastrac Engine Turbopump are described in a viewgraph presentation format. The bent inducer blade dilemma and observations of unsteady data and oscillation components are discussed. The pump-feed system stability modeling assessment is outlined. Recommendations are made urging further investigation.

  5. Mechanoluminescence and sonoluminescence from acoustic cavitation

    NASA Astrophysics Data System (ADS)

    Eddingsaas, Nathan C.

    The intense shock wave launched from collapsing bubbles during the sonication of slurries allows for the study of chemical and physical events that occur when a solid is stressed or fractured. One such event is mechanoluminescence (ML): light produced by any mechanical action on a solid. ML has been studied for over 400 years, but much is still not known about it because the emission is inherently weak. Sonicating slurries of mechanoluminescent crystals (such as sucrose, sodium chloride, resorcinol, m-aminophenol, or coumarin) in long chain alkanes has produced very bright ML, up to 1,000 fold more intense than from manual grinding. The large increase in intensity has revealed a number of new emitting species including C2, CH, CO, CO+, CO2+, H, and He+, many of which have not been reported from ML before. In addition, the emission products show that gas phase reactions are occurring within the plasma generated from the ML discharge. The intense ML induced by acoustic cavitation allowed the plasma to be characterized in terms of heavy atom temperature of ˜400 K, electron density of 1014 cm-1, and electron energy of ˜3.5 eV. These conditions are very similar to other highly reactive microdischarges. To further extend the knowledge of the conditions generated within a cloud of cavitating bubbles, multi-bubble sonoluminescence (MBSL) of sulfuric acid has been studied. The MBSL spectrum from 95 wt % H2SO 4 consists of a broad continuum extending into the UV with SO and Ar emission lines also observed. The Ar lines were used to determine an effective emission temperature of ˜8,000 K, which is substantially greater than in other low vapor pressure systems (e.g., silicone oil, where MBSL emission temperature is only ˜5,000 K). The observation of Ar lines at this temperature also indicates that a hot plasma core is probably generated during multi-bubble cavitation in sulfuric acid. In addition, the effect of solution composition was studied by varying the acid

  6. Effect of Shock-Induced Cavitation Bubble Collapse on the damage in the Simulated Perineuronal Net of the Brain.

    PubMed

    Wu, Yuan-Ting; Adnan, Ashfaq

    2017-07-13

    The purpose of this study is to conduct modeling and simulation to understand the effect of shock-induced mechanical loading, in the form of cavitation bubble collapse, on damage to the brain's perineuronal nets (PNNs). It is known that high-energy implosion due to cavitation collapse is responsible for corrosion or surface damage in many mechanical devices. In this case, cavitation refers to the bubble created by pressure drop. The presence of a similar damage mechanism in biophysical systems has long being suspected but not well-explored. In this paper, we use reactive molecular dynamics (MD) to simulate the scenario of a shock wave induced cavitation collapse within the perineuronal net (PNN), which is the near-neuron domain of a brain's extracellular matrix (ECM). Our model is focused on the damage in hyaluronan (HA), which is the main structural component of PNN. We have investigated the roles of cavitation bubble location, shockwave intensity and the size of a cavitation bubble on the structural evolution of PNN. Simulation results show that the localized supersonic water hammer created by an asymmetrical bubble collapse may break the hyaluronan. As such, the current study advances current knowledge and understanding of the connection between PNN damage and neurodegenerative disorders.

  7. Numerical prediction of impact force in cavitating flows

    NASA Astrophysics Data System (ADS)

    Zhu, B.; Wang, H.

    2010-08-01

    An analytical method including a macroscopic cavitation model based on the homogeneous flow theory and a microscopic cavitation model based on the bubble dynamic was proposed for the prediction of the impact force caused by cavitation bubbles collapse in cavitating flows. A Large Eddy Simulation (LES) solver incorporated the macroscopic cavitation model was applied to simulate the unsteady cavitating flows. Based on the simulated flow field, the evolution of the cavitation bubbles was determined by a microscopic cavitation model from the resolution of a Rayleigh-Plesset equation including of the effects of the surface tension, the viscosity and compressibility of fluid, thermal conduction and radiation, the phase transition of water vapor at interface and chemical reactions. The cavitation flow around a hydrofoil was simulated to validate the macroscopic cavitation model. A good quantitative agreement was obtained between the prediction and the experiment. The proposed analytical method was applied to predict the impact force at cavitation bubbles collapse on a KT section in cavitating flows. It was found that the shock pressure caused by cavitation bubble collapse is very high. The impact force was predicted accurately comparing with the experimental data.

  8. Cloud cavitation effects in shockwave lithotripsy

    NASA Astrophysics Data System (ADS)

    Colonius, Tim; Tanguay, Michel

    2003-10-01

    Cavitation has already been identified as an important damage mechanism in the comminution of kidney stones in shockwave lithotripsy (SWL). However, the precise conditions that maximize the damage caused by the collapsing bubbles are still unknown. Numerical simulations are used to investigate shock propagation and the consequent growth and collapse of a bubble cloud in the focal region of a lithotripter. In the simulations, a continuum two-phase flow model for the ensemble-averaged macroscale is coupled to a Gilmore model for individual spherical bubble dynamics at the microscale. The simulations show agreement with experimental pressure measurements and high-speed photography of the bubble cloud. At void fractions commensurate with experiments, it is found that the collective collapse of the bubble cloud provides a significant increase to the energy available for comminution (beyond what a single bubble would produce). Relatively small increases in the pressure at the center of the cloud in advance of collapse (two orders of magnitude smaller than the initial shock) can more than double the energy of the collapsing bubble.

  9. Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review.

    PubMed

    Bagal, Manisha V; Gogate, Parag R

    2014-01-01

    Advanced oxidation processes such as cavitation and Fenton chemistry have shown considerable promise for wastewater treatment applications due to the ease of operation and simple reactor design. In this review, hybrid methods based on cavitation coupled with Fenton process for the treatment of wastewater have been discussed. The basics of individual processes (Acoustic cavitation, Hydrodynamic cavitation, Fenton chemistry) have been discussed initially highlighting the need for combined processes. The different types of reactors used for the combined processes have been discussed with some recommendations for large scale operation. The effects of important operating parameters such as solution temperature, initial pH, initial pollutant concentration and Fenton's reagent dosage have been discussed with guidelines for selection of optimum parameters. The optimization of power density is necessary for ultrasonic processes (US) and combined processes (US/Fenton) whereas the inlet pressure needs to be optimized in the case of Hydrodynamic cavitation (HC) based processes. An overview of different pollutants degraded under optimized conditions using HC/Fenton and US/Fenton process with comparison with individual processes have been presented. It has been observed that the main mechanism for the synergy of the combined process depends on the generation of additional hydroxyl radicals and its proper utilization for the degradation of the pollutant, which is strongly dependent on the loading of hydrogen peroxide. Overall, efficient wastewater treatment with high degree of energy efficiency can be achieved using combined process operating under optimized conditions, as compared to the individual process.

  10. Effects of non-condensable gas on the dynamic oscillations of cavitation bubbles

    NASA Astrophysics Data System (ADS)

    Zhang, Yuning

    2016-11-01

    Cavitation is an essential topic of multiphase flow with a broad range of applications. Generally, there exists non-condensable gas in the liquid and a complex vapor/gas mixture bubble will be formed. A rigorous prediction of the dynamic behavior of the aforementioned mixture bubble is essential for the development of a complete cavitation model. In the present paper, effects of non-condensable gas on the dynamic oscillations of the vapor/gas mixture bubble are numerically investigated in great detail. For the completeness, a large parameter zone (e.g. bubble radius, frequency and ratio between gas and vapor) is investigated with many demonstrating examples. The mechanisms of mass diffusion are categorized into different groups with their characteristics and dominated regions given. Influences of non-condensable gas on the wave propagation (e.g. wave speed and attenuation) in the bubbly liquids are also briefly discussed. Specifically, the minimum wave speed is quantitatively predicted in order to close the pressure-density coupling relationship usually employed for the cavitation modelling. Finally, the application of the present finding on the development of cavitation model is demonstrated with a brief discussion of its influence on the cavitation dynamics. This work was financially supported by the National Natural Science Foundation of China (Project No.: 51506051).

  11. Cold Spraying of Cu-Al-Bronze for Cavitation Protection in Marine Environments

    NASA Astrophysics Data System (ADS)

    Krebs, S.; Gärtner, F.; Klassen, T.

    2015-01-01

    Traveling at high speeds, ships have to face the problem of rudder cavitation-erosion. At present, the problem is countered by fluid dynamically optimized rudders, synthetic, and weld-cladded coatings on steel basis. Nevertheless, docking and repair is required after certain intervals. Bulk Cu-Al-bronzes are in use at ships propellers to withstand corrosion and cavitation. Deposited as coatings with bulk-like properties, such bronzes could also enhance rudder life times. The present study investigates the coating formation by cold spraying CuAl10Fe5Ni5 bronze powders. By calculations of the impact conditions, the range of optimum spray parameters was preselected in terms of the coating quality parameter η on steel substrates with different temperatures. As-atomized and annealed powders were compared to optimize cavitation resistance of the coatings. Results provide insights about the interplay between the mechanical properties of powder and substrate for coating formation. Single particle impact morphologies visualize the deformation behavior. Coating performance was assessed by analyzing microstructures, bond strength, and cavitation resistance. These first results demonstrate that cold-sprayed bronze coatings have a high potential for ensuring a good performances in rudder protection. With further optimization, such coatings could evolve towards a competitive alternative to existing anti-cavitation procedures.

  12. Inertial cavitation threshold of nested microbubbles.

    PubMed

    Wallace, N; Dicker, S; Lewin, Peter; Wrenn, S P

    2015-04-01

    Cavitation of ultrasound contrast agents (UCAs) promotes both beneficial and detrimental bioeffects in vivo (Radhakrishnan et al., 2013) [1]. The ability to determine the inertial cavitation threshold of UCA microbubbles has potential application in contrast imaging, development of therapeutic agents, and evaluation of localized effects on the body (Ammi et al., 2006) [2]. This study evaluates a novel UCA and its inertial cavitation behavior as determined by a home built cavitation detection system. Two 2.25 MHz transducers are placed at a 90° angle to one another where one transducer is driven by a high voltage pulser and the other transducer receives the signal from the oscillating microbubble. The sample chamber is placed in the overlap of the focal region of the two transducers where the microbubbles are exposed to a pulser signal consisting of 600 pulse trains per experiment at a pulse repetition frequency of 5 Hz where each train has four pulses of four cycles. The formulation being analyzed is comprised of an SF6 microbubble coated by a DSPC PEG-3000 monolayer nested within a poly-lactic acid (PLA) spherical shell. The effect of varying shell diameters and microbubble concentration on cavitation threshold profile for peak negative pressures ranging from 50 kPa to 2 MPa are presented and discussed in this paper. The nesting shell decreases inertial cavitation events from 97.96% for an un-nested microbubble to 19.09% for the same microbubbles nested within a 2.53 μm shell. As shell diameter decreases, the percentage of inertially cavitating microbubbles also decreases. For nesting formulations with average outer capsule diameters of 20.52, 14.95, 9.95, 5.55, 2.53, and 1.95 μm, the percentage of sample destroyed at 1 MPa was 51.02, 38.94, 33.25, 25.27, 19.09, and 5.37% respectively.

  13. The numerical research of runner cavitation effects on spiral vortex rope in draft tube of Francis turbine

    NASA Astrophysics Data System (ADS)

    Yang, J.; Zhou, L. J.; Wang, Z. W.

    2015-12-01

    The spiral cavitating vortex rope developed in the draft tube of Francis turbine under part load condition maybe causes serious pressure fluctuations and power swings, which threatens the safety and stability of the power plant operations. Many works have been performed to explore the mechanisms of it. In this paper, the runner cavitation and spiral vortex rope under part load conditions were studied to investigate the relations of runner cavitation and the spiral vortex rope. The results proved the existence of obvious interaction between them. The swirl flow at the runner outlet plays an important role in the formation of vortex rope. And the periodic procession of vortex rope in turn intensifies the uneven pressure distribution near the runner outlet and causes the asymmetric cavitation on the runner blades, which then give rise to the modification of swirl flow at the runner blades and thereby affects the characteristics of vortex rope.

  14. Experimental study of temperature effect on the growth and collapse of cavitation bubbles near a rigid boundary

    NASA Astrophysics Data System (ADS)

    Liu, Xiu-mei; Long, Zheng; He, Jie; Li, Bei-bei; Liu, Xin-hua; Zhao, Ji-yun; Lu, Jian; Ni, Xiao-wu

    2013-07-01

    The effect of temperature on the dynamics of a laser-induced cavitation bubble is studied experimentally. The growth and collapse of the cavitation bubble are measured by two sensitive fiber-optic sensors based on optical beam deflection (OBD). Cavitation bubble tests are performed in water at different temperatures, and the temperature ranges from freezing point (0°C) to near boiling point. The results indicate that both the maximum bubble radius and bubble lifetime are increased with the increase of temperature. During the stage of bubble rapidly collapsing in the vicinity of a solid surface, besides laser ablation effect, both the first and second liquid-jet-induced impulses are also observed. They are both increased with liquid temperature increasing, and then reach a peak, followed by a decrease. The peak appears at the temperature which is approximately the average of freezing and boiling points. The mechanism of liquid temperature influence on cavitation erosion is also discussed.

  15. The effect of regime and structural parameters of an inclined Archimedean screw forepump on the volume of cavitation cavities, their elasticity, and cavitation resistance

    NASA Astrophysics Data System (ADS)

    Grigorev, Iu. E.; Pilipenko, V. V.

    Improved empiricotheoretical dependences of the volume of cavitation cavities and cavitation resistance on the cavitation number and liquid flowrate at the inlet to an inclined Archimedean centrifugal screw pump are derived. An analysis is presented of the influence of cavitation number, flowrate, and structural parameters of the forepump on the volume and elasticity of cavities, and on cavitation resistance.

  16. On cavitation and macroscopic behaviour of amorphous polymer-rubber blends.

    PubMed

    Belayachi, Naima; Benseddiq, Noureddine; Naït-Abdelaziz, Moussa; Hamdi, Adel

    2008-04-01

    The macroscopic behaviour of rubber-modified polymethyl methacrylate (PMMA) was investigated by taking into account the microdeformation mechanisms of rubber cavitation. The dependence of the macroscopic stress-strain behaviour of matrix deformation on the cavitation of rubber particles was discussed. A phenomenological elastic-viscoplastic model was used to model the behaviour of the matrix material, while the rubber particles were modelled with the hyperelasticity theory. A two-phase composite material with a periodic arrangement of reinforcing particles of a circular unit cell section was considered. Finite-element analysis was used to determine the local stresses and strains in the two-phase composite. In order to describe the cavitation of the rubber particles, a criterion of void nucleation is implemented in the finite-element (FE) code. A comparison of the numerically predicted response with experimental result indicates that the numerical homogenisation analysis gives satisfactory prediction results.

  17. On cavitation and macroscopic behaviour of amorphous polymer-rubber blends

    PubMed Central

    Belayachi, Naima; Benseddiq, Noureddine; Naït-Abdelaziz, Moussa; Hamdi, Adel

    2008-01-01

    The macroscopic behaviour of rubber-modified polymethyl methacrylate (PMMA) was investigated by taking into account the microdeformation mechanisms of rubber cavitation. The dependence of the macroscopic stress–strain behaviour of matrix deformation on the cavitation of rubber particles was discussed. A phenomenological elastic-viscoplastic model was used to model the behaviour of the matrix material, while the rubber particles were modelled with the hyperelasticity theory. A two-phase composite material with a periodic arrangement of reinforcing particles of a circular unit cell section was considered. Finite-element analysis was used to determine the local stresses and strains in the two-phase composite. In order to describe the cavitation of the rubber particles, a criterion of void nucleation is implemented in the finite-element (FE) code. A comparison of the numerically predicted response with experimental result indicates that the numerical homogenisation analysis gives satisfactory prediction results. PMID:27877983

  18. Effect of laser-induced cavitation bubble on a thin elastic membrane

    NASA Astrophysics Data System (ADS)

    Orthaber, U.; Petkovšek, R.; Schille, J.; Hartwig, L.; Hawlina, G.; Drnovšek-Olup, B.; Vrečko, A.; Poberaj, I.

    2014-12-01

    A study of the effects of a cavitation bubble on a thin elastic membrane is presented. A cavitation bubble was produced by focusing a high-energy laser beam near an elastic membrane submerged in water, which corresponds to conditions often encountered in ophthalmology. The bubble effects on the membrane were studied as a function of distance between the bubble and membrane and laser pulse energy. Recordings of bubble dynamics with an ultra-high-speed camera were performed on both sides of the membrane, providing better insight into the mechanisms of membrane rupture. Observations have revealed distinct bubble behavior regimes with respect to coefficient γ. Cavitation bubbles centered on the membrane produce less damage than bubbles shifted slightly away. Significant damages were observed at intermediate distances between the bubble and membrane after bubble collapse, while weaker interactions were recorded at larger distances with less or no damaging effect to the membrane.

  19. Controlled Cavitation for Scale-Free Heating, Gum Hydration and Emulsification in Food and Consumer Products

    NASA Astrophysics Data System (ADS)

    Mancosky, Douglas G.; Milly, Paul

    Cavitation is defined as the sudden formation and collapse of bubbles in liquid by means of a mechanical force. As bubbles rapidly form and collapse, pressurized shock waves, localized heating events and tremendous shearing forces occur. As microscopic cavitation bubbles are produced and collapse, shockwaves are given off into the liquid, which can result in heating and/or mixing, similar to ultrasound. These shockwaves can provide breakthrough benefits for the heating of liquids without scale buildup and/or the mixing of liquids with other liquids, gases or solids at the microscopic level to increase the efficiency of the reaction.

  20. Heat pipe stability. 1: A preliminary investigation into thermally assisted cavitation

    NASA Technical Reports Server (NTRS)

    1973-01-01

    The notion is introduced of thermally assisted cavitation by localized fluctuations in capillary forces. Because cavitation in liquids can be closely approximated by an isothermal process, only momentum and mass balances are used to introduce the notion for liquids under mechanical tension. Brief attention is given to developing a stability theory in terms of the stiffness and compliance coefficients for a working fluid. Interestingly, the particular thermodynamic approach taken can be used to suggest experiments relating working fluid performance to meniscus behavior. A correction to the liquid flow equation is suggested.

  1. Initial stage of cavitation in liquids and its observation by Rayleigh scattering

    NASA Astrophysics Data System (ADS)

    Pekker, M.; Shneider, M. N.

    2017-06-01

    A theory is developed for the initial stage of cavitation in the framework of Zel’dovich-Fisher theory of nucleation in the field of negative pressure, while taking into account the surface tension dependence on the nanopore radius. A saturation mechanism is proposed that limits the exponential dependence of the nucleation rate on the energy required to create nanopores. An estimate of the saturated density of nanopores at the nucleation stage is obtained. It is shown that Rayleigh scattering can detect nanopores arising at the initial stage of cavitation development.

  2. The restoration of obliterated stamped serial numbers by ultrasonically induced cavitation in water

    NASA Technical Reports Server (NTRS)

    Young, S. G.

    1973-01-01

    Seventeen out of 21 obliterated stamped serial numbers on test specimens of copper, brass, steel, and aluminum were successfully restored. Cavitation induced in water by a piezoelectric transducer was the mechanism used. Primarily, smeared metal was removed from the number grooves by the force of the cavitation, however, numbers were also restored at depths at or below the level of the stamped grooves. The feasibility of this technique as a low cost tool for crime laboratories has been clearly demonstrated. The technique is applicable to a variety of materials, and no previous surface or chemical treatments are necessary.

  3. Cavitational Hydrothermal Oxidation: A New Remediation Process - Final Report

    SciTech Connect

    Suslick, K. S.

    2001-07-05

    During the past year, we have continued to make substantial scientific progress on our understanding of cavitation phenomena in aqueous media and applications of cavitation to remediation processes. Our efforts have focused on three separate areas: sonoluminescence as a probe of conditions created during cavitational collapse in aqueous media, the use of cavitation for remediation of contaminated water, and an addition of the use of ultrasound in the synthesis of novel heterogeneous catalysts for hydrodehalogenation of halocarbons under mild conditions.

  4. Monitoring Cavitation in HIFU as an Aid to Assisting Treatment

    NASA Astrophysics Data System (ADS)

    Hsieh, Chang-yu; Smith, Penny Probert; Kennedy, James; Leslie, Thomas

    2007-05-01

    Rapid hypothermia resulting in tissue necrosis is often associated with bubble activity (normally from cavitation) in HIFU treatment. Indeed in some HIFU protocols, the evidence of cavitation is taken as an indicator of tissue lesions. In this paper we discuss two methods to delineate reliably the region in which cavitation occurs, so that a history of the cavitation events can be provided automatically during treatment. Results are shown on simulated images and from a clinical treatment session.

  5. The effect of chloride ions on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation.

    PubMed

    Wan, Tong; Xiao, Ning; Shen, Hanjie; Yong, Xingyue

    2016-11-01

    The effects of Cl(-) on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation in chloride solutions were investigated using nanoindentation in conjunction with XRD and XPS. The results demonstrate that Cl(-) had a strong effect on the nano-mechanical properties of the corroded surface layer under cavitation, and there was a threshold Cl(-) concentration. Furthermore, a close relationship between the nano-mechanical properties and the cavitation corrosion resistance of 00Cr22Ni5Mo3N duplex stainless steel was observed. The degradation of the nano-mechanical properties of the corroded surface layer was accelerated by the synergistic effect between cavitation erosion and corrosion. A key factor was the adsorption of Cl(-), which caused a preferential dissolution of the ferrous oxides in the passive film layer on the corroded surface layer. Cavitation further promoted the preferential dissolution of the ferrous oxides in the passive film layer. Simultaneously, cavitation accelerated the erosion of the ferrite in the corroded surface layer, resulting in the degradation of the nano-mechanical properties of the corroded surface layer on 00Cr22Ni5Mo3N duplex stainless steel under cavitation.

  6. The issue of cavitation number value in studies of water treatment by hydrodynamic cavitation.

    PubMed

    Šarc, Andrej; Stepišnik-Perdih, Tadej; Petkovšek, Martin; Dular, Matevž

    2017-01-01

    Within the last years there has been a substantial increase in reports of utilization of hydrodynamic cavitation in various applications. It has came to our attention that many times the results are poorly repeatable with the main reason being that the researchers put significant emphasis on the value of the cavitation number when describing the conditions at which their device operates. In the present paper we firstly point to the fact that the cavitation number cannot be used as a single parameter that gives the cavitation condition and that large inconsistencies in the reports exist. Then we show experiments where the influences of the geometry, the flow velocity, the medium temperature and quality on the size, dynamics and aggressiveness of cavitation were assessed. Finally we show that there are significant inconsistencies in the definition of the cavitation number itself. In conclusions we propose a number of parameters, which should accompany any report on the utilization of hydrodynamic cavitation, to make it repeatable and to enable faster progress of science and technology development.

  7. Static and Transient Cavitation Threshold Measurements for Mercury

    SciTech Connect

    Moraga, F.; Taleyarkhan, R.P.

    1999-11-14

    Transient and static cavitation thresholds for mercury as a function of the cover gas (helium or air), and pressure are reported. Both static and transient cavitation onset pressure thresholds increase linearly with cover gas pressure. Additionally, the cavitation thresholds as a function of dissolved gases were also measured and are reported.

  8. Studies reveal effects of pipe bends on fluid flow cavitation

    NASA Technical Reports Server (NTRS)

    Stonemetz, R. E.

    1966-01-01

    Incipient cavitation in liquids flowing in pipes curved in one plane are affected by the pipe bend radii and pipe diameters, but little by pipe bend angles ranging from 60 to 120 degrees. Critical cavitation indices decrease with higher Reynolds number and pressure ratio. Bulk liquid temperature increase lowers the mean critical velocity at which cavitation occurs.

  9. Numerical Simulation of Cavitation Characteristics for Pump-jet Propeller

    NASA Astrophysics Data System (ADS)

    Shi, Yao; Pan, Guang; Huang, Qiaogao; Du, Xiaoxu

    2015-09-01

    With k — ε turbulent model, non-cavitating performance of a pump-jet propeller was obtained by calculating RANS equations. The comparison between calculation results and experiment data shown that the numerical model and method was reliable. The cavitating hydrodynamic performance of it was calculated and analyzed with mixture homogeneous flow cavitation model based on Rayleigh-Plesset equations and sliding mesh. The effects of different inlet velocity ratio, cavitation number and flow velocity on cavitation characteristics of pump-jet were studied. When the cavitation occurred on the blades, the propeller thrust and torque decreased significantly, thereby causing open water efficiency reduced 15%. For the same cavitation number, as the inlet velocity ratio decreased, the pump-jet propeller blade cavitation phenomenon was more obvious. While for the same ratio, the smaller the number of cavitation, cavitation phenomenon was more remarkable. The more significant was that while the cavitation number was greater than a certain value, the blade cavitation phenomenon disappeared.

  10. Real-time two-dimensional imaging of microbubble cavitation

    NASA Astrophysics Data System (ADS)

    Vignon, Francois; Shi, W. T.; Powers, J. E.; Liu, J.; Drvol, L.; Lof, J.; Everbach, C.; Gao, S.; Xie, F.; Porter, T.

    2012-10-01

    Ultrasound cavitation of microbubble contrast agents has a potential for therapeutic applications, including sonothrombolysis in acute ischemic stroke. For safety, efficacy, and reproducibility of treatment, it is critical to evaluate the cavitation state (e.g. stable versus inertial forms of cavitation) and intensity in and around a treatment area. Acoustic Passive Cavitation Detectors (PCDs) have been used but do not provide spatial information. This paper presents a prototype of a 2D cavitation imager capable of producing images of the dominant cavitation state and intensity in a region of interest at a frame rate of 0.6Hz. The system is based on a modified ultrasound scanner (iE33, Philips) with a sector imaging probe (S5-1). Cavitation imaging is based on the spectral analysis of the acoustic signal radiated by the cavitating microbubbles: ultraharmonics of the excitation frequency indicate stable cavitation, while noise bands indicate inertial cavitation. The system demonstrates the capability to robustly identify stable and inertial cavitation thresholds of Definity microbubbles (Lantheus) in a vessel phantom through 3 ex-vivo human temporal bones, as well as to spatially map cavitation activities.

  11. Activating Molecules, Ions, and Solid Particles with Acoustic Cavitation

    PubMed Central

    Pflieger, Rachel; Chave, Tony; Virot, Matthieu; Nikitenko, Sergey I.

    2014-01-01

    The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO2 powder in pure water yields stable colloids of plutonium due to both effects. PMID:24747272

  12. Activating molecules, ions, and solid particles with acoustic cavitation.

    PubMed

    Pflieger, Rachel; Chave, Tony; Virot, Matthieu; Nikitenko, Sergey I

    2014-04-11

    The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO2 powder in pure water yields stable colloids of plutonium due to both effects.

  13. String cavitation formation inside fuel injectors

    NASA Astrophysics Data System (ADS)

    Reid, B. A.; Gavaises, M.; Mitroglou, N.; Hargrave, G. K.; Garner, C. P.; McDavid, R. M.

    2015-12-01

    The formation of vortex or ‘string’ cavitation has been visualised at pressures up to 2000 bar in an automotive-sized optical diesel fuel injector nozzle. The multi-hole nozzle geometry studied allowed observation of the hole-to-hole vortex interaction and, in particular, that of a bridging vortex in the sac region between the holes. Above a threshold Reynolds number, their formation and appearance during a 2 ms injection event was repeatable and independent of upstream pressure and cavitation number. In addition, two different hole layouts and threedimensional flow simulations have been employed to describe how, the relative positions of adjacent holes influenced the formation and hole-to-hole interaction of the observed string cavitation vortices, with good agreement between the experimental and simulation results being achieved.

  14. Numerical simulations of cryogenic cavitating flows

    NASA Astrophysics Data System (ADS)

    Kim, Hyunji; Kim, Hyeongjun; Min, Daeho; Kim, Chongam

    2015-12-01

    The present study deals with a numerical method for cryogenic cavitating flows. Recently, we have developed an accurate and efficient baseline numerical scheme for all-speed water-gas two-phase flows. By extending such progress, we modify the numerical dissipations to be properly scaled so that it does not show any deficiencies in low Mach number regions. For dealing with cryogenic two-phase flows, previous EOS-dependent shock discontinuity sensing term is replaced with a newly designed EOS-free one. To validate the proposed numerical method, cryogenic cavitating flows around hydrofoil are computed and the pressure and temperature depression effect in cryogenic cavitation are demonstrated. Compared with Hord's experimental data, computed results are turned out to be satisfactory. Afterwards, numerical simulations of flow around KARI turbopump inducer in liquid rocket are carried out under various flow conditions with water and cryogenic fluids, and the difference in inducer flow physics depending on the working fluids are examined.

  15. Large eddy simulation of cavitating flows

    NASA Astrophysics Data System (ADS)

    Gnanaskandan, Aswin; Mahesh, Krishnan

    2014-11-01

    Large eddy simulation on unstructured grids is used to study hydrodynamic cavitation. The multiphase medium is represented using a homogeneous equilibrium model that assumes thermal equilibrium between the liquid and the vapor phase. Surface tension effects are ignored and the governing equations are the compressible Navier Stokes equations for the liquid/vapor mixture along with a transport equation for the vapor mass fraction. A characteristic-based filtering scheme is developed to handle shocks and material discontinuities in non-ideal gases and mixtures. A TVD filter is applied as a corrector step in a predictor-corrector approach with the predictor scheme being non-dissipative and symmetric. The method is validated for canonical one dimensional flows and leading edge cavitation over a hydrofoil, and applied to study sheet to cloud cavitation over a wedge. This work is supported by the Office of Naval Research.

  16. Inducer Hydrodynamic Forces in a Cavitating Environment

    NASA Technical Reports Server (NTRS)

    Skelley, Stephen E.

    2004-01-01

    Marshall Space Flight Center has developed and demonstrated a measurement device for sensing and resolving the hydrodynamic loads on fluid machinery. The device - a derivative of the six-component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This rotating balance was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining the amplitude and frequency content associated with operating in various cavitation modes. The rotating balance was calibrated statically using a dead-weight load system in order to generate the 6 x 12 calibration matrix later used to convert measured voltages to engineering units. Structural modeling suggested that the rotating assembly first bending mode would be significantly reduced with the balance s inclusion. This reduction in structural stiffness was later confirmed experimentally with a hammer-impact test. This effect, coupled with the relatively large damping associated with the rotating balance waterproofing material, limited the device s bandwidth to approximately 50 Hertz Other pre-test validations included sensing the test article rotating assembly built-in imbalance for two configurations and directly measuring the assembly mass and buoyancy while submerged under water. Both tests matched predictions and confirmed the device s sensitivity while stationary and rotating. The rotating balance was then demonstrated in a water test of a full-scale Space Shuttle Main Engine high-pressure liquid oxygen pump inducer. Experimental data was collected a scaled operating conditions at three flow coefficients across a range of cavitation numbers for the single inducer geometry and radial clearance. Two distinct cavitation modes were observed symmetric tip vortex cavitation and alternate-blade cavitation. Although previous experimental tests on the same inducer demonstrated two additional

  17. Fundamental studies on cavitation melt processing

    NASA Astrophysics Data System (ADS)

    Tzanakis, I.; Hodnett, M.; Lebon, G. S. B.; Eskin, D. G.; Pericleous, K.

    2016-05-01

    The application of ultrasound to industrial casting processes has attracted research interest during the last 50 years. However, the transfer and scale-up of this advanced and promising technology to industry has been hindered by difficulties in treating large volumes of liquid metal due to the lack of understanding of certain fundamentals. In the current study experimental results on ultrasonic processing in deionised water and in liquid aluminium (Al) are reported. Cavitation activity was determined in both liquid environments and acoustic pressures were successfully measured using an advanced high-temperature cavitometer sensor. Results showed that highest cavitation intensity in the liquid bulk is achieved at lower amplitudes of the sonotrode tip than the maximum available, suggesting nonlinearity in energy transfer to the liquid, while the location of the sonotrode is seen to substantially affect cavitation activity within the liquid. Estimation of real-time acoustic pressures distributed inside a crucible with liquid Al was performed for the first time.

  18. Towards numerical prediction of cavitation erosion.

    PubMed

    Fivel, Marc; Franc, Jean-Pierre; Chandra Roy, Samir

    2015-10-06

    This paper is intended to provide a potential basis for a numerical prediction of cavitation erosion damage. The proposed method can be divided into two steps. The first step consists in determining the loading conditions due to cavitation bubble collapses. It is shown that individual pits observed on highly polished metallic samples exposed to cavitation for a relatively small time can be considered as the signature of bubble collapse. By combining pitting tests with an inverse finite-element modelling (FEM) of the material response to a representative impact load, loading conditions can be derived for each individual bubble collapse in terms of stress amplitude (in gigapascals) and radial extent (in micrometres). This step requires characterizing as accurately as possible the properties of the material exposed to cavitation. This characterization should include the effect of strain rate, which is known to be high in cavitation erosion (typically of the order of several thousands s(-1)). Nanoindentation techniques as well as compressive tests at high strain rate using, for example, a split Hopkinson pressure bar test system may be used. The second step consists in developing an FEM approach to simulate the material response to the repetitive impact loads determined in step 1. This includes a detailed analysis of the hardening process (isotropic versus kinematic) in order to properly account for fatigue as well as the development of a suitable model of material damage and failure to account for mass loss. Although the whole method is not yet fully operational, promising results are presented that show that such a numerical method might be, in the long term, an alternative to correlative techniques used so far for cavitation erosion prediction.

  19. Towards numerical prediction of cavitation erosion

    PubMed Central

    Fivel, Marc; Franc, Jean-Pierre; Chandra Roy, Samir

    2015-01-01

    This paper is intended to provide a potential basis for a numerical prediction of cavitation erosion damage. The proposed method can be divided into two steps. The first step consists in determining the loading conditions due to cavitation bubble collapses. It is shown that individual pits observed on highly polished metallic samples exposed to cavitation for a relatively small time can be considered as the signature of bubble collapse. By combining pitting tests with an inverse finite-element modelling (FEM) of the material response to a representative impact load, loading conditions can be derived for each individual bubble collapse in terms of stress amplitude (in gigapascals) and radial extent (in micrometres). This step requires characterizing as accurately as possible the properties of the material exposed to cavitation. This characterization should include the effect of strain rate, which is known to be high in cavitation erosion (typically of the order of several thousands s−1). Nanoindentation techniques as well as compressive tests at high strain rate using, for example, a split Hopkinson pressure bar test system may be used. The second step consists in developing an FEM approach to simulate the material response to the repetitive impact loads determined in step 1. This includes a detailed analysis of the hardening process (isotropic versus kinematic) in order to properly account for fatigue as well as the development of a suitable model of material damage and failure to account for mass loss. Although the whole method is not yet fully operational, promising results are presented that show that such a numerical method might be, in the long term, an alternative to correlative techniques used so far for cavitation erosion prediction. PMID:26442139

  20. Correlations of thermodynamic effects for developed cavitation

    NASA Technical Reports Server (NTRS)

    Billet, M. L.; Holl, J. W.; Weir, D. S.

    1978-01-01

    The net positive suction head (NPSH) requirements for a pump are determined by the combined effects of cavitation, fluid properties, pump geometry, and pump operating point. An important part of this determination is the temperature depression (Delta T). Correlations are presented of the temperature depression for various degrees of developed cavitation on venturis and ogives. These correlations, based on a semi-empirical entrainment theory, express Delta T in terms of the dimensionless numbers of Nusselt, Reynolds, Froude, Weber, and Peclet, and dimensionless cavity length (L/D). The Delta T data were obtained in Freon 114, hydrogen and nitrogen for the venturis and in Freon 113 and water for the ogives.

  1. Ideas in action: Solving a cavitation mystery

    SciTech Connect

    1995-12-31

    Cavitation caused significant erosion from 1985 through 1990 on turbine runners at the 970-MW Murray 1 Power Station operated by Snowy Mountains Hydro-Electric Authority (SMHEA) in Australia. The problem was perplexing because no obvious cause could be found. Investigation eventually showed the problems stemmed form the runners sagging slightly from the correct height. Corrective measures, which included adjustment of runners and new control settings for the units, appear to have relieved the cavitation. The adjustments also reduced stress on the unit thrust-bearings, eliminating a future maintenance headache.

  2. Surge instability on a cavitating propeller

    NASA Astrophysics Data System (ADS)

    Duttweiler, Mark Edward

    2001-11-01

    The present study details results from experiments investigating a surge instability on a cavitating propeller. Initially, the stable behavior of the propeller is explored, and the nature and extent of the cavitation is documented at various experimental conditions, including propeller yaw. The cavitation surge instability is first explored through visual observation of the cavitation on the propeller blades and in the tip vortices. Particular note is made of similarities between the behavior of the re-entrant jets and that noted by other investigators. It is also observed that the nature of the instability is closely related to the partial cavity instability observed on single, two-dimensional hydrofoils. The flow conditions that lead to instability are determined and it is shown that onset corresponds to a specific configuration of attached cavity lengths on an individual propeller blade. Pressure measurements are obtained from transducers within the experimental facility, and the acoustic signature of the instability is identified. The magnitude of the fluctuating pressures is very large, presumably capable of producing severe hull vibration. A simple model is developed based on cavity volume estimates obtained from high speed video footage, and the predictions of the model are compared with the experimentally obtained pressures. To assess the significance of the surrounding facility in initiating and sustaining the instability, a model is developed for the experimental facility dynamics. The predictions of this model are then compared with an experimentally determined facility response to a volumetric excitation imposed by an oscillating piston. To quantify the response of the cavitation to fluctuations in test section conditions, quasistatic estimates are obtained for the cavitation compliance and mass flow gain factor of the propeller. These parameters have previously been employed in developing system transfer functions for cavitating pumps. Finally, a model

  3. Cavitation wear resistance of engine bearing materials

    NASA Astrophysics Data System (ADS)

    Rac, Aleksandar

    1994-04-01

    The resistance to cavitation erosion of aluminum alloy, and cast and sinte-red lead-bronze, materials which are most frequently used for engine bearings, has been evaluated. The tests were carried out in motor oil at a temperature of 80 C, using a magnetostrictive vibratory tester (20 kHz). The results showed that the cavitation erosion resistance was the greatest in cast lead-bronze. On the contrary, sintered lead-bronze, though of the same chemical composition, had the greatest erosion rate. Additionally, the investigation of the overlay plated bearings showed the overlay was nonresistive to this type of wear.

  4. Modeling hydrodynamic nonequilibrium in cavitating flows

    SciTech Connect

    Chen, Y.; Heister, S.D.

    1996-03-01

    A nonlinear numerical model has been developed to assess nonequilibrium effects in cavitating flows. The numerical implementation involves a two-phase treatment with the use of a pseudo-density which varies between the liquid and gas/vapor extremes. A new constitutive equation for the pseudo-density is derived based on the bubble response described by a modified form of the Rayleigh-Plesset equation. Use of this constitutive equation in a numerical procedure permits the assessment of nonequilibrium effects. This scheme provides a quantitative description of scaling effects in cavitated flows. With minimal modifications, the model can also be used for bubbly two-phase flows.

  5. Revisiting a runner cavitation repair job

    SciTech Connect

    Witman, J.K.

    1996-05-01

    This article reviews the efforts to repair turbine runner cavitation damage. The particular runner was originally repaired in 1990 with the application of a layer of beaded epoxy to areas of severe cavitation on the suction side of the blades on the upper runner. A year later, the runner was inspected, with no damage to the epoxy. In June of 1994, the runner was again inspected, and this and the most recent inspection shows that the epoxy coating is holding up well. The last inspection did show the beginnings on some erosion of the repair material. Based on this long-term series of inspections, maintenance recommendations are set forth.

  6. Dynamics of cavitating cascades. [transfer functions

    NASA Technical Reports Server (NTRS)

    Brennen, C. E.; Acosta, A. J.

    1980-01-01

    The unsteady dynamics of cavitating cascades and inducer pumps were studied with a view to understanding (and possibly predicting) the dynamic characteristics of these devices. The chronology of the research is summarized as well as the final conculsions for each task. The construction of a dynamic pump test facility and its use in making experimental measurements of the transfer function is described as well as tests conducted using a scale model of the low pressure liquid oxygen turbopump inducer in the shuttle main engine. Auto-oscillation and unsteady inlet flow characteristics are discussed in addition to blade cavity influence and bubbly cavitation.

  7. Ultrasound-induced cavitation enhances the delivery and therapeutic efficacy of an oncolytic virus in an in vitro model.

    PubMed

    Bazan-Peregrino, Miriam; Arvanitis, Costas D; Rifai, Bassel; Seymour, Leonard W; Coussios, Constantin-C

    2012-01-30

    We investigated whether ultrasound-induced cavitation at 0.5 MHz could improve the extravasation and distribution of a potent breast cancer-selective oncolytic adenovirus, AdEHE2F-Luc, to tumour regions that are remote from blood vessels. We developed a novel tumour-mimicking model consisting of a gel matrix containing human breast cancer cells traversed by a fluid channel simulating a tumour blood vessel, through which the virus and microbubbles could be made to flow. Ultrasonic pressures were chosen to maximize either broadband emissions, associated with inertial cavitation, or ultraharmonic emissions, associated with stable cavitation, while varying duty cycle to keep the total acoustic energy delivered constant for comparison across exposures. None of the exposure conditions tested affected cell viability in the absence of the adenovirus. When AdEHE2F-Luc was delivered via the vessel, inertial cavitation increased transgene expression in tumour cells by up to 200 times. This increase was not observed in the absence of Coxsackie and Adenovirus Receptor cell expression, discounting sonoporation as the mechanism of action. In the presence of inertial cavitation, AdEHE2F-Luc distribution was greatly improved in the matrix surrounding the vessel, particularly in the direction of the ultrasound beam; this enabled AdEHE2F-Luc to kill up to 80% of cancer cells within the ultrasound focal volume in the gel 24 hours after delivery, compared to 0% in the absence of cavitation.

  8. Spatial-temporal ultrasound imaging of residual cavitation bubbles around a fluid-tissue interface in histotripsy.

    PubMed

    Hu, Hong; Xu, Shanshan; Yuan, Yuan; Liu, Runna; Wang, Supin; Wan, Mingxi

    2015-05-01

    Cavitation is considered as the primary mechanism of soft tissue fragmentation (histotripsy) by pulsed high-intensity focused ultrasound. The residual cavitation bubbles have a dual influence on the histotripsy pulses: these serve as nuclei for easy generation of new cavitation, and act as strong scatterers causing energy "shadowing." To monitor the residual cavitation bubbles in histotripsy, an ultrafast active cavitation imaging method with relatively high signal-to-noise ratio and good spatial-temporal resolution was proposed in this paper, which combined plane wave transmission, minimum variance beamforming, and coherence factor weighting. The spatial-temporal evolutions of residual cavitation bubbles around a fluid-tissue interface in histotripsy under pulse duration (PD) of 10-40 μs and pulse repetition frequency (PRF) of 0.67-2 kHz were monitored by this method. The integrated bubble area curves inside the tissue interface were acquired from the bubble image sequence, and the formation process of histotripsy damage was estimated. It was observed that the histotripsy efficiency decreased with both longer PDs and higher PRFs. A direct relationship with a coefficient of 1.0365 between histotripsy lesion area and inner residual bubble area was found. These results can assist in monitoring and optimization of the histotripsy treatment further.

  9. Cellular High-Energy Cavitation Trauma - Description of a Novel In Vitro Trauma Model in Three Different Cell Types.

    PubMed

    Cao, Yuli; Risling, Mårten; Malm, Elisabeth; Sondén, Anders; Bolling, Magnus Frödin; Sköld, Mattias K

    2016-01-01

    The mechanisms involved in traumatic brain injury have yet to be fully characterized. One mechanism that, especially in high-energy trauma, could be of importance is cavitation. Cavitation can be described as a process of vaporization, bubble generation, and bubble implosion as a result of a decrease and subsequent increase in pressure. Cavitation as an injury mechanism is difficult to visualize and model due to its short duration and limited spatial distribution. One strategy to analyze the cellular response of cavitation is to employ suitable in vitro models. The flyer-plate model is an in vitro high-energy trauma model that includes cavitation as a trauma mechanism. A copper fragment is accelerated by means of a laser, hits the bottom of a cell culture well causing cavitation, and shock waves inside the well and cell medium. We have found the flyer-plate model to be efficient, reproducible, and easy to control. In this study, we have used the model to analyze the cellular response to microcavitation in SH-SY5Y neuroblastoma, Caco-2, and C6 glioma cell lines. Mitotic activity in neuroblastoma and glioma was investigated with BrdU staining, and cell numbers were calculated using automated time-lapse imaging. We found variations between cell types and between different zones surrounding the lesion with these methods. It was also shown that the injured cell cultures released S-100B in a dose-dependent manner. Using gene expression microarray, a number of gene families of potential interest were found to be strongly, but differently regulated in neuroblastoma and glioma at 24 h post trauma. The data from the gene expression arrays may be used to identify new candidates for biomarkers in cavitation trauma. We conclude that our model is useful for studies of trauma in vitro and that it could be applied in future treatment studies.

  10. Effects of ultrasound frequency and tissue stiffness on the histotripsy intrinsic threshold for cavitation.

    PubMed

    Vlaisavljevich, Eli; Lin, Kuang-Wei; Maxwell, Adam; Warnez, Matthew T; Mancia, Lauren; Singh, Rahul; Putnam, Andrew J; Fowlkes, Brian; Johnsen, Eric; Cain, Charles; Xu, Zhen

    2015-06-01

    Histotripsy is an ultrasound ablation method that depends on the initiation of a cavitation bubble cloud to fractionate soft tissue. Previous work has indicated that a cavitation cloud can be formed by a single pulse with one high-amplitude negative cycle, when the negative pressure amplitude directly exceeds a pressure threshold intrinsic to the medium. We hypothesize that the intrinsic threshold in water-based tissues is determined by the properties of the water inside the tissue, and changes in tissue stiffness or ultrasound frequency will have a minimal impact on the histotripsy intrinsic threshold. To test this hypothesis, the histotripsy intrinsic threshold was investigated both experimentally and theoretically. The probability of cavitation was measured by subjecting tissue phantoms with adjustable mechanical properties and ex vivo tissues to a histotripsy pulse of 1-2 cycles produced by 345-kHz, 500-kHz, 1.5-MHz and 3-MHz histotripsy transducers. Cavitation was detected and characterized by passive cavitation detection and high-speed photography, from which the probability of cavitation was measured versus pressure amplitude. The results revealed that the intrinsic threshold (the negative pressure at which probability = 0.5) is independent of stiffness for Young's moduli (E) <1 MPa, with only a small increase (∼2-3 MPa) in the intrinsic threshold for tendon (E = 380 MPa). Additionally, results for all samples revealed only a small increase of ∼2-3 MPa when the frequency was increased from 345 kHz to 3 MHz. The intrinsic threshold was measured to be between 24.7 and 30.6 MPa for all samples and frequencies tested in this study. Overall, the results of this study indicate that the intrinsic threshold to initiate a histotripsy bubble cloud is not significantly affected by tissue stiffness or ultrasound frequency in the hundreds of kilohertz to megahertz range.

  11. Post hoc analysis of passive cavitation imaging for classification of histotripsy-induced liquefaction in vitro.

    PubMed

    Bader, Kenneth B; Haworth, Kevin J; Maxwell, Adam D; Holland, Christy K

    2017-08-02

    Histotripsy utilizes focused ultrasound to generate bubble clouds for transcutaneous tissue liquefaction. Image guidance of histotripsy pulses is required to provide spatially resolved monitoring of treatment progress. The aim of this study was to investigate the feasibility of plane wave B-mode and passive cavitation images to be used as binary classifiers of histotripsy-induced liquefaction. Prostate tissue phantoms were exposed to mechanically ablative histotripsy pulses over a range of pulse durations (5 - 20 μs) and peak negative pressures (12 - 23 MPa). Acoustic emissions were recorded during the insonation and beamformed to form passive cavitation images. Plane wave B-mode images were acquired following the insonation to detect the hyperechoic bubble cloud. Phantom samples were sectioned and stained to delineate the liquefaction zone. Correlation between passive cavitation and plane wave B-mode images and the liquefaction zone was assessed using receiver operating characteristic (ROC) curve analysis. Liquefaction of the phantom was observed for all insonation conditions. The area under the ROC (0.94 vs. 0.82), accuracy (0.90 vs. 0.83), and sensitivity (0.81 vs. 0.49) was greater for passive cavitation images relative to B-mode images (p < 0.05) along the azimuth of the liquefaction zone. The specificity was greater than 0.9 for both imaging modalities. These results demonstrate here denote a stronger correlation between histotripsy-induced liquefaction and passive cavitation imaging compared to plane wave B-mode imaging, albeit with limited passive cavitation image range resolution.

  12. A tissue phantom for visualization and measurement of ultrasound-induced cavitation damage.

    PubMed

    Maxwell, Adam D; Wang, Tzu-Yin; Yuan, Lingqian; Duryea, Alexander P; Xu, Zhen; Cain, Charles A

    2010-12-01

    Many ultrasound studies involve the use of tissue-mimicking materials to research phenomena in vitro and predict in vivo bioeffects. We have developed a tissue phantom to study cavitation-induced damage to tissue. The phantom consists of red blood cells suspended in an agarose hydrogel. The acoustic and mechanical properties of the gel phantom were found to be similar to soft tissue properties. The phantom's response to cavitation was evaluated using histotripsy. Histotripsy causes breakdown of tissue structures by the generation of controlled cavitation using short, focused, high-intensity ultrasound pulses. Histotripsy lesions were generated in the phantom and kidney tissue using a spherically focused 1-MHz transducer generating 15 cycle pulses, at a pulse repetition frequency of 100 Hz with a peak negative pressure of 14 MPa. Damage appeared clearly as increased optical transparency of the phantom due to rupture of individual red blood cells. The morphology of lesions generated in the phantom was very similar to that generated in kidney tissue at both macroscopic and cellular levels. Additionally, lesions in the phantom could be visualized as hypoechoic regions on a B-mode ultrasound image, similar to histotripsy lesions in tissue. High-speed imaging of the optically transparent phantom was used to show that damage coincides with the presence of cavitation. These results indicate that the phantom can accurately mimic the response of soft tissue to cavitation and provide a useful tool for studying damage induced by acoustic cavitation. Copyright © 2010 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  13. Influence of the empirical coefficients of cavitation model on predicting cavitating flow in the centrifugal pump

    NASA Astrophysics Data System (ADS)

    Liu, Hou-lin; Wang, Jian; Wang, Yong; Zhang, Hua; Huang, Haoqin

    2014-03-01

    The phenomenon of cavitation is an unsteady flow, which is nearly inevitable in pump. It would degrade the pump performance, produce vibration and noise and even damage the pump. Hence, to improve accuracy of the nu¬merical prediction of the pump cavitation performance is much desirable. In the present work, a homogenous model, the Zwart-Gerber-Belamri cavitation model, is considered to investigate the influence of the empirical coefficients on predicting the pump cavitation performance, concerning a centrifugal pump. Three coefficients are analyzed, namely the nucleation site radius, evaporation and condensation coefficients. Also, the experiments are carried out to validate the numerical simulations. The results indicate that, to get a precise prediction, the approaches of declining the initial bubble radius, the condensation coefficient or increasing the evaporation coefficient are all feasible, especially for de¬clining the condensation coefficient, which is the most effective way.

  14. THE ROLE OF INERTIAL CAVITATION IN ACOUSTIC DROPLET VAPORIZATION

    PubMed Central

    Fabiilli, Mario L.; Haworth, Kevin J.; Fakhri, Nasir H.; Kripfgans, Oliver D.; Carson, Paul L.; Fowlkes, J. Brian

    2011-01-01

    The vaporization of a superheated droplet emulsion into gas bubbles using ultrasound – termed acoustic droplet vaporization (ADV) – has potential therapeutic applications in embolotherapy and drug delivery. The optimization of ADV for therapeutic applications can be enhanced by understanding the physical mechanisms underlying ADV, which are currently not clearly elucidated. Acoustic cavitation is one possible mechanism. This paper investigates the relationship between the ADV and inertial cavitation (IC) thresholds (measured as peak rarefactional pressures) by studying parameters that are known to influence the IC threshold. These parameters include bulk fluid properties such as gas saturation, temperature, viscosity, and surface tension; droplet parameters such as degree of superheat, surfactant type, and size; and acoustic properties such as pulse repetition frequency and pulse width. In all cases the ADV threshold occurred at a lower rarefactional pressure than the IC threshold indicating that the phase-transition occurs before IC events. The viscosity and temperature of the bulk fluid are shown to influence both thresholds directly and inversely, respectively. An inverse trend is observed between threshold and diameter for droplets in the 1 to 2.5 μ range. Based on a choice of experimental parameters, it is possible to achieve ADV with or without IC. PMID:19473917

  15. Laser-nucleated acoustic cavitation in focused ultrasound

    NASA Astrophysics Data System (ADS)

    Gerold, Bjoern; Kotopoulis, Spiros; McDougall, Craig; McGloin, David; Postema, Michiel; Prentice, Paul

    2011-04-01

    Acoustic cavitation can occur in therapeutic applications of high-amplitude focused ultrasound. Studying acoustic cavitation has been challenging, because the onset of nucleation is unpredictable. We hypothesized that acoustic cavitation can be forced to occur at a specific location using a laser to nucleate a microcavity in a pre-established ultrasound field. In this paper we describe a scientific instrument that is dedicated to this outcome, combining a focused ultrasound transducer with a pulsed laser. We present high-speed photographic observations of laser-induced cavitation and laser-nucleated acoustic cavitation, at frame rates of 0.5×106 frames per second, from laser pulses of energy above and below the optical breakdown threshold, respectively. Acoustic recordings demonstrated inertial cavitation can be controllably introduced to the ultrasound focus. This technique will contribute to the understanding of cavitation evolution in focused ultrasound including for potential therapeutic applications.

  16. Kaplan turbine tip vortex cavitation - analysis and prevention

    NASA Astrophysics Data System (ADS)

    Motycak, L.; Skotak, A.; Kupcik, R.

    2012-11-01

    The work is focused on one type of Kaplan turbine runner cavitation - a tip vortex cavitation. For detailed description of the tip vortex, the CFD analysis is used. On the basis of this analysis it is possible to estimate the intensity of cavitating vortex core, danger of possible blade surface and runner chamber cavitation pitting. In the paper, the ways how to avoid the pitting effect of the tip vortex are described. In order to prevent the blade surface against pitting, the following possibilities as the change of geometry of the runner blade, dimension of tip clearance and finally the installation of the anti-cavitation lips are discussed. The knowledge of the shape and intensity of the tip vortex helps to design the anti-cavitation lips more sophistically. After all, the results of the model tests of the Kaplan runner with or without anti-cavitation lips and the results of the CFD analysis are compared.

  17. Laser-nucleated acoustic cavitation in focused ultrasound.

    PubMed

    Gerold, Bjoern; Kotopoulis, Spiros; McDougall, Craig; McGloin, David; Postema, Michiel; Prentice, Paul

    2011-04-01

    Acoustic cavitation can occur in therapeutic applications of high-amplitude focused ultrasound. Studying acoustic cavitation has been challenging, because the onset of nucleation is unpredictable. We hypothesized that acoustic cavitation can be forced to occur at a specific location using a laser to nucleate a microcavity in a pre-established ultrasound field. In this paper we describe a scientific instrument that is dedicated to this outcome, combining a focused ultrasound transducer with a pulsed laser. We present high-speed photographic observations of laser-induced cavitation and laser-nucleated acoustic cavitation, at frame rates of 0.5×10(6) frames per second, from laser pulses of energy above and below the optical breakdown threshold, respectively. Acoustic recordings demonstrated inertial cavitation can be controllably introduced to the ultrasound focus. This technique will contribute to the understanding of cavitation evolution in focused ultrasound including for potential therapeutic applications.

  18. Numerical study of cavitation flows inside a tubular pumping station

    NASA Astrophysics Data System (ADS)

    Tang, X. L.; Huang, W.; Wang, F. J.; Yang, W.; Wu, Y. L.

    2012-11-01

    Based on RNG k-epsilon turbulence model and the full cavitation model, the cavitation flows inside a low-head tubular-pump model were predicted by using the FLUENT software. For a operating case of given flow rate, cavitation happens near the inlet on the suction surfaces of the impeller blades at the initial cavitating stage, and the cavitating area spreads to the impeller passage and hub as NPSH (net positive suction head) decreases, which will affect energy transformation. For various operating cases of cavitation flows at the given flow rates, the predicted velocity and pressure distributions as well as the vapor volumetric fraction are systematically analyzed. Finally, the cavitation performance curve of the tubular-pump model is obtained by means of the further post-processing. All the comparisons and analysis can be further employed to optimize the hydraulic and structural design of the tubular pump and to guide its safe operation.

  19. Real-time visualization of joint cavitation.

    PubMed

    Kawchuk, Gregory N; Fryer, Jerome; Jaremko, Jacob L; Zeng, Hongbo; Rowe, Lindsay; Thompson, Richard

    2015-01-01

    Cracking sounds emitted from human synovial joints have been attributed historically to the sudden collapse of a cavitation bubble formed as articular surfaces are separated. Unfortunately, bubble collapse as the source of joint cracking is inconsistent with many physical phenomena that define the joint cracking phenomenon. Here we present direct evidence from real-time magnetic resonance imaging that the mechanism of joint cracking is related to cavity formation rather than bubble collapse. In this study, ten metacarpophalangeal joints were studied by inserting the finger of interest into a flexible tube tightened around a length of cable used to provide long-axis traction. Before and after traction, static 3D T1-weighted magnetic resonance images were acquired. During traction, rapid cine magnetic resonance images were obtained from the joint midline at a rate of 3.2 frames per second until the cracking event occurred. As traction forces increased, real-time cine magnetic resonance imaging demonstrated rapid cavity inception at the time of joint separation and sound production after which the resulting cavity remained visible. Our results offer direct experimental evidence that joint cracking is associated with cavity inception rather than collapse of a pre-existing bubble. These observations are consistent with tribonucleation, a known process where opposing surfaces resist separation until a critical point where they then separate rapidly creating sustained gas cavities. Observed previously in vitro, this is the first in-vivo macroscopic demonstration of tribonucleation and as such, provides a new theoretical framework to investigate health outcomes associated with joint cracking.

  20. Real-Time Visualization of Joint Cavitation

    PubMed Central

    Rowe, Lindsay

    2015-01-01

    Cracking sounds emitted from human synovial joints have been attributed historically to the sudden collapse of a cavitation bubble formed as articular surfaces are separated. Unfortunately, bubble collapse as the source of joint cracking is inconsistent with many physical phenomena that define the joint cracking phenomenon. Here we present direct evidence from real-time magnetic resonance imaging that the mechanism of joint cracking is related to cavity formation rather than bubble collapse. In this study, ten metacarpophalangeal joints were studied by inserting the finger of interest into a flexible tube tightened around a length of cable used to provide long-axis traction. Before and after traction, static 3D T1-weighted magnetic resonance images were acquired. During traction, rapid cine magnetic resonance images were obtained from the joint midline at a rate of 3.2 frames per second until the cracking event occurred. As traction forces increased, real-time cine magnetic resonance imaging demonstrated rapid cavity inception at the time of joint separation and sound production after which the resulting cavity remained visible. Our results offer direct experimental evidence that joint cracking is associated with cavity inception rather than collapse of a pre-existing bubble. These observations are consistent with tribonucleation, a known process where opposing surfaces resist separation until a critical point where they then separate rapidly creating sustained gas cavities. Observed previously in vitro, this is the first in-vivo macroscopic demonstration of tribonucleation and as such, provides a new theoretical framework to investigate health outcomes associated with joint cracking. PMID:25875374

  1. Cavitation in ultrasound and shockwave therapy

    NASA Astrophysics Data System (ADS)

    Colonius, Tim

    2014-11-01

    Acoustic waves, especially high-intensity ultrasound and shock waves, are used for medical imaging and intra- and extra-corporeal manipulation of cells, tissue, and urinary calculi. Waves are currently used to treat kidney stone disease, plantar fasciitis, and bone nonunion, and they are being investigated as a technique to ablate cancer tumors and mediate drug delivery. In many applications, acoustic waves induce the expansion and collapse of preexisting or newly cavitating bubbles whose presence can either mediate the generation of localized stresses or lead to collateral damage, depending on how effectively they can be controlled. We describe efforts aimed at simulating the collapse of bubbles, both individually and in clusters, with the aim to characterize the induced mechanical stresses and strains. To simulate collapse of one or a few bubbles, compressible Euler and Navier-Stokes simulations of multi-component materials are performed with WENO-based shock and interface capturing schemes. Repetitive insonification generates numerous bubbles that are difficult to resolve numerically. Such clouds are also important in traditional engineering applications such as caveating hydrofoils. Models that incorporate the dynamics of an unresolved dispersed phase consisting of the bubble cloud are also developed. The results of several model problems including bubble collapse near rigid surfaces, bubble collapse near compliant surfaces and in small capillaries are analyzed. The results are processed to determine the potential for micron-sized preexisting gas bubbles to damage capillaries. The translation of the fundamental fluid dynamics into improvements in the design and clinical application of shockwave lithotripters will be discussed. NIH Grant PO1-DK043881.

  2. Transfection effect of microbubbles on cells in superposed ultrasound waves and behavior of cavitation bubble.

    PubMed

    Kodama, Tetsuya; Tomita, Yukio; Koshiyama, Ken-Ichiro; Blomley, Martin J K

    2006-06-01

    The combination of ultrasound and ultrasound contrast agents (UCAs) is able to induce transient membrane permeability leading to direct delivery of exogenous molecules into cells. Cavitation bubbles are believed to be involved in the membrane permeability; however, the detailed mechanism is still unknown. In the present study, the effects of ultrasound and the UCAs, Optison on transfection in vitro for different medium heights and the related dynamic behaviors of cavitation bubbles were investigated. Cultured CHO-E cells mixed with reporter genes (luciferase or beta-gal plasmid DNA) and UCAs were exposed to 1 MHz ultrasound in 24-well plates. Ultrasound was applied from the bottom of the well and reflected at the free surface of the medium, resulting in the superposition of ultrasound waves within the well. Cells cultured on the bottom of 24-well plates were located near the first node (displacement node) of the incident ultrasound downstream. Transfection activity was a function determined with the height of the medium (wave traveling distance), as well as the concentration of UCAs and the exposure time was also determined with the concentration of UCAs and the exposure duration. Survival fraction was determined by MTT assay, also changes with these values in the reverse pattern compared with luciferase activity. With shallow medium height, high transfection efficacy and high survival fraction were obtained at a low concentration of UCAs. In addition, capillary waves and subsequent atomized particles became significant as the medium height decreased. These phenomena suggested cavitation bubbles were being generated in the medium. To determine the effect of UCAs on bubble generation, we repeated the experiments using crushed heat-treated Optison solution instead of the standard microbubble preparation. The transfection ratio and survival fraction showed no additional benefit when ultrasound was used. These results suggested that cavitation bubbles created by the

  3. The making of a cavitation children's book

    NASA Astrophysics Data System (ADS)

    Henry de Frahan, Marc; Patterson, Brandon; Lazar, Erika

    2016-11-01

    Engaging young children in science is particularly important to future scientific endeavors. From thunderstorms to the waterpark, children are constantly exposed to the wonders of fluid dynamics. Among fluid phenomena, bubbles have always fascinated children. Yet some of the most exciting aspects of bubbles, such as cavitation, are scarcely known to non-experts. To introduce cavitation to a five year old audience, we wrote "Brooke Bubble Breaks Things", a children's book about the adventures of a cavitation bubble learning about all the things she could break. In this talk, we discuss how a children's book is made by walking through the steps involved in creating the book from concept to publication. We focus on strategies for successfully communicating a technical message while balancing entertainment and fidelity to nature. To provide parents, teachers, and young inquiring minds with a detailed explanation of the physics and applications of cavitation, we also created a website with detailed explanations, animations, and links to further information. We aim to convince the fluids community that writing picture books is an intellectually stimulating and fun way of communicating fluids principles and applications to children. ArtsEngine Microgrant at the University of Michigan.

  4. Relating xylem cavitation to transpiration in cotton

    USDA-ARS?s Scientific Manuscript database

    Acoustic emmisions (AEs) from xylem cavitation events are characteristic of transpiration processes. Even though a body of work employing AE exists with a large number of species, cotton and other agronomically important crops have either not been investigated, or limited information exists. A few s...

  5. Size scale effect in cavitation erosion

    NASA Technical Reports Server (NTRS)

    Rao, P. V.; Rao, B. C.; Buckley, D. H.

    1982-01-01

    An overview and data analyses pertaining to cavitation erosion size scale effects are presented. The exponents n in the power law relationship are found to vary from 1.7 to 4.9 for venturi and rotating disk devices supporting the values reported in the literature. Suggestions for future studies were made to arrive at further true scale effects.

  6. Cavitation and multiphase flow forum - 1987

    SciTech Connect

    Furuya, O

    1987-01-01

    These proceedings collect papers on cavitation phenomena. Topics include: multiphase flow, the two-phase water hammer in a nuclear power plant, phase separation of dispersed annular flow, liquid films, shock waves propagating through two-phase magnetic fluid, venturimeters, gas-particle flows, particle-wall interactions, and the evaluation of wear in centrifugal slurry pumps.

  7. Film temperatures in the presence of cavitation

    NASA Technical Reports Server (NTRS)

    Elrod, Harold G.; Vijayaraghavan, D.

    1995-01-01

    Numerical algorithms are developed and implemented for the treatment of laminar lubricating-film temperatures associated with cavitated regions. The reformation front, with its film-content discontinuity and flow reversal, is given special attention. Computational economy is achieved through the use of Lobatto-point locations for flow-property determinations.

  8. Hot spot conditions during cavitation in water

    SciTech Connect

    Didenko, Y.T.; McNamara, W.B. III; Suslick, K.S.

    1999-06-23

    Liquids irradiated with high-intensity ultrasound undergo acoustic cavitation--the formation, growth, and implosive collapse of bubbles. The energy stored during the growth of the bubble in the rarefaction phase of the acoustic field is released when the bubble violently collapses in the compression phase of the acoustic field, as acoustic noise, shock waves, chemical reactions, and the emission of light (sonoluminescence, SL). This violent collapse is predicted to generate a hot spot of thousands of Kelvin within the bubble, but, to date, there have been only a limited number of experimental measurements of the temperature of this hot spot. Although the SL of water has been studied for more than 50 years, the effective hot spot temperature during aqueous cavitation remains unresolved. Given the importance of aqueous cavitation (sonography and bioeffects of ultrasound, sonochemical remediation of aqueous pollutants, synthetic applications of sonochemistry, etc.), the authors decided to apply previous spectroscopic analysis of SL of nonaqueous liquids to aqueous solutions doped with small amounts of hydrocarbons. The authors have collected and analyzed excited-state C{sub 2} NBSL (multi-bubble sonoluminescence, light emission from the clouds of cavitating bubbles) spectra from mixtures of organic liquids in water at 20 kHz and find an effective emission temperature of 4,300 {+-} 200 K.

  9. A New Unsteady Model for Dense Cloud Cavitation in Cryogenic Fluids

    NASA Technical Reports Server (NTRS)

    Hosangadi, Ashvin; Ahuja, Vineet

    2005-01-01

    Contents include the following: Background on thermal effects in cavitation. Physical properties of hydrogen. Multi-phase cavitation with thermal effect. Solution procedure. Cavitation model overview. Cavitation source terms. New cavitation model. Source term for bubble growth. One equation les model. Unsteady ogive simulations: liquid nitrogen. Unsteady incompressible flow in a pipe. Time averaged cavity length for NACA15 flowfield.

  10. Cavitation-Induced Synthesis of Biogenic Molecules on Primordial Earth.

    PubMed

    Kalson, Natan-Haim; Furman, David; Zeiri, Yehuda

    2017-09-27

    Despite decades of research, how life began on Earth remains one of the most challenging scientific conundrums facing modern science. It is agreed that the first step was synthesis of organic compounds essential to obtain amino acids and their polymers. Several possible scenarios that could accomplish this step, using simple inorganic molecules, have been suggested and studied over the years. The present study examines, using atomistic reactive molecular dynamics simulations, the long-standing suggestion that natural cavitation in primordial oceans was a dominant mechanism of organic molecule synthesis. The simulations allow, for the first time, direct observation of the rich and complex sonochemistry occurring inside a collapsing bubble filled with water and dissolved gases of the early atmosphere. The simulation results suggest that dissolved CH4 is the most efficient carbon source to produce amino acids, while CO and CO2 lead to amino acid synthesis with lower yields. The efficiency of amino acid synthesis also depends on the nitrogen source used (i.e., N2, NH3) and on the presence of HCN. Moreover, cavitation may have contributed to the increase in concentration of NH3 in primordial oceans and to the production and liberation of molecular O2 into the early atmosphere. Overall, the picture that emerges from the simulations indicates that collapsing bubbles may have served as natural bioreactors in primordial oceans, producing the basic chemical ingredients required for the beginning of life.

  11. Treatment of cyanide containing wastewater using cavitation based approach.

    PubMed

    Jawale, Rajashree H; Gogate, Parag R; Pandit, Aniruddha B

    2014-07-01

    Industrial wastewater streams containing high concentrations of biorefractory materials like cyanides should ideally be treated at source. In the present work, degradation of potassium ferrocyanide (K4Fe(CN)6) as a model pollutant has been investigated using cavitational reactors with possible intensification studies using different approaches. Effect of different operating parameters such as initial concentration, temperature and pH on the extent of degradation using acoustic cavitation has been investigated. For the case of hydrodynamic cavitation, flow characteristics of cavitating device (venturi) have been established initially followed by the effect of inlet pressure and pH on the extent of degradation. Under the optimized set of operating parameters, the addition of hydrogen peroxide (ratio of K4Fe(CN)6:H2O2 varied from 1:1 to 1:30 mol basis) as process intensifying approach has been investigated. The present work has conclusively established that under the set of optimized operating parameters, cavitation can be effectively used for degradation of potassium ferrocyanide. The comparative study of hydrodynamic cavitation and acoustic cavitation suggested that hydrodynamic cavitation is more energy efficient and gives higher degradation as compared to acoustic cavitation for equivalent power/energy dissipation. The present work is the first one to report comparison of cavitation based treatment schemes for degradation of cyanide containing wastewaters.

  12. Controlled Cavitation to Augment SWL Stone Comminution: Mechanistic Insights In-Vitro

    PubMed Central

    Duryea, Alexander P.; Roberts, William W.; Cain, Charles A.; Hall, Timothy L.

    2013-01-01

    Stone comminution in shock wave lithotripsy (SWL) has been documented to result from mechanical stresses conferred directly to the stone, as well as the activity of cavitational microbubbles. Studies have demonstrated that the presence of this cavitation activity is crucial for stone subdivision; however, its exact role in the comminution process remains somewhat weakly defined, in part due to the fact that it is difficult to isolate the cavitational component from the shock waves themselves. In this study, we further explored the importance of cavitation in SWL stone comminution through the use of histotripsy ultrasound therapy. Histotripsy was utilized to target model stones designed to mimic the mid-range tensile fracture strength of naturally occurring cystine calculi with controlled cavitation at strategic time points in the SWL comminution process. All SWL was applied at a peak-positive pressure (p+) of 34 MPa and a peak-negative pressure (p−) of 8 MPa; a shock rate of 1 Hz was used. Histotripsy pulses had a p− of 33 MPa and were applied at a pulse repetition frequency (PRF) of 100 Hz. Ten model stones were sonicated in-vitro with each of five different treatment schemes: A. 10 minutes SWL (600 shocks) with 0.7 seconds of histotripsy interleaved between successive shocks (totaling to 42,000 pulses); B. 10 minutes SWL (600 shocks) followed by 10 minutes histotripsy applied in 0.7 second bursts (1 burst per second, totaling to 42,000 pulses); C. 10 minutes histotripsy applied in 0.7 second bursts (42,000 pulses) followed by 10 minutes SWL (600 shocks); D. 10 minutes SWL-only (600 shocks); E. 10 minutes histotripsy-only applied in 0.7 second bursts (42,000 pulses). Following sonication, debris was collected and sieved through 8, 6, 4, and 2 mm filters. It was found that SWL-only generated a broad range of fragment sizes, with an average of 14.9 ± 24.1% of the original stone mass remaining >8 mm. Histotripsy-only eroded the surface of stones to tiny

  13. Laser surface modification of stainless steels for cavitation erosion resistance

    NASA Astrophysics Data System (ADS)

    Kwok, Chi Tat

    1999-12-01

    Austenitic stainless steel UNS S31603 (Fe -17.6Cr -11.2Ni -2.5Mo -1.4Mn -0.4Si -0.03C) has higher pitting corrosion resistance but lower cavitation erosion resistance than that of UNS S30400. This is because of its lower tendency for strain induced martensitic transformation and higher stacking fault energy as compared with those of UNS S30400. In order to improve its cavitation erosion resistance, surface modification of S31603 was performed by laser surface melting and laser surface alloying using a 2-kW CW Nd-YAG laser and a 3-kW CW CO2 laser. For laser surface melting, austenitic stainless steel UNS S30400, super duplex stainless steel UNS S32760 and martensitic stainless steel UNS S42000 were also investigated for comparison purpose. For laser surface alloying, alloying materials including various elements (Co, Cr, Ni, Mo, Mn, Si & C), alloys (AlSiFe & NiCrSiB), ceramics (Si3N 4, SiC, Cr3C2, TiC, CrB & Cr2O 3) and alloys-ceramics (Co-WC, Ni-WC, Ni-Al2O3, Ni-Cr2C3) were used to modify the surface of S31603. The alloyed surface was achieved first by flame spraying or pre-placing of the alloy powder on the S31603 surface and then followed by laser surface remelting. The cavitation erosion characteristics of laser surface modified specimens in 3.5% NaCl solution at 23°C were studied by means of a 20-kHz ultrasonic vibrator at a peak-to-peak amplitude of 30 mum. In addition, their pitting corrosion behaviour was evaluated by electrochemical techniques. The microstructures, compositions, phase changes and damage mechanisms under cavitation erosion were investigated by optical microscopy, SEM, EDAX and X-ray diffractometry. Mechanical properties such as microhardness profile were also examined. The cavitation erosion resistance Re (reciprocal of the mean depth of penetration rate) of laser surface melted S31603 was found to be improved by 22% and was attributed to the existence of tensile residual stress. Improvement on the Re of S42000 was found to be 8.5 times

  14. Reversible Leaf Xylem Collapse: A Potential “Circuit Breaker” against Cavitation1[OPEN

    PubMed Central

    Zhang, Yong-Jiang; Rockwell, Fulton E.; Graham, Adam C.; Alexander, Teressa; Holbrook, N. Michele

    2016-01-01

    We report a novel form of xylem dysfunction in angiosperms: reversible collapse of the xylem conduits of the smallest vein orders that demarcate and intrusively irrigate the areoles of red oak (Quercus rubra) leaves. Cryo-scanning electron microscopy revealed gradual increases in collapse from approximately −2 MPa down to −3 MPa, saturating thereafter (to −4 MPa). Over this range, cavitation remained negligible in these veins. Imaging of rehydration experiments showed spatially variable recovery from collapse within 20 s and complete recovery after 2 min. More broadly, the patterns of deformation induced by desiccation in both mesophyll and xylem suggest that cell wall collapse is unlikely to depend solely on individual wall properties, as mechanical constraints imposed by neighbors appear to be important. From the perspective of equilibrium leaf water potentials, petioles, whose vessels extend into the major veins, showed a vulnerability to cavitation that overlapped in the water potential domain with both minor vein collapse and buckling (turgor loss) of the living cells. However, models of transpiration transients showed that minor vein collapse and mesophyll capacitance could effectively buffer major veins from cavitation over time scales relevant to the rectification of stomatal wrong-way responses. We suggest that, for angiosperms, whose subsidiary cells give up large volumes to allow large stomatal apertures at the cost of potentially large wrong-way responses, vein collapse could make an important contribution to these plants’ ability to transpire near the brink of cavitation-inducing water potentials. PMID:27733514

  15. Numerical investigation of three-dimensional cloud cavitation with special emphasis on collapse induced shock dynamics

    NASA Astrophysics Data System (ADS)

    Schnerr, Günter H.; Sezal, Ismail H.; Schmidt, Steffen J.

    2008-04-01

    The aim of the present investigation is to model and analyze compressible three-dimensional (3D) cavitating liquid flows with special emphasis on the detection of shock formation and propagation. We recently developed the conservative finite volume method CATUM (Cavitation Technische Universität München), which enables us to simulate unsteady 3D liquid flows with phase transition at all Mach numbers. The compressible formulation of the governing equations together with the thermodynamic closure relations are solved by a modified Riemann approach by using time steps down to nanoseconds. This high temporal resolution is necessary to resolve the wave dynamics that leads to acoustic cavitation as well as to detect regions of instantaneous high pressure loads. The proposed two-phase model based on the integral average properties of thermodynamic quantities is first validated against the solution of the Rayleigh-Plesset equation for the collapse of a single bubble. The computational fluid dynamics tool CATUM is then applied to the numerical simulation of the highly unsteady two-phase flow around a 3D twisted hydrofoil. This specific hydrofoil allows a detailed study of sheet and cloud cavitation structures related to 3D shock dynamics emerging from collapsing vapor regions. The time dependent development of vapor clouds, their shedding mechanism, and the resulting unsteady variation of lift and drag are discussed in detail. We identify instantaneous local pressure peaks of the order of 100bar, which are thought to be responsible for the erosive damage of the surface of the hydrofoil.

  16. Changes in cell morphology due to plasma membrane wounding by acoustic cavitation

    PubMed Central

    Schlicher, Robyn K.; Hutcheson, Joshua D.; Radhakrishna, Harish; Apkarian, Robert P.; Prausnitz, Mark R.

    2010-01-01

    Acoustic cavitation-mediated wounding (i.e., sonoporation) has great potential to improve medical and laboratory applications requiring intracellular uptake of exogenous molecules; however, the field lacks detailed understanding of cavitation-induced morphological changes in cells and their relative importance. Here, we present an in-depth study of the effects of acoustic cavitation on cells using electron and confocal microscopy coupled with quantitative flow cytometry. High resolution images of treated cells show that morphologically different types of blebs can occur after wounding conditions caused by ultrasound exposure as well as by mechanical shear and strong laser ablation. In addition, these treatments caused wound-induced non-lytic necrotic death resulting in cell bodies we call wound-derived perikarya (WD-P). However, only cells exposed to acoustic cavitation experienced ejection of intact nuclei and nearly instant lytic necrosis. Quantitative analysis by flow cytometry indicates that wound-derived perikarya are the dominant morphology of nonviable cells, except at the strongest wounding conditions, where nuclear ejection accounts for a significant portion of cell death after ultrasound exposure. PMID:20350691

  17. Stable cavitation induces increased cytoplasmic calcium in L929 fibroblasts exposed to 1-MHz pulsed ultrasound.

    PubMed

    Tsukamoto, Akira; Higashiyama, Satoru; Yoshida, Kenji; Watanabe, Yoshiaki; Furukawa, Katsuko S; Ushida, Takashi

    2011-12-01

    An increase in cytoplasmic calcium (Ca(2+) increase) is a second messenger that is often observed under ultrasound irradiation. We hypothesize that cavitation is a physical mechanism that underlies the increase in Ca(2+) in these experiments. To control the presence of cavitation, the wave type was controlled in a sonication chamber. One wave type largely contained a traveling wave (wave type A) while the other wave type largely contained a standing wave (wave type B). Fast Fourier transform (FFT) analysis of a sound field produced by the wave types ascertained that stable cavitation was present only under wave type A ultrasound irradiation. Under the two controlled wave types, the increase in Ca(2+) in L929 fibroblasts was observed with fluorescence imaging. Under wave type A ultrasound irradiation, an increase in Ca(2+) was observed; however, no increase in Ca(2+) was observed under wave type B ultrasound irradiation. We conclude that stable cavitation is involved in the increase of Ca(2+) in cells subjected to pulsed ultrasound.

  18. Shock wave and cavitation bubble measurements of ultrashort-pulse laser-induced breakdown in water

    NASA Astrophysics Data System (ADS)

    Hammer, Daniel X.; Thomas, Robert J.; Frenz, Martin; Jansen, E. Duco; Noojin, Gary D.; Diggs, Sarah J.; Noack, Joachim; Vogel, Alfred; Rockwell, Benjamin A.

    1996-05-01

    Laser-induced breakdown (LIB) has long been used in ophthalmic microsurgery as a mechanism for disruption of tissue. The goal of this surgery has been precise tissue cutting by plasma formation and a minimization of collateral damage due to shock wave and cavitation bubble formation. We investigate the strength of the shock wave emission, the size of the cavitation bubble, and the amount of plasma shielding to determine the efficacy of using femtosecond pulses in surgery to reduce collateral photoacoustic damage. A pump-probe technique is used to image the time-resolved evolution of the cavitation bubble produced by focused laser pulses with pulsewidths of 130 fs, 300 fs, 3 ps, and 60 ps. Simultaneously, a hydrophone is used to measure the pressure response generated by the initial plasma shock wave and subsequent shock waves generated by the collapse and rebound of the cavitation bubbles. In addition, transmission measurements are made which indicate the amount of energy shielded beyond the focus by the plasma. These measurements give a good indication of the degree to which collateral damage may be reduced as the pulsewidths is decreased from the picosecond to the femtosecond time regime.

  19. Study of cavitation bubble dynamics during Ho:YAG laser lithotripsy by high-speed camera

    NASA Astrophysics Data System (ADS)

    Zhang, Jian J.; Xuan, Jason R.; Yu, Honggang; Devincentis, Dennis

    2016-02-01

    Although laser lithotripsy is now the preferred treatment option for urolithiasis, the mechanism of laser pulse induced calculus damage is still not fully understood. This is because the process of laser pulse induced calculus damage involves quite a few physical and chemical processes and their time-scales are very short (down to sub micro second level). For laser lithotripsy, the laser pulse induced impact by energy flow can be summarized as: Photon energy in the laser pulse --> photon absorption generated heat in the water liquid and vapor (super heat water or plasma effect) --> shock wave (Bow shock, acoustic wave) --> cavitation bubble dynamics (oscillation, and center of bubble movement , super heat water at collapse, sonoluminscence) --> calculus damage and motion (calculus heat up, spallation/melt of stone, breaking of mechanical/chemical bond, debris ejection, and retropulsion of remaining calculus body). Cavitation bubble dynamics is the center piece of the physical processes that links the whole energy flow chain from laser pulse to calculus damage. In this study, cavitation bubble dynamics was investigated by a high-speed camera and a needle hydrophone. A commercialized, pulsed Ho:YAG laser at 2.1 mu;m, StoneLightTM 30, with pulse energy from 0.5J up to 3.0 J, and pulse width from 150 mu;s up to 800 μs, was used as laser pulse source. The fiber used in the investigation is SureFlexTM fiber, Model S-LLF365, a 365 um core diameter fiber. A high-speed camera with frame rate up to 1 million fps was used in this study. The results revealed the cavitation bubble dynamics (oscillation and center of bubble movement) by laser pulse at different energy level and pulse width. More detailed investigation on bubble dynamics by different type of laser, the relationship between cavitation bubble dynamics and calculus damage (fragmentation/dusting) will be conducted as a future study.

  20. Effect of hydrodynamic cavitation in the tissue erosion by pulsed high-intensity focused ultrasound (pHIFU).

    PubMed

    Zhou, Yufeng; Gao, Xiaobin Wilson

    2016-09-21

    High-intensity focused ultrasound (HIFU) is emerging as an effective therapeutic modality in clinics. Besides the thermal ablation, tissue disintegration is also possible because of the interaction between the distorted HIFU bursts and either bubble cloud or boiling bubble. Hydrodynamic cavitation is another type of cavitation and has been employed widely in industry, but its role in mechanical erosion to tissue is not clearly known. In this study, the bubble dynamics immediately after the termination of HIFU exposure in the transparent gel phantom was captured by high-speed photography, from which the bubble displacement towards the transducer and the changes of bubble size was quantitatively determined. The characteristics of hydrodynamic cavitation due to the release of the acoustic radiation force and relaxation of compressed surrounding medium were found to associate with the number of pulses delivered and HIFU parameters (i.e. pulse duration and pulse repetition frequency). Because of the initial big bubble (~1 mm), large bubble expansion (up to 1.76 folds), and quick bubble motion (up to ~1 m s(-1)) hydrodynamic cavitation is significant after HIFU exposure and may lead to mechanical erosion. The shielding effect of residual tiny bubbles would reduce the acoustic energy delivered to the pre-existing bubble at the focus and, subsequently, the hydrodynamic cavitation effect. Tadpole shape of mechanical erosion in ex vivo porcine kidney samples was similar to the contour of bubble dynamics in the gel. Liquefied tissue was observed to emit towards the transducer through the punctured tissue after HIFU exposure in the sonography. In summary, the release of HIFU exposure-induced hydrodynamic cavitation produces significant bubble expansion and motion, which may be another important mechanism of tissue erosion. Understanding its mechanism and optimizing the outcome would broaden and enhance HIFU applications.

  1. Effect of hydrodynamic cavitation in the tissue erosion by pulsed high-intensity focused ultrasound (pHIFU)

    NASA Astrophysics Data System (ADS)

    Zhou, Yufeng; Gao, Xiaobin Wilson

    2016-09-01

    High-intensity focused ultrasound (HIFU) is emerging as an effective therapeutic modality in clinics. Besides the thermal ablation, tissue disintegration is also possible because of the interaction between the distorted HIFU bursts and either bubble cloud or boiling bubble. Hydrodynamic cavitation is another type of cavitation and has been employed widely in industry, but its role in mechanical erosion to tissue is not clearly known. In this study, the bubble dynamics immediately after the termination of HIFU exposure in the transparent gel phantom was captured by high-speed photography, from which the bubble displacement towards the transducer and the changes of bubble size was quantitatively determined. The characteristics of hydrodynamic cavitation due to the release of the acoustic radiation force and relaxation of compressed surrounding medium were found to associate with the number of pulses delivered and HIFU parameters (i.e. pulse duration and pulse repetition frequency). Because of the initial big bubble (~1 mm), large bubble expansion (up to 1.76 folds), and quick bubble motion (up to ~1 m s-1) hydrodynamic cavitation is significant after HIFU exposure and may lead to mechanical erosion. The shielding effect of residual tiny bubbles would reduce the acoustic energy delivered to the pre-existing bubble at the focus and, subsequently, the hydrodynamic cavitation effect. Tadpole shape of mechanical erosion in ex vivo porcine kidney samples was similar to the contour of bubble dynamics in the gel. Liquefied tissue was observed to emit towards the transducer through the punctured tissue after HIFU exposure in the sonography. In summary, the release of HIFU exposure-induced hydrodynamic cavitation produces significant bubble expansion and motion, which may be another important mechanism of tissue erosion. Understanding its mechanism and optimizing the outcome would broaden and enhance HIFU applications.

  2. Study of Traverse Speed Effects on Residual Stress State and Cavitation Erosion Behavior of Arc-Sprayed Aluminum Bronze Coatings

    NASA Astrophysics Data System (ADS)

    Hauer, Michél; Henkel, Knuth Michael; Krebs, Sebastian; Kroemmer, Werner

    2017-01-01

    Within a research project regarding cavitation erosion-resistant coatings, arc spraying was used with different traverse speeds to influence heat transfer and the resulting residual stress state. The major reason for this study is the lack of knowledge concerning the influence of residual stress distribution on mechanical properties and coating adhesion, especially with respect to heterogeneous aluminum bronze alloys. The materials used for spray experiments were the highly cavitation erosion-resistant propeller alloys CuAl9Ni5Fe4Mn (Ni-Al-Bronze) and CuMn13Al8Fe3Ni2 (Mn-Al-Bronze). Analyses of cavitation erosion behavior were carried out to evaluate the suitability for use in marine environments. Further microstructural, chemical and mechanical analyses were realized to examine adhesive and cohesive coating properties. Residual stress distribution was measured by modified hole drilling method using electronic speckle pattern interferometry (ESPI). It was found that the highest traverse speed led to higher tensile residual stresses near the surface and less cavitation erosion resistance of the coatings. Moreover, high oxygen affinity of main alloying element aluminum was identified to severely influence the microstructures by the formation of large oxides and hence the coating properties. Overall, Mn-Al-Bronze coatings showed lower residual stresses, a more homogeneous pore and oxide distribution and less material loss by cavitation than Ni-Al-Bronze coatings.

  3. Cavitation and non-cavitation regime for large-scale ultrasonic standing wave particle separation systems--In situ gentle cavitation threshold determination and free radical related oxidation.

    PubMed

    Johansson, Linda; Singh, Tanoj; Leong, Thomas; Mawson, Raymond; McArthur, Sally; Manasseh, Richard; Juliano, Pablo

    2016-01-01

    We here suggest a novel and straightforward approach for liter-scale ultrasound particle manipulation standing wave systems to guide system design in terms of frequency and acoustic power for operating in either cavitation or non-cavitation regimes for ultrasound standing wave systems, using the sonochemiluminescent chemical luminol. We show that this method offers a simple way of in situ determination of the cavitation threshold for selected separation vessel geometry. Since the pressure field is system specific the cavitation threshold is system specific (for the threshold parameter range). In this study we discuss cavitation effects and also measure one implication of cavitation for the application of milk fat separation, the degree of milk fat lipid oxidation by headspace volatile measurements. For the evaluated vessel, 2 MHz as opposed to 1 MHz operation enabled operation in non-cavitation or low cavitation conditions as measured by the luminol intensity threshold method. In all cases the lipid oxidation derived volatiles were below the human sensory detection level. Ultrasound treatment did not significantly influence the oxidative changes in milk for either 1 MHz (dose of 46 kJ/L and 464 kJ/L) or 2 MHz (dose of 37 kJ/L and 373 kJ/L) operation.

  4. Detection of Xylem Cavitation in Corn under Field Conditions 1

    PubMed Central

    Tyree, Melvin T.; Fiscus, Edwin L.; Wullschleger, S. D.; Dixon, M. A.

    1986-01-01

    We report the detection of cavitation events in corn (Zea mays) plants growing under field conditions in Greeley, CO. To our knowledge this study reports the first successful attempt to monitor continuously for long periods the cavitation events of a crop plant using acoustic detection techniques. Cavitation events occur in corn plants using acoustic detection techniques. Cavitation events occur in corn plants irrigated daily when the xylem pressure potentials fall below about −1.0 megapascals. In unirrigated corn we estimate that approximately half of all vessels cavitate on any one day when xylem pressure potentials fall below about −1.8 megapascals. We postulate that root pressure developed every night in irrigated and unirrigated corn is adequate to rejoin cavitated water columns. PMID:16665075

  5. Compressive spherical beamforming for localization of incipient tip vortex cavitation.

    PubMed

    Choo, Youngmin; Seong, Woojae

    2016-12-01

    Noises by incipient propeller tip vortex cavitation (TVC) are generally generated at regions near the propeller tip. Localization of these sparse noises is performed using compressive sensing (CS) with measurement data from cavitation tunnel experiments. Since initial TVC sound radiates in all directions as a monopole source, a sensing matrix for CS is formulated by adopting spherical beamforming. CS localization is examined with known source acoustic measurements, where the CS estimated source position coincides with the known source position. Afterwards, CS is applied to initial cavitation noise cases. The result of cavitation localization was detected near the upper downstream area of the propeller and showed less ambiguity compared to Bartlett spherical beamforming. Standard constraint in CS was modified by exploiting the physical features of cavitation to suppress remaining ambiguity. CS localization of TVC using the modified constraint is shown according to cavitation numbers and compared to high-speed camera images.

  6. PIV Analysis of Cavitation Flow Characteristics of He II

    SciTech Connect

    Harada, K.; Murakami, M.

    2006-04-27

    In the present experimental study cavitation phenomena in both He I and He II flows were investigated through the application of the PIV technique and visual observation under the saturated vapor pressure condition. The cavitation flow was generated in the downstream regions of a Venturi channel and a converging jet nozzle driven by a contracting metal bellows. It is seen that cavitation inception is a kind of stochastic process and has definite temperature dependence. The spatial distribution of the cavitation bubble velocity is measured by using the PIV technique. Some differences in the cavitating flow pattern and the void fraction are found between He II and He I cavitating flows. The PIV result indicates that the void fraction for He II flow is larger than that for He I flow.

  7. Cavitation measurement during sonic and ultrasonic activated irrigation.

    PubMed

    Macedo, Ricardo; Verhaagen, Bram; Rivas, David Fernandez; Versluis, Michel; Wesselink, Paul; van der Sluis, Luc

    2014-04-01

    The aims of this study were to quantify and to visualize the possible occurrence of transient cavitation (bubble formation and implosion) during sonic and ultrasonic (UAI) activated irrigation. The amount of cavitation generated around several endodontic instruments was measured by sonochemiluminescence dosimetry inside 4 root canal models of human dimensions and varying complexity. Furthermore, the spatial distribution of the sonochemiluminescence in the root canal was visualized with long-exposure photography. Instrument oscillation frequency, ultrasonic power, and file taper influenced the occurrence and amount of cavitation. In UAI, cavitation was distributed between the file and the wall extending beyond the file and inside lateral canals/isthmuses. In sonic activated irrigation, no cavitation was detected. Cavitation was shown to occur in UAI at clinically relevant ultrasonic power settings in both straight and curved canals but not around sonically oscillating instruments, driven at their highest frequency. Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  8. U-shaped Vortex Structures in Large Scale Cloud Cavitation

    NASA Astrophysics Data System (ADS)

    Cao, Yantao; Peng, Xiaoxing; Xu, Lianghao; Hong, Fangwen

    2015-12-01

    The control of cloud cavitation, especially large scale cloud cavitation(LSCC), is always a hot issue in the field of cavitation research. However, there has been little knowledge on the evolution of cloud cavitation since it is associated with turbulence and vortex flow. In this article, the structure of cloud cavitation shed by sheet cavitation around different hydrofoils and a wedge were observed in detail with high speed camera (HSC). It was found that the U-shaped vortex structures always existed in the development process of LSCC. The results indicated that LSCC evolution was related to this kind of vortex structures, and it may be a universal character for LSCC. Then vortex strength of U-shaped vortex structures in a cycle was analyzed with numerical results.

  9. Negative capillary-pressure-induced cavitation probability in nanochannels

    NASA Astrophysics Data System (ADS)

    Zhang, Ruijing; Ikoma, Yoshifumi; Motooka, Teruaki

    2010-03-01

    The capillarity-induced negative pressure of water flow has been investigated in nanochannels of a rectangular cross section by using computational fluid dynamics (CFD) simulation. As a consequent effect of negative pressure, the cavitation probability has been analyzed numerically. The numerical relation between the critical radius of cavitation (Rc) and geometrical characteristics of channels shows that cavitation does not occur in channels of uniform cross section (UCS), since 2Rc is larger than the smallest dimension of the channel. However, it may occur in channels of non-uniform cross section (NUCS), except for planar or high aspect ratio channels. The inequality in height and width is favorable for the absence of cavitation. The findings can also be applied to channels of elliptical or circular cross section. The results show the influence of geometrical characteristics of channels on the cavitation probability, which is important to engineer the channel geometrical structure in order to avoid undesirable filling problem 'cavitation' during the flow process.

  10. Hydrodynamic cavitation in Stokes flow of anisotropic fluids

    NASA Astrophysics Data System (ADS)

    Stieger, Tillmann; Agha, Hakam; Schoen, Martin; Mazza, Marco G.; Sengupta, Anupam

    2017-05-01

    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.

  11. Numerical and Experimental Study on Unsteady Shedding of Partial Cavitation

    NASA Astrophysics Data System (ADS)

    Ji, Bin; Luo, Xianwu; Wu, Yulin; Peng, Xiaoxing; Xu, Hongyuan

    Periodically unsteady shedding of partial cavity and forming of cavitation cloud have a great influence on hydraulic performances and cavitation erosion for ship propellers and hydro machines. In the present study, the unsteady cavitating flow around a hydrofoil has been calculated by using the single fluid approach with a developed cavitation mass transfer expression based on the vaporization and condensation of the fluid. The numerical simulation depicted the unsteady shedding of partial cavity, such as the process of cavity developing, breaking off and collapsing in the downstream under the steady incoming flow condition. It is noted that good agreement between the numerical results and that of experiment conducted at a cavitation tunnel is achieved. The cavitating flow field indicates that the cavity shedding was mainly caused by the re-entrant jet near cavity trailing edge, which was also clearly recorded by high-speed photographing.

  12. Use of ultrasonics in shear layer cavitation control.

    PubMed

    Chatterjee, Dhiman

    2003-08-01

    In this paper we report results from some investigations on the use of ultrasonics in controlling hydrodynamic cavitation in the shear layer downstream of a sudden expansion. Control of this type of cavitation has been achieved by modulating the local pressure that was experienced by a nucleus present in the shear layer. This modulation was made possible by using a piezoelectric device, termed as Ultrasonic Pressure Modulator (UPM). The performance of UPM has been studied at different dissolved gas concentrations with electrolysis bubbles as nuclei. Control of cavitation due to natural nuclei has also been attempted. Efficiency of UPM, in reducing cavitation, was seen to be dependent on the driving frequency employed. Experimental and numerical studies have been conducted to bring out the physics behind this approach of cavitation control. Different measures of cavitation control have been identified and some possible applications of this method have also been outlined.

  13. Variations of bubble cavitation and temperature elevation during lesion formation by high-intensity focused ultrasound.

    PubMed

    Zhou, Yufeng; Gao, Xiaobin Wilson

    2013-08-01

    High-intensity focused ultrasound (HIFU) is emerging as an effective therapeutic modality in both thermal ablations for solid tumor/cancer and soft-tissue fragmentation. Mechanical and thermal effects, which play an important role in the HIFU treatment simultaneously, are dependent on the operating parameters and may vary with the progress of therapy. Mechanical erosion in the shape of a "squid," a "dumbbell" lesion with both mechanical and thermal lesions, or a "tadpole" lesion with mechanical erosion at the center and thermal necrosis on the boundary in the transparent gel phantom could be produced correspondingly with the pulse duration of 5-30 ms, which is much longer than histotripsy burst but shorter than the time for tissue boiling, and pulse repetition frequency (PRF) of 0.2-5 Hz. Meanwhile, variations of bubble cavitation (both inertial and stable cavitation) and temperature elevation in the focal region (i.e., z = -2.5, 0, and 2.5 mm) were measured by passive cavitation detection (PCD) and thermocouples during the therapeutic procedure, respectively. Stable cavitation increased with the pulse duration, PRF, and the number of pulses delivered. However, inertial cavitation was found to increase initially and then decrease with long pulse duration and high PRF. Temperature in the pre-focal region is always higher than those at the focal and post-focal position in all tests. Great variations of PCD signals and temperature elevation are due to the generation and persistence of large bubble, which is resistant to collapse and occurs with the increase of pulse duration and PRF. Similar lesion pattern and variations were also observed in ex vivo porcine kidneys. Hyperechoes in the B-mode ultrasound image were comparable to the shape and size of lesions in the dissected tissue. Thermal lesion volume increased with the increase of pulse duration and PRF, but mechanical erosion reached its maximum volume with the pulse duration of 20 ms and PRF of 1

  14. Application of the "Full Cavitation Model" to the fundamental study of cavitation in liquid metal processing

    NASA Astrophysics Data System (ADS)

    Lebon, G. S. B.; Pericleous, K.; Tzanakis, I.; Eskin, D.

    2015-01-01

    Ultrasonic cavitation treatment of melt significantly improves the downstream properties and quality of conventional and advanced metallic materials. However, the transfer of this technology has been hindered by difficulties in treating large volumes of liquid metal. To improve the understanding of cavitation processing efficiency, the Full Cavitation Model, which is derived from a reduced form of the Rayleigh-Plesset equation, is modified and applied to the two-phase problem of bubble propagation in liquid melt. Numerical simulations of the sound propagation are performed in the microsecond time scale to predict the maximum and minimum acoustic pressure amplitude fields in the domain. This field is applied to the source term of the bubble transport equation to predict the generation and destruction of cavitation bubbles in a time scale relevant to the fluid flow. The use of baffles to limit flow speed in a launder conduit is studied numerically, to determine the optimum configuration that maximizes the residence time of the liquid in high cavitation activity regions. With this configuration, it is then possible to convert the batch processing of liquid metal into a continuous process. The numerical simulations will be validated against water and aluminium alloy experiments, carried out at Brunel University.

  15. Time-evolving statistics of cavitation damage on metallic surfaces.

    PubMed

    Diodati, P; Marchesoni, F

    2002-11-01

    The statistics of surface damage on polycrystalline aluminium plates caused by acoustic cavitation is studied experimentally as a function of time. Cavitation is shown to produce a uniform distribution of crater-like holes with different depth, area and eccentricity. Most notably, the size distribution of such craters evolves with time from a gamma function into a power law. By contrast, on the surface of a martensitic Cu-Ni-Al crystal cavitation damage generates ramified patterns, reminiscent of a fractal object.

  16. L-Area Cavitation Tests Final Analysis - Limits Application

    SciTech Connect

    Wood, D.C.

    2001-06-26

    The L-Area cavitation test was designed to better define the onset of cavitation in the reactor system. The onset of gas evolution in the effluent piping and pump cavitation was measured using state-of-the-art equipment to provide data with a high confidence and low uncertainty level. The limits calculated from the new data will allow an approximate two percent increase in reactor power if the reactor is effluent temperature-limited with no compromise in reactor safety.

  17. Inverse Analysis of Cavitation Impact Phenomena on Structures

    DTIC Science & Technology

    2007-07-02

    Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6390--07-9051 Inverse Analysis of Cavitation Impact Phenomena on Structures July 2, 2007...ABSTRACT c. THIS PAGE 18. NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Inverse Analysis of Cavitation Impact Phenomena on Structures S.G. Lambrakos and N.E...signature analysis A general methodology is presented for in situ detection of cavitation impact phenomena on structures based on inverse analysis of

  18. Excitation of cavitation bubbles in low-temperature liquid nitrogen

    NASA Astrophysics Data System (ADS)

    Sasaki, Koichi; Harada, Shingo

    2017-06-01

    We excited a cavitation bubble by irradiating a Nd:YAG laser pulse onto a titanium target that was installed in liquid nitrogen at a temperature below the boiling point. To our knowledge, this is the first experiment in which a cavitation bubble has been successfully excited in liquid nitrogen. We compared the cavitation bubble in liquid nitrogen with that in water on the basis of an equation reported by Florschuetz and Chao [J. Heat Transfer 87, 209 (1965)].

  19. Experiments in thermosensitive cavitation of a cryogenic rocket propellant surrogate

    NASA Astrophysics Data System (ADS)

    Kelly, Sean Benjamin

    Cavitation is a phase-change phenomenon that may appear in practical devices, often leading to loss of performance and possible physical damage. Of particular interest is the presence of cavitation in rocket engine pumps as the cryogenic fluids cavitate in impellers and inducers. Unlike water, which has been studied exhaustively, cryogenic fluids undergo cavitation with significant thermal effect. Past attempts at analyzing this behavior in water have led to poor predictive capability due to the lack of data in the regime defined as thermosensitive cavitation. Fluids flowing near their thermodynamic critical point have a liquid-vapor density ratio that is orders of magnitude less than typical experimental fluids, so that the traditional equation-of-state and cavitation models do not apply. Thermal effects in cavitation have not been fully investigated due to experimental difficulties handling cryogenics. This work investigates the physical effects of thermosensitive cavitation in a model representative of a turbopump inducer in a modern rocket engine. This is achieved by utilizing a room-temperature testing fluid that exhibits a thermal effect equivalent to that experienced by cryogenic propellants. Unsteady surface pressures and high speed imaging collected over the span of thermophysical regimes ranging from thermosensitive to isothermal cavitation offer both quantitative and qualitative insight into the physical process of thermal cavitation. Physical and thermodynamic effects are isolated to identify the source of cavity conditions, oscillations and growth/collapse behavior. Planar laser imaging offers an instantaneous look inside the vapor cavity and at the behavior of the boundary between the two-phase region and freestream liquid. Nondimensional parameters are explored, with cavitation numbers, Reynolds Numbers, coefficient of pressure and nondimensional temperature in a broad range. Results in the form of cavitation regime maps, Strouhal Number of cavity

  20. Cavitation-based hydro-fracturing simulator

    SciTech Connect

    Wang, Jy-An John; Wang, Hong; Ren, Fei; Cox, Thomas S.

    2016-11-22

    An apparatus 300 for simulating a pulsed pressure induced cavitation technique (PPCT) from a pressurized working fluid (F) provides laboratory research and development for enhanced geothermal systems (EGS), oil, and gas wells. A pump 304 is configured to deliver a pressurized working fluid (F) to a control valve 306, which produces a pulsed pressure wave in a test chamber 308. The pulsed pressure wave parameters are defined by the pump 304 pressure and control valve 306 cycle rate. When a working fluid (F) and a rock specimen 312 are included in the apparatus, the pulsed pressure wave causes cavitation to occur at the surface of the specimen 312, thus initiating an extensive network of fracturing surfaces and micro fissures, which are examined by researchers.

  1. Cavitation in liquid cryogens. 3: Ogives

    NASA Technical Reports Server (NTRS)

    Hord, J.

    1973-01-01

    Experimental results for three, scaled, quarter-caliber ogives are given. Both desinent and developed cavity data, using liquid hydrogen and liquid nitrogen, are reported. The desinent data do not exhibit a consistent ogive size effect, but the developed cavity data were consistently influenced by ogive size; B-factor increases with increasing ogive diameter. The developed cavity data indicated that stable thermodynamic equilibrium exists throughout the vaporous cavities. These data were correlated by using the extended theory derived in NASA-CR-2156 (volume II of this report series). The new correlating parameter MTWO, improves data correlation for the ogives, hydrofoil, and venturi and appears attractive for future predictive applications. The cavitation coefficient and equipment size effects are shown to vary with specific equipment-fluid combinations. A method of estimating cavitation coefficient from knowledge of the noncavitating pressure coefficient is suggested.

  2. Transient cavitation in fluid-structure interactions

    SciTech Connect

    Kot, C.A.; Hsieh, B.J.; Youngdahl, C.K.; Valentin, R.A.

    1981-11-01

    A generalized column separation model is extended to predict transient cavitation associated with fluid-structure interactions. The essential feature of the combined fluid-structure interaction calculations is the coupling between the fluid transient, which is computed one dimensionally, and the structural response which can be multidimensional. Proper coupling is achieved by defining an average, one-dimensional, structural velocity and by assuming a spatially uniform pressure loading of the structure. This procedure is found to be effective even for complex finite element structural models for which the required computational time step is orders of magnitude smaller than that for the fluid transient. Computational examples and comparison with experimental data show that neglecting cavitation and setting the fluid velocity at all times equal to that of the structural boundary leads to unreal negative pressure predictions. A properly coupled column separation model reproduces the important features of fluid-structure interactions, converges rapidly, and gives reasonable fluid and structural response predictions. 9 refs.

  3. Laser-induced cavitation based micropump.

    PubMed

    Dijkink, Rory; Ohl, Claus-Dieter

    2008-10-01

    Lab-on-a-chip devices are in strong demand as versatile and robust pumping techniques. Here, we present a cavitation based technique, which is able to pump a volume of 4000 microm3 within 75 micros against an estimated pressure head of 3 bar. The single cavitation event is created by focusing a laser pulse in a conventional PDMS microfluidic chip close to the channel opening. High-speed photography at 1 million frames s(-1) resolves the flow in the supply channel, pump channel, and close to the cavity. The elasticity of the material affects the overall fluid flow. Continuous pumping at repetition rates of up to 5 Hz through 6 mm long square channels of 20 microm width is shown. A parameter study reveals the key-parameters for operation: the distance between the laser focus and the channel, the maximum bubble size, and the chamber geometry.

  4. Numerical simulation of cavitating flows under uncertainty

    NASA Astrophysics Data System (ADS)

    Rodio, M. G.; Abgrall, R.; Congedo, P. M.

    2017-03-01

    Cavitation is characterized by vapor bubbles creation in the liquid phase as a consequence of a pressure drop. This phenomenon can be reproduced by means of several two-phase models. An equation of state is commonly used in order to define the thermophysical properties of the two fluids and to close the model. The aim of this work is to study how the uncertain parameters of the equation of state (EOS) can influence the prediction of the cavitation structures. These uncertainties are propagated through a two-phase numerical solver for evaluating the impact on the predictive character of the numerical solution. The variability of the mixture velocity and the mixture pressure are analyzed.

  5. Bubble Dynamics and Cavitation Inception Theory.

    DTIC Science & Technology

    1986-07-30

    appearing in the forcing function, with the result that this problem involves only a soft excitation. Expanding the forced Rayleigh - Plesset equation and...Expanding the forced Rayleigh - Plesset equation and its initial conditions to the second order in 6, we find that the zeroth-order problem is the well...involves only an ordinary pulsed (e) This interaction causes the cavitation Rayleigh - Plesset differential equation. bubble to be removed from the

  6. Impact of acoustic cavitation on food emulsions.

    PubMed

    Krasulya, Olga; Bogush, Vladimir; Trishina, Victoria; Potoroko, Irina; Khmelev, Sergey; Sivashanmugam, Palani; Anandan, Sambandam

    2016-05-01

    The work explores the experimental and theoretical aspects of emulsification capability of ultrasound to deliver stable emulsions of sunflower oil in water and meat sausages. In order to determine optimal parameters for direct ultrasonic emulsification of food emulsions, a model was developed based on the stability of emulsion droplets in acoustic cavitation field. The study is further extended to investigate the ultrasound induced changes to the inherent properties of raw materials under the experimental conditions of sono-emulsification.

  7. Some stochastic aspects of intergranular creep cavitation

    SciTech Connect

    Fariborz, S.J.; Farris, J.P.; Harlow, D.G.; Delph, T.J.

    1987-10-01

    We present some results obtained from a simplified stochastic model of intergranular creep cavitation. The probabilistic features of the model arise from the inclusion of random cavity placement on the grain boundary and time-discrete stochastic cavity nucleation. Among the predictions of the model are Weibull-distributed creep rupture failure times and a Weibull distribution of cavity radii. Both of these predictions have qualitative experimental support. 18 refs., 7 figs.

  8. Numerical Simulation of Cavitation in Ultrasound Field

    NASA Astrophysics Data System (ADS)

    Tamura, Yoshiaki; Tsurumi, Nobuo; Matsumoto, Yoichiro

    2011-09-01

    In the present paper, numerical simulation of cavitation in HIFU is proposed. The overning equations are 1) linearized acoustic wave equation (with/without attenuation) and 2) Rayleigh-Plesset equation (bubble volume motion equation). The two equations are coupled through pressure and void fraction. Pressure affects the motion of bubble and the void fraction changes the local density and the local sound speed. Some computed results are presented to show the validity of the present method.

  9. Numerical investigation of cavitation performance on bulb tubular turbine

    NASA Astrophysics Data System (ADS)

    Sun, L. G.; Guo, P. C.; Zheng, X. B.; Luo, X. Q.

    2016-05-01

    The cavitation flow phenomena may occur in the bulb tubular turbine at some certain operation conditions, which even decrease the performance of units and causes insatiably noise and vibration when it goes worse. A steady cavitating flow numerical simulations study is carried out on the bulb tubular unit with the same blade pitch angle and different guide vane openings by using the commercial code ANSYS CFX in this paper. The phenomena of cavitation induction areas and development process are obtained and draws cavitation performance curves. The numerical results show that the travelling bubble cavity is the main types of cavitation development over a wide operating range of discharge and this type of cavitation begins to sensitive to the value of cavitation number when the discharge exceeding a certain valve, in this condition, it can lead to a severe free bubble formation with the gradually decrement of cavitation number. The reported cavitation performance curves results indicate that the flow blockage incident would happen because of a mount of free bubble formation in the flow passage when the cavity developed to certain extend, which caused head drop behavior and power broken dramatically and influenced the output power.

  10. Cavitation inception on microparticles: a self-propelled particle accelerator.

    PubMed

    Arora, Manish; Ohl, Claus-Dieter; Mørch, Knud Aage

    2004-04-30

    Corrugated, hydrophilic particles with diameters between 30 and 150 microm are found to cause cavitation inception at their surfaces when they are exposed to a short, intensive tensile stress wave. The growing cavity accelerates the particle into translatory motion until the tensile stress decreases, and subsequently the particle separates from the cavity. The cavity growth and particle detachment are modeled by considering the momentum of the particle and the displaced liquid. The analysis suggests that all particles which cause cavitation are accelerated into translatory motion, and separate from the cavities they themselves nucleate. Thus, in the research of cavitation nuclei the link is established between developed cavitation bubbles and their origin.

  11. High Speed Imaging of Cavitation around Dental Ultrasonic Scaler Tips.

    PubMed

    Vyas, Nina; Pecheva, Emilia; Dehghani, Hamid; Sammons, Rachel L; Wang, Qianxi X; Leppinen, David M; Walmsley, A Damien

    2016-01-01

    Cavitation occurs around dental ultrasonic scalers, which are used clinically for removing dental biofilm and calculus. However it is not known if this contributes to the cleaning process. Characterisation of the cavitation around ultrasonic scalers will assist in assessing its contribution and in developing new clinical devices for removing biofilm with cavitation. The aim is to use high speed camera imaging to quantify cavitation patterns around an ultrasonic scaler. A Satelec ultrasonic scaler operating at 29 kHz with three different shaped tips has been studied at medium and high operating power using high speed imaging at 15,000, 90,000 and 250,000 frames per second. The tip displacement has been recorded using scanning laser vibrometry. Cavitation occurs at the free end of the tip and increases with power while the area and width of the cavitation cloud varies for different shaped tips. The cavitation starts at the antinodes, with little or no cavitation at the node. High speed image sequences combined with scanning laser vibrometry show individual microbubbles imploding and bubble clouds lifting and moving away from the ultrasonic scaler tip, with larger tip displacement causing more cavitation.

  12. High Speed Imaging of Cavitation around Dental Ultrasonic Scaler Tips

    PubMed Central

    Vyas, Nina; Pecheva, Emilia; Dehghani, Hamid; Sammons, Rachel L.; Wang, Qianxi X.; Leppinen, David M.; Walmsley, A. Damien

    2016-01-01

    Cavitation occurs around dental ultrasonic scalers, which are used clinically for removing dental biofilm and calculus. However it is not known if this contributes to the cleaning process. Characterisation of the cavitation around ultrasonic scalers will assist in assessing its contribution and in developing new clinical devices for removing biofilm with cavitation. The aim is to use high speed camera imaging to quantify cavitation patterns around an ultrasonic scaler. A Satelec ultrasonic scaler operating at 29 kHz with three different shaped tips has been studied at medium and high operating power using high speed imaging at 15,000, 90,000 and 250,000 frames per second. The tip displacement has been recorded using scanning laser vibrometry. Cavitation occurs at the free end of the tip and increases with power while the area and width of the cavitation cloud varies for different shaped tips. The cavitation starts at the antinodes, with little or no cavitation at the node. High speed image sequences combined with scanning laser vibrometry show individual microbubbles imploding and bubble clouds lifting and moving away from the ultrasonic scaler tip, with larger tip displacement causing more cavitation. PMID:26934340

  13. Prediction of cavitating flow noise by direct numerical simulation

    NASA Astrophysics Data System (ADS)

    Seo, Jung H.; Moon, Young J.; Shin, Byeong Rog

    2008-06-01

    In this study, a direct numerical simulation procedure for the cavitating flow noise is presented. The compressible Navier-Stokes equations are written for the two-phase fluid, employing a density-based homogeneous equilibrium model with a linearly-combined equation of state. To resolve the linear and non-linear waves in the cavitating flow, a sixth-order compact central scheme is utilized with the selective spatial filtering technique. The present cavitation model and numerical methods are validated for two benchmark problems: linear wave convection and acoustic saturation in a bubbly flow. The cavitating flow noise is then computed for a 2D circular cylinder flow at Reynolds number based on a cylinder diameter, 200 and cavitation numbers, σ=0.7-2. It is observed that, at cavitation numbers σ=1 and 0.7, the cavitating flow and noise characteristics are significantly changed by the shock waves due to the coherent collapse of the cloud cavitation in the wake. To verify the present direct simulation and further analyze the sources of cavitation noise, an acoustic analogy based on a classical theory of Fitzpatrik and Strasberg is derived. The far-field noise predicted by direct simulation is well compared with that of acoustic analogy, and it also confirms the f-2 decaying rate in the spectrum, as predicted by the model of Fitzpatrik and Strasberg with the Rayleigh-Plesset equation.

  14. Understanding Cavitation Intensity through Pitting and Pressure Pulse Analysis

    NASA Astrophysics Data System (ADS)

    Jayaprakash, A.; Singh, S.; Choi, J.-K.; Chahine, G.

    2011-11-01

    Cavitation erosion is of interest to the designers of ship propulsion devices because of its detrimental effects. One of the difficulties of predicting cavitation erosion is that the intensity of cavitation is not well predicted or defined. In this work we attempt to define the intensity of a cavitation erosion field through analysis of cavitation induced erosion pits and pressure pulses. In the pitting tests, material samples were subjected to cavitation field for a short duration of time selected within the test sample's incubation period, so that the test sample undergoes plastic deformation only. The sample material reacts to these cavitation events by undergoing localized permanent deformation, called pits. The resulting pitted sample surfaces were then optically scanned and analyzed. The pressure signals under cavitating jets and ultrasonic horns, for different conditions, were experimentally recorded using high frequency response pressure transducers. From the analysis of the pitting data and recorded pressure signals, we propose a model that describes the statistics, which in the future can be used to define the cavitation field intensity. Support for this work was provided by Office of Naval Research (ONR) under contract number N00014-08-C-0450, monitored by Dr. Ki-Han Kim.

  15. Acoustic methods for cavitation mapping in biomedical applications

    NASA Astrophysics Data System (ADS)

    Wan, M.; Xu, S.; Ding, T.; Hu, H.; Liu, R.; Bai, C.; Lu, S.

    2015-12-01

    In recent years, cavitation is increasingly utilized in a wide range of applications in biomedical field. Monitoring the spatial-temporal evolution of cavitation bubbles is of great significance for efficiency and safety in biomedical applications. In this paper, several acoustic methods for cavitation mapping proposed or modified on the basis of existing work will be presented. The proposed novel ultrasound line-by-line/plane-by-plane method can depict cavitation bubbles distribution with high spatial and temporal resolution and may be developed as a potential standard 2D/3D cavitation field mapping method. The modified ultrafast active cavitation mapping based upon plane wave transmission and reception as well as bubble wavelet and pulse inversion technique can apparently enhance the cavitation to tissue ratio in tissue and further assist in monitoring the cavitation mediated therapy with good spatial and temporal resolution. The methods presented in this paper will be a foundation to promote the research and development of cavitation imaging in non-transparent medium.

  16. Experimental Investigation of Cavitation Induced Feedline Instability from an Orifice

    NASA Technical Reports Server (NTRS)

    Hitt, Matthew A.; Lineberry, David M.; Ahuja, Vineet; Frederick, Robert A,

    2012-01-01

    This paper details the results of an experimental investigation into the cavitation instabilities created by a circular orifice conducted at the University of Alabama in Huntsville Propulsion Research Center. This experiment was conducted in concert with a computational simulation to serve as a reference point for the simulation. Testing was conducted using liquid nitrogen as a cryogenic propellant simulant. A 1.06 cm diameter thin orifice with a rounded inlet was tested in an approximately 1.25 kg/s flow with inlet pressures ranging from 504.1 kPa to 829.3 kPa. Pressure fluctuations generated by the orifice were measured using a high frequency pressure sensor located 0.64 tube diameters downstream of the orifice. Fast Fourier Transforms were performed on the high frequency data to determine the instability frequency. Shedding resulted in a primary frequency with a cavitation related subharmonic frequency. For this experiment, the cavitation instability ranged from 153 Hz to 275 Hz. Additionally, the strength of the cavitation occur red as a function of cavitation number. At lower cavitation numbers, the strength of the cavitation instability ranged from 2.4 % to 7 % of the inlet pressure. However, at higher cavitation numbers, the strength of the cavitation instability ranged from 0.6 % to 1 % of the inlet pressure.

  17. Propeller sheet cavitation noise source modeling and inversion

    NASA Astrophysics Data System (ADS)

    Lee, Keunhwa; Lee, Jaehyuk; Kim, Dongho; Kim, Kyungseop; Seong, Woojae

    2014-02-01

    Propeller sheet cavitation is the main contributor to high level of noise and vibration in the after body of a ship. Full measurement of the cavitation-induced hull pressure over the entire surface of the affected area is desired but not practical. Therefore, using a few measurements on the outer hull above the propeller in a cavitation tunnel, empirical or semi-empirical techniques based on physical model have been used to predict the hull-induced pressure (or hull-induced force). In this paper, with the analytic source model for sheet cavitation, a multi-parameter inversion scheme to find the positions of noise sources and their strengths is suggested. The inversion is posed as a nonlinear optimization problem, which is solved by the optimization algorithm based on the adaptive simplex simulated annealing algorithm. Then, the resulting hull pressure can be modeled with boundary element method from the inverted cavitation noise sources. The suggested approach is applied to the hull pressure data measured in a cavitation tunnel of the Samsung Heavy Industry. Two monopole sources are adequate to model the propeller sheet cavitation noise. The inverted source information is reasonable with the cavitation dynamics of the propeller and the modeled hull pressure shows good agreement with cavitation tunnel experimental data.

  18. An Experimental and Theoretical Study on Cavitating Propellers.

    DTIC Science & Technology

    1982-10-01

    between partially cavitating and 0 fully supercavitating conditions. Therefore, the? heat treated stainless steel 17 - 4PH was used for the center...ION 0@WN4AAOING t4. CHSTR$SUtOW STATEMENT (e tis Repa) Approved for public release; distribution unlimited 17 . OISTrIlUTION STATZMt 4"T (of the ae euet...cavitation number for a - 40 39 17 Lift coefficient vs. cavitation number for a = 60 40 18 Lift coefficient vs. cavitation number for a - 80 41 19 Drag

  19. Cavitation effects in ultrasonic cleaning baths

    NASA Technical Reports Server (NTRS)

    Glasscock, Barbara H.

    1995-01-01

    In this project, the effect of cavitation from aqueous ultrasonic cleaning on the surfaces of metal and non-metal sample coupons was studied. After twenty cleaning cycles, the mass loss from the aluminum coupons averaged 0.22 mg/sq cm surface area and 0.014 mg/sq cm for both stainless steel and titanium. The aluminum coupons showed visual evidence of minor cavitation erosion in regions of previously existing surface irregularities. The non-metal samples showed some periods of mass gain. These effects are believed to have minor impact on hardware being cleaned, but should be evaluated in the context of specific hardware requirements. Also the ultrasonic activity in the large cleaning baths was found to be unevenly distributed as measured by damage to sheets of aluminum foil. It is therefore recommended that items being cleaned in an ultrasonic bath be moved or conveyed during the cleaning to more evenly distribute the cavitation action provide more uniform cleaning.

  20. Computational fluid dynamic modelling of cavitation

    NASA Technical Reports Server (NTRS)

    Deshpande, Manish; Feng, Jinzhang; Merkle, Charles L.

    1993-01-01

    Models in sheet cavitation in cryogenic fluids are developed for use in Euler and Navier-Stokes codes. The models are based upon earlier potential-flow models but enable the cavity inception point, length, and shape to be determined as part of the computation. In the present paper, numerical solutions are compared with experimental measurements for both pressure distribution and cavity length. Comparisons between models are also presented. The CFD model provides a relatively simple modification to an existing code to enable cavitation performance predictions to be included. The analysis also has the added ability of incorporating thermodynamic effects of cryogenic fluids into the analysis. Extensions of the current two-dimensional steady state analysis to three-dimensions and/or time-dependent flows are, in principle, straightforward although geometrical issues become more complicated. Linearized models, however offer promise of providing effective cavitation modeling in three-dimensions. This analysis presents good potential for improved understanding of many phenomena associated with cavity flows.

  1. Multiscale Modeling of Cavitating Bubbly Flows

    NASA Astrophysics Data System (ADS)

    Ma, J.; Hsiao, C.-T.; Chahine, G. L.

    2013-03-01

    Modeling of cavitating bubbly flows is challenging due to the wide range of characteristic lengths of the physics at play: from micrometers (e.g., bubble nuclei radius) to meters (e.g., propeller diameter or sheet cavity length). To address this, we present here a multiscale approach which integrates a Discrete Bubble Model for dispersed microbubbles and a level set N-S solver for macro cavities, along with a mesoscale transition model to bridge the two. This approach was implemented in 3DYNAFScopyright and used to simulate sheet-to-cloud cavitation over a hydrofoil. The hybrid model captures well the full cavitation process starting from free field nuclei and nucleation from solid surfaces. In low pressure region of the foil small nuclei are seen to grow large and eventually merge to form a large scale sheet cavity. A reentrant jet forms under the cavity, travels upstream, and breaks it, resulting in a bubble cloud of a large amount of microbubbles as the broken pockets shrink and travel downstream. This is in good agreement with experimental observations based of sheet lengths and frequency of lift force oscillation. DOE-SBIR, ONR (monitored by Dr. Ki-Han Kim)

  2. Creep cavitation in 304 stainless steel

    SciTech Connect

    Chen, I.W.; Argon, A.S.

    1981-01-01

    Creep cavitation in 304 stainless steel at 0.5 T/sub m/ was investigated. Two specially developed techniques were used to study the nucleation and growth of grain-boundary cavities. It was found that cavities nucleated heterogeneously throughout the creep history and those observed were well in their growth stage. Comparison of these observations with the theory for cavity nucleation requires that a high interfacial stress be present. Experiments suggest that such stress concentrations are present in the early stages of boundary sliding, and in additional transients associated with intermittent sliding of boundaries throughout the creep life. It was found that microstructural variations such as those caused by twins which strongly affect initial particle densities on boundaries can alter cavitation behavior drastically. Our results also show that wedge cracks are the result of accelerated linking of growing cavities in the triple point region of stress concentration and are not a separate phenomenon. Furthermore, at higher strain rates growth of cavities can be accelerated by grain boundary sliding. Lastly, evidence is given to support the view that in engineering alloys which contain complex phas constitutents particularly along grain-boundaries, cavitation in long term service is likely to be caused by cavities nucleated in connection with a prior cold forming operation. 15 figures.

  3. Optic cavitation with CW lasers: A review

    NASA Astrophysics Data System (ADS)

    Padilla-Martinez, J. P.; Berrospe-Rodriguez, C.; Aguilar, G.; Ramirez-San-Juan, J. C.; Ramos-Garcia, R.

    2014-12-01

    The most common method to generate optic cavitation involves the focusing of short-pulsed lasers in a transparent liquid media. In this work, we review a novel method of optic cavitation that uses low power CW lasers incident in highly absorbing liquids. This novel method of cavitation is called thermocavitation. Light absorbed heats up the liquid beyond its boiling temperature (spinodal limit) in a time span of microseconds to milliseconds (depending on the optical intensity). Once the liquid is heated up to its spinodal limit (˜300 °C for pure water), the superheated water becomes unstable to random density fluctuations and an explosive phase transition to vapor takes place producing a fast-expanding vapor bubble. Eventually, the bubble collapses emitting a strong shock-wave. The bubble is always attached to the surface taking a semi-spherical shape, in contrast to that produced by pulsed lasers in transparent liquids, where the bubble is produced at the focal point. Using high speed video (105 frames/s), we study the bubble's dynamic behavior. Finally, we show that heat diffusion determines the water superheated volume and, therefore, the amplitude of the shock wave. A full experimental characterization of thermocavitation is described.

  4. Intensely oscillating cavitation bubble in microfluidics

    NASA Astrophysics Data System (ADS)

    Siew-Wan, Ohl; Tandiono; Klaseboer, Evert; Dave, Ow; Choo, Andre; Claus-Dieter, Ohl

    2015-12-01

    This study reports the technical breakthrough in generating intense ultrasonic cavitation in the confinement of a microfluidics channel [1], and applications that has been developed on this platform for the past few years [2,3,4,5]. Our system consists of circular disc transducers (10-20 mm in diameter), the microfluidics channels on PDMS (polydimethylsiloxane), and a driving circuitry. The cavitation bubbles are created at the gas- water interface due to strong capillary waves which are generated when the system is driven at its natural frequency (around 100 kHz) [1]. These bubbles oscillate and collapse within the channel. The bubbles are useful for sonochemistry and the generation of sonoluminescence [2]. When we add bacteria (Escherichia coli), and yeast cells (Pichia pastoris) into the microfluidics channels, the oscillating and collapsing bubbles stretch and lyse these cells [3]. Furthermore, the system is effective (DNA of the harvested intracellular content remains largely intact), and efficient (yield reaches saturation in less than 1 second). In another application, human red blood cells are added to a microchamber. Cell stretching and rapture are observed when a laser generated cavitation bubble expands and collapses next to the cell [4]. A numerical model of a liquid pocket surrounded by a membrane with surface tension which was placed next to an oscillating bubble was developed using the Boundary Element Method. The simulation results showed that the stretching of the liquid pocket occurs only when the surface tension is within a certain range.

  5. Cavitation technology - a greener processing technique for the generation of pharmaceutical nanoemulsions.

    PubMed

    Sivakumar, Manickam; Tang, Siah Ying; Tan, Khang Wei

    2014-11-01

    Novel nanoemulsion-based drug delivery systems (DDS) have been proposed as alternative and effective approach for the delivery of various types of poorly water-soluble drugs in the last decade. This nanoformulation strategy significantly improves the cell uptake and bioavailability of numerous hydrophobic drugs by increasing their solubility and dissolution rate, maintaining drug concentration within the therapeutic range by controlling the drug release rate, and reducing systemic side effects by targeting to specific disease site, thus offering a better patient compliance. To date, cavitation technology has emerged to be an energy-efficient and promising technique to generate such nanoscale emulsions encapsulating a variety of highly potent pharmaceutical agents that are water-insoluble. The micro-turbulent implosions of cavitation bubbles tear-off primary giant oily emulsion droplets to nano-scale, spontaneously leading to the formation of highly uniform drug contained nanodroplets. A substantial body of recent literatures in the field of nanoemulsions suggests that cavitation is a facile, cost-reducing yet safer generation tool, remarkably highlighting its industrial commercial viability in the development of designing novel nanocarriers or enhancing the properties of existing pharmaceutical products. In this review, the fundamentals of nanoemulsion and the principles involved in their formation are presented. The underlying mechanisms in the generation of pharmaceutical nanoemulsion under acoustic field as well as the advantages of using cavitation compared to the conventional techniques are also highlighted. This review focuses on recent nanoemulsion-based DDS development and how cavitation through ultrasound and hydrodynamic means is useful to generate the pharmaceutical grade nanoemulsions including the complex double or submicron multiple emulsions.

  6. Interspecific variation in xylem vulnerability to cavitation among tropical tree and shrub species.

    PubMed

    Lopez, Omar R; Kursar, Thomas A; Cochard, Hervé; Tyree, Melvin T

    2005-12-01

    In tropical moist forests, seasonal drought limits plant survival, productivity and diversity. Drought-tolerance mechanisms of tropical species should reflect the maximum seasonal water deficits experienced in a particular habitat. We investigated stem xylem vulnerability to cavitation in nine tropical species with different life histories and habitat associations. Stem xylem vulnerability was scored as the xylem water potential causing 50 and 75% loss of hydraulic conductivity (P50 and P75, respectively). Four shade-tolerant shrubs ranged from moderately resistant (P50=-1.9 MPa for Ouratea lucens Kunth. Engl.) to highly resistant to cavitation (P50=-4.1 MPa for Psychotria horizontalis Sw.), with shallow-rooted species being the most resistant. Among the tree species, those characteristic of waterlogged soils, Carapa guianensis Aubl., Prioria copaifera Griseb. and Ficus citrifolia Mill., were the most vulnerable to cavitation (P50=-0.8 to -1.6 MPa). The wet-season, deciduous tree, Cordia alliodora (Ruiz and Pav.) Oken., had resistant xylem (P50=-3.2 MPa), whereas the dry-season, deciduous tree, Bursera simaruba (L.) Sarg. was among the most vulnerable to cavitation (P50=-0.8 MPa) of the species studied. For eight out of the nine study species, previously reported minimum seasonal leaf water potentials measured in the field during periods of drought correlated with our P50 and P75 values. Rooting depth, deciduousness, soil type and growth habit might also contribute to desiccation tolerance. Our results support the functional dependence of drought tolerance on xylem resistance to cavitation.

  7. PTEN induces apoptosis and cavitation via HIF-2-dependent Bnip3 upregulation during epithelial lumen formation

    PubMed Central

    Qi, Y; Liu, J; Saadat, S; Tian, X; Han, Y; Fong, G-H; Pandolfi, P P; Lee, L Y; Li, S

    2015-01-01

    The tumor suppressor phosphatase and tensin homolog (PTEN) dephosphorylates PIP3 and antagonizes the prosurvival PI3K-Akt pathway. Targeted deletion of PTEN in mice led to early embryonic lethality. To elucidate its role in embryonic epithelial morphogenesis and the underlying mechanisms, we used embryonic stem cell-derived embryoid body (EB), an epithelial cyst structurally similar to the periimplantation embryo. PTEN is upregulated during EB morphogenesis in parallel with apoptosis of core cells, which mediates EB cavitation. Genetic ablation of PTEN causes Akt overactivation, apoptosis resistance and cavitation blockade. However, rescue experiments using mutant PTEN and pharmacological inhibition of Akt suggest that the phosphatase activity of PTEN and Akt are not involved in apoptosis-mediated cavitation. Instead, hypoxia-induced upregulation of Bnip3, a proapoptotic BH3-only protein, mediates PTEN-dependent apoptosis and cavitation. PTEN inactivation inhibits hypoxia- and reactive oxygen species-induced Bnip3 elevation. Overexpression of Bnip3 in PTEN-null EBs rescues apoptosis of the core cells. Mechanistically, suppression of Bnip3 following PTEN loss is likely due to reduction of hypoxia-inducible factor-2α (HIF-2α) because forced expression of an oxygen-stable HIF-2α mutant rescues Bnip3 expression and apoptosis. Lastly, we show that HIF-2α is upregulated by PTEN at both transcriptional and posttranscriptional levels. Ablation of prolyl hydroxylase domain-containing protein 2 (PHD2) in normal EBs or inhibition of PHD activities in PTEN-null EBs stabilizes HIF-2α and induces Bnip3 and caspase-3 activation. Altogether, these results suggest that PTEN is required for apoptosis-mediated cavitation during epithelial morphogenesis by regulating the expression of HIF-2α and Bnip3. PMID:25394489

  8. Smooth particle hydrodynamics method for modeling cavitation-induced fracture of a fluid under shock-wave loading

    NASA Astrophysics Data System (ADS)

    Davydov, M. N.; Kedrinskii, V. K.

    2013-11-01

    It is demonstrated that the method of smoothed particle hydrodynamics can be used to study the flow structure in a cavitating medium with a high concentration of the gas phase and to describe the process of inversion of the two-phase state of this medium: transition from a cavitating fluid to a system consisting of a gas and particles. A numerical analysis of the dynamics of the state of a hemispherical droplet under shock-wave loading shows that focusing of the shock wave reflected from the free surface of the droplet leads to the formation of a dense, but rapidly expanding cavitation cluster at the droplet center. By the time t = 500 µs, the bubbles at the cluster center not only coalesce and form a foam-type structure, but also transform to a gas-particle system, thus, forming an almost free rapidly expanding zone. The mechanism of this process defined previously as an internal "cavitation explosion" of the droplet is validated by means of mathematical modeling of the problem by the smoothed particle hydrodynamics method. The deformation of the cavitating droplet is finalized by its decomposition into individual fragments and particles.

  9. Moving beyond the cambium necrosis hypothesis of post-fire tree mortality: cavitation and deformation of xylem in forest fires.

    PubMed

    Michaletz, S T; Johnson, E A; Tyree, M T

    2012-04-01

    • It is widely assumed that post-fire tree mortality results from necrosis of phloem and vascular cambium in stems, despite strong evidence that reduced xylem conductivity also plays an important role. • In this study, experiments with Populus balsamifera were used to demonstrate two mechanisms by which heat reduces the hydraulic conductivity of xylem: air seed cavitation and conduit wall deformation. Heat effects on air seed cavitation were quantified using air injection experiments that isolate potential temperature-dependent changes in sap surface tension and pit membrane pore diameters. Heat effects on conduit wall structure were demonstrated using air conductivity measurements and light microscopy. • Heating increased vulnerability to cavitation because sap surface tension varies inversely with temperature. Heating did not affect cavitation via changes in pit membrane pore diameters, but did cause significant reductions in xylem air conductivity that were associated with deformation of conduit walls (probably resulting from thermal softening of viscoelastic cell wall polymers). • Additional work is required to understand the relative roles of cavitation and deformation in the reduction of xylem conductivity, and how reduced xylem conductivity in roots, stems, and branches correlates and interacts with foliage and root necroses to cause tree mortality. Future research should also examine how heat necrosis of ray parenchyma cells affects refilling of embolisms that occur during and after the fire event. © No claim to original US government works. New Phytologist © 2012 New Phytologist Trust.

  10. The role of ultrasonic cavitation in refining the microstructure of aluminum based nanocomposites during the solidification process.

    PubMed

    Xuan, Yang; Nastac, Laurentiu

    2017-07-01

    Recent studies showed that the microstructure and mechanical properties of aluminum based nanocomposites can be significantly improved when ultrasonic cavitation and solidification processing is used. This is because ultrasonic cavitation processing plays an important role not only in degassing and dispersion of the nanoparticles, but also in breaking up the dendritic grains and refining the as-cast microstructure. In the present study, A356 alloy and Al2O3 nanoparticles are used as the matrix alloy and the reinforcement, respectively. Nanoparticles were added into the molten A356 alloy and dispersed via ultrasonic cavitation processing. Ultrasonic cavitation was applied over various temperature ranges during molten alloy cooling and solidification to investigate the grain structure formation and the nanoparticle dispersion behavior. Optical Microscopy and Scanning Electron Microscopy were used to investigate in detail the differences in the microstructure characteristics and the nanoparticle distribution. Experimental results indicated that the ultrasonic cavitation processing and Al2O3 nanoparticles play an important role for microstructure refinement. In addition, it was shown in this study that the Al2O3 nanoparticles modified the eutectic phase. Copyright © 2017 Elsevier B.V. All rights reserved.

  11. The effect of microstructure on cavitation during hot deformation in fine-grained AA5083 aluminum alloy sheet material

    NASA Astrophysics Data System (ADS)

    Chang, Jung-Kuei

    Aluminum alloys are of great interest to the automobile industry for vehicle mass reduction, which improves vehicle performance and reduces emissions. Hot forming processes, such as superplastic forming (SPF) and quick-plastic forming (QPF) have been developed to take advantage of the improved formability of certain aluminum materials at elevated temperature. Commercial fine-grained aluminum alloy AA5083 sheet is the most commonly used material in the SPF and QPF forming processes. Hot formability of AA5083 is often limited by material cavitation during forming, which makes understanding and controlling cavitation an issue of primary importance for improving hot sheet forming processes. The thermomechanical processing history of AA5083 can strongly affect superplastic performance, causing variations in formability between material lots. These variations are closely related to microstructure, and intermetallic particles are prime suspects for controlling cavitation behavior. However, there has been little more than anecdotal evidence available that these particles nucleate or influence cavitation. Interactions between intermetallic particles and cavities were, thus, analyzed using both two-dimensional (2-D) and three-dimensional (3-D) microstructure characterization techniques. Analysis of 3-D microstructures from AA5083 specimens deformed under conditions similar to the SPF and QPF processes provide conclusive proof that cavities form at specific types of intermetallic particles. Differences in cavitation between materials deformed under the SPF and QPF processes result from differences in deformation mechanisms. These differences are illustrated by the formation of filaments on fracture surfaces of superplastically deformed AA5083 specimens, which have been characterized.

  12. The relationship between the nuclei population and the cavitation event rate for cavitation on a Schiebe body

    SciTech Connect

    Liu, Z.; Brennen, C.E.

    1994-12-31

    Simultaneous measurements were made of the cavitation event rates on a Schiebe body and the nuclei number distributions in the oncoming stream in the Low Turbulence Water Tunnel at Caltech. Cavitation inception occurred at an average cavitation number of 0.57. Cavitation event rates increased dramatically as the cavitation number was decreased. It was also found that both the magnitude and the shape of the nuclei distribution changed substantially with the operating condition. These changes had very strong effect on the event rate and therefore on cavitation inception number based on a fixed event rate. At the same cavitation number, the changes in the event rate due to different free stream nuclei populations can be as much as a decade. The changes in the shape of the nuclei distribution occurred mostly in the nuclei size range above 15 {micro}m. The nuclei concentration tended to increase as cavitation number was decreased. And the cavitation event rate increased with he free stream nuclei concentration. The measured nuclei density distributions are used in an analytical model which attempts to correlate the even rate with the nuclei population. The predicted event rates are compared with those observed experimentally.

  13. Nucleus factory on cavitation bubble for amyloid β fibril

    PubMed Central

    Nakajima, Kichitaro; Ogi, Hirotsugu; Adachi, Kanta; Noi, Kentaro; Hirao, Masahiko; Yagi, Hisashi; Goto, Yuji

    2016-01-01

    Structural evolution from monomer to fibril of amyloid β peptide is related to pathogenic mechanism of Alzheimer disease, and its acceleration is a long-running problem in drug development. This study reveals that ultrasonic cavitation bubbles behave as catalysts for nucleation of the peptide: The nucleation reaction is highly dependent on frequency and pressure of acoustic wave, and we discover an optimum acoustical condition, at which the reaction-rate constant for nucleation is increased by three-orders-of magnitudes. A theoretical model is proposed for explaining highly frequency and pressure dependent nucleation reaction, where monomers are captured on the bubble surface during its growth and highly condensed by subsequent bubble collapse, so that they are transiently exposed to high temperatures. Thus, the dual effects of local condensation and local heating contribute to dramatically enhance the nucleation reaction. Our model consistently reproduces the frequency and pressure dependences, supporting its essential applicability. PMID:26912021

  14. Nucleus factory on cavitation bubble for amyloid β fibril.

    PubMed

    Nakajima, Kichitaro; Ogi, Hirotsugu; Adachi, Kanta; Noi, Kentaro; Hirao, Masahiko; Yagi, Hisashi; Goto, Yuji

    2016-02-25

    Structural evolution from monomer to fibril of amyloid β peptide is related to pathogenic mechanism of Alzheimer disease, and its acceleration is a long-running problem in drug development. This study reveals that ultrasonic cavitation bubbles behave as catalysts for nucleation of the peptide: The nucleation reaction is highly dependent on frequency and pressure of acoustic wave, and we discover an optimum acoustical condition, at which the reaction-rate constant for nucleation is increased by three-orders-of magnitudes. A theoretical model is proposed for explaining highly frequency and pressure dependent nucleation reaction, where monomers are captured on the bubble surface during its growth and highly condensed by subsequent bubble collapse, so that they are transiently exposed to high temperatures. Thus, the dual effects of local condensation and local heating contribute to dramatically enhance the nucleation reaction. Our model consistently reproduces the frequency and pressure dependences, supporting its essential applicability.

  15. Cavitation-induced ignition of cryogenic hydrogen-oxygen fluids

    NASA Astrophysics Data System (ADS)

    Osipov, V. V.; Muratov, C. B.; Ponizovskaya-Devine, E.; Foygel, M.; Smelyanskiy, V. N.

    2011-03-01

    The Challenger disaster and purposeful experiments with liquid hydrogen (H2) and oxygen (Ox) tank breaches demonstrated that cryogenic H2/Ox fluids always self-ignite in the process of their sudden mixing. Here, we propose a cavitation-induced self-ignition mechanism that may be realized under these conditions. In one possible scenario, self-ignition is caused by the strong shock waves generated by the collapse of pure Ox vapor bubble near the surface of the Ox liquid that may initiate detonation of the gaseous H2/Ox mixture next to the gas-liquid interface. This effect is further enhanced by H2/Ox combustion inside the collapsing bubble in the presence of admixed H2 gas.

  16. Nucleus factory on cavitation bubble for amyloid β fibril

    NASA Astrophysics Data System (ADS)

    Nakajima, Kichitaro; Ogi, Hirotsugu; Adachi, Kanta; Noi, Kentaro; Hirao, Masahiko; Yagi, Hisashi; Goto, Yuji

    2016-02-01

    Structural evolution from monomer to fibril of amyloid β peptide is related to pathogenic mechanism of Alzheimer disease, and its acceleration is a long-running problem in drug development. This study reveals that ultrasonic cavitation bubbles behave as catalysts for nucleation of the peptide: The nucleation reaction is highly dependent on frequency and pressure of acoustic wave, and we discover an optimum acoustical condition, at which the reaction-rate constant for nucleation is increased by three-orders-of magnitudes. A theoretical model is proposed for explaining highly frequency and pressure dependent nucleation reaction, where monomers are captured on the bubble surface during its growth and highly condensed by subsequent bubble collapse, so that they are transiently exposed to high temperatures. Thus, the dual effects of local condensation and local heating contribute to dramatically enhance the nucleation reaction. Our model consistently reproduces the frequency and pressure dependences, supporting its essential applicability.

  17. Pre-breakdown cavitation nanopores in the dielectric fluid in the inhomogeneous, pulsed electric fields

    NASA Astrophysics Data System (ADS)

    Pekker, Mikhail; Shneider, Mikhail N.

    2015-10-01

    This paper discusses the nanopores emerging and developing in a liquid dielectric under the action of the ponderomotive electrostrictive forces in a nonuniform electric field. It is shown that the gradient of the electric field in the vicinity of the rupture (cavitation nanopore) substantially increases and determines whether the rupture grows or collapses. The cavitation rupture in the liquid (nanopore) tends to stretch along the lines of the original field. The mechanism of the breakdown associated with the generation of secondary ruptures in the vicinity of the poles of the nanopore is proposed. The estimations of the extension time for nanopore in water and oil (polar and nonpolar liquids, respectively) are presented. A new mechanism of nano- and subnanosecond breakdown in the insulating (transformer) oil that can be realized in the vicinity of water microdroplets in nanosecond high-voltage devices is considered.

  18. Generation of abnormal acoustic noise: Singing of a cavitating tip vortex

    NASA Astrophysics Data System (ADS)

    Peng, Xiaoxing; Wang, Benlong; Li, Haoyu; Xu, Lianghao; Song, Mingtai

    2017-05-01

    We present experimental results and a theoretical analysis for the singing of a cavitating tip vortex (SCTV), which has been occasionally observed under special conditions in a few experimental facilities around the world since the 1990s. Due to lack of repeatability, little is known about the generation mechanism of SCTV [R. E. A. Arndt, Annu. Rev. Fluid Mech. 34, 143 (2002), 10.1146/annurev.fluid.34.082301.114957]. In the present work we propose an experimental procedure to produce the SCTV phenomenon at selected flow conditions in the China Ship Scientific Research Center cavitation mechanism tunnel. By analyzing the frequency characteristics of the acoustical signal and the bubble dynamics, it is found that the tone of SCTV matches the natural frequency of radial oscillation of the cylinder bubble and a formulation to predict SCTV is developed. Good agreement is obtained between the proposed formulation and the experimental data from different facilities.

  19. A Three-Component Model Suitable for Natural and Ventilated Cavitation

    NASA Astrophysics Data System (ADS)

    Ji, Bin; Luo, Xian-Wu; Zhang, Yao; Ran, Hong-Juan; Xu, Hong-Yuan; Wu, Yu-Lin

    2010-09-01

    A three-component model based on mass transfer equation is proposed to simulate both the natural and ventilated cavitations. In the present cavitation model, the content of nuclei in the local flow field is updated synchronously, and is coupled with the Rayleigh-Plesset equation so as to capture the cavity development. The proposed model is applied for simulating the cavitating flow around a super-cavitating vehicle in different cavitation conditions. In the case of the natural cavitation simulation, the predicted cavitation characteristics including the cavity length and cavity diameter agrees fairly well with the analytical results. In the case of the mixed cavitation simulation, the gas ventilation obviously influences the development of cavity. With the increase of the gas ventilated rate, the natural cavitation is suppressed remarkably, and a super cavitation is formed even at a relatively larger natural cavitation number.

  20. Initial stages of cavitation damage and erosion on copper and brass tested in a rotating disk device

    NASA Technical Reports Server (NTRS)

    Rao, P. V.; Rao, B. C. S.; Rao, N. S. L.

    1982-01-01

    In view of the differences in flow and experimental conditions, there has been a continuing debate as to whether or not the ultrasonic method of producing cavitation damage is similar to the damage occurring in cavitating flow systems, namely, venturi and rotating disk devices. In this paper, the progress of cavitation damage during incubation periods on polycrystalline copper and brass tested in a rotating disk device is presented. The results indicate several similarities and differences in the damage mechanism encountered in a rotating disk device (which simulates field rotary devices) and a magnetostriction apparatus. The macroscopic erosion appears similar to that in the vibratory device except for nonuniform erosion and apparent plastic flow during the initial damage phase.

  1. Transient cavitation produced by extracorporeal shock wave lithotripsy

    NASA Astrophysics Data System (ADS)

    Cioanta, Iulian

    1998-12-01

    Two decades ago, a new medical procedure was introduced, allowing the fragmentation of kidney stones from outside the human body (noninvasively) using a shock wave device termed lithotripter ('stone crusher'). Considered as one of the most important medical inventions of this century, lithotripsy is currently used in more than 80% of urolithiasis cases. Experimental studies have shown that transient or inertial cavitation is generated by this procedure near the stones and in renal tissue. To find a correlation between the number of shocks delivered and the treatment efficiency, the acoustic emission (AE) generated by the oscillation of cavitation bubbles, and its relation with stone fragmentation and tissue damage during shock wave lithotripsy were studied. In vitro experiments were carried out to identify the correlation between the AE signals and the expansion and collapse of cavitation bubbles, which were captured by high-speed photography (20,000 frames per second). This correlation has been verified on four different electrohydraulic lithotripters, under multiple experimental conditions. The effects of tissue attenuation on AE and stone fragmentation were also studied. The in vitro results have further allowed the interpretation of AE signals from in vivo experiments with pigs. Although similar in general trend, in vivo AE signals are found to be shorter in expansion and longer in the total ringing times (including the rebound phenomenon) than for in vitro AE signals, indicating a tissue constraining effect on bubble oscillation. Based on this observation a new mechanism for renal vascular and tubular injury is proposed. In addition, changes in AE signals have been observed as the total number of shocks increases, and this dose dependence feature has allowed the determination of a threshold value for extended tissue injury at 20 kV. This result has been confirmed by histological analysis and by results of a theoretical model study of bubble oscillation in a

  2. Cavitation erosion by single laser-produced bubbles

    NASA Astrophysics Data System (ADS)

    Philipp, A.; Lauterborn, W.

    1998-04-01

    In order to elucidate the mechanism of cavitation erosion, the dynamics of a single laser-generated cavitation bubble in water and the resulting surface damage on a flat metal specimen are investigated in detail. The characteristic effects of bubble dynamics, in particular the formation of a high-speed liquid jet and the emission of shock waves at the moment of collapse are recorded with high-speed photography with framing rates of up to one million frames/s. Damage is observed when the bubble is generated at a distance less than twice its maximum radius from a solid boundary ([gamma]=2, where [gamma]=s/Rmax, s is the distance between the boundary and the bubble centre at the moment of formation and Rmax is the maximum bubble radius). The impact of the jet contributes to the damage only at small initial distances ([gamma][less-than-or-eq, slant]0.7). In this region, the impact velocity rises to 83 m s[minus sign]1, corresponding to a water hammer pressure of about 0.1 GPa, whereas at [gamma]>1, the impact velocity is smaller than 25 m s[minus sign]1. The largest erosive force is caused by the collapse of a bubble in direct contact with the boundary, where pressures of up to several GPa act on the material surface. Therefore, it is essential for the damaging effect that bubbles are accelerated towards the boundary during the collapse phases due to Bjerknes forces. The bubble touches the boundary at the moment of second collapse when [gamma]<2 and at the moment of first collapse when [gamma]<1. Indentations on an aluminium specimen are found at the contact locations of the collapsing bubble. In the range [gamma]=1.7 to 2, where the bubble collapses mainly down to a single point, one pit below the bubble centre is observed. At [gamma][less-than-or-eq, slant]1.7, the bubble shape has become toroidal, induced by the jet flow through the bubble centre. Corresponding to the decay of this bubble torus into multiple tiny bubbles each collapsing separately along the

  3. Cavitation Along Surfaces of Separation

    DTIC Science & Technology

    1960-08-30

    Engineering _________________ Mechanics, The University This docLunen* has bee prv~ ansa, lwrene, an. for Pubic’ release and sale; its distribution is...produced by a Peerless axial- mation which must be associated with reduced flow hydrofoil pump passes through a honeycomb to pressure within individual

  4. In situ observation of ultrasonic cavitation-induced fragmentation of the primary crystals formed in Al alloys.

    PubMed

    Wang, Feng; Tzanakis, Iakovos; Eskin, Dmitry; Mi, Jiawei; Connolley, Thomas

    2017-11-01

    The cavitation-induced fragmentation of primary crystals formed in Al alloys were investigated for the first time by high-speed imaging using a novel experimental approach. Three representative primary crystal types, Al3Ti, Si and Al3V with different morphologies and mechanical properties were first extracted by deep etching of the corresponding Al alloys and then subjected to ultrasonic cavitation processing in distilled water. The dynamic interaction between the cavitation bubbles and primary crystals was imaged in situ and in real time. Based on the recorded image sequences, the fragmentation mechanisms of primary crystals were studied. It was found that there are three major mechanisms by which the primary crystals were fragmented by cavitation bubbles. The first one was a slow process via fatigue-type failure. A cyclic pressure exerted by stationary pulsating bubbles caused the propagation of a crack pre-existing in the primary crystal to a critical length which led to fragmentation. The second mechanism was a sudden process due to the collapse of bubbles in a passing cavitation cloud. The pressure produced upon the collapse of the cloud promoted rapid monotonic crack growth and fast fracture in the primary crystals. The third observed mechanism was normal bending fracture as a result of the high pressure arising from the collapse of a bubble cloud and the crack formation at the branch connection points of dendritic primary crystals. The fragmentation of dendrite branches due to the interaction between two freely moving dendritic primary crystals was also observed. A simplified fracture analysis of the observed phenomena was performed. The specific fragmentation mechanism for the primary crystals depended on their morphology and mechanical properties. Copyright © 2017 The Author(s). Published by Elsevier B.V. All rights reserved.

  5. A continuum damage relation for hydrogen attack cavitation

    SciTech Connect

    Burg, M.W.D. van der; Giessen, E. van der

    1997-07-01

    A continuum damage relation (CDR) is proposed to describe the failure process of hydrogen attack, i.e., grain boundary cavitation of steels under conditions of high temperature and high hydrogen pressure. The cavitation is caused by the chemical reaction of hydrogen with grain boundary carbides forming cavities filled with high pressure methane. The micromechanisms described are the grain boundary cavitation and the dislocation creep of the grains. The CDR is based on two extreme cavitation rate distribution modes. In the first mode, the cavitation rate along the facets is uniform, resulting in a hydrostatic dilatation while the creep deformations remain relatively small. In the second mode, cavitation proceeds predominantly on grain boundary facets transverse to the principal macroscopic stress. This part of the CDR builds on Tvergaard`s constitutive relation for intergranular creep rupture [Tvergaard, V., Acta Metallurgica, 1984, 32, 1977] where the facet cavitation is constrained by creep of the surrounding grains. The mode corresponding to the highest cavitation rate is the active mode. The two-dimensional version of the CDR is verified against detailed finite element analyses of hydrogen attack in planar polycrystalline aggregates. Finally, the generalization to a three-dimensional CDR is discussed.

  6. Characterizing the cavitation development and acoustic spectrum in various liquids.

    PubMed

    Tzanakis, I; Lebon, G S B; Eskin, D G; Pericleous, K A

    2017-01-01

    A bespoke cavitometer that measures acoustic spectrum and is capable of operating in a range of temperatures (up to 750°C) was used to study the cavitation behaviour in three transparent liquids and in molten aluminium. To relate these acoustic measurements to cavitation development, the dynamics of the cavitation bubble structures was observed in three Newtonian, optically transparent liquids with significantly different physical properties: water, ethanol, and glycerine. Each liquid was treated at 20kHz with a piezoelectric ultrasonic transducer coupled to a titanium sonotrode with a tip diameter of 40mm. Two different transducer power levels were deployed: 50% and 100%, with the maximum power corresponding to a peak-to-peak amplitude of 17μm. The cavitation structures and the flow patterns were filmed with a digital camera. To investigate the effect of distance from the ultrasound source on the cavitation intensity, acoustic emissions were measured with the cavitometer at two points: below the sonotrode and near the edge of the experimental vessel. The behaviour of the three tested liquids was very different, implying that their physical parameters played a decisive role in the establishment of the cavitation regime. Non dimensional analysis revealed that water shares the closest cavitation behaviour with liquid aluminium and can therefore be used as its physical analogue in cavitation studies; this similarity was also confirmed when comparing the measured acoustic spectra of water and liquid aluminium.

  7. A comprehensive analysis of cavitation and liquid impingement erosion data

    NASA Technical Reports Server (NTRS)

    Rao, P. V.; Young, S. G.

    1983-01-01

    Cavitation-erosion experimental data previously covering several materials tested in a rotating disk device and a magnetostriction apparatus were analyzed using new normalization and curve-fitting techniques. From this process a universal approach is derived which can include data from cavitation and liquid impingement studies for specific materials from different test devices.

  8. An objective comparison of commercially-available cavitation meters.

    PubMed

    Sarno, Daniel; Hodnett, Mark; Wang, Lian; Zeqiri, Bajram

    2017-01-01

    With a number of cavitation meters on the market which claim to characterise fields in ultrasonic cleaning baths, this paper provides an objective comparison of a selection of these devices and establishes the extent to which their claims are met. The National Physical Laboratory's multi-frequency ultrasonic reference vessel provided the stable 21.06kHz field, above and below the inertial cavitation threshold, as a test bed for the sensor comparison. Measurements from these devices were evaluated in relation to the known acoustic pressure distribution in the cavitating vessel as a means of identifying the mode of operation of the sensors and to examine the particular indicator of cavitation activity which they deliver. Through the comparison with megahertz filtered acoustic signals generated by inertial cavitation, it was determined that the majority of the cavitation meters used in this study responded to acoustic pressure generated by the direct applied acoustic field and therefore tended to overestimate the occurrence of cavitation within the vessel, giving non-zero responses under conditions when there was known to be no inertial cavitation occurring with the reference vessel. This has implications for interpreting the data they provide in user applications.

  9. Control of Acoustic Cavitation with Application to Lithotripsy.

    DTIC Science & Technology

    2007-11-02

    cavitation contributes to kidney stone comminution and tissue damage. An electrical spark at the near focus of an underwater ellipsoidal reflector was the...Control of acoustic cavitation (sound-induced bubble activity) is the subject of this dissertation. Application is to clinical lithotripsy where

  10. Radiation induced cavitation: A possible phenomenon in liquid targets?

    SciTech Connect

    West, C.D.

    1998-07-01

    The proposed design of a new, short-pulse spallation neutron source includes a liquid mercury target irradiated with a 1 GeV proton beam. This paper explores the possibility that cavitation bubbles may be formed in the mercury and briefly discusses some design features that could avoid harmful effects should cavitation take place.

  11. Instabilities in confined elastic layers under tension: Fringe, fingering and cavitation

    NASA Astrophysics Data System (ADS)

    Lin, Shaoting; Mao, Yunwei; Radovitzky, Raul; Zhao, Xuanhe

    2017-09-01

    Under tension, confined elastic layers can exhibit various modes of mechanical instabilities, including cavitation, fingering and fringe instabilities. While the cavitation has been extensively studied, the fingering and fringe instabilities have not been well understood, and the relations and interactions of these instabilities have not been explored yet. In this paper, we systematically study the formation, transition, interaction and co-existence of mechanical instabilities in confined elastic layers under tension. Through combined experimental, numerical and theoretical analysis, we find that the mode of instability is determined by both geometry and mechanical properties of the elastic layer through two non-dimensional parameters: layer's lateral dimension over its thickness and elastocapillary length over the defect size. A phase diagram is calculated to quantitatively predict the occurrence of any mode of instability. We further show cavitation instability and fingering instability can coexist and interact with each other in one elastic layer. The current work can help the design of robust adhesives by rationally harnessing the desired mode of instabilities while suppressing the other modes.

  12. Cavitation erosion - corrosion behaviour of ASTM A27 runner steel in natural river water

    NASA Astrophysics Data System (ADS)

    Tôn-Thât, L.

    2014-03-01

    Cavitation erosion is still one of the most important degradation modes in hydraulic turbine runners. Part of researches in this field focuses on finding new materials, coatings and surface treatments to improve the resistance properties of runners to this phenomenon. However, only few studies are focused on the deleterious effect of the environment. Actually, in some cases a synergistic effect between cavitation erosion mechanisms and corrosion kinetics can establish and increase erosion rate. In the present study, the cavitation erosion-corrosion behaviour of ASTM A27 steel in natural river water is investigated. This paper state the approach which has been used to enlighten the synergy between both phenomena. For this, a 20 kHz vibratory test according ASTM G32 standard is coupled to an electrochemical cell to be able to follow the different corrosion parameters during the tests to get evidence of the damaging mechanism. Moreover, mass losses have been followed during the exposure time. The classical degradation parameters (cumulative weight loss and erosion rate) are determined. Furthermore, a particular effort has been implemented to determine the evolution of surface damages in terms of pitting, surface cracking, material removal and surface corrosion. For this, scanning electron microscopy has been used to link the microstructure to the material removal mechanisms.

  13. Control of acoustic cavitation with application to lithotripsy

    NASA Astrophysics Data System (ADS)

    Bailey, Michael Rollins

    Control of acoustic cavitation, which is sound-induced growth and collapse of bubbles, is the subject of this dissertation. Application is to extracorporeal shock wave lithotripsy (ESWL), used to treat kidney stones. Cavitation is thought to help comminute stones yet may damage tissue. Can cavitation be controlled? The acoustic source in a widely used clinical lithotripter is an electrical spark at the near focus of an underwater ellipsoidal reflector. To control cavitation, we used rigid reflectors, pressure release reflectors, and pairs of reflectors aligned to have a common focus and a controlled delay between sparks. Cavitation was measured with aluminum foil, which was placed along the axis at the far focus of the reflector(s). Collapsing bubbles pitted the foil. Pit depth measured with a profilometer provided a relative measure of cavitation intensity. Cavitation was also measured with a focused hydrophone, which detected the pressure pulse radiated in bubble collapse. Acoustic pressure signals produced by the reflectors were measured with a PVdF membrane hydrophone, digitally recorded, and input into a numerical version of the Gilmore equation (F. R. Gilmore, 'The growth or collapse of a spherical bubble in a viscous compressible liquid,' Rep#26-4, California Institute of Technology, Pasadena (1952), pp.1-40.). Maximum pressure produced in a spherical bubble was calculated and employed as a relative measure of collapse intensity. Experimental and numerical results demonstrate cavitation can be controlled by an appropriately delayed auxiliary pressure pulse. When two rigid-reflector pulses are used, a long interpulse delay (150-200 μs) of the second pulse 'kicks' the collapsing bubble and intensifies cavitation. Foil pit depth and computed pressure three times single pulse values were obtained. Conversely, a short delay (<90 μs) 'stifles' bubble growth and weakens cavitation. A single pressure release reflector time- reverses the rigid-reflector waveform

  14. Non-cavitating propeller noise modeling and inversion

    NASA Astrophysics Data System (ADS)

    Kim, Dongho; Lee, Keunhwa; Seong, Woojae

    2014-12-01

    Marine propeller is the dominant exciter of the hull surface above it causing high level of noise and vibration in the ship structure. Recent successful developments have led to non-cavitating propeller designs and thus present focus is the non-cavitating characteristics of propeller such as hydrodynamic noise and its induced hull excitation. In this paper, analytic source model of propeller non-cavitating noise, described by longitudinal quadrupoles and dipoles, is suggested based on the propeller hydrodynamics. To find the source unknown parameters, the multi-parameter inversion technique is adopted using the pressure data obtained from the model scale experiment and pressure field replicas calculated by boundary element method. The inversion results show that the proposed source model is appropriate in modeling non-cavitating propeller noise. The result of this study can be utilized in the prediction of propeller non-cavitating noise and hull excitation at various stages in design and analysis.

  15. Dynamics of dissolved gas in a cavitating fluid.

    PubMed

    Mastikhin, Igor V; Newling, Benedict

    2008-12-01

    A strong acoustic field in a liquid separates the liquid and dissolved gases by the formation of bubbles (cavitation). Bubble growth and collapse is the result of active exchange of gas and vapor through the bubble walls with the surrounding liquid. This paper details a new approach to the study of cavitation, not as an evolution of discrete bubbles, but as the dynamics of molecules constituting both the bubbles and the fluid. We show, by direct, independent measurement of the liquid and the dissolved gas, that the motions of dissolved gas (freon-22, CHClF2 ) and liquid (water) can be quite different during acoustic cavitation and are strongly affected by filtration or previous cavitation of the solvent. Our observations suggest that bubbles can completely refresh their content within two acoustic cycles and that long-lived ( approximately minutes) microbubbles act as nucleation sites for cavitation. This technique is complementary to the traditional optical and acoustical techniques.

  16. Dynamics of dissolved gas in a cavitating fluid

    NASA Astrophysics Data System (ADS)

    Mastikhin, Igor V.; Newling, Benedict

    2008-12-01

    A strong acoustic field in a liquid separates the liquid and dissolved gases by the formation of bubbles (cavitation). Bubble growth and collapse is the result of active exchange of gas and vapor through the bubble walls with the surrounding liquid. This paper details a new approach to the study of cavitation, not as an evolution of discrete bubbles, but as the dynamics of molecules constituting both the bubbles and the fluid. We show, by direct, independent measurement of the liquid and the dissolved gas, that the motions of dissolved gas (freon-22, CHClF2 ) and liquid (water) can be quite different during acoustic cavitation and are strongly affected by filtration or previous cavitation of the solvent. Our observations suggest that bubbles can completely refresh their content within two acoustic cycles and that long-lived (˜minutes) microbubbles act as nucleation sites for cavitation. This technique is complementary to the traditional optical and acoustical techniques.

  17. Effect of vibration amplitude on vapor cavitation in journal bearings

    NASA Technical Reports Server (NTRS)

    Brewe, D. E.; Jacobson, B. O.

    1986-01-01

    Computational movies were used to analyze the formation and collapse of vapor cavitation bubbles in a submerged journal bearing. The effect of vibration amplitude on vapor cavitation was studied for a journal undergoing circular whirl. The boundary conditions were implemented using Elrod's algorithm, which conserves mass flow through the cavitation bubble as well as through the oil-film region of the bearing. The vibration amplitudes for the different cases studied resulted in maximum eccentricity ratios ranging from 0.4 to 0.9. The minimum eccentricity ratio reached in each case was 0.1. For the least vibration amplitude studied in which the eccentricity ratio varied between 0.1 and 0.4, no vapor cavitation occurred. The largest vibration amplitude (i.e., eccentricity ratios of 0.1 to 0.9) resulted in vapor cavitation present 76 percent of one complete orbit.

  18. Numerical simulation of viscous cavitating flow around a ship propeller

    NASA Astrophysics Data System (ADS)

    Zhu, Zhi-Feng; Fang, Shi-Liang; Wang, Xiao-Yan; Meng, Zhao-Wen; Liu, Ping-Xiang; Du, Xuan-Min

    2011-09-01

    In the present study, cavitation and a ship propeller wake are reported by computed fluid dynamics based on viscous multiphase flow theory. Some recent validation results with a hybrid grid based on unsteady Navier-Stokes (N-S) and bubble dynamics equations are presented to predict velocity, pressure and vapor volume fraction in propeller wake in a uniform inflow. Numerical predictions of sheet cavitation, tip vortex cavitation and hub vortex cavitation are in agreement with the experimental data, same as numerical predictions of longitudinal and transversal evolution of the axial velocity. Blade and shaft rate frequency of propeller is well predicted by the computed results of pressure, and tip vortex is the most important to generate the pressure field within the near wake. The overall results indicate that the present approach is reliable for prediction of cavitation and propeller wake on the condition of uniform inflow.

  19. Experiments on the dynamic behavior of cavitating pumps

    NASA Technical Reports Server (NTRS)

    Ng, S. L.; Brennen, C.

    1978-01-01

    This paper describes experiments performed to measure the dynamic transfer matrices for cavitating (and noncavitating) pumps. These transfer matrices describe the relationship between small linear oscillatory perturbations in the pressures and mass flow rates at inlet and discharge from the hydraulic machine. The matrices were deduced from direct measurements of these fluctuating quantities for different modes of excitation of the machine. Results for a cavitating inducer are presented as functions of frequency and mean operating state. Though some of the trends in the data are consistent with existing theoretical models of inducer dynamics, others are not, indicating a need for further theoretical investigation of the dynamic characteristics of such flows. The results exhibit increasingly complex dynamics with increasing cavitation; it appears that the hydraulic machine deviates from an essentially passive response without cavitation to an increasingly active response as the cavitation number is reduced.

  20. Cavitation measurements on a pump-turbine model

    NASA Astrophysics Data System (ADS)

    Schmidt, H.; Kirschner, O.; Riedelbauch, S.

    2015-12-01

    When a hydraulic turbine is operated at off-design conditions, cavitation on the runner and other machine parts can occur. Vibration, noise and erosion caused by cavitation can damage the turbine and lead to a limitation of the operational range. To avoid damage of the turbine, it is fundamental to get knowledge of the presence of cavitation. In this paper, the acoustic emissions at a pump-turbine model at different operating conditions with and without the presence of cavitation were recorded and analysed. High speed video recordings were carried out simultaneously to validate the acoustic measurements. The main goal of the investigation was to compare the acoustic emissions with the visual observations at operating conditions with cavitation on the leading edge of the turbine runner. The analysis of the recorded signals and the visual observations are in good accordance for the investigated operating points.

  1. Mechanistic analysis of cavitation assisted transesterification on biodiesel characteristics.

    PubMed

    Sajjadi, Baharak; Abdul Aziz, A R; Ibrahim, Shaliza

    2015-01-01

    The influence of sonoluminescence transesterification on biodiesel physicochemical properties was investigated and the results were compared to those of traditional mechanical stirring. This study was conducted to identify the mechanistic features of ultrasonication by coupling statistical analysis of the experiments into the simulation of cavitation bubble. Different combinations of operational variables were employed for alkali-catalysis transesterification of palm oil. The experimental results showed that transesterification with ultrasound irradiation could change the biodiesel density by about 0.3kg/m(3); the viscosity by 0.12mm(2)/s; the pour point by about 1-2°C and the flash point by 5°C compared to the traditional method. Furthermore, 93.84% of yield with alcohol to oil molar ratio of 6:1 could be achieved through ultrasound assisted transesterification within only 20min. However, only 89.09% of reaction yield was obtained by traditional macro mixing/heating under the same condition. Based on the simulated oscillation velocity value, the cavitation phenomenon significantly contributed to generation of fine micro emulsion and was able to overcome mass transfer restriction. It was found that the sonoluminescence bubbles reached the temperature of 758-713K, pressure of 235.5-159.55bar, oscillation velocity of 3.5-6.5cm/s, and equilibrium radius of 17.9-13.7 times greater than its initial size under the ambient temperature of 50-64°C at the moment of collapse. This showed that the sonoluminescence bubbles were in the condition in which the decomposition phenomena were activated and the reaction rate was accelerated together with a change in the biodiesel properties. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. AN EFFICIENT TREATMENT STRATEGY FOR HISTOTRIPSY BY REMOVING CAVITATION MEMORY

    PubMed Central

    Wang, Tzu-Yin; Xu, Zhen; Hall, Timothy L.; Fowlkes, J. Brian; Cain, Charles A.

    2012-01-01

    Cavitation memory effects occur when remnants of cavitation bubbles (nuclei) persist in the host medium and act as seeds for subsequent events. In pulsed cavitational ultrasound therapy, or histotripsy, this effect may cause cavitation to repeatedly occur at these seeded locations within a target volume, producing inhomogeneous tissue fractionation or requiring an excess number of pulses to completely homogenize the target volume. We hypothesized that by removing the cavitation memory, i.e., the persistent nuclei, the cavitation bubbles could be induced at random locations in response to each pulse; therefore, complete disruption of a tissue volume may be achieved with fewer pulses. To test the hypothesis, the cavitation memory was passively removed by increasing the intervals between successive pulses, Δt, from 2, 10, 20, 50 and 100, to 200 ms. Histotripsy treatments were performed in red blood cell tissue phantoms and ex vivo livers using 1-MHz ultrasound pulses of 10 cycles at P−/P+ pressure of 21/59 MPa. The phantom study allowed for direct visualization of the cavitation patterns and the lesion development process in real time using high-speed photography; the ex vivo tissue study provided validation of the memory effect in real tissues. Results of the phantom study showed an exponential decrease in the correlation coefficient between cavitation patterns in successive pulses from 0.5 ± 0.1 to 0.1 ± 0.1 as Δt increased from 2–200 ms; correspondingly, the lesion was completely fractionated with significantly fewer pulses for longer Δts. In the tissue study, given the same number of therapy pulses, complete and homogeneous tissue fractionation with well-defined lesion boundaries was achieved only for Δt ≥ 100 ms. These results indicated that the removal of the cavitation memory resulted in more efficient treatments and homogeneous lesions. PMID:22402025

  3. Peripapillary intrachoroidal cavitation in pathological myopia.

    PubMed

    Marticorena-Álvarez, P; Clement-Fernández, F; Iglesias-Ussel, L

    2014-08-01

    A 54 year old woman with pathological myopia, presented with an elevated, yellowish-white lesion at the inferior border of the myopic conus in her left eye. The optical coherence tomography (OCT) demonstrated an intrachoroidal hyporeflective space. The fluorescein angiography examination (FA) showed early hypofluorescence with delayed staining, with no leakage of contrast. Recognition of «peripapillary intrachoroidal cavitation» as an own entity associated with pathological myopia is important to avoid confusion with other possible retinal lesions which require further investigation and treatment. Copyright © 2012 Sociedad Española de Oftalmología. Published by Elsevier Espana. All rights reserved.

  4. Ultrasonic cavitation erosion of 316L steel weld joint in liquid Pb-Bi eutectic alloy at 550°C.

    PubMed

    Lei, Yucheng; Chang, Hongxia; Guo, Xiaokai; Li, Tianqing; Xiao, Longren

    2017-11-01

    Liquid lead-bismuth eutectic alloy (LBE) is applied in the Accelerator Driven transmutation System (ADS) as the high-power spallation neutron targets and coolant. A 19.2kHz ultrasonic device was deployed in liquid LBE at 550°C to induce short and long period cavitation erosion damage on the surface of weld joint, SEM and Atomic force microscopy (AFM) were used to map out the surface properties, and Energy Dispersive Spectrometer (EDS) was applied to the qualitative and quantitative analysis of elements in the micro region of the surface. The erosion mechanism for how the cavitation erosion evolved by studying the element changes, their morphology evolution, the surface hardness and the roughness evolution, was proposed. The results showed that the pits, caters and cracks appeared gradually on the erode surface after a period of cavitation. The surface roughness increased along with exposure time. Work hardening by the bubbles impact in the incubation stage strengthened the cavitation resistance efficiently. The dissolution and oxidation corrosion and cavitation erosion that simultaneously happened in liquid LBE accelerated corrosion-erosion process, and these two processes combined to cause more serious damage on the material surface. Contrast to the performance of weld metal, base metal exhibited a much better cavitation resistance. Copyright © 2017. Published by Elsevier B.V.

  5. Enhanced cavitation and heating of flowing polymer- and lipid-shelled microbubbles and phase-shift nanodroplets during focused ultrasound exposures

    NASA Astrophysics Data System (ADS)

    Zhang, Siyuan; Cui, Zhiwei; Li, Chong; Zhou, Fanyu; Zong, Yujin; Wang, Supin; Wan, Mingxi

    2017-03-01

    Cavitation and heating are the primary mechanisms of numerous therapeutic applications of ultrasound. Various encapsulated microbubbles (MBs) and phase-shift nanodroplets (NDs) have been used to enhance local cavitation and heating, creating interests in developing ultrasound therapy using these encapsulated MBs and NDs. This work compared the efficiency of flowing polymer- and lipid-shelled MBs and phase-shift NDs in cavitation and heating during focused ultrasound (FUS) exposures. Cavitation activity and temperature were investigated when the solution of polymer- and lipid-shelled MBs and NDs flowed through the vessel in a tissue-mimicking phantom with varying flow velocities when exposed to FUS at various acoustic power levels. The inertial cavitation dose (ICD) for the encapsulated MBs and NDs were higher than those for the saline. Temperature initially increased with increasing flow velocities of the encapsulated MBs, followed by a decrease of the temperature with increasing flow velocities when the velocity was much higher. Meanwhile, ICD showed a trend of increases with increasing flow velocity. For the phase-shift NDs, ICD after the first FUS exposure was lower than those after the second FUS exposure. For the encapsulated MBs, ICD after the first FUS exposure was higher than those after the second FUS exposure. Further studies are necessary to investigate the treatment efficiency of different encapsulated MBs and phase-shift NDs in cavitation and heating.

  6. Numerical 3D analysis of cloud cavitation shedding frequency on a circular leading edge hydrofoil with a barotropic cavitation model

    NASA Astrophysics Data System (ADS)

    Blume, M.; Skoda, R.

    2015-12-01

    A compressible density-based time-explicit low Mach number consistent viscous flow solver is utilised in combination with a barotropic cavitation model for the analysis of cloud cavitation on a circular leading edge (CLE) hydrofoil. For 5° angle of attack, cloud structure and shedding frequency for different cavitation numbers are compared to experimental data. A strong grid sensitivity is found in particular for high cavitation numbers. On a fine grid, a very good agreement with validation data is achieved even without explicit turbulence model. The neglect of viscous effects as well as a two-dimensional set-up lead to a less realistic prediction of cloud structures and frequencies. Comparative simulations with the Sauer-Schnerr cavitation model and modified pre-factors of the mass transfer terms underestimate the measured shedding frequency.

  7. A unified electrostatic and cavitation model for first-principles molecular dynamics in solution

    SciTech Connect

    Scherlis, D A; Fattebert, J; Gygi, F; Cococcioni, M; Marzari, N

    2005-11-14

    The electrostatic continuum solvent model developed by Fattebert and Gygi is combined with a first-principles formulation of the cavitation energy based on a natural quantum-mechanical definition for the surface of a solute. Despite its simplicity, the cavitation contribution calculated by this approach is found to be in remarkable agreement with that obtained by more complex algorithms relying on a large set of parameters. The model allows for very efficient Car-Parrinello simulations of finite or extended systems in solution, and demonstrates a level of accuracy as good as that of established quantum-chemistry continuum solvent methods. They apply this approach to the study of tetracyanoethylene dimers in dichloromethane, providing valuable structural and dynamical insights on the dimerization phenomenon.

  8. Morphological Evaluation of Plasma Sprayed Ceramic Coatings using Cavitation Erosion Test

    NASA Astrophysics Data System (ADS)

    Uematsu, Susumu; Tani, Kazumi; Sugasawa, Shinobu; Kawanami, Yasutaka; Namba, Yoshio; Takabatake, Tsuyoshi; Yoshioka, Masaru; Ishihara, Yasuaki

    The microstructure of plasma sprayed ceramic coatings is characterized by the existence of splats along with other morphological features such as interlamellar and globular pores, intrasplat microcracks and splat boundaries. These various process-dependant micro- defects extremely influence physical and mechanical properties such as thermal conductivity and elastic modulus and then influence coating behavior. In this approach, the process involved in the cavitation erosion of plasma sprayed ceramic coatings have been studied using the ultrasonic vibratory technique. The weight loss occurring during fifteen minute intervals of exposure to cavitational erosion was determined, the surface of specimens and the wear debris were examined by Scanning electron microscopy (SEM). The results suggest that the improvement in coating performance could be achieved by controlling the effective contact between lamellae of which the coating is made up using the plasma spray conditions, such as sufficient preheat, short standoff distance and slow gun traversing movement.

  9. Effect of temperature and strain rate on cavitation in a superplastic duplex stainless steel

    SciTech Connect

    Pulino-Sagradi, D.; Nazar, A.M.M.; Ammann, J.J.; Medrano, R.E.

    1997-11-01

    The effect of temperature and strain rate on cavitation during superplastic deformation of a duplex stainless steel has been studied at 1,223 K and 1,253 K for initial strain rates ranging from 2 {times} 10{sup {minus}4} s{sup {minus}1} to 2 {times} 10{sup {minus}3} s{sup {minus}1}. The cavitation was analyzed quantitatively for a specifically developed image processing technique that allows an accurate determination of the volume fraction and size distribution of the voids. The results show that increasing temperature and/or decreasing strain rate cause a more homogeneous deformation of the specimen characterized by a uniform size and distribution of the cavities. The increase of the strain rate results in an increase in cavity volume fraction related to more cavity nucleation and interlinkage. This reflects the lack of accommodation process during the mechanism of grain boundary sliding.

  10. The Role of Acoustic Cavitation in Ultrasound-triggered Drug Release from Echogenic Liposomes

    NASA Astrophysics Data System (ADS)

    Kopechek, Jonathan A.

    Cardiovascular disease (CVD) is the leading cause of death in the United States and globally. CVD-related mortality, including coronary heart disease, heart failure, or stroke, generally occurs due to atherosclerosis, a condition in which plaques build up within arterial walls, potentially causing blockage or rupture. Targeted therapies are needed to achieve more effective treatments. Echogenic liposomes (ELIP), which consist of a lipid membrane surrounding an aqueous core, have been developed to encapsulate a therapeutic agent and/or gas bubbles for targeted delivery and ultrasound image enhancement. Under certain conditions ultrasound can cause nonlinear bubble growth and collapse, known as "cavitation." Cavitation activity has been associated with enhanced drug delivery across cellular membranes. However, the mechanisms of ultrasound-mediated drug release from ELIP have not been previously investigated. Thus, the objective of this dissertation is to elucidate the role of acoustic cavitation in ultrasound-mediated drug release from ELIP. To determine the acoustic and physical properties of ELIP, the frequency-dependent attenuation and backscatter coefficients were measured between 3 and 30 MHz. The results were compared to a theoretical model by measuring the ELIP size distribution in order to determine properties of the lipid membrane. It was found that ELIP have a broad size distribution and can provide enhanced ultrasound image contrast across a broad range of clinically-relevant frequencies. Calcein, a hydrophilic fluorescent dye, and papaverine, a lipophilic vasodilator, were separately encapsulated in ELIP and exposed to color Doppler ultrasound pulses from a clinical diagnostic ultrasound scanner in a flow system. Spectrophotometric techniques (fluorescence and absorbance measurements) were used to detect calcein or papaverine release. As a positive control, Triton X-100 (a non-ionic detergent) was added to ELIP samples not exposed to ultrasound in order

  11. Filter-based modeling of unsteady turbulent cavitating flow computations

    NASA Astrophysics Data System (ADS)

    Wu, Jiongyang

    Cavitation plays an important role in the design and operation of fluid machinery and devices because it causes performance degradation, noise, vibration, and erosion. Cavitation involves complex phase-change dynamics, large density ratio between phases, and multiple time scales. Noticeable achievements have been made in employing homogeneous two-phase Navier-Stokes equations for cavitating computations in computational and modeling strategies. However, these issues pose challenges with respect to accuracy, stability, efficiency and robustness because of the complex unsteady interaction associated with cavitation dynamics and turbulence. The present study focuses on developing and assessing computational modeling techniques to provide better insight into unsteady turbulent cavitation dynamics. The ensemble-averaged Navier-Stokes equations, along with a volume fraction transport equation for cavitation and turbulence closure, are employed. To ensure stability and convergence with good efficiency and accuracy, the pressure-based Pressure Implicit Splitting of Operators (PISO) algorithm is adopted for time-dependent computations. The merits of recent transport equation-based cavitation models are first re-examined. To account for the liquid-vapor mixture compressibility, different numerical approximations of speed-of-sound are further investigated and generalized. To enhance the generality and capability of the recent interfacial dynamics-based cavitation model (IDM), we present an improved approximation for the interfacial velocity via phase transformation. In turbulence modeling, a filter-based model (FBM) derived from the k-epsilon two-equation model, an easily deployable conditional averaging method aimed at improving unsteady simulations, is introduced. The cavitation and turbulence models are assessed by unsteady simulations in various geometries including square cylinder, convergent-divergent nozzle, Clark-Y hydrofoil, and hollow-jet valve. The FBM reduces eddy

  12. Temperature and stress fields produced by ultrasound-induced cavitation in a viscoelastic medium

    NASA Astrophysics Data System (ADS)

    Mancia, Lauren; Johnsen, Eric

    2016-11-01

    Ultrasound contrast agents can act as cavitation nuclei that mechanically damage surrounding tissue when they oscillate in diagnostic ultrasound. Encapsulated microbubbles have also been proposed as a means to improve the efficiency and efficacy of therapeutic ultrasound by increasing the rate of tissue heating. However, the thermal and mechanical effects of cavitation are difficult to distinguish from each other and to quantify experimentally as they often occur simultaneously. To address this challenge, we study the cavitation-induced temperature and stress fields produced by a spherical bubble oscillating in a Kelvin-Voigt viscoelastic medium with nonlinear elasticity using a model that also accounts for energy transport inside and outside the bubble. We find that the primary contribution to heating is viscous dissipation, which itself depends on both the material (viscosity) and the bubble dynamics. We examine the rate of viscous heating and the magnitude of stresses over a relevant range of tissue properties and waveform parameters to determine regimes where heating is expected to be dominant. A means of estimating the expected significance of viscous dissipation from given tissue properties and waveform parameters is proposed.

  13. High speed imaging of bubble clouds generated in pulsed ultrasound cavitational therapy--histotripsy.

    PubMed

    Xu, Zhen; Raghavan, Mekhala; Hall, Timothy L; Chang, Ching-Wei; Mycek, Mary-Ann; Fowlkes, J Brian; Cain, Charles A

    2007-10-01

    Our recent studies have demonstrated that mechanical fractionation of tissue structure with sharply demarcated boundaries can be achieved using short (< 20 micros), high intensity ultrasound pulses delivered at low duty cycles. We have called this technique histotripsy. Histotripsy has potential clinical applications where noninvasive tissue fractionation and/or tissue removal are desired. The primary mechanism of histotripsy is thought to be acoustic cavitation, which is supported by a temporally changing acoustic backscatter observed during the histotripsy process. In this paper, a fast-gated digital camera was used to image the hypothesized cavitating bubble cloud generated by histotripsy pulses. The bubble cloud was produced at a tissue-water interface and inside an optically transparent gelatin phantom which mimics bulk tissue. The imaging shows the following: (1) Initiation of a temporally changing acoustic backscatter was due to the formation of a bubble cloud; (2) The pressure threshold to generate a bubble cloud was lower at a tissue-fluid interface than inside bulk tissue; and (3) at higher pulse pressure, the bubble cloud lasted longer and grew larger. The results add further support to the hypothesis that the histotripsy process is due to a cavitating bubble cloud and may provide insight into the sharp boundaries of histotripsy lesions.

  14. Cavitation-enhanced delivery of a replicating oncolytic adenovirus to tumors using focused ultrasound.

    PubMed

    Bazan-Peregrino, Miriam; Rifai, Bassel; Carlisle, Robert C; Choi, James; Arvanitis, Costas D; Seymour, Leonard W; Coussios, Constantin C

    2013-07-10

    Oncolytic viruses (OV) and ultrasound-enhanced drug delivery are powerful novel technologies. OV selectively self-amplify and kill cancer cells but their clinical use has been restricted by limited delivery from the bloodstream into the tumor. Ultrasound has been previously exploited for targeted release of OV in vivo, but its use to induce cavitation, microbubble oscillations, for enhanced OV tumor extravasation and delivery has not been previously reported. By identifying and optimizing the underlying physical mechanism, this work demonstrates that focused ultrasound significantly enhances the delivery and biodistribution of systemically administered OV co-injected with microbubbles. Up to a fiftyfold increase in tumor transgene expression was achieved, without any observable tissue damage. Ultrasound exposure parameters were optimized as a function of tumor reperfusion time to sustain inertial cavitation, a type of microbubble activity, throughout the exposure. Passive detection of acoustic emissions during treatment confirmed inertial cavitation as the mechanism responsible for enhanced delivery and enabled real-time monitoring of successful viral delivery.

  15. Experimental investigation of the flow-induced vibration of hydrofoils in cavitating flows

    NASA Astrophysics Data System (ADS)

    Wang, Guoyu; Wu, Qin; Huang, Biao; Gao, Yuan

    2015-12-01

    The objective of this paper is to investigate the correlation between fluid induced vibration and unsteady cavitation behaviours. Experimental results are presented for a modified NACA66 hydrofoil, which is fixed at α=8°. The high-speed camera is synchronized with a single point Laser Doppler Vibrometer to analyze the transient cavitating flow structures and the corresponding structural vibration characteristics. The results showed that, with the decreasing of the cavitation number, the cavitating flows in a water tunnel display several types of cavitation patterns, such as incipient cavitation, sheet cavitation and cloud cavitation. The cavity shedding frequency reduces with the decrease of the cavitation number. As for the cloud cavitation regime, the trend of the vibration velocity goes up with the growth of the attached cavity, accompanied with small amplitude fluctuations. Then the collapse and shedding of the large-scale cloud cavities leads to substantial increase of the vibration velocity fluctuations.

  16. Augmentation of Muscle Blood Flow by Ultrasound Cavitation Is Mediated by ATP and Purinergic Signaling.

    PubMed

    Belcik, J Todd; Davidson, Brian P; Xie, Aris; Wu, Melinda D; Yadava, Mrinal; Qi, Yue; Liang, Sherry; Chon, Chae Ryung; Ammi, Azzdine Y; Field, Joshua; Harmann, Leanne; Chilian, William M; Linden, Joel; Lindner, Jonathan R

    2017-03-28

    Augmentation of tissue blood flow by therapeutic ultrasound is thought to rely on convective shear. Microbubble contrast agents that undergo ultrasound-mediated cavitation markedly amplify these effects. We hypothesized that purinergic signaling is responsible for shear-dependent increases in muscle perfusion during therapeutic cavitation. Unilateral exposure of the proximal hindlimb of mice (with or without ischemia produced by iliac ligation) to therapeutic ultrasound (1.3 MHz, mechanical index 1.3) was performed for 10 minutes after intravenous injection of 2×10(8) lipid microbubbles. Microvascular perfusion was evaluated by low-power contrast ultrasound perfusion imaging. In vivo muscle ATP release and in vitro ATP release from endothelial cells or erythrocytes were assessed by a luciferin-luciferase assay. Purinergic signaling pathways were assessed by studying interventions that (1) accelerated ATP degradation; (2) inhibited P2Y receptors, adenosine receptors, or KATP channels; or (3) inhibited downstream signaling pathways involving endothelial nitric oxide synthase or prostanoid production (indomethacin). Augmentation in muscle perfusion by ultrasound cavitation was assessed in a proof-of-concept clinical trial in 12 subjects with stable sickle cell disease. Therapeutic ultrasound cavitation increased muscle perfusion by 7-fold in normal mice, reversed tissue ischemia for up to 24 hours in the murine model of peripheral artery disease, and doubled muscle perfusion in patients with sickle cell disease. Augmentation in flow extended well beyond the region of ultrasound exposure. Ultrasound cavitation produced an ≈40-fold focal and sustained increase in ATP, the source of which included both endothelial cells and erythrocytes. Inhibitory studies indicated that ATP was a critical mediator of flow augmentation that acts primarily through either P2Y receptors or adenosine produced by ectonucleotidase activity. Combined indomethacin and inhibition of

  17. Numerical 3D flow simulation of ultrasonic horns with attached cavitation structures and assessment of flow aggressiveness and cavitation erosion sensitive wall zones.

    PubMed

    Mottyll, Stephan; Skoda, Romuald

    2016-07-01

    As a contribution to a better understanding of cavitation erosion mechanisms, a compressible inviscid finite volume flow solver with barotropic homogeneous liquid-vapor mixture cavitation model is applied to ultrasonic horn set-ups with and without stationary specimen, that exhibit attached cavitation at the horn tip. Void collapses and shock waves, which are closely related to cavitation erosion, are resolved. The computational results are compared to hydrophone, shadowgraphy and erosion test data. At the horn tip, vapor volume and topology, subharmonic oscillation frequency as well as the amplitude of propagating pressure waves are in good agreement with experimental data. For the evaluation of flow aggressiveness and the assessment of erosion sensitive wall zones, statistical analyses of wall loads and of the multiplicity of distinct collapses in wall-adjacent flow regions are applied to the horn tip and the stationary specimen. An a posteriori projection of load collectives, i.e. cumulative collapse rate vs. collapse pressure, onto a reference grid eliminates the grid dependency effectively for attached cavitation at the horn tip, whereas a significant grid dependency remains at the stationary specimen. The load collectives show an exponential decrease towards higher collapse pressures. Erosion sensitive wall zones are well predicted for both, horn tip and stationary specimen, and load profiles are in good qualitative agreement with measured topography profiles of eroded duplex stainless steel samples after long-term runs. For the considered amplitude and gap width according to ASTM G32-10 standard, the analysis of load collectives reveals that the distinctive erosive ring shape at the horn tip can be attributed to frequent breakdown and re-development of a small portion of the tip-attached cavity. This partial breakdown of the attached cavity repeats at each driving cycle and is associated with relatively moderate collapse peak pressures, whereas the

  18. [Particle size reduction using acoustic cavitation].

    PubMed

    Bartos, Csilla; Ambrus, Rita; Szabóné, Révész Piroska

    2014-01-01

    Different pharmaceutical technological processes have been used for modification of the physico-chemical and biopharmaceutical properties of drugs. Changes of crystal size, distribution and morphology can open up new, alternative administration routes, e.g. intranasally and the pulmonary route, where the particle size is a determining factor. A wet grinding method based on acoustic cavitation (the collapse of bubbles or voids formed by sound waves) is a novel possibility for modification of the properties of particles. During our work this wet grinding technique was studied. The effect of this method was investigated on particle size reduction. The samples were treated with extreme sonication parameters. The effect of the concentration of the polymer was examined on the particle size reduction. Meloxicam was chosen as a model crystalline drug because of its poor aqueous solubility. The structural characterization and the morphological analysis of the dried products were carried out by DSC, XRPD and SEM. It was found that the acoustic cavitation resulted in crystalline micronized product.

  19. Passive cavitation imaging with ultrasound arrays.

    PubMed

    Salgaonkar, Vasant A; Datta, Saurabh; Holland, Christy K; Mast, T Douglas

    2009-12-01

    A method is presented for passive imaging of cavitational acoustic emissions using an ultrasound array, with potential application in real-time monitoring of ultrasound ablation. To create such images, microbubble emissions were passively sensed by an imaging array and dynamically focused at multiple depths. In this paper, an analytic expression for a passive image is obtained by solving the Rayleigh-Sommerfield integral, under the Fresnel approximation, and passive images were simulated. A 192-element array was used to create passive images, in real time, from 520-kHz ultrasound scattered by a 1-mm steel wire. Azimuthal positions of this target were accurately estimated from the passive images. Next, stable and inertial cavitation was passively imaged in saline solution sonicated at 520 kHz. Bubble clusters formed in the saline samples were consistently located on both passive images and B-scans. Passive images were also created using broadband emissions from bovine liver sonicated at 2.2 MHz. Agreement was found between the images and source beam shape, indicating an ability to map therapeutic ultrasound beams in situ. The relation between these broadband emissions, sonication amplitude, and exposure conditions are discussed.

  20. Correlating Inertial Acoustic Cavitation Emissions with Material Erosion Resistance

    NASA Astrophysics Data System (ADS)

    Ibanez, I.; Hodnett, M.; Zeqiri, B.; Frota, M. N.

    The standard ASTM G32-10 concerns the hydrodynamic cavitation erosion resistance of materials by subjecting them to acoustic cavitation generated by a sonotrode. The work reported extends this technique by detecting and monitoring the ultrasonic cavitation, considered responsible for the erosion process, specifically for coupons of aluminium-bronze alloy. The study uses a 65 mm diameter variant of NPL's cavitation sensor, which detects broadband acoustic emissions, and logs acoustic signals generated in the MHz frequency range, using NPL's Cavimeter. Cavitation readings were made throughout the exposure duration, which was carried out at discrete intervals (900 to 3600 s), allowing periodic mass measurements to be made to assess erosion loss under a strict protocol. Cavitation measurements and erosion were compared for different separations of the sonotrode tip from the material under test. The maximum variation associated with measurement of cavitation level was between 2.2% and 3.3% when the separation (λ) between the transducer horn and the specimen increased from 0.5 to 1.0 mm, for a transducer (sonotrode) displacement amplitude of 43.5 μm. Experiments conducted at the same transducer displacement amplitude show that the mass loss of the specimen -a measure of erosion- was 67.0 mg (λ = 0.5 mm) and 66.0 mg (λ = 1.0 mm).

  1. Numerical research on unsteady cavitating flow over a hydrofoil

    NASA Astrophysics Data System (ADS)

    Homa, D.; Wróblewski, W.

    2016-10-01

    Cavitation is a widely known phenomenon in pumps and water turbines installations. It can lead to significant damage of blades and walls of the rotor therefore it is crucial during pump designing and exploitation to avoid working in flow conditions, that enabled cavitation to occur. Nowadays numerical simulations of flow can provide valuable information concerning pressure and velocity distribution and can indicate if there is a risk of cavitating flow appearance. There are a few mathematical models which describe cavitating flow. In the paper Schnerr & Sauer model was chosen for simulation. Aim of the paper is to verify its utility in case of different cavitating flow regimes over Clark-Y hydrofoil. After performing the grid independence study four different cavitation regimes were investigated. The vapour areas appearance, their shapes and changes in time were observed. The assumption of isothermal, two - phase flow was made. The calculations were performed using OpenFOAM and were compared to the available measurements data. The presented results concerned sheet and cloud cavitation regimes.

  2. Cavitating vortex characterization based on acoustic signal detection

    NASA Astrophysics Data System (ADS)

    Digulescu, A.; Murgan, I.; Candel, I.; Bunea, F.; Ciocan, G.; Bucur, D. M.; Dunca, G.; Ioana, C.; Vasile, G.; Serbanescu, A.

    2016-11-01

    In hydraulic turbines operating at part loads, a cavitating vortex structure appears at runner outlet. This helical vortex, called vortex rope, can be cavitating in its core if the local pressure is lower that the vaporization pressure. An actual concern is the detection of the cavitation apparition and the characterization of its level. This paper presents a potentially innovative method for the detection of the cavitating vortex presence based on acoustic methods. The method is tested on a reduced scale facility using two acoustic transceivers positioned in ”V” configuration. The received signals were continuously recorded and their frequency content was chosen to fit the flow and the cavitating vortex. Experimental results showed that due to the increasing flow rate, the signal - vortex interaction is observed as modifications on the received signal's high order statistics and bandwidth. Also, the signal processing results were correlated with the data measured with a pressure sensor mounted in the cavitating vortex section. Finally it is shown that this non-intrusive acoustic approach can indicate the apparition, development and the damping of the cavitating vortex. For real scale facilities, applying this method is a work in progress.

  3. Visualization of acoustic cavitation effects on suspended calcite crystals.

    PubMed

    Wagterveld, R M; Boels, L; Mayer, M J; Witkamp, G J

    2011-01-01

    The acoustic cavitation (42,080 Hz, 7.1 W cm(-2) or 17 W) effects on suspended calcite crystals, sized between 5 and 50 μm, have been visualized for the first time using high speed photography. High speed recordings with a duration of 1 s containing up to 300,000 frames per second, revealed the effect of cluster and streamer cavitation on several calcite crystals. Cavitation clusters, evolved from cavitation inception and collapse, caused attrition, disruption of aggregates and deagglomeration, whereas streamer cavitation was observed to cause deagglomeration only. Cavitation on the surface gave the crystals momentum. However, it is shown that breakage of accelerated crystals by interparticle collisions is unrealistic because of their small sizes and low velocities. Crystals that were accelerated by bubble expansion, subsequently experienced a deceleration much stronger than expected from drag forces, upon bubble collapse. Experiments with pre-dried crystals seemed to support the current theory on bubble nucleation through the presence of pre-existing gas pockets. However, experiments with fully wetted crystals also showed the nucleation of bubbles on the crystal surface. Although microjet impingement on the crystal surface could not be directly visualized with high speed photography, scanning electron microscopy (SEM) analysis of irradiated calcite seeds showed deep circular indentations. It was suggested that these indentations might be caused by shockwave induced jet impingement. Furthermore, the appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can also cause the breakage of single crystal structures.

  4. Experimental determination of cavitation thresholds in liquid water and mercury

    SciTech Connect

    Taleyarkhan, R.P.; Gulec, K.; West, C.D.; Haines, J.

    1998-09-01

    It is well-known that fluids (like solids) will break apart or form voids when put under sufficient tension. The present study has been motivated by the need to evaluate the impact of fluid cavitation in spallation neutron source target systems, more specifically for the proposed 1-MW Spallation Neutron Source (SNS) project, which is being designed in collaboration between Oak Ridge National Laboratory (ORNL), Los Alamos National Laboratory, Lawrence Berkeley National Laboratory, Brookhaven National Laboratory, and Argonne National Laboratory. Indeed, results of SNS-specific simulations have indicated that the onset of cavitation could play a very significant role in reducing imposed stresses in structural components of the SNS. In general, the cavitation of fluids is target systems is important to consider for a variety of reasons. Its occurrence can have significant impact on heat transfer, pressure pulse generation, fluid jetting on to structures, surface erosion, stresses induced in enclosures, etc. Therefore, it is important to evaluate the threshold pressure under which the fluid in tension will undergo cavitation. Another major aspect concerns the possible onset of cavitation in an oscillating pressure field; i.e., one would need to know if fluids such as mercury and water will cavitate if the imposed tensile pressure in the fluid is of short duration. If indeed it takes sufficiently long for cavitation bubbles to nucleate, then it would be possible to disregard the complexities involved with addressing cavitation-related issues. This paper provides an overview of preliminary work done to date to derive information on cavitation onset in a relatively static and in a high-frequency environment.

  5. Counterbalancing the use of ultrasound contrast agents by a cavitation-regulated system.

    PubMed

    Desjouy, C; Fouqueray, M; Lo, C W; Muleki Seya, P; Lee, J L; Bera, J C; Chen, W S; Inserra, C

    2015-09-01

    The stochastic behavior of cavitation can lead to major problems of initiation and maintenance of cavitation during sonication, responsible of poor reproducibility of US-induced bioeffects in the context of sonoporation for instance. To overcome these disadvantages, the injection of ultrasound contrast agents as cavitation nuclei ensures fast initiation and lower acoustic intensities required for cavitation activity. More recently, regulated-cavitation devices based on the real-time modulation of the applied acoustic intensity have shown their potential to maintain a stable cavitation state during an ultrasonic shot, in continuous or pulsed wave conditions. In this paper is investigated the interest, in terms of cavitation activity, of using such regulated-cavitation device or injecting ultrasound contrast agents in the sonicated medium. When using fixed applied acoustic intensity, results showed that introducing ultrasound contrast agents increases reproducibility of cavitation activity (coefficient of variation 62% and 22% without and with UCA, respectively). Moreover, the use of the regulated-cavitation device ensures a given cavitation activity (coefficient of variation less 0.4% in presence of UCAs or not). This highlights the interest of controlling cavitation over time to free cavitation-based application from the use of UCAs. Interestingly, during a one minute sonication, while ultrasound contrast agents progressively disappear, the regulated-cavitation device counterbalance their destruction to sustain a stable inertial cavitation activity.

  6. Effect of cavitation in high-pressure direct injection

    NASA Astrophysics Data System (ADS)

    Aboulhasanzadeh, Bahman; Johnsen, Eric

    2015-11-01

    As we move toward higher pressures for Gasoline Direct Injection and Diesel Direct Injection, cavitation has become an important issue. To better understand the effect of cavitation on the nozzle flow and primary atomization, we use a high-order accurate Discontinuous Galerkin approach using multi-GPU parallelism to simulate the compressible flow inside and outside the nozzle. Phase change is included using the six-equations model. We investigate the effect of nozzle geometry on cavitation inside the injector and on primary atomization outside the nozzle.

  7. Ultrasound-induced inertial cavitation from gas-stabilizing nanoparticles.

    PubMed

    Kwan, J J; Graham, S; Myers, R; Carlisle, R; Stride, E; Coussios, C C

    2015-08-01

    The understanding of cavitation from nanoparticles has been hindered by the inability to control nanobubble size. We present a method to manufacture nanoparticles with a tunable single hemispherical depression (nanocups) of mean diameter 90, 260, or 650 nm entrapping a nanobubble. A modified Rayleigh-Plesset crevice model predicts the inertial cavitation threshold as a function of cavity size and frequency, and is verified experimentally. The ability to tune cavitation nanonuclei and predict their behavior will be useful for applications ranging from cancer therapy to ultrasonic cleaning.

  8. An advanced cavitation resistant austenitic stainless steel for pumps

    SciTech Connect

    McCaul, C.

    1996-10-01

    Cavitation damage is a chronic problem leading to impaired pump performance, and eventual failure in a wide range of industrial applications. Pump manufacturers recognize that cavitation damage can be minimized by utilizing advanced hydraulic designs and employing new state-of-the-art materials. The materials solution is particularly attractive because it does not involve detailed engineering studies, new pattern equipment, or long lead times. This paper traces the development, over the past decade, of a new class of cavitation resistant stainless steels. The properties and engineering characteristics of these alloys are described, and several initial field applications are discussed.

  9. Experimental determination of cavitation thresholds in liquid water and mercury

    SciTech Connect

    Taleyarkhan, R.P.; West, C.D.; Moraga, F.

    1998-11-01

    An overview is provided on cavitation threshold measurement experiments for water and mercury. Various aspects to be considered that affect onset determination are discussed along with design specifications developed for construction of appropriate apparatus types. Both static and transient-cavitation effects were studied using radically different apparatus designs. Preliminary data are presented for cavitation thresholds for water and mercury over a range of temperatures in static and high-frequency environments. Implications and issues related to spallation neutron source target designs and operation are discussed.

  10. Cavitation and Electrochemical Characteristics in Seawater by Water Cavitation Peening of 5083-O al Alloy for Ships

    NASA Astrophysics Data System (ADS)

    Hyun, Koangyong; Kim, Seong-Jong

    Aluminum (Al) alloy ships are vulnerable to both damage from chlorine ions in seawater environments and cavitation-erosion due to fast relative motion of metal and liquid resulting from lightweight and high-speed vessels moving through seawater. These corrosive processes cause damage to the hulls of ships, resulting in large economic losses. Recently, cavitation peening technology to improve the durability of a material has been in development. The technology works by forming compressive residual stress on the surface layer of the material in order to improve fatigue strength and fatigue life. In this study, we performed a water cavitation peening (WCP) on a 5083-O Al alloy for ships by applying an ultrasonic piezoelectric effect and cavitation effect, as described in ASTM-G32. From these experiments, we determined an optimum WCP duration, 2.5min, for sufficient cavitation resistance characteristics. This timing improved cavitation resistance by 48.68% compared to the untreated condition. A comprehensive comparison of all of results revealed that the optimum WCP duration was 3min with respect to the point of cavitation and corrosion resistance.

  11. Testing hypotheses that link wood anatomy to cavitation resistance and hydraulic conductivity in the genus Acer.

    PubMed

    Lens, Frederic; Sperry, John S; Christman, Mairgareth A; Choat, Brendan; Rabaey, David; Jansen, Steven

    2011-05-01

    • Vulnerability to cavitation and conductive efficiency depend on xylem anatomy. We tested a large range of structure-function hypotheses, some for the first time, within a single genus to minimize phylogenetic 'noise' and maximize detection of functionally relevant variation. • This integrative study combined in-depth anatomical observations using light, scanning and transmission electron microscopy of seven Acer taxa, and compared these observations with empirical measures of xylem hydraulics. • Our results reveal a 2 MPa range in species' mean cavitation pressure (MCP). MCP was strongly correlated with intervessel pit structure (membrane thickness and porosity, chamber depth), weakly correlated with pit number per vessel, and not related to pit area per vessel. At the tissue level, there was a strong correlation between MCP and mechanical strength parameters, and some of the first evidence is provided for the functional significance of vessel grouping and thickenings on inner vessel walls. In addition, a strong trade-off was observed between xylem-specific conductivity and MCP. Vessel length and intervessel wall characteristics were implicated in this safety-efficiency trade-off. • Cavitation resistance and hydraulic conductivity in Acer appear to be controlled by a very complex interaction between tissue, vessel network and pit characteristics.

  12. Cavitation dynamics on a NACA0015 hydrofoil using time resolved X-ray densitometry

    NASA Astrophysics Data System (ADS)

    Ganesh, Harish; Wu, Juliana; Ceccio, Steven

    2015-11-01

    Recent investigations of partial cavitation have shown that the transition from stable to shedding cavities can be related to the presence of both propagating bubbly shocks and re-entrant liquid jets originating in the cavity closure region. In the present study, formation of sheet cavitation and its transition to periodically shedding cavities is studied on a NACA0015 hydrofoil in a recirculating water tunnel at different attack angles. Using high-speed videos and time resolved X-ray densitometry, the instantaneous void fraction flow fields are obtained to identify the principal mechanism responsible for transition from stable to shedding cavities over a range of attack angles and cavitation numbers. The role of attack angle is of particular interest, since is it related to the pressure gradient at cavity enclosure, and can lead to the formation of stronger reentrant flows. The relative importance of reentrant liquid flow and bubbly shock wave propagation will be discussed This work is supported by Office of Naval Research.

  13. Large-eddy simulation of cavitating nozzle flow and primary jet break-up

    NASA Astrophysics Data System (ADS)

    Ã-rley, F.; Trummler, T.; Hickel, S.; Mihatsch, M. S.; Schmidt, S. J.; Adams, N. A.

    2015-08-01

    We employ a barotropic two-phase/two-fluid model to study the primary break-up of cavitating liquid jets emanating from a rectangular nozzle, which resembles a high aspect-ratio slot flow. All components (i.e., gas, liquid, and vapor) are represented by a homogeneous mixture approach. The cavitating fluid model is based on a thermodynamic-equilibrium assumption. Compressibility of all phases enables full resolution of collapse-induced pressure wave dynamics. The thermodynamic model is embedded into an implicit large-eddy simulation (LES) environment. The considered configuration follows the general setup of a reference experiment and is a generic reproduction of a scaled-up fuel injector or control valve as found in an automotive engine. Due to the experimental conditions, it operates, however, at significantly lower pressures. LES results are compared to the experimental reference for validation. Three different operating points are studied, which differ in terms of the development of cavitation regions and the jet break-up characteristics. Observed differences between experimental and numerical data in some of the investigated cases can be caused by uncertainties in meeting nominal parameters by the experiment. The investigation reveals that three main mechanisms promote primary jet break-up: collapse-induced turbulent fluctuations near the outlet, entrainment of free gas into the nozzle, and collapse events inside the jet near the liquid-gas interface.

  14. Evidence of grain-boundary-sliding-induced cavitation in ceramics under compression

    SciTech Connect

    Blanchard, C.R.; Chan, K.S. )

    1993-07-01

    Detailed microscopy of two crept aluminas, one with (AD99) and one without (Lucalox) a grain boundary glassy phase, has been performed to determine the pertinent damage mechanisms during creep. Evidence is presented for a nucleation-controlled cavitation process where creep cavities nucleate primarily on two-grain facets, followed by cavity growth and coalescence to form grain-facet-sized cavities and microcracks. A variety of creep cavity morphologies were observed in Lucalox, including spheroidal and irregularly shaped cavities. The latter finding implies a strong influence of crystallographic orientation and the corresponding surface energy of the cavitated planes on the cavity shaped. In contrast, classical spheroidal cavities were observed in AD99 due to the presence of a viscous phase along grain boundaries. Direct evidence for grain boundary sliding as the process driving force for cavitation in Lucalox is presented together with evidence for the nucleation of creep cavities at grain boundary ledges. These findings are compared to the grain boundary sliding (GBS) and small-angle neutron scattering (SANS) measurements performed previously on the same systems. Based on this study, the cavity nucleation process in the glassy-phase- and non-glassy-phase-containing aluminas is apparently similar as both involve the nucleation of rows of equally sized and equally spaced cavities.

  15. Large-eddy simulation of cavitating nozzle flow and primary jet break-up

    SciTech Connect

    Örley, F. Trummler, T.; Mihatsch, M. S.; Schmidt, S. J.; Adams, N. A.; Hickel, S.

    2015-08-15

    We employ a barotropic two-phase/two-fluid model to study the primary break-up of cavitating liquid jets emanating from a rectangular nozzle, which resembles a high aspect-ratio slot flow. All components (i.e., gas, liquid, and vapor) are represented by a homogeneous mixture approach. The cavitating fluid model is based on a thermodynamic-equilibrium assumption. Compressibility of all phases enables full resolution of collapse-induced pressure wave dynamics. The thermodynamic model is embedded into an implicit large-eddy simulation (LES) environment. The considered configuration follows the general setup of a reference experiment and is a generic reproduction of a scaled-up fuel injector or control valve as found in an automotive engine. Due to the experimental conditions, it operates, however, at significantly lower pressures. LES results are compared to the experimental reference for validation. Three different operating points are studied, which differ in terms of the development of cavitation regions and the jet break-up characteristics. Observed differences between experimental and numerical data in some of the investigated cases can be caused by uncertainties in meeting nominal parameters by the experiment. The investigation reveals that three main mechanisms promote primary jet break-up: collapse-induced turbulent fluctuations near the outlet, entrainment of free gas into the nozzle, and collapse events inside the jet near the liquid-gas interface.

  16. Synchrotron quantification of ultrasound cavitation and bubble dynamics in Al-10Cu melts.

    PubMed

    Xu, W W; Tzanakis, I; Srirangam, P; Mirihanage, W U; Eskin, D G; Bodey, A J; Lee, P D

    2016-07-01

    Knowledge of the kinetics of gas bubble formation and evolution under cavitation conditions in molten alloys is important for the control casting defects such as porosity and dissolved hydrogen. Using in situ synchrotron X-ray radiography, we studied the dynamic behaviour of ultrasonic cavitation gas bubbles in a molten Al-10 wt%Cu alloy. The size distribution, average radius and growth rate of cavitation gas bubbles were quantified under an acoustic intensity of 800 W/cm(2) and a maximum acoustic pressure of 4.5 MPa (45 atm). Bubbles exhibited a log-normal size distribution with an average radius of 15.3 ± 0.5 μm. Under applied sonication conditions the growth rate of bubble radius, R(t), followed a power law with a form of R(t)=αt(β), and α=0.0021 &β=0.89. The observed tendencies were discussed in relation to bubble growth mechanisms of Al alloy melts. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. Fluid-structure interaction in case of water hammer with cavitation

    NASA Astrophysics Data System (ADS)

    Tijsseling, A. S.

    1993-06-01

    The transient behavior of liquid-filled pipe systems is studied. The time scale is acoustic. Pressure waves in the liquid, and axial, lateral, and torsional stress waves in the pipes are the dominant phenomena. The phenomena in the liquid (water hammer) and the phenomena in the pipe system (structural dynamic) influence each other if significant radial and axial pipe motions occur. When, in addition, the dynamic pressure drops to the vapor pressure, vapor bubbles will form in the liquid (cavitation). The major new element of the present work is in the simultaneous occurrence of fluid-structure interaction (FSI) and cavitation, which is investigated both theoretically and experimentally. An extensive review of literature on the subject is given. One dimensional basic equations are obtained by integration of general three dimensional equations for fluid dynamics and structural linear elasticity. Three FSI-mechanisms (junction, Poisson, and friction-coupling) are taken into account. The governing equations, formulated as a hyperbolic set of fourteen first-order partial differential equations, are solved by the method of characteristics. Vapor cavitation is numerically simulated by the relatively simple concentrated cavity model.

  18. Cavitation erosion of low-density polyethylene coatings for pipe liners

    NASA Astrophysics Data System (ADS)

    Hattori, S.; Benitani, E.; Ruan, W.; Suda, Y.; Takeuchi, R.; Iwata, T.

    2015-12-01

    The relationship between mechanical properties and the erosion rate was examined for chloroprene rubber and a number of polyethylene materials produced by different methods. As electric power plants are in operation over long periods of time, the effect of aging was also examined by testing material intended for use in pipes in electric power plants. Cavitation erosion tests were carried out by using a flowing apparatus as specified in the American Society for Testing Materials G134-95 standard. A flow velocity of 150 m/s and a test time of 24hours, were the experimental conditions used for a cavitating liquid jet test on polyethylene. The maximum depth of erosion rate (MaxDER) of polyethylene was found to decrease with the increase in hardness. Among all the tested materials, the relatively high molecular weight polyethylene with low density (m-LLDPE-H), showed the best resistance to cavitation erosion in terms of MaxDER. The effect of aging on the erosion rate of polyethylene was limited.

  19. The effect of boundary slip and cavitation on hydrodynamic pressure generation in pocket bearings

    NASA Astrophysics Data System (ADS)

    Muchammad, Tauviqirrahman, Mohammad; Pratomo, Ariawan Wahyu; Jamari, J.; Schipper, Dirk J.

    2016-04-01

    Surface texturing as well as boundary slip is an effective approach to increase the tribological performance, friction and load support of lubricated mechanical components. However, in a textured bearing with boundary slip, cavitation, which is generally neglected, is important, and it alters the flow behavior. Therefore, in this paper a novel analytical equation was proposed based on a modified Reynolds equation considering boundary slip and cavitation. The modified Reynolds equation was derived by following the general approach to deduce the Reynolds equation from the Navier-Stokes equation by assuming classical assumptions, except that boundary slip was present. A theoretical investigation was carried out to study the effect of boundary slip including cavitation on the pressure distribution of a pocket bearing. Different slip configurations (full slip, single slip and semi slip) were studied and compared to various pocket depths. The results indicated that the presence of boundary slip both on the leading edge of the contact and the pocket area (i.e. the "semi slip" case) could result in a significant improvement in the hydrodynamic pressure generation; thus, it causes an increased load support. The above improvement depends on the pocket depth of the bearing.

  20. Dynamic analysis on cavitation and embolization in vascular plants under tension

    NASA Astrophysics Data System (ADS)

    Ryu, Jeongeun; Hwang, Bae Geun; Kim, Yangmin; Lee, Sang Joon

    2014-11-01

    Plants can transport sap water from the soil to the tip of their leaves using the tensile forces created by leaf transpiration without any mechanical pumps. However, the high tension adversely induces a thermodynamically metastable state in sap water with negative pressure and gas bubbles are prone to be formed in xylem vessels. Cavitation easily breaks down continuous water columns and grows into embolization, which limits water transport through xylem vessels. Meanwhile, the repair process of embolization is closely related to water management and regulation of sap flow in plants. In this study, the cavitation and embolization phenomena of liquid water in vascular plants and a physical model system are experimentally and theoretically investigated in detail under in vivo and in vitro conditions. This study will not only shed light on the understanding of these multiphase flows under tension but also provide a clue to solve cavitation problems in micro-scale conduits and microfluidic network systems. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2008-0061991).

  1. Cavitation bands control porosity and fluid flow in lower crustal shear zones

    NASA Astrophysics Data System (ADS)

    Menegon, Luca; Fusseis, Florian; Stunitz, Holger

    2014-05-01

    Shear zones channelize fluid flow in the Earth's crust. A number of mechanisms were suggested to control fluid migration pathways in upper- and midcrustal shear zones, amongst them creep cavitation, which is well-known from deforming metals and ceramics. Deep crustal fluid migration is hardly constrained by any observations, and so it remains unclear how fluids are channelized and distributed in an actively deforming lower crustal shear zone. This study investigates the deformation mechanisms, fluid-rock interaction and development of porosity in a mangerite ultramylonite from Lofoten, northern Norway. The synkinematic mineral assemblage consists of plagioclase, K-feldspar, hornblende, quartz, calcite and biotite, and yields P, T conditions of deformation of 700-730° C, 0.65-0.8 GPa. Mass-balance calculations indicate (1) a volume increase of 2.3%, and (2) fluid infiltration during the protolith-ultramylonite transformation. Microstructural observations and EBSD analysis are consistent with diffusion creep as the dominant deformation mechanism in the ultramylonite. The microstructure shows extensive evidence of synkinematic nucleation of new phases in dilatant sites resulting from the concomitant operation of grain boundary sliding and cavitation during grain-size sensitive creep. EBSD maps show the occurrence of isolated quartz grains along C' shear bands in feldspathic layers. Quartz does not show a crystallographic preferred orientation in these bands, suggesting that it precipitated in cavities. The occurrence of such quartz bands is consistent with the coalescence of individual pores originally formed at dilatant sites resulting from the operation of grain boundary sliding. Opening of pores implies local dilatancy. Positive volume change accompanied by fluid infiltration, as inferred from the mass balance calculations, is consistent with the precipitation of new phases in pores from intragranular fluids. We used synchrotron X-ray microtomography to analyse

  2. Physical insights into the sonochemical degradation of recalcitrant organic pollutants with cavitation bubble dynamics.

    PubMed

    Sivasankar, Thirugnanasambandam; Moholkar, Vijayanand S

    2009-08-01

    This paper tries to discern the mechanistic features of sonochemical degradation of recalcitrant organic pollutants using five model compounds, viz. phenol (Ph), chlorobenzene (CB), nitrobenzene (NB), p-nitrophenol (PNP) and 2,4-dichlorophenol (2,4-DCP). The sonochemical degradation of the pollutant can occur in three distinct pathways: hydroxylation by ()OH radicals produced from cavitation bubbles (either in the bubble-bulk interfacial region or in the bulk liquid medium), thermal decomposition in cavitation bubble and thermal decomposition at the bubble-liquid interfacial region. With the methodology of coupling experiments under different conditions (which alter the nature of the cavitation phenomena in the bulk liquid medium) with the simulations of radial motion of cavitation bubbles, we have tried to discern the relative contribution of each of the above pathway to overall degradation of the pollutant. Moreover, we have also tried to correlate the predominant degradation mechanism to the physico-chemical properties of the pollutant. The contribution of secondary factors such as probability of radical-pollutant interaction and extent of radical scavenging (or conservation) in the medium has also been identified. Simultaneous analysis of the trends in degradation with different experimental techniques and simulation results reveals interesting mechanistic features of sonochemical degradation of the model pollutants. The physical properties that determine the predominant degradation pathway are vapor pressure, solubility and hydrophobicity. Degradation of Ph occurs mainly by hydroxylation in bulk medium; degradation of CB occurs via thermal decomposition inside the bubble, degradation of PNP occurs via pyrolytic decomposition at bubble interface, while hydroxylation at bubble interface contributes to degradation of NB and 2,4-DCP.

  3. Removal of residual nuclei following a cavitation event: a parametric study.

    PubMed

    Duryea, Alexander P; Tamaddoni, Hedieh A; Cain, Charles A; Roberts, William W; Hall, Timothy L

    2015-09-01

    The efficacy of ultrasound therapies such as hock-wave lithotripsy and histotripsy can be compromised by residual cavitation bubble nuclei that persist following the collapse of primary cavitation. In our previous work, we have developed a unique strategy for mitigating the effects of these residual bubbles using low-amplitude ultrasound pulses to stimulate their aggregation and subsequent coalescence—effectively removing them from the field. Here, we further develop this bubble removal strategy through an investigation of the effect of frequency on the consolidation process. Bubble removal pulses ranging from 0.5 to 2 MHz were used to sonicate the population of residual nuclei produced upon collapse of a histotripsy bubble cloud. For each frequency, mechanical index(MI) values ranging from 0 to approximately 1.5 were tested.Results indicated that, when evaluated as a function of bubble removal pulse MI, the efficacy of bubble removal shows markedly similar trends for all frequencies tested. This behavior divides into three distinct regimes (with provided cutoffs being approximate): 1) MI < 0.2: Minimal effect on the population of remanent cavitation nuclei; 2) 0.2 < MI < 1: Aggregation and subsequent coalescence of residual bubbles, the extent of which trends toward a maximum; and 3) MI > 1: Bubble coalescence is compromised as bubble removal pulses induce high-magnitude inertial cavitation of residual bubbles. The major distinction in these trends came for bubble removal pulses applied at 2 MHz, which were observed to generate the most effective bubble coalescence of all frequencies tested. We hypothesize that this is a consequence of the secondary Bjerknes force being the major facilitator of the consolidation process, the magnitude of which increases when the bubble size distribution is far from resonance such that the phase difference of oscillation of individual bubbles is minimal.

  4. Removal of Residual Nuclei Following a Cavitation Event: A Parametric Study

    PubMed Central

    Duryea, Alexander P.; Tamaddoni, Hedieh A.; Cain, Charles A.; Roberts, William W.; Hall, Timothy L.

    2015-01-01

    The efficacy of ultrasound therapies such as shock wave lithotripsy and histotripsy can be compromised by residual cavitation bubble nuclei that persist following the collapse of primary cavitation. In our previous work, we have developed a unique strategy for mitigating the effects of these residual bubbles using low amplitude ultrasound pulses to stimulate their aggregation and subsequent coalescence—effectively removing them from the field. Here, we further develop this bubble removal strategy through an investigation of the effect of frequency on the consolidation process. Bubble removal pulses ranging from 0.5 – 2 MHz were used to sonicate the population of residual nuclei produced upon collapse of a histotripsy bubble cloud. For each frequency, mechanical index (MI) values ranging from 0 to approximately 1.5 were tested. Results indicated that, when evaluated as a function of bubble removal pulse MI, the efficacy of bubble removal shows markedly similar trends for all frequencies tested. This behavior divides into three distinct regimes (with provided cutoffs being approximate): (1) MI < 0.2: Minimal effect on the population of remnant cavitation nuclei; (2) 0.2 < MI < 1: Aggregation and subsequent coalescence of residual bubbles, the extent of which trends toward a maximum; (3) MI > 1: Bubble coalescence is compromised as bubble removal pulses induce high magnitude inertial cavitation of residual bubbles. The major distinction in these trends came for bubble removal pulses applied at 2 MHz, which were observed to generate the most effective bubble coalescence of all frequencies tested. We hypothesize that this is a consequence of the secondary Bjerknes force being the major facilitator of the consolidation process, the magnitude of which increases when the bubble size distribution is far from resonance such that the phase difference of oscillation of individual bubbles is minimal. PMID:26719861

  5. Inactivation of food spoilage microorganisms by hydrodynamic cavitation to achieve pasteurization and sterilization of fluid foods.

    PubMed

    Milly, P J; Toledo, R T; Harrison, M A; Armstead, D

    2007-11-01

    Hydrodynamic cavitation is the formation of gas bubbles in a fluid due to pressure fluctuations induced by mechanical means. Various high-acid (pH < [corrected]/= 4.6) fluid foods were processed in a hydrodynamic cavitation reactor to determine if commercial sterility can be achieved at reduced processing temperatures. Sporicidal properties of the process were also tested on a low-acid (pH > [corrected] 4.6) fluid food. Fluid foods were pumped under pressure into a hydrodynamic cavitation reactor and subjected to 2 rotor speeds and flow rates to achieve 2 designated exit temperatures. Thermal inactivation kinetics were used to determine heat-induced lethality for all organisms. Calcium-fortified apple juice processed at 3000 and 3600 rpm rotor speeds on the reactor went through a transient temperature change from 20 to 65.6 or 76.7 degrees C and the total process lethality exceeded 5-log reduction of Lactobacillus plantarum and Lactobacillus sakei cells, and Zygosaccharomyces bailii cells and ascospores. Tomato juice inoculated with Bacillus coagulans spores and processed at 3000 and 3600 rpm rotor speeds endured a transient temperature from 37.8 to 93.3 or 104.4 degrees C with viable CFU reductions of 0.88 and 3.10 log cycles, respectively. Skim milk inoculated with Clostridium sporogenes putrefactive anaerobe 3679 spores and processed at 3000 or 3600 rpm rotor speeds endured a transient temperature from 48.9 to 104.4 or 115.6 degrees C with CFU reductions of 0.69 and 2.84 log cycles, respectively. Utilizing hydrodynamic cavitation to obtain minimally processed pasteurized low-acid and commercially sterilized high-acid fluid foods is possible with appropriate process considerations for different products.

  6. A study of cavitating and non-cavitating performances of valveless micropump through dynamic measurement of chamber pressure

    NASA Astrophysics Data System (ADS)

    Chandrasekaran, Arvind; Packirisamy, Muthukumaran

    2015-03-01

    A lot of work has gone into the study of valveless micropumps for various applications. However, the complex fluid-structure interactional physics and associated phenomena such as cavitation affects the characterization of valveless micropumps, for applying them reliably in any real-time applications. This paper presents a method of characterization of valveless micropump performance through dynamic measurement of chamber pressure. Experimental investigation has been carried out to study the micropump behavior through pressure measurement under both cavitation and non-cavitation conditions, and the results show that this technique is useful for the characterization of micropump.

  7. Cavitation in liquid cryogens. 2: Hydrofoil

    NASA Technical Reports Server (NTRS)

    Hord, J.

    1973-01-01

    Boundary layer principles, along with two-phase concepts, are used to improve existing correlative theory for developed cavity data. Details concerning cavity instrumentation, data analysis, correlative techniques, and experimental and theoretical aspects of a cavitating hydrofoil are given. Both desinent and thermodynamic data, using liquid hydrogen and liquid nitrogen, are reported. The thermodynamic data indicated that stable thermodynamic equilibrium exists throughout the vaporous cryogen cavities. The improved correlative formulas were used to evaluate these data. A new correlating parameter based on consideration of mass limiting two-phase flow flux across the cavity interface, is proposed. This correlating parameter appears attractive for future correlative and predictive applications. Agreement between theory and experiment is discussed, and directions for future analysis are suggested. The front half of the cavities, developed on the hydrofoil, may be considered as parabolically shaped.

  8. Cavitation microstreaming and material transport around microbubbles

    NASA Astrophysics Data System (ADS)

    Manasseh, Richard; Tho, Paul; Ooi, Andrew; Petkovic-Duran, Karolina; Zhu, Yonggang

    2010-01-01

    It has been suggested that cavitation microstreaming plays a role in the therapeutic action of microbubbles driven by ultrasound, such as the sonothrombolytic and sonoporative phenomena. Microscopic particle-image velocimetry experiments are presented, showing that many different microstreaming patterns are possible around a microbubble when it is on a surface. Each pattern is associated with a particular oscillation mode of the bubble and generates a different shear stress distribution. It was found that it is possible to change the flow pattern by changing the sound frequency. Microstreaming flows around bubbles could be responsible for mixing therapeutic agents into the surrounding blood, as well as assisting sonoporative delivery of molecules across cell membranes. Appropriate tuning of the driving frequency may benefit therapies.

  9. Localization in an Acoustic Cavitation Cloud

    NASA Astrophysics Data System (ADS)

    Miao, Bo-Ya; An, Yu

    2017-03-01

    Using a nonlinear sound wave equation for a bubbly liquid in conjunction with an equation for bubble pulsation, we predict and experimentally demonstrate the appearance of a gap in the frequency spectrum of a sound wave propagating in a cavitation cloud comprising bubbles. For bubbles with an ambient radius of 100 {\\mu}m, the calculations revealed that this gap corresponds to the phenomenon of sound wave localization. For bubbles with an ambient radius of 120 {\\mu}m, this spectral gap relates to a forbidden band of the sound wave. In the experiment, we observed the predicted gap in the frequency spectrum in soda water; however, in tap water, no spectral gap was present because the bubbles were much smaller than 100 {\\mu}m.

  10. Ultrasonic cavitation for disruption of microalgae.

    PubMed

    Greenly, Justin M; Tester, Jefferson W

    2015-05-01

    Challenges with mid-stream fractionation steps in proposed microalgae biofuel pathways arise from the typically dilute cell density in growth media, micron scale cell sizes, and often durable cell walls. For microalgae to be a sustainable source of biofuels and co-products, efficient fractionation by some method will be necessary. This study evaluates ultrasonic cell disruption as a processing step that fractionates microalgae. A range of species types with different sizes and cell wall compositions were treated. The initial seconds of sonication offered the most significant disruption, even for the more durable Nannochloropsis cells. Following this initial period, diminishing effectiveness was attributed, by acoustic measurements, to attenuation of the ultrasound in the ensuing cloud of cavitating bubbles. At longer exposure times, differences between species were more pronounced. Processing higher concentrations of Isochrysis slowed cell disintegration only marginally, making the expenditure of energy more worthwhile. Copyright © 2014 Elsevier Ltd. All rights reserved.

  11. Experimental investigation of cavitation in superfluid [sup 4]He

    SciTech Connect

    Pettersen, M.S.; Balibar, S. ); Maris, H.J. )

    1994-05-01

    We present the results of experiments to study cavitation in liquid [sup 4]He at negative pressures. A focused sound wave is used to generate a negative pressure in a small region of the liquid, and the cavitation is detected by light scattering. We have studied the cavitation as a function of the temperature and static pressure applied to the liquid. We are able to observe the statistical nature of the cavitation process, and to determine the nucleation barrier and the attempt frequency. The results for the attempt frequency are lower than expected for homogeneous nucleation. We discuss the possibility that the nucleation is occurring on quantized vortices. The tensile strength at constant pressure decreases slowly with increasing temperature in the range 0.8 to 1.5 K, drops rapidly as the temperature approaches the [lambda] point, and then decreases slowly above [ital T][sub [lambda

  12. Metal of cavitation erosion of a hydrodynamic reactor

    NASA Astrophysics Data System (ADS)

    Zakirzakov, A. G.; Brand, A. E.; Petryakov, V. A.; Gordievskaya, E. F.

    2017-02-01

    Cavitation erosion is a major cause of the petroleum equipment hydraulic erosion, which leads to the metal weight loss of the equipment and its breakdown, which can be followed by the full stop of the plant or company work. The probability of the metal weight loss and equipment failure can be reduced by the use of special protective coatings or rivets, made of the sacrificial metals, the use of which significantly increases the service life and the production equipment reliability. The article investigates the cavitation erosion effect, occurred under the condition of the advanced hydrodynamic cavitation on the hydrodynamic cavitation reactor. This article presents the results of the experiments and recommendations for increasing the operational resource.

  13. Hign-speed penetration of projectile with cavitator into sand

    NASA Astrophysics Data System (ADS)

    Daurskikh, Anna; Veldanov, Vladislav

    2011-06-01

    Cavitators are used in underwater projectiles design to form a cavern in which projectile could move with no or significantly reduced drag. An investigation of possible application of this structural element for penetration into porous media was conducted. High-speed impact of a conical-shaped head projectile with cavitator was studied in terms of its influence on penetration capacity and projectile stability in sand for impact velocity about 1500 m/s. Cavitators were manufactured of steel with different strength moduli, and thus two penetration regimes (with eroding/non-eroding cavitator) were compared. Numerical simulations showing wave propagation in target and projectile were performed in AUTODYN with Johnson-Cook model for projectile and granular model for sand.

  14. Synergistic degradation of chitosan by impinging stream and jet cavitation.

    PubMed

    Huang, Yongchun; Wang, Pengfei; Yuan, Yuan; Ren, Xian'e; Yang, Feng

    2015-11-01

    Chitosan degradation was investigated using a combination of jet cavitation and impinging stream. Different operating parameters such as the initial concentration (1-5 g L(-1)), initial pH (3.2-4.8), solution temperature (30, 40, 50, 60, and 70°C), inlet pressure (0.1-0.45 MPa), and treatment time (0-120 min) were optimized to achieve the maximum degradation of chitosan. After the optimization of jet cavitation parameters, chitosan degradation was carried out using venturi tubes of different structures (the fluidic generator). The efficiency of the jet cavitation degradation was improved significantly by combining with impinging stream. The structures of the degradation products were characterized by Fourier-transform infrared spectroscopy and X-ray diffraction. This study has conclusively established that a combination of jet cavitation and impinging stream can be effectively used for the complete degradation of chitosan.

  15. Dental Pulp Reaction to Cavit Temporary Filling Material.

    DTIC Science & Technology

    1976-09-22

    histologically evaluated at three time periods to identify initial, early and final response. There were no statistically significant differences in pulpal response between Cavit and the zinc oxide- eugenol controls. (Author)

  16. Cavitation Performance of a Centrifugal Pump with Water and Mercury

    NASA Technical Reports Server (NTRS)

    Hammitt, F. G.; Barton, R. K.; Cramer, V. F.; Robinson, M. J.

    1961-01-01

    The cavitation performance of a given centrifugal pump with water (hot and cold) and mercury is compared. It is found that there are significant scale effects with all fluids tested, with the Thoma cavitation parameter decreasing in all cases for increased pump speed or fluid Reynolds' number. The data for a fixed flow coefficient fall into a single curve when plotted against pump speed (or fluid velocity), rather than against Reynolds' number. Conversely, the Thoma parameter for a given Reynolds' number is approximately twice as large for mercury as for water. The direction of this variation is as predicted from consideration of the cavitation thermodynamic parameters which vary by a factor of 10(exp 7) between these fluids. No difference in cavitation performance between hot and cold water (approximately 160 F and 80 F) was observed, However, the thermodynamic parameters vary only by a factor of 5.

  17. Optimization of centrifugal pump cavitation performance based on CFD

    NASA Astrophysics Data System (ADS)

    Xie, S. F.; Wang, Y.; Liu, Z. C.; Zhu, Z. T.; Ning, C.; Zhao, L. F.

    2015-01-01

    In order to further improve the cavitation performance of a centrifugal pump, slots on impeller blade near inlet were studied and six groups of hydraulic model were designed. Base on cavitating flow feature inside a centrifugal pump, bubble growth and implosion are calculated from the Rayleigh-Plesset equation which describes the dynamic behavior of spherical bubble and RNG κ-epsilon model was employed to simulate and analyze the internal two-phase flow of the model pump under the same conditions. The simulation results show that slots on blade near inlet could improve the cavitation performance and cavitation performance improvement of the second group was more obvious. Under the same conditions, the pressure on the back of blade near inlet was higher than the pressure on the back of unmodified blade near inlet, and energy distribution in the flow channel between the two blades was more uniform with a small change of head.

  18. Design method of water jet pump towards high cavitation performances

    NASA Astrophysics Data System (ADS)

    Cao, L. L.; Che, B. X.; Hu, L. J.; Wu, D. Z.

    2016-05-01

    As one of the crucial components for power supply, the propulsion system is of great significance to the advance speed, noise performances, stabilities and other associated critical performances of underwater vehicles. Developing towards much higher advance speed, the underwater vehicles make more critical demands on the performances of the propulsion system. Basically, the increased advance speed requires the significantly raised rotation speed of the propulsion system, which would result in the deteriorated cavitation performances and consequently limit the thrust and efficiency of the whole system. Compared with the traditional propeller, the water jet pump offers more favourite cavitation, propulsion efficiency and other associated performances. The present research focuses on the cavitation performances of the waterjet pump blade profile in expectation of enlarging its advantages in high-speed vehicle propulsion. Based on the specifications of a certain underwater vehicle, the design method of the waterjet blade with high cavitation performances was investigated in terms of numerical simulation.

  19. Cavitation Damage Mechanisms: Experimental Study of Cavitation in a Spool Valve.

    DTIC Science & Technology

    1980-02-01

    an infinite distance from the bubble. The bubble responds with an oscillating radius r. Upon linearizing the perturbations in the Rayleigh equation ...equal to Cc The above equation suggests a linear relationship between Q and b. Because of the relatively small values of b employed in this study and... Plesset and Prosperetti (I27], the natural frequency of the oscillating bubble can be expressed W 4 ~i +3(p.-p v )ro02~ (Cl) in which S is the surface

  20. Cavitational synthesis of nanostructured inorganic materials for enhanced heterogeneous catalysis

    NASA Astrophysics Data System (ADS)

    Krausz, Ivo Michael

    The synthesis of nanostructured inorganic materials by hydrodynamic cavitation processing was investigated. The goal of this work was to develop a general synthesis technique for nanostructured materials with a control over crystallite size in the 1--20 nm range. Materials with crystallite sizes in this range have shown enhanced catalytic activity compared to materials with larger crystallite sizes. Several supported and unsupported inorganic materials were studied to understand the effects of cavitation on crystallite size. Cavitation processing of calcium fluoride resulted in more spherical particles, attached to one another by melted necks. This work produced the first evidence of shock wave heating of nanostructured materials by hydrodynamic cavitation processing. Hydrodynamic cavitation synthesis of various catalytic support materials indicated that their phase composition and purity could be controlled by adjustment of the processing parameters. Zirconia/alumina supports synthesized using hydro-dynamic cavitation and calcined to 1368 K retained a high purity cubic zirconia phase, whereas classically prepared samples showed a phase transformation to monoclinic zirconia. Similarly, the synthesis of alumina resulted in materials with varying Bohmite and Bayerite contents as a function of the process parameters. High temperature calcination resulted in stable alumina supports with varying amounts of delta-, and theta-alumina. Synthesis studies of palladium and silver showed modest variations in crystallite size as a function of cavitation process parameters. Calcination resulted in larger grain materials, indicating a disappearance of intergrain boundaries. Based on these results, a new synthesis method was studied involving controlled agglomeration of small silver crystallites by hydrodynamic cavitation processing, followed by deposition on alumina. The optimal pH, concentration, and processing time for controlling the silver crystallite size in the cavitation