•Strong nonlinear interactions between one and two underwater explosion bubbles with a free surface are numerically studied.•Numerical method is based on axisymmetrical fully compressible three-phase ...homogeneous model coupled with two interface advection equations.•Numerical and experimental data agree well regarding the shape of bubbles and free surface.•Detailed pressure and velocity contours during the interaction process are obtained and can better reveal the mechanism underlying the dynamics between the bubbles and free surface.•Motion characteristics of the free surface and bubbles are investigated under different non-dimensional standoff parameters.
In this study, strong nonlinear interactions of one and two underwater explosion bubbles with a free surface are numerically studied using an axisymmetrical fully compressible three-phase homogeneous model. The bubble interfaces and free surface are captured by solving two interface advection equations of vapor and air phases. The numerical results are validated via comparisons with the experimental results. The single-bubble case is validated first, and good quantitative and qualitative agreements are achieved. Special features of the interactions, such as jet impact, toroidal bubble, and primary and secondary water spike, are observed in our numerical model. The detailed pressure and velocity contours during the interaction process are obtained and can better reveal the mechanism underlying the bubbles and free surface dynamics. Afterward, the characteristics of the motion of the free surface and the bubbles are investigated considering different non-dimensional standoff parameters. Four distinct patterns of free surface motion are identified. Next, strong interactions between two bubbles and a free surface are simulated. The essential physical phenomena, such as coalesced bubble, annular residual, and bubble splitting, are reproduced well in the representative experiments. Finally, a parametric study reveals the dependence of the center water spike on the interaction between the bubbles and the free surface.
Evolution of strong nonlinear interaction between a spark-genarated underwater explosion bubble with a free surface. Special characteristic motions including jet impact, toroidal bubble, center and secondary free surface spike are well captured with experimental images. Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Laser-induced cavitation bubble dynamics near a rigid surface were numerically studied using a three-dimensional fully compressible model.•Bubble dynamics under the various standoff were discussed ...in detail based on pressure field and velocity field.•Violent high-speed jet impact with extremely hot internal bubble temperature were well captured and analyzed.•Critical standoffs for wall impact pressure and the maximum bubble temperature based on the shape of the microjet were suggested.
Cavitation bubble dynamics include the releasing shock wave, violent jet impact, and extremely local high temperature at the collapse phase. Notably, in the case of a bubble collapsing near a rigid boundary, a high-velocity microjet toward structure is an important issue and significantly related to various engineering fields. A fully compressible mixture model based on the three-dimensional Navier-Stokes equation was used for numerical simulation of laser-induced single bubble dynamics near a rigid surface. Beside, a preconditioned dual-time stepping method and high-resolution interface capturing scheme were coupled with the numerical model for the stability and high-accuracy of simulation. The numerical results were validated by comparing with experimental data and good agreements were achieved. In near-field bubble dynamics, length scale dimensionless parameter is strongly affecting its behavior. Thus, the aspect ratio, jet velocity, wall impact pressure, and peak temperature were discussed in detail based on bubble behavior under different standoffs. Finally, we suggested the critical standoff for wall impact pressure and the maximum temperature.
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•Influence of phase-change on the collapse and rebound stages of spark-generated explosion bubbles was numerically studied.•A reasonable agreement of the bubble radius with the experimental data was ...obtained, particularly at the second cycle.•The condensation process had the highest influence and mainly occurred at the bubble interfaces with a thin boundary layer.•Secondary cavitation regions in the water field induced by rarefaction waves were observed.•The effects of source term by temperature changes on the bubble dynamics were estimated thoroughly.
Influences of phase-change are generally ignored by current numerical models that are used to study spark-generated cavitation bubble dynamics. However, this assumption was limited to predicting bubble behaviors only at the first expansion and collapse stages. In this study, we aimed to explore the phase-change effects on the cavitation bubble dynamics over multiple cycles. A combination of a two-phase homogeneous mixture model and interface-capturing method was adopted to simulate the bubble dynamics. The full compressibility of the water and vapor phases, heat transfer, condensation, and evaporation were involved in our numerical model. Phase-change processes due to pressure changes and temperature changes were evaluated to explore the major influence phenomenon on the bubble dynamics. By comparing with experimental data, a compatible bubble shape and radius evolution under a free-field condition was obtained, particularly at the rebound and collapse stages. Disturbance secondary cavitation regions in the water field induced by rarefaction waves were observed immediately after the second rebound stage. In addition, bubble dynamic behaviors were mainly affected by the condensation phenomenon. The condensation mass transfer rate increases, becomes extremely high at the final collapse stage, and decreases during the rebound stage. Moreover, the condensation phenomenon mainly occurs at the vapor–water bubble interfaces with a thin boundary layer. The evaporation phenomenon occurred purely inside bubbles with a uniform region. Finally, we discuss the effects of phase-change by temperature changes on the cavitation bubble dynamics. In general, these effects were sufficiently small during the first two-cycle bubble oscillations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Compressible multiphase model based on a geometrical PLIC-VOF based simulation method.•Fully conservative hyperbolic system is solved based on a Riemann solver.•Reconstruction of the Riemann solver ...for oscillation-free behavior near contact discontinuity.•Dynamic behavior of bubble collapses, high-speed jets, and pressure loads.•3D bubble collapse near a free surface and an oblique wall.
The dynamic behavior of bubble collapses, water jets, and pressure loads during the collapse of the bubble near walls and a free surface were numerically investigated via a geometrical volume of fluid (VOF)-based simulation method. The numerical method is based on the compressible Navier–Stokes equations in a conservative form that describe the flow of compressible viscous fluids. The equations are discretized on a general curvilinear grid using an associated Godunov-type numerical scheme, and a reconstruction of a computational finite-volume Riemann solver is introduced for suppression of oscillation near the interface between fluids. The interface was tracked using the VOF reconstruction method. The VOF method is based on a geometrical tool and Lagrangian propagation of the interface reconstructed by a piecewise linear interface calculation (PLIC), resulting in strictly mass-conserving and sharp interface solutions. The numerical procedure was validated for capturing sharp interface and strong shock waves. For the simulation of bubble collapse, grid dependence studies of a spark-generated bubble were studies of both spherical and non-spherical bubbles were conducted. The results showed good agreement between the simulation and experiment of the bubble dynamics during the collapse process. Subsequently, an investigation of a single bubble near a wall with different standoff distances was performed. The pressure loads induced by the jets impacting the walls were calculated and analyzed. Furthermore, a more complex case of bubble collapse near an oblique wall and free surface was simulated. The resulting bubble dynamics with the jets and free surface shape were compared via photographs of the experiments.
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•Dynamics of an underwater explosion bubble are numerically investigated.•The numerical method is based on a compressible homogeneous mixture model.•Good agreement is obtained between numerical and ...experimental results.•Details of the pressure pulse, water jet impact, and velocity field are discussed.•Effects of the buoyancy parameter on the bubble dynamics are carefully analyzed.
A compressible homogeneous mixture model was adopted to numerically investigate the dynamics of an underwater explosion bubble. The bubble-water interfaces were captured by solving an interface advection equation using a compressive high-resolution interface capturing method. The numerical model was validated by comparison with experimental results for a free-field underwater explosion. The results exhibited good agreement overall. Complex phenomena of dynamic bubble motion, including the bubble expansion, contraction, collapse, jet, and rebound, were accurately predicted. Under the effects of buoyancy on the dynamic motions, the upward migration process of the bubble was determined and analyzed in detail. Furthermore, the pressure pulse and jet velocity fields at typical moments were examined. Additionally, the effects of the buoyancy parameter on the bubble dynamics were carefully investigated. It was found that the upward migration behavior was stronger and the non-dimensional maximum jet velocity decreases for a larger buoyancy parameter.
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•A three-phase numerical model for air–steam mixture condensation flows is presented.•A fully compressible multiphase homogeneous mixture flow model is adopted.•The numerical results are in good ...agreement with experimental data.•Condensate water film layer thickness of almost 4.0 mm is observed at the outlet tube.•The effects of air mass fraction on condensation rate are investigated.
In this study, a fully compressible three-phase numerical model for steam condensation flow in the presence of air is presented. The model solves the Reynolds-averaged Navier–Stokes equation coupled with two interface advection equations. The Lee condensation model was applied to simulate the mass and energy transfer processes via interfaces. Several test cases were simulated for the air–steam mixture condensation flow in a vertical tube with different air mass fractions to verify the numerical model. The validity was demonstrated through comparisons of the centerline temperatures along the tube and experimental data; the results were in good agreement with experimental data. A detailed radial profile of the temperature, species mass fraction, and velocity was analyzed. A developing thin condensate water film along the tube and the thickest film layer at the outlet tube wall of approximately 4.0 mm were observed. Air accumulation at the steam–water interface was also represented. In addition, the effects of air mass fraction on the characteristics of the condensation rate were investigated.
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•An unsteady natural cavitating flow around an axisymmetric projectile is numerically studied using fully compressible homogeneous multiphase approach.•Good agreement is obtained regarding the cavity ...structures and dynamics evolution with the experimental data.•Detailed mechanisms of the cavity shedding with periodic cavity–vortex–pressure interaction behaviors are revealed.•The cavity shape tends to be mushier with increasing water temperature under the same reference cavitation number and reynolds number.
Here, an unsteady natural cavitating flow around an axisymmetric projectile is computationally studied using a homogeneous multiphase approach. The numerical models used are based on a dual-time preconditioning method, an interface-capturing scheme, and a modified cavitation model, to capture unsteady cavitation structure behaviors. Full compressibility of two phases and an energy equation are used to determine the effects of temperature on a cavitating flow. First, the experimental data were validated at a cavitation number of σ = 0.435. Both quantitatively and qualitatively good agreements were achieved, including the evolution of the cavity shape, cavity length, and cavity thickness. Then, the key characteristics of an unsteady cavitation structure regarding the cavity growth, re-entrant jet, cavity shedding, and collapse were analyzed. In particular, the mechanism of the re-entrant jet inside the cavity, causing the periodic cavity shedding, was explored. Furthermore, detailed mechanisms of cavity shedding with periodic cavity–vortex–pressure interaction behaviors were analyzed. Finally, the influences of free-stream temperature on the cavitation structure behaviors were carefully investigated. It was found that both the cavity length and thickness increased with the free-stream temperature under the atmospheric pressure condition. The most sensitive effects occurred when the free-stream temperature approached its boiling point. In case of the same reference cavitation number and Reynolds number, the cavity shape tended to be mushier with increasing water temperature.
Evolution of the cavity shape of unsteady natural cavitating flow around an axisymmetric projectile with the cavitation number σ= 0.435. Special characteristic motions including cavity incipient, growth, re-entryre-entrant jet, shedding, and collapse are well captured with experimental images. Display omitted
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Cryptococcal meningitis has high mortality. Flucytosine is a key treatment but is expensive and rarely available. The anticancer agent tamoxifen has synergistic anti-cryptococcal activity with ...amphotericin in vitro. It is off-patent, cheap, and widely available. We performed a trial to determine its therapeutic potential.
Open label randomized controlled trial. Participants received standard care - amphotericin combined with fluconazole for the first 2 weeks - or standard care plus tamoxifen 300 mg/day. The primary end point was Early Fungicidal Activity (EFA) - the rate of yeast clearance from cerebrospinal fluid (CSF). Trial registration https://clinicaltrials.gov/ct2/show/NCT03112031.
Fifty patients were enrolled (median age 34 years, 35 male). Tamoxifen had no effect on EFA (-0.48log10 colony-forming units/mL/CSF control arm versus -0.49 tamoxifen arm, difference -0.005log10CFU/ml/day, 95% CI: -0.16, 0.15, p=0.95). Tamoxifen caused QTc prolongation.
High-dose tamoxifen does not increase the clearance rate of
from CSF. Novel, affordable therapies are needed.
The trial was funded through the Wellcome Trust Asia Programme Vietnam Core Grant 106680 and a Wellcome Trust Intermediate Fellowship to JND grant number WT097147MA.
•An accurate shock- and interface-capturing method for compressible multiphase flows.•A high-resolution Godunov-type numerical scheme for a five-equation two-phase model.•An interface-sharpening ...technique (IST) for compressible flows.•Consistent thermodynamic laws for the mixture can be obtained during numerical simulations.•The compressible multiphase flow problems with the presence of both shock waves and the dynamics of interfaces.
An accurate shock- and interface-capturing method is introduced for simulations of compressible multiphase flows. First, an associated Godunov-type numerical scheme is established for a five-equation two-phase model obtained from a seven-equation model by assuming a single velocity and a single pressure between two phases. The computational finite-volume Riemann solver using the scheme and computing algorithms is presented. Next, an interface-sharpening technique (IST) is extended for the compressible two-phase model to improve numerical simulations and correct diffusion errors. The modified IST was applied as postprocessing to correct the numerical diffusion error in the solution of the discretization scheme while maintaining a sharp interface with a desired thickness after each time step. A mixture-consistent interface regularization approach of all conservative variables is combined with the IST to obtain consistent thermodynamic laws for the mixture, ensuring the consistency of the variables in the correction process. Several examples of fluid interface simulations including shock-tube, shock-bubble interactions, and underwater explosions were performed to demonstrate the accuracy and capability of the proposed method. Those compressible multiphase flow problems are complicated by the presence of both shock waves and the dynamics of interfaces. Comparisons of the numerical method with theoretical results and experimental data indicate that the present method can simulate interface dynamics with the presence of shock waves and large density differences.
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