Pulsation Period Research Articles

Model of R134a Liquid–Vapor Two-Phase Heat Transfer Coefficient for Pulsating Flow Boiling in an Evaporator Using Response Surface Methodology

The present study proposes a model to predict the heat transfer coefficient in R134a liquid–vapor two-phase pulsating flow boiling in an evaporator using the experimental data and response surface methodology (RSM). The model is based on the current existing empirical correlation for R134a liquid–vapor two-phase continuous flow with an imposed modification factor. The model for the imposed modification factor is the function of the pulsating period and inlet/outlet vapor quality, which is obtained using the limited experimental data. An analysis of variance (ANOVA) is carried out to test the significance of the model and normal probability of residuals is analyzed as well. Results show that the regression model produces a mean error of −4.3% and a standard deviation of 15.4%, compared to experimental results. Of the data 95.1% is contained inside a ±50% error window, which indicates that the proposed model could predict the heat transfer coefficient of R134a liquid–vapor two-phase pulsating flow boiling well.

SOFIA/FORCAST Observations of R Aqr: Monitoring the Dust Emission

Abstract We present mid-infrared spectra of the symbiotic Mira, R Aqr obtained with the Faint Object infraRed CAmera instrument on the Stratospheric Observatory for Infrared Astronomy in 2016 and 2017. These data, supplemented with Infrared Space Observatory observations from 20 yr earlier, allow us to study the variation of the silicate dust emission over short and long timescales. Radiative transfer models for the dust emission from the circumstellar shell indicate that changes that occur within a pulsation period are driven mainly by the variation properties of the asymptotic giant branch star, and do not require any change in the grain composition. The models show that the longer-term changes are due to variations in the dust density, probably modulated by the orbital separation of the binary companion stars. The models also suggest the presence of micron-size dust grains at all epochs.

V363 Cassiopeiae: a new lithium-rich Galactic Cepheid

Context. Classical Cepheids (DCEPs) are important astrophysical objects not only as standard candles in the determination of the cosmic distance ladder, but also as a testbed for the stellar evolution theory. This is based on the strict connection between their pulsation (period(s) and amplitudes) and stellar parameters (luminosity, mass, effective temperature, and metallicity). Aims. We examine the nature of the Galactic DCEP V363 Cas and other DCEPs that show cosmic abundances of lithium in their atmospheres. Methods. We collected three epochs of high-resolution spectroscopy for V363 Cas with HARPS-N at the TNG. We measured accurate stellar parameters: the effective temperatures, gravities, microturbulences, radial velocities, and metal abundances. Results. We detected a lithium abundance of A(Li) = 2.86 ± 0.10 dex, along with iron, carbon, and oxygen abundances of [Fe/H] = −0.30 ± 0.12 dex, [C/H] = −0.06 ± 0.15 dex, and [O/H] = 0.00 ± 0.12 dex. V363 Cas is the fifth of the Milky Way DCEPs to exhibit a Li-rich feature. An analysis of historical time-series spanning a 100-year interval shows that the period of V363 Cas is increasing, with a sharp acceleration after HJD = 2 453 000 days. This is a clear indication of a first crossing of the instability strip. Conclusions. Our results favour the scenario in which the five Galactic Li-rich DCEPs are on their first crossing of the instability strip and have had slowly rotating progenitors during their main-sequence phase.

Two-dimensional flow movement in the area of protective regulatory structures

The article discusses the results of numerical studies of the flow movement with a sharp change in the parameters of the channel. Basically, the results of the study using the system of two-dimensional equations of hydrodynamics-Saint-Venant are analyzed. The divergent form of two-dimensional equations describing the movement of a water stream at a site of regulation of a channel by protective and regulatory dams is given. The influence of the length step on the results of numerical experiments is investigated numerically. Graphs of the time variation of the longitudinal velocity component behind the sudden double expansion of the channel are compiled. The flow was unsteady all the time and had the character of stationary pulsations, and the finer the grid, the richer the spectrum of these pulsations. It was noted that in numerical calculations, the time step in the calculations was always much less than the minimum pulsation period, therefore, these pulsations were not associated with difference oscillations that can arise when approximating by central differences. It is concluded that, according to the authors from the following and the present work, they collectively show that the pulsations on different grids differ significantly, the average values of the velocities are close, and thereby the solution for the average values is well converged, this shows that the pulsations are a property source equations of Saint-Venant. The applicability of the numerical model, consisting of two-dimensional shallow water equations, the vector equation of momentum conservation and the scalar equation of mass conservation, in description the flow with the presence of circulation zones, which is typical when water flows are constrained by protective-regulatory structures. In this case, the solution pulsates around a certain average value, and the average length of the circulation zone behind the sudden expansion of the open flow is in good agreement with the laboratory experiments of G.L. Mazhbits.

Experimental study on liquid-vapor two-phase pressure drop of pulsating flow in an evaporator

Pulsating liquid-vapor, two-phase, flows, characterized primarily by periodic oscillations in the mass flux, can occur naturally due to thermal-hydraulic conditions imposed on a flow, and they can be created by design in pursuit of improved thermal performance in heat pumping, air-conditioning, and refrigeration systems. Such flows are not fully understood, especially if the flow oscillations give rise to significant changes in liquid-vapor interface morphology (changes in two-phase flow regime). In this work, the pressure drop of R134a liquid-vapor, two-phase pulsating flows is measured under varying pulsation periods (2s to 24s), mass fluxes (100 to 200 kg•m−2•s−1), and inlet/outlet vapor qualities (0.1-0.4/0.6-0.8). The flow regimes and liquid-vapor interface evolution are also observed. Experimental results show the pressure drop increases sharply at the start of flow and drops quickly as the flow ceases in a pulsation cycle. The peak of pressure drop as the pulsation starts is larger at a higher inlet vapor quality, but the valley as flow ceases is lower. With an increasing mass flux, the rate of pressure drop increase is closely related to the pulsation period and vapor quality. A higher rate of increasing pressure drop is observed in flows with a shorter pulsation period and higher inlet vapor quality. Fluctuations in the pressure drop are also observed, and are more pronounces in low mass flux and low inlet vapor quality flows, a result attributed to fluctuations in the liquid-vapor interface and changes in two-phase flow regimes.

Periodically repeating fast radio bursts: Lense–Thirring precession of a debris disk?

Abstract Recently, repeating fast radio bursts (FRBs) with a period of PFRB = 16.35 ± 0.18 d from FRB 180916.J0158+65 were reported. It still remains controversial how such a periodicity might arise for this FRB. In this Letter, based on an assumption of a young pulsar surrounding by a debris disk, we attempt to diagnose whether Lense–Thirring precession of the disk on the emitter can produce the observed periodicity. Our calculations indicate that the Lense–Thirring effect of a tilted disk can result in a precession period of 16 d for a mass inflow rate of 0.5–1.5 × 1018 g s−1, a pulsar spin period of 1–20 ms, and an extremely low viscous parameter α = 10−8 in the disk. The disk mass and the magnetic field of the pulsar are also constrained to be ∼10−3 M⊙ and <2.5 × 1013 G. In our model, a new-born pulsar with normal magnetic field and millisecond period would successively experience the accretion and propeller phases, and is visible as a strong radio source in the current stage. The rotational energy of such a young neutron star can provide the observed radio bursting luminosity for 400 yr.

Updated theoretical period–age and period–age–colour relations for Galactic Classical Cepheids: an application to the Gaia DR2 sample

ABSTRACT Updated evolutionary and pulsational model predictions are combined in order to interpret the properties of Galactic Classical Cepheids in the Gaia Data Release 2. In particular, the location of the instability strip boundaries and the analytical relations connecting pulsation periods to the intrinsic stellar parameters are combined with evolutionary tracks to derive reliable and accurate period–age and the first theoretical period–age–colour relations in the Gaia bands for a solar chemical abundance pattern (Z = 0.02, Y = 0.28). The adopted theoretical framework takes into account possible variations in the mass–luminosity relation for the core helium-burning stage as due to changes in the core convective overshooting and/or mass-loss efficiency, as well as the impact on the instability strip boundaries due to different assumptions for superadiabatic convection efficiency. The inferred period–age and period–age–colour relations are applied to a selected sample of both fundamental and first overtone Gaia Cepheids, and individual ages for the various adopted theoretical scenarios are derived. The retrieved age distributions confirm that a variation in the efficiency of superadiabatic convection in the pulsational model computations has a negligible effect, whereas a brighter mass–luminosity relation, as produced by mild overshooting, rotation, or mass-loss, implies significantly older age predictions. Moreover, older Cepheids are found at larger Galactocentric distances, while first overtone Cepheids are found to be systematically older than the fundamental ones. The comparison with independent age distribution analysis in literature supports the predictive capability of current theoretical framework.

Astrometry and infrared observations of the Mira variable stars AP Lyncis, V837 Herculis, and BX Camelopardalis: Implications for the period–luminosity relation of the Milky Way

Abstract AP Lyn and V837 Her are long-period Mira variable stars in the Milky Way. We performed VLBI Exploration of Radio Astrometry (VERA) phase-referenced observations towards H2O masers associated with AP Lyn and V837 Her. The annual parallaxes of AP Lyn and V837 Her were obtained to be 2.008 ± 0.038 mas and 1.090 ± 0.014 mas, corresponding to distances of 498 ± 10 pc and 917 ± 12 pc, respectively. From our multi-epoch infrared observations using the Kagoshima University 1 m telescope, we derived the mean J-, H-, and K′-band magnitudes of AP Lyn, V837 Her, and an additional long-period Mira variable BX Cam, whose parallax is known. We derived their pulsation periods to be 433 ± 1 d, 520 ± 1 d, and 458 ± 1 d, respectively, using the K′-band light curves. The MK–log P relation of long-period Mira variables seem to be violated by Mira variable stars with larger-than-expected MK values (like OZ Gem) in the Milky Way because of circumstellar extinction leading to an observed dimming effect. AP Lyn, V837 Her, and BX Cam (like OZ Gem) are dimming from the trend to O-rich stars in the Large Magellanic Cloud. This implies that the high metallicity of the Milky Way galaxy increases the opacity of the Mira-type variable stars and strengthens mass loss.

Distinct intensification pathways for a shallow-water vortex subjected to asymmetric “diabatic” forcing

Observational studies and cloud resolving numerical simulations have shown that developing tropical cyclones often have markedly asymmetric distributions of moist convection. The present study uses a shallow-water model on the f-plane to gain further insight into the variety of vortex intensification pathways that may exist under such conditions. The diabatic forcing associated with asymmetric convection is represented by a localized mass sink displaced from the initial center of rotation. The pathway of vortex intensification is found to depend on whether the velocity-convergence generated by the mass sink exceeds a critical value sc, and thereby prevents the escape of fluid that flows into the mass sink. The critical value is approximately given by sc=2Vl/ρs, in which ρs is the radial size of the mass sink, and Vl is the magnitude of the local vector-difference between the broader cyclonic velocity field and the drift velocity of the mass sink. If the convergence is supercritical so as to exceed sc, the core of the vortex reforms in the vicinity of the mass sink and rapidly intensifies. Two other modes of intensification are found in subcritical systems. One common mode occurs at a moderate pace and entails a gradual drift of the vortex center toward the mass sink, coinciding with significant contraction of the radius of maximum azimuthal velocity. A slower mode can occur when a subcritical mass sink has substantial azimuthal drift. The slower mode resembles that expected for a symmetric system in which the mass sink is uniformly spread over its orbital annulus, whose radius from the vortex center is roughly constant over time. If the mass sink pulsates so as to periodically generate modestly supercritical values of convergence, a transition may occur from a subcritical mode of intensification to a supercritical mode as the pulsation period increases beyond a certain threshold. In a distinct set of simulations where the mass sink drifts radially outward from the initial vortex center with velocity r˙s, supercritical convergence determined with Vl=r˙s in the formula for sc is generally necessary for major vortex intensification.

On the Metamorphosis of the Bailey Diagram for RR Lyrae Stars

Abstract We collected over 6000 high-resolution spectra of four dozen field RR Lyrae (RRL) variables pulsating either in the fundamental (39 RRab) or in the first overtone (9 RRc) mode. We measured radial velocities (RVs) of four strong metallic and four Balmer lines along the entire pulsational cycle and derived RV amplitudes with accuracies better than 1–2 km s−1. The new amplitudes were combined with literature data for 23 RRab and 3 RRc stars (total sample of 74 RRLs), which allowed us to investigate the variation of the Bailey diagram (photometric amplitude versus period) when moving from optical to mid-infrared bands and to recast the Bailey diagram in terms of RV amplitudes. We found that RV amplitudes for RRab are minimally affected by nonlinear phenomena (shocks) and multiperiodicity (Blazhko effect). The RV slope (logP–A(V r )) when compared with the visual slope (logP–A(V)) is shallower, and the dispersion, at fixed period, decreases by a factor of two. We constructed homogeneous sets of horizontal branch evolutionary models and nonlinear, convective pulsation models of RRLs to constrain the impact of evolutionary effects on their pulsation properties. Evolution causes, on the Bailey diagram based on RV amplitudes, a modest variation in pulsation period and a large dispersion in amplitude. The broad dispersion in period of the Bailey diagram is mainly caused by variation in RRL intrinsic parameters (stellar mass, chemical composition). Empirical evidence indicates that RV amplitudes are an optimal diagnostic for tracing the mean effective temperature across the RRab instability strip.

Identification of temperature anomaly RR Lyrae stars in LAMOST survey, misclassification and binarities

RR Lyrae stars, a well-known type of pulsating variable stars, have been known about for more than a century. A large amount of photometric data on RR Lyrae stars has been accumulated by space- and ground-based sky surveys, but the spectral data are relatively poor. Fortunately, the LAMOST sky survey project provides an opportunity to view them from the point of view of spectra. We collect the atmospheric parameters of 1685 RR Lyrae stars provided by the LAMOST catalog, and carry out research by using the reliable Teff. We find that there is a clear correlation between their Teff and pulsation periods, which is consistent with the pulsation and evolution theories of RR Lyrae stars. In addition, we focus on those RR Lyrae stars with abnormal temperatures. After analyzing the data from several photometric surveys, we find that some of these temperature anomalies are misclassified variable stars (e.g., eclipsing binaries, pulsating stars on main sequence), and some are RR Lyrae binary candidates. For the latter, the temperatures of potential companions should be lower and their luminosities should not be neglected (e.g., red giant stars). We obtain that the ratio of temperature anomaly stars to all the sample stars is 4%, which means that the impact on the further analysis (e.g., kinematics analysis) is low. We also present the catalogs of spectral anomaly RR Lyrae stars.

Trigonometric parallax of O-rich Mira variable star OZ Gem (IRAS 07308+3037): A confirmation of the difference between the P–L relations of the Large Magellanic Cloud and the Milky Way

Abstract OZ Geminorum (OZ Gem) is a galactic Mira variable in the Milky Way (MW). We measured its annual parallax with VLBI Exploration of Radio Astrometry to be π = 0.806 ± 0.039 mas, corresponding to a distance of D = 1.24 ± 0.06 kpc. Based on multi-epoch infrared observations with the Kagoshima University 1 m telescope, we also derived the mean J-, H-, and K′-band magnitudes of OZ Gem to be 5.75 ± 0.47 mag, 4.00 ± 0.16 mag, and 2.65 ± 0.16 mag, respectively. We derived a pulsation period of OZ Gem as 592 ± 1 d from the K′-band lightcurve. From the period–luminosity (P–L) relation and two-color diagram of the Large Magellanic Cloud (LMC), the property of OZ Gem suggests that OZ Gem is assigned among the carbon-rich Mira variables. However, our optical spectroscopic observational results (with the 1.5 m Kanata telescope) confirmed OZ Gem to be an oxygen-rich Mira star with the detection of multiple titanium oxide transition absorption lines. We suggest that OZ Gem is a low-mass star evolving to an OH/IR star with large mass loss and dust formation. It is predicted that the lower limit to the initial mass of AGB stars for developing the C-rich surface chemistry is larger in the MW than in the LMC because of larger metallicity, and OZ Gem is likely to be the first example to prove this. Our results highlight the necessity of deriving the PL relation of the Milky Way with high accuracy.

High Productivity Ethanol from Solid-State Fermentation of Steam-Exploded Corn Stover Using Zymomonas mobilis by N2 Periodic Pulsation Process Intensification.

Solid-state fermentation, featured by water-saving, eco-friendly and high concentration product, is a promising technology in lignocellulosic ethanol industry. However, in solid-state fermentation system, large gas content inside the substrate directly leads to high oxygen partial pressure and inhibits ethanol fermentation. Z. mobilis can produce ethanol from glucose near the theoretical maximum value, but this ethanol yield would be greatly decreased by high oxygen partial pressure during solid-state fermentation. In this study, we applied N2 periodic pulsation process intensification (NPPPI) to ethanol solid-state fermentation, which displaced air with N2 and provided a proper anaerobic environment for Z. mobilis. Based on the water state distribution, the promotion effects of NPPPI on low solid loading and solid-state fermentation were analyzed to confirm the different degrees of oxygen inhibition in ethanol solid-state fermentation. During the simultaneous saccharification solid-state fermentation, the NPPPI group achieved 45.29% ethanol yield improvement and 30.38% concentration improvement compared with the control group. NPPPI also effectively decreased 58.47% of glycerol and 84.24% of acetic acid production and increased the biomass of Z. mobilis. By coupling the peristaltic enzymatic hydrolysis and fed-batch culture, NPPPI made the ethanol yield and concentration reach 80.11% and 55.06g/L, respectively, in solid-state fermentation.

Active Control of Passive and Active Particle Distribution at the Outlet of Double Y-Microchannel Using Pulsatile Flow

Abstract While a variety of active and passive techniques have been proposed for steady flows, pulsatile flow has received much less attention. Pulsation makes more control parameters available for passive methods and enables them to separate particles. The purpose of this work is to determine the effects of the phase shift between two entering flows (only one includes the particles) on particle separation inside a double Y-microchannel. Numerical simulations were carried out for both steady and pulsating flow conditions. The results showed that when the velocity amplitude ratio (β) is less than 2, the separation index increases with the phase shift (φ) and the highest efficiency occurs at φ = 180 deg. A similar trend can be observed for higher values of β only if the pulsation period is short enough. A series of experiments qualitatively validated the numerical results.

The VMC Survey

Context. Variability is a key property of stars on the asymptotic giant branch (AGB). Their pulsation period is related to the luminosity and mass-loss rate of the star. Long-period variables (LPVs) and Mira variables are the most prominent of all types of variability of evolved stars. The reddest, most obscured AGB stars are too faint in the optical and have eluded large variability surveys. Aims. We obtained a sample of LPVs by analysing K-band light curves (LCs) of a large number of sources in the direction of the Magellanic Clouds with the colours expected for red AGB stars ((J − K) > 3 mag or equivalent in other colour combinations). Methods. Selection criteria were derived based on colour-colour and colour-magnitude diagrams from the combination of the VISTA Magellanic Cloud (VMC) survey, Spitzer IRAC and AllWISE data. After eliminating LPVs with known periods shorter than 450 days, a sample of 1299 candidate obscured AGB stars was selected. K-band LCs were constructed by combining the epoch photometry available in the VMC survey with literature data, were analysed for variability, and fitted with a single period sine curve to derive mean magnitudes, amplitudes, and periods. A subset of 254 stars are either new variables, known variables where the period we find is better determined than the literature value, or variables with periods longer than 1000 days. The spectral energy distributions (SEDs) of these stars were fitted to a large number of templates. For this purpose the SEDs and Spitzer IRS spectra of some non-AGB stars (Be stars, HII regions and young stellar objects – YSOs) were also fitted to have templates of the most likely contaminants in the sample. Results. A sample of 217 likely LPVs is found. Thirty-four stars have periods longer than 1000 days, although some of them have alternative shorter periods. The longest period of a known Mira in the Magellanic Clouds from Optical Gravitational Lensing Experiment data (with P = 1810 d) is derived to have a period of 2075 d based on its infrared LC. Two stars are found to have longer periods, but both have lower luminosities and smaller pulsation amplitudes than expected for Miras. Mass-loss rates and luminosities are estimated from the template fitting. Period-luminosity relations are presented for carbon (C-) and oxygen (O-) rich Miras that appear to be extensions of relations derived in the literature for shorter periods. The fit for the C stars is particularly well defined (with 182 objects) and reads Mbol = (−2.27 ± 0.20) ⋅ log P + (1.45 ± 0.54) mag with an rms of 0.41 mag. Thirty-four stars show pulsation properties typical of Miras while the SEDs indicate that they are not. Overall, the results of the LC fitting are presented for over 200 stars that are associated with YSOs.

Effects of a centered conducting body on natural convection of a non-Newtonian fluid in a square enclosure with time-periodic temperature distribution

In this paper, a modified lattice Boltzmann model that incorporates the effect of heat capacity is adopted to study the effects of a centered conducting body on the natural convection of a non-Newtonian fluid in a square cavity with time-periodic temperature distribution. The effects of power-law index, Rayleigh number, heat capacity ratio, thermal conductivity ratio, body size, temperature pulsating period, and temperature pulsating amplitude on fluid flow and heat transfer are analyzed in detail. The results showed that the increase of Rayleigh number and thermal conductivity ratio as well as the decrease of power-law index can strengthen both transient and global heat transfer, while the increase of heat capacitance of the fluid to the solid wall can enhance the transient heat transfer and has little effect on the overall heat transfer. Furthermore, the increase of body size will reduce both the transient heat transfer ratio and the overall heat transfer ratio. In addition, the decrease of temperature pulsating period can enhance the transient heat transfer, but will slightly weaken the overall heat transfer. Finally, the results show that both the transient and overall heat transfer ratios increase with the increase of temperature pulsating amplitude.

Blazhko effect in the Galactic bulge fundamental mode RR Lyrae stars – II. Modulation shapes, amplitudes, and periods

ABSTRACT The number of stars observed by the Optical Gravitational Lensing Experiment (OGLE) project in the Galactic bulge offers an invaluable chance to study RR Lyrae stars in a statistical manner. We used data of 3141 fundamental-mode RR Lyrae stars showing the Blazhko effect observed in OGLE-IV to investigate a possible connection between modulation amplitudes and periods, light curve, and pulsation characteristics. We found that there is no simple monotonic correlation between any combination of two parameters concerning the Blazhko and pulsation amplitudes, periods, and the shape of the light curves. There are only systematic limits. There is a bottom limit of the modulation period with respect to the pulsation period. We also found that the possible range of modulation amplitudes decreases with increasing pulsation period, which could point towards that the Blazhko effect is suppressed in cooler, larger, more luminous, and less metal abundant bulge RR Lyrae stars. Our investigation revealed that the distribution of the modulation periods can be described with two populations of stars with the mean modulation periods of 48 and 186 d. There is a certain region with a low density of the modulated stars, which we call the Blazhko valley, in the pulsation period–modulation period plane. Based on the similarity of the modulation envelopes, basically every star can be assigned to one of six morphological classes. The double modulation was found in 25 per cent of the studied stars. Only 6.3 per cent of modulated stars belong to the Oosterhoff group II.

Experimental Investigation of the Performance and Spray Characteristics of a Supersonic Two-Phase Flow Ejector with Different Structures

A two-phase flow ejector is an important part of a water mist fire suppression system, and these devices have become a popular research topic in recent years. This paper proposes a supersonic ejector that aims to improve the efficiency of water mist fire suppression systems. The effects of ejector geometric parameters on the entrainment ratio (ER) were explored. The effects of primary flow pressure (PP) on the mixing process and flow phenomena were studied by a high-speed camera. The experimental results show that the ER first increases and then decreases with increasing PP. ER increases with increasing ejector area ratio (AR). The PP corresponding to the maximum ER of ejectors with a different nozzle exit position (NXP) is 3.6 bar. The ejector with an NXP of +1 and AR of 6 demonstrate the best performance, and the ER of this ejector reaches 36.29. The spray half-cone angle of the ejector increases with increasing ER, reaching a maximum value of 7.07°. The unstable atomization half-cone angle is mainly due to a two-phase flow pulsating phenomenon. The pulsation period is 10 ms. In the present study, a general rule that provides a reference for ejector design and selection was obtained through experiments.

Study on the influence of rigid wall surface on the bubble characteristics of underwater explosion

In order to investigate the influence of rigid wall surface on the bubble characteristics of underwater explosion, the underwater explosion experiment under the boundary conditions of free surface and rigid wall surface was carried out on 2.5g cylindrical charge TNT in a 2×2×2m tank. The time history curves of shock wave and bubble pulsation were obtained by underwater pressure sensor, and the bubble pulsation process was observed by high-speed photography. The experimental results show that compared with the free surface underwater explosion, the shock wave peak pressure and the bubble pulse peak pressure in rigid wall surface underwater explosion are increased, and a large cavitation area appeared at the junction of rigid wall and water surface. After the bubbles contacted the rigid wall surface, the bubble morphology changed significantly, the first bubble pulsation period and the maximum radius of bubble expansion became larger. After the first bubble pulsation, the bubble partially collapsed and split into two parts, bubbles continued to pulsate in the direction of the rigid wall and the bottom of the water. Finally, combined with the experimental data of rigid wall surface at different explosion depths, the relationship between the first bubble pulsation period, the maximum bubble expansion radius and the explosion depth of 2.5gTNT under rigid wall conditions is given.

Dynamic behaviors of a laser-induced bubble and transition mechanism of collapse patterns in a tube

The pulsation of cavitation bubbles under constraint conditions has complex dynamic characteristics and has been widely applied in various fields, such as liquid pumping, underwater propulsion, and clinical applications. In this study, the dynamic behaviors of a laser-induced bubble in a tube are investigated under different initial conditions. A high-speed optical visualization is carried out in the experiments. The numerical simulation based on the volume-of-fluid method is implemented on the open source code OpenFOAM. From the experimental observation and numerical analysis, an axial jet pointing toward the front end of the tube is generated during bubble shrinkage. According to the type of the axial jet, the collapse patterns are classified into three regimes: one-dimensional, transitional, and three-dimensional. Furthermore, it is also found that the normalized initial energy of the bubble and the length-to-diameter ratio affect the maximum length and the pulsation period of the bubble. Finally, the transition mechanism of the collapse patterns from one dimension to three dimension is obtained through a phase diagram by combining experimental observations with numerical simulation.