共查询到20条相似文献,搜索用时 31 毫秒
1.
Obreschkow D Kobel P Dorsaz N de Bosset A Nicollier C Farhat M 《Physical review letters》2006,97(9):094502
We studied spark-generated cavitation bubbles inside water drops produced in microgravity. High-speed visualizations disclosed unique effects of the spherical and nearly isolated liquid volume. In particular, (1) toroidally collapsing bubbles generate two liquid jets escaping from the drop, and the "splash jet" discloses a remarkable broadening. (2) Shock waves induce a strong form of secondary cavitation due to the particular shock wave confinement. This feature offers a novel way to estimate integral shock wave energies in isolated volumes. (3) Bubble lifetimes in drops are shorter than in extended volumes in remarkable agreement with herein derived corrective terms for the Rayleigh-Plesset equation. 相似文献
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Small para-H2 clusters (pH2)N with N=2,...,8 have been identified by Raman spectroscopy in cryogenic free jets of the pure gas, near the Q(0) Raman line of the H2 monomer. The high resolution in space, time, and number size makes it possible to follow their growth kinetics with distance from the orifice. At lower source temperatures liquid clusters appear early in the expansion and then undergo a gradual phase transition to the solid state. The technique is very promising for exploring superfluidity in pure (pH2)N clusters. 相似文献
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Motivated by its importance for microfluidic applications, we study the stability of jets formed by pressure-driven concentric biphasic flows in cylindrical capillaries. The specificity of this variant of the classical Rayleigh-Plateau instability is the role of the geometry which imposes confinement and Poiseuille flow profiles. We experimentally evidence a transition between situations where the flow takes the form of a jet and regimes where drops are produced. We describe this as the transition from convective to absolute instability, within a simple linear analysis using lubrication theory for flows at low Reynolds number, and reach remarkable agreement with the data. 相似文献
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Cylindrical liquid jets are inherently unstable and eventually break into drops due to the Rayleigh-Plateau instability, characterized by the growth of disturbances that are either convective or absolute in nature. Convective instabilities grow in amplitude as they are swept along by the flow, while absolute instabilities are disturbances that grow at a fixed spatial location. Liquid jets are nearly always convectively unstable. Here we show that two-phase jets can breakup due to an absolute instability that depends on the capillary number of the outer liquid, provided the Weber number of the inner liquid is >O(1). We verify our experimental observations with a linear stability analysis. 相似文献
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Lonzaga JB Osterhoudt CF Thiessen DB Marston PL 《The Journal of the Acoustical Society of America》2007,121(6):3323-3330
Experimental evidence shows that a liquid jet in air is an acoustic waveguide having a cutoff frequency inversely proportional to the jet diameter. Ultrasound applied to the jet supply liquid can propagate within the jet when the acoustic frequency is near to or above the cutoff frequency. Modulated radiation pressure is used to stimulate large amplitude deformations and the breakup of the jet into drops. The jet response to the modulated internal ultrasonic radiation pressure was monitored along the jet using (a) an optical extinction method and (b) images captured by a video camera. The jet profile oscillates at the frequency of the radiation pressure modulation and where the response is small, the amplitude was found to increase in proportion to the square of the acoustic pressure amplitude as previously demonstrated for oscillating drops [P.L. Marston and R.E. Apfel, J. Acoust. Soc. Am. 67, 27-37 (1980)]. Small amplitude deformations initially grow approximately exponentially with axial distance along the jet. Though aspects of the perturbation growth can be approximated from Rayleigh's analysis of the capillary instability, some detailed features of the observed jet response to modulated ultrasound are unexplained neglecting the effects of gravity. 相似文献
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Previous 2D simulations of reconnection using a standard model of initially antiparallel magnetic fields have detected electron jets outflowing from the x point into the ion outflow exhausts. Associated with these jets are extended "outer electron diffusion regions." New PIC simulations with an ion to electron mass ratio as large as 1836 (an H(+) plasma) now show that the jets are strongly deflected and the outer electron diffusion region is broken up by a very weak out-of-plane magnetic guide field, even though the diffusion rate itself is unchanged. Jet outflow and deflection are interpreted in terms of electron dynamics and are compared to recent measurements of jets in the presence of a small guide field in Earth's magnetosheath. 相似文献
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着重介绍了瑞利在测量氮气密度过程中发现惰性气体氩的研究和创新历程,以及瑞利对光学、声学等物理学的各个领域的主要贡献,指出正是求实的科学态度、锲而不舍的钻研精神和以创新为乐趣的事业追求是瑞利一生中取得丰硕的研究成果的主要原因。 相似文献
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Continuous high-speed water jets are presently used in many industrial applications such as cutting of various materials, cleaning and removal of surface layers. However, there is still a need for further research to enhance the performance of pure water jets. An obvious method is to generate water jets at ultra-high pressures (currently up to 700 MPa). An alternate approach is to eliminate the need for such high pressures by pulsing of the jet. This follows from the fact that the impact pressure on a target generated by a slug of water is considerably higher than the stagnation pressure of a corresponding continuous jet. Ultrasonically forced modulation of a continuous stream of water represents the most promising method of pulsed jet generation because of its simplicity and practicality. A pulsed jet is generated by modulating a continuous stream of water by ultrasonic waves. A velocity transformer connected to a piezoelectric transducer is located axially inside a nozzle to induce longitudinal pulsations in the water. An extensive laboratory research program is in progress to understand the basic principles of the process and to optimize the nozzle design for several applications. The results reported in this paper show that the performance of such a pulsed jet is far superior to that of a continuous jet operating at the same parameters. Experimental results obtained with the ultrasonic vibration of a tip situated inside the nozzle indicate that using this technique one can achieve performance of the jet even order of magnitude higher in comparison to continuous jet at the same hydraulic parameters. Performance of ultrasonically modulated jets in cutting of various materials was tested in laboratory conditions. In this paper, results of measurement of dynamic pressure in the nozzle and force effects of modulated jets are presented together with results obtained in cutting of various materials using ultrasonically modulated water jets. The results are compared with those obtained with continuous jets at the same operating parameters. Potential of forced modulation of the jet in applications of cleaning, paint and coating removal from surfaces and concrete cutting in the process of repair of concrete structures is mentioned. 相似文献
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Dombrowski C Cisneros L Chatkaew S Goldstein RE Kessler JO 《Physical review letters》2004,93(9):098103
Suspensions of aerobic bacteria often develop flows from the interplay of chemotaxis and buoyancy. We find in sessile drops that flows related to those in the Boycott effect of sedimentation carry bioconvective plumes down the slanted meniscus and concentrate cells at the drop edge, while in pendant drops such self-concentration occurs at the bottom. On scales much larger than a cell, concentrated regions in both geometries exhibit transient, reconstituting, high-speed jets straddled by vortex streets. A mechanism for large-scale coherence is proposed based on hydrodynamic interactions between swimming cells. 相似文献
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由于岩石破碎过程的复杂性,目前对水射流的破岩机理的认识仍然不十分清楚。先采用超高压万能水射流切割机冲蚀切割岩石,然后用扫描电镜对水射流切割岩石断口形貌进行观测,分析了岩石在超高压水射流作用下的破坏形式。观测分析表明,超高压射流切割岩石形成的切槽主要有长形规则和漏斗状两种形状。岩石在水射流作用下的破坏机制主要有拉伸破坏和剪切破坏两种,剥落岩块以穿晶断裂为主,其微观断裂机制是脆性拉伸破坏;切槽凹侧面主要是剪切错动,其微观破坏机制是剪脆性破坏。实验为水射流破岩机理分析提供了实测依据。 相似文献
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Water samples from three quarry lakes and the surrounding fractured rock aquifer were investigated for delta18O and delta2H (H2O), delta15N and delta18O (NO3-), as well as anions and cations. Lake water and groundwater can be distinguished by their different chemical and isotopic composition. Because of evaporation processes, 18O and 2H are enriched in the lake water and can be used as natural tracers for the water dynamic of the lakes. The groundwater is characterised by high nitrate concentrations (up to 120 mg/l). Lake internal processes reduce the nitrate concentration in the quarry lakes. However, no enrichment of delta15N and delta18O in nitrate, typical for microbial nitrate degradation, is observed in the lake water. Because of the complex flow paths in the fractured rock aquifer and the intense chemical transformations at the interface between groundwater and lake water, isotopic and hydrochemical data of lake water and groundwater alone do not conclusively explain hydrological and hydrochemical processes of the investigated lake-groundwater system. 相似文献
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For coarse drops of binary concentrated solutions with the double phase transition that move in a ternary gaseous mixture via thermophoresis, a theory including thermal diffusion effects is elaborated. The drops consist of water with ethanol dissolved in it. Numerical estimates are made and plots are constructed for the rate of thermophoresis of drops with radii 5, 10, and 15 μm at different ethanol concentrations with and without allowance for volume thermal diffusion. 相似文献
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M. Attalla 《实验传热》2015,28(2):139-155
The heat transfer characteristics in a stagnation region were investigated experimentally for five circular free jets impinging into a heated flat plate. The local temperature distributions are estimated from the thermal images obtained from an infrared camera. To get a precise heat transfer data over the plate, fully developed straight pipe jets were used in this study. Mean jet Reynolds number varied from 1,000 to 45,000, jet-to-plate vertical non-dimensional distance H/D varied from 2 to 6, and the spacing distance jet-to-jet S/D varied from 2 to 8. A geometrical arrangement of one jet surrounded by four jets an in-line array was tested. The results show that the stagnation point Nusselt number is correlated to a jet Reynolds number as Nust∝Re0.61. The average Nusselt number is higher at a separation distance of 2D for three cases of spacing distances, S/D = 2, 4, and 6. 相似文献
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Ratios of azimuthal angle correlations between two jets produced at large rapidity separation are studied in the N = 4 maximally supersymmetric Yang-Mills (MSYM) theory. It is shown that these observables, which directly prove the SL(2,C) symmetry present in gauge theories in the Regge limit, exhibit an excellent perturbative convergence. They are compared to those calculated in QCD for different renormalization schemes concluding that the momentum-substraction scheme with the Brodsky-Lepage-Mackenzie scale-fixing procedure captures the bulk of the MSYM results. 相似文献
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利用溢流恒压装置产生具有稳定出流速度的圆管潜射流, 结合染色液流态显示方法, 在多种射流无量纲潜深d/H、雷诺数Re以及限制数C的组合下, 实验研究了该潜射流动量在有限深密度均匀流体中的演化特性, 其中d为射流潜深, H为水深. 研究表明, 当C<1时潜射流表现为深水特征, 而当1≤ C<2时潜射流表现为过渡特征, 在这两种情况下均不产生任何形式的大尺度相干结构; 当2≤ C<10时潜射流表现为浅水特征, 而C≥10时潜射流表现为极浅水特征, 在这两种情况下均产生大尺度的偶极子涡结构. 对极浅水特征潜射流, 在各种无量纲潜深下, 偶极子涡结构的无量纲形成时间tf*与无量纲射流时间Tinj*均满足相同的正比例关系; 对浅水特征潜射流, 当d/H=0.5时, tf*与Tinj*满足某种线性关系, 但对其他无量纲潜深, tf*与Tinj*之间无明显规律.
关键词:
圆管潜射流
限制数
偶极子涡结构
形成时间 相似文献
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An image analysis technique has been developed in order to determine the drop size distributions of sprays produced by low‐velocity plain cylindrical jets. The particle sizing method is based on incoherent backlight images. Each drop is analyzed individually in the image. The two‐dimensional image resulting from the projection of the three‐dimensional object shape (the drop) on a screen (the video sensor surface) is modeled. The model, based on the point spread function formulation, has been developed to derive a relation between contrast and relative width of individual drops. This relation is used to extend the domain of validity of drop size in terms of size range, out of focus and image resolution. The shape parameter is determined for each drop image through morphological analysis. Spherical and non‐spherical droplets are then sorted on the basis of this parameter. Non‐spherical drops are regarded as non‐fully atomized liquid bulks or coalesced drops. Finally, the droplet size distribution of true spherical droplets is established for a low‐velocity plain cylindrical liquid jet. 相似文献