Upwash formation on splash plate atomization

The present study investigated the formation of upwash by the impingement of two liquid sheets on a solid wall. Here I considered the case when two liquid jets impinge on a solid wall, generating two liquid sheets, which in turn generates an upwash. The upwash greatly affects the spray characteristics and the spatial dispersion of spray droplets of a splash plate atomizer. Therefore, the upwash formation should be taken into account in the design of an atomizer. The formation of an upwash was experimentally observed under different experimental conditions, and the shape of the upwash was classified. Furthermore, the formation conditions and the shape of the upwash were theoretically analyzed, and the results of the theoretical analysis were verified experimentally.     

Acoustically excited air-assisted liquid sheets

The effect of acoustic excitation on the disintegration characteristics of air-assisted liquid sheets, which utilize water at ambient temperature, and for velocities up to 1.8 m/s, is investigated. The study using high-speed imaging techniques revealed that optimum frequency modulation of the perturbation generator has a pronounced influence on the associated surface waves and the subsequent breakup of the liquid sheet. The analysis includes characterization of critical wave amplitude, breakup length, and breakup frequency, for Weber numbers in the range 0.30<We_abs<0.44, which are compared with flow features in the absence of acoustic excitation. The results show that acoustic perturbation can effectively suppress the dominance of gravitational and surface tension effects. As a consequence, for low Weber number flows, the interfacial waves exhibit regularity, and thus a better control of primary breakup processes of liquid sheet may be accomplished.     

Turbulent liquid metal flow in rectangular shaped contraction nozzles for target applications

Owing to the high beam power densities envisaged in advanced nuclear targets, liquid metal-operated free surface targets are conceived as one feasible option. There, the free surface is formed by an adequately shaped upstream located nozzle. Target boundary conditions necessitate a detailed knowledge on the turbulent flow in contraction nozzles in order to identify turbulence models accurately predicting experimental findings within the velocity range of interest for nuclear target and hence can then act as design optimisation tools. In this context, a combined experimental and numerical study is conducted on the basis of the turbulent flow in the contraction nozzle of the Super-FRS target. Two aspects determining the turbulent flow in the nozzle have been investigated. The first is a potential relaminarisation of the boundary layer caused by the acceleration within the contraction and the second is a development of the secondary flows due to the pressure gradient in the rectangular shaped ducts cross-section. Regarding the three different turbulence models investigated here only the V2F model exhibited the capability to predict the relaminarisation of the turbulent boundary layer both qualitatively and quantitatively. All turbulence models are able to predict the development of secondary flows induced by pressure gradients in transverse direction with an acceptable accuracy.     

A study on the aerodynamic instability of attenuating liquid sheets

We describe the characteristics of a radially spreading unstable liquid sheet in quiescent air via optical measurement techniques and linear instability theory. A high speed CCD camera system and a complimentary laser refraction method were employed to measure the intact sheet diameter, unstable wave lengths, wave speed, wave frequency spectrum and spatial wave growth rates. Linear instability models for thinning, viscous and inviscid liquid sheets, which are available from the literature, allow for a comparison of experimental data and predicted sheet behaviour. The last section evaluates the differences and similarities between the current liquid sheet experiment and industrial spray applications such as fuel atomisation via pressure-swirl nozzles.     

Shock and wave dynamics in cavitating compressible liquid flows in injection nozzles

Due to the exceptional high inlet pressures up to 2,000 bar flow dynamics and efficiency of modern injection systems are controlled by high frequency wave dynamics of the compressible liquid flow. Corresponding to alternating shock and expansion waves the liquid fluid evaporates and recondenses instantaneously. Here we present CFD simulations of the time accurate evolution of cavitating flows in 2-D plane and in six-hole injection nozzles with focus on the wave dynamics just after initialisation of the flow and within the time scale Δt ≤ 10^?4 s of pilot and multi-point injection. Due to shock reflections at the bottom of the sack hole the instantaneous maximum pressure increases more than three times higher as compared with the prescribed pressure at the nozzle inlet. For instance, in case of an inlet pressure of 600 bar the maximum pressure in the sack and therefore ahead of the nozzle bore holes reaches about 2,100 bar. It is quite reasonable that this amplification of the pressure affects the evolution of the convective flow and therefore the mass flow through the nozzle bore holes.     

An experimental study of liquid jets formed by bubble-shock wave interaction in dilute polymer solutions

 This paper describes experiments in which a shock wave, emanating from the collapse of a cavitation bubble, causes a second bubble to collapse, thereby producing a liquid jet. A comparison of the jets formed by bubble collapse in dilute solutions of polyacrylamide and polyethylene oxide, and in their Newtonian counterparts, shows that in the polymer solutions liquid jet development is markedly suppressed. The implications of these findings are discussed in the context of cavitation damage. Received: 3 September 1998/Accepted: 23 July 1999     

A procedure for the design of nozzles used for the production of turbulent liquid jets

Where turbulent liquid jets are used for cutting and mining purposes the pressure generated by impact must be maximized. Initial jet behaviour has an important influence on subsequent jet impact pressures at medium range. Nozzle wall boundary layer history has a strong influence on the initial jet, and certain boundary layer features can be linked to poor jet performance. The procedure outlined in this paper was developed to eliminate new nozzle designs or changes in operating conditions on the grounds of badly behaved nozzle boundary flow. The design procedure consists of a potential flow analysis and a boundary layer analysis coupled to empirical correlations for boundary layers in accelerated flows. The procedure is exemplified by application to the design of a nozzle to be used for the specific purpose of mining china clay.     

Extensional flow of liquid jets formed by bubble collapse in oils under cavitation-generated pressure waves

We report a study of liquid jets which are formed by bubble collapse under cavitation-generated pressure waves. The results obtained for jets formed from samples of a multigrade motor oil provide the first evidence that such jets experience a significant degree of extensional deformation, at high rates of extension. The results support the conclusion that the reduced velocity and final length of such jets, relative to their Newtonian counterparts, is due to an increased resistance to extensional flow. Insofar as the multigrade oils studied here are made viscoelastic by polymer additives and evidently possess significant levels of resistance to extension, the results provide evidence in support of a mitigating effect of viscoelasticity on a cavitation damage mechanism, as mooted by Berker et al. (J Non Newton Fluid Mech 56:333, 1995).     

The generation of a draining liquid film by the vertical withdrawal of a flat plate from an elastico-viscous liquid

The analysis of Waters and Keeley [1] for the start-up of the drainage of an elastico-viscous liquid from a vertical surface is extended to include the effect of the vertical surface moving vertically with an arbitrary velocity. This is used to examine the effect of elasticity on the interesting drainage problems associated with the sudden withdrawal of a vertical plate from an elastico-viscous liquid.     

A two-phase stream containing liquid particles in the sub- and transonic regions of plane nozzles

The results of experimental studies of the influence of the entrance conditions, the particle size, the profiles of the sub- and transonic parts of the nozzle, and the initial concentration on the distribution of the solid discrete phase in the exit cross sections of axisymmetric nozzles were analyzed in [1]. The results of a study of the influence of the profiling of the nozzle and the size of the particles at the nozzle entrance on the formation of the distribution fields of the discrete liquid phase and its size at the cut of a plane nozzle are presented in the present report, which is a continuation of [1]. The experimental data presented permit a deeper understanding of the mechanism of flow of a two-phase medium in a nozzle and are required for an evaluation of efficiency of the calculation methods.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 167–170, March–April, 1978.     

Penetration of a compressible liquid by a plate and a disk of finite mass

The incidence of a plate and a disk of finite mass on a free water surface and the subsequent inertial motion are investigated. The effect of the air medium above the liquid is neglected.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 177–179, May–June, 1989.     

Cavitation flow around a plate in a channel by a stream of heavy liquid

The nonlinear problem of cavitation flow around a plate by a stream of heavy liquid is investigated in precise formulation; the plate is located on the horizontal floor of a channel when the gravity vector is directed perpendicular to the wall of the channel. Two flow systems are considered-Ryabushinskii's and Kuznetsov's system [1]. This problem was investigated in linear formulation in [2], Similar problems were considered earlier in [3–7] for unrestricted flow. Below, on the basis of a method proposed by Birkhoff [8, 9], all the principal hydrodynamic and geometric characteristics are calculated for the problem being considered.Translated from Ivestiya Akademii Nauk SSSR. Mekhanika Zhidkosti i Gaza, No. 3, pp. 3–9, May–June, 1973.     

Some rheological properties of lyotropic liquid crystals formed by phosphated polyoxyethylene surfactants,n-hexane and water

Summary Rheological measurements have been carried out using continuous shear viscometry and creep testing on two major mesophases previously found in systems containing phosphated nonyphenol ethoxylate (PNE), phosphated fatty alcohol ethoxylate (PFE), water andn-hexane. Systems containing lamellar liquid crystals exhibited a clockwise (rheopectic) hysteresis loop on the Ferranti-Shirley cone-and-plate viscometer which increased in area with increasing water content. On the other hand, both the hexagonal liquid crystalline phase and an intermediate amorphous gel phase showed an antì-clockwise (thixotropic) hysteresis.Creep tests with an air-bearing viscometer indicated that the majority of the lamellar phase systems tested had a linear visco-elastic behavior which could generally be characterised by one Maxwell unit combined with two Voigt units.The results are discussed in relation to the effects that water produces on the probable structure of the mesomorphic structures, in particular the coiling of the polyoxyethylene chains on the surfactant molecules.

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Zusammenfassung Rheologische Messungen mit den Methoden der kontinuierlichen Scherviskosimetrie und der Kriech-Prüfung wurden an zwei neu gefundenen Haupt-Mesophasen in Systemen von phosphatisiertem Nonylphenol-Äthoxylat (PNE), phosphatisiertem Fettalkohol-Äthoxylat (PFE), Wasser undn-Hexan durchgeführt. Die Systeme mit lamellaren flüssigen Kristallen zeigten im Ferranti-Shirley Kegel-Platte-Viskosimeter eine im Uhrzeigersinne verlaufende (rheopexe) Hysteresis-Schleife, deren Fläche mit zunehmendem Wassergehalt größer wurde. Dagegen zeigten sowohl die hexagonale flüssigkristalline Phase als auch eine intermediäre amorphe Gelphase eine entgegen dem Uhrzeigersinn verlaufende (thixotrope) Hysteresis.Kriech-Versuche mit einem luftgelagerten Viskosimeter ergaben, daß die Mehrzahl der untersuchten lamellaren Systeme ein linear-viskoelastisches Verhalten zeigte, welches durch Kombination von einem Maxwell- und zwei Voigt-Elementen beschrieben werden kann.Die Ergebnisse werden im Hinblick auf die Wirkung des Wassers auf die wahrscheinliche Anordnung der mesomorphen Strukturen diskutiert, insbesondere die Verknäuelung der Polyoxyäthylen-Ketten auf die oberflächenaktiven Moleküle.

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With 4 figures and 2 tables     

Impact of a rectangular plate on a liquid half-space

The potential flow of an ideal incompressible fluid occupying a half-space resulting from the impact of a rectangular plate on its surface is considered. Outside the plate the surface of the fluid is free. An integral equation of the first kind is obtained for the impulsive pressure beneath a flexible plate. It is solved on a computer by the power series method for the particular case of a rigid nondeformable plate. The accuracy of the method is estimated. The theoretical dependence of the virtual mass and virtual moment of inertia coefficients of a rigid nondeformable plate on the plate geometry is constructed and compared with the experimental data and with empirical formulas [1-3] not directly related with the solution of the Laplace equation.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.5, pp. 120–126, September–October, 1992.