EFFECT OF A PROPELLER AND GAS DIFFUSION ON BUBBLE NUCLEI DISTRIBUTION IN A LIQUID

A multi-bubble dynamics code accounting for gas diffusion in the liquid and through the bubble wall was developed and used to study the modification of a bubble nuclei population dynamics by a propeller.The propeller flow field was obtained using a Reynolds-Averaged Navier-Stokes(RANS) solver and bubble nuclei populations were propagated in this field.The numerical pro-cedure enabled establishment of the possibility of production behind the propeller of relatively large visible bubbles starting from typical ocean nuclei size distributions.The resulting larger bubbles are seen to cluster in the blade wakes and tip vortices.Parametric investigations of the initial nuclei size distribution,the dissolved gas concentration,and the cavitation number were conducted to ide-ntify their effects on bubble entrainment and the resultant void fractions and bubble distribution modifications downstream from the propeller.Imposed synthetic turbulence-like fluctuations unto the average RANS flow field were also used to study the effect avera-ging in the RANS procedure has on the results.     

THE MOTION OF A BUBBLE IN WAVES

The motion of a single spherical bubble due to buoyancy in the ideal fluid with waves is studied in this article. Assuming that the bubble has no effect on the wave field, equations of a bubble motion are attained. The equations are solved. It is found that the nonlinear effect increases with the increase of the bubble radius. Since the difference between the frequencies of gravity waves and the eigenfrequency of bubbles is great for small bubbles, their oscillations can not be coupled. During the rising of a bubble, the oscillation of the bubble decays very fast, so it can be ignored. The rising time and the motion orbit are given. When the wave is high and the bubble is small, the spiral orbit may appear.     

INTERACTION OF A CAVITATION BUBBLE AND AN AIR BUBBLE WITH A RIGID BOUNDARY

The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography. Several dimensionless parameters are used to describe the geometrical configuration of the bubble-bubble-boundary interaction. The bubble-bubble interaction can be considered in two different conditions. The cavitation bubble will collapse towards the air bubble if the air bubble is relatively small, and away from the air bubble if the air bubble is relatively large. The two zones are identified in the bubble-boundary interaction, and they are the danger zone and the safety zone. The relative position, the bubble-boundary distance and the bubble-bubble distance play important roles in the bubble-bubble-boundary interaction, which can be considered in several conditions according to the responses of the bubbles. Air jets are found to penetrate into the cavitation bubbles. The cavitation bubble and the air bubble (air jet) move in their own way without mixing. The motion of a cavitation bubble may be influenced by an air bubble and/or a rigid boundary. The influence of the air bubble and the influence of the boundary may be combined, like some thing of a vector.     

VISCOSITY EFFECTS ON THE BEHAVIOR OF A RISING BUBBLE

In the incompressible fluid flow regime,without taking consideration of surface tension effects,the viscosity effects on the behavior of an initially spherical buoyancy-driven bubble rising in an infinite and initially stationary liquid are investigated numerically by the Volume Of Fluid(VOF) method.The ratio of the gas density to the liquid density is taken as 0.001,and the gas viscosity to the liquid viscosity is 0.01,which is close to the case of an air bubble rising in water.It is found by numerical exp...     

EFFECTS OF LIQUID COMPRESSIBILITY ON RADIAL OSCILLATIONS OF GAS BUBBLES IN LIQUIDS

For forced radial oscillations of gas bubbles in liquids, a more rigorous expression of the acoustic damping constant based on Keller’s equation is developed. Comparison with those in published papers is also made. The expression offered in this paper will improve the predictions of total damping constant in particular for high frequencies and large bubbles, i.e., large ωR0/c1(ω is the frequency of driving sound field,R0 is the equilibrium bubble radius, c1 is the sound speed in the liquid). Examples in ultrasound imaging and acoustical oceanography are demonstrated.     

A MODEL FOR LIQUID SLUG LENGTH DISTRIBUTION IN VERTICAL GAS-LIQUID SLUG FLOW

The slug length and the trailing Taylor bubble velocity in an upward vertical slug flow were measured by using the optical probes and the EKTAPRO 1000 high speed motion analyzer. The correlation between the trailing bubble velocity and the length of liquid slug ahead of that bubble is derived from the experimental data. Based on this correlation as well as the bubble overtaking mechanism, a model for the slug length distribution at any designated locations along the pipe is proposed. The predicted results are in agreement with the experimental data.     

A LEVEL SET METHOD FOR SIMULATION OF RISING BUBBLE

A level set method, the TVD scheme of second-order upwind procedure coupled with flux-limiter, and SIMPLE algorithm were incorporated to simulate the flow and interracial motion of immiscible two-fluids with large density ratio and viscosity ratios, large topology distortion and surface tension. As a numerical example axi-symmetric rising bubbles were investigated. It is found that the method is numerically stable and has good convergence property and the results are in good agreement with other works.     

THE COUNTER-JET FORMATION IN AN AIR BUBBLE INDUCED BY THE IMPACT OF SHOCK WAVES

The interaction of an air bubble (isolated in water or attached to a boundary) with shock waves induced by electric sparks is investigated by high-speed photography.The interaction is closely related to the counter-jet induced by the impact of shock waves.The formation of a counter-jet in an air bubble is related to the liquid jet formed in the same air bubble,but the mechanism is different with that of the counter-jet formation in a collapsing cavitation bubble.The formation of a counter-jet in an air bubb...     

A COUPLING MODEL OF WATER FLOWS AND GAS FLOWS IN EXHAUSTED GAS BUBBLE ON MISSILE LAUNCHED UNDERWATER

The gas and water flows during an underwater missile launch are numerically studied. For the gas flow, the explicit difference scheme of Non-oscillation and Non-free-parameter Dissipation (NND) is utilized to solve the Euler equations for compressible fluids in the body-fitted coordinates. For the water flow, the Hess-Smith method is employed to solve the Laplace equation for the velocity potential of irrotational water flows based on the potential theory and the boundary element method. The hybrid Eulerian-Lagrangian formulation for the free boundary conditions is used to compute the changes of the free surface of the exhausted gas bubble in time stepping. On the free surface of the exhausted gas bubble, the matched conditions of both the normal velocities and pressures are satisfied. From the numerical simulation, it is found that the exhausted gas bubble grows more rapidly in the axial direction than in the radial direction and the bubble will shrink at its "neck" finally. Numerical results of the movement of the shock wave and the distribution of the Mach number and the gas pressure within the bubble were presented, which reveals that at some time, the gas flow in the Laval nozzle is subsonic and the gas pressure in the nozzle is very high. Influences of various initial missile velocities and chamber total pressures and water depths on both the time interval when the gas flow in the nozzle is subsonic and the peak of the gas pressure at the nozzle end were discussed. It was suggested that a reasonable adjustment of the chamber total pressure can improve the performance of the engine during the underwater launch of missiles.     

DYNAMIC CHARACTERISTICS OF LIQUID SLOSHING IN A RECTANGULAR TANK UNDER LOW GRAVITY

1. INTRODUCTION The stability and the directional precision of liquid-filled spacecraft are influenced by the sloshing of liquid in the tank of spacecraft, which has been studied since 1960’s[1]. The major studies have been focused on the sloshing of liq…     

VIBRATION CHARACTERISTICS OF FLUID-STRUCTURE INTERACTION OF CONICAL SPIRAL TUBE BUNDLE

Heat transfer enhancement is achieved by flow-induced vibration in elastic tube bundles heat exchangers.For a further understanding of heat transfer enhancement mechanism and tube structure optimization,it is of importance to study the vibration characteristics of fluid-structure interaction of tube bundles.The finite element method is applied in the study of fluid-structure interaction of a new type elastic heat transfer element,i.e.,the dimensional conical spiral tube bundle.The vibration equation and ele...     

NUMERICAL STUDY OF NON-AQUEOUS PHASE LIQUID TRANSPORT IN A SINGLE FILLED FRACTURE BY LATTICE BOLTZMANN METHOD

In this article,the Non-Aqueous Phase Liquid(NAPL)transport in the single filled fracture was studied with the Shan-Chen multi-component multiphase Lattice Boltzmann Method(LBM)with special consideration of wettability effects.With the help of the model,the contact angle of the non-wetting phase and wetting phase interface at a solid wall could be adjusted.By considering a set of appropriate boundary conditions,the fractured conductivity was investigated in condition that the NAPL blocks the channels in the single filled fracture.In order to study the wettability effects on the NAPL transport,a constant driving force was introduced in the Shan-Chen multi-component multiphase LBM.Flow regimes with different wettabilities were discussed.Simulated results show that the LBM is a very instrumental method for simulating and studying the immiscible multiphase flow problems in single filled fracture.     

THEORETIC SOLUTION OF TRANSIENT FLOW OF LIQUID IN THE PIPE WITH FLUID MACHINERY

The transient flow of liquid in the pipe with fluid machinery is analysed in this pa-per.The theoretic solution of the transient flow produced due to the regulation of fluid machin-ery is found by use of the method of the Laplace transformation.     

THE EQUIVALENT MECHANICAL MODELS OF LIQUID SLOSHING IN A SPHERICAL TANK WITH SPACER UNDER LOW GRAVITY

The dynamics of liquid sloshing in a spherical tank with spacer under low gravity was investigated. By extending the characteristic functions, the frequencies of liquid free-sloshing, reaction force and moments on the wall of tank were obtained. By mechanical equivalent principle, the equivalent models of spring-vibrator-damper of liquid sloshing were given. The numerical results obtained show when a spacer is inserted in the tank, the sloshing frequency of liquid and the sloshing mass of liquid will decrease.     

NUMERICAL SIMULATION OF FLOW-INDUCED VIBRATION ON TWO CIRCULAR CYLINDERS IN TANDEM ARRANGEMENT

Flow-induced vibration of two circular cylinders in tandem arrangement elastically mounted with a massspring-damping system was studied by solving the primitive variable Navier Stokes equations incorporating the Arbitrary Lagrangian-Eulerian （ALE） method. The convection term and dissipation term were discretized using the third-order upwind compact scheme and the fourth-order central compact scheme, respectively. The typical spacing between the cylinders is 4 diameters, which is close to the critical value. The dynamic response of the vibrations on two cylinders with two-degreeof-freedom motion is different from that of an isolated cylin der, and also different from that of a cylinder vibrating in the wake of a fixed upstream one. Different flow patterns were found in the wake, and proved to be relevant to the discontinuities observed in the response of the oscillatory cylinders.     

NUMERICAL PREDICTION OF FATIGUE DAMAGE IN STEEL CATENARY RISER DUE TO VORTEX-INDUCED VIBRATION

For studying the characteristics of Steel Catenary Riser (SCR), a simplified pinned-pinned cable model of vibration is established. The natural frequencies, the normalized mode shapes and mode curvatures of the SCR are calculated. The fatigue damage of the SCR can be obtained by applying the modal superposition method combined with the parameters of S - N curve. For analyzing the relation between the current velocity and the SCR’s fatigue damage induced by the vortex-induced vibration, ten different current states are evaluated. Then, some useful conclusions are drawn, especially an important phenomenon is revealed that the maximum fatigue damage in the riser usually occurs near the area of the boundary ends.     

QUADRANT ANALYSIS OF BUBBLE INDUCED VELOCITY FLUCTUATIONS IN A TRANSITIONAL BOUNDARY LAYER

Our previous study showed that the frictional drag decreases with increasing void fraction at Re > 1300, while it increases at Re < 1000. Decomposition of the Reynolds shear stress also implied that bubbles induce isotropy of turbulence. In order to confirm our previous analysis and to further investigate flow fields in the vicinity of bubbles, we analyze velocity fluctuations on the quadrant space in the streamwise and transverse directions ( u′ – v′ plane). Here, we focus on two specific Reynolds numbers ...     

ANALYSIS OF LIQUID SLUG MOTION IN A VOIDED LINE

A quasi two-dimensional two-phase flow cylinder model of slug motion in avoided line developed in this paper can predict reasonably the change of flow pattern of the slug,air entrainment,“holdup” and the distribution of axial velocity.However,if using the theoryof transfer momentum to estimate the pressure-time history of slug at the elbow,the result ofcalculation is not good in agreement with that of experiment.Analysis of the experiment resultsand the estimations of using the theory of transient two-phase flow indicate that an evident wa-terhamrner-response occurs in the slug,when the high-speed slug impacts on the elbow,and thepeaks and waveform of pressure-time history are dependent mainly on the propagation of tran-sient two-phase flow in the slug.     

A NEW WAKE OSCILLATOR MODEL FOR PREDICTING VORTEX INDUCED VIBRATION OF A CIRCULAR CYLINDER

This article proposes a new wake oscillator model for vortex induced vibrations of an elastically supported rigid circular cylinder in a uniform current. The near wake dynamics related with the fluctuating nature of vortex shedding is modeled based on the classical van der Pol equation, combined with the equation for the oscillatory motion of the body. An appropriate approach is developed to estimate the empirical parameters in the wake oscillator model. The present predicted results are compared to the experimental data and previous wake oscillator model results. Good agreement with experimental results is found.     

水平液面式孔内电视系统测量孔斜的误差因素

提出水平液面式孔内电视系统测量孔斜的误差因素。并对液体的毛细作用、误差精度、钻孔顶角、容器直径引起的误差进行分析。