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The Yunkai massif is a key region to decipher the tectonic evolution of the south China block since the contained high-grade metamorphic rocks experienced a polyphase deformation. The earliest event ([D.sub.1]) corresponds to a top-to-the-northwest ductile shearing, coeval with amphibolite facies metamorphism, probably developed during a postorogenic synmigmatization extensional event occurred in early Paleozoic time. The main ductile deformation ([D.sub.2]) is top-to-the-northeast shearing, occurred in early Mesozoic time, coeval with amphibolite to greenschist facies metamorphism and associated with the development of northeast verging recumbent folds within the Neoproterozoic-Paleozoic sedimentary cover of the south China block. The tectonic significance of D2 is possibly linked with the subduction of Indochina beneath south China along the Song Ma belt of North Vietnam. Another compressional event ([D.sub.3]) of Late Jurassic to Cretaceous age is indicated by SE verging recumbent folds with NE-SW trending axes developed both in the sedimentary cover and gneissic basement. The northwestward subduction of the Pacific plate or the SE thrusting of the Songpan-Ganzi fold belt upon the Yangtze craton can be considered as the geodynamic causes of this late Mesozoic event. Last, NE SW trending brittle sinistral strike-slip and normal faulting ([D.sub.4]) control the massif uplifting and the subsiding of continental half grabens. This structure, which is widespread in the eastern margin of the Eurasia continent, can be related either to the westward subduction of the Paleo-Pacific plate or to lithosphere removal during the late Mesozoic.

A computational fluid dynamics model for cavitation simulation was investigated and compared with experimental results in the case of a three-blade industrial inducer. The model is based on a homogeneous approach of the multiphase flow coupled with a barotropic state law for the cool water vapor/liquid mixture. The numerical results showed a good prediction of the head drop for three flow rates. The hydrodynamic mechanism of the head drop was investigated through a global and local study of the flow fields. The evolution of power, efficiency, and the blade loading during the head drop were analyzed and correlated with the visualizations of the vapor/liquid structures. The local flow analysis was made mainly by studying the relative helicity and the axial velocity fields. A first analysis of numerical results showed the high influence of the cavitation on the backflow structure. [DOI: 10.1115/1.2969272]

Flows past a free surface piercing cylinder are studied numerically by large eddy simulation at Froude numbers up to [Fr.sub.D] = 3.0 and Reynolds numbers up to [Re.sub.D] = 1 x [10.sup.5]. A two-phase volume of fluid technique is employed to simulate the air-water flow and a flux corrected transport algorithm for transport of the interface. The effect of the free surface on the vortex structure in the near wake is investigated in detail together with the loadings on the cylinder at various Reynolds and Froude numbers. The computational results show that the free surface inhibits the vortex generation in the near wake, and as a result, reduces the vorticity and vortex shedding. At higher Froude numbers, this effect is stronger and vortex structures exhibit a 3D feature. However, the free surface effect is attenuated as Reynolds number increases. The time-averaged drag force on the unit height of a cylinder is shown to vary along the cylinder and the variation depends largely on Froude number. For flows at [Re.sub.D] = 2.7 x [10.sub.4], a negative pressure zone is developed in both the air and water regions near the free surface leading to a significant increase of drag force on the cylinder in the vicinity of the free surface at about [Fr.sub.D] = 2.0. The mean value of the overall drag force on the cylinder increases with Reynolds number and decreases with Froude number but the reduction is very small for [Fr.sub.D] = 1.6-2.0. The dominant Strouhal number of the lift oscillation decreases with Reynolds number but increases with Froude number. Keywords: free surface piercing cylinder, two-phase volume of fluid, large eddy simulation

Eulerian equations for the vertical flux and momentum of suspended particles in dilute sediment-laden open-channel flow in equilibrium have been derived using the two-fluid approach. Reynolds averaging has been applied in order to allow validation of individual terms with experimental data. Consideration of the various terms of the vertical momentum balance with experimental flume data indicates that the drag force has to be separated into a mean and a turbulent contribution with different timescales, respectively, the (gravitational) particle timescale and the integral turbulence timescale. The resulting formulation further provides a new theoretical closure for the turbulent Schmidt number. DOI: 10.1061/(ASCE)0733-9429(2008) 134:9(1225) CE Database subject headings: Suspended sediments; Open channel flow; Turbulence; Two-phase flow.

This paper focuses on the formulation and assessment of a second-order accurate finite volume (FV) shock-capturing scheme for simulating one- and two-phase water hammer flows. The two-phase flow model is based on the single-equivalent fluid concept. The proposed scheme for one- and two-phase flows is the same, except for the Riemann solvers used to evaluate fluxes between computational cells. For one-phase flows, the accuracy and numerical efficiency of the proposed scheme is contrasted against the fixed-grid method of characteristics (MOC) and a recently proposed FV scheme. For two-phase flows, the accuracy and numerical efficiency of the proposed scheme are compared to the fixed-grid MOC scheme. The results for one-phase flows show that, when a Courant number (Cr) very close to 1.0 (around 0.99 or higher) is used, the MOC scheme is more efficient than the proposed scheme and the other FV scheme. In this case, the latter two schemes have similar numerical efficiency. When Cr drops below about 0.95, the proposed scheme is more efficient than the MOC scheme and the other FV scheme, especially for smooth transient flows (no discontinuities). For two-phase water hammer flows, all the simulations were carried out using a maximum Courant number of 0.95 to avoid numerical instability problems. The results for two-phase flows show that the proposed scheme is much more efficient than the fixed-grid MOC scheme. The fixed-grid MOC and the proposed scheme are also used to reproduce a set of two-phase flow experiments reported in the literature. Good agreement between simulated and experimental data is found. CE Database subject headings: Pressurized flow; Two phase flow; Water hammer; Hydraulic transients.

Stratified flows are encountered in many industrial applications. The determination of the flow characteristics is essential for the prediction of pressure drop and holdup in the system. The aim of this study is to gain insight into the interaction of a gas and a liquid phase flowing in a stratified regime, with especial focus on the effect of interfacial waves on the turbulence structure of the liquid phase. Measurements of mean velocities and turbulent intensities in the liquid phase of a stratified air-water duct flow are performed. Mean velocity profiles and turbulence structure are affected differently for different wave amplitudes. The effect of small amplitude waves is restricted to the. near-interface region, resembling the effect of increasing shear rate on a flat interface. On the other hand, large amplitude waves modify the flow structure throughout the whole liquid depth. The mean velocity is greatly enhanced, resulting in a higher bulk velocity. Turbulent intensities are also significantly enhanced especially in the interface region. This big difference in flow structure is not observed after the appearance of the first waves but rather when a certain critical wave amplitude is triggered, indicating that the prediction of this critical wave type turns out to be more important than the determination of the transition from a smooth to a stratified wavy regime. [DOI: 10.1115/1.2928295]

This work simulated the flow pattern of the sludge blanket clarifier at the Bansin Water Treatment Plant, Taiwan by multiphase flow, three-dimensional analysis. The following three models were developed individually: One-phase flow (water) in the clarifier--this model acquires the basic water-flow pattern; a homogeneous porous medium at the bottom of the clarifier--this porous medium represents the sludge blanket; and, the Eulerian granular multiphase model, which was utilized to obtain solid effluent flux and to determine the effects of particle size and density on sludge blanket stability. Analytical results indicated that the clarifier has two principal circulations inside and outside the reaction well. A plentiful, dense and thick sludge blanket should exist at the clarifier bottom; otherwise particles could flow out through the gap between bottom of the reaction well and top of blanket surface, resulting in poor water quality. In the multiphase flow model, large particles and a high particle density are positively correlated with sludge blanket stability. DOI: 10.1061/(ASCE)0733-9372(2008)134:6(443) CE Database subject headings: Computational fluid dynamics technique; Two phase flow; Three-dimensional analysis; Porous media.

We present a generalized integral model for multiphase plumes in stratified ambient conditions based on the double-plume approach, where the plume is composed of a rising, multiphase core plume surrounded by a counterflowing outer ring plume of dense fluid. The generalized model captures as limiting cases the current approaches in the literature, including two-fluid and mixed-fluid equations, continuous and discrete detrainment, dispersed-phase mass transfer, and two models for entrainment in the counterflow region. These modeling approaches are compared and validated against both laboratory and field-scale data. In unstratified conditions, all model formulations perform equally well. In stratification, entrainment in the counterflow region is best represented by correlation to the inner plume velocity instead of the difference between the inner and outer plume velocities. The vertical distribution of the exchange between the inner and outer plumes in the models differs from that measured in the prototype due to enhanced entrainment at the detrainment zone and forced entrainment from the collapsing intrusion layer. Nonetheless, the models predict well the length scales and volume fluxes at the detrainment zone and intrusion layer. Applications are demonstrated for reservoir air bubble plumes. The mass transfer and near-field mixing in the double-plume integral model prove sufficiently accurate to predict the depth of maximum plume rise (both the locations of total dissolution of the bubbles and the maximum height of the decelerating plume) and the volume flux, dissolved constituent mass flux, and trap height of the intrusion. DOI: 10.1061/(ASCE)0733-9429(2008)134:6(772) CE Database subject headings: Bubbles; Plumes; Two phase flow; Entrainment; Integral equations; Numerical models; Mass transfer.

This paper focuses on an experimental study of the two-phase flow downstream of a laboratory model fish bypass. Experiments were performed on a 1:24 scale laboratory model of a fish bypass under consideration for construction at Wanapum Dam, on the Columbia River in Washington. The model was operated at the design condition of skimming flow regime and at the possible off-design plunging and surface jump regimes. Void fraction data were collected using an optical phase detection probe on a three-dimensional grid, and the phase indicator function was recorded at selected locations. It was found that in the laboratory model, the skimming flow regime effectively prevents bubbles from reaching deep into the tailrace, resulting in a considerably lower void fraction than plunging and surface jump regimes. For this geometry, the surface jump regime entrains air deeper than the plunging regime. To observe trends, the instantaneous source of total dissolved gas was estimated for the three regimes using the model data and several simplifying assumptions. Time distributions of the indicator function are also reported. DOI: 10.1061/(ASCE)0733-9429(2008)134:6(763) CE Database subject headings: Bubbles; Spillways; Dissolved gas; Two phase flow; Columbia River; Dams; Washington.

The breakup of a liquid droplet induced by a high-speed gas stream is a known multiphase flow problem. Among various breakup modes of liquid droplets impinged by shock waves, the stripping breakup takes place over a wide range of Weber numbers, from 100 to approximately 20,000. In this study, the evolution of the stripping breakup of a water droplet is simulated by using a multiphase flow solver with a five-equation model. Several test cases such as gas-gas shock tube, water-air shock tube, and underwater explosion problems are performed to validate the present numerical methods. To compare with the experimental results, the water droplets with diameters of 6.4 and 4.8 nun and Mach numbers of 1.3 and 1.47 are chosen in this study. The stripping breakup of a water droplet, including the shape deformation, vortex shedding, unsteady drag force, and flow instability, is investigated. The computed displacement, acceleration, and volume change of the water droplet are in agreement with the experimental data in dimensionless form. The evolution of a water droplet during the stripping breakup for an inviscid flow is presented by flow visualization.

The rolling stream trail (RST) model introduces a new formulation of cavitation analysis of an eccentric journal bearing; it is presented as a preferred foundation for cavitation analysis of a journal bearing to replace Floberg's streamer hypothesis that had been adopted by many investigators in recent past. Based on a careful reinterpretation of published experimental photographic data, noting the blunt-nosed shape of the interspersing space that separates adjacent wetting outlines at the rupture boundary, it stipulates a 3D flow structure for transition from the filled fluid film (FFF) to a cross-void fluid transportation process. The transition starts as a two-component composite rupture front and becomes an adhered film (AF) that is masked by rolled-on stream trails, which are drawn from the rupture front. The AF moves with the journal surface across the void to feed the FFF at the formation boundary. Upon averaged across a full period of the rupture front, Olsson's equation for flow continuity relative to a moving cavitation boundary yields a moving speed of the rupture front that is proportional to the reciprocal of the width fraction of the wet pockets multiplied into the FFF pressure gradient. For all nonvanishing width fraction of the wet pockets, both rupture and formation boundaries move with finite speeds. RST is an initial value time-dependent problem that deals with both the FFF and AF that are joined at rupture and formation boundaries. The initial fluid content in the void span is bracketed between a dry void and a freshly cavitated wet void. As time progresses, transportation of AF across the void space and boundary motions form a coupled evolution process. Formulas for the boundary motions indicate that the formation boundary would become stationary simultaneously as the rupture boundary approaches the Swift-Stieber condition. For implementation of RST analysis, analytic functions originally derived by Sommerfeld in his classical paper are employed to construct FFF pressure profile and subsequently to calculate boundary speeds. Precision and robustness achieved in this approach assure viability of RST cavitation analysis. Results include temporal evolution profiles of the FFF pressure and the cavitation boundary trajectories. Basic concepts and mathematical formulation of RST are applicable to 2D problems. A scheme to include squeeze film motion is outlined. [DOI: 10.1115/1.2908912] Keywords: cavitation analysis, fluid film lubrication, hydrodynamic lubrication, journal bearing, two-phase flow

This paper presents a comprehensive analysis of suspended sediment transport in open channels under various flow conditions through a kinetic-model-based simulation. The kinetic model, accounting for both sediment-turbulence and sediment-sediment interactions, successfully represents experimentally observed diffusion and transport characteristics of suspended sediments with different densities and sizes. Without tuning any model coefficients, the nonmonotonic concentration distribution and the noticeable lag velocity with a negative value close to the wall are reasonably reproduced. Examination of flow conditions typical of suspension dominated rivers shows that the conventional method may overestimate or underestimate unit suspended-sediment discharge, depending on the Rouse number, sediment size, as well as shear velocity. The error may be less than 20% for [d.sub.p]< 0.5 mm and might exceed 60% for [d.sub.p] > 1.0 mm under typical flow conditions where shear velocity ranges from 1.0 to 12.5 cm/s and flow depth ranges from 1.0 to 5.0 m. CE Database subject headings: Sediment transport; Open channel flow; Simulation; Two phase flow; Turbulence.

The incipience of two-phase flow in discharging branches from a stratified gas-liquid region has major implications in industrial applications where safety is of concern. An experimental investigation of the liquid side flow field at the onset of gas entrainment, in a single downward oriented discharging branch, was presented. Particle image velocimetry was used to measure the liquid side flow field in horizontal and vertical planes. Averaged velocity profiles were presented and demonstrated a highly radial flow. The particle image velocimetry data were validated using continuity and showed that the mass flow rate to be in the range of 10-25% of the expected value. Further, the vortex-free flow field assumption, used previously in the development of analytical and empirical models, was found to be reasonable. [DOI: 10.1115/1.2801356] Keywords: onset of gas entrainment, two-phase flow visualization, particle image velocimetry

In the present paper, experimental work concerning the effect of water injection on a compressor stage is presented. The effect on compressor stage performance and stability is examined for water injection up to 2%. The behavior of the airflow in the blade rows is examined through aerodynamic measurements. The results indicate that although the water injection appears to not have any significant effect on the flow pattern and to stage pressure rise and stall margin, there is a measurable effect on compression efficiency, which seems to result mainly from losses of a mechanical nature and water acceleration. The efficiency degradation is proportional to the water ratio entering the engine. [DOI: 10.1115/1.2718223] Keywords: water injection, wet compression, two-phase flow

Air in water flow is a frequent phenomenon in hydraulic structures. The main reason for air entrainment is vortices at water intakes, pumping stations, tunnel inlets, and so on. The accumulated air, in a conduit, can evolve to a different flow pattern, from stratified to pressurized. Among different patterns, slug is most complex with extreme pressure variations. Due to lack of firm relations between pressure and influential parameters, study of slug flow is very important. Based on an experimental model, pressure fluctuations inside a circular, horizontal, and inclined pipe (90 mm inside diameter and 10 m long) carrying tow-phase air-water slug flow has been studied. Pressure fluctuations were sampled simultaneously at different sections, and longitudinal positions. The pressure fluctuations were measured using differential pressure transducers (DPT), while behavior of the air slug was studied using a digital camera. The objective of the paper is to predict the pressure variation in a pipeline or tunnel, involving resonance and shock waves experimentally. The results show that the more intensive phase interaction commences stronger fluctuations. It is shown, that the air-water mixture entering the pipe during rapid filling of surcharging can cause a tremendous pressure surge in the system and may eventually cause failure of the system (e.g., the maximum pressure inside the pipe would reach up to 10 times of upstream hydrostatic pressure as suggested by others too). Relations for forecasting pressure in these situations are presented as a function of flow characteristics, pipe geometry, longitudinal, and cross-sectional positions and head water [DOI: 10.1115/1.2375134] Keywords: two-phase flow, water tunnel, pressure fluctuation, experimental model slug flow

Pulsed dielectric barrier discharges are generated within bubbles of a gas-liquid two-phase flow that consists of argon bubbles and water. Discharge images were captured by using a high-speed video camera to understand the motion of discharge within bubbles, and an intensified charge-coupled device camera captured temporal discharge images at a nanosecond timescale. Index Terms--Gas bubbles, gas-liquid two-phase flow, pulsed barrier discharge.