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Soil layers including shallow gas threaten underground structures. Considering the special geological conditions of the gas-bearing layers under the Yangtze River for the Sutong River-crossing unity tunnel project, a solid-liquid-gas coupled 3-D numerical model was established to consider two different gas pocket conditions (a single gas pocket and multiple random gas pockets), and the effects of shallow gas on the tunnel segment and the adjacent soils in the long-term process of gas leakage were analyzed and discussed. A brief discussion of the displacement results and a comparison of the stress results determined by simulation and the designed data indicated that as the maximum displacement is on the order of millimeters for both gas pocket conditions and the simulated maximum bending moment is less than the design value for the bending moment, the structure of the tunnel segment has remained in a safe state during the leakage of the gas pocket, and the normal operation of the tunnel segment is basically not affected by the leakage of the gas pocket.

To investigate the gas–liquid two-phase flow in a three-stage multiphase pump, numerical simulations and visualization experiments were performed. A mixture of air and water was selected as the medium. A three-dimensional flow field of the three-stage multiphase pump designed by authors was simulated employing the commercial computational fluid dynamics software ANSYS-CFX to solve the Navier–Stokes equations for steady flow and unsteady flow. The differential pressure of each stage and change characteristic of gas volume fraction under various inlet gas volume fraction were compared via steady simulations. The distribution characteristics of pressure and gas volume fraction in three stages were studied, and the movement of gas pockets in impellers was discovered via unsteady simulations as well. Four types of flow patterns were observed during the visualization experiments with the increasing inlet gas volume fraction. The results of the experiment reveal that the positions and characteristics of the gas pocket were similar to the results from the unsteady simulations, which verify the reliability of the simulations.

The results of physical modeling of geomechanical processes in outer zones of coal beds with the main roof caveable with difficulty. The scope of the modeling embraces the inlfuence seams on gas release by gas temperature and pressure variation during stage-wise outlet of gas from a pressure bomb, which simulates cyclical mechanical impact on a coal seam in the zones of a gas pocket. It is found that the low-frequency (2.0–4.5 Hz) attenuating vibrations generated in the main roof can induce both secondary rock mass disintegration as well as methane desorption and decomposition of gas hydrates (if present) accompanied by an increases in gas pressure and in number of gas-dynamic events in outer zones of coal beds.

When illuminated by a laser, plasmonic nanoparticles immersed in water can very quickly and strongly heat up, leading to the nucleation of so-called plasmonic vapor bubbles. While the long-time behavior of such bubbles has been well-studied, here, using ultrahigh-speed imaging, we reveal the nucleation and early life phase of these bubbles. After some delay time from the beginning of the illumination, a giant bubble explosively grows, and collapses again within 200 μs (bubble life phase 1). The maximal bubble volume Vmax remarkably increases with decreasing laser power, leading to less total dumped energy E. This dumped energy shows a universal linear scaling relation with Vmax , irrespective of the gas concentration of the surrounding water. This finding supports that the initial giant bubble is a pure vapor bubble. In contrast, the delay time does depend on the gas concentration of the water, as gas pockets in the water facilitate an earlier vapor bubble nucleation, which leads to smaller delay times and lower bubble nucleation temperatures. After the collapse of the initial giant bubbles, first, much smaller oscillating bubbles form out of the remaining gas nuclei (bubble life phase 2). Subsequently, the known vaporization dominated growth phase takes over, and the bubble stabilizes (life phase 3). In the final life phase 4, the bubble slowly grows by gas expelling due to heating of the surrounding. Our findings on the explosive growth and collapse during the early life phase of a plasmonic vapor bubble have strong bearings on possible applications of such bubbles.

Pumps handling two-phase flows are essential parts of industrial process mainly in oil and gas facilities and power plants. It is known that for centrifugal pumps the presence of gas phase in liquid flow causes the performance to deteriorate. Knowledge improvement of the highly complex internal flow is the way to design more efficient and reliable pumps. The paper describes the results of studies conducted in a centrifugal pump operating in two-phase air/water mixture flows, for performance determination and flow field investigation using numerical simulations. The aim is to provide a new highlight on the performance evolution and to identify the physical mechanism responsible for the deterioration. The work is carried out at design flow rate with varying inlet gas volume fraction. The results show significant performance deterioration compared to single-phase situation. The analysis of flow fields in case of two-phase flows reveals an accumulation of the gas in the impeller passages, causing an alteration of the conventional single-phase flow structure. The effect of interaction with volute is also investigated and it is found to play a key role in changing the flow pattern inside the impeller. At the conclusion of the study, special design features are suggested as concepts for enhancing two-phase pumping behavior of centrifugal pumps.

Pressure reduction in liquids may result in vaporization and bubble formation—a process known as cavitation. It is commonly observed in hydraulic machinery, ship propellers and even in the context of medical therapy within the human body. Although cavitation may be beneficial for the removal of malign tissue, in many cases it is unwanted due to its ability to erode nearly any material in close contact. The current understanding is that the origins of heterogeneous cavitation are nucleation sites where stable gas cavities reside, for example, on contaminant particles, submerged surfaces or shell-stabilized microscopic bubbles 1 , 2 . Here we present the discovery of an atomically smooth interface between two immiscible liquids acting as a nucleation site. The non-polar liquid has a higher gas solubility and, upon pressure reduction, it acts as a gas reservoir as gas accumulates at the interface. We describe experiments that reveal the formation of cavitation on non-polar droplets in contact with water, and elucidate the working mechanism that leads to the nucleation of gas pockets through simulations. Cavitation refers to the emergence of bubbles from liquids undergoing pressure reduction. A hitherto unknown cavitation scenario is now reported, with bubbles originating from the atomically smooth interface between two immiscible liquids.

Gas escape from volcanic systems is regulated by permeable pathways. When gas escape is hindered, pressure within the edifice can increase, possibly resulting in explosive eruptions. We present a study on enclave bearing dome lavas from Chaos Crags and Lassen Peak, California, to understand the impact of mechanical and textural heterogeneities on the permeability fabric of dome lavas. We combine field and laboratory measurements of permeability and porosity. The data show that in the presence of mechanical heterogeneities, shear deformation induces permeability anisotropy and heterogeneity with higher permeability parallel to the shear fabric and varying on decimeter scale around mechanical heterogeneities. Based on these insights we discuss implications for the accumulation of gas pockets in the conduit margin, which may contribute to cyclic explosive gas venting commonly observed at dome forming volcanoes.

Gas injection into a liquid cross-flow is examined for the case where the gas is injected beneath a horizontal flat surface. For moderate Froude numbers, the gas pocket that is formed will rise toward the flow boundary under the action of buoyancy, a condition that is conducive to the formation of gas layers for friction-drag reduction on the surface. At the location of gas injection, a plume whose geometry is related to the mass and momentum flux of the injected gas and liquid cross-flow is formed, and the influence of buoyancy is minimal. However, as the gas pocket convects downstream, buoyancy brings the gas back upward to the flow boundary, and leads to the bifurcation of the pocket into two distinct branches, forming a stable ‘V’-shape. Under some conditions, the flow between the two gas branches is almost entirely liquid, while for others there exists a bubbly flow or a continuous sheet of gas between the branches. The sweep angle and cross-sectional geometry of the gas branches are related to free-stream speed and boundary-layer thickness of the liquid cross-flow, the mass-injection rate of the gas, the diameter of the injection orifice and the gas outlet mean velocity and gas–jet angle. Data for a range of experimental conditions are used to scale the flow and results are compared to numerical computations of the flow, and these data are used to illustrate the underlying flow processes responsible leading to the formation the stable and straight gas branches. A simple model based on the balance of forces around a stable gas branch is presented and used to scale the observed data, and we use the results of this analysis and the computations to discuss how the process of gas injection may interact with the formation of the stable gas pockets farther downstream.

Two-dimensional gaseous detonations near critical propagation state were studied numerically in a channel with stoichiometric H\\(_2\\)/air and H\\(_2\\)/O\\(_2\\) mixtures. Detonation waves exhibit a mode-locking effect (MLE) in a single-headed mode regime. Increasing the channel width alters the strength and propagation period of the single transverse wave. This leads to MLE failure and the occurrence of the single-dual-headed critical mode, featuring the emergence of a new transverse wave. For a stoichiometric H\\(_2\\)/air mixture, generation of the new transverse wave is due to interactions between the detonation front and the local explosion wave originating from interactions between the transverse wave and unreacted gas pocket downstream. Whereas, for a stoichiometric H\\(_2\\)/O\\(_2\\) mixture, a transverse wave interacting with the wall produces Mach reflection bifurcation, causing MLE failure and generation of the new transverse wave. Our results show that all transverse waves manifest as strong transverse wave (STW) structures, with most belonging to the second kind, and an acoustic coupling exists between the typical second kind of STW structure and the acoustic wave in the induction zone behind the Chapman–Jouguet detonation front. A high-pressure region close to the STW structure plays a crucial role in exploring the transverse dynamics of this structure. Shock polars with rational assumptions are adopted to predict flow states in this region. The roles of pivotal factors in influencing the flow states and wave structure are clarified, and characteristic pressure values derived adequately represent the STW structure’s transverse dynamic behaviours. Lastly, the relationship between the kinematics and kinds of STW structures is unveiled.

Superhydrophobic surfaces are able to entrap gas pockets in between surface roughness elements when submerged in water. These entrapped gas pockets give these surfaces the potential to reduce drag due to the overlying flow being able to locally slip over the gas pockets, resulting in a mean slip at the surface. In this work we assess the separate effects that surface slip and surface texture have on turbulence over superhydrophobic surfaces. We show that the direct effect of surface slip does not modify the dynamics of the overlying turbulence, which remains canonical or smooth-wall like. The surface drag is governed by the difference between two virtual origins, the virtual origin of the mean flow and the virtual origin experienced by the overlying turbulence, in an extension of the theory from Luchini, Manzo & Pozzi (J. Fluid Mech., vol. 228, 1991, pp. 87–109) for riblets. Streamwise slip deepens the virtual origin of the mean flow, while spanwise slip deepens the virtual origin perceived by the overlying turbulence. Drag reduction is then proportional to the difference between the two virtual origins. We decompose the near-wall flow into background-turbulence and texture-coherent components, and show that the background-turbulence component experiences the surface as homogeneous slip lengths. The validity of the slip-length model can then be extended to larger texture size $L^{+}$ than thought in previous studies. For $L^{+}\\gtrsim 25$ , however, we observe that a nonlinear interaction with the texture-coherent flow develops that alters the dynamics of the background turbulence, exhibiting a modified distribution of turbulent energy across length scales. This has the effect of reducing the velocity increment $\\unicode[STIX]{x0394}U^{+}$ compared to that predicted using homogeneous slip lengths and sets the upper limit of applicability of slip-length models.