Search Results (112)

This study utilizes a large-scale numerical simulation model to investigate the hydrodynamic behavior and particle transport characteristics of gas–liquid–solid three-phase flow in vertical wellbores featuring multi-source confluence and curved geometries. Simulation results indicate that increasing flow velocity shifts the dominant control mechanism from surface tension to inertial forces, transitioning the flow pattern from slug flow to churn flow. In curved pipe sections, centrifugal phase separation and geometric shielding effects cause significant flow asymmetry and maintain large bubble stability at the inner wall. Additionally, the multi-inlet structure induces shear rate gradients that result in the spatial coexistence of two distinct bubble scales. Furthermore, localized gas concentrations exceeding 70% at the upper inlet can trigger severe gas-locking phenomena and intense pressure pulsations. Full article

In gas drilling, the local annular contraction caused by a drillpipe tool joint can markedly reduce cuttings’ carrying capacity and increase the risk of localized blockage and sand bridging near the tool-joint region, thereby threatening hole cleaning and drilling safety. To investigate this problem, a three-dimensional CFD–DEM two-way coupling model was established by considering the geometric features of the drillpipe tool joint and gas–solid interaction. The effects of gas mass flow rate, solids feed rate, and particle diameter on local cuttings’ transport states and annular pressure-drop responses near the tool joint were systematically analyzed. The results show that three typical local transport states can develop near the tool-joint region, namely continuous passage, fallback, and clogging accompanied by sand-bridge formation. Fallback cases occur only within a finite interval around the critical gas mass flow rate for cuttings’ transport. Under the geometric and operating conditions considered in this study, localized clogging first appears when the particle diameter reaches approximately 10.5 mm, and the proportion of clogging cases increases rapidly with a further increase in particle diameter. Increasing the solids feed rate intensifies particle retention, accumulation, and collision near the tool joint, promotes earlier clogging, and markedly narrows the operating range of continuous passage; stable clogging is difficult to form when the solids feed rate is below 8 kg/s. Distinct annular pressure-drop histories correspond to different local transport states, with low amplitude fluctuation for continuous passage, repeated pulsation for fallback, and sustained growth in pressure difference magnitude for developing clogging accompanied by sand bridge formation. These results demonstrate a clear correspondence between local transport states near the tool joint and annular pressure-drop responses under the investigated geometry and operating window. They provide a mechanism-level basis for interpreting localized blockage near the drillpipe tool joint, while quantitative field application requires calibration for the specific annular clearance, monitoring interval, gas-injection condition, and cuttings’ loading condition. Full article

Closed-circuit axial piston pumps in the travel hydraulic systems of heavy-duty engineering vehicles are highly vulnerable to severe transient cavitation during emergency braking. Rapid pressure reversal at the interface between the cylinder bore and the valve plate causes volumetric efficiency loss, intensified pressure pulsation, and erosion damage; however, the coupled mechanism by which throttling, vortex formation, and cavitation interact in this region, together with its structural regulation pathway, remains insufficiently understood. To address this gap, a closed-circuit axial piston pump for cotton pickers was investigated under emergency braking as a representative extreme loading scenario. A full-passage transient CFD model was established and validated against steady-state volumetric efficiency tests on a heavy-load test bench, as well as against PIV internal flow visualization on a Reynolds-scaled transparent model. Parametric transient CFD sweeps were then performed, and a multi-objective optimization model was developed and solved using a Kriging-assisted NSGA-II algorithm with entropy-weighted TOPSIS decision-making. The results identify the interface between the cylinder bore and the valve plate as the primary cavitation zone, with cavitation driven by local throttling and wall-attached vortices rather than by global low pressure. The optimized cylinder bore configuration reduces the peak gas volume fraction by 34.7% in the total flow domain and by 15.7% in the valve plate region, while maintaining volumetric efficiency above 97.8%; the port plate pressure pulsation increases by 12.97%. The key takeaway is that targeted optimization of the cylinder bore alone, without altering the overall valve plate or piston block architecture, can effectively suppress transient cavitation, while revealing an inherent trade-off with pressure pulsation control. In conclusion, this work clarifies the cavitation mechanism, provides a validated numerical and experimental framework, and offers an implementable design pathway for transient cavitation control of closed-circuit piston pumps under extreme loading conditions. Full article

Under high-frequency commutation conditions, the Single-Piston Two-Dimensional Electro-Hydraulic Pump suffers from severe reverse flow and pressure pulsation, which limit its volumetric efficiency and operational stability. To address this issue, this study proposes a surrogate-assisted multi-objective optimization framework for the pump distribution structure. First, a dynamic model is established to analyze the influence of triangular damping groove geometry on flow and pressure characteristics, and four key parameters are selected as design variables. Then, sample data generated from AMESim simulations are used to train a Genetic Algorithm-optimized Backpropagation neural network surrogate model. Finally, the surrogate model is integrated with NSGA-II to minimize the peak reverse flow and pressure pulsation amplitude simultaneously. The results show that the GA-BP model predicts reverse flow and pressure pulsation with mean relative errors of 2.72% and 2.99%, respectively. Compared with the initial design, the optimized structure reduces the peak reverse flow by 27.6% and decreases the pressure pulsation amplitude from 0.78 MPa to 0.41 MPa. These results indicate that, within the parameter ranges and operating conditions considered in this study, the proposed framework provides an effective tool for the coordinated optimization of damping groove parameters for the Single-Piston Two-Dimensional Electro-Hydraulic Pump. Full article

This study investigates the unsteady gas flow structure in a cyclone separator using high-resolution Large Eddy Simulation (LES). Unlike traditional approaches, a method for analyzing velocity field dynamics based on velocity increments is proposed and validated. This technique enables the identification of coherent structures and high-frequency pulsations even on relatively coarse computational grids—a task beyond the capabilities of classical RANS models. Comparative analysis reveals that standard two-equation isotropic turbulence models systematically overestimate tangential velocity near the walls, suggesting they should be used with caution in cyclone applications. While the anisotropic RSM provides better agreement for the mean tangential velocity, it fails to capture the episodic “superbursts” and near-wall streaks resolved by LES. Numerical experiments revealed two distinct dynamic regimes in the conical section: continuous background pulsations caused by stochastic vortex migration and periodic superbursts triggered by vortex core–wall interactions. Special emphasis is placed on the identification of near-wall velocity streaks resulting from hydrodynamic instability in the viscous sublayer. It is shown that the unsteadiness and subsequent bursting of these structures induce high-frequency gas pulsations directly at the wall, which can significantly affect the dynamics of solid particles near the surfaces. These findings provide new insights into turbulent transport in swirling flows and establish a robust framework for further investigation of separation mechanisms. Full article

Air flotation is widely used in wastewater treatment for the removal of emulsified oils and suspended solids. The complex flow disturbances generated during the flotation process play a critical role in determining separation efficiency. This study employs the volume-of-fluid (VOF) method within the OpenFOAM framework to simulate the aggregation and rising behavior of microbubbles (40–100 μm) and oil droplets under various perturbation conditions. The effects of different airflow disturbance patterns on the flotation dynamics of oil–gas compounds are systematically investigated. Results show that negative pulsation promotes the rising of bubble–oil aggregates, whereas positive pulsation hinders their coalescence and upward motion. Furthermore, recirculation vortices induced by surface disturbances increase the residence time of oil–gas compounds in the water column, thereby affecting overall separation performance. The findings demonstrate that introducing vertical upward flow and bilateral oblique upward airflow can enhance flotation efficiency. This work provides insights into optimizing airflow configurations for improved oil removal in wastewater treatment applications. Full article

Screw compressors are critical equipment in oil and gas production and transportation, where efficiency losses caused by rotor geometry, inlet pressure pulsations, and harsh climatic conditions can accumulate into substantial annual energy penalties and reliability degradation. This study provides a quantitative assessment of these coupled effects within a unified multiphysics framework that combines time-accurate transient CFD simulations based on a fixed Cartesian immersed-boundary formulation with a climate-calibrated offline physics-based digital twin—functioning as a digital shadow with one-way data flow from archival SCADA records—a reduced-order seasonal model with no real-time updating, calibrated against a full calendar year of SCADA records and validated against a held-out cold-season dataset (October–December 2022, T_amb = −15 to +8 °C); summer-period predictions rely on calibrated extrapolation beyond the validation window—an integration not previously demonstrated for oil-flooded screw compressors. Two rotor profile configurations (Type A and Type B) were analyzed to quantify geometry-driven differences in static pressure distribution, leakage tendency, and pulsation sensitivity. Transient suction conditions were modeled using harmonic and quasi-random inlet pressure disturbances to evaluate pressure amplification, phase lag, leakage intensification, and efficiency degradation. Seasonal performance was assessed by integrating temperature-dependent gas properties, oil viscosity behavior, and external heat transfer into an annual climatic load framework. The results show that inlet oscillations are amplified inside the chambers (pressure amplification factor П_p ≈ 1.95; П_p up to 2.3 under quasi-random excitation), reducing mass flow and volumetric efficiency by 8–10% and decreasing polytropic efficiency from 0.78 to 0.69–0.71, while increasing leakage by up to 27% and raising peak contact pressures to 167–171 MPa. Seasonal variability (+30 to −30 °C) increased suction density by 38% but raised drive power by ~9% due to viscosity-driven mechanical losses, producing an energy penalty up to 10.8% and an estimated annual additional consumption of approximately 186 MWh per compressor, decomposed as: cold-season contribution ~113 MWh (±10 MWh, directly field-validated against October–December 2022 SCADA data) and summer-season contribution ~51 MWh (calibrated extrapolation; additional uncertainty unquantified and not included in the ±10 MWh bound). The full annual figure of 186 MWh should be interpreted as a model-based estimate rather than a fully validated result. These findings demonstrate that rotor design optimization and mitigation of nonstationary suction effects, coupled with climate-aware offline physics-based digital shadow operation, represent high-priority levers for improving efficiency and reducing energy penalties in field conditions; reliability implications require further validation against summer-season field measurements. Full article

Performance deterioration and unstable operation are common when multistage centrifugal pumps handle gas–liquid mixtures. Here, we investigate a two-stage centrifugal pump over a wide speed range and inlet gas volume fractions (IGVFs) using experiments and CFD. The two-phase flow is simulated with a Eulerian–Eulerian two-fluid approach (liquid as the continuous phase; gas as a dispersed bubbly phase with a representative bubble diameter of 0.3 mm). Turbulence is closed using the SST k–ω model for the liquid phase and the built-in dispersed-phase turbulence treatment in ANSYS CFX. Transient pressure signals are analyzed in the time and frequency domains (FFT) to assess how rotational speed affects void-fraction distribution, overall performance, and the dominant unsteady components within the adopted modeling framework. The results show that IGVF primarily controls gas accumulation in the impeller passages: as IGVF increases, the gas phase evolves from dispersed bubbles to a central core, whereas speed mainly alters the detailed morphology via centrifugal effects. Similarity-law scaling is strongly speed-dependent in this pump: agreement is better at higher speeds and deteriorates at lower speeds where viscous effects become more influential. The dominant unsteady content also changes with speed, shifting from low-speed broadband features associated with gas redistribution to high-speed periodic components linked to blade–vane rotor–stator interaction (RSI). In addition, the downstream stage exhibits more uniform void fraction and more regular periodic signatures, consistent with an inter-stage flow-rectification effect. These observations provide practical guidance for hydraulic design and variable-speed operation of multistage pumps under gas entrainment. Full article

The straddle packer fracturing technique represents a core technology for reservoir stimulation in horizontal wells targeting deep shale gas formations. However, the fracturing string constrained by dual packers is highly susceptible to severe vibrations induced by high-pressure pulsating fluid flow, which subsequently leads to collisions between the string and the casing. These collisions may compromise the sealing integrity of the packers or cause fatigue damage to the string. The existing design of packer spacing primarily relies on static mechanical experience and lacks the support of nonlinear dynamics theory. As a result, it is difficult to maximize operational efficiency while ensuring safety. Therefore, this paper establishes a fluid–solid coupling fracturing string model that takes into account fluid pulsation, geometric nonlinearity and gap collision constraints. Using the Galerkin discretization and the fourth-order Runge–Kutta algorithm, the influence laws of packer spacing and flow rate on the system stability are systematically studied. Studies have shown that the spacing of packers non-monotonically controls the system stability. Both too short or too long packer spacings will induce chaotic instability. However, there exists a highly robust, stable contact window near the ratio. Within this interval, the fracturing string is locked onto a stable period-doubling orbit. Based on this proposed optimization criterion, compared with the traditional conservative design, the spacing of the packers can be extended by approximately 90%. This not only avoids the risk of chaos but also significantly improves the efficiency of the fracturing operation. Full article

The generation of atmospheric pressure nonequilibrium plasma using electrical discharges is an active area of research due to its significance in a wide spectrum of applications including medicine, combustion, and manufacturing. In our attempt to create a helium plasma jet in a pin-plane discharge with a constant current source, we observed self-pulsating behavior. We present the results of the electrical, optical, and spectroscopic measurements carried out to characterize the discharge. The duration of the discharge is a few tens of nanoseconds, and the repetition rate is in the few tens of kHz. The effect of the gap distance and gas flow is discussed. The effective capacitance formed by the space charge in the discharge region plays an important role in determining the pulsing frequency. The results of voltage swing, current pulse, and light emission are also discussed. Such self-pulsating discharges can be used to produce helium plasmas under ambient conditions in applications such as plasma medicine. Full article

The production of a stable and uniform spray is a primary concern in fuel atomization applications, such as in fluid catalytic cracking reactors, directly affecting the process quality and gas emissions. However, depending on nozzle geometry and operating conditions, undesired pulsed spray behavior may occur. This phenomenon originates from the internal multiphase flow interaction in Y-jet nozzles and leads to unstable sprays. Understanding the formation of spray pulsations is challenging due to limited internal flow visualization in the nozzle and the fast dynamics involved. Accordingly, this work elucidates the mechanisms of the pulsed spray formation through 3D transient numerical multiphase simulations inside a mixing chamber. The model is validated against internal pressure measurements and applied to investigate the internal mixing behavior across several operating conditions. Results show that the liquid-to-gas momentum flux ratio governs the internal flow regimes. A higher liquid momentum flux obstructs the gas flow, leading to periodic spray bursts when the gas overcomes the liquid back pressure. The simulations also reveal self-sustained oscillatory flow patterns and cyclic transitions between gas penetration and liquid accumulation, which produce periodic pressure fluctuations and nozzle discharge pulsations. The findings offer valuable guidance for optimizing nozzle operation and geometry to suppress pulsation and improve atomization performance. Full article

As the power density of microelectronic devices and components continues to increase, thermal management has become a critical bottleneck limiting their performance and reliability. With its advantages of effective heat dissipation, no need for external power, and good safety, the micro pulsating heat pipe (MPHP) exhibits unique application advantages and enormous development potential when compared to other cutting-edge thermal management solutions, such as embedded microchannel cooling technology, which has complicated manufacturing processes and is prone to leakage, or thermoelectric material cooling technology, which is limited by material efficiency and self-heating. However, a pulsating heat pipe (PHP) is vulnerable to the combined impacts of several elements (scale effects, wall effects, and interfacial effects) at the micro-scale, which can lead to highly variable heat transfer characteristics and complex two-phase flow behavior. There are still few thorough experimental reviews on this subject, despite the fact that many researchers have concentrated on the MPHP and carried out in-depth experimental investigations on their flow and heat transmission mechanisms. In order to provide strong theoretical support for optimizing the design of the MPHP cooling devices, this paper reviews previous experimental research on the MPHP with the goal of thoroughly clarifying the mechanisms of gas–liquid two-phase flow and heat/mass transfer within them. The definition of MPHP is first explained, along with its internal energy transmission principles and structural features. The motion states of gas–liquid two-phase working fluids in the MPHP from previous experimental investigations are then thoroughly examined, highlighting their distinctive flow patterns and evolution mechanisms. Lastly, the variations in thermal performance between different kinds of MPHPs are examined, along with the factors that affect them. Full article

This study investigates the combustion behavior of H₂–CH₄ mixtures with oxygen-enriched air, achieved through injecting ozone (O₃) into the air intake of the burner fan. The motivation for this approach lies in the high reactivity of hydrogen compared to methane, with the aim of promoting a more favorable oxidizing environment for overall combustion. The research combines theoretical analysis with experimental validation using a diffusion-type burner operating at a fuel flow rate of 1.2 Nm³/h. For this flow rate, the ozone injection led to an equivalent O₂ concentration of approximately 21.7%. At this enrichment level, flame temperature was calculated to increase by 70–90 °C. The burner was specifically designed for the diffusion combustion of H₂–CH₄ mixtures and features three fuel injection nozzles, each surrounded by five air inlets. Experiments employed premixed H₂-CH₄ gas cylinders (Linde) with hydrogen concentrations of 20% and 30%, respectively. The results confirmed slight combustion intensification due to elevated oxygen concentration, with no issues related to flame stability or pulsations observed. Core flame temperature and flue gas emissions, including CO₂, were measured. The results support the further development of this combustion technology by increasing the allowable oxygen concentration limit. Full article

Deep coal seams have low permeability and poor wettability, making gas extraction difficult. This study presents a zero-energy consumption pulsating water hammer fracturing technique that uses the gravitational potential energy of high-elevation water and the pulsating pressure waves from the water hammer effect to induce fatigue damage in coal, creating an interconnected network of cracks. The research included experiments on water hammer pressure waves, multi-physics field coupling simulations at different flow rates, and discrete element simulations to analyze the fracture behavior of underwater hammer pressure. Results showed that initial flow velocity impacts the water hammer pressure’s intensity, range, and duration. Pressure shock waves propagate as expansion and compression waves, with peaks rising from 4.99 to 19.91 MPa within a 2–12 m/s flow rate range. Water hammer pressure reduced fracture initiation pressure by 23% compared to static pressure loading and increased fracture numbers by 13.4%. With pressure amplitudes between 2–18 MPa, fractures tripled, and the damaged area grew from 2.2 to 11%. A variable frequency combination loading strategy, starting with low frequency and then high frequency, was more effective for fracture propagation. This study offers a theoretical foundation for applying this technology to enhance coal seam permeability and gas pumping efficiency. Full article

This paper takes a small three-stage centrifugal pump as the research object. Based on the RNG k-ε turbulence model and the TFM two-phase flow model, the numerical simulation of the internal gas–liquid two-phase flow was carried out, and the influence of the inlet gas content rate of the small multistage centrifugal pump on its internal flow was analyzed. The research results show that the head and efficiency of the multistage centrifugal pump will decrease with the increase in the inlet gas content rate. As the gas content increases from 0% to 5%, the head of the multistage centrifugal pump decreases by 3% and its efficiency drops by 5%. The trend of the continuous increase in the pressure on the blade surface does not change with the increase in the inlet gas content rate. The bubble area on the surface of the first-stage impeller blade increases with the increase in the gas content rate. When the inlet gas content rate condition reaches 5%, the bubbles cover the middle section of the blade suction surface. The flow vortex structure is mainly composed of blade separation vortices and mouth ring clearance leakage vortices. The vortices inside the impeller are concentrated in the blade outlet and rim area, while the vortices inside the guide vanes are located in the flow channel area of the anti-guide vanes. With the increase in the gas content rate, the amplitude of pressure pulsation in the flow channel inside the pump decreases. Full article