Search Results (886)

Sediment buildup in storage tanks over extended operation periods may compromise their efficiency. To prevent pollutant deposition in storage tanks and enhance their hydraulic self-cleaning efficiency, this study addressed the unique structural configuration of lateral flow in storage tanks. Conducting numerical simulations to investigate the hydraulic characteristics within storage tanks, an integrated approach combining physical experiments and response surface methodology (RSM) was employed to optimize flow distribution. Key findings reveal that tangential and normal velocity differences lead to flow distribution nonuniformity, exacerbated by increased inflow Froude number (F_r) and reduced relative weir height (h_i). Based on the flow-splitting mechanism, an optimized “combined raised baffle” was proposed. Through single-factor experiments, Plackett–Burman (PB) screening, and RSM experiments, the optimal combination for maximal flow uniformity was determined as h₁ = 1.27, h₂ = 1.23, and h₃ = 1.24, achieving an 87.18% improvement in Q_y compared to the initial design. After optimization, the incoming flow pattern of the inlet channel of the storage pond was improved, and the difference between tangential and normal flow velocity in the flow field was significantly reduced. This research provides a novel approach and methodological paradigm for optimizing storage tanks and other hydraulic structures, demonstrating significant academic and engineering value. Full article

The unsteady and discontinuous liquid flow in the microchannel affects the efficiency of sample mixing, molecular detection, target acquisition, and biochemical reaction. In this work, an active method of reducing the flow pulsation in the microchannel of a pneumatic microfluidic chip is proposed by using an on-chip membrane microvalve as a valve chamber damping hole or a valve chamber accumulator. The structure, working principle, and multi-physical model of the reducing element of reducing the flow pulsation in a microchannel are presented. When the flow pulsation in the microchannel is sinusoidal, square wave, or pulse, the simulation effect of flow pulsation reduction is given when the membrane valve has different permutations and combinations. The experimental results show that the inlet flow of the reducing element is a square wave pulsation with an amplitude of 0.1 mL/s and a period of 2 s, the outlet flow of the reducing element is assisted by 0.017 and the fluctuation frequency is accompanied by a decrease. The test data and simulation results verify the rationality of the flow reduction element in the membrane valve microchannel, the correctness of the theoretical model, and the practicability of the specific application, which provides a higher precision automatic control technology for the microfluidic chip with high integration and complex reaction function. Full article

The secondary air system plays important roles in gas turbines, such as cooling hot-end components, sealing the rim, and balancing axial forces. In this paper, the flow structure and the heat transfer characteristics of the rotating disk cavity with two inlets and single outlet is studied by CFD (Computational Fluid Dynamics) approach. The effect and mechanism under higher rotational speed and larger mass flow rate are also discussed. The results show that a large-scale vortex is induced by the central inlet jet in the low-radius region of the cavity, while the flow structure in the high-radius region is significantly influenced by rotational speed and flow rate. Increasing the rotational speed generally enhances heat transfer because it amplifies the differential rotational linear velocity between the disk surface and nearby wall flow, consequently thinning the boundary layer. Increasing the mass flow rate enhances heat transfer through two primary mechanisms: firstly, it elevates the turbulence intensity of the near-wall fluid; secondly, the higher radial velocity results in a thinner boundary layer. Full article

After an aero-engine shuts down, the high temperature within the core flow path prevents conventional borescope probes from performing immediate internal inspections due to their limited thermal resistance, thereby constraining rapid turnaround capabilities for aircraft. To address this challenge, this study proposes an active cooling strategy using coolant flow to keep the probe within a safe temperature range. Three cooling structures incorporating pressure-drop modules—annular, annular-slit, and round-hole configurations—were designed and numerically investigated to assess the effects of geometric parameters and coolant properties (temperature, pressure, nitrogen mixing ratio) on cooling performance. The results demonstrate that the round-hole structure with a 1.0 mm diameter achieves optimal cooling, maintaining an average probe mirror temperature of 286.2 K under coolant conditions of 285 K and 0.5 MPa. Cooling efficiency exhibits a strong linear negative correlation with coolant temperature, while its relationship with pressure is highly structure-dependent. Nitrogen doping significantly improves the heat transfer capacity of the coolant. The implemented three-stage pressure-drop module performs consistently, with the pressure loss per stage determined solely by the inlet pressure. This study provides valuable insights and a theoretical foundation for the design of high-temperature-resistant borescope equipment capable of operating in the harsh environments of aero-engines. Full article

Nitrogen compression requires centrifugal compressors to operate under relatively high ambient pressure. However, the internal instability characteristics of compressors handling high-density working fluids remain unclear. Therefore, this study employs Dynamic Mode Decomposition (DMD) to investigate unsteady flow fluctuations within an isolated centrifugal impeller under both best efficiency and near-stall conditions at high ambient pressure. Results show that as the throttling process progresses, distinct unsteady phenomena emerge within the impeller. Under near-stall conditions, the frequency of the instability is 0.44 times the blade passage frequency (BPF), manifesting as periodic pressure fluctuations throughout the entire blade passage. This instability originates from periodic passage blockages caused by fluctuations in tip leakage flow. Additionally, the pressure fluctuations at the impeller inlet exhibit a noticeable lag compared to those in the latter half of the passage. Through DMD analysis, it is found that after the tip leakage vortex exits the blade, it interacts with the pressure surface of the adjacent blade, affecting the tip loading of the neighboring blade and forming a dynamic cycle. However, this vortex is not the primary flow structure responsible for the instability. These insights into the nature of unsteady disturbances provide valuable implications for future stall warning and instability prediction technologies. Full article

This work evaluates a hydrogen-fueled planar micro-combustor featuring three triply periodic minimal surface (TPMS) structures, namely, gyroid, lidinoid, and Neovius matrix lattices, aiming to advance heat transfer processes and enhance system efficiency in micro-thermophotovoltaic (MTPV) applications. Through three-dimensional numerical investigations, a series of simulations are conducted under varying TPMS lengths, inlet volume flow rate, and inlet equivalence ratios to optimize the design and operating conditions. The outcomes reveal that increasing the length of the TPMS structures is an effective means of improving heat transfer from the combustion zone to the walls, as indicated by significant increases in both mean wall temperature and radiation efficiency. However, longer internal structures reduce the uniformity of wall temperature and slightly increase entropy generation. Of the three topologies, the Neovius lattice demonstrates superior performance in all length scales, exhibiting a marginal improvement over the gyroid and a substantially greater advantage over the lidinoid structure. Increasing the inlet volume flow rate enhances wall temperature and its uniformity; however, the performance parameters decrease for all structures, indicating a limitation of the micro-combustor in benefiting from higher input power. Notably, the gyroid structure shows a lower rate of performance degradation at higher velocities, making it a potentially ideal design under such conditions. Finally, varying the equivalence ratio identifies the stoichiometric condition as optimal, yielding superior performance metrics compared to both lean and rich mixtures. Full article

The significant potential loss of proton exchange membrane fuel cells (PEMFCs) at high current densities is primarily attributed to the high mass transfer resistance of the gas diffusion layer (GDL). The underlying mechanism of how structural parameters of the GDL under actual assembly conditions affect oxygen transport resistance remains unclear, particularly the quantitative relationship between the compression ratio (α) and tortuosity (γ). This study systematically evaluated the output performance and mass transfer overpotential of three commercially available GDLs with similar thickness and porosity under different compression ratios (5.4% to 27%) and four inlet humidity conditions (RH0% to RH100%). By accurately extracting and comparing mass transfer overpotentials, it was observed that the mass transfer overpotential initially decreased and then increased with the rising compression ratio, with an optimum observed at 21.6%. An empirical correlation between the compression ratio (α) and tortuosity (γ) was established as γ = 3.42α + 2.1. Based on this, a modified oxygen diffusion equation was proposed to accurately describe oxygen transport behavior within the GDL under compressed conditions. A modified oxygen diffusion equation was proposed to more accurately characterize the oxygen transport process within compressed GDLs. These findings establish a foundation for optimizing GDL design and stack assembly processes. Future work will build upon this study by incorporating multiphysics conditions such as stack clamping pressure, number of cells, intercell contact resistance, and assembly conditions (temperature and relative humidity), with the aim of elucidating the force–thermal–electrical–mass coupling mechanisms within the stack, thereby enhancing the overall performance and reliability of high-power-density proton exchange membrane fuel cell (PEMFC) stacks. Full article

This paper evaluated the operation of a universal cryopanel designed to cool surfaces to cryogenic temperatures using an experimental and computer study. The cryopanel’s structure comprises prefabricated parts: a lower plate and a top plate featuring 2.3 mm high pins, through which cooled nitrogen flows. The main aim of this work was to assess the performance of the universal cryopanel design through thermal and mechanical numerical modeling to meet the demands of different operating modes. Using the COMSOL Multiphysics software version 6.1, it has been shown that the optimized design achieves the required temperature of 150 K and lower on the top surface of the panel with a constant inlet temperature of 80 K and a flow rate of 0.05 m/s. Experimental data on the operation of cryopanels was compared with the resulting model. Data on the cryopanel and research at cryotemperatures will find application in medicine, the food industry, electronics, and scientific research on deposition and condensation, where it is important to observe operating modes and maintain low temperatures. Full article

This article presents an experimental study on the hydrodynamics of coolant flow within the pressure vessel of a small modular reactor (SMR) cooled with water, including areas such as the annular downcomer, bottom chamber, and core-simulating channels that are being developed for use in land-based nuclear power plants. This paper describes the experimental setup and test model, measurement techniques used, experimental conditions under which this research was conducted, and results obtained. This study was conducted at the Nizhny Novgorod State Technical University (NNSTU) using a high-pressure aerodynamic testing facility and a scale model that included structural components similar to those found in loop-type reactors. Experiments were performed with Reynolds numbers (Re) ranging from 20,000 to 50,000 in the annular downcomer space of the test model. Two independent techniques were used to simulate the non-uniform flow field in the pressure vessel: passive impurity injection (adding propane to the airflow) and hot tracer (heating one of the reactor circulation loops). The axial velocity field at the inlet to the reactor core was also investigated. This study provided information about the spatial distribution of a tracer within the coolant flow in the annular downcomer and bottom chamber of the pressure vessel. Data on the distribution of the contrasting admixture are presented in plots. The swirling nature of the coolant flow within the pressurized vessel was analyzed. It was shown that the intensity of mixing within the bottom chamber of the pressure vessel is influenced by the presence of a central vortex. Parameters associated with the mixing of admixtures within the model for the pressure vessel were estimated. Additionally, the possibility for simulating flow with different temperature mixing processes using isothermal models was observed. Full article

Dual-inlet tail escapes, combining an orifice and a weir, are key hydraulic structures that evacuate excess water from canal termini during maintenance and protect berms by discharging surplus irrigation flows. Conventional sizing methods typically depend on trial and error, which is time-consuming and may yield suboptimal design. This study introduces a graphical design approach and a MATLAB-based tool, TAILOPT, developed to streamline tail escape design. The tool incorporates both the Fanning and Darcy–Weisbach friction formulations for head loss estimation and can automatically generate an “.inp” file for EPA-SWMM, enabling direct unsteady-state hydraulic assessment. This integration reduces design effort and supports evaluation of alternative hydraulic and drainage scenarios within a single workflow. Two applications illustrate the framework. The first shows that overly steep drainage slopes (Sp > 2%) are impractical, while vertical drops may require larger pipe diameters. The second application applies TAILOPT to a distributary canal, determining the optimal pipe size and verifying its performance in EPA-SWMM under emergency surplus flow and routine dewatering conditions. The results demonstrate that the method yields economical, robust, and practitioner-friendly designs; however, modeling simplifications, such as assuming continuously submerged orifice flow, can introduce minor deviations in the predicted channel emptying times. Full article

To investigate the time-varying influence of oil viscosity and water content on flow behavior in crossing pipelines, we developed a three-dimensional finite element/CFD model using advanced simulation software with fluid dynamics capabilities. Simulations were performed under varying viscosity and water-cut conditions, and the analyses covered fluid velocity, pressure distribution, and secondary flow characteristics. The results show clear quantitative trends: in the horizontal span, the stabilized centerline velocity reached 2.46 m/s (+23.0% versus the 2.00 m/s inlet). At Node 10, increasing viscosity from 0.306 to 0.603 Pa·s reduced the mean pressure by 11.2 kPa (−11.2% relative to a 0.10 MPa baseline), and a further increase to 1.185 Pa·s produced an additional 4.5 kPa (−4.5%) drop. At Node 1, the low-viscosity case yielded a centerline velocity 1.1× higher than the high-viscosity case (+10.0%). Consistent with these observations, higher viscosity and water cut decreased the average flow velocity and lengthened the duration of pressure fluctuations. These findings provide quantitative insight into the dynamic behavior of multiphase flow and offer a basis for understanding fluid–structure interaction phenomena in crude oil pipeline transport systems. Full article

In order to meet the harsh working environment and complex and changeable stress conditions, the low-temperature and high-pressure liquid carbon dioxide conveying system used in oil extraction will choose metal bellows for transportation. In this paper, the bellows in an accident section are investigated and observed by the working environment and characterization methods such as macroscopic analysis, metallographic analysis, EDS component analysis, fracture scanning electron microscopy analysis, and related mechanical performance test methods. The failure mechanism of the accident is preliminarily judged, and the unidirectional fluid–structure coupling model and the standard k-ω turbulence model are used as the calculation models for subsequent simulation. Combined with Fluent finite element simulation analysis, it is verified that the failure is caused by a welding defect, the maximum stress of the metal bellows under normal conditions is less than its own yield strength, and the material can work normally. When the welding crack is greater than 2 mm, the strength of the workpiece weld will be reduced, and the stress concentration has exceeded the yield strength that the workpiece can bear, causing failure fracture at the welding defect part. Combined with ANSYS simulation of accident defects, compared with bellows without defects, the stress at the crack will increase with the increase in the inlet flow velocity and decrease with the increase in temperature, and the flow rate will have a greater influence on it. Therefore, in actual working conditions, the stiffness and fatigue life of the conveying system can be improved by appropriately reducing the liquid flow rate and increasing the temperature. It provides a reference for the future application research of bellows and the research on bellows fracture failure. Full article

As a key device for precise feeding in aquaculture, feeders directly affect feed utilization efficiency and farming profitability; however, pneumatic pond feeders commonly exhibit poor spreading uniformity and low feed utilization. In this study, a dual-sided air intake structure incorporating a triangular flow-splitter plate was added inside the feed chamber, and the spreading process was simulated using a coupled computational fluid dynamics–discrete element method approach to analyze the motion mechanisms of feed pellets within the feeding device. A rotatable orthogonal composite experimental design was employed for the multiparameter collaborative optimization of the feed chamber height ($h$), the triangular flow-splitter plate width ($d$), and its inlet angle ($\alpha$). The results demonstrated that the triangular flow-splitter plate renders the velocity field within the device chamber more uniform and reduces the coefficient of variation ($CV$) of circumferential pellet distribution to 18.27%, a 22.19% decrease relative to the unmodified design. Experimental validation using the optimal parameter combination confirmed a mean $CV$ of 17.02%, representing a 24.45% reduction compared with the original structure. This study provides a theoretical foundation and reliable technical solution for precise feeding equipment in aquaculture. 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

Adverse pressure gradients are intrinsic to compressor flow behavior and are further intensified by secondary effects associated with rotor tip clearance flow interactions. Tip clearance generates leakage flow, which leads to the formation of tip leakage vortices, a major contributor to aerodynamic losses in axial compressors. These vortices significantly influence both compressor performance and operational stability. Extensive prior research has demonstrated that passive casing treatments, particularly axial slots, can substantially improve the stall margin in axial compressors. In this work, the performance of a new casing treatment geometry is investigated using the concept of recirculating flow within semi-circular axial slots. The proposed casing treatment geometry builds upon recent experimental findings involving single-rotor configurations. It was applied to the first rotor row of a three-and-a-half-stage (3.5-stage) axial compressor comprising an inlet guide vane followed by three rotor–stator stages. The numerical model incorporates axial slots with a novel periodic interface approach implemented in a multistage compressor simulation. Three-dimensional steady-state RANS (Reynolds Average Navier-Stokes) simulations were performed to investigate the aerodynamic effects of the casing treatment across various rotational speeds. The results for the casing treatment configuration were compared with those of a baseline smooth casing. The introduction of the new casing treatment produced noticeable modifications to the internal flow structure, particularly in the tip region, resulting in improved overall compressor stability within the operating range of 85 to 100% of design speed. Full article