Search Results (53)

Natural gas hydrate (NGH) is a highly promising alternative energy source for the future, which is widely distributed in marine clayey-silty sediments. Permeability is the key factor determining the efficiency of NGH exploitation. However, clay particles can migrate and clog the pores, leading to a decrease in reservoir permeability during the development of NGH. This review summarizes the permeability damage law during the NGH production from clayey-silty sediments, with a focus on the influence of clay particle migration. For the scientific problem of clay particle migration, the governing equation of clay particle migration was first clarified through force balance analysis. Then, the influencing factors and laws of clay particle migration were systematically summarized from two aspects: internal factors such as clay type, content, particle size, reservoir heterogeneity, and external conditions such as salinity, flow rate, temperature, pH, and stress field. The detachment, migration, aggregation and clogging characteristics of clay particles in porous media were observed and outlined based on microscopic visualization technology. Thirdly, the numerical simulation methods of particle migration were summarized, and the permeability damage laws and its influence mechanism were analyzed. Finally, the limitations on clay particle migration and permeability damage in the current research were discussed, and corresponding suggestions were given to promote the efficient development of NGH. Full article

The research objectives of engine plume radiation calculation primarily encompass two aspects: (1) addressing the additional heating induced by plume radiation on rocket thermal protection systems and (2) elucidating the variation patterns of spectral radiation intensity for infrared signature identification and tracking. Focusing on the thermal effects of radiation, this study first calculates the radiative properties of high-temperature combustion gases and particles separately. Subsequently, the radiative properties of mixed droplets with alumina caps are computed and analyzed. Building upon this and incorporating empirical formulas for aluminum droplet combustion, the engine’s radiative properties are calculated, accounting for the presence of mixed droplets. Ultimately, an integrated computational method for engine radiative properties (both internal and external flow fields) is established, which considers the non-equilibrium processes during droplet transformation. The radiative property parameters are then embedded into the fluid dynamics software via multidimensional interpolation. The radiation transfer equation is solved using the discrete ordinates method (DOM) to obtain the radiation intensity distribution within the plume flow field. This work provides technical support for investigating the radiative characteristics of solid rocket engine plumes. Full article

To achieve efficient and sustainable marine aquaculture, STAR-CCM+ was used to simulate the internal and external field characteristics of a semi-submersible aquaculture platform based on a porous media model, focusing on the influence of incoming flow velocity and net solidity ratio. The results indicate that the flow field distribution around the platform exhibits no significant regularity and that low-velocity vortex regions are primarily concentrated near the pillars and nets. After velocity attenuation, the velocity reduction coefficients at the centers of the three cages are 90.26%, 63.65%, and 52.56%, respectively. Furthermore, the velocity attenuation inside the cages is minimally influenced by incoming flow velocity, with a maximum difference of 3.10%. In contrast, differences in net solidity ratio significantly affect velocity attenuation, particularly in downstream regions. The velocity reduction coefficient in the third cage varies by up to 43.25% depending on the net solidity ratio. These findings provide practical insights for the engineering design and application of aquaculture platforms. Full article

This paper presents the results of laboratory tests on the intensity of mass and heat exchange in a polytunnel, with a focus on the synergy between the polytunnel and a stone accumulator. The subject of study was a standard polytunnel made of double polythene sheathing. In the process of selecting the appropriate working conditions for such a polytunnel, the characteristic operating parameters were modeled and verified. They were related to the process of mass and energy exchange, which takes place in regular controlled-environment agriculture (CEA). Then, experimental tests of a heat accumulator on a fixed stone bed were carried out. The experiments were carried out for various accumulator surfaces ranging from 18.7 m² to 74.8 m², which was measured perpendicularly to the heat medium. To standardize the results obtained, the analysis included the unit area of the accumulator and the unit time of the experiment. In this way, 835 heat and mass exchange events were analyzed, including 437 accumulator charging processes and 398 discharging processes from April to October, which is a standard period of polytunnel use in the Polish climate. During the tests, internal and external parameters of the process were recorded, such as temperature, relative humidity, solar radiation, wind speed and air flow speed in the accumulator system. Based on the parameters, a set of empirical relationships was developed using mathematical modeling. This provided the foundation for calculating heat gains as a result of its storage in a stone accumulator and its discharging process. The research results, including the developed dependencies, not only fill the scientific gap in the field of heat storage, but can also be used in engineering design of polytunnels supported by a heat storage system on a stone bed. In addition, the proposed methodology can be used in the study of other heat accumulators, not only in plant production facilities. Full article

In practical applications, the fully enclosed structure is always required by self-starting permanent magnet synchronous motors for safety. However, internal heat dissipation can be obstructed as a result, which affects operational reliability. To resolve the issue, this study takes a 3 kW self-starting permanent magnet synchronous motor as the research object. Based on fluid dynamics and fluid solid coupling heat transfer theory, the model is reasonably simplified according to the characteristics of the structure of motor cooling, and basic assumptions and boundary conditions are given to establish a three-dimensional, whole machine solution domain model. The finite element method is used to numerically analyze and calculate under rated conditions. The fluid flow characteristics, heat transfer characteristics, motion trajectories of the cooling medium on the surface of the external casing, fan, and internal stator and rotor domains, and winding ends are analyzed. Therefore, the internal rheological characteristics and temperature rise distribution law of the self-starting permanent magnet synchronous motor can be revealed. Based on the aforementioned research, a novel method to design the wind spur structure on the surface of the rotor end is proposed. By comparing the simulation results of the fluid field and temperature field of the motor under wind spur structures with different lengths and equidistant distributions in the circumferential direction of the rotor end, the influence of the convective heat characteristics can be systematically studied. Lastly, the accuracy of the calculation results and the rationality of the solution method are verified through experiments of temperature rise, and the flow temperature distribution characteristics of the motor can be optimized by the wind spur structure, which can be used in practical applications. Full article

Film cooling, a vital method for controlling surface temperatures in components subjected to intense heat, strives to enhance efficiency through innovative technological advancements. Over the last several decades, considerable advancements have been made in film cooling technologies for applications such as liquid rocket engines, combustion chambers, nozzle sections, gas turbine components, and hypersonic vehicles, all of which operate under extreme temperatures. This review presents an in-depth investigation of film cooling, its applications, and its key mechanisms and performance characteristics. The review also explores design optimization for combustion chamber components and examines the role of gaseous film cooling in nozzle systems, supported by experimental and numerical validation. Gas turbine cooling relies on integrated methods, including internal and external cooling, material selection, and coolant treatment to prevent overheating. Notably, the cross-flow jet in blade cooling improves heat transfer and reduces thermal fatigue. Film cooling is an indispensable technique for addressing the challenges of high-speed and hypersonic flight, aided by cutting-edge injection methods and advanced transpiration coolants. Special attention is given to factors influencing film cooling performance, as well as state-of-the-art developments in the field. The challenges related to film cooling are reviewed and presented, along with the difficulties in resolving them. Suggestions for addressing these problems in future research are also provided. Full article

Based on Graph Balancing Theory, this study proposes an anomaly detection algorithm, the Supply Chain Proof of Relation (PoR), applied to enterprise procurement networks formalized as weighted directed graphs. A mathematical framework is constructed by integrating Laplacian flow conservation and the Sheaf topological coherence principle to identify anomalous nodes whose local characteristics deviate significantly from the global features of the supply network. PoR was empirically implemented on a dataset comprising 856 Taiwanese enterprises, successfully detecting 56 entities exhibiting abnormal behavior. Anomaly intensity was visualized through trend plots, revealing nodes with rapidly increasing deviations. To validate the effectiveness of this detection, the study further analyzed the correlation between internal and external performance metrics. The results demonstrate that anomalous nodes exhibit near-zero correlations, in contrast to the significant correlations observed in normal nodes—indicating a disruption of information consistency. This research establishes a graph-theoretic framework for anomaly detection, presents a mathematical model independent of training data, and highlights the linkage between structural deviations and informational distortions. By incorporating Sheaf Theory, the study enhances the analytical depth of topological consistency. Moreover, this work demonstrates the observability of flow conservation violations within a highly complex, non-physical system such as the supply chain. It completes a logical integration of Sheaf Coherence, Graph Balancing, and High-Dimensional Anomaly Projection, and achieves a cross-mapping between Graph Structural Deviations and Statistical Inconsistencies in weighted directed graphs. This contribution advances the field of graph topology-based statistical anomaly detection, opening new avenues for the methodological integration between physical systems and economic networks. Full article

To investigate the size effect on the energy characteristics of axial flow pumps, this study scaled the original model size based on the head similarity principle, resulting in four size schemes (Schemes 2–4 correspond to 3, 5, and 10 times the size of Scheme 1, respectively). By solving the unsteady Reynolds-averaged Navier–Stokes (URANS) equations with the Shear Stress Transport (SST) k-omega turbulence model, the external characteristic parameters and internal flow field structures were predicted. Additionally, the spatial distribution of internal hydraulic losses was analyzed using entropy generation theory. The results revealed three key findings: (1) the efficiency of axial flow pumps significantly improves with increasing size ratio, with Scheme 4 exhibiting a 6.1% efficiency increase compared to Scheme 1; (2) as the size ratio increases, the entropy production coefficients of all hydraulic components decrease, with the impeller and guide vanes in Scheme 4 showing reductions of 55.1% and 56.5%, respectively, compared to Scheme 1; (3) the high entropy generation coefficient regions in the impeller and guide vanes are primarily concentrated near the rim, with their area decreasing as the size ratio increases. Specifically, the entropy production coefficients at the rim of impeller and guide vanes in Scheme 4 decreased by 84.85% and 58.2%, respectively, compared to Scheme 1. These findings provide valuable insights for the selection and optimization of axial flow pumps in applications such as cross-regional water transfer, agricultural irrigation, and urban drainage systems. Full article

Reciprocating liquid metal magnetohydrodynamic (MHD) power generation is a new MHD power generation method in which the working fluid is a single-phase liquid metal with a low melting point and high conductivity. The internal combustion stroke of automobiles, ocean waves, sound waves and other reciprocating external forces drive the liquid metal to flow back and forth in an applied magnetic field, generating single-phase alternating current (AC) energy. Reciprocating liquid metal MHD (LMMHD) power generation has the advantages of a high power density, high efficiency, a fast start and good stability, and it provides a new solution for space static nuclear power conversion, variable-stroke automobile engines, distributed power supply and ocean energy utilization. According to the mode of action of an electromagnetic field, reciprocating LMMHD generators can be divided into the inductive type and conductive type. Compared with the inductive type, the conductive type has a simple structure and is the current research hot spot. Firstly, the classification and characteristics of reciprocating LMMHD power generation are introduced. Then, the working characteristics of conductive reciprocating LMMHD (CRLMMHD) generators are analyzed. On this basis, technical key points and issues in the current research of CRLMMHD generators are elaborated. Finally, conclusions and the future research direction of CRLMMHD generators are pointed out. Full article

As the inlet temperature of the gas turbine exceeds the high temperature limit of the blade materials, efficient leading edge cooling technologies are crucial for the further development of gas turbines. Therefore, this paper reviews the research progress on external cooling technology, internal cooling technology, and composite cooling technology for gas turbine rotating blade leading edge cooling. It focuses on the impact of the geometric shape, arrangement, and flow parameters of film cooling holes on external cooling performance, the influence of jet hole design, configuration, crossflow, ribs on internal cooling efficiency, and the characteristics and influencing factors of composite cooling technologies are also discussed. Among the most promising composite cooling techniques, the impingement jet film composite cooling technology and swirl film composite cooling technology stand out. For impingement jet film composite cooling technology, this paper explores the effects of blowing ratio, nozzle parameters, jet hole characteristics, and flow field parameters on the overall cooling performance of the rotating blade leading edge. Impingement jet film composite cooling technology has been shown to significantly improve the cooling performance of the leading edge compared to traditional single cooling techniques. For applications requiring large area cooling or maintaining film integrity, swirl film composite cooling technology not only enhances heat transfer efficiency but also improves the uniformity of heat transfer. The design of swirl nozzles, coolant flow rate, Reynolds number, and jet temperature all have significant effects on the heat transfer efficiency of swirl film composite cooling. To further advance the development of gas turbine rotating blade leading edge cooling technologies, it is recommended to focus on the study of film composite cooling techniques, particularly investigating the effects of various parameters of impingement, swirl on composite cooling performance. Full article

In order to improve the sealing performance of a sealing ring in order to improve the efficiency of the centrifugal pump, based on the bionics principle, a calculation model for the bionic groove surface sealing ring structure of the centrifugal pump is established, based on the Realizable k-ε turbulence model. The external characteristics, internal flow field distribution and leakage characteristics of centrifugal pumps with different bionic groove surface structures and groove diameters are analyzed, and the influence of bionic surface structure on the sealing performance of the centrifugal pump sealing ring is studied. The results show that the bionic groove structure has a certain promoting effect on the external characteristics of the pump; a sealing ring with a circular groove structure can improve the efficiency, greatly reduce the leakage, and has better sealing performance, which are important influences on the performance and stability of the centrifugal pump. Among the three different diameters of the circular groove, the optimal groove diameter of the surface structure is 0.2 mm, where leakage is the least, volume efficiency is the largest, and sealing performance is the best. Full article

This study investigates the transient behavior of a single-blade centrifugal pump under variable frequency speed regulation, with the objective of enhancing both pump efficiency and operational stability under variable frequency conditions. By integrating numerical simulations, external characteristic tests, and Particle Image Velocimetry (PIV) flow field experiments, the research provides a comprehensive analysis of the dynamic performance of the pump. The accuracy of the numerical simulations is first validated through a comparison between CFD results and experimental data, both at rated and variable speeds. This study then explores the transient external performance, internal flow patterns, and radial force characteristics of the pump under various speed-change schemes. In the process of acceleration, the variation trend of the centrifugal pump head and speed is basically the same, and Scheme 3 shows better stability; Scheme 2 minimizes the fluctuation of shaft power; with the increase in speed, the pressure and flow field in the pump will appear to be unstable. In the deceleration process, the Scheme 3 head fluctuates less, the change in shaft power is the most stable, and the more uniform pressure distribution and stable flow field can be maintained. The radial force increases with the increase in speed, but the degree of radial force fluctuation is different among different schemes. These findings offer valuable insights into the dynamic performance of centrifugal pumps under variable speed conditions and provide a foundation for optimizing both pump design and operational strategies. Full article

An approach to estimate the dynamic characteristic of multilayered three-dimensional cubic quasicrystal cylindrical shells, annular plates, and truncated conical shells with different boundary conditions is presented. These investigated structures can be in a vacuum, totally filled with quiescent fluid, and subjected to internal flowing fluid where the fluid is incompressible and inviscid. The velocity potential, Bernoulli’s equation, and the impermeability condition have been applied to the shell–fluid interface to obtain an explicit expression, from which the fluid pressure can be converted into the coupled differential equations in terms of displacement functions. The state-space method is formulated to quasicrystal linear elastic theory to derive the state equations for the three structures along the radial direction. The mixed supported boundary conditions are represented by means of the differential quadrature technique and Fourier series expansions. A global propagator matrix, which connects the field variables at the internal interface to those at the external interface for the whole structure, is further completed by joint coupling matrices to overcome the numerical instabilities. Numerical examples show the correctness of the proposed method and the influence of the semi-vertical angle, different boundary conditions, and the fluid debit on the natural frequencies and mode shapes for various geometries and boundary conditions. Full article

To investigate the hydraulic characteristics during the start-up process of a full-flow pumped storage unit under low-head conditions, numerical simulations were conducted to study the dynamic characteristics during the process, providing a detailed analysis of the dynamic behavior of the internal flow field during the transition period as well as the associated variation in external performance parameters. Study results revealed a vortex-shedding phenomenon during the initial phase of the start-up process. These vortices restrict the flow, initiating a water hammer effect that abruptly elevates the upstream pressure within the runner. As the high-pressure water hammer dissipated, the flow rate rapidly increased, leading to a secondary but relatively weaker water hammer effect, which caused a momentary drop in pressure. This series of events ultimately resulted in significant oscillations in the unit’s head. After the guide vanes stop opening, the vortex structures at the runner inlet and outlet gradually weaken. As the runner torque continues to decline, the unit gradually approaches a no-load condition and enters the S-shaped region. Concurrently, pressure pulsations intensify, and unstable vortex formations reemerge along the leading and trailing edges of the runner blades. The escalated flow velocity at the runner’s exit contributes to the elongation of the vortex band within the draft tube, ultimately configuring a double-layer vortex structure around the central region and the pipe walls. This configuration of vortices precipitates the no-load instability phenomenon experienced by the unit. Full article

Currently, the field of microgear manufacturing faces various processing challenges, particularly in terms of size reduction; these challenges increase the complexity and costs of manufacturing. In this study, a technique for microgear manufacturing is aimed at reducing subsequent processing steps and enhancing material utilization. This technique involves the use of trough dies with extrusion-cutting processing, which enables workpieces to undergo forming in a negative clearance state, thus reducing subsequent processing time for micro products. We conducted finite element simulations using microgear dies, measuring stress, velocity, and flow during the forming process of four types of dies-flat, internal-trough, external-trough, and double-trough dies. The results indicated that the buffering effect of the troughs reduced the rate of increase in the material’s internal stress. In the cavity, the material experiences a significant increase in hydrostatic pressure, leading to the formation of a “hydrostatic pressure wall”. This pressure barrier imposes substantial constraints on the flow of the material during dynamic processes, making it difficult for the material to move into the remaining areas. This effectively enhances the blockage of material flow, demonstrating the critical role of hydrostatic pressure in controlling material distribution and movement. In addition, combining the characteristics of both into a double-trough die enhances the overall stability of forming velocity, reduces forming load and energy consumption, and maximizes material utilization. Results further revealed that microgears manufactured using double-trough dies exhibited defect-free surfaces, with a dimensional error of less than 5 μm and tolerances ranging from IT5 to IT6. Overall, this study offers new insights into the traditional field of microgear manufacturing, highlighting potential solutions for the challenges encountered in current microstamping processes. Full article