Search Results (1,510)

The design of tubular flocculators has advanced in the pursuit of more efficient and compact water treatment systems. Helically coiled tube flocculators (HCTFs) are known for generating stable secondary flows and uniform hydrodynamic patterns after the development length. However, their constant geometry restricts the hydrodynamic variability required for optimized flocculation. This study introduces the spirally coiled tube flocculator (SCTF), characterized by a winding diameter that varies along its length. CFD simulations and laboratory-scale experiments compared HCTFs and SCTFs in terms of turbidity removal capacity, axial velocity profiles, secondary flows, streamlines, and global velocity gradients. The SCTF outperformed the HCTFs under all evaluated configurations, achieving up to 98.2% turbidity removal. The results emphasize the potential of spiral geometries to enhance process efficiency and highlight the need to reconsider hydrodynamic strategies in the design of tubular flocculators. Full article

This study numerically investigates the growth and dynamics of a single vapor bubble in a rectangular microchannel under subcooled and saturated inlet conditions using the phase-field method coupled with the Lee phase-change model. Results demonstrate that subcooled flow induces early bubble nucleation, pronounced lateral expansion along the heated wall, and prolonged bubble-wall contact due to stronger condensation at the interface and thinner microlayer formation. Enhanced recirculating vortices and steeper thermal gradients promote vigorous evaporation and increased local heat flux, resulting in faster downstream bubble propagation driven by significant axial pressure gradients. Analysis of temperature gradient and heat flux profiles confirms that subcooled conditions produce higher wall heat flux and more frequent peaks in evaporative flux compared to the saturated case, indicating intensified phase-change activity and thermal transport. Conversely, saturated conditions produce more spherical bubbles with dominant vertical growth, weaker condensation, and symmetrical thermal and pressure fields, leading to slower growth and delayed detachment near the nucleation site. These findings highlight the critical influence of inlet subcooling on bubble morphology, flow structures, heat transfer, and pressure distribution, underscoring the thermal management advantages of subcooled boiling in microchannel applications. Full article

During perforation operations, high-speed jet penetration into the casing-cement sheath-formation assembly damages the bonding interfaces, resulting in fluid flow along these interfaces within the wellbore. This can compromise the wellbore seal integrity and shorten the lifespan of the oil and gas well. To address this, a numerical model was developed using fluid-solid coupling algorithms, combined with a cohesive zone damage model and the ALE algorithm. The model was employed to analyze the dynamic damage evolution of the bonding interfaces during the jet penetration process and quantify the effects of the cement sheath’s mechanical parameters (shear modulus and compressive strength) and geological stress on the axial damage length and area. The results indicate that both the casing-cement sheath and cement sheath-formation interfaces exhibit significant damage, with the former showing a larger damage area under identical mechanical conditions; as the cement sheath’s shear modulus increases, the damaged area at the casing-cement sheath interface expands, while that at the cement sheath-formation interface reduces. Conversely, an increase in the cement sheath’s compressive strength reduces the damage extent at both interfaces, as does elevated geological stress. Based on engineering cases, different cement slurry types were compared to minimize perforation-induced interface damage. This study provides theoretical and practical guidance for optimizing cement selection and assessing bonding interface integrity during perforation. Full article

The aerodynamic performance of nacelle inlets under crosswind conditions is crucial for engine stability and efficiency. Current parametric investigations are predominantly focused on cruise operations, with minimal consideration given to crosswind conditions. This study employs an iCST-based parametric modeling approach to construct geometric models. A systematic examination of key geometric parameters—including the throat axial location, fan face radius, and leading-edge radii of the inner and outer contours is conducted. The reliability of the numerical methodology was established through a two-step validation process using both the iCST-generated non-axisymmetric model and the DLR-F6 benchmark model, followed by a geometric sensitivity analysis based on parametrically generated axisymmetric models. The results demonstrate that the inner contour leading-edge radius (ROC_I/R_hi) has the most substantial influence on flow separation. When ROC_I/R_hi decreases from 7.84% to 3.46%, the peak maximum circumferential total pressure distortion index (IDCmax) is increased by 86.78% with a 53.85% rearward shift in the complete reattachment mass flow rate. Correspondingly, a similar reduction in the outer contour leading-edge radius (ROC_O/R_hi) from 9.38% to 4.69% results in a 55.50% increase in peak IDCmax and a 33.33% rearward shift. Comparatively, the fan face radius shows minimal impact on flow distortion (increases by 9.72%), but more pronounced effects on total pressure recovery, while rearward movement of the throat axial location (35.00% to 69.00%) causes a 30.03% rise in IDCmax and 43.75% complete flow reattachment delay. It is concluded that the leading-edge optimization is crucial for crosswind resilience, with the inner contour geometry being particularly influential, providing parametric foundations for robust inlet design across a wide range of operating regimes. In addition, it is also found that the effects of Reynolds number (Re) lie in two folds: (1) For a fixed model scale, the aerodynamic performance of the inlet suffers a remarkable degradation with rapidly rising IDCmax as the crosswind velocity-based Re is increased to cause significant flow separations. (2) For a fixed crosswind velocity, the peak IDCmax progressively decreases with the increasing scale based Re, while σ exhibits an overall enhancement as Re rises. Full article

This article presents the results of an experimental study on the hydrodynamics of the coolant at the inlet of the fuel assembly in the RITM reactor core. The importance of these studies stems from the significant impact that inlet flow conditions have on the flow structure within a fuel assembly. A significant variation in axial velocity and local flow rates can greatly affect the heat exchange processes within the fuel assembly, potentially compromising the safety of the core operation. The aim of this work was to investigate the effect of different designs of orifice inlet devices and integrated absorber grids on the flow pattern of the coolant in the rod bundle of the fuel assembly. To achieve this goal, experiments were conducted on a scaled model of the inlet section of the fuel assembly, which included all the structural components of the actual fuel assembly, from the orifice inlet device to the second spacer grids. The test model was scaled down by a factor of 5.8 from the original fuel assembly. Two methods were used to study the hydrodynamics: dynamic pressure probe measurements and the tracer injection technique. The studies were conducted in several sections along the length of the test model, covering its entire cross-section. The choice of measurement locations was determined by the design features of the test model. The loss coefficient (K) of the orifice inlet device in fully open and maximally closed positions was experimentally determined. The features of the coolant flow at the inlet of the fuel assembly were visualized using axial velocity plots in cross-sections, as well as concentration distribution plots for the injected tracer. The geometry of the inlet orifice device at the fuel assembly has a significant impact on the pattern of axial flow velocity up to the center of the fuel bundle, between the first and second spacing grids. Two zones of low axial velocity are created at the edges of the fuel element cover, parallel to the mounting plates, at the entrance to the fuel bundle. These unevennesses in the axial speed are evened out before reaching the second grid. The attachment plates of the fuel elements to the diffuser greatly influence the intensity and direction of flow mixing. A comparative analysis of the effectiveness of two types of integrated absorber grids was performed. The experimental results were used to justify design modifications of individual elements of the fuel assembly and to validate the hydraulic performance of new core designs. Additionally, the experimental data can be used to validate CFD codes. Full article

The fluid flow in underground reservoirs is directly related to resource recovery and hazard prevention. In this study, the evolution of fractured sandstone deformation and permeability under an in situ stress influence is investigated using the true triaxial percolation system. The results show that the strain of fractured sandstone increases logarithmically with the increase in axial stress. The evolution of axial strain is dominated by the maximum principal stress, and the minimum principal stress and the intermediate principal stress affect the strain amplitude. The fracture morphology of low-permeability sandstone affects permeability and strain evolution. Small fractures are more sensitive to the increase in the maximum principal stress, and the response in principal strain to the increase in principal stress is obvious in large fractures. There is a negative exponential relationship between pore pressure and the conductivity of fractures. When pore pressure is 0.3 MPa, the conductivity is the highest; meanwhile, when pore pressure is 1.8 MPa, the conductivity is the lowest. The decreasing range of the conductivity increases with the increase in fracture size. In situ stress significantly affects the evolution of principal strain and related permeability. The permeability decreases with an increase in the minimum and middle principal stresses. Under low pore pressure (0.3–0.6 MPa), the permeability decreases with an increase in the principal stress; meanwhile, under high pore pressure (0.6–1.8 MPa), permeability changes slightly with an increase in the principal stress. The findings provide reference to the engineering practice of underground mining. Full article

The hydrodynamic and reaction characteristics of poly-alpha-olefin (PAO) polymerization in a continuous stirred tank reactor (CSTR) under Eulerian–Eulerian multiphase flow and a finite-rate chemical kinetics model were studied in this paper. A mathematical framework correlating 1-decene conversion with operational and structural parameters was established. Numerical simulations revealed an axial circulation flow pattern driven by combined impellers, with internal coils enhancing heat exchange and flow guidance. The gaseous catalyst, injected below the turbine impeller, achieved rapid dispersion and low gas holdup. The results demonstrated that 1-decene conversion exhibited insensitivity to impeller speed under fully turbulent mixing (mixing time <0.15% of space time), suggesting limited mass transfer benefits from further speed increases. Conversion positively correlated with temperature and space time, albeit with diminishing returns at prolonged durations. Series reactor configurations improved conversion efficiency, though incremental gains decreased with additional units. Optimal reactor design should balance conversion targets with economic factors, including energy consumption and capital investment. These findings provide critical insights into scaling PAO polymerization processes, emphasizing the interplay between reactor geometry, mixing dynamics, and reaction kinetics for industrial applications. Full article

This study investigates the role of toroidal vortex formation in torque-flow pumps and its influence on pump performance. A mathematical model of viscous fluid motion in toroidal coordinates was developed to describe the two-stage energy transfer mechanism, in which the impeller drives the toroidal vortex and the vortex subsequently imparts momentum to the main throughflow. The model identifies vortex deformation as a primary source of hydraulic losses. The theoretical framework was validated by computational fluid dynamics (CFD) simulations of a torque-flow pump. Analysis of the axial, circumferential, and vertical velocity components revealed a closed three-dimensional toroidal circulation loop within the free chamber, confirming the predictions of the mathematical model. A parametric study was conducted to assess the influence of impeller extension into the free chamber (Δb₂) on pump performance. Three characteristic regimes were identified. At Δb₂ ≈ 6 mm, the shaft power decreased to 120.3 kW (an 8.1% decrease compared to the baseline), with efficiency improving to 39.2%. At Δb₂ ≈ 10 mm, the pump achieved its best balance of parameters: efficiency increased from 34.0% to 42.8% (+8.7 percentage points), while head rose from 32.8 m to 38.5 m (+17.4%), with moderate power demand (122.3 kW). At Δb₂ ≈ 70 mm, the head reached 45.6 m (+39%), but power consumption rose to 146.9 kW (+12%), and the design shifted toward centrifugal-type operation, reducing reliability for abrasive fluids. Overall, the results provide both a validated mathematical description of toroidal vortex dynamics and practical guidelines for optimizing torque-flow pump design, with Δb₂ ≈ 10 mm identified as the most rational configuration. Full article

Prediction of the maneuvering performance of autonomous underwater vehicles equipped with pump–jet propulsion remains computationally intensive when relying solely on high-fidelity computational fluid dynamics. To overcome this limitation, a surrogate maneuvering model is developed to achieve comparable accuracy with drastically reduced computational cost. The model is constructed from numerical results obtained using unsteady Reynolds-averaged Navier–Stokes equations with the k–ω shear stress transport turbulence model, and formulated through a Taylor-expansion-based framework. The propulsion and rudder modules are refined to enhance physical representation and efficiency: a conventional open-water-based formulation is adopted to embed the pump–jet propulsive model, incorporating axial flow velocities near the duct inlet for improved thrust prediction; meanwhile, the rudder force model minimizes the number of captive simulations by employing a kinematic approach that compensates for limited datasets. The surrogate model is applied to free-running simulations and validated against high-fidelity computational results. The findings confirm that the proposed framework reproduces the dominant trends of kinematic responses, forces, and moments with high consistency, providing a practical and time-efficient alternative for maneuvering prediction of underwater vehicles equipped with pump–jet propulsion systems. Full article

Mesenchymal stem cells are widely cultivated in stirred tank bioreactors. Due to their adhesion properties, they are attached to small spherical spheres called microcarriers. To understand the hydromechanical stresses encountered by the cells, it is essential to characterize the flow using the PIV technique. However, the usual solid–liquid system used in cell cultures has poor optical properties. Thus, shifting to one with better optical properties, while respecting the physical characteristics, is mandatory to achieve a relevant representation. PMMA microparticles suspended with 61 wt% ammonium thiocyanate solution NH₄SCN were found to be a robust candidate. The refractive index (RI) of both sides is of the order of 1.491 with a density ratio of ${\rho }_f/{\rho }_p\approx$ 0.96, and particle size averaged around 168 μm. Using the RIM-PIV (refractive index matched particle image velocimetry) technique for a 0.7 L volume stirred tank equipped with an HTPG down-pumping axial impeller and operating at full homogeneous speed $N=150$ rpm, mean and turbulence quantities of the liquid phase were measured as a function of PMMA particle volume fractions ${\alpha }_p$, which ranged from 0.5 to 3 v%. This corresponds to a particle number density of $n=12$ particles/mm³, which is considered original and challenging for the PIV technique. At 3 v%, the addition of particles dampened the turbulent kinetic energy (TKE) of the liquid phase locally by 20% near the impeller. This impact became trivial (<10%) at the local-average level. The structure and direction of the recirculation loop also shifted. Full article

This study aims to enhance total pressure probe performance in transonic axial compressors using passive flow control via circular grooves. Simulations in ANSYS CFX were performed on six probe configurations, one smooth baseline and five with groove depths of 0.1 to 0.5 mm, across Mach numbers 0.3 to 0.86. The 0.1 mm grooved probe showed optimal results, reducing the drag coefficient from 15.23 to 14.33 and the lift from 0.0169 to 0.0042. A spanwise analysis from the hub to tip (55–95%) confirmed improved flow uniformity, while a streamwise analysis (zones 0–2) showed steadier downstream pressure and reduced wake-induced distortion. The 0.1 mm groove also minimized the shock strength and flow separation near blade tips. Results confirm that micro-grooving at 0.1 mm significantly stabilizes measurements and enhances aerodynamic efficiency, offering a practical optimization strategy for high-speed compressor applications. Full article

An efficient cooling configuration is critical for ensuring the safe operation of electrical machines and is key for optimizing the iterative design of motors. To improve the heat dissipation performance of high-power, explosion-proof, integrated variable-frequency permanent magnet motors used in mining and reduce the risk of permanent magnet demagnetization, this study considers a 1600 kW mining explosion-proof variable-frequency permanent magnet motor as its research object. Based on the zigzag-type water channel structure of the frame, a novel rotor-cooling scheme integrating axial–radial ventilation structures and axial flow fans was proposed. The temperature field of the motor was simulated and analyzed using a fluid–thermal coupling method. Under rated operating conditions, the flow characteristics of the frame water channel and the temperature distribution law inside the motor were compared when the water supply flow rates were 5.4, 4.8, 4.2, 3.6, 3, 2.4, and 1.8 m³/h, respectively, and the relationship between the motor temperature rise and the variation in water flow rate was revealed. A production prototype was developed, and temperature rise tests were conducted for verification. The test results were in good agreement with the simulation calculation results, thereby confirming the accuracy of the simulation calculation method. The results provide an important reference for enterprises in the design optimization and upgrading of high-power explosion-proof integrated variable-frequency permanent-magnet motors. Full article

Mean flow velocities and the corresponding turbulence fluctuation velocities were measured within the suction port of a standard twin-screw compressor using LDV and PIV optical techniques. Time-resolved velocity measurements were carried out over a time window of 1° at a rotor speed of 1000 rpm, a pressure ratio of 1, and an air temperature of 55 °C. Detailed LDV measurements revealed a very stable and slow inflow, with almost no influence from rotor movements except near the rotors, where a more complex flow formed in the suction port. The axial velocity near the rotors exhibited wavy profiles, while the horizontal velocity showed a rotational flow motion around the centre of the port. The turbulence results showed uniform distributions and were independent of the rotors’ motion, even near the rotors. PIV measurements confirmed that there is no rotor movement influence on the inflow structure and revealed complex flow structures, with a crossflow dominated by a main flow stream and two counter-rotating vortices in the X-Y plane; in the Y-Z plane, the presence of a strong horizonal stream was observed away from the suction port, which turned downward vertically near the entrance of the port. The corresponding turbulence results in both planes showed uniform distributions independent of rotor motions that were similar in all directions. Full article

Micro-combustion-powered thermoelectric generators (μ-CPTEGs) combine the high energy density of hydrocarbons with solid-state conversion, offering compact and refuelable power for long-endurance electronics. Such characteristics make μ-CPTEGs particularly promising for aerospace systems, where conventional batteries face serious limitations. Their achievable performance hinges on how a swirl-stabilized flame transfers heat into the hot ends of thermoelectric modules. This study uses a conjugate CFD framework coupled with a lumped parameter model to examine how input power and equivalence ratio shape the flame/flow structure, temperature fields, and hot-end heating in a swirl combustor-powered TEG. Three-dimensional numerical simulations were performed for the swirl combustor-powered TEG, varying the input power from 1269 to 1854 W and the equivalence ratio from φ = 0.6 to 1.1. Results indicate that the combustor exit forms a robust “annular jet with central recirculation” structure that organizes a V-shaped region of high modeled heat release responsible for flame stabilization and preheating. At φ = 1.0, increasing Q_in from 1269 to 1854 W strengthens the V-shaped hot band and warms the wall-attached recirculation. Heating penetrates deeper into the finned cavity, and the central-plane peak temperature rises from 2281 to 2339 K (≈2.5%). Consistent with these field changes, the lower TEM pair near the outlet heats more strongly than the upper module (517 K to 629 K vs. 451 K to 543 K); the inter-row gap widens from 66 K to 86 K, and the incremental temperature gains taper at the highest power, while the axial organization of the field remains essentially unchanged. At fixed Q_in = 1854 W, raising φ from 0.6 to 1.0 compacts and retracts the reaction band toward the exit and weakens axial penetration; the main-zone temperature increases up to φ = 0.9 and then declines for richer mixtures (peak 2482 K at φ = 0.9 to 2289 K at φ = 1.1), cooling the fin section due to reduced transport, thereby identifying φ = 0.9 as the operating point that best balances axial penetration against dilution/convective-cooling losses and maximizes the TEM hot-end temperature at the fixed power. Full article

The complex jet-ground interactions of Short Take-off and Vertical Landing (STOVL) aircraft are critical to flight safety and performance, yet studying them with traditional full-scale wind tunnel tests is prohibitively expensive and time-consuming, hindering design optimization. This study addresses this challenge by developing and numerically verifying a “pressure ratio–momentum–geometry” multi-dimensional similarity framework, enabling accurate and efficient scaled-model analysis. Systematic simulations of an F-35B-like configuration demonstrate the framework’s high fidelity. For a representative curved nozzle configuration (e.g., the F-35B three-bearing swivel duct nozzle, 3BSD), across scale factors ranging from 1:1 to 1:15, the plume deflection angle remains stable at 12° ± 1°. Concurrently, axial force (F) and mass flow rate (Q) strictly follow the square scaling relationship ($F\propto 1/n^2, Q\propto 1/n^2)$, with deviations from theory remaining below 0.15% and 0.58%, respectively, even at the 1:15 scale, confirming high-fidelity momentum similarity, particularly in the near-field flow direction. Second, a 1:13.25 scale aircraft model, constructed using Froude similarity principles, exhibits critical parameter agreement (intake total pressure and total temperature) of the prototype-including vertical axial force, lift fan mass flow, and intake total temperature—all less than 1.5%, while the critical intake total pressure error is only 2.2%. Fountain flow structures and ground temperature distributions show high consistency with the full-scale aircraft, validating the reliability of the proposed “pressure ratio–momentum–geometry” multi-dimensional similarity criterion. The framework developed herein has the potential to reduce wind tunnel testing costs and shorten development cycles, offering an efficient experimental strategy for STOVL aircraft research and development. Full article