Search Results (135)

The present paper reports for the first time the comparison of radar-derived eddy dissipation rate (EDR) and vertical velocity with measurements from six aircraft for an intense squall line crossing Hong Kong. The study objectives are three-fold: (i) to characterise the structural dynamics of the intense squall line; (ii) to identify the dynamical change in EDR and vertical velocity during its eastward propagation across Hong Kong with a view to gaining insight into the intensity change of the squall line and the severity of its impact on aircraft flying near it; (iii) to carry out quantitative comparison of EDR and vertical velocity derived from remote sensing instruments, i.e., weather radars and in situ measurements from aircraft, so that the quality of the former dataset can be evaluated by the latter. During the passage of the squall line and taking reference of the radar reflectivity, vertical circulation and the subsiding flow at the rear, it appeared to be weakening in crossing over Hong Kong, possibly due to land friction by terrain and urban morphology. This is also consistent with the maximum gusts recorded by the dense network of ground-based anemometers in Hong Kong. However, from the EDR and the vertical velocity of the aircraft, the weakening trend was not very apparent, and rather severe turbulence was still recorded by the aircraft flying through the squall line into the region with stratiform precipitation when the latter reached the eastern coast of Hong Kong. In general, the radar-based and the aircraft-based EDRs are consistent with each other. The radar-retrieved maximum vertical velocity may be smaller in magnitude at times, possibly arising from the limited spatial and temporal resolutions of the aircraft data. The results of this paper could be a useful reference for the development of radar-based turbulence products for aviation applications. Full article

With growing reliance on hydraulic fracturing to develop tight oil and gas reservoirs characterized by low porosity and permeability, optimizing proppant transport and placement has become critical to sustaining fracture conductivity and production. However, how fracture geometry influences proppant distribution under varying field conditions remains insufficiently understood. This study employed computational fluid dynamics to investigate proppant transport and placement in hydraulic fractures of which the aperture tapers linearly along their length. Four taper rate models (δ = 0, 1/1500, 1/750, and 1/500) were analyzed under a range of operational parameters: injection velocities (1.38–3.24 m/s), sand concentrations (2–8%), proppant particle sizes (0.21–0.85 mm), and proppant densities (1760–3200 kg/m³). Equilibrium proppant pack height was adopted as the key metric for pack morphology. The results show that increasing injection rate and taper rate both serve to lower pack heights and enhance downstream transport, while a higher sand concentration, larger particle size, and greater density tend to raise pack heights and promote more stable pack geometries. In tapering fractures, higher δ values amplify flow acceleration and turbulence, yielding flatter, “table-top” proppant distributions and extended placement lengths. Fine, low-density proppants more readily penetrate to the fracture tip, whereas coarse or dense particles form taller inlet packs but can still be carried farther under high taper conditions. These findings offer quantitative guidance for optimizing fracture geometry, injection parameters, and proppant design to improve conductivity and reduce sand-plugging risk in tight formations. These insights address the challenge of achieving effective proppant placement in complex fractures and provide quantitative guidance for tailoring fracture geometry, injection parameters, and proppant properties to improve conductivity and mitigate sand plugging risks in tight formations. Full article

We develop a symmetry-based variational theory that shows the coarse-grained balance of work inflow to heat outflow in a driven, dissipative system relaxed to the golden ratio. Two order-2 Möbius transformations—a self-dual flip and a self-similar shift—generate a discrete non-abelian subgroup of $\mathrm{PGL}(2,\mathbb{Q}\left(\sqrt{5}\right))$. Requiring any smooth, strictly convex Lyapunov functional to be invariant under both maps enforces a single non-equilibrium fixed point: the golden mean. We confirm this result by (i) a gradient-flow partial-differential equation, (ii) a birth–death Markov chain whose continuum limit is Fokker–Planck, (iii) a Martin–Siggia–Rose field theory, and (iv) exact Ward identities that protect the fixed point against noise. Microscopic kinetics merely set the approach rate; three parameter-free invariants emerge: a $62\%:38\%$ split between entropy production and useful power, an RG-invariant diffusion coefficient linking relaxation time and correlation length ${\mathcal{D}}_{\alpha }={\xi }^z/\tau$, and a $\vartheta ={45}^{\circ }$ eigen-angle that maps to the golden logarithmic spiral. The same dual symmetry underlies scaling laws in rotating turbulence, plant phyllotaxis, cortical avalanches, quantum critical metals, and even de-Sitter cosmology, providing a falsifiable, unifying principle for pattern formation far from equilibrium. Full article

To explore the influence of guide vanes on the energy loss of hydraulic turbines, a pump characterized by a simple structure and convenient operation was selected as the research subject. Entropy generation theory was utilized to analyze entropy generation losses at different flow rates, with a particular emphasis on the mechanisms in the impeller and draft tube. The findings indicate that turbulent entropy production dominates energy dissipation. Under the best efficiency point (BEP), the total entropy generation loss of Z₀ = 11 turbine was 7.18% and 5.76% lower than that of Z₀ = 7 and Z₀ = 9, respectively. The proportion of entropy generation loss in the impeller was highest under low-flow and optimal operating conditions, while the proportion of entropy generation loss in the draft tube was highest under high-flow conditions. In guide-vane-free turbines, the impeller’s high turbulent entropy generation rate was attributed to vortices and backflow caused by significant velocity gradients. For guide-vane-equipped turbines, high turbulent entropy generation rates arose from rotor–stator interactions and flow separation at blade inlets. Under high-flow-rate conditions, the entropy generation loss in the draft tube was significantly larger than that in other flow components, primarily due to vortices generated by excessive velocity circulation at the impeller outlet near the upstream draft tube flow passages, leading to high turbulent entropy generation rates. Full article

The transesterification process for biodiesel production is constrained by high thermal input, prolonged residence time, and intensive mechanical agitation. This study investigates process intensification via hydrodynamic cavitation using a custom-built Shockwave Power Reactor (SPR), enabling continuous biodiesel synthesis from soybean and used cooking oils. A statistically designed experimental matrix was applied to evaluate the reactor’s transient–stable thermal regime and the influence of operational parameters: rotor speed (1700–3415 rpm), volumetric flow rate (60–105 mL/min), methanol-to-oil molar ratio (6:1 to 12:1), and alkali catalyst type (NaOH or KOH). For benchmarking, conventional alkaline transesterification was optimized. The FAME yields from the SPR system exceeded 96.5% and complied with EN14103 standards. Specific energy analysis showed that cavitation-enhanced transesterification reduced energy consumption and peak temperature compared to traditional methods. The SPR’s capacity to induce high shear and localized turbulence under controlled cavitation offers a promising pathway for low-energy, scalable biodiesel production. Full article

Autonomous inflow control devices (AICDs) offer a promising means of delaying early water breakthrough in heavy oil horizontal wells; yet, current design practices remain largely empirical. A three-dimensional, field-calibrated computational fluid dynamics (CFD) model was developed to establish a mechanistic basis that solves the transient Navier–Stokes equations for turbulent two-phase flow via a volume-of-fluid formulation. Pressure-controlled inflow boundaries were tuned to build up data from four Colombian heavy oil producers, enabling a quantitative comparison with production logs. Model predictions deviate by no more than ±14% for oil rate and ±10% for water rate over a 500-day horizon, providing confidence in subsequent scenario analysis. Replacing a slotted liner completion with optimally sized AICDs lowers cumulative water-cut by up to 93%, reduces annular friction losses by 18%, and cuts estimated life cycle CO₂ emissions per stock-tank barrel by 82%. Sensitivity analysis identifies nozzle diameter as the dominant design variable, with a nonlinear interaction between local drawdown pressure and the oil–water viscosity ratio. These findings demonstrate that CFD-guided AICD design can materially extend wells’ economic life while delivering substantial environmental benefits. The validated workflow establishes a low-risk, physics-based path for tailoring AICDs to reservoir conditions before field deployment. Full article

Theoretical and experimental investigations were conducted to predict permeate flux in direct contact membrane distillation (DCMD) modules equipped with turbulence promoters. These DCMD modules operate at moderate temperatures (45 °C to 60 °C) using a hot saline feed stream while maintaining a constant temperature for the cold inlet stream. The temperature difference between the two streams creates a gradient across the membrane surfaces, leading to thermal energy dissipation due to temperature polarization effects. To address this challenge, 3D-printed turbulence promoters were incorporated into the DCMD modules. Acting as eddy promoters, these structures aim to reduce the temperature polarization effect, thereby enhancing permeate flux and improving pure water productivity. Various designs of promoter-filled channels—with differing array configurations and geometric shapes—were implemented to optimize flow characteristics and further mitigate polarization effects. Theoretical predictions were validated against experimental results across a range of process parameters, including inlet temperatures, volumetric flow rates, hydraulic diameters, and flow configurations, with deviations within 10%. The DCMD module with the inserted 3D-printed turbulence promoters in the flow channel could provide a relative permeate flux enhancement up to 91.73% under the descending diamond-type module in comparison with the module of using the no-promoter-filled channel. The modeling equations demonstrated technical feasibility, particularly with the use of both descending and ascending hydraulic diameters of 3D-printed turbulence promoters inserted into the saline feed stream, as compared to a module using an empty channel. Full article

Tetrafluoroethylene (TFE), as a key basic chemical raw material, has an irreplaceable position in strategic emerging industries involving high-end materials, electronics, chemicals, and pharmaceuticals. Currently, TFE is industrially produced via the vapor cracking of difluoromonochloromethane (R22). However, there is a gap between China and the developed countries in the high-end tetrafluoroethylene monomer, the purity of tetrafluoroethylene monomer is difficult to reach the high purity requirement of 99.999%, and the content of the key impurities that determine the nature of the functional materials is high, which leads to a series of problems of instability in the performance of the high-end and special products and high media loss. To enhance the purity of TFE monomers produced by the pyrolysis reactor of R22 and water vapor, the fluid dynamics simulations of the reactor model were conducted using Ansys Fluent. The reactor model was initially constructed using Space Claim, followed by mesh generation with Fluent Meshing and other relevant configurations. Both cold-state and thermal-state simulations were performed. The cold-state simulation analyzed the effects of temperature, flow velocity, and turbulence models on the turbulent gas flow and mixing processes within the reactor model. The thermal-state simulation examined the impacts of reaction process variations on internal temperature, turbulence, component distribution, and outlet component concentrations during the actual reaction process. Finally, the inlet flow rate and structure of the reactor were optimized. The results indicated that the optimal inlet flow rates for R22 and water vapor were 0.2–0.3 kg/s and 0.4–0.5 kg/s, respectively. In practical production, the internal fluid mixing achieved an optimal value after modifying the inlet structure to a T shape. This study provides new insights into the pyrolysis reaction and lays the foundation for further improving the purity of TFE monomers. Full article

Flow characteristic monitoring includes parameters such as flow regime, fluid characteristic frequency, and flow rate, which are crucial for optimizing production and ensuring the safety of oil and gas transportation systems. Existing fluid monitoring technologies, such as various flow meters, often face limitations in providing distributed and real-time monitoring data. In contrast, distributed acoustic sensing offers a spatial resolution of 1 m with high frequency sampling capability, allowing for long-term, multi-point dynamic monitoring of fluid migration characteristics. We developed an indoor physical simulation pipeline loop to assess the feasibility of using distributed acoustic sensing for monitoring flow migration characteristics. The experiment collected signal characteristics under different conditions, including background noise, single gas-phase flow, single liquid-phase flow, and gas–liquid two-phase flow. In the frequency–power spectral density analysis, single gas-phase flow signals are concentrated at lower frequencies, single liquid-phase flow displays noticeable spikes over a broader frequency range, and gas–liquid two-phase flow covers the widest frequency range with stronger amplitude signals. Autocorrelation analysis shows larger oscillations for gas–liquid two-phase flow, smoother signals for gas-phase flow, and more turbulent signals for liquid-phase flow. By examining root mean square energy changes, flow rates can be qualitatively estimated, revealing a positive correlation between energy and flow velocity. Finally, the study discussed the limitations of the experimental setup and proposed improvements and advanced research directions of distributed acoustic sensing in fluid monitoring. Full article

Achieving precise seed distribution is essential for optimizing crop yields and agricultural productivity. This study examines the impact of divider head geometry on seed distribution accuracy in pneumatic air seeder systems using rapeseed, wheat, and rice. Three custom-designed divider heads—funnel distributor (A1), closed-funnel distributor (A2), and cone-shaped distributor (A3)—were developed for an eight-furrow opener seeding system, each featuring eight outlets per opener. Bench tests at air pressures of 3, 3.5, 4, 4.5, 5, and 5.5 kPa and speeds of 4 and 5 km/h revealed significant variations in seed distribution accuracy among the designs. The A2 distributor demonstrated the lowest coefficient of variation (CV) across all seed types: 4.3%, 2.6%, and 6.95% for A1, A2, and A3 in wheat, respectively; 4.5%, 3.4%, and 6.2% in rice, respectively; and 0.3%, 0.1%, and 1.0% in rapeseed, respectively. Seed types also significantly influenced feed rate uniformity, with average CVs of 2.91% for rapeseed, 3.85% for rice, and 4.90% for wheat. CFD-DEM simulations validated the superior performance of the A2 distributor by analyzing flow fields and velocity distributions, showing reductions in CVs by 19.09–54.55% compared to A1 and A3. Thus, the A2 distributor was identified as the optimal design, significantly improving seeding uniformity across all seed types. In conclusion, this study provides critical insights for redesigning seed drill distribution heads to minimize turbulence in the seed–air mixture transport, enhancing seeding uniformity and increasing crop yields and agricultural productivity. Full article

Flat drippers are widely used in agricultural irrigation systems to ensure precise water distribution. This study investigates the optimization of flat drippers through Computational Fluid Dynamics (CFDs) simulations, focusing on the channel geometry. These emitters have a particular configuration of the labyrinth channel appropriately shaped to ensure high turbulence and dissipation of the hydraulic load. CFDs techniques are particularly suitable to investigate the labyrinth design and optimization. Here, by analyzing seven different dripper models with varying dissipation channel sizes, the relationship between flow rate (liters per hour) and pipe pressure (kPa) was studied. Simulations were performed for six inlet pressures in the range between 50 and 175 kPa, with steps of 25 kPa, allowing for the derivation of the pressure–flow curve and the optimization of the emitter exponent. The value of the exponent is closely linked to the conformation of the channel and is standardized by the International Organization for Standardization (ISO) 9261:2004. Additionally, the influence of the labyrinth channel’s cross-sectional area on flow rate was examined, providing insights into design improvements for enhanced hydraulic performance. The proposed optimization could lead to significant water savings and enhanced agricultural productivity by improving the efficiency of irrigation systems. Full article

With the development of a power system predominantly reliant on new energy sources, turbine generator sets are increasingly required to operate under wide load conditions, resulting in numerous unstable flow phenomena and substantial economic losses for power stations. This study employs the Shear Stress Transport (SST) k-ω turbulence model to combine numerical simulations with experimental methods. It calculates the guide vane opening at the rated head of a Francis turbine and examines the internal flow field characteristics and pressure pulsations under various operating conditions. The findings indicate that the entropy production ratio in the draft tube is the highest among all load conditions, ranging from about 72.7% to 95.9%. Energy dissipation in the vaneless zone and the runner increases with greater opening. At 45% and 100% load conditions, the draft tube is mainly influenced by dynamic and static interference, single and double frequencies induced by runner rotation, and low-frequency fluctuations of the vortex and. Under 60% load conditions, pressure fluctuations in the draft tube are primarily caused by the eccentric vortex band, characterized by higher intensity and a frequency of 0.2 f_n. Numerical results closely align with experimental observations. The findings provide essential guidance for ensuring the stable operation of power plant units. Full article

This article examines the impact of fluid flow dynamics on microbial growth, distribution, and control within food processing systems. Fluid flows, specifically laminar and turbulent flows, significantly influence microbial behaviors, such as biofilm development and microbial adhesion. Laminar flow is highly conducive to biofilm formation and microbial attachment because the flow is smooth and steady. This smooth flow makes it much more difficult to sterilize the surface. Turbulent flow, however, due to its chaotic motion and the shear forces that are present, inhibits microbial growth because it disrupts attachment; however, it also has the potential to contaminate surfaces by dispersing microorganisms. Computational fluid dynamics (CFD) is highlighted as an essential component for food processors to predict fluid movement and enhance numerous fluid-dependent operations, including mixing, cooling, spray drying, and heat transfer. This analysis underscores the significance of fluid dynamics in controlling microbial hazards in food settings, and it discusses some interventions, such as antimicrobial surface treatments and properly designed equipment. Each process step from mixing to cooling, which influences heat transfer and microbial control by ensuring uniform heat distribution and optimizing heat removal, presents unique fluid flow requirements affecting microbial distribution, biofilm formation, and contamination control. Food processors can improve microbial management and enhance product safety by adjusting flow rates, types, and equipment configurations. This article helps provide an understanding of fluid–microbe interactions and offers actionable insights to advance food processing practices, ensuring higher standards of food safety and quality control. Full article

To investigate the impact of airfoil angle of attack on the output performance of a valveless piezoelectric pump with airfoil baffles, this study conducted comprehensive performance tests and full-flow field simulations of piezoelectric pumps across a range of angles. At a driving voltage of 100 V and with a Clark Y airfoil set at an angle of 0°, the piezoelectric pump reached a peak output flow rate of 200.7 mL/min. An increase in the angle of attack corresponded to a decline in both the maximum output flow rate and the maximum back pressure of the pump. Flow field simulation results demonstrated that an increased airfoil angle of attack led to a gradual increase in entropy production within the piezoelectric pump. Turbulent dissipation and wall entropy production were found to be more pronounced compared to viscous entropy production. High turbulent dissipation was primarily observed at the pump chamber inlet, the trailing edges of the airfoils in both the inlet and outlet pipes, and the outlet bend. As the angle of attack increased, the complexity of the vortex core structures within the flow field escalated as well. Regions with significant wall entropy production were notably concentrated at the outlet bend. Full article

In connection with subsonic jet noise production, this study investigates acoustic noise reduction in micro turbojet engines by comparing ejector and chevron nozzle configurations to a baseline. Through detailed statistical analysis, including assessments of stationarity and ergodicity, the current work validates that the noise signals from turbojet engines could be treated as wide-sense ergodic. This further allows to use time averages in acoustic measurements. Acoustic analysis reveals that the chevron nozzle reduces overall SPL by 1.28%, outperforming the ejector’s 0.51% reduction. Despite the inherent challenges of Schlieren imaging, an in-house code enabled a more refined analysis. By examining the fine-scale turbulent structures, one concludes that chevrons promote higher mixing rates and smaller vortices, aligning with the statistical findings of noise reduction. Schlieren imaging provided visual insight into turbulence behavior across operational regimes, showing that chevrons generate smaller, controlled vortices near the nozzle, which improve mixing and reduce noise. At high speeds, chevrons maintain a confined, high-frequency turbulence that attenuated noise more effectively, while the ejector creates larger structures that contribute to low-frequency noise propagation. Comparison underscores the superior noise-reduction capabilities of chevrons with respect to the ejector, particularly at high-speed. The enhanced Schlieren analysis allowed for new frame-specific insights into turbulence patterns based on density gradients, providing a valuable tool for identifying turbulence features and understanding jet flow dynamics. Full article