Three-dimensional Simulations Research Articles

Optimizing Flow and Heat Transfer With Guiding Pin Fins in a Wedge-Shaped Cooling Channel for Gas Turbine Blade Trailing Edge

Abstract In this study, an innovative guiding pin-fin array optimization has been developed through three-dimensional numerical simulations to enhance the cooling efficiency of gas turbine blade trailing edge. The guiding pin-fin array is optimized using the Kriging surrogate model and Genetic Algorithm (GA), aiming to significantly improve the heat transfer rates and uniformity within the wedge-shaped channel. The design parameter chosen for optimization is the deflection angle of each guiding pin fin, and the optimization process is conducted in two rounds. The first-round optimization yields a first-optimized guiding pin-fin array, which exhibits superior overall heat transfer performance and reasonable pressure loss compared to conventional circular, oblong, and parallel pin-fin arrays. For the first-optimized guiding pin-fin (1st-OGP) channel at the Reynolds number of Re = 50,000, the total Nusselt number and pressure loss are 44.1% higher and 9.9% lower than those of the baseline circular pin-fin array (CP), respectively. An experimental validation using the transient liquid crystal (TLC) thermography method is carried out and proves the effectiveness of the optimization process. However, it is noted that the first-optimized guiding pin-fin exhibits even lower heat transfer at a low Reynolds number of Re = 10,000, particularly in the channel middle region, which is mainly due to the incapable turning flow control in the root region of the wedged channel. To address this issue and further improve the heat transfer performance at low Reynolds numbers, a second-round optimization is performed by specifically adjusting the deflection angle of the selected guiding pin fins near the root region of the wedged channel. This secondary optimization demonstrates significant heat transfer improvements over the whole studied Reynolds number range with a reasonably reduced consumption of computational resources. The total Nusselt number and pressure loss are 69.3% higher and 11.9% lower than those of the baseline circular pin-fin array, respectively, at Re = 50,000. The optimization process proposed in this paper produces a high-performance cooling structure design with elaborate guiding pin-fin arrangements in the wedge-shaped channel, which indicates high heat transfer enhancement and relatively lower pressure loss in the wedged channel for the turbine blade trailing edge.

Three-dimensional simulation of the coupled electromagnetic-mechanical responses in a no-insulation racetrack coil

Three-dimensional simulation of the coupled electromagnetic-mechanical responses in a no-insulation racetrack coil

Equivalent Simulation Study of Delta-Rotor Engine

The mechanical structure, movement mode, and combustion process of a triangular rotor engine differ from those of a conventional engine with a crank connecting rod mechanism as the core. This makes it impossible to directly use existing simulation software to simulate the performance of the entire engine, rendering it difficult to conduct structural evaluation and performance prediction during the engine development stage. Therefore, using existing performance simulation software to establish a performance-equivalent model for a triangular rotor engine is crucial. To solve the above problems, this study proposes a performance-equivalent simulation modelling method for a triangular rotor engine based on a three-dimensional simulation model and the operating principles of the triangular rotor and four-stroke engines. Compared to various performance indicators obtained from the three-dimensional simulation model, the results show that the equivalent model established in this study has sufficient accuracy for key indicators such as the cylinder pressure, cylinder temperature, and in-cylinder quality under various working conditions. This can satisfy the requirements of the complete machine-performance simulation of a triangular rotor engine.

The Effect of Dam Break Speed on Flood Evolution in a Downstream Reservoir of a Cascade Reservoir System

The dam break flood is one of the potential causes of catastrophic events in cascade hydropower hub groups. Investigating the movement patterns of dam break flooding among reservoir groups under different dam break speeds is crucial for flood prevention and emergency response. In this study, the evolution characteristics of dam break floods were investigated in a cascading reservoir system, focusing on different break speeds of the upstream dam. The results indicate that the dam break speed determines the concavity or convexity of the water level curve changes in the upstream reservoir. Accordingly, dam breaks are classified into three modes: instant dam break, fast dam break, and slow dam break. An approximate critical speed has been identified to differentiate between the fast dam break and slow dam break. Further investigation into the evolution patterns of dam break floods in downstream reservoirs under different break modes was conducted. Correspondingly, the flood peak discharge and peak arrival time of the dam break floods vary differently with break speed under different break modes. Finally, a theoretical analysis for the flood peak discharge at the dam site during gradual dam break at a certain speed was established, which is able to predict the over-dam flood peak discharge in fast and slow dam break modes. This study is based on a combination of laboratory flume experiments and three-dimensional numerical simulations. This study has theoretical significance for the reinforcement of public infrastructure safety and the prevention of natural disasters.

Heat Transfer in Carbon-Nanotube Dispersions: A Simulation Study of the Role of Nanotube Morphology and Connectivity

Simulation of the behavior of carbon nanotubes (CNTs) can become a very challenging task considering their complicated shape and large aspect ratio. This study aims to elucidate the role of CNT shape, length, and connectivity during heat transfer in CNT dispersions through a three-dimensional (3D) simulator. Three characteristic shapes for the CNTs are considered, namely, straight, moderately curved, and strongly curved. The results reveal that the commonly used assumption of viewing CNTs as straight cylinders leads to significant overestimation of the overall medium conductivity. The CNT length has an important effect on the nanofluid conductivity for all types of CNT shapes considered here. In addition, use of CNTs with higher conductivity than a certain value appears to have no further beneficial effect, thus relaxing the need for extremely pure or single-wall CNTs. On the contrary, the conductivity remains a strong function of the CNT concentration and may be even increased upon organization of CNTs into loose clusters. The overall approach and concept can be extended to CNT composites in a straightforward manner.

Three-dimensional discrete element simulations on pressure ridge formation

Abstract. This study presents the first three-dimensional discrete element method simulations of pressure ridge formation. Pressure ridges are an important feature of the sea-ice cover, as they contribute to the mechanical thickening of ice and likely limit the strength of sea ice at large scales. We validate the simulations against laboratory-scale experiments, confirming their accuracy in predicting ridging forces and ridge geometries. Then we demonstrate that Cauchy–Froude scaling applies for translating laboratory-scale results on ridging to full-scale scenarios. We show that non-simultaneous failure, where an ice floe fails at distinct locations across the ridge length, is required for an accurate representation of the ridging process. This process cannot be described by two-dimensional simulations. We also find a linear relationship between the ridging forces and the ice thickness, contrasting with earlier results in the literature obtained by two-dimensional simulations.

3D simulation estimation and experimental validation of droplet generation in CFD-based flow-focusing microfluidic chips

Abstract Microdroplets generated using microfluidic techniques offer significant advantages over those generated using conventional methods, including high accuracy and excellent monodispersity. However, there remains a paucity of literature regarding the influence of fluid operating conditions and physical properties on droplet generation, specifically in relation to size and frequency, using computational fluid dynamics (CFD) techniques. In this study, we present a simplified microfluidic chip capable of flexibly adjusting the structure and size of the microchannels based on specific requirements. Subsequently, three-dimensional numerical simulations of this chip were conducted using CFD techniques and fitted a dimensionless model to estimate the droplet generation size and frequency through multivariate nonlinear regression methods. The experimental validation results demonstrated a strong correlation between the fitted data and the experimental observations, with size differences not exceeding 8% and good monodispersity, indicated by a coefficient of variation of less than 2.4%. This study provides valuable insights and a reference for future research.

Numerical simulation of deposit-landslide instability induced by water level decrease: a case study of RS deposit in Lancang River

Changes in reservoir water level often trigger landslides along the reservoir banks, which are common geological hazards that significantly affect the construction and operation of hydropower projects. In this paper, the stability of the RS reservoir landslide in the southwestern region of China is investigated. A discrete element seepage analysis model is constructed based on the theory of changes in the infiltration surface of the deposit caused by water level drawdown. The model is then embedded into a continuous-discontinuous three-dimensional numerical simulation method to systematically investigate the influence of reservoir water level decrease on the stability of the RS deposit. The results indicate that, under the condition of a sudden drop in reservoir water level decrease, the deposit experiences destabilization failure. Its sliding velocities are mainly influenced by seepage forces and gravity, while sliding displacements are influenced by seepage forces and topographic conditions. The landslide process shows distinct stratification characteristics. The portion of the deposit that slides into the river channel is mainly distributed between an altitude of 2655 m and 2870 m. The research results provide a scientific basis for studying the mechanism of slope failure and landslide disaster chain under the condition of reservoir water level lowering.

Performance assessment of a high-efficiency indirect dew-point evaporative cooler through three-dimensional modeling

The escalating demand for eco-friendly air cooling, driven by concerns over global warming, necessitates sustainable alternatives to air conditioners. Dew-point evaporative coolers offer a green alternative yet face challenges due to high flow resistances caused by the U-turn of the working air. Recently, we have developed a new compact counterflow dew-point cooler that eliminates the U-turn of the working air, mitigating flow resistance. In this paper, a precise three-dimensional simulation, based on fluid dynamics, heat transfer and mass transportation, is developed to assess the cooler's performance. The validation against experiments shows maximum 8 % deviation in input pressure and 3 % in product air temperature. The simulation provides insights into the cooler's operation, efficiency, and performance, which are not easily obtained experimentally. Optimal cooling coefficients of performance occurs at working ratios of 0.5–0.6. Notably, while metallic channel separator excels at higher flow rates, plastic ones like high-density polyethylene and polycarbonate match performance at lower rates. Furthermore, the cooler performs better in hotter, drier climates. In locales like Xian and New Delhi, the cooler is suitable for standalone use, while in regions like Dubai, Texas, Singapore, Beijing, and Monterrey, it can be coupled with air conditioners to enhance the ventilation and energy efficiency.

Three-Dimensional Numerical Simulation of High-Speed Shear Crushing of High-Density Fluid

Plasma atomization is a technology that can produce high sphericity, small particle diameters, and high-purity copper powder, which is of great significance for the development of metal additive manufacturing. At present, although plasma atomization can realize the industrial preparation of spherical copper powder, there are still some problems, such as unclear understanding of the atomization process and a lack of theoretical support for powder quality control. This leads to the inability to predict the average particle diameter of powder in advance based on the actual atomization conditions and to optimize the process parameters, which seriously affects the further development of the plasma atomization process. We mainly studied the non-stationary simulation of a DC argon plasma torch. The purpose of this paper was to study the specific influence law of the average particle diameter of the powder in the process of plasma atomization by means of numerical simulation and experimental observation. The aim was to establish the mapping relationship between the atomization condition and the average particle diameter of the powder and realize the controllable preparation of the plasma atomized powder. At the same time, we used industrial-grade plasma atomization equipment to carry out pulverizing experiments to verify the plasma atomization theory and the powder average particle diameter control scheme proposed in this paper, thus proving the reliability of this study.

Rapid simulation of knitted fabrics based on a ribbon yarn model

In the study, an innovative three-dimensional ribbon-based yarn model simulation technique is introduced, aimed at significantly enhancing the realism and speed of knitted fabric simulation through efficient model construction and rendering processes. The method successfully overcomes the limitations of traditional two-dimensional loop models and tubular yarn models, accurately capturing the textural details of knitted fabrics with a vivid three-dimensional representation. Experimental results demonstrate the outstanding performance of this simulation system in simulating the fuzz effects of yarn and in processing speed. This technology offers significant potential in textile design and production, notably in boosting design efficiency and accelerating new product development. By employing low-cost image capture methods, the study effectively reduces technical and financial barriers in knitted fabric simulation, enhancing its practical and industrial applicability.

Experimental and numerical study on scroll compressor under different profile correction and discharge ports shapes

The scroll compressor is an essential component in air conditioning and heat pump systems. This study examined an electric scroll compressor using R22 refrigerant, focusing on how modifications in the scroll head profile and discharge structure affect its performance. Initially, a semi-empirical model based on mathematical formulas was developed to predict the performance improvements of the updated scroll compressor. Three-dimensional simulation software was then used to illustrate changes in the internal flow dynamics before and after enhancements. The predictions were validated through experimental testing. Both the semi-empirical model and the three-dimensional unsteady numerical calculation model analyzed the effects of modifications to the tooth head profile and discharge port shape on compressor performance. The adoption of a PMP profile correction delayed the compressor discharge process, shifting the starting discharge angle from 315°to 344°, thereby reducing under-compression occurrences during operation and increasing volumetric efficiency by 1.31%. Additionally, mathematical formulas correlating temperature with compressor performance were developed from fitting data, predicting compressor behavior under various conditions. Moreover, replacing a circular discharge port with a waist-shaped port reduced power consumption by 0.59 kW, resulting in a more uniform temperature distribution and enhanced mass flow rate during compressor operation.

Analysis and structure optimization of the flow and temperature fields of the large-scale hot air drying room

Large-scale hot air drying rooms play a crucial role as efficient drying equipment across various industries. The uniform distribution of hot air is a crucial factor influencing the drying quality of large-scale hot air drying rooms. This study focuses on camellia seeds as the drying subject. Building on a porous media model and the drying kinetics of camellia seeds, a CFD model of the drying room was established. Three-dimensional simulations of the internal flow and temperature fields were performed using CFD software, and the simulated results aligned well with experimental data. To improve the uniformity, this study introduced an optimized design featuring a combination of a Type E3 air guide hood with five guiding plates and a fan, selected based on optimized angles (θ1 = 5°, θ2 = 10°). Under the condition of improving the structure without introducing a new heat source, the optimization ensured a significant improvement in flow field uniformity while making the temperature field closer to the desired ideal temperature. This offers a reference for the design and research of hot air drying equipment and hot air drying rooms.

Comfort weight analysis for optimising ergonomic cabin design of a drilling rig machine using three-dimensional human simulation

Ergonomics in product design enhance user comfort, correlating with increased efficiency and usability between the user and the product. Anthropometry is an important part of creating ergonomic design that correlates with human body size. By utilising anthropometry data, this research aims to analyse the cabin's comfort in drilling rig machine by creating 3D simulations for human-machine interaction. The comfort values will be assessed using Jack software. An experimental orthogonal design is applied to generate 81 optimal combination samples. The sample with the optimal comfort value can also be obtained. Following that, the extreme learning machine and mean impact value (ELM-MIV) algorithm is employed to evaluate the comfort weight analysis of each influencing factor. The accuracy value of the prediction model assessed using mean squared error (MSE) is 0.004, and the squared correlation coefficient (R2 ) value is 0.996. It can be inferred that the prediction error is apparently minimal, indicating the reliability of ELM implementation in data training. It will optimise the redesign of a drilling rig machine cabin to solve work-related health issues and improve operator comfort and efficiency.

Directed pulsed neutron source generation from inverse kinematic reactions driven by intense lasers

Neutron production driven by intense lasers utilizing inverse kinematic reactions is explored self-consistently by a combination of particle-in-cell simulations for laser-driven ion acceleration and Monte Carlo nuclear reaction simulations for neutron production. It is proposed that laser-driven light-sail acceleration from ultrathin lithium foils can provide an energetic lithium-ion beam as the projectile bombarding a light hydrocarbon target with sufficiently high flux for the inverse p(Li7,n) reaction to be efficiently achieved. Three-dimensional self-consistent simulations show that a forward-directed pulsed neutron source with ultrashort pulse duration 3 ns, small divergence angle 26°, and extremely high peak flux 3 × 1014n/(cm2⋅s) can be produced by petawatt lasers at intensities of 1021 W/cm2. These results indicate that a laser-driven neutron source based on inverse kinematics has promise as a novel compact pulsed neutron generator for practical applications, since the it can operate in a safe and repetitive way with almost no undesirable radiation.

Research on the Dynamic Leaking and Diffusion Law of Hydrogen-Blended Natural Gas under the Soil–Atmosphere Coupled Model

With the breakthrough in mixing hydrogen into natural gas pipelines for urban use, the widespread application of hydrogen-blended natural gas (HBNG) in energy delivery is imminent. However, this development also introduces significant safety concerns due to notable disparities in the physical and chemical properties between methane and hydrogen, heightening the risks associated with gas leaks. Current models that simulate the diffusion of leaked HBNG from buried pipelines into the atmosphere often employ fixed average leakage rates, which do not accurately represent the dynamic nature of gas leakage and diffusion. This study uses computational fluid dynamics (CFD) 2024R1 software to build a three-dimensional simulation model under a soil–atmosphere coupling model for HBNG leakage and diffusion. The findings reveal that, in the soil–atmosphere coupling model, the gas diffusion range under a fixed leakage rate is smaller than that under a dynamic leakage rate. Under the same influencing factors in calm wind conditions, the gas primarily diffuses in the vertical direction, whereas under the same influencing factors in windy conditions, the gas mainly diffuses in the horizontal direction.

Thermo-hydraulic performance of concentric tube heat exchangers with turbulent flow: Predictive correlations and iterative methods for pumping power and heat transfer

This research addresses the problem of predicting the thermo-hydraulic performance of concentric tube heat exchangers (CTHE) under turbulent flow conditions, a critical aspect in energy-efficient industrial systems such as HVAC, power generation, and chemical processing. Existing studies often lack accurate predictive methods for balancing heat transfer performance with pumping power requirements. To tackle this issue, novel correlations and an iterative Newton–Raphson method were developed for predicting pumping power and heat transfer rates. Three-dimensional CFD simulations of a water-to-water counter-flow CTHE were conducted, with Reynolds numbers ranging from 4000 to 8000 for both the hot and cold fluids. The simulations employed the Reynolds-Averaged Navier–Stokes (RANS) equations with the k−ω SST turbulence model. The results demonstrated that increasing the Reynolds number enhances both heat transfer rates and pumping power, with the cold fluid requiring consistently higher pumping power. New correlations were developed to predict pumping power, capturing the impact of both entry and fully developed flow regions. These correlations showed an average error of less than 2.33% when compared with the CFD data. The iterative Newton–Raphson method for predicting heat transfer rates demonstrated high accuracy, with an average error of 0.66% for heat transfer rate, 0.03% for hot fluid outlet temperature, and 0.01% for cold fluid outlet temperature. Additionally, we identified optimal operating conditions for efficient cooling and heating based on the heat capacity ratio (Cr). The novelty of this work lies in the development of new, highly accurate predictive correlations and iterative methods for optimizing CTHE performance, going beyond existing literature by providing comprehensive insights into the relationship between pumping power, heat transfer efficiency, and flow conditions.

A unifying bubble-layer-based theoretical model for flow boiling and application to a rod bundle

Current analyses of flow boiling primarily utilize two−/three-dimensional numerical simulations or one-dimensional empirical correlations/models. To develop a quasi-two-dimensional theoretical model, a unifying bubble-layer-based theoretical model is proposed, which can be applicable to the entire flow boiling process, from the single-phase liquid flow to the dryout point. This model considers bubble behaviors in each region and heat and mass transfer at the interfaces of two regions, consisting of conservation equations of mass, momentum, and energy, supplemented by a few empirical correlations. A sensitivity analysis of these correlations is conducted, revealing that the slip ratio correlation and bubble condensation rate correlation have the most significant impacts. Using experimental data on void fraction, the most accurate combination of empirical correlations is identified, with a total absolute error of 27.9 %. The verification ranges are 0.1-8Mpa for pressure, 182-1700 kW/m2 for heat flux, 240-2200 kg/m2s for mass flux, 0.83–1.76 for Prandtl number, and 4.4e3–2.98e5 for Reynold number. Finally, this model is applied to the analysis of the NHR200-II rod bundle, revealing the variations of several two-phase parameters under micro-boiling conditions and the influence of operating conditions on the length proportion of different flow sections, serving as important references for analyzing the impact of boiling on reactor reactivity.

Influence of electron cyclotron current drive on the pressure crashes caused by the 2/1 double tearing modes

Abstract A module with self-consistent evolution of driven current is developed and coupled with the resistive-MHD equations in the three-dimensional, toroidal, and nonlinear simulation code (CLT). The driven current equation is solved with a second-order accuracy symmetric scheme, which exhibits good conservation properties. With the new module, we find that the driven current can self-consistently concentrate inside the magnetic island when the parallel diffusion of the driven current is sufficiently large. The efficiency of the driven current on tearing mode suppression will then be much higher than those with stationary distributions. With the new module, the influence of electron cyclotron current drive (ECCD) on the nonlinear evolution of the 2/1 double tearing modes (DTMs) is investigated. When co-ECCD deposits on the outer resonant surface, the local magnetic shear is reduced, and the growth rates of the DTMs decrease; if ctr-ECCD deposits on the outer resonant surface, the local magnetic shear increases, and the DTMs become more unstable. However, things will be different if ECCD deposits on the inner resonant surface since the local magnetic shear is negative. The co-ECCD deposited on the inner resonant surface increases the negative shear and then promotes the growth of the DTMs; while the ctr-ECCD suppresses the DTMs. It is also found that the off-axis and central pressure crashes associated with the 2/1 DTMs can be converted to each other by properly depositing the driven current. To convert a central crash to an off-axis crash, the co-ECCD should be deposited on the outer resonant surface, or the ctr-ECCD deposited on the inner resonant surface. While, the co-ECCD should be deposited on the inner rational surface, or the ctr-ECCD deposited on the outer rational surface to convert an off-axis crash to a central crash. The co- or ctr-ECCD should be larger than a threshold for such transitions, and the threshold value is mainly determined by the location of the inner resonant surface.

Enhancing stimulated Brillouin scattering in suspended silicon waveguides through subwavelength nanostructuration [Invited

Brillouin optomechanics is playing a key role in the development of groundbreaking devices and novel functionalities in integrated silicon photonics, such as narrow linewidth filtering and lasers, tunable frequency, non-reciprocity, etc. Most silicon-based optomechanical waveguides, which use anchoring arms or perforated slabs to ensure mechanical stability and operate for transverse-electric polarized light, face challenges with acoustic mode leakage into the lateral Si slab, limiting the photon-phonon overlap and the Brillouin gain. Here, we propose new waveguide designs based on subwavelength nanostructuration to tailor near-infrared photons and GHz phonons and maximize the Brillouin gain. We introduce six different geometries suitable for both membrane or fully suspended configurations (i.e., without transversal arms anchoring the core to the Si slab). Our three-dimensional optomechanical simulations predict that subwavelength silicon membranes with strip, slot, and SWG slot core waveguides achieve gains up to 12257 W-1m-1 at mechanical frequencies of 12-13 GHz. Moreover, suspended silicon waveguides with SWG slots achieve a high gain of 43542 W-1m-1 at 4.45 GHz, with the ability to adjust the mechanical frequency from 4 to 9 GHz. Further enhancements in the Brillouin gain are studied by integrating side arms to amplify the moving boundaries effect in the suspended SWG slot waveguides and leveraging the slow light regime, which can significantly increase the Brillouin gain up to 17 × 106 W-1m-1 for a mechanical mode at 11.18 GHz.