Computational Fluid Dynamics Numerical Simulation Research Articles

Temperature Analysis of Waveform Water Channel for High-Power Permanent Magnet Synchronous Motor

Abstract High-power permanent magnet synchronous motors (HPMSM) face extremely harsh cooling conditions due to their high power and complex structure. An efficient cooling system is pivotal to ensuring the safety and operational reliability of HPMSM. To improve the uneven axial temperature distribution in HPMSM and enhance the cooling effect, this paper presents an optimization of the water channels within the motor's cooling system. Initially, targeting the maximum temperature of the motor, the number and width of the traditional water channel (TWC) ribs are parameterized, and the optimal parameters are determined. Subsequently, based on the optimal parameters, three different waveform water channels are designed: circular channel (CC), triangular channel, and square channel. By employing the computational fluid dynamics numerical simulation, the influence of three kinds of water channels on the temperature of an HPMSM is analyzed under rated conditions. When the depth is 36 mm and the span is 40 mm for the CC, the average temperature rise of the motor winding is 9.88% lower than that of the TWC, reaching 48.77 °C. Results indicate that the cooling effect of the CC is better than others, which improves the cooling effect and operation performance of the motor.

A fast quadrupole-based analytical model for solving transient heat transfer in ventilated double-skin walls and assessing their energy saving potential

This research proposes a fast and accurate method for modeling transient heat transfer in ventilated double-skin façades (VDFs) with forced ventilation to predict their energy-saving potential. Using the thermal quadrupole formalism, the method solves the VDF problem in the Laplace domain while considering the full transient nature of the heat transfer; the only approximation is in space. The solution involves obtaining a general transfer function that predicts heat transfer rates or air temperatures at ventilated cavity's exit. The quadrupole method is validated against computational fluid dynamic numerical simulations conducted under similar meteorological, design and boundary conditions. A very good agreement was found (less than 3 % average deviation) with a significant reduction in computation time (less than 3s against 6h for CFD calculations). The model is computationally efficient and can consider important factors such as the opacity of the walls, construction materials, and air cavity design parameters. Finally, the model allows the assessment of the energy-saving potential of VDFs under various scenarios compared to conventional systems, which helps contributing to more sustainable building design practices. The energy efficiency of a VDF configuration was compared against a conventional wall system. Energy savings of 8.4 and 5.2 % were obtained, in cold and hot climates respectively.

Numerical simulation of falling film dehumidification with rectangular cylinder insertion modification at different elevations

ABSTRACT A falling film dehumidifier is one type of desiccant-based dehumidifier with superior performance and has a simple design and working mechanism. Geometric modifications of falling film dehumidifiers can impact their fluid flow and effectiveness. For further investigations, a CFD (Computational Fluid Dynamics) numerical simulation was carried out on the dehumidifier geometric innovation equipped with a rectangular cylinder with variations in different height positions. Falling film dehumidifier with four variations of rectangular cylinder height positions (3/12 h, 5/12 h, 7/12 h, and 9/12 h) was analyzed to determine its impact on dehumidification performance for each incoming airflow of 0.5 m/s, 1 m/s, and 1.5 m/s. Based on the results, it was evident that adding a rectangular cylinder to the humid air passage can change the flow characteristics, enhance the distribution rate of mass and air temperature, and ultimately enhance the dehumidification performance. The decrease in humidity and temperature increased by 11–14% and 11–27%, respectively, for the air velocity range of 0.5–1.5 m/s. In addition, the dehumidification performance was obtained to increase by 11–14% at the same air velocity range. Variations in the position of a rectangular cylinder show different results, where the lowest position delivers the best dehumidification performance.

Performance of the multi-U-style structure based flow field for polymer electrolyte membrane fuel cell

The design of the reactant gas flow field structure in bipolar plates significantly influences the performance of proton exchange membrane fuel cells (PEMFCs). In this study, we introduced four innovative U-shaped flow field designs, namely: In-Out Multi-U, Out-In Multi-U, Distro In-Out Multi-U, and Distro Out-In Multi-U. To investigate the impact of these various flow fields on PEMFC performance, we conducted computational fluid dynamics (CFD) numerical simulations, validated through model experiments. Our results indicate that the Distro Out-In Multi-U flow field offers notable advantages compared to the conventional parallel flow field (CPFF) and conventional serpentine flow field (CSFF). These benefits include reduced inlet and outlet pressures, lower liquid water content, more uniform liquid water distribution, and a more even current density distribution. Furthermore, the Distro Out-In Multi-U design demonstrates improved efficiency, consuming less H2 (91.9%) than the CSFF while achieving a higher net power density output (10.1%). As a result, for the same power output, the Distro Out-In Multi-U utilizes only 83.5% of the H2 consumed by the CSFF. In summary, the U-shaped structured flow field exhibits superior output performance, enhanced energy efficiency, and improved resistance to flooding. These findings suggest that the U-shaped flow field design holds significant potential as a reactive flow field for PEMFCs.

Study on gas–liquid–solid multiphase flow and erosion in ball valves

In industrial processes involving ball valves, gas–liquid–solid multiphase flows with continuous carrier and discrete particle phases are characterised by erosion challenges. These challenges reduce sealing performance and can lead to leakage and valve failure. To explore the characteristics of gas–liquid–solid multiphase flow and flow-induced erosion in ball valves, we conducted a combination of computational fluid dynamics numerical simulations and experimental testing. Results indicate that an increase in the gas content increases the flow coefficient, accelerates both liquid flow and particle movement and exacerbates erosion. In addition, particles are less concentrated in regions with higher gas concentrations. Erosion is primarily observed on the upstream surface and rear wall of the valve core as well as the upper side of the downstream pipeline. Severe erosion occurs more at smaller valve openings, and affected regions expand as the valve opening increases.

Dynamics of non-Newtonian fluid–fiber interactions and void formation mechanism based on fused filament fabrication

Due to the presence of internal defects such as voids in the composites manufactured by material extrusion additive manufacturing (MEX AM), the mechanical properties of the composites are significantly below the theoretical optimum. Under this circumstance, this paper is intended to investigate the effects of nozzle feeding angles and to analyze the void formation and evolution of multiphase flow, in which systematic computational fluid dynamics numerical simulations are conducted. The volume of fluid model and overset grid method are used to simulate the extrusion deposition process of carbon fiber-reinforced polymer composites, and the Carreau model is used to represent the shear-thinning behavior of molten polymer. The numerical method is validated against previously experimental and numerical simulation data. The numerical results show that the key factor leading to void formation is the vortices caused by fiber oscillation. The intense vortex at the front end of the fibers disrupts the interface between molten polymer and air, creating a beneficial condition for air to enter. Nozzle tilting can effectively reduce the probability of void formation by decreasing the fiber oscillation velocity. The results of the present study provide insights into the development and optimization of printer nozzles to enable the printing of longer fibers with less probability of potential void formation.

Simulating conjugate heat and mass transfer by the advanced perforated wall model for effusion cooling

Full-scale Computational Fluid Dynamics (CFD) numerical simulations can accurately predict the heat flux and metal wall temperature of gas turbine combustor liners, but they require considerable computational resources. In present work, an Advanced Perforated Wall model (A-PWM) has been developed to resolve the flow and heat transfer behaviors in this confined region. The geometric structure of the effusion cooling perforated plate is simplified, while the fluid-solid coupling heat transfer processes are still fully considered in details. The three-dimensional Reynolds Average Navier–Stokes simulations have been carried out for both a single-hole cooling plate and a multi-hole perforated cooling plate by using A-PWM. For simulations of the single-hole cooling plate, the cooling effectiveness in the downstream of the jet flow with the x/D ranging from 2 to 8 predicted by A-PWM shows good agreement with conjugate heat transfer model and experimental results. For multi-hole perforated cooling plate, the differences of cooling effectiveness between the prediction results by A-PWM and experimental results are just within 5%, confirming the developed model’s accuracy in predicting the effusion cooling. In addition, the A-PWM can also be employed to analyze the temperature distribution inside the solid zone. In simulations of both the single-hole cooling plate and the multi-hole perforated cooling plate, the use of the A-PWM model can lead to a reduction of over 35% in grid count compared to the conjugate heat transfer model, significantly reducing the computational time.

Centralized exhaust system simulation and parameter optimization

With the increase in high-rise buildings in cities, public flue exhaust systems have a direct impact on residential air quality and the living environment. Although existing studies have analyzed the problems in public flue exhaust systems through computational fluid dynamics (CFD) numerical simulations and experimental tests, these studies often lack an in-depth exploration of the specific impacts of individual components in the system. To solve this problem, this study not only thoroughly analyzes the key components in the public flue system, such as branch pipes, check valves, and tee pipes, but also develops a parametric public flue simulation system software based on C# and verifies the accuracy of the simulation through experiments. The study first determines the key parameters affecting the comprehensive resistance coefficient of the branch pipe, check valve, tee pipe, and other components through CFD simulation and experimental testing. Subsequently, a visualization program is developed using the C# language, which can quickly simulate and visualize the flow changes in the flue according to different building parameters such as the number of floors, height of floors, and size of the flue. The results confirm that the program can efficiently predict the flow distribution under different design options, providing a practical tool for the optimal design and performance evaluation of public flues, which is important for improving the air quality of the living environment.

The indoor thermal environment performance of various air-conditioning system configurations and airflow modes in a large space museum building

Optimizing air distribution in site museums is crucial for the long-term protection of heritage sites and the thermal comfort of visitors and staff. This study examined a site museum, analyzing the traditional suspended ceiling air-conditioning system and proposing a more rational renovation. Using computational fluid dynamics (CFD) numerical simulations, the study evaluated the effects of both systems on site protection and thermal comfort. The results indicated that the retrofit scheme could significantly reduce the indoor air velocity and temperature with the same air supply parameters, which would improve human thermal comfort and also reduce the negative impact of temperature and wind speed on the site. Additionally, the retrofit scheme cut air-conditioning energy consumption by 40% and reduced initial investment costs for a unit with a rated airflow of 62,000 m³/h. The optimization of the air-conditioning system ends was also carefully considered, resulting in a safer and easier installation and maintenance process, as well as enhancing the visual appeal of the museum’s interior. The proposed retrofit scheme can provide a reference for the design of air-conditioning systems in similar types of buildings.

Numerical study on bifurcation characteristics of wind-induced vibration for an H-shaped section

In order to reveal the influence of initial excitation on the bifurcation phenomenon of bridge decks, a new perspective of flow characteristics is developed based on the computational fluid dynamics numerical simulation method. Then, the bifurcation mechanism of vortex-induced vibration (VIV) response and nonlinear flutter response of the H-shaped section is investigated. The results show that when the wind speed is 2 m/s, under a small torsional excitation of 0.5°, the flow field of the H-shaped section will develop into the vortex shedding mode of the vertical vibration, resulting in vertical VIV. However, while under a large excitation of 6°, the flow field will directly transform into the vortex shedding mode of the torsional vibration, resulting in torsional VIV. Therefore, the bifurcation phenomenon of the VIV response is observed. When the wind speed is 4 m/s, the H-shaped section exhibits a nonlinear flutter limit cycle oscillation under a large excitation of 8°, but its response can be ignored under a small excitation of 0.5°. This phenomenon is attributed to the significant change in the transition of the vortex shedding mode from a small amplitude to a stable large amplitude, and the flow field lacks enough energy to complete the transition of the vortex shedding mode, resulting in the bifurcation phenomenon of the nonlinear flutter response. When the wind speed is 3.0 m/s, the large excitation will change the vortex shedding frequency of the new H-shaped section, resulting in the torsional VIV.

Aerodynamic configuration of a wide-range reversible vehicle

The design of wide-range high-efficiency aerodynamic configurations is one of the most important key technologies in the research of near-space hypersonic vehicles. A double-sided intake configuration with different inlets on the upper and lower surfaces is proposed to adapt to wide-range flight. Firstly, the double-sided intake configuration’s design method and flight profile are delineated. Secondly, Computational Fluid Dynamics (CFD) numerical simulation based on multi-Graphics Processing Unit (GPU) parallel computing is adopted to evaluate the vehicle’s performance comprehensively, aiming to verify the feasibility of the proposed scheme. This evaluation encompasses a wide-range basic aerodynamic characteristics, inlet performance, and heat flux at critical locations. The results show that the inlets of the designed integration configuration can start up across Mach number 3.5 to 8. The vehicle possesses multi-point cruising capability by flipping the fuselage. Simultaneously, a 180°rotation of the fuselage can significantly decrease the heat accumulation on the lower surface of the vehicle, particularly at the inlet lip, further decreasing the temperature gradient across the vehicle structure. This study has some engineering value for the aerodynamic configuration design of wide-range vehicles. However, further study reveals that the flow phenomena at the intersection of two inlets are complex, posing potential adverse impacts on propulsion efficiency. Therefore, it is imperative to conduct additional research to delve into this matter comprehensively.

The influence of warning lights on the truck cabins on aerodynamic performance

Abstract In recent development of goods transportation by road, there has been a growing interest in truck aerodynamics as a consequence of increased desire to reduce fuel consumption and emissions. Commercial vehicles have undergone continuous modifications in terms of body design (cabin) and trailers or semi-trailers. There have been and still are areas that disrupt air flow and can be optimized for an improved aerodynamic performance. As part of this areas, the paper will study the influence of beacon lights and light ramps positioned on cabin roof for European type trucks (tractor units). These warning equipment’s are imposed by transportation laws, reason for which eliminating them for achieving described purpose is not an option. In this context, the reduction of aerodynamic coefficient (Cd) can be pursued by analysing and optimizing the dimensions, shape and position for warning lights, in order to reduce the magnitude level of swirling effect. Different configurations of these elements will be tested and their impact in terms of air flow on the truck body will be analysed, with focus on roof area. The study will be done by simulating the interaction between airflow and truck in a virtual aerodynamic wind tunnel. The results will be analysed with the help of parameters like velocities, streamlines and pressures from a theoretical and experimental point of view to find the most viable option for each of the presented elements. The CFD (computational fluid dynamics) numerical simulations for chosen tests will be performed at a speed of 110 km/h considering that it is an often-encountered speed for trucks and also that aerodynamic phenomenology can be BETTER observed. By analysing the results obtained from the performed CFD simulations, the best positions and shapes for the beacon and ramp lights are desired to be identified. The paper conclusions will contain best configurations of warning lights and emissions improvement.

Influence of hot water pipe position on the performance of radiant floor heating systems integrated with PCM

To address the slow heating and low efficiency issues of traditional macro-packed phase change material (PCM) radiant floor heating systems, this study innovatively explores the impact of altering the eccentric positions of hot water pipes within the PCM encasement, based on computational fluid dynamics (CFD) numerical simulations. Starting with a concentric case as a baseline, the investigation extends to six different configurations achieved by displacing the hot water pipes vertically (upward and downward) and horizontally. The analysis encompasses the PCM's thermal state, temperature dynamics, spatial distribution, and heat flux. The results indicate that the arrangement of hot water pipes with upward and horizontal displacements demonstrates a more positive impact on improving the thermal performance of the PCM radiant floor heating system, with the effect becoming more pronounced as the displacement distance increases. Cases with upward eccentric movement of r/4 (where r is the encasement radius) and r/2 reached the optimal floor temperature of 297.15 K faster than the concentric case by 2 h and 3.8 h, respectively, during the heating phase. Cases with horizontal eccentric movement advanced by 0.5 h and 2.5 h, respectively. Cases with horizontal displacements of r/4 and r/2 caused smaller temperature fluctuations and provided greater comfort and energy efficiency than those with upward displacements, with average heat flux values being 4.75 % and 11.82 % lower, respectively. These findings offer theoretical support for the optimization and application of macro-packed PCM floor heating systems.

Equilibrium atmospheric boundary layer model for numerical simulation of urban wind environment

The numerical simulation of urban wind environments faces difficulties in capturing the turbulent characteristics due to the large computational domain. Traditional Reynolds-averaged methods (RANS) can effectively capture the average wind characteristics of urban areas. However, due to the significant dissipation and attenuation of turbulent energy in the downstream direction, this method fails to provide accurate turbulent characteristics after time-averaging processing. Therefore, in order to obtain a higher-precision turbulent wind field distribution within urban areas, this paper proposed a new numerical method named an equilibrium atmospheric boundary layer model (EABL) by modifying the control equation of the shear stress transport k–ω model. During the process, the equilibrium atmospheric boundary layer was achieved successfully, and the attenuation problem of the turbulent kinetic energy and dissipation rate during the computational fluid dynamics numerical simulation was resolved. Simultaneously, a wind tunnel experiment and six turbulence models [standard k–ε, realizable k–ε, renormalization group k–ε, large eddy simulation—narrowband synthesis random flow generator (LES-NSRFG) and LES vortex method and EABL] were employed to simulate the wind field characteristics in an actual residential area. The simulation results demonstrate that, relative to traditional RANS models, the EABL model enhances the simulation accuracy of turbulence characteristics by over two times. Furthermore, compared to LES models, the EABL model can reduce computational time by threefold.

Identification of an Unknown Stationary Emission Source in Urban Geometry Using Bayesian Inference

Estimating the parameters of an unidentified toxic pollutant source is crucial for public safety, especially in densely populated urban areas. Implementing source term estimation methods in real-world urban environments is challenging due to complex phenomena and the absence of concentration observational data. This work combines a computational fluid dynamics numerical simulation with the Metropolis–Hastings MCMC algorithm to identify the location and quantify the release rate of an unknown source within the geometry of Augsburg city center. To address the lack of concentration measurements, synthetic observations are generated by a forward dispersion model. The methodology is tested using these datasets, both as directly calculated by the forward model and with added Gaussian noise under different source release and wind flow scenarios. The results indicate that in most cases, both the source location and the release rate are estimated accurately. Although a higher performance is achieved using synthetic datasets without additional noise, high accuracy predictions are also obtained in many applications of noisy measurement datasets. In general, the outcomes demonstrate that the presented methodology can be a useful tool for estimating unknown source parameters in real-world urban applications.

Innovative coupled cooling strategy for enhanced battery thermal management: Synergistic optimization of jet impingement and immersion cooling

This study introduces an innovative, synergistically optimized coupled cooling design that enhances lithium-ion battery thermal management for electric vehicles, merging jet impingement with immersion cooling techniques. Utilizing Computational Fluid Dynamics (CFD) numerical simulation, distributed iterative optimization is conducted. Initially, the inlet and outlet configurations are determined. Subsequently, the number of jet pipes and the flow distribution are optimized. Finally, the diameters of the jet pipes are refined. This process aims to enhance heat transfer efficiency and reduce total input cost. The results indicate that a design with three inlets and one outlet, using an inlet flow rate of 0.075 kg/s alongside the flow rate of 0.025 kg/s, achieves optimal thermal performance for the batteries. This configuration reduces the maximum battery temperature and average temperature by 17.61% and 15.05%, respectively. Furthermore, an excessive or insufficient number of jet pipes is detrimental to cooling within the battery. Relying solely on mainstream inlet or jet pipe coolant for refrigeration is far less effective than proportionally distributing flow between the two. Selecting 6 jet pipes and a distribution ratio of 2꞉1 can reduce the maximum temperature by 10.10%. In contrast to adjusting jet pipe diameters, optimizing flow distribution exerts a more significant influence on battery cooling efficiency. Ultimately, the optimized solution, compared to the original design (with a flow rate of 0.025 kg/s), reduces the maximum temperature and average temperature by 26.41% and 10.61%, respectively. These improvements demonstrate the effectiveness of coupling jet impingement and immersion methods in battery thermal management, offering valuable insights for the future development of EVs battery cooling technologies.

Calculation method for the dynamic temperature distribution of winding area in dry-type on-board traction transformer

Dry-type on-board traction transformers have attracted considerable attention because of their lightweight and flameproof characteristics. The temperature distribution of winding areas is a critical indicator for representing operation performance. This study developed a calculation model for the dynamic temperature distribution of winding areas in dry-type on-board traction transformers under time-varying environments. First, a dynamic temperature calculation model was proposed based on the principle of thermoelectric analogy. Next, for addressing the transient outlet temperature of air ducts in the model, the influences of environment parameters and air duct size on heat dissipation were investigated, and a calculation model for the transient outlet temperature was proposed. Finally, the validity of the proposed dynamic temperature calculation method was verified experimentally, and the method was compared with conventional computational fluid dynamics numerical simulation using line data. The results revealed that for various structural parameters and time-varying operation scenarios, the proposed method could accurately obtain the temperature distribution in the winding area and could save more than 99% of the time cost compared with the conventional method.© 2017 Elsevier Inc. All rights reserved.

Prediction of engine combustion chamber outlet temperature field based on deep Learning: Application in aero-engine life extension control

One of the current research hotspots is the prediction of combustion chamber flow field based on deep learning methods, but how to effectively utilize these prediction results is a key issue that needs to be addressed urgently. This paper further proposes a study on the predictive control method for engine life extension considering the dangerous point temperature of turbine guide vane based on the prediction of combustion chamber outlet temperature field. Firstly, a combustion chamber outlet temperature distribution prediction model is established through Computational Fluid Dynamics (CFD) numerical simulation and inception deconvolution network, and integrated into the variable cycle engine component level model to achieve real-time prediction of combustion chamber outlet temperature distribution. Furthermore, based on this, the dangerous point temperature of the high-pressure turbine (HT) guide vanes is introduced as a constraint into the prediction optimization, and a predictive control method for engine life extension considering the thermal mechanical fatigue life (TMFL) of the guide vanes is proposed. The simulation results show that compared to the traditional LEC control method, the temperature at the critical point of the blade is reduced by 12.28 K, and the TMFL of the blade is increased by 29.23 %. The research results of this article provide a good application example for predicting the temperature distribution at the outlet of the combustion chamber, expanding the application scenarios for predicting the flow field parameters inside the engine.

Numerical Simulation and Comparison of Different Steady-State Tumble Measuring Configurations for Internal Combustion Engines

To enhance air–fuel mixing and turbulence during combustion, spark ignition internal combustion engines commonly employ tumble vortices of the charge inside the cylinder. The intake phase primarily dictates the generated tumble, which is influenced by the design of the intake system. Utilizing steady-state flow rigs provides a practical method to assess an engine’s cylinder head design’s tumble-generating characteristics. This study aims to conduct computational fluid dynamics (CFD) numerical simulations on various configurations of steady-state flow rigs and compare the resulting tumble ratios. The simulations are conducted for different inlet valve lifts of a four-valve cylinder head with a shallow pent-roof. The findings highlight variations among these widely adopted configurations.

Multi-Objective Optimization Design of Dynamic Performance of Hydrofoil with Gurney Flap

The horizontal axis tidal turbine, as a crucial device for capturing tidal energy, has gained significant attention because it has better energy efficiency performance. Enhancing the performance of foils, a vital part of tidal turbine blades, can significantly improve tidal turbine performance. Among numerous methods to enhance the foil performance, the Gurney flap has gained significant attention due to its avoidance of complex structural design. Currently, there is limited research on optimizing the design of Gurney flaps while considering the dynamic performance of foils. In this study, the S809 foil with a blade cross-section was selected as the research subject, a multi-objective optimization design platform was created by integrating a multi-objective optimization algorithm with Computational Fluid Dy-namics (CFD) numerical simulation techniques. The objective of this platform is to enhance the dynamic performance of the hydrofoil by optimizing the geometric structure of the Gurney flap. The improvement of dynamic lift and the size of the dynamic stall hysteresis loop are used as objective variables in this study to evaluate the hydrofoil’s dynamic performance. The optimal Latin hypercube design method is used in the optimization process to choose sample locations, and the Kriging approximation model is used to determine the relationship between the design variables and the objective variables. Meanwhile, the Non-Dominated Sorting Genetic Algorithm-II (NSGA-II) is used to create a multi-objective optimization platform for solving the optimization problem, and the optimized results are validated using CFD. Comparative validation results show that quantifying the dynamic performance during hydrofoil pitching oscillation and using the optimal Latin hypercube design method and Kriging approximation model for optimizing the Gurney flap structure is rational and accurate. This study explores the mechanism of the Gurney flap through in-depth CFD numerical simulations and finds that the Gurney flap affects the flow characteristics at the hydrofoil’s trailing edge, thereby influencing the performance. It increases the pressure difference between the pressure and suction surfaces, thus enhancing the hydrofoil’s lift. Finally, this article provides three recommended parameters to improve the dynamic performance of the hydrofoil. This research can serve as a reference for the application of Gurney flaps in tidal turbine blade design.