CFD Numerical Simulation and Road Prediction for Sine-Wave-Class Road Overtaking

Transportation has become one of the primary sources of urban atmospheric pollutants and it causes severe diseases among city residents. This study focuses on assessing the pollutant dispersion pattern using computational fluid dynamics (CFD) numerical simulation, with the effect and results validated by the results from wind tunnel experiments. First, the wind tunnel experiment was carefully designed to preliminarily assess the flow pattern of vehicle emissions. Next, the spatiotemporal distribution of pollutant concentrations around the motor vehicle was modeled using a CFD numerical simulation. The pollutant concentration contours indicated that the diffusion process of carbon monoxide mainly occurred in the range of 0−2 m above the ground. Meanwhile, to verify the correctness of the CFD simulation, pressure distributions of seven selected points that were perpendicular along the midline of the vehicle surface were obtained from both the wind tunnel experiment and the CFD numerical simulation. The Pearson correlation coefficient between the numerical simulation and the wind tunnel measurement was 0.98, indicating a strong positive correlation. Therefore, the distribution trend of all pressure coefficients in the numerical simulation was considered to be consistent with those from the measurements. The findings of this study could shed light on the concentration distribution of platoon-based vehicles and the future application of CFD simulations to estimate the concentration of pollutants along urban street canyons.

On the basis of the simulation results of premixed jet flame using liquid hydrocarbon fuel, an optimization method for the component of aviation kerosene surrogate fuels based on chemical reactor network (CRN) model is proposed. Firstly, computational fluid dynamics (CFD) numerical simulation is carried out for three hydrocarbon fuel jet flames of n-dodecane (C12H26), n-decane (C10H22), n-heptane (C7H16) to obtain the characteristics of the temperature field under different working conditions. Based on this, the CRN partition topological geometry of jet flame is generated. The genetic algorithm is used to optimize the parameters of each reactor, and the algebraic relationship between the CRN parameter and the inlet parameters (dimensionless inlet temperature, Reynolds number and mixing fraction) is obtained. Then, topological geometry of the CRN which is suitable for different working conditions is established, and the best CRN model of hydrocarbon fuel jet flame is constructed. Combined with the experimental data, the optimal proportion of three-component surrogate fuels is determined by the above method. As a result, the optimal ratio is 56.41% C12H26, 26.36% C10H22 and 17.23% C7H16. Finally, the CFD numerical simulation was performed and the results agreed well with the experimental data, indicating the effectiveness of optimization method for the CRN-based aviation kerosene surrogate fuels. This method can be applied to the component optimization of aviation kerosene surrogate fuels.

The movement and distribution of the airflow field of the sprayer are very important for the distribution and penetration of the droplets. It is the focus and difficulty of the research to find the airflow field distribution of the fan outlet that matches the parameters of the canopy of the fruit tree. In order to study the influence of the angle change of the deflector of the orchard air-driven sprayer on the three-dimensional spatial distribution of the external air velocity field, this paper numerically simulated the external flow field based on computational fluid dynamics. The spray requirements of different fruit tree crown shapes were analyzed. The ICEM CFD software was used to model the external flow field. In order to improve the calculation efficiency, the model was divided into mixed grids. The k-ε turbulence model and Fluent solver are used for numerical solution. The flow fields of different deflectors are analyzed, and the influence of different positions and different sizes of deflector angles on the external flow field is determined.

Countercurrent-cocurrent dissolved air flotation (CCDAF), the popular water purification device, which consists of collision and adhesion contact zones, showed favorable flotation conditions for micro-bubble adhesion and stability. In this study, computational fluid dynamics (CFD) numerical simulation was employed to confirm that the unique CCDAF configuration create reasonable and that the flow field characteristics were good no matter for single phase or gas-liquid two-phase conditions. In addition, the turbulence of the flow field was enhanced with the increasing influent load; the swirling was remarkably reduced with the increase of gas holdup. Meanwhile, a thick micro-bubble filter layer was formed in the separation zone, which favored bubble-flocs agglomerating and rising. The force analysis also showed that the cross section within the tank contribute to the uniformity of the bottom water collection as well as enlargement of the bottom outflow area, therefore improving the overall flotation performance. The simulation results revealed for the CCDAF process can provide technical guidance for engineering design and application.

The effects of projectile rotation on the internal and external flow fields of the supersonic fluidic element are numerically studied using sliding grid technique and the RNG k-ε turbulence model. The effects of rotating speed on internal and external flow fields, switching time and output characteristics are studied. The results show that: for the external flow field, there is no obvious change in the flow field structure at low angular velocity; when the angular velocity increases to 20 r/s, the flow field structure becomes obviously asymmetric due to the Coriolis force; the flow field far away from the surface of the projectile body (more than 0.3 m) is much more affected than the flow field near the surface of the projectile body. The influence of projectile rotation on the internal flow field is much weaker than on the external flow field, and the change of internal flow field is not obvious when the rotational speed is less than 20 r/s. The switching time decreases with the increase in angular velocity, and within normal range of the angular velocity, the deviation of switching time from that without rotation is within 5%. The change of thrust distribution is not obvious when the rotational speed is less than 20 r/s. However, when the rotational speed reaches 50 r/s, the thrust of the middle part of the right nozzle increases by about 20 N.

Flotation process is a multi‐phase and multi‐scale complex flow system, in which hydrodynamics plays an indispensable role. In recent years, computational fluid dynamics (CFD) numerical simulation has gradually become a powerful tool for studying flotation. In this review, the theories of CFD numerical simulation in flotation research were reviewed, involving various turbulence models and multi‐phase flow simulation approaches. An attempt has been made to analyze and discuss the characteristics and applicability of different turbulence models and multi‐phase flow simulation approaches in flotation researches in detail. The CFD simulation of two commonly used flotation devices, that is, mechanically agitated flotation machine and flotation column, has been reviewed in detail. The detailed principles, operation, and hydrodynamic of flotation devices were discussed from the viewpoint of CFD. The advances made in CFD simulation for studying flotation process, including particle suspension, bubble dispersion, particle–bubble collision, attachment, and detachment subprocesses have been critically analyzed. Focused analysis was given on the influence mechanism of turbulence on the particle–bubble interactions. Finally, the gaps in the available literature are discussed and potential research directions are also proposed.

There are many kinds of turbulence models for automobile external flow field simulation. It is a very important significance to find a kind of turbulence model with high calculation efficiency and precision from the turbulence models for vehicle external flow field simulation. Three equation k- e-v2 turbulent model is used to simulate automobile external flow field, because the effect of turbulence spatial scale and turbulence time scale to turbulence transportation is involved in the calculation of eddy viscidity coeffi- cient μ tand more physical mechanism of turbulence transportation is described in the model, therefore, k-e-v2 turbulent model has higher calculation precision than shear stress transport (SST) and k-eturbulent model. So, three-equation model is a compara- tively ideal numerical simulation model of vehicle external flow field. The presented simulation example of car external flow field with the eddy viscosity type three equation k-e-v2, SST model and k-eturbulent model, through comparison of calculated drag coefficients of car with experimental date, validate the advantages of k-e-v2 turbulent model. In additional, the curve of pressure coefficient of car longitudinal symmetry face calculated by three models and wind tunnel pressure coefficient experimental data is compared. Turbulent kinetic energy distribution, velocity vector, exterior streamline graph at the position of 0.1 m away from the car rear simulated by k-e-v2 turbulent model, are also shown.

Numerical simulation was conducted to investigate the secondary explosion in the external flow field following horizontal explosion venting of a narrow and long vessel. The study utilized Fluent software, employing the standard k–ε turbulence model and SIMPLE algorithm, to analyze the secondary explosion under different explosion venting pressures, equivalence ratios, and length–diameter ratios. The results show that after the explosion of the pipeline, the flame lagging behind the pressure wave ignites the residual methane discharged into the external flow field again, which is the cause of the secondary explosion. When the explosion venting pressure exceeds 240 kPa, a distinct peak in overpressure is observed in the external flow field with its strength and range increasing proportionally to the venting pressure, reaching a maximum influence range of 0.4 m. At an explosion venting pressure of 290 kPa, three explosions can be detected. The equivalence ratio primarily affects the overpressure rise rate within the container prior to membrane rupture but has no significant impact on secondary explosion intensity. On the other hand, the length–diameter ratio significantly influences the overpressure rise rate within the container before membrane rupture as well as affecting secondary explosion intensity.

In this paper, computational fluid dynamics (CFD) numerical simulation is employed to analyze and discuss the effect of obstacle gradient on the flame propagation characteristics of premixed hydrogen/air in a closed chamber. With a constant overall volume of obstacles, the obstacle blocking rate gradient is set at +0.125, 0, and −0.125, respectively. The study focuses on the evolution of the flame structure, propagation speed, the dynamic process of overpressure, and the coupled flame–flow field. The results demonstrate that the flame front consistently maintains a jet flame as the obstacle gradient increases, with the wrinkles on the flame front becoming increasingly pronounced. When the blocking rate gradients are +0.125, 0, and −0.125, the corresponding maximum flame propagation speeds are measured at 412 m/s, 344 m/s, and 372 m/s, respectively, indicating that the obstacle gradient indeed increases the flame propagation speed. Moreover, the distribution of pressure is closely related to changes in the flame structure, with the overpressure decreasing in the obstacle channel as the obstacle gradient increases. Furthermore, the velocity vector and vortex distribution in the flow field are revealed and compared. It is found that the obstacle tail vortex is the main factor inducing flame evolution and flow field changes in a closed chamber. The effect of the blocking rate gradient on flow velocity is also quantified, with instances of deceleration occurring when the blocking rate gradient is −0.125.

This research aims to provide insight on the experimental results obtained induring hydraulic flume channel testing of a multifunctional artificial reef (MFAR) prototype employing various turbulence models and discretization schemes for Computational Fluid Dynamics (CFD) numerical simulations. The recently developed Multifunctional Artificial Reef is believed to be an effective tool to support marine ecosystem regeneration. Innovative design of the reef structure involves reticulated unconventional geometry, which results in complex interactions with the surrounding environment. To evaluate the structures behavior in water flow, hydraulic water flume tests were performed, to obtain the horizontal and vertical mean water flow velocity profiles.Additionally, the experimental setup and conditions were replicated in numerical simulation models to obtain comparative results, using different turbulence models and solution controls. Finally, these physical experimental results could be compared against numerical models within the CFD. This proved that the second order discretization scheme, and particularly k − ω turbulence model, had the closest approximation to experimentally obtained data.

In the course of study on aerodynamic change and its effect on steering stability and controllability of automobiles in passing, because there are multi-interaction streams, it is difficult to use traditional methods, such as wind tunnel test and road experiment methods. If the process of passing is divided into many time segments, and the segments are simulated with CFD (Computational Fluid Dynamics) method, then the approximate computational results about external flow field will be obtained. Based on the idea, numerical simulation analysis of side force coefficient of car in the course of passing Heavy Goods Vehicle and preliminary discussion of aerodynamic characteristics of correlative situations for car are presented in the paper, by means of dividing the passing process into many time segments and then simulating external flow field of every time segment through solving three-dimensional, steady and uncompressible N-S equations with Finite Volume Method, it avoids the use of moving mesh, which takes a large calculation resource and CPU processing time in calculating. Finally, the result of the side force coefficient of car is presented and coincident well with the experimental data, which shows creditability of numerical simulation methods is presented.

The method of Computational Fluid Dynamics (CFD) simulation has been extensively employed in the stack and tower integration technology (STIT) research; however, a significant number of studies overlooked the impact of thermal buoyancy on the external flow field of cooling tower. In light of this, an improved approach is proposed in this study. A model of a cooling tower and its surrounding flow field was established, and its reliability was confirmed too. Based on our model, the performance of three enhancement strategies under various crosswind speeds and ambient temperatures was simulated. The results indicate that all three enhancement strategies can effectively simulate the effects of thermal buoyancy. In the simulations, the elevation of the flue gases increased from 306 m to either 426 m or 476 m. In the present study, ambient conditions characterized by crosswind speeds below 4 m/s and temperatures below 297.15 K were deemed suitable for the dispersion of stack and tower integration (STI) flue gases. A power function distribution was identified between crosswind speed and the mean height of the plume, while a linear relationship was observed between ambient temperature and the mean height of the plume.

Hydropower is considered to be an important way to achieve the sustainable development goal of human progress. The performance of turbines is very important to the safety and stability of hydropower stations. Most of the hydraulic turbine performance studies only use Computational Fluid Dynamics (CFD) for performance simulation, lacking the integration of Building Information Modeling (BIM) technology and CFD. Therefore, a performance analysis model of a Francis turbine based on BIM was put forward in this paper. The BIM software OpenBuildings Designer CONNECT Edition Update 10 was used to build the hydraulic turbine model, and then the BIM model was transferred to the CFD numerical simulation platform ANSYS through the intermediate format conversion. In the ANSYS environment, the numerical simulation of different working conditions was carried out with the help of Fluent 2021 R1 software. The numerical simulation results show that the fluid velocity gradient in the volute was 2~3 m/s under the three working conditions, which was relatively stable. The water flow could progress the guide vane mechanism at a higher speed, and the drainage effect of the volute was better. There were some negative pressure areas at the back of the runner blades and the inlet of draft tube, and the negative pressure value was as high as −420,000 Pa and −436,842 Pa under maximum head conditions, which were prone to cavitation erosion. It is proven that BIM supported the hydraulic turbine performance analysis and provided a geometric information model for hydraulic turbine CFD numerical simulation, meaning that the performance analysis model based on BIM is feasible. This study can expand the application value of BIM and provide guidance for the study of hydraulic turbine numerical simulation using BIM technology in combination with CFD methods.

Research assessing on-road emission flow patterns from motor vehicles is essential in monitoring urban air quality, since it helps to mitigate atmospheric pollution levels. To reveal the influence of vehicle induced turbulence (VIT) caused by both front- and rear-vehicles on traffic exhaust and verify the applicability of the simplified line source emission model, a Computational Fluid Dynamics (CFD) numerical simulation was used to investigate the micro-scale vehicle pollutant flow patterns. The simulation results were examined through sensitivity analysis and compared with the field measured carbon monoxide (CO) concentration. Conclusions indicate that the vehicle induced turbulence caused by the airflow blocking effect of both front- and rear-vehicles impedes the diffusion of front-vehicle traffic exhaust, compared with that of the rear vehicle. The front-vehicle isosurface with the CO mass fraction of 0.0012 extended to 6.0 m behind the vehicle, while that of the rear-vehicle extends as far as 12.7 m. But for the entire motorcade, VIT is beneficial to the diffusion of pollutants in car-following situations. Meanwhile, within the range of 9 m behind the rear of the lagging vehicle lies a vehicle induced turbulence zone. Furthermore, the influence of vehicle induced turbulence on traffic exhaust flow pattern is obvious within a range of 1 m on both sides of the vehicle body, where the concentration gradient of on-road emission is larger and contains severe mechanical turbulence. As a result, in the large concentration gradient area of the pollutant flow field, which accounts for 99.85% of the total concentration gradient, using the line source models to represent the on-road emission might introduce considerable errors due to neglecting the influence of vehicle induced turbulence. Findings of this study may shed lights on predicting emission concentrations in multiple locations by selecting appropriate on-road emission source models.

CFD(Computational Fluid Dynamics) numerical simulation method was adopted to study on the solid expansion character in flow process of two phases fluidized bed including liquid and solid phases and testify the reliability. Commercial CFD software-Fluent was used in the study under some proper boundary conditions, such as velocity inlet, pressure outlet, symmetry condition for free liquid surface, standard k-ϵ model for turbulence and Gidapow model for inter-phase drag forces. Beside these, time dependent method was used in numerical simulation. Results of simulation were verified with calculation results of Richardson-Zaki experiential relations which were approved widely and they agreed well. The results of simulation could predict bed height and volume fraction of solids for expanded fluidized bed accurately; dynamical simulation could illustrate the start-up process of fluidized bed visually; numerical simulation in CFD could give some theoretical instructions for scale-up design of fluidized bed.