Computational Fluid Dynamics Analysis Method Research Articles

Research on CFD Simulation of the Cement Slurry Mixer

Numerical simulation method of the internal flow field of fluid machinery has become an important technology in the study of fluid machinery design. In order to obtain a high-performance cement slurry mixer, computational fluid dynamics (CFD) techniques are used to simulate the flow field in the mixer, and the simulation results are studied. According to the analysis results, the structural parameters of the mixer are modified. The results show the mixer under the revised parameters meet the design requirements well. So CFD analysis method can shorten design period and provide valuable theoretical guidance for the design of fluid machinery.

Optimization of variables in air conditioning control systems: Applications of simulations integrating CFD analysis and response factor method

The integration of three-dimensional spatial distributions into building simulations is of significant interest, and computational fluid dynamics (CFD) analysis is widely employed in building design processes. For example, based on the experience of architects and engineers, CFD analyses are often conducted under steady boundary conditions to determine the degree of attainment of indoor environments. However, CFD analyses have large calculation costs and cannot be often used for simulations with unsteady boundary conditions such as energy simulations in the building design processes. Thus, we developed a method that calculates sensitivities from heat sources to an arbitrary point in an indoor environment and integrates them into simulations with unsteady boundary conditions. In the proposed method, CFD analysis is employed under steady boundary conditions to calculate the response factors, and the resulting sensitivities are integrated into simulations under unsteady boundary conditions. In the present study, the proposed method was applied to optimize the variables of an air conditioning control system. With our method, temperature changes at a sensor over time are calculated from the time series of air supply temperature. In total, 800 calculations were conducted, and the optimal variables that allow the temperature at the sensor to reach the target value quickly were obtained. Except for the time required to calculate the response factors, the optimization in the present study took only a few seconds. If only CFD analysis was used for the optimization, the calculations would take a year. Thus, calculating the sensitivities via CFD analysis and utilizing the results in simulations is a useful approach for solving optimization problems. Moreover, the proposed method is applicable to simulations that require three-dimensional spatial distributions to enhance the accuracy of the calculation such as energy simulations.

Computational Fluid Dynamics Study of a Small Vertical Axis Wind Turbine with Ball-Shaped Blades

The computational fluid dynamics analysis of a small vertical axis wind turbine with ball-shaped blades has been done in this paper. First, a three-dimensioned model of the wind turbine with the ball-shaped blades has been constructed by using the software of FLUENT 6.3. Then, by giving the size parameters and shape parameters of the blades, the simulation has been done and the corresponding simulation results have been obtained. The contuours of static pressure around the wind blade area has been shown. The simulated model and the results can be used for finding the factors which will affect the power efficiency of this type of wind turbine in the future. Finally, the simulation results of the blade with zero curvature radius and curvature radius of 2 are shown and compared in order to demonstrate the effectiveness of this computational fluid dynamics analysis method. It can be concluded that the blades with curvature of 2 can obtain more toruqe comparing with the zero one and it would be the more suitable option in the blade design.

ICONE19-43536 Development of CFD Analysis Method Based on Droplet Tracking Model for BWR Fuel Assemblies

It is well known that the minimum critical power ratio (MCPR) of the boiling water reactor (BWR) fuel assembly depends on the spacer grid type. Recently, improvement of the critical power is being studied by using a spacer grid with mixing devices attaching various types of flow deflectors. In order to predict the critical power of the improved BWR fuel assembly, we have developed an analysis method based on the consideration of detailed thermal-hydraulic mechanism of annular mist flow regime in the subchannels for an arbitrary spacer type. The proposed method is based on a computational fluid dynamics (CFD) model with a droplet tracking model for analyzing the vapor-phase turbulent flow in which droplets are transported in the subchannels of the BWR fuel assembly. We adopted the general-purpose CFD software Advance/FrontFlow/red (AFFr) as the base code, which is a commercial software package created as a part of Japanese national project. AFFr employs a three-dimensional (3D) unstructured grid system for application to complex geometries. First, AFFr was applied to single-phase flows of gas in the present paper. The calculated results were compared with experiments using a round cellular spacer in one subchannel to investigate the influence of the choice of turbulence model. The analyses using the large eddy simulation (LES) and re-normalisation group (RNG) k-ε models were carried out. The results of both the LES and RNG k-ε models show that calculations of velocity distribution and velocity fluctuation distribution in the spacer downstream reproduce the experimental results qualitatively. However, the velocity distribution analyzed by the LES model is better than that by the RNG k-ε model. The velocity fluctuation near the fuel rod, which is important for droplet deposition to the rod, is also simulated well by the LES model. Then, to examine the effect of the spacer shape on the analytical result, the gas flow analyses with the RNG k-ε model were performed for three kinds of spacers of actual fuel assemblies: a lattice type spacer, a round cell type spacer, and a grid spacer with mixing vanes, respectively. The results indicate that the swirling flow is generated by the mixing vane, and the turbulence energy increases near the surface of fuel rod. The Lagrangian method was applied to droplet behavior in turbulent gas flow around the round cell type spacer and that around a mixing vane spacer as trial analyses. It was confirmed that liquid droplet deposition is promoted in downstream from the mixing vane spacer because of swirling flow.

Measurement of airflow of air-conditioning in a car with PIV

In the present study, a model experiment is performed in order to clarify the airflow characteristics of a car cabin. In addition, this study provides high precision data for a benchmark test using the CFD (Computational Fluid Dynamics) analysis method. Initially, the study focuses on the ventilation mode that describes the flow field in the car cabin obtained from an experiment with PIV. The car cabin model is made of transparent acrylic resin and measures 1,450 mm × 700 mm × 900 mm, almost half the size of a real car, and was installed in a thermostatic chamber. In the experiment, the cabin model was controlled by an orifice tube and a pressure gauge in order to confirm the airflow rate. The PIV measurement was performed at a total of 18 regions within the section. The analyzed PIV data provides the mean velocity profile, the standard deviation distribution and the turbulence intensity distribution at each region.

High-Accuracy Thermal Analysis Methodology for Semiconductor Junction Temperatures by Considering Line Patterns of Three-Dimensional Modules

A novel computational fluid dynamics analysis method of predicting semiconductor junction temperatures precisely without modeling printed circuit board (PCB) line patterns was developed. First, PCBs are divided into multiple regions. The effective anisotropic thermal conductivity of each region is then assigned as follows. All the regions are divided into smaller subregions whose size is below the pattern width. The thermal conductivity of each subregion is defined by the property of the material at the center of the subregion. Next, a thermal circuit network composed of all the subregions is generated, and finally the anisotropic thermal conductivities of each region are computed by solving this thermal network matrix. When boards are divided into multiple regions, there is a convergence region size under which the analytical results show no further change. In this paper, the relationship between the size of the divided regions and the accuracy of the analytical results was investigated. It was confirmed that the calculated semiconductor junction temperatures were precisely coincident with the experimental results when the size of the regions was less than 20 times the line pattern width.

Regulatory Issues on the Safety Distance between a VHTR and a H2 Production Facility and an Overpressure Prediction Using Correlations and a CFD Analysis for the JAEA Explosion Test in an Open Space

Regulatory issues are discussed to establish Korean regulations on the safety distance between a very high temperature reactor (VHTR) and a hydrogen production facility. The major issues for the regulations concerning a gas explosion are an overpressure criteria, a regulation philosophy, and an overpressure prediction method. The overpressure can be predicted using empirical correlations of the trinitrotuluene (TNT) equivalent method and the multi-energy method (MEM). A comparison work of the predicted values using these correlations and the Japan Atomic Energy Agency (JAEA) explosion test results was performed to evaluate the applicability of these correlations to a VHTR. The MEM predicts the peak overpressure better than the TNT equivalent method because the explosion test results in a deflagration phenomenon. Thus, the MEM may be used effectively to estimate the peak overpressure for the gas explosion simply. A CFD analysis for the explosion test was also performed to establish an analysis methodology for a gas explosion. A spark ignition model to simulate an electric spark of 40 J in the JAEA explosion test was developed based on an energy conservation law. A sensitivity computational fluid dynamics (CFD) calculation was performed to elucidate the optimized pressure, temperature, and radius value of the spark ignition model. The CFD analysis results showed that the peak overpressure and the flame front time of arrival may be predicted better by the CFD analysis than by the MEM if the proper pressure and radius for the spark ignition model are chosen. So, the CFD analysis may be used as an accurate evaluation tool to provide the three-dimensional information of an overpressure and a time history of the overpressure variation. Therefore, it is recommended that the risk-informed regulation, the MEM, and the CFD analysis method should be used together to determine a safety distance.