Nariaki Horinouchi

Large eddy simulation analysis of engine steady intake flows using a mixed-time-scale subgrid-scale model

Abstract Large eddy simulation (LES) using a mixed-time-scale (MTS) subgrid-scale (SGS) model is applied to the intake flows in simplified internal combustion engine geometry. A modified colocated grid system is employed to obtain results as precise as possible and to perform calculations in a stable way with a central difference scheme for convective terms. The results are compared with corresponding experimental data and the Reynolds averaged Navier—Stokes (RANS) equation model results obtained using the low-Reynolds-number linear k— In addition, it is made clear that when the QUICK scheme is used in LES for the convective terms instead of the central difference scheme, the result obtained deteriorates owing to the numerical viscosity. The importance of the discretization method in practical LES is also confirmed.

Application of a three-equation cubic eddy viscosity model to 3-D turbulent flows by the unstructured grid method

Abstract The three-equation cubic k – e – A 2 model proposed by Craft et al. (Int. J. Heat Fluid Flow 18 (1997) 15–28) is evaluated in three-dimensional (3-D) turbulent flows pertinent to engineering applications, especially in the automobile industry. For the computations of complex industrial flows, a numerical scheme has been developed using the cell vertex unstructured grid method. This scheme treats a mixture of tetrahedral, pyramidal, prismatic and hexahedral computational cells with high accuracy. The industrial flows chosen are internal combustion (IC) engine port-cylinder flows and flows around aerodynamic bluff bodies. The model performance in U-bend duct flows and a flow around a surface-mounted cubical obstacle is also examined. These fundamental flows include essential features of the industrial flows presently focused on. The model performs generally satisfactorily. However, the performance in a 3-D separating wake flow behind a bluff body suggests that the model needs further improvements.

A knowledge-based mesh generation system for forging simulation

We developed a knowledge-based system GENMAI (Artificial Intelligence Mesh GENerator) to auto-generate two-dimensional structured meshes. GENMAI is easily applicable to various kinds of application domains. Mesh generation is one of the major tasks confronted in computational simulation. The quality of generated meshes affects computational accuracy and computing time. Since various kinds of domain knowledge are needed to generate high quality structured meshes, the knowledge-based approach has been found effective and successful. Before designing GENMAI, we analyzed mesh generation jobs in plastic deformation analysis and computational fluid dynamics. Then, we formulate GENMAI so that it searches feasible plural divided patterns combinatorially and selects the best pattern. The characteristics of GENMAI are as follows: the meta-inference mechanism and its knowledge representation are widely applicable to various kinds of application domains; and plural patterns can be efficiently obtained at the same time by a search technique based on global dependency and local dependency. We applied GENMAI to forging simulation and developed AI-FESTE, which integrated a rigid-plastic deformation analysis program and GENMAI. Forging designers can easily decide shapes of a forging product and dies and also plan the forming sequence using AI-FESTE. AI-FESTE automates a series of forging analysis operations and shortens the execution time from 1 or 2 day(s) to a few hours. As a result, not only can AI-FESTE shorten the turn-around time, but it can improve the quality of product and die design.

Application of a Higher Order GGDH Heat Flux Model to Three-Dimensional Turbulent U-Bend Duct Heat Transfer

A higher order version of the generalized gradient diffusion hypothesis (HOGGDH) for turbulent heat flux is applied to predict heat transfer in a square-sectioned U-bend duct. The flow field turbulence models coupled with are a cubic nonlinear eddy viscosity model and a full second moment closure. Both of them are low Reynolds number turbulence models. The benefits of using the HOGGDH heat flux model are presented through the comparison with the standard GGDH

LES Analysis of Engine Steady Intake Flows Using a Mixed-Time-Scale SGS Model

Large eddy simulation (LES) using a mixed-time-scale (MTS) SGS model is applied to the intake flows in simplified internal combustion engine geometry. A modified colocated grid system is employed so as to perform calculations stably with a central difference scheme for convection terms. The results are compared with corresponding experimental data and the computational results obtained by using the low-Reynolds-number linear k-e and cubic nonlinear k-e -A2 turbulence models. The LES results show the best agreement with experimental data in three computational cases, not only in the mean velocity profiles but also in the profiles of turbulent energy. These results suggest that LES using the MTS model is an effective method for accurately predicting the performance of a combustion engine involving turbulent diffusion of spray and combustion flame. In addition, it is clarified that the numerical viscosity from the QUICK scheme for the convection term has a great influence on the computational results and decreases the prediction accuracy of LES.Copyright

Wall Thermal Conductivity Effects on Nucleation Site Interaction During Boiling: An Experimental Study

The past decades have witnessed the diverse applications of boiling heat transfer enhancement in the removal of high density heat flux released by electronic components or power devices. People have developed many enhanced surfaces to obtain the highest heat transfer coefficient in nucleate boiling or to raise the CHF. In the boiling arena bubbling and nucleation site density play core parts, and hence it is crucial to correlate them quantitatively with surface structure and heat transfer conditions. For example one can determine by that correlation the best arrangement of boiling cavities for a given heat flux. However, the bubbling is highly influenced by inter-bubble actions. It has been found that the interactions can considerably change the bubble’s size, frequency and spatial distribution. The interactions are needed to be taken accounts of for a good correlation. Researchers tried to formulate the interactions as a single function of the inter-site spacing but have obtained contradictory conclusions, as suggests that they depend also on other parameters. In the present study we conducted a saturated boiling heat transfer experiment to investigate the interactions with respects to both the inter-site spacing and the wall thermal conductivity. The test section was fabricated by both copper and stainless steel, whose surface has two cylindrical artificial cavities of 50μm in diameter. It was heated with a uniform heat flux. The results show that both the bubble diameter Db and frequency f are functions of the inter-cavity distance s, but they vary in different manners in the copper and the stainless steel surfaces. In the copper surface, we observed evident enhancement of the boiling heat transfer at 1> S >0.4 and a slight inhibitive effect at 1.6> S >1, where S = s/Db . On the contrary the two nucleate sites in the stainless steel surface interfere with each other giving rise to evident suppression of boiling heat transfer at 1.6> S >0.65 and only slight enhancement at 0.65> S >0.3. Note that the copper’s thermal conductivity is 22 times larger than the stainless steel. Numerical simulation has revealed that the temperature variation beneath the copper cavities is much less than the stainless steel, which partly explains the differences in our experimental results. It is suggested that modeling the bubble interactions should take accounts of not only the distance-to-diameter ratio but also the fluid and wall properties.Copyright