In order to clarify an aerodynamic performance of cylinder with spiral fins used for Magnus wind turbines, wind tunnel experiments and numerical simulations (LES) were conducted. Reynolds number based on the diameter of the cylinder and uniform velocity is 1.1×104 and computational grid used for numerical simulations consists of nearly 6 million points. The experiments made the relations between force worked on the cylinder and rotational speed ratio clear, and numerical simulations made clear how the two-dimensional flow around the cylinder with and without spiral fins are.
Presented in this paper is large eddy simulation (LES) of turbulent incompressible flow around NACA0012 wing tip and numerical prediction of aerodynamic sound in the far field. Reynolds number based on the chord length of the wing and uniform velocity is 3×105 and the angle of attack is 9 degrees. Computational grid consists of nearly 10 million grid points. LES results give good corelation with measured data. It made clear that two primary vortexes are generated from the upper and lower edge of the wing tip. The far-field sound predicted by Lighthill tensor and Curle’s equation both show a similar tendency to the measured data.
We investigate the fluid-acoustic interactions in the fluid-resonant oscillations in a flow over a two-dimensional cavity by directly solving the compressible Navier-Stokes equations. The upstream boundary layer is turbulent, and the freestream Mach number is 0.15 or 0.3. The computational results show that the mechanisms of the formation of large-scale vortices and the radiation of acoustic waves are essentially the same as those in the fluid-dynamic oscillations. However, the acoustic resonance amplifies the acoustic energy radiated by the collision of the vortices along the downstream wall. Moreover, the acoustic feedback becomes more intense due to the acoustic resonance. As a result, the fluid-resonant oscillations occur even at a low Mach number such as 0.15.
A large eddy simulation (LES) of magnetohydrodynamic turbulent channel flow is carried out and turbulent statistics are obtained to investigate the dynamo effect. The transport equations for the turbulent energy and the turbulent electromotive force are examined. It is shown that the energy is transferred from the turbulent kinetic energy to the mean magnetic-field energy as the dynamo effect. The wall-normal and spanwise components of the turbulent magnetic energy are produced due to the Lorentz force term, which corresponds to the energy transfer from the turbulent kinetic energy. It is also shown that the cross-helicity dynamo actually produces the turbulent electromotive force that sustains the mean magnetic field. [This abstract is not included in the PDF]
Turbulent cross helicity (correlation between the velocity and magnetic-field .uctuations) is expected to play an important role in several magnetohydrodynamic (MHD) plasma phenomena such as global magnetic-field generation, turbulence suppression, etc. First we present physical interpretation of the cross-helicity effect; A combination of the local angular-momentum conservation and the cross-correlation between the velocity and magnetic-field fluctuation gives rise to the contribution to the turbulent electromotive force parallel to the large-scale vorticity. A microscopic origin of the effect is also presented with the aid of the notion of polarization drift. The conservative nature of the cross helicity is examined with special reference to the cross-helicity supplying mechanism to turbulence and mean flows. This point is important in considering the boundary condition for the numerical test of the cross-helicity effect. [This abstract is not included in the PDF]
In this study, large-eddy simulation of Rayleigh-B%eacute;nard convection using a novel subgrid scale model is carried out. The model, which is one-equation-type SGS model with SGS kinetic energy, does not have any length scales. Compared with the result of some conventional models such as standard Smagorinsky model, present model is in good agreement with DNS data and applicable to turbulent thermal convection. [This abstract is not included in the PDF]
The calculation of EHL film thickness is important in rolling bearing design. The film thickness analysis under starved condition requires following two technologise. (a) EHL analysis with prescribed inlet oil distribution. (b) Inlet oil distribution analysis with prescribed oil feed rate for a bearing. There are some studies of (a), but (b) has never been studied. Thus, this paper aims to develop a new method for coupled simulation of micro (EHL) and macro flow (oil flow outside an EHL). The macro flow is modeled as liquid film (LF). The present method is applied to a rolling bearing. The relationship between oil feed rate and oil film thickness is investigated. [This abstract is not included in the PDF]
Numerical simulation was carried out for the effects of eutrophication and global climate change between 1955 and 2005. The date of overturn of waters is different by 1 month and annually minimum concentration of dissolved oxygen decreases by 0.5-1 mg L-1 if overturn of waters delays by one month. In order to mitigate the effects of global climate change, 10 % of the external loading of total phosphorus, which controls phytoplankton growth, should be removed in comparison with the present external loading of total phosphorus. [This abstract is not included in the PDF]
Numerical simulation by means of three-dimensional hydrostatic model was carried out with the effect of icing event for water current field in the Caspian Sea. As a result, prediction of water temperature field was improved by considering the icing event. The salinity field contributes to formation of the surface gyre system, while the accuracy of predicting salinity field was not enough. The water current field in the Caspian Sea is formed by adding wind-driven current to the dominant density-driven current, which is based on horizontal differences in water temperature and salinity, and Coriolis force. [This abstract is not included in the PDF]
The effect of large-scale greenery is expected to mitigate urban heat islands. However, most research is measurement-based, with limited research using numerical simulations. In order to investigate the effect of thermal mitigation by large-scale greenery, a tree model was built into the CFD code. The air temperature leeward of an urban block with large-scale greenery is approximately 1.5°C lower than without such greenery. This result showed that large-scale greenery provides an effective way to mitigate urban heat islands.
This research is focused on the wind characteristics and the ventilation performance in the street canyon. In order to achieve the same flow as the actual wind, four cases with varying building height and array were made. To confirm the relevance of affection of region of pollutants and the form of canyon, the height of 7.5 m for the pollutants release was set in each case. About the performance of ventilation, SVE3 and Exchange Ratio were obtained from the pollution solutions which was calculated in each case. And we analyzed the ventilation efficiency in canyon, based on which, how ventilation performance is influenced by the form of canyon and the pollution region has been studied.
Pollutants in atmosphere are chemically reactive, and the reaction plays a main role in the genesis of air pollution. In this paper, chemical reaction and wall deposition are modeled with Large-Eddy Simulation (LES) to investigate the effect of these phenomena in turbulent flow. Ozone and Limonene which is a kind of Terpene are employed as chemical species. As the gas-phase reaction between these substances is regarded as bi-molecular reaction, the Second Order Rate Constant model is used for the reaction between these chemicals. The CFD simulations are conducted for a two-dimensional enclosed region. The results of computational analysis are consistent with experimental data.
Indoor thermal environment is composed of various heat factors both from outdoors and indoors. The contribution ratio of indoor climate (CRI) based on CFD is developed to estimate the individual contribution of these factors to any location inside a room. Since most of the studies related to CRI are considered in forced convection air flow field, the purpose of this paper is to analyze the heat transfer by convection and radiation respectively by using CRI in an atrium dominated by a strong natural convection.
Nowadays, reverse simulation seems to be a promising topic in term of environment research. Mathematically, reverse simulation is the solution of the transport equation in the negative time advancing. The process of transport equation is equivalent to that of positive time advancing with negative convection and diffusion. However, there is a numerical instability problem in solving diffusion term. This research introduces a method to improve numerical stability in reverse simulation. Two examples are given in this paper. In the first one, a simple laminar flow is considered and pollutant is emitted for uniformity time. In the second example, the wind flow around a single building is considered.
In the present study, the extended Brinson’s constitutive equation for shape memory alloy considering asymmetric tensile and compressive deformation and multi-axial stress state has been simplified and applied to the one-dimensional and three-dimensional dynamic simulations, which have furthermore been extended to the simulations considering the cyclic effect. [This abstract is not included in the PDF]
The computational modeling based on continuum damage mechanics has been studied for gray cast iron FC250. The damage mechanics model considering asymmetric tensile and compressive deformation has been presented and its material parameters have been identified, based on the uniaxial tension/compression and fatigue test results. The validity of the damage mechanics model has been demonstrated by conducting the finite element analysis based on locally-coupled and fully-coupled approach. [This abstract is not included in the PDF]
Advanced Mobility Research Center (ITS Center), Institute of Industrial Science, The University of Tokyo has approached to improvement of realistic sensation on the Universal Driving Simulator (DS). Some functions such as a turntable mechanism, new visual system with the target projector to improving visibility, improvement of a sound system, etc. have been added before now. Moreover, new mechanism consisting of the XY-stage and the turntable mechanism for upgrading realistic sensation of the DS and applying the DS to experiments on automobiles was developed. The new mechanism is installed on the top of a motion platform of DS. In this paper, concept and structure of new mechanism are described. [This abstract is not included in the PDF]
In order to achieve the new transportation mode, we have investigated the personal mobility vehicle (PMV), which is friendly for the human and the environment. The PMV consists of the bicycle mode and parallel two-wheel mode. The parallel two-wheel mode has the human-powered type that applies human pedaling for its driving. In this paper, the steering systems especially the method of turning and steering input are investigated. We made the prototype vehicle with the steering reaction motor. Using the prototype vehicle, we confirmed its successful maneuvering. [This abstract is not included in the PDF]