Akisato Mizuno

Numerical Estimation of Exhaust Gas Emission From Tunnel Portal With Forced Extraction System

In recent years, exhaust gas emission out of tunnel portals has been a problem. In order to maintain the environment around the tunnel portal, a concentrated exhaustion system is installed in some tunnels. In the area between the suction port and the portal, the air flows in the opposite direction to the traffic, so that the pollutant is sucked toward the exhaustion port. In order to grasp the detailed phenomena, the authors investigated quantitatively the extent of the pollutant, which is brought out of the tunnel portal, in terms of a three-dimensional numerical analysis. This simulation system includes a sliding mesh algorithm in order to express the movement of vehicles. A typical result of the suction velocity of 1.0 m/s showed that almost no emission out of the tunnel is observed in small car traffic.Copyright

Prediction of Aerodynamic Noise Radiated From a Vertical-Axis Wind Turbine

Unsteady flow field and flow induced noise of vertical axis wind turbine are numerically investigated. The flow field is numerically calculated by the vortex method with core-spreading model. This simulation obtains aerodynamic performance and aerodynamic forces. Aerodynamic noise is also simulated by using Ffowcs Williams-Hawkings equation with compact body and low-Mach number assumptions. Tip speed of rotor blades are not so high, then the contribution of the moving sound source is smaller than that of the dipole sound source. Since the maximum power coefficient of VAWT can be obtained at lower tip-speed ratio compared to the conventional, horizontal axis wind turbines, the aerodynamic noise from vertical axis wind turbine is smaller than that of the conventional wind turbines at the same aerodynamic performance. This result indicates that the vertical axis wind turbines are useful to develop low-noise wind turbines.Copyright

Numerical Study on Securing Evacuation Environment Under Fire at an Inclined Tunnel Part

We have experienced severe fire accidents in tunnels, such as in the Mont Blanc Tunnel or Tauern Tunnel. These accidents triggered a series of studies for securing safe environments in case of tunnel fire. Plenty of research has been done so far, experimentally or numerically, on the phenomena of tunnel fire, and the behavior of smoke and heat has been discussed for the flat part of the tunnel. At the inclined part, however, the analysis is not sufficient, and it is necessary to be studied. The authors estimated the behavior of heat and smoke by fire at an inclined tunnel part by means of a 3-D numerical analysis. The analysis was done utilizing a freeware, named “FrontFlow/red” developed by a group at Tokyo University. The simulation results give a detailed flow field as well as heat and smoke distribution, which can be used to establish tunnel facilities as ventilation systems and their control, so that safe environments can be attained. It is also available to decide the interval of cross passages for evacuation.Copyright

Wavelet analysis of stock market prices

Wavelet analysis is one of the suitable methods to estimate characteristics of unsteady phenomena. In this paper, wavelet analysis was applied to predict the stock prices. Stock-broking timing can be estimated by using wavelet signal which depends on the wavelet coefficient. However, profit does not always accord in change magnitude of wavelet coefficient. Short term trade provides much profit compare to that of the maximum wavelet coefficient. The profit of the stock trade on the basis of human judgment compared with the wavelet analysis. After 1700 business-days trade, the wavelet based prediction brought higher profit. It reveals that the wavelet is useful for stock prices prediction.

Visualization of aerodynamic noise source of a rotating circular cylinder

Vorticity structures and flow field around a rotating circular cylinder at Reynolds numbers between 102 and 104 was numerically visualized. Velocity ratio of the uniform velocity and the rotational velocity of the cylinder was changed from 0 to 3. At low velocity ratio, the wake has anti-symmetric vorticity structure and lift-drag ratio is rapidly increasing. However, when the velocity ratio exceeds about 2, an absolute value of lift-drag ratio becomes small and alternative vorticity structure disappears. As a result, fluctuation of the aerodynamic forces turn weakness and the resulting aerodynamic sound becomes small. Source term of aerodynamic sound was also visualized by using results of CFD analysis. Sound source term generated large scale eddies disappeared at high velocity ratio. It reveals that rotating cylinders are effective for reduction of aerodynamic sound.

Numerical Prediction of Contaminant Emission from a Road Tunnel Portal

The purpose of this investigation is to predict contaminant emission from a automotive tunnel portal by using 2-D flow simulation. In order to simulate flow around moving vehicles in the road tunnel, sliding mesh technique is utilized. The sliding mesh for moving vehicles moves relatively for the fixed mesh for the tunnel and outer region. The amount of the contaminant emission depends on the carrying out quantity by the moving vehicles only without the ventilation effect of the tunnel facilities. In the case of a forward flow ventilation (4m/s), moving vehicles carry out 6.4% of the contaminant gas. On the other hand, in the case of a backward flow ventilation (4m/s), carrying out quantity decreases from 6.4 % to 2% and overall emission is almost zero. It reveals that the massive exhaustion at the exit portal is useful for reducing the contaminant emission.

VISUALIZATION OF AERODYNAMIC SOUND SOURCE WITH COMPACT GREEN'S FUNCTION

The objective of this investigation is to develop a method for detecting the aerodynamic sound source in a low-Mach number turbulent wake. In order to evaluate vorticity contribution for the dipole sound generation, a compact Greens function is utilized for identification of the aerodynamic sound source. The compact Greens function (1) (2) denotes the acoustic efficiency of the surface dipole caused by the interaction between the vorticity fluctuation and solid surfaces. The surface dipole sources and vorticity fluctuation are measured (3)(4) in the wake of a circular cylinder with Reynolds number of 4.0×10 4 . The compact Greens function model can be estimate instantaneous sound source distribution, however, this method requires the spatial derivative of vorticity fluctuations. Therefore, experimental evaluation is difficult. To evaluate the compact Greens function method, we introduce coherent output power (COP) in terms of surface dipole and vorticity fluctuation (4) . This method can be estimated vorticity contribution to the dipole sound generation with measurement of the coherence output power in terms of the vorticity fluctuation and the surface (dipole) pressure. This method is based on the conventional Lighthill-Curles theory (5) , which shows the aerodynamic sound is calculated with the surface pressure fluctuation. The COP method makes use of the coherent output power instead of the surface pressure fluctuation, it is found that the intensity of COP corresponds to the distribution of the dipole sound source caused by unsteady vorticity fluctuation. The estimated sound source distribution with the compact Greens function model is good agreement with that of the COP method.

On the Regular Publication of the Journal: Preface

Since then, the regular quarterly distribution has been the major target to be attained for the editorial board, as well as maintaining its quality and expanding international circulation. One of the important characteristics of this journal is that all papers are published in full color in order to promote better understanding of complex phenomena. We are happy to report that this journal enjoys a very favorable reputation, and the numbers of contributors and subscribers are increasing. Editorial Board consists of 17 Regional Editors, 17 Managing Editors and 33 Advisory Editors from all over the world in variety of fields related to Visualization. These Editors cooperate together to publish this outstanding Journal periodically. It is a great honor for me to have an opportunity of acting as the managing editor of the current issue, which is published and distributed in October 2002, and to carry out the spirit of the Journal, even though I am rather new to have joined in the editorial board. I called for papers through the regional editors worldwide, and saw two notable outcomes. One is the contribution of the invited paper from Prof. R. A. Robb, which appears at the top of this issue. The other is a group of papers by Russian authors organized by Prof. Chashechkin (Moscow University). For the latter, I owe much to Prof. Ryuji Kimura (Tokyo University) who has a close relationship with Prof. Chashechkin. But to my regret, due to the delay in the review process, none of these papers could be included in this issue. I hope they will appear in the following issues. We are happy that the journal is now published periodically. On the other hand, we still have to undertake some challenges, in particular to boost circulation. On behalf of the editorial board, I would sincerely like to ask the readers to help raise the number of subscription including that from libraries. It would be of great appreciation if the readers would solicit their colleagues and acquaintances interested in the field to subscribe to the Journal of Visualization.