Sun M.,Tohoku University |
Sun M.,Institute of Fluid Science |
Hirao K.,Tohoku University
51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013 | Year: 2013
A simple method is proposed to evaluate the curvature of interfaces. The essence of the method is to treat the surface normal (SN) vectors as independent variables, and to integrate them separately. The curvature is then evaluated from the SN vectors. It is found that the curvature can be evaluated with uniform second-order accuracy for circles as small as two grid cells in diameter, which has never been reported before. In addition, the method is based on the numerical solution of the partial differential equations, so it can be straightforwardly extended to unstructured grid systems. Three possible methods to evaluate the curvature from the SN vectors have been compared. It turns out that only the curvature interpolated from that of the centroid to the center of an interface segment achieves the second-order accuracy. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Iga Y.,Tohoku University |
Iga Y.,Institute of Fluid Science |
Yoshida Y.,Japan Aerospace Exploration Agency |
Yoshida Y.,Kakuda Space Center
Journal of Propulsion and Power | Year: 2011
The propagation mechanism of rotating cavitations, especially that of supersynchronous rotating cavitation, is still unclear. The direction of propagation of supersynchronous rotating cavitation is in the direction of rotation of an impeller, which is opposite of the direction of rotating stall in general pumps and fans. Also, neither the mechanism of the order of appearance of rotating cavitations (supersynchronous, synchronous, and subsynchronous propagation) nor the mechanism of the discontinuity of the propagation speed during the transition between different types of rotating cavitations has been determined thus far. The present study indicates that they can be explained by the existence of latent rotating stall and a specific feature of cavitation: A decrease in the break-off frequency of a cavitation according to its development. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.
News Article | October 20, 2015
Spoilers on the back of cars aren't anything new. However, spoilers on tires are cutting-edge technology if you ask Yokohama. The Japanese tire manufacturer has fastened small, subtle spoilers onto its tires' outer walls, alleging the aerodynamic advance will increase fuel efficiency. Yokohama will roll out its concept tire at the 2015 Tokyo Motor Show next week on Oct. 28. Yokohama added spoilers onto tires by installing the thin fins at distinct angles on their tires' outer sidewalls. According to CNET, the spoilers work in two ways — fighting aerodynamic drag, allowing tires to work with more fuel efficiency, and lowering aerodynamic lift, positively affecting traction. The tire manufacturer thought of the idea after gathering data from the Tohoku University's Institute of Fluid Science and learning the effects of tiny fins attached to the sidewalls of tires. Yokohama says the study used a Supercomputer "K" to run aerodynamic simulations at different parameter values. From the simulations, they devised the idea to add spoilers to their tires. Overall, this development seeks to control aerodynamic flow throughout the vehicle's body by using the spoilers. If this concept hits the market, it will be interesting to see if the average driver invests in these tires and overall technology they boast or whether the advance will be relegated to car enthusiasts, ready to do anything to improve their vehicle's performance. Whether you fall in the former or latter category, anything designed to promote fuel efficiency can be deemed a positive.
Tokumasu T.,Institute of Fluid Science |
Ogawa I.,Institute of Fluid Science |
Koyama M.,Kyushu University |
Ishimoto T.,Kyushu University |
Miyamoto A.,Tohoku University
Journal of the Electrochemical Society | Year: 2011
The bond dissociation energy of a perfluorosulfonic acid (PFSA) molecule was investigated by density functional theory (DFT) to provide some dissociation trends of the PFSA molecule and the basic information for the design of more durable PFSA membranes. As the preliminary analysis, the chemical bond strengths of the PFSA molecule were analyzed exhaustively, and the vulnerable bond was identified by comparison of the results. The same calculations were performed for an ionized PFSA molecule to determine the influence of the ionization state on the bond strength. The C-S bond was the weakest among the side chain backbone in the neutral molecule; however, the C-S bond became stronger when ionized while it weakened the C-O bond connecting the side chain with the main chain. Analysis of the C-F bonds in the side chain showed that the dissociation energy decreases in the order of primary, secondary, and tertiary bonds, as also reported in the literature. Analysis of the main chain showed that the secondary C-F bonds neighboring the tertiary C-F bond connecting the side and main chains were the weakest. Ionization of the PFSA molecule weakens the average dissociation energy of C-F bonds. As the realistic analysis, the same calculations were performed considering the solvation effects to analyze the effects on the dissociation trend. Moreover, the possibility for improving the durability of PFSA membranes was investigated by partial substitution of H atoms or CH3 groups for F atoms. © 2010 The Electrochemical Society.
Yamashita H.,Tohoku University |
Yamashita H.,Institute of Fluid Science |
Obayashi S.,Tohoku University |
Obayashi S.,Institute of Fluid Science
Journal of Aircraft | Year: 2013
The article discusses the global variation of sonic boom overpressure due to seasonal changes in the atmosphere with temperature, pressure, and density gradients. Seasonal variations and geographic differences in overpressure due to a nonstandard atmosphere were examined in comparison with the standard atmospheric conditions. Differences in altitude were taken into consideration; however, the effects of wind, atmospheric absorption, and turbulence were not taken into account. The meteorological observations were obtained from a radiosonde, which is a balloon-borne instrument platform. These upper-air observations are performed twice a day at 0000 and 1200 coordinated universal time (UTC) in many parts of the world. The average vertical resolution of the observations is several hundred meters. The observations were assumed to be the values in the upper air directly above each station.