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Thwe Thwe, A.; Kadowaki, Satoshi; Nagaishi, Ryuji
Journal of Nuclear Science and Technology, 60(6), p.731 - 742, 2023/06
Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)In this study, we performed numerical calculations of unsteady reaction flow considering detailed chemical reactions, investigated the unstable behavior of hydrogen-air dilute premixed flame due to intrinsic instability, and clarified the effects of unburned gas temperature and pressure. I made it. The unstable behavior of the flame in a wide space was simulated, and the burning rate of the cellular flame was obtained. Then, the effects of heat loss and flame scale on flame unstable behavior were investigated. The burning velocity of a planar flame increases as the unburned-gas temperature increases and it decreases as the unburned-gas pressure and heat loss increase. The normalized burning velocity increases when the pressure increases and heat loss becomes large, and it decreases when the temperature increases. This is because the high unburned-gas pressure and heat loss promote the unstable behavior and instability of flame.
Katsumi, Toshiyuki; Thwe Thwe, A.; Kadowaki, Satoshi
Journal of Visualization, 25(5), p.1075 - 1083, 2022/10
Times Cited Count：1 Percentile：19.38(Computer Science, Interdisciplinary Applications)Lean combustion and inert-gas addition are useful to control the burning velocity of hydrogen premixed flames, and it is well known that the cellular structure forms on the front of lean hydrogen flames owing to intrinsic instability. However, the influences of inert-gas addition on the instability phenomena of lean hydrogen premixed flames are not understood fully, and then it is needed to be investigated the flame instability experimentally. In the experiments, the cellular structure and fluctuation of H
/O/inert gases (Ar, N,CO) premixed flames on a flat burner were obtained using direct observation, laser diagnostics and light emission intensity to elucidate the characteristics of instability phenomena. As the results, the correlation of inert-gas addition, equivalence ratio and total flow rate with the characteristics of cellular flames was revealed, and the influences of these parameters on flame instability were discussed.
Kadowaki, Satoshi; Thwe Thwe, A.; Furuyama, Taisei*; Kawata, Kazumasa*; Katsumi, Toshiyuki; Kobayashi, Hideaki*
Journal of Thermal Science and Technology (Internet), 16(2), p.20-00491_1 - 20-00491_12, 2021/00
Times Cited Count：4 Percentile：29.17(Thermodynamics)Effects of pressure and heat loss on the unstable motion of cellular-flame fronts in hydrogen-air lean premixed flames were numerically investigated. The reaction mechanism for hydrogen-oxygen combustion was modeled with seventeen reversible reactions of eight reactive species and a diluent. Two-dimensional unsteady reactive flow was treated, and the compressibility, viscosity, heat conduction, molecular diffusion and heat loss were taken into account. As the pressure became higher, the maximum growth rate increased and the unstable range widened. These were due mainly to the decrease of flame thickness. The burning velocity of a cellular flame normalized by that of a planar flame increased as the pressure became higher and the heat loss became larger. This indicated that the pressure and heat loss affected strongly the unstable motion of cellular-flame fronts. In addition, the fractal dimension became larger, which denoted that the flame shape became more complicated.
Katsumi, Toshiyuki; Yoshida, Yasuhito*; Nakagawa, Ryo*; Yazawa, Shinya*; Kumada, Masashi*; Sato, Daisuke*; Thwe Thwe, A.; Chaumeix, N.*; Kadowaki, Satoshi
Journal of Thermal Science and Technology (Internet), 16(2), p.21-00044_1 - 21-00044_13, 2021/00
Times Cited Count：6 Percentile：35.68(Thermodynamics)The effects of addition of CO and water vapor on characteristics of dynamic behavior of hydrogen/air premixed flames were elucidated experimentally. By Schlieren photography, wrinkles on the flame surface were clearly observed in low equivalence ratios. The propagation velocity increased monotonically as the flame radius became larger and flame acceleration was found. Increasing the addition of inert gas, the propagation velocity decreased, especially in the case of CO addition. Moreover, the Markstein length and the wrinkling factor decreased. This indicated that the addition of Co or HO promoted the unstable motion of hydrogen flames, which could be due to the enhancement of the diffusive-thermal effect. Based on the characteristics of dynamic behavior of hydrogen flames, the parameters used in the mathematical model on propagation velocity including flame acceleration was obtained, and then the flame propagation velocity under various conditions was predicted.
Wang, Z.; Iwasawa, Yuzuru; Sugiyama, Tomoyuki
Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 12 Pages, 2020/08
states in UPd
Al
and valence crossover in the Vicinity of Heavy-Fermion superconductivityMetoki, Naoto; Haga, Yoshinori; Yamamoto, Etsuji; Matsuda, Masaaki*
Journal of the Physical Society of Japan, 87(11), p.114712_1 - 114712_9, 2018/11
Times Cited Count：3 Percentile：29(Physics, Multidisciplinary)The localized 5
states with 5 (
) configuration of U
ion have been revealed in UPdAl. We found that the low-lying states are the same as PrPdAl flat orbitals with large 
are stabilized by a two-dimensional CEF potential in the unique crystal structure. The present study involves the valence crossover from tetravalent to trivalent in a series of AnPdAl, demonstrated by lattice and/or transport anomaly as well as many body effects in the vicinity of the boundary. The valence instability plays important role for the unusual heavy fermion superconductivity in NpPdAl.
Pozdeyev, E.*; Tennant, C.*; Bisognano, J. J.*; Sawamura, Masaru; Hajima, Ryoichi; Smith, T. I.*
Nuclear Instruments and Methods in Physics Research A, 557(1), p.176 - 188, 2006/02
Times Cited Count：13 Percentile：63(Instruments & Instrumentation)no abstracts in English
Takase, Kazuyuki; Yoshida, Hiroyuki; Ose, Yasuo*; Akimoto, Hajime
Computational Fluid Dynamics 2004, p.649 - 654, 2006/00
no abstracts in English
Matsumoto, Taro; Naito, Hiroshi*; Tokuda, Shinji; Kishimoto, Yasuaki*
Nuclear Fusion, 45(11), p.1264 - 1270, 2005/11
Times Cited Count：14 Percentile：43.56(Physics, Fluids & Plasmas)A gyrokinetic particle simulation is executed to clarify the effect of the electron inertia on the MHD phenomena in the reversed shear configuration (RSC) of a cylindrical tokamak plasma. It is found that the collisionless (kinetic) double tearing modes grow up at the Alfv
n time scale, and nonlinearly induce the internal collapse when the helical flux at the magnetic axis is less than that at the outer resonant surface. After the internal collapse, the secondary reconnection is induced by the current concentration due to the 
convective flow. It is also clarified that a nonlinear dynamics accompanied with the elementary processes caused by the flow can generate a new RSC with resonant surfaces. In the presence of the density gradient, after the full reconnection induced by the mode, the radial electric field is found to be generated due to the difference of the 
motion between ions and electrons. However, the intensity of the radial field is not so large as that induced by the collisionless kink mode.
100
systemsFujieda, Shinji*; Miura, Yoshinao*; Saito, Motofumi*; Teraoka, Yuden; Yoshigoe, Akitaka
Microelectronics Reliability, 45(1), p.57 - 64, 2005/01
Times Cited Count：11 Percentile：51.31(Engineering, Electrical & Electronic)To characterize the interface defects that are responsible for the negative-bias temperature instability (NBTI) of a thin plasma-nitrided SiON/Si system, we carried out inerface trap density measurements, electron-spin resonance spectroscopy and synchrotron radiation XPS. The NBTI was shown to occur mainly through the dehydrogenation of the interfacial Si dangling bonds (P
defects). Although we suggest that non- P defects are also generated by the negative-bias temperature stress, nitrogen dangling bonds do not seem to be included. The plasma-nitridation process was confirmed to generate sub-oxides at the interface and thus increase the interface trap density. Furthermore, it was found that the nitridation induces another type of P
defect than that at pure-SiO/Si interfacec. Such an increase and structural change of the interfacial defects are likely the causes of the nitridation-enhanced NBTI.
Takase, Kazuyuki; Yoshida, Hiroyuki; Ose, Yasuo*; Tamai, Hidesada
JSME International Journal, Series B, 47(2), p.323 - 331, 2004/05
no abstracts in English
Ida, Masato; Taniguchi, Nobuyuki*
Physical Review E, 69(4), p.046701_1 - 046701_9, 2004/04
Times Cited Count：1 Percentile：5.79(Physics, Fluids & Plasmas)This paper extends our recent theoretical work concerning the feasibility of stable and accurate computation of turbulence using a large eddy simulation. In our previous paper, it was shown, based on a simple assumption regarding the instantaneous streamwise velocity, that the application of the Gaussian filter to the Navier-Stokes equations can result in the appearance of a numerically unstable term. In the present paper, based on assumptions regarding the statistically averaged velocity, we show that in several situations, the shears appearing in the statistically averaged velocity field numerically destabilize the fluctuation components because of the derivation of a numerically unstable term that represents negative diffusion in a fixed direction. This finding can explain the problematic numerical instability that has been encountered in large eddy simulations of wall-bounded flows. The present result suggests that if there is no failure in modeling, the resulting subgrid-scale model can still have unstable characteristics.
Li, J.; Kishimoto, Yasuaki
Physics of Plasmas, 11(4), p.1493 - 1510, 2004/04
Times Cited Count：59 Percentile：85.15(Physics, Fluids & Plasmas)The electron temperature gradient (ETG) driven turbulence in tokamak core plasmas is numerically investigated based on three-dimensional gyrofluid model with adiabatic ion response. Attentions are focused on the zonal flow dynamics in ETG fluctuations and the resultant electron heat transport. A high electron energy confinement mode is found in the weak magnetic shear regime, which is closely relevant with self-organization behavior of turbulence through the enhanced zonal flow dynamics rather than the weak shear stabilization of ETG fluctuations. It is demonstrated that the weak shear is favorable for the enhancement of zonal flows in ETG turbulence.
Li, J.; Kishimoto, Yasuaki; Idomura, Yasuhiro; Miyato, Naoaki; Matsumoto, Taro
Journal of Plasma and Fusion Research SERIES, Vol.6, p.585 - 588, 2004/00
An enhanced zonal flow is observed in collisionless electron temperature gradient (ETG) driven turbulence with weak magnetic shears. The Kelvin-Helmholtz (KH) instability is proposed as a primary damping mechanism of such flow. Some considerable evidences for the KH mode excitation are presented. Results seem to suggest a possibility of turbulence transition from the ETG-dominated one to the KH-dominated one due to the zonal flow dynamics in weak shear plasmas.
JT-60 Team
JAERI-Review 2003-029, 197 Pages, 2003/11
JAERI-Review-2003-029.pdf:13.06MB
no abstracts in English
Iguchi, Tadashi; Shibamoto, Yasuteru; Asaka, Hideaki; Nakamura, Hideo
Proceedings of 10th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-10), 16 Pages, 2003/10
Thermal-hydraulic and neutronic dynamics are always interrelated in BWR core. This is called thermal-hydraulic and neutronic (T/N) coupling. Channel stability experiments with T/N coupling under non-nuclear condition are very limited. This is mainly due to the difficulties in the real-time simulation of neutron dynamics and in the fast-response void fraction measurement under high-pressure and temperature conditions. Authors have developed techniques to solve the above difficulties, and have succeeded in experimentally simulating T/N coupling under non-nuclear conditions with the THYNC facility. Using THYNC facility, T/N coupling effect on channel stability was investigated. Experiments were performed under Pressure=2-7MPa, Subcooling=10-40K, and Mass flux=270-660kg/m
s. THYNC results indicated T/N coupling lowered the channel stability threshold. The reduction of channel stability threshold due to T/N coupling was small within 10% at 7MPa in the present THYNC experiment, although the experimental condition was set to be more severe than that supposed in a reactor.
Shibamoto, Yasuteru; Iguchi, Tadashi; Nakamura, Hideo; Kukita, Yutaka*
Proceedings of 11th International Conference on Nuclear Engineering (ICONE-11) (CD-ROM), 11 Pages, 2003/04
The pressure effect on the onset of flow instability in a vertical upflow through a boiling channel is studied both analytically and experimentally. The analytical model is based on the Wallis-Heasley model for linear analysis of one-dimensional homogeneous two-phase flow in thermal equilibrium. The dead-time elements commonly used to represent the time lag in the responses of variables to the inlet velocity perturbation is replaced by first-order lag elements to allow the system characteristic equation to be solved analytically. This approach, although approximate, makes it much easier to identify the main contributor to the instability because the individual components are represented by separate terms in the characteristic equation. The predictions are in reasonable agreement with the data when the system pressure effect on the irreversible pressure loss in the two-phase region is appropriately considered based on calibration experiments.
Iguchi, Tadashi; Shibamoto, Yasuteru; Asaka, Hideaki; Nakamura, Hideo
Proceedings of 11th International Conference on Nuclear Engineering (ICONE-11) (CD-ROM), 8 Pages, 2003/04
Authors investigated the cooling limit under flow instability, by conducting THYNC experiments using a 2
2 bundle test section of electrical rod heaters、whose heated lengths and diameters were 3.71m and 12.3mm. The experimental result indicated periodic rise and rapid drop of the rod temperature under flow oscillation, indicating periodic film boiling. When the heating power increased further, the rod temperature indicated continuous film boiling. The power at the onset of continuous film boiling (cooling limit) under flow oscillation was about 50%-80% of the cooling limit under steady flow condition in THYNC. The ratio of both cooling limits almost agreed with the Umekawa model prediction in cases of P2MPa and G400kg/m2s. For high pressure and high mass flux conditions, the ratio almost agreed with the empirical model based on the heat balance during one cycle of flow oscillation. TRAC-BF1 code simulated periodic film boiling qualitatively, but the cooling limit under the flow oscillation was not predicted well probably due to inaccurate rewetting prediction.
Utsumi, Takayuki*; Koga, J. K.; Kunugi, Tomoaki*
Parallel Computational Fluid Dynamics; New Frontiers and Multi-Disciplinary Applications, p.539 - 546, 2003/00
no abstracts in English
Zhu, X. D.; Naramoto, Hiroshi; Xu, Y.; Narumi, Kazumasa; Miyashita, Kiyoshi*
Physical Review B, 66(16), p.165426_1 - 165426_5, 2002/10
Times Cited Count：14 Percentile：57.54(Materials Science, Multidisciplinary)no abstracts in English
