-
Yoshiaki UEDA, Teruhiko KIDA, Manabu IGUCHI
Article type: Article
Session ID: 1758
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
Numerical simulation of the collision of two vortex rings is a classic problem. The vortex reconnection or/and the merging phenomena of the vortex rings has been often simulated by the spectral method or LES modeling, etc. In the aspect of the discrete vortex method, it seems to be much difficult in this flow to satisfy the necessary conditions in which the Navier-Stokes equations have a strong solution when the vorticity vector is satisfied with sinβ(x, x', t) ⩽ |x - x'|/ρ (see Constantin, SIAM Review, 36, 1994). In the previous paper, the clear vortex reconnection did not occur in the numerical results which was simulated by the dynamic Smagorinsky model proposed by Cottet et al. (see M2AN, 37, 2003, 187-207). In this paper, we investigate the filtering model in which each cutoff radius is locally increased by taking account of the necessary condition of Constantin.
View full abstract
-
Wataru FUKUSAWA, Norimasa MIYAGI, Motoaki KIMURA, Hajime FUJITA, Hideo ...
Article type: Article
Session ID: 1759
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
In order to control the vortex structure within a turbulent boundary layer, the small vortex generating jet was applied. The visualization and analysis of a generating vortex in each jet conditions by the laser light sheet method using YAG laser were performed. Moreover, comparison with the speed distribution measured using the hot wire flow velocity meter performed before was carried out. It turns out that the vortex by which the time of jet angle α=45° was stabilized most is generated from this result.
View full abstract
-
Fujio AKAGI, Sumio YAMAGUCHI, Youichi ANDO
Article type: Article
Session ID: 1760
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
The method for measuring the circulation of vortex ring induced by pulsatile jet flow in a stenosed pipe is studied using Hierarchical Recursive PIV. In this method, relative velocity vectors are initially estimated by deducting a propagation velocity of vortex ring from phase mean velocity vectors. A propagation velocity of vortex ring is regarded to be equal to a propagation velocity of vorticity peak point. Because the vorticity profile in vortex region is similar to the laminar vortex ring with the Gaussian vorticity profile and with peak vorticity at the center of vortex. In deciding the vortex core region inside the vortex region defined by closing streamline, the threshold level of vorticity defined at the maximum point of circumference velocity around the vortex center. The vortex core region, similar to the forced vortex flow in the Rankine-Vortex, is defined as the region where the vorticity is higher than the threshold level. The circulation of vortex ring is estimated by the integrated vorticity in the vortex core region.
View full abstract
-
Nobuhiko TANAKA, Yasuhiko SAKAI, Mutsumi YAMAMOTO
Article type: Article
Session ID: 1761
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
To investigate the coherent structure in a turbulent plane jet. it is important to estimate the convective velocity of the coherent structure. In this study, the simultaneous measurement at 2 points by the X-type hot wire probe has been performed, and the new method was suggested to estimate the convective velocity more accurately by using the power spectrum and the spatial correlation of the lateral velocity fluctuation v. It is found that the convective velocity for the turbulent plane jet of this study is 0.676 times of the mean velocity of the jet centerline.
View full abstract
-
Taketo YAMADA, Yoshiaki UEDA, Hiroyuki TAKAHIRA, Manabu IGUCHI, Teruhi ...
Article type: Article
Session ID: 1762
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
When a three-dimensional flow is simulated with vortex methods, the break-down of the vorticity occurs many times, in particular, in the case of the flow field with the velocity discontinuity. The purpose of this paper is to study the mechanism of the break-down of the vorticity in the vortex method. The present paper deals with the flow field in which the ring vortex with core is issued at each time step. This flow is similar to the ring jet, so that the flow changes from laminar flow to turbulent flow. In the present paper, the flow with initial disturbance is simulated with the discrete vortex method in which the PSE (Particle Strength Exchange) method is used for the viscous diffusion. Numerical results show that the flow is almost similar to the free jet and the break-down of the vorticity field occurs when the core radius is small.
View full abstract
-
Masahiro IWANAGA, Kazuya HARADA, Yoshiki KIRIU
Article type: Article
Session ID: 1763
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
It was investigated how flow-phenomena usually observed changed with the Coriolis force. At first we constructed a turntable, on which we studied two types of basic flows, that is, flow around a circular cylinder and a vortex flow in a cylindrical container. In the case of the flow around a circular cylinder perpendicular to the rotating axis, we found that there was the critical Rossby number, under which no Karman vortex could exist. Above the critical Rosbby number, Karman vortex could exist but the axis of vortexes were found inclined relative to the axis of cylinder, which was also explained with the effects of Coriolis force. In the case of vortex flow in a cylindrical container perpendicular to the rotating axis, we found also that there was the critical Rossby number, under which the vortex could not exist. Above the critical Rosbby number, the vortex could exist but the axis of vortex was found inclined relative to the axis of cylinder.
View full abstract
-
Fumihito OHYA, Kazuie NISHIWAKI
Article type: Article
Session ID: 1764
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
The scalar and velocity scale distributions were measured using laser light scattering image in steady round jet and steady impinging jet which were issued through a straight pipe nozzle at several Reynolds numbers. Numerical simulations were also carried out with two-equation turbulence model and the results were compared with measurements. Discussions were made on model constants for integral length scales.
View full abstract
-
Yoshihiro TANAKA, Koji MORINISHI, Kenichi MATSUNO
Article type: Article
Session ID: 1765
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
The purpose of this study is to propose the numerical simulation method of computational fluid dynamics in order to solve the unsteady state undergoing elastic deformation of interforcial object. This study employs GCL (Geometric Conservation Low) method because metrics and Jacobians should be evaluated in the finite volume method to satisfy the conservation in the discretized form of Navier-Stokes equations. And to solve the elastic deformation the finite element method is used. So this problem is solved the fluid-structure weak interaction analysis using both FDM and FEM.
View full abstract
-
Kunihiro YANAGIDA, Hiroyuki SHIRAISHI
Article type: Article
Session ID: 1766
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
The unsteady flow oscillation caused by nozzle-edge interaction is analyzed by the discrete vortex method which has been used for an incompressible and moderately high Reynolds number flows as a simple numerical simulation method. Though some instability was caused by the original method because of the oscillation flow, the approaches using a sub-element method and a second-order time-marching are suitable in this case. Calculation results show that the wall at the nozzle exit performs an important role in the nozzle-edge interaction.
View full abstract
-
Kazuhiko HAMADA, Reima IWATSU
Article type: Article
Session ID: 1767
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
Numerical study was performed for flows driven by oscillating bottom wall in two-dimensional square cavity. The unsteady flows are studied for representative values of Reynolds number Re and Froude number Fr with the frequency parameter varied in the range of 0.1 ⪇ ω' (= ωL/U) ⪇ 10.0. It is observed that for high frequency values, i. e. √<(2ν/ω)> / H << 1, the lid-oscillation does not penetrate much into the cavity and top surface naintains flat linear shape. For moderate to low frequency values, i.e. √<(2ν/ω)> / H ⪈ 1, depending on the values of Fr, free-surface motion is stimulated at a particular values of ω'= O (Fr^<-1>).
View full abstract
-
Akira Rokugou, Toshihiro Ueda, Atsushi Okajima
Article type: Article
Session ID: 1768
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
Numerical simulation of a flow around a circular or square cylinder with finite span-length is carried out at Reynolds number of 1000 by using finite difference method. We have investigated three-dimensional flow structures for cylinders with aspect ratios of 5 and 8. The numerical result shows the time history of the coefficients of drag, lift and side forces. The flow pattern of the cylinder with aspect ratio of 5 is influenced by downwash more than that of aspect ratio 8. We confirm that the change of fluid forces closely relates to that of the flow pattern and the difference between fluid-dynamic force of a circular cylinder and a square cylinder.
View full abstract
-
Masayoshi OKAMOTO, Nobuyuki SHIMA
Article type: Article
Session ID: 1769
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
Turbulent concentric annular pipe flows with thin inner rods were investigated by means of the direct numerical simulation (DNS). In the inner region, the mean velocity shifts downward from the logarithmic law and the Reynolds stresses decrease monotonously as the radius ratio decreases. We found that the skewness, flatness, two-point correlation and instantaneous field for very small radius ratios are much different from those for large radius ratios.
View full abstract
-
Toshiya KIMURA, Mitsuru SHIMAGAKI, Yoshiki YOSHIDA
Article type: Article
Session ID: 1770
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
CFD simulations were applied to cavitating flow around a turbopump inducer. Unsteady simulations were performed for the full 3D model of an inducer, changing cavitation coefficients in the range between 0.02 and 0.07. The calculated results were compared with those of experiments conducted at the cavitation tunnel at JAXA-KSPL. The break-down of the suction performance as decrease of a cavitation coefficient was reasonably reproduced, and the simulation clearly showed the growth of the cavity for lower cavitation number and unsteady change of cavity structure appeared on inducer blades.
View full abstract
-
Article type: Appendix
Pages
App4-
Published: September 04, 2004
Released on J-STAGE: August 01, 2017
CONFERENCE PROCEEDINGS
RESTRICTED ACCESS
