著者

吉川 穣 西尾 悠 伊澤 精一郎 福西 祐

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

pp.17-00478, (Released:2017-12-20)

参考文献数

15

被引用文献数

2

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Numerical simulations are carried out aimed at finding a key flow structure which leads to a laminar-turbulent transition of a boundary layer with streaky structures. In the preliminary computation, an array of cuboids is used to form streaky structures inside a boundary layer. Then, a disturbance is introduced into the boundary layer by ejecting a short-duration jet from a hole in the wall into a low-speed region in the streaky structures. Although the boundary layer returns to a laminar state when the jet velocity is set to 18% of the uniform flow velocity, it eventually turns into a turbulent state downstream in the 20% case. The differences are investigated in detail in terms of the vortical structures. As a result, only in the stronger jet case, a flat spanwise vortex is generated beside one leg of a hairpin vortex and it merges with the streamwise vortex nearby forming an inclined streamwise vortex. On the other hand, the flat spanwise vortex disappears without being connected to the streamwise vortex in the weaker jet case. The inclined streamwise vortex is stretched by the mean velocity gradient of the boundary layer growing into a strong vortex, and new vortex structures are generated around the inclined one, which leads to turbulence. Therefore, the results suggest that formation of the inclined vortex is the key to transition of the boundary layer.

著者

黒田 将史 岡地 範明 伊澤 精一郎 福西 祐

出版者

一般社団法人日本機械学会

雑誌

講演論文集

巻号頁・発行日

vol.2002, no.37, pp.50-51, 2002-03-16

著者

多田 修平 佐竹 正俊 茂田 正哉 伊澤 精一郎 福西 祐

出版者

一般社団法人 日本機械学会

雑誌

年次大会

巻号頁・発行日

vol.2011, pp._G050093-1-_G050093-5, 2011

被引用文献数

1

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Water splash caused by an elastic tire rolling on a wet road is simulated using SPH method. Fluid-structure inter action model is newly proposed to couple the fluid motion and the elastic tire. The result shows that the water discharge capability strongly depends on the grooved patterns, and the tire receives lift and drag forces from the water.

著者

多田 修平 茂田 正哉 伊澤 精一郎 福西 祐

出版者

一般社団法人 日本機械学会

雑誌

東北支部総会・講演会 講演論文集

巻号頁・発行日

vol.2010, pp.206-207, 2010

著者

寺島 修 伊澤 精一郎 稲澤 歩 福西 祐

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.77, no.773, pp.56-65, 2011 (Released:2011-01-25)

参考文献数

19

被引用文献数

4 2

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The streamwise interface of an isolated turbulent region in a laminar flat plate boundary layer is investigated by performing a wind tunnel experiment. In the experiment, bimorph-type piezoceramic actuators are used to generate a trapezoidal-shaped turbulent region that has a wide interface in the spanwise direction. With the use of the piezoceramic actuators, the interference of the spanwise interface with the streamwise interface of the turbulent region is eliminated. Therefore, the streamwise interface can be considered as an independent interface. The experimental results show that the rms value of the velocity fluctuation and the turbulent fluctuation rapidly changes at the leading edge of the turbulent region. On the other hand, the rms value of the velocity fluctuation remains high after the turbulent fluctuation disappears at the trailing edge of the turbulent region. It is also shown that the traveling speed of the trailing edge of the turbulent region is faster than the ensemble-averaged streamwise velocity at the trailing edge of the turbulent region near the wall (η≤1.3). In addition, the velocity profile at the trailing edge of the turbulent region indicates the existence of the acceleration of the turbulent fluid near the wall. From the above results, it is found that the inverse transition occurs at the trailing edge of the turbulent region near the wall due to the acceleration of the turbulent fluid.

著者

伊澤 精一郎 磯 拓朗 西尾 悠 福西 祐

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.84, no.862, pp.18-00132, 2018 (Released:2018-06-25)

参考文献数

23

被引用文献数

1

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Behaviors of liquid films scattering from a disk-type or cup-type rotary atomizer are studied using computations based on the three-dimensional Smoothed Particle Hydrodynamics (SPH) method. To reduce computational costs while maintaining a high spatial resolution, the computational domain is limited to a fan-shaped region near the edge of the atomizers using a periodic boundary condition in the circumferential direction. Steady inflow is considered as the inlet condition. In both disk- and cup-type cases, the liquid film leaving the atomizer edge becomes wavy in the circumferential direction and forms elongated ligaments, which break up into droplets. When the atomizer is equipped with grooves on its outer edge, the process of ligament formation and droplet break up is strongly affected by the number and shape of the grooves, particularly for the cup-type atomizer, in which the centrifugal force works more effectively. Two ligament formation patterns are observed: one ligament from each groove and a pairing of ligaments from two neighboring grooves. Droplets of uniform sizes are likely to be generated when the former pattern appears. The results suggest that droplets of uniform sizes can be obtained by choosing the appropriate shape and number of grooves.