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551 results on '"Rinoshika A"'

15. Analysis of coherent structures over interacting barchan dunes based on tomographic particle image velocimetry.

Author

Han, Xiaolei, Rinoshika, Hiroka, Zhou, Yuyang, Li, Jiawei, and Rinoshika, Akira

Abstract

The influence of barchan dune interaction upon unsteady flow separation and wake dynamics around the fixed-bed downstream barchan dune (DBD) model are experimentally investigated at a Reynolds number of 2640 based on the tomographic particle image velocimetry (PIV) system. The time-averaged statistics including the mean velocities, recirculation area, vortex spatial topology, Reynolds stress, and turbulent kinetic energy were used to characterize the flow field and large-scale anisotropy. It was found that arch-shaped vortex "chains" with strong spanwise coherence shedding from isolated barchan crestline populate the whole wake region, while elongated rod-shaped vortex structures with strong streamwise coherence induced by the up-downwash flow around the DBD were found to fill the whole measurement range, which is closely related to "sheltering" effect on the incoming flow acting at DBD due to the presence of upstream barchan dune (UBD). Additionally, in order to study the complex dynamic features of these predominated vortex structure transformations, time-resolved planar particle image velocimetry was applied. This technique allows for providing complementary insights into the temporal behavior of the unsteady coherent flow structures populating the wake field in different experimental configurations. It was found that the basic unsteady flapping motion, vortex roll-up, and complex vortex interactions including vortex pairing, merging, and breaking up can all be analyzed by dividing into certain scales with ease in a combination wavelet and Lagrangian framework. [ABSTRACT FROM AUTHOR]

Published
2024
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24. Application of multi-dimensional wavelet transform to fluid mechanics

Author

Akira Rinoshika and Hiroka Rinoshika

Subjects
Engineering (General). Civil engineering (General), TA1-2040
Abstract

ABSTRACT: This paper first reviews the application research works of wavelet transform on the fluid mechanics. Then the theories of continuous wavelet transform and multi-dimensional orthogonal (discrete) wavelet transform, including wavelet multiresolution analysis, are introduced. At last the applications of wavelet transform on 2D and 3D turbulent wakes and turbulent boundary layer flows are described based on the hot-wire, 2D particle image velocimetry (PIV) and 3D tomographic PIV. Keywords: Continuous wavelet transform, Fluid mechanics, Multi-scale flow structures, Orthogonal wavelet transform, Turbulence, Wavelet multiresolution analysis

Published
2020
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43. Particle image velocimetry measurements of the flow structures induced by the free-falling spin flight of maple seeds

Author

Lin Dong, Guoan Wen, and Akira Rinoshika

Subjects
Instrumentation
Abstract

Most measurements of flow field caused by a rotating maple seed were performed in a vertical wind tunnel limited to fixing the vertical axis to simulate the stable falling spin period. In the nature, however, the free-falling motion of maple seeds induces airflow, which makes the seeds spin and generates lift to reduce falling speed. In this study, the flow structures around free-falling Japanese maple seeds in spin are measured using particle image velocimetry. In general, the free-falling spin flight of a seed is divided into three stages: transition period I, transition period II, and the stable period. In transition period II, it can be observed that the sizes of wingtip and root vortices increase with decreasing coning angle of the seed wing and result in an increase in seed rotation speed and decrease in free-falling speed. We also find that the flow structures induced by the free-falling motion of the maple seed in the stable period are different from those that suspend the rotation seed in a vertical wind tunnel. The leading-edge vortex (LEV) and trailing-edge vortex (TEV) are observed above the front of the leading edge and at the top back of the trailing edge, respectively. The position of the LEV core is located above the front of the leading edge, and it gradually approaches the leading edge of the seed along the spanwise direction, toward the wing tip. As the seed enters the stable period, the root vortex shrinks, and the tip vortex grows.

Published
2022

47. Three-Dimensional Flow Structures Behind a Wall-Mounted Short Cylinder with a Rear Inclined Hole

Author

Akira Rinoshika, Masato Akamatsu, Yan Zheng, and Hiroka Rinoshika

Subjects
Particle image velocimetry, Turbulence, Turbulence kinetic energy, Flow (psychology), Shear stress, Aerospace Engineering, Cylinder, Geometry, Boundary layer thickness, Stagnation point, Geology
Abstract

Three-dimensional (3-D) flow structures around a wall-mounted short circular cylinder, into which was drilled a rear inclined hole (RIH) going from the rear surface to the top surface of the cylind...

Published
2021

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