2002 Fiscal Year Final Research Report Summary
Elucidation and Modeling of Particle Interactions in Dispersed Two-Phase Turbulence
| Project/Area Number |
11450073
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Fluid engineering
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| Research Institution | Yokohama National University |
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Principal Investigator |
NISHINO Koichi Yokohama National University, Faculty of Engineering, Associate Professor, 大学院・工学研究院, 助教授 (90192690)
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| Co-Investigator(Kenkyū-buntansha) |
TORII Kohoru Yokohama National University, Faculty of Engineering, Professor, 大学院・工学研究院, 教授 (00017998)
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| Project Period (FY) |
1999 – 2002
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| Keywords | Multi-Phase Flow / Dispersed Two-Phase Flow / Turbulent Flow / Grid Turbulence / Particle / Interaction / PIV / Flow Visualization |
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| Research Abstract |
Turbulence modification by solid particles in grid turlbulence of water is examined experimentally. Glass particles, 2450kg/m^3 in density, are suspended in an upwarl turbulent flow behind a grid with M=12mm. Two particle diameters, d_p=1.00mm and 1.25mm, are examined. The flow velocity is adjusted so that the particles stay quasi-stationary in the test section by the force balance between gravity and drag exerting on the particles. The resultant Reynolds numbers based on Mand d_p are respectively 1660 and 140 for d_p=1.00mm and 2000 and 210 for d_p=1.25mm. Kolmogorov length scales in single-phase flows are 0.43mm Re_M=1740) and 0.40mm Re_M=2000). PIV measurements of turbulence are carried out by using fluorescent tracer particles 26mm in diameter to avoid the effect of strong light scattering by the glass particles. It is found that the turbulence in the streamwise direction increases remarkably and selectively with C, the volumetric concentration of glass particles, in the range of C
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<0.50%. This increase is associated with the occurrence of columnar particle accumulation (CPA) into a region elongated in the streamwise direction. CPA alters significantly the longitudinal two-point velocity correlation, R_uu (Δx) , and vorticity correlation, R_<ω_z><ω_z> (Δx) , while it affects little the transverse two-point velocity correlation, R_vv(Δx), where Δx is the streamwise separation between the two points.
Flow visualization is performed to find out particle structures responsible for generation of CPA. It is found that particles tend to accumulate in region being elongated in the streamwise direction at particle volume fraction larger than 0.05%. Probability density functions indicate that the probability for two particles being aligned in the streamwise direction is significantly larger than that in transverse direction. Three-dimensional measurements of particle behaviors made at a condition of low particle volume fraction have revealed a notable interaction between two particles. In the interaction, (1) the downstream particle starts to approach the upstream particle, (2) they suddenly exchange their position whey they come very close to each other, and (3) the downstream particle stays at that position while the upstream particle starts to leave downstream at a relatively high velocity. Less
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Research Products
(16 results)
