Yasutaka Hayamizu

Visualization of the flow in a helical pipe

The secondary flow structure in a helical pipe with large torsion is investigated by using a numerical calculation of a fluid particle trajectory and an experiment using a smoke visualization technique. Good agreement is obtained between the experiment and the numerical calculation. The secondary flow in a cross-section is transformed from a two counter-rotating vortices structure to a one-recirculation structure with increase of the torsion of the pipe at a constant Dean number. The line dividing two vortices varies its direction from horizontal to vertical as the torsion increases.

Chaotic Mixing in a Curved-Square Duct Flow at Very Low Reynolds Numbers

Chaotic mixing in a curved-square duct flow is studied experimentally and numerically. Two walls of the channel (inner and top walls) rotate around the center of curvature and a pressure gradient i...

Effect of Torsion on the Friction Factor of Helical Pipe Flow

Three-dimensional direct numerical simulations of a viscous incompressible fluid flow through a helical pipe with a circular cross section were conducted for three Reynolds numbers, Re (= 80, 300, and 1000), and two nondimensional curvatures, δ (= 0.1 and 0.05), over a wide range of torsion parameters, β (= nondimensional torsion/\(\sqrt{2\delta } \)), from 0.02 to 2.8. Well-developed axially invariant regions were obtained where the friction factors were calculated, in good agreement with the experimental data obtained by Yamamoto et al. [Fluid Dyn. Res. 16, 237 (1995)]. It was found that the friction factor sharply increases as β increases from zero, then decreases after taking a maximum, and finally slowly approaches that of a straight pipe when β tends to infinity. It is interesting that a peak of the friction factor exists in the region 0.2 ≤ β ≤ 0.3 for all the Reynolds numbers and curvatures studied in the present paper, which manifests the importance of the torsion parameter in helical pipe flow.

The Estimation of the Mechanical Property of the Porous Material by Numerical Analysis

Porous materials, such as filters made of sintered metals, lagging materials, and fireproof materials, are utilized in various fields. The porosity changes the characteristics of the materials. For example, with heat-insulating foam, the higher the porosity, the greater is the insulation factor. However, increased porosity leads to a decline in mechanical properties. Thus, when using porous materials, analyzing the mechanical strength is necessary. We modeled a porous structure of sintered metal sample and estimated the Youngs modulus using the numerical analysis software “ADVENTURE” and compared the estimated value with the experimental value. Also, we modeled the effect of porosity and pore diameter on the mechanical property of the material. From the results, the Youngs modulus decreases with increases in porosity and pore diameter, as expected.