| Autor: |
Thiriet, M., Graham, J. M. R., Issa, R. I., Thiriet, M., Graham, J. M. R., Issa, R. I. |
| Zdroj: |
Journal de Physique III; January 1993, Vol. 3 Issue: 1 p85-103, 19p |
| Abstrakt: |
A finite-volume model of steady flow of an incompressible viscous fluid has been carried out in a smooth rigid 90° bend of circular cross-section. The inlet boundary conditions for laminar flow are either an entry Poiseuille regime or a constant injection velocity for a range of Dean number 140 ≤ De ≤430. A numerical test of turbulent flow was performed for De ∼22100 with a flat velocity profile at the model entry. The lower the role played by the viscous forces, the larger the distance necessary to set an outer shift of the peak axial velocity. The axial velocity of laminar flow depends not only on the value of the Dean number, but also on separate effects of the Reynolds number and of the tube curvature. The larger the laminar boundary layer at the bend inlet, the nearer from the entry the bend segment where the strongest secondary motion is located. With increasing Reynolds number, the secondary flow develops over a longer bend region and the wall shear rises. Upstream and downstream effect of the bend on the shear stress, as well as flow disturbances induced by very small curvature, were observed. The residence time of conveyed particles is enhanced by the presence of a curved section in the conduit with respect to a straight pipe only at the inner edge of the straight section located downstream from the bend. When the Reynolds number rises, the flow regime remaining laminar, the residence time is smaller in the whole pipe. However for turbulent flow, the residence time, which has much smaller values, takes its highest values in the exit straight section. |
| Databáze: |
Supplemental Index |
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