Experimental study of a horizontal round tube jet in a vertical crossflow at different momentum flux ratios
| Autor: | Sheng-shiang Yang, 楊盛翔 |
|---|---|
| Rok vydání: | 2011 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 99 The purpose of this research is to study the flow field structure at different momentum flux ratios of a horizontal cylindrical tube jet into a vertical crossflow, R. Experimental observations include a vertical crossflow passing around a horizontal cylindrical tube (R = 0), interaction between a horizontal cylindrical tube jet and vertical crossflow (R = 0.16 ∼ 48) and a horizontal cylindrical tube jet in a stationary flow (R = ∞) by using flow visualization and Particle Image Velocimeter (P.I.V) techniques. Crossflow is generated by a vertical water tunnel with ReD = 250 ∼ 1080, based on the char- acteristic length of the exterior diameter of a cylindrical tube. The round jet has a range of Rej = 250 ∼ 2580, based on the character- istic length of the interior diameter. Experimental observations on crossflow passing around a cylindrical tube includes transverse sections of X/D = -1.5, -2.5, -7.5. At X/D = -1.5, there is a confined region of a reverse vortex pairs at the lee- side of the cylindrical tube. Except for the confined region, stream- lines and pathlines of the flow field are shown straight downward. At X/D = -2.5, the confined region is affected by varied strength of downwash crossflow and vortices are generated irregularly. Beneath the covered region streamlines show S-shaped to swing. At X/D = -7.5, eddy traveling frequency are generated periodically. Higher ReD induces higher eddy traveling frequency. Experimental observations on interaction between a horizontal cylindrical tube jet flow and vertical crossflow at different momentum flux ratios include a vertical longitudinal (Z/D = 0) and several trans- verse sections. The vertical longitudinal section of the flow field is located at Z/D = 0. The curvature of jet trajectory gradually de- creases the higher R. R = 2.1 seems to be a transition value of crossflow domination and two momentum flows interaction. When 2.1 < R < 37, the bifurcation lines induce concave at the lee-side of the jet. When R > 37, the bifurcation lines become a convergent point. Transverse sections of flow field at the lee-side of cylindrical tube can be divided into four groups. When R = 0.16 at X/D = -3.5, the vortices in the confined region become irregular because of downwash crossflow of various strength. When R = 2.1 at X/D = -3.5, eddy traveling frequency is generated periodically and eddy traveling cycle of non-dimensional time interval is Δt∗ = 4.36. When R = 8.5 at X/D = -0.5, because of strong downwash crossflow and close to cylindrical tube, the confined region becomes smaller and vortices generation are suppressed. When R = 26 at X/D = 0, be- cause crossflow passes a jet and mixes with the jet fluid, a pair of counter rotation vortices are generated at the same time. When R = 48 at X/D = 4.5, the confined region has not generated. Beneath the jet streamlines show S-shaped to swing. Experimental observations on a horizontal cylindrical tube jet in a stationary flow include a vertical longitudinal section(Z/d = 0) for Rej = 350, 550, 730, 900. At Rej = 350, the environmental fluid close to the shear layer is slightly driven and vortices appear near the shear layer. As Rej increases, environmental fluid is driven more significantly. By P.I.V. calculation of velocity distribution in a jet at X/d = 2, 4, 8, 12, the axial velocity shows consistent parabolic distribution and the center maximum velocity decreases gradually when the jet moves downstream. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|