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作者 Saelim, Nattapong
書名 Flow past a cylinder: Effect of surface modification on structure of the near-wake
國際標準書號 0496347543
book jacket
說明 259 p
附註 Source: Dissertation Abstracts International, Volume: 64-04, Section: B, page: 1880
Adviser: Donald O. Rockwell
Thesis (Ph.D.)--Lehigh University, 2003
The near-wake of a cylinder with a surface nonuniformity is addressed. A helical wire pattern about the surface of a cylinder, whereby the wire has a diameter an order of magnitude smaller than the cylinder diameter, induces substantial alterations of both the quasi-two-dimensional (sectional) and the three-dimensional wake structure. A technique of high-image-density particle image velocimetry is employed in order to characterize the instantaneous and averaged flow patterns in three orthogonal planes in the near-wake
In order to provide a basis for interpretation of the wake induced by the helical wire pattern, reference states of the wake from the plain cylinder are defined over a range of Reynolds number, based on cylinder diameter, up to 10,000
For the case of the cylinder with the helical winding, extreme cases of quasi-laminar and turbulent near-wakes from the corresponding plain (smooth) cylinder are considered. Quasi-two-dimensional (sectional) patterns of instantaneous or phase-referenced vorticity show large variations with the effective angle of incidence of the helical wire at a given spanwise location. Extreme types of patterns involve: (i) a relatively narrow wake with lack of large-scale vorticity concentrations; and (ii) a wide wake with well-defined, large-scale concentrations that are formed well downstream of the cylinder. The effective width of the near-wake can vary by as much as 50%, despite the very small diameter of the helical wire. A distinctive, additional feature at Re = 104 is the occurrence of coherent patterns of small-scale, shear layer vortices, which are evident at all values of incidence angle
Corresponding patterns of the flow structure in planes oriented along the span of the cylinder show deterministic features of three-dimensionality, which are linked to the aforementioned sectional patterns. For the quasi-laminar wake at low Reynolds number, the three-dimensional structure of the near-wake undergoes a well-defined transformation with increasing distance from the base. Space-time volumes of vorticity and velocity evolve from a predominantly in-line form to a staggered form. For the turbulent wake at higher Reynolds number, the three-dimensional patterns are less deterministic, but they show a spanwise spatial periodicity that is correlated to the helical wire pattern
School code: 0105
DDC
Host Item Dissertation Abstracts International 64-04B
主題 Engineering, Mechanical
Physics, Fluid and Plasma
0548
0759
Alt Author Lehigh University
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