Dunn, Warren R2013-11-082013-11-0820042004Source: Dissertation Abstracts International, Volume: 66-05, Section: B, page: 2781.http://hdl.handle.net/10393/29103http://dx.doi.org/10.20381/ruor-12771Cylinders with a single step-change in diameter, symmetric double step-changes, and a free end were studied at Reynolds numbers between 40 and 1250, in uniform and shear flows. The diameter ratio of the step-cylinders was 0.51. Streamwise velocity measurements were taken with laser Doppler velocimetry, and observations were made using flow visualization. Spectral analysis showed that step-changes in diameter caused vortex shedding to occur in cells of constant frequency, with a change in frequency across the cell boundaries. In uniform flow, vortices behind the large cylinder near the step were shed in a cell with a lower frequency compared to the rest of the cylinder, while, in shear flow, cellular shedding was observed behind both the large and small cylinders. Flow visualization showed that the ends of vortices shed in-phase from two adjacent cells in the step region connected across the cell boundary, while those shed out-of-phase looped 180° and joined with vortices shed from the opposite side of the cylinder, in the same cell. Wavelet analysis of velocity signals showed that the two dominant shedding frequencies at the step could be detected in the signal either simultaneously, in which case the signal had a modulated appearance, or alternating, in which case the signal had a quasi-periodic appearance, whose frequency changed with time. The vortices shed from both cylinders were inclined with respect to the cylinder axes. Spanwise convection of the wakes occurred near the step, in the direction of the large cylinder, caused by flow over the step normal to the cylinder axis. Streamwise vortices were released from the sharp edges of the step, which aided in the formation of vortex loops. Most of the vortex shedding patterns behind the double-step cylinders and the cylinders with free ends were similar to those observed in the single-step case. In addition, the flow around each of the steps of the double-step cylinder influenced the other, an effect that increased as the step separation decreased. The increased flow over the tip of a finite cylinder, as compared to the step-cylinders, resulted in highly-inclined, cusp-like connections between the streamwise and shed vortices.231 p.enEngineering, Mechanical.Thesis