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Mesoscale convective vortices (MCVs), which typically form within the stratiform rain of some mesoscale convective systems (MCSs), may persist for days, often regenerating convection daily. Long-lived MCVs can produce as much precipitation as a landfalling hurricane and lead to catastrophic flooding. The number of studies using multi-Doppler radar observations for validation of the kinematics, or three-dimensional (3-D) wind structure, of MCV genesis is limited. For this study, the Oklahoma City (KTLX) and Tulsa, Oklahoma (KINX) Weather Surveillance Radar – 1988 Doppler (WSR-88D) were used to examine the genesis of a long-lived MCV from 0000 to 0300 UTC on 11 June 2003. Traditional dual-Doppler techniques were used to determine the 3-D wind field. To relate MCV genesis within the associated larger MCS, time series of convective and stratiform precipitation, divergence, vertical vorticity, and vertical velocity were created for multiple levels within the MCS. The role of vertical vorticity generated in the convective region in MCV development was determined using vertical profiles of the terms in the vorticity tendency equation at 15 minute temporal resolution during the three hour period of investigation. The results of this study provide a detailed three hour examination for the initiation and early evolution of a long-lived MCV and can provide model validation of MCV generation.

Circular cylinders in cross-flow have been extensively studied in the last century. However, there are still many unsolved problems in this area, one of which is the flow structure around two staggered finite circular cylinders. This thesis mainly focuses on an experimental investigation of the vortex shedding characteristics of two staggered finite circular cylinders of equal diameter in cross-flow. Wind tunnel experiments were conducted to measure the vortex shedding frequency at the mid-height of the two cylinders and along the height of the two cylinders. Two identical circular cylinders of aspect ratio AR = 9 were partially immersed in a flat-plate turbulent boundary layer, where the boundary layer thickness to cylinder height ratio at the location of the cylinders was δ/H = 0.4. The Reynolds number based on the cylinder diameter was Re<i>D</i> = 2.4z_x~104. Centre-to-centre pitch ratios of <i>P/D</i> = 1.125, 1.25, 1.5, 2, 2.5, 3, 4 and 5 were examined and the incidence angle was incremented in small steps from á = 0° to 180°. For each configuration of the cylinders, the vortex shedding frequency, represented in dimensionless form as the Strouhal number, St, was measured with a single-component hot-wire anemometer. Also, a seven-hole pressure probe was used to measure the time-averaged wake velocity field behind the cylinders at selected configurations in order to get a better understanding of the wake structure.<p>The vortex shedding frequencies measured at the mid-height of the cylinders clearly showed the similarities and differences of vortex shedding between two staggered finite and infinite circular cylinders. The Strouhal number behavior of the two finite circular cylinders is generally similar to that of two infinite circular cylinders, but the values of St for the two finite cylinders were found for most cases to be smaller than the case of the infinite cylinders.<p>The measurements of vortex shedding frequency along the heights of each finite cylinder revealed that, for most incidence angles, the value of the Strouhal number remains constant along the height of the cylinder, but a notable variation in the shape and strength of the vortex shedding peak along the heights of the cylinders is observed. Sharp and strong peaks in the power spectra are measured around the mid-height of the cylinder. Broader and weaker peaks are found both at the base of the cylinder and near the free end. At several particular configurations, the vortex shedding frequency changes along the height of the cylinder, caused by the varying flow pattern in the vertical direction.<p>Wake measurements showed the velocity field behind the two finite circular cylinders arranged in tandem configurations of P/D = 1.125, 2 and 5. The experimental data revealed that the flow structure behind two finite circular cylinders arranged in a tandem configuration is much more complicated than that of the single finite circular cylinder. The downwash flow from the tip of the downstream cylinder is weaker due to the flow interaction between the free ends of two cylinders, and this downwash flow becomes stronger with increasing P/D. A similar trend happens to the vorticity of the tip vortex structures. However, the upwash flow behind the downstream cylinder is not strongly affected by the existence of the upstream cylinder.

Circular cylinders in cross-flow have been extensively studied in the last century. However, there are still many unsolved problems in this area, one of which is the flow structure around two staggered finite circular cylinders. This thesis mainly focuses on an experimental investigation of the vortex shedding characteristics of two staggered finite circular cylinders of equal diameter in cross-flow. Wind tunnel experiments were conducted to measure the vortex shedding frequency at the mid-height of the two cylinders and along the height of the two cylinders. Two identical circular cylinders of aspect ratio AR = 9 were partially immersed in a flat-plate turbulent boundary layer, where the boundary layer thickness to cylinder height ratio at the location of the cylinders was δ/H = 0.4. The Reynolds number based on the cylinder diameter was Re<i>D</i> = 2.4z_x~104. Centre-to-centre pitch ratios of <i>P/D</i> = 1.125, 1.25, 1.5, 2, 2.5, 3, 4 and 5 were examined and the incidence angle was incremented in small steps from á = 0° to 180°. For each configuration of the cylinders, the vortex shedding frequency, represented in dimensionless form as the Strouhal number, St, was measured with a single-component hot-wire anemometer. Also, a seven-hole pressure probe was used to measure the time-averaged wake velocity field behind the cylinders at selected configurations in order to get a better understanding of the wake structure.<p>The vortex shedding frequencies measured at the mid-height of the cylinders clearly showed the similarities and differences of vortex shedding between two staggered finite and infinite circular cylinders. The Strouhal number behavior of the two finite circular cylinders is generally similar to that of two infinite circular cylinders, but the values of St for the two finite cylinders were found for most cases to be smaller than the case of the infinite cylinders.<p>The measurements of vortex shedding frequency along the heights of each finite cylinder revealed that, for most incidence angles, the value of the Strouhal number remains constant along the height of the cylinder, but a notable variation in the shape and strength of the vortex shedding peak along the heights of the cylinders is observed. Sharp and strong peaks in the power spectra are measured around the mid-height of the cylinder. Broader and weaker peaks are found both at the base of the cylinder and near the free end. At several particular configurations, the vortex shedding frequency changes along the height of the cylinder, caused by the varying flow pattern in the vertical direction.<p>Wake measurements showed the velocity field behind the two finite circular cylinders arranged in tandem configurations of P/D = 1.125, 2 and 5. The experimental data revealed that the flow structure behind two finite circular cylinders arranged in a tandem configuration is much more complicated than that of the single finite circular cylinder. The downwash flow from the tip of the downstream cylinder is weaker due to the flow interaction between the free ends of two cylinders, and this downwash flow becomes stronger with increasing P/D. A similar trend happens to the vorticity of the tip vortex structures. However, the upwash flow behind the downstream cylinder is not strongly affected by the existence of the upstream cylinder.

Mesoscale convective vortices (MCVs), which typically form within the stratiform rain of some mesoscale convective systems (MCSs), may persist for days, often regenerating convection daily. Long-lived MCVs can produce as much precipitation as a landfalling hurricane and lead to catastrophic flooding. The number of studies using multi-Doppler radar observations for validation of the kinematics, or three-dimensional (3-D) wind structure, of MCV genesis is limited. For this study, the Oklahoma City (KTLX) and Tulsa, Oklahoma (KINX) Weather Surveillance Radar – 1988 Doppler (WSR-88D) were used to examine the genesis of a long-lived MCV from 0000 to 0300 UTC on 11 June 2003. Traditional dual-Doppler techniques were used to determine the 3-D wind field. To relate MCV genesis within the associated larger MCS, time series of convective and stratiform precipitation, divergence, vertical vorticity, and vertical velocity were created for multiple levels within the MCS. The role of vertical vorticity generated in the convective region in MCV development was determined using vertical profiles of the terms in the vorticity tendency equation at 15 minute temporal resolution during the three hour period of investigation. The results of this study provide a detailed three hour examination for the initiation and early evolution of a long-lived MCV and can provide model validation of MCV generation.

This dissertation presents the turbulence of multiphase plumes and tidal vortices by studying and quantifying coherent structures that affect the dynamics of the flow. The measurements presented in this dissertation were taken using particle image velocimetry (PIV). After preprocessing the images and conducting the PIV analysis to get the final velocity fields, the local swirl strength was used to identify coherent structures (vortices) in the flow. This dissertation used the identified vortices to quantify the turbulent properties of the flows. The mean and turbulent properties of bubble plumes are found to be self-similar within the measured air flow rates when appropriately nondimensionalized. The timeaveraged velocity profile was shown to have a Gaussian distribution when nondimensionalized by the centerline velocity and plume radius. The bubble plumes were found to have the most energetic vortices along the plume edge and a modulated turbulent energy spectrum with a slope in the inertial subrange from -7/6 instead of the classical -5/3. The mean and turbulent properties of an inertial particle plume are presented, revealing the time-averaged velocity and vorticity profiles to be self-similar for all cases when nondimesionalized by the centerline velocity and plume radius. The average vortex properties were not self-similar for all flow cases with the largest two particles sizes being self-similar and the smallest particle vortex properties being similar to bubble plume data. Despite the difference in vortex properties, the turbulent energy spectra in inertial particle plumes followed the same modulation as the bubble plumes. PIV experiments from the tidal starting-jet vortices detail the influence of a finite channel length using identified vortice. The results show the trajectory and development of the tidal starting-jet vortices to be changed by a region of vorticity that develops inside the channel and is expelled as a vortex during the ebb tide. This expelled lateral boundary layer vortex is shown to move the starting-jet vortex away from the tidal jet shear layer thus reducing the input vorticity. When the expelled boundary layer vortex strength is 1/5 the starting-jet vortex the system dynamics change resulting in a deviation in the starting-jet vortices' trajectory. This dissertation successfully uses the local swirl strength to quantify the turbulence of multiphase plumes and tidal starting-jet vortices. Using these results, engineers will be able to better predict the efficiency of CO2 ocean sequestration and tidal flushing. Furthermore, the techniques of quantifying coherent structures developed in this dissertation can be applied to a multitude of turbulent flows.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 109-120).

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 92-96).

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 185-191).