When a liquid drains through a hole in a container, a vortex may form between the surface and the drainage hole. An interesting phenomenon occurs in the presence of two drainage holes. Only one vortex forms, while the other hole will mostly drain as sink flow. In addition, the vortex can switch between one hole and the other with regular periodicity. The primary goal of this study is to measure this periodicity under varying conditions (height of water in the container, diameter of the drainage holes, and distance between drainage holes). Additionally, a study concerning the volume flow rates of vortical vs. sink flow out of the drainage holes was conducted. In the case of two drainage holes, when the height of the water was decreased in the container, the diameter of drainage holes decreased, or the distance between drainage holes was increased, the switching period was shown to decrease. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

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Although complex, inconsistent and fickle, the time-averaged flow over a stationary slender forebody is generally well-understood. However, the nature of unsteady, time-varying flows over slender forebodies - whether due to the natural unsteadiness or forced maneuvering - is not well-understood. This body of work documents three experimental investigations into the unsteadiness of the flow over a 3.5 caliber tangent-ogive cylinder at high angles of incidence. The goal of the investigations is to characterize the natural and forced flow unsteadiness, using a variety of experimental tools. In the first investigation, flow data are collected over a stationary model in a water tunnel. Particle-Image Velocimetry (PIV) is employed to acquire time-dependent planes of velocity data with the model at several angles of attack. It is discovered that the asymmetric flow associated with the tangent-ogive forebody exhibits a large degree of unsteadiness, especially for data planes located far from the forebody tip. Vortex shedding of the type exhibited by a circular cylinder in crossflow is observed, but this shedding is skewed by the presence of the tip, the shedding process does not require equal periods of time from each side of the body, and this results in a time-averaged flowfield that is asymmetric, as expected. The rms values of the time-averaged velocity, as well as the turbulent kinetic energy and axial vorticity are calculated. In the second investigation, surface pressure data are acquired from several circumferential rings of pressure ports located on two models undergoing ramp coning motions in two different wind tunnel facilities. The surface pressure data are integrated to determine the sectional yaw forces. Coning motions were performed at several different reduced frequencies, and pneumatic control actuation from the nose was employed. The chosen control actuation method used a small mass flow rate ejected very close to the forebody tip, so as to leverage the inherent convective instability. The data resulting from these tests were analyzed in order to determine how the coning motions affect the distribution of surface pressure and yaw forces, how quickly the flow reacts to the motion, and the extent of control authority of the pneumatic actuation. It was discovered that the yaw forces increase in the direction of the motion for small reduced frequencies, but in the direction opposite to the motion for large reduced frequencies. The effects of the motion tend to dominate the control method, at least for the reduced frequencies and setup tested in the low-speed wind tunnel. The results from the high-speed testing with transitional separation give a preliminary indication that the control method could have sufficient control authority when the reduced frequencies are low. The third investigation involves tangent-ogive cylinder undergoing a pitching maneuver in a water tunnel. Laser-Doppler Velocimetry (LDV) is used in order to map out several planes of velocity data as the model is pitched. The LDV data is used to calculate vorticity and turbulent kinetic energy. Variables that are proportional to the flow asymmetry and proximity to the steady-state flow are defined. All of these variables are displayed as a function of time and space (where appropriate). The delay in the development of the asymmetry and the flow progression to the steady state are determined to be a function of pitch-axis location. The propagation velocity of the convective asymmetry is faster than expected, most likely because of the increased axial velocity in the vortex cores. Vortex breakdown of one of the vortices is observed, with loss of axial velocity and dilution of the vorticity over a large area. The cause of this phenomenon is not yet understood, but it is reminiscent of vortex breakdown over delta wings. / Ph. D.

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An experimental study in air has been performed to determine what effect fins have on the flow over circular cylinders. The tubes under investigation included one bare tube and three segmented-finned tubes of different fin densities with the same root diameter as the bare tube. The tests were performed at two Reynolds numbers (2.61 x 104 and 4.98 x 104) and two downstream distances (2.5 & 5 diameters) and involved the use of hotwire anemometry. Measurements of mean and fluctuating velocities were taken across the wake as well as two-point fluctuating velocity correlations. It was discovered that the use of fins can result in significant differences. Fins cause larger mean velocity deficits in the wake profiles and significant shape differences in the total turbulence intensity profiles. Fins also increase the strength of vortex shedding, contrary to what would be expected, and increase the number of harmonic frequency peaks in the frequency spectra as three harmonic peaks were observed for the bare tube, while as many as ten were seen for the densest finned tube. Correlation length measurements, and thus radiated sound intensity, proved to be inconclusive. It was discovered that correlation length changed with angular rotation suggesting that this phenomenon needs to be investigated further before making any comparisons. Based on the differences seen with increased fin density, it is thought that there may be a critical fin density which causes fundamental changes in the cylinder wake. Also, during the course of this investigation, it was concluded that while the use of an effective diameter, De, proved adequate in collapsing the finned tube data, this approximation could be improved. / Thesis / Master of Applied Science (MASc)

An experimental study in air has been performed to determine what effect fins have on the flow over circular cylinders. The tubes under investigation included one bare tube and three segmented-finned tubes of different fin densities with the same root diameter as the bare tube. The tests were performed at two Reynolds numbers (2.61 x 104 and 4.98 x 104) and two downstream distances (2.5 & 5 diameters) and involved the use of hotwire anemometry. Measurements of mean and fluctuating velocities were taken across the wake as well as two-point fluctuating velocity correlations. It was discovered that the use of fins can result in significant differences. Fins cause larger mean velocity deficits in the wake profiles and significant shape differences in the total turbulence intensity profiles. Fins also increase the strength of vortex shedding, contrary to what would be expected, and increase the number of harmonic frequency peaks in the frequency spectra as three harmonic peaks were observed for the bare tube, while as many as ten were seen for the densest finned tube. Correlation length measurements, and thus radiated sound intensity, proved to be inconclusive. It was discovered that correlation length changed with angular rotation suggesting that this phenomenon needs to be investigated further before making any comparisons. Based on the differences seen with increased fin density, it is thought that there may be a critical fin density which causes fundamental changes in the cylinder wake. Also, during the course of this investigation, it was concluded that while the use of an effective diameter, De, proved adequate in collapsing the finned tube data, this approximation could be improved. / Thesis / Master of Applied Science (MASc)

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No description available.

Approved for public release; distribution is unlimited / The flowfield downstream of a vertically-launched surface-to-air missile model at an angle of attack of 50° and a Reynolds number of 1.1 x 10(5) was investigated in a wind tunnel of the Naval Postgraduate School. The goal of this thesis is to experimentally validate the pressure measurement system for flowfield variables with elevated levels of turbulence; to determine the location and intensity of the asymmetric vortices in the wake of the VLSAM model at a raised level of freestream turbulence; and to display the asymmetric vortices by velocity mapping and pressure contours. The purpose is to correlate the results with the force measurements of Rabang to provide a greater understanding of the vortex flowfield. The body-only configuration was tested. Two flowfield conditions were treated: the nominal ambient wind tunnel condition, and a condition with grid­ generated turbulence of 3.8% turbulence intensity and a dissipation length scale of 1.7 inches. The following conclusions were reached: 1) The relative strengths of the asymmetric vortices can be noted by the sharp spike shape in the ambient condition; this condition becomes diffused and becomes fatter in the turbulent condition; 2) The right side vortex has greater strength than the left side one as seen by the diffusion in the total pressure coefficient and static pressure coefficient contours with and without a turbulent condition; 3) an increase in turbulence intensity tends to reduce the strength of the asymmetric nose-generated vortices; also pushes the two asymmetric vortices closer together; 4) and crossflow velocities were examined and were found to indicate the behavior denoted by the pressure contours. / http://archive.org/details/flowfieldmeasure00lung / Lieutenant, Republic of China Navy

"Optical vortices are singularities in phase fronts of optical beams. They are characterized by a dark core in the center and by a helical wave front. Owing to azimuthal components of wave vectors, an optical vortex carries orbital angular momentum. Previously, optical vortices were studied only in coherent beams with a well-defined phase. The object of this dissertation is to explore vortices in partially coherent systems where statistics are required to quantify the phase. We consider parametric scattering of a vortex beam and a vortex placed on partially coherent beam. Optical coherence theory provides the mathematical apparatus in the form of the mutual coherence function describing the correlation properties of two points in a beam. Experimentally, the wave-front folding interferometer allows analysis of the cross-correlation function, which may be used to study partial coherence effects even when traditional interferometric techniques fail. We developed the theory of composite optical vortices, which can occur when two coherent beams are superimposed. We then reported the first experimental observation of vortices in a cross-correlation function (which we call spatial correlation vortices). We found numerically and experimentally how the varying transverse coherence length and position of a vortex in a beam may affect the position and existence of spatial correlation vortices. The results presented in this thesis offer a better understanding of the concept of phase in partially coherent light. The spatial correlation vortex presents a new tool to manipulate coherence properties of an optical beam."