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Öğe Assessment of turbulence models for flow around a surface-mounted cube(International Journal of Mechanical Engineering and Robotics Research, 2017) Dogan S.; Yagmur S.; Goktepeli I.; Ozgoren M.Flow over a bluff body constitutes one of the most fundamental phenomena for engineering applications. Even though a cube is considered as a simple bluff body to examine with respect to the flow structure, there is more complicated flow physics around the cube than expected. Thus, a cube just like other bluff bodies is mostly used in the comparison process of numerical and experimental results to determine the more suitable turbulence model in case of undertaken problem. For this reason, in this paper, turbulence models have been employed to investigate the flow characteristics around a surface-mounted cube at Re = 3700 based on the edge length of the cube in terms of Computational Fluid Dynamics (CFD) and then compared with experimental results in the literature. Normalized and time-averaged results of velocity vector fields, streamwise and cross-stream velocity components, vorticity contours and streamline patterns have been numerically obtained by using k-? Re-Normalization Group (RNG), k-? Shear Stress Transport (SST) and Large Eddy Simulation (LES) turbulence models. LES turbulence model has presented the best prediction of hydrodynamic characteristics for the body among the investigated turbulence models in this study. Although k-? SST turbulence model was the second successful one after LES method among the investigated turbulence models for the estimation of flow structure around the cube, k-? RNG turbulence model was failed to capture the flow fluctuations in the wake region of the geometry. © 2017 Int. J. Mech. Eng. Rob. Res.Öğe Experimental investigation of flow structures around a torpedo-like geometry placed in a boundary layer flow(Horizon Research Publishing, 2018) Hayder M.A.H.; Goktepeli I.; Yagmur S.; Ozgoren M.; Kose F.; Kavurmacioglu L.A.Defense applications for both under oceans and seas, particularly underwater vehicles have been considered in this research. With this aim, flow characteristics around a torpedo-like geometry under the effect of the boundary layer flow over a smooth flat plate have been experimentally examined by using PIV technique. All of the experiments have been done for Re = 20000 and Re = 40000 based on the length (L) of the geometry as a characteristic length. As a result, time-averaged streamwise velocity components < u* >, velocity vectors < v >, streamline topologies < ? > and Reynolds stress correlations < u'v'/U?2 > in the wake region of the torpedo-like geometry have been acquired in the range of 0 ? G/D ? 1.5. Here, G is the space between the bottom point of the geometry and flat plate surface; D stands for the diameter of the geometry. It is found that at the smallest value of G/D = 0.25, jet-like flow occurs between the plate and the model which causes a powerful scouring. As the gap ratio is increased to G/D = 0.5 and G/D = 1.0, the jet-like flow diminishes slightly and then the flow structure in the wake region becomes similar to the uniform incoming flow condition for G/D = 1.50. Due to the effect of the jet-like flow and boundary layer flow, time-averaged flow patterns present asymmetrical distributions which are clearly shown a bigger size focus close to the plate in streamline topology. Reynolds stress patterns form more powerful viscous forces in the boundary layer flow due to the occurrence of eddy vortices and viscosity effect. It is observed from the aforementioned flow patterns that interaction between the flow structure, the model and boundary layer flow yields very complex structure. In order to decrease the energetic flow in this condition, passive or active flow control method can be integrated on the torpedo-like geometry. © 2018 by authors.Öğe Interaction of a deep-water wave with a vertical cylinder: Effect of self-excited vibrations on quantitative flow patterns(2007) Ozgoren M.; Rockwell D.Interaction of a deep-water wave with a cylinder gives rise to ordered patterns of the flow structure, which are quantitatively characterized using a technique of high-image-density particle image velocimetry. When the cylinder is stationary, the patterns of instantaneous flow structure take on increasingly complex forms for increasing Keulegan-Carpenter number KC. These patterns involve stacking of small-scale vorticity concentrations, as well as large-scale vortex shedding. The time-averaged consequence of these patterns involves, at sufficiently high KC, an array of vorticity concentrations about the cylinder. When the lightly damped cylinder is allowed to undergo bidirectional oscillations, the trajectories can be classified according to ranges of KC. At low values of KC, the trajectory is elliptical, and further increases of KC allow, first of all, both elliptical and in-line trajectories as possibilities, followed by predominantly in-line and figure-of-eight oscillations at the largest value of KC. Representations of the quantitative flow structure, in relation to the instantaneous cylinder position on its oscillation trajectory, show basic classes of patterns. When the trajectory is elliptical, layers of vorticity rotate about the cylinder surface, in accordance with rotation of the relative velocity vector of the wave motion with respect to the oscillating cylinder. Simultaneously, the patterns of streamline topology take the form of large-scale bubbles, which also rotate about the cylinder. When the cylinder trajectory is predominantly in-line with the wave motion, generic classes of vortex formation and shedding can be identified; they include sweeping of previously shed vorticity concentrations past the cylinder to the opposite side. Certain of these patterns are directly analogous to those from the stationary cylinder. © 2007 Cambridge University Press.
