09:40   Data processing and visualization II Unsteady Dynamics of an Elliptical Vortex Ring with AR=1.5: Flow Visualization Study Rijin Rajan, Kamal Poddar, Debopam Das Abstract: This work investigates the unsteady dynamics in the propagation of elliptical vortex rings (EVR) arising from their inherent geometric asymmetry. Here, we present flow visualization results of a vortex ring generated with an aspect ratio of 1.5, which is a moderately elongated orifice with an ellipticity of 0.75. Elliptic vortex rings have the ability to entrain more fluid from its vicinity as compared to a circular vortex rings of same cross-section (Ho & Gutmark 1986). This results in greater mixing and growth rate. As the vorticity is distributed about an asymmetric contour, the self-induction of the vortex leads to azimuthal distortion in the elliptic vortex ring. The axis switching of an elliptic jet based on the dynamics of azimuthal vorticity is explained by Hussain & Husain (1989). This study is motivated by the lacking of clear information on the characteristics of elliptic vortex rings in the literature. In this study, the elliptic vortex rings are formed by ejecting fluid through an elliptic orifice. The Major diameter of the orifice is 60.04 mm and minor diameter is 39.96 mm which gives an aspect ratio of 1.5 with an ellipticity of 0.75. The fluid motion is given by the piston connected to a 100 W speaker, which in turn is driven by the signal from the function generator. The Reynolds number based on hydraulic diameter is in range of 4200-840. The flow Reynolds number is changed using the amplitude of the wave (Das 2016). The hydraulic diameter is 47.52 mm and equivalent diameter is 48.98 mm. The major axis and minor axis are illuminated (one plane at a time) using a 10 W PSU-H-LED variable laser and the flow through the orifice is captured along the axial direction of flow using two high speed cameras until the flow dies down or becomes turbulent. The high speed cameras used are 9 MP IDT and 5 MP Microvec respectively along the downstream. The cameras and function generator are synchronised using a 5V TTL signal generated by the NI-PXI 6289 DAQ, which is operated through LabVIEW software. The main aim of the study described here is to visulaize the flow through an elliptical orifice of aspect ratio 1.5. The figure 2 below shows the evolution of EVR for Reynolds number of 4272 and an exit velocity of 1.43 m/s. The slug flow model estimates the exit velocity by assuming that the fluid leaving the orifice has a uniform velocity distribution across the entire flow area. The elliptic vortex rings switches its axes under self induced motion in axial direction due to azimuthal instabilities. The deformation and bending of the major and minor axis can be seen in the visualization. In the high Reynolds number cases, the formation of secondary vortex rings can be seen which are due to the rolling up of shear layers. The secondary vortices exhibit a leap-frogging phenomenon as they interact with the leading vortex. Further investigation requires the use of planar PIV and tomographic PIV techniques. Classification of Turbulent Flow between Corotating Disks using Image Analysis Kohei Kuroda, Katsuya Hirata Abstract: In an area enclosed by co-rotating disks that share the same axis of rotation and rotate in the same direction with the same angular velocity, when the gap between the disks is much smaller than the disk radius, the flow field often exhibits three distinct regions: a core region near the center of the axis, where velocity fluctuations are small and rigid body rotation is dominant, an outer region where turbulent effects are dominant, with large velocity fluctuations, and boundary layer flow region. The boundary between a core region and an outer region forms a non-axisymmetric polygonal shape in the r-θ plane. This non-axisymmetric flow remains poorly understood, and a detailed study is required both for fundamental fluid machinery modeling and for addressing important challenges in the miniaturization and precision improvement of magnetic disk devices and surface finishing in semiconductor manufacturing processes. In this study, grayscale image analysis was conducted in the r-θ plane to quantitatively classify the core shape modes (CSM) which classifies core regions by their shapes and examine the changes in shape. The results indicated that pixel values were obtained in concentric circles around the rotation axis, and spectral analysis of these values allowed for a quantitative classification of the shapes. Moreover, the image analysis revealed that the core region's shape changes with the rotational angle, indicating that the core shape is not centered around the rotation axis. Characterization of the Ship Deck Flow Field of a medium-sized Tanker Hendrik Fischer, Federico Taruffi, Axelle Viré, Alberto Rius-Vidales Abstract: This abstract describes an experimental series at the Low Turbulence Tunnel (LTT) at TU Delft to characterize the flow field on the deck of an MR2-class tanker using 2D-2C PIV, pressure measurements and force balance measurements. The visualization of the ship deck flow features are intended to provide a basis for a physics-informed model of the inflow conditions of wind-assisted ship propulsion devices and therefore improve accuracy of performance predictions as well as make informed decisions on optimal device placement in the design phase of wind-assisted ships.

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