Adaptive synthetic Schlieren imaging

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009."June 2009." Vita. Cataloged from PDF version of thesis.Includes bibliographical references (p. 20).Traditional schlieren photography has several important disadvantages when designing a system to image refractive index gradients including the relatively high cost of parabolic mirrors and the fact that the technique does not easily yield quantitative data. Both these issues are resolved by using synthetic Schileren photography, but this technique produces images with a lower resolution than traditional schlieren imaging. Synthetic schlieren imaging measures a refractive index gradient by comparing the distortion of two or more images with high frequency backgrounds. This method can either yield low-resolution quantitative data in two dimensions or high-resolution quantitative data in one dimension, but cannot give high-resolution data in two dimensions simultaneously. In order to yield high resolution imaging in two dimensions, a technique is described that based upon previously measured fields, adaptively modifies the high resolution background in order to maximize the resolution for a given flow field.by Roderick R. La Foy.S.B

Quantitative Flow Field Imaging about a Hydrophobic Sphere Impacting on a Free Surface

This fluid dynamics video shows the impact of a hydrophobic sphere impacting a water surface. The sphere has a mass ratio of m* = 1.15, a wetting angle of 110 degrees, a diameter of 9.5 mm, and impacts the surface with a Froude number of Fr = 9.2. The first sequence shows an impact of a sphere on the free surface illustrating the formation of the splash crown and air cavity. The cavity grows both in the axial and radial direction until it eventually collapses at a point roughly half of the distance from the free surface to the sphere, which is known as the pinch-off point. The second set of videos shows a sphere impacting the free surface under the same conditions using Particle Image Velocimetry (PIV) to quantify the flow field. A laser sheet illuminates the mid-plane of the sphere, and the fluid is seeded with particles whose motion is captured by a high-speed video camera. Velocity fields are then calculated from the images. The video sequences from left to right depict the radial velocity, the axial velocity, and the vorticity respectively in the flow field. The color bar on the far left indicates the magnitude of the velocity and vorticity. All videos were taken at 2610 fps and the PIV data was processed using a 16 x 16 window with a 50% overlap.Comment: American Physical Society Division of Fluid Dynamics 2008 Annual Meeting Replaced previous version because abstract had LaTex markup and was too long, missing periods on middle initial of first two name

Three-Dimensional Fluid Flow Measurement Techniques with Applications to Biological Flows

The accuracy of plenoptic and tomographic particle image velocimetry (PIV) experimental methods is measured by simulating three-dimensional flows and measuring the errors in the estimated versus true velocity fields. Parametric studies investigate the accuracy of these methods by simulating a range of camera numbers, camera angles, calibration errors, and particle densities. The plenoptic simulations combine lightfield imaging techniques with standard tomographic techniques and are shown to produce higher fidelity measurements than either technique alone. The tomographic PIV simulations are centered around testing software developed for processing large quantities of data that were produced during an experimental investigation of the flow field about a 3D printed model of the flying snake Chrysopelea paradisi. A description of this tomographic PIV experiment is given along with basic results and recommendations for future investigation.Doctor of PhilosophyTwo different experimental measurement techniques that can be used to measure three-dimensional fluid flow fields are discussed. The first measurement technique that is investigated in simulations uses cameras with arrays of lenses to simultaneously capture images of a flow field from multiple different angles. A method of combining the data from multiple cameras is discussed and shown to yield more accurate estimates of the three-dimensional flow fields than from a single camera alone. An additional measurement technique that uses a group of standard cameras to measure three-dimensional flow fields is also discussed with respect to software that was developed for processing a large volume dataset. This software was developed for processing data collected during an experimental investigation of the flow field about a 3D printed model of the flying snake Chrysopelea paradisi. A description of this experiment is given along with basic results and recommendations for future investigation

Long Term Dynamics of Water-Entry Cavity

Many engineering applications involve the motion of objects crossing a fluid interface. The dynamics of this process are often complicated due to the interplay of surface tension, gravity, and inertia. Nevertheless, a simple analysis using potential flow theory works well to predict the interfacial profile of the air cavity formed during an impact. Most current theories however, cannot predict the behavior of the air cavity after pinch off occurs. We therefore investigated the long term dynamics of water entry in both experiment and theory. It was found that shortly after pinch off the cavity dynamics become governed primarily by thermodynamic gas relations. The internal pressure slowly rises due to the cavity volume decreasing while the ambient liquid pressure quickly increases as a result of the descent of the projectile. This effect is incorporated into our model to correctly predict the cavity geometry.</jats:p

Main results of the 4th International PIV Challenge

In the last decade, worldwide PIV development efforts have resulted in significant improvements in terms of accuracy, resolution, dynamic range and extension to higher dimensions. To assess the achievements and to guide future development efforts, an International PIV Challenge was performed in Lisbon (Portugal) on July 5, 2014. Twenty leading participants, including the major system providers, i.e., Dantec (Denmark), LaVision (Germany), MicroVec (China), PIVTEC (Germany), TSI (USA), have analyzed 5 cases. The cases and analysis explore challenges specific to 2D microscopic PIV (case A), 2D time-resolved PIV (case B), 3D tomographic PIV (cases C and D) and stereoscopic PIV (case E). During the event, 2D macroscopic PIV images (case F) were provided to all 80 attendees of the workshop in Lisbon, with the aim to assess the impact of the user's experience on the evaluation result. This paper describes the cases and specific algorithms and evaluation parameters applied by the participants and reviews the main results. For future analysis and comparison, the full image database will be accessible at http://www.pivChallenge.org.The authors like to thank Springer Science+Business Media (www.springer.com), PCO AG (www.pco.de) and InnoLas Laser GmbH (www.innolas-laser.com) for their financial support to make the workshop possible in Lisbon on the July 5, 2014. Without the participants of the 4th International PIV Challenge, this paper could not be written, and we would like to thank all of them for their effort and the fruitful discussions

Oil droplet in alcohol

The elegant patterns formed by fluid droplets falling through a dissimilar liquid were first studied over a century ago.1 The emerging patterns are driven by hydrodynamic instabilities set up by velocity and density gradients between the liquids. We perform experiments using 3 mm droplets of naphthenic oil released from two heights 25 mm, 50 mm into isopropyl alcohol