David J. Daily

Cavitation onset caused by acceleration

Significance In this paper we propose an alternative derivation of the cavitation number and validate the threshold. The proposed dimensionless number is more suitable to predict the cavitation onset caused by a sudden acceleration rather than a large velocity as prescribed by the traditional cavitation number. Systematic experiments were conducted for validation, confirming that the alternative cavitation number predicts the threshold at which cavitation will occur (Ca<1). Striking the top of a liquid-filled bottle can shatter the bottom. An intuitive interpretation of this event might label an impulsive force as the culprit in this fracturing phenomenon. However, high-speed photography reveals the formation and collapse of tiny bubbles near the bottom before fracture. This observation indicates that the damaging phenomenon of cavitation is at fault. Cavitation is well known for causing damage in various applications including pipes and ship propellers, making accurate prediction of cavitation onset vital in several industries. However, the conventional cavitation number as a function of velocity incorrectly predicts the cavitation onset caused by acceleration. This unexplained discrepancy leads to the derivation of an alternative dimensionless term from the equation of motion, predicting cavitation as a function of acceleration and fluid depth rather than velocity. Two independent research groups in different countries have tested this theory; separate series of experiments confirm that an alternative cavitation number, presented in this paper, defines the universal criteria for the onset of acceleration-induced cavitation.

Determining 3D flow fields via multi-camera light field imaging.

In the field of fluid mechanics, the resolution of computational schemes has outpaced experimental methods and widened the gap between predicted and observed phenomena in fluid flows. Thus, a need exists for an accessible method capable of resolving three-dimensional (3D) data sets for a range of problems. We present a novel technique for performing quantitative 3D imaging of many types of flow fields. The 3D technique enables investigation of complicated velocity fields and bubbly flows. Measurements of these types present a variety of challenges to the instrument. For instance, optically dense bubbly multiphase flows cannot be readily imaged by traditional, non-invasive flow measurement techniques due to the bubbles occluding optical access to the interior regions of the volume of interest. By using Light Field Imaging we are able to reparameterize images captured by an array of cameras to reconstruct a 3D volumetric map for every time instance, despite partial occlusions in the volume. The technique makes use of an algorithm known as synthetic aperture (SA) refocusing, whereby a 3D focal stack is generated by combining images from several cameras post-capture 1. Light Field Imaging allows for the capture of angular as well as spatial information about the light rays, and hence enables 3D scene reconstruction. Quantitative information can then be extracted from the 3D reconstructions using a variety of processing algorithms. In particular, we have developed measurement methods based on Light Field Imaging for performing 3D particle image velocimetry (PIV), extracting bubbles in a 3D field and tracking the boundary of a flickering flame. We present the fundamentals of the Light Field Imaging methodology in the context of our setup for performing 3DPIV of the airflow passing over a set of synthetic vocal folds, and show representative results from application of the technique to a bubble-entraining plunging jet.

Simultaneous Tracking of Vocal Fold Superior Surface Motion and Glottal Jet Dynamics

Synthetic aperture particle image velocimetry is used with an excised human vocal fold model to study the airflow between the vocal folds during voice production. A whole field, time-resolved, 3D description of the flow is presented over multiple cycles of vocal fold oscillations. The 3D flow data are synchronized with a 3D reconstruction of the superior surface of the vocal folds and with the subglottal pressure signal.© 2013 ASME

Three‐dimensional whole‐field measurements of pulsatile glottal jets using synthetic aperture particle image velocimetry.

The use of synthetic aperture particle image velocimetry (SAPIV) to measure the three‐dimensional (3‐D) jet velocity field generated by the human vocal folds during speech is described. SAPIV uses an array of cameras to acquire 3D flow velocity data throughout a volume of interest. In the present application, eight high‐speed cameras are synchronized with a volume‐illuminating pulsed laser to image the supraglottal jet exiting from self‐oscillating synthetic vocal fold models. The images from the eight cameras are transformed and reconstructed to generate different image planes within the flow field, to which traditional particle image velocimetry (PIV) techniques are applied to calculate 3‐D velocity vectors throughout the flow field. Two‐dimensional PIV using thin laser sheets has been previously used to study the supraglottal jet, but 3‐D measurements have been typically limited to either (1) quasisteady measurements as the laser sheet traverses the glottal jet volume, or (2) 3‐D measurements over a na...

Effects of the airway surface liquid on vocal fold vibration.

A two‐layer airway surface liquid (ASL), comprised of a Newtonian sublayer and a non‐Newtonian surface layer, lines the laryngeal lumen. During phonation the layers on opposing vocal folds experience merging, squeezing, stretching, and rupture. Various aspects of the ASL have been studied, but its role in vocal fold vibration remains largely understudied. This presentation describes the results of experiments and computational simulations aimed at improving our understanding of the role of the ASL, in particular the non‐Newtonian layer, in phonation. The experimental setup for measuring the liquid properties is described, and results are presented. The measured liquid properties are input into a finite element model of the vocal folds, which includes a simulated non‐Newtonian layer, using the software package ADINA. The non‐Newtonian liquid is also incorporated into a two‐mass vocal fold model, which includes the effects of the ASL during collision and separation. The finite element and two‐mass models ar...