The acoustic emissions of cavitation bubbles in stretched vortices

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98657/1/JAS003209.pd

The influence of developed cavitation on the flow of a turbulent shear layer

Developed cavitation in a shear layer was studied experimentally in order to determine the effect that the growth and collapse of cavitation have on the dynamics of shear flows. Planar particle imaging velocimetry (PIV) was used to measure the velocity field, the vorticity, strain rates, and Reynolds stresses of the flow downstream of the cavitating and noncavitating shear layer; the flow pressures and void fraction were also measured. The flow downstream of a cavitating shear flow was compared to the noncavitating shear flow. For cavitating shear layers with void fractions of up to 1.5%, the growth rate of the shear layer and the mean flow downstream of the shear layer were modified by the growth and collapse of cavitation bubbles. The cross-stream velocity fluctuations and the Reynolds stresses measured downstream of the cavitating shear layer were reduced compared to the entirely noncavitating flow. This result is inconsistent with a scaling of the shear stress within the shear flow based on the mean flow. The decrease in the cross-stream fluctuations and Reynolds stresses suggests that the cavitation within the cores of strong streamwise vortices has decreased the coupling between the streamwise and cross-stream velocity fluctuations. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70602/2/PHFLE6-14-10-3414-1.pd

Cavitation scaling experiments with headforms : bubble dynamics

Utilizing some novel instrumentation which allowed detection and location of individual cavitation bubbles in flows around headforms. Ceccio and Brennen (1991 and 1989) recently examined the interaction between individual bubbles and the structure of the boundary layer and flow field in which the bubble is growing and collapsing. They were able to show that individual bubbles are often fissioned by the fluid shear and that this process can significantly effect the acoustic signal produced by the collapse. Furthermore they were able to demonstrate a relationship between the number of cavitation events and the nuclei number distribution measured by holographic methods in the upstream flow. More recently Kumar and Brenncn (1991-1992) have closely examined further statistical properties of the acoustical signals from individual cavitation bubbles on two different headformsm in order to learn more about the bubble/flow interactions. However the above experiments were all conducted in the same facility with the same size of headform (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified in those earlier experiments change with changes of speed, scale and facility. The present paper will describe experiments conducted in order to try to answer some of these important qucstions regarding the scaling of the cavitation phenomena. We present data from experiments conducted in the Large Cavitation Channel of the David Taylor Research Center in Memphis, Tennessee, on similar headforms which are 5.08, 25.4 and 50.8cm in diameter for speeds ranging up to 15m/s and for a range of cavitation numbers. In this paper we focus on visual observations of the cavitation patterns and changes in these patterns with speed and headform size

The collapse of a cavitation bubble in shear flows—A numerical study

The collapse of a cavitation bubble is examined by direct numerical simulations of the Navier–Stokes equations, using a finite difference/front tracking technique. Bubbles in both a quiescent fluid as well as shear flows are examined. For quiescent fluid, the results are compared with theoretical and previous computational results. For bubbles in a shear flow it is shown that large shear can increase the rate of collapse, and for bubbles near boundaries shear can eliminate the re‐entrant jet seen for bubbles in a quiescent flow. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69789/2/PHFLE6-7-11-2608-1.pd

Cinemagraphic PIV investigation of the lifted turbulent jet diffusion flame stabilization region

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76915/1/AIAA-2001-698-809.pd

Cavitation Scaling Experiments with Axisymmetric Bodies

Several experiments by Ceccio and Brennen (1991, 1989) and Kumar and Brennen (1992, 1991) have closely examined the interaction between individual cavitation bubbles and the boundary layer, as well as statistical properties of the acoustical signals produced by the bubble collapse. All of these experiments were, however, conducted in the same facility with the same headform size (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified change with speed, scale and facility. The present paper describes experiments conducted in order to try to answer some of these important questions regarding the scaling of the cavitation phenomena. The experiments were conducted in the Large Cavitation Channel of the David Taylor Research Center in Memphis Tennessee, on geometrically similar Schiebe headforms which are 5.08, 25.4 and 50.8cm in diameter for speeds ranging up to 15m/s and for a range of cavitation numbers

The effects of electrostatic forces on the distribution of drops in a channel flow: Two-dimensional oblate drops

Numerical simulations are used to examine the effect of an electrostatic field on an emulsion of drops in a channel. The leaky-dielectric theory of Taylor is used to find the electric field, the charge distribution on the drop surface, and the resulting forces. The Navier-Stokes equations are solved using a front-tracking/finite-volume technique. Depending on the ratios of conductivity and permittivity of the drop fluid and the suspending fluid the drops can become oblate or prolate. In addition to normal forces that deform the drops, tangential forces can induce a fluid motion either from the poles of the drops to their equator or from the equator to the poles. In this paper we focus on oblate drops, where both the dielectrophoretic and the electrohydrodynamic interactions of the drops work together to “fibrate” the emulsion by lining the drops up into columns parallel to the electric field. When the flow through the channel is slow, the fibers can extend from one wall to the other. As the flow rate is increased the fibers are broken up and drops accumulate at the channel walls. For high enough flow rate, when the drop interactions are dominated by the fluid shear, the drops remain in suspension. Only two-dimensional systems are examined here, but the method can be used for fully three-dimensional systems as well.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87286/2/093302_1.pd

The New Mechanical Engineering Curriculum at the University of Michigan

This paper describes the new undergraduate program in the Department of Mechanical Engineering and Applied Mechanics at the University of Michigan, Ann Arbor. The restructuring of the program was initiated by a comprehensive review in 1992 that included surveys of alumni, students, and industrial representatives, as well as faculty assessment of current trends and future needs. The program is intended to address the changing backgrounds of incoming students, to prepare the students for new and diverse challenges in the workplace, and to provide a structure for the curriculum to evolve with changing technology. The new curriculum consists of three integrated courses in Design and Manufacturing, two Laboratory courses, and several redesigned courses in the Engineering Sciences. The redesigned program provides students with extensive hands‐on experience, a comprehensive experience in teamwork and technical communication, and the opportunity to exercise and develop their creativity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94791/1/j.2168-9830.2001.tb00624.x.pd

Measurement of near-wall stratified bubbly flows using electrical impedance

The impedance measurement between a pair of flush-mounted electrodes was used to measure the characteristics of a stratified near-wall bubbly flow. The variation in cross electrode impedance with liquid layer thickness and mixture void fraction was examined using numerical simulations and static experiments. The experimental realization of the measurement system was used to measure the solid fraction of a water–glass sphere mixture to an uncertainty of ±2.4%, where the diameter of the glass spheres ranged from 0.1 to 0.2 of the electrode diameter. A stratified bubbly flow was produced over a flat surface, and optical measurements of the bubble distributions were used to understand the measured impedances across the electrode pair. Comparison between the computed impedance change (based on the observed void fraction and liquid layer height) and the inferred quantities from the impedance measurement alone yielded a variation from 12 to 28% on average. The use of multiple electrode pairs is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49059/2/mst5_4_015.pd