Showing papers by "Steven L. Ceccio published in 1994"

Influence of orientation of electric field on shear flow of electrorheological fluids

Abstract: It is possible, in experimental flows of electrorheological (ER) fluids or in actual ER devices based on shear flows, that the electric field may have a component normal to and/or parallel to the fluid velocity. An analytical study of this possibility is presented here. The analysis is carried out using a constitutive equation for the three‐dimensional response of ER fluids [Rajagopal and Wineman, Acta Mechanica 91 (1992)] in which the electric field influences the response in two ways: (a) by affecting the material parameters, and (b) by contributing to stress components because of the interaction of the electric field vector and the shearing. It is shown that the viscosity is altered by a component of the electric field in the direction of the fluid velocity. Moreover, the viscosity is changed if the shear direction is reversed. The model is used in a study of the flow between parallel plates. It is found that the velocity field need not be symmetric about the midplane and the tractions on the plates may differ.

Cavitation Scaling Experiments With Headforms: Bubble Acoustics

Abstract: 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.