Abstract: The transient evolution of the particle-size probability density functions resulting from the break up of an immiscible fluid particle of size D injected into a fully developed turbulent flow has been measured experimentally by using Phase Doppler Particle sizing (PDPA) and image processing techniques. These measurements are used to determine the break-up frequency and the size probability density functions of the resulting daughter particles as a function of the particle size and the critical capillary diameter Dc. This is defined as being proportional to the (3/5)th power of the ratio (sigma/rho) and (-2/5)th power of epsilon, which is the rate of dissipation of turbulent kinetic energy per unit mass and per unit time of the underlying turbulence. A phenomenological model is proposed showing the existence of two distinct turbulent break-up regimes. For particles of sizes comparable to Dc, the break-up frequency is shown to increase as [ (sigm/rho)^-2/5 (epsilon)^3/5 (D/Dc - 1)^1/2 ], while for large particles whose sizes are greater than 1.63 Dc, the break-up frequency is shown to decrease with size as [ (epsilon)^1/3 D^-2/3 ]. The models for both the break-up frequency and the probability density functions of the daughter particles are shown to be in good agreement with the measurements performed over a wide range of sizes and magnitude of the turbulent kinetic energy of the underlying turbulence.

Biography: Dr. Lasheras received his undergraduate degree in Aerospace Engineering from the Universidad Politecnica de Madrid in 1975, and received his M.S. and Ph.D. degrees in Mechanical and Aerospace Engineering from Princeton University under the sponsorship of a Guggenheim Fellowship. After completing his studies in 1982, he was at the Shell Oil Company for three years prior to accepting a faculty appointment at the University of Southern California. He moved to the University of California, San Diego in 1991. Dr. Lasheras is currently a Professor and Chairman of the Department of Mechanical and Aerospace Engineering. He is the recipient of the F. N. Frenkiel Award for Fluid Dynamics and he has been appointed as a Fellow of the Royal Academy of Engineering in Spain. His research interests include three-dimensional instabilities in free shear flows, particle mechanics in turbulent flows, particle sedimentation and suspension mechanisms, turbulent multi-phase flows, and flame instabilities.

Time:March 10, 2000 @ 2:30 P.M
Place:Room 1202, Martin Hall
Hosts: Professors K. Kiger and J. Wallace, Department of Mechanical Engineering