TURBULENT INSTABILITIES IN A THIN SLAB MOLD Rodolfo D. Morales 1) , Saul G. Hernandez 2) . 1) Professor at the Department of Metallurgy and Materials Engineering, National Polytechnic Institute-ESIQIE, Apdo. Postal 75-874, México D.F. rmorales@ipn.mx , ketechnologies@prodigy.net.mx 2) Graduate Students at the Department of Metallurgy and Materials Engineering, National Polytechnic Institute-ESIQIE, Apdo. Postal 75-874, México, D.F. iq_sagahz@hotmail.com Key words: funnel thin slab mold, meniscus oscillation, dynamic distortion. Abstract A water-physical model of a funnel-type thin slab mold fed by a 2 ports SEN was employed to characterize the flow of liquid steel using dye tracer, PIV and video recording experiments. A cyclic and energetic flow distortion of short live inducing high meniscus oscillation was identified. Its intensity grows with high casting speeds of 7 m/min and at a shallow immersion position of a SEN. This distortion is originated by the apparent existence of vortex flows located below the two discharging jets which are formed by the existence of shear stresses in their ends and acting on the surrounding fluid. It is inferred, under the ground of experimental results, that this flow distortion is originated by an instantaneous unbalance of the turbulent kinetic energy in the discharging jets. Negative production of kinetic energy is ascribed as the source of this unbalance which is compensated by higher contribution of the turbulent kinetic energy by mean convection and turbulent transport mechanisms manifested through higher velocities. After the restoration of the energy balance the system yields a stable meniscus to repeat the cycle. Introduction Design of submerged entry nozzles (SEN) is critical for controlling steel flow turbulence in continuous casting molds and especially in confined spaces such as funnel-type thin slab molds which operate at higher casting speeds than conventional thick molds. Controlling turbulence is very important to avoid flux particles entrainment which transforms into slivers in the final product [1,2] , to avoid meniscus instability [3,4] , distribute evenly heat transfer aiming at uniform shell growth [5] and attainment of steady flow conditions. Some thin slab and conventional mold SEN designs induce strong meniscus instability and high amplitude oscillations of liquid in the mold [6] . Takatani et al. [7] found that the horizontal velocity under the meniscus fluctuates strongly through the width of a conventional slab mold. Using a physical model Yoshida et al. [8] identified a meniscus descending flow along the outer surface of the SEN due to the existence of differential pressure in this region. According to those authors driven force for the descending flow is the instantaneous meniscus velocity difference between metal and liquid flux provided by bath oscillations. Morales et al. [9] reported that in a four ports SEN strong backflows, from the upper roll flow, are responsible for the existence of strong bath oscillations indicating that full port utilization (FPU) is a key factor for SEN design. A second key factor for SEN design is to avoid high free shear strain rates induced by long discharging jets, especially when the casting speed increases as Torres-Alonso et al. [10] indicated. In other work the same author reported also the existence of energetic vortexes formed very close to the SEN due to the existence of biased 87 Jim Evans Honorary Symposium Edited by: Ben Q. Li, Brian G. Thomas, Lifeng Zhang, Fiona M. Doyle and Andrew P. Campbell TMS (The Minerals, Metals & Materials Society), 2010