Oscillatory Flow in a Physical Model of a Thin Slab Casting Mould With a Bifurcated Submerged Entry Nozzle

Abstract

Laser Doppler anemometry (LDA) measurements are presented of the oscillatory flow in a 33% scale water model of thin slab casting mould when the flow enters as two lateral jets through a bifurcated nozzle. The submerged entry nozzle (SEN) and the mould were geometrically scaled to be representative of industrial thin slab casters. Mean and RMS LDA velocity measurements were taken at three selected points in the region surrounding the SEN, at 500 points in the central plane parallel to the broad face of the mould, and at points in selected transverse sections, for casting rates up to 1.53 m/min. Flow visualization was also taken at two selected planes in the mould. The LDA results showed each jet to form an upper and lower recirculation zone with the lower zones adjacent to one another bounded by the jets and the mould walls and the upper zones bounded by the jet, the SEN, the mould walls and the free surface. Both jets were found to have most oscillatory energy at frequencies below 5 Hz with high energy low frequency modes occurring at frequencies below 0.2 Hz. However, no single dominant frequency occurred in the spectrum and flow visualization revealed an apparently chaotic flow pattern in the oscillation. Midpoint jet deflection was restricted to 6–8 mm RMS, and no coherence was observed between jet (and free surface) movements on either side of the mould. The time averaged flow pattern was found to be almost symmetric across the wide face of the mould. It is concluded that both shear layer instability in the impinging jets, and deflection of the jets due to cross-flow at the SEN-mould wall, contribute to the flow oscillation.