Secondary Vortex Formation in Bifurcated Submerged Entry Nozzles: Numerical Simulation of Gas Bubble Entrapment
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N continuous casting of slab steel, the flow condition at the ports of the submerged entry nozzle (SEN) is believed to determine the global flow behavior in the mold.[1–3] Subsequently, many efforts have been put into the design of SEN geometries and an investigation of the effect of SEN operation on port outflow conditions.[4,5] In addition to SEN geometry, gas injection through the stopper rod is believed to significantly affect the flow behavior inside and outside of the SEN, leading to reduced clogging rates and altered convective mold flow pattern.[6–8] Since the effect of SEN flow on mold flow is difficult to detect under real operating conditions, commonly, water models are applied to substitute the real process.[3,8] While liquid steel can be assumed as a Newtonian fluid and Reynolds analogy can be applied for pure single-phase flows, similarity is violated in case of multiphase flows. Because of this water–air experiments cannot be directly used to predict the behavior of gas flow in liquid steel. Recently, new experimental methods evolved, which allow for an analysis of gas bubble behavior in liquid metal SEN flow at low temperatures.[9] In supplement to experimental investigation methods, SEN flow and downstream mold flow have been subject to numerical simulations.[1,2,7,8,10–14] In case of a bifurSTEFAN PIRKER, Head of Department, and SIMON SCHNEIDERBAUER, Deputy Head of Department, are with the Department of Particulate Flow Modelling, Johannes Kepler University, Linz, Austria. Contact e-mail: [email protected] DAMIR KAHRIMANOVICV, Senior Researcher, is with the Department of Particulate Flow Modelling, Johannes Kepler University, also with the Department of Process Technologies, University of Sarajevo, Sarajevo, Bosnia and Herzegovina. Manuscript submitted November 6, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
cated SEN, numerical simulations predict an unsteady and asymmetrical mold flow pattern, which agrees to experimental observations.[13] At the SEN port outlet, axisymmetric flow profiles have been reported,[4] which indicate the existence of a superposed horizontally orientated secondary vortex. From a fluid dynamical point of view, the existence of secondary vortex formation in flow bifurcations is well known from T-shaped conjunction in piping networks. The physical mechanism for the establishment of these secondary vortices as well as their interaction with gas bubbles is well described in a recent PNAS paper.[15] However, to the best knowledge of the authors, there is no investigation of secondary vortex formation in bifurcated SEN flow available in the literature. Numerical simulation of secondary vortex formation in SEN flow requires the resolution of turbulent length and time scales which are significantly smaller than the dimensions of the secondary vortices. Consequently, this requires a fine grid resolution in combination with a local, scale resolving turbulence model. Recently, SEN flow and mold flow have been considered by highly resolved large eddy simulation (LES) on regular grids.[13,16] While these simu
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