This paper presents a water experiment benchmark for evaluation of the numerical models for the particle motion in a continuous casting tundish. The particles are optically tracked in the model tundish and additionally are captured by instrumented wooden frames at the water surface. In the meantime, an attempt is made to simulate the water flow and motion of the particles by using the Eulerian-Lagrangian approach. It is shown that for the experiment with large particles (f3.5 mm) the experimentally determined distribution of the particles as captured by the wooden frames can be numerically simulated, but for the small particles (with a diameter distribution between 50 and 600 mm) there is still relative large mismatch between the simulation and the experiment. Some modeling options and parameters must be tuned carefully. This raises concern for the future application of the models in real engineering process where experimental calibration and evaluation are not possible. Therefore, the goal of this paper is to (i) call contributions from researchers to propose their models and evaluate them against the same benchmark; (ii) verify the agreement of the numerical solutions obtained by different contributors, and (iii) comment on further improvements and modifications to the existing models.

In continuous casting of steel, the casting rate is often controlled by a stopper rod placed in the tundish outlet where the submerged entry nozzle (SEN) tube begins. The flow pattern inside the SEN plays an important role for the bubble formation at the argon injection nozzle at the stopper rod tip. High flow velocities are reached in the small gap between stopper rod and the surrounding SEN walls, and a flow separation has to be expected after the gap due to the fast expansion of the cross section. According to theoretical considerations and to the simulations, the absolute pressure in the gap becomes very low for liquid steel, which can cause cavitation-like effects. PIV-flow measurements in a 1:1 scaled water model of the caster show a highly oscillating and asymmetric flow pattern with rapidly changing separation regions. The low pressure effects expected in liquid steel cannot be investigated on the water-model due to the lower density of water. In numerical simulations of the water-model, the choice of the turbulence model and the usage or the non-usage of geometrical symmetries for the bound of the computational domain have a great impact on the resulting flow pattern and the accuracy of the predicted pressure drop. The results of various turbulence models are compared with results from measurements on a water-model. It turns out that only a 3D model using advanced turbulence models (SST k-v or Large Eddy) produce acceptable results, while 2D simulations completely fail and the standard turbulence models (e.g. k-e) significantly underestimate the pressure drop even in a 3D simulation.

The impact on the mold flow of inert gas bubbles originating from a gas injection at the top of the submerged entry nozzle is investigated. Results from a physical model using water and air are compared with corresponding numerical flow simulation results. In numerical models, the bubble velocities are determined by calculating the force equilibrium between buoyancy, drag force, and other forces acting on the bubbles. For the observed bubble size in the physical model, the so‐determined rising velocity of the bubbles is significantly too high in comparison to the water model experiment. Various effects can influence the rising velocity of bubbles. One of them is that the presence of turbulence obviously reduces the rising velocity. The influence of turbulence models and of a turbulence‐induced bubble drag modification is analyzed in numerical flow simulations and compared to water model results.

In continuous slab casting, the liquid steel is introduced into the mould via a submergered entry nozzle. This nozzle usually has two opposed orifices on its side walls, generating two diametrically opposed turbulent jets that are declined about 20° to the horizontal axis. These jets interact with the surrounding walls of the mould, which leads to an unstable flow situation and a self induced oscillation of the jets. Although both mould and nozzle geometry have two perpendicular symmetry planes, the oscillations are asymmetric. The fluid flow inside the mold is calculated with a 3D finite volume solver using turbulence models based on Reynolds‐averaging. The massflow of the jets and the mould extensions are varied, and the numerical results are partially compared with PIV‐measurements at a 1:1 scaled watermodel of the mould. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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