Study on the Asymmetric Fluid Flow in the Continuous Casting Mold

학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2014. 8. 이경우.It is very important to understand flow patterns within the continuous casting mold because they have a significant impact on product quality. Water model experiment and numerical simulation conducted to identify the fluid flow pattern in the steel slab continuous casting mold. The fluid flow pattern in the mold is not steady but instead an oscillatory flow with a specific oscillation frequencies. We identified the physical origins of various specific oscillation frequencies, and confirmed through experimentation and simulation that each frequency is related to the cross flow and injection stream oscillation. Moreover, the degree of oscillation at each frequency appears differently depending on the location within the mold, and is shown to have a effect near the mold wall. Water model experiment was conducted to observe the surface fluctuation corresponding to different port angles of the submerged entry nozzle in the steel slab continuous casting mold. When the port angle has low values, the amplitude of the surface fluctuation is relatively larger than for higher angles. We demonstrate that these phenomena are related to the fluid flow patterns in the mold by numerical simulation. Fluid flow patterns are asymmetric and unsteady for low port angles, with repetition of vortex nucleation and annihilation. However, fluid flow patterns become symmetric with increased SEN port angles. These results not only provide a better understanding of complex oscillatory flow patterns, but also provide a method to obtain a stabilized surface within the mold.Contents Abstract i List of Figures iii List of Tables vii Chapter 1 Introduction 1 1. 1 Continus Casting 1 1. 1. 1 Historical Developments of Continuous Casting 1 1. 1. 2 Continuous Casting Equipments 2 1. 1. 3 New Continuous Casting Technology 8 1. 2 Fluid Flow in the Mold 12 1. 3 Quality Problems Related to the Fluid Flow 14 1. 3. 1 Inclusion Flotation 14 1. 3. 2 Mold Slag Entrainment 16 1. 3. 3 Defect from the Surface Level Fluctuation 18 1. 3. 4 Injection Stream Impingement 19 1. 4 Previous Researches 19 1. 4. 1 Asymmetric Flow in the Mold 19 1. 4. 2 Origin of Oscillatroy Flow 20 1. 5 Goals of the Research 22 Chapter 2 Research Methods 23 2. 1 Water Model Experiment 23 2. 1. 1 Water Model Equipments 23 2. 1. 2 Similarity of Water Model Equipment 28 2. 2 Numerical Calculation 32 2. 2. 1 Governing Equation 32 2. 2. 2 Turbulent Model 34 2. 2. 3 Simulation Geometries 36 2. 2. 4 Simulation Mesh 37 2. 2. 5 Boundary Conditions 40 Chapter 3 Origin of Periodic Oscillatory Flow 42 3. 1 Experiment Conditions 42 3. 2 Simulation Conditions 42 3. 3 Results and Dicussions 44 3. 3. 1 Velocity Variations in the Mold 44 3. 3. 2 FFT Power Spectrums of Velocity Magnitude 47 3. 3. 3 The Periodicity of Velocity Variation 51 3. 3. 4 The Origin of Oscillation Frequencies 53 3. 3. 5 Position Dependence of Oscillation Frequencies 64 3. 3. 6 Periodic Oscillatory Flow of Molten Steel 68 Chapter 4 Surface Level Fluctuation 73 4. 1 Experiment Conditions 73 4. 2 Simulation Conditions 73 4. 3 Results and Dicussions 75 4. 3. 1 Surface Level Fluctuations for the Different SEN Port Angles 75 4. 3. 2 Surface Level Fluctuation Behaviors 78 4. 3. 3 Fluid Flow Patterns for the Different SEN Port Angles 83 4. 3. 4 Surface Velocities for the Different SEN Port Angles 87 4. 3. 5 Surface Level Fluctuations of Molten Steel 89 Chapter 5 Conclusions 92 References 94 Korean Abstract 104 Acknowledgement 106Docto