1. Introduction

In modern continuous steel casting, the submerged entry nozzle (SEN) plays a crucial role in delivering molten steel from the tundish into the mold in a controlled, stable manner. The flow behavior of the liquid steel as it exits the SEN significantly impacts the hydrodynamics within the mold, which in turn influences solidification patterns, meniscus stability, inclusion distribution, and ultimately the final steel quality. Among various geometric features of the SEN, the bottom well — a recessed region at the base of the nozzle — has been shown to be a key factor affecting the internal flow patterns and the characteristics of the exit jets that emerge from the nozzle ports.

This article examines how the presence or absence of a bottom well in a SEN affects the shape, alignment, spread angle, and impact point of exit jets — all of which are important for controlling mold flow and ensuring uniform solidification in slab casting. The discussion draws on experimental and numerical studies using scaled water analogs and computational fluid dynamics that provide detailed insights into the hydrodynamic consequences of bottom-well geometry.

2. Background: SEN Jets and Mold Flow Dynamics

2.1 Continuous Casting and SEN Function

In vertical continuous casting machines, molten steel is transferred from the tundish to the mold through the submerged entry nozzle, which has multiple exit ports oriented towards the wide faces of the mold. These jets deliver steel with specified momentum and direction into the mold pool, where fluid flow establishes recirculation zones that influence meniscus level, slag movement, and inclusion transport.

The dynamics of these jets depend on:

• Nozzle geometry

• Exit port configuration

• Internal flow patterns inside the SEN

• Steel velocity and turbulence characteristics

If jets are misaligned or uneven, they can generate asymmetric recirculation patterns that increase meniscus oscillation and promote slag entrainment — both detrimental to steel quality.

3. Bottom Well Geometry: What It Is and Why It Matters

The “bottom well” refers to a recessed cavity built into the internal bottom wall of the SEN, between the inlet bore and the exit ports. When present, it creates a region where flow can recirculate before leaving the nozzle.

Two basic SEN designs have been compared experimentally and numerically:

1. Type A SEN — with a bottom well

2. Type B SEN — without a bottom well

Both designs have the same inlet flow and port area, but the internal hydrodynamics differ dramatically because of how the deep region alters vortex formation and momentum distribution before the jets exit.

4. Internal Flow Patterns Inside SENs

4.1 Flow with Bottom Well (Type A)

Experiments and simulations show that when a bottom well is present, the internal flow tends to form a single large vortex occupying much of the nozzle’s internal volume. This single, dominant recirculation zone has two important consequences:

• Asymmetric flow patterns, because the vortex core may be biased toward one side.

• Unsteady jet exit directions, since the vortex alters instantaneous local momentum vectors at the exit ports.

The single-vortex scenario increases flow mixing within the SEN and produces broader, more irregular exit jets, which have larger spread angles and misalignment relative to the mold center plane.

4.2 Flow without Bottom Well (Type B)

In contrast, SENs without a bottom well tend to produce two smaller, counter-rotating vortices in the internal flow field. These vortices are more balanced in size and occur symmetrically about the nozzle’s center plane. This symmetry yields:

• More uniform velocity profiles at the exit

• Compact, collimated jets

• Better alignment with the mold center plane

This dual-vortex configuration generally produces jets that are narrower, less turbulent, and more predictable in their trajectories.

5. Exit Jet Characteristics and Differences

5.1 Jet Shape and Spread Angle

One of the key measurable effects of bottom well geometry is the spread angle of the exit jets — the angle between the jet core direction and a reference axis perpendicular to the exit port.

• Type A (with bottom well): Jets are wider and more irregular, exhibiting larger downward and lateral spread. This indicates lower collimation and higher disruption from internal turbulence.

• Type B (without bottom well): Jets are narrower, more compact, and more consistent in direction.

In experimental observations using scaled water models, the measured difference in vertical jet falling angle between the two configurations was roughly 5°, with the bottom-well jets being steeper on average. In a full-scale industrial caster, this difference could translate into a shift in the impact height on the narrow mold wall of about 0.150 m (15 cm).

5.2 Jet Alignment and Mold Impact

Jet alignment relative to the mold’s central plane affects where the jets strike the narrow faces once they exit the ports and travel downward in the mold pool. Misaligned jets can cause:

• Uneven heat transfer

• Asymmetric recirculation zones

• Increased meniscus fluctuations

• Greater slag entrainment

Type A SEN jets, because of their broader angles and asymmetry, are more likely to produce lateral oscillations and uneven wall impacts. Type B SEN jets, being more compact and symmetric, tend to promote more stable mold flows.

6. Hydrodynamics Inside SEN and Jet Formation Mechanisms

6.1 Vortex Influence on Jet Momentum

The internal vortices alter the direction and magnitude of velocity components just upstream of the exit ports. These altered momentum fields map directly onto jet characteristics:

• In type A SENs, the dominant single vortex imposes higher turbulence coupling between ports, creating jets with higher angular spread and significant upward components near edges.

• In type B SENs, the counter-rotating vortices help stabilize flow and produce jets with less turbulence, lower transverse motion, and more downward-directed momentum.

Numerical simulations using Large Eddy Simulation (LES) models capture these patterns and confirm that the bottom well depth and configuration play a role in vortex formation.

7. Turbulence and Jet Behavior Correlation

Analyses also quantify turbulent kinetic energy near the exit ports. High turbulence levels near an exit correlate with broader jets and less predictable trajectories:

• Type A SEN jets exhibit higher local turbulent kinetic energy and more chaotic jet fronts.

• Type B SEN jets show lower turbulence intensity, corresponding to smoother, better-collimated jets.

These observations are consistent with parametric CFD studies that show how nozzle geometry influences interior turbulence structures and, subsequently, jet dynamics.

8. Impact of Jets on Mold Flow and Steel Quality

The characteristics of jets leaving the SEN significantly influence mold flow patterns:

8.1 Flow Patterns in the Mold

Narrow, symmetric jets tend to:

• Promote stable recirculation loops

• Reduce meniscus oscillation

• Lower slag entrainment risk

• Achieve more uniform heat extraction

Wider, asymmetric jets can:

• Drive stronger lateral flows

• Increase turbulence near the free surface

• Create unstable meniscus behavior

• Increase risk of inclusion entrapment

These conditions arise because the jets’ momentum vectors and angles determine how steel initially circulates and interacts with the mold’s boundaries.

9. Engineering Implications

Understanding the influence of bottom well geometry is critical for:

• SEN design optimization

• Improving casting stability

• Reducing defect rates (e.g., surface cracks, segregation)

• Lowering operational cost by improving nozzle performance

SEN designers can use this knowledge to tailor the bottom well shape, size, and port arrangement to produce jets with desired characteristics for specific casting speeds and mold geometries.

10. Conclusions

The presence of a bottom well in a submerged entry nozzle strongly influences the internal flow dynamics and the subsequent characteristics of the jets produced by the exit ports. Specifically:

• A bottom well tends to generate a single dominant vortex, which results in broader, misaligned, and more turbulent jets.

• Absence of a bottom well encourages dual vortex formation, leading to compact, symmetric, and better-collimated jets.

• Differences in jet behavior can significantly affect where and how the jets impact the mold surfaces, with implications for meniscus stability, slag entrainment, and overall steel quality.

This understanding provides a scientific basis for improving SEN design and optimizing continuous casting operations.More information please visit Henan Yangyu Refractories Co.,Ltd