Simulation Analysis and Optimization Design of Y-Shaped Tee Flow Field Characteristics for Liquid Rocket Engine Ignition

Literature Overview

This paper by Zhang Jingyu and colleagues from Beijing Institute of Technology and Beijing Aerospace Propulsion Institute investigates the flow field characteristics of Y-shaped tee structures used in liquid rocket engine ignition systems. Published in Equipment Environmental Engineering (2025, Vol. 22, Issue 4), the study compares single-propellant igniter straight tube structures with dual-propellant igniter Y-shaped tee structures and presents optimization results for improved ignition reliability in next-generation heavy-lift launch vehicle engines.

Core Technical Approach

Comparative Study Design

The researchers conducted a systematic comparison between two ignition system architectures:

1. Single-propellant igniter with straight tube structure: A conventional configuration with one igniter feeding a straight tube.
2. Dual-propellant igniter with Y-shaped tee structure: A redundant configuration with two igniters feeding through a Y-shaped tee junction.

CFD Simulation Methodology

ANSYS Fluent was used for fluid simulation, analyzing pressure, temperature, and velocity distributions along the flow path for both configurations. Two optimized Y-shaped tee structures were also simulated to evaluate the impact of geometric modifications on output performance.

Key Technical Findings

Performance Comparison

Optimization Results

Flow Field Characteristics

Both configurations exhibit the following flow behavior:

• Pressure and temperature decrease along the flow direction
• Velocity increases along the flow direction
• Changes are more pronounced at the downstream end

Engineering Practice Integration

Significance for Rocket Engine Design

The Y-shaped tee structure serves as a critical flow distribution component in rocket engine ignition systems. The 126.3% improvement in exit pressure achieved by the dual-igniter Y-tee configuration has direct implications for:

• Ignition reliability: Higher exit pressure ensures more reliable combustion initiation in the main combustion chamber.
• Redundancy: The system maintains acceptable performance even when one igniter fails, providing critical redundancy for mission safety.
• Heavy-lift capability: The enhanced ignition performance supports the development of next-generation heavy-lift launch vehicles requiring more robust ignition systems.

Connection to Welding and Fabrication

The Y-shaped tee structure in rocket engine applications presents unique manufacturing challenges:

• Material selection: High-temperature alloys (Inconel, Hastelloy, or similar) are typically used, requiring specialized welding procedures.
• Welding process: GTAW (Tungsten Inert Gas Welding) is the preferred process for thin-walled Y-tee junctions, requiring precise heat input control to minimize distortion.
• Fillet geometry: The addition of fillets at the Y-junction (which improved pressure by 14%) requires careful welding technique to ensure smooth internal contour without undercut or excess reinforcement.
• Inspection requirements: Critical aerospace components require 100% NDE inspection including RT, UT, and often internal borescope examination of weld joints.

Quality Control Considerations

Standards and Specifications

For aerospace rocket engine components, the following standards apply:

Key Questions and Reflections

Failure mode analysis: The study shows that single igniter failure reduces exit pressure by 15.8%, yet the system still performs comparably to a single-igniter straight tube. This suggests that the Y-tee design provides meaningful redundancy. However, a complete failure mode analysis should consider:

• Partial clogging of one branch
• Differential igniter response times
• Thermal expansion effects on the Y-junction geometry during operation
• Vibration-induced fatigue at the Y-junction weld

Temperature effects on flow performance: The study reports exit temperatures within 5% of the baseline, but in actual rocket engine operation, the temperature rise along the flow path can be substantial. The interaction between thermal expansion of the Y-tee structure and flow performance should be evaluated under realistic thermal conditions.

Manufacturing tolerance sensitivity: The 102.3% pressure improvement from reducing tube diameter to 6 mm suggests high sensitivity to dimensional parameters. In manufacturing, maintaining tight tolerances on such small diameters requires precision machining or forming capabilities.

Study Insights and Implications

This study demonstrates the significant performance enhancement achievable through geometric optimization of Y-shaped tee structures in rocket engine ignition systems. The 126.3% pressure improvement and the built-in redundancy capability make the dual-igniter Y-tee configuration a compelling design choice for next-generation launch vehicles.

The optimization findings — particularly the beneficial effects of Y-junction fillets and reduced tube diameters — provide clear design guidelines for engineers developing ignition system components. The fillet addition is especially notable as it represents a simple geometric modification with substantial performance benefits, and it can be implemented through careful weld procedure design.

For aerospace engineers and fitting manufacturers, this study highlights the importance of computational fluid dynamics in optimizing flow distribution components. The ability to predict and optimize flow field characteristics before fabrication reduces development risk and accelerates the design cycle for critical propulsion system components.

The redundancy capability demonstrated in this study — maintaining acceptable performance with single igniter failure — aligns with the safety philosophy of aerospace systems where single-point failures must not result in mission failure. The Y-tee design provides an elegant solution that combines performance enhancement with inherent redundancy in a single component.