Design and Development of a Variable Converging-Diverging Nozzle with CFD and FEA

Challenge

The research program needed a single nozzle that could change its convergence, divergence and outlet flow direction, instead of relying on multiple fixed nozzles. The mechanism had to hold an accurate internal flow path in every configuration while withstanding pressure loads, without deflection or leakage that would compromise the flow.

Approach

The full variable-geometry mechanism was designed to adjust the throat area, the expansion section and the outlet direction. Compressible-flow CFD evaluated each configuration for acceleration, shock behaviour and outlet flow quality. FEA assessed stresses and deformation of the moving walls and the mechanism under the predicted pressure loads, so that geometry and structure were refined together.

Key Findings

• Throat and exit area settings controlled flow acceleration and outlet Mach number, and CFD confirmed the target conditions were achievable across the design range.
• Off-design expansion ratios produced internal shocks and flow separation in the diverging section, which defined the practical operating envelope of the mechanism.
• Directional adjustment deflected the outlet flow while keeping the core flow attached, confirming the steering capability.
• FEA showed that wall stiffness and support locations were critical for holding the flow geometry under load, and this led to structural refinements before manufacture

Deliverables

Mechanical design of the variable nozzle mechanism, CFD results for all configurations, FEA stress and deformation assessment, and design recommendations for manufacture and operation.