starship ascent cfd simulation

1. Geometry and Grid Generation

I started by working with a simplified Starship geometry, modeling half of the vehicle using symmetry to reduce computational cost.

Key work:

• Generated a 3D structured grid using a multi-block (T-Rex) approach

• Captured the external flow field around the full vehicle, including control surfaces

• Added grid refinement to resolve shock structures (bow shock and expansions)

• Kept total cell count under ~1 million while maintaining accuracy

This stage focused on building a high-quality grid capable of resolving compressible flow features without explicitly modeling boundary layers.

2. Flow Solver Setup

The simulation was performed in ANSYS Fluent, modeling compressible, inviscid flow around the vehicle and through the engines.

What I implemented:

• Freestream conditions representing ascent trajectory (Mach, altitude, pressure)

• Species transport to model realistic air and exhaust gas mixtures

• Pressure inlet boundary conditions for the rocket nozzles

• Separate cases for:

  • Thrust OFF (external aerodynamics only)

  • Thrust ON (fully coupled external + internal flow)

This allowed direct comparison between purely aerodynamic forces and propulsion-influenced flow.

3. Nozzle and Internal Flow Modeling

The internal nozzle flow was approximated using geometry generated from Method of Characteristics principles.

Key features:

• Diverging nozzle section with realistic area ratio

• Pressure-driven inflow conditions to simulate combustion chamber output

• Tracking of exhaust species through the nozzle and into the external flow

This enabled analysis of how the exhaust plume interacts with the surrounding flow field.

4. Grid Adaptation and Shock Resolution

To improve accuracy, I applied grid adaptation based on pressure gradients.

• Refined regions with strong curvature (shock locations)

• Improved resolution of bow shocks and plume structures

• Ensured stable and converged solutions for both cases

This step was important for accurately capturing high-speed compressible flow features.

5. Performance Analysis

From the simulations, I extracted key aerodynamic and propulsion metrics:

• Drag, lift, and pitching moment coefficients

• Force and moment distributions across the vehicle

• Thrust generated by integrating pressure forces inside the nozzle

• Comparison between thrust-on and thrust-off cases

This provided a complete picture of how propulsion affects vehicle aerodynamics during ascent.