A Strategy for Faster Aerodynamics Analysis using Stallion 3D

Solving Half-Geometry Models in Stallion 3D Using Symmetry

In many aerodynamic problems, the geometry is symmetric about a plane. When this is the case, the computational model can be reduced to half the physical geometry. This approach either:

• Increases solution resolution for the same computational cost, or
• Reduces runtime by approximately 50% while maintaining resolution.

This short example demonstrates how to apply symmetry in Stallion 3D for a full aircraft configuration.

Purpose of Half-Model Analysis

When symmetry exists:

• The flow physics are mirrored across a plane.
• Only half the domain must be solved.
• Grid density can be increased for the same memory footprint.
• Turnaround time is reduced without sacrificing accuracy.

This is especially useful for:

• Conceptual aircraft design
• Wing-body configurations
• Early trade studies
• Parametric geometry comparisons

Step-by-Step Workflow

Step 1 – Import the STL Geometry

1. Go to Design → Import STL
2. Load the aircraft geometry.
3. Confirm the orientation and scale.

If you intend to use symmetry, only half of the geometry needs to be present (aligned with the symmetry plane).

Step 2 – Define the Computational Boundaries

1. Select Size / Scale
2. Set the CFD boundaries relative to the STL geometry.
3. Leave default settings unless refinement is required.
4. Click OK

The boundaries should extend sufficiently far from the geometry to prevent artificial blockage.

Step 3 – Inspect the Geometry

Use either:

• Visualization → View Geometry Only, or
• The wireframe view in the Design window

Verify:

• No unintended gaps
• Proper orientation
• Symmetry plane alignment at Y = 0 (or your chosen plane)

Step 4 – Configure the CFD Solver

Navigate to CFD Solver → Setup CFD Solver.

Recommended starting settings:

• Approximately 1,000,000 cells
• Initial X, Y, Z divisions appropriate to domain size
• Enable near-body refinement splitting

Confirm:

• RANS (Reynolds-Averaged Navier-Stokes) model selected
• Turbulence model appropriate for your case

Click OK.

Step 5 – Apply the Mirror Boundary Condition

This is the key step.

1. Select Ground Effect → Mirror Image
2. Choose Mirror at Minimum Y
3. Click Apply
4. Go to the Dimensions tab
5. Set Minimum Y = 0

This aligns the lower boundary with the symmetry plane. Stallion 3D reflects the solution across that plane internally.

Step 6 – Verify the Mirror Setup

Return to the geometry view. You should observe:

• The physical half-geometry
• A mirrored computational image
• A symmetry plane replacing the removed half

Step 7 – Generate Grid and Solve

1. Go to CFD Solver
2. Select Generate Grid and Solve Flow

After the solver converges (for example, ~4,000 iterations in this demo), the pressure field will be available for post-processing.

The solution shows pressure distribution on the physical half, with the symmetry plane replacing the opposite side, providing a full aerodynamic solution at roughly half the computational expense.

Step 8 – Extract Pressure Coefficient (Cp) Slices

Use surface graphs and spanwise Cp slices to compare stations across the wing. Example span stations:

• y = 3 m
• y = 4 m
• y = 5 m

These results are commonly used for load integration, structural sizing input, performance analysis, and validation against reference data.

Why This Matters

Using symmetry correctly enables faster iteration during early design, higher resolution grids within memory limits, and efficient conceptual evaluation of aircraft configurations. For UAV designers and small engineering teams, this can significantly reduce turnaround time while preserving fidelity.

Summary

To solve half-geometry models in Stallion 3D:

1. Import STL
2. Define CFD boundaries
3. Set solver parameters
4. Apply mirror boundary at the symmetry plane
5. Generate grid and solve
6. Extract aerodynamic data

The same method applies to wings, fuselages, hydrofoils, and other symmetric configurations.

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