Executive Summary

This project presents a complete aerodynamic evaluation of a ducted coaxial UAV propulsion system using high‑fidelity CFD analysis. The system features a NACA‑profiled duct, a central hub, and two contra‑rotating rotors designed to maximize thrust density within a compact footprint. The study investigates flow behavior, rotor‑to‑rotor interaction, duct pressure recovery, and overall aerodynamic performance under realistic operating conditions.

The analysis combines CAD‑driven geometry with a refined CFD workflow, forming a robust foundation for future optimization, acoustic studies, and structural validation.

Geometry Overview (CAD Section)

NACA‑Profiled Duct

The duct uses a NACA 0010‑style profile to promote smooth inlet pressure recovery and reduce lip separation. Six internal struts support the centerbody while maintaining structural rigidity.

Coaxial Rotor Pair

The propulsion module incorporates two four‑bladed coaxial rotors with:

• 0.213 m radius

• Contra‑rotation for torque cancellation

• Swept aerodynamic blade profiles

• Optimized hub geometry

Centerbody & Struts

A 120 mm centerbody houses the coaxial shaft system. The six struts are positioned to minimize flow blockage while ensuring mechanical stability.

CFD Methodology

Meshing

A multi‑zone mesh was generated with refinement around:

• Rotor blades

• Duct lip

• Struts

• Rotor‑to‑rotor interaction region

• Wake region

The mesh ensures accurate resolution of tip vortices, swirl, and duct boundary layer behavior.

Simulation Setup

• Solver: Steady/Transient (depending on your actual setup)

• Rotor Modeling: MRF / Sliding Mesh / AMI (whichever you used)

• Inlet: Uniform velocity or mass flow

• Outlet: Pressure outlet

• Walls: No‑slip

• RPM: 3500 RPM design basis

Objectives

• Evaluate flow acceleration through the duct

• Study rotor‑to‑rotor aerodynamic interference

• Analyze pressure rise and swirl behavior

• Assess duct contribution to thrust density

CFD Results

Velocity Magnitude

The duct accelerates flow through the rotor pair, producing a concentrated jet with reduced radial losses. The coaxial configuration increases axial momentum while maintaining compact geometry.

Pressure Distribution

Pressure contours show:

• High suction at rotor leading edges

• Pressure rise across each rotor stage

• Smooth pressure recovery along the duct interior

Streamlines & Swirl

Streamlines reveal:

• Swirl cancellation due to contra‑rotation

• Reduced rotational losses

• Improved axial flow alignment

Rotor Interaction

The lower rotor experiences modified inflow due to the wake of the upper rotor. CFD visualizes:

• Wake contraction

• Tip vortex interaction

• Localized pressure disturbances

These insights guide future optimization.

Technical Specifications

Parameter Value

Duct Profile NACA 0010

Centerbody Diameter 120 mm

Rotor Configuration Coaxial, contra‑rotating

Rotor Radius 213 mm

Blade Count 4 + 4

Internal Struts 6

Operating RPM 3500 RPM

Simulation Type CFD (MRF/AMI/Sliding Mesh)

Application Mid‑scale UAV propulsion

Conclusion

This ducted coaxial propulsion system demonstrates strong aerodynamic performance under CFD evaluation. The NACA‑profiled duct improves pressure recovery, while the contra‑rotating rotor pair reduces swirl and enhances axial thrust density. Flow visualizations highlight rotor‑to‑rotor interference regions and duct‑induced acceleration, providing clear pathways for future optimization.

While this study focuses on aerodynamic behavior, upcoming work will include structural FEA, aeroacoustic analysis, and performance optimization across varying inflow conditions and rotor speeds.