Numerical Investigation Into the Fluidic Adaptation of the Throat Cross-Section of Coanda Coflow Fluidic Thrust Vectoring Nozzles for Mid-Sized Mixed Turbofan Engines

This study presents a numerical investigation into the aerodynamic effects and scalability of a novel symmetric Coanda coflow nozzle concept for fluidic thrust vectoring (FTV) in unmanned aerial systems (UAS). Unlike traditional asymmetric configurations used for lateral jet deflection, the proposed design introduces tangential Coanda injection on both upper and lower nozzle walls to modulate the effective throat area and adapt nozzle exit conditions across varying flight regimes. Using a validated two-dimensional RANS-based CFD framework combined with NPSS engine performance data, over 470 flight conditions were evaluated for a medium-thrust class mixed-flow turbofan engine. Key performance metrics—such as gross thrust, specific thrust, jet velocity, effective throat area, and exit pressure ratio—were analyzed across a wide range of Mach numbers, altitudes, and injection mass flow ratios. Results show that symmetric Coanda injection consistently increases gross and specific thrust by reshaping the internal flow geometry, particularly through displacement-thickness-driven throat contraction. However, thrust augmentation comes at the cost of pressure mismatch at higher injection levels and off-design conditions. The trade-off analysis highlights the need for adaptive control strategies. Optimal injection ratios were found to lie between 5–10\% at low Mach numbers and altitudes, shifting to lower values at higher flight speeds or altitudes. The findings demonstrate that symmetric Coanda coflow enables dynamic performance tuning of FTV nozzles, providing a promising pathway toward mechanically passive yet aerodynamically adaptive nozzle designs for next-generation UAS propulsion systems.