Bottom-up computational design of a hybrid tricopter agricultural spray UAV: propeller, nozzle, tank and airframe CFD optimization

Abstract

This paper aims to develop and validate a hybrid tri-agri-copter (TAC) unmanned aerial vehicle (UAV) for precision agricultural spraying using a bottom-up computational fluid dynamics (CFD)-first design methodology that sequentially evaluates each sub-system before full-vehicle integration. A 2.5 kg payload is adopted as the primary design driver. Critical components, including a coaxial propeller unit, Y-shaped airframe, three nozzle configurations and two tank geometries, are modeled in 3DEXPERIENCE and evaluated using ANSYS Fluent under vertical take-off and landing, hover and forward-flight conditions. Validation is conducted via wind tunnel drag measurements and laboratory nozzle flow tests. Nozzle-2 produces a uniform, well-collimated jet free of recirculation, with an exit velocity of 16.46 m/s at 2 bar; the proposed rectangular-convergent tank provides superior flow uniformity and a 29.4% higher exit velocity than the conventional conical tank. Wind tunnel validation yields a root-mean-square error of 0.00013 on the drag coefficient; the nozzle flow rate matches CFD within 3.3%. The thrust margin of the design payload is 3.6%. Only three nozzle and tank geometries are compared; field trials remain as future work. The validated CFD-first framework enables agricultural UAV developers to select components before hardware commitment, reducing development cost and iteration time. To the best of the authors’ knowledge, this is the first study to apply sequential, component-level CFD to the propeller, nozzle, tank and full airframe in a single bottom-up design chain for an agricultural TAC.