Development of a numerical simulation methodology for propellers and ducted fans of transport unmanned aerial vehicles with a takeoff weight of 80 to 350 kg
For transport unmanned aerial vehicles, selecting propulsion characteristics is a key consideration. A distinction must be made between lift propulsors, which must provide sufficient thrust within limited dimensions, and cruise propulsors, which primarily require high efficiency in both hover and forward flight. The results of developing a numerical simulation methodology for isolated propellers and ducted fans are presented, including the selection of turbulence models under conditions of a potential laminar-turbulent transition. The studied objects include K184V propellers and VK1 ducted fans, developed at the Central Aerohydrodynamic Institute (TsAGI) for hovercraft propulsion systems. The one-equation Spalart-Allmaras model and two-equation models based on k-ε and k-ω variables are investigated. The turbulence models are verified against benchmark data to account for the laminar-turbulent transition and the presence of separation bubbles on the blade and duct surfaces. One method for dividing the flow region into laminar, turbulent, and transitional zones is introducing the intermittency parameter γ into the turbulence model equations, where γ is equal to unity in fully developed turbulent flow and zero in laminar flow. The Langtry-Menter k-ω SST Reθ-γ transition model is one such turbulence model that uses the intermittency parameter and accounts for the laminar flow region effect. A geometric multigrid method is used to solve the difference equations. The numerical simulation yields pressure and velocity fields both in the computational domain and directly on the blade and duct surfaces, allowing the determination of aerodynamic characteristics of the ducted fan under various operating conditions. For hover and forward-flight conditions, the calculated dependencies of thrust and power coefficients, as well as propulsive efficiency, are obtained for a wide range of rotational speeds and engine power inputs. The results are compared with benchmark experimental data from TsAGI. Accounting for the laminar-turbulent transition and the associated formation of thin laminar separation bubbles significantly improves the agreement between the computational results and experimental data.