Aerodynamic performance and transition prediction of low-speed fixed-wing unmanned aerial vehicles in full configuration based on improved γ − Reθ model

Abstract

A transition prediction method based on the coupled Michel transition Criterion and γ−Reθ transition model has been proposed for aerodynamic analysis of low-speed fixed-wing UAVs. Firstly the Michel transition criterion is utilized to estimate the transition momentum thickness Reynolds number R˜eθt. Then an empirical relation is used to obtain the critical momentum thickness Reynolds number Reθc and the length of the transition region Flength. Finally, the improved transition model is coupled with Reynolds Averaged Navier-Stokes (RANS) equations to conduct the aerodynamic analysis based on FLUENT platform. The method is validated through the cases of SD7032 airfoil and FX 63-137 wing, which prove that the new method can improve the stability and convergence of the original γ−Reθ transition model in FLUENT. Comparison study of the new method and S-A fully turbulent model is implemented to analyze aerodynamic characteristic of a low speed UAV. The results show that the maximum lift-to-drag ratio is about 17.1 and 15.6 by transition model and S-A model, respectively. Compared to S-A model, the computed lift coefficient with transition model is basically similar, but the drag coefficient is less by 15%. The results demonstrate that the improved transition model can predict transition phenomenon well.