The Numerical Research On Transient Aerodynamic Performances And Configurations Of Low Speed UAVs

Unmanned Aerial Vehicles(UAVs),with characteristics of low price and light weight configuration, have widely applied in military and civil areas, such as battlefield situation awareness and SAR missions in disaster areas. In recent years, large amounts of UAVs have been developed, thus the low speed UAVs experience a quickly development for their unique advantages. Quickly obtaining the steady and unsteady aerodynamics parameters is playing a significant role in designing control system and evaluating flying quality during aerodynamics configuration design. Therefore, how to make a good use of CFD technique to get the performance of UAVs more effectively and economically has become a hot point in the research areas. This article will choose the low speed UAVs as the research object and mainly concern about the steady and unsteady aerodynamics performances. The main work of this thesis may be described with the following several aspects:(1)Several low speed UAVs were investigated and the features of them were analyzed, then a new definition of low speed UAVs is proposed at view of fluid dynamic. Finally the methods which are used in steady and unsteady aerodynamics performances analysis are concluded.(2)Numerical simulation of the flow over airfoil are performed using the RANS model by solving the Navier-Stokes equations with widely used turbulence model operating at a Reynolds number 3×105.The ability in numerical simulation of the turbulence model are evaluated by comparing the results with the experiment data. A novel simulation approach of fixing the transition point is built and validated in the skin friction coefficient distribution, the drag coefficient of airfoil and the separation bubble simulation. The results show good agreement with experiment data.(3)The trimming process and stability analysis of the UAV are based on the VB scripts and VLM code. With this method, the original mounted angel of main lift surfaces can be calculated quickly. After that, numerical simulation is conducted to get the viscous flow field of the UAV, the final results are used to modify the results previously obtained by inviscid flow theory.(4)Based on the Etkin’s theory, formulations of pitching and rolling aerodynamics derivatives are presented to calculate stability derivatives in various of angels of attack. The demonstration of its feasibility is given by theoretical derivation. Flowing this, several cases are given to check the ability of CFD technique in dynamics simulation. Finally the various parameters which influence the dynamics derivatives calculation are investigated and the stability derivatives of the UAV are calculated.(5)With the foundation of CFD technique which we built above to analyze the dynamic aerodynamics performances, we will explore and design a flying-wing aerodynamics configuration of the low speed UAV at the last part of this article. The problems of stability and trimming are discussion in this part.