Simulating unsteady flow phenomena involving moving boundaries is a challenging task, one key requirement of which is a reliable and fast algorithm to deform the computational mesh. Radial basis functions (RBFs) interpolation is a very simple and robust method to deform the mesh. However, the number of operations and the requirement of memory storage will be increased rapidly as the number of grid nodes increases, which limits the application of RBFs to three-dimensional (3D) moving mesh. Moving submesh approach (MSA) is an efficient method, but its robustness depends on the method used to deform the background mesh. A hybrid method which combines the benefits of MSA and RBFs interpolation, which is called RBFs-MSA, has been presented. This hybrid method is proved to be robust and efficient via several numerical examples. From the aspect of the quality of deforming meshes, this hybrid method is comparable with the RBFs interpolation; from the aspect of computing efficiency, one test case shows that RBFs-MSA is about two orders of magnitude faster than RBFs interpolation. For these benefits of RBFs-MSA, the new method is suitable for unsteady flow simulation which refers to boundaries movement

Most unmanned aerial vehicles which fly with moving wings or encounter gusts at low Reynolds number conditions make pitching oscillation motions. The aerodynamic forces and flow field around the wings vary dramatically with the unsteady motion parameters (reduced frequency, mean angle of attack, and amplitude). This study conducts numerical simulations to investigate the influence of such parameters on the aerodynamic characteristics of a pitching NACA 0012 airfoil. The respective cases are researched through computational fluid dynamics (CFD) based on the finite-volume method (FVM). The governing equations are the unsteady, incompressible two-dimensional Navier–Stokes (N-S) equations. The airfoil performs sinusoidal pitching oscillations with respect to the quarter chord at the Reynolds number $2.53\times {10}^5$ . A detailed analysis of the force coefficients and how their evolution is affected by the dynamics of flow structures generated during pitch oscillations is presented. The results show that these parameters change the instantaneous force coefficients quantitatively and qualitatively. The effective angle of attack is different at various locations of the airfoil chord during the oscillation motion, which determines the deviations of forces at the same angle of attack during pitch-up and pitch-down periods. It is also observed that the strength, interaction, and convection of the vortex surrounding the airfoil are significantly affected by the variations of these parameters.

Owning to the requirements for longer endurance, larger payloads as well as simpler mechanical structure of tactical UAV, the two-element airfoil technology is introduced. Firstly, the aerodynamic characteristics of five common low-speed airfoils are calculated and compared. The airfoil with good aerodynamic performance after segmentation is selected as initial airfoil. Then, the influence of different segmentation types on the aerodynamic characteristics of airfoils is analyzed, and the segmentation type which brings the best aerodynamic benefits is selected. The slot parameters are optimized by NSGA-II optimization algorithm under cruising, take-off, and a large angle of attack states to obtain a high-performance self-adaption tactical UAV airfoil. Finally, the new airfoil is applied to Sparrow-hawk tactical UAV, the CL^1.5 /CD of acceleration state increases 15.5%, the CL of large angle of attack increases 20.4% and the CL^1.5 /CD of cruising state after enlarge the aspect ratio increase12.3%.

The ground taxiing phase is a crucial stage for the autonomous takeoff and landing of fixed-wing unmanned aerial vehicles (UAVs), and its trajectory tracking accuracy and stability directly determine the success of the UAV’s autonomous takeoff and landing. Therefore, researching the adaptive robust optimal control technology for UAV taxiing is of great significance for enhancing the autonomy and environmental adaptability of UAVs. This study integrates the linear quadratic regulator (LQR) with sliding mode control (SMC). A compensation control signal is generated by the SMC to mitigate the potential effects of uncertain parameters and random external disturbances, which is then added onto the LQR output to achieve a robust optimal controller. On this basis, through ANFIS (Adaptive Neuro-Fuzzy Inference System), the nonlinear mapping relationship between multiple state parameters such as speed, lateral/heading deviation and the weight matrix of the LQR controller is learned, realizing a data-driven adaptive adjustment mechanism for controller parameters to improve the tracking accuracy and anti-interference stability of the UAV’s taxiing trajectory.

The lift of an aircraft can be effectively enhanced by circulation control (CC) technology at subsonic speeds, but the efficiency at transonic speeds is greatly decreased. The underlying mechanism of this phenomenon is not fully understood. In this study, Reynolds averaged Navier—Stokes simulation with $k-\omega$ shear stress transport model was utilized to investigate the mechanism of lift enhancement by CC in transonic flow. For validation, the numerical CC results were compared with the NASA experimental data obtained for transonic CC airfoil. Thereafter, the RAE2822 airfoil was modified with a Coanda surface. The lift enhancement effects of CC via steady blowing with different momentum coefficients were tested at $Ma=0.3$ and 0.8 at $\alpha =3^{\circ }$, and various fluid mechanics phenomena were investigated. The results indicate that the flow structure of the CC jet is insensitive to the incoming flow conditions because of the similarity to the local static pressure field around the trailing edge of the airfoil. Owing to the appearance of shockwaves on the airfoil surface in the transonic regime, the performance of the CC jet is restricted to the trailing edge of the airfoil. Transonic CC achieved a slight improvement in aerodynamic performance owing to a favorable shift in the shockwave pattern and accelerated flow in the separation region on the airfoil surfaces. Revealing the mechanism of lift enhancement of CC in the transonic regime can facilitate the rational design of new fluidic actuators with high activity and expand the potential applications of CC technology.