In the past decades, most of the research studies on airfoil shape design and optimization were focused on high Reynolds number airfoils. However, low Reynolds number airfoils have attracted significant attention nowadays due to their vast applications, ranging from micro-aerial vehicles (MAVs) to small-scale unmanned aerial vehicles. For low Reynolds number airfoils, the unsteady effects caused by boundary layer separation cannot be neglected. In this paper, we present an aerodynamic shape optimization framework for low Reynolds number airfoil that we developed based on the unsteady laminar N–S equation and the adjoint method. Finally, using the developed framework, we performed a test case with NACA0012 airfoil as a baseline configuration and the inverse of lift to drag ratio as the cost function. The optimization was carried out at Re = 10,000 and Ma = 0.2. The results demonstrate the effectiveness of the framework.

This paper investigates the influence of forward-swept wing (FSW) positions on the aerodynamic characteristics of aircraft under supersonic condition (Ma=1.5). The numerical method based on Reynolds-averaged Navier-Stokes (RANS) equations, Spalart-Allmaras (S-A) turbulence model and implicit algorithm is utilized to simulate the flow field of the aircraft. The aerodynamic parameters and flow field structures of the horizontal tail and the whole aircraft are presented. The results demonstrate that the spanwise flow of FSW flows from the wingtip to the wing root, generating an upper wing surface vortex and a trailing edge vortex nearby the wing root. The vortexes generated by FSW have a strong downwash effect on the tail. The lower the vertical position of FSW, the stronger the downwash effect on tail. Therefore, the effective angle of attack of tail becomes smaller. In addition, the lift coefficient, drag coefficient and lift-drag ratio of tail decrease, and the center of pressure of tail moves backward gradually. For the whole aircraft, the lower the vertical position of FSW, the smaller lift, drag and center of pressure coefficients of aircraft. The closer the FSW moves towards tail, the bigger pitching moment and center of pressure coefficients of the whole aircraft, but the lift and drag characteristics of the horizontal tail and the whole aircraft are basically unchanged. The results have potential application for the design of new concept aircraft.

To reduce aerodynamic coupling between the canards and the tail fins of a canard-controlled projectile, the afterbody of the projectile is decoupled from the forebody by a bearing structure, namely, a free-spinning tail. A series of numerical simulations was conducted for different angles of attack using NASA’s canard-controlled projectile with a free-spinning tail. The results were then compared with the wind tunnel test data. The spin rate of the free-spinning tail shows that, with the canard roll control, the tail section will rotate at lower angles of attack and “lock-in” at higher ones, demonstrating nonlinearization between the rotating rate and the angle of attack. According to a flow structure analysis, the circular flow velocity induced by canards is responsible for the non-linear characteristics of the tail. Moreover, the change in position of the circular flow velocity results in a reverse of the rolling moment of the “+” fixed tail projectile at different angles of attack. Furthermore, a comparison of the aerodynamic characteristics of the fixed (“+” and “x”) and free-spinning tail configurations proves that when the tail is spinning, all the aerodynamic coefficients of the free-spinning tail projectile are between those of the “+” and “x” fixed tail projectiles. The longitudinal difference in aerodynamic characteristics is related to the rolling angle, whereas the lateral difference is related to both the rolling angle and rotation rate. When the tail section “locks-in,” different rolling angles lead to different characteristics in both the longitudinal and lateral directions.