A numerical study was conducted on the influence of turbulence intensity and Reynolds number on the mean topology and transition characteristics of flow separation to provide better understanding of the unsteady jet flow of turboelectric distributed propulsion (TeDP) aircraft. By solving unsteady Reynolds averaged Navier-Stokes (URANS) equation based on C-type structural mesh and $\gamma -{\widetilde{\mathrm{Re}}}_{\theta t}$ transition model, the aerodynamic characteristics of the NACA0012 airfoil at different turbulence intensities was calculated and compared with the experimental results, which verifies the reliability of the numerical method. Then, the effects of varied low Reynolds numbers and turbulence intensities on the aerodynamic performance of NACA0012 and SD7037 were investigated. The results show that higher turbulence intensity or Reynolds number leads to more stable airfoil aerodynamic performance, larger stalling angle, and earlier transition with a different mechanism. The generation and evolution of the laminar separation bubble (LSB) are closely related to Reynolds number, and it would change the effective shape of the airfoil, having a big influence on the airfoil’s aerodynamic characteristics. Compared with the symmetrical airfoil, the low-Reynolds-number airfoil can delay the occurrence of flow separation and produce more lift in the same conditions, which provides guidance for further airfoil design under TeDP jet flow.

A cellular-based evolutionary topology optimization scheme over a small curvature big contour wing surface is proposed for the design of an ultralight surface structure. Using this method, a ground-structure technique is first applied to obtain homogeneous mesh generation with a predefined weight value over the design domain. Secondly, the stiffener path’s description is guided by a modified map L system topology method that simulates the growth of the bionic branch, and the structural components are obtained by the specified searching method according to weights of the previous mesh vertexes. Thirdly, an optimal curved stiffener layout is achieved using an agent-based algorithm to create individual instances of designs based on a small number of input parameters. These parameters can then be controlled by a genetic algorithm to optimize the final design according to goals like minimizing weight and structural weakness. A comparison is implemented for long-span panel stiffener layout generation between an initial straight case and a bionic optimal case via our method, thereby indicating the significant improvement of the buckling loads by steering the stiffener’s path. Finally, this bionic method is applied to the wing box structure design and achieves remarkable weight loss at last.

In recent years, the air-drop launch technology of near-space UAVs has attracted much attention. Between downfall from the carrier and the flight control system’s initiation, the UAV presents free-fall movement. This free-fall process is very important for the control effect of the flight control system and is also crucial for the safety of the UAV and the carrier. Focus is required on two important dynamic parameters of the UAV: the moment of inertia and the center of mass position. In this paper, we used a quasi-steady model proposed by predecessors to address the flat-plate falling problem with modifications to describe the freely falling motion of the wing. Computational fluid dynamics (CFD) were used to simulate the free-fall movement of the wing with various parameters, and the wing release behavior was analyzed to check the quasi-steady model. Research shows that the movement characteristics of the falling wing are mostly reflected in the longitudinal plane, and the developed quasi-steady analytical model can more accurately describe the dynamic behavior of free-fall to some extent. By using CFD methods, we further investigated the aerodynamic performance of the free-fall wing. The results show that the wing mainly presents tumbling and fluttering motion. Changing the moment of inertia around the tumbling axis changes the tumbling frequency and the time point as the wing enters tumbling. In contrast, changing the position of the center of mass significantly changes the form of falling and makes the free-fall motion more complex. Therefore, it is necessary to carefully configure the center of mass in the UAV design process.

This paper establishes an analytical model for component mass, takeoff weight, and performance constraints of distributed electric propulsion (DEP) propeller-driven short takeoff and landing (STOL) unmanned aerial vehicles (UAV), and develops a conceptual design method considering propulsive/aerodynamic coupling effects. The proposed approach was applied to design a 350 kilogram-class DEP UAV with STOL capability, verifying the feasibility and effectiveness of the design method. To investigate the layout design and propulsive/aerodynamic coupling characteristics of DEP UAV, three UAV configurations with different DEP arrangements are formulated and studied, and the results indicate that the flap deflection significantly increases the lift coefficient of the UAV during takeoff, and under the same total thrust and power conditions, the lift-enhancement using DEP arrangement is more significant. In addition, it is necessary to fully consider the propulsive/aerodynamic coupling effects in the conceptual design process, and this is of great significance for the future development of DEP STOL UAV.

According to the development and research background of the next generation civil aircraft, the aerodynamic characteristics and stall mechanism of a specified distributed propulsion (DP) blended-wing-body (BWB) aircraft are analyzed and studied by combining the numerical simulation and the wind tunnel tests. Firstly, the DP BWB configuration and the numerical simulation methods are introduced. Secondly, the aerodynamic performance of the DP BWB aircraft between with and without the DP induced effects into consideration are compared and analyzed by using the numerical simulation. Finally, the stall mechanism is sorted out based on the wind tunnel flow-field visualization, and at the same time, the numerical simulation method is also validated. The results show that the span-wise flow along the leading edge (LE) of the plane platform for DP installation is the main factor to induce stall at high angle of attack (AOA), while the middle fuselage can still provide enough lift to maintain flight at high angle of attack, and the DP system has an obvious combination effect on the flow on the wing, which maybe is an effective way to control and improve the BWB stall characteristics at high AOA.

Hand-launched unmanned aerial vehicles require adequate low-speed lift and cruise efficiency. This study investigates a 3 kg propeller-aided biplane (PAB) with distributed electric propulsion using unsteady computational fluid dynamics. Propeller–wing arrangements are examined, followed by complete-aircraft simulations with transition modeling and sliding meshes. A conventional tractor configuration (CONV) provides a reference under comparable design constraints. Among the arrangements examined, over-the-wing and leading-edge tractor installations provide substantial lift augmentation. Predicted airframe loads are sensitive to transition modeling and the representation of propeller rotation. Although PAB has a lower clean-airframe lift-to-drag ratio, its smaller propeller-induced airframe drag penalty largely offsets this disadvantage at sampled fixed-rpm cruise conditions. At the 5 m/s hand-launch condition and angles of attack of 8–12°, PAB provides greater lift per unit shaft power with a comparable positive net forward force. At 12°, the lift-per-power gain is approximately 4%. About the respective design reference centers of gravity, cycle-mean nose-down moment magnitudes are approximately 77% and 49% smaller for PAB than for CONV at 8° and 12°. These predictions indicate hand-launch benefits for this non-optimized configuration pair under the prescribed conditions.