Over the last decade, many flight tests of the conventional/canard/flying-wing layout UAVs (unmanned aerial vehicle) have proven that the trailing-edge circulation control (CC) is an effective method to generate a significant rolling moment for the rolling control. However, the Coanda jet’s three-dimensional effects, especially the Coanda jet direction, on the design of UCAVs (unmanned combat air vehicle) have not been revealed and discussed clearly yet. In order to solve this problem, the effects of the Coanda jet direction on the swept wing’s aerodynamics and flow physics are investigated in detail in this paper. An in-house CFD(computational fluid dynamics) solver HyperFLOW with the Spalart–Allmaras for Rotation and Curvature turbulence model and the velocity inlet boundary has been validated by 2-D and 3-D CC cases and is used in this work. The research reveals that compared with the Coanda jet in the freestream direction (FJ jet), the Coanda jet perpendicular to the trailing edge (PJ jet) has a more significant impact on the aerodynamic loads and flow structures for swept wings, including increasing lift, drag, and nose-down moment, enhancing the wingtip vortex and weakening the thickness vortex. In contrast, the FJ jet performs better in improving the lift-to-drag ratio of swept wings. On a typical UCAV, the generalizability of the conclusion about the Coanda jet direction effects on the aerodynamic characteristics is verified. The current research gets an insight into the three-dimensional effects of the trailing-edge CC and provides solid support for implementing the CC technology into practical aircraft concepts.

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.

A restricted 2D necklace theory is proposed to extend the application of Flower constellations theory with regard to Earth discontinuous coverage. Firstly, the 2D lattice theory, the restricted Flower constellations, as well as the necklace theory are introduced and combined to deduce the restricted 2D necklace theory. Then, the design process of Flower constellations using the restricted 2D necklace theory is presented. Finally, numerical examples are implemented. Results indicate that the proposed restricted 2D necklace theory can be an extension of the traditional Flower constellation theory and generate a large number of configurations. Also, the superiority analysis shows that aiming at the Earth discontinuous coverage issues, the restricted 2D necklace Flower constellations perform better than the traditional Walker constellations in most of the design cases. This research can be instrumental in the evolution of the Flower constellation design theory for Earth discontinuous coverage.

Premature jet separation severely limits the control authority of transonic circulation control (CC) airfoils. This study investigates the flow physics governing Coanda jet attachment and develops a progressive-curvature Coanda surface at Ma=0.72 through shape optimization of the NASA-SC(2)-0714-CC supercritical airfoil. Relative to the constant-radius baseline, the optimized progressive-curvature surface achieves 37.0% lift enhancement and extends jet deflection from 79.4° to 125.0°. Flow-field analysis shows that the performance improvement is governed by two coordinated curvature effects. A locally smaller curvature radius near the slot exit lets the under-expanded jet expand more fully along the wall. A confined shock-induced separation bubble is then bridged and reattached, and shock-cell oscillations are damped. The subsequent progressive increase in the curvature radius reduces the required centripetal acceleration as the jet momentum decays, thereby sustaining the wall-normal pressure gradient and delaying separation. The optimized geometry also retains its effectiveness at Ma=0.3, yielding 23.2% higher lift-to-drag ratio than the baseline configuration. These results demonstrate that matching surface curvature to evolving jet momentum governs transonic CC effectiveness.

To address the critical issue of weakened control authority in transonic circulation control (CC) airfoil due to premature jet separation, this study proposes a discrete-adjoint-driven, global-local hybrid optimization framework. The framework couples a GEKPLS surrogate, Parallel EGO utilizing a hybrid PI+EI acquisition strategy for global exploration, and the L-BFGS-B algorithm for final local polishing. The Coanda surface of a baseline NASA-SC(2)-0714-CC supercritical airfoil is parametrically modeled using a radially varying function based on Bernstein polynomials. By incorporating gradient information, this three-stage workflow successfully overcomes the inherent challenges of high gradients and even discontinuities within the design space. Results demonstrate that the proposed framework is highly robust to initial point selection and exhibits excellent convergence efficiency. The optimized airfoil achieves a substantial 22.6% improvement in the lift coefficient under transonic design conditions. Aerodynamic analysis reveals that the optimal Coanda surface evolves into a quasi-single-sided Laval nozzle configuration. This unique geometry forces the underexpanded jet to undergo a controlled initial compression followed by expansion, which significantly deepens and extends the low-pressure region. The sustained low pressure provides stronger centripetal force, significantly enhancing flow entrainment, and delivers a substantially higher lift coefficient than the baseline prior to jet separation. This research offers an efficient, robust optimization paradigm for transonic CC airfoils and establishes a solid technical foundation for the application of active flow control in high-speed aircraft.