Aerospace

For high-speed compound helicopters, such as the S-97 Raider, the reflection and diffraction effects of vertical/horizontal tails on pusher propeller noise are inevitable. To investigate the noise distortion effect of the rear-mounted pusher propeller, this study first relies on the Chinese Laboratory of Rotorcraft Navier-Stokes (CLORNS) solver, adopting the high-resolution Perturbed polynomial reconstructed Targeted Essentially Non-Oscillatory scheme (TENO-P) combined with the Delayed Detached Eddy Simulation based on the Spalart–Allmaras (SA-DDES) turbulence model to resolve the multi-scale rotor flowfield. Additionally, a continuous and conserved acoustic source extraction method is proposed to eliminate non-physical waves at the one-way Computational Fluid Dynamics and Computational AeroAcoustics (CFD–CAA) coupling interface, addressing the temporal inconsistency between flowfield evolution and acoustic propagation. Finally, numerical investigations are conducted on the instantaneous acoustic wave propagation and acoustic directivity of the pusher propeller under the influence of vertical/horizontal tails. The results show that significant acoustic distortion occurs when pusher propeller-generated noise interacts with vertical/horizontal tails. This interaction not only produces reflected and diffracted acoustic waves but also leads to wavefront discontinuities, the formation of short acoustic waves, and changes in acoustic directivity. The maximum variation in the sound pressure level reaches 10 dB at local azimuths. The distortion effect of tails on pusher propeller noise is closely correlated with the number of propeller blades. The interaction process between the propeller and tails becomes more complex with the increase in blade count, resulting in the generation of shorter acoustic waves. For the six-blade rotor, the originally continuous acoustic wave branch can be split into up to four short waves. This study confirms that the proposed Hybrid Computational AeroAcoustics (HCAA) method holds significant application prospects in the aeroacoustic research of compound helicopters.

This paper addresses the attitude tracking control problem for laterally symmetric vehicles during the boost phase under aerodynamic parameter variations and high-altitude wind disturbances. A neural disturbance observer-based nonsingular predefined-time sliding mode control scheme is proposed. First, a Lyapunov-based predefined-time stability criterion is established, which facilitates the design of an adaptive predefined-time observer using radial basis function neural networks. Without requiring prior knowledge of disturbance bounds, this observer ensures that disturbance estimation errors converge to a neighborhood of the origin within a predefined time parameter. Second, a novel nonsingular predefined-time sliding surface is constructed using hyperbolic tangent functions, leading to an integrated predefined-time sliding mode controller. The proposed scheme guarantees that the upper bound of the convergence time for initial attitude tracking errors is independent of the initial boost-phase states and can be arbitrarily predefined. Unlike conventional predefined-time control methods, the proposed approach eliminates controller singularity issues while avoiding the introduction of piecewise continuous functions or double-integral terms in either the sliding surface or the control law, thereby reducing structural complexity. Theoretical analysis confirms the boundedness of all closed-loop signals during attitude tracking. Numerical simulations demonstrate the effectiveness of the proposed control strategy under complex flight conditions.

Lunar dust exhibits exceptionally strong adhesion, abrasiveness, and electrostatic charging due to long-term exposure to extreme temperature cycling (−183 °C to 127 °C), high vacuum, and intense radiation. With the rapid advancement of global lunar exploration programs and the planned construction of lunar bases, lunar dust has become a critical threat to exploration equipment, spacesuits, and spacecraft sealing systems. This paper systematically reviews recent progress in lunar dust mitigation technologies from the perspective of engineering application requirements. Key micro-mechanism factors governing dust adhesion and removal efficiency are analyzed, and the protection mechanisms and application scenarios of traditional lunar dust mitigation technologies are comprehensively discussed, including both active and passive approaches. Active protection technologies generally provide effective dust removal but suffer from high energy consumption, whereas passive strategies can reduce dust adhesion but face challenges in mitigating dynamic dust accumulation. To overcome these limitations, recent studies have increasingly focused on active–passive synergistic strategies that integrate surface modification with dynamic dust removal. Such approaches enable improved efficiency and adaptability by combining long-term dust resistance with real-time removal capability. Based on the latest research advances, this paper further proposes an integrated technical framework for the engineering design of efficient lunar dust protection.