Related references
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Article
Mechanics
Jeongwoo Ko et al.
Summary: A comprehensive multirotor noise assessment framework is developed to predict the noise of rotational-speed-controlled rotor configurations in real-time. The framework can synthesize frequency-modulated multirotor noise and analyze its characteristics. It includes modules for flight control, aerodynamics, time reconstruction, noise prediction, and time-frequency analysis. Validation and verification studies have confirmed the effectiveness of the framework for different configurations and flight conditions.
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S. B. Yucel et al.
Summary: The vortex dynamics of biplane configuration with pure plunging airfoils is studied using experimental and numerical methods. The effects of different frequencies and amplitudes of plunging motion on vortex shedding and interaction mechanisms are investigated. Numerical simulations reveal that the phase difference has an impact on vortex structures and propulsive characteristics, with opposing plunge at 180 degrees showing the highest efficiency and 90 degrees beneficial for lift production.
Article
Mechanics
B. Fenyvesi et al.
Summary: Counter-rotating rotor configurations are becoming more common in fixed-wing aircraft and unmanned aerial vehicle sectors due to their higher efficiency. However, the noise generated by these configurations is significant, and understanding and reducing the noise is important. This paper presents an automated method for analyzing noise source maps to identify the dominant noise generation mechanisms associated with interaction tones.
Article
Mechanics
Qiaogao Huang et al.
Summary: A numerical analysis based on detached eddy simulations is conducted to investigate vortex dynamics of a pre-swirl pumpjet propulsor (PJP) in oblique inflow. The effects of incidence alpha and propeller loading on the wake dynamics of PJP as well as the mechanism leading to its destabilization are discussed. The results show that high hydrodynamic efficiency loss is found for PJP operating in drift, and a different secondary vortex structure caused by the duct is found for PJP in both axisymmetric and oblique flow conditions. Furthermore, the instability mechanism of tip vortices shows obvious asymmetry.
Article
Mechanics
Zi-wei Hou et al.
Summary: This study numerically investigates the pressure evolution of shock waves and high-pressure zones between two detonation tubes in a dual-tube detonation-powered underwater engine. The results reveal the formation and interaction of shock waves and discuss the influence of different factors on the engine's performance.
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Mechanics
Ao Xu et al.
Summary: A numerical study is conducted to train a self-propelling agent to migrate in an unsteady flow environment. The results show that the smart agent can learn to migrate efficiently by utilizing background flow currents, and the training process is more challenging in turbulent flow compared to simple periodic flow.
Article
Mechanics
Chunyu Wang et al.
Summary: Birds and bats can enhance aerodynamic performance through a combination of flapping and local sweep morphing, providing a possible approach for improving micro aerial vehicles.
Article
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Xuehao Wang et al.
Summary: Autonomous underwater vehicles (AUVs) are cost-effective platforms for ocean acoustic measurements and surveys. This study presents the acoustic observation application of the Petrel acoustic AUV in marine monitoring, evaluates its self-noise characteristics, and proposes a solution to address the impact of attitude adjustment on acoustic data quality.
Article
Mechanics
T. M. Faure et al.
Summary: This study focuses on the cetacean propulsion mechanism and validates low-order models on a benchmark flexible straight wing. The research highlights the importance of incorporating viscous drag modeling into the discrete vortex method for accurate thrust results. Additionally, a lifting line theory is introduced to extend the three-dimensional leading-edge-suction-parameter modulated discrete vortex method, considering the wing dihedral resulting from spanwise flexibility. The results show that excessive flexibility is detrimental while intermediate flexibility improves the thrust coefficient.
Article
Mechanics
Yan Wu et al.
Summary: This paper presents a detailed investigation of tonal noise generated by an unmanned aerial vehicle propeller with a circular strut mounted downstream. Experimental measurements and computational fluid dynamics simulations were used to analyze the acoustic pressure and the noise generation mechanism. The study showed that the magnitude and shape of the pressure impulse caused by the propeller-strut interaction varied with observer location and decreasing the distance between the propeller and the strut reduced the impulse magnitude. The analysis also revealed that both the propeller and strut contributed to the noise generation, and the combined signals had a complex directivity. Analytical models were developed to estimate the unsteady loading on the propeller and strut and predictions made using these models showed reasonable agreement with experimental and computational results.
Article
Mechanics
Chunyu Wang et al.
Summary: The study finds that spanwise oscillation can enhance the power factor of a gliding wing, with the optimal reduced frequency ranging from 0.47 to 0.56. Analysis of vortex structures and the Lamb vector field suggests that the interaction between stable leading-edge vortices and side-edge vortices associated with spanwise oscillation leads to the enhanced power factor.
Article
Mechanics
Jaeheon Jeong et al.
Summary: This study conducted a stochastic numerical analysis on a multirotor to investigate its acoustic characteristics, taking into account the effects of rotational speed fluctuation. The analysis was validated through noise measurements in an anechoic chamber, showing that the stochastic approach could effectively predict the noise features of the multirotor.
Article
Mechanics
Liwei Liu et al.
Summary: This study uses computational fluid dynamics (CFD) simulations to predict the self-propulsion performance of a full-scale submarine propelled by a high-skew propeller. Model- and full-scale simulations are conducted and compared, showing consistent results with minor discrepancies after adequate corrections. Discussions are provided on the differences between model- and full-scale self-propulsion results, including propeller performance, pressure distribution, boundary layer, and wake flow.
Article
Mechanics
Talib Dbouk et al.
Summary: This study focuses on the noise induced by drone swarms, revealing that a V-flight formation emits less noise and induces reduced drag compared to a U-shape (or rectangular) formation, thus saving energy. The research has broad impacts on defense and security, public health, transportation, and surveillance, among other fields.
