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The impact of the clocking effect of the pre-swirl stator on the excitation force of a pump-jet propeller is investigated in this paper. The clocking effect, a common concept in fluid machinery, is applied and extended to the relative circumferential position between the pre-swirl stator and the submarine hull in this paper. The research is conducted using computational fluid dynamics (CFD) and water tunnel experiments. The CFD results demonstrate that the clocking effect exerts a negligible influence on the steady performance of the pump-jet. However, the excitation force of the rotor is greatly influenced by it. This is due to the fact that the stator, when positioned at various clocking positions, generates different wakes that change the amplitude and phase distribution of the rotor strips' excitation force. Furthermore, the experimental results demonstrate that the influence of the clocking effect on the duct vibration and the noise radiated by the pump-jet should not be ignored, the trend of which is consistent with that of the excitation force obtained by CFD, thereby establishing a clear correlation between the excitation force and the vibration and noise level. This paper is of guiding significance for the low-noise design of submarine pump-jets. • Discovered and defined the clocking effect of the pre-swirl stator. • Investigated the mechanism of the clocking effect on excitation force. • Verified the clocking effect through water tank experiments. [ABSTRACT FROM AUTHOR]

When compared with horizontal-axis wind turbines, vertical-axis wind turbines (VAWTs) have the primary advantages of insensitivity to wind direction and turbulent wind, simple structural configuration, less fatigue loading, and easy maintenance. In recent years, large-scale VAWTs have attracted considerable attention. Wind loads on a VAWT must be determined prior to structural analyses. However, traditional blade element momentum theory cannot consider the effects of turbulence and other structural components. Moreover, a large VAWT cannot simply be regarded as a planar structure, and 3D computational fluid dynamics (CFD) simulation is computationally prohibitive. In this regard, a practical wind load simulation method for VAWTs based on the strip analysis method and 2D shear stress transport (SST) k-ω model is proposed. A comparison shows that the wind pressure and aerodynamic forces simulated by the 2D SST k-ω model match well with those obtained by 2.5D large eddy simulation (LES). The influences of mean wind speed profile, turbulence, and interaction of all structural components are considered. A large straight-bladed VAWT is taken as a case study. Wind loads obtained in this study will be applied to the fatigue and ultimate strength analyses of the VAWT in the companion paper.

When compared with horizontal-axis wind turbines, vertical-axis wind turbines (VAWTs) have the primary advantages of insensitivity to wind direction and turbulent wind, simple structural configuration, less fatigue loading, and easy maintenance. In recent years, large-scale VAWTs have attracted considerable attention. Wind loads on a VAWT must be determined prior to structural analyses. However, traditional blade element momentum theory cannot consider the effects of turbulence and other structural components. Moreover, a large VAWT cannot simply be regarded as a planar structure, and 3D computational fluid dynamics (CFD) simulation is computationally prohibitive. In this regard, a practical wind load simulation method for VAWTs based on the strip analysis method and 2D shear stress transport (SST) k-ω model is proposed. A comparison shows that the wind pressure and aerodynamic forces simulated by the 2D SST k-ω model match well with those obtained by 2.5D large eddy simulation (LES). The influences of mean wind speed profile, turbulence, and interaction of all structural components are considered. A large straight-bladed VAWT is taken as a case study. Wind loads obtained in this study will be applied to the fatigue and ultimate strength analyses of the VAWT in the companion paper. [ABSTRACT FROM AUTHOR]