A cylindrical rod placed at the leading edge of the S809 airfoil is used as an alternative for the conventional vortex generators. In this paper, extensive numerical investigations have been conducted on the effects of the rod on the static and dynamic stall performance of the S809 airfoil. The flows around the stationary and sinusoidally oscillating S809 airfoils at Re = 10⁶ are simulated by solving the unsteady two-dimensional Reynolds-averaged Navier–Stokes equations with the Shear Stress Transport k–ω model. For the stationary airfoil, the leading edge rod can effectively enhance the aerodynamic characteristics of the airfoil and delay the stall angle, with the maximum lift–drag ratio increased by 30.7%. For the airfoil undergoing deep dynamic stall, the rod shows the capacity of eliminating the dynamic stall vortex at the leading edge and suppressing the flow separation at the tailing edge. It also reduces the peak of the negative pitching moment and the hysteresis effects substantially, and eliminates the negative damping sub-loop of the moment coefficient. Moreover, the distance between the rod and the airfoil has a strong influence on the lift forces but little effect on drag and moment coefficients of airfoil under deep dynamic stall.

In this paper, large eddy simulation (LES) was performed to investigate the shock wave/boundary layer interaction (SBLI) phenomenon in transonic compressor cascades with a chord Reynolds number of 2.12 × 106. A comprehensive analysis was conducted on both the SBLI structures inherent to the transonic compressor cascade and the coherent vortex structures within the boundary layer. The underlying mechanisms of the shock-induced boundary layer transition and the shock low-frequency unsteadiness in the transonic compressor cascade were elucidated through spectral and dynamic mode decomposition (DMD) analysis. The results revealed that boundary layer separation induced by the SBLI cannot reattach, leading to the formation of large-scale coherent vortex structures. Spectral analysis revealed that the shock-induced boundary layer transition in the transonic compressor cascade was dominated by inviscid Kelvin–Helmholtz (K–H) and secondary instability mechanisms, characterized by a dimensionless Strouhal number of 0.06. Additionally, pressure signals showed the variations in sub-frequency from the separated shear layer to the main flow. The oscillation amplitude of the shock foot was significantly greater than that of the shock main body, and the oscillation frequency of the shock foot was consistent with the sub-frequency. The oscillation frequency of the shock main body coincided with that of the compression ramp and flat plate configurations. Finally, DMD modal analysis indicated that high-frequency modes were correlated with turbulent fluctuations in the boundary layer, while medium- and low-frequency modes corresponded to shedding motion in the separated shear layer and low-frequency motion of the shock. This work promotes the understanding of the complex flow mechanisms of SBLI in the transonic compressor cascades.

The central shaft is an important and indispensable part of a small scale urban vertical axis wind turbines (VAWTs). Normally, it is often operated at the same angular velocity as the wind turbine. The shedding vortices released by the rotating shaft have a negative effect on the blades passing the wake of the wind shaft. The objective of this study is to explore the influence of the wake of rotating shaft on the performance of the VAWT under different operational and physical parameters. The results show that when the ratio of the shaft diameter to the wind turbine diameter (α) is 9%, the power loss of the wind turbine in one revolution increases from 0% to 25% relative to that of no-shaft wind turbine (this is a numerical experiment for which the shaft of the VAWT is removed in order to study the interactions between the shaft and blade). When the downstream blades pass through the wake of the shaft, the pressure gradient of the suction side and pressure side is changed, and an adverse effect is also exerted on the lift generation in the blades. In addition, α = 5% is a critical value for the rotating shaft wind turbine (the lift-drag ratio trend of the shaft changes differently). In order to figure out the impacts of four factors; namely, tip speed ratios (TSRs), α, turbulence intensity (TI), and the relative surface roughness value (k_s/d_s) on the performance of a VAWT system, the Taguchi method is employed in this study. The influence strength order of these factors is featured by TSRs > k_s/d_s > α > TI. Furthermore, within the range we have analyzed in this study, the optimal power coefficient (C_p) occurred under the condition of TSR = 4, α = 5%, k_s/d_s = 1 × 10⁻², and TI = 8%.

Drop impact on cylindrical substrates is more common than on flat substrates in many natural and engineering settings. Quantifying the transient impact force in drop-cylinder collisions is, therefore, crucial for understanding drop dynamics on curved substrates and for applications, such as icing mitigation, heat-transfer enhancement, and erosion reduction. Here, we experimentally investigate the transient impact force and morphological evolution of water drops impacting superhydrophobic cylinders, using a piezoelectric force sensor synchronized with high-speed imaging. The cylinder diameter ranges from 2 mm, which is comparable to the drop diameter of 2.05 mm, up to the flat-surface limit, while the Weber number varies from 4.5 to 102.2. Our results show that, on both flat and cylindrical superhydrophobic substrates, the impact force exhibits two distinct peaks. For the first peak, we find that at low Weber numbers the dynamics are governed by the combined effects of inertia and surface tension, while the influence of curvature remains weak. As the Weber number increases, the dependence of the first peak on curvature becomes increasingly pronounced. Based on the scaling analysis, we establish a quantitative relationship between the normalized first peak and the ratio of cylinder diameter to drop diameter. In contrast, the second peak is highly sensitive to curvature at low Weber numbers. The singular Worthington jet that forms on flat surfaces and cylinders with large diameter is suppressed on cylinders with small diameter due to the strongly asymmetric interfacial evolution. Consequently, the second peak decreases significantly as the cylinder diameter is reduced.