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A hydrofoil is a basic shape of fluid machinery blades, and its drag reduction performance is an important reference index in the field of fluid transportation. When fluid flows around a hydrofoil, it generates friction drag and pressure drag, greatly reducing the hydrofoil's hydraulic performance. This study designs a bionic drag reduction structure by arranging fish scales on a Clark-Y hydrofoil. The overlapping size, thickness, and coverage area of fish scales are taken as design parameters, and the optimal design scheme is attained by using the Taguchi method. Large eddy simulation is used to numerically simulate various schemes. Results show that when the overlapping size O is 2.00 mm, the thickness h is 0.36 mm, the initial position x/C of the fish scale covering is 0 (where C is the chord length of the hydrofoil), and the hydrofoil exhibits excellent drag reduction performance. The total drag reduction rate of the hydrofoil is up to 35.15%, and the drag reduction rate of friction drag and pressure drag is up to 39.56% and 25.64%, respectively. The lift–drag ratio of the hydrofoil increases by 18.04%. The bionic fish scale structure effectively inhibits turbulence, thereby reducing the drag caused by the transformation of laminar flow to turbulence. [ABSTRACT FROM AUTHOR]

As a core component in high-pressure hydrogen storage systems for hydrogen fuel cell vehicles, the spring-loaded hydrogen decompression valve (SHDV) directly affects the performance of the hydrogen fuel cells. In this study, the transient flow characteristics of fluid– structure interaction in SHDV are investigated using the dynamic mesh method and real gas model. The complete closure of the valve spool is realized by the porous medium model. Adverse pressure gradients, flow separation, and unsteady vortex evolution in the decompression valve are numerically calculated with large eddy simulation, and the reliability of the calculation is verified by the experiments and theoretical model. Results show that the characteristic curve of the SHDV startup process can be divided into three phases: rapid response phase, closure phase, and equilibrium phase. The change in spool angle slightly affects the rapid response phase but substantially affects the fluctuations of pressure and flow during the closure and equilibrium phases. In the equilibrium phase, typical adverse pressure gradients and flow separation occur downstream of the spool, gradually propagating into the control chamber and causing pressure instability. Backflow under the large-angle spool is primarily caused by adverse pressure gradient and wall shear stresses, whereas backflow under the small-angle spool is mainly formed by the obstruction of the upper wall at the control chamber. By adding a convex cylinder structure to the spool, adverse pressure gradients and flow separation downstream of the large-angle spool can be effectively suppressed. [Display omitted] • The transient flow characteristics of fluid-structure interaction are investigated. • The complete closure of the spool is realized by the porous medium model. • The adverse pressure gradient and flow separation are investigated. • The evolution mechanisms of unstable vortices are clarified. • Optimization of unsteady flow downstream of the spool by convex cylinder. [ABSTRACT FROM AUTHOR]

The retainer in the faulty piston pump exhibits abnormal wear and fracture. To investigate the early failure mechanism of the fractured retainer, a model is presented for calculating the transient contact between the overturning retainer and the slipper. The trajectory equations between the overturning retainer and the slipper are established based on the transformation matrix and the operating mechanism of the slipper in the oil-sucking and oil-discharging areas. The push point trajectory between the overturning retainer and the slipper is determined, while also identifying the failure mechanism of the retainer extrusion wear. The results demonstrate that as the degree of overturning increases, there is an escalation in both the extent and range of extrusion and wear between the failure retainer and the slipper. This research elucidates the failure mechanism of the retainer, thereby establishing a fundamental basis for dynamic modeling and coupled vibration analysis of overturning retainers. [ABSTRACT FROM AUTHOR]