Search

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]

Hydrofoil sections are broadly used in the field of fluid machinery. The leading edge of a hydrofoil structure is closely related to drag and cavitation performance. In this study, we adopt the concept of a bionic design. The fin structure of a fish is simplified and applied to the traditional National Advisory Committee for Aeronautics 0015 hydrofoil. We adopt the Grey–Taguchi method to calculate the best layout. This helps obtain the best drag and cavitation performance. Large eddy simulations are used to verify the scheme. When the ratio of fin depth to length h/L is 0.3, the fin layout length Xn is 7 L, the inclination of fins θ is 7°, and the bionic hydrofoil exhibits the best hydrodynamic performance. Application of the best bionic hydrofoil to the fluid machinery (pump) demonstrates that the hydraulic performance of the pump has been considerably improved. [ABSTRACT FROM AUTHOR]

Focusing on the current limited vertical adjustment technique of large-scale drillings,a 6-DOF parallel adjustment equipment with 12 inputs is designed for the working condition of vertical drilling.The equipment mechanism consists of 6branched chains with redundancy which are symmetrical in structure.Each of the chains is composed by a compound of rotate joint and a compound of spherical joint,while the two pairs are connected by two prismatic pairs.The modal analysis is carried out on the body which is based on ANSYS software,first six order frequency distribution and modal vibration mode,and along the X、Y、Zdirection of the displacement frequency response about the moving platform are got.The analysis consequence shows that the most sensitive of external forces to the moving platform is 46 Hz frequency.Otherwise,the working space of the 6-DOF platform is obtained by using the 3-D searching algorithm.The results have significant meanings in the further research on the correlation between the parameters and the whole mechanism,as well as the optimization of the parameter.

This paper proposes to improve the output performance of a piezoelectric pump by matching the resonant frequency of the resonator to the optimal operating mode of bridge-type polydimethylsiloxane (PDMS) check valves. Simulation analyses reveal that the side-curling mode of the PDMS valve is conducive to liquid flow and exhibits a faster frequency response compared with the first bending mode. The first bending resonant frequency of a beam-type piezoelectric resonator was tuned close to the side-curling mode of the PDMS valve by adjusting the weight of two mass blocks installed on both ends of the resonator, so that both the resonator and the valve could work at their best conditions. Experiments were conducted on a detachable prototype piezoelectric pump using PDMS valves with three different lengths. The results confirm that the peak flowrate at the resonant point of the pump reaches its maximum when the resonant frequencies between the resonator and the valve are matched. Maximum peak flowrates of 88 mL/min, 72 mL/min and 70 mL/min were achieved at 722 Hz, 761 Hz and 789 Hz, respectively, for diaphragm pumps using five-, four- and three-inlet-hole PDMS valves, under a driving voltage of 300 Vpp. [ABSTRACT FROM AUTHOR]

The gas–solid fluidized bed is the key structure of industrial fluidization, and it is widely used in fields such as chemical reactors and industrial material conveying. To study the uniformity of velocity distribution (Vu) in a fluidized bed and clarify the interaction mechanism between the geometric structure of the air chamber and the gas flow, in this paper, 16 novel chamber structures for powder unloading were designed based on the Taguchi method. Computational fluid dynamics was used to simulate the different chamber schemes, and the effects of various geometric factors on the response were analyzed based on the Taguchi method. The effect of the novel optimization model for powder unloading was verified by tests. The results show that the optimal combination of geometrical parameters is air chamber capacity (V) at level 4, separation ratio (K) at level 1 and clearance of splitter plate (δ) at level 1, and δ has the greatest effect on the Vu1 and Vu2 in the fluidized bed. With the increase in δ and K, the velocity of the airflow away from the inlet side increases, and the area of the vortex near the splitter plate increases. Compared with the baseline model, the fluidized bed with the novel air chamber can effectively reduce the residual rate of powder unloading. [ABSTRACT FROM AUTHOR]