Zhenyu Wang

Hydraulic motors and pumps are the core components in hydraulic systems. The plunger assembly is a key component for the realization of the function of the axial piston pump and motor. The coupling between the slipper and the plunger body is completed through the closing process. With the application of computational science and finite element technology, DEFORM-3D metal forming process simulation is used to establish the corresponding closing device model of the plunger assembly. Through simulation, we analyze the change law of metal flow during plastic deformation process, and carry out structural optimization design based on the simulation results. We found that the closing is completed under the appropriate cone angle and distance line of the shoe, the quality is relatively uniform, and there is no closing defects such as metal flow overflow and cracks. The pull-off force and the clearance value after rolling can meet the design requirements. This method not only can effectively shorten the product verification cycle and reduce the cost, but also can reduce the defects of the finished product and improve the yield rate, providing a new way for the design of the closing structure and closing model of the plunger assembly.

With the increased prominence of multicopter micro-aerial vehicles, more importance has been placed on the aerodynamic and acoustic performance of these systems, as their small-scale and lower Reynolds number regime provide results that are different from full-scale rotors. A computational methodology was employed in order to study the aerodynamic and aeroacoustic performance from different small-scale rotors used in a multicopter configuration. Three rotor design variables (twist, taper, and pitch) were investigated in order to understand their influence on aerodynamic and acoustic performance of a hovering rotor. Variables such as rotor rotation rate and rotor radius were kept constant. Common aerodynamic performance metrics such as the ratio of coefficient of thrust to coefficient of power and figure of merit (FM) were used to assess aerodynamic hover performance of the designed rotors. Acoustic performance was assessed by recording acoustic pressure in the far-field at two separate receivers. Acoustic results are presented in the frequency domain as one-third octave band data and as overall sound pressure level (SPL). Flow fields and pressure contours were calculated and displayed in order to help explain aerodynamic and acoustic results. From the results, insights are provided for rotor designs that are more aerodynamically and acoustically efficient in hover. Specifically, rotors that provided lower values of disk loading and higher values of power loading were typically more acoustically efficient. Using greater rotor twist and taper increased both aerodynamic and acoustic performance.

With the rapid increase in the number of multi-rotor small unmanned aerial systems (sUAS) in recent years and a plethora of possible applications, the aerodynamic and aeroacoustic characteristics of these vehicles become very important issues. Due to the limited research on the aerodynamic and aeroacoustic characteristics of sUAS which include an airframe or support arm, this paper presents a comprehensive analysis of the flow and acoustic features with the inclusion of said geometry. The influence of rotor orientation—either mounted above or below the airframe—was comprehensively studied through experimental and computational analyses. Detailed experimental investigations—including particle image velocimetry (PIV), pressure transducer readings, and acoustic measurements—were employed to assess the aerodynamic and acoustic characteristics of a rotor–airframe system used on typical multirotor sUAS. The results from the computational methodology were also compared to those from the experiment to assess accuracy and possible benefits.

Vertical-axis wind turbines (VAWTs) are a promising solution for the use of renewable energy in residential areas. Compared to traditional horizontal-axis wind turbines (HAWTs), VAWTs are usually smaller, quieter, and insensitive to the wind direction and can be installed in a wide range of urban, suburban and rural places such as top of buildings, backyard, etc. In addition, VAWTs require a lower wind speed to self-start which increases the capability of wind energy extraction in the areas with low wind speed. However, VAWTs are less efficient and the power output of VAWTs is substantially affected by the phenomenon of dynamic stall induced by the variations of angle of attack of rotating blades, especially at low tip speed ratios (λ_TSRRe5), dynamic stall occurs periodically throughout the rotation of the blades. This results a sharp drop in lift coefficient and therefore rotor torque and power output are substantially reduced. The purpose of the present study is to investigate the prospects for improving the flow performances of small VAWTs using serrated leading-edge configurations on straight blades in a conventional H-type VAWT design to control dynamic flow separation. A numerical study is carried out to obtain the detailed flow fields for analysis and visualization. The results show that the turbine blade with the serration profiles of h = 0.025c (amplitude) and λ_s = 0.33c (wavelength) not only increased the power generation at low TSRs, but also enhanced the capability of wind energy extraction at the optimum TSR in comparison to the baseline model. The dynamic stall was suppressed significantly in the range of the azimuth angle from 80° to 160°. The flow separation induced by large angles of attack was essentially alleviated in the modified turbine model due to the serrated configuration implemented on the blade leading-edge.

A numerical study on sunroof noise reduction is carried out. One of the strategies to suppress the noise is to break down the strong vortices impinging upon the trailing edge of the sunroof into smaller eddies. In the current study, a serrated sunroof trailing edge with sinusoidal profiles of wavelengths is investigated for the buffeting noise reduction. A number of combinations of wavelengths and amplitudes of sinusoidal profiles is employed to examine the effects of trailing edge serrations on the noise reduction. A generic vehicle model is used in the study and a straight trailing edge is considered as a baseline. The results indicate that the trailing edge serration has a significant impact on the sound pressure level (SPL) in the vehicle cabin and it can reduce the SPL by up to 10~15 dB for the buffeting frequency. In addition, the transient flow field visualization and vorticity magnitude contours substantiate that the large shedding vortices are broken down into small eddies by using the serrated trailing edges. As a result, the SPL in the cabin is reduced. Furthermore the effectiveness of the trailing edge serrations is investigated for various freestream velocities. The results demonstrate that the trailing edge serration strategy is a promising solution for reducing automobile sunroof buffeting noise.