###### Abstract  
Coupling systems play a vital role in hydraulic power transmission equipment. In recent years, flat-face coupling systems have been extensively studied due to their environment friendly features. The difficulty of the connection process of hydraulic equipment increases with the increase in their working pressure. To improve the convenience of making high-pressure connections, a novel flat-face coupling system is proposed in this article. In the proposed design, which is based on the conventional flat-face coupling system, the resistance caused by high hydraulic fluid pressure during coupling is drastically reduced by the addition of an instantaneous pressure relief module. In this study, the theoretical model of the system kinetics is established to illustrate the operational mechanism of the novel design, and a series of computational fluid dynamics numerical investigations based on the novel dynamic mesh technology and Ansys Mosaic meshing technology are implemented to verify the rationality of the proposed design. Additionally, an optimal design of the novel flat-face coupling system is proposed to reduce the energy loss during hydraulic power transmission. computational fluid dynamics (CFD); hydraulic power transmission; flat-face coupling; dynamic mesh; poly-hexcore mesh; turbulent kinetic energy; mechanism design +
Footnote †: journal: Applied Sciences
circuits flexibly and quickly without the need for extra tools or special equipment [12]. In these couplings, the energy losses occur mainly in the valves, coupling gaps and the gaps of the working mechanism of positive displacement machines such as pumps and motors. [PERSON] proposed a new design for satellite pumps and investigated their volumetric and hydraulic-mechanical losses, their efficiencies and their noise characteristics [13]. [PERSON] also established a theoretical energy loss model for a hydraulic motor composed of planetary gears and verified it through experiments [14]. Taking inspiration from these works, this article presents a series of numerical investigations on the energy losses occurring in the proposed novel hydraulic coupling system. According to the shape of the connector, hydraulic quick couplings can be divided into three main categories: (1) poppet type, (2) spherical type and (3) flat-face type [15; 16; 17]. Compared to poppet type and spherical type couplings, flat-face type is a recent development that can minimize the leakage of hydraulic fluid during connection and disconnection to reduce the environmental pollution. However, the complicated geometry of the flat-face connection system leads to a higher energy consumption during hydraulic transmission. Therefore, a number of studies proposing different optimization schemes have been carried out to reduce this pressure loss problem, [18; 19; 20; 21; 22]. The working pressure of hydraulic power systems has increased with the development of industry [23]. This increase in the working pressure of the system also increases the difficulty of the coupling process of hydraulic circuits. A variety of methods have been proposed to improve the convenience of the coupling process under high operating pressures [24; 25]. However, it has been difficult to greatly improve the conventional flat-face coupling system (CFFCS) due to the size limitations of hydraulic circuits. In this research, a novel flat-face coupling system (NFFCS) design with an instantaneous pressure relief based on [PERSON]'s law is proposed, and validated through a series of comparative numerical investigations of 10 mm CFFCS and NFFCS. The instantaneous pressure relief effect of the proposed NFFCS design is verified through transient simulation results based on the novel dynamic mesh analysis method. In order to reduce the energy loss during hydraulic power transmission, the optimization of the hydraulic flow characteristics of NFFCS is implemented based on Ansys Mosaic meshing technology and CFD simulation technology.