In this study, design of experiment, three-dimensional free surface flow analysis, response surface method, and the multi-objective optimization method were combined to develop a multi-objective optimization design method for an undershot cross-flow water turbine. This design method was applied to a water turbine runner, and multi-objective optimization was performed to achieve low head and high power output. The resulting optimized runner was tested, and the flow field around the runner and the torque fluctuation acting on the blade were investigated. The results showed that the effective head of the optimized runner was 20.2% higher than that of the original runner, but the turbine output was significantly higher (98.3%). This is because, although the optimized runner had fewer blades, the torque of each blade increased significantly, since the optimized runner had a narrower negative torque range and a larger positive torque range than the original runner in terms of the torque fluctuation of one blade during one runner rotation, resulting in a significant increase in total torque.

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Two-vane pumps, as the core equipment for sewage treatment, are subject to severe clogging and wear during operation. This paper proposes a multi-objective optimization strategy based on the CFD-DEM coupling method, random forest, and NSGA-III to improve the discharge performance of a two-vane pump. Firstly, the optimal Latin hypercube sampling is used to generate 60 samples. Secondly, the random forest algorithm is used to build an approximate model between the design variables and optimization objectives, and then NSGA-III is used to search the Pareto front. Finally, the TOPSIS with entropy weight is used to objectively select the optimal pump for the Pareto optimal solution set. Under clear water conditions, the optimized pump has a significantly higher head and efficiency. Under the rated solid-liquid two-phase flow conditions, the head and efficiency of the optimized pump are increased by 4.14% and 1.45%, respectively. The passing ability of the rag in the pump is significantly improved and the wear of the rag on the pump is greatly reduced by 36.4%.

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The paper presents the calculation of 2D pressure distribution of lubricated oil film in the internal gear motors and pumps considering to misalignment of the ring gear by using the finite difference method (FDM). The equation of film thickness in case of misalignment is firstly established. The Reynold equation is then solved to obtain 2D pressure distribution. The results point out that the pressure distribution is greatly affected by the misaligned angle of the ring gear. If the ring gear is aligned then the pressure distribute evenly. However, if the ring gear is misaligned then the oil pressure distribution is not even. The maximum pressure will be transitioned to one side in axial direction of ring gear. Moreover, the misalignment causes the negative pressure area which leads to cavitation phenomenon and reduces the capacity of the oil film.

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The unreasonable design of pressure differential valve may lead to unstable oil supply of aero-engine lubrication system. In order to find the optimization method of pressure differential valve structure, taking the oil supply subsystem of lubrication system as the research object, to study the effect of different pressure differential valve structure parameters on the oil supply pressure characteristics of aero-engine lubrication system by using a combination of numerical simulation and experimental verification. The results show that: (1) The reduction of spool damping hole diameter can improve the stability of oil supply pressure, but the dynamic performance becomes worse, and there is a large pressure peak; (2) Increase the diameter of the overflow hole can optimize the dynamic characteristics and stability of the oil supply pressure at the same time, to achieve stable oil supply; (3) Reduce the spring stiffness can weaken the oil supply pressure fluctuations and improve the stability of oil supply, but the pressure overshoot and rise time increase, resulting in poor dynamic performance.

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To reduce the failure, deformation, and damage of slipper pair in radial piston pumps, Theoretical research and numerical modeling were conducted on the structure, kinematics principle, and stroke ring-slipper components force analysis of the radial piston pump, Through the theoretical analysis of the hydrostatic bearing oil film of the slipper pair, The obtained the static characteristic curve of the slipper pair, the oil film backthrust, the oil film stiffness, the power loss, and the optimal oil film thickness, reflecting the relationship between the oil film thickness, operating pressure, and the former. Subsequently, the dynamic characteristics equation of the oil film for the slipper pair under impact load was established, and the conclusion obtained by using the fourth-order Runge-Kutta method is as follows: during the oil film squeezing process, the fluctuation of the oil film increases monotonically with time t, during the establishment of the oil film, oil film fluctuation generates damping oscillations, eventually tending to balance the oil film thickness. Conversely, without considering the squeezing effect, the dynamic process of the oil film diverges. Finally, the influence of the slipper structural parameters on the dynamic characteristics of the slipper pair oil film under impact load was studied, The results show that when the sealing strip area decreases or Δp and h0 increases, the fluctuation caused by oil film squeezing becomes larger. However, as the oil film establishes, the fluctuation amplitude of the oil film varies directly with the sealing strip area、Δp and h0, When the adjustment time ts＜t is reached, the ratio of the fluctuation of the oil film to the equilibrium oil film thickness is less than 3%.

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This study investigates the impact of blade gap angle on spiral axial flow gas–liquid multiphase pump performance. Using five numerical models and the shear stress transport k-omega (SST k-ω) turbulence model, we incorporated gas compressibility to analyze the influence of blade gap angle on pump performance. Results revealed alterations in the gap angle affected gas–liquid slip velocity distribution, turbulence eddy frequency within the impeller region, and the distribution of gas separation areas at the gap inlet and outlet. Increasing the gap deflection angle inhibited gas flow separation at the hub-side inlet while simultaneously enlarging separation area at the outlet of the gap, with the optimal gap angles enhancing flow separation in a helicoaxial gas–liquid multiphase pump.

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