No abstract

Axial-flow pumps, in addition to providing high anti-cavitation properties, must have high anti-erosion properties to ensure the required lifetime of the pump. Erosion damage of surfaces occurs when the net positive suction head (NPSH) significantly exceeds its critical value. The object of the study in this article is the axial-flow pump with a specific speed of 600 in two alternatives: № 1 and № 2. By analysis of the flow in the impeller blade systems, the ratio value between the NPSH, which ensures the absence of erosion, and the NPSH3, at which pump operational failure occurs, was determined. Impeller variant № 1 did not provide the required ratio. Impeller variant № 2 had higher cavitation qualities, and the required ratio was achieved for it. Energy, cavitation, and erosion characteristics of the axial-flow pump with impeller № 2 in rotational frequency n = 2000 rpm were investigated. Easily breakable paint coatings were used for the accelerated study of cavitation erosion. The experiment was carried out at three different flow rates and confirmed the assumptions made—the pump with impeller № 2 was not affected by cavitation erosion at the optimum flow rate. Patterns of erosion zones were accompanied by calculations of vapor zones in the impeller. At flow rates less than the optimum, cavitation disruptions occurred and appeared behind the vapor region. As a result, the condition of ensuring erosion-free flow in the impeller of an axial pump with a specific speed of 600 was obtained, ensuring the ratio NPSH/NPSH3 > 2.5. Recommendations on designing of erosion-free flow part of the axial pump impeller were also obtained.

Hydraulic shock that occurs in pipeline systems can cause accidents and destroy pipelines, valves and equipment. If the pressure fluctuates due to a hydraulic shock, the pressure in the rarefaction phase may drop below the pressure of saturated vapours, resulting in a cavitation. This phenomenon is accompanied by an additional increase in the amplitude of pressure fluctuation, which leads to additional loads occurring in the hydraulic system. The aim of the paper is to provide the method for calculation of the hydraulic shock with the help of OpenFOAM soft-ware complex, which considers the cavitation formation.

Studies of dynamic frequencies are an important stage in designing multistage vane pumps. This research aimed to confirm the rigidity and vibrational reliability of the pump rotor. Based on the recommendations of J.F. Gülich, the nominal rotational speed of the rotor shaft should differ from the cutoff speed by no less than 25 %. The Lomakin effect supposes taking into consideration the hydrodynamic forces acting in the gap seals and having a damping effect on the pump rotor. This research solved the problem of developing and verifying a numerical method of calculating hydrodynamic forces, which arise in seals of vane pumps at critical speeds. The studies were conducted on a ‘dry’ model of the rotor using ANSYS Mechanical software package. During computational modeling of bearings and seals, the COMBIT214 ele¬ment was used where the stiffness coefficient values were set. These values were determined by calculating the flow parameters in the gap seal using ANSYS CFX. The proposed method was verified using the experimental data obtained. The seal rigidity was calculated for different operating modes of the pump. It was shown that the hydrodynamic forces which arose in the gap seals had a significant influence on the rotor’s critical speed. Accounting for these forces increased the main own frequency of the rotor by approximately 44 %. This fact had a significant qualitative and quantitative impact on the vibrational characteristics of the pump. This study showed that the value of the hydrodynamic force was influenced by several factors: shaft deflection, differential pressure and geometry of the gap seal. The proposed method is recommended for use for multistage centrifugal pumps.

The results are presented of numerical and experimental research of fluid flow in the flow path of a torque flow pump with specific speed ns ;: 55. The 3D methods of CFD have been shown to allow for predicting energy characteristics of this type of pumps with a sufficient accuracy. According to the results of flow visualization the work process has been analysed and conclusions drawn to enhance TFP efficiency.