Rotor Dynamic Characteristics of Oblique Flow Pump under Action of Fluid-structure Interaction

Taking a certain type of oblique flow pump as the research object, the computational fluid dynamics software CFX 2021 Rl and the finite element analysis software ANSYS Workbench 2021 Rl platform were used to solve the natural frequency and mode shape of the dry and wet mode of the oblique flow pump rotor system. The critical speed and the transient dynamics based on fluid-structure coupling, the deformation and stress distribution of the impeller blades at different positions were studied, and the influence of different flow conditions on the deformation and stress distribution of the impeller blades was compared and analyzed. The results showed that with an increase in the order, the natural frequency was gradually decreased. The 3rd order mode had the least decline rate at 9.82% while the 6th order mode had the highest decline rate at 44.31%. This confirmed the findings that the natural frequency of the rotor would decrease in the wet mode. The critical speed of the calculated second-order mode was 7 369 r/min, which was much greater than the rotor working speed. This indicated that the design requirements of the rotor dynamics met as the rotor system would not resonate when operating at working speed hence resulting in a stable operation. The deformation trends between the rear side of the blade and the working side of the impeller blade were quite similar. On the working surface, the deformation at the upper span of the blade towards the outlet was the largest. When the amplitude reached 2. 675 5 mm, the deformation at each given position on the impeller blade working surface was higher than the rear surface with a maximum deformation of 0. 035 8 mm. The deformation at the upper span of the blade was higher than at the root of the blade with the maximum difference being 1. 017 7 mm. The highest amplitude reached 2. 675 5 mm. Considering the stress change and stress amplitude trend, it was revealed that at the upper span of the blade near the inlet part were roughly similar on both sides. The stress amplitude graphs showed that towards the outlet portion of the blade, the upper span and root on the working surface had higher amplitudes than on the corresponding rear surface. The amplitude of the monitoring point at the outlet of the blade was significantly greater than that of the monitoring point at the inlet. On the rear surface, the equivalence force at the root of the blade towards blade was the largest, and the largest value reached about 6 MPa. The change trend of blade deformation under different flow conditions was similar, and as the flow rate increased, the amount of deformation at each position of the impeller blade gradually decreased. At 0.6。,the amount of blade deformation fluctuated the most with time. The maximum deformation was 3.067 2 mm, which appearred at the upper span of the impeller blade towards the outlet. At the upper span of the blade, as the flow rate increased, the stress fluctuation gradually decreased, at the blade root, the stress amplitude fluctuated the most at Q. The smallest fluctuations in inlet and outlet stress occurred under 0.6Q and 0.8Q flow conditions, respectively, and the maximum equivalent force was 12.456 MPa. At the blade root, after each stress fluctuation, the 0.6Q and 0.8Q stress curve would have an additional small fluctuation, therefore operating the pump under small flow conditions must be avoided and also the blade thickness at the impeller root should be strengthened. The research results can provide a reference for the operation stability analysis of the oblique flow pump rotor system and the structural optimization design of the impeller blades. © 2022 Chinese Society of Agricultural Machinery. All rights reserved.