Effect of incidence angle on cavity blockage and flow stability in the net positive suction head drop of mixed-flow pumps

Abstract

The cavitation is an inevitable factor in pumps used in the whole industry, which is a major cause of energy loss and mechanical breakdown. In this study, the cavitation phenomena at the design flow rate were numerically analyzed for two pumps with different incidence angles. The design flow rate for both models was located near the best efficiency point (BEP). The incidence angle was determined with the impeller inlet diameter and the blade angle. A pump with a smaller incidence angle consistently showed a stable flow pattern as the inlet pressure decreased, whereas a pump with a larger incidence angle contained non-uniform flow streamlines despite a very small amount of the generated cavities. The flow pattern at the impeller inlet was handled by the shape and thickness of the generated cavities which could act as an additional blockage in the pumps. The inception and growth of the cavity with a decrease of inlet pressure were also inferred, which was specifically quantified as the blockage ratio. A pump with a larger incidence angle performed poor cavitation characteristics and obtained the pressure fluctuation and cavity oscillation. The magnitude of pressure fluctuation was indicated using the fast Fourier transform (FFT) analysis. The experimental tests were performed on both pumps to validate the numerical results.

Influence of blade leading edge shape on hydraulic and suction performance of a mixed-flow pump

“…In the other three sets, the flow patterns near the blade LE were slightly deformed, and it seems that the thickness (blockage) of the vapor decreased in the tangential direction as the ER increased. In Figure 4, despite the decrease in inlet pressure, the reason why the head drop was delayed in the larger ER set can be considered because the flow was able to pass near the LE with less obstruction due to the thinner vapor [14,15]. Meanwhile, the single-passage (shown in Figure 2) was rotationally copied as if it is a full-passage, so that the limiting streamline appears to be broken at each periodic boundary.…”

“…These patterns tend to be consistent with the description in Figure 5. As a possibility of further research on this study, the tendency at the off-design flow rates needs to be analyzed, and the thickness (blockage) of the vapor can be quantified [14] to link with the characteristics of the head drop. In addition, in Figure 4, the ER0 set repeated decrease and increase in the head at the range 𝜎 < 1.0 with a peak just before the 3% head drop, and the ER1 set obtained a sudden decrease in the head at the point 𝜎 ≈ 0.6, in this study.…”

Numerical Investigation on Hydraulic Performance at Low Flow Rates of a Mixed-flow Pump with Impeller Inlet Diameter Effects

“…First, the numerical results were validated through experimental tests in the Korea Institute of Industrial Technology (KITECH), Korea [10]. The international standards for pump tests, ISO 5198 and ANSI/HI 1.6 [11,12], had been fully applied to the closed-loop system.…”