Abstract
Cavitation has a significant effect on the flow fields and structural behaviors of a centrifugal pump. In this study, the unsteady flow and structural behaviors of a centrifugal pump are investigated numerically under different cavitation conditions. A strong two-way coupling fluid-structure interaction simulation is applied to obtain interior views of the effects of cavitating bubbles on the flow and structural dynamics of a pump. The renormalization-group k-ε turbulence model and the Zwart–Gerbe–Belamri cavitation model are solved for the fluid side, while a transient structural dynamic analysis is employed for the structure side. The different cavitation states are mapped in the head-net positive suction head (H-NPSH) curves and flow field features inside the impeller are fully revealed. Results indicate that cavitating bubbles grow and expand rapidly with decreasing NPSH. In addition, the pressure fluctuations, both in the impeller and volute, are quantitatively analyzed and associated with the cavitation states. It is shown that influence of the cavitation on the flow field is critical, specifically in the super-cavitation state. The effect of cavitation on the unsteady radial force and blade loads is also discussed. The results indicate that the averaged radial force increased from 8.5 N to 54.4 N in the transition progress from an onset cavitation state to a super-cavitation state. Furthermore, the structural behaviors, including blade deformation, stress, and natural frequencies, corresponding to the cavitation states are discussed. A large volume of cavitating bubbles weakens the fluid forces on the blade and decreases the natural frequencies of the rotor system. This study could enhance the understanding of the effects of cavitation on pump flow and structural behaviors.
Highlights
1 Introduction A centrifugal pump is a critical fluid transportation device and an important part of the petrochemical process loops. It is well-known that cavitation, which is inevitable in a centrifugal pump, can decrease the head-flow curve and increase noise and vibrations
Blade surfaces have been eroded by the collapse of cavitation bubbles, which results in long-term damage [1]
The vibration characteristics of centrifugal pumps under cavitation conditions were measured and the results indicated that the vibration amplitude increased significantly from non-cavitation to severe cavitation conditions [12, 13]. d’Agostino et al [14], Fu et al [15], and Valentini et al [16] studied the rotor-dynamic forces on cavitating pumps and the variations of rotor-dynamic forces corresponding to the cavitation states were reported
Summary
A centrifugal pump is a critical fluid transportation device and an important part of the petrochemical process loops. Hassan et al [6] measured the vapor fraction through the turbopump using an X-ray technique and determined the spectra of dynamic pressure in the housing under different cavitation conditions This provided a better understanding of the overall flow structures inside the pump inducer. To better understand the correlations between unsteady flow and the structural dynamic response in a centrifugal pump, a fluid-structure interaction (FSI) was conducted to investigate the interaction between fluids and structures in a pump. Pei et al [22] expanded on this by investigating the unsteady flow-induced impeller oscillations for a single-blade pump by strong two-way coupling FSI simulations and non-contact deflection measurements under off-design conditions. More information of unsteady flow and structural behaviors of a centrifugal pump under cavitation conditions are investigated. A number of new features, for instance, the deformation, stress, and natural frequency data of a rotor system in a centrifugal pump under cavitation conditions, are analyzed by means of the FSI method
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