Browsing by Author "Van der Spuy, SJ"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Simulation and testing of centrifugal pump cavitation.
    (Stellenbosch : Stellenbosch University, 2024-02) Van der Spuy, SJ; Bekker, A; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Cavitation, the formation of vapour filled bubbles in areas of low pressure, can be deleterious to centrifugal pump operation. Cavitating flow may cause efficiency loss, damage to impeller surfaces, and excessive vibration in pump systems. Some cavitation is unavoidable and even harmless, however, preventing cavitation will in general enhance pump reliability, and efficiency. In this research question, computational fluid dynamics was used to simulate cavitation inception using single‑phase, steady‑state flow, in a centrifugal pump. The pump was a low specific speed radial flow centrifugal pump that is used for the conveyance of water or other products. Simulations were performed using Cadence (NUMECA) Fine Turbo 16.1 and AutoGrid 5 meshing software. The simulated performance characteristics were compared to experimental performance measurements. The cavitation model determined the net positive suction head (NPSH) of cavitation inception (NPSHi) in the post‑processing stage of the simulation. The cavitation model is based solely on the inlet pressure and minimum static pressure in the impeller to determine cavitation inception. The simulated NPSHi values were 0.903 m, 1.53 m, and 2.33 m, at shaft speeds of 800 RPM, 1000 RPM, and 1200 RPM respectively. This was compared against scaled NPSH3 values of 0.281 m, 0.475 m, and 0.722 m respectively. As expected, the simulated NPSHi values were consistently higher than NPSH3 values. Vibration sensors were employed to measure cavitation inception in the pump, but due to stall occurring in the impeller, the point of cavitation inception could not be distinguished above the noise caused by backflow vibration. Broadband excitation was measured on the pump, which was consistent with other test setups where backflow was present. Backflow was also confirmed by the simulations. Experimental performance measurements showed that for accurate performance simulation, a model containing only the impeller and diffuser was insufficient. Adherence to the predicted NPSHi will prevent operating pumps under damaging cavitating conditions, however, the correspondence of these values with true cavitation inception is tenuous.