Analysis of flow evolution mechanism in variable speed control of semi-open impeller centrifugal pump

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Abstract
To investigate the transient flow characteristics and flow field hysteresis mechanism within a centrifugal pump during variable speed regulation, this paper selects a double-volute, semi-open impeller centrifugal pump as the research object, through the Pro/E software modeling for centrifugal pump 3-d full port, choosing Renault N-S equation and standard k - ε turbulence model, using CFX software perform numerical simulations process of centrifugal pump up or slow down the transient flow characteristics to carry on the numerical simulation, the evolution law of flow field in centrifugal pump during variable speed adjustment is studied and analyzed. The results demonstrate that the internal pressure, flow velocity, turbulent kinetic energy, and vorticity within the centrifugal pump exhibit distinct transient characteristics during variable speed regulation. During the acceleration phase, as the rotational speed elevates, the internal pressure of the pump increases along with an expanded pressure fluctuation range, the vorticity within the impeller passage increases, the vorticity in the volute chamber decreases, and the fluid velocity and turbulent kinetic energy change obviously in the middle region of the blade working face and the blade tip region. In the process of deceleration, with the decrease of rotational speed, the pressure in the centrifugal pump decreases, the vorticity in the impeller passage decreases, and the vorticity in the volute increases first and then weakens. When t =   0.4 s, pressure on the outlet wall of the volute of the centrifugal pump increases obviously, and the flow velocity and turbulent kinetic energy likewise change obviously in the middle region of the blade working face and the blade tip region. Quantitative comparison further reveals an obvious transient hysteresis effect: under identical rotational speed, the overall pressure and turbulent kinetic energy in deceleration process are higher than those in acceleration process, which provides a new physical understanding of flow discrepancy between two variable-speed modes lacking in previous qualitative researches.

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