Abstract
The energy performance and radial force of a mixed flow pump with symmetrical and unsymmetrical tip clearance are investigated in this paper. As the tip clearance increases, the pump head and efficiency both decrease. The center of the radial force on the principal axis is located at the coordinate origin when the tip clearance is symmetrical, and moves to the third quadrant when the tip clearance is unsymmetrical. Analysis results show that the total radial force on the principal axis is closely related to the fluctuation of mass flow rate in each single flow channel. Unsteady simulations show that the dominant frequencies of radial force on the hub and blade correspond to the blade number, vane number, or double blade number because of the rotor stator interaction. The radial force on the blade pressure side decreases with the tip clearance increase because of leakage flow. The unsymmetrical tip clearances in an impeller induce uneven leakage flow rate and then result in unsymmetrical work ability of each blade and flow pattern in each channel. Thus, the energy performance decreases and the total radial force increases for a mixed flow pump with unsymmetrical tip clearance.
Highlights
Mixed-flow pumps are important devices with the advantage of a wide, high-efficiency operating region; these pumps are widely used in hydraulic engineering, petrochemical engineering, power supply, agricultural irrigation and other fields [1]
Flow phenomena owing to blade tip clearance are extremely complicated and involve leakage flow, vortex shedding and cavitation
The energy performance of the pump decreases as the tip clearance increases
Summary
Mixed-flow pumps are important devices with the advantage of a wide, high-efficiency operating region; these pumps are widely used in hydraulic engineering, petrochemical engineering, power supply, agricultural irrigation and other fields [1]. The impeller is the key component that performs energy conversion and exerts a marked effect on pump performance [2,3]. Turbulent flow in an impeller is highly complicated especially when there is blade tip clearance. The extent of tip clearance is extremely small, usually 0.1–2 mm; this tip clearance causes leakage flow and vortex motion, which directly affect the flow of nearly 50% of the area in the impeller passage and thereby affect the efficiency and stability of the impeller. Flow phenomena owing to blade tip clearance are extremely complicated and involve leakage flow, vortex shedding and cavitation. Gearhart [4] investigated the effect of tip clearance configuration on the flow pattern and cavitation performance of a turbomachine and found that a slightly divergent gap configuration provided poor gap cavitation performance. You et al [6]
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