Numerical analysis for the effect of tip clearance in a low specific speed mixed-flow pump

• Published in: Advances in mechanical engineering Vol. 11; no. 3
• Main Authors: Yu, Zhiyi, Zhang, Wenwu, Zhu, Baoshan, Li, Yongjiang
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01.03.2019; Sage Publications Ltd; SAGE Publishing
• Subjects: Computational fluid dynamics; Computer simulation; Design optimization; Discharge; External pressure; Impellers; Low pressure; Numerical analysis; Power efficiency; Tip clearance; Variations; low specific speed; tip clearance; pressure fluctuation; tip loss; Mixed-flow pump; external characteristics
• ISSN: 1687-8132; 1687-8140
• DOI: 10.1177/1687814019832222

To study the influence of tip clearance on performance (external characteristics, pressure fluctuation and tip loss) of a low specific speed mixed-flow pump, unsteady simulation was performed for the whole flow passage with five tip clearance sizes (δ0 = 0 mm, δ1 = 0.10 mm, δ2 = 0.25 mm, δ3 = 0.75 mm and δ4 = 1 mm). The reliability of the numerical methodology was verified in external characteristics (efficiency, head and power) and fluctuation. The performance of the pump was obtained under different discharges and tip clearance sizes using ANSYS CFX. The results showed that the variation of tip clearance size has greater effect on the external characteristics under large discharges. Meanwhile, along the flow direction, the fluctuation coefficients near the impeller shroud increase gradually with the smaller tip clearance sizes (δ = 0.10 and 0.25 mm), while for the larger tip clearance sizes (δ = 0.75 and 1.00 mm), the significant increase of fluctuation near the shroud of impeller inlet is closely associated with the clear leakage vortex and the large region of low pressure. Besides, with the increase of tip clearance size, the effect of tip clearance will become more remarkable under different discharge conditions. According to this study, for the optimization design of such pumps, the size of the tip clearance is suggested to be about 0.9% times the blade height at middle of the impeller passage.