Abstract
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.
Highlights
Because the tip clearance (TC) of the mixed-flow pumps exists between impeller shroud and pump case, so the leakage of fluid is to happen
Bing et al.[10] experimentally determined the external characteristics of a mixed-flow pump with different TCs and found that they all decrease with the TC increases
When the TC size is small enough, the pressure fluctuation will be enhanced as a result of the enhancement of the rotor–stator interaction between impeller shroud and pump case, while few studies have been performed on this case
Summary
Because the tip clearance (TC) of the mixed-flow pumps exists between impeller shroud and pump case, so the leakage of fluid is to happen. Many studies have been carried out in the aspects of the effect of TC on external characteristics, pressure fluctuation and tip leakage for pumps. By setting different TC sizes of a mixed-flow pump, Li et al.[7] found the positive slope characteristic of the head curve could be effectively suppressed when TC was 0.5 mm. Zhang et al.[12] found that the tip leakage had larger impact on the pressure fluctuation in impeller than that in diffuser by investigating the TC effect of a mixed-flow pump. When the TC size is small enough, the pressure fluctuation will be enhanced as a result of the enhancement of the rotor–stator interaction between impeller shroud and pump case, while few studies have been performed on this case. The relevant content of experiment has been described in previous published literature[12] ns
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