Analysis of hydraulic performance for vertical axial-flow pumping system with cube-type inlet passage

Abstract: In order to better understand the effect of a submerged vortex on the hydraulic performance of a vertical axial-flow pumping system and the trajectory characteristics of a submerged vortex, a vertical axial-flow pumping system with a cube-type inlet passage was chosen as the research object, and CFD (computational fluid dynamic) technology and high-speed photography technology were used. The flow patterns in the cube-type inlet passage, calculated by a numerical simulation of CFD, can be classified into three types: the straight line adjustment stage, a flare tube contraction, and a flare tube adjustment pattern. The second and third stages of the flow pattern are especially important in the cube-type inlet passage. A submerged vortex occurs in the flare tube contraction stage under different conditions. A submerged vortex trajectory of an inlet passage was captured successfully based on a numerical simulation in different operating conditions, which was basically the same as the experimental results. A submerged vortex occurs first in the bottom of inlet passage, and then it flows into the flare tube. When a submerged vortex flows from the bottom of an inlet passage into the inlet of a flare tube, the position of maximum vorticity is closer to the center point of the bell-mouth than the initial position. A submerged vortex trajectory is oscillating. If it flows into the impeller chamber, it will affect the safe operation stability of the pumping system and the hydraulic efficiency of the pumping system. With the increase of flow coefficient KQ, the maximum vorticity magnitude of every measuring line increases gradually, and the increased amplitude of maximum vorticity magnitude decreases gradually. In the flow coefficient KQ range from 0.30-0.62, the hydraulic loss of an inlet passage with an anti-submerged vortex device (AVD) decreases, the maximum difference is 0.50 cm, the minimum difference is 0.34 cm. The uniformity of axial velocity distribution improves by 0.77%, the velocity-weighted average swirl angle improves by 0.22° for the outlet section of inlet passage, compared with the inlet passage without AVD. There is a little difference between the hydraulic performance of inlet passage with and without ADV, except for hydraulic loss. The variation range of the relative ratio value of the axial force is 0-7.0%, and the axial force decreases gradually with the increase of flow coefficient KQ. The variation range of the relative ratio value of radial force is 5.0%-110.0%, and the submerged vortex has a great influence on the radial force of the impeller. The submerged vortex should be suppressed by AVD installation on the bottom of an inlet passage for a pumping system.