Numerical analysis of the influences of balance hole diameter on the flow characteristics of the back chamber of centrifugal pump

The flow characteristic inside a pump chamber is the core problem in the study of the thrust force of a centrifugal pump. A numerical study on the IS150-125-315-type centrifugal pump with four different balance hole diameters was conducted. By selecting clear water as the medium, the time-averaged continuity equation with relative coordinates and the Navier- Stokes equation are established on the basis of the FLUENT software. The RNG k-ϵ equation turbulence model and the SIMPLEC algorithm are used to conduct a numerical simulation. The numerical results match the accuracy of the design values on the performance of the pump. The test results match the accuracy of the numerical results on the pressure of the back chamber and clearance leakage of the back seal ring. The influence of balance hole diameters is revealed in the flow field of the back chamber of the centrifugal pump. In detail, the patterns of the axial and radial distributions of the dimensionless tangential and radial velocities and the spanwise distribution of their average values in the back chamber of the centrifugal pump with different balance hole diameters are investigated. The relationship is also obtained between fluid rotational angular velocity in the back chamber of the centrifugal pump and rotational angular velocity of the impeller. The results reveal that the turbulent boundary layer and core region of the flow always exist in the pump chamber, even if there are no balance holes. The increase in diameter of the balance holes is associated with the increase in the radial component in the core region velocity and the decrease in the value range of its tangential component. At a certain radius and angular position, the diameter of larger balance holes leads to higher normalized tangential velocity in the core region. At the same time, a higher absolute value of the normalized radial velocity near the pump cover corresponds to greater radial leakage. At the same balance hole diameters, the rotating speed of the core region fluid generally keeps constant along the axial direction, whereas a significant difference is observed along the radial and tangential directions. The dimensionless radial and tangential velocities are significantly influenced by the flow of the volute chamber in the pump and are rarely influenced by the changes in the balance hole diameters, and vice versa. The dimensionless radial velocity will exert more power on large sections, such as sections 5 and 7, than the dimensionless tangential velocity, and vice versa. For cases with balance hole diameters less than its design value, dimensionless tangential average velocity is less than 0.5 with increases and dimensionless radial average velocity is less than 0 with decreases along the radial direction in the flow core area. Otherwise, dimensionless tangential average velocity is approximately equal to 0.59 and dimensionless radial average velocity is approximately equal to 0 in the flow core area. The balance hole diameter changes from 0 mm to 12 mm, and the rotating speed of the core region fluid is 0-0.8 times, rather than half, that of the impeller. Key words: Centrifugal pump, balance holes, back chamber, tangential velocity, radial velocity.