The diameter of the impeller balance hole in a centrifugal pump is closely related to axial force.Thus,to select the appropriate diameter of a balance hole is crucial for balancing the axial force of the centrifugal pump.After the validation of the CFD method and the grids independence study,the characteristics of flow in the hub cavity have been analyzed in 4 cases with different diameters of balance holes.The leakage rate of the liquid in the hub cavity of the centrifugal pump is calculated and compared with the test result.According to the research,when no balance hole exists,the distribution of liquid velocity in the core area of the hub cavity exhibits axial symmetry,and the circumferential velocity component is approximately 0.4 times of the impeller's rotational speed.When the balance hole exists,the distribution of liquid velocity in the hub cavity does not exhibit axial symmetry,and the circumferential velocity component is larger than 0.4 times of the impeller's rotational speed.The radial leakage velocity on the turbulent boundary layer of the pump cover will increase with the increasing diameter of the balance hole.
A numerical investigation on the aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor is conducted through three-dimensional CFD analysis.The results show that the flow,especially near the diffuser inlet,is influenced by the axial misalignment obviously.When the impeller offsets to one side,the pressure at diffuser inlet close to this side will descend,and the vortex in the cavity on the other side will partially enter the diffuser and then result in the back flow.The performances of the stage and its components also change with the impeller-diffuser axial misalignment.There exists an optimum offset making the efficiency maximum at a given operating point.Furthermore,the effect of impeller-diffuser axial misalignment on the axial thrust is pronounced.The axial thrust is nearly increased linearly with the increase of axial misalignment.The aerodynamic effects of impeller-diffuser axial misalignment in the low-flow-coefficient centrifugal compressor behaves more remarkably at the large flow rate.To alleviate the aerodynamic effects of impeller-diffuser misalignment,a rounding in the meridional plane at the diffuser inlet can be applied.
