Effects of Inlet-Loss Coefficient on Dynamic Coefficients and Stability of Multistage Pump Annular Seal

In order to explore the influence of inlet-loss coefficient on dynamic coefficients and stability of finite-length annular seal, and then to provide theoretical basis for multistage pump rotor system vibration and stability, the bulk-flow model is taken into account to model the fluid control equations of clearance flow, and perturbation method is applied to calculate the first-order functions and dynamic coefficients. The calculated results are validated by comparing them with reference results, and the minimum and maximum error percentage are 1.4 and 5.6%, respectively. The dynamic coefficients change rule and stability of annular seal under the multifactor-coupled effects are researched in a detailed manner. The numerical results show that the inlet-loss coefficient plays an important role in dynamic coefficients of finite-length annular seal, especially for direct stiffness. All of the dynamic coefficients increase with the increase in inlet-loss coefficient, and the growth trends are the most distinct for large length–diameter ratio, small clearance or high rotating speed. Moreover, reducing the inlet-loss coefficient can improve the stability of annular seal. The research results and conclusions can provide references for the structure design of multistage pump and optimal design of rotor system.