Numerical Simulation And Experimental Study On The Dynamic Characteristics Of Herringbone-grooved Annular Seals In Centrifugal Pumps

Centrifugal pumps is widely used in aerospace, petrochemical and nuclear power industry as the key device for fluid transport. These pumps, especially multi-stage centrifugal pumps, employ several annular seals to satisfy the sealing demands and to balance the pressure gap, such as seal rings, interstage seals and balance pistons. With the rapid development of industry, users and manufacturers are looking forward to seals with better hydraulic and rotordynamic characteristics. The sealing performance and dynamic characteristics of traditional annular seals with smooth rotor and smooth stator are difficult to meet the demands. Therefore, analytic methods for the sealing performance and dynamic characteristics of labyrinth seals, damper seals and the optimum design methods for these seals have been investigated in detail. While, investigations on the characteristics of the seals with pumping actions, such as helical-grooved seals and herringbone-grooved seals are rare. How to calculate the characteristics, especially the dynamic characteristics of these seals accurately is an important issue.Taking the the herringbone-grooved annular seals in centrifugal pumps as the research object of this dissertation. A series of detailed analysis was done on the dynamic characteristics of the seals with helical grooves on the rotor and seals with herringbone grooves either on the rotor or on the stator. An experiment facility was also established to validate the proposed analysis method. The major contents of the current dissertation consist of the following four aspects.First, the circumferential momentum equation, first-order circumferential velocity perturbation and its change with axial location were added to the governing equations of helical-grooved seals for a more accuracy description for the flow within the seal clearance. Besides, a numerical solution was developed to solve the new governing equations. Based on the new method, the effects of operating conditions, gemometric parameters on the sealing performance and dynamic characteristics were investigated.Second, combining the new calculation method for helical-grooved seals with the finite-length solutions for smooth annular seals, an analytic method for calculating the leakag flow rate and dynamic characteristics of the seals with herringbone grooves on the rotor was proposed. Both the Blasius lubrication model and the Moody model can be used in this method. A series of numerical simulations were completed to investigate the influence of operating conditions, structure design and geometric parameters on the leakage and dynamic characteristics of these seals.Third, to accurately describe the flow conditions of within the seal clearance of the labyrinth seals with helical grooves on the stator, the pressure gap caused by the pumping effects of helical grooves was added to the governing equations, which significantly improved the accuracy of the steady flow solutions within helical-grooved seal clearance. At the same time, combined with finite-length solutions for smooth annular seals, dynamic and sealing performnce prediction method for labyrinth seals with herrinbone grooves on the stator was also proposed. The calculated leakage flow rate, rotordynamic coefficients and instability ratio of this kind of seals were compared to those of the seals with grooves on the rotor.Fourth, a test rig was built to measure the fluid force within seal clearances. The eccentricity, rotating speed and whirling speed can be controlled independently and accurately. A series of experiments under different operating conditions for different kinds of seals were conducted. The reliability of the proposed methods was validated by comparisons between the numerical and experimental results, which established the foundation of the conlusions presented in this dissertation.Research results indicate that, leakage and dynamic characterisitcs calculated by the new analytic method for helical-grooved seals show better agreement with the experimental results compared to the original method developed by Iwatsubo. The predicted leakage flow rate and dynamic characteristics of seals with herringbone grooves on the rotor and the stator coordinate with the experimental results. Besides, the results show that pressure difference acting on the seal has greater influence than rotating speed on the characteristics of herringbone-grooved seals and helical-grooved seals. Geometric parameters have different effects on the characteristics of the seals, such as spiral angle, L/D ratio, groove depth and so on.The content and conclusions of the current dissertation can provide references for the performance prediction and optimum design for annular seals as well as the whole shafting of a centrifugal pump.