采用Bulk-Flow模型的直通式迷宫密封转子动力特性研究

Investigation on the Rotordynamic Characteristics of Straight-Through Labyrinth Seal Using Bulk-Flow Model

为了选择最佳泄漏模型并探究运行工况参数对直通式迷宫密封转子动力特性的影响规律,基于单控制体等熵过程Bulk-Flow模型发展了迷宫密封转子动力特性预测方法并开发了计算程序。通过对72种泄漏模型进行适用性分析,获得的最佳泄漏模型是采用Neumann泄漏方程、Chaplygin流量系数、Swamee&Jain切应力系数以及Kurohashi动能输运系数(正预旋工况)或Neumann动能输运系数(负预旋工况)的模型。所发展的方法结合这一模型对迷宫密封交叉刚度和直接阻尼的平均预测误差约为10%。研究了压比(0.3,0.5,0.7)和预旋比(-0.8,-0.4,0,0.4,0.8)对迷宫密封转子动力特性的影响,结果表明:迷宫密封交叉刚度和直接阻尼对密封进口压力敏感,而受出口压力的影响有限,穿越频率几乎不受进出口压力的影响;迷宫密封有效阻尼随预旋比增大而减小,在正预旋时出现负值,且其穿越频率随预旋比增大而显著增大,不利于转子系统的稳定运行;进口预旋速度的影响在密封上游腔室更为显著,应在迷宫密封进口采用防旋流装置来抑制泄漏流的周向流动。所发展的预测方法和计算程序可为迷宫密封转子动力特性系数的快速评估提供技术手段。

To select the best leakage model and investigate the effects of the operational conditions on the rotordynamic characteristics of the straight-through labyrinth seal,the rotordynamic characteristics prediction method and program of labyrinth seals are developed based on the one-control-volume Bulk-Flow model considering the isentropic process.Through the applicability analysis of 72 leakage models,it is found that the best leakage model is the one that uses Neumann’s leakage equation,Chaplygin’s discharge coefficient,Swamee&Jain’s friction factor and Kurohashi’s kinetic energy carryover coefficient(for positive preswirl conditions)or Neumann’s kinetic energy carryover coefficient(for negative preswirl conditions).The developed method combined with the best leakage model has an average prediction error of about 10%for the cross-coupled stiffness and direct damping of labyrinth seals.The developed prediction program is used to investigate the effects of pressure ratios(0.3,0.5,0.7)and preswirl ratios(-0.8,-0.4,0,0.4,0.8)on the rotordynamic characteristics of labyrinth seals.The results show that the cross-coupled stiffness and direct damping of labyrinth seals are sensitive to the inlet pressure,but are insensitive to the outlet pressure.The crossover frequency is hardly affected by the inlet and outlet pressures.Increasing preswirl ratio results in a decrease in the effective damping of labyrinth seals.For positive preswirl conditions,negative effective damping exists and the crossover frequency significantly increases with the preswirl ratio,which is a destabilizing factor for rotor system.The influence of inlet preswirl velocity is more significant at the upstream cavities of the seal.Therefore,anti-swirl devices should be installed at the seal entrance to suppress the circumferential flow of the leakage flow.The presented prediction method and program can provide technical approaches for rapid evaluation of the rotordynamic coefficients of labyrinth seals.