Theoretical and experimental study on static stability of fully partitioned pocket damper seals
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摘要:
阻尼密封稳定性是影响透平机械转子安全性与稳定性的关键因素之一。以贯通式袋型阻尼密封为研究对象，提出密封静态直接刚度实验识别方法，建立密封三维计算流体力学模型，通过实验测试及数值模拟，对贯通式袋型阻尼密封静态直接刚度系数、气流力进行对比研究，分析其静态稳定性。结果表明：同一偏心率下，随进口压力增大，气流力先增大后减小；同一进口压力下，随偏心率增大，静态直接刚度系数逐渐减小，在进口压力为0.321 MPa、偏心率为0.8时，密封静态刚度系数趋于负值；堵塞工况下，低偏心率也会产生负的气流力及静态刚度系数。间隙处轴向压力分布存在大、小间隙压差零点，该点前压差产生恢复力，交叉点后压差会加剧转子偏离中心。阻塞工况下，间隙处马赫数在出口段发生剧烈增长产生的惯性效应是导致系统静态不稳定的原因之一。
Abstract:The stability of damper seal is one of the key factors affecting the security and stability of the turbomachinery rotor. An experimental method was proposed to identify the static stiffness coefficients for fully partitioned pocket damper seal. A fluid domain numeric model was established. And based on experiments and simulation, the static stiffness coefficient, fluid-induced force, and the static stability were studied. The results indicated that at the same eccentricity, with the increase of inlet pressure, the overall fluid-induced force increased first and then decreased, and at the same inlet pressure, with the eccentricity increasing, the static direct stiffness coefficient decreases gradually. When the inlet pressure at 0.321 MPa and the eccentricity is 0.8, the static stiffness coefficient tends to be negative, and at the choked flow condition, negative fluid-induced force and static stiffness coefficient appeared at low eccentricity. There was a pressure difference zero point in the axial pressure distribution at the large and small clearances. The pressure difference before the point produced restoring force, and after the point aggravated the rotor deviation. At the choked condition, the inertia effect caused by the sharp increase of the clearance Mach number in the outlet section was one of the reasons for the static instability.
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图 1 贯通式袋型阻尼密封几何结构示意图
Figure 1. Geometric structure of fully partitioned pocket damper seal
图 5 贯通式袋型阻尼密封网格分布
Figure 5. Computational grid of fully partitioned pocket damper seal
图 7 不同偏心率下气流力随进口压力的变化
Figure 7. Change of fluid-induced force with inlet pressure at different eccentric conditions
图 8 不同进口压力下末齿间隙马赫数分布情况
Figure 8. Mach number distribution of the last tooth clearance at different inlet pressures
图 9 不同进口压力下静态直接刚度随偏心率的变化
Figure 9. Change of static stiffness coefficient with eccentricity at different inlet pressures
图 11 不同进口压力下密封结构内部压力及马赫数
Figure 11. Internal pressure and Mach number distribution of the sealing structure at different inlet pressures
图 12 密封间隙轴向压力及马赫数变化（pin=0.261 MPa）
Figure 12. Change of internal axial pressure and Mach number of the sealing structure （pin=0.261 MPa）
图 13 密封间隙轴向压力及马赫数变化（pin=0.381 MPa）
Figure 13. Change of internal axial pressure and Mach number of the sealing structure （pin=0.381 MPa）
表 1 密封几何尺寸
Table 1. Seal geometry
参数 数值 转子直径D/mm 60.00 密封间隙Cr/mm 0.20 密封齿数N1 8 密封齿厚t1/mm 1.46 挡板数N2 8 挡板厚度t2/mm 1.50 周向×轴向主腔室个数N3 8×4 主腔室长度l1/mm 4.50 周向×轴向副腔室个数N4 8×3 副腔室长度l2/mm 2.00 腔室深度h/mm 3.30 密封长度L/mm 35.70 
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表 2 系统刚度测量结果
Table 2. System stiffness measurement results
载荷/N 系统刚度/（kN/m） 0.98 249.25 1.50 245.00 2.25 242.78 2.99 234.07 3.97 224.91
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表 3 网格无关性验证
Table 3. Grid independent verification
网格数/104 泄漏量/（g/s） 相对误差 57 11.0157 140 11.1014 0.00772 274 11.0884 0.00117 470 11.0316 0.00515
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表 4 工况参数
Table 4. Calculation conditions
计算工况 设置 湍流模型 标准k-ε 工质 理想气体 壁面 光滑、绝热 温度T/K 298.15 偏心率ε 0，0.2，0.4，0.6，0.8 进口压力pin/MPa 0.151，0.201，0.261，0.321，0.381 出口压力pout/MPa 0.101 转子转速n/（r/min） 0
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