Static and Rotordynamic Characteristics for Two Novel Hole-Pattern Annular Liquid Seals With Circumferentially- /Axially- Oblique Hole Cavities

Abstract

Abstract Non-contacting annular damper seals, such as hole-pattern seals are gradually used in the multiple-stage centrifugal pumps, as a replacement of the conventional labyrinth seal to reduce the fluid leakage and stabilize the rotor-bearing system.The hole-pattern seal (HPS) possesses numerous radial hole cavities on the seal stator, and the geometric constructions of the hole cavity (such as the hole depth and diameter) have been demonstrated to have significant influences on the leakage and rotordynamic characteristic for hole-pattern seals. Due to the inevitable manufacturing variability, particulate impurity deposition and abrasion during operation, these hole cavities can be non-radial, which may affect the performance of the hole-pattern seal. However, the effects of the non-radical hole cavities on the performance of the hole-pattern seal are still unknown due to the lack of numerical or experimental research. Thus, in this paper, two types of novel hole-pattern seals possessing circumferentially- or axially-oblique hole cavities (C-HPS, A-HPS) with various oblique angles were designed and assessed to better understand the influences of the non-radial hole cavities. To assess the leakage and rotordynamic characteristics of the novel liquid hole-pattern seals, a proposed 3D transient CFD-based perturbation method was utilized for the predictions of seal rotordynamic forces coefficients, based on the multi-frequency one-dimensional rotor whirling model and mesh deformation technique. The accuracy and reliability of the present steady and transient numerical methods were demonstrated based on published experimental data of leakage and rotordynamic force coefficients for an experimental hole-pattern seal with radial hole cavities. The leakage and rotordynamic force coefficients were presented for the novel hole-pattern seals with various circumferentially-oblique angle (α = −30°∼30°) or axially-oblique angle (β = −30°∼30°) at various rotational speeds (n = 0.05, 2.0, 4.0, 6.0 krpm), and compared with the ideal hole-pattern seal with radial hole cavities. Numerical results show that the non-radial hole cavity can result in a modest deviation (∼10%) from the design value for the seal leakage, and the oblique direction is crucial for the sealing performance. The flow field in hole cavities and the pressure distribution in the seal clearance suggest that the oblique hole cavities with positive α or β can strengthen the vortex-dissipation of kinetic energy in the hole cavities, thus reduce the leakage (about 5% ∼ 10%). The non-radial cavity with a positive oblique angle results in a modest increase (∼15% for the circumferentially-oblique angle α = 30°, ∼ 6% for the axially-oblique angle β = 30°) in the effective stiffness of the hole-pattern seal, but shows very weak influence (< 4.0%) on the effective damping of the hole-pattern seals, especially for the circumferentially-oblique hole. Therefore, in view of the inevitable manufacturing variability and abrasion effects, a designed non-radial hole with suitable positive α or β (10°∼20°) is beneficial to be applied to new designs in early design phases for the robust design of hole-pattern seals.