The study deals with optimization of leakage and rotordynamic characteristics of liquid annular seals. A nonlinear constrained multi-objective optimization problem is considered. An objective function is a weighted sum of leakage and whirl-frequency ratio of the seal. Side constraints are imposed on design variables. The seal consists of two rings which shape can be either cylinder or converging taper or diverging taper. There are four design variables — seal length and diameters of the rings. A non-gradient-based method is used for solving the optimization problem. Analysis of the seal performance is based on computational fluid dynamics (CFD). A full 3D eccentric CFD model of the seal including upstream and downstream regions is constructed in ANSYS CFX. The solution procedures for prediction of rotordynamic coefficients are discussed and compared. The whirling rotor method under the assumption of centered circular orbit is used in optimization runs. The CFD model of the seal is validated against experimental data taken from the literature. A mesh independence study is carried out. An optimization environment includes automatic grid generation, parallel CFD calculations of the seal, and optimization algorithm. Two optimization runs corresponding to low-speed and high-speed cases are performed. Seals with improved characteristics include near-cylindrical and divergent-tapered rings. Performance of three seals from the Pareto set is calculated for different rotational speeds and inlet pressures. Generally, the rotordynamic performance degrades at other operating conditions. Additional study for the seals with enlarged clearance is carried out to model effect of wear.
Smart Material Planning Optimization Problem Analysis
