CFD-Predicted Rotordynamic Coefficients for a 20-Teeth-on-Stator Labyrinth Seal at High Supply Pressure Conditions

Abstract

A twenty-teeth-on-stator labyrinth seal with a tooth radial clearance of 0.1 mm is modeled using a CFD method to predict leakage performance, as well as stiffness and damping coefficients. The calculations are performed at a supply pressure of 70 bar for three shaft rotational speeds (10200 rpm, 15200 rpm, and 20200 rpm), three preswirl ratios (low, medium, and high), and three pressure ratios (0.1, 0.35, and 0.5). The predicted performance of the seal is compared to experimental data obtained by Picardo and Childs (Picardo, A. and Childs, D.W., 2005, “Rotor-dynamic Coefficients for a Tooth-on-Stator Labyrinth Seal at 70 Bar Supply Pressures: Measurements Versus Theory and Comparison to a Hole-Pattern Stator Seal,” ASME J. Eng. Gas Turbines Power, 127, pp. 843–855). The results from CFD simulations follow the experimental data. Leakage performance is underpredicted by up to 19.8%. Direct and cross-coupled stiffness coefficients are in reasonable agreement with the measurements. However, predicted cross-coupled stiffness increases slower with increasing preswirl ratio than the experimental cross-coupled stiffness. Direct damping is also in agreement with the measured values with the exception of the high preswirl ratio at 20200 rpm. Cross-coupled damping reveals the largest deviations between predictions and experiments. Additionally, the coefficient of determination is calculated for all experimental rotordynamic coefficients to estimate the goodness of fit for the raw test data.