CFD Comparison to 3D Laser Anemometer and Rotordynamic Force Measurements for Grooved Liquid Annular Seals

Abstract

A pressure-based computational fluid dynamics (CFD) code is employed to calculate the flow field and rotordynamic forces in a whirling, grooved liquid annular seal. To validate the capabilities of the CFD code for this class of problems, comparisons of basic fluid dynamic parameters are made to three-dimensional laser Doppler anemometer (LDA) measurements for a spinning, centered grooved seal. Predictions are made using both a standard and low Reynolds number κ-ε turbulence model. Comparisons show good overall agreement of the axial and radial velocities in the through flow jet, shear layer, and recirculation zone. The tangential swirl velocity is slightly under-predicted as the flow passes through the seal. By generating an eccentric three-dimensional, body fitted mesh of the geometry, a quasi-steady solution may be obtained in the whirling reference frame allowing the net reaction force to be calculated for different whirl frequency ratios, yielding the rotordynamic force coefficients. Comparisons are made to the rotordynamic force measurements for a grooved liquid annular seal. The CFD predictions show improved stiffness prediction over traditional multi-control volume, bulk flow methods over a wide range of operating conditions. In cases where the flow conditions at the seal inlet are unknown, a two-dimensional, axisymmetric CFD analysis may be employed to efficiently calculate these boundary conditions by including the upstream region loading to the seal. This approach is also demonstrated in this study.