CFD development for rotordynamic force coefficients of plain and labyrinth seals

To improve the prediction of the swirl flow field in seals, which is important to the rotordynamic coefficients calculation, Bradshaw's (1973) modified turbulent mixing length analogy for the streamline curvature effect was used to develop a new law of the wall for strong swirl flow along a curved surface. Also a new wall function for CFD codes was developed from the new law of the wall. The results were compared with Morrison's (1988, 1991a, 1991b, 1995) measurements. The comparisons show an improvement of the predictions of swirl velocity with the new wall function over the standard wall function.; For prediction of rotordynamic force coefficients of complex geometry seals, a 3-D Navier-Stokes model was established. By adopting the bipolar coordinate system, the model can be used for a wide range of shaft eccentricity (0.1% to 99.9%) cases. Several benchmark test cases were calculated to validate the code. The comparison shows the predictions of the 3-D model are in fairly close agreement with the measurements.; A new coordinate transformation, based on a new axial dividing concept, was developed to convert an eccentric physical seal domain to a concentric computational domain. This new transformation eliminates the limitation of previous transformations so that it can be applied to almost any complex geometry seal. Under the assumptions of small displacement of the shaft from the center of the housing and sinusoidal circumferential variation of the flow quantities, the 3-D Navier-Stokes equations were perturbed with the perturbation parameter of eccentricity ratio. Zeroth-order equations, which represent the concentric axisymmetric flow field, and first-order equations for the perturbed eccentric flow field, were derived. The equations were solved numerically. The CFD/Perturbation model was applied to a labyrinth gas seal, a grooved liquid seal, an interlocking gas seal and a stepped labyrinth seal. The results were compared with measurements. The comparisons show the CFD/Perturbation model gives a fairly close agreement result with measurements.