Abstract
Dynamic pressure and shear stress measurements on the stator wall of whirling annular seals are presented. Two flow conditions (Re=12,000 & 24,000), two seal speeds (Ta=3,300 & 6,600) and three eccentricity ratios (0, 10, & 50% of the clearance) are studied at a whirl ratio of 1.0 (seal center precesses around stator center at same speed as the shaft). Also included are mean velocity and Reynolds stresses measured 0.016 clearances from the stator wall using a 3-D LDA (Thames, 1992) for Re=24,000, Ta--6,600 and c=0.50. A simple integration scheme is used to calculate axial, azimuthal (tangential), and radial forces and moments on the stator wall, using the phase averaged fluctuating shear stress and pressure measurements. A vena contracts and large axial and azimuthal velocity gradients at the seal inlet cause high levels of turbulence and wall pressure and shear stress fluctuations. The highest pressures and axial velocities reside on the pressure side at the entrance and migrate towards the suction side at the exit. Generally the high shear stresses lag the high pressures by 90' at the seal entrance with both the degree of migration and the mean direction of the shear stresses dependent on the test conditions. The pressure and shear stress fluctuations decrease along the seal to the exit where increased azimuthal momentum and decreased axial velocity cause them to increase again. A correlation between the ratio of Ta/Re is seen to exist, suggesting that the flow field shear stress and pressure characteristics are not only dependent on F,, Ta, and Re, but also on the Ta/Re ratio. The forces and moments due to the shear stresses and pressures in a whirling annular seal are significant and should be accounted for in CFD models used to predict seal performance. The radial shear stress forces are negligible compared to the pressure forces, however, the axial shear stress forces are not. In general, the flow field is quite complex with interaction between the mean velocities, turbulence, wall pressures, wall shear stresses, and forces.
Winslow, Robert Bradley (1994). Dynamic pressure and shear stress measurements on the stator wall of whirling annular seals. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1994 -THESIS -W781.