Additional Test Results for Round-Hole-Pattern Damper Seals: Leakage, Friction Factors, and Rotordynamic Force Coefficients

Abstract

Test results are presented for round-hole-pattern damper seals at Reynolds numbers on the order of 90,000 to 250,000. The seals have roughened stators; Cr/R = 0.0075 and L/D = 1/2. The fluid CBrF3 entering the test seals has no intentional prerotation, i.e., the fluid is injected radially into the apparatus. There is no tangential injection; and no “slinger” is provided upstream of the seals. Test results consist of leakage rates, axial pressure gradients, friction factors, and rotordynamic-force coefficients. The hole-pattern-stator seals leak approximately one third less than smooth seals at the same clearances, have approximately the same damping performance, and about 20 percent lower stiffness values. Unlike earlier tests (Childs and Kim, 1986), variations in hole depth to radial clearance ratios h/Cr showed no clear optimum with respect to damping. Increasing the ratio of hole area to surface area from 0.27 to 0.34 to 0.42 showed no damping change, in moving from 0.27 to 0.34, but a substantial drop in moving from 0.34 to 0.42. Measured friction factors showed serious deviations from the assumed Blasius friction-factor model for wall-shear stress for some stators, particularly in regard to speed dependency. Despite these deviations, theoretical predictions based on measured friction factors are generally reasonable. Direct stiffness predictions are generally within 20 percent. Damping predictions are generally within 5 percent.