Analyzing the Influence of a Swirl Brake on a Smooth Liquid Annular Seal Through Measuring Static and Rotordynamic Characteristics

Abstract

Data are available for a previously tested annular seal with no swirl brakes (NSB). The NSB seal design was modified by adding slots at the inlet to produce a swirl brake (SB) seal. Tests were conducted to evaluate the static and dynamic characteristics of the modified SB seal. The SB data was then compared to the NSB data to understand how the seal rotordynamic coefficients are affected when swirl brakes are added. The SB and NSB seals had a radial clearance (Cr) of 203.2 um with the diameter of the seals (D) being 102 mm. The length to diameter ratio (L/D) of the NSB seal was 0.50, while the SB seal had an L/D of 0.45 due to the addition of swirl brakes. The SB seal was tested at three different inlet pre-swirl ratios (PSR): high preswirl, medium pre-swirl, and radial injection. During testing, operational conditions were varied by changing differential pressure (?P), running speed (w), and eccentricity ratio (e0). The test points were at w = 2, 4, 6, 8 krpm, ?P = 2.07, 4.14, 6.21, 8.27 bar and e0 = 0.00, 0.27, 0.53, 0.80. The test fluid was ISO VG 2 oil. The static data for SB showed that the flow rate (Q) increased as the imposed PSR increased, meaning the high pre-swirl case produced the highest Q values. Swirl brakes deliver the greatest reduction in PSR compared to that of NSB seals at high ?P, low w, and toward the centered position (e0=0.00). A vector Reynolds number was produced over the range of 1300 to 4400. The flow through the test stand was predicted to be transitional and turbulent.