Session: 25-01 Annular Seals 1

Paper Number: 83504

83504 - "Negative Centering Forces of Wet-Gas Hole-Pattern Seals at Low Excitation Frequencies" 

Zhang and Childs (2021) investigated the behaviors of a hole-pattern HP seal (the length-to-diameter ratio is 0.75, hole depth is 1.9 mm, area ratio is 65%) with wet-gas mixtures. The HP seal’s rotordynamic coefficients were strongly frequency-dependent. Direct stiffness K increased as excitation frequency increased and was close to zero at low excitation frequencies. Cross-coupled damping c is negative and makes effective stiffness K_eff lower than K. This paper calculates the K_eff values of the HP seal presented by Zhang and Childs (2021) and finds K_eff generally decreases after the oil is injected into the air stream and changes from positive to negative in many cases. This paper also presents the test data for a new HP seal that has the same geometric dimensions except with a deeper hole depth of 2.5 mm. Tests for the new HP seal are performed at 62.1 bars inlet pressure, 0.5 pressure ratio, three speeds from 10 to 20 krpm, and two inlet liquid volume fractions (inlet LVF = 0 and 2%). The new HP seal shows negative K and K_eff values at low excitation frequencies. The negative stiffness of the new HP seal at low excitation frequencies can lead to negative destabilizing forces and prevent testing for cases with inlet LVF higher than 2%.

Presenting Author: Min Zhang Praxair, Inc.

Presenting Author Biography: Min Zhang is a Development Specialist within the Turbomachinery R&D Unit of Praxair Inc. in Tonawanda, NY. He earned his Bachelor and Master degrees from Harbin Institute of Technology (Harbin, China) and received his Ph.D. degree in Mechanical Engineering from Texas A&M University (College Station, TX).

Authors:

Min Zhang Linde, Inc.
Dara Childs Texas A&M University