Abstract
This paper conducts a comprehensive study on the effects of the air presence in the oil on the leakage and rotordynamic coefficients of a long-smooth seal (inner diameter D = 89.306 mm, radial clearance Cr = 0.140 mm, and length-diameter ratio L/D = 0.65) under laminar-two-phase flow conditions. The mixture consists of air and silicone oil with inlet GVF (gas volume fraction) up to 10%.
Tests are performed at inlet temperature Ti = 39.4 °C, exit pressure Pe = 6.9 bars, pressure drop PD = 31 and 37.9 bars, and rotor speed ω = 5, 7.5, and 10 krpm. The test seal is always concentric with the rotor, and no intentional fluid pre-rotation is provided at the seal inlet.
The complex dynamic stiffness coefficients Hij of the test seal are measured and fitted by the frequency-independent direct stiffness K, cross-coupled stiffness k, direct damping C, cross-coupled damping c, direct virtual-mass M, and cross-coupled virtual-mass mq coefficients.
Under laminar flow conditions, increasing inlet GVF has negligible effects on K, k, C, and effective damping Ceff, while it decreases c and M. These trends are correctly predicted by San Andrés’s bulk-flow model with laminar flow friction formula. As inlet GVF increases, measured leakage flow rate ṁ increases slightly. In general, the predictions of K, k, C, c, Ceff, and ṁ are reasonably close to measurements.