Leakage performance and rotordynamic characteristics of bump floating ring seals for turbopump

Floating ring seal with bump foil(BFRS) was newly proposed and tested. BFRS which has a thickness of bump (0.076, 0.1 and 0.12 mm) are separately tested for pressuredrops of 3.0, 5.0 and 7.0 MPa and rotor-speed up to 24,800 rpm. The measured data included leakage performance, attitude angle, lock-up eccentric ratio, and rotordynamic coefficients such as stiffness, damping and equivalent whirl frequency ratio to decide the whirling stability of seal were compared with floating ring seal. When the thickness of bump floating ring seals is increasing, leakage flow rate somewhat increases. Also, the lock-up eccentric ratio of the bump floating ring seal with large thickness is lower than that of the floating ring seal or small thickness of bump foil. The attitude angle increases linearly with the operating speeds in both cases. The direct damping coefficients increase significantly with the increments in bumpfoil thickness and hydrostatic pressure-drop, but diminish with the rising rotor-speed. Especially, Coulomb friction damping force between the bump foil and housing surface contributes to the enhancement of direct damping coefficient value. Whirl frequency ratio of the floating ring seal without bump shows somewhat small in low speed ranges. When bump foil thickness is 0.074mm or 0.1mm, WFR is insensitive in rotating speed and pressure. But BFRS(0.12mm) shows up more stable tendency according to decreasing whirl frequency ratio in high speed ranges. The design parameters determined from these test results will be used to enhance the stability in high pressure and high speed turbomachinery seals.