Experimental rotordynamic characterization of annular seals: Facility and methodology

Annular seals are known to enhance rotordynamic stability margins and minim ize vibration response levels in high-speed rotating machinery. Theoretical predictions SOY the rotordynamic characteristics of annular seals exist bu t additional experimental data is needed to properly anchor these results. NASA's Marshall Space Flight Center (MSFC) has developed an annular seal te st rig and facility to experimentally characterize axially fed annular seal s. The objective of MSFC's annular seal test rig is to obtain the rotordyna mic coefficients (direct and cross-coupled stiffness, damping, and added ma ss) for a variety of high Reynolds number annular seals. The MSFC test, rig supports centered-seal testing with inlet pressures up to 138 bars (2000 p si) and flow rates of over 946 liters per minute (250 gpm). The rig's shaft is powered by a 186 kilowatt (250 horsepower) steam turbine capable of rot ational speeds of over 20,000 revolutions per minute (rpm). A description o f the identification process used to obtain rotordynamic coefficients is gi ven as well as procedures for ensuring quality data. Experimental results f or a smooth annular seal with an L/D = 0.5 is presented Excellent agreement between experimental and theoretical results is obtained.