DYNAMIC FORCE PERFORMANCE OF ANNULAR GAS SEALS AT OFF-CENTER CONDITIONS

A numerical analysis to predict the static and dynamic performance cha racteristics of gas annular seals at Off-center conditions is presente d. Isothermal rotor and stator surfaces are assumed according to condi tions observed on an existing test rig. Heat flow to the rotor and sta tor is modeled by bulk-flow heat transfer coefficients. The non-linear differential equations for the turbulent bulk flow in the annular sea l are solved using an efficient CFD algorithm. A perturbation method f or calculation of the zeroth- and first-order flow fields determines t he seal steady-state response and dynamic force coefficients. Numerica l predictions for a test seal show that heat transfer from the boundin g solid surfaces to the fluid film is important to correctly predict t he temperature field. An adiabatic flow assumption leads to unrealisti cally large temperature drops across the seal length. The seal leakage and the direct stiffness coefficients are insensitive to the position of the rotor center in the seal, while the seal forces, the cross-cou pled stiffness, and the direct damping coefficients increase with the rotor static eccentricity.