Identification of force coefficients in a squeeze film damper with a mechanical seal

 

MAJOR APPLICATION: Attenuate vibrations and enhance mechanical isolation in Aircraft Gas Turbines, Power Gas Turbines, Centrifugal Compressors

 

Sponsors: Turbomachinery Research Consortium (03-08) with technical & grant support from Honeywell AeroSpace (phoenix)

 

Objective: To assess effect of end seal on dynamic forced performance of a test SFD.

Rotating machinery operation at high speeds induces severe dynamic loading with large amplitude journal motions at the bearing supports. At these conditions, oil lubricated dampers with low levels of external pressurization are prone to air ingestion leading to an inhomogeneous lubricant film with large striations of entrapped gas. This pervasive phenomenon affects greatly the dynamic force capability and reduces the reliability of the rotor-bearing system.

Status: properly designed end seals increase the damping capability of short length SFDs. The test rig accommodates an industrial contacting mechanical seal SFD. The end seal introduces a dry friction (non-linear) force into the system. The system dynamic force coefficients have been identified from circular centered orbit tests. The parameter identification method allows discerning between the linear (squeeze film) and non-linear (end seal-dry friction) contributions to the overall system response. The SFD dynamic response is characterized in terms of squeeze film damper coefficients, seal dry friction force and added mass coefficients. Identification of damping and inertia force coefficients for multiple frequency (non-circular orbits) will be forthcoming in 2008. The tests aim to replicate operating conditions of intershaft dampers found in multi-spool turbine engines. 

 

Current Work

The SFD vertical test rig was revamped with an end sealed SFD, replicating closely an industrial application. One damper end is flooded while the other end is fully sealed through an end seal ring with a wave spring and O-ring. There is a lubricant recirculation annulus and orifice discharge ports to reduce or eliminate pervasive air ingestion. Structural parameters of the “dry” system (i.e. with no lubricant across the SFD land) were identified from static load and impact load tests .

 

The objective is to identify the damping and inertia force coefficients of an end sealed squeeze film damper. The major tasks are:

2003-07

a)      To measure pressure drop and leakage to determine the end seal coefficient as a function of pressure, lubricant temperature (viscosity), wave spring preload, journal centering, and orifice size. 

b)      To perform dynamic load tests (shakers) with lubricated SFD for increasing oil temperatures and feed pressures.

c)       To develop test and DAQ procedures. Perform analysis of test data using frequency domain identification techniques to extract SFD force coefficients (damping and inertia).  Forward estimated parameters as a function of excitation frequency and amplitude of whirl, lubricant flow rate, feed temperature and pressure, sealing conditions, etc.

d)      To validate predictive model with comparisons to experimental values.

 

      2007-08

a)      Conduct tests with multiple frequency excitations for centered and off-centered bearing positions to simulate operating conditions in multi-spool gas turbine engines.

b)      Development/adaptation of identification method for multiple frequency excitation and off-centered operation.

c)       Increase contact force at the mechanical seal interface and evaluate its impact on the SFD forced performance for centered and off-centered operation.

d)      Estimate parameters as a function of excitation frequency and motion amplitude.

 

The research is of interest for applications such as squeeze film dampers in multiple spool gas turbines, floating ring bearings in turbochargers, hydrodynamic bearings in compressors, etc.

 

 

 

TEST RIG FACILITY

 

 

 

 

 

Squeeze film damping coefficients (CSFDxx, CSFDyy) versus orbit amplitude

 

Dynamic pressure measurements at SFD land and discharge groove, and film thickness.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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Updated May 1, 2008 (LSA)