Shoed Brush Seals to Improve Gas Turbine Efficiency

Hybrid Brush Seals with Reverse Rotation Ability

MAJOR APPLICATION: Gas Turbines, Steam Turbines

Sponsors: Turbomachinery Research Consortium (04-05), Advanced Turbomachinery Solutions-US-NAVY SBIR II (02-03), Siemens Power Generation (2006-2008)

Objective: Measurements of leakage, power loss and structural parameters in a hybrid brush seals for gas turbine applications

Status: Rotating test rig constructed for shaker load measurements. Leakage vs. supply pressure tests at increasing rotor speeds completed. Hybrid brush seals offer markedly low leakages and reduced power losses as pressure supply increases with little detrimental effect from rotor speed.

Hardware from Advanced Turbomachinery Solutions (ATS)

Sponsor Project #

Amount

Project

Dates(GS support)

Siemens 32525/3465A	$ 67,000	High temperature Brush Seal Test Rig	10/01/07 9/30/08 (1)
Siemens 32525/34650	$ 75,993	Brush Seals with Reverse Rotation	01/01/06-09/30/07 (1)
ATS 32525/66260/ME	$ 79,580	Computational Analysis of Reverse Rotation Brush Seals	10/15/01-03/31/03 (1)

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Justification: Labyrinth seals are the primary seal type used in gas turbines due to their simplicity, low cost and easy installation. However, leakage through a labyrinth seal increases with operation due to inevitable wear, thermal growth and rotor excursions. Furthermore, labyrinth seals are poor rotordynamic elements, often producing negative effective damping and leading to dangerous rotordynamic sub synchronous instabilities. Brush seals effectively control leakage in air breathing engines. However, their current state of the art limits their application to relatively low-pressure differentials.

Objective: To measure & predict brush seal leakage, to measure mechanical parameters (stiffness and damping) from brush seal, and to advance computational models for prediction of the dynamic forced performance of shoed brush seals.

Status: Analysis and software complete. Effect of dry-friction in bristle bed is paramount to generate enough damping enhancing rotordynamic stability of multiple-shoed brush seals. In 2004, Test rig constructed to perform dynamic force measurements with pressurized brush seals and identification of brush seal structural stiffness and damping (dissipation) coefficients. The physical parameter characterization using nonlinear methods is in progress. IN 2008, test rig for operation at high temperature (500 F) manufactured for measurement of seal leakage.

Prior/Current Work: leakage, Stiffness and Damping Coefficients of Brush Seals with Reverse Rotation Ability

Multiple-shoed brush seals represent an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for shaft reverse rotation. The novel brush seal incorporates pads contacting the shaft; and which under rotor spinning; lift off due to the generation of hydrodynamic pressure. The ensuing gas film prevents intermittent contact; thus lowering the operating temperature and thermal distortions, and even eliminating bristles wear.

A computational model was advanced in 2003 with funding from Advanced Technology Group through a US-NAVY SBIR grant. The brush seal model relies on the physical characterization of the bristle bed structural stiffness and damping coefficients. This can only be achieved through exhaustive testing rather than complicated computational analyses.

In 2004 a test rig was constructed for identification of brush seal parameters. The experimental work included leakage and dynamic load tests (shakers) for increasing supply gas pressures. An identification method was developed to determine the shoed-brush seal force response. Force coefficients are given as a function of excitation frequency, supply temperature and pressure, etc. The SBS energy dissipation mechanism is characterized using a dry-friction (coulomb damping) and a loss factor (structural damping) coefficient. The total system damping is also given in terms of an equivalent viscous damping coefficient.

In 2006 the test rig was revamped to conduct rotordynamic tests and accommodate a hybrid brush seal (HBS- third generation shoed brush seal) also developed by Advanced Technology Group. The leakage and dynamic performance of this seal was also characterized and compared to results obtained for the shoed brush seal. The HBS has better leakage and dynamic performance than the first generation brush seal.

In 2008, a high temperature test rig is near completion to test an improved version of the HBS up to 300 ^oC. Turbomachinery users will benefit from a planned effort to characterize the dynamic and leakage performance of the seal for various pressure drop and temperature conditions. The current tasks are:

a) To perform dynamic load tests (shakers) for increasing supply gas pressures and temperatures. Single and multiple frequency experiments are planned.

b) To identify structural stiffness and damping coefficients. Force coefficients will be given as a function of excitation frequency and amplitude of whirl motion, supply temperature and pressure, seal interference, etc.

c) To measure leakage flow across a HBS, SBS and labyrinth seal for increasing supply gas pressures and temperatures.

2008 TEST RIG FACILITY

2006 TEST RIG FACILITY

2004 TEST RIG FACILITY

VIRTUAL TOUR

To be Included 30 sec video clip

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