Measurement of leakage in a novel all metal non-contacting

annular seal at high temperatureAlain AndersonGraduate Research Assistant

Luis San AndrésMast-Childs Professor

TRC project 2010-2011 TRC 32513/15193S/ME

START DATE: September 1, 2010

Trends in High Performance Turbomachinery• Higher speeds & more compact units• Extreme operating temperatures and pressures• More efficient & reliable

JUSTIFICATION

Issues of Importance• Reduce secondary flows

(parasitic leakage)• Reduce specific fuel consumption & COST• Increase power delivery• Eliminate potential for rotordynamic instability

Source: GE Energy

TRC funded a two-year program- Conduct non-proprietary leakage tests with a

HALOTM seal- Conduct leakage tests with a three tooth labyrinth

seal for comparison

OBJECTIVE

Desired outcomes- Enable the application of state of the art sealing

technology- Increase system efficiency

- Reducing leakage- Eliminating wear of components- Extending maintenance intervals

PRIOR WORK 2007-2009 [1]

• To measure leakage in three test seals by varying:• Supply pressure (upstream) from 1 bar to 3.5 bar• Air inlet temperature from 30ºC to 300ºC• Rotor speed from 0 rpm to 3,000 rpm

• To estimate drag torque (power loss) from each seal• Compare three seals and provide recommendations

A power gas turbine OEM wished to benchmark novel seal types against a (traditional) labyrinth seal to realize benefits and to ensure potential gains

TEST SEALS 2007-2009 [1]

Labyrinth Seal Brush Seal

Hybrid Brush Seal

EXPERIMENTAL FACILITY

Heater

Exhaust duct

Air pressurization cylinder

Motor Test seal

Roller bearings

cm

50 25 75 0

Flow in

Flow out

Rotor

Voltage Power OutputHeater 240 V 12 kW 300°CMotor 90 V 850 W 3,000 rpm

Maximum

1 Hot air inlet 5 Optical displacement sensor2 Pressurized cylinder & shaft 6 Centering mechanism

3 Radial support bearings 7 Coupling and quill shaft4 Disc and test seal location 8 Electric drive motor

8

3

2

5

4

6

1

7

Flow in (supply pressure)

Flow out (ambient pressure)

0 10 20

cm

Properties Magnitude

Specific gas constant, R 287 J/kg-K

Supply pressure, Ps 101-760 kPa

Inlet temperature, T 298-573 K

Exhaust pressure, Pe 101 kPa

Ambient temperature 298 K

EXPERIMENTAL FACILITY

Test seal

Maximum air pressure: 100 psig

EXPERIMENTAL FACILITY

Rollerbearing assembly

Eddy current sensor

Spring

Ball bearing

Shaft

Disk

High pressure air

Flow

Flow Flexible coupling to motor

Hybrid brush sealDetail of brush seal test rig

Rollerbearing assembly

Eddy current sensor

Spring

Ball bearing

Shaft

Disk

High pressure air

Flow

Flow Flexible coupling to motor

Hybrid brush seal

Rollerbearing assembly

Eddy current sensor

Spring

Ball bearing

Shaft

Disk

High pressure air

Flow

Flow Flexible coupling to motor

Hybrid brush sealDetail of brush seal test rig

Centering mechanism

Test seal

a) Revamp test rig for operation at higher rotor speeds to reach a tip surface speed of 120 m/s (15 krpm). Thermal and centrifugal growth at high speeds is expected to further decrease leakage

b) Perform clearance and leakage measurements with a three teeth labyrinth seal and the HALOTM seal operating with pressure ratios as high as 8, temperatures to 300ºC, and tip surface speeds to 120 m/s

c) Compare the labyrinth seal measured leakage with XLLaby® predictions at high temperature. The benchmarking is essential to trust, modify or discard current predictive models

Proposal to TRC (2 years)TRC members benefit from existing high temperature seal test rig

a) Revamp test rig for operation at higher rotor speeds to reach a tip surface speed of 120 m/s (15 krpm). Thermal and centrifugal growth at high speeds is expected to further decrease leakage

b) Perform clearance and leakage measurements with a three teeth labyrinth seal and the HALOTM seal operating with pressure ratios as high as 8, temperatures to 300ºC, and tip surface speeds to 120 m/s

c) Compare the labyrinth seal measured leakage with XLLaby® predictions at high temperature. The benchmarking is essential to trust, modify or discard current predictive models

TRC funded project (2 years)TRC members benefit from existing high temperature test rig

(a) Learn operation of test rig and DAQ system(b) Install two seals (labyrinth and HALO) and perform

leakage measurements with air for:

(c) Revamp test rig for high speed operation

Non-rotating and centered rotor

Inlet temperature (30ºC-300ºC)

Supply pressure (1 bar- 7 bar)

Work to date for TRC funded project

TEST LABYRINTH SEAL

LEAKAGE: Labyrinth Seal

Flow rate increases with supply pressure and decreases with inlet temperature due to changes in seal clearance and gas density.

TESTS for low pressure ratios to 3.5 (> choking)

30C

300C

Modified Flow Factor

lDP

Tm

s

Modified flow factor: Labyrinth Seal

Flow factor allows comparison of different types of seals. For labyrinth seal, it removes effect of supply pressure and temperature.

30C

300C

Hydrostatic Advanced Low Leakage Seal All metal (no bristles) non-contacting seal

TEST HALOTM Seal

0 2010

mm

Direction of flow

Direction of flow

http://www.atgi.us

TEST CONDITIONS (HALOTM SEAL)

Hydrostatic Advance Low Leakage (HALO) Seal

*Clearance between seal pad and disc not to scale.

Axial profile of a resilient pad in HALO™ seal (Courtesy of ATG)

Direction of flow

Exhaust Pressure

Supply pressure

Seal pad

Disc 0 1 mm

2 3

0

0.05

0.1

0.15

0.2

0.25

1 1.2 1.4 1.6 1.8

Pressure Ratio [Ps/Pe]

Ra

dia

l C

lea

ran

ce

[m

m]

PR: upstream pressure /ambient (exit) pressure

HALO™ seal clearance closes with pressurization.

Measurements at room temperature (30 °C) and no shaft rotation

LEAKAGE: HALOTM Seal

Flow rate increases with supply pressure and decreases with air inlet temperature. TESTS conducted with much higher pressure ratios

30C

300C

Modified Flow Factor

lDP

Tm

s

Modified flow factor: HALOTM Seal

Modified flow factor much lower than for labyrinth seal

30C300C

Leakage Comparison: Labyrinth & HALO)

LABYRINTH

HALO seal

The HALOTM seal leaks 50% or less than the labyrinth seal. For pressure ratios (Ps/Pa) > 3.0, the HALOseal leaks ~¼ the flow rate of the labyrinth seal

Flow factor (Labyrinth & HALO) 300 C

Labyrinth seals are an outdated technology. Industries seeking to increase efficiency by reducing (parasitic) secondary leakage losses will benefit greatly from a change in seal technology

LABYRINTH

HALO seal

REVAMP TEST RIG

Issues

• Large vibrations of cantilevered rotor

• Critical speeds too low& air temperature too high

• Safety: containment at high speeds

• Drive motor speed limitations

Solutions• Balance rotor

• For high temperature, use a metal mesh foil bearing (MMFB) as a support.

• Use high speed router motor & construct containment guard.

For operation at higher rotor speeds to reach a tip surface speed of 120 m/s (15 krpm)

REVAMP TEST RIGXLTRC2 rotordynamic analysis

f=5953.2 cpmd=.0602 zetaN=10000 rpm

forwardbackward

Metal mesh bearing support adds stiffness and damping to original cantilevered rotor.

Bearing Cartridge Metal mesh

donut

Formed top foil

XLTRC2 imbalance response predictions

0.000

0.040

0.080

0.120

0.160

0.200

0 5000 10000 15000 20000

rotor speed (krpm)

amp

litu

de

mic

ro-m

0-p

k

thin shaft 0.5 inch (current rotor)

shaft 1 inch diam

shaft 1.5 inch

shaft 2.0 inch

original (0.5 inch) - no MMFB

original 0.5 in OD shaft- no MMFB

shaft OD increases(0.5 in to 2.0 in)OD=0.5 in

rotor supported on MMFBs

MMFB increases critical speed and determines a well damped system

With MMFB

Amplitude of motion at disc

Shaft13430

25

2015

105Shaft11

-0.12

-0.08

-0.04

0

0.04

0.08

0.12

0 0.08 0.16 0.24 0.32 0.4 0.48

Axial Location, meters

Sh

aft

Rad

ius,

met

ers

rolling bearings

connecting rod to drive

Disc

Shaft (1/2 inch)

Metal mesh bearing& rods support

journal

Test gas seal

TRC Budget

Year IISupport for graduate student (20 h/week) x $ 1,700 x 12 months $ 20,400

Fringe benefits (0.6%) and medical insurance ($191/month) $ 2,412

Travel to (US) technical conference $ 1,500

Tuition three semesters ($3,802 x 3) $ 10,138

Equipment and supplies for test rig $ 550

Year II $ 35,000Year I $ 39,863

High Temperature Seals

Research will quantify the leakage performance of a novel gas seal for high temperature gas turbines and steam turbines.

RESEARCH PRODUCTS•Reliable leakage database•ASME journal publication•Technical report (M.S. thesis)

Questions (?)

[1] San Andrés, L., and Ashton, Z., 2010, "Comparison of LeakagePerformance in Three Types of Gas Annular Seals Operating at a High Temperature (300°C)," Tribol. Trans., 53(3), pp. 463-471.

Learn more athttp://rotorlab.tamu.edu

References

[2] Justak, J., and Doux, C., 2009, “Self-Acting Clearance Control forTurbine Blade Outer Air Seals,” ASME Paper GT2009-59683.