UNCERTAINTY REDUCTION IN GAS TURBINE PERFORMANCE ...€¦ · Uncertainty Reduction in Gas Turbine Performance Diagnostics by Accounting for Humidity Effects 01-021 Page 3 of 22 Modeling

LABORATORY OF THERMAL TURBOMACHINES NATIONAL TECHNICAL UNIVERSITY OF ATHENS

ASME TURBO EXPO 2001 - Land, Sea, & Air, The 46th ASME International Gas Turbine & Aeroengine Technical Congress New Orleans, Louisiana, USA, June 4-7, 2001

2001-GT-010 1

UNCERTAINTY REDUCTION IN GAS TURBINE PERFORMANCE DIAGNOSTICS

BY ACCOUNTING FOR HUMIDITY EFFECTS

K. Mathioudakis, A. Tsalavoutas,

Laboratory of Thermal Turbomachines National Technical University of Athens


Uncertainty Reduction in Gas Turbine Performance Diagnostics by Accounting for Humidity Effects 01-021

Page 2 of 22

Uncertainty Reduction in Gas Turbine Performance Diagnostics by Accounting for

Humidity Effects

• Modelling humidity effects on gas turbine performance

• Impact on Monitoring

o Effects on Measurements

o Effects on "Health Indices"

• Demonstration on Test Data

• Summary-Conclusions



Page 3 of 22

Modeling Humidity effects on gas turbine performance

Layout of twin shaft gas turbine, used for constituting a component based performance model.

1 41

3

2 5 4

C PTCT

Working medium: mixture of air and water vapor for calculations of thermodynamic processes

water content: ad

w

mmwar

,

=



Page 4 of 22


Component performance parameters transformation

Compressor

ddwwdw

RRT

NT

Nγγ ⋅=

⋅

dwwd

dw

RRP

TWP

TWγγ ⋅⋅=

ddwwdw

RRTh

Th

γγ ⋅⋅=

∆

∆

Turbines

( ) )1(1 wdddwwdw

RRT

NT

Nγγγγ +⋅⋅+⋅⋅=

⋅

( ) ( )12

112

1

21

12 −⋅

+−⋅

+

⋅

+⋅

+⋅

⋅⋅

=

d

d

w

w

d

wdw

wd

dwRR

PTW

PTW γ

γγ

γ

γγγ

γ

( ) ( )wdddwwdw

RRTh

Th

γγγγ +⋅⋅+⋅⋅=

∆

∆

11



Page 5 of 22


Referred ("Corrected") quantities

Rotational speed: θγ

⋅×⋅

=2874.1RNN cor

Mass flow rate: θ

γδ⋅×=

4.1287RWWcor

Temperature: θTTcor =

Pressure:

5,31

14,011

−

−

+=

−

γ

γ

δγ ppcor

Power: θγ

δγ

⋅⋅⋅=2874.14.1RPPcor



Page 6 of 22

Effect of Humidity on Quantities used for Monitoring

Effect On Measured Quantities

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04war

-2

-1

0

1

2

Load

Wf

CDT

W

GG Speed

GGET

CDP

-1

0

1

2

3

4

Perc

enta

ge D

evia

tion

(%)

LoadWf

CDT

W

GG SpeedGGETEGTCDP

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04Water Air Ratio

-2

-1

0

1

2

0 20 40 60 80 100

GG SpeedWf

EGT

WCDT

CDP

GGET

0 20 40 60 80 100

0 20 40 60 80 100

Relative Humidity

15 C

25 C

35 C

(a) P=ct

(b)TIT=ct

(c)EGT=ct



Page 7 of 22


Percentage change of referred quantities for constant referred load.

-5

-4

-3

-2

-1

0

1

0 0.01 0.02 0.03 0.04war

Δ %

CDPcorr

CDTcor

EGTcor

Wcor

N1cor



Page 8 of 22

Compressor delivery temperature - power output

Different relative humidity levels, related uncertainty bands

-15

-10

-5

0

5

88 90 92 94 96 98 100 102

Load %

CD

T-C

DT n

om (

o C)

0 %

30%

60%

90%

. If humidity is not accounted for: -ability for diagnosing malfunction is reduced, when based on performance quantity interrelations - changes caused by humidity may be large enough to be misinterpreted as the occurrence of a malfunction, and thus have a false alarm.



Page 9 of 22


Effect on Measurement Deviation Patterns

-3

-2

-1

0

P W1 CDP CDT(C) EGT(C)

(a)Δ %

-3

-2

-1

0

P W1 CDP CDT(C) EGT(C)

(b)Δ %

(a) war=0.009 (b) IGV fault. Signatures for N1 constant



Page 10 of 22

Effects On Monitored Parameters Condition assessed using “health indices” Technique used "ADAPTIVE MODELLING" Compressor

( ) ( )refPTWPTWf 2222221 //)/= ,

refCCf ,2 /ηη= Gas Generator Turbine

( ) ( )refPTWPTWf 4444445 ///= ,

refGGTGGTf ,6 /ηη= Power Turbine

( ) ( )ref

PTWPTWf 1.41.41.41.41.41.47 /// ⋅⋅=

refPTPTf ,8 /ηη= Measurements collected from the engine, fed to the adaptive model, without properly accounting for humidity, produce health parameters different form their nominal values.



Page 11 of 22

Humidity Effect on Component Health Indices

Modification factors deviation, for humid air data processed by dry-air adaptive-model

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04war

-6

-5

-4

-3

-2

-1

0

1

2

Perc

enta

ge D

evia

tion

(%)

f8

f2

f1

f4f6

f5f7

.



Page 12 of 22

Measurement data from an industrial gas turbine

Layout of gas turbine and quantities measured for monitoring

Inlet pressure, Temperature

CDP,CDT

EGT N1

Airflow

Load

.



Page 13 of 22

Daily variation of ambient conditions

15

20

25

30

35

40

45

0 2 4 6 8 10 12 14 16 18 20 22 24

Hour

Ambi

ent T

empe

ratu

re

Day 1 Day 2 Day 3 Day 4Day 5 Day 6 Day 7 Day 8

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14 16 18 20 22 24

Rela

tive H

umid

ity

0.008

0.01

0.012

0.014

0.016

0 2 4 6 8 10 12 14 16 18 20 22 24Time of Day (h)

war



Page 14 of 22

Variation of ambient conditions over a week

70

75

80

85

90

95

100

1 2 3 4 5 6 7 8Time (Days)

Load

(%)

15

20

25

30

35

40

45

1 2 3 4 5 6 7 8Time (Days)

Tam

b (o

C)

0.008

0.01

0.012

0.014

0.016

1 2 3 4 5 6 7 8Time (Days)

war



Page 15 of 22

Referred measured quantities for low and high humidity level

96.0

97.0

98.0

99.0

100.0

90.00 91.00 92.00 93.00 94.00 95.00 96.00Load/(δ θ) %

CD

Pco

r %

99.0

99.5

100.0

100.5

90.00 91.00 92.00 93.00 94.00 95.00 96.00Load/(δ θ) %

EG

Tcor

99.0

99.2

99.4

99.6

99.8

90.00 91.00 92.00 93.00 94.00 95.00 96.00Load/(δ θ) %

N1c

or %

98

99

100

101

90.50 91.00 91.50 92.00 92.50 93.00 93.50 94.00 94.50 95.00 95.50Load/(δ θ) %

CDTc

or

94

95

96

97

90.00 91.00 92.00 93.00 94.00 95.00 96.00Pcor %

W1c

or

Points around Instants A and B



Page 16 of 22

Estimation of Measurement Deviations

Predicted and measured differences

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

CDT CDP W NGG EGT

Δ %

Predicted Measured

Comparison of Operating conditions of low(war~0.008) and high ambient humidity ( war~0.014)



Page 17 of 22

.

Health indices deviation for different levels of humidity

.

Sensitivity of the individual indices to humidity

0 0.01 0.02 0.03 0.04war

-5

-4

-3

-2

-1

0

1

Perc

enta

ge D

evia

tion

(%)

f2

f1

f6

f5

f7

f1,f2,f5,f6,f7 estimated from N1, CDP, CDT, EGT, W2 Indices mostly influenced: f1 , f7



Page 18 of 22

Time evolution of Health-Indices

Compressor flow capacity evolution

-3-2-10123

0 1 2 3 4 5 6 7 8

df1(

%)

-3-2-10123

0 1 2 3 4 5 6 7 8Time (days)

df1(

%)

(a)

(b)

(a) standard humidity of 60%, (b) actual measured humidity



Page 19 of 22

Humidity induced variation compared to actually expected variations

-3-2-10123

0 1 2 3 4 5 6 7 8

df1(

%)

-3-2-10123

0 1 2 3 4 5 6 7 8Time (days)

df1(

%)

(a)

(b)

Impact of fouling on Compressor flow capacity, and the effect of compressor wash

-3

-2

-1

0

1

2

3

0 10 20 30 40 50Time (Days)

Df1

%

Compressor Wash



Page 20 of 22

Time evolution of Health-Indices

Power turbine swallowing capacity evolution

-3

-2

-1

0

1

2

3

0 1 2 3 4 5 6 7 8Time (Days)

df7

(%)

-3-2-10123

0 1 2 3 4 5 6 7 8Time (Days)

df7

(%)

(b)

(a)

(a) standard humidity of 60%, (b) measured humidity



Page 21 of 22

Some Practical Aspects

• Humidity measurement essential for accurate monitoring

• Humidity influence more important when large

variations in ambient absolute humidity are expected.

o (This would be the case more for hot and humid climates)

• Referred variables to be used for comparing data from different humidity levels.

o The reference condition can be chosen to be representative of an average day, but it does not practically influence the magnitude of observed changes, if it is consistently used.

• It is preferable to use the standard absolute humidity

for calculations instead of keeping the relative humidity constant or assuming dry air (if a measurement is not available)

• Monitoring turbines with inlet humidification

requires the support by models incorporating humidity.



Page 22 of 22

SUMMARY-CONCLUSIONS

• Effect of humidity on quantities related to gas turbine performance monitoring analyzed. A twin shaft industrial gas turbine was used as a test case.

• A method of incorporating humidity effects in an engine performance model described, as well as a method to "refer" measured performance variables

• The model was used to demonstrate how measured quantities deviate from their values in operation with dry air.

• If humidity is not taken into account, uncertainty bands in measured quantities may be too broad reducing the discriminative ability for diagnostics.

• Measurement deviations caused by humidity changes could be of magnitude similar to the magnitude of deviation caused by faults

• "Health” parameters exhibit apparent deviations if humidity is not correctly accounted for

• Incorporating a measurement of humidity in calculations eliminates apparent trends while it reduces the scattering of “health” parameter values.

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UNCERTAINTY REDUCTION IN GAS TURBINE PERFORMANCE ...€¦ · Uncertainty Reduction in Gas Turbine Performance Diagnostics by Accounting for Humidity Effects 01-021 Page 3 of 22 Modeling