erosion of dust-filtered helicopter turbine engines

7/21/2019 Erosion of Dust-Filtered Helicopter Turbine Engines

1/6

J O U R N A L O F

A I R C R A F T

V o l .

32, No. 1, January -F ebruary

1995

Erosion ofDust-Filtered HelicopterTurbineEngines

Part

II:

Erosion

Reduction

Joh a n n e s P. van der Wa lt* and A l a n N u r i c k t

University

of the

Witwatersrand, Johannesburg, South

Africa

The effects of erosion of filteredand

unfiltered

dusts ingested by a helicopter gas turbine engine are investigated

for

the case where particle-on-particle interactions are negligible. The effects of the particle size distribution of

th e

dust

in the

ingested airstream

on

engine life

are

included

in the

analysis.

An

erosion reduction factor, which

may be used to predict the increase in life of a gas turbine engine in terms of a filtration efficiency factor and

the effective particle sizes of the filtered and unfiltered dusts, is presented. The method is validated using

experimental results obtained on a T urmo

IV B

gas turbine engine.

Nomenclature

E

=

erosion, g or cm

3

E, =

erosion rate,

g/g or

cm

3

/g

/ S A E ( $ )

=

fractional particle size distribution

of SAE

coarse

test dust

/((/>) = fractio nal particle size distribution of

ingested dust

k =

constant dependent

on

engine

and

erodent

properties

M =

mass

of

ingested particles,

kg

M

fe d

=

dust mass

fed to the

filtration system,

kg

M j =

dust mass

in

each particle size band

/,

kg

^scav

dust mass scavenged

by the

filtration

system,

kg

m

t

=

M-JM

P

2

IP \

=

pressure ratio of the first-stage compressor

S

scavenge ratio

V =

impact velocity, m/s

W

r

= rate of engine power loss, % / k g

a =

exponent

in Eq. (3)

A V K = percentage eng ine power loss, %

T J m a s s

=

mass-based

filtration

efficiency

= particle size,^m

0

ef f

= effective

particle size,

jam

0 m a x

=

max imum part icle size,^m

0 m a x

S A E

=

m a x i m u m u n f i l te r e d S A E

coarse

particle size,

f j u m

c / >

m in

= min imu m particle size,

ju m

^ m i n S A E

=

m i n i m u m u n fi l t e re d S A E c oa rs e

particle

size,

ju m

^ S A E

e f t

=

effective

particle size

o f S A E

coarse

test dust, ) L t m

Introduction

T

H E

p e r f o r m a n c e

of an air filtration

system

is

often

ex -

pressed in terms of a

filtration

efficiency parameter that

gives th e

reduct ion

of the

mass

(o r

concentration)

of

i m p u -

rities in the through-f low ai rs t ream. T h e impuri t ies in the

airstream

ingested

b y a

helicopter

ga s

turbine engine result

in engine erosion, wh ich can be greatly reduced by the use

of

a dust

filter fitted

to the engine in take. A simple mass-

R ecei v ed May 5,

1993;

revision received A pril 20 ,

1994;

accepted

fo r

p u b l i cat i o n

May 3, 1994.

C o p y ri g h t

1994by the

A m e r i c a n

I n s t i t u t e o f

A e r o n a u t i c s

an d

A s t r o n a u t i c s ,

Inc.A ll

rights reserved.

^ G r a d u a t e

S t u d en t , S ch o o l

of

M ech an i cal E n g i n eer i n g , B ran ch

of

A e r o n a u t i c a l E n g i n e e r i n g .

tProfessor, School

of

M ech an i cal E n g i n eer i n g , B ran ch

of

Aero-

based

filtration

efficiency

p a r a m e t e r

doesnot,

however,

pro-

vide

a

complete measure

of the

engine erosion,

and it is

pro-

posed that

filtration efficiencies

be expressed in terms of an

erosion reduction factor that provides a direct measure o f

engine

life

extension.

A l t h o u g h

some research has been done on helicopter en-

gine

erosion characteristics,

i t

appears tha t l i t t le

ha sbeen

done

to incorporate these parameters into a practical fi l tration as-

sessment method.

D u f f y

et

al.

1

presented

a

complete

set of

en gin e

erosion curves

for theT7

engine where

th e

engine

erosion

is

expressed

in

t e r m s

of initial

engine power,

influ-

enced

by the

mass

an d

mass mean particle sizes

of

ingested

dust. However, no attempt to construct a

filtration

assessment

correla tion

that is based on these erosion curves could be

fo und

in the open l i terature.

Mass-Based Filtration Efficiency

Mass-based

filtration efficiencies can be

defined

as

1?mass

Mass

of

dust removed

Mass of dust fed

( i )

W h e n

filtration

systems feature dual

flow

paths (i .e., through-

flow

an d

scavenge

f lo w ), a

correction

to the

dust mass

fed to

th e system is required. A f o r m u l a t i o n of this relationship

expressed

in

terms

of the

ingested

an d

scavenge particle mass

fractions can be written

2

:

T/mass

=

1

M

sca

-

S

(2 )

Relationship

Between Engine Power Deterioration

andErosion

A relat ionshipby van der W a l t an d Nurick

3

relates filtered

helicopter

engine power deteriorat ion

to

erosion,

o r

more

specifically

to the mass an d size of the ingested particles. I t

w as

shown that

E = k M < f > V

a

or

E,

=

k c / > V

u

3)

an d

t h a t

a

l inear relat ionship

can be

assumed between engine

erosion and

power deteriorat ion

for a filtered

helicopter

en -

gin e,

which may be w r i t t e n

a


2/6

VANDER WALT AND

NURICK:

DUST-FILTERED

HELICOPTER ENGINES

PARTII 113

Percentage by Mass in

Band

[ ]

0.1

1 1

Particle

Size [Microns]

1000

Fig.

1 SAE

coarse

and Donaldson

through-flow (SAE coarse

dust

ingested) particle size distribution

expressed

as

mass

fractions.

or

W

r

=

4)

For the

case

of a

sparse

dust d istr ibution in

wh ich

particle-

on-particle

interactions are

negligible,

th e engine p o w e r loss

is given by

A W

=

k M

n

< f >

H

V

a

=

kV

a

5)

Practical Application of

Erosion

Analysis

Procedure

Th e p rimary ob ject ive of th e

engineerosion analysis

is to

establish

a first-order relationship between th e mass-based

filtration efficiency of a filter and the associated increase in

engine

life.

Sincea whole spectrum ofparticle

sizes

isingested

d uring

n o r m a l

flight

condit ions,

th e

re la tionship

mu st in clu de

th e effects of a

dust

size distr ibution. To

enable realistic

an d

repeatable simulations to be obtained in the experimental

w o r k ,

graded test

dusts

(MIL-E-5007E a n d S A E coarse) were

used

to

r e p r e s e n t a m b i e n t

dusts. The particle-size

distribu-

tions of the u n fi l tered S A E coarse dust and of the filtered

dust t h a t entered the engine in the tests

carried

out are given

in

F i g .

1.

The

size distributions given

in Fig. 1 are expressed as

mass

fractions

fo r

small

particle size bands. T o a d e q u a t e l y predict

th e

erosion

of an engine, it was fou n d t h a t it is

necessary

to

divide th e

particle

size distribution into 20-25

size

bands,

s u m m i n g th e erosive effects of each band. T he masses fo r

each particle size

band

can be rewritten in

terms

of

mass

fractions,

wh ich

ar e

directly

obtained

from

Fig.

1.

The re-

duction in engine

p o w e r

given by the sum of the

effects

of

each size band is given by

A W-kVM

= kVM

(6 )

Su b st i tu t ion of th e mass-based filtration efficiency [Eq. (2)]

of th e

par ticular filtration system

being

used

into Eq. (6)

results in acorrelation

between

enginepow er loss, mass-based

fil tration efficiency,

total dust mass

fed to the system, and

thro ugh-flo w

particle

size dis tr ib u t ion ,

giving

a

re la tionship

between

engine

erosion and overall filtration system perfor-

m a n c e ,

wh ich may be

expressed

as

A W=kV(l - t / J M

fc d

f W 4 >

7)

A n erosion reduction factor for the

filtration

system can be

expressed in terms of Eq. (7)

u sin g, e.g. ,

S A E

coarse dust

as

a reference:

*7erosion

p f r m a x S A E

'^min

S A E

SA

\

f*

1

1?mass)

^ mn

1

7mass)0eff

8)

This re la t ionship provides a direct measure of engine

life

extension

for a specific filtration

system

relative to an

engine

ingesting

unfiltered

S A E coarse test

dust .

A

value

of

i7

erosion

of ,

e.g. , 10, would m e a n that the engine

life

is extended by

a

factor

of 10

relative

to an engine

w h e r e

no

filtration

system

isfitted

a n d S A E

coarse

testdust isingested. Sincet he erosion

is ap p rox imately proport ional to the ingested

dust mass

fo r

cases of limited

erosion

(typically 10% or less

power

loss),

th e

erosion

rate of the engine is obtained by dividing Eq. (7)

by th e

dust mass

fed:

W~

e(J

(9 )

W h e n a

comparison

is drawn

between

tw o different fi l tra-

tion

systems

using the same

test d u s t ,

th e

rate

of

p o w e r

de -

ter ioration given by Eq. (9) can be

expressed

in terms of one

of th e

fi l trat ion

sy stems.

This results

in a relat ion sh ip giving

the rate of power deterioration of one system relative to the

other,

w hich

is in fact a

filtration system

i m p r o v e m e n t

in dex :

a W i

a W o

J t

T 7

2

f^tmx

ass

) '

Jmin2

10

Experimental

Test

Results on a

Turbomeca Turmo

IV B

Turboshaft Engine

Tests w e r e carried

out on a Turbomeca

Turmo

IVB

P u m a

h elicop ter en gin e ( F i g . 2) , w hich w as

installed

an d

tested

in

th e en gin eerosion test facility sh own in Fig. 3.

2

In the first

test,

th e

filtered engine intake

w as

removed

a n d S A E

coarse

test

dust

was fed directly into the engine. The engine

p o w e r

w as

m o n i t o r e d regularly

as a function of the mass of dust

fed .

T h e test w as repeated on the

same en gin e w ith

th e

filtered

air intake in

place.

T he

results obtained from these tests

are

presented

in

Fig.

4 .

F or

both

th e u n fi l tered an d filtered dusts

ingested

into th e

engine, the dust concentrations (1.1 g/m

3

and 0.055 g/m

3

,

respectively)

were

significantly

lower

t h a n

th e concentra tion

of 49

g/ m

3

p r o v e nearlier

3

to

h a v e negligible p ar tic le-on-par-

ticle in teract ion s. Th e filtered airi n t a k ew as fitted withvortex

tubes

and had atested mass-based

filtration efficiency

of

9 5 % .

Due to the extremely high

cost

ofengineoverh aul, the filtered

air intake

was not

tested with o t h e r

vortex

tube

types or dust

grades.

O n e of th e s trik in g observations th at can b e made

from

F i g .

4 is the w el l -kno w n ini t ia l p o w e r

increase

due to

dust

polishing th e

blade su rface. D u r i n g this

in cu b ation

phase,

typically

5% of the engine

life,

2

the

erosionrate

is a

function

of

th e

ingested

dust

mass

an d

will

be referred to as the un-

steady phase. Variat ions in the length of the unsteady phase

will m ainly be due to var ia tions in the

filtration

efficiency.

D u r i n g the steadyphase, engine power reduction ispropor-

tional to the

mass

of dust fed and,

h e n c e ,

th e slope of this

p ort ion

of the curve represents th e rate of

en gin e p o w e r

d e-


3/6

114

VAN

DER WALT AND

NURICK:

DUST-FILTERED HELICOPTER

ENGINES

PARTII

Fig. 2 Turbomeca

Turmo

IV B

turboshaft

engine layout.

DYNAMOMETER

Initial Engine Power

[ ] Pressure Ratio

P2/P1

102 , I6.32

DUST FEEDER

Fig. 3 Engine

erosion

test

facility

showing

dust

feeder system sus-

pended from a load

cell, filtered

engine

intake,

Turmo

IVB

engine

and dynamometer.

Initial

Engine Power [ ] Pressure Ratio

P2/P1

102 i ; I5.32

98

96

94

92

Initial

Power

Initial Power

PressureRatio P2/P1

Unsteady

Phase

FILTRATION

ON

Steady Phase

5.3

5.28

5.26

5.24

5.22

5.2

0 20 40 60 80 100 120

Dust Mass Fed [kg]

TURMOIVBENGINE AirDenaity 1.0kg/m

3

Fig.

4 Engine power and

pressure ratio deterioration

rates as

func-

tions of SAE

coarse

dustmassfed fortestswithand without afiltration

system

(95 efficient

by mass) on a Turmo IV B

engine.

teriorat ion

a n d ,

t h u s , erosion.

I t i s thus

con clu ded t h a t suf-

ficiently

accurate

valu es

of the erosion rates for the two test

casesa re representedb y theslopesof the steady-stateportions

of

th e curves.

When the steady

phase

i s

r e a c h e d ,

a near-linear relationship

between engine p o w e r

and

ingested dust mass exists. D u r i n g

this

linearphaseit is assum ed,based on the experimental

data

avai lab le,

2

that the engine p o w e r , for a

given

particle

size

distribution, is a

function

of only the mass of

ingested

d u s t .

This enables

th e

analysis

of

filtration p e r f o r m a n c e

to be

car-

ried out

i n d e p e n d e n t l y

of

other

factors . Th e deter ioration of

th e

e n g i n e

compressor pressure ra tio P

2

/P

l

as a function of

dust

mass

fe d (fil tration

systemactive)

is

sh own

in

Fig.

4 for

the steady

region.

L i n e a r regressions on th e s teady p ort ion s of th e twopower

deter ioration curves (i.e., ign orin g the initial

point

in each

case) as well as thepressure ra tio deteriorat ion cu rve in F i g .

4 as

f u n ct i on s

of the du st mass fed are

s h o w n

in F i g. 5 . Within

th e

first 5-10%

power loss,

w hich

is the

area

of

interest,

a

l inear relat ion sh ipseems to

exist

for all t h r e e relat ion sh ip s .

F o r t h e test

case

wi t h

n o

fi l trat ion

system

f i t t ed,

a least-

sq u ares

correlat ion coefficient

of 0.9678 w as

obtained,

an d

fo r

th e

t e s t w h e r e

the 95%

efficient fi l trat ion system

w as

fi t ted,

a

correlat ion

coefficient o f

0.9893 resu l ted

for the en-

10 0

98

96

94

92

D

Initial

Power

X initial Power

Pressure Ratio

P2/P1

\FILTRATIONON

FILTRATION

ON

SLOPE

-0.03505)

0 20

TURMO IVB

ENGINE

40 60

Dust Mass Fed

[kg]

6.3

6.28

6.26

6.24

6.22

6.2

80 100

Ai r

Density

1.0kg/m

3

Fig.

5

Steady-state

engine power and

pressure

ratio deterioration

ratesas functions of dust

mass

fed fortests

with

and without a

filtration

system

(95%

efficient by

mass)

on a

Turmo

IV B

engine.

ginepower

deterioration

and a correlation

coefficient

of

0.9920

fo r

th e pressure

ratio

deter ioration.

These

linear

re la tionships

were

n o t p r o v e n fo r

en gin es

wi t h

excessiveerosion d a m a g e

(10% or m o r e

p o w e r

d e t e r i o r a t i o n ) , a n d a r e

u n l i k el y

to exist.

I t

appears

from

Fig. 5 th at a n ear-l in ear relat ion sh ip ex is ts

b etween th e p ressu rera tio deter iorationan d th e in gested du st

mass.T h isresultsupportsthe observation m a d eduring earlier

tests on electrical scavenge blowers

3

that blower performance

and blower erosion ar e directly related. A lso, th e correlation

given by Eq. (3) can be

readily

applied to

provide

measures

of

p ower deteriorat ion for th e Turmo I V B engine as

given

by Eqs. ( 4) an d

(5) .

T he data in

F i g .

5

give

th e

steady-state

rate of loss of engine p o w e r

with

dust mass fed to the engine

fo r th e

case

of no

dust

filtration as

well

as wh en filtration w as

used.

T he

influence

of particle size

d is trib u tion s

on engine power

deteriorat ion

can b e isolated b y

p lot t in g

th e

deter iorations

as

f u n ct i on s

of the ingested dust mass as shown in Fig. 6 rather

than dust mass fed as given by

Fig.

5.

T h e r e f o r e ,

th e

erosion

rates represented

by the

slopes

of the

curves

in

Fig.

6 is the

result of the di f f er en t du st d is t r ibut io ns used and

sh ou ld

b e

correlated to the

respective

effective

particle sizes <

ef f

[Eqs.

(5 )

an d

(6)].

T he

erosion rates represented

by the

slopes

of

th e

curv es

in F i g . 5,

h o w e v e r ,

includes the

variat ion s

in the

respective mass-based filtration efficiencies

of the

systems used,

and hav ebeen includ ed in the fi l trat ion

sy stem p erforman ce

correlat ion s givenbyEqs. (7-10).

Sincethe

enginepower loss, ingested

dust

particle size

dis-

t r ibut io ns , and ingested

dust

mass is

k n o w n

fo r

both cases,

the constant k can be calculated. T h i s

constant

is d e p e n d e n t

on the en gin e

characteristics

as

well

as

some dust

properties

th at

are all

assumed

to be

constant

for a

specific engine

an d

dust

t y p e . In this analysisprocedure, which is

d e m o n s t r a t ed

in

T a b l e

1, the

percentage

mass

fractions fo r

each particle-

size band

obtained

from

Fig.

1

(columns

2 and 5 in

T a b le

1)

is m ult ipl ied

by the total

mass

of

ingested

dust to

d e t e r m i n e

the massof particles in

each

band ( colu mn s3 and 6 inTable

1) . Th e p art icle mass an d s ize p er b an d are

t h e n

m ult ipl ied

( c o l u m n s

4 and 7). S u m m a t i o n of the M , , t e r m s in Eq. (5)


4/6

VAN

DER

WALT

AN D

NURICK:

DUST-FILTERED

HELICOPTER

ENGINESPARTII

Table

1 Derivation

procedure

of the

proposedeffective particle

s izeEq. (5)

A v e r a g e

particle

size in

S A E

coarse reference

D on a l ds on

through-flow

mass fed M = 0.8 kg

Effi ci ency r/

m a ss

= 0 %

Mass ingested

= 0.8 kg

Total mass fed M = 9 1 . 6 k g

Effi ci ency

r/

m a s s

= 95.0%

.- .

Mass

ingested = 4.58 kg

b a n d ,

//-m

(0,)

0.32

0.72

0.90

1.15

1.45

1.80

2.30

2.90

3.60

4.55

5.75

7.20

9.00

11.50

14.50

18.00

22.75

28.75

36.25

45.25

57.00

72.50

91.50

116.00

155.00

2:

A W :

kV

a

:

^ o f t -

Percent in

b a n d ,

/,()

x 100

12.1

14.7

11.0

10.0

10.2

7.1

4 .4

4.2

3.1

3.3

3.8

1.6

1.9

1.9

1.8

1.5

1.5

1.3

1.3

0. 9

0. 6

0.3

0. 1

0.01

100.0

( P ercen t init ia l

( A W / 2 AW,-)

(2 AW,-/2

M,.)

Mass per

b a n d ,

M,

0.5548

0.6742

0.5060

0.4622

0.4716

0.3262

0.2041

0.1964

0.1431

0.1531

0.1747

0.0776

0.0898

0.0887

0.0854

0.0732

0.0721

0.0621

0.0632

0.0443

0.0316

0.0177

0.0061

0.0004

4.5800

p owe r

loss)

A W

0.1775

0.4854

0.4554

0.5315

0.6838

0.5872

0.4696

0.5696

0.5153

0.6968

1.0050

0.5593

0.8090

1.0209

1.2390

.3183

.6410

.7866

.2930

.0086

.8027

.2873

0.5584

0.0579

22.560

-3.271

-0.145

4.926

is obtained by the summation of columns 4 and 7. Since the

en gin e

p o w e r

deteriorat ion is known, Eq. (5) can be

applied

to

d e t e r m i n e

th e

factor kV

a

. < / >

e f f

ca n then be

calculated

as

th e total M is also k n o w n .

A p p l i c a t i o n of Eq. (6) ra ther t h a n Eq. (5) results in a sim-

plif ied

analys is ,

since

th e

f u n ct i on

representing

th e

mass

frac-

tion

of the particle-size distribution can be

integrated direct ly ,

an d

therefore, no calculation of actualmassesforeach particle

size band is n e e d e d . I n

fact,

if the

function

representing

th e

particle size distribution

is known, no

calculation using

dis-

crete particle size

b a n d s is

n e e d e d ,

as the

function

is

merely

integrated.T h i s

simplified analysis

procedurei sdemonstrated

in T a b l e 2 . T h e particle size distributions represented by Fig.

1 are

tabled

in the

first ,

second, an d

fou rth

columns

in

Table

2.

It should be noted that in this

case,

th e

s u m m a t i o n

of the

ra,$,

terms directly results in <

e f f

.

Since the through-flow effective

particle

size for the D o n -

aldson

vortex

tubes , as

well

as its

mass-based filtration

effi-

ciency

is known, the

erosion

reduct ion

factor i7

erosion

can be

calculated

by m e a n s of Eq.

(8).

U sing

u n fi l tered

S A E

coarse

test dust as the reference, the erosion reduction factor is

given

by

E r o s i o n =

[38.74/(l

- 0.95)4.93] = 157

U

Physically, this result

provides

a direct

measure

of theero-

sion reduction

( a n d , t h u s , life

i m p r o v e m e n t ) b r o u g h t

a b o u t

by

the vortex

t u b e

filtration

system. The engine would

take

157 times as long to

reach

the same level of

deterioration

as

an unfiltered

engine

at the same

operating conditions

an d

ingesting

the same

q u an ti ty

o f S A E

coarse dust . A vailable

data in dicates

t h a t

an

i m p r o v e m e n t

in en gin e life of thisorder

in d us ty e n v i r o n m e n t s

is

feas ible .

A l t h o u g hAPME

4

o nly

claimed

en gin e life

i m p r o v e m e n t s

of b e t w e e n

10-26 times, it is i m p o r t a n t to

bear

in min d t h a t

engine

erosionwill

vary with du st

t y p e ,

composition,filtration

efficiency, as

well

as the particle

size distribution

of the

th rou gh -

flow stream ( the du st

p assin g th rou gh

th e

filters

into th e en -

g i n e ) .

F u r t h e rm o r e ,

fi l trat ion efficiencies

o ffilter sy stemsm ay

vary with du st

concentra tions fo r e x t r e m ecases.

Discussions

on

Proposed Helicopter Engine

Erosion Correlations

T he filtration systemtestresults andassessment conclusions

ar e given in T a b l e 3.

Comparisons

Between

th e Effective and Mass Mean Particle

Sizes

T he first important observat ion

fromTable

3 is the signif-

icant

difference

between

the calculated

$

eff

and the

mass mean

particle sizes

< / >

m a s s

m e a n

.

It is

also

significant

that

th e effective

particle sizes for the thro ugh-flo w

streams

are ap p rox imately

4

t imes

larger than themass mea n particle sizes, whe reasthose

fo r

u n f i l t er ed

S A E coarse are q u i te

similar.

This observation

can be explained in

t e r m s

of the di f f er en t size distributions

as

in dicated

inFig.

1.Since

the larger

portion

o f S A E coarse

dust is centered around the larger particle sizes(30-50^m),

the mass

m e a n

an d effective

particle

sizes are not all that

different.

However,

since the largest

portion

of the

Donaldson through-

flow

s t ream is centered aroun d the

smaller

particle sizes

(0.2-

1 / L t m ) , the small fraction largerparticles

significantly

influ-

ences

the calculated effective

particle size,

wh ich is not the

case for the calculation of the

mass

mean particle size.

This

demonstratest he relevance of the

effective

particle sizein the

analysis.


5/6

116

VAN DER WALT ANDNURICK: DUST-FILTERED HELICOPTER ENGINESPARTII

Table 2 Improved derivation

procedure

of theproposed effective particle

s izeEq.

(6 )

S A E c o a r s e

referen ce

D on a l ds on

through-flow

Average

T o t a l mass

fe d

M

=

Efficiency T /

mass

=

.

.- .

Mass ingested

=

nartrrle

6

size

in b an d , F ract i on in

( J i m

M

0.32

0.72

0.90

1.15

1.45

1.80

2.30

2.90

3.60

4.55

5.75

7.20

9.00

11.50

14.50

18.00

22.75

28.75

36.25

45.25

57.00

72.50

91.50

116.00

155.00

y .

f a f f -

W:

W .

b a n d ,

m,=/,(*)

0.005

0.007

0.006

0.007

0.010

0.010

0.010

0.015

0.015

0.020

0.035

0.035

0.045

0.050

0.055

0.055

0.065

0.070

0.095

0.100

0.095

0.080

0.055

0.045

0.015

1.0

(S 771,4,.)

(% I n i t i a l p owe r )

[ ( & W / M ) /f a f f]

T ab l e3 S u m m a r yof filtration test results and proposed erosion

related filtration

performance

F i l t r a t i o n p e r f o r m a n c e

p a r a m e t e r

1. Mass-based f i l t r a t i o n

effic iency

T /

m

.

lss

,

E q . ( 2 )

2. Mass mean

particle

size < / >

m a s s

m c a n

3. Effect i v e

particle

size

f a f

f

,

T a b l e s

1 and 2

4. E x p er i men t al erosion

r a t e

dW/dM ,

Eq. (6)

(slopes

in

Fig. 6

based

on dust mass

i n g e s t e d )

5.

C al cu l at ed ero si o n

rate

dW/dM, E q . ( 6 )

(based

on dust mass ingested)

6. E x p e r i m e n t a l erosion

r a t e dW/dM , Eq. (9)

slopes

in Fig.

5

based on

dust

mass

fed)

7.

Calculated erosion rate

dW/dM ,

Eq. (9)

(based

on

dust mass fed)

8 .

E ro si o n

reduction factor

T /

c ro sio n

,

Eq. (8)

9 . R e l a t i v e erosion rat e

dWi/BW

2

, Eq. (10)

\Eq. (5)

C

and

assessmentmethodology

D o n a l d s o n Unfi l tered

through-flow

S A E

coarse

95

0

1.21

30

4.93

38.737

-0.733 -5.367

-0.714

-5.423

-0.0351 -5.367

-0.0357

-5.423

157 1

1 157

-0.145 -0.140

-0.590

-0.181

0.8 kg

T o t a l mass

fe d

M = 91.6

kg

0 %

Effi ci ency

r/

m a s s

=

95.0%

0.8 kg .- . Mass ingested =

4.58

kg

Fract ion in

b a n d ,

m, ,.

m f

=

/

2

((/>)

771,4,.

0.0016

0.1211

0.0387

0.0050 0.1472 0.1060

0.0054

0.1104 0.0994

0.0080

0.1009 0.1160

0.0145

0.1029

0.1493

0.0180 0.0712 0.1282

0.0230

0.0445 0.1025

0.0435

0.0428 0.1243

0.0540 0.0312

0.1125

0.0910 0.0334

0.1521

0.2012 0.0381 0.2194

0.2520 0.0169

0.1221

0.4050 0.0196

0.1766

0.5750 0.0193 0.2229

0.7975 0.0186

0.2705

0.9900 0.0159

0.2878

1.4787 0.0157

0.3583

2.0125

0.0135

0.3901

3.4437 0.0138 0.5006

4.5250 0.0096 0.4385

5.4150 0.0069 0.3936

5.8000 0.0038 0.2810

5.0325 0.0013

0.1219

5.2200

0.0001

0.0126

o 3050

38.737

1.0

4.9258

38.737

(2 m,4,.) 4.9258

-4.328 (% I n i t i a l p o w e r )

-3.271

-0.140 [ ( b W / M ) /f a f f ] -0.145

I n i t i a l

Engine Power [ ] Pressure Ratio

P2/P1

102r

-

i

5.32

^ ^v. D

%

I n i t i a l Power

100\

^

X

*

n i t ia lPower 5

'

3

^^

+

Pressure

R a t i o

P2/P1

H

-5.28

98

NO

F I L T R A T I O N^\

\(SLOPE=-5.367) >\ - 5 26

2 S -

^v x \ ^\FILTRATIONON

96 ^^ ~-__

x

^

^^ -* ^ -5.24

F I L T R A T I O NON~^^_ ~

94

( S L O P E =

-0.733)

- -5.22

92

5.2

0 1 2 3 4 5

D u s t Mass Ingested [kg]

T U R M O

IV BE N G I N E A ir

D e n s i t y

- 1 .0

kg/m

3

Fig. 6 Steady-state

engine power

and pressure ratio deterioration

rates as

functions

ofdust

mass

ingested for

tests

with an d w i t h o u t a

filtration

system

(95%

efficient

by mass) on a

Turmo

IV B

engine.

Experimental Investigations on a

Turbomeca Turmo

I V B

T u r b o s h a f t

Engine

T h e

ex p erimen tal lyd e t e r m i n e d erosion rates,wh ich

are the

slopesof the

en gin e

power deterioration

curves

i n

Fig.

6

[refer

to Eq. (6)],

shows

the isolated effect of particle size on the

engine

erosion

for the different

particle

size

distr ibutions

in -

gested. T h e s e

gradients can now be used to

verify

the engine

erosion correlations

established in the

previous

sections.

Since engine

p o w e r

deteriorated linearly

(during,the steady

phase) with ingested mass

of

du st

fo r

both

tests, th e obser-

vation

m a d e

earl ier

t h a t

over th e

range

of testscarried

out,

en g i n e

erosion

is

p r o p o r t i o n a l

to th e in gested mass of du st ,


6/6

VAN DER WALT ANDNURICK: DUST-FILTERED HELICOPTER ENGINESPARTII

117

is

co nfi rm ed . T h e

e x p e r i m e n t s

on the axial scaven ge b lowers

also

con firmed

thisconclusion.

3

Th e con clu sion

d r a w n ear l ier that

th e

erosion

rate of an

engine is e q u a l to theproduct of an en gin e con stan t k, c /> an d

V

a

[Eqs. ( 3) an d(4)], together wi t h th e

definit ion

of an ef-

fective particle size[Eq.

(5)] ,

can b e evalu ated us ing th e

3rd,

4 t h ,

and 10th

r o w s

in

Table

3. The ra t io of

power

deter ioration

rate

( erosion

rate,

f ou r t h row) , an d th e effective p art icle

size

(third

row), for both th e

unfiltered

S A E

coarse

dust and the

D o n a l d s o n th rou gh -flow dust results

in the

factor

kV

a

given

in row 10, and can be seen to be fairly

constant (for

these

experiments

th e

engine

speed was kept constant) .

A l t h o u g h

some d us t properties m ay

i n f l u en ce

k, itseems from th e ex -

p e r i m e n t a l

results

t h a t

this

influence,

at least for the

test dusts

used, is m i n i m a l . It is

also

sh own th at p redictederosion rates

correlated well with th e ex p erimen tal resu l ts ( rows 4 an d 5) .

T he erosion redu ct ion factor T ?

crosion

(row 8)

includ es

t he effect

of

th e

filtration system (plotted against

the dust

mass fed) ,

an d w as d efined as the

ra tio

of the erosion rates in Eq . ( 8)

(ro w

7) and is shown to be ingood agreement with the ex-

p e r i m e n t a l results (row

6 and

Fig.

5) .

Particle

c o n c e n t r a t i o n w a s el im inated from th e erosion

analysis

3

since the concentrations ingested by helicopter en-

gines

are ex tremely low. F u r t h e r m o r e ,t h econcentra tions that

th eTurmo IVB engine ingested

with

an d with ou t filtration

systems varied su b stan t ial ly . Since the proposed erosion cor-

relations fit the e x p e r i m e n t a ldata well ,this serves as further

p roof th at

p art icle con cen trat ion s

at these lo w

levels

do n ot

influence th eerosion rate.

A l t h o u g h t h e r e l a ti o n s h i p b e t w e e nerosion in

t e r m s

o f mass

or

compressor

b lade

dimen sion

a n d p o w e r d e t e r i o r a t i o n w a s

sufficiently

estab l ish ed

fo r

small

levels of erosion ,

3

th e final

tests on th e Turmo I V B e n g i n e proved th e

validity

of th e

assumption that th e power

will

deteriorate linearly with in -

gested

du st

mass as well as pressure

ratio

in the steady-state

region(Fig. 6) .

Conclusions

I n

th e case of the gas turbine ingesting sparse dust concen-

trations where particle-on-particle interactions are negligible,

the loss inp o w e r is

given

by the sum of the losses attr ibutable

to each particle size. The total p o w e r loss is proport ional to

th e weighted average

particle

size, referred to as the

effective

particle

size.

T he increase in

life

of a gas turbine ingesting filtered dust

m ay

be

u n iq u ely expressed

in

terms

of the effective

particle

sizes

of the

unfi l tered

and filtered dust s t reams and the

effi-

ciency

of the dust

fi l ter.

T he

redu ction

of

p o w e r

of a gas

t u r b i n e

en gin e du e to du st

erosion is

p r o p o r t i o n a l

to the mass of

du st ingested

by the

ga s

t u r b i n e .

References

' D u f f y ,

R. J. , et al. , I n t e g r a l E n g i n e Particle Se p a r a t or . V ol u m e

I I Design G u i d e ,

General Electr ic

Co.,

A ug. 1975.

2

V an

de r

W al t ,

J. P.,

Parameters Governing

Fi l tered

Helicopter

I n t a k e P erfo rman ce, P h . D .

D i s s e r t a t i on ,

U n i v . of the Witwaters-

r a n d ,

J o h a n n e s b u r g ,

S o u t h A f r i c a , 1991.

3

V an de r W a l t , J. P., and

N u r i c k ,A.,

E r o s i o n of Dust Fi l tered

H e l i c o p t e r T u r b i n e E n g i n e s P ar t I: Basic T h eo ret i cal C o n si d era-

tions, Journal of Aircraft, Vol.

32, No. 1,1995, pp . 106-111.

4

The C e n t r i s e p Ai r C l e a n e r S ys t em , A i r c r a f t Porous M ed i a

E u r o p e ,

Ltd. , a

division

of PallCorp., B r o c h u r e 5 0 5 COD/LM/11/

91 ,

P o r t s m o u t h , E n g l a n d ,

U K , 1991,

PracticalIntake

Aerodynamic

Design

E .L.

Goldsmith

and }.Seddon,editors

Thisbook provides,for the

f irst

time,thedis-

tilled

experience

ofauthors who have been

closely involved in design of air intakes for

botha i r f r a m eandengine

manufacturers.

Much

valuable

data f r o m systematic experimental

measurementson intakes formissiles,combat

and

V/STOL

aircraf t f rom

research

sourcesin

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erosion of dust-filtered helicopter turbine engines

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