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Impact of dust erosion on the reduction of axial compressor efficiency of a

turboshaft engine and on the stability of its operation

Article in MATEC Web of Conferences · October 2022

DOI: 10.1051/matecconf/202236700008

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MATEC Web of Conferences 367, 00008 (2022) https://doi.org/10.1051/matecconf/202236700008
Power System Engineering 2022

Impact of dust erosion on the reduction of axial

compressor efficiency of a turboshaft engine
and on the stability of its operation
Marián Hocko1*, Samer Al-Rabeei2
1Technical University of Kosice, Faculty of Aeronautics, Department of Aerospace Engineering,
Rampová 7, 041 21 Kosice, Slovakia
2 Technical University of Kosice, Faculty of Aeronautics, Department of Aerospace Engineering,

Rampová 7, 041 21 Kosice, Slovakia

Abstract. This paper aimed to solve the impact of operational abrasive

wear on the rotor blades of the axial compressor of the turboshaft engine
on the decrease in its total compression efficiency ηCt and its transition into
unstable work mode (surge). This process is analyzed based on the
obtained data by operating TV3-117 helicopter turboshaft engines in high
dust atmosphere conditions. Abrasive wear of the rotor blades of axial
compressors causes mechanical damage to the blades, reducing their
strength, changing their geometry, and aerodynamic properties, reducing
the life of the whole compressor and thus the entire engine. Destruction of
the compressor of a turboshaft engine may occur suddenly as a result of
unstable compressor operation caused by damaged axial compressor blades
due to their damage by the abrasive effect of dust.

1 Introduction
The first research on the dust erosion impacts was carried out in Germany already in 1930.
These studies were based on a theoretical analysis of the influence of erosion on various
materials based on elaborated models for registration of the volume of worn material,
deformation and abrasive wear, particle motion, etc. A great scientific contribution to the
creation of erosive wear models was brought by I. Finnie, J. G. Bitter, J. Neilson, A.
Gilchrist, W. Tabakoff, G. Grant, and others. In the Russian Federation, scientists from
many universities and organizations (CIAM, UGATU, SGAU, IAIA, VIVA, and others)
have made a major contribution to experimental and numerical research of the influence of
operational factors on the characteristics of aircraft turbo-compressor engine (ATCE)
(CIAM, UGATU, CGAU, MAI, VVIA, and others). [2, 3, 4].

The basic wear mechanism is a complex function of the physical properties of the damaged
material, a composition of abrasive particles, their dimensions, the angle of a collision
(interaction), and the collision velocity. This mechanism has been investigated by many
scientists and it has resulted in a definition of an experimental correlation between the

* Corresponding author: marian.hocko@tuke.sk

© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons
Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).
MATEC Web of Conferences 367, 00008 (2022) https://doi.org/10.1051/matecconf/202236700008
Power System Engineering 2022

material wear level as a function of erosion parameters. [5] J. Goodwin and others have
found that the erosion level practically directly depends on the percentage of quartz in the
dust. [6] This is due to the fact that quartz is one of the most present dust components. At
the same time, they have shown that the degree of erosion at the given interaction velocity
increases with a growing dust particle diameter. The dust particle size is one of the
important factors determining the level and nature of erosive wear. Particles with
dimensions of less than 70 micrometres are classified as dust.
The results of further research illustrate that the level of wear increases with growing
particle size. [7] In the case of high dust levels, the turboshaft turbo compressor engine
(TsTCE) shows equal wear and tear on the first stage blades and increased wear on the
peripheral parts of the last stage blades. With a moderate dust content in the air, the blade's
wear is local in nature and depends on the specificity of the flow, which causes a local
increase in particle concentration and their velocity with regard to the compressor blades.
The wear of the compressor blades results in a change in the shape of the blade's
aerodynamic profile and an increase in the blade surface roughness. Due to decreasing the
total efficiency of the compressor ηCt, the total compression rate πCt, the mass flow rate
QAir, the gas-dynamic stability of each stage of the compressor, and the compressor as a
whole of Ky decreases, resulting in unstable operation of the TsTCE and combustion
turbine (CT) compressors. [8]

2 TV3-117 turboshaft helicopter engine

To analyze the influence of the erosive wear of the rotor blades of the axial compressor of a
turboshaft engine on the unstable work of the axial compressor, one of the most widely
used turboshaft helicopter engines at present, the TV3-117, was selected. Its selection was
also influenced by the fact that the mentioned turboshaft engine was and still is massively
used in the conditions of countries with atmosphere with considerable dust content
(Afghanistan, Iraq, Iran, Syria, Egypt, Algeria and others). The advantage of this selection
is that statistical data of individual parameters are available and usable from the operation
of these turboshaft engines in the above conditions.

Fig. 1. TV3-117 turboshaft helicopter engine section. [ 6]

The TV3-117 is a turboshaft engine with an axial inlet, a twelve-stage axial compressor
with rotary vane blades and two air bleed valves, an annular combustion chamber, a two-
stage axial, cooled gas turbine compressor, a two-stage axial, free gas turbine, and an outlet

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Power System Engineering 2022

system with the outlet tube rotated at an angle of 60° to the right or left with respect to the
engine [11].
Two TV3-117 3rd series turboshaft engines are used to drive the Mi-24D and Mi-24DU
helicopters, two TV3-117V engines of the Mi-24V drive the helicopter, and two TV3-
117MT engines drive the medium transport Mi-17 helicopter [11].

Table 1. Modes of the turboshaft engine TV3-117, 3rd series.

Mode Pe ce T3t nTC nMR Operating time (min.)
kW kg.kW-1.h-1 K % % Continuously 3x for TL
Take off 1628 0,314 1248 97,6 98±1 6 ≤5%
Nominal 1427 0,342 1208 94,7 98±1 60 ≤ 40 %
1. Travel 1244 0,369 1173 93,5 100±2 Unlimited Unlimited
2. Travel 1098 0,396 1143 91,5 100±2 Unlimited Unlimited
Idle 879 ≤ 155 kg.h-1 1103 73+1 65 20 -

The TV3-117 turboshaft engine compressor is an axial, single-shaft, twelve-stage

compressor with adjustable guide vanes on the first four stages of the compressor stator.
The adjustment of the guide vanes is carried out automatically in the range from αGV = 27°
to αGV = 0°, depending on the calculated rotor speed of the turbo-compressor. To ensure the
stable operation of the compressor, two air release valves are also used downstream of the
seventh compressor stage.

Fig. 2. Compressor section of the turboshaft helicopter engine TV3-117.

To protect against the occurrence of unstable compressor operation, the compressor uses
adjustable stator vanes (variable stator vanes) of the first four stages and the inlet rectifier,
which are set to a given position according to the specified program αGV = f(nC,calc.). A
deviation from the program of 1,5 ° to the opening side results in a reduction of the Ky
compressor's steady-state operating margin of 1,5 % to 2,0 %. A deviation of 1° to the
closing side results in a reduction of 66 kW in engine power. Control of the compressor
vane rotation mechanism is provided by two hydraulic slave cylinders, which are supplied
with pressurised fuel from the NR-3A pump-regulator.
Two blow-off valves, which discharge part of the air outside the compressor depending on
the recalculated speed of the turbo-compressor rotor according to a program controlled by
the pump-controller NR-3A, also provide an increase in the supply of stable operation of
the engine compressor on the transient modes.

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Power System Engineering 2022

Fig. 3. Control program for the adjustable guide vanes of the inlet rectifier and the first four
stages of the compressor stator of the TV3-117 engine.

Table 2. Gas-dynamic parameters of the compressor of the turboshaft engine TV3-117 in

take-off mode

Compressor stage
Parameter
1 2 3 4 5 6 7 8 9 10 11 12
T2t (K) 312 340 370 398 427 456 484 511 533 564 589 613
ΔTt (K) 24 28 30 29 29 29 28 27 27 26 25 24
πCc (1) 1,289 1,314 1,298 1,271 1,246 1,228 1,205 1,192 1,175 1,159 1,146 1,28
ηCc (1) 0,889 0,899 0,904 0,907 0,902 0,904 0,904 0,904 0,901 0,896 0,823 0,857
zstator 60 60 60 60 80 84 84 86 88 90 90 114
zrotor 37 43 59 67 73 81 89 89 89 89 89 89

Where:
T2t – temperature at the outlet of the stage;
ΔTt – heating the air to v degree;
πCt – the overall degree of compression of the grade;
ηCt – overall degree efficiency;
The total efficiency of the compressor is ηCt = 0,86.

3 Effect of dust erosion on the characteristics of a turboshaft

engine axial compressor
The disturbance of the stable work of the axial compressor of a turboshaft helicopter
engine, caused by the loss of gas-dynamic stability, is one of its most dangerous failures.
For this reason, operation on modes, where the working point in the compressor
characteristic is close to the limit of unstable work, i.e. where the stock of stable work is
small, is inadmissible.

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Power System Engineering 2022

Fig. 4. Characteristics of TV3-117 turboshaft engine axial compressor.

The steady-state workload of an axial compressor can be expressed by the equation

𝜋
( 𝐶𝑡 )
𝑄𝐴𝑖𝑟
𝑆𝐿
∆𝐾𝑦 = [ 𝜋 − 1] . 100 % (1)
( 𝐶𝑡 )
𝑄𝐴𝑖𝑟
𝑊𝑃

Where:
πCt,SL – the overall degree of compression at the limit of unstable work (on surge line),
QAir,SL – air mass flow rate at the limit of unstable work (on surge line),
πCt,WP – the total degree of air compression at the working point,
QAir,WP – air mass flow rate at the working point.

Fig. 5. Dependence of the steady-state work reserve of the axial compressor of the TV3-117
turboshaft engine on the engine operation mode.

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Power System Engineering 2022

When the compressor is tested above the calculation mode, the compressor's steady-state
operating margin reaches Ky = 2 - 5 %.

Fig. 6. Characteristics of a compressor with intact rotor blades and blades damaged by dust
erosion.

Statistical analysis of the measurement results of the blades of different stages of the axial
compressor of the TV3-117 engine, which were subjected to abrasive action of dust in
operation, showed that the shortening of the blade bowstring was manifested only in the
peripheral part of the blades, at the level of the upper third of the blade (Fig. 5). The
analysis of the blade leaf wear values in the individual stages of the axial compressor
allowed to detect the regularities caused by the design peculiarities of the compressor of the
TV3-117 engine. It was confirmed that there are close correlations between the value of
blade wear of the second to the twelfth stage of the compressor, which is due to the
homogeneity of the processes that lead to blade wear. Maximum wear occurs in the first
and sixth stage blades of an axial compressor. However, the nature of the wear is different.
The rotor blades of the first stage show signs of damage mainly on the leading edge and on
the front face, which is the result of contact with the largest abrasive particles that are
fragmented in other parts of the axial compressor. The rotor blades of stages one to four had
basic wear at the leading edges and in the blade trough. Rotor blades of the fifth to twelfth
stages had wear at the inlet and outlet edges and the trailing edge of the blade. The above
wear patterns can be explained by the fact that large dispersive abrasive particles encounter
the leading edges of the rotor blades of the first stage of the axial compressor, fragment and
move with the air stream towards the next stages. As the rotor blades of the first stage
encounter relatively large particles, these blades are the most damaged. Already in the
second stage, the shortening of the bowstring due to wear is considerably less, but it is of an
increasing character up to the sixth (seventh) stage of the compressor. This effect is due to
the fact that the rotor blades of the subsequent stage have a smaller profile thickness
compared to the previous blade, but the volume of abrasive particles acting on it remains

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Power System Engineering 2022

constant. At the same time, the rotor blades of each successive stage operate at a higher
temperature (Table 2) resulting in a reduced ability of the material to resist wear.
The blades from the eighth to the twelfth stage have considerably less, approximately equal
wear when compared to the sixth and seventh stages. This is due to the air intake chamber
to the blow-off valves located after the seventh stage (Fig. 6).
When the engine is running at low speed (idle, right correction) on the ground, under dusty
conditions, some of the dust (sand) along with the air escapes through the blow-off valves
to the atmosphere. As a result, less abrasive particles reach the next stages, resulting in less
blade wear.
Change in overall adiabatic compressor efficiency ηCt,ad. as a function of the engine
operating mode is shown in Fig. 7.

Fig. 7. Change in the total adiabatic efficiency of the axial compressor of the TV3-117
turboshaft engine ηCt,ad. as a function of the engine operating mode.

The research results in the change of the TV3-117 compressor condition as a function of the
number of hours worked in dusty atmosphere conditions, which with the increase of the leaf
erosion intensity leads to a shift of the whole compressor characteristic (Fig. 8 ), as a result
of which the overall compressor compression ratio π Ct and the overall compression
efficiency ηCt decreases.

Fig. 8. Characteristics of TV3-117 turboshaft engine compressor with marked changes after
working different number of hours in dusty environment.
_____ 0 working hours, _ _ _ _ 200 working hours, _ . _ . _ . _ 400 working hours, _ .. _ ..
_ 600 working hours, - - - - - - - 800 working hours

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Power System Engineering 2022

Fig. 9. Characteristics of TV3-117 turboshaft engine compressor with marked changes total
compressor efficiencies after working different number of hours in dusty environment.
_____ 0 working hours, _ _ _ _ 200 working hours, _ . _ . _ . _ 400 working hours, _ .. _ ..
_ 600 working hours, - - - - - - - 800 working hours

It is known that a 15 % reduction in the gasodynamic stability margin of an axial

compressor induces the development of unstable compressor operation in bench tests of the
TV3-117 turboshaft engine.

Table 3. Change in the gasodynamic stability reserve of the compressor after working
different periods of operation

Earned 𝑛 𝑛 𝑛 𝑛
= 95 % = 98 % = 100 % = 103 %
time (hours) √𝑇1𝑐 √𝑇1𝑐 √𝑇1𝑐 √𝑇1𝑐
0 25,25 % 22,14 % 20,58 % 19,10 %
200 21,30 % 18,32 % 16,52 % 15,13 %
400 17,35 % 14,51 % 12,46 % 11,16 %
600 13,39 % 10,69 % 8,39 % 7,18 %
800 9,44 % 6,87 % 4,33 % 3,21 %

In addition to the influence of flow section erosion, damage, erosion, pollution, frost and
others, the characteristic of the TV3-117 engine compressor is affected by the angle of
adjustment of the engine compressor guide gear. The compressor motor alignment gear
enables better coordination of the operation of the individual stages and the achievement of
high values of the overall compression efficiency η Ct and the stock of stable work of the
axial compressor. Such research requires technical personnel to periodically check the
characteristics of the directing gear and achieve their nominal values through control.
For a helicopter turboshaft helicopter turbo-compressor engine operated in dusty
atmosphere conditions, one of the current challenges is to evaluate the effect of compressor
blade erosion on its gasodynamic characteristics. Its solution, simultaneously with the
evaluation of the influence of blade erosion on the vibro frequency characteristics, allows to
elaborate recommendations in terms of the compressor blade boundary condition.

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Power System Engineering 2022

To evaluate the influence of dust erosion on the change of the compressor's gasodynamic
characteristics, calculations of the air velocity and pressure in the flow section for the
nominal (initial) blade geometry, as well as the geometry corresponding to the operating
time of the engine in operation during 200, 400, 600 and 800 hours, were carried out. [1]
The results of calculations of the compressor characteristics (Fig. 8., 9.) π Kc, ηKc = f(Qv)
from the operating time in dusty atmosphere showed that with the increase of the blade
erosion intensity, the overall compression ratio in the compressor and its overall
compression efficiency decreases. This implies that the limit of stable operation decreases,
while at the same time the stable work margin of turboshaft engine ΔK y decreases. The
steady-state work reserve of the turboshaft engine was calculated according to the relation
(1).
The results of the calculation are shown in Table 3.
It is known that a reduction of the compressor's gasodynamic stability margin below 15 %
causes the compressor to develop unstable compressor operation (pumping) during bench
tests of turboshaft engine TV3-117.
The analysis of the obtained results shows that the investigated compressor reaches its
limit state when working in conditions of dusty atmosphere for 730 to 750 hours. The
analysis of the absolute current velocity in the peripheral region of the flow area of the
compressor with blades having different degree of wear, as well as the absolute current
velocity fields at the height of 90 % from the compressor blade root, showed that due to the
erosive wear in the peripheral region of the blades 6. Up to the 9th stage of the compressor
develops air stream tear-off, which induces the development of unstable compressor
operation. The cause of the phenomenon was the reduction of the rotor blade chord and the
increase of the radial gap above the blades.

4 Conclusion

Maximum wear of the rotor blades of the axial compressor of the TV3-117 turboshaft
engine due to dust erosion occurs at the first and sixth rotor blade stages.
From the point of view of the gas-dynamic stability of the axial compressor of the TV3-117
turboshaft engine, the erosive wear of the rotor blades of the sixth stage of the axial
compressor is limiting, which can cause the jet to break off and cause the axial compressor
to work unstably. When the bowstring in the peripheral part of the rotor blades is shortened
by 6.19 mm, the stock of stable work of the axial compressor decreases by ΔK y = 15 % to
17 %.
Determination of the limit value of permissible erosive wear of rotor blades of all stages of
the TV3-117 turboshaft engine is possible on the basis of the required level of gas-dynamic
stability.

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Power System Engineering 2022

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