The Egyptian International Journal of

Engineering Sciences and Technology

Vol. 18 No. 4 (2015) 218–228

http://www.eijest.zu.edu.eg

EFFECTS OF VARYING TIP CLEARANCE AND AXIAL

GAP ON AXIAL-FLOW TURBINE STAGE PERFORMANCE
( PRESENT STATE OF THE ART)
Wael M. Elwan, Mohamed R. Shaalan,
Mofreh M. Nassief, Mohamed H. Gobran
Mech. Power Engineering Department, Zagazig University., Egypt
ARTICLE I NFO ABSTRACT
Article history: The leakage flow near the tip of rotor and stator blade rows of an axial-flow turbine
Received 00 March 2014
Received in revised form: stage imposes significant thermal loads on such blades. It is also responsible for the
Accepted 00 June 2014 aerodynamic losses therein. This leakage flow is induced mainly by the pressure
Available online:
difference across the tip section for both the rotor and the stator. Most research has
hitherto focused on the effect of varying the tip clearance ratio, but a rather little
Keywords:
Leakage flow,
amount of published work on axial gap effect is found. This paper presents the
Rotor Tip, outcome of scanning the available research on tip clearance and axial gap
axial gap, parameters and effects of their variation on the flow characteristics and
Losses.
performance of a typical axial–flow turbine stage. The prime objective here is to
throw some light upon the state of the art in this area of research. The surveyed
literature is discussed and criticized, giving suggestions for further investigation of
the problem.

1-INTRODUCTION

stage is referred to as “ axial gap“(see Fig.(2)). In the

Gas turbine engines are widely used in power following section of this paper available published
plants marine power and aircraft propulsion. Hence, work in this area is reviewed . The results of the
attempts to improve the performance of such engines reviewed work is next discussed and evaluated in
are encouraged through investigation of the effects of terms of the sufficiency of the information obtained
various parameters on their flow characteristics, for the understanding of the problem.
hence on the performance. Two important parameters
here are the tip clearance and axial gap ratios. A
typical axial-flow turbine stage is given in Fig. (1), 2- LITERATURE SURVEY
showing the tip leakage flow occurring between the 2.1 Active and Passive Control
rotor blade tip and the shroud. A similar situation
Hass et al10. (1984) studied experimentally as well
occurs between the stator tip and the rotor hub. The
as numerically the effect of stator end wall contouring on
gap between the casing, in the case of the rotor blade
(or between the hub , in the case of stator blade ) and turbine stage performance. In his investigation three stator
the blade end section is referred to as “ tip clearance end wall configurations were evaluated with the same
gap “The gap between the stator and the rotor of a rotor. One configuration was a cylindrical end wall and the

* Co Corresponding author: Tel: +201119765043 ; E-mail Address: apoelwan@yahoo.com el

 EIJEST Vol. 18 No. 4 (2015) 218–228

other two were contoured end walls , one of S-shaped

profile and the other of conical-shaped. The results showed
total efficiencies of 0.845, 0.851, and 0.853 , respectively.
Dey4 (2001) indicates that the leakage flow near the tip of
an unshrouded rotor blade in an axial turbine imposes
significant thermal load on such blade. It is also responsible
for up to a third of the aerodynamic losses occurring in a
turbine stage. This study used several concepts to reduce
the severity of losses caused by the leakage vortex. Three
desensitization techniques, both active and passive, were
examined. For example, a coolant flow from a tip trench
was used to counter the momentum of the leakage jet.
(b) Axial Gap
(N.B. : the fact that the leakage vortex is weakened
by closing the tip gap has been well established in
literature). Fig. (2) : Definition of Tip clearance
and Axial gap

Pfau16 (2003) studied the interaction flows associated

with open cavities in shrouded high pressure turbines.
The measurements focused on the rotor tip labyrinth
seal, comprising two seal gaps, 0.3% and 0.8% of
blade height. The labyrinth seal consisted of an open
inlet cavity, closed labyrinth cavities and an open exit
cavity. The size of those cavities was small in
compared to the main flow channel height (15% of
blade height). He attributed a loss generation to the
Fig. (1) : Tip Leakage Flow seen from the
labyrinth seal of around 16% of the stage loss in the
pressure side (Saxena19 2003)
case of 0.3% gap and 28% in the case of 1%
Saxena19 (2003) studied the effect of various tip
Casing sealing geometries on the blade tip leakage flow and
the associated heat transfer. Several tip sealing
Tip clearance
Blade tip techniques were investigated in this study. Crosswise
trip strips were used to reduce the leakage flow and
the associated heat transfer by placing the trip strips
Rotor
blade in different orientations. Cylindrical pin fins were
examined and compared to the trip strip geometries
Blade root as shown in Fig. (3). Full and three partial squealers
were also investigated. The partial squealers were
placed on the suction side, pressure side and mid
(a) Tip Clearance
chord of the blade tip section . Detailed heat transfer
measurements were obtained using a steady state

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 Wael M. Elwan / EFFECTS OF VARYING TIP CLEARANCE AND AXIAL GAP ON AXIAL-FLOW
TURBINE STAGE PERFORMANCE ( PRESENT STATE OF THE ART)

HSI-based liquid crystal technique. The upstream by means of a 5-hole probes as well as temperature
wake effect was simulated with a spoked wheel wake probes. The vortices caused substantial flow
generator placed upstream of the tested cascade. A blockage and turbulence near the end wall . The
turbulence grid placed even farther upstream unsteady measurements in the rotor tip clearance
generated the required free-stream turbulence of showed that one of the second-rotor blades had a
4.8%. He concluded that the squealers and the trip little bigger clearance than the others.
strips placed against the leakage flow direction Rao et al.18 (2004) studied the effect of discrete
produced the lowest heat transfer on the tips coolant jets issuing from a tip platform trench in
compared to all the other cases. Results also showed reducing the total pressure deficit caused by tip
that the full squealer had a strongest effect on the leakage flow. In their work they examined the effect
overall reduction of tip heat transfer. of the injection hole location on tip leakage flow. The
investigation was carried out in a large scale rotor test
rig. Total pressure downstream of the rotor was
measured using a Kulite sensor. The injection holes
were located at 61%, 71%, 81%, and 91% of blade
axial chord from leading edge and made in the tip
trench of one blade and with a tip clearance of 1.40%
of blade height. The results showed that injection at
61% and 71% chord reduced the leakage vortex size
and that coolant injection at 81% chord was the most
(a) Blade tip with rectangular pin fins successful in reducing the total pressure deficit in the
leakage vortex. However, the injection at 91% chord
had no effect on the leakage vortex and most of the
leakage flow that is responsible for the greatest total
pressure deficit occurs with injection at around 80%
chord. Van Ness et al.2 (2006) studied the effect of
tip clearance leakage flow on efficiency, where active
flow control using a blade-tip-mounted unsteady
(b) Blade tip with cylindrical pin fins plasma actuator was implemented in a low pressure
Fig. (3) Blade tip with different trip strips linear turbine cascade. Downstream flow velocity and
19
Saxena (2003) pressure were obtained using a five-hole probe to
detect changes in leakage vortex size and strength.
Ma et al.8 (2004) studied the flow field at both inlet Reynolds numbers of 5*104 and 1x104 for tip gaps of
and outlet of a 2-stage axial turbine with shrouded 4% and 1.56% of axial chord were
rotor. The flow field at inlet and outlet was surveyed
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 EIJEST Vol. 18 No. 4 (2015) 218–228

examined for unactuated and actuated cases. Due to squealer caused a maximum increase of 52%. These
the large flow angles observed in the leakage vortex results showed that the plasma actuator was able to
at a 4% gap size, the probe was unable to give the favorably mitigate the adverse effects of the tip
downstream pressure as the calibration region of the clearance flow in a similar manner as the squealer tip,
probe was then exceeded. With the strong three- without the drawbacks of the passive squealer
dimensionality of the flow-field in the tip region it method. QingJun et al.17 (2009) studied
was difficult to measure low velocities. The results experimentally the unsteady pressure fluctuation of
showed that for the 1.56% gap, the leakage vortex rotor tip region in high pressure stage turbine. The
size had been reduced . The 4% gap allowed for experiment was carried out on a blow-down short
actuator to be effective on the downstream flow field. duration turbine facility. Through this experimental
Also, the actuation gave 29.5% reduction in the investigation, a distinct blade-to-blade variations
maximum pressure loss at a Reynolds number of were observed. The results indicated that the
5 4
1x10 , while at a Reynolds number of 5 * 10 , a combined effects of vane wake , tip leakage flow,
14.7% reduction was obtained. complicated wave systems and rotor wake had
3
Van Ness et al. (2009) examined the use of passive induced the remarkable blade-to- blade variations.
and active on-blade flow control to reduce the losses The results showed also that the unsteady effect is
associated with blade tip clearance flow in a intensified along the flow direction.
rectilinear turbine cascade. An SDBD plasma Lei et al.15 (2010) gave experimental and numerical
actuator and a passive partial suction-side squealer investigations of the unsteady interaction of
were tested over a Reynolds number range from secondary flow vortices in turbine end wall region as
5.3×104 to 1.03×105 at a fixed tip clearance of 2.18 well as the effect of upstream periodic wakes. The
% of axial chord. Flow field measurement were made flow field was investigated in a linear turbine cascade
with a five-hole-probe at 1 axial chord length as well as a turbine rotor. The study revealed the
downstream of the test cascade blade and within the physical mechanisms of unsteady interaction between
clearance by wall pressure taps located on the end upstream wake and secondary vortices. The influence
wall opposite the blade tip. These tests allowed the of the upstream wake on the performance of turbine
loss associated with the flow and the change in this end wall region was discussed. Also, two interaction
loss with applied flow control to be recorded. The mechanisms were proposed whereby passage vortex
plasma actuator caused an improvement in the loss would decrease. The results indicated that the
downstream flow, with a reduction in the total flow field at the exit of the turbine blade row showed
pressure loss coefficient within the tip leakage vortex a decrease in passage vortex strength and the loss due
ranging between 2% to 12%, depending on Reynolds to the upstream wake transport, the upstream wake–
number, while the passive squealer showed a change pressure side leg of the horseshoe vortex interaction
of approximately 40%. On the end wall within the and the upstream wake passage vortex interaction.
clearance, the plasma actuator generated a 19% peak The transport of upstream wake is expected to
increase in wall static pressure while the passive suppress the development of pressure side leg of the

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TURBINE STAGE PERFORMANCE ( PRESENT STATE OF THE ART)

horseshoe vortex and passage vortex as a result of the passage secondary flows, and then reduce the total
‘‘negative jet” influence of the wake. losses in turbines. Different types of axially uniform
11
Junnarkar (2010) studied experimentally the and non-uniform rotor tip clearances were used in
ingestion of main air into the aft rotor-stator, disk this investigation, which include uniform, expanding,
cavity in a model 1.5-stage (stator-rotor-stator) shrinking, and back- and front-step tip clearances.
axial air turbine. The cavity featured rotor and The results show that, for the axially uniform tip
stator rim seals with radial clearance and axial clearances, the interaction mechanism between tip
overlap and an inner labyrinth seal. First, time- leakage and passage secondary flows is different in
average static pressure distribution was measured the relatively small and large tip clearance heights.
in the main gas path upstream and downstream of With the tip clearance height gradually increasing, tip
the rotor as well as in the cavity to ensure that a passage vortex at the passage exit is first enhanced,
nominally steady run condition had been achieved. and then it becomes weak. Tip static pressure
Main gas ingestion was determined by measuring the coefficient distribution in axially non- uniform tip
concentration distribution of tracer gas (CO2) in the clearance changes the chordwise distribution of over
cavity. Static-pressure readings were taken at: (i) tip leakage mass flow is shown in Fig.( 5).
seven radial locations on the stator surface, (ii) Binghui, et al.1 (2012) Improved blade tip clearance
three axial positions on the outer shroud management in high pressure turbine can provide
downstream of the rotor blades and (iii) on the outer dramatic improvements in specific fuel consumption
shroud 3 mm downstream of first stage blades. The (SFC), time on wing, engine efficiency, increased
results showed that the pressure on the stator surface payload and mission range capabilities. Also, studied
had dropped by a significant amount across the the active tip clearance control, and then a controller
labyrinth seal and then increased radially outward in based on fuzzy algorithm was designed; An
the rim cavity. The overall effect of the isolated innovative piezoelectric actuator was provided, and
injection cases is more readily seen in Fig (4), which then the actuating system be modeled as a second-
shows the radial distribution of the passage average order mass-spring-damper system for verified the
total pressure coefficient for the passage bounded by performance of the controller. This simulation result
the suction side of the test blade. Injection from H1 shows: fuzzy self-setting controller can track the tip
and H2 shows a consistent increase in the total clearance changes accurately.
pressure drop coefficient above 90% span. 2.2 Tip Leakage Losses
6
Gao, et al. (2011) studied the effect of axially non- Lakshminarayana et al.14 (1998) Studied the
uniform tip clearance on the aerodynamic experimental and computational effects of the nozzle
performance of an unshrouded axial turbine at design wake-rotor interaction and effects of the unsteady
and off-design conditions, in an attempt to seek an flow in turbine rotors. This paper is organized in two
optimal tip clearance chordwise distribution to parts. Part1 deals with the experimental and
control the interaction between tip leakage and
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 Fig. (4) Combined Effect of ingestion on test blade Cpt,p (Junnarkar 13)

compared with the predictions from the Navier-

Stokes code. The second part deals with the
integrated interpretation of the unsteady velocity and
pressure field as well as the flow physics associated
with the nozzle wake transport and decay. The results
show that, the high negative incidence angle at off-
design Condition leads to a significant increase in the
unsteady pressurewithin15%ofthe chord down -
stream of the leading edge on the pressure surface. At
Fig. (5) Grid independency study of blade
the suction surface the peak of the unsteady pressure
loading distribution near the tip
decays more rapidly in comparison to the design
( Jie Gao6)
condition. The experimental data shows large
numerical program and interpretation of the blade
fluctuation of the Pressure near the leading edge of
pressure field. The experiment was carried out in a
the hub surface. It decays rapidly down- stream due
low speed turbine at 22.6% of the nozzle chord
to the interaction with the corner and end wall flow.
spacing between the rotor and the nozzle. A
He9 (2000) studied three-dimensional full Navier–
systematic study has been carried out to evaluate the
Stokes method of unsteady flows through multiple
effect of the turbulence model and artificial
blade rows in axial-flow turbo-machinery. The solver
dissipation on the accuracy of the numerical
adopts the cell-centred finite volume discretization
prediction. The steady flow field, unsteady pressure
and the four-stage Runge–Kutta time-marching
at design and off-design conditions on both blade
scheme. Unsteady calculations are effectively
surfaces and the hub are presented, interpreted and
accelerated by using a time-consistent multi-grid

* Co Corresponding author: Tel: +201119765043 ; E-mail Address: apoelwan@yahoo.com el

 Wael M. Elwan / EFFECTS OF VARYING TIP CLEARANCE AND AXIAL GAP ON AXIAL-FLOW
TURBINE STAGE PERFORMANCE ( PRESENT STATE OF THE ART)

technique, resulting in a speed-up by a factor of 10–

20 with adequate temporal accuracy. The
computational efficiency and validity of the present
multi-grid technique are illustrated by comparisons
with the results of the conventional dual time-
stepping scheme. The results show that the
computational study of turbine stage performances at
different stator–rotor axial gaps reveals a marked
three-dimensional behavior of the interaction
between incoming wakes and rotor passage-vortex
structures. Also, the time-averaged losses from
unsteady calculations show a noticeable spanwise
redistribution compared with the steady results and
two dimensional and three-dimensional calculations
indicate opposite trends in stage efficiency variation
when the stator–rotor gap is reduced. Fig. (6) The schematic shape of vortices
7 (Han8 2001)
Han et al. (2001) studied numerical analysis of the
three-dimensional flow fields in an annual cascade Li et al.12 (2007) studied the percentage of tip
with tip clearance and rotation and in a linear cascade leakage flow losses of the shrouded rotor blade
is carried out. A comparison with flow visualization contribute significantly to overall losses of the
verifies the computational result. The results show turbine stage. Effects of the shrouded rotor
that the numerical analysis captures the separation on blade tip leakage flow in stator blade/shrouded rotor
the tip edge of the pressure side of the blade and the blade/stator blade on
flow direction over the tip surface. Also, rotation the aerodynamic performance of a 1. 5
weakens the leakage flow so that the size of the axial turbine stage were numerical investigated using
separation bubble decreases on the tip surface and commercial CFD software CFX-TASC flow. Three
large tip clearance increases leakage flow so that the conditions with different numbers of sealing fins in
tip vortex is larger and moves to the suction side. Fig. the rotor blade shroud were simulated. The structure
(6), is a representation of the tip vortex, leakage of the leakage flow and its influence to the next stator
vortex, and passage vortex as they occur in some of were presented. The results show that for shrouded
the sections. rotor blade the leakage flow is from upstream to
downstream of the blade when the leakage flow of
the unshrouded blade follows a circumferential way.
It is also found that the direction of the up-half span

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 EIJEST Vol. 18 No. 4 (2015) 218–228

of the flow field is affected obviously when the

leakage flow mixed with the main flow and lead to
incidence losses to the next stator. The leakage flow
which has high radial velocity tends to the mid-span
in the following stator and change the flow field
structure of the up-half passage. With more sealing
fins, the loss of the isentropic efficiency of the stator
is reduced. The influence of the leakage flow to the
performance of the turbine stage is carefully studied. (a)
20
Yadav et al. (2008) studied the effect of change
in parameters such as axial gap and tip clearance
on axial -flow gas turbine used in power
generation. Different combinations of axial gap
and tip clearance have been tested to analyze the
performance of the turbine. The results show that
the axial gap of 3.5 mm and 5% tip clearance is the
optimum set value for the maximum performance
as shown in Fig. (7). (b)
5
Da Silva et al. (2011) studied the influence of the Fig. (7) Performance curves of turbine stage
rotor tip clearance on the performance of a multistage (Yadav23)
axial flow turbine, the performance parameters such
as turbine efficiency, mass flow and pressure ratios,
for several tip clearances. The influence of the rotor
tip clearance on the performance of a multistage axial
flow turbine is evaluated by means of turbulent,
viscous, 3D flow calculations. The results from CFD
calculations show clearly the influence of the tip
clearance and its gap values on the efficiency and
pressure ratio of a low pressure multi-stage axial flow
turbine. A very high difference of 3.1% in efficiency
was found if the first and the third cases. This is a
large difference that would cause significant drop in Fig. (8) Representation of flows in the tip
the engine thermal efficiency. The flow schematic for gap of an unshrouded blade (da Silva5 2011)
the region at the tip of a turbine rotor is shown in Fig.
(8).

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TURBINE STAGE PERFORMANCE ( PRESENT STATE OF THE ART)

3. EVALUATION OF REVIEWED WORK paid much attention . Also, work on an optimum, if

It is noticed that previous investigators whose articles any , of tip clearance / axial gap combination insofar
have been reviewed here did not give attention to as stage performance is concerned is in fact absent in
what may be referred to as “Passive control” Casing published literature . Moreover, steady and unsteady
Treatment) . Also, relatively little work is noticeably cases ought to be considered.
available on the combined effect of varying tip
clearance and axial gap on stage performance. One REFERENCES
suggestion of “casing treatment” is shown in Fig.(9) , [1] Binghui, J., Zhang, X., and Hou, Y., "
where circumferential grooving is suggestively made Active Control of Turbine Tip
in the casing opposite the rotor blade tip section, Clearance by Fuzzy Parameter
instead of the regular (non-grooved) casing in normal Self-setting PID Algorithms", 8th IEEE
practice. Consideration of this arrangement is International Conference on
worthwhile . Automation Science and Engineering
August 20-24, 2012, Seoul, Korea.
Tip clearance Casing [2] Daniel K., Van Ness II, Corke, T., C.,
Blade tip and Morrisz, S., C., "Turbine Tip
Clearanc Flow Control using Plasma
Actuators", 44th Aerospace Sciences
Meeting and Exhibit, January 9-12,
Stator Rotor Stator
blade blade blade 2006, Reno, Nevada.
[3] Daniel K. Van Ness I,_ Corke, T. C.,
Shaft and Morris, S. C., " Tip Clearance
Flow Control in a Linear Turbine
Cascade using Plasma Actuation", 47th
Axial gap Blade root
AIAA Aerospace Sciences Meeting
Fig. (9) Suggested Treated Casing Including The New Horizons Forum
and Aerospace Exposition, 5 - 8
4. CONCLUSION AND NEED FOR MORE January, 2009, Orlando, Florida.
WORK
The flow field in the tip clearance, and pressure [4] Dey, D., "Aerodynamic Tip
distributions have been studied by numerous Desensitization In Axial Flow
Investigators . In the majority of studied reviewed Turbines", Phd, December, 2001 The
here, conclusions are that a means a large leakage Pennsylvania State University.
flow , hence less efficiency . The geometrical [5] Da Silva, L. M., Tomita, J. T., and
configuration of the tip clearance region has not been
226
 EIJEST Vol. 18 No. 4 (2015) 218–228

Barbosa, J. R., " A study Of The and space Administration, 1984.

Influence Of The Tip-Clearance Of An [11] Junnarkar, N., " Experimental Study
Axial Turbine On The Tip-Leakage of the Flow Field in a Model 1.5-Stage
Flow Using CFDTechniques", 21st Gas Turbine Rotor-Stator Disk Cavity",
Brazilian Congress of Mechanical master, December, 2010.
Engineering 2011, October ,24-28, [12] Li, J., Xin, Y., Qiang L., Yonghui,
2011, Natal, RN, Brazil. Natal, RN, X., Zhenping, F., "The Effect of the
Brazil. Shrouded Rotor Blade Tip Leakage
[6] Gao, J., Zheng, Q., Li, Y., and Yue, Flow on the Aerodynamic Performance
G., " Effect of axially non-uniform of a One and Half Turbine Stage",
rotor tip clearance on erodynamic International Conference on Power
performance of an unshrouded axial Engineering October, 23-27, 2007,
turbine", Journal of Power and Energy, Hangzhou, China.
November, 2011. [13] Kavurmacioglu, L., Dey, D., and
[7] Han, S., Han, B., Jin, P., and Camci, C., "Aerodynamic character Of
Goldstein, R. J., " Numerical Partial Squealer Tip Arrangements In
Prediction Of The Flow Field Near The An Axial Flow Turbine", IGTI/ASME
Tip Of A Rotating Turbine Blade", Turbo Expo, June 2002 Amsterdam
Journal of Engineering Physics and
Thermo physics, Vol. 74, No. 4, 2001
[14] Lakshminarayana, B.,
[8] Hongwei, MA., Bohn, D. E.,
Chernobrovkin, A., and Ristic, D.,
Kreitmeier, F., and Sell, M.,
“Experimental and Numerical Study Of
"Measurements of a 2-Stage Axial
Unsteady Viscous Flow Duo To Rotor-
Turbine with Shrouded Rotor Cavities"
Stator Interaction In Turbines”, 34th
J. of thermal Science, October ,Vol. 13,
AIAA/ASME/SAE/ASEE Joint
No. 4, 2004.
Propulsion Conference & Exhibit Jul
[9] He, L., "Three-dimensional unsteady
y13-15,1998/Cleveland, OH.
Navier–Stokes analysis of stator–rotor
[15] Lei, Q., Zhengping , Z., Huoxign, L. ,
interaction in axial-flow turbines",
Wei, L., "Upstream wake–secondary
Journal of Power and energy, 2000.
flow interactions in the endwall
region of high-loaded turbines",
[10] Hass. J.E, Boyle, R.J, “Analytical and Computers & Fluids, 2010,PP.
Experimental Investigation Of Statoe 1575–1584
Endwall Contouring In A Small Axial- [16] PFAU, A., "Loss Mechanisms in
Flow Turbine”, National Aeronautics Labyrinth Seals of Shrouded Axial

227
 Wael M. Elwan / EFFECTS OF VARYING TIP CLEARANCE AND AXIAL GAP ON AXIAL-FLOW
TURBINE STAGE PERFORMANCE ( PRESENT STATE OF THE ART)

Turbines", Phd, Zurich, Germany,2003.

[17] QingJun, Z., XiYang, L., HuiShe, W.,
XiaoLu, Z. and JianZhong, X., "
Experimental investigation on unsteady
pressure fluctuation of rotor tip region
in high pressure stage of a vaneless
counter-rotating turbine", Science in
China Series E: Technological Science,
2009, vol. 52,1478-1483.
[18] Rao, N., and Camci, C., "Injection
From A Tip Trench As A Turbine Tip
Desensitization Method", ASME
(2004). Department of Aerospace
Engineering Turbo machinery Heat
Transfer Laboratory The Pennsylvania
State University.
[19] Saxena, V., "Effect of Unsteady
Wake, Free Stream Turbulence, Tip
Geometry on Blade Tip Flow And Heat
Transfer", Phd, B.Tech., Indian
Institute of Technology, May, 2003.

[20] Yadav, R., Gulati, V., and Katyal, P.,

“Investigations of Gas Turbine
Characteristics by Varying Tip
Clearance and Axial Gap”,
International Journal of Engineering
Research and Applications (IJERA) ,
Vol. 1, Issue 3, pp.1058-1064., 2008.

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