TPFL: Turbine Cascade Unsteady Boundary Layer Research
Cascade Flow Research Capability
Following figures present experimental results dealing with the
measurement of boundary layer development along the suction
surface of a low pressure turbine blade under periodic unsteady
wake flow conditions.
For more details, please see the publication list in CV
CV of Dr. Schobeiri
Introduction: Wake Interaction

Boundary transition in turbomachines is determined by:

Change of frame of reference that inherently causes periodic unsteady flow
consisting of wakes with high TI- vortical cores and low TI- flow region

Wake flow impinges on the surface of the following cascade and periodically
changes the portion of the laminar boundary layer to turbulent and affects the
turbine aerodynamics, efficiency, performance and heat transfer
Schematics of Rotor-Stator Interaction
TPFL Unsteady Turbine Cascade Research Facility
Simulation of periodic unsteady wakes impinging on turbine blades
U
U
Wake generator
Air supply unit
S1
V
U
8
W
S2
6
5
Spacing S3
1
2
1
Spacing S4
Test section
7
15
16
(a) Wakes from turbine blades
4
U
16
End View
V
12
10
14
U
W
11
Adjustable height: y =130 mm
(b) Wakes from turbine rods
1
Static pressure blade
5 Traversing system
9
Inlet nozzle
13
2
Blade with hot film sensors
6 Transition duct
10
Hydraulic cylinders
14
3
Wake generating rods
7 Straight duct
11
Pivot point
15
Honeycomb flow straightener
4
Wake generator
8 Timing belts with rod attachments 12
Wake generator e-motor
16
Traversing slots
TPFL: The Turbomachinery Performance and Flow Research Laboratory
Texas A&M University
M. T. Schobeiri
Large silence chamber with
honeycom and five screens
Telescope supprt
INTRODUCTION: LOW-PRESSUER TURBINE AERODYNAMICS
Low Pressure Turbine (LPT) stage of aircraft gas turbine engines operates
within the following Re-range:

Take off:
Re = 400,000
(high Re)

Cruise:
Re = 100,000
(low Re)

Routine operations
Re = 400,000 to 100,000
LP-Turbine
Fig. 1: A twin-spool aircraft gas turbine with a fan-stage, HP, IP, and LP
compressor and turbine stages
Introduction: LPT-Aerodynamics
Suction Surface
S
te
a
d
yIn
le
tF
lo
w
: R
e
=
1
0
0
0
0
0
-4
-3
.5
-3
S
u
c
tio
ns
u
rfa
c
e
-2
.5
Cp
-2
-1
.5
-1
-0
.5
Pressure Surface
0
P
re
s
s
u
res
u
rfa
c
e
0
.5
1
0
0
.2
0
.4
s
/s
o
0
.6
0
.8
Fig. 2: LPT-blade, suction side
Fig. 3: Pressure distribution
On Suction surface:
Negative pressure gradient: Acceleration, stable laminar boundary layer
Change of pressure gradient: Onset of a separation bubble, manifestation
Further change of pressure gradient: Re-attachment of separated flow
1
Parameters Affecting LPT-Aerodynamics
Flow parameters:

Re Number, Mach Number

Unsteady Wakes
- Wake Frequency
- Wake Width
- Wake Turbulence

Freestream Turbulence Intensity
Blade geometry:

Suction, pressure surface configuration (front, aft-load)

Inlet, exit angle (total flow deflection)
- Responsible for pressure distribution, location of separation bubble
RESEARCH OBJECTIVES

To investigate the impact of the periodic unsteady inlet flow conditions on the development of
the boundary layer separation.

To provide detailed steady and unsteady boundary flow information to understand the
underlying physics of the onset and the extent of the separation zone under the unsteady
wake effects.

To extend the intermittency based unsteady boundary layer transition model developed by
Schobeiri and his co-workers to the boundary layer cases with separation.

To create a bench mark data base for comparison with numerical computation using DNS or
RANS-codes.
UNSTEADY FLOW TURBINE CASCADE RESEARCH FACILITY
SIMULATION OF PERIODIC UNSTEADY WAKE FLOW CONDITION
S3= 80 mm
S2=160 mm
S1=
RESULTS AND DISCUSSIONS:Unsteady Wake Flow
Investigations
Time-averaged velocity profiles along the suction surface of the blade at Ω=0
Periodic Generation and Suppression of the Separation Bubble
Contour plot of the ensemble averaged velocity distribution showing the effect of
periodic wakes an the separation zone at different streamwise positions at Ω =1.59
=1.59,s/so=0.52
(a)
10
10
9
9
y(mm)
7
6
5
4
3
2
1
V(m/s)
7.79
7.46
7.13
6.80
6.46
6.13
5.80
5.47
5.13
4.80
4.47
4.14
3.80
3.47
3.14
2.00
8
7
y(mm)
V(m/s)
8.29
7.94
7.58
7.22
6.87
6.51
6.15
5.80
5.44
5.08
4.72
4.37
4.01
3.65
3.30
2.00
8
=1.59,s/so=0.546
(b)
6
5
4
3
2
1
1
t/
2
1
t/
2
Periodic Generation and Suppression of the Separation Bubble
Contour plot of the ensemble averaged velocity distribution showing the effect of
periodic wakes an the separation zone at different streamwise positions at Ω =1.59
=1.59,s/so=0.651
(e)
=1.59,s/so=0.674
(f)
10
14
V(m/s)
8.16
7.69
7.22
6.75
6.28
5.81
5.34
4.87
4.40
3.92
3.45
2.98
2.51
2.04
2.00
8
y(mm)
7
6
5
4
3
V(m/s)
8.40
7.93
7.46
6.99
6.52
6.05
5.58
5.11
4.64
4.17
3.70
3.23
2.76
2.29
2.00
12
10
y(mm)
9
8
6
4
2
2
1
1
t/
2
1
t/
2
Periodic Generation and Suppression of the Separation Bubble
Temporal behavior of the separation zone behavior unsteady case Ω =1.59
(SR =160mm)
=1.59, t/=0.05
=1.59, t/=0.25
10
10
9
9
y(mm)
7
6
5
4
3
7
6
5
4
3
2
2
1
1
0.5
0.6
s/so
0.7
0.8
V/Uµ
1.12
1.05
0.98
0.91
0.83
0.76
0.69
0.62
0.55
0.48
0.40
0.33
0.26
0.19
0.12
8
y(mm)
V/Uµ
1.08
1.01
0.94
0.88
0.81
0.74
0.67
0.60
0.54
0.47
0.40
0.33
0.27
0.20
0.13
8
0.5
0.6
s/so
0.7
0.8
Periodic Generation and Suppression of the Separation Bubble
Temporal behavior of the separation zone behavior unsteady case Ω =1.59
(SR =160mm). Note the development of the separation bubble.
=1.59, t/=0.50
=1.59, t/=0.75
10
10
9
9
y(mm)
7
6
5
4
3
7
6
5
4
3
2
2
1
1
0.5
0.6
s/so
0.7
0.8
V/Uµ
1.07
1.00
0.93
0.86
0.80
0.73
0.66
0.60
0.53
0.46
0.39
0.33
0.26
0.19
0.13
8
y(mm)
V/Uµ
1.01
0.95
0.89
0.83
0.77
0.71
0.65
0.59
0.53
0.47
0.41
0.35
0.29
0.23
0.17
8
0.5
0.6
s/so
0.7
0.8
Periodic Generation and Suppression of the Separation Bubble
Physics of Contraction, Separation and Regeneration of the Separation Zone
4
2
Suppression ends
regeneration begins
at t/ = 2.0
y(mm)
3
Contraction ends
at t/ = 1.41
Contraction begins
at t/ = 1.25
SR=160mm, s/so=0.651
1
0.5
1
1.5
t/
2
2.5
More Details on Generation and Suppression of the Separation Bubble
Contraction, Separation and Regeneration of the Separation Zone
velocity
3
2
1
0
high v
vx4, V(m/s)
4
high V
Wake external region
5
s/s0=0.651, y= 2.85mm
fluctuation
Vortical
core
1
t/
2
3
Periodic Generation and Suppression of the Separation Bubble
5
Contraction end
at t/ = 1.41
vx4, V(m/s)
4
Contraction begin
at tt = 1.25
Re-generation
starts at t/ = 2.0
3
(a) (b) (c) (d)
2
suppression from 1.41 to 2.0
1
0
1
t/
2
3
Details: Contraction phase starts at the point, where vrms/t > 0 start,
Regeneration phase starts at the point, where of vrms/t < 0 starts
Boundary Layer Integral Quantities
Boundary layer ensemble-averaged integral momentum deficiency thickness for
steady case Ω =0 (SR = )and unsteady cases Ω =1.59(SR =160mm) and Ω =3.18
(SR =80mm)
1.15
1.15
(a)
1.10
SR=160mm
(b)
s/so=0.588
1.05
2/(2)=0
1.05
1.00
1.00
0.95
0.95
0.90
0.90
0.85
s/so=0.368
0.85
0
1
t/
2
0.80
0
3
1
1.80
1.70 (c)
SR=160mm
1.60
1.50
1.40
s/so=0.705
s/so=0.767
1.30
1.20
1.10
1.00
0.90
0.80
0.70
0.60
0
s/so=0.617
s/so=0.52
s/so=0.384
2/(2)=0
2/(2)=0
SR=160mm
1.10
s/so=0.422
s/so=0.805
1
s/so=0.849
t/
2
3
t/
2
3
Boundary Layer Integral Quantities
Boundary layer momentum thickness time-averaged
25
160mm
80mm
norod
1

10
160mm
80mm
norod
20
15
5
10
5
0.2
0.4
s/so
0.6
0.8
0.2
s/so
0.6
0.8
8
5
7
160mm
80mm
norod
6
H12
4
2
0.4
3
160mm
80mm
norod
5
4
2
3
1
2
0.2
0.4
s/so
0.6
0.8
0.4
0.6
s/so
0.8