Cascade Flow Research CapabilityFollowing 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 CVCV of Dr. Schobeiri

TPFL: Turbine Cascade Unsteady Boundary Layer Research

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: The Turbomachinery Performance and Flow Research LaboratoryTexas A&M University

M. T. Schobeiri

TPFL Unsteady Turbine Cascade Research Facility

(a) Wakes from turbine blades

V

WU

U

V

WU

U

U

(b) Wakes from turbine rods

Pivot point

Hydraulic cylinders

Inlet nozzle

Wake generator e-motorWake generator

Wake generating rods

Blade with hot film sensors

Static pressure blade

Adjustable height: y =130 mm

End View

1

3

2

4

Traversing system

Straight duct

Transition duct

Timing belts with rod attachments

5

7

6

8

9

11

10

12

4

12 14

11

16

Wake generator

Test section

Spa

cing

S3

Spa

cing

S4

S1

S2

1

2

8

1

16

Honeycomb flow straightener

Telescope supprthoneycom and five screensLarge silence chamber with

Traversing slots

13

15

14

16

10

Air supply unit

15

5

7

6

Simulation of periodic unsteady wakes impinging on turbine blades

INTRODUCTION: LOW-PRESSUER TURBINE AERODYNAMICS

Fig. 1: A twin-spool aircraft gas turbine with a fan-stage, HP, IP, and LP compressor and turbine stages

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 100,000LP-Turbine

Introduction: LPT-Aerodynamics

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

Fig. 3: Pressure distribution

0 0.2 0.4 0.6 0.8 1s/so

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

Cp

Steady Inlet Flow: Re=100000

Pressure surface

Suction surface

Fig. 2: LPT-blade, suction side

Suction Surface

Pressure Surface

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

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

t/

y(m

m)

1 2

1

2

3

4

5

6

7

8

9

10

V(m/s)8.297.947.587.226.876.516.155.805.445.084.724.374.013.653.302.00

=1.59,s/so=0.52(a)

t/

y(m

m)

1 2

1

2

3

4

5

6

7

8

9

10

V(m/s)7.797.467.136.806.466.135.805.475.134.804.474.143.803.473.142.00

=1.59,s/so=0.546(b)

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

t/

y(m

m)

1 2

2

4

6

8

10

12

14V(m/s)8.407.937.466.996.526.055.585.114.644.173.703.232.762.292.00

=1.59,s/so=0.674(f)

t/

y(m

m)

1 2

1

2

3

4

5

6

7

8

9

10

V(m/s)8.167.697.226.756.285.815.344.874.403.923.452.982.512.042.00

=1.59,s/so=0.651(e)

Temporal behavior of the separation zone behavior unsteady case Ω =1.59

(SR =160mm)

s/so

y(m

m)

0.5 0.6 0.7 0.8

1

2

3

4

5

6

7

8

9

10

V/U1.081.010.940.880.810.740.670.600.540.470.400.330.270.200.13

=1.59, t/=0.05

s/so

y(m

m)

0.5 0.6 0.7 0.8

1

2

3

4

5

6

7

8

9

10

V/U1.121.050.980.910.830.760.690.620.550.480.400.330.260.190.12

=1.59, t/=0.25

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.

s/so

y(m

m)

0.5 0.6 0.7 0.8

1

2

3

4

5

6

7

8

9

10

V/U1.071.000.930.860.800.730.660.600.530.460.390.330.260.190.13

=1.59, t/=0.75

s/so

y(m

m)

0.5 0.6 0.7 0.8

1

2

3

4

5

6

7

8

9

10

V/U1.010.950.890.830.770.710.650.590.530.470.410.350.290.230.17

=1.59, t/=0.50

Periodic Generation and Suppression of the Separation Bubble

Physics of Contraction, Separation and Regeneration of the Separation Zone

Su

pp

ress

ion

end

sre

gen

erat

ion

beg

ins

att/

=2

.0

Co

ntr

actio

nb

egin

sat

t/

=1

.25

Co

ntr

actio

nen

ds

att/

=1

.41

t/

y(m

m)

0.5 1 1.5 2 2.5

1

2

3

4SR=160mm, s/so=0.651

Periodic Generation and Suppression of the Separation Bubble

Contraction, Separation and Regeneration of the Separation Zone

t/

vx4

,V(m

/s)

0 1 2 31

2

3

4

5s/s0=0.651, y= 2.85mm

hig

hv

Wak

eex

tern

alre

gio

n

Vorticalcore

fluctuation

velocity

hig

hV

More Details on Generation and Suppression of the Separation Bubble

Periodic Generation and Suppression of the Separation Bubble

Details: Contraction phase starts at the point, where vrms/t > 0 start,

Regeneration phase starts at the point, where of vrms/t < 0 starts

Contraction beginat tt = 1.25

(d)(a) (b) (c)

t/

vx4

,V(m

/s)

0 1 2 31

2

3

4

5

Re-generationstarts at t/ = 2.0

suppression from 1.41 to 2.0

Contraction endat t/ = 1.41

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)s/so=0.422

s/so=0.368s/so=0.384

t/

2/( 2

) =

0

0 1 2 30.85

0.90

0.95

1.00

1.05

1.10

1.15

SR=160mm(a)

s/so=0.588

s/so=0.617s/so=0.52

t/

2/( 2

) =

0

0 1 2 30.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

SR=160mm(b)

s/so=0.705

s/so=0.849s/so=0.805

s/so=0.767

t/

2/( 2

) =

0

0 1 2 30.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

SR=160mm(c)

Boundary Layer Integral Quantities

Boundary layer momentum thickness time-averaged

s/so

H12

0.4 0.6 0.8

2

3

4

5

6

7

8

160mm80mmnorod

s/so

2

0.2 0.4 0.6 0.8

1

2

3

4

5

160mm80mmnorod

s/so

0.2 0.4 0.6 0.8

5

10

15

20

25

160mm80mmnorod

s/so

1

0.2 0.4 0.6 0.8

5

10160mm80mmnorod

Boundary Layer Integral Quantities