Study of Oscillating Blades from Stable to Stalled

Conditions

1 CFD Lab, Department of Aerospace Engineering, University of Glasgow

2 Volvo Aero Corporation

3 Rolls-Royce Plc

S. Svensdotter3, G. Barakos1 and U. Johansson2

Motivation

Turbomachinery Turbomachinery blades flutterblades flutter

During flutter During flutter blades may breakblades may break

Implications on Implications on the safe operation the safe operation of the engineof the engine

Flutter

Structural vibration involving Structural vibration involving bending and twistingbending and twisting

A result of interactions between A result of interactions between aerodynamics, stiffness and aerodynamics, stiffness and inertial forcesinertial forces

Can be experienced on all flexible Can be experienced on all flexible structuresstructures

Engine Working Line

Possible Fan or Compressor Flutter Zones

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

0.15 0.20 0.25 0.30 0.35 0.40

Total Flow/Area (non-dim)

Ro

tor

Pre

ssu

re R

atio

(u

nit

s d

epen

ds

on

cas

e)

Typical Nominal Working Line

Typical High Working Line

Low Speed Stall Flutter

Transonic Stall Flutter

Supersonic Stall Flutter

Supersonic Unstalled Flutter

Choke Flutter

Low-speed Stall Flutter

Transonic Stall Flutter

Typical nominal working line

Typical high working line

Supersonic Unstalled Flutter

Supersonic Stall Flutter

50%

60%

70%

80%

90%

100%

Corrected Speed

Choke Flutter

Objectives

Study a simple peculiar case of Study a simple peculiar case of flutterflutter

Use CFD to assess the quality of Use CFD to assess the quality of experimental dataexperimental data

Shed some light in the argument Shed some light in the argument raised about this particular flutter raised about this particular flutter casecase

Background Three key publications on the subjectThree key publications on the subject

(1) Parametric Study of the Pressure (1) Parametric Study of the Pressure Stability of an Oscillating Airfoil from Stability of an Oscillating Airfoil from Stable to Stalled Flow Conditions (S. Stable to Stalled Flow Conditions (S. Svensdotter, U. Johansson, T. Svensdotter, U. Johansson, T. Fransson)Fransson)

(2) Boundary-Layer Transition, (2) Boundary-Layer Transition, Separation and Reattachment on an Separation and Reattachment on an Oscillating Airfoil (T. Lee, G. Petrakis)Oscillating Airfoil (T. Lee, G. Petrakis)

(3) An Experiment on Unsteady Flow (3) An Experiment on Unsteady Flow Over an Oscillating Airfoil (L. He, J.D. Over an Oscillating Airfoil (L. He, J.D. Denton)Denton)

Experimental Method

EquipmentEquipmentSymmetrical 2D NACA 63A006, Symmetrical 2D NACA 63A006, chord length 80mm, span 150mmchord length 80mm, span 150mm

13 pressure transducers on the 13 pressure transducers on the suction surface of the bladesuction surface of the blade

Pitching axis at 43% chordPitching axis at 43% chord Performed in a wind tunnel with Performed in a wind tunnel with test section 150mm by 180mmtest section 150mm by 180mm

Experimental Method Test program and data interpretationTest program and data interpretation

High oscillating frequencies (up to High oscillating frequencies (up to 210Hz)210Hz)

Inlet Mach number was 0.5Inlet Mach number was 0.5Reynolds number was 850 000Reynolds number was 850 000Unsteady pressure signals were Unsteady pressure signals were analysed in terms of amplitude of analysed in terms of amplitude of perturbation and the phase difference perturbation and the phase difference between the pressure signal and between the pressure signal and blade motionblade motion

Test rig

Test equipment

Amplitude and Phase, 0° Incidence

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80

x/c [%]

alpha=0deg, f=60Hz, dalpha=0.8deg

alpha=0deg, f=60Hz, dalpha=2.7deg

alpha=0deg, f=60Hz, dalpha=4.2deg

Pitching axis

-180

-90

0

90

180

0 10 20 30 40 50 60 70 80

x/c [%]

[

deg

]

alpha=0deg, f=60Hz, dalpha=0.8deg

alpha=0deg, f=60Hz, dalpha=2.7deg

alpha=0deg, f=60Hz, dalpha=4.2deg

Exciting

Exciting

Damping

Damping

Pitching axis

-180

-90

0

90

180

0 10 20 30 40 50 60 70 80

x/c [%]

[

deg

]

alpha=0deg, f=110Hz, dalpha=0.8deg

alpha=0deg, f=210Hz, dalpha=0.8deg

Exciting

Damping

Damping

Exciting

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80

x/c [%]

alpha=0deg, f=110Hz, dalpha=0.8deg

alpha=0deg, f=210Hz, dalpha=0.8deg

Amplitude and Phase, 6° Incidence

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80

x/c [%]

alpha=6deg, f=60Hz, dalpha=0.8deg

alpha=6deg, f=60Hz, dalpha=2.7deg

alpha=6deg, f=60Hz, dalpha=4.2deg

-180

-90

0

90

180

0 10 20 30 40 50 60 70 80

x/c [%]

[

deg

]

alpha=6deg, f=60Hz, dalpha=0.8deg

alpha=6deg, f=60Hz, dalpha=2.7deg

alpha=6deg, f=60Hz, dalpha=4.2deg

Damping

DampingExciting

Exciting

-180

-90

0

90

180

0 10 20 30 40 50 60 70 80

x/c [%]

[d

eg]

alpha=6deg, f=110Hz, dalpha=0.8deg

alpha=6deg, f=110Hz, dalpha=2.7deg

alpha=6deg, f=210Hz, dalpha=0.8deg

Exciting

Exciting

Damping

Damping

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80

x/c [%]

alpha=6deg, f=110Hz, dalpha=0.8deg

alpha=6deg, f=110Hz, dalpha=2.7deg

alpha=6deg, f=210Hz, dalpha=0.8deg

Summary of measurements

Highly non-linear behaviour at and above static Highly non-linear behaviour at and above static stall anglestall angle

Below stall angleBelow stall angle Airfoil dampedAirfoil damped Increase amplitude => increased excitationIncrease amplitude => increased excitation Increase to 210Hz => blade excitedIncrease to 210Hz => blade excited

Above stall angleAbove stall angle Airfoil excitedAirfoil excited Increased amplitude => decreased excitationIncreased amplitude => decreased excitation Increase to 210Hz => blade dampedIncrease to 210Hz => blade damped

210Hz phase shift possibly due to lagging LE 210Hz phase shift possibly due to lagging LE separation vortex or migration of stagnation separation vortex or migration of stagnation pointpoint

Summary Of Findings (2) Transition & Separation, (2) Transition & Separation,

Relaminarisation & Reattachment Relaminarisation & Reattachment delayed with increasing reduced delayed with increasing reduced frequency (T. Lee, G. Petrakis).frequency (T. Lee, G. Petrakis).

(3) Increasing frequency delays (3) Increasing frequency delays dynamic stall (L. He, J.D. Denton)dynamic stall (L. He, J.D. Denton)

Analysis

Use CFD to simulate the Use CFD to simulate the experimentexperiment

Used the University of Glasgow Used the University of Glasgow PMB code to analyse the dataPMB code to analyse the data

Cross-plotted the CFD results and Cross-plotted the CFD results and the experimental results in order the experimental results in order to make a comparisonto make a comparison

CFD Grid

1st block41*85*2

3rd block41*85*2

2nd block222*85*2

CFD results on the pressure field

Table of Cases

FrequencyFrequency 60Hz60Hz 110Hz110Hz 210Hz210Hz

Inlet mach No.Inlet mach No. 0.50.5 0.50.5 0.50.5

Inlet stagnation Inlet stagnation temperaturetemperature

280K280K 280K280K 280K280K

Reynolds Reynolds numbernumber

850 000850 000 850 000850 000 850 000850 000

Time Domain Comparison 60Hz

Frequency Domain Comparison 60Hz

Time Domain Comparison 110Hz

Frequency Domain Crossplots 110Hz

Time Domain Crossplots 210Hz

Frequency Domain Crossplots 210Hz

Reference case

Boundary layer behaviourTurbulent Reynolds Number indicating laminar flow up to30% of the chord

Pressure taps indicating transitionat ~50% chord

1.9

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

0 10 20 30 40 50 60

P (

-)

Time Step

Probe 1Probe 6Probe 9

Incidence

Mean incidence 7 degreesAmplitude 1 degreeFrequency 210 Hz

1.6

1.8

2

2.2

2.4

2.6

2.8

0 20 40 60 80 100 120

P (

-)

Time Step

Probe 1Probe 6Probe 9

Incidence

Mean incidence 7 degreesAmplitude 1 degreeFrequency 210 HzTrip x/c=0.5

BL trip at 50% chord

Mean incidence 0 degreesAmplitude 1 degreeFrequency 120 HzTransition at x/c=0.5

1.9

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

0 20 40 60 80 100 120 140 160 180

P (

-)

Time Step

Probe 1Probe 6Probe 9

Incidence

2.4

2.45

2.5

2.55

2.6

2.65

2.7

2.75

2.8

0 20 40 60 80 100 120 140 160 180

P (

-)

Time Step

Probe 1Probe 6Probe 9

IncidenceMean incidence 0 degreesAmplitude 1 degreeFrequency 210 HzTransition at x/c=0.5

BL trip at 50% chord

Conclusions The 60Hz and 110Hz cases were The 60Hz and 110Hz cases were

reasonably the samereasonably the same 210Hz Experiment suggests a change in 210Hz Experiment suggests a change in

phase, CFD maintains the same trend, for phase, CFD maintains the same trend, for reference casereference case

BL trip at 50% chord gives phase shift, BL trip at 50% chord gives phase shift, even for zero incidenceeven for zero incidence

The higher mean incidence the easier to The higher mean incidence the easier to get phase shiftget phase shift

State of boundary layer seems to affect State of boundary layer seems to affect phasephase

Investigate difference of BL between 110Hz Investigate difference of BL between 110Hz and 210Hz frequencesand 210Hz frequences

Further work needs to be carried outFurther work needs to be carried out