CONJUGATE HEAT TRANSFER ANALYSIS FOR GAS TURBINE … · 2016. 12. 7. · CONJUGATE HEAT TRANSFER...

15th ISRAELI SYMPOSIUM ON JET ENGINES & GAS TURBINES

CONJUGATE HEAT TRANSFER ANALYSIS

FOR GAS TURBINE FILM-COOLED BLADE Bruno Aguilar

November 17th, 2016

© 2015 by Honeywell International Inc. All rights reserved.

Agenda

• Introduction and Motivation

• Geometry and Computational Domain

• Model Mesh Details

• Numerical Set Up and Boundary Conditions

• Model Convergence

• Results and Discussion

- Comparison against thermocouple data

• Conclusions and Further Investigation



Introduction and Motivation

• Modern gas turbine engines operate at high temperatures and

speed to obtain high power. High turbine inlet temperature can lead

to excessive thermal stress and reduced component life.

• In order to correctly calculate cyclic thermal stress and component

life, blade metal temperature predictions within the accuracy range

of ± 4K (7°F) are required.

• CHT Tm calculation is within hth=5-10% which implies DTm=20-73K

(50-140oF). This may cause 10-20x error in life prediction.

• Accuracy of CHT in film cooled blades will be explored in this

presentation.

Calculating Blade Temperature Is Challenging

3


Common Thermal Analysis Process

CHT CFD CFD

HTC

Conduction Thermal Model

Stress Analyses Life Calculations

Cycle Sheet Materials

Secondary Flows

Blade Tm Validation

No

Yes

Calibration Factors DTm ≤ 4K

DTm > 4K

Blade Tm Validation

No

DTm > 4K

Yes DTm ≤ 4K


Geometry and Computational Domain


Model Mesh Details

• Grid sensitivity was completed with different Y+ values.

- Y+ values near wall is less than 3.

• A combination of tetrahedral (Unstructured) and prism elements are used.

• The CFX CHT model consisted of 9.8 million elements:

- 1.2 million cells in the solid domain (Blade) and 8.6 million cells in the fluid domain.

• Conformal contact interface between solid and fluid region. Prism are wrapped around the

blade surface to resolve the boundary layer (higher accuracy).


Numerical Set Up and Boundary Conditions

• ANSYS CFX 14.0

• Steady State RANS

• Turbulence model - Turbulence intensity factor of 15%.

- Shear stress transport (SST) turbulence model with automatic wall function.

- Sensitivity study completed for 4 turbulence models: SA, k-ε, RNG and SST w/ transition.

• Heat transfer - Total energy and viscous work term

• Wall function - Automatic

• Static structures assumed adiabatic

7

• Boundary Conditions



Numerical Set Up and Boundary Conditions

• Inlet total gas temperature obtained using Fine Turbo.

• Harmonic and mixing plane yielded similar absolute radial total temperature profiles.

Mixing Plane Tt(r) is Used

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20

Ra

dia

l s

pa

n

Tt/Tt_ref

TFE1042 Blade Inlet Temperature Profile

Harmonic

Steady

1.10

1.04

Tt /Tt_ref

0.98

0.86

0.92

0.80


Model Convergence

• CHT steady state solution achieved

- RMS residuals between 10-4 and 10-5

- Mass flow imbalance ≤ 0.05% of core flow.

- Blade temperatures at different locations stable.

9



1.00

0.95

0.90

0.85

0.80

0.70

0.75

0.65

0.60

0.55

0.50

Ts/Tref

1.00

0.96

0.91

0.86

0.81

0.72

0.76

0.67

0.62

0.57

0.52

Tt/ Tref

Results – External Gas Flow

• Low pressure region in the throat

due to supersonic flow.

Why is suction side so cool relative to pressure side?

1.00

0.92

0.83

0.75

0.67

0.50

0.58

0.41

0.33

0.25

0.17

Ps/Ps_ref Mn

• Migration of hot gas towards the pressure side due to flow accelerating on the suction side.

• Low temperature layer covering most of suction side.

50% radial span

50% radial span




Secondary flows impact film cooling effectiveness

11

LE

TELETE

Inlet

plane

• Secondary flow vortices roll the end

wall flows from hub and shroud

toward mid-span in suction side.

• These vortices also disperse the flow

to the entire span on pressure side.




• Secondary flow vortices gradually roll

blade hub and tip cooling flows as

flow progresses from the blade

leading edge towards the trailing

edge.

• The cool flow migration causes the

trailing edge metal temperature radial

gradient to worsen.

• Temperature gradients are directly

promotional to stress.

TE durability will suffer due to secondary flow effects

12

Tt_rel

Tt-ref

TE

LE

(a) Inlet plane (b) 15% axial chord

(e) 60% axial chord

(c) Exit plane

(f) 35% axial chord

(d) 75% axial chord


• Pressure drop due to entrance losses compensated by pumping effect.

• Recirculation zones detected inside the blade core, seal plate cavity and Tangential on

board ejector (TOBI). This will adversely affect heat transfer and cause pressure loses.

• Cooling air temperature increases as it travel through the serpentine. The cooling air

temperature in the trailing edge region might not be adequate.

13

1.00

0.93

0.86

0.78

0.71

0.57

0.64

0.50

0.43

0.36

Ps /Pref

(a) Ps

Mn

(b) Mn

1.00

0.94

0.88

0.81

0.69

0.75

0.63

0.56

Ts/Tref

(c) Ts

Results – Internal Cooling Flows


Results – Internal Cooling Flows

• Secondary flow vortices disrupt

the cooling effectiveness from

the film cooling. This effect is

mainly seen on the suction side.

• Last row of cooling flows on the

pressure side seem to have

some ingestion.

14

SSPS

SSPS

film cooling

flow is low


• Blade tip hot due to cooling flow rolling over from pressure side to suction side. Also, internal flow recirculation affected some zones.

• Trailing edge too hot due to last row of pressure side cooling holes not providing adequate cooling.

• Heat tinting field experience validate these results.

15

1.00

0.95

0.89

0.84

0.78

0.73

0.67

Tm/Tref

Results – Metal Temperatures


Results – Comparison Against TC Data

• CHT

16

• Three blades instrumented at 50% radial span. 7 TCs on the suction

side and 5 TCs on the pressure side. Blade to blade variation within

2%.

• Results within 20K (~50F) except the locations 1, 2, 3 on the suction

side where DTm can be as high as 73K (~140oF).

Mid-section

2

1

3

4

5

6

8

10

9

7

1112

-13

1

-19

14

-9

-18

-73

-28

14

8-16

-68

DT(k)

DT=(TT/C-TCHT)

1.00

0.85

0.98

0.88

0.95

0.93

0.90

0.83

0.80

Tm/Tref


Results – Comparison Against TC Data

• CHT model with SST with transition does an adequate job

predicting metal temperatures except on a few points on the suction

side.

17

2

1

3

4

5

68

10

9

7

1112


Results – Sensitivity to other Turbulent Models

• All models fail to adequately predict metal temperatures for a few

points on the suction side.SA being the worst.

• Best model to predict metal temperatures on LE and TE is SST +

Transition. K-ε being the worst in these locations.

18

2

1

3

4

5

68

10

9

7

1112


• CHT reasonably predicts metal temperature for a filmed cooled

blade. However, the metal temperature accuracy might not meet the

life prediction requirements.

• Although temperature accuracy may not meet the life prediction

requirement, CHT results can still provide detailed guidance for

model calibration.

• Therefore, the CHT simulation could be a valuable design and

analysis tool during the preliminary analysis or trade-off studies.

• Further investigation: - Investigate potential issues with combustor profile.

- Explore different turbulence models with better fluid flow transition

prediction capability.

- Apply an unsteady inlet boundary condition for the CHT simulation to

obtain the blade temperature response.

Conclusions


Thank you !

CONJUGATE HEAT TRANSFER ANALYSIS FOR GAS TURBINE … · 2016. 12. 7. · CONJUGATE HEAT TRANSFER...

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