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UTSR Presentation

Heat Transfer Development

Andrew ChenAugust, 2017

Mentor: Yong Kim

Group Manager: Michael Fox

Department Manager: Daniel Burnes

General Questions to All Manufacturers

Caterpillar Confidential - YELLOW

Presentation Outline

Personal Background

Projects

I. Pressure Side Trailing Edge Slot Discharge Coefficient Study

II. Labyrinth Seal Flow Parameter Study

III. Labyrinth Seal CFD Simulation

Takeaways

Q&A

2



Background

3

B.S. degree from National Taiwan University

M.S. degree from Texas A&M University

Research on Gas Turbine Heat

Transfer/Film Cooling

Pursuing Ph.D. degree at Texas A&M University

Research on Gas Turbine Film Cooling and Internal

Cooling under Stationary or Rotating Conditions)



Experience

Research assistant at

Foxconn Communication Technology Corp.

Institute of Atomic and Molecular Sciences, Academia Sinica.

National Synchrotron Radiation Research Center, Taiwan.

4



PS Slot Discharge Coeff.─

Introduction

5

Why cooling?

Engine operates under mainstream temp. > metal yielding temp.

Use cooling air to cool the turbine blade both internally and

externally.

External (film) cooling.

Credit: Je-Chin Han, 2013, “Fundamental Gas Turbine Heat Transfer”

Trailing edge slot ejection

For a gas turbine vane or blade,

a thin trailing edge is usually

preferred from the aerodynamic

point of view.

Pressure side (PS) slots are

ideal for providing adequate

cooling in this thin-wall region.




Introduction

A trailing edge slot rig was built to study the heat transfer as

well as flow behavior.

Mainstream flow acceleration was achieved by an adjustable

door (inclined top wall).

6

Mainstream

Coolant

6 in2.85 in

9.4 in

21.9 in

3.8 in

3.9 in

0.83 in

Vin = 65 ft/s

Coolant mass flow rate

= 0.03 ~ 0.15 lb/s

Pout = 14.5 psi




Background

7

Discharge coefficient:

𝐶𝑑 =𝐴𝑐𝑡𝑢𝑎𝑙 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒

𝐼𝑑𝑒𝑎𝑙 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒≤ 1

Important for estimating the actual coolant flow rate

𝐴𝑐𝑡𝑢𝑎𝑙 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 = C𝑑 × 𝐼𝑑𝑒𝑎𝑙 𝑚𝑎𝑠𝑠 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒

Provide adequate cooling with less amount of coolant.

Increase power, efficiency and durability.

Orifice or Slot

Pup Pdown




Finesse Model

Finesse is an in-house 1-D fluid network solver with

specialized components specifically for turbomachinery.

Used for engine hot-gas-path heat/mass predictions.

A 1-D flow simulation network was built for the PS slot.

Mass flow rate, pressures, and velocities are fairly close to the

experimental data.

8




Results

Existing experimental results showed:

Cd higher than one.

Cd drops abruptly at higher coolant blowing ratios (M).

9

Blowing ratio M =

𝐶𝑜𝑜𝑙𝑎𝑛𝑡 𝑚𝑎𝑠𝑠 𝑓𝑙𝑢𝑥

𝑀𝑎𝑖𝑛𝑠𝑡𝑟𝑒𝑎𝑚 𝑚𝑎𝑠𝑠 𝑓𝑙𝑢𝑥




Results

CFD result showed Cd gradually increases with blowing ratio

up to around 1.

Discrepancy between CFD and experimental results.

10




Results

Tried to use different reference pressures.

No significant change in results.

11

Ref. 1

Ref. 2




Results

Three different mainstream flow conditions were investigated:

Accelerated (baseline case)

Accelerated, door was shifted 1.8” downstream (DS)

Non-accelerated (NA)

Nearly no effect on Cd.12

Baseline

Door-Shifted (DS)

Non-accelerated (NA)




Slot Inlet Static Pressure

Slot inlet static pressure was examined. An abrupt change in

slope was identified in the experimental data.

13




Mainstream Static Pressure

Use Bernoulli’s equation, the -0.07 psi static pressure

difference corresponds to a velocity of 96 ft/s, which is far

higher than the specified mainstream inlet velocity of 65 ft/s.

Higher than expected uncertainties in pressure measurement

may be responsible for the discrepancies between

experimental and CFD results.

14




Conclusions

CFD Showed that Cd increases with increasing coolant flow

rate up to around 1.

Different reference pressures will lead to different results.

The mainstream acceleration, or the door (top wall) location,

has minimal effect on the discharge coefficient.

Uncertainty in the pressure measurement may be responsible

for the discrepancies between the experimental and CFD

results.

15



Labyrinth Seal Flow Coeff. Study

Background

An accurate prediction of flow parameters of labyrinth seals is

important to the resultant coolant consumption,

pressure/temperature distributions, and engine performance.

Based on engine test data, the leakage mass flow rate of the

labyrinth seal was found ~10% higher than the value

predicted by Finesse.

Objectives:

Compare Finesse with available NASA data.

Check if Finesse is working properly.

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Straight Seal Test Matrix

The NASA test data [1] includes the following cases. There

are three clearances: CL = 0.02”, 0.01” and 0.005”

Cases include smooth land and honeycomb land.

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Test # Kϴ (°) KN KT (in) KP (in) CL (in) X (in)

1 90 5 0.010 0.100 0.005 0.031

2 90 5 0.010 0.100 0.005 0.062

3 90 5 0.010 0.100 0.005 0.125

4 90 5 0.010 0.100 0.005 Solid

5 90 5 0.010 0.100 0.010 0.031

6 90 5 0.010 0.100 0.010 0.062

7 90 5 0.010 0.100 0.010 0.125

8 90 5 0.010 0.100 0.010 Solid

9 90 5 0.010 0.100 0.020 0.031

10 90 5 0.010 0.100 0.020 0.062

11 90 5 0.010 0.100 0.020 0.125

12 90 5 0.010 0.100 0.020 Solid

[1] Donald L. Tipton, Thomas E. Scott, and Rodney E. Vogel, 1986, “Volume III – Analytical and Experimental

Development of a Design Model for Labyrinth Seals”, Technical Report by Allison Gas Turbine.




NASA vs. Finesse

Comparison between NASA data and Finesse model showed

significant discrepancies at CL = 0.01”.

Finesse model is around 9% lower than the NASA data.

18




Vermes Model

Vermes model [2] is an improved version from the Martin’s

formula [3] and is the theory base of Finesse.

The mass flow through a labyrinth seal is expressed by:

The result is dependent on the clearance factor K value [4]:

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𝑊 = 5.76𝐾𝐴𝑔

𝑅𝑇0

𝑃0

1 − 𝛼𝛽

L/C

K

• Smaller K variation when

0.4 < L/C < 1

[2] Vermes G. “A Fluid Mechanics Approach to the

Labyrinth Seal Leakage Problem”, ASME. J. Eng.

Power. 1961;83(2):161-169. doi:10.1115/1.3673158.

[3] H. M. Martin, “Labyrinth Packings,” Engineering,

January 10, 1908, pp. 35-36.

[4] Myer Kutz, “Mechanical Engineers' Handbook,

Volume 3: Manufacturing and Management”, John Wiley

& Sons, 2015




Vermes vs. Finesse

Comparison between Finesse and Vermes model was done

and the results suggest that the Finesse outputs are correct.

20




NASA vs. Vermes

NASA data was converted into weight flow (lb/s) and

overlapped with the figure in Vermes paper [2] .

Vermes model under-predicts at CL = 0.01” to 0.015”

21

lb/s




Conclusions

The results confirmed that there is no internal error of

Finesse.

Both Vermes paper and the comparison with NASA data

suggest that the Vermes model may under predict the flow at

a clearance level between 0.01” to 0.015”.

The clearance factor (K) directly affects the outcome of the

prediction. It seems that having 0.4 < L/C < 1.0 will be a more

conservative way in the design point of view due to smaller

variations of the K value.

According to Bell and Bergelin (1957): “For the flows in the

transition region (40 < Re < 4000), experimental values

should be used whenever possible.”

Further study is needed.

22



Labyrinth Seal CFD Simulation

Background

CFD models using two different reference frame setups were

run using STAR CCM+. Different results were obtained.

23

Setup 1

Rotate_wall

Setup 2

Rotate_fluid

stationary

rotating




Challenges

Complex geometry with tiny gaps and high losses.

Convergence is challenging.

Issues remained even with higher mesh densities:

Mass imbalance

High residual values

Occasional floating point errors

24




Simplified Model

To rule out other factors that might affect the CFD calculation

with such complex geometry, a half cylinder fluid domain was

generated.

Similar boundary conditions were applied.

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Periodic

1

Periodic

2

Ω

stator




Results

Static pressures are almost identical.

Simulation on the cylinder model using different reference

settings showed different total temperature results.

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inlet middle outlet inlet middle outlet

2000 rpm




Results

Run at higher rpms.

27

2k rpm

2k rpm

5k rpm

5k rpm

10k rpm

10k rpm

Rotate fluid

Rotate wall

Residuals




Conclusions

Both results from the full model and the simplified model

showed significant difference in total temperature.

Total temperature from either setup may be questionable.

Some observations:

28

Rotate fluid Rotate wall

CPU time >

Residual level >

Stability <



Takeaways

STAR CCM+

Finesse

Labyrinth seal models and theories

Work in a company

Connections inside/outside company

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