Film cooling aerodynamic performance

170 Pages·2017·12.02 MB·English

Film cooling aerodynamic performance:
flow structures and aerodynamic losses
in an airfoil with pressure side injection

MSc Thesis

Clara Paula Moreno Castán
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Film cooling aerodynamic performance

Flow structures and aerodynamic losses in an airfoil
with pressure side injection

By

Clara Paula Moreno Castán

in partial fulfilment of the requirements for the degree of
Master of Science in Aerospace Engineering

at the Delft University of Technology,

to be defended publicly on
Friday 8th June 2018 at 9:00

Student number: 4421760
Project duration: March 2017 - June 2018
Thesis committee: Dr. A. G. Rao, TU Delft supervisor
Dr. A. Sciacchitano, TU Delft advisor
Dr. G.A. Bohlin TU Delft
Dr. D. Ragni TU Delft

This thesis is confidential and cannot be made public until 8th June 2018

An electronic version of this thesis is available at http://repository.tudelft.nl/.

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Abstract

As a response to a socio-economic framework which demands lower fuel consumption and
CO emissions, gas turbine manufacturers strive to attain higher thermal efficiency and specific work
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output in their engines. The enhancement of these two performance parameters is linked to higher
turbine inlet temperatures (TIT), which explains the increasing trend in TIT accompanying aero
engines industrial development.

Turbine cooling technology is one of the disciplines strongly contributing to this aim, enabling
operating hot gas temperatures to be higher than the melting temperature of the material. This study
deals with film cooling: an external type of turbine cooling. Coolant air, bled from the compressor,
is injected into the turbine blades and vanes and discharged through small holes into the airfoil´s
external boundary layer, creating a thin insulating layer that reduces convective heat transfer from
the hot gas to the surface. However, this gain in thermal capability brings along an aerodynamic
penalty.

The purpose of this work is to understand the aerodynamic performance of a NACA 0012 airfoil with
multi-row film cooling on the pressure side, as a follow-up experimental study of a previous one
using the same model but with suction side injection. A configuration with angle of attack 𝛼 = 0°,
freestream velocity 𝑉 = 15 m/s ( 𝑅𝑒 = 1.18· 105) and air as secondary flow is tested as a
∞ ∞,
𝑐
baseline to understand the effect of blowing ratio 𝐵𝑅 ∈ (0,2) on flow field characteristics. Then,
other configurations are tested to analyse the effect of angle of attack, freestream velocity, single row
injection and density ratio by using CO as secondary flow to simulate the temperature ratio existing
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in real gas turbine applications. With this experimental setup and operating conditions, the measured
aerodynamic losses are limited to viscous effects in the airfoil boundary layer and wake shear layer
including flow separation, and coolant-related losses due to mixing processes between primary and
secondary flows.

Pointwise pressure measurements at a location downstream of the airfoil (x = 1.25·c) and planar and
stereo PIV are used as flow measurement techniques. Wake velocity profile characteristics and
aerodynamic losses are retrieved from pressure measurements. Results for the baseline configuration
show how the wake velocity profile displaces towards the pressure side when blowing is introduced.
For low blowing ratios, the low momentum of the coolant induces high mixing losses whereas for
high blowing ratios, the energizing effect of the high momentum coolant outweighs the mixing losses
resulting in an aerodynamic gain. Maximum losses are found for BR = 0.5 and they decrease for
higher blowing ratios. For BR = 1.4, a shift from wake to jet local behaviour is observed. The high
and low velocity regions in the 2D average velocity fields computed from planar PIV measurements
show the same trend with blowing ratio in the wake region and provide further information about the
mixing shear layer at a location close to the cooling holes. Finally, 3D average velocity fields
computed from stereo PIV display the evolution of the mixing shear layer and jet in crossflow at
different streamwise locations.

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Table of Contents

Nomenclature .................................................................................................................................. 9
List of Abbreviations .................................................................................................................... 10
List of Figures ............................................................................................................................... 11
List of Tables ................................................................................................................................ 15

1 Introduction ............................................................................................................................... 17
1.1. Framework and motivation ............................................................................................. 17
1.2. Document structure ......................................................................................................... 20

2 Literature review ........................................................................................................................ 21
2.1. Research scope ............................................................................................................... 21
2.2. Aerodynamic losses and flow structures .......................................................................... 24
2.2.1. Theoretical background..................................................................................... 24
2.2.2. Literature study ................................................................................................. 29
2.3. Experimental conditions and scaling parameters ............................................................. 30
2.3.1. Theoretical background..................................................................................... 30
2.3.2. Literature study ................................................................................................. 33
2.4. Flow measurement techniques and use of PIV ................................................................. 34
2.4.1. Theoretical background..................................................................................... 34
2.4.2. Literature study ................................................................................................. 35
2.5. Chapter remarks .............................................................................................................. 36

3 Testing methodology and experimental setup ............................................................................. 40
3.1. Research objective .......................................................................................................... 40
3.2. Testing methodology and experimental matrix ................................................................ 41
3.3. Equipment specifications and experimental approach ...................................................... 44
3.3.1. Windtunnel ....................................................................................................... 44
3.3.2. Secondary flow system ..................................................................................... 45
3.3.3. Airfoil model .................................................................................................... 47
3.3.4. Pressure measurements system.......................................................................... 48
3.3.5. PIV setup .......................................................................................................... 52
3.3.6. Equipment uncertainties .................................................................................... 58
3.4. Chapter remarks .............................................................................................................. 59

4 Pressure measurements results.................................................................................................... 60
4.1. Air as secondary flow ..................................................................................................... 60
4.1.1. Baseline configuration, 𝑉 =15 m/s and AoA=10º: effect of BR ........................ 60
∞
4.1.2. Effect of angle of attack .................................................................................... 72
4.1.3. Effect of freestream velocity ............................................................................. 76
4.1.4. Effect of partial injection .................................................................................. 78
4.2. CO as secondary flow .................................................................................................... 80
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4.2.1. Baseline configuration, 𝑉 =15 m/s and AoA=10º: effect of BR ........................ 81
∞
4.2.2. Effect of angle of attack .................................................................................... 84
4.2.3. Effect of scaling parameter: momentum flux ratio ............................................. 88
4.3. Uncertainty analysis ........................................................................................................ 89
4.4. Chapter remarks .............................................................................................................. 90

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5 PIV results ................................................................................................................................. 92
5.1. Planar PIV: Global flowfield ........................................................................................... 92
5.2. Planar PIV: local flowfield .............................................................................................. 93
5.3. Comparison with pressure measurements results ............................................................. 96
5.4. Stereo-PIV ...................................................................................................................... 97
5.5. Uncertainty analysis ...................................................................................................... 100
5.6. Chapter remarks ............................................................................................................ 103

6 Conclusions and outlook .......................................................................................................... 105
6.1. Concluding remarks......................................................................................................... 105
6.2. Recommendations for future work .................................................................................. 110

Bibliography ............................................................................................................................... 112

Appendices ................................................................................................................................. 120
Appendix I: Literature study tables .......................................................................................... 120
Appendix II: Bronkhorst flow controller .................................................................................. 141
Appendix III: Pressure measurements results........................................................................... 145
Air as secondary flow .................................................................................................. 146
CO as secondary flow ................................................................................................. 154
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Appendix IV: Planar PIV results ............................................................................................. 162

Acknowledgements ..................................................................................................................... 169

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Nomenclature
Latin symbol Parameter
A Area
C Conversion factor in flowcontroller
c Chord
𝑐 Heat capacity at constant pressure
𝑝
C Discharge coefficient
d
d Distance
𝐷 Hole diameter
f Focal length
f f-stop in PIV
#
h Enthalpy
k Coverage factor
L Hole length
M Mach number
N Number of image pairs
ṁ Mass flow
P Pressure
q Dynamic pressure
s Entropy
R Gas constant

T Temperature
V Velocity

Greek symbol Parameter
 Aerodynamic loss
 Ratio of specific heats
 Aerodynamic loss
 Aerodynamic loss
α Angle of attack
𝜎 Standard deviation
𝛿 Laser sheet thickness
𝑧
𝛽 Hole injection angle
 Density

Subscript Meaning
amb Ambient
avg Average
c Coolant
cs Cross-sectional
∞ Mainstream
is Isentropic
i Image
o Object
s Static magnitude
t Total magnitude
1 Inlet
2 Exit
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List of Abbreviations

Abbreviation Meaning
AOA Angle Of Attack
BR Blowing Ratio
CCD Charged Coupled Device
CFD Computational Fluid Dynamics
CRVP Counter Rotating Vortex Pair
DAS Data Acquisition System
DLR German Aerospace Center
DR Density Ratio
FOV Field of view
FREP Fast Response Entropy Probe
FS Full-scale
HSC High-accuracy Silicon Ceramic
HWA Hot Wire Anemometry
IAL Integrated Aerodynamic Losses
IIM Ideal Isentropic Mixing
IR InfraRed
JICF Jet In Cross Flow
KE Kinetic Energy
LDV Laser Doppler Velocimetry
LE Leading Edge
MFR Mass Flow Ratio
MRV Magnetic Resonance Velocimetry
NGV Nozzle Guide Vane
PIV Particle Image Velocimetry
PS Pressure Side
PSP Pressure Sensitive Paint
PTU Programmable Timing Unit
RD Reading
SS Suction Side
TBC Thermal Barrier Coating
TIT Turbine Inlet Temperature
TR Temperature Ratio
VR Velocity Ratio

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