Contactless Localization of Premature Laminar–Turbulent Flow Transitions on Wind Turbine Rotor Blades in Operation
Abstract
:Featured Application
Abstract
1. Introduction
1.1. Motivation
1.2. State of the Art
1.3. Aim and Outline
2. Measurement Approach
2.1. Actual Flow Transition
2.1.1. Method A: No Image Rotation and 2D Gradient Evaluation
2.1.2. Method B: Image Rotation and 1D Gradient Evaluation
2.2. Natural Flow Transition
2.3. Parameter Definition to Quantify the Laminar Flow Reduction (LFR)
3. Experimental Setup
3.1. Image Acquisition
3.2. Implementation
- Pre-evaluation of the thermographic image
- Obtaining all local gradient maxima positions representing the natural and premature flow transition
- Selection of all gradient maxima with plausibility and outliers analysis
- Creating a final actual and natural flow transition line from the selected gradient maxima
- Calculation of the laminar flow reduction (LFR)
- 1.
- Pre-Evaluation
- 2.
- Obtaining Positions of Local Gradient Maxima
3.2.1. Method A: No Image Rotation and 2D Gradient Evaluation
3.2.2. Method B: Image Rotation and 1D Gradient Evaluation
- 3.
- Selection of Local Gradient Maxima
- 4.
- Acquiring Flow Transition Line
- 5.
- Calculation of the Laminar Flow Reduction (LFR)
4. Results
4.1. Verification
4.1.1. Simulation
4.1.2. Contrast of Turbulence Wedge
4.1.3. Image Noise
4.1.4. Overlapping of Turbulence Wedges
4.2. Validation
4.2.1. Flow Transition Line
4.2.2. Laminar Flow Reduction
5. Conclusions and Outlook
Author Contributions
Funding
Conflicts of Interest
Abbreviations
CNR | contrast to noise ratio |
IFOV | instantaneous field of view |
LFR | laminar flow reduction |
method A | image processing with no image rotation and 2D gradient evaluation |
method B | image processing with image rotation and 1D gradient evaluation |
NETD | noise equivalent temperature difference |
rotation angle in degrees | |
gradient direction in degrees | |
relative contrast of turbulence wedge in % | |
contrast to noise ratio between area a and b in arbitrary units | |
gradient threshold for premature flow transitions without unit | |
gradient threshold for natural flow transitions without unit | |
collection of premature flow transitions in pixels | |
collection of natural flow transitions in pixels | |
G | gradient magnitude without unit |
gradient magnitude in direction without unit | |
counting variable without unit | |
mean intensity without unit | |
relative laminar flow reduction in image column i in arbitrary units | |
relative laminar flow reduction in arbitrary units | |
standard deviation without unit | |
temperature profile of image column j without unit | |
image coordinates in pixels | |
rotated image coordinates in pixels | |
actual transition position in image column i in pixels | |
natural transition position in image column i in pixels | |
rotor blade leading edge position in image column i in pixels | |
rotor blade trailing edge position in image column i in pixels | |
y-coordinates of actual flow transition line in pixels | |
y-coordinates of natural flow transition line in pixels |
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Gleichauf, D.; Sorg, M.; Fischer, A. Contactless Localization of Premature Laminar–Turbulent Flow Transitions on Wind Turbine Rotor Blades in Operation. Appl. Sci. 2020, 10, 6552. https://doi.org/10.3390/app10186552
Gleichauf D, Sorg M, Fischer A. Contactless Localization of Premature Laminar–Turbulent Flow Transitions on Wind Turbine Rotor Blades in Operation. Applied Sciences. 2020; 10(18):6552. https://doi.org/10.3390/app10186552
Chicago/Turabian StyleGleichauf, Daniel, Michael Sorg, and Andreas Fischer. 2020. "Contactless Localization of Premature Laminar–Turbulent Flow Transitions on Wind Turbine Rotor Blades in Operation" Applied Sciences 10, no. 18: 6552. https://doi.org/10.3390/app10186552
APA StyleGleichauf, D., Sorg, M., & Fischer, A. (2020). Contactless Localization of Premature Laminar–Turbulent Flow Transitions on Wind Turbine Rotor Blades in Operation. Applied Sciences, 10(18), 6552. https://doi.org/10.3390/app10186552