Laminar-Turbulent Boundary Layer Transition Imaging Using IR Thermography

Crawford, Brian K.; Duncan, Glen T.; West, David E.; Saric, William S.

doi:10.4236/opj.2013.33038

Cited by 57 publications

(13 citation statements)

References 7 publications

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“…Comparison of the skin-friction distribution and mean temperature profiles suggested that the separation and reattachment locations correspond approximately to locations of local maximum and minimum surface temperature, respectively. Furthermore, as suggested by other studies [19,20,24,[82][83][84][85], the transition location was shown to coincide with the location of maximum streamwise gradient in surface temperature.…”

Section: Temperature Measurementssupporting

confidence: 74%

“…In the subsonic regime, less pronounced temperature differences between the outer flow and the model surface made diagnostics using infrared thermography more difficult. In attempts to improve thermal contrast in the subsonic regime, external [21,22,25,26,[89][90][91] or internal [19,20,24,90] heating elements were often incorporated [82]. With the use of additional heating, both laboratory [19][20][21][22][23][24][25] and in-flight experiments [20,26] have performed successful detection of mean transition using infrared…”

Section: Temperature Measurementsmentioning

confidence: 99%

“…With recent developments in infrared camera technology, infrared thermography has been successfully applied in subsonic flows to identify boundary layer transition in both laboratory [19][20][21][22][23][24][25] and in-flight experiments [20,26]. Additionally, analysis of separating near-wall flows has been pursued, such as detection and characterization of laminar separation bubbles.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of Laminar Separation Bubbles Using Infrared Thermography

Wynnychuk

Yarusevych

2019

AIAA Aviation 2019 Forum

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Boutilier & Yarusevych [7] for estimation of the characteristic points in a laminar separation bubble using static pressure distributions shown with an example pressure distribution (Re L = 27, 000) 4.2 Comparison of inviscid and measured pressure distributions at Re L = 27, 000 4.3 Distribution of static pressure coefficient for highlighted flow conditions. . ix 4.4 Contours of mean streamwise velocity at highlighted Reynolds numbers. .

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Section: Temperature Measurementssupporting

confidence: 74%

Section: Temperature Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Characterization of Laminar Separation Bubbles Using Infrared Thermography

Wynnychuk

Yarusevych

2019

AIAA Aviation 2019 Forum

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“…For many years, experimental studies have been devoted to laminar‐turbulent transition, to understand in detail the transition process and to generate transition detection databases for computational validations and improvements. Some of the most common experimental methods are using pressure transducers, hot film sensors, and infrared thermography . Although there are many experiments conducted in literature for detection of the laminar‐turbulent transition in aircraft applications, research on wind turbine blades are comparably rare.…”

Section: Introductionmentioning

confidence: 99%

Laminar‐turbulent transition detection on airfoils by high‐frequency microphone measurements

et al. 2019

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In the present work, various data processing methods for laminar to turbulent transition detection on airfoils are assessed based on experimental data. For this purpose, NACA 63-418 airfoil profile with surface microphones flush mounted both on the suction and the pressure side is used in the wind tunnel experiments. Reynolds numbers are changed in the range from 1.6 · 10 6 to 6 · 10 6 for various angles of attack. In this way, the transition behaviour of the airfoil is characterized.Time signals and spectrogram of the data, chordwise pressure level changes, and first moments are investigated. Standard deviations of pressure are observed to exhibit a peak at transition and slightly decreases for the fully turbulent flow staying always higher than the laminar flow. The most robust method to detect the transition location is found to be the characteristic frequency approach by spectral moments provided that the inflow turbulence is low. The numerical results are in agreement with experimental results on the pressure side where natural transition occurs.However, the transition due to surface irregularity and microphone placement occurs on the suction side. This cannot be predicted by the numerical tools. The Tollmien-Schlichting wave frequencies and neutral curve points are determined from the experiments. The analysis shows that the most common curve length of the transition process is around 15% to 20%, and it can vary between 0% to 30 % of the chord. Increasing the Reynolds number leads to an earlier transition position closer to leading edge at both upper and lower surfaces. KEYWORDSboundary layer, laminar-turbulent transition, transition detection, wind tunnel experiments, wind turbine airfoil INTRODUCTIONAs the size of modern wind turbines is steadily growing, high Reynolds number experimental data for the wind turbine airfoils and blades are needed for verification and improvement of the aerodynamic prediction tools in the design process. In order to contribute to the development of the airfoil design and to accurately predict airfoil characteristics, the determination of the laminar-turbulent transition point is very important. 1Power curves, which are the indication of the electrical power output at different incoming wind speeds, are highly affected by the lift to drag ratio of the aerodynamic profiles of wind turbines. However, the maximum lift coefficient must be limited due to structural load constraints, which makes drag force one of the major parameters to be studied. 2 Skin friction drag of a laminar boundary layer is significantly lower than that of a turbulent boundary layer. Therefore, by the detection of the transition location from laminar to turbulent flow, it is possible to have an improved frictional drag estimation. Moreover, transition location control mechanisms can be applied to obtain higher lift to drag ratio airfoils.It was hypothesized by Reynolds that the transition is a result of instabilities in the laminar flow, which was further developed by Rayleigh. 3On a given body, starting f...

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“…For example, Bouchardy and Durand (1983) measured the adiabatic temperature distribution on the surface of a blade in a wind tunnel with an infrared camera to detect the transition region. Quast (1987) and more recently Crawford et al (2013) and Richter and Schülein (2014) applied this technique also in free flight experiments and moving rotor blades. Major drawbacks are, however, the always present reflections of surrounding surfaces on the investigated blade, the varying emissivity of the surface and the dependency on the viewing angle.…”

mentioning

confidence: 99%

Temperature decline thermography for laminar–turbulent transition detection in aerodynamics

et al. 2017

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a post-processing method was developed and qualified to determine a quantity proportional to the heat transfer coefficient into the flow. By plotting this quantity for each pixel of the surface, a qualitative, two-dimensional heat transfer map was obtained. The results clearly depicted the areas of onset and end of transition over the full span of the model and agreed with the expected behavior based on the respective flow condition. To validate the approach, surface hotfilm measurements were conducted simultaneously on the same NACA profile. Both techniques showed excellent agreement. The temperature decline method allows to visualize laminarturbulent transitions on static or moving parts and can be applied on a very broad range of scales-from tiny airfoils up to large airplane wings.

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Laminar-Turbulent Boundary Layer Transition Imaging Using IR Thermography

Cited by 57 publications

References 7 publications

Characterization of Laminar Separation Bubbles Using Infrared Thermography

Characterization of Laminar Separation Bubbles Using Infrared Thermography

Laminar‐turbulent transition detection on airfoils by high‐frequency microphone measurements

Temperature decline thermography for laminar–turbulent transition detection in aerodynamics

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