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Research Papers

Infrared Based Wall Shear Stress Measurement Techniques

[+] Author and Article Information
Ilka Rudolph1

 Institute of Aeronautics and Astronautics, Technical University Berlin, Berlin 10587, Germanyilka.rudolph@ilr.tu-berlin.de

Matthias Reyer, Wolfgang Nitsche

 Institute of Aeronautics and Astronautics, Technical University Berlin, Berlin 10587, Germany

1

Corresponding author.

J. Thermal Sci. Eng. Appl 3(3), 031001 (Aug 10, 2011) (7 pages) doi:10.1115/1.4004107 History: Received September 10, 2010; Revised March 22, 2011; Published August 10, 2011; Online August 10, 2011

The paper presented here introduces two novel, infrared based wall shear stress measurement techniques. The first provides wall shear stress visualizations with a high spatial and temporal resolution as well as spatial quantitative information. The other technique enables sensor-based measurements of the wall shear stress magnitude and direction. Both techniques are based on the close link between momentum and heat transport in the boundary layer and correlate the surface temperature distribution of a heated surface (first technique) or a heated spot (second technique), which is measured using infrared thermography, with the wall shear stress. For the spatial qualification and quantification, the temporal surface temperature evolution of a heated structure subjected to a flow is linked to the wall shear stress distribution. The second, sensor-based technique heats a small spot on an otherwise unheated surface. The temperature distribution, or thermal tuft, around this heated spot is closely related to the local wall shear stress magnitude and direction. Results are presented for both techniques and compared to reference measurements and visualizations, respectively. Reference measurements of the wall shear stress were obtained using a skin friction balance; oilflow visualizations were used as a reference visualization technique.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 5

Setup for the visualization experiments with heatable areas (left) and flow topology of the flow around a wall mounted cylinder (right)

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Figure 6

Visualization of the horseshoe vortex system (left). Comparison of infrared visualization and surface hotwire measurements (right).

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Figure 7

Visualization of the cylinder top (left) and visualization of the cylinder circumference (right)

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Figure 8

Sketch of a thermal tuft in two and three dimensions (left) and experimental setup for the thermal tuft sensor (right)

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Figure 9

Infrared images of the temperature field around the sensor for four different heat flux values and a skin friction of τw  = 0.7 N/m2

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Figure 10

Infrared images of the temperature field around the sensor for two different shear stress values and a heat flux of q = 0.25 W/mm2 (left). Calibration curves and shear stress angle for various heat flux values (right).

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Figure 1

Fundamental principle of the technique with details of the heated structure (left) and cooling curves for various free stream velocities at a fixed streamwise position (right)

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Figure 2

Detailed view of the experimental setup with heated measurement area (gray) and points for reference measurements marked by a cross (left). Exemplary wall shear stress measurements for tripped and untripped flow (right).

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Figure 3

Area ratio over wall shear stress for various Reynolds numbers and laminar and turbulent flow conditions (left). Mean deviation from the reference measurements for laminar and turbulent flow conditions (right).

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Figure 4

Corrected laminar data and resulting mean wall shear stress deviations (left). Spatial deviation of the shear stress values from the reference measurements for two free stream velocities (right).

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