Abstract
The results of an investigation of the influence of free stream disturbances on the lift and drag performance of the Lissaman 7769 airfoil are presented. The wind tunnel disturbance environment is described using hot-wire anemometer and sound pressure level measurements. The disturbance level is increased by the addition of a ‘turbulence screen’ upstream of the test section and/or the addition of a flow restrictor downstream of the test section. For the Lissaman airfoil it was found that the problems associated with obtaining accurate wind tunnel data at low chord Reynolds numbers (i.e., below 200,000) are compounded by the extreme sensitivity of the boundary layers to the free stream disturbance environment. The effect of free stream disturbances varies with magnitude, frequency content, and source of the disturbance.
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Abbreviations
- c d :
-
section profile drag coefficient
- c l :
-
section lift coefficient
- R c :
-
Reynolds number based on airfoil chord and free stream conditions
- URMS:
-
root-mean-square of the fluctuating velocity, m/s
- U :
-
test section velocity, m/s
- x :
-
distance measured from beginning of test section, cm
- :
-
distance measured along airfoil chord from the leading edge divided by chord length, percent
- a :
-
angle of attack, degrees
- max:
-
maximum value
- min:
-
minimum value
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Mueller, T.J., Pohlen, L.J., Conigliaro, P.E. et al. The influence of free-stream disturbances on low Reynolds number airfoil experiments. Experiments in Fluids 1, 3–14 (1983). https://doi.org/10.1007/BF00282261
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DOI: https://doi.org/10.1007/BF00282261