Evaluation of three techniques for wall-shear measurements in three-dimensional flows
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Recent improvements in three techniques for measuring skin friction in two- and three-dimensional turbulent wall-bounded shear flows are presented. The techniques are: oil-film interferometry, hot wires mounted near the wall, and surface hot-film sensors based on MEMS technology. First, we demonstrate that the oil-film interferometry technique can be used to measure the skin-friction magnitude and its direction in two- and three-dimensional wall-bounded shear flows. Second, a simple method is outlined to measure the skin friction with a wall wire located outside of the viscous sublayer. Finally, a systematic study of the parameters influencing wall-friction measurements with MEMS sensors is presented. The results demonstrate that accurate measurements of the mean skin friction with MEMS sensors are possible in two- and three-dimensional wall flows. Measurements by the three techniques are compared to each other and to past measurements in the same facility.
This work was funded by the Swiss Federal Office for Education and Science (OFES) under contract BBWN2.97.0294. The present study was also part of the European project AEROMEMS, contract BRPR-CT97–0573, which investigates the feasibility of using MEMS technology for boundary layer control on aircraft. The contributions of the second author were supported by the Air Force Office of Scientific Research, USAF, under grant number F49620–01–1-0445, and ERCOFTAC.
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