平板に作用する壁面せん断応力のオイルフィルム干渉法による測定

抄録

Reduction of air resistance is a very important design element in aircraft engineering, and at subsonic speeds, skin friction resistance accounts for half of the total resistance. Surface shearing stress can be measured by Oil Film Interferometry. In the OFI it is important to know the direction in which the shearing stress acts, and corrections must be made if the direction is different from the mainstream direction. In this study, the shearing stress direction was identified using a path of a center of the ring-shaped fringes, the OFI is applied the region upstream of the center of fringes, and the shear stress was estimated. The flow field along the flat plate was the object of measurement. The flow field was formed using a wind tunnel, and a tripping wire was placed in the nozzle rip of the wind tunnel to form turbulence. A drop of oil placed 320 mm downstream from the front edge of the flat plate gradually spread and was transformed into an oil film of about 15 mm in diameter over time. The center of the ring fringe moved linearly through the oil film for about 300 seconds after the wind tunnel was started. The film gradually became thinner upstream of the oil film and thicker downstream. The skin friction resistance was calculated and was underestimated by 5 % compared to the theoretical value.