Approximate Estimation of Skin Friction by Oil Dot Method

Abstract

An approximate skin friction estimation method by tracking oil dot movement under the effect of skin friction is proposed. The method uses the correlation between oil dot velocity and skin friction obtained by measurements for flat plate laminar boundary layer in a wind tunnel. The correlation is divided into two zones. Linear correlations at early stage of oil dot streak developments are observed. But, the correlation factors are much differ among oil dots. If oil dots streaks develop enough after a long period, the correlations converge into a certain band. Present method uses the later correlation to estimate skin friction values. Skin friction values on a very low aspect ratio rectangular wing having NACA 4412 wing section are estimated. The results show approximate skin friction values on bodies can be easily estimated by the present method.