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The flow on a rotating disk is the simplest example of three-dimensional boundary layers where two kinds of instabilities can appear in general. One is the familiar cross-flow instability of the inflexion-point type essentially described by Rayleigh's inviscid stability equation, and the other is streamline-curvature instability, whose rigorous mathematical description is not yet established. The present study gives an asymptotic series solution of the exact partial differential equations governing small but wavy disturbances superimposed on rotating-disk flow and compares the results with some known properties of streamline-curvature instability., 資料番号: NALSP0059026, レポート番号: NAL SP-59

An iterative calculation method was applied to identify two different instability modes in a three-dimensional boundary layer near attachment-line on a yawed cylinder. The point disturbance originating from a small hole on the cylinder was dispersed in the wedge-shaped region which consists of two types of unstable waves. Detailed hot-wire measurements illustrated the wave crests suggesting the each distribution of phase line for the two instability modes. The iterative calculation based on an assumption for the distribution function of the amplitude successfully provided the decomposition of the original experimental data into the two modes. The decomposition enabled us the comparison with the prediction by Itoh's linear stability theory and the identification of these modes, the streamline-curvature (S-C) modes and cross-flow (C-F) modes., 資料番号: NALSP0059012, レポート番号: NAL SP-59