Decomposition of two kinds of instability waves in three-dimensional boundary layer near yawed attachment line

摘要

Artificial excitation from a point source near the attachment line on a yawed circular cylinder is found to yield highly modulated amplitude and phase distributions of unsteady disturbances due to superposition of both cross-flow and streamline-curvature instabilities, and this modulation makes it difficult to determine their individual critical Reynolds numbers. On the assumption that the modulation is simply due to linear superimposition of two modes, a mathematical model is proposed to decompose the measured distributions of amplitude and phase into those of the individual mode. Application of this method of decomposition to experimental data at various downstream locations shows that the basic assumption is valid even near the peak positions of amplitudes. After the decomposition of two modes, it is possible to clarify the characteristics of each instability mode such as phase velocity, magnitude and direction of wave-number vector and even to determine the critical Reynolds number of each mode.