EXPERIMENTAL INVESTIGATION OF INSTABILITY WAVE-PROPAGATION IN A 3-DIMENSIONAL BOUNDARY-LAYER FLOW

Wave propagation phenomena in three-dimensional boundary-layer flows w ith crossflow instability were investigated experimentally. A 10-eleme nt hot-film sensor was flush-mounted on a rotatable insert in a swept flate plate with imposed favorable pressure gradient. By means of cros s-spectral analysis it was possible to obtain direction and magnitude of the phase velocity and the group velocity of the traveling instabil ity waves, thus filling a gap in the knowledge of crossflow instabilit y characteristics. The waves were found to propagate approximately nor mal to the potential streamline direction, according to linear theory. Phase velocity and the resulting wavelengths also agree satisfactoril y, whereas the measured direction and magnitude of the group velocity shows significant differences.