Experimental Investigation of Instablility Wave Propagation in a 3-D Boundary-Layer Flow.

Abstract

Wave propagation phenomena in 3-d boundary-layer flows with crossflow instability were investigated experimentally. A 10 element hot-film sensor was flush-mounted on a rotatable insert in a swept flate plate with imposed favourable pressure gradient. By means of cross spectral analysis it was possible to obtain direction and magnitude of the phase velocity and the group velocity of the traveling instability waves, thus filling a gap in the know-ledge of crossflow instability characteristics. The waves were found to propagate approximately normal to the portential streamline direction, according to linear theory. Phase velocity and the resulting wavelengths also agree satisfactorily, whereas the measured direction and magnitude of the group velocity shows significant differences.