Traveling disturbances on a spinning disk boundary layer

Spinning disk boundary layer provides a flow field convenient for a swept wing boundary layer transition study. In order to examine the randomization process in crossflow dominant three-dimensional (3-D) boundary-layer transition region experimental investigation is performed and two kinds of traveling disturbances with frequencies differing by more than an order of magnitude are detected for the first time. The properties of these disturbances is measured using a rotatable parallel hot wire probe. Results showed that the low frequency disturbance seems to be due to the unsteady crossflow instability (primary instability), while the high frequency one to be inflexional instability (high frequency, secondary instability) and coincides with the structure visualized by smoke visualization technique.