An experimental study of boundary-layer transition over a rotating, compliant disk

An experimental study is described which investigates the laminar-turbulent transition of the boundary layer over rigid and compliant disks rotating under water. Hot-film data are presented and analyzed to produce neutral-stability curves. It appears to be the first time that such data has become available for a compliant disk. Our experiments employing a rigid disk essentially confirm the results of previous authors. For the flow over the compliant disk the turbulence levels in the transitional and fully turbulent flow regimes are found to be considerably lower than the corresponding levels for the rigid disk. The analysis of our experimental data suggests that wall compliance has a stabilizing influence in the frequency range associated with the Type I cross-flow instability. Nevertheless, compliance is found to have an overall destabilizing effect on the boundary-layer flow. This results in a substantially lower transitional Reynolds number compared to the case of the rigid disk. The experimental observations are in qualitative agreement with our theoretical predictions. It is argued that the reduced transitional Reynolds number for the compliant disk might indicate that transition for such a disk results from a convective-instability mechanism and not from an absolute-instability mechanism as has recently been suggested in the literature to be the case for a rigid disk. (C) 1999 American Institute of Physics. [S1070- 6631(99)00111-7].