Stabilisation of Tollmien-Schlichting waves by streaky base flow

Authors: Fransson, J. H. M., Talamelli, A., Brandt, L.B., Cossu, C.
Document Type: Conference
Pubstate: Published
Journal: 56th Meeting of the APS Division of Fluid Dynamics, Nov. 23-25, East Rutherford (NJ), USA. Abstract in Bull. Am. Phys. Soc.
Volume: 48  
Year: 2003


The stabilisation of Tollmien-Schlichting (TS) waves 1 in a spanwisely modulated Blasius boundary layer, has been experimentally verified in the MTL wind tunnel at KTH. The alternating high and low speed streaks were created by regularly spaced cylindrical roughness elements mounted near the leading edge of the plate. Their amplitude was varied between 5% and 12% of the free stream velocity simply by change of ditto. The streaks show good agreement with spatial optimal perturbation theory calculated for the present experimental conditions. The TS-waves were generated by means of blowing and suction through a spanwise slot in a plug mounted in the plate. TS-waves are suppressed by high amplitude streaks (>10%) after an initial transient behaviour, whilst moderate streak amplitudes (<8%) shifts branch II downstream compared with the corresponding TS-wave in a Blasius boundary layer. The amplitude profiles compare qualitatively well with theory although the measured phase speed for the high amplitude streaks seems to be higher than the theoretical value.