Experimental investigation on the steady and unsteady disturbances in a flat plate boundary layer
2014 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 26, no 12, 124103- p.Article in journal (Refereed) Published
Recent experiments have shown that miniature vortex generators (MVGs) are coveted devices to stabilize unsteady disturbances in flat plate boundary layers and to delay the onset of turbulence by modulating the base flow in the spanwise direction. The spanwise modulation is a result from the non-modal transient growth of steady and spanwise periodic streamwise vortices being generated by the MVGs. The present experimental investigation aims at studying the transient growth of non-modal disturbances induced by a spanwise periodic array of MVGs and its stabilizing effect on non-linear unsteady disturbances in the boundary layer originating from planar Tollmien-Schlichting (TS) waves. Measurements consist of cross-stream planes at different downstream locations in the boundary layer and a spatio-temporal analysis of different modes of the disturbances is carried out. In the streaky boundary layer generated by the MVGs the fundamental spanwise mode, with the same wavelength as the MVG pairs in the array, and its first harmonic, both undergo transient growth whereas the higher harmonics decay immediately downstream of the array. In the unstable region formed in the wake of the MVG blades, i.e., just downstream of the array, a wide range of spanwise modes contributes to an initial growth in the energy of unsteady disturbances. Similar behavior is observed upstream of branch II position of the neutral stability curve where the unsteady disturbances undergo a second energy growth in the unstable region. It is shown that the spatial gradients of the base flow in the wall-normal and spanwise directions are contributing to the amplification and attenuation of the TS wave disturbances, respectively, in the streaky boundary layer.
Place, publisher, year, edition, pages
2014. Vol. 26, no 12, 124103- p.
Tollmien-Schlichting Waves, Number-Independent Instability, Streamwise Vortices, Bypass Transition, Transient Growth, Shear Flows, Streaks, Stability, Surface, Stabilization
Fluid Mechanics and Acoustics
IdentifiersURN: urn:nbn:se:kth:diva-139047DOI: 10.1063/1.4902395ISI: 000347161600037ScopusID: 2-s2.0-84918789723OAI: oai:DiVA.org:kth-139047DiVA: diva2:682767
FunderEU, European Research Council
QC 20150203. Updated from manuscript to article in journal.
Previous title: "Experimental investigation on the steady and traveling disturbances in a flat plate boundary layer". 2013-12-302013-12-302016-02-08Bibliographically approved