FLOW-FIELD DECOMPOSITION APPLIED TO EXPERIMENTAL-DATA OBTAINED FOR A TRANSITIONAL BOUNDARY-LAYER

Using experimental data from Particle Image Velocimetry (PIV) measurem ents, coherent structures of a transitional spatially developing bound ary layer are determined. The coherent structures are determined utili zing the Proper Orthogonal Decomposition (POD), which is based on an e xpansion of the flow field variables into a set of eigenfunctions or m odes. For having constant and reproducible flow field conditions, the flow is artificially excited by means of periodic velocity fluctuation s, The used excitation device allows the generation of different trans ition scenarios, where this paper focuses on the case of the fundament al transition. Phase locked excitation signals allow the recording of instantaneous velocity fields of the how field at certain instants of time. It can be shown that PIV is a suitable technique to provide expe rimental data for POD. The results of the POD show that already a smal l number of modes cover most of the kinetic energy of the flow.