Proper orthogonal decomposition applied to PIV data for the oblique transition in a Blasius boundary layer

Kurzfassung

Using experimental data from Particle Ima Velocimetry (PIV) measurements, coherent structures of a transitional, spatially developing boundary layer are determined. The coherent structures are calculated utilizing the Proper Orthogonal Decomposition (POD), which is based on an expansion of the flow field variables into so- called Karhunen Loeve eigenfunctins. To get reproducible flow conditions we excite the flow with controlled disturbances by means of periodic velocity fluctuations. We are able to introduce two-and three-dimensional traveling waves. Therefore it is possible to investigate different transition scenarios. This paper focus on the oblique transition. Phase locked signals allows to record the flow field at certain instants of time. We can show that PIV is a suitable technique to provide experimental data for POD. The POD shows that already a small number of modes cover most of the energy.