Analysis of an Axisymmetric Bluff Body Wake using Fourier Transform and POD

The data from u nforced and open loop forced simulations of the wake behind an axisymmetric bluff body at Re D=1,500 is analyzed to explore the effect of forcing. In the unforced wake, because of the axial symmetry of the body , structures do no t maintain a constant azimuthal phase over time , which leads to inaccurate predictions of the flow field when applying POD . Forcing inside the “lock -in” region in amplitude -frequency space with a fixed azimuthal phase is therefore introduced to study the w ake in detail. The resulting flow field is analyzed using three methods , namely an azimuthal Fourier transform, a moment of inertia calculation, and a velocity vector histogram, to determine the a zimuthal phase of the wake structures . The overall goal is t o minimize the necessary data volume to analyze the flow for eventual implementation in real time feedback flow control experiments. It is shown that the methods used to determine the azimuthal phase all yield a measure of the phase angle of the symmetry p lane in the wake .