Extracting dominant three-dimensional coherent structures from timeresolved planar PIV measurements in the wakes of cylindrical bodies

The present study investigates two techniques for phase averaging time resolved two-dimensional PIV measurements for the purpose of extracting dominant three-dimensional wake characteristics. The first one is the classical phase averaging which uses a reference wake velocity signal measured via Laser Doppler Velocimetry (LDV). The second technique involves obtaining the phase information in each measurement plane using Proper Orthogonal Decomposition (POD) of PIV data and then establishing the relative phase between the planes utilizing the reference LDV signal. These techniques are applied to the results of numerical simulations and experiments on the flow past a circular cylinder immersed in a uniform shear flow. Numerical simulations are completed for ReD = 100 and 300, and experiments are completed for ReD = 2100. The phase-averaged results show that both techniques are able to reconstruct the oblique shedding of dominant spanwise vortices. For the basic case of laminar shedding at ReD = 100, the techniques perform equally well. However, the new POD-based approach is superior when there are temporal variations in the threedimensional wake topology present in the uniform cylinder wake for ReD = 300 and 2100