A modification to extended proper orthogonal decomposition-based correlation analysis: The spatial consideration

The so-called proper orthogonal decomposition (POD) method has been used in numerous research items, mainly in the field of turbulence, as a reduced-order model to describe transient complex turbulence by a set of deterministic functions. One of the modifications of POD known as the extended POD method (EPOD) has been successfully used mainly to analyse correlations between the flow field and synchronized vector or scalar fields such as correlations between velocity and temperature fields. However, its bottleneck in the correlation identification is demonstrated in this paper, and then the issue is addressed by a suitable modification. For this, a set of unsteady fully turbulent simulation results in the presence of different arrays of vortex generators, enhancing heat transport, is analysed by POD and EPOD. As a major result, a spatial filtering procedure is proposed to be applied prior to EPOD analysis. It is demonstrated that, in contrast to a conventional application of EPOD, the proposed procedure enables correct separation of thermally active and inactive flow modes.