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

•A bottleneck of the EPOD method for correlation analysis is described.•The role of the spatial distribution of the modes is clarified, and a procedure to take this into account is proposed.•This is started by thermally active zone detection using spatial modes of temperature.•Then damping of temporal coefficients is used as a spatial filter.•The procedure provides a more meaningful correlation study in the example of turbulence enhanced heat transfer. 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.