Dissimilar heat transfer enhancement by introduction of a vortex tube in plane Couette flow

Abstract

Recent studies have suggested that a cyclonic vortex, which has the same signed vorticity as that of background shear, can lead to dissimilar heat transfer enhancement, i.e. more heat transfer than momentum transfer. However, it has not yet been known how the cyclonic vortex achieves dissimilarity, or if other types of vortices would also lead to dissimilarity. In order to tackle these problems, we introduce a straight vortex tube into laminar plane Couette flow under various conditions and numerically investigate heat and momentum transfer therein. The essential process for dissimilarity is isolated from complex ingredients of realistic flow to consider the interaction of a vortex with background shear. It is found that introduction of a strong spanwise anti-cyclonic vortex, which has the opposite signed vorticity to that of background shear, can realize more dissimilar heat transfer than the known cyclonic vortex as a consequence of the long-term interaction with the background flow, whereas the spanwise cyclonic vortex achieves larger dissimilarity in the early stage of its time evolution. The physical mechanisms of dissimilarity due to these vortices are elucidated by interpreting the distribution of the streamwise pressure gradient and the resulting difference between temperature and streamwise velocity around the vortex.