Dean instability and thermal characteristic in sinusoidal structure

Sinusoidal structures have been widely used in various heat exchangers and micro heat sinks. In this paper, the flow and heat transfer characteristics in sinusoidal channels are numerically investigated. In particular, the unsteady fluctuation of Dean vortices has been studied in detail. It is found that a critical Reynolds number exists in sinusoidal channel. When the Reynolds number exceeds the critical Reynolds number, the flow is in an unsteady state, which is manifested by the irregular fluctuation of the Dean vor-tices. In addition, the POD (Proper Orthogonal Decomposition) method is used to perform mode analysis of the Dean vortices motion, and the Swirling number is used to quantify the degree of Dean instability for the first time. It is found that the fluctuations of the Dean vortices have similarity in the decompo-sition of modes when reaching the critical state, and the locations of the main fluctuations at 90 degrees and 180 degrees cross sections change. It is also found that the Dean instability has a significant effect on improving the thermal homogenization of the channel wall. In detail, 82.83% and 20.20% enhancements of thermal homogenization at the upper and lower walls at the 90 degrees cross section are obtained, respectively. 14.06% and 14.33% enhancements of thermal homogenization are obtained at the upper and down walls at the 180 degrees cross section, respectively.(c) 2023 Elsevier Ltd. All rights reserved.