Vortices and Heat Transfer

Abstract

AbstractFor internal flow the influence of vortices on heat transfer is studied mainly numerically. Laminar channel flows with two types of periodic vortex generators (VGs), transverse ribs and rectangular winglets, are considered. The transverse ribs generate transverse vortices (TVs), and the rectangular winglets at 45° angle of attack generate longitudinal vortices (LVs). Velocity and temperature fields, local and global friction, flow losses, and heat transfer are computed from the full unsteady, three‐dimensional conservation equations. Point comparisons with experimental results are given. For steady flow the TVG configuration strongly influences heat transfer locally, but not globally. The stationary TVs don't provide an additional mechanism for convective thermal energy transport, but cause additional flow losses for their generation. The LVG configuration enhances local and global heat transfer for both steady and unsteady flow. For steady flow the LVs generate swirl which is an additional mode of convective thermal energy transport. When the flow reaches a critical Re‐number, which is more than an order of magnitude lower than the normal transition Re‐number, self‐sustained oscillations set in. They provide an additional heat transfer mode due to “Reynolds” averaged transport which further increases the heat transfer. For the same heat transfer increase the LVG configuration causes only half the flow losses of the TVG configuration. For practical applications, where high heat transfer and low flow losses are important, LVG configurations are better suited than TVG configurations.