Heat Transfer Around Longitudinal and Parallel Arranged Wedge-Shaped Vortex Generators

Abstract

In order to enhance convective heat transfer, turbulence promoters or vortex generators (VGs) are often used to manipulate the flow field and to benefit from their effect on thermal performance. The current investigation is directed towards a detailed understanding of the generated vortex flows and their impact on heat transfer for wedge shaped full-body VGs in internal flows. The main focus is on longitudinal and parallel arrangements of two or three VGs, where interaction of the induced flow field plays an important role. A single VG introduces a main vortex pair moving longitudinally downstream which is symmetric to the mid-plane of the turbulator itself. By using arrangements of several VGs it is possible to take advantage of the vortex interaction and define or deflect zones of enhanced heat transfer. In certain cases (e.g. due to manufacturing reasons) sharp edges on the elements cannot be realized. The effect of this discrepancy in the designated geometry is also investigated. Data for heat transfer behind a sharp-edged VG is compared with data for VGs manufactured with two different edge radii. In the present experimental setup the VGs are mounted on the bottom wall of a rectangular channel. For Reynolds numbers of 150,000 up to 550,000 the heat transfer coefficient is measured with the transient thermochromic liquid crystal (TLC) thermometry which is based on the measurement of the wall temperature response to a given step change in the fluid temperature. Numerical simulations using a Reynolds-Stress Model describe the flow field around the arrangements and are used for further interpretation of the experimental heat transfer distributions. Effects of vortex interactions on the heat transfer distribution are described for parallel and longitudinal arrangements. In the experimental data for elements with rounded edges a significant reduction in heat transfer can be observed.