Heat Transfer Enhancement of a Turbulent Duct Flow by Means of Vortex Generators Attached to a Large Eddy Break-Up Manipulator.

Abstract

An experimental study was conducted to investigate the characteristics of wall heat transfer and momentum loss for a turbulent duct flow disturbed by insertion of a complicated body composed of a LEBU (Large Eddy Break-Up) plate and winglet-type vortex generators. It was found that the LEBU plate reduces the wall heat transfer in the region downstream of the insertion position and that this suppression of heat transfer could be recovered by attaching vortex generators to the LEBU plate, i.e., conspicuous heat transfer enhancement was achieved over a large streamwise distance. The obtained spatial distribution of heat transfer coefficient shows the same features as that observed in the previous study of a flat plate turbulent boundary layer. Therefore, the flow and thermal field structure of the turbulent duct flow downstream of the inserted body should be basically the same as those in the same region of the turbulent boundary layer. The effect of a notch, open in the LEBU plate behind the vortex generator, on heat transfer and pressure drop was also examined. The notch simulates the hole of the LEBU plate to be produced in practical application, when a vortex generator is produced by punching from the original plain LEBU plate. A vortex generator having an open notch was found to work best not only in augmentation of the wall heat transfer but also in suppression of the increase of momentum loss.