Vortex-Generator Pairs for Vortex-Induced Heat-Transfer Enhancement in Heat-Exchanger Channels Markus R ¨ utten and Lars Krenkel German Aerospace Center, Institute of Aerodynamics and Flow Technology, Bunsenstrasse 10, G ¨ ottingen, Germany, Markus.Ruetten@dlr.de, WWW home page: http://www.dlr.de/as Summary The objective of the presented work is to investigate possibilities for increasing the heat-transfer in heat-exchanger channels for aircraft applications by using flow- manipulating devices. Focal point of the investigation are different arrangements of vortex-generator pairs within a generic heat-exchanger channel. The DLR URANS CFD solver THETA has been used to carry out numerical simulations of the laminar flow within a rectangular channel with integrated vortex generators. In particular, the analysis of the interaction of generated vortices with the stratified thermal bound- ary layer, the impact of vortical flow structures on heated walls and the enforced mixed-convection flow is of special interest. The final goal is the evaluation of the applicability of oppositely arranged vortex-generator pairs for the enhancement of vortex-induced heat-transfer. 1 Introduction The increase of fuel prices and the general increasing environmental awareness to- gether with the demand for unlimited, fast and cheap air transport enforces the air- craft manufactureres to cut the full potential of all aircraft sub-systems to guarantee an economical success. One possibility to reduce the specific fuel consumption of modern aircraft is to increase the performance of the environmental control system (ECS), mainly by increasing the performance of the cooling capacity of its heat ex- changers. A higher cooling capacity might allow for reducing the size of the heat exchangers, which may also enlarge the space envelope for the ducting of the cool- ing channel giving leeway for flow optimization. Therefore, the scientific goal of the work is, firstly to improve the understanding of the effect of large scale vortical flow structures on mixed thermal convection and, secondly to reveal possibilities to enhance the heat transfer in heat-exchanger channels while avoiding or minimising additional drag and pressure losses. The enhancement of heat transfer in energy- conversion systems is subject of extensive ongoing research. One way to achieve an enhancement of heat transfer is to utilize additional devices in heat exchanger