Heat transfer in the stagnation point area of a heated cylinder is investigated using Direct Numerical Simulation (DNS). The heated cylinder is subjected to the turbulent wake of a smaller cylinder placed upstream. Two Reynolds numbers based on the diameter of the heated cylinder of 13,200 and 48,000 are chosen. In accordance with correlations in the literature, an increase in heat transfer compared to fully laminar flow is found for all angles along the front circumferential area of the heated cylinder. However, due to the presence of the wake, the maximum increase is shifted away from the centerline. The characteristic turbulence level and Nusselt number in the present study are an order of magnitude higher than those reported in previous simulations. The DNS results obtained, are in good agreement with an existing experimental correlation. Finally, relevant flow structures and instantaneous temperature fields are visualized.@en

Predicting fuel spray interaction with large scale vortex structures still is a major challenge for state-of-the-art CFD codes. In order to elucidate the mechanisms involved, a fundamental study has been carried out in which the interaction of water droplets with a Karman vortex street is investigated. The disperse two-phase flow around a cylinder has been computed taking into account the mass, momentum and heat transfer between both phases. Flow conditions are chosen such that large scale vortices are generated by periodic flow separations of the well known Karman vortex street. A homogeneous distribution of water droplets is injected into the hot air up-stream of the computational domain. The mixing process as well as the impact of the droplets on the gas phase instabilities is analyzed in the downstream region where large scale vortex structures are present.@en

From experimental studies it is well established that free-stream and wake-induced turbulence can increase the heat transfer on curved surfaces such as turbine blades or cylinders even if the mean flow matches corresponding laminar velocity profiles. Here, preliminary results of an investigation using (embedded) Direct Numerical Simulation (DNS) are reported that aim at identifying the responsible physical mechanisms for this phenomenon. The setup follows an existing experiment where a heated cylinder is subjected to the turbulent wake of a smaller cylinder placed upstream. The Reynolds number based on the diameter of the heated cylinder is Re = 48, 000. A key parameter identified in an experimental correlation is the characteristic turbulence level Tua that includes a dependency on Re and the mean flow acceleration. For the present study, Tua is an order of magnitude higher than those reported in any previous DNS. The obtained Nusselt number is in good agreement with the experimental correlation. More and better resolved data is currently produced for further analysis.@en