Comparison of DNS of compressible and incompressible turbulent droplet-laden heated channel flow with phase transition

• Comparison of incompressible and compressible channel flow.
• Studying of dependence of the heat transfer on the Mach number.
• Evaporating droplets increase the heat transfer up to by factor of 5.

Direct numerical simulation is used to assess the importance of compressibility in turbulent channel flow of a mixture of air and water vapor with dispersed water droplets. The dispersed phase is allowed to undergo phase transition, which leads to heat and mass transfer between the phases. We compare simulation results obtained with an incompressible formulation with those obtained for compressible flow at various low values of Mach number. We discuss differences in fluid flow, heat- and mass transfer and dispersed droplet properties. Results for flow properties such as mean velocity obtained with the compressible model converge quickly to the incompressible results in case the Mach number is reduced. In contrast, thermal properties such as the heat transfer, characterized by the Nusselt number, display a systematic difference between the two formulations on the order of 15%, even in the low-Mach limit. This shows the necessity of the use of a compressible formulation for accurate prediction of heat transfer, even in case of an initial relative humidity of 100%. Mass transfer properties display a difference between the models on the order of 5%, for example in the prediction of the droplet mean diameter near the walls.