DNS of turbulent droplet-laden heated channel flow with phase transition at different initial relative humidities

In this paper a turbulent channel flow of a mixture of dry air and water vapor with water droplets is examined. Direct numerical simulation is used to quantify the importance of variations in the initial relative humidity. We focus on the droplet behavior along with the thermal properties of the system, such as the Nusselt number. During the initial stages of the simulations droplets evaporate more if the initial relative humidity is lower in order to reach the saturation condition. The difference in the Nusselt number between the cases of the lowest initial relative humidity and the saturation initial condition is on the order of 10% and this is connected with the different total heat capacity of the system. At the same time, we confront compressible and incompressible formulations comparing the results for both phases. A lower initial relative humidity leads to a larger difference in the mean gas mass density between the two formulations because of larger heat and mass transfer. Moreover, we find a larger relative difference in the Nusselt number between the two formulations in case of a lower initial relative humidity. These findings motivate the need to adopt the complete compressible flow model.