Turbulence modulation effects caused by small droplets using one-dimensional-turbulence

Sammanfattning: This thesis presents a stochastic model to study turbulence modulation effects on gas phases caused by small droplets or more generally speaking particles to achieve a better understanding about the physics and with the aim to provide data for a subgrid-scale (SGS) model for Large-eddy-simulations. The one-dimensional-turbulence (ODT) model addresses one of the major issues for multiphase flow simulations, namely computational costs. It is a dimension-reduced model resolving all turbulent time and length scales and reaching parameter ranges, which are inaccessible for Direct-Numerical-Simulations (DNS). ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps which represent the effect of individual turbulent eddies on property fields. For an efficient investigation of turbulence modulation effects, ODT has been extended in this thesis in many ways. First, the Lagrangian particle tracking method developed by Schmidt et al. was modified for spatial, cylindrical flow simulations. Therefore, the two-way coupling mechanism was extended as well. This case serves to study the overall influence of particles on a jet configuration, which conforms with the droplet-laden flow in the dilute region of a spray. Here, the most significant effects are expected. Secondly, a concept for developing a SGS model is presented. Based on this concept, ODT was modified to capture two canonical test cases of stationary, forced isotropic turbulence (HIT) and homogeneous shear turbulence (HST). For this purpose, a forcing scheme that maintains statistical stationarity and a new energy redistribution mechanism during  the eddy events are introduced. The latter enables ODT to predict anisotropic turbulent structures. ODT is validated against several data sets of DNS studies and showed its capability to access parameter ranges beyond previous limits. It turned out to have a lot of potential to contribute to a SGS closure of LES for turbulence modulation caused by small droplets.