Temporal numerical simulations of turbulent Coanda wall jets

In a novel application of the temporal numerical simulation, an investigation of turbulence modeling techniques is carried for the turbulent wall jet over a convex surface (Coanda wall jet.) The simultaneous presence of multiple instability mechanisms and the interaction with the turbulence dynamics at the solid boundary produces a unique combination of different large turbulent coherent structures that constitutes both a consistent challenge for numerical simulations and an ideal test bed for turbulence models.; The Temporal Direct Numerical Simulation (TDNS) of the Coanda wall jet restricts the focus from the global turbulent Coanda wall jet to a smaller, local portion of the flow and offers a wide array of advantages to the present work. In particular, the size of the computational domain can be arbitrarily chosen in both the spanwise and the streamwise directions. This allows to either suppress or enhance individual physical mechanisms and, consequently, to selectively reproduce different large coherent structures within the local flow. In the first part, temporal numerical simulations are employed to reproduce four different flow scenarios of the local Coanda wall jet with a level of numerical resolution that, because of the reduced size of the computational domain, cannot be matched by standard DNS of the entire physical flow (spatial DNS, or SDNS .); The TDNS of these four flow scenarios are then used in the second part for an a-posteriori analysis of different turbulence models in order to address common shortcomings shown by Hybrid Turbulence Models (HTM). For each flow scenario, the turbulent flow field is deliberately decomposed in resolved and unresolved flows by the application of different filters in space corresponding to different grid resolution. The behavior of turbulence models can be reproduced from the resolved flow and compared to the turbulent stress tensor directly calculated from the unresolved part of the flow field. Starting from the RANS limit, turbulence models with different levels of complexity are studied. Successively, the performance of these models is analyzed at intermediate numerical resolutions between RANS, LES, and DNS . Finally, an improved formulation of the Flow Simulation Methodology (FSM) is proposed.