Numerical Simulations of Turbulent Flows at Widely Different Mach Numbers

University dissertation from KFS AB

Abstract: The present thesis mainly focuses on the numerical simulation of the turbulent flow field and acoustics developed in different industrial applications. The study covers a large range of Mach numbers, starting from incompressible regimes and ending with a fully compressible flow. In the first part of the thesis, several computations of an incompressible flow, are performed in order to study the behavior of an aircraft engine running close to the ground. The ground vortex interaction and particle ingestion are the investigated topics. The methods involved for solving the flow are the Reynolds Averaged Navier Stokes with a k-epsilon turbulence model closure, Large Eddy Simulation with Smagorinsky sub grid scale model. The particle ingestion problem is investigated using a one way coupling lagrangian particle tracking algorithm. The second part concerns the study of the flow around moving bodies and the acoustical field generated by it. Based on the flow incompressibility assumption, the problem is decoupled: first the flow solution is computed using Large Eddy Simulation frame work, then the acoustic sources are extracted and finally the acoustical wave propagation is studied using an acoustic analogy developed by Ffowcs-Williams and Hawkings. Three different cases are presented in the papers, all involving rotating bodies: an axial fan, a wind turbine and a propeller. From these three cases, only the wind turbine computation is presented in more detail in the thesis. The dynamics of a shock wave in a transonic flow in a channel are investigated in the third part of this thesis using the Large Eddy Simulation framework. Similar phenomena with those encountered in supersonic flows are found: Mach reflection shock wave, regular reflection shock wave, outlet pressure induced hysteresis, unsteady shock wave.