Methodology for the Numerical Characterization of a Radial Turbine under Steady and Pulsating Flow

Doctoral Thesis / Dissertation from the year 2012 in the subject Engineering - Mechanical Engineering Universidad Politécnica de Valencia (Departamento de M´aquinas y Motores T´ermicos) language: English abstract: The increasing use of turbochargers is leading to an outstanding research tounderstand the internal flow in turbomachines. In this frame computationalfluid dynamics (CFD) is one of the tools that can be applied to contributeto the analysis of the fluid-dynamic processes occurring in a turbine. Theobjective of this thesis is the development of a methodology for performingsimulations of radial turbomachinery optimizing the available computationalresources. This methodology is used for the characterization of a vaned-nozzleturbine under steady and pulsating flow conditions.An important effort has been devoted in adjusting the case configurationto maximize the accuracy achievable with a certain computational cost. Concerningthe cell size a local mesh independence analysis is proposed as aprocedure to optimize the distribution of cells in the domain thus allowing touse a finer mesh in the most suitable places. Particularly important in turbomachinerysimulations is the influence of the approach for simulating rotormotion. In this thesis two models have been compared: multiple referenceframe and sliding mesh. The differences obtained using both methods werefound to be significant in off-design regions. Steady flow CFD results havebeen validated against global measurements taken on a gas-stand.The modeling of a turbine installed either on a turbocharger test rig oran engine requires the calculation of the flow in the ducts composing thesystem. Those ducts could be simulated assuming a one-dimensional (1D)approximation and thus reducing the computational cost. In this frame ofideas two CFD boundary conditions have been developed. The first one allowsperforming coupled 1D-3D simulations communicating the flow variables fromeach dom